JP7168176B1 - Method for removing chlorides from surface-conditioned steel structures - Google Patents

Abstract

A method for removing chlorides from a surface-conditioned steel structure capable of effectively removing even chlorides that have permeated the surface layer of the steel structure is provided. A water-based wetting agent containing water and a water-soluble polymer is applied to the surface of a steel structure having chlorides remaining on the surface layer after surface preparation, and the surface is undried. Leave for 4 hours or longer. As a result, chloride ions generated by the dissolution of chloride are eluted into the aqueous wetting agent. The aqueous wetting agent is then removed. The aqueous wetting agent preferably further contains an anion exchange layered pigment. [Selection drawing] Fig. 1

Description

TECHNICAL FIELD The present invention relates to a method for removing chlorides from a surface-conditioned steel structure, which removes chlorides remaining after surface preparation when repainting a protective coating film on the steel structure.

BACKGROUND ART Conventionally, steel structures such as bridges and steel towers are surface-protected with a protective coating film in order to prevent the generation of rust and maintain strength. However, the protective coating film also deteriorates over time due to exposure to wind, rain, ultraviolet rays, etc., and the protective function (anticorrosion function) of the steel structure, which is the object to be coated, gradually declines. For this reason, maintenance work is periodically performed to remove the existing deteriorated protective coating and replace it with a new protective coating. At that time, the existing protective coating that has deteriorated is scraped off, and the rust layer caused by corrosion is removed by physical scraping using a power tool, etc., to form a surface suitable for repainting. is carried out. However, rust removal is likely to be insufficient at locations where a strong adherent rust layer adheres to a steel structure is formed, and at locations where base preparation is difficult such as narrow areas and uneven areas. If repainting is carried out in this state, corrosion progresses at an early stage under the newly repainted protective coating, causing blistering and rusting of the protective coating, and the original anti-corrosion function of the protective coating is lost. I will not be able to do it.

Above all, under conditions of severe corrosive environments such as coastal areas, a large amount of airborne chloride containing sodium chloride and magnesium chloride as main components adheres to steel structures. Moreover, when calcium chloride or sodium chloride is sprayed as a road surface anti-freezing agent in the cold season, it adheres to surrounding steel structures as salt water, not only in coastal areas. These chlorides are highly soluble in water, so rain and snow are trapped inside deteriorated protective coatings and brittle rust (layered peeling rust that does not adhere to steel structures and can be removed relatively easily). It penetrates with water as a medium, and further accumulates in the interior of the adherent rust layer existing in the lower layer and in the interface with the steel structure. Chloride ions produced by dissolving these chlorides in water become substances that promote corrosion of steel structures. Therefore, when repainting is carried out, if these are not sufficiently removed together with the rust, the rust will reappear in a much shorter period of time than expected. In particular, when a strong adhering rust layer is formed on the surface of a corroded steel structure, it takes a considerable amount of time and effort to completely remove the adhering rust layer even with a power tool. For this reason, even after surface preparation, chlorides may remain inside the remaining adherent rust layer and at the interface with the steel structure (hereinafter, both regions are referred to as the "surface layer"). .

On the other hand, according to the blasting method, which has the highest precision as a surface preparation method among physical keren, it is relatively easy to remove the adhered rust layer, but even so, some chlorides remain on the surface of the blasted steel structure. It is contained and difficult to completely remove. In addition, recently, Non-Patent Document 1 has proposed a method using laser or induction heating (IH) as a substrate conditioning method with less environmental load, and it is reported that this also reduces the residual amount of chloride to some extent. ing. However, the method of Non-Patent Document 1 is not a method for the direct purpose of removing chlorides, and the reduction in the residual amount of chlorides is only a secondary effect, and the effect is the general effect using a power tool. There is no big difference from physical keren.

In addition, the Steel Highway Bridge Corrosion Prevention Handbook (Japan Road Association) describes a measurement example in which the average amount of salt content (NaCl) deposited on a painted steel bridge in a coastal area is several hundred mg/m ² . In addition, if salt content of 50 mg/m ² or more adheres to the old coating film (existing protective coating film), defects in the coating film tend to occur early after repainting. Washing with water is said to be effective. However, it does not refer to the amount of salt remaining on the surface layer of the steel structure after removing the brittle rust including the old coating film by surface preparation and the method of removing it. On the other hand, in the case of weathering steel that can be used without coating, it is described that the amount of salt adhering to the dense rust layer on a bridge that has been built for a long time is about 50 to 1000 mg/m ² . When repairing by painting due to delamination rust, after removing delamination rust by base preparation, the amount of adhering salt should be reduced to 50 mg/m ² or less by washing with water or the like.

Conventionally, the chlorides remaining after surface preparation have been removed by washing with water or the like. However, environmental pollution due to harmful substances contained in the old coating film has become a problem, and it is now difficult to implement washing with water. Therefore, it is desired to develop a construction method that can efficiently and safely remove the chloride remaining in the steel structure even after surface preparation, instead of washing with water.

Techniques for that purpose are disclosed in, for example, Patent Documents 1 to 4 below. In Patent Document 1, as a coating method using a salt remover, when applying an intermediate coat to a steel structure that has been factory-coated up to the undercoat and brought into the site, the undercoated surface is exposed to a salty environment during installation for a long period of time. If the amount of salt above the specified value adheres to the undercoated surface, spray a salt remover containing an alkanolamine and hydroxycarboxylic acid mixture with a high pressure washer on the undercoated surface, and then apply the intermediate coat. In addition, if the middle coat is contaminated with airborne salt during the curing period and the amount of salt above the specified value adheres, a top coat is applied after spraying the salt remover in the same manner. In addition, when painting areas submerged at high tide using the ebb and flow of the tide, such as painting work on pier piers, a salt remover containing a mixture of alkanolamine and hydroxycarboxylic acid is sprayed with a high-pressure washer to prepare the surface. A method is disclosed in which a post-undercoat is applied, and a desalting agent is sprayed in the same manner before each coating after the undercoat step to remove salt from the surface to be coated. According to this, it is said that the salt removal effect is brought about without damaging the surface to be coated due to the action of scavenging chlorine ions due to the complex formation of the mixture of alkanolamine and hydroxycarboxylic acid.

In Patent Document 2, for repair or paint repair, the steel structure surface of the steel structure to be processed is ground, polished, or subjected to ground treatment such as shot blasting to make the base exposed area ratio 60% or more. and then a step B of applying an aqueous solution of sodium carbonate having a predetermined concentration. The sodium carbonate aqueous solution as the pretreatment liquid penetrates into the fixed rust remaining on the surface preparation surface and passivates the rust/steel interface to stop or suppress corrosion. The surface chemical action of the rust material exchanges the chloride ions incorporated in the adhering rust to carbonate ions, thereby desorbing the salt from the corrosion interface. When this pre-treatment liquid is applied, the remaining fixed rust turns dark brown, and even if it is in a state where moisture adheres, it does not generate back rust. In other words, the corrosion active points are dead. Since the pretreatment liquid is an aqueous solution, sodium carbonate powder crystallizes when dried. After that, the crystallized powder should be removed with a nylon cup wire brush or the like attached to an electric rotating tool, and the next painting process should be started.

Patent Document 3 discloses a surface treatment method for a steel structure that is performed before painting of the steel structure, wherein the surface of the steel structure is coated with glycolic acid as a rust decomposing agent and hydrotal as an anion adsorbent. A method is disclosed for removing rust decomposers and anionic adsorbents from the surface of steel structures after applying a surface treatment agent containing sites and hydrocalumite. According to this, the rust decomposing agent decomposes the rust and converts the adhering chloride ions into soluble chloride ions, and the anion adsorbent adsorbs the soluble chloride ions. After that, by removing the surface treatment agent by wiping with water or the like, it is possible to improve the durability of the repainted coating film.

Patent Literature 4 discloses a base paint composition for repair that exhibits long-term anticorrosion properties with mild scraping during repainting. Specifically, in a base coating composition for repair consisting of an organic zinc-rich paint containing zinc dust as a main component, the content of zinc dust is 50 to 90% by mass with respect to the total solid content of the composition, Further, it contains 0.5 to 3.5% by mass of stannous sulfate with respect to the total solid content of the composition. This undercoating composition for repair is said to be applied to the surface of a steel structure having a residual chloride content of 50 mg/m ² or more in terms of NaCl.

In addition, although it is not a method for removing chlorides remaining in a steel structure after surface preparation, Patent Document 5 discloses an aqueous wetting agent that can suppress scattering of dust-like fine coating film fragments generated by physical cleaning work A method for removing existing coatings using is disclosed. Specifically, an aqueous wetting agent having a viscosity of 500 to 20000 mPa s and containing an alkali-swelling water-soluble polymer whose solubility in water is promoted by an alkali component is applied to the surface of the existing coating film, After removing the existing coating film with the aqueous wetting agent attached by physical scraping, the aqueous wetting agent remaining on the scraped surface is selected from sodium carbonate, sodium sesquicarbonate, and sodium bicarbonate. It is washed with an alkaline aqueous solution of pH 8.5-12.0 containing one or more.

Japan Corrosion Prevention Technology Association, "Corrosion Prevention Management", Vol. 64, No. 3, 2020, pp. 79-87

JP-A-10-237417 JP 2007-283237 A JP 2017-193768 A JP 2016-040350 A JP 2020-132874 A

Patent Documents 1 to 3 describe removing or detoxifying chlorides remaining on the surface preparation surface by adsorbing or passivating them with a chloride removing agent. However, even if the chloride remover is applied to the surface preparation surface by coating or the like, the contact efficiency between the chloride remover and chloride, and the reactivity between the chloride remover and chloride, are still low compared to water. has limits. In particular, there is concern about how far the chloride remover can react with chlorides that have permeated the inside of the adhering rust layer and the surface layer of the steel structure, including the interface with the steel structure.

Patent document 4 improves the anti-corrosion property against chlorides of the repainting paint, and does not remove residual chlorides in the first place. Patent Document 5 does not focus on the residual chloride, and removes the aqueous wetting agent by shaving and alkaline water immediately after applying the aqueous wetting agent to the surface preparation surface.

Therefore, the present invention solves the above problems, and provides a method for removing chlorides from a surface-conditioned steel structure, which can effectively remove even chlorides that have permeated the surface layer of the steel structure. intended to

As a means for that purpose, a water-based wetting agent containing water and a water-soluble polymer is applied to the surface preparation surface of a steel structure in which chloride remains on the surface layer even after surface preparation, and the surface is not dried. Chloride ions generated by dissolution of chlorides are eluted into the aqueous wetting agent by leaving the steel structure as it is for 4 hours or more, and then the aqueous wetting agent is removed. provide a way.

The aqueous wetting agent preferably further contains an anion-exchange layered pigment.

<Mechanism of rust generation under the protective coating>
When the surface of the protective coating on the steel structure is moistened with water, the water penetrates into the protective coating, forming a water layer at the interface with the steel structure under the protective coating, and the protective coating Reduced adhesion. If oxygen exists in the water layer under the protective coating, a local battery is formed on the surface of the steel structure, iron ions (Fe ²⁺ ) are eluted at the anode and corrosion occurs, and at the cathode, the electrode The reaction produces hydroxide ions (OH ⁻ ). Since these electrode reaction products dissolve in the water layer under the protective coating, the action of osmotic pressure promotes the infiltration of moisture on the surface side of the protective coating under the protective coating. Blistering occurs. Since oxygen also penetrates together with moisture, the electrode reaction at the cathode further progresses, the corrosion current increases, and the corrosion of the steel structure is accelerated. In addition, the iron ions (Fe ²⁺ ), which are the anode reaction products, and the hydroxide ions (OH ⁻ ), which are the cathode reaction products, combine to deposit insoluble matter, and the oxidation progresses to produce a reddish-yellow color. It becomes iron oxyhydroxide and black iron oxide, which promotes blistering and deterioration of the protective coating.

<Effect of chloride ion>
The presence of chloride ions (Cl ⁻ ) further accelerates the progress of rust. If a protective coating is formed with chlorides remaining on the surface of a steel structure after surface preparation, chloride ions, which promote corrosion, are eluted under the protective coating as water penetrates later. As a result, corrosion current flows easily under the protective coating, and at the same time, the action of osmotic pressure increases, which promotes penetration of moisture and dissolved oxygen under the protective coating, further advancing corrosion. As a result, blistering and rusting of the protective coating occur early, and the original anti-corrosion function of the protective coating cannot be achieved.

<Solution principle>
When repairing steel structures such as bridges and steel towers, in order to prevent the early recurrence of blistering and rusting of the protective coating after repainting, it is necessary to maintain the surface layer of the steel structure even after surface preparation. It is necessary to remove chlorides sufficiently before recoating. Therefore, the inventor of the present application applied an aqueous wetting agent containing water and a water-soluble polymer to the steel structure after surface preparation to form a water retention layer on the surface of the steel structure. It was found that the chloride remaining on the surface layer of the structure dissolved and the dissociated chloride ions were eluted into the aqueous wetting agent.

Therefore, in the present invention, an aqueous wetting agent containing water and a water-soluble polymer is applied to a steel structure having chlorides remaining on the surface layer even after surface preparation, and left undried for a predetermined time or more. . This makes it possible to easily remove chloride ions produced by the dissolution of chlorides together with the aqueous wetting agent after the chloride ions are eluted.

Furthermore, by including an anion-exchange layered pigment in the aqueous wetting agent, chloride ions are adsorbed by the aqueous wetting agent, and the chloride ion absorption and thus the chloride removal performance are improved. However, the use of the anion-exchange layered pigment is only for the improvement of the chloride removal performance, and the main chloride removal is water that can permeate to the surface layer of the steel structure.

It is the graph which showed the relationship between the immersion time of a rust steel plate, and the amount of elution of a chloride ion, and an elution rate.

≪Aqueous Wetting Agent≫
The aqueous wetting agent used in the present invention can be obtained by mixing water and a water-soluble polymer.

<Water-soluble polymer>
The water-soluble polymer dissolves in water and imparts an appropriate viscosity to the aqueous wetting agent. As a result, the water-based wetting agent becomes gel-like with a certain water-retaining property, and can be retained for a predetermined time even when applied to almost vertical surfaces of steel structures. As a specific example of the water-soluble polymer, any one or both of a hydroxyl group and a carboxyl group may be included in the structural unit of the polymer. Examples include methylcellulose, hydroxyethylcellulose, methylhydroxypropylcellulose, carboxymethylcellulose, guar gum, carrageenan, alginic acid, xanthan gum, starch, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, water-soluble polyurethane, and modified products thereof. can. These water-soluble polymers can be used singly or in combination of two or more.

When dissolving the water-soluble polymer in water, the dissolution of the water-soluble polymer can be promoted by adding a basic substance as necessary. Examples of basic substances that can be used include hydroxides of alkali metals, hydroxides of alkaline earth metals, ammonia, amines, and aminoalcohols. Among them, ammonia is preferable because it has good volatility and is less likely to remain on the cleaning work surface after use.

When a basic substance is added, the amount added is preferably 0.01 to 1% by weight, more preferably 0.05 to 0.5% by weight. If the amount of the basic substance added is too small, it will be difficult to obtain the effect of promoting the dissolution of the water-soluble polymer. On the other hand, if the amount of the basic substance to be added is too large, it becomes an excessive addition to the water-soluble polymer, which is a waste of cost.

The viscosity (23°C) of the aqueous wetting agent is preferably 500 to 20,000 mPa s, more preferably 1,000 to 10,000 mPa s, and more preferably 1,500 to 5,000 mPa s before application. More preferred. If the viscosity of the water-based wetting agent is too low, the water-based wetting agent tends to run off when applied to a vertical surface, making it difficult to retain the water-based wetting agent on the surface of the steel structure. As a result, the amount of the water-based wetting agent adhered decreases, making it difficult to maintain a wet state for a long time, and the water in the water-based wetting agent does not sufficiently penetrate the surface layer of the steel structure, and the water-based wetting agent is salted. Insufficient elution of compound ions. However, the viscosity of the water-based wetting agent may be somewhat low when applied to a substantially horizontal surface of a steel structure. On the other hand, even if the viscosity of the water-based wetting agent is high to some extent, the effect of removing chlorides is not greatly reduced, but the manufacturability and coating workability are reduced.

The content of the water-soluble polymer may be within a range that allows the viscosity of the aqueous wetting agent to be adjusted within the above range. Specifically, the content of the water-soluble polymer in the aqueous wetting agent is preferably 0.1 to 10% by weight, more preferably 0.3 to 5% by weight. The viscosity of the aqueous wetting agent is linked to the content of the water-soluble polymer. , the viscosity of the aqueous wetting agent becomes too high.

<Anion exchange type layered pigment>
The aqueous wetting agent can further enhance the effect of removing chloride ions by containing an anion-exchange layered pigment. The anion-exchange layered pigment is a compound classified as a layered double hydroxide having an anion-exchange function, or a fired product thereof, and a hydroxide layer containing two or more divalent and trivalent metals. Alternatively, it is possible to form a structure that has oxide layers and anions are sandwiched between the layers. Using this characteristic, chloride ions existing outside can be taken in between the layers and fixed. Examples of the anion-exchange layered pigment include hydrotalcite, Mg—Al oxide which is a sintered product thereof, and hydrocalumite. Among them, Mg—Al oxide, which is a sintered product of hydrotalcite, is preferable. General hydrotalcite intercalates carbonate ions, which are difficult to replace with chloride ions unless in an acidic atmosphere. On the other hand, the calcined product of hydrotalcite reproduces the layered double hydroxide structure in an aqueous solution and can intercalate chloride ions even in a neutral atmosphere. In the case of hydrotalcite and hydrocalmite, both of which intercalate nitrite ions exchange with nitrite ions to adsorb chloride ions, and the released nitrite ions have an anticorrosive effect. It is more preferable because it has

When an anion-exchange layered pigment is blended, the content is preferably 0.1 to 10% by weight, more preferably 0.5 to 8% by weight, and even more preferably 1 to 5% by weight. If the content of the anion-exchanged layered pigment rust is too small, the ability to adsorb chloride ions eluted into the aqueous wetting agent is lowered. On the other hand, if the content of the anion-exchanged layered pigment is too large, it becomes excessively added relative to the eluted chloride ions, which is a waste of cost.

In addition, polyols can be blended into the aqueous wetting agent as necessary in order to increase the durability of the wetting effect. Polyols are mainly polyether polyols for polyurethane, and are obtained by addition polymerization of polyhydric alcohols with alkylene oxides such as propylene oxide and ethylene oxide. Polyols are liquid at normal temperature (room temperature) and are sparingly soluble in water, but the water-soluble polymer functions as a surfactant to emulsify and uniformly disperse in the aqueous wetting agent. By blending polyols in the aqueous wetting agent, the water retention capacity of the aqueous wetting agent is further improved, and the wet state can be maintained for a longer period of time.

The polyol preferably has a number average molecular weight of 200 to 3,000. Specific examples of polyols include polyoxypropylene glycol, polyoxypropylene glycer ether, polyethylene adipate, polyethylene butylene adipate, polybutylene adipate, neopentyl adipate, polyoxyethylene bisphenol A ether, polyoxypropylene bisphenol A ether, and Examples thereof include polymers of these acrylic acid esters. Among them, polyoxypropylene glycol or polyoxypropylene glycerol ether having a number average molecular weight of 400 to 2,000 is preferable because it is relatively easily available and inexpensive. These polyols can be used singly or in combination of two or more.

When polyols are added to the aqueous wetting agent, the content thereof is preferably 0.5 to 30% by weight, more preferably 1 to 25% by weight. When the content of polyols is too small, it is difficult to obtain the effect of improving water retention. However, since polyols are components added as necessary, the content may be 0% by weight. On the other hand, if the content of the polyols is too high, it takes a long time to clean the water-based wetting agent, resulting in wasted effort.

In order to increase the wetting speed, the water-based wetting agent may optionally contain a rust penetrating wetting agent. The rust-penetrating wetting agent dissolves or disperses in water and lowers the surface tension of water, thereby facilitating the penetration of water into the rust layer. Types of rust penetrating wetting agents include nonionic surfactants, silicone surfactants, anionic surfactants, and cationic surfactants. Not limited.

Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyalkylene derivatives, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, sorbitan fatty acid esters, Examples include polyoxyethylene fatty acid esters, polyoxyethylene hydrogenated castor oil, polyoxyethylene alkylamines, alkylalkanolamides, and the like. Among them, those having an HLB (Hydrophilic-Lipophilic Balance) of 12 or more are excellent in water permeability to the rust layer.

Examples of silicone-based surfactants include polyether-modified silicones, polyester-modified silicones, aralkyl-modified silicones, and the like. Examples of anionic active agents include fatty acid salts, sulfonates, sulfate ester salts, naphthalenesulfonic acid-formalin condensates, and polycarboxylates. Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Amphoteric surfactants include, for example, alkylbetaines and alkylamine oxides. These rust penetrating wetting agents may be used alone or in combination of two or more.

When a rust penetrating wetting agent is blended, the content is preferably 0.01 to 1% by weight, more preferably 0.05 to 0.5% by weight. If the content of the rust-penetrating wetting agent is too small, it will be difficult to obtain the wetting promotion effect of the water-based wetting agent. On the other hand, if the content of the rust-penetrating wetting agent is too high, a large amount of the rust-penetrating wetting agent tends to remain on the surface of the steel structure even after washing with the water-based wetting agent, resulting in the water resistance of the repainted protective coating. and corrosion resistance.

Further, the water-based wetting agent may contain additives such as preservatives, antifungal agents, antifoaming agents, initial rust inhibitors, gelling agents, and fluorescent brightening agents within the range that does not impair the effects of the present invention. It can be added as needed. The gelling agent is mixed with the aqueous wetting agent before the aqueous wetting agent is applied to the substrate preparation surface or when the aqueous wetting agent is applied (simultaneously with the application of the aqueous wetting agent), not when the aqueous wetting agent is prepared. may be brought into contact.

≪Method for adjusting aqueous wetting agent≫
The water-based wetting agent can be prepared by gradually adding a water-soluble polymer into water while stirring the water to uniformly disperse the polymer, and then stirring until the polymer is sufficiently dissolved. When the water-soluble polymer powder is in the form of powder, when the water-soluble polymer powder is put into water all at once, the swollen water-soluble polymer particles agglomerate and form a coating film around them, forming splinters (so-called lumps). ”) is formed, and the solubility in water may deteriorate. Therefore, it is also preferable to wet the water-soluble polymer powder in advance with a hydrophilic solvent such as alcohol, if necessary.

<<Method for removing chloride ions>>
When repainting steel structures such as bridges and steel towers, the water-based wetting agent is applied to the surface preparation surface after performing surface preparation by physical cleaning on the deteriorated existing protective coating and corroded areas. . The method of applying the water-based wetting agent is not particularly limited, and typical examples include roller coating using a flocked roller, porous sponge roller, etc., brush coating, and injection coating using a sprayer, an injector, or the like. . At this time, since the aqueous wetting agent has a viscosity with moderately suppressed fluidity, it stays attached to the surface of the steel structure. In addition, the water-based wetting agent has good water-retaining properties, does not easily evaporate, and maintains a moist state for a long period of time.

In order to form a water-retaining layer on the steel structure surface, the coating amount of the aqueous wetting agent is preferably 0.1 to 1.0 kg/m ² , more preferably 0.2 to 0.6 kg/m ² . If the amount of the water-based wetting agent applied is too small, the water in the water-based wetting agent will not sufficiently permeate the surface layer of the steel structure, and the chloride will not be removed sufficiently. On the other hand, even if the amount of the water-based wetting agent applied is large, there is no problem with the chloride removal effect, but the amount applied to the steel structure is excessive, and on the horizontal surface, part of the water-based wetting agent reaches the periphery of the surface preparation surface. Some water-based wetting agent may run off on vertical surfaces, which may require wiping.

In order to prevent such useless spreading and running down of the water-based wetting agent, the surface of the water-based wetting agent may be covered with a water-absorbent sheet such as a non-woven fabric to impregnate the water-based wetting agent with the water-based wetting agent. As a result, even when the viscosity of the aqueous wetting agent is low, or when the amount of the aqueous wetting agent applied is large, it is possible to prevent the water-based wetting agent from spreading and running down. In addition, if the water-absorbing sheet is removed when removing the aqueous wetting agent from the substrate preparation surface after sufficiently eluting the chloride ions into the aqueous wetting agent, a certain amount of the aqueous wetting agent is removed together with the water-absorbing sheet. be able to.

After the aqueous wetting agent is applied to the surface preparation surface, the aqueous wetting agent is left undried for at least 4 hours, preferably 10 hours or longer, and more preferably 16 hours or longer. Since the water-based wetting agent has a certain level of water retention, it remains wet for a certain period of time after it is applied to the substrate preparation surface. In order to maintain the wettability, the surface of the applied aqueous wetting agent may be covered with a drying prevention sheet such as a vinyl sheet, if necessary. Then, as the water in the aqueous wetting agent permeates the surface layer of the steel structure while it is left standing, the chloride remaining on the surface preparation surface dissolves to generate chloride ions, and the water in the aqueous wetting agent eluted to Therefore, if the standing time is less than 4 hours, the water in the aqueous wetting agent will not sufficiently permeate the surface layer of the steel structure, and the time required for chloride ions to dissolve into the aqueous wetting agent will be insufficient. There is no upper limit to the time allowed to stand as long as the aqueous wetting agent does not dry out.

After the chloride ions are sufficiently eluted into the aqueous wetting agent, the undried aqueous wetting agent is scooped up with a spatula or the like, or wiped off with a cloth waste, absorbent paper, or the like to remove the eluted chloride ions. can be removed with an aqueous wetting agent.

At this time, if necessary, a gelling agent may be added to the aqueous wetting agent to gel (increase the viscosity) of the aqueous wetting agent. The gelling agent can be applied by applying water containing the gelling agent to the surface of the aqueous wetting agent. The method of applying the gelling agent-containing water may be the same as the method of applying the water-based wetting agent. Gelation of the water-based wetting agent can be achieved by a method of hydrogen-bonding the hydroxyl groups in the water-soluble polymer with the hydroxyl groups in the gelling agent, or a method of metal-crosslinking the carboxyl groups in the water-soluble polymer with polyvalent metal ions. can be used. Examples of the former include polyvinyl alcohol and borax, guar gum and borax, and examples of the latter include carboxymethyl cellulose and alum, and alginic acid and calcium lactate. Two or more of these gelation methods can be combined. However, chloride, which is a substance that promotes corrosion of steel structures, is not preferable as a gelling agent. The combination and ratio of the water-soluble polymer and the gelling agent may be appropriately adjusted according to the required degree of gelation, adhesiveness, and the like.

The aqueous wetting agent gelled by the gelling agent has an increased cohesive force, so that it becomes easier to separate in a mass, and is less likely to dissipate when removed, making it easier to collect. In addition to gelling with a gelling agent, the water-based wetting agent can be dried to form a film to some extent and then removed. Film-forming reduces the weight of waste as compared to the case of using a gelling agent, and can reduce disposal costs. However, if the film formation progresses too much, the adhesion strength increases, and it may become difficult to peel off.

The steps from application to removal of the aqueous wetting agent may be repeated multiple times as necessary. The water-based wetting agent that cannot be completely removed by scraping or wiping may be washed away by wiping with water. At this time, even if the chloride is not completely removed from the steel structure surface layer with the aqueous wetting agent, the chloride is ionized by the aqueous wetting agent, so at the same time as cleaning and removing by wiping with water, Residual chloride ions can also be easily removed.

In addition to water, it is also preferable to use alkaline water for washing after wiping off the aqueous wetting agent. Since the water-soluble polymer used in the present invention has an alkali-swelling property, even if the aqueous wetting agent remaining on the surface of the steel structure dries and forms a film, it can be quickly re-dissolved in alkaline water. is possible. Alkaline water also has the effect of suppressing the generation of return rust.

As alkaline water, an aqueous solution containing sodium carbonate, sodium sesquicarbonate, sodium hydrogencarbonate, or a mixture thereof and adjusted to pH 8.5 to 12.0 can be used. Alternatively, an aqueous solution containing potassium hydroxide and adjusted to pH 11.0 to 13.0 can also be used. In order to effectively suppress the generation of return rust, the pH is preferably 11.0 or higher. On the other hand, when the safety of handling by workers is important, the pH is preferably less than 11.5 in order to avoid corrosive effects on the skin.

The method of washing with alkaline water is not particularly limited, but if alkaline water is simply sprayed or poured onto the ground and there is concern about soil contamination, alkaline water should be applied to a sponge, brush, scrubbing brush, cloth waste, etc. It is also possible to rub the base material while applying it little by little, or to rub the base material with a sponge, a brush, a scrubbing brush, a cloth waste, etc. while applying the alkaline water in a mousse state and applying it little by little.

After washing with the water-based wetting agent, it should be dried quickly to prevent back rust. Therefore, it is preferable to wipe off moisture with a cloth waste, water-absorbing paper, or the like, and then improve ventilation.

EXAMPLES Examples embodying the present invention will be described below, but the present invention is not limited to the following examples.

In evaluating the chloride removability according to the present invention, a rusted steel sheet having a strongly adhered rust layer on the surface and prepared so that the amount of chloride ions contained in the rust does not exceed 1000 mg/m ² was used. Used as test substrate. A specific procedure for producing the rusted steel plate is shown below.

<Procedure for producing rusted steel plate>
A rusted steel plate, which is a base material for testing, was produced by the following procedures 1 to 6.
Procedure 1: The base material is a structural steel plate SS400 (size: length 150 mm x width 70 mm x thickness 3.2 mm) specified in JIS G 3101, and the surface on the side to be rusted is JIS K 5551 7.14 ( Cycle corrosiveness).
Step 2: Apply molten paraffin (petroleum wax defined in JIS K 2235, melting point 55-65°C) to the back and sides of the base material with a brush and solidify at room temperature.
Procedure 3: 5 of JIS K 5600-7-9. Using the cyclic corrosion tester specified in (Apparatus), perform 60 cycles of cyclic corrosion of the base material under the conditions of Annex 1 (Cycle D) to form a rust layer on the surface, then remove the base material from the tester take out from
Step 4: Substrate is soaked in tap water for 1-16 hours to remove excess salt content, then dried at room temperature for 24 hours.
Step 5: Remove the fragile rust layer on the surface of the base material by hitting it with a hammer, and then scrape the surface with a wire brush until it has a metallic luster to remove the powder adhering to the surface.
Step 6: Confirm that the amount of chloride ions contained in one of the multiple rusted steel plates produced by steps 1 to 5 does not exceed 1000 mg/m ² , and test the remaining rusted steel plates. used as a base material for When the amount of chloride ions contained exceeds 1000 mg/m ² , the above steps 4 to 6 are repeated until the content does not exceed 1000 mg/m ² to prepare a rusted steel sheet.

As a method for measuring the amount of chloride ions contained in the rusted steel sheet, a method of immersing the steel sheet in deionized water to allow natural elution (hereinafter referred to as the "immersion method"), and/or immersing the steel sheet in an electrolyte solution. A measurement method (hereinafter referred to as "energization method") was used in which an electric current is passed through and electrophoresis is used to force elution in a short period of time. Then, the saturated elution amount by the energization method was regarded as the total amount of chloride ions contained in the rusted steel sheet. Specific measurement methods for these are shown below.

<Measurement of chloride ion content by immersion method>
Place a rusted steel plate on the bottom of a rectangular plastic container (size: length 18 cm x width 12 cm x depth 6 cm), pour 500 mL of deionized water (sample load factor 21 m ² /m ³ ), seal the container, and cool to room temperature. for 16 hours. The rusted steel plate is taken out, and the concentration (mg/L) of chloride ions eluted in deionized water is measured using a water quality detector tube for measuring chloride ions "201SC" (manufactured by Komyo Rikagaku Kogyo Co., Ltd.). Then, the amount (mg) of chloride ions eluted is calculated to determine the amount (mg/m ² ) of chloride ions contained in the rusted steel sheet. The sample load factor (m ² /m ³ ) is based on the following formula.
Sample load factor (m ² /m ³ ) = Area of rusted surface of rusted steel plate (m ² ) ÷ Volume of water (m ³ )

<Measurement of chloride ion content by current method>
Scrape off a small portion of the rust on the top of the rusted steel plate with abrasive paper, and connect the wiring for energization with a crocodile clip. Next, the rusted steel plate was placed on the bottom of a square plastic container (size: length 18 cm x width 12 cm x depth 6 cm), and a spacer with grid-like holes was placed on top of it to keep it from coming into contact with the steel plate. cover the Furthermore, a graphite sheet electrode of the same size as the rusted steel plate is fixed on top of the rusted steel plate so as to be directly above the rusted steel plate, and the wiring for energization is connected with a crocodile clip. Finally, 500 mL of a 0.1 N potassium nitrate aqueous solution is poured into the graphite sheet electrode until it is completely immersed (sample load factor: 21 m ² /m ³ ), and the container is sealed. In this state, with the graphite sheet side as the anode and the rusted steel sheet side as the cathode, a 2.0 V direct current is supplied from a stabilized power source to elute chloride ions in the rust and attract them to the anode side by electrophoresis. Power is turned off every 10 minutes, and the concentration (mg/L) of eluted chloride ions is measured with a water quality detector tube for chloride ion measurement "201SC". Then, energization and measurement are repeated until the increase in the concentration of chloride ions almost disappears, and the amount of chloride ions (mg/m ² ) contained in the rusted steel sheet is obtained from the saturated elution amount (mg).

FIG. 1 is a graph showing the relationship between the immersion time and the chloride ion elution amount and elution rate for a rusted steel sheet in which the saturated elution amount of chloride ions by the immersion method was about 1100 mg/m ² . The immersion was continued until 72 hours, and the amount of elution became almost saturated after 16 hours. After that, the elution of the rusted steel sheet by an electric current method was further attempted, and the presence or absence of residual chloride ions was confirmed. As a result, the amount of elution was less than the lower measurement limit (1 ppm) of the water quality detector tube "201SC" for measuring chloride ions, so it was found that almost all of the chloride ions were eluted by the immersion method without remaining chloride ions. did. For this reason, using a rusted steel sheet prepared so that the amount of chloride ions contained does not exceed 1000 mg/m ² , after removing chloride ions, chloride ions are measured by an immersion method that is easy to measure. was measured.

≪Preparation of aqueous wetting agent≫
To evaluate the chloride removability according to the present invention, aqueous wetting agents 1-3 were prepared according to the following procedure. Table 1 shows these raw materials and their blending amounts (% by weight).
<Aqueous wetting agent 1>
Water was weighed into a 1-liter plastic cup, and the water-soluble polymer A was added little by little while stirring with a stirrer to disperse it. Polyols were added thereto and stirred for about 1 hour to prepare an aqueous wetting agent 1 .
<Aqueous wetting agent 2>
Water was weighed into a 1-liter plastic cup, and the water-soluble polymer A was added little by little while stirring with a stirrer to disperse it. An anion-exchange layered pigment and polyols were sequentially added to this, and the mixture was stirred for about 1 hour to prepare an aqueous wetting agent 2 .
<Aqueous wetting agent 3>
Water was weighed into a 1 L plastic cup, and the water-soluble polymer B was added little by little while stirring with a stirrer to disperse it. An anion-exchange layered pigment was added to this, and the mixture was stirred for about 1 hour to prepare an aqueous wetting agent 3.

As each raw material shown in Table 1, the following were used.
Water-soluble polymer A: hydroxyethyl cellulose ("BG15" manufactured by Sumitomo Seika Co., Ltd.)
Water-soluble polymer B: hydroxypropyl guar gum (“MYPRO HPG8111” manufactured by Sansho Co., Ltd.)
Anion-exchange layered pigment: calcined product of synthetic hydrotalcite ("KW-2000" manufactured by Kyowa Chemical Industry Co., Ltd.)
Polyols: Polyoxypropylene glycol ("Sannics PP-1000" manufactured by Sanyo Chemical Industries, Ltd.)

The viscosities of aqueous wetting agents 1 to 3 are also shown in Table 1. The viscosity was measured by adjusting the temperature of the aqueous wetting agents 1 to 3 to 23° C. and using a B8H type viscometer (rotation speed: 20 rpm, measurement time: 2 minutes).

The resulting aqueous wetting agents 1-3 were evaluated for chloride removal.
<Chloride ion removal>
The chloride removability by the water-based wetting agent was evaluated by applying the water-based wetting agents 1 to 3 to the rusted steel plate, which is the test substrate, and leaving the water-based wetting agents for different times. , the amount of chloride ions remaining in the substrate was measured and evaluated from the ratio of the eluted amount to the total amount. Specific test procedures for these examples and comparative examples are shown below, and the test results are shown in Table 2.

<Chloride ion removal test procedure>
(Examples 1 and 2 and Comparative Example 1)
The test was performed according to procedures 1 to 6 below.
Procedure 1: A water-based wetting agent is applied to the rusted steel plate, which is the substrate for testing, with a brush so that the coating amount is 4.2 g (0.4 kg / m ² ), and immediately the whole is covered with a transparent plastic film (Asahi Kasei Wrapped in "Saran Wrap" (registered trademark) manufactured by Home Products Co., Ltd. and sealed. After leaving for a specified period of time, the test substrate is unsealed and taken out, the applied aqueous wetting agent is scooped out with a piece of paper, and 2.0 g of the sample is collected in a 100 cc plastic cup.
Procedure 2: Wipe off the aqueous wetting agent remaining on the test substrate with absorbent paper.
Procedure 3: The substrate for testing in Procedure 2 is further washed by wiping off the residue with water absorbing paper while spraying alkaline water. The alkaline water is adjusted to pH 10.3 by dissolving sodium sesquicarbonate (“Sodium sesquicarbonate” manufactured by Niwakyu Co., Ltd.) in deionized water.
Procedure 4: Measure the chloride ion concentration (ppm) of the test solution obtained by diluting the sample collected in Procedure 1 by 50 times with deionized water using a water quality detector tube for chloride ion measurement "201SC". From this, the chloride ion concentration (ppm) before dilution is calculated, and the amount of dissolved chloride ions (mg/m ² ) converted per 1 m ² is calculated from the application amount (0.4 kg/m ² ) of the aqueous wetting agent. This is regarded as the eluted chloride ion amount (mg/m ² ) from the test substrate.
Procedure 5: The amount of residual chloride ions (mg/m ² ) of the test substrate washed in Procedure 3 is measured by the immersion method described above.
Procedure 6: Chloride ion content (mg/m ² ) and chloride ion removal rate (%) of the test base material are determined by the following equations.
Chloride ion content (mg/m ² ) = eluted chloride ion amount + residual chloride ion amount Chloride ion removal rate (%) = (eluted chloride ion amount / chloride ion content) x 100

(Examples 3 and 6)
The test was performed in the same manner as in Example 1, etc., except that Procedure 3 in Examples 1 and 2 and Comparative Example 1 was not performed, and the chloride ion removal rate (%) was determined.

(Examples 4 and 5)
A test was carried out in the same procedure as up to Procedure 4 in Example 1, etc., and the amount of dissolved chloride ions (mg/m ² ) of the aqueous wetting agent was determined. Next, 0.01 g of sodium bicarbonate was added to the test solution and stirred for 10 minutes to dissolve, thereby replacing the chloride ions adsorbed to the anion-exchange layered pigment with carbonate ions and desorbing them. Chloride ions were eluted into the test solution. Then, the chloride ion concentration (ppm) was measured using a water quality detector tube "201SC" for measuring chloride ions. Then, the chloride ion concentration (ppm) before dilution is calculated, and the amount of eluted chloride ions (mg/m ² ) converted per 1 m ² is calculated from the applied amount (0.4 kg/m ² ) of the aqueous wetting agent. asked. Furthermore, the amount of adsorbed chloride ions (mg/m ² ) was calculated by subtracting the amount of dissolved chloride ions (mg/m ² ) from the amount of eluted chloride ions (mg/m ² ). After that, the test was conducted in the same procedure as Procedure 5 to Procedure 6 in Example 1, etc., and the chloride ion removal rate (%) was obtained. The amount of sodium bicarbonate required for desorption of chloride ions is determined in advance by measuring the saturated adsorption amount of chloride ions to the anion-exchange layered pigment, and is equal to or more than the equivalent amount that carbonate ions completely replace the chloride ions saturated and adsorbed. was determined to be

<Evaluation criteria for chloride ion removal>
The chloride removal property was evaluated from the chloride ion removal rate according to the following criteria.
◎: 90% or more ○: 75% or more and less than 90% △: 60% or more and less than 75% ×: less than 60%

As shown in Table 2, each example and comparative example was prepared such that the chloride ion content of the test substrate did not exceed 1000 mg/m ² . Example 1, in which the standing time after application of the aqueous wetting agent was left for 4 hours, had a chloride ion removal rate of 61%, and Example 2, in which the standing time was left for 16 hours, had a chloride ion removal rate of 75. % improved. In Examples 4 and 5, in which the anion-exchange layered pigment was added, the chloride ion removal rate was higher than in Examples 1 and 2, in which no addition was added. The product ion removal rate was shown. Example 6, which required water-soluble polymer B, also showed a high chloride ion removal rate.

Moreover, Example 2, in which cleaning was performed after wiping off the aqueous wetting agent, had a higher chloride ion removal rate than Example 3, in which cleaning was not performed. As a result, even if all the chlorides were not eluted into the aqueous wetting agent, it was confirmed that the remaining chloride ions could be easily reduced by washing with water because the chlorides were ionized.

On the other hand, in Comparative Example 1, the removal of chloride ions was insufficient because the standing time was as short as 1 hour. This is because the water in the aqueous wetting agent does not sufficiently permeate the surface layer of the steel structure, and the chloride ions are not sufficiently eluted into the aqueous wetting agent. Moreover, although washing was also performed after wiping off the aqueous wetting agent, the chloride ion removal rate was still as low as 37%.

Claims (2)

Applying an aqueous wetting agent containing water and a water-soluble polymer to the surface of a steel structure having chlorides remaining on the surface after surface preparation,
After the chloride ions generated by the dissolution of chloride are eluted into the aqueous wetting agent by leaving it undried for 4 hours or more, the aqueous wetting agent is removed while it is undried . A method for removing chlorides from a structure. 2. The method for removing chlorides from a surface-conditioned steel structure according to claim 1, wherein said aqueous wetting agent further contains an anion-exchange layered pigment.

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