Concentrated solution for preparing surface conditioners, and surface conditioners

Abstract

To provide a concentrated solution for preparing a surface conditioner having excellent dispersion stability. [Solution] A concentrated solution for preparing a surface conditioner, 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 concentrated solution is 3 mass% or more and 60 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 concentrated solution is 0.1 mass% or more and 20 mass% or less, and the layered clay mineral is natural hectorite and / or synthetic hectorite.

Description

[Technical Field]

[0001] The present disclosure relates to a concentrate for preparing a surface conditioner, and a surface conditioner. [Background technology]

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

[0003] One surface conditioning technique has been proposed (see Patent Document 1), which involves pretreating a metal surface with an aqueous pre-washing bath containing an activator prior to phosphate treatment, and which is characterized by contacting the metal surface with a pre-washing bath additionally containing montmorillonite. Another technique has been proposed (see Patent Document 2), which relates to a surface conditioning pre-treatment solution containing one or more phosphate salts containing at least one divalent or trivalent metal with particles having a particle size of 5 μm or less, an alkali metal salt, an ammonium salt, or a mixture thereof, and which has a pH adjusted to 4 to 13. Another technique has been proposed (see Patent Document 3), which relates to a surface conditioning treatment solution for metals prior to phosphate conversion coating, characterized by containing one or more phosphate particles selected from phosphate salts containing at least one divalent and / or trivalent metal, and one or more promoters selected from monosaccharides, polysaccharides, and their derivatives. [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 Application Laid-Open No. 2000-96256 Summary of the Invention [Problem to be solved by the invention]

[0005] The surface conditioning treatment liquids disclosed in the above patent documents have a problem in that the dispersion stability of the concentrated liquids used to prepare the treatment liquids is particularly poor.

[0006] The present disclosure has been made in view of the above, and has an object to provide a concentrated liquid for preparing a surface conditioner that has excellent dispersion stability. [Means for solving the problem]

[0007] (1) The present disclosure relates to a concentrated solution for preparing a surface conditioner, the concentrated solution containing zinc phosphate particles and a dispersion stabilizer, the zinc phosphate particles having a D50 of 3 μm or less, a content of the zinc phosphate particles relative to the total mass of the concentrated solution of 3% by mass or more and 60% by mass or less, the dispersion stabilizer containing 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 of 0.1% by mass or more and 20% by mass or less, and the layered clay mineral being natural hectorite and / or synthetic hectorite.

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

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

[0010] (4) The concentrated solution for preparing a surface conditioner according to (2), wherein 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 a total amount of 2-acrylamido-2-methylpropanesulfonic acid and / or allylsulfonic acid.

[0011] (5) The concentrated solution for preparing a surface conditioner 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) The concentrated solution for preparing a surface conditioner 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 7,500 or less.

[0013] (7) The present disclosure also relates to a surface conditioner containing zinc phosphate particles and a dispersion stabilizer, wherein the zinc phosphate particles have a D50 of 3 μm or less, and the content of the zinc phosphate particles relative to the total mass of the surface conditioner is 50 ppm by mass or more and 20,000 ppm by mass or less, the dispersion stabilizer contains a layered clay mineral and a sulfur-containing compound, and the content of the layered clay mineral relative to the total mass of the surface conditioner 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 the present disclosure, a concentrated solution for preparing a surface conditioner having excellent dispersion stability can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present disclosure will be described, but the present disclosure is not limited to the following embodiments.

[0016] <Concentrated solution for preparing surface conditioners> The concentrate for preparing a surface conditioner according to this embodiment (hereinafter sometimes referred to as "concentrate") is a concentrate (stock solution) used to prepare a surface conditioner by dilution or the like. The surface conditioner used at the site of coating of metal molded objects is provided as a concentrate, stored, and then diluted as needed before being used as a surface conditioner. The concentrate contains zinc phosphate particles and a dispersion stabilizer.

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

[0018] The zinc phosphate particles have a D50 of 3 μm or less. By including zinc phosphate having a D50 of 3 μm or less in the concentrated solution, many crystal nuclei can be provided on the metal surface to be treated before the phosphating conversion treatment, allowing fine phosphate crystals to precipitate in a relatively short chemical conversion treatment. The zinc phosphate particles are not particularly limited as long as they have a D50 of 3 μm or less, and may be, for example, a mixture of particles having a D50 of 3 μm or less.

[0019] The lower limit of D50 of the zinc phosphate particles is preferably 0.001 μm. If D50 is less than 0.001 μm, the particles may aggregate due to the phenomenon of overdispersion. If D50 exceeds 3 μm, the proportion of fine zinc phosphate particles decreases, making it difficult to obtain the desired effects of the present invention. The lower limit is more preferably 0.005 μm, and the upper limit is more preferably 1 μm.

[0020] The D90 of the 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 low proportion of coarse particles. As described above, using zinc phosphate with a D50 of 3 μm or less allows for the precipitation of fine phosphate crystals in a short chemical conversion treatment. However, when using means such as grinding, excessive grinding can result in a shortage of layered clay minerals due to an increase in specific surface area, causing overdispersed particles to aggregate, resulting in the formation of coarse particles and impairing dispersion stability, resulting in overdispersion. Furthermore, variations in dispersibility can occur depending on the formulation of the concentrated solution and dispersion conditions, potentially leading to aggregation and thickening due to close packing of coarse and fine particles, as well as aggregation of fine particles themselves. However, when the D90 of the zinc phosphate particles is 4 μm or less, the above-mentioned problems can be more effectively prevented.

[0021] The lower limit of D90 of the zinc phosphate particles is preferably 0.01 μm. If D90 is less than 0.01 μm, the particles may aggregate due to the phenomenon of overdispersion. If D90 exceeds 4 μm, the proportion of fine zinc phosphate particles decreases, making it difficult to obtain the desired effects of the present invention. The lower limit is more preferably 0.05 μm, and the upper limit is more preferably 2 μm.

[0022] In this specification and claims, D50 refers to the volume average particle diameter (median diameter) measured by dynamic light scattering. D90 refers to the 90% volume diameter. The D50 (volume 50% diameter) and D90 (volume 90% diameter) are determined as the particle diameters at 50% and 90%, respectively, of a cumulative curve calculated based on the particle size distribution in a dispersion, with the total volume of the particles being 100%. The D50 and D90 can be measured using a particle size measuring device, such as an optical diffraction particle size measuring device (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, based on the total mass of the concentrated solution. If the content is less than 3% by mass, when surface conditioning is performed using a surface conditioner obtained from the concentrated solution, there may be a shortage of phosphate to serve as crystal nuclei, and sufficient surface conditioning effects may not be achieved. Furthermore, a large amount of concentrated solution is required to maintain the required zinc phosphate concentration in the surface conditioning bath, which may result in poor workability and be uneconomical. If the content exceeds 60% by mass, the dispersion stability of the zinc phosphate particles in the concentrated solution may decrease, causing them to settle. The lower limit of the content is preferably 5% by mass, and the upper limit of the content is more preferably 50% by mass.

[0024] (Dispersion stabilizer) The dispersion stabilizer contains a layered clay mineral and a sulfur-containing compound. It is presumed that the dispersion stabilizer acts as an anti-settling agent for zinc phosphate particles in the concentrated solution. That is, the dispersion stabilizer not only prevents the settling of zinc phosphate particles in the surface conditioner obtained by diluting the concentrated solution, but also prevents the settling of zinc phosphate particles in the concentrated solution, thereby maintaining the dispersion stability of the concentrated solution for a long period of time. It is preferable that the dispersion stabilizer further contains a water-soluble organic polymer.

[0025] The layered clay mineral is at least one of natural hectorite and synthetic hectorite. The layered clay mineral can suppress the sedimentation of zinc phosphate particles contained in the concentrated solution. While the reason for this is unclear, the following reasons are presumed. Adding the layered clay mineral to the concentrated solution can exhibit an excellent thickening effect. It can also exhibit a repulsive effect on charged particles. The synergistic effect of this thickening effect and the repulsive effect of charged particles exhibits an extremely excellent effect of suppressing the sedimentation of zinc phosphate particles. As a result, it is presumed that the sedimentation of zinc phosphate particles can be further suppressed even in the concentrated solution, and long-term dispersion stability can be maintained. Furthermore, the layered clay mineral itself has an electrical repulsive effect. Therefore, when the layered clay mineral adheres around zinc phosphate particles, the electrical repulsion can stabilize the zinc phosphate particles in the concentrated solution. Therefore, when components such as zinc phosphate particles are dispersed in the concentrated solution during preparation of the concentrated solution, the zinc phosphate particles can be further refined and the dispersion efficiency can be further improved.

[0026] Natural hectorite is a trioctahedral clay mineral belonging to the montmorillonite group and 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 include BENTON EW and BENTON AD (manufactured by ELEMENTIS).

[0029] Synthetic hectorite has a three-layered crystalline structure and is similar to hectorite, which belongs to the unlimited layer expansion type trioctahedral with an expanded lattice, and is composed mainly of 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. 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 replaceable cations outside the lattice structure of the plate surface, and 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 an ordinary 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 plates becomes negatively charged and repels each other electrostatically, resulting in 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] ​The use of synthetic hectorite can thus exhibit excellent thickening properties, which is believed to prevent the settling of zinc phosphate particles not only in the surface conditioner obtained by diluting the concentrate, but also in the concentrate itself, thereby presumably maintaining the dispersion stability of the concentrate for a long period of time. Furthermore, because the zinc phosphate particles can be further stabilized in the concentrate, it is believed that the zinc phosphate particles can be further refined when dispersing components such as zinc phosphate particles, thereby further improving dispersion efficiency. It is also believed that the same effect can be obtained with the above-mentioned natural hectorite.

[0035] Commercially available synthetic hectorites include, for example, Laponite B, S, RD, RDS, XLG, and XLS (trade names) manufactured by Laporte Industries Ltd. The commercially available products are white powders that readily form sols (Laponite S, RDS, and XLS) or gels (Laponite B, RD, and XLG) when added to water. Another example is Lucentite SWN manufactured by Co-op Chemical Co. These natural and synthetic hectorites may be used alone or in combination.

[0036] The content of the layered clay mineral in the concentrated solution is 0.1% by mass or more and 20% by mass or less, based on the total mass of the concentrated solution. If the content is less than 0.1% by mass, the zinc phosphate particles may not be sufficiently prevented from settling. If the content exceeds 20% by mass, the solution may become too thick, making it difficult to disperse the concentrated solution or to remove the product from the container, which may cause handling problems. 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 layered clay mineral preferably has an average particle size (= average value of maximum dimensions) of 5 μm or less, more preferably 1 μm or less. If the average particle size exceeds 5 μm, dispersion stability may decrease. The average aspect ratio (= average value of maximum dimension / minimum dimension) of the 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, dispersion stability may decrease.

[0038] The concentrated solution according to this embodiment may contain layered clay minerals other than the natural hectorite and synthetic hectorite, provided that the effects of the invention are not impaired. Examples include smectites such as montmorillonite, beidellite, and saponite; kaolinites such as kaolinite and halloysite; vermiculites such as dioctahedral vermiculite and trioctahedral vermiculite; micas such as taeniolite, tetrasilicic mica, muscovite, illite, sericite, phlogopite, and biotite; hydrotalcite; pyrophyllolite; and layered polysilicates such as kanemite, makatite, ileite, magadiite, and Kenyaite. These layered clay minerals may be natural or synthetic minerals synthesized by hydrothermal synthesis, melting, solid-state synthesis, or the like. Note that when layered clay minerals other than the natural hectorite and synthetic hectorite are contained, these layered clay minerals are not included in the definition of the content of the layered clay mineral in the concentrated solution.

[0039] In addition, intercalation compounds of the layered clay minerals (pillared crystals, etc.), those that have been subjected to ion exchange treatment, and those that have been subjected to surface treatment (silane coupling treatment, composite treatment with organic binder, etc.) can also be used. These layered clay minerals can be used alone or in combination of two or more.

[0040] The sulfur-containing compound improves the dispersion stability of the concentrated solution. Although the reason why the sulfur-containing compound improves the dispersion stability is unclear, it is presumed to be due to electrical repulsion caused by the polarization state of the sulfur-containing compound.

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

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

[0043] The content of the sulfur-containing compound in the concentrated solution is preferably 2 ppm by mass or more and 100 ppm by mass or less based on 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 in the concentrated solution (layered clay mineral / sulfur-containing compound) is preferably 7500 or less. The mechanism by which the ratio of the mass of the sulfur-containing compound to the mass of the layered clay mineral in the concentrated solution affects the state of the concentrated solution is unclear, but it is presumed that the dispersion of zinc phosphate particles is further stabilized by the interaction between the polarized sulfur compound and the layered clay mineral polarized at the flat and edge portions. The 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 2-acrylamido-2-methylpropanesulfonic acid and / or allylsulfonic acid. The water-soluble organic polymer functions as a dispersant and can accelerate the chemical conversion treatment during chemical conversion treatment. This allows for the formation of a dense chemical conversion coating and improved corrosion resistance. While the reason why the use of a surface conditioner containing a water-soluble organic polymer can accelerate the chemical conversion treatment and form a dense chemical conversion coating is unclear, it is presumed to be due to the ease with which the ends of these components are adsorbed to the substrate.

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

[0047] Examples of the organic amine salt include aliphatic or aromatic monoamine salts such as 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, isooctadecylamine salt, octyldodecylamine salt, docosylamine salt, decyltetradecylamine salt, oleylamine salt, linoleamine salt, dimethylamine salt, trimethylamine salt, and aniline salt; ethylenediamine salt, tetramethylenediamine salt, and dodecylpropylene diamine salt. Examples of suitable salts include polyamine salts such as diamine salts, tetradecyl-propylenediamine salts, hexadecyl-propylenediamine salts, octadecyl-propylenediamine salts, oleyl-propylenediamine salts, diethylenetriamine salts, triethylenetetramine salts, tetraethylenepentamine salts, and pentaethylenehexamine salts; alkanolamine salts such as monoethanolamine salts, diethanolamine salts, triethanolamine salts, monoisopropanolamine salts, diisopropanolamine salts, and triisopropanolamine salts; salts of alkylene oxide adducts of these salts; and salts of alkylene oxide adducts of primary or secondary amines; and 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 water-soluble organic polymer, the content of acrylic acid is less than 50% by mass based on 100% by mass of the monomer composition. If the content is 50% by mass or more, a chemical conversion coating may not be formed well on the portion of the aluminum-based substrate where the iron- or zinc-based substrate and the aluminum-based substrate contact each other. Furthermore, a sufficient amount of chemical conversion coating may not be formed on the aluminum-based substrate or high-tensile steel plate. The lower limit of the content is preferably 20% by mass, more preferably 25% by mass. The upper limit of the content is more preferably 45% by mass, even more preferably 40% by mass.

[0049] In the water-soluble organic polymer, the total content of 2-acrylamido-2-methylpropanesulfonic acid and / or allylsulfonic acid is more than 50% by mass based on 100% by mass of the monomer composition. If it is less than 50% by mass, a chemical conversion coating may not be formed well on the aluminum substrate at the contact point between the iron- or zinc-based substrate and the aluminum substrate. Furthermore, a sufficient amount of chemical conversion coating may not be formed on the aluminum substrate or high-tensile steel sheet. The lower limit of the content is more preferably 55% by mass, and even more preferably 60% by mass. The upper limit of the content is preferably 80% by mass, and more preferably 75% by mass.

[0050] The acid value of the water-soluble organic polymer preferably has a lower limit of 10 and an upper limit of 1,000. If the acid value is less than 10 or exceeds 1,000, 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 water-soluble organic polymer preferably has a lower limit of 100 and an upper limit of 30,000. If it is less than 100, a sufficient dispersing effect may not be obtained. If it exceeds 30,000, a sufficient dispersing effect may not be obtained and aggregation may 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 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. 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 unclear, but 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. It is more preferable that the ratio be 25,000 or less and 1,600 or more.

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

[0054] The organic solvent is not particularly limited, and examples thereof 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 alone or in combination of two or more.

[0055] The concentrated solution according to this embodiment preferably contains a divalent or trivalent metal nitrite compound. Surface conditioning is typically performed on clean metal surfaces after degreasing and water rinsing, which can lead to problems such as oxidation and corrosion of the metal surface during the surface conditioning process. However, when the concentrated solution contains a divalent or trivalent metal nitrite compound, rust formation on the metal surface after surface conditioning can be sufficiently suppressed. Furthermore, the ability to suppress rust formation can significantly improve the chemical conversion properties of the chemical conversion treatment.

[0056] The divalent or trivalent metal nitrite compound is not particularly limited as long as it is a nitrite containing a divalent or trivalent metal, and examples thereof include zinc nitrite, copper nitrite, nickel nitrite, and alkaline earth metal nitrites such as magnesium nitrite, calcium nitrite, strontium nitrite, and barium nitrite. Of these, zinc nitrite is preferred. When zinc nitrite is used in surface conditioning, accumulation of foreign metals in the chemical conversion treatment bath is prevented when forming a zinc phosphate conversion coating in the chemical conversion treatment step, facilitating bath management of the chemical conversion treatment solution. Furthermore, rust formation on the metal surface after surface conditioning can be further suppressed. These compounds may be used alone or in combination of two or more.

[0057] The content of the 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 surface conditioner obtained from the concentrated solution may not exhibit good rust prevention and metal substitution. If the content exceeds 10% by mass, when a metal nitrite compound is used, the cationic components in the metal nitrite compound may inhibit dispersibility, and the product may 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] A thickener can be added to the concentrated solution according to this embodiment as needed to further improve stability. The thickener is not particularly limited, and examples thereof include inorganic thickeners such as white clay, diatomaceous earth, calcium carbonate, barium sulfate, titanium oxide, alumina white, silica, and aluminum hydroxide; organic thickeners such as polyacrylic esters, polyurethanes, polyesters, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polysiloxanes, thickening polysaccharides, phenolic resins, epoxy resins, and benzoguanamine resins; and thickeners made of polymers thereof. The amount of the thickener added is not particularly limited as long as it does not impair the effects of the present disclosure. The thickeners may be used alone or in combination of two or more.

[0059] An alkali salt such as soda ash may be added to the concentrate according to this embodiment in order to stabilize the zinc phosphate particles and form a fine chemical conversion coating in the subsequent phosphate coating chemical treatment step.

[0060] (pH) The pH of the concentrated solution according to this embodiment is preferably 3 or more and 12 or less. If the pH is less than 3, the zinc phosphate particles tend to dissolve easily, becoming unstable and potentially affecting the subsequent step. If the pH is more than 12, this may result in a decrease in the pH of the chemical conversion bath in the subsequent step, potentially resulting in poor chemical conversion. The lower limit is preferably 6, and the upper limit is preferably 11.

[0061] <How to prepare concentrated solution for preparing surface conditioner> The method for preparing the concentrated solution for preparing the surface conditioner preferably includes, for example, a step of wet-pulverizing the raw material zinc phosphate and a dispersion stabilizer in a dispersion medium at a predetermined mass ratio. The wet-pulverization method is not particularly limited, and any common wet-pulverization means may be used, such as a bead mill typified by a disk type or pin type, a high-pressure homogenizer, or a media-less disperser typified by an ultrasonic disperser.

[0062] For example, zinc phosphate tetrahydrate (Zn3(PO4)2·4H2O), a crystalline precipitate, can be obtained 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 aqueous solution of phosphoric acid with zinc oxide or zinc carbonate. The tetrahydrate crystals are orthorhombic and have three modifications. When heated, they become a dihydrate at 100°C, a monohydrate at 190°C, and an anhydrate at 250°C. Any of these forms, tetrahydrate, dihydrate, monohydrate, and anhydrous, can be used as the raw material. Commercially available tetrahydrates may also be used. Commercially available products may be in any form, such as fine particles, plates, or flakes.

[0063] The zinc phosphate raw material may be one that has undergone various surface treatments. For example, 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 may be used. Alternatively, silicic acid-modified zinc phosphate may be used, in which zinc phosphate is microparticulated by adding silica and polyphosphoric acid when reacting a zinc compound with phosphoric acid. Alternatively, zinc phosphate may be one in which a portion of the zinc has been substituted 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, 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 the raw material, the zinc phosphate particles can be dispersed in a liquid with a D50 of 3 μm or less. This also prevents over-dispersion and prevents aggregation, thickening, and aggregation of fine particles.

[0065] The wet grinding process reduces the proportion of coarse particles, which are particles with a particle size exceeding D90. In particular, it is possible to obtain a dispersion with a D90 distribution of 4 μm or less, further 2.6 μm or less, and even 0.3 μm or less. This allows zinc phosphate to be dispersed with a fine dispersion size and to maintain a highly stable dispersion. Furthermore, the low proportion of coarse particles allows the zinc phosphate particles in the solution to efficiently contribute to the formation of crystal nuclei. Furthermore, the sharp dispersion size distribution and uniform particle size allow for the formation of more uniform crystal nuclei in the surface conditioning treatment process, leading to the formation of uniform zinc phosphate crystals in the subsequent chemical conversion treatment, resulting in uniform and excellent surface quality for the resulting chemically treated steel sheet. Furthermore, this improves the treatability of steel sheets that are difficult to convert, such as the pockets of components with complex structures and black steel sheets.

[0066] After the wet-milling step, the resulting aqueous dispersion is mixed with other components that constitute the concentrated liquid to prepare the concentrated liquid according to this embodiment. The mixing method is not particularly limited, and for example, the other components may be added to the aqueous dispersion and mixed, or the other components may be blended during the preparation of the aqueous dispersion. Instead of the wet-milling step, the concentrated liquid may be prepared in advance using zinc phosphate particles having a predetermined average particle size.

[0067] <Surface conditioner> The surface conditioner according to this embodiment is used in the surface conditioning process, which is a pretreatment for phosphate coating chemical conversion treatment, to deposit fine zinc phosphate particles on the metal surface to be treated. This promotes the formation of a zinc phosphate coating using these fine particles as crystal nuclei during the zinc phosphate chemical conversion treatment process, resulting in the formation of a good zinc phosphate coating. When this surface conditioner is used to condition a metal material and then chemical conversion treatment is performed, fine phosphate crystals are precipitated in a relatively short time, completely covering the metal surface. The surface conditioner can be obtained, for example, by diluting the above-mentioned concentrated solution for preparing the surface conditioner to a predetermined concentration. Alternatively, the surface conditioner may be prepared directly so that the concentrations of each component are as desired.

[0068] The surface conditioner contains the zinc phosphate particles and the dispersion stabilizer. The surface conditioner may contain the water-soluble organic polymer and other components. It may also contain an antifoaming agent to suppress foaming during processing, and an antiseptic or antifungal agent to prevent bacteria and mildew in the dispersion.

[0069] In the surface conditioner, the content of the zinc phosphate particles relative to the total mass of the surface conditioner is preferably 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 a shortage of phosphate salts to serve as crystal nuclei, and a sufficient surface conditioning effect may not be obtained. If the content exceeds 20,000 ppm by mass, the desired effect will not be obtained, and this is not economical. 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 conditioner, the content of the layered clay mineral relative to the total mass of the surface conditioner is preferably 3 ppm by mass or more and 600 ppm by mass or less. If the content is less than 3 ppm by mass, the effect of preventing the sedimentation of zinc phosphate particles in the surface conditioner may not be sufficiently obtained. If the content exceeds 600 ppm by mass, the mineral may be easily adsorbed to the metal surface, which may affect the subsequent chemical conversion process. The lower limit of the content is more preferably 10 ppm by mass, and the upper limit of the content is more preferably 300 ppm by mass.

[0071] The surface conditioner preferably has a pH of 3 or more and 12 or less. If the pH is less than 3, the zinc phosphate particles tend to dissolve easily, becoming unstable and potentially affecting the subsequent step. If the pH is more than 12, the pH of the subsequent chemical conversion bath may be reduced, potentially resulting in poor chemical conversion. The lower limit of the pH is preferably 6, and the upper limit of the pH is preferably 11.

[0072] <Surface conditioning method> The surface conditioning method according to this embodiment includes a step of contacting the surface conditioner with a metal surface. This allows fine zinc phosphate particles to adhere well to the metal surface, resulting in the formation of a good chemical conversion coating in the chemical conversion treatment step. In particular, the chemical conversion coating can be more effectively formed on the portion of the aluminum-based substrate where the iron- or zinc-based substrate contacts the aluminum-based substrate, and a chemical conversion coating of a sufficient amount can be formed on the aluminum-based substrate, high-tensile steel plate, or the like.

[0073] In the above surface conditioning method, the method for bringing the surface conditioning agent into contact with the metal surface is not particularly limited, and any conventionally known method such as immersion or spraying can be appropriately employed.

[0074] The metal material to be subjected to the surface conditioning is not particularly limited, and can be applied to various materials that are generally subjected to phosphate chemical conversion treatment, such as steel, galvanized steel sheet, aluminum or aluminum alloy, magnesium alloy, etc. It can also be suitably applied to the contact portion between steel or galvanized steel sheet and aluminum or aluminum alloy.

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

[0076] After the above-mentioned surface conditioning, a phosphate conversion treatment can be carried out to produce a phosphate conversion-treated steel sheet. The phosphate conversion treatment method is not particularly limited, and various known methods such as immersion treatment, spray treatment, and electrolysis treatment can be applied. A combination of these methods may also be used. The phosphate coating to be deposited is also not particularly limited as long as it is a phosphate, and examples include zinc phosphate, iron phosphate, manganese phosphate, and zinc calcium phosphate. The contact time between the chemical conversion treatment agent and the metal surface and the temperature of the chemical conversion treatment agent are not particularly limited in the above-mentioned phosphate conversion treatment, and the treatment can be carried out under conventionally known conditions.

[0077] After the surface conditioning and chemical conversion treatment, a coated plate can be produced by further painting. Examples of the painting method include electrodeposition painting. The paint used for painting is not particularly limited, and examples include various paints commonly used for painting phosphate-treated steel sheets, such as epoxy melamine paint, cationic electrodeposition paint, polyester-based intermediate paint, and polyester-based top coat paint. After the chemical conversion treatment, a known process such as a cleaning process may be carried out before painting. [Example]

[0078] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to the following examples.

[0079] Example 1 To 66.5 parts by weight of water, 1.5 parts by weight of natural hectorite "BENTON EW" (manufactured by ELEMENTIS) was added, and the mixture was stirred at 3,000 rpm for 30 minutes using a disperser to obtain a pregel. To the resulting pregel, 5 parts by weight of "Aron A-6020" (a copolymer of 40% by weight of acrylic acid and 60% by weight of sulfonic acid, manufactured by Toa Gosei Co., Ltd.) as a water-soluble organic polymer, 30 parts by weight of zinc phosphate particles, and 10 ppm by weight of a sulfur-containing compound (1,2-benzisothiazolin-3-one (BIT)) as a dispersion stabilizer were added, and the mixture was dispersed with zirconia beads until the viscosity reached 600 cps or less, to obtain a concentrated solution for preparing the surface conditioner according to Example 1.

[0080] (Other Examples and Comparative Examples) Concentrated solutions according to 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 the layered clay mineral, the concentration of the water-soluble organic polymer, and the type and concentration of the sulfur-containing compound 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 or more and 12 or less.

[0081] [Table 1]

[0082] Details of the abbreviations shown in Table 1 are as follows. 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-benzisothiazolin-3-one MIT: 2-methyl-4-isothiazolin-3-one CIT: 5-chloro-2-methyl-4-isothiazolin-3-one OIT: 2-n-octyl-4-isothiazolin-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 the average particle size (D50) of zinc phosphate particles] Particle size distribution was measured using an optical diffraction particle size analyzer ("LA-500", manufactured by Horiba, Ltd.) to measure the average particle diameter D50 of the zinc phosphate particles (median particle diameter of the dispersion). The results are shown in Table 2. Note that in Comparative Example 4, the particles settled, making measurement impossible.

[0084] [Dispersion stability evaluation] The concentrated solutions for preparing surface conditioners obtained in the Examples and Comparative Examples were each allowed to stand at room temperature in a room, and the 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: Uniform appearance. 2: No sediment is observed, but a small amount of supernatant liquid is observed. 1: The thick liquid is completely separated into two layers and sediment is visible.

[0086] [Viscosity measurement] The surface conditioning concentrates obtained in the examples and comparative examples were each allowed to stand at room temperature, and after six months, the viscosity at 15°C was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.). Evaluation was based on 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 600cps 3: 600 cps or more and less than 1100 cps 2: 1100 cps or more and less than 1600 cps 1: Over 1600cps or not measurable

[0088] [Zeta potential measurement] The surface conditioning concentrates obtained in the Examples and Comparative Examples were diluted 500 times with ion-exchanged 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 -60 mV or less was considered acceptable. The results are shown in Table 2. Note that in Comparative Example 4, the particles had aggregated, making measurement impossible.

[0089] [Coating appearance] The concentrated solutions for preparing surface conditioners obtained in the Examples and Comparative Examples were left to stand at room temperature for six months, and then diluted 500 times with ion-exchanged water to prepare solutions. The pH of the prepared solutions (surface conditioners) was within the range of 3 to 12. Using the prepared solutions, SPC test panels were each subjected to surface conditioning. After the surface conditioning, the panels were immersed in a zinc phosphate treatment agent (Surfdyne SD5350, manufactured by Nippon Paint Surf Chemicals Co., Ltd.) at 35°C for two minutes to form a zinc phosphate conversion coating. The appearance of the formed coating was visually evaluated according to the following criteria. The results are shown in Table 2. Surface conditioning was not possible for Comparative Example 4.

[0090] (Evaluation criteria) 2: Uniform 1: At least some rust has occurred

[0091] [Table 2]

[0092] From the results in Table 2, it was confirmed that the concentrates according to the Examples had superior dispersion stability compared to the concentrates according to the Comparative Examples.

Claims

1. A concentrated solution for preparing a surface conditioner, comprising zinc phosphate particles and a dispersion stabilizer, 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 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; The sulfur-containing compound is a compound having an isothiazolinone structure. Concentrated solution for preparing surface conditioners.

2. 2. The concentrated liquid for preparing a surface conditioner according to claim 1, further comprising a water-soluble organic polymer as the dispersion stabilizer.

3. The concentrated solution for preparing a surface conditioner according to claim 2, wherein 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 a total of 2-acrylamido-2-methylpropanesulfonic acid and / or allylsulfonic acid.

4. 3. The concentrated solution for preparing a surface conditioner 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.

5. 2. The concentrated solution for preparing a surface conditioner 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 7,500 or less.

6. A surface conditioner containing zinc phosphate particles and a dispersion stabilizer, 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 conditioner 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 conditioner 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; The sulfur-containing compound is a compound having an isothiazolinone structure. Surface conditioner.

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