Water-based substrate preparation agent composition and substrate preparation method

Abstract

The present invention provides a water-based surface preparation agent composition that combines paint film stripping and rust removal properties. [Solution] This is a surface preparation agent composition for removing rust along with the existing paint film when repainting an existing paint film applied to existing steel materials. It contains at least benzyl alcohol, a hydroxy acid, and water. The hydroxy acid is citric acid, malic acid, or an acidic salt thereof. Furthermore, it contains hydroxyethyl cellulose as an emulsifier for benzyl alcohol. The pH is preferably 4.0 to 6.0. This water-based surface preparation agent composition is applied to the existing steel material to remove rust along with the existing paint film.

Description

[Technical Field]

[0001] The present invention relates to a water-based surface preparation agent composition for removing rust along with the existing paint film when repainting an existing paint film applied to existing steel materials, and to a method for preparing the surface of existing steel materials using the same. [Background technology]

[0002] Steel materials used in existing structures such as buildings, plants, towers, bridges, ships, and vehicles (hereinafter collectively referred to as "existing steel materials") are exposed to ultraviolet rays, wind and rain, and corrosion-promoting substances from the atmosphere and surrounding environment adhere to them, causing deterioration of the existing protective coating and the occurrence of rust due to corrosion over time. Such deterioration of the existing coating and the occurrence of rust not only impair the aesthetic appearance of the existing structure but also lead to a decrease in structural strength and shorten the service life of the existing structure. For this reason, existing structures need to be refurbished by repainting the existing coating as needed, and in such cases, surface preparation is carried out in advance to remove the deteriorated existing coating and rust.

[0003] Traditionally, the main method used for surface preparation has been physical scraping, which removes existing paint and rust simultaneously. Typical physical scraping methods include large-scale methods using blasting, and methods using power scraping tools and manual scraping tools (hereinafter, power scraping tools and manual scraping tools are collectively referred to as "scraping tools").

[0004] Furthermore, rust can be present not only as exposed rust mixed with the existing paint film (hereinafter referred to as exposed rust), but also as rust and mill scale that have formed beneath the existing paint film (hereinafter referred to as sub-paint rust). Both of these adversely affect the quality of the repainted film, and therefore need to be removed by physical scraping before repainting.

[0005] Furthermore, if the removal is limited to the removal of existing paint films, chemical surface preparation using paint strippers is also employed. Chemical surface preparation allows the removal of existing paint films to be carried out in a wet environment, thus reducing the impact on workers and the surrounding environment. However, since rust is not affected by the paint-removing solvents contained in paint strippers, chemical surface preparation using paint strippers cannot be applied to rust removal. For this reason, if the existing steel material is corroded in an uneven manner, or if the adhesion between the bottom layer of paint film and the rust beneath the paint film is strong, conventional paint strippers cannot completely remove the existing paint film, and it is necessary to remove the remaining paint film along with the rust beneath the paint film by physical surface preparation separately. Moreover, if the existing paint film on the surface of the existing steel material has partially disappeared due to deterioration or corrosion, exposing rust, or if rust has penetrated the existing paint film and is occurring in a dotted manner, it is necessary to remove this exposed rust by physical surface preparation after chemical surface preparation.

[0006] On the other hand, when surface-treated steel products are processed in factories, the steel is first washed with inorganic acids (acid pickling) to remove surface oxide layers such as mill scale and rust. The rust removal action by acid (hereinafter referred to as "rust removal") is based on the principle of an electrochemical reaction (electrochemical oxidation-reduction reaction) consisting of an anode reaction and a cathode reaction, and the acid dissolution reaction of rust. However, chemical rust removal using acids is not widely used in surface preparation at repainting construction sites for existing steel materials. The reason for this is that inorganic acids such as hydrochloric acid and sulfuric acid are frequently used as active ingredients in acid pickling, but these inorganic acids are strong acids, and their use at construction sites is sometimes undesirable from a safety and environmental perspective. In addition, there are concerns that such strong acids may cause thinning of existing steel materials and a decrease in strength due to hydrogen embrittlement. Furthermore, even if rust is removed using hydrochloric acid, rust is quickly induced (back-rusting), making it unsuitable for use at construction sites.

[0007] Therefore, the inventors of this application have developed a new surface preparation method (electrochemical surface preparation) (Patent Document 1) in which, after preliminary scraping off the rust from existing steel materials, exposed areas of the base iron that serve as areas for promoting electrochemical reactions are formed in places of the remaining rust (hereinafter referred to as electrochemical treatment), and the rust removal process is advanced by applying an aqueous solution of hydroxy acid, a type of organic acid, thereby thoroughly removing the weakened rust. According to this method, the rust removal work when repainting existing steel materials is safe because strong acids are not used, and the rust removal work can be carried out with high quality and at low cost. Moreover, since residual salt in the rust is also removed along with the rust, the durability of the repainted coating and the existing steel material is improved.

[0008] In addition, a surface preparation method has been disclosed in which an aromatic alcohol such as benzyl alcohol, which has a paint film peeling effect, is applied to remove the existing paint film, and then an inorganic acid and organic acid-containing mill scale remover is applied to the mill scale present beneath the existing paint film to remove the mill scale, etc. (Patent Document 2). [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Patent No. 7426641 [Patent Document 2] Japanese Patent Publication No. 2009-179860 [Overview of the project] [Problems that the invention aims to solve]

[0010] However, the electrochemical surface preparation method described in Patent Document 1 cannot be applied to the removal of existing paint films, so it is necessary to remove the paint film separately by performing physical surface preparation or chemical surface preparation using a paint film remover. The surface preparation method described in Patent Document 2 consists of two steps: a paint film removal step using a paint film penetrating softener and a mill scale removal step using a mill scale remover. This requires two types of liquids, making it complicated and less efficient than physical surface preparation. Furthermore, it targets the removal of mill scale formed on the surface of newly installed steel materials, and does not target the removal of rust formed by corrosion over time.

[0011] If rust removers containing hydroxy acids, a type of organic acid, could be used to remove rust from existing steel materials, they would be safe to use at construction sites, environmentally friendly, and free from concerns about thinning of existing steel materials or strength reduction due to hydrogen embrittlement. On the other hand, chemical surface preparation using paint strippers containing paint-removing solvents such as benzyl alcohol is not intended to remove rust, so it is necessary to remove the rust separately using physical surface preparation. Therefore, there has been a problem in that the work efficiency is lower compared to physical surface preparation, which can remove existing paint and rust simultaneously. Furthermore, in the conventional understanding, paint strippers containing benzyl alcohol as an active ingredient and rust removers containing acids as an active ingredient were different types of surface preparation agents with different purposes.

[0012] Therefore, the present invention aims to solve the above problems and to provide a water-based surface preparation agent composition containing benzyl alcohol, which is a paint film peeling solvent, and a hydroxy acid, which is a rust remover component, thereby possessing both paint film peeling and rust removal properties, and a method for preparing the surface of existing steel materials using this composition. [Means for solving the problem]

[0013] <Water-based substrate conditioning agent composition> The aqueous substrate preparation composition of the present invention contains benzyl alcohol, a hydroxy acid, and water, wherein the hydroxy acid is citric acid, malic acid, or an acidic salt thereof, and contains hydroxyethylcellulose as an emulsifier for benzyl alcohol. Preferably, it is weakly acidic with a pH of 4.0 to 6.0.

[0014] <Rust removal and paint film stripping effects of water-based surface preparation agent compositions> When iron comes into contact with water, the iron dissolves and iron ions (Fe) are formed. 2+ The anodic reaction (anodic dissolution) in which iron ions (Fe) are eluted, and the cathode reaction in which dissolved oxygen and hydrogen ions are reduced, form a local cell and generate a corrosion current. This electrochemical reaction proceeds more rapidly in an acidic atmosphere. On the other hand, if rust, which is an iron corrosion oxide, is formed on the surface of existing steel material, impregnating the rust with an acidic solution will, in addition to the above reaction, cause the rust to dissolve in the acid and release iron ions (Fe). 2+ In addition to eluting ) the rust components are reduced by a cathodic reaction to other rust components that are highly acid-soluble, and these then dissolve in acid to form iron ions (Fe 2+ ) dissolves. Therefore, when an acid solution is applied to rust on the surface of steel, iron ions (Fe) are released through an electrochemical reaction and an acid dissolution reaction. 2+ As the rust dissolves, it weakens. At the same time, the interface between the base iron and the rust is eroded, and the adhesion of the rust to the base iron decreases, making the rust easier to peel off and thus easier to remove.

[0015] The hydroxy acids contained in the water-based surface preparation agent composition not only have a rust-removing effect on exposed rust mixed with the existing paint film, but also penetrate into the interior of the existing paint film, thereby removing rust beneath the paint film. The synergistic effect of this rust-removing effect beneath the paint film and the paint-stripping effect of benzyl alcohol further promotes the paint-stripping effect of the water-based surface preparation agent composition. Furthermore, even if the existing paint film is strongly adhered to the rust beneath the paint film or the base metal iron, the rust-removing effect on the rust beneath the paint film and the anode dissolution of the base metal iron reduce the adhesion of the existing paint film, making it easier to remove. Moreover, the rust beneath the paint film can be removed simultaneously with the existing paint film.

[0016] Since the aqueous substrate conditioner composition uses hydroxy acid as a rust-removing component, the dissolution of the base iron is so slight that it is hardly perceptible visually compared to strong acids such as inorganic acids, and there is almost no concern about the reduction of the existing steel material due to pickling with inorganic acids. Also, in pickling with inorganic acids, scale is removed by the pressure of hydrogen gas generated by the cathodic reaction. However, if it is weakly acidic with a higher pH than strong acids, the reduction reaction of hydrogen ions is suppressed, so there is almost no concern about the reduction in the strength of the existing steel material due to hydrogen embrittlement. Furthermore, the rust-removing operation can be carried out safely compared to inorganic acids which are strong acids. Among them, if the hydroxy acid is citric acid, malic acid, or their acidic salts (partially neutralized salts), the risks of health hazards and corrosiveness can be avoided.

[0017] <Method for conditioning the substrate of existing steel materials> The method for conditioning the substrate of the existing steel materials of the present invention involves applying the above aqueous substrate conditioner composition to the existing coating film and removing rust together with the existing coating film.

Advantages of the Invention

[0018] According to the aqueous substrate conditioner composition of the present invention, by applying this aqueous substrate conditioner composition, the rust-removing action and the coating film peeling action automatically proceed, so the substrate conditioning work can be labor-saving. Even for existing coating films that are difficult to peel with a coating film peeling agent, the peeling work of the existing coating film becomes easy due to the rust-removing action of the rust under the coating film. It can be carried out with higher quality than physical chipping using only a chipping tool, and can be carried out safely at a lower cost than large-scale physical chipping by blasting. Since the residual salt content after substrate conditioning is almost eliminated, it contributes to preventing the early recurrence of rust due to corrosion after repainting, and the durability of the existing steel material is improved. If the aqueous substrate conditioner composition is weakly acidic, there is almost no concern about the reduction of the existing steel material due to reduction of the thickness of the existing steel material and hydrogen embrittlement, and the corrosive effect on the human body is also low. And since the removal work of the existing coating film and rust is carried out in a wet state, dust generation can be suppressed, and the safety for workers and the surrounding environment is improved.

[0019] Also, if physical chipping with a chipping tool or chemical chipping with a coating film remover is preliminarily carried out in advance, then the aqueous substrate conditioner composition is applied to the remaining coating film and the exposed rust mixed therein, and the remaining coating film and the rust are removed simultaneously to enable the exposure of the base metal iron. Thereby, it becomes possible to assist the conventional physical chipping operation and chemical chipping operation, and furthermore, the quality of substrate conditioning is further improved.

Embodiments for Carrying Out the Invention

[0020] ≪Aqueous Substrate Conditioner Composition≫ The aqueous substrate conditioner composition of the present invention (hereinafter abbreviated as "substrate conditioner") contains at least benzyl alcohol, hydroxy acid, and water. A typical substrate conditioner according to the present invention is emulsified simply by mixing and stirring the above components to form an aqueous emulsion liquid. Therefore, the substrate conditioner of the present invention contains hydroxyethyl cellulose as an emulsifier for benzyl alcohol.

[0021] <Benzyl Alcohol> Benzyl alcohol is known to effectively act as a stripping solvent for various types of organic coating films. Therefore, the existing coating films to which the present invention is applied are organic coating films. Since benzyl alcohol has good affinity with organic resins, it penetrates into the organic coating film to soften and swell the existing coating film, reducing the adhesion between the existing coating film and the coated object. Furthermore, when it acts significantly, the existing coating film is lifted from the coated object. These make it easier to remove the existing coating film with a hand chipping tool.

[0022] The content of benzyl alcohol in the substrate conditioner is preferably 15 to 55% by weight, more preferably 25 to 50% by weight, and even more preferably 35 to 45% by weight. If the content of benzyl alcohol is too low, the coating film stripping action tends to be insufficient. On the other hand, if the content of benzyl alcohol is too high, the content of water and hydroxy acid relatively decreases, so the rust removal action decreases.

[0023] <Hydroxy Acid> The rust removal process using hydroxy acids is based on electrochemical reactions involving anode and cathode reactions, as well as the acid dissolution of rust. In the cathode reaction, the reduction of rust components and dissolved oxygen competes with the reduction of hydrogen ions. As the pH decreases, the electrochemical reaction is accelerated, making the base iron more susceptible to erosion by the anode reaction. Furthermore, as the pH decreases, the reduction of hydrogen ions becomes dominant, making the base iron more susceptible to hydrogen embrittlement due to hydrogen penetration, a tendency that is particularly pronounced below pH 1.0.

[0024] Suitable hydroxy acids as substrate conditioners are aliphatic hydroxy acids or their acidic salts, which have high solubility in water, high boiling points, low odor, and low health hazards. Examples of such aliphatic hydroxy acids include malic acid, which has 4 to 6 carbon atoms in a chain-like structure and contains one hydroxyl group and two carboxyl groups per molecule, or citric acid, which contains one hydroxyl group and three carboxyl groups per molecule. Malic acid and citric acid are less likely to cause the pH to fall below 1.0 even at high concentrations, and can be expected to promote the elution of iron ions through chelating action.

[0025] An acidic salt of a hydroxy acid is an electrolyte obtained by partially neutralizing a hydroxy acid with a monovalent base component such as Li, K, Na, or NH3, and its aqueous solution exhibits an acidic pH range of 1.0 to 6.0.

[0026] The hydroxy acid content of the surface conditioner is preferably 5 to 25% by weight, more preferably 6 to 20% by weight, and even more preferably 7 to 15% by weight. If the hydroxy acid content is too low, the rust removal action tends to be insufficient. On the other hand, if the hydroxy acid content is too high, it will exceed the solubility limit and will not dissolve in the surface conditioner. Since hydroxy acids have high solubility in water, they dissolve easily in a short time by mixing and stirring with water within the above-mentioned content range. Hydroxy acids also act as emulsification accelerators for benzyl alcohol.

[0027] <Benzyl alcohol as an emulsifier> The substrate preparation agent is an oil-in-water (O / W) emulsion in which benzyl alcohol is dispersed in water. Therefore, hydroxyethyl cellulose is added as an emulsifier for benzyl alcohol. Hydroxyethyl cellulose is a type of polysaccharide derivative and acts as a protective colloid for the micronized benzyl alcohol, providing emulsification without necessarily requiring emulsifiers such as surfactants. This is a property specific to hydroxyethyl cellulose, and other polysaccharides or their derivatives do not exhibit this function. In addition, hydroxyethyl cellulose is less susceptible to salting-out by hydroxy acids, thus minimizing viscosity reduction of the substrate preparation agent.

[0028] The hydroxyethylcellulose content is moderate and preferable at 0.1 to 5.0% by weight. If the hydroxyethylcellulose content is too low, the emulsifying effect of benzyl alcohol will be insufficient, and if it is too high, the viscosity of the substrate conditioner will become excessively high, making it difficult to manufacture and apply. Hydroxyethylcellulose can be added by direct mixing as is, or by indirectly mixing a thickened liquid obtained by dissolving or swelling it in water beforehand.

[0029] The pH of the surface preparation agent should be at least 1.0 to 6.0, preferably weakly acidic with a pH of 4.0 to 6.0. If the pH is 1.0 or higher, the anodic reaction, which is the dissolution reaction of the base iron, is less likely to occur. Furthermore, if the pH is 4.0 or higher, the cathode reaction, which is the reduction reaction of hydrogen ions, is less likely to occur, and hydrogen embrittlement due to hydrogen penetration into the base iron is suppressed. On the other hand, if the pH is higher than 6.0, the rust removal action will not proceed easily.

[0030] When using basic components to adjust the pH of a surface conditioner, monovalent Li, K, Na, NH3, etc., are suitable. Adjusting the pH with divalent or higher basic components inhibits the dissolution of hydroxy acids, making hydroxy acid precipitation more likely. Furthermore, instead of adjusting the pH of the surface conditioner with these basic components, using the acidic salts of hydroxy acids derived from these basic components simplifies the pH adjustment process. For this reason, malic acid and citric acid are preferred as hydroxy acids, but diammonium hydrogen citrate, an acidic salt of citric acid, is even more preferred because it easily adjusts the pH of a weakly acidic surface conditioner to 4.0-6.0 without the need for additional basic components, and is readily available at a relatively low cost.

[0031] While hydroxyethylcellulose alone, used as an emulsifier for benzyl alcohol, imparts some viscosity to the substrate preparation agent, other water-soluble polymers can be used as viscosity modifiers if further adjustment of the viscosity of the substrate preparation agent is desired. Specific viscosity modifiers include polysaccharides and their derivatives, such as guar gum, carrageenan, xanthan gum, tamarind seed gum, methylcellulose, hydroxypropyl methylcellulose, carboxymethylcellulose, alginates, starch, and their cationized modified forms, or chitosan. In addition to polysaccharides and their derivatives, polyvinyl alcohol, polyvinylpyrrolidone, acrylic thickeners, water-soluble polyurethanes, and their cationized modified forms can also be used as viscosity modifiers. These water-soluble polymers can be used individually or in combination of two or more.

[0032] Since each of these viscosity modifiers has a different pH range in which it can increase viscosity, it is preferable that they be able to maintain a viscous state in the acidic range of pH 1.0 to 6.0. Furthermore, to prevent dripping on downward surfaces and sagging on vertical and inclined surfaces, it is preferable that they impart thixotropic viscosity.

[0033] The viscosity of the surface conditioner (at 23°C) is preferably 1,000 to 40,000 mPa·s, more preferably 3,000 to 35,000 mPa·s, and even more preferably 5,000 to 30,000 mPa·s before application. If the viscosity of the surface conditioner is too low, it is prone to falling on downward surfaces and sagging on vertical and inclined surfaces. On the other hand, if the viscosity of the surface conditioner is too high, it becomes difficult to manufacture and application becomes difficult.

[0034] Surface preparation agents may contain wax to ensure sufficient time for rust removal and to facilitate removal of the coating by delaying the drying and solidification of the coating solution. Examples of waxes include paraffin wax, microcrystalline wax, montan wax, polyethylene wax, polypropylene wax, Fischer-Tropsch wax, ethylene vinyl acetate copolymer wax, ethylene acrylic acid copolymer wax, beeswax, carnauba wax, lanolin wax, and modified versions thereof. Among these, paraffin wax is preferred. Because paraffin wax has low polarity and is hydrophobic, it further suppresses the evaporation of water from the rust remover, and the liquid state inside the rust remover is prolonged, ensuring sufficient time for rust removal. One or more of these waxes can be used. The method of adding the wax is to atomize or emulsify these waxes, which are solid at room temperature, and mix them in the form of a water-dispersible wax, which makes it easy to add to the rust remover. As the water-dispersible wax, commercially available products in which the wax has already been dispersed and stabilized with surfactants or emulsifiers can be used.

[0035] The wax content is preferably 1-7% by weight as solid content, more preferably 2-6% by weight, and even more preferably 3-5% by weight. If the wax content is less than 1% by weight, the above effects tend to be insufficient. On the other hand, if the wax content exceeds 7% by weight, the rust removal effect is inhibited because the water content is relatively reduced, and the cost becomes unnecessarily high, which is undesirable.

[0036] The surface preparation agent of the present invention may further contain, as an electrochemical reaction accelerator, inorganic anions or inorganic cations derived from an electrolyte with a solubility in water of 10 g / 100 mL or more. Among such inorganic anions, chloride ions are preferred due to their high corrosiveness to iron, and examples of electrolytes that dissociate chloride ions include sodium chloride, calcium chloride, and iron(III) chloride. In existing steel materials that have rusted in an outdoor environment, chloride ions, which are corrosion-promoting substances, are often inherent in the rust, so in such cases, it is not necessary to replenish chloride ions. However, if a small amount of inorganic anions are added to the rust remover in advance, the original rust removal accelerating effect can be obtained even in rusted steel materials with a low amount of inherent salt.

[0037] On the other hand, among inorganic cations, the oxidizing agent is the trivalent iron ion (Fe 3+ ) is preferred because it promotes the anodic dissolution of iron, and examples of electrolytes that dissociate iron(III) ions include iron(III) chloride and ammonium iron(III) citrate. The electrolyte can be dissolved and dissociated in the rust remover, and can be included in a limit that does not exceed the pH range of the rust remover and does not excessively adversely affect the viscosity.

[0038] The electrolyte content is preferably 0.01 to 3% by weight, more preferably 0.05 to 2% by weight, and even more preferably 0.1 to 1% by weight. If the electrolyte content is too low, the rust removal accelerator effect tends to be insufficient. On the other hand, if the electrolyte content is too high, it inhibits the viscosity-imparting effect of the water-soluble polymer contained in the rust remover.

[0039] Aliphatic polyhydric alcohols or carbohydrates can be added to the substrate conditioner as a water syneresis inhibitor, to the extent that they do not inhibit the effects of the substrate conditioner. Preferred aliphatic polyhydric alcohols are those with 2 to 6 carbon atoms that have high solubility in water, such as dihydric alcohols like ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and dipropylene glycol; and trihydric alcohols like glycerol. Examples of carbohydrates include monosaccharides such as glucose, fructose, and galactose; disaccharides such as sucrose, lactose, and maltose; oligosaccharides such as oligosaccharides; polysaccharides such as dextrin; and sugar alcohols such as xylitol, sorbitol, erythritol, pentaerythritol, and dipentaerythritol. The aliphatic polyhydric alcohols or carbohydrates added to the substrate conditioner can be used individually or in combination of two or more.

[0040] Furthermore, especially when organic substances such as oils are attached to existing steel materials, the penetration of the surface preparation agent into the existing coating or rust is inhibited. For this reason, a penetrating wetting agent can be added to the surface preparation agent, to the extent that it does not inhibit the effects of the present invention. The type of penetrating wetting agent is not particularly limited, and includes nonionic surfactants, silicone surfactants, anionic surfactants, cationic surfactants, etc., as long as it facilitates the penetration of water into the rust. These penetrating wetting agents can be used individually or in combination of two or more types.

[0041] Furthermore, the surface preparation agent may optionally contain organic acids, inorganic acids, preservatives, fungicides, defoamers, initial rust inhibitors, fluorescent whitening agents, gelling agents, synthetic resin emulsions, and drying retarding solvents, provided that they do not hinder the effects of the present invention.

[0042] 《Method for preparing the surface of existing steel materials》 The method for preparing the surface of existing steel materials according to the present invention (chemical surface preparation method) consists of three steps: a preliminary step, an action step, and a removal step.

[0043] <Preliminary process> Regardless of the presence or absence of existing paint film, areas with thick rust such as loose rust, layered rust, or scale rust are pre-treated by striking them with a specialized impact tool to break them up and remove them, exposing the solidified rust. Furthermore, conventional physical rust removal is performed on the exposed solidified rust using a scraping tool to remove the rust until only a thin layer remains. Specifically, it is preferable that the thickness of the solidified rust be 100 μm or less. By pre-treating the rust to this extent, exposed areas of the base iron are almost always formed in various places, whether intentionally or inevitably. The rust removal action of the surface conditioner is due to the acid dissolution reaction of rust and the electrochemical reaction consisting of the anodic and cathode reactions, and the exposed areas of the base iron become areas that promote the anodic reaction. Therefore, the rust removal action of the surface conditioner is further promoted by the exposure of the base iron in various places. Furthermore, in areas where existing paint film remains, conventional chemical surface preparation using a conventionally known paint film remover may be performed beforehand to remove some of the existing paint film on the surface until only the bottom layer of the existing paint film, which is difficult to remove, remains. The existing paint film, which has swollen and softened after applying the paint film remover, is peeled off and removed with a scraper or similar tool. It is preferable that this operation creates scratches that reach the rust beneath the paint film, and it is even preferable that the base iron is exposed in some places.

[0044] <Coating process> After the preliminary steps, the surface conditioner is applied to any remaining existing paint film (residual paint film) and any exposed rust present. The method of applying the surface conditioner is not particularly limited; typical examples include roller application using a flocked roller or porous sponge roller, brush application, and spray application using a sprayer or aerosol machine. The application rate is 0.1 to 2.4 kg / m². 2 Preferably, 0.3 to 2.2 kg / m 2 More preferably, 0.5-2.0 kg / m 2 A larger amount is preferable. If too little is applied, the coating will dry out easily, and the rust-removing action will be insufficient. On the other hand, if too much is applied, the coating will not stay in place easily, and it will be more prone to dripping on downward surfaces and sagging on vertical and inclined surfaces.

[0045] After applying the substrate conditioner, if the liquid temperature is 23 °C, leaving it for generally 1 to 24 hours allows the coating film peeling action and rust removal action to proceed, reducing the adhesion of the existing coating film and rust to the base iron. If the leaving time is too short, these actions tend to proceed insufficiently. Conversely, if the leaving time is too long, the construction time will be unnecessarily extended. In addition, in the remaining coating film part, the existing coating film softens and swells, and more significantly, the existing coating film floats, so it can be used as a measure of the progress of the coating film peeling action. Also, in the exposed part of the rust, iron ions (Fe 2+ ) elute into the coating liquid and are further oxidized by air, causing the coating liquid to turn dark brown, so this degree of color change can be used as a measure of the progress of the rust removal action.

[0046] <Removal process> Remove the existing coating film and rust with reduced adhesion to the base iron due to the coating process using a brush, scraper, leather skin, brush sander, etc. Whether it is necessary to remove the substrate conditioner before removing the rust is not questioned, but if the rust removal operation is carried out without removing the substrate conditioner, the scattering of dust can be suppressed. Also, before removing the existing coating film and rust, the substrate conditioner can be wiped off with a spatula, leather skin, waste cloth, etc., or washed away by high-pressure water washing. In that case, the scattering of dust can be suppressed by carrying out the removal operation of the existing coating film and rust while the rust surface remains wet without drying. After removing the existing coating film and rust, wash the powder and salt remaining on the treated surface with water, alkaline water, etc., and quickly dry it to prevent the generation of re-rust and make the substrate suitable for painting.

Example

[0047] The following describes examples embodying the present invention, but the present invention is not limited to the following examples. The compositions of the examples are shown in Table 1, and the compositions of the comparative examples are shown in Table 2.

[0048]

Table 1

[0049]

Table 2

[0050] <Materials used> The materials shown in Tables 1 and 2 are as follows: (Benzyl alcohol emulsifier) Polysaccharide 1: "Natrozole 250HR Hydroxyethylcellulose," a polysaccharide derivative manufactured by Ashland Japan Co., Ltd. Polysaccharide 2: "HEC Daicel SP-900 Hydroxyethylcellulose," a polysaccharide derivative manufactured by Daicel Finechem Co., Ltd. Polysaccharide 3: BG-15 Hydroxyethylcellulose, a polysaccharide derivative manufactured by Sumitomo Seika Co., Ltd. Polysaccharide 4: MP Gokyo Food & Chemical Co., Ltd.'s "Grilloid 6C Tamarind Seed Gum" is a polysaccharide. Polysaccharide 5: "Snow Algin H Sodium Alginate," a polysaccharide manufactured by Fuji Chemical Industry Co., Ltd. Polysaccharide 6: KELZAN AP Xanthan Gum, manufactured by Sansho Co., Ltd., is a polysaccharide. Polysaccharide 7: Combizell HF4M methylhydroxypropylcellulose, a polysaccharide derivative manufactured by Tianpu Cemicals Co. Ltd. (Hydroxy acid) Hydroxy acid 1: "Citric acid (crystalline)" manufactured by Fujifilm Wako Pure Chemical Corporation. Hydroxy Acid 2: "DL-Malic Acid" manufactured by Marubeni Corporation Hydroxy acid 3: Diammonium hydrogen citrate, manufactured by Kanto Chemical Co., Ltd., is an acidic salt of citric acid. (pH adjuster) Base 1: "25% Ammonia Water" manufactured by Goto Chemical Co., Ltd. Base 2: Sodium citrate (trisodium citrate) manufactured by Matsuba Pharmaceutical Co., Ltd.

[0051] <Preparation of water-based substrate conditioners> The substrate preparation agents for the examples and comparative examples were prepared using the following procedure. First, a predetermined amount of water was measured into a 150cc poly cup, and the predetermined polysaccharides (except for Comparative Example 7) were added and dissolved while stirring with a mixer. Next, the predetermined hydroxy acid (except for Comparative Example 6) was added and dissolved while stirring with the mixer. Furthermore, for Examples 1, 2, and 4, the predetermined base was added while stirring with the mixer. Finally, a predetermined amount of benzyl alcohol was added while stirring with the mixer (except for Comparative Example 5), and the miscibility (whether or not it could be emulsified) was evaluated according to the following criteria. In addition, the pH of Examples 1-12 and Comparative Examples 5 and 6 was measured using a glass electrode pH meter.

[0052] <Mixibility> ○: Good white emulsion □: White emulsion layer is fairly good (partially separated) △: Insufficient whitening, which is an indicator of the degree of emulsification. ×: Does not emulsify, does not mix.

[0053] Examples 1-12 and Comparative Example 6 showed generally good miscibility. Comparative Examples 1 and 2 showed insufficient whitening, which is an indicator of the degree of emulsification, while Comparative Examples 3 and 7 did not emulsify and were not miscible. Comparative Example 4 produced aggregates due to salting out. Comparative Example 5 did not contain benzyl alcohol and was therefore not evaluated.

[0054] Examples 1-11 and Comparative Example 5 had a pH range of 4-6. Example 12, which was not pH-adjusted, had a pH of slightly over 2. Comparative Example 6 did not contain hydroxy acids, so its pH was 7.4. Comparative Examples 1-4 and Comparative Example 7 were excluded from pH measurement due to poor miscibility of benzyl alcohol.

[0055] <Procedure for preparing test substrates> The test substrate was prepared using the following procedure. Procedure 1: The base material will be structural steel plate SS400 as specified in JIS G 3101 (size: 150 mm long x 70 mm wide x 3.2 mm thick), and the test surface will be blast-treated in accordance with JIS K 5551 7.14 (cyclic corrosion resistance). Step 2: Dilute EpoMild Gray (manufactured by Suzuka Fine Co., Ltd.), a one-component, low-solvent, reaction-curing epoxy resin-based rust-preventive paint, with paint thinner to a ratio of 50%. Step 3: Divide the test surface vertically into two sections, and apply diluted EPOMild Gray to one section at a rate of 0.1 kg / m². 2 Apply with an air sprayer to achieve the desired finish, and allow to dry at 23°C for 7 days. Step 4: Apply molten paraffin (petroleum wax specified in JIS K 2235, with a melting point of 55-65°C) to the back and sides of the substrate using a brush, and allow it to solidify at room temperature. Step 5: Treat the test surface with a neutral salt spray test as specified in JIS Z 2371:2015, 6.2, for 110 hours. Step 6: Remove the substrate from the test machine and allow it to dry at room temperature for 24 hours. Step 7: Remove any fragile rust layers on the untreated surfaces of the Epomild by tapping them with a hammer. Scrub any remaining rust with a wire brush, then remove any powdery material adhering to the surface with a cloth.

[0056] <Testing Method> The substrate is divided horizontally into six equal parts, and Examples 1-12 and Comparative Examples 5 and 6 are applied to each area, ensuring that the application spans both the Epomild-coated surface and the uncoated (rusted) surface. The size of the application area is 6 cm vertically and 1.2 cm horizontally, with a coating amount of 1.0 kg / m². 2 Apply with a brush in the manner shown. After 16 hours at 23°C, remove the Epomild coating and weakened rust along with the coating solution using a metal spatula. Furthermore, wash the test surface with water using a poly brush to remove any remaining Epomild coating and rust simultaneously.

[0057] <Evaluation Method> Table 1 shows the evaluation results for the examples, and Table 2 shows the evaluation results for the comparative examples. The evaluation criteria for each evaluation item are shown below.

[0058] (Paint film peelability) The peeling rate of the EPOMild coating was evaluated according to the following criteria. ○: More than 90% △: 50-90% ×: Less than 50%

[0059] (rust removal) The rust removal rate (exposure rate of the steel surface) on the uncoated surface (rusted surface) of Epomild was evaluated according to the following criteria. ◎:More than 70% ○: 30-70% □: 10-30% ×: Less than 10%

[0060] Examples 1-12 showed nearly good paint film peeling and rust removal properties. Comparative Example 5 showed good rust removal properties but poor paint film peeling properties. Comparative Example 6 showed good paint film peeling properties but poor rust removal properties. Comparative Examples 1-4 and Comparative Example 7 had poor miscibility with benzyl alcohol and were therefore excluded from evaluation.

Claims

1. This is a water-based surface preparation agent composition for removing rust along with the existing paint film when repainting existing paint films applied to existing steel materials. It contains benzyl alcohol, a hydroxy acid, and water. The hydroxy acid is citric acid, malic acid, or an acidic salt thereof. A water-based substrate preparation composition containing hydroxyethylcellulose as an emulsifier for the benzyl alcohol.

2. The aqueous substrate conditioning agent composition according to claim 1, wherein the pH is 4.0 to 6.

0.

3. A method for preparing the surface of existing steel materials, comprising applying the water-based surface preparation agent composition described in claim 1 or claim 2 to the existing steel material, thereby removing rust along with the existing coating.

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