Scale remover and method for producing metal material

Abstract

To provide a scale remover which can remove scale while keeping plating film.SOLUTION: A scale remover contains a chelating agent, an organic acid, a fluorochemical and a surfactant. The chelating agent contains an aminocarboxylic acid type chelating agent. The aminocarboxylic acid type chelating agent has equal to or more than 2 carboxyalkyl groups binding to nitrogen atom in the molecule. The carboxyalkyl group is structured by linear alkylene groups. Equal to or more than 2 of the carboxyalkyl group are carboxymethyl groups.SELECTED DRAWING: Figure 1B

Description

[Technical field]

[0001] The present invention relates to a scale remover and a method for producing a metal material. [Background technology]

[0002] Welding of metal materials is generally performed at high temperatures. As a result, the area around the welded surface oxidizes and discolors. This discoloration is called scale. Scale not only changes the appearance of the metal material, but also inhibits the formation of a chemical conversion coating. As a result, the corrosion resistance of the metal material is easily reduced.

[0003] Therefore, Patent Document 1 proposes a scale remover containing an organic phosphonic acid or a salt thereof. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-70805 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, it has been found that when a scale remover containing an organic phosphonic acid or the like is applied to a metal material having a plated coating, the plated coating dissolves.

[0006] An object of the present invention is to provide a scale remover capable of removing scale while maintaining a plating coating. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides the following aspects. [1] The composition includes a chelating agent, an organic acid, a fluorine compound, and a surfactant, The chelating agent includes an aminocarboxylic acid type chelating agent, The aminocarboxylic acid type chelating agent has two or more carboxyalkyl groups bonded to a nitrogen atom in the molecule, The carboxyalkyl group is composed of a linear alkylene group, A scale remover, wherein two or more of the carboxyalkyl groups are carboxymethyl groups.

[0008] [2] The scale remover according to [1] above, wherein the aminocarboxylic acid type chelating agent has three or more carboxymethyl groups bonded to nitrogen atoms in the molecule.

[0009] [3] The scale remover according to the above [1] or [2], wherein the aminocarboxylic acid type chelating agent contains nitrilotriacetic acid.

[0010] [4] Content C of the aminocarboxylic acid type chelating agent C1 and the organic acid content C A Mass ratio to: C C1 / C A The scale remover according to any one of the above [1] to [3], wherein the ratio of the scale remover to the total scale is 10 / 90 to 90 / 10.

[0011] [5] Content C of the aminocarboxylic acid type chelating agent C1 The scale remover according to any one of the above [1] to [4], wherein the content of 3,000 ppm by mass or more and 60,000 ppm by mass or less is 3,000 ppm by mass or more and 60,000 ppm by mass or less.

[0012] [6] The organic acid content C A The scale remover according to any one of the above [1] to [5], wherein the content of ammonium nitrate is 3,000 ppm by mass or more and 60,000 ppm by mass or less.

[0013] [7] The scale remover according to any one of the above [1] to [6], wherein the organic acid includes an alkyl carboxylic acid.

[0014] [8] The scale remover according to [7] above, wherein the alkyl carboxylic acid has two or more carboxy groups.

[0015] [9] The scale remover according to any one of the above [1] to [8], which is for a metal material having a plated coating.

[0016]

[10] The method includes a step of contacting a scale remover with a metal material, The scale remover includes a chelating agent, an organic acid, a fluorine compound, and a surfactant, The chelating agent includes an aminocarboxylic acid type chelating agent, The aminocarboxylic acid type chelating agent has two or more carboxyalkyl groups bonded to a nitrogen atom in the molecule, The carboxyalkyl group is composed of a linear alkylene group, The method for producing a metal material, wherein two or more of the carboxyalkyl groups are carboxymethyl groups.

[0017]

[11] The method for producing a metal material described in

[10] above, wherein in the contacting step, the metal material is immersed in the scale remover.

[0018]

[12] The method for producing a metal material described in

[11] above, wherein the metal material is immersed in the scale remover at a temperature of 40°C or more and 70°C or less for 1 minute or more and 50 minutes or less.

[0019]

[13] The method for producing a metal material according to any one of the above

[10] to

[12] , wherein the metal material includes a metal material having a plating film.

[0020]

[14] The method for producing a metal material according to the above-mentioned

[13] , wherein the metal material having a plating coating includes a zinc-plated steel sheet. Effect of the Invention

[0021] According to the present invention, a scale remover capable of removing scale while maintaining a plating coating can be provided. [Brief description of the drawings]

[0022] [Figure 1A] 1 is an image (magnification 5x) taken through a magnifying glass of the periphery of a weld bead portion of a test piece prepared in Example 1. [Figure 1B] 1B is an image taken through a magnifying glass (magnification 5x) of the area corresponding to FIG. 1A after treatment with a descaling agent. [Diagram 2] 1 is a scanning electron microscope (SEM) image (magnification: 1,500 times) of the periphery of a weld bead portion of the test piece prepared in Example 1 after chemical conversion treatment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Scale is a metal oxide that is produced when metal components combine with oxygen in the air during welding of metal materials such as steel plates. Scale may contain carbon as well as metal oxides. Scale is also called welding burn.

[0024] Similarly, when welding metal materials having a plated coating, scale is formed on the plated coating. If a descaling agent containing a phosphonic acid chelating agent is used to remove this scale, the plated coating also dissolves.

[0025] In view of this, the present embodiment proposes a scale remover containing a specific aminocarboxylic acid-type chelating agent, and a method for manufacturing a metal material using the same. The scale remover according to the present embodiment can remove scale while maintaining the plating film.

[0026] A. Scale remover The scale remover according to this embodiment includes a chelating agent, an organic acid, a fluorine compound, and a surfactant. The chelating agent includes a specific aminocarboxylic acid type chelating agent (hereinafter referred to as a first chelating agent) having two or more carboxyalkyl groups bonded to nitrogen atoms in the molecule. The carboxyalkyl groups are composed of linear alkylene groups. Two or more of the carboxyalkyl groups are carboxymethyl groups.

[0027] The pH of the scale remover is 6 or more and 8 or less. Even though the scale remover is almost neutral, it can efficiently remove scale by containing a chelating agent, an organic acid, a fluorine compound and a surfactant. Furthermore, discoloration of metal materials and environmental load are suppressed.

[0028] The scale remover is prepared by adding each of the above components to an aqueous solvent and mixing them. Examples of the aqueous solvent include various types of water such as pure water, ion-exchanged water, tap water, and industrial water. The scale remover may contain a small amount of a water-miscible organic solvent (e.g., alcohols) together with water as necessary.

[0029] [Chelating agents] The scale remover according to the present embodiment contains a chelating agent. The chelating agent peels off and captures scale from the surface of the metal material.

[0030] The chelating agent includes a first chelating agent having two or more carboxyalkyl groups bonded to a nitrogen atom in the molecule. The carboxyalkyl groups in the first chelating agent are composed of linear alkylene groups. Furthermore, the two or more carboxyalkyl groups are carboxymethyl groups.

[0031] (First Chelating Agent) The first chelating agent has two or more carboxymethyl groups (-CH2-COOH) bound to a nitrogen atom in the molecule. The two or more carboxymethyl groups may all be bound to the same nitrogen atom, or may be bound to different nitrogen atoms, or two carboxymethyl groups may be bound to the same nitrogen atom and the other carboxymethyl group may be bound to a different nitrogen atom.

[0032] The first chelating agent has an amino group and a carboxy group. Both groups allow the first chelating agent to adsorb to the metal material. The carboxy group has an etching ability, which contributes to the removal of scale, but at the same time dissolves the plating film. On the other hand, the amino group does not exhibit an etching effect, but acts to protect the surface of the metal material. Although the reason is unclear, it is thought that the carboxyalkyl group bonded to the nitrogen atom does not have a branched structure, which makes it easier for the amino group to adsorb to the metal material, making it easier to exert the effect of suppressing the dissolution of the plating film.

[0033] At least two of the carboxyalkyl groups (-R-COOH) bonded to the nitrogen atom are required to be carboxymethyl groups, and the others are not particularly limited. However, all of the carboxyalkyl groups bonded to the nitrogen atom must be linear alkylene groups (R=C n H 2n The number of carbon atoms, n, of the alkylene group constituting the carboxyalkyl group is, for example, about 1 or more and 3 or less.

[0034] The first chelating agent has one or more nitrogen atoms in the molecule. The number of nitrogen atoms may be two or more. That is, the first chelating agent may be a monoaminopolycarboxylic acid or a polyaminopolycarboxylic acid. The first chelating agent may be an alkali metal salt (typically, a sodium salt) of a mono- or polyaminopolycarboxylic acid.

[0035] In the polyaminopolycarboxylic acid, a plurality of nitrogen atoms may be bonded to each other via an alkylene group. The alkylene group linking the nitrogen atoms is preferably linear and has about 1 to 3 carbon atoms.

[0036] From the viewpoint of inhibiting dissolution of the plating film, the number of carboxymethyl groups bonded to nitrogen atoms in the molecule is preferably 3 or more, and more preferably 4 or more.

[0037] The first chelating agent may further have a hydroxy group (-OH). However, the number of hydroxy groups present in the molecule is preferably less than the number of carboxy groups (specifically, carboxyalkyl groups). This prevents the hydrophilicity of the first chelating agent from becoming excessively high. Scale usually contains carbon and is therefore hydrophobic. Since the hydrophilicity of the first chelating agent is not excessively high, diffusion into the aqueous solvent is suppressed and the first chelating agent is easily brought into contact with the scale. As a result, the scale removal effect can be further improved.

[0038] The molecular weight of the first chelating agent is not particularly limited. In terms of being able to easily obtain the effect with a small amount, the molecular weight of the first chelating agent is preferably 350 or less, more preferably 300 or less, and particularly preferably 250 or less.

[0039] Examples of the first chelating agent include ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA), hydroxyethylethylenediaminetriacetic acid (HEDTA), triethylenetetraaminehexaacetic acid (TTHA), 1,3-propanediaminetetraacetic acid (PDTA), 1,3-diamino-2-hydroxypropanetetraacetic acid (DPTA-OH), hydroxyethyliminodiacetic acid (HIDA), glycoletherdiaminetetraacetic acid (GEDTA), and L-glutamic acid diacetic acid (GLDA). Some structural formulas of the first chelating agent are shown below.

[0040] [ka]

[0041] [ka]

[0042] [ka]

[0043] [ka]

[0044] [ka]

[0045] [ka]

[0046] [ka]

[0047] [ka]

[0048] The first chelating agent may be used alone or in combination of two or more. Among them, NTA, EDTA, and PDTA are preferred because they are more likely to inhibit dissolution of the plating film. NTA is particularly preferred. NTA, EDTA, and PDTA have relatively small molecular weights and therefore have high adsorption to metal materials. Therefore, they exhibit a higher effect of inhibiting dissolution of the plating film.

[0049] Content of the first chelating agent C C1The content of C is preferably 3,000 ppm by mass or more and 60,000 ppm by mass or less. This makes it easier to exhibit the effect of inhibiting dissolution of the plating film and the effect of removing scale. C1 is more preferably 5,000 mass ppm or more, particularly preferably 7,000 mass ppm or more. C1 is more preferably 50,000 ppm by mass or less, particularly preferably 30,000 ppm by mass or less.

[0050] (Second Chelating Agent) An aminocarboxylic acid type chelating agent other than the first chelating agent (hereinafter referred to as a second chelating agent) may be included. Even in this case, the effect of inhibiting dissolution of the plating film and the effect of removing scale can be exerted.

[0051] From the viewpoint of suppressing dissolution of the plating film and removing scale, the content of the second chelating agent C C2 is the content C of the first chelating agent C1 It is preferably 30% by mass or less, and more preferably 10% by mass or less.

[0052] Content of second chelating agent C C2 The content of C is preferably 18,000 mass ppm or less. This makes it easier to obtain the effect of removing scale while suppressing dissolution of the plating film. C2 is more preferably 15,000 ppm by mass or less, particularly preferably 9,000 ppm by mass or less.

[0053] Examples of the second chelating agent include an aminocarboxylic acid type chelating agent having an alkylene group with a branched structure and an aminocarboxylic acid type chelating agent having only one carboxyalkyl group bonded to a nitrogen atom. These may be used alone or in combination of two or more.

[0054] Examples of aminocarboxylic acid type chelating agents having branched alkylene groups include methylglycine diacetate (MGDA), (S,S)-ethylenediaminedisuccinic acid (EDDS), aspartic acid diacetate (ASDA), and glutamic acid diacetate (CMGA). The structural formulae of MGDA, EDDS, and CMGA are shown below.

[0055] [ka]

[0056] [ka]

[0057] [ka]

[0058] An example of an aminocarboxylic acid type chelating agent having only one carboxyalkyl group bonded to a nitrogen atom in the molecule is dihydroxyethylglycine (DHEG), the structural formula of which is shown below.

[0059] [ka]

[0060] (Third Chelating Agent) A chelating agent other than the aminocarboxylic acid type chelating agent (hereinafter referred to as a third chelating agent) may be included, which can improve the scale removal effect.

[0061] However, from the viewpoint of suppressing dissolution of the plating film, the content of the third chelating agent C C3 is the content C of the first chelating agent C1 It is preferably 30% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less.

[0062] Content of the third chelating agent CC3 is preferably 5,000 mass ppm or less, more preferably 2,000 mass ppm or less, and particularly preferably 1,500 mass ppm or less. C3 may be 600 ppm by mass or more, or 1,000 ppm by mass or more.

[0063] Examples of phosphonic acid chelating agents include hydroxyethylidene diphosphonic acid (HEDP), nitrilotrismethylenephosphonic acid (NTMP), phosphonobutanetricarboxylic acid (PBTC), and ethylenediaminetetramethylenephosphonic acid (EDTMP). The structural formulae of HEDP, NTMP, PBTC, and EDTMP are shown below.

[0064] [ka]

[0065] [ka]

[0066] [ka]

[0067] [ka]

[0068] [Organic acid] The organic acid improves the solubility of the scale, helping the chelating agent to dislodge the scale, without excessively lowering the pH of the descaling agent.

[0069] The organic acid is not particularly limited. From the viewpoint of scale removal effect, an alkyl carboxylic acid having no aromatic ring is preferable. The hydrocarbon group in the alkyl carboxylic acid may be a chain or an alicyclic group. The chain hydrocarbon group may be a straight chain or a branched chain. The hydrocarbon group may be saturated or unsaturated. The number of carbon atoms in the hydrocarbon group may be 1 or more and 20 or less, or 2 or more and 10 or less. The organic acid is used alone or in combination of two or more.

[0070] Examples of saturated aliphatic carboxylic acids include monovalent carboxylic acids such as acetic acid, propionic acid, butyric acid, valeric acid, lauric acid, palmitic acid, and stearic acid; and divalent carboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid. Examples of unsaturated aliphatic carboxylic acids include monovalent carboxylic acids such as acrylic acid, methacrylic acid, oleic acid, and linoleic acid; divalent carboxylic acids such as fumaric acid and maleic acid; and trivalent carboxylic acids such as aconitic acid. Examples of alicyclic carboxylic acids include cyclohexane carboxylic acid and 1,4-cyclohexane dicarboxylic acid. Among these, alkyl carboxylic acids having two or more carboxy groups (divalent or higher) are preferred. The number of carboxy groups may be 4 or less.

[0071] The organic acid may further have a hydroxy group. This makes it easier to further enhance the scale removal effect. However, it is preferable that the number of hydroxy groups is less than the number of carboxy groups in the molecule. As described above, scale exhibits hydrophobicity. By having a small number of hydroxy groups, the hydrophilicity of the organic acid is not excessively high, which suppresses diffusion into the aqueous solvent and makes it easier to contact the scale. As a result, the scale removal effect can be further improved. The number of hydroxy groups may be 1 or 2.

[0072] Examples of alkyl carboxylic acids having a hydroxy group (alkyl hydroxy carboxylic acids) include lactic acid, malic acid, and citric acid. Among these, malic acid and citric acid, which are divalent or higher alkyl hydroxy carboxylic acids, are more preferred.

[0073] Organic acid content C A The content of C is preferably 3,000 ppm by mass or more and 60,000 ppm by mass or less. This makes it possible to more efficiently remove scale and to easily suppress dissolution of the plating film. A is more preferably 5,000 mass ppm or more, particularly preferably 7,000 mass ppm or more. C1 is more preferably 50,000 ppm by mass or less, particularly preferably 30,000 ppm by mass or less.

[0074] Content of the first chelating agent C C1 and organic acid content C A Mass ratio to: C C1 / C A The ratio is preferably in the range of 10 / 90 to 90 / 10. This allows scale to be removed more efficiently and makes it easier to suppress dissolution of the plating film. C1 / C A More preferably, the ratio is in the range of 30 / 70 to 70 / 30, and particularly preferably in the range of 45 / 55 to 55 / 45.

[0075] An acid (inorganic acid) other than an organic acid may be included. However, from the viewpoint of suppressing dissolution of the plating film, the content of inorganic acids other than hydrofluoric acid is preferably as small as possible. The content of inorganic acids is preferably 200 ppm by mass or less, more preferably 100 ppm by mass or less, and particularly preferably below the detection limit. Examples of inorganic acids other than hydrofluoric acid include hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, and boric acid. These may be used alone or in combination of two or more.

[0076] [Fluorine compounds] The fluorine-containing compound is a source of fluorine ions. The fluorine ions stabilize the metal ions contained in the scale in the scale remover, making it easier for the scale to dissolve from the surface of the metal material, and the scale is removed efficiently.

[0077] The fluorine-containing compound is not particularly limited as long as it liberates fluorine ions. Examples of the fluorine-containing compound include hydrofluoric acid, acidic sodium fluoride, acidic ammonium fluoride, fluorotitanic acid, fluorozirconic acid, fluorosilicic acid, ammonium fluoride, sodium fluoride, potassium fluoride, and potassium hydrogen difluoride. These compounds may be used alone or in combination of two or more.

[0078] Fluorine ion content C F The content C is preferably 500 ppm by mass or more and 10,000 ppm by mass or less in terms of the amount of fluorine atoms. This further increases the stability of the metal ions contained in the scale in the scale remover. F is more preferably 1,000 mass ppm or more, particularly preferably 3,000 mass ppm or more. F is more preferably 8,000 ppm by mass or less, particularly preferably 7,000 ppm by mass or less.

[0079] [Surfactants] The surfactant further enhances the scale removal performance. The surfactant may be at least one of an anionic surfactant and a nonionic surfactant.

[0080] The anionic surfactant is not particularly limited, and known surfactants can be used. Examples of the anionic surfactant include phosphate ester surfactants, carboxylic acid surfactants, sulfonic acid surfactants (including sulfosuccinic acid surfactants), and sulfate ester surfactants. These can be used alone or in combination of two or more.

[0081] Commercially available anionic surfactants include, for example, DOW TRITON H66 (registered trademark) (manufactured by Dow Chemical Japan, a potassium phosphate type surfactant), NEOGEN AS-20 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., a sulfonic acid type surfactant), SANMOLIN OT-70 (manufactured by Sanyo Chemical Industries, Ltd., a sulfosuccinic acid type surfactant), NOIGEN ES-99 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and SANSPEARL PDN-173 (manufactured by Sanyo Chemical Industries, Ltd., a carboxylic acid type surfactant).

[0082] The nonionic surfactant is not particularly limited, and any known surfactant can be used. Examples of the nonionic surfactant include polyoxyalkylene glycol fatty acid esters, polyalkylene glycol fatty acid esters, and polyoxyalkylene alkyl ethers.

[0083] Commercially available nonionic surfactants include, for example, Adekanol UA series (manufactured by ADEKA Corporation), Genapol EP 2564 (manufactured by Clariant Japan KK), Noigen XL100 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and Genagen C 100 (manufactured by Clariant Japan KK).

[0084] Surfactant content C S The content C is preferably 300 ppm by mass or more and 3,000 ppm by mass or less. This makes it easier to further improve the scale removal performance. S is more preferably 400 mass ppm or more. S More preferably, the content is 2,000 ppm by mass or less.

[0085] [Rust inhibitor] The scale remover may contain a rust inhibitor, which enhances the rust prevention of the metal material after scale removal and before chemical conversion treatment is performed.

[0086] Examples of the rust inhibitor include so-called P-based, N-based, S-based, and acetylene-based rust inhibitors. Examples of the P-based rust inhibitor include phosphates. Examples of the N-based organic acids include alkylamines, imidazoles, and triazoles. Examples of the S-based rust inhibitor include santhiol and thiourea. Examples of the acetylene-based rust inhibitor include 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol, 2,5-dimethyl-3-hexyne-2,5-diol, and 3,6-dimethyl-4-octyne-3,6-diol. Examples of commercially available rust inhibitors include KORANTIN PM (manufactured by BASF Japan).

[0087] Rust inhibitor content C R The content of the fluorine-containing compound is preferably from 50 ppm by mass to 300 ppm by mass, which makes it easier to further improve the rust prevention properties of the metal material.

[0088] [Other ingredients] The scale remover may contain other components within the range that does not impair the effect, such as a pH adjuster, a preservative stabilizer, an antifoaming agent, an antifreeze agent, a preservative, and an antifungal agent.

[0089] [Metal material] The scale remover is used for metal materials. The scale remover is particularly used for removing weld scale from metal materials having welded parts. The metal materials are not particularly limited, and examples thereof include iron materials, cold-rolled steel sheets, hot-rolled steel sheets, galvanized steel sheets, and aluminum alloy materials.

[0090] The scale remover according to this embodiment can efficiently remove scale while suppressing dissolution of the plating film. Therefore, the scale remover according to this embodiment is particularly suitable for removing scale from metal materials having a plating film (typically, galvanized steel sheets) and materials in which a metal material having a plating film and a metal material not having a plating film are welded together.

[0091] B.Metal material manufacturing method The scale remover according to the present embodiment can be used to manufacture a metal material from which scale has been removed. The metal material is manufactured by a method including a step of contacting the scale remover according to the present embodiment with the metal material.

[0092] (1) Contact process The method of contacting the scale remover with the metal material is not particularly limited. Examples of the contact method include spraying and immersion. Among these, immersion is preferred because of its high contact efficiency. The immersion method is suitable as a method for continuously processing metal materials because it can achieve a scale removal effect in a relatively short time.

[0093] In the spraying method, the spray pressure may be 0.08 MPa or more and 2 MPa or less, and may be 0.1 MPa or more and 1.5 MPa or less.

[0094] In the immersion method, ultrasonic waves may be applied to the surface of the metal material while the metal material is immersed in a bath of the scale remover. The frequency of the ultrasonic waves may be 25 kHz or more and 100 kHz or less, or 30 kHz or more and 50 kHz or less.

[0095] In the immersion method, the scale remover may be stirred while the metal material is immersed in a bath of the scale remover. This causes the scale remover to flow. The flow velocity of the scale remover on the surface of the metal material may be 10 cm / sec to 40 cm / sec, or 15 cm / sec to 35 cm / sec. The surface flow velocity can be measured using a commercially available surface current meter (e.g., JFE Advantech Co., Ltd., three-axis electromagnetic flow sensor, ACM3-RS, etc.).

[0096] The temperature of the scale remover may be 40° C. or higher and 70° C. or lower. This makes it easier to achieve the scale removal effect and reduces the burden on the equipment. The temperature of the scale remover is preferably 50° C. or higher and 70° C. or lower, and particularly preferably 55° C. or higher and 65° C. or lower.

[0097] The contact time between the scale remover and the metal material may be appropriately set depending on the contact method. The contact time in the spraying method may be, for example, 3 minutes or more and 30 minutes or less, or 5 minutes or more and 20 minutes or less. The contact time in the immersion method may be, for example, 1 minute or more and 50 minutes or less, or 1 minute or more and 30 minutes or less, or 1 minute or more and 15 minutes or less.

[0098] (2)Chemical conversion process After the contact step of the scale remover, the surface of the metal material may be subjected to a chemical conversion treatment. Since the scale remover according to the present embodiment efficiently removes scale, a chemical conversion film is easily formed on the obtained metal material. Examples of the chemical conversion treatment include zinc phosphate chemical conversion treatment and zirconium chemical conversion treatment.

[0099] In the zinc phosphate chemical conversion treatment, a chemical conversion treatment agent containing zinc phosphate is used. The chemical conversion treatment agent containing zinc phosphate is not particularly limited, and a conventionally known one can be used. A preferred chemical conversion treatment agent contains zinc ions of 0.5 g / L or more and 2 g / L or less (more preferably 0.7 g / L or more and 1.2 g / L or less), phosphate ions of 5 g / L or more and 30 g / L or less (more preferably 10 g / L or more and 20 g / L or less), and manganese ions of 0.2 g / L or more and 2 g / L or less (more preferably 0.3 g / L or more and 1.2 g / L or less).

[0100] Prior to the zinc phosphate conversion treatment, the metal material may be subjected to a surface conditioning treatment. This facilitates the formation of crystals of the zinc phosphate coating on the surface of the metal material, making it easier to obtain a uniform and dense conversion coating. The surface treatment agent is, for example, a weak alkaline solution containing dispersed titanium colloids. The titanium colloids become the nuclei of the crystals. The crystals are generated and grow from the titanium colloids.

[0101] In the zirconium chemical conversion treatment, a chemical conversion treatment agent containing zirconium ions (zirconium chemical conversion treatment agent) is used. The concentration of zirconium ions in the zirconium chemical conversion treatment agent is preferably 10 ppm or more and 10,000 ppm or less.

[0102] The descaled and chemically treated metal materials are particularly suitable for use in the manufacture of automobile bodies and parts thereof, such as passenger cars, trucks, motorcycles, buses, and the like. EXAMPLES

[0103] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In the examples, "parts" and "%" are by weight unless otherwise specified.

[0104] [Example 1] (a) Preparation of scale agent NTA (chelating agent), ADEKA NOL UA90N (nonionic surfactant, manufactured by ADEKA Corporation, polyoxyalkylene alkyl ethers), citric acid (organic acid), acidic ammonium fluoride (fluorine compound), and KORANTIN PM (rust inhibitor, manufactured by BASF Japan Ltd.) were mixed into water. The pH was then adjusted to 6 using an aqueous NaOH solution (40%) to obtain a scale remover. The content of the chelating agent was 10,000 ppm, the content of the surfactant was 300 ppm, the content of the organic acid was 10,000 ppm, the content of the fluorine compound was 5,000 ppm, and the content of the rust inhibitor was 300 ppm.

[0105] (b) Preparation of metal materials Two galvanized steel sheets were prepared and welded together. Scale was formed near the weld bead. The welded product with the scale was used as a test piece.

[0106] (c) Contact with descaling agents The scale remover obtained above was placed in a 10 L treatment bath, and the temperature was adjusted to 60°C. The test piece was immersed in the treatment bath for 10 minutes. After that, the test piece was taken out and thoroughly washed. After washing, it was dried at 40°C for about 10 minutes.

[0107] (d) Degreasing, surface preparation and chemical conversion treatment After the treatment (c), the test pieces were degreased using Surf Cleaner EC90 (manufactured by Nippon Paint Surf Chemicals Co., Ltd.) with a pH adjusted to 11. The treatment temperature was 45°C and the treatment time was 120 seconds. After the degreasing treatment, the test pieces were washed with water. Next, the surface of the test piece was conditioned using Surf Fine 7 (manufactured by Nippon Paint Surf Chemicals Co., Ltd.) whose pH was adjusted to 10. The treatment temperature was room temperature, and the treatment time was 30 seconds. Finally, the test pieces were treated with zinc phosphate conversion coating using Surfdyne SD5300 (a zinc phosphate conversion coating agent manufactured by Nippon Paint Surf Chemicals Co., Ltd.) at a treatment temperature of 35°C for 120 seconds.

[0108] [evaluation] The test pieces after treatment (c) or (d) were subjected to the following evaluations. The evaluation results are shown in Table 1.

[0109] (i) Plating retention The plating thickness (Mi) before the process (c) and the plating thickness (Mt) after the process (c) but before the process (d) were measured using a film thickness meter (Fisher Instruments, DELTASCOPE MP30ES). From these measurements, the plating remaining rate was calculated according to the following formula. Plating remaining rate (%) = 100 x plating thickness after treatment (Mt) / plating thickness before treatment (Mi)

[0110] The plating remaining rate was evaluated according to the following criteria. Best: Plating remaining rate is 90% or more Good: Plating remaining rate is between 70% and 90% Acceptable: Plating remaining rate is between 50% and 70% Defective: Less than 50% of the plating remains

[0111] (ii) Scale removal The scale width (bi) before the treatment (c) and the scale width (bt) after the treatment (c) but before the treatment (d) were measured using a vernier caliper. From these measurements, the scale remaining rate was calculated according to the following formula. The scale width is the width of the widest part of the scale generated around the weld bead. Scale remaining rate (%) = 100 x scale width after treatment (bt) / scale width before treatment (bi)

[0112] The scale remaining rate was evaluated according to the following criteria. Best: Less than 30% scale remaining Good: Scale remaining rate is 30% to less than 40% Acceptable: Scale remaining rate is 40% or more but less than 50% Poor: Scale remaining rate is 50% or more

[0113] FIG. 1A is an image (magnification 5x) taken through a magnifying glass of the periphery of the weld bead of the test piece prepared in Example 1. The dark black parts are scale. FIG. 1B is an image (magnification 5x) taken through a magnifying glass of the part corresponding to FIG. 1A after treatment with a scale remover. As can be seen from FIG. 1B, most of the scale has been removed.

[0114] (iii) Chemical properties The periphery of the weld bead after treatment (d) was observed using a SEM (JEOL, JSM6510A) (magnification: 1,500x). The area of ​​the periphery of the weld bead within the observation field was taken as 100%, and the area ratio of the part where the chemical conversion coating was formed (chemical conversion rate) was calculated.

[0115] The conversion rate was evaluated according to the following criteria. Best: conversion rate is 90% or more Good: conversion rate is between 70% and 90% Acceptable: conversion rate is 50% or more but less than 70% Poor: conversion rate is less than 50%

[0116] Figure 2 is an SEM image (magnification 1,500x) of the periphery of the weld bead after treatment (d) of the test piece prepared in Example 1. As can be seen from Figure 2, a chemical conversion coating is formed around the entire periphery of the weld bead.

[0117] [Examples 2-3, Comparative Examples 1-4] A scale remover was prepared, treatment (c) and treatment (d) were carried out, and evaluation was carried out in the same manner as in Example 1, except that the chelating agent was changed as shown in Table 1. The evaluation results are shown in Table 1.

[0118] [Table 1]

[0119] [Examples 4-8] A scale remover was prepared, treatment (c) and treatment (d) were carried out, and evaluation was performed in the same manner as in Example 1, except that the organic acid was changed as shown in Table 2. The evaluation results are shown in Table 2.

[0120] [Table 2]

[0121] [Examples 9-13] A scale remover was prepared, and treatments (c) and (d) were carried out and evaluated in the same manner as in Example 1, except that the first chelating agent and the third chelating agent (HEDP) were mixed as shown in Table 3. The evaluation results are shown in Table 3.

[0122] [Table 3] [Industrial Applicability]

[0123] The scale remover according to the present embodiment is capable of removing scale while maintaining the plating coating, and is therefore preferably applied to metal materials having a plating coating.

Claims

1. The composition includes a chelating agent, an organic acid, a fluorine compound, and a surfactant, The chelating agent includes an aminocarboxylic acid type chelating agent, The aminocarboxylic acid type chelating agent has two or more carboxyalkyl groups bonded to a nitrogen atom in the molecule, The carboxyalkyl group is composed of a linear alkylene group, two or more of the carboxyalkyl groups are carboxymethyl groups; The organic acid includes an alkyl carboxylic acid having two or more carboxy groups, A scale remover for metal materials with plated coatings.

2. The scale remover according to claim 1 , wherein the aminocarboxylic acid type chelating agent has three or more carboxymethyl groups bonded to nitrogen atoms in the molecule.

3. The scale remover according to claim 1 or 2, wherein the aminocarboxylic acid type chelating agent includes nitrilotriacetic acid.

4. The scale remover according to any one of claims 1 to 3, wherein the mass ratio of the aminocarboxylic acid type chelating agent content CC1 to the organic acid content CA: CC1 / CA is 10 / 90 to 90 / 10.

5. The scale remover according to any one of claims 1 to 4, wherein the content CC1 of the aminocarboxylic acid type chelating agent is 3,000 ppm by mass or more and 60,000 ppm by mass or less.

6. The scale remover according to any one of claims 1 to 5, wherein the organic acid content CA is 3,000 ppm by mass or more and 60,000 ppm by mass or less.

7. The method includes a step of contacting a metal material having a plated coating with a scale remover, The scale remover includes a chelating agent, an organic acid, a fluorine compound, and a surfactant, The chelating agent includes an aminocarboxylic acid type chelating agent, The aminocarboxylic acid type chelating agent has two or more carboxyalkyl groups bonded to a nitrogen atom in the molecule, The carboxyalkyl group is composed of a linear alkylene group, two or more of the carboxyalkyl groups are carboxymethyl groups; The organic acid comprises an alkyl carboxylic acid having two or more carboxy groups.

8. The method for producing a metal material according to claim 7 , wherein in the contacting step, the metal material is immersed in the scale remover.

9. The method for producing a metal material according to claim 8, wherein the metal material is immersed in the scale remover at a temperature of 40°C or higher and 70°C or lower for a period of 1 minute to 50 minutes.

10. The method for producing a metal material according to any one of claims 7 to 9, wherein the metal material having the plating film includes a zinc-plated steel sheet.

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