JP7572940B2 - Film-forming salt-reducing agent - Google Patents

Description

The present invention relates to a film-forming salt content reducing agent that contains at least one type of resin as a film-forming component. The present invention also relates to a method for reducing the amount of salt adhering to the surface of a steel structure using the film-forming salt content reducing agent. This method can be used particularly when the steel structure has undergone surface preparation in a repainting work for the steel structure.

Steel bridges and other steel structures are part of the infrastructure of a nation and society. Steel structures have a coating to protect the base from the environment, but because the coating deteriorates over time in outdoor environments that are subject to the weather, they generally require periodic repainting, about once every 5 to 50 years. When repainting steel structures, the old coating is removed by preparing the base, and any substances adhering to the surface of the steel structure (rust, salt, etc.) are removed, and then a new coating is formed.

Surface preparation is generally called "cleaning". There are several types of cleaning (class 1 to class 4 cleaning), and among these, class 1 cleaning is the most thorough surface preparation (i.e. the highest level of surface preparation) (for definitions of each type of cleaning, refer to the Japan Road Association's "Handbook for Steel Highway Bridge Corrosion Prevention, March 2014"). Class 1 cleaning is usually done by blasting. When surface preparation is done using class 1 cleaning, all of the old paint film and all of the rust adhering to the surface of the steel structure are removed. However, since the presence of attached salt is often not visible to the naked eye, a large amount of salt may remain on the surface of the steel structure even after surface preparation using class 1 cleaning. For example, when a steel structure is located in a coastal area or a cold region, salt (mainly sodium chloride) that has flown in from the ocean or salt (sodium chloride, calcium chloride, magnesium chloride, etc.) that is derived from snow-melting agents sprayed in cold regions adheres to the steel structure, and even if surface preparation is performed using a type 1 scraper, a large amount of salt still adheres to the surface of the steel structure. If a large amount of salt is left unremoved, it will have a negative effect not only on the steel structure but also on the newly formed coating film. Therefore, it is necessary to remove the salt adhering to the surface of the steel structure and reduce the amount of salt to a certain value or less, and then apply a new coat of paint. The above-mentioned "Handbook for Steel Highway Bridge Corrosion Prevention" and other publications recommend reducing the amount of sodium chloride to 50 mg/m2 ^{or less} before applying a new coat of paint. In this specification, "salt" refers to a compound containing chloride ions. Examples of salt include sodium chloride, potassium chloride, calcium chloride, and magnesium chloride.

Removal of remaining salt on the surface of steel structures has traditionally been done using high-pressure water washing or power tools.

The high-pressure water washing method is a method for removing salt by spraying large amounts of high-pressure water on the surface of a steel structure. This method has the problem that it requires a large amount of water, and also generates a large amount of wastewater that requires treatment, which is costly and environmentally problematic. Another problem with this method is that it can only be carried out in seasons when the water does not freeze.

The power tool method is a method of removing salt using power tools. This method has the problem that it requires specialized tools, as well as being labor-intensive. This method also has the problem that it generates noise and dust from the use of power tools, and has a large environmental impact due to the need to deal with industrial waste such as used power tools. Furthermore, with this method, there is a risk that the use of power tools may damage the surface of the steel structure, and that such damage may cause the salt on the surface of the steel structure to penetrate into the interior of the steel structure.

Furthermore, especially when the steel structure is a bridge, the parts other than the supporting parts are often located in high spaces, making it difficult to carry out salt removal work, whether by high-pressure water washing or power tools.

In this situation, there is a demand for simple, environmentally friendly alternatives to conventional technologies.

JP 2002-045811 A (Patent Document 1) discloses a method for removing contaminants adhering to the surface of a building or furniture. In this document, an aqueous solution of polyvinyl alcohol resin is applied to the surface of the building or furniture, dried, and the formed film is peeled off and removed together with the contaminants, thereby removing the contaminants adhering to the surface of the building or furniture. In this document, a house is assumed as the building, and the contaminants to be removed are assumed to be contaminants in the house, but the removal of salt remaining on the surface of a steel structure such as a bridge is not assumed. In this document, a preferred embodiment is to allow the formed film to function as a protective film on the surface of the building or furniture until it is peeled off and removed.

JP 2007-283237 A (Patent Document 2) discloses a method for removing salt remaining on the surface of a steel structure after surface preparation in a repainting work for the steel structure to expose 60% or more of the steel structure's surface. In this method, an aqueous solution of sodium carbonate is applied to the surface of the steel structure, chloride ions are ion-exchanged with carbonate ions to remove salt from the surface of the steel structure, sodium carbonate powder is crystallized by drying, this powder is removed with a nylon cup wire brush attached to an electric rotary tool, and then a new coating is formed. In this document, a power tool is used to remove the powder, so the problems associated with the use of power tools mentioned above inevitably occur.

JP 2017-213557 A (Patent Document 3) discloses a method for removing salt remaining on the surface of a steel structure after the exposed surface area of the steel structure is adjusted to 30% or more by adjusting the surface during repainting work on the steel structure. In this method, a corrosion inhibitor containing hydrocalumite and/or hydrotalcite, which are ion scavengers, is applied to the surface of the steel structure and dried to form a film that captures chloride ions. This document assumes that the formed film will be strongly attached to the surface of the steel structure and will remain unpeeled for a long period of time, and that a power tool method must be used to remove the film. Therefore, the method of this document inevitably causes the problems associated with the use of power tools as described above.

Thus, Patent Document 1 is a technology unrelated to removing salt remaining on the surface of steel structures such as bridges. Furthermore, Patent Documents 2 and 3 form a crystalline powder or film to remove salt remaining on the surface of a steel structure after surface preparation, but because power tools are required to remove the powder or film, the problems associated with the power tool method remain unresolved. Therefore, there remains a need for a simpler method that is environmentally friendly and can replace the high-pressure water washing method and the power tool method.

Japanese Patent Application Publication No. 2002-045811 Japanese Patent Application Publication No. 2007-283237 Japanese Patent Application Publication No. 2017-213557

The objective of the present invention is to provide a method for reducing the amount of salt adhering to the surface of a steel structure, which is a simple and environmentally friendly alternative to conventional high-pressure water washing methods and power tool methods.

In the course of research to develop the above method, the inventors discovered that when a viscous aqueous solution containing a film-forming resin is applied to the surface of a steel structure and dried to form a film, the film incorporates chloride ions, and further discovered that some such films can be peeled off by hand without using power tools (i.e., without the need for power tools) from the surface of the steel structure. In other words, they discovered that a viscous aqueous solution containing a specific resin as a film-forming component functions as a salt content reducer for reducing the amount of salt adhering to the surface of a steel structure, that the aqueous solution, which is a film-forming salt content reducer, is applied to the surface of a steel structure and dried to obtain a film that can be peeled off by hand without using power tools from the surface of the steel structure, and that the problems of the present invention are solved by the method of applying the aqueous solution to the surface of a steel structure to form a film and then peeling off the film from the surface, and thus completed the present invention.

The method for reducing salt content of the present invention using a film-forming salt-reducing agent can be easily performed from film formation to peeling, and in particular, the peeling of the film can be performed manually without using power tools (i.e., without the need for power tools). Therefore, the method of the present invention is a simple method that does not put a burden on the environment, and can solve all the problems of the conventional high-pressure water washing method and power tool method. Specific examples of the effects of the present invention include that it can be easily performed, that it puts a burden on the environment, that it is inexpensive, that it does not require a large amount of water, that it does not generate a large amount of wastewater, that it does not require equipment for treating the wastewater, that it can be performed regardless of the location of the steel structure, that it can be performed regardless of the season, that it does not require power tools, and that there is no risk of damage to the surface of the steel structure caused by the use of power tools, or that the salt on the surface of the steel structure will penetrate into the interior of the steel structure due to the damage. Furthermore, by combining the method of the present invention with a conventional method, the problems of the conventional method can be alleviated. For example, the number of times and the time required for high-pressure water washing when reducing salt content using the conventional high-pressure water washing method can be reduced by combining the method of the present invention.

The present invention is a chloride reducer for the surface of a steel structure that has been subjected to surface preparation using a type 1 or type 2 scraper, which is then dried to form a film that absorbs the chlorides remaining on the surface of the steel structure, and which then peels off the film together with the chlorides to remove the chlorides remaining on the surface. The chloride reducer for the surface of a steel structure is a film-forming chloride reducer that is made of a viscous aqueous solution composed of a mixture of polyvinyl alcohol and ethylene-vinyl acetate copolymer and water, and contains 24 to 26 mass % of the mixture based on the total mass of the chloride reducer .

The present invention is a method for reducing the chlorides on the surface of a steel structure by applying a coating to the surface of a steel structure that has been subjected to surface preparation using a type 1 or type 2 scraping process , drying the coating to form a film that absorbs the chlorides remaining on the surface of the steel structure, and then peeling off the film together with the chlorides , the method comprising the following steps:
(1) The film-forming chloride reducer for the surface of a steel structure as described in claim 1 is applied to the surface of the steel structure and dried to form a film that absorbs the chlorides remaining on the surface of the steel structure.
(2) The film is peeled off from the surface of the steel structure together with the chlorides .

To facilitate understanding of the present invention, the basic features and preferred aspects of the present invention are listed below.

1. A film-forming salt-reducing agent that is a viscous aqueous solution containing at least one type of resin as a film-forming component.

2. The film-forming salt-reducing agent according to the preceding paragraph 1, which does not contain an ion scavenger.

3. The film-forming salt-reducing agent according to paragraph 1 or 2 above, characterized in that the resin is a vinyl resin.

4. A film-forming salt-reducing agent according to any one of the preceding paragraphs 1 to 3, which is used to reduce the amount of salt adhering to the surface of a steel structure.

5. A method for reducing the amount of salt adhering to the surface of a steel structure, comprising the steps of:
(1) The film-forming salt reducing agent described in any one of the preceding paragraphs 1 to 4 is applied to the surface of a steel structure having salt attached thereto, and then dried to form a film on the surface of the steel structure.
(2) Peel the membrane off from the surface of the steel structure.

6. The method according to paragraph 5 above, wherein the salt contains at least one selected from the group consisting of sodium chloride, potassium chloride, calcium chloride, and magnesium chloride.

7. The method according to paragraph 5 or 6 above, characterized in that the steel structure has undergone surface preparation in a repainting job.

8. The method according to item 7 above, characterized in that the salt contains sodium chloride, the surface preparation is a type 1 cleaning, and the amount of sodium chloride adhering to the surface of the steel structure after the surface preparation exceeds 50 mg/ ^m2 .

The present invention will be described in detail below.

As will be explained in detail later, the film-forming salt content reducing agent of the present invention can be used to reduce the amount of salt adhering to the surface of a steel structure. The amount of salt is reduced by applying the film-forming salt content reducing agent to the surface of a steel structure to which salt has adhered and drying the agent to form a film on the surface of the steel structure, and then peeling off the film. As mentioned above, in this specification, "salt" means a compound containing chloride ions, and examples of salt include sodium chloride, calcium chloride, and magnesium chloride.

The film-forming salt content reducer of the present invention is a viscous aqueous solution containing at least one type of resin as a film-forming component (hereinafter, the resin as a film-forming component is often abbreviated as "film-forming resin"). From the viewpoint of rust prevention, the pH of the film-forming salt content reducer is preferably in the alkaline region. There are no particular limitations on the viscosity of the film-forming salt content reducer, so long as it is capable of forming a film and can be peeled off by hand without using a power tool after film formation.

The components of the film-forming salt-reducing agent of the present invention are as follows:

(A) Film-forming resin The film-forming resin is an essential component. The film-forming resin may be used alone or in combination. The amount of the film-forming resin is not particularly limited as long as the object of the present invention can be achieved, but is preferably 5 to 39 mass %, more preferably 11 to 33 mass %, and particularly preferably 22 to 30 mass % of the total mass of the film-forming salt-reducing agent.

The resin used is not particularly limited, so long as it is capable of forming a film and can be peeled off by hand without the use of power tools. The film-forming resin may be a homopolymer or a copolymer. Examples of film-forming resins include vinyl resins. Examples of vinyl resins include polyvinyl alcohol and vinyl acetate resins (such as ethylene-vinyl acetate copolymers). Further examples of film-forming resins include polyvinyl butyral resins, acrylic resins, and urethane resins.

From the viewpoint of film-forming properties and ease of peeling after film formation, vinyl resins are preferred as film-forming resins, and polyvinyl alcohol and vinyl acetate resins (such as ethylene-vinyl acetate copolymers) are even more preferred.

There are no particular restrictions on the degree of polymerization of polyvinyl alcohol. The degree of polymerization can be selected appropriately depending on the manner in which the salt-reducing agent is applied to the steel structure.

When applying by spraying, the degree of polymerization of the polyvinyl alcohol is preferably 300 to 4000, more preferably 400 to 2500, and particularly preferably 500 to 1000. Also, polyvinyl alcohol in the particularly preferred range (500 to 1000) may be used as the main component, and polyvinyl alcohol with a higher degree of polymerization may be used in combination.

When applying by a method other than a spray method (for example, using a brush or roller), the degree of polymerization is preferably 500 to 4000, more preferably 2000 to 3000, and particularly preferably 2400 to 2600. Also, polyvinyl alcohol in the particularly preferred range (2400 to 2600) may be used as the main component, and polyvinyl alcohol with a lower degree of polymerization may be used in combination.

There are no particular limitations on the degree of saponification of polyvinyl alcohol, so long as it is capable of forming a film and can be peeled off by hand without the use of power tools. In general, the higher the degree of saponification, the lower the fluidity of the film-forming salt-reducing agent, which is a viscous aqueous solution. However, when the amount of polyvinyl alcohol blended is relatively small, the use of a fully saponified type does not impair fluidity, and the fully saponified type has superior film strength. Those skilled in the art can appropriately determine up to what degree of saponification polyvinyl alcohol can be used, taking into account the amount of polyvinyl alcohol blended.

There are no particular limitations on the degree of polymerization of the ethylene-vinyl acetate copolymer, so long as it is capable of forming a film and can be peeled off by hand after film formation without the use of power tools.

There are no particular limitations on the ratio of ethylene to vinyl acetate in the ethylene-vinyl acetate copolymer, so long as a film can be formed and the film can be peeled off by hand without the use of power tools.

Two or more types of film-forming resins may be used in combination. When two or more types of resins are used in combination, there is no particular restriction on the ratio of the resins, so long as a film can be formed and the film can be peeled off by hand without using a power tool. Those skilled in the art can determine the ratio of the resins while taking into consideration the degree of polymerization of each resin. For example, when polyvinyl alcohol and ethylene-vinyl acetate copolymer are used in combination, if the degree of polymerization of polyvinyl alcohol is high, the strength of the film will be high even if the amount of polyvinyl alcohol is relatively small, so the ratio of polyvinyl alcohol may be small. Note that if the amount of polyvinyl alcohol is large, it may not be possible to apply it by spraying it with an airless spray, but in such a case, it is possible to apply it using a brush or roller.

(B) Water Water is an essential component. There is no particular limitation on the amount of water as long as the object of the present invention can be achieved. In general, the greater the amount of water, the greater the contact between the salt on the steel structure surface and moisture, and therefore the greater the salt reduction effect, but if the amount of water is too large, drying will be slow. From this perspective, the amount of water is preferably 10 to 70 mass %, more preferably 20 to 60 mass %, and particularly preferably 35 to 50 mass % of the total mass of the film-forming salt reducer.

It is also preferable to use water with a low ionic content, such as distilled water, ion-exchanged water, or pure water.

(C) Removal property improver The release property improver is an optional component. It can be used to improve the release property after film formation. When a release property improver is used, the amount thereof depends on the type of release property improver, but is preferably 0.5 to 5 mass %, more preferably 1 to 4 mass %, and particularly preferably 2 to 3 mass % of the total mass of the film-forming salt-reducing agent.

Examples of peeling enhancers include fatty acid esters (such as sorbitan fatty acid esters), fatty acid salts (such as sodium oleate and potassium oleate), alkylamine ethylene oxide adducts, and fluorine-based surfactants.

(D) Thickener The thickener is an optional component. It can be used to improve film-forming properties. The thickener may be an inorganic thickener or an organic thickener. The thickener may be used alone or in combination of multiple types. When used in combination, any multiple types may be selected from the group consisting of a single or multiple inorganic thickeners and a single or multiple organic thickeners and used in combination. In addition, when a thickener is used, the amount thereof is preferably 0.5 to 20 mass%, more preferably 1.0 to 10 mass%, and particularly preferably 1.5 to 5.0 mass% of the total mass of the film-forming salt-reducing agent.

The inorganic thickener may be natural or synthetic. Examples of inorganic thickeners include silica, kaolin minerals, serpentine, talc, mica, vermiculite, smectite (including montmorillonite, beidellite, nontronite, saponite, hectorite, sauconite, and stevensite), bentonite, sepiolite, organoclay, and organobentonite.

Examples of organic thickeners include anionic thickeners such as polyacrylic acid or its salts, acrylic acid-acrylic acid ester copolymers or their salts, acrylic acid-acrylamide copolymers or their salts, olefin-maleic acid copolymers or their salts, styrene-maleic acid copolymers or their salts, methylcellulose, carboxymethylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose or its salts, and nonionic thickeners such as polyacrylamide, alkylcellulose, polyethylene oxide, and polyethylene oxide.

(E) Rust inhibitor The rust inhibitor is an optional component. When a rust inhibitor is used, the amount thereof is preferably 0.1 to 3 mass %, more preferably 0.5 to 1.0 mass %, of the total mass of the film-forming salt-reducing agent.

Examples of rust inhibitors include organic acid salts, fatty acid salts, organic acid amine salts, alkanolamines, alkylamine ethylene oxide adducts, alkyl phosphate ester salts, and 3-(2-benzothiazylthio)propionic acid alkanolamine salts.

(F) pH adjuster The pH adjuster is an optional component. It is preferable to add the pH adjuster from the viewpoint of rust prevention. When an alkaline pH adjuster is used, if the amount of the adjuster is large, it tends to be reflected in the measured value when the surface salt content is measured by a surface salinity meter. Therefore, from the viewpoint of the accuracy of the measurement by the surface salinity meter, when an alkaline pH adjuster is used, it is desirable to add the pH of the film-forming salt content reducer containing the pH adjuster in the weak alkaline region. When a pH adjuster is used, the amount is preferably 0.1 to 5 mass%, more preferably 0.5 to 3 mass%, and particularly preferably 0.8 to 1.5 mass% of the total mass of the film-forming salt content reducer.

Examples of pH adjusters include ammonia, 2-methylaminoethanol, monoisopropanolamine, diisopropanolamine, 2-dimethylaminoethanol, triethanolamine, triethylamine, sodium hydroxide, potassium hydroxide, lactic acid, succinic acid, gluconic acid, citric acid, malic acid, oxalic acid, and phosphoric acid.

(G) Ion Scavenger The ion scavenger is an optional component. Basically, it is preferable not to use an ion scavenger for the reasons described below, but use of the ion scavenger is not excluded.

Examples of ion trapping agents include the IXE series manufactured by Toagosei Co., Ltd. of Japan, and hydrotalcite (such as Kyoward 500 manufactured by Kyowa Chemical Industry Co., Ltd. of Japan). The IXE series has a higher ion trapping ability than hydrotalcite. Of the IXE series, IXE-600, IXE-6107, IXE-100 and IXE-700F are preferred.

Since it takes time for the ion trapping agent to exert its ion trapping ability, if you try to peel off the film about 24 hours after applying the film-forming salt content reducing agent, the use of the ion trapping agent will not be very effective. In addition, since it is preferable to use the ion trapping agent in a neutral or acidic region, it is not preferable to include it in the film-forming salt content reducing agent of the present invention, which is preferably used in an alkaline range from the viewpoint of rust prevention. Furthermore, when the film-forming salt content reducing agent of the present invention contains an ion trapping agent, the peelability of the resulting film tends to decrease. However, if the resulting film is to be maintained for a certain amount of time and sufficient measures are taken to address the above problems associated with the use of the ion trapping agent, the ion trapping agent may be used.

The film-forming salt-reducing agent of the present invention may contain additives other than those mentioned above in order to improve film-forming properties, peelability, drying properties, thixotropy, etc. Examples of additives (some of which overlap with the additives mentioned above) include organic solvents, thickeners, film-forming assistants, plasticizers, thixotropy-imparting agents, pigments, dyes, emulsifiers, solubilizers, surfactants, dispersants, release agents, anti-settling agents, leveling agents, rust inhibitors, preservatives, antioxidants, defoamers, ultraviolet absorbers, chelating agents, and ion traps.

The film-forming salt-reducing agent of the present invention can be used to reduce the amount of salt adhering to the surface of a steel structure. A method of using the agent includes the following steps.
(1) The film-forming salt reducing agent of the present invention is applied to the surface of a steel structure having salt attached thereto, and then dried to form a film on the surface of the steel structure.
(2) Peel the membrane off from the surface of the steel structure.

There are no particular limitations on the steel structure. Examples of steel structures include steel bridges, steel plants, steel buildings, steel pipes, steel materials, steel plates, and other steel structures.

There are no particular limitations on the application method, and application can be done using a spray, brush, roller, or the like, as appropriate, taking into consideration the characteristics of the film-forming salt-reducing agent, which is the application liquid, the size, shape, and installation location of the steel structure, etc. If the film thickness is not uniform, it may tear when peeled off, so it is preferable to apply it as uniformly as possible. When using a spray, a wide area can be applied in a short time compared to manual work using a brush or roller. The spray may be an air spray or an airless spray. The air spray may be a handy air spray or a non-handy air spray. The airless spray may also be a handy airless spray or a non-handy airless spray. It is easier to fill the application liquid with a non-handy airless spray than with a handy airless spray, so from this point of view, a non-handy airless spray is more suitable for applying a wide area than a handy airless spray.

The coating amount is an amount that allows the resulting film to have a desired thickness. There is no particular limitation on the thickness of the film. From the viewpoint of easy peeling of the film after drying, the wet film thickness is preferably 500 to 1500 μm, more preferably 800 to 1200 μm, and the dry film thickness is preferably 10 to 300 μm, more preferably 50 to 200 μm, and particularly preferably 75 to 150 μm. If the film thickness is not uniform, it may cause the film to tear when peeled off, so the film thickness is preferably uniform. In addition, the coating weight is preferably 0.5 to 1.5 kg/m ² , more preferably 0.8 to 1.2 kg/m ^2. It is easy to manage the coating amount by the wet film thickness and the coating weight. In addition, when the time from coating to peeling of the film is relatively short, such as about 24 hours, the film is not required to have a particularly high strength.

There are no particular limitations on the method of drying; it may simply be left to dry, or a fan may be used to speed up the drying. In the case of leaving to dry, the drying should be carried out for a period of time that allows the film to dry sufficiently and be easily peeled off. The specific time of leaving to dry varies depending on the season and weather. For example, in winter, a longer time of leaving to dry is required. From the viewpoint of the number of days required for the process, it is not preferable to leave to dry for too long. Taking these factors into consideration, the time of leaving to dry is generally preferably 10 to 48 hours, more preferably 15 to 35 hours, and particularly preferably 20 to 30 hours. It is also preferable to leave to dry at a temperature of 5°C or higher and a humidity of 85% or lower. Note that "humidity" here means "relative humidity", and the same applies below.

It was verified in several test environments whether the film could be peeled off within 24 hours after application. Specifically, a salt content reducing agent having the same composition as Sample 5 used in the examples described later was applied to a blasted steel test piece (size: 200 x 100 x 6 mm, material: SM400A) with a brush at a coating amount of 1.0 kg/ ^m2 , dried using an explosion-proof thermostatic and hygroscopic chamber PR-4KPH (manufactured by ESPEC Corporation, Japan), and whether the film could be peeled off within 24 hours after application was verified under several temperature and humidity conditions. The verification results are as follows. When the temperature was 10°C and the humidity was 85%, the film could not be peeled off within 24 hours after application. On the other hand, when the temperature was 10° C. and the humidity was 50%, when the temperature was 20° C. and the humidity was 85%, when the temperature was 20° C. and the humidity was 50%, when the temperature was 30° C. and the humidity was 85%, and when the temperature was 30° C. and the humidity was 50%, the film was able to be peeled off within 24 hours after application.

There are no particular limitations on the method of peeling. The film can be peeled off by hand without using a power tool. When peeling off by hand without using a power tool, peel off the film from the edge and pull the film with a constant force to remove it. If the edge of the film is difficult to peel off, insert a simple tool (for example, a tool with a thin blade such as a cutter or scraper) into the interface between the steel base material and the film, lift it up, and then peel it off.

The method of the present invention can be preferably used when the steel structure has undergone surface preparation in a repainting job.

There are no particular limitations on the surface preparation for repainting work. Scraping may be type 1 scraping, type 2 scraping, type 3 scraping, or type 4 scraping, and type 3 scraping may be type 3A, type 3B, or type 3C. In the present invention, surface preparation is preferably by type 1 scraping (the highest degree of surface preparation), but it is acceptable for there to be many areas of the old coating film that are not removed, as with type 3 and type 4 scraping.

There are no limitations on the method of surface preparation, and conventional surface preparation methods, such as blasting or the use of tools such as grinders with rotating grindstones or grinding disks attached to an electric rotary drive, or disk grinders, can be used. There are also no particular limitations on the amount of salt remaining on the surface of the steel structure after surface preparation.

When surface preparation is performed by type 1 scraping, all of the old coating film and all of the rust on the steel structure surface are removed. The amount of sodium chloride remaining on the steel structure surface after surface preparation by type 1 scraping may exceed 50 mg/ ^m2 or may be 50 mg/m2 or ^less . When surface preparation is performed by type 1 scraping and the amount of sodium chloride remaining on the steel structure surface exceeds 50 mg/ ^m2 , it is preferable to apply the present invention to reduce the amount of sodium chloride remaining on the steel structure surface to 50 mg/ ^m2 or less. The above-mentioned "Handbook for Steel Highway Bridge Corrosion Prevention" and other publications recommend reducing the amount of sodium chloride remaining on the steel structure surface to 50 mg/ ^m2 or less before applying a new paint coat. Note that even when the amount of sodium chloride remaining on the steel structure surface after surface preparation by type 1 scraping is 50 mg/ ^m2 or less, the present invention can be applied to further reduce the amount of sodium chloride.

After reducing the amount of salt remaining on the surface of the steel structure, a new coating film is applied to the steel structure. There are no particular limitations on the coating composition used for the new coating, the type of coating film obtained, or the coating method, and these may be determined appropriately taking into account factors such as the period for which the coating film will be maintained.

The present invention will be described more specifically below with reference to Examples 1 to 3, Comparative Examples 1 and 2, and Reference Examples 1 to 3 (hereinafter, these are often collectively referred to as "Examples, etc.").
As described later, Example 1 , Comparative Examples 1 and 2 , and Reference Example 1 were carried out in parallel over a period of three days, and Examples 2 and 3 and Reference Examples 2 and 3 were also carried out in parallel over a period of two days. Examples 1 to 3, Comparative Examples 1 and 2, and Reference Example 3 were carried out in parallel with the salt content reduction agent, and Reference Examples 1 and 2 were carried out in parallel with the salt content reduction by water washing treatment. The examples and the like do not limit the scope of the present invention.

The test steel materials and sample film-forming salt-reducing agents used in the examples are as follows:

Test steels (test steels 1 to 4) used in Example 1 , Comparative Examples 1 and 2, and Reference Example 1
Test steels 1 to 4 are waste materials of corroded lower cross struts that were removed from a bridge (under the jurisdiction of the Tosa National Highway Office of the Ministry of Land, Infrastructure, Transport and Tourism) along the coast of Kochi Prefecture due to replacement work of components caused by corrosion. This bridge was erected in 1970 and repainted (with polyurethane paint) in 1999. The corroded lower cross struts were removed in 2013 (43 years after erection) and transported to the Kamogawa Exposure Test Site of the Civil Engineering Research Center (Kamogawa City, Chiba Prefecture) on October 29, 2013, where they were exposed, and were provided to the applicant this time. The horizontal dimensions of the flange undersides of test steels 1 to 4 are 0.17 m x 1.2 m. For an overview of the Kamogawa Exposure Test Site of the Civil Engineering Research Center and the test steels that are waste materials of corroded lower cross struts, please refer to the technical journal "Civil Engineering Technical Information" 57-1 (2015) pp. This is explained in 60-63.

Test steel materials 1 to 4 are used in Example 1 , Comparative Examples 1 and 2, and Reference Example 1, respectively.

Test steel material (test steel material 5) used in Examples 2 and 3 and Reference Example 2
Test steel material 5 is a scrap material that was used as the main girder of a bridge built in an area free from salt damage, and was removed for replacement work and stored at the Inagawa Warehouse (Inagawa-cho, Kawabe-gun, Hyogo Prefecture) of Japan Far East Metallicon Industries Co., Ltd. The Inagawa Warehouse is located in an area free from salt damage. Test steel material 5 was provided to the applicant this time. The dimensions of the vertical surface of test steel material 5, which corresponds to the main girder web surface, are 1.17 m long and 0.92 m wide. Hereinafter, this vertical surface will be referred to simply as the "vertical surface of test steel material 5", or even more simply as the "vertical surface".

First, a high-concentration calcium chloride aqueous solution was applied evenly to both vertical surfaces (i.e., the front and rear surfaces) of the test steel 5 on weekdays (every day except Saturdays, Sundays, and other holidays) for one month using a roller twice each, so that calcium chloride was fixed on both vertical surfaces. Furthermore, from the salt content reduction process stage described below, a vertical partition 0.02 m wide was provided in the center of both surfaces, and each surface was divided into two parts, a left part and a right part, for a total of four sections (each section has a dimension of 1.17 m length x 0.45 m width). Hereinafter, the front and rear vertical surfaces of the test steel 5 are often referred to simply as the "front" and "rear", respectively, and the left section of the front, the right section of the front, the left section of the rear, and the right section of the rear are often referred to as the "front A", "front B", "rear A" and "rear B", respectively.

The front surface A, the front surface B, the rear surface A and the rear surface B are used in Example 2 , Example 3 , Reference Example 2 and Reference Example 3 , respectively.

Samples of film-forming salt-reducing agents used in Example 1 and Comparative Examples 1 and 2 (Samples 1 to 3)
The components and amounts of Samples 1 to 3 are shown in Table 1.

Sumikaflex 455HQ and Sumikaflex 456HQ in Table 1 contain moisture, as described below. Therefore, the total amount of "film-forming resin" listed in item (A) does not represent the total amount of resin in Sample 1 or Sample 2, and the amount of "moisture" listed in item (B) does not represent the total amount of moisture in Sample 1 or Sample 2. The resin amount and moisture amount of Sample 1 are approximately 26% by mass and 64% by mass, respectively. The resin amount and moisture amount of Sample 2 are approximately 28% by mass and 53% by mass, respectively.

The details of the components shown in Table 1 are as follows:

JC-25 (manufactured by Japan Vinyl Acetate & Poval Co., Ltd.)
Polyvinyl alcohol resin polymerization degree: 2500
Saponification degree: 99 mol%

Sumikaflex 455HQ (manufactured by Sumika Chemtex Co., Ltd., Japan)
Ethylene-vinyl acetate copolymer emulsion non-volatile content: 54 to 57% by mass (moisture: 46 to 43% by mass)
Glass transition temperature (Tg): 0 ° C.

Sumikaflex 456HQ (manufactured by Sumika Chemtex Co., Ltd., Japan)
Ethylene-vinyl acetate copolymer emulsion non-volatile content: 54 to 56% by mass (moisture: 46 to 44% by mass)
Glass transition temperature (Tg): 0 ° C.

IONET T-80V (manufactured by Sanyo Chemical Industries, Ltd., Japan)
A surfactant whose main component is polyoxyethylene sorbitan fatty acid ester

hiMetolose 90SH-15000 (manufactured by Shin-Etsu Chemical Co., Ltd., Japan)
Hydroxypropyl methylcellulose (glyoxal treated)

Aron B-500 (manufactured by Toagosei Co., Ltd., Japan)
Carboxylic acid copolymer emulsion solid content: 36±1% by mass

Kiresuto Light W-510 (manufactured by Kiresuto Co., Ltd., Japan)
Organic acid amine salts

Sanhibitor No. 50 (manufactured by Sanyo Chemical Industries, Ltd., Japan)
Amine-based nonionic surfactants

DIPA (85%)
Diisopropanolamine: 85% by mass
Moisture: 15% by weight

Samples used in Examples 2 and 3 and Reference Example 3 (Samples 4 and 5)
The components and amounts of Samples 4-5 are shown in Table 2.

Sumikaflex 400HQ and Sumikaflex 408HQE in Table 2 contain moisture, as described below. Therefore, the total amount of "film-forming resin" listed in item (A) does not represent the total amount of resin in Sample 4 or Sample 5, and the amount of "moisture" listed in item (B) does not represent the total amount of moisture in Sample 4 or Sample 5. The resin amount and moisture amount of Sample 4 are approximately 24% by mass and 71% by mass, respectively. The resin amount and moisture amount of Sample 5 are also approximately 24% by mass and 71% by mass, respectively.

The details of the components shown in Table 2 are as follows:

JF-05 (manufactured by Japan Vinyl Acetate & Poval Co., Ltd.)
Polyvinyl alcohol resin polymerization degree: 500
Saponification degree: 98 to 99 mol%

Sumikaflex 400HQ (manufactured by Sumika Chemtex Co., Ltd., Japan)
Ethylene-vinyl acetate copolymer emulsion non-volatile content: 54 to 56% by mass (moisture: 46 to 44% by mass)
Glass transition temperature (Tg): 0 ° C.

Sumikaflex 408HQE (manufactured by Sumika Chemtex Japan Co., Ltd.)
Ethylene-vinyl acetate copolymer emulsion non-volatile content: 49 to 51% by mass (moisture: 51 to 49% by mass)
Glass transition temperature (Tg): -30°C

IONET T-80V (manufactured by Sanyo Chemical Industries, Ltd., Japan)
A surfactant whose main component is polyoxyethylene sorbitan fatty acid ester

Laponite EP (BYK-Chemie, Germany)
Synthetic Hectorite

Kiresuto Light W-510 (manufactured by Kiresuto Co., Ltd., Japan)
Organic acid amine salts

MMEA amine 2-methylaminoethanol

BYK-014 (BYK-Chemie, Germany)
Antifoaming agent that is a mixture of foam-busting polymer and hydrophobic particles

The method of applying the sample to the test steel material and the method of washing the test steel material in the examples are as follows:

Method of sample application in Example 1 and Comparative Examples 1 and 2 Sample application was performed using a brush on the horizontal surface corresponding to the underside of the flange of test steel materials 1 to 3. However, as described above, the dimensions of the horizontal surface were 0.17m x 1.2m, but since there were holes on both sides of the test steel material, application was performed on the area excluding both sides (0.17m x 1.0m), resulting in an application area of ^0.17m2 . The application amount was 1.0kg/ ^m2 for each.

Method of sample application in Examples 1 and 3 and Reference Example 3 Sample application was performed using a spray on the entire surfaces (1.17 m long x 0.45 m wide) of the front surface A, front surface B, and rear surface B, respectively, with the vertical surface (1.17 m long x 0.92 m wide) of the test steel material 5 in an upright position. The spray used was a handy airless spray (Ultramax Cordless) (manufactured by GRACO, USA) for the front surface A and rear surface B, and a high-pressure airless sprayer (Ecopon series) (manufactured by Asahi Sanac Co., Japan) for the front surface B. LP525 (manufactured by GRACO, USA) was used as the nozzle tip for the high-pressure airless sprayer. The application amount was 1.0 kg/m ² for each.

Method of Water Rinsing in Reference Example 1 Water rinsing was performed using a handy airless spray (Ultramax Cordless) (manufactured by GRACO, USA) on the horizontal surface corresponding to the lower surface of the flange of the test steel material 4. However, as in the case of painting, the parts rinsed with water were the parts excluding both sides of the test steel material, so the rinsed area was 0.17 ^m2 . The amount of water used per ^m2 of rinsed area was 7 L, so the total amount of water was about 1.2 L.

The reason for setting the amount of water used per square ^meter of washing area at 7L is as follows. In a lecture entitled "Experiments for Removing Salt Adhering to Bridges" (56th Annual Academic Lecture Meeting of the Japan Society of Civil Engineers, October 2001, pp.340-341), an experiment was conducted to remove salt adhering to the surface of a steel bridge, and it was concluded that "in order to satisfy the allowable amount of salt adhering during repair, the minimum amount of water required is sufficient, and an appropriate amount of washing water is 6 to 8 liters/ ^m2 ." Therefore, the amount of water used per square ^meter of washing area was set at 7L, taking the middle point between the lower limit (6L) and the upper limit (8L) of the range of 6 to 8L.

Method of Water Rinsing in Reference Example 2 Water rinsing was performed using the above-mentioned handy airless sprayer on the rear surface A of the vertical surface of the test steel material 5 (a steel plate measuring 1.17 m long x 0.92 m wide) in an upright position. The amount of water used per square meter of water-rinsed area was reduced from that in Reference Example 1, and set to 1 L (i.e., 1.0 kg/ ^m2 ) in accordance with the sample application amount in Examples 2 and 3 and Reference Example 3 .

The measurements taken in the examples are as follows:

Measurements using a surface salinity meter in Example 1 , Comparative Examples 1 and 2, and Reference Example 1 A portable surface salinity meter (SSM-21P) manufactured by DKK Toa Corporation of Japan was used as the surface salinity meter.

The amount of salt remaining on the surface of test steels 1 to 4 after the blast treatment described below, and the amount of salt remaining on the surface of test steels 1 to 4 after the salt reduction treatment process described below, were measured using a surface salinity meter. Since the main component of the salt contained on the surface of test steels 1 to 4 is sodium chloride, the measured salt concentration, which converts the measured electrical conductivity value into the concentration of sodium chloride, was used as the amount of salt.

Measurements were taken at five locations for all test steels (test steels 1 to 4). Specifically, looking at the test steels longitudinally from left to right, measurements were taken at five locations: left, left center, center, right center, and right (one end of the test steel is considered the left end, and the other end the right end, and from the left end to the right end, the locations are left, left center, center, right center, and right). However, due to the nature of the surface salinity meter, there is a possibility that the measurement water will leak from the surface salinity meter, and since leakage will have a significant effect on the measurement values, if leakage occurs, the measurement value at that location is not counted.

Additionally, the average of the counted measurements was calculated.

Measurements using a surface salinity meter in Examples 2 and 3 and Reference Examples 2 and 3 The above-mentioned surface salinity meter was used as the surface salinity meter.

The amount of salt remaining on the surface of the test steel 5 after the blast treatment described below, and the amount of salt remaining on the surface of the test steel 5 after the salt reduction treatment process described below were measured using a surface salinity meter. Since the salt contained on the surface of the test steel 5 was essentially calcium chloride only, the measured salt concentration, which converts the measured electrical conductivity value into the concentration of water-soluble salt based on the IMO PSPC, was used as the amount of salt.

Measurements were taken at multiple locations as follows. For measurements after blasting (at this point, the front and rear of test steel 5 had not yet been divided into two), nine locations on each of the front and rear were selected as measurement locations. For measurements after the salt reduction treatment process (at this point, the front was divided into front A and front B, and the rear was divided into rear A and rear), five locations each on front A, front B, and rear A were selected as measurement locations, and six locations on rear B were selected as measurement locations. However, due to the nature of the surface salinity meter, there is a possibility that the measurement water will leak from the surface salinity meter, and since leakage will have a significant effect on the measurement values, if leakage occurs, the measurement value at that location was not counted.

Additionally, the average of the counted measurements was calculated.

Measurement by Ion Chromatography in Examples 1 to 3 , Comparative Examples 1 and 2, and Reference Examples 1 to 3 As an ion chromatograph, Dionex ICS-1100 manufactured by Thermo Fisher Scientific, Inc., USA, was used.

The liquid used for the surface salinity meter measurements (only those for which the measured values were counted ⁾ was collected and used as a sample in an ion chromatograph to measure the ^amounts of chloride ions ( ^Cl- ), nitrite ions ( _NO2- ⁾ , nitrate ions ( _NO3- ), and sulfate ions ( _SO42- ), and the total amount of these four anions was calculated. Note that because the measurement principles of ion chromatographs and surface salinity meter differ and measurement errors are possible, the amount of chloride ions ( ^Cl- ) obtained by measurement with the ion chromatograph does not necessarily correlate with the amount of salt (amount of sodium chloride or calcium chloride) obtained by measurement with the surface salinity meter.

In addition, the average values of the measurements were calculated.

Example 1 , Comparative Examples 1 and 2, and Reference Example 1
Salt content reduction experiments were conducted in parallel on test steels 1 to 4 from the first to third days as follows. As described below, the experiments using test steels 1 to 3 are Example 1 , Comparative Examples 1 and 2, respectively , and the experiment using test steel 4 is Reference Example 1. Reference Example 1 is an experimental example of salt content reduction using a conventional high-pressure water washing method, and was conducted to serve as a reference for evaluating the salt content reduction effect of the present invention.

In the afternoon of the first day, test steels 1 to 4 were blasted (equivalent to type 1 scraping). In the morning of the second day, the amount of salt on the surface of test steels 1 to 4 after blasting was measured using a surface salt meter. The liquid used for the measurement with the surface salt meter was also collected and measured later using an ion chromatograph.

After the above-mentioned surface salinity measurements were performed on test steels 1 to 3 using a surface salinity meter, samples 1 to 3 were applied to each steel in the morning of the second day and left to dry for 24 hours to form a film, and the film was peeled off by hand in the morning of the third day. In the afternoon of the third day, the amount of salt on the surface of test steels 1 to 3 after the film was peeled off was measured using a surface salinity meter. The liquid used for the measurements using the surface salinity meter was also collected and measured using an ion chromatograph at a later date.

After the above-mentioned surface salinity measurements were performed using a surface salinity meter on test steel 4, it was washed with water in the afternoon of the second day. In the afternoon of the third day, the amount of salt on the surface of test steel 4 after washing with water was measured using a surface salinity meter. The liquid used for the measurements using the surface salinity meter was also collected and was measured using an ion chromatograph at a later date.

On the second day, the temperature was 27.2°C and the humidity was 50%. On the third day, the temperature was 28.1°C and the humidity was 45%.

The experiments using test steels 1 to 3 (salt reduction was performed using samples 1 to 3, respectively) were designated Example 1 , Comparative Examples 1 and 2 , respectively, and the experiment using test steel 4 (salt reduction was performed by water washing treatment) was designated Reference Example 1. In Example 1 and Comparative Examples 1 and 2 , the process from application of the sample to peeling and removal of the film is referred to as the salt reduction treatment process, and in Reference Example 1 (water washing experiment example), the water washing process is referred to as the salt reduction treatment process.

Table 3 shows the results of measurements using a surface salinity meter after blasting (only those for which measurements were counted), and the results of measurements using an ion chromatograph conducted at a later date on the measurement liquid used in the measurements (only those for which measurements were counted using the surface salinity meter). Table 4 also shows the average values of the measurements.

Table 5 shows the results of measurements using a surface salinity meter after the salt reduction process (only those for which measurements were counted), and the results of measurements using an ion chromatograph conducted at a later date on the measurement solutions used in the measurements (only those for which measurements were counted using the surface salinity meter). Table 6 also shows the average values of the measurements.

Table 7 shows the salt removal rate calculated based on the measurements taken with the surface salinity meter. Table 7 also shows the removal rate of ^each of the four types of anions (i.e., chloride ion ( ^Cl- ), nitrite ion ( _NO2- ), nitrate ion ( ^NO3- ), and sulfate ion ( _SO42- )) calculated based on measurements taken with an ion chromatograph, as well as the total removal rate of these four types of anions. The removal rate indicates how much ^the amount of salt or anions has been reduced by carrying out _the salt reduction treatment process, and was calculated using the following formula.

Removal rate (%)
= (measurement value after blasting treatment - measurement value after salt reduction treatment process) ÷ measurement value after blasting treatment × 100

Table 8 shows the overall evaluation for each of Example 1 , Comparative Examples 1 and 2 , and Reference Example 1. This overall evaluation includes evaluation of film formation, evaluation of manual peelability, and evaluation of salt reduction effect. However, in the case of Reference Example 1, since no film is formed, there is no evaluation of manual peelability.

As can be seen from Table 8, the evaluation of film formation, evaluation of manual peelability, and salt content reduction effect all reached practical levels in the cases of Example 1 and Comparative Examples 1 and 2. Therefore, the film formed from the film-forming salt content reducing agent of the present invention reduces the salt content adhering to the surface of the steel sheet, and the film can be peeled off and removed by hand without using a power tool.

The evaluation criteria shown in Table 8 are as follows:

Evaluation of film formation A liquid (sample film-forming salt-reducing agent in the case of Example 1 , Comparative Examples 1 and 2 , and water in the case of the Reference Example) was applied to the test steel material, and whether a film could be formed was evaluated together with the degree of dripping. The specific evaluation criteria were as follows:

⊚: No dripping, film can be formed.
Good: There is a small amount of dripping (some of the liquid causes an avalanche), but a film can be formed.
△: There is considerable dripping (some of the liquid drips from the steel material onto the floor), but a film can be formed.
×: Dripping was so severe that a film could not be formed.

Evaluation of peelability by hand Whether or not the film after drying could be peeled off by hand from the surface of the test steel material was evaluated together with the ease of peeling. The specific evaluation criteria are as follows:

: Very easy to peel off.
◯: Easy to peel off, but since there are weak parts of the film, it cannot be said that it is very easy to peel off.
Δ: Peelable, but not peelable as a unit, so not easily peelable.
×: Cannot be peeled off.

Evaluation of Salt Reduction Effect The salt reduction effect was evaluated based on the salt removal rate (A) measured by a surface salt content meter and the chloride ion removal rate (B) measured by an ion chromatograph. The specific evaluation criteria are as follows:

⊚: Particularly significant effect (both A and B exceed 70%).
○: There is a significant effect (either A or B exceeds 70%).
△: Somewhat effective (both A and B are below 70%).

Examples 2 and 3 and Reference Examples 2 and 3
From the first to the second day, salt reduction experiments were conducted in parallel on the front surface (divided into front surface A and front surface B after blasting) and rear surface (divided into rear surface A and rear surface B after blasting) of test steel material 5 as follows. As described below, the experiments using front surface A, front surface B, rear surface A and rear surface B are Example 2 , Example 3 , Reference Examples 2 and 3 , respectively. Reference Example 2 is an example of a salt reduction experiment using a conventional high-pressure water washing method, and was conducted to serve as a reference for evaluating the salt reduction effect of the present invention.

At 11:00 am on the first day, the front and rear surfaces were blasted (equivalent to type 1 scraping). After blasting, the front surface was divided into front A and front B, and the rear surface was divided into rear A and rear B. At 1:00 pm on the first day, the surface salt content of front A, front B, rear A, and rear B after blasting was measured using a surface salt meter. The liquid used for the measurements with the surface salt meter was also collected and measured using an ion chromatograph at a later date.

For the front surface A, the front surface B and the rear surface B, the above-mentioned surface salt content measurement was performed using a surface salt content meter, and then at 4:00 p.m. on the first day, Sample 4, Sample 5 and Sample 5 were applied, respectively (thus, Sample 5 was applied to the front surface B and the rear surface B), and the film was formed by leaving it to dry. For the front surface A and the front surface B, the formed film was peeled off and removed by hand at 11:00 a.m. on the second day (thus, the front surface A and the front surface B were left to dry for 19 hours), and the amount of salt on the surface after the film was peeled off and removed was measured using a surface salt content meter at 11:30 a.m. on the second day. For the rear surface B, the formed film was peeled off and removed by blasting (equivalent to a type of scraping) at 1:00 p.m. on the second day (thus, the rear surface B was left to dry for 21 hours), and the amount of salt on the surface after the film was peeled off and removed was measured using a surface salt content meter at 3:00 p.m. on the second day. The liquid used for the measurement with the surface salinity meter was collected for each of the front surface A, the front surface B, and the rear surface B, and was later measured with an ion chromatograph. In the experiment using the rear surface B (i.e., Reference Example 3 ), the film was peeled off and removed by blasting, so two blasting treatments were performed, including the first blasting treatment, but in order to distinguish between these two blasting treatments, the first blasting treatment is simply referred to as "blasting treatment" and the second blasting treatment (i.e., the blasting treatment for peeling off and removing the film) is referred to as "further blasting treatment".

The wet and dry film thicknesses were measured for the films formed on the front surface A, front surface B, and rear surface B. The wet film thickness was measured using a wet gauge, and the dry film thickness was measured using a film thickness gauge, at three locations each. As accurate measurements could not be obtained for the wet film thickness, measurements were taken at three locations to obtain an approximate value. The dry film thickness was the average of the measurements at the three locations. For the film formed on the front surface A, the wet film thickness was 1000 μm and the dry film thickness was 169 μm. For the film formed on the front surface B, the wet film thickness was 800-1300 μm and the dry film thickness was 215 μm. For the film formed on the rear surface B, the wet film thickness was 800-900 μm and the dry film thickness was 183 μm.

After the above-mentioned surface salinity measurement was performed using a surface salinity meter on rear surface A, it was washed with water at 2:00 p.m. on the first day. At 11:30 a.m. on the second day, the amount of salt on the surface after the washing process was measured using the surface salinity meter. The liquid used for the measurement using the surface salinity meter was also collected and measured using an ion chromatograph at a later date.

On the first day, the temperature was 29°C and the humidity was 50%. On the second day, the temperature was 26°C and the humidity was 43%.

The experiments using front surface A, front surface B, and rear surface B (salt reduction was performed using sample 4, sample 5, and sample 5, respectively) were set as Examples 2 and 3 and Reference Example 3 , respectively, and the experiment using rear surface A (salt reduction was performed by water washing treatment) was set as Reference Example 2. In Examples 2 and 3 and Reference Example 3 , the process from application of the sample to peeling and removal of the film is referred to as the salt reduction treatment process, and in Reference Example 2 (water washing experiment example), the water washing process is referred to as the salt reduction treatment process.

Table 9 shows the average values measured by the surface salinity meter after blasting, and the average values measured by ion chromatography at a later date after recovering the measurement solution used in the measurement.

Table 10 shows the average values measured by the surface salinity meter after the salt reduction treatment process, and the average values measured by ion chromatography at a later date after recovering the measurement solution used in the measurement.

Table 11 shows the salt removal rate calculated based on the measurements taken with the surface salinity meter. Table 11 also shows the removal rate of ^each of the four types of anions (i.e., chloride ion ( ^Cl- ), nitrite ion ( _NO2- ), nitrate ion ( ^NO3- ), and sulfate ion ( _SO42- )) calculated based on measurements taken with _an ion chromatograph, as well as the total removal rate of these four types of anions. The removal rate indicates how much the amount of ^salt or the amount of anions has been reduced by carrying out the salt reduction treatment process, and was calculated using the same formula as in the above-mentioned Example 1 , Comparative Examples 1 and 2, and Reference Examples 1 and 2 .

Table 12 shows the overall evaluation for each of Examples 2 and 3 and Reference Examples 2 and 3. This overall evaluation includes evaluation of film formation, evaluation of manual peelability, and evaluation of salt reduction effect, and the criteria for these evaluations are the same as those for the above-mentioned Examples 1 to 3 and Reference Example 1. However, in the case of Example 6, peeling and removal by hand is not performed, and in the case of Reference Example 2, no film is formed, so there is no evaluation of manual peelability.

As can be seen from Table 12, in the cases of Examples 2 and 3 , the evaluation of film formation, evaluation of manual peelability, and salt reduction effect all reached practical levels. Therefore, the film formed from the film-forming salt-reducing agent of the present invention reduces the salt adhering to the surface of the steel sheet, and the film can be peeled off and removed by hand without using a power tool.

The film-forming salt-reducing agent of the present invention can eliminate all of the problems associated with conventional high-pressure water washing and power tool methods, and is an excellent, simple, and economical method of reducing salt content, without causing any environmental impact. It can reduce the amount of salt adhering to the surface of steel structures, such as steel bridges, steel plants, steel buildings, steel pipes, steel materials, steel plates, and other steel structures.

Claims (3)

A chloride reducer for the surface of a steel structure that has been subjected to surface preparation using a type 1 or type 2 scraper is applied and dried to form a film that absorbs the chlorides remaining on the surface of the steel structure, and the film is then peeled off together with the chlorides to remove the chlorides remaining on the surface. The chloride reducer for the surface of a steel structure is a film-forming chloride reducer that is made of a viscous aqueous solution consisting of a mixture of polyvinyl alcohol and ethylene-vinyl acetate copolymer and water, and contains 24 to 26 mass % of the total mass of the chloride reducer. A method for reducing the chloride content on the surface of a steel structure by applying a coating material to the surface of the steel structure that has been subjected to surface preparation using a type 1 or type 2 scraper , and drying the coating material to form a film that incorporates the chlorides remaining on the surface of the steel structure, and then peeling off the film together with the chlorides , the method comprising the steps of:
(1) The film-forming chloride reducer for the surface of a steel structure as described in claim 1 is applied to the surface of the steel structure and dried to form a film that absorbs the chlorides remaining on the surface of the steel structure.
(2) The film is peeled off from the surface of the steel structure together with the chlorides . The method according to claim 2, characterized in that the chloride is at least one selected from the group consisting of sodium chloride, potassium chloride, calcium chloride and magnesium chloride.