Concentrated solution for preparing surface modifiers, and surface modifiers

Abstract

To provide a concentrated solution for preparing surface modifiers with excellent dispersion stability. [Solution] A concentrated liquid for preparing a surface modifier containing zinc phosphate particles and a dispersion stabilizer, wherein the zinc phosphate particles have a D50 of 3 μm or less, the content of zinc phosphate particles relative to the total mass of the concentrated liquid is 3% by mass or more and 60% by mass or less, the dispersion stabilizer contains layered clay mineral and sulfur-containing compound, the content of layered clay mineral relative to the total mass of the concentrated liquid is 0.1% by mass or more and 20% by mass or less, and the layered clay mineral is natural hectorite and / or synthetic hectorite.

Description

[Technical Field]

[0001] This disclosure relates to a concentrated solution for preparing surface modifiers and to surface modifiers. [Background technology]

[0002] Traditionally, the painting of metal molded products used in automobile bodies, home appliances, etc., has been carried out through various processes such as degreasing, surface preparation, chemical conversion treatment, and electrodeposition coating. Surface preparation treatment is a process applied to form a film containing phosphate crystals uniformly, quickly, and at high density across the entire metal surface in the subsequent phosphate film conversion treatment.

[0003] Regarding surface conditioning treatment techniques, a method for pre-treating a metal surface with an activator-containing aqueous pre-wash bath prior to phosphate treatment has been disclosed, characterized by contacting the metal surface with a pre-wash bath additionally containing montmorillonite (see Patent Document 1). Furthermore, a technique has been proposed for a surface conditioning pre-treatment solution containing one or more phosphates selected from those containing at least one divalent or trivalent metal with a particle size of 5 μm or less, an alkali metal salt or ammonium salt or a mixture thereof, and having a pH adjusted to 4-13 (see Patent Document 2). In addition, a technique has been proposed for a surface conditioning treatment solution before phosphate coating treatment of metals, characterized by containing one or more phosphate particles selected from phosphates containing one or more divalent and / or trivalent metals, and one or more accelerating components selected from monosaccharides, polysaccharides and their derivatives (see Patent Document 3). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 59-226181 [Patent Document 2] Japanese Patent Application Publication No. 10-245685 [Patent Document 3] Japanese Patent Publication No. 2000-96256 [Overview of the project] [Problems that the invention aims to solve]

[0005] The surface conditioning treatment solutions disclosed in the above-mentioned patent document had a particular problem: the dispersion stability of the concentrated solution used to prepare the treatment solution was poor.

[0006] This disclosure has been made in view of the above, and aims to provide a concentrated liquid for preparing surface modifiers that exhibits excellent dispersion stability. [Means for solving the problem]

[0007] (1) This disclosure relates to a concentrated solution for preparing a surface modifier containing zinc phosphate particles and a dispersion stabilizer, wherein the zinc phosphate particles have a D50 of 3 μm or less, the content of the zinc phosphate particles relative to the total mass of the concentrated solution is 3% by mass or more and 60% by mass or less, the dispersion stabilizer contains a layered clay mineral and a sulfur-containing compound, the content of the layered clay mineral relative to the total mass of the concentrated solution is 0.1% by mass or more and 20% by mass or less, and the layered clay mineral is natural hectorite and / or synthetic hectorite.

[0008] (2) The concentrated solution for preparing the surface modifier according to (1), further containing a water-soluble organic polymer as the dispersion stabilizer.

[0009] (3) The sulfur-containing compound is a compound having an isothiazolinone structure, the concentrated solution for preparing a surface modifier according to (1) or (2).

[0010] (4) The water-soluble organic polymer is obtained by polymerizing a monomer composition containing less than 50% by mass of acrylic acid and more than 50% by mass of the total amount of 2-acrylamido-2-methylpropanesulfonic acid and / or allylsulfonic acid, as described in (2), a concentrated solution for preparing a surface modifier.

[0011] (5) The concentrated solution for preparing a surface modifier according to (2) or (4), wherein the ratio of the mass of the sulfur-containing compound to the mass of the water-soluble organic polymer (water-soluble organic polymer / sulfur-containing compound) is 25,000 or less.

[0012] (6) A concentrated solution for preparing a surface modifier according to any one of (1) to (5), wherein the ratio of the mass of the sulfur-containing compound to the mass of the layered clay mineral (layered clay mineral / sulfur-containing compound) is 7500 or less.

[0013] (7) The present disclosure also relates to a surface modifier comprising zinc phosphate particles and a dispersion stabilizer, wherein the zinc phosphate particles have a D50 of 3 μm or less, the content of the zinc phosphate particles relative to the total mass of the surface modifier is 50 ppm by mass or more and 20,000 ppm by mass or less, the dispersion stabilizer comprises a layered clay mineral and a sulfur-containing compound, the content of the layered clay mineral relative to the total mass of the surface modifier is 3 ppm by mass or more and 600 ppm by mass or less, and the layered clay mineral is natural hectorite and / or synthetic hectorite. [Effects of the Invention]

[0014] According to this disclosure, a concentrated liquid for preparing surface modifiers with excellent dispersion stability can be provided. [Modes for carrying out the invention]

[0015] The embodiments of this disclosure are described below. This disclosure is not limited to the embodiments described below.

[0016] <Concentrated solution for preparing surface modifiers> The concentrated solution for preparing surface modifiers according to this embodiment (hereinafter sometimes referred to as "concentrated solution") is a concentrated solution (undiluted solution) used to prepare surface modifiers by dilution or other means. Surface modifiers used in the painting of metal molded products are provided as a concentrated solution, stored, and then used as surface modifiers after being diluted as needed. The concentrated solution contains zinc phosphate particles and a dispersion stabilizer.

[0017] (Zinc phosphate particles) Zinc phosphate particles are used to form a film containing phosphate crystals on the metal surface to be treated. Zinc phosphate particles can be obtained, for example, using commercially available zinc phosphate as a raw material. The raw material zinc phosphate is represented by the chemical formula: Zn3(PO4)2·4H2O.

[0018] The D50 of the zinc phosphate particles is 3 μm or less. When the concentrated solution contains zinc phosphate with a D50 of 3 μm or less, many crystal nuclei can be imparted to the metal surface to be treated before the phosphatization treatment, so that fine phosphate crystals can be precipitated by a phosphatization treatment for a relatively short time. The zinc phosphate particles are not particularly limited as long as the D50 is 3 μm or less. For example, they may be a mixture of particles such that the D50 is 3 μm or less.

[0019] The lower limit of the D50 of the zinc phosphate particles is preferably 0.001 μm. When the D50 is less than 0.001 μm, there is a risk that the particles will aggregate due to overdispersion. When the D50 exceeds 3 μm, the proportion of fine zinc phosphate particles decreases, so that the effects of the present invention cannot be preferably obtained. The above lower limit is more preferably 0.005 μm, and the above upper limit is more preferably 1 μm.

[0020] The D90 of zinc phosphate particles is preferably 4 μm or less. In this case, the zinc phosphate particles not only have a D50 of 3 μm or less, but also a D90 of 4 μm or less, resulting in a relatively small proportion of coarse particles in the zinc phosphate particles. As described above, by using zinc phosphate with a D50 of 3 μm or less, fine phosphate crystals can be precipitated by short-time chemical conversion treatment. However, when using methods such as grinding, excessive grinding can lead to a deficiency of layered clay minerals, etc., due to an increase in specific surface area, causing overdispersion of particles to aggregate and form coarse particles, thus impairing dispersion stability. Furthermore, variations in dispersibility can occur depending on the composition of the concentrated liquid and dispersion conditions, potentially leading to aggregation and thickening due to the close packing of coarse and fine particles, as well as aggregation of fine particles among themselves. However, when the D90 of zinc phosphate particles is 4 μm or less, the above-mentioned problems can be more effectively prevented.

[0021] The lower limit of the D90 of zinc phosphate particles is preferably 0.01 μm. If the D90 is less than 0.01 μm, the particles may aggregate due to overdispersion. If the D90 exceeds 4 μm, the proportion of fine zinc phosphate particles decreases, and the effects of the present invention cannot be desirablely obtained. The lower limit is more preferably 0.05 μm, and the upper limit is more preferably 2 μm.

[0022] In this specification and in the claims, D50 means the volume-average particle diameter (median diameter) measured by dynamic light scattering. D90 means the 90% volume diameter. The above D50 (50% volume diameter) and D90 (90% volume diameter) are determined as the particle size at the point where the cumulative curve reaches 50% and 90%, respectively, when the total volume of particles is taken as 100% based on the particle size distribution in the dispersion. The above D50 and D90 can be measured using particle size analyzers such as a light diffraction particle size analyzer ("LA-500", manufactured by Horiba, Ltd.) or a laser Doppler particle size analyzer ("Microtrac UPA150", manufactured by Nikkiso Co., Ltd.).

[0023] The content of zinc phosphate particles in the concentrated solution is 3% by mass or more and 60% by mass or less relative to the total mass of the concentrated solution. If the above content is less than 3% by mass, when surface conditioning is performed using a surface conditioning agent obtained from the concentrated solution, there may be insufficient phosphate salts to serve as crystal nuclei, and a sufficient surface conditioning effect may not be obtained. In addition, a large amount of concentrated solution is required to maintain the required amount of zinc phosphate concentration in the surface conditioning bath, which may result in poor workability and be uneconomical. If the above content exceeds 60% by mass, the dispersion stability of zinc phosphate particles in the concentrated solution may decrease, and they may settle. The lower limit of the above content is preferably 5% by mass, and the upper limit of the above content is more preferably 50% by mass.

[0024] (Dispersion stabilizer) The dispersion stabilizer contains layered clay minerals and sulfur-containing compounds. It is presumed that the dispersion stabilizer acts as a sedimentation inhibitor for zinc phosphate particles in the concentrated solution. That is, the dispersion stabilizer not only prevents sedimentation of zinc phosphate particles in the surface modifier obtained by diluting the concentrated solution, but also prevents sedimentation of zinc phosphate particles in the concentrated solution, thereby maintaining the long-term dispersion stability of the concentrated solution. Preferably, the dispersion stabilizer further contains a water-soluble organic polymer.

[0025] The layered clay mineral is either natural hectorite or synthetic hectorite, at least one of the above. The layered clay mineral can suppress the sedimentation of zinc phosphate particles contained in concentrated liquids. The reason for this is not clear, but the following reasons are speculated: Adding the layered clay mineral to a concentrated liquid can produce an excellent thickening effect. It can also produce a repulsive effect on charged particles. The synergistic effect of this thickening effect and the repulsive effect of charged particles results in an extremely excellent suppression of zinc phosphate particle sedimentation. As a result, it is presumed that sedimentation of zinc phosphate particles can be further suppressed even in concentrated liquids, and dispersion stability can be maintained over a long period of time. In addition, the above layered clay mineral itself has an electrical repulsive effect. Therefore, when the above layered clay mineral adheres to zinc phosphate particles, the zinc phosphate particles in the concentrated liquid can be stabilized by electrical repulsion. Accordingly, when dispersing components such as zinc phosphate particles in the liquid during the preparation of concentrated liquids, the zinc phosphate particles can be made finer, and the dispersion efficiency can be further improved.

[0026] Natural hectorite is a trioctahedral clay mineral belonging to the montmorillonite group, represented by the following formula (I).

[0027] [Si8(Mg 5.34 Li 0.66 )O 20 (OH)4M + 0.66 ·nH2O] (I)

[0028] Examples of commercially available natural hectorite products include BENTON EW and BENTON AD (manufactured by ELEMENTIS).

[0029] Synthetic hectorite has a three-layer crystalline structure and approximates hectorite belonging to the unlimited-layer expansion type trioctahedral with an expansion lattice. Its main components are magnesium, silicon, sodium, and trace amounts of lithium and fluorine. Synthetic hectorite is represented by the following formula (II).

[0030] [Si8(Mg a Li b )O 20 (OH) c F 4-c X- M X+ (II)

[0031] In the above formula (II), 0 < a ≤ 6, 0 < b ≤ 6, 4 < a + b < 8, 0 ≤ c < 4, and X = 12 - 2a - b. Examples of M in the above formulas (I) and (II) include Na.

[0032] The above synthetic hectorite has a three-layer structure, and each layer of the crystal structure in the layered structure consists of two-dimensional small plates with a thickness of about 1 nm. And a part of the magnesium atoms existing in the middle layer of this small plate unit is isomorphously substituted with low-valence lithium atoms. As a result, the small plate unit is negatively charged. In the dry state, this negative charge is balanced with the replaceable cations outside the lattice structure of the plate surface. In the solid phase, these particles are bonded to each other by van der Waals forces to form a bundle of flat plates.

[0033] When the synthetic hectorite is dispersed in an aqueous phase, the replaceable cations are hydrated and the particles swell. When dispersed using a normal disperser such as a high-speed dissolver, a stable sol can be obtained. In the state of being dispersed in the aqueous phase like this, the surface of the small plate becomes negatively charged and repels each other electrostatically, becoming a stable sol that is subdivided into small plate-shaped primary particles. However, when the particle concentration or the ion concentration is increased, the repulsive force due to the surface negative charge decreases, and it becomes possible for the positively charged ends of other small plates to be electrically oriented on the negatively charged small plate surface, forming a so-called card house structure and exhibiting thickening properties.

[0034] ​By using synthetic hectorite, excellent viscosity can be achieved in this way, which can prevent not only the sedimentation of zinc phosphate particles in the surface modifier obtained by diluting the concentrated liquid, but also the sedimentation of zinc phosphate particles in the concentrated liquid. As a result, it is presumed that the dispersion stability of the concentrated liquid can be maintained over a longer period. Furthermore, since zinc phosphate particles can be more stabilized in the concentrated liquid, it is presumed that the zinc phosphate particles can be made finer when dispersing components such as zinc phosphate particles, thereby improving dispersion efficiency. It is also presumed that similar effects can be obtained with the above-mentioned natural hectorite.

[0035] Examples of commercially available synthetic hectorite include Laponite B, S, RD, RDS, XLG, and XLS (trade names) manufactured by Laporte Industries Ltd. These commercial products are white powders that readily form sols (Laponite S, RDS, XLS) or gels (Laponite B, RD, XLG) when added to water. Another example is Lucentite SWN from Coop Chemical. These natural and synthetic hectorites may be used individually or in combination of two or more types.

[0036] The content of the above-mentioned layered clay mineral in the concentrated liquid is 0.1% by mass or more and 20% by mass or less relative to the total mass of the concentrated liquid. If the content is less than 0.1% by mass, the effect of preventing the sedimentation of zinc phosphate particles may not be sufficiently obtained. If the content exceeds 20% by mass, there is a risk of excessive viscosity, difficulty in dispersing the concentrated liquid, and handling problems such as difficulty in removing the product from the container. The lower limit of the content is preferably 0.3% by mass, and the upper limit of the content is preferably 10% by mass.

[0037] The above-mentioned layered clay mineral preferably has an average particle size (= average of the maximum dimensions) of 5 μm or less, and more preferably 1 μm or less. If the average particle size exceeds 5 μm, the dispersion stability may decrease. Furthermore, the average aspect ratio (= average of the maximum dimension / minimum dimension) of the above-mentioned layered clay mineral is preferably 10 or more, more preferably 20 or more, and even more preferably 40 or more. If it is less than 10, the dispersion stability may decrease.

[0038] The concentrated liquid according to this embodiment may contain layered clay minerals other than the natural hectorite and synthetic hectorite described above, to the extent that they do not impair the effects of the invention. Examples include smectites such as montmorillonite, beiderite, and saponite; kaolinites such as kaolinite and halosite; vermiculites such as dioctahedral vermiculite and trioctahedral vermiculite; micas such as teniolite, tetrasilicic mica, muscovite, illite, sericite, phlogopite, and biotite; hydrotalcite; pyrophyllolite; and layered polysilicates such as kanemite, makatites, islaite, magadiite, and kenyaite. These layered clay minerals may be natural minerals or synthetic minerals produced by hydrothermal synthesis, melting, solid-phase synthesis, etc. If layered clay minerals other than the natural hectorite and synthetic hectorite described above are included, these layered clay minerals are not included in the definition of the content of the layered clay minerals in the concentrated liquid.

[0039] Furthermore, intercalation compounds of the above-mentioned layered clay minerals (such as pyramidal crystals), those that have undergone ion exchange treatment, and those that have undergone surface treatment (such as silane coupling treatment or compounding treatment with an organic binder) can also be used. These layered clay minerals may be used individually or in combination of two or more types.

[0040] Sulfur-containing compounds improve the dispersion stability of concentrated liquids. The reason why sulfur-containing compounds improve dispersion stability is not entirely clear, but it is presumed to be due to electrical repulsion caused by the polarization state of the sulfur-containing compounds.

[0041] The sulfur-containing compound preferably has an isothiazolinone structure. The sulfur-containing compound having an isothiazolinone structure is not particularly limited, but examples include derivatives of isothiazolinone. Specific examples of derivatives of isothiazolinone include 1,2-benzoisothiazolinone-3-one (BIT), 2-methyl-4-isothiazolinone-3-one (MIT), 5-chloro-2-methyl-4-isothiazolinone-3-one (CIT), 2-n-octyl-4-isothiazolinone-3-one (OIT), and dichlorooctylisothiazolinone (DCOIT, DCOI). Preferred derivatives of isothiazolinone are 2-methyl-4-isothiazolinone-3-one (MIT) and 5-chloro-2-methyl-4-isothiazolinone-3-one (CIT).

[0042] As the sulfur-containing compound, sulfur-containing compounds other than those having an isothiazolinone structure may be used. The above sulfur-containing compounds may be used alone or in combination of two or more.

[0043] The content of the above sulfur-containing compound in the concentrated solution is preferably 2 ppm by mass or more and 100 ppm by mass or less, relative to the total mass of the concentrated solution.

[0044] The ratio of the mass of the sulfur-containing compound to the mass of the layered clay mineral (layered clay mineral / sulfur-containing compound) in the concentrated liquid is preferably 7500 or less. Although the mechanism by which this ratio affects the state of the concentrated liquid is not clear, it is presumed that the interaction between the polarized sulfur compound and the layered clay mineral, which is polarized in both planar and edge portions, further stabilizes the dispersion of zinc phosphate particles. The above ratio is more preferably 5000 or less, and even more preferably 500 or more.

[0045] The water-soluble organic polymer is preferably obtained by polymerizing a monomer composition containing less than 50% by mass of acrylic acid and more than 50% by mass of the total amount of 2-acrylamido-2-methylpropanesulfonic acid and / or allylsulfonic acid. The water-soluble organic polymer described above acts as a dispersant and can also promote the chemical conversion treatment. As a result, a dense chemical conversion film can be formed during the chemical conversion treatment, improving corrosion resistance. The reason why the chemical conversion treatment can be promoted and a dense chemical conversion film can be formed by using a surface modifier containing a water-soluble organic polymer is not clear, but it is presumed that the edges of these components are easily adsorbed to the substrate.

[0046] The above-mentioned water-soluble organic polymer can be easily obtained by conventionally known methods, such as copolymerizing a monomer composition containing acrylic acid and sulfonic acid monomers under a catalyst such as a peroxide. The above-mentioned water-soluble organic polymer may also be a salt of the copolymer obtained as described above. This salt is formed by acrylic acid units forming a salt, and examples include alkali metal salts such as lithium salts, sodium salts, potassium salts, magnesium salts, and calcium salts, as well as alkaline earth metal salts, ammonium salts, and organic amine salts.

[0047] The above organic amine salts include methylamine salt, ethylamine salt, propylamine salt, butylamine salt, amylamine salt, hexylamine salt, octylamine salt, 2-ethylhexylamine salt, decylamine salt, dodecylamine salt, isotridecylamine salt, tetradecylamine salt, hexadecylamine salt, isohexadecylamine salt, octadecylamine salt, isooctadylamine salt, octyldodecylamine salt, docosylamine salt, decyltetradecylamine salt, oleylamine salt, linoleamine salt, dimethylamine salt, trimethylamine salt, aniline salt, and other aliphatic and aromatic monoamine salts, ethylenediamine salt, tetramethylenediamine salt, and dodecylpropylene. Examples of polyamine salts include diamine salts, tetradecyl-propylenediamine salts, hexadecyl-propylenediamine salts, octadecyl-propylenediamine salts, oleyl-propylenediamine salts, diethylenetriamine salts, triethylenetetramine salts, tetraethylenepentamine salts, pentaethylenehexamine salts, monoethanolamine salts, diethanolamine salts, triethanolamine salts, monoisopropanolamine salts, diisopropanolamine salts, triisopropanolamine salts, salts of alkylene oxide adducts thereof, alkanolamine salts such as salts of alkylene oxide adducts of primary or secondary amines, amino acid salts such as lysine salts and arginine salts. Among these, alkali metal salts, ammonium salts, and alkanolamine salts are preferred.

[0048] In the above-mentioned water-soluble organic polymer, the acrylic acid content is less than 50% by mass per 100% by mass of the monomer composition. If it is 50% by mass or more, there is a risk that a chemical conversion film cannot be properly formed on the aluminum substrate portion at the contact point between the iron or zinc substrate and the aluminum substrate. Furthermore, there is a risk that a sufficient amount of chemical conversion film cannot be formed on the aluminum substrate or high-tensile steel plate. The lower limit of the above content is preferably 20% by mass, and more preferably 25% by mass. The upper limit of the above content is more preferably 45% by mass, and even more preferably 40% by mass.

[0049] In the above-mentioned water-soluble organic polymer, the total content of 2-acrylamido-2-methylpropanesulfonic acid and / or allylsulfonic acid is greater than 50% by mass per 100% by mass of the monomer composition. If it is 50% by mass or less, there is a risk that a chemical conversion film cannot be properly formed on the aluminum substrate portion at the contact point between the iron or zinc substrate and the aluminum substrate. Furthermore, there is a risk that a sufficient amount of chemical conversion film cannot be formed on the aluminum substrate or high-tensile steel plate. The lower limit of the above content is more preferably 55% by mass, and even more preferably 60% by mass. The upper limit of the above content is preferably 80% by mass, and more preferably 75% by mass.

[0050] The acid value of the above water-soluble organic polymer is preferably between a lower limit of 10 and an upper limit of 1000. If it is less than 10 or more than 1000, the dispersibility of the zinc phosphate particles may decrease. The lower limit is more preferably 30, and the upper limit is more preferably 800.

[0051] The number-average molecular weight of the above water-soluble organic polymer is preferably between a lower limit of 100 and an upper limit of 30,000. If it is less than 100, sufficient dispersion may not be achieved. If it exceeds 30,000, not only will sufficient dispersion not be achieved, but aggregation may also occur. The lower limit is more preferably 1,000, and the upper limit is more preferably 20,000.

[0052] When the concentrated solution contains the above-mentioned water-soluble organic polymer, the ratio of the mass of the sulfur-containing compound to the mass of the water-soluble organic polymer in the concentrated solution (water-soluble organic polymer / sulfur-containing compound) is preferably 25,000 or less. Although the mechanism by which the ratio of the mass of the sulfur-containing compound to the mass of the water-soluble organic polymer in the concentrated solution affects the state of the concentrated solution is not clear, it is presumed that the interaction between the polarized sulfur compound and the functional groups of the water-soluble organic polymer further stabilizes the dispersion of zinc phosphate particles. The above ratio is more preferably 25,000 or less, and 1,600 or more.

[0053] (Other ingredients) The concentrated liquid according to this embodiment may contain a dispersion medium for dispersing zinc phosphate particles. Examples of the dispersion medium include aqueous media such as water, and various organic solvents. The dispersion medium may be water alone.

[0054] The above-mentioned organic solvents are not particularly limited, and examples include alcohol-based solvents such as methanol, isopropanol, ethylene glycol, and ethylene glycol monopropyl ether; hydrocarbon-based solvents such as hexane, heptane, xylene, toluene, cyclohexane, and naphtha; ketone-based solvents such as methyl isobutyl ketone, methyl ethyl ketone, isophorone, and acetophenone; amide-based solvents such as dimethylacetamide and methylpyrrolidone; and ester-based solvents such as ethyl acetate, isobutyl acetate, octyl acetate, ethylene glycol monomethyl ether acetate, and diethylene glycol monomethyl ether acetate. These may be used individually or in combination of two or more.

[0055] The concentrated solution according to this embodiment preferably contains a divalent or trivalent metal nitrite compound. Normally, surface conditioning is a treatment applied to a clean metal surface after degreasing and washing, and problems such as oxidation and corrosion of the metal surface may occur during the surface conditioning process. However, if the concentrated solution contains a divalent or trivalent metal nitrite compound, the occurrence of rust on the metal surface after surface conditioning can be sufficiently suppressed. Furthermore, as a result of suppressing the occurrence of rust, the chemical conversion performance in the chemical conversion treatment can also be significantly improved.

[0056] The above-mentioned divalent or trivalent metal nitrite compounds are not particularly limited as long as they are nitrites containing a divalent or trivalent metal, and examples include zinc nitrite, copper nitrite, nickel nitrite, and alkaline earth metal nitrites such as magnesium nitrite, calcium nitrite, strontium nitrite, and barium nitrite. Among these, zinc nitrite is preferred. When zinc nitrite is used in surface preparation, the accumulation of dissimilar metals in the chemical conversion treatment bath is prevented when a zinc phosphate conversion film is formed in the chemical conversion treatment process, making bath management of the chemical conversion solution easier. Furthermore, the occurrence of rust on the metal surface after surface preparation can be further suppressed. These may be used individually or in combination of two or more.

[0057] The content of the above-mentioned divalent or trivalent metal nitrite compound in the concentrated solution is preferably 0.1% by mass or more and 10% by mass or less based on the total mass of the concentrated solution. If the content is less than 0.1% by mass, the rust prevention and metal substitution properties of the surface modifier obtained from the concentrated solution may not be satisfactory. If the content exceeds 10% by mass, when the metal nitrite compound is used, the cationic component in the metal nitrite compound may inhibit dispersibility and may also be uneconomical. The lower limit of the content is more preferably 0.5% by mass, and the upper limit of the content is more preferably 5% by mass.

[0058] To further improve the stability of the concentrated liquid according to this embodiment, a thickening agent may be added as needed. The thickening agent is not particularly limited and may include, for example, inorganic thickening agents such as clay, diatomaceous earth, calcium carbonate, barium sulfate, titanium dioxide, alumina white, silica, and aluminum hydroxide; organic thickening agents such as polyacrylic acid esters, polyurethanes, polyesters, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polysiloxane, thickening polysaccharides, phenolic resins, epoxy resins, and benzoguanamine resins; or thickening agents made from polymers thereof. The amount of thickening agent added is not particularly limited as long as it does not hinder the effects of this disclosure. The thickening agents may be used alone or in combination of two or more.

[0059] The concentrated liquid according to this embodiment may contain an alkali salt such as soda ash for the purpose of stabilizing the zinc phosphate particles and forming a fine chemical conversion film in the subsequent phosphate coating treatment step.

[0060] (pH) The pH of the concentrated solution according to this embodiment is preferably 3 or higher and 12 or lower. If the pH is less than 3, the zinc phosphate particles will dissolve more easily and become unstable, which may affect the next step. If the pH exceeds 12, it may cause a decrease in the pH of the chemical bath in the next step, which may result in poor chemical conversion. The lower limit is preferably 6, and the upper limit is preferably 11.

[0061] <Method for preparing concentrated solution for surface conditioning agent preparation> The method for preparing the concentrated solution for surface conditioning agents described above preferably includes a step of wet grinding, for example, by placing the raw material zinc phosphate and the dispersion stabilizer in a dispersion medium in a predetermined mass ratio. The wet grinding method described above is not particularly limited, and any general wet grinding method may be used. For example, bead mills such as disc type and pin type, high-pressure homogenizers, and media-less dispersers such as ultrasonic dispersers can be used.

[0062] As a method for producing the above-mentioned raw material, zinc phosphate (Zn3(PO4)2·4H2O), for example, zinc phosphate tetrahydrate can be obtained as a crystalline precipitate by mixing and heating a diluted solution of zinc sulfate and disodium hydrogen phosphate in a molar ratio of 3:2. Alternatively, zinc phosphate tetrahydrate can be obtained by reacting a dilute phosphoric acid aqueous solution with zinc oxide or zinc carbonate. The tetrahydrate crystals are orthorhombic and undergo three transformations. When heated, it becomes dihydrate at 100°C, monohydrate at 190°C, and anhydrous at 250°C. Any of these forms—tetrahydrate, dihydrate, monohydrate, or anhydrous—can be used as the raw material. Commercially available tetrahydrate products that are generally easy to obtain may also be used. Commercial products may be in any form, such as fine particles, plates, or flakes.

[0063] The zinc phosphate used as the raw material may be one that has undergone various surface treatments. For example, it may be one that has been surface-treated with a silane coupling agent, rosin, a silicone compound, or a metal alkoxide such as silicon alkoxide or aluminum alkoxide. Alternatively, silicate-modified zinc phosphate may be used, in which zinc phosphate is micronized by adding silica and polyphosphate when reacting a zinc compound with phosphoric acid. Alternatively, some of the zinc in the zinc phosphate may be replaced with a metal such as magnesium, calcium, or aluminum. In this case, it is preferable that the zinc phosphate contains 25% by mass or more in terms of ZnO, and 15% by mass or more in terms of P2O5.

[0064] In the wet grinding process described above, the average particle size of the zinc phosphate particles can be adjusted to a desired range by monitoring the D50 and, if necessary, the D90 of the zinc phosphate particles. That is, even when zinc phosphate with an average particle size exceeding 3 μm is used as a raw material, the zinc phosphate particles can be dispersed in the liquid with a D50 of 3 μm or less. Furthermore, this prevents overdispersion and prevents phenomena such as aggregation, thickening, and aggregation of fine particles.

[0065] The wet grinding described above reduces the proportion of coarse particles, which are defined as particles with a particle size greater than D90. In particular, the dispersion can be made such that the dispersion diameter distribution is 4 μm or less, 2.6 μm or less, and even 0.3 μm or less. As a result, zinc phosphate is dispersed with a fine dispersion diameter, and the dispersion state can be made extremely stable. In addition, because the proportion of coarse particles is low, the zinc phosphate particles in the liquid efficiently contribute to the formation of crystal nuclei. Furthermore, because the dispersion diameter distribution is sharp and the particle size is uniform, more uniform crystal nuclei are formed in the surface conditioning process, and the subsequent chemical conversion treatment leads to the formation of uniform zinc phosphate crystals, resulting in a uniform and excellent surface property of the resulting chemically converted steel sheet. Moreover, this can improve the processability of difficult-to-convert steel sheets such as bag sections of complex structural members and black scale steel sheets.

[0066] After the wet grinding step described above, the concentrated liquid according to this embodiment can be prepared by mixing the obtained aqueous dispersion with other components constituting the concentrated liquid. The mixing method is not particularly limited; for example, other components may be added to the aqueous dispersion and mixed, or other components may be added during the preparation of the aqueous dispersion. Instead of the wet grinding step described above, the concentrated liquid may be prepared using zinc phosphate particles having a predetermined average particle size.

[0067] <Surface modifier> The surface modifier according to this embodiment is used for surface conditioning, which is a pretreatment for phosphate film conversion treatment, to deposit fine zinc phosphate particles onto the metal surface to be treated. In the zinc phosphate conversion treatment process, it promotes the formation of a zinc phosphate film using the fine particles as crystal nuclei, thereby forming a good zinc phosphate film. When a metal material is surface-conditioned using this and then subjected to conversion treatment, fine phosphate crystals can be precipitated in a relatively short time, completely covering the metal surface. The surface modifier can be obtained, for example, by diluting the concentrated solution for preparing the surface modifier described above to adjust it to a predetermined concentration. Alternatively, the surface modifier may be prepared directly so that the concentrations of each component reach the predetermined concentrations.

[0068] The surface modifier contains the above zinc phosphate particles and the above dispersion stabilizer. The surface modifier may also contain the above water-soluble organic polymer and other components. Furthermore, an antifoaming agent may be used to suppress foaming during work, and preservatives and fungicides may be used to prevent bacteria and fungi in the dispersion.

[0069] In the surface modifier, it is preferable that the content of zinc phosphate particles relative to the total mass of the surface modifier is 50 ppm by mass or more and 20,000 ppm by mass or less. If the content is less than 50 ppm by mass, there may be insufficient phosphate to serve as crystal nuclei, and a sufficient surface modifier effect may not be obtained. Even if the content exceeds 20,000 ppm by mass, it is not economical as it does not necessarily provide an effect beyond the desired effect. The lower limit of the content is more preferably 150 ppm by mass, and the upper limit of the content is more preferably 10,000 ppm by mass.

[0070] In the surface modifier, it is preferable that the content of the above-mentioned layered clay mineral relative to the total mass of the surface modifier is 3 ppm by mass or more and 600 ppm by mass or less. If the above content is less than 3 ppm by mass, the effect of preventing the sedimentation of zinc phosphate particles in the surface modifier may not be sufficiently obtained. If it exceeds 600 ppm by mass, adsorption to the metal surface may occur, which may affect the subsequent chemical conversion process. The lower limit of the above content is more preferably 10 ppm by mass, and the upper limit of the above content is more preferably 300 ppm by mass.

[0071] The surface modifier preferably has a pH of 3 to 12. If the pH is less than 3, the zinc phosphate particles become easily soluble and unstable, which may affect the next process. If the pH exceeds 12, it may cause a decrease in the pH of the subsequent chemical bath, potentially leading to poor chemical conversion. The lower limit of the above pH is preferably 6, and the upper limit of the above pH is preferably 11.

[0072] <Surface conditioning method> The surface conditioning method according to this embodiment includes a step of bringing the surface conditioning agent into contact with a metal surface. This allows fine particles of zinc phosphate to adhere well to the metal surface, and enables the formation of a good chemical conversion coating in the chemical conversion treatment step. In particular, the chemical conversion coating can be formed more effectively on the aluminum substrate portion at the contact point between the iron or zinc substrate and the aluminum substrate, and a more sufficient amount of chemical conversion coating can be formed on aluminum substrates, high-tensile steel plates, etc.

[0073] The method for bringing the surface conditioning agent into contact with the metal surface in the above surface conditioning method is not particularly limited, and conventionally known methods such as immersion and spraying can be used as appropriate.

[0074] The metal material to which the above surface treatment is applied is not particularly limited and is generally applicable to various materials that undergo phosphate chlorination treatment, such as steel, galvanized steel sheets, aluminum or aluminum alloys, magnesium alloys, etc. It can also be suitably applied to contact areas between steel or galvanized steel sheets and aluminum or aluminum alloys.

[0075] The above surface conditioning agent can be used in a degreasing and surface conditioning process. This eliminates the need for a water rinsing step after degreasing. In the above degreasing and surface conditioning process, known inorganic alkali builders, organic builders, and surfactants may be added to enhance cleaning power. Known chelating agents, condensed phosphates, etc., may also be added. In the above surface conditioning, the contact time between the surface conditioning agent and the metal surface and the temperature of the surface conditioning agent are not particularly limited and can be carried out under conventionally known conditions.

[0076] The above surface preparation can be performed, followed by a phosphate chlorination treatment to produce a phosphate chlorination treated steel sheet. The phosphate chlorination treatment method is not particularly limited, and various known methods such as dipping, spraying, and electrolytic treatment can be applied. Multiple methods may be combined. The phosphate film to be deposited is also not particularly limited as long as it is a phosphate, and is not limited in any way, such as zinc phosphate, iron phosphate, manganese phosphate, zinc calcium phosphate, etc. In the above phosphate chlorination treatment, the contact time between the chemical treatment agent and the metal surface and the temperature of the chemical treatment agent are not particularly limited and can be carried out under conventionally known conditions.

[0077] After performing the above surface preparation and chemical conversion treatment, a painted board can be manufactured by further painting. Examples of the painting method include electrodeposition coating. The paint used for painting is not particularly limited and can be any of the various types commonly used for painting phosphate-chlorinated steel sheets, such as epoxy melamine paint, cationic electrodeposition paint, polyester-based intermediate coating paint, and polyester-based topcoat paint. After the chemical conversion treatment, known processes such as a cleaning process may be performed before painting. [Examples]

[0078] The contents of this disclosure will be described in more detail below based on the examples. The contents of this disclosure are not limited to the examples described below.

[0079] (Example 1) To 66.5 parts by mass of water, 1.5 parts by mass of natural hectorite "BENTON EW" (manufactured by ELEMENTIS) was added, and the mixture was stirred at 3000 rpm for 30 minutes using a disperser to obtain a pregel. To the obtained pregel, 5 parts by mass of "Aron A-6020" (a copolymer of 40% by mass of acrylic acid and 60% by mass of sulfonic acid, manufactured by Toagosei Co., Ltd.) as a water-soluble organic polymer, 30 parts by mass of zinc phosphate particles, and 10 ppm by mass of a sulfur-containing compound (1,2-benzoisothiazolin-3-one (BIT)) as a dispersion stabilizer were added, and the mixture was dispersed with zirconia beads until the viscosity was 600 cps or less to obtain a concentrated solution for preparing a surface modifier according to Example 1.

[0080] (Other examples and comparative examples) Concentrated solutions for the other examples and comparative examples were prepared in the same manner as in Example 1, except that the concentration of zinc phosphate particles, the concentration of layered clay minerals, the concentration of water-soluble organic polymers, and the type and concentration of sulfur-containing compounds were modified as shown in Table 1. The pH of the concentrated solutions prepared in the examples (including Example 1) and comparative examples was within the range of 3 to 12.

[0081] [Table 1]

[0082] The details of the abbreviations shown in Table 1 are described below. In Table 1, "mass ratio (B) / (A)" means the mass ratio of layered clay mineral / sulfur-containing compound. Similarly, "mass ratio (C) / (A)" means the mass ratio of water-soluble organic polymer / sulfur-containing compound. BIT: 1,2-Benzisothiazoline-3-one MIT:2-methyl-4-isothiazolin-3-one CIT:5-Chloro-2-methyl-4-isothiazolin-3-one OIT:2-n-octyl-4-isothiazoline-3-one (a): 1,3,5-Triazine-1,3,5(2H,4H,6H)-Tris(ethanol) (b): 2-bromo-2-nitropropane-1,3-diol (c): Morpholine

[0083] [Measurement of average particle size (D50) of zinc phosphate particles] Particle size distribution was measured using a photodiffraction particle size analyzer ("LA-500," manufactured by Horiba, Ltd.), and the average particle size D50 (median particle size of the dispersion) of zinc phosphate particles was measured. The results are shown in Table 2. Note that in Comparative Example 4, the particles settled, making measurement impossible.

[0084] [Dispersion stability assessment] The concentrated solutions for surface modifier preparation obtained in the examples and comparative examples were left to stand at room temperature indoors, and their stability after 6 months was visually confirmed according to the following criteria. A rating of 3 was considered acceptable. The results are shown in Table 2.

[0085] (Evaluation Criteria) 3: It has a uniform appearance. 2: No sediment was observed, but a small amount of supernatant liquid was detected. 1: The concentrated liquid has completely separated into two layers, and sediment is visible.

[0086] [Viscosity measurement] The concentrated surface-conditioning solutions obtained in the examples and comparative examples were left to stand at room temperature indoors for 6 months, and their viscosity at 15°C was measured using a Type B viscometer (manufactured by Toki Sangyo Co., Ltd.). The solutions were evaluated according to the following criteria, with a rating of 3 or higher being considered acceptable. The results are shown in Table 2.

[0087] (Evaluation Criteria) 4: Less than 600 cps 3: 600 cps or more and less than 1100 cps 2: 1100 cps or more, less than 1600 cps 1: 1600 cps or higher, or unmeasurable.

[0088] [Zeta potential measurement] The concentrated surface preparation solutions obtained in the examples and comparative examples were diluted 500 times with deionized water to prepare solutions, and the zeta potential was measured using a zeta potential measuring device (model: Zetasizer Nano ZS, manufactured by Malvern Panalytical). A value of -60mV or less was considered acceptable. The results are shown in Table 2. Note that in Comparative Example 4, the particles were aggregated, making measurement impossible.

[0089] [Appearance of the coating] The concentrated solutions for surface conditioning obtained in the examples and comparative examples were left to stand at room temperature for 6 months, and then diluted 500 times with deionized water to prepare the solutions. The pH of the prepared solutions (surface conditioning agents) was within the range of 3 to 12. The surfaces of SPC test plates were prepared using the above-prepared solutions. After the above surface conditioning, a zinc phosphate conversion coating was formed by immersion treatment with a zinc phosphate treatment agent (Surfdyne SD5350, manufactured by Nippon Paint Surf Chemicals Co., Ltd.) at 35°C for 2 minutes. The appearance of the formed coating was evaluated visually according to the following criteria. The results are shown in Table 2. Note that surface conditioning could not be performed on Comparative Example 4.

[0090] (Evaluation Criteria) 2: Uniform 1: At least some rust has formed.

[0091] [Table 2]

[0092] The results in Table 2 confirm that the concentrated solutions in each example exhibit superior dispersion stability compared to the concentrated solutions in the comparative examples.

Claims

1. A concentrated solution for preparing a surface modifier containing zinc phosphate particles and a dispersion stabilizer, The zinc phosphate particles have a D50 of 3 μm or less. The content of zinc phosphate particles relative to the total mass of the concentrated liquid is 3% by mass or more and 60% by mass or less. The aforementioned dispersion stabilizer comprises a layered clay mineral and a sulfur-containing compound. The content of the layered clay mineral relative to the total mass of the concentrated liquid is 0.1% by mass or more and 20% by mass or less. The layered clay mineral is natural hectorite and / or synthetic hectorite. Concentrated solution for preparing surface conditioning agents.

2. The concentrated solution for preparing the surface modifier according to claim 1, wherein the concentrated solution for preparing the surface modifier further contains a water-soluble organic polymer as the dispersion stabilizer.

3. The sulfur-containing compound is a compound having an isothiazolinone structure, as described in claim 1, a concentrated solution for preparing a surface modifier.

4. The water-soluble organic polymer is obtained by polymerizing a monomer composition containing less than 50% by mass of acrylic acid and more than 50% by mass of the total amount of 2-acrylamido-2-methylpropanesulfonic acid and / or allylsulfonic acid, as described in claim 2.

5. The concentrated solution for preparing a surface modifier according to claim 2, wherein the ratio of the mass of the sulfur-containing compound to the mass of the water-soluble organic polymer (water-soluble organic polymer / sulfur-containing compound) is 25,000 or less.

6. The concentrated liquid for preparing a surface modifier according to claim 1, wherein the ratio of the mass of the sulfur-containing compound to the mass of the layered clay mineral (layered clay mineral / sulfur-containing compound) is 7500 or less.

7. A surface modifier containing zinc phosphate particles and a dispersion stabilizer, The zinc phosphate particles have a D50 of 3 μm or less. The content of zinc phosphate particles relative to the total mass of the surface modifier is 50 ppm by mass or more and 20,000 ppm by mass or less. The aforementioned dispersion stabilizer comprises a layered clay mineral and a sulfur-containing compound. The content of the layered clay mineral relative to the total mass of the surface modifier is 3 ppm by mass or more and 600 ppm by mass or less. The layered clay mineral is natural hectorite and / or synthetic hectorite, and is a surface modifier.

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