JP2008150654A - Metal substrate, pretreatment method for metal, and method for forming composite coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-treated metal substrate which has superior anticorrosion properties and can prevent a coating film formed on the surface of the substrate from peeling. <P>SOLUTION: A surface-treated cold-rolled steel sheet has an iron substrate, and bismuth metal nanoparticles of 100 mg/m<SP>2</SP>or more in terms of bismuth fixed on the surface of the iron substrate so as to come in contact with the surface. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a metal substrate, a metal pretreatment method, and a composite film forming method.

Cathodic electrodeposition coating with high throwing power is applied in applications that require high anticorrosion performance such as automobiles, but it is generally used as a coating base treatment to ensure adhesion between the electrodeposition coating and the base steel. Chemical conversion treatment represented by zinc phosphate treatment is performed. However, improvements have been sought for the zinc phosphate treatment process because of the need for a dedicated and large facility, the need for maintenance such as sludge recovery, and the long process time.

On the other hand, lead compounds such as lead chromate and basic lead silicate have conventionally been added to such electrodeposition coatings used for cationic electrodeposition coating as corrosion resistance imparting agents. In recent years, since lead compounds have an adverse effect on the environment, Patent Document 1 discloses an example in which a cationic electrodeposition coating composition containing a metal bismuth colloid is applied to a zinc phosphate-treated steel sheet as a corrosion resistance imparting agent instead of a lead compound. It is disclosed.

Further, Patent Document 2 discloses a coating composition that can be obtained from a thermosetting aqueous coating material based on an organic main component containing metal bismuth dispersed in a colloidal form.

Examples of applying a cationic electrodeposition coating composition containing a bismuth salt (bismuth hydroxide, bismuth silicate) other than metal bismuth to a zinc phosphate-treated steel sheet are disclosed in Patent Documents 3, 4 and the like.

However, even if the coating composition described in Patent Documents 1 to 4 is applied to a steel sheet such as an untreated steel sheet that has not been subjected to zinc phosphate treatment, the anticorrosion property is not necessarily sufficient, and the coating film is not There was a case of peeling. That is, it is not described in Patent Documents 1 to 4 that such a composition is used as an alternative means of chemical conversion treatment performed as pre-coating treatment.
JP 2006-083305 A Special table 2003-525970 gazette Japanese Patent Laid-Open No. 5-140487 JP-A-5-247385

In view of the above-mentioned present situation, the present invention has an object of providing a metal substrate that has excellent anticorrosive properties and can prevent peeling of a film. In addition, the present invention can provide corrosion resistance equivalent to that of zinc phosphate treatment and adhesion between a steel sheet substrate and a coating film, and does not require maintenance such as sludge recovery without using a long facility. The object is to provide a simple metal pretreatment method and composite film forming method.

The present invention has a surface-treated metal substrate characterized by having an iron substrate and bismuth metal nanoparticles of 100 mg / m ² or more in terms of bismuth fixed so as to be in contact with the surface of the iron substrate. It is.
In the surface-treated metal substrate, the average particle diameter of the bismuth metal nanoparticles is preferably 1 to 50 nm.
In the surface-treated metal base material, it is preferable that the iron base material is not subjected to chemical conversion treatment. In the surface-treated metal base material, the iron base material is preferably a steel plate.
The present invention is also a composite film-coated metal substrate characterized by having the surface-treated metal substrate and an organic resin film formed on the surface of the surface-treated metal substrate.

The present invention is also a metal pretreatment method comprising a step of applying a dispersion of bismuth metal nanoparticles on the surface of a steel plate in an amount of 100 mg / m ² or more in terms of bismuth.
In the metal pretreatment method, the steel plate is preferably not subjected to chemical conversion treatment.
In the metal pretreatment method, the coating amount of the dispersion of bismuth metal nanoparticles is preferably 2000 mg / m ² or less in terms of bismuth.

In the metal pretreatment method, the average particle size of the bismuth metal nanoparticles in the dispersion is preferably 1 to 50 nm.
In the metal pretreatment method, the bismuth metal nanoparticle dispersion preferably contains bismuth metal nanoparticles having an average particle diameter of 1 to 50 nm, a high molecular weight pigment dispersant, and a solvent.

This invention is also a composite film formation method characterized by including the process of forming an organic resin film | membrane on the surface of the steel plate which gave the pre-treatment obtained by using the above-mentioned metal pre-treatment method.
In the composite film forming method, the organic resin film is preferably formed using a cationic electrodeposition coating composition containing an amine-added epoxy resin and a blocked polyisocyanate.
In the composite film forming method, the amine-added epoxy resin is preferably a cation-modified epoxy resin obtained by modifying an oxirane ring in a resin skeleton with an organic amine compound.

The present invention is also a composite film-coated steel sheet having a composite film obtained by using the above-described composite film forming method.
In the composite coated steel sheet, the composite film preferably includes bismuth metal nanoparticles and an organic resin film bonded to the surface of the steel sheet.
The present invention is described in detail below.

The surface-treated metal substrate of the present invention has an iron substrate and bismuth metal nanoparticles fixed so as to contact the surface of the iron substrate. For this reason, a composite film-coated metal substrate can be obtained by further forming an organic resin film on the surface-treated metal substrate. The composite film-coated metal base material has good adhesion between the iron base material and the coating film and corrosion resistance. In the normal metal corrosion mechanism, if a noble metal exists from the base material, the base metal is likely to be corroded, which is undesirable from the viewpoint of obtaining corrosion resistance of the metal. However, in the present invention, corrosion resistance can be improved by bismuth, which is a noble metal, by suppressing a decrease in the adhesion of the coating film over a long period of time. The reason why excellent adhesiveness and anticorrosiveness can be obtained in the present invention is not clear, but it is presumed that it is manifested by the following actions and functions.

FIG. 1 is an example of a conceptual diagram of the composite film-coated metal substrate of the present invention. In this example, the case where the iron substrate is a steel plate is shown. In this coated metal substrate, the bismuth metal nanoparticles or aggregates (aggregates) thereof are dispersed and joined on the steel plate, and the exposed portion of the steel plate not covered with the metal nanoparticles becomes a fine anode portion. In addition to being formed in a dispersed manner, the surface of the metal nanoparticles or their aggregates will be dispersed as a fine cathode part, and the local part in a state where the fine anode part and the cathode part are in close proximity and fixed It is assumed that a battery is formed.

FIG. 2 is an example of a conceptual diagram (estimated diagram) of the anticorrosion mechanism when bismuth metal nanoparticles are dispersed and coated on a steel plate. As shown in FIG. 2, in the fixed anode part, it is assumed that an anode reaction represented by the following reaction formulas (1) and (2) occurs, which causes a decrease in pH at the site. The
Fe → Fe ²⁺ + 2e ⁻ (1)
Fe ²⁺ + 2H ₂ O → Fe (OH) ₂ + 2H ⁺ (2)
On the other hand, in the cathode part, it is presumed that the cathode reaction represented by the following reaction formula (3) occurs, resulting in an increase in pH at that site.
1 / 2O ₂ + H ₂ O + 2e ⁻ → 2OH ⁻ (3)

Usually, the coating film is vulnerable to alkali, and an increase in pH at the cathode portion causes a decrease in adhesion, resulting in coating blistering or peeling of the coating film, and corrosion progresses. That is, when a coating film is formed on an untreated metal base material, the peripheral part of the scratched part or the initial defect part becomes a cathode, and adhesion decreases at the cathode part. It tends to occur. Once the coating film is separated from the substrate, the surrounding area becomes the cathode, and the peeling of the coating film spreads side by side one after another, and the cathode part and the anode part are easily expanded from the site, Corrosion begins to progress rapidly.

On the other hand, in the present invention, bismuth metal nanoparticles are used, and the anode part and the cathode part are fixed in proximity to each other, so that the adhesion force is maintained in the adjacent anode part even if the adhesion is lowered in the cathode part. Therefore, as a result, swelling and peeling of the coating film are suppressed, and expansion of corrosion is prevented. In this way, it is presumed that the coating film can exhibit good adhesion and anticorrosion properties despite bonding of a noble metal (bismuth). In view of the above effects, the bismuth metal nanoparticles are preferably fixed so as to be in contact with the iron base and are unevenly distributed near the surface of the iron base.

On the other hand, in the coating compositions described in Patent Documents 1 to 4, since bismuth metal nanoparticles are dispersed in the coating composition, even if the coating composition is applied to a steel plate, Only a small amount of contact with the steel plate. For this reason, even if the coating composition is used, a local battery in which the fine anode portion and the cathode portion are close and fixed is not formed, and good adhesion and corrosion resistance cannot be exhibited. Inferred.

In the surface-treated metal substrate, bismuth metal nanoparticles are fixed to 100 mg / m ² or more in terms of metal bismuth with respect to the surface of the iron substrate. Therefore, the surface-treated metal substrate has excellent anticorrosion properties and adhesion between the iron substrate and the film. If it is less than 100 mg / m ² , adhesion and anticorrosion may be reduced.
The average particle diameter of the bismuth metal nanoparticles is preferably 1 to 50 nm. This is because excellent adhesion and corrosion resistance can be obtained.
The iron base is preferably not subjected to chemical conversion treatment. In the present invention, the bismuth metal nanoparticles are brought into contact with the iron substrate to form a local battery, thereby exhibiting excellent corrosion resistance and adhesion between the iron substrate and the film. This is because there is no need for processing. For this reason, it is not necessary to use long equipment, and maintenance such as sludge recovery is not necessary.
Moreover, although the said iron base material is not specifically limited, It is preferable that it is a steel plate, and it is more preferable that it is a cold-rolled steel plate. This is because it has excellent adhesion and anticorrosion properties and can be suitably used for automobile bodies and the like.

The surface-treated metal substrate of the present invention can be produced by applying the metal pretreatment method of the present invention to an iron substrate such as a steel plate. Moreover, the composite film-coated steel sheet of the present invention can be produced by applying the composite film forming method of the present invention to the surface-treated metal substrate.

In the metal pretreatment method of the present invention, a specific amount (in terms of bismuth) of a bismuth metal nanoparticle dispersion is applied to an untreated steel plate (not subjected to chemical conversion treatment) to thereby form bismuth metal nanoparticles on the steel plate surface. Are dispersed and joined.

The metal pretreatment method of the present invention is a method including a step of applying 100 mg / m ² or more of a bismuth metal nanoparticle dispersion liquid in terms of bismuth on the surface of a steel plate. The chemical conversion treatment is a conventionally known chemical conversion treatment such as zinc phosphate treatment. The steel plate is preferably a cold-rolled steel plate. This is because it has excellent adhesion and anticorrosion properties and can be suitably used for automobile bodies and the like. The steel sheet is preferably not subjected to chemical conversion treatment. In the present invention, the metal nanoparticles and the steel plate are in contact with each other to form a local battery, thereby exhibiting excellent corrosion resistance and adhesion between the steel plate and the film. Therefore, the steel plate needs to be subjected to chemical conversion treatment. Because there is no. For this reason, it is not necessary to use long equipment, and maintenance such as sludge recovery is not necessary.

The bismuth metal nanoparticle dispersion is a liquid in which bismuth metal nanoparticles are dispersed in a liquid. In the present invention, it is important to use metal nanoparticles of bismuth having an average particle diameter in the above range, and thereby excellent adhesion and corrosion resistance can be obtained.

The average particle diameter of the bismuth metal nanoparticles in the dispersion is preferably 1 to 50 nm, and more preferably 5 to 50 nm. In the present invention, the use of metal nanoparticles having an average particle diameter within the above range is preferable in that excellent adhesion and corrosion resistance can be obtained. In the present specification, the method for measuring the average particle diameter is to measure the average of the major diameters of metal nanoparticles obtained by taking a photograph using a transmission electron microscope. In addition, the said average particle diameter is a primary particle diameter of a metal nanoparticle.

The bismuth metal nanoparticle dispersion is not particularly limited as long as it is a dispersion containing bismuth metal nanoparticles, but contains bismuth metal nanoparticles having an average particle diameter of 1 to 50 nm, a high molecular weight pigment dispersant, and a solvent. Bismuth metal nanoparticle dispersions are preferred. Thereby, adhesiveness and anticorrosion can be improved favorably.

In the bismuth metal nanoparticle dispersion, the high molecular weight pigment dispersant coexists with the bismuth metal nanoparticles and serves to stabilize the dispersion of the bismuth metal nanoparticles in the solvent. It is thought that there is. The above high molecular weight pigment dispersant is an amphiphilic copolymer having a structure containing a solvated portion and a functional group having a high affinity for the pigment surface introduced into a high molecular weight polymer. It is used as a pigment dispersant when producing a pigment paste.

The high molecular weight pigment dispersant is considered to have a function of stabilizing the generation of metal nanoparticles by reduction of the metal compound and the dispersion in the solvent after the generation.
The number average molecular weight of the high molecular weight pigment dispersant is preferably 1,000 to 1,000,000. If it is less than 1000, the dispersion stability may not be sufficient, and if it exceeds 1,000,000, the viscosity may be too high and handling may be difficult. More preferably, it is 2000-500,000, More preferably, it is 4000-500,000.

The high molecular weight pigment dispersant is not particularly limited as long as it has the above-mentioned properties, and examples thereof include those exemplified in JP-A-11-80647. A variety of high molecular weight pigment dispersants can be used, but commercially available ones can also be used.

The high molecular weight pigment dispersant may be polar or nonpolar. When the solvent of the bismuth metal nanoparticle dispersion is aqueous, the high molecular weight pigment dispersant is a polar high molecular weight pigment dispersant. When the solvent of the bismuth metal nanoparticle dispersion is a nonpolar solvent, the high molecular weight pigment is dispersed. The dispersant is a nonpolar high molecular weight pigment dispersant. In addition, the solvent is aqueous, which means water, a lower alcohol miscible with water in an arbitrary ratio, a mixture of water and lower alcohol, and those containing another polar solvent. The nonpolar solvent is an organic solvent that is immiscible with water. Specific examples include aromatic hydrocarbons such as toluene, xylene, and ethylbenzene, and aliphatic carbonizations such as hexane, heptane, decane, octane, and heptane. Examples thereof include ester groups such as hydrogen, ethyl acetate and butyl acetate, long chain alcohols such as α-terpineol and butyl carbitol, and esters of long chain alcohols and carboxylic acids.

Examples of commercially available polar high molecular weight pigment dispersants include Dispersic R, Dispersic 154, Dispersic 180, Dispersic 187, Dispersic 184, Dispersic 190, Dispersic 191, Dispersic 192, Dispersic 193, Dispersic 194 (above made by Big Chemie), Solsperse 20000, Solsperse 27000, Solsperse 12000, Solsperse 40000, Solsperse HP90 (above Lubrizol), EFKA-450, EFKA-451, EFKA-452, EFKA -453, EFKA-4540, EFKA-4550, EFKA-1501, EFKA-1502 (manufactured by Fuka Additives) , Floren TG-720W, Floren TG-730W, Floren TG-740W, Floren TG-745W, Floren TG-750W, Floren G-700DMEA, Floren G-WK-10, Floren G-WK-13E (manufactured by Kyoeisha) Dispar Aid W-30, Dispar Aid W-39 (made by Elementis), K-SPERSE XM2311 (made by King), Neoletz BT-24, Neoletts BT-175 (manufactured by Generalca), SMA 1440H (manufactured by Atchem) , Orotan 731DP, Orotan 963 (made by Rohm and Haas), Yonelin (made by Yoneyama Chemical), Sunspearl PS-2 (made by Sanyo Kasei), Triton CF-10 (made by Union Carbide), John Crill 678, John Kuril 679, G John Krill 683, John Krill 611, John Krill 680, John Krill 682, John Krill 52, John Krill 57, John Krill 60, John Krill 63, John Krill 70, John Krill HPD-71, John Krill 62 (manufactured by Johnson Polymer Co., Ltd.) Surfynol CT-111 (made by Air Products) etc. can be mentioned.

On the other hand, as the commercially available non-polar high molecular weight pigment dispersant, Dispervic 110, Dispersic LP-6347, Dispersic 170, Dispersic 171, Dispersic 174, Dispersic 161, Dispersic 166, Dispersic 182, Disperbic 183, Disperbic 185, Disperbic 2000, Disperbic 2001, Disperbic 2050, Disperbic 2150, Disperbic 2070 (manufactured by Vic Chemie), Solsperse 24000, Solsperse 28000, Solsperse 32500, Solsperse 32550, Solsperse 31845 Solsparse 26000, Solsparse 36600, Solsparse 38500 (above Avisi EFKA-46, EFKA-47, EFKA-48, EFKA-4050, EFKA-4055, EFKA-4009, EFKA-4010, EFKA-400, EFKA-401, EFKA-402, EFKA-403 (Chemicals), Floren DOPA-15B, Floren DOPA-17, Floren DOPA-22 (manufactured by Kyoeisha), Dispalon 2150, Disparon 1210 (manufactured by Enomoto Kasei) and the like.

The above bismuth metal nanoparticles have a triangle and rhombus shape with a size of 20 to 30 nm, and a triangle, quadrangle, ellipse, circle, and rod shape with a size of 5 to 15 nm as seen in an electron micrograph. There are some indefinite shapes that are mixed with various shapes. When the bismuth metal nanoparticles are amorphous and the solvent is aqueous, the high molecular weight pigment dispersant is polar and turbid when bismuth ions coexist. When the metal nanoparticles are amorphous and the solvent is nonpolar, the high molecular weight pigment dispersant is nonpolar.

Among the above polar high molecular weight pigment dispersants, those that cause turbidity when bismuth ions coexist include Dispersic 191, EFKA-4540, EFKA-4550, Floren G-WK-10, Floren G-WK-13E, and the like. . These all have an amino group and are considered to cause interaction with bismuth ions.

The solid content of the bismuth metal nanoparticles and the high molecular weight pigment dispersant is preferably 2 to 70% by mass in the bismuth metal nanoparticle dispersion. If it is less than 2% by mass, the concentration of the dispersion is too thin and not efficient, and if it exceeds 70% by mass, there may be a problem in stability. The mass ratio between the bismuth metal nanoparticles and the high molecular weight pigment dispersant is preferably 5/100 to 100/10. If it is less than 5/100, the concentration of bismuth is low and inefficient, and if it exceeds 100/10, there may be a problem in stability.

Examples of the method for producing the bismuth metal nanoparticle dispersion include a method of reducing a bismuth ion dispersion described in JP-A-2004-99991 with a reducing agent in the presence of a high molecular weight pigment dispersant.
The bismuth ion solution is a solution in which a compound serving as a supply source of bismuth ions is dissolved in an aqueous solvent. The compound serving as the source of bismuth ions is not particularly limited as long as it is a compound containing bismuth capable of supplying colloidal bismuth metal nanoparticles by dissolving in a solvent and reducing, for example, chloride Inorganic bismuth-containing compounds such as bismuth, bismuth oxychloride, bismuth bromide, bismuth silicate, bismuth hydroxide, bismuth trioxide, bismuth nitrate, bismuth subnitrate, bismuth oxycarbonate; bismuth lactate, triphenyl bismuth, bismuth gallate In addition to bismuth benzoate, bismuth citrate, bismuth methoxyacetate, bismuth acetate, bismuth formate, bismuth 2,2-dimethylolpropionate, and the like (for example, bismuth oxide, bismuth hydroxide, basic bismuth carbonate, etc. A) Bismuth compound and organic acid mixed in an aqueous medium And the like organic bismuth-containing compounds such as organic acid-modified bismuth as can be produced by dispersing (see International Publication No. WO99 / 31187). Especially, when water is included as a solvent, bismuth chloride and bismuth nitrate are preferable from the viewpoint of solubility in water.

Examples of the aqueous solvent include water, methanol, ethanol, ethylene glycol, isopropanol, and a mixture thereof, and may contain other organic solvents as long as the solubility of the raw material components is not inhibited. Considering the solubility of the reducing agent described later, it is preferable that water is contained. Moreover, it is preferable that methanol and ethanol are contained from the solubility of a bismuth compound. Furthermore, it is particularly preferable to contain ethanol having an ability to inhibit oxidation of bismuth metal.

In the method for producing the bismuth metal nanoparticle dispersion, the reaction is performed under acidic conditions. This is because bismuth compounds generally have low water solubility, higher solubility in acids, and bismuth is more stable in Bi ⁰ than Bi ³⁺ under acidic conditions, so that the reduction reactivity is increased. Conversely, when the reaction is carried out with the interior of the system being basic, bismuth hydroxide or an oxybismuth compound precipitates to hinder the progress of the reaction. The pH of the reaction solution is preferably 4 or less, and more preferably 2 or less. The acid is preferably added in an amount of 2 to 50 times the molar amount of the Bi compound. More preferably, it is 5 to 20 times the molar amount.

Examples of the acid added to the solution to make the reaction solvent acidic include hydrohalic acids such as hydrochloric acid and hydrobromic acid; perchloric acid, chloric acid, acetic acid, glycolic acid, and lactic acid. Of these, hydrochloric acid, perchloric acid, and acetic acid are preferable.

The reducing agent used in the method for producing the bismuth metal nanoparticle dispersion has a reducing ability even under acidic conditions. That is, as described above, the reaction solvent is acidic in consideration of the solubility and reduction reactivity of the bismuth compound. Since the reduction reaction is caused in such an acidic solution, the selection of the reducing agent is important. In addition, the amine compound often used as a reducing agent in the production of a copper or noble metal metal nanoparticle dispersion does not function as a reducing agent under acidic conditions.

The reducing agent having the reducing ability even under the above acidic conditions is not particularly limited. For example, dithionic acid, sodium formaldehyde sulfoxylate (called Rongalite) which is a derivative of dithionite, formaldehyde sulfoxylic acid Examples thereof include zinc, citric acid, tartaric acid, alcorbic acid, malic acid, lithium borohydride, sodium aluminum hydride, dimethylamine borane, hydrazine, hypophosphorous acid, hydrosulfite and the like. Among the above reducing agents, when using citric acid, tartaric acid, ascorbic acid, malic acid, which are relatively mild reducing agents, a solution of iron (II) sulfate, tin (II) chloride, titanium (III) chloride and Reduction ability can be improved by mixing and using together. Among the reducing agents, sodium formaldehyde sulfoxylate (Longalite) is more preferable from the viewpoint of safety and reaction efficiency.

The amount of the reducing agent added is preferably equal to or greater than the amount necessary to reduce bismuth in the bismuth-containing compound. If the amount is less than this amount, reduction may be insufficient. Moreover, although an upper limit is not specifically limited, It is preferable that it is 30 times or less of the quantity required for reducing the bismuth in the said bismuth containing compound, and it is more preferable that it is 10 times or less.

When sodium formaldehyde sulfoxylate is used as the reducing agent, the amount of sodium formaldehyde sulfoxylate added is preferably 1.5 to 20 mol with respect to 1 mol of the bismuth-containing compound. When the amount is less than 1.5 mol, the reduction is not sufficiently performed, and when the amount exceeds 20 mol, the aggregation stability of the generated metal nanoparticles decreases. More preferably, it is 3-10 mol. Further, when using sodium formaldehyde sulfoxylate, iron (II) sulfate may be used in combination.

In the method for producing the bismuth metal nanoparticle dispersion, the reduction reaction is performed in the presence of a high molecular weight pigment dispersant. It is considered that the high molecular weight pigment dispersant can stably disperse the bismuth metal nanoparticles in a solvent. As the high molecular weight pigment dispersant, one suitable for the kind of bismuth metal nanoparticle dispersion to be produced is selected. A polar high molecular weight pigment dispersant is selected when the solvent is water-based, and a nonpolar high molecular weight pigment dispersant is selected when the solvent is non-polar. Hereinafter, the procedure of the production method will be described separately for a case where the solvent is an aqueous solvent and a case where the solvent is a nonpolar solvent.

In the case of an aqueous solvent, first, an acidic solution of the bismuth-containing compound is prepared. The amount of the bismuth-containing compound used at this time is not particularly limited, and can be, for example, about 0.1 mol / l. At this time, the bismuth-containing compound can be efficiently dissolved by heating to about 40 ° C. in a hot water bath or the like.

Next, a polar high molecular weight pigment dispersant is added here. The polar high molecular weight pigment dispersant is preferably dissolved in an aqueous solvent. The amount of the polar high molecular weight pigment dispersant is preferably 5 to 1000 parts by mass with respect to 100 parts by mass of the bismuth metal of the bismuth-containing compound. If it is less than 5 parts by mass, there may be a problem in the stability of the bismuth metal nanoparticle dispersion, and if it exceeds 1000 parts by mass, the amount of the high-molecular-weight pigment dispersant with respect to the metal nanoparticles of bismuth increases. May affect physical properties. The amount of the polar high molecular weight pigment dispersant is more preferably 20 to 200 parts by mass.

The addition of the polar high molecular weight pigment dispersant may make the liquid turbid and translucent. This is seen when a polar high molecular weight pigment dispersant having an amino group such as Disparvic 191, EFKA-4540, EFKA-4550, Floren G-WK-10, or Floren G-WK-13E is used. It is a phenomenon. Among these, it is preferable in terms of stability to use Big Chemie 191 and EFKA-4550. In this case, even if the liquid becomes turbid, precipitation does not occur in a short time, and the process can proceed to the next stage as it is.

Next, a reducing agent is added. When the reducing agent is sodium formaldehyde sulfoxylate, the addition can be performed at room temperature. After the addition, the solution turns from colorless and transparent to black indicating the formation of bismuth metal nanoparticles. Thereafter, for example, aging is performed for about 2 hours to complete the reaction.
The reduction reaction can take various forms such as adding a bismuth-containing compound solution to a mixture of a polar high molecular weight pigment dispersant and a reducing agent.

In addition to the bismuth metal nanoparticles and the above-described high molecular weight pigment dispersant, the bismuth metal nanoparticle dispersion obtained in this way is mixed ions such as chloride ions derived from raw materials such as bismuth-containing compounds. The resulting salt and, in some cases, contain a reducing agent. These miscellaneous ions, salt and reducing agent may adversely affect the stability of the resulting bismuth metal nanoparticle dispersion. It is desirable to remove it.

The ultrafiltration (UF) has a screen size smaller than that of a filtration membrane used for microfiltration (MF). Ultrafiltration is usually used for the purpose of separating high molecular weight substances and colloidal substances. In the present invention, it is used to increase the concentration of metal bismuth in the solid content of the bismuth metal nanoparticle dispersion. The ultrafiltration can be performed by a conventionally known method.

By the ultrafiltration treatment, the miscellaneous ions and the reducing agent are removed from the bismuth metal nanoparticle dispersion. Furthermore, since a part of high molecular weight pigment dispersant is removed simultaneously, the bismuth density | concentration in solid content in a bismuth metal nanoparticle dispersion liquid can be raised compared with a process. In addition to the ultrafiltration, the miscellaneous ions and the reducing agent can be removed by centrifugation. Even in this case, the bismuth concentration can be increased as compared with that before the treatment.

Next, the procedure of the production method when the solvent is a nonpolar solvent will be described. First, as in the case of an aqueous solvent, an acidic solution of the bismuth-containing compound is prepared. Next, a solution of a nonpolar high molecular weight pigment dispersant is prepared. When this nonpolar high molecular weight pigment dispersant solution is mixed with the previously prepared acidic solution of a bismuth-containing compound, the solution must not become separated into two layers but become cloudy. Therefore, the solvent used to adjust the solution of the nonpolar high molecular weight pigment dispersant is preferably methanol or ethanol which is an alcohol having an affinity for water.

The obtained acidic solution of the bismuth-containing compound and the solution of the nonpolar high molecular weight pigment dispersant are mixed and left in a cloudy state, and a reducing agent is added thereto to advance the reduction reaction. Here, the blending ratio and reaction conditions in the reduction reaction can be set in the same manner as when the polar high molecular weight pigment dispersant is used.

As the reaction proceeds, a black oil that appears to consist of non-polar high molecular weight pigment dispersant and bismuth metal nanoparticles precipitates. Here, by removing the colorless and transparent supernatant by decantation and further washing with water, the above-mentioned miscellaneous ions and the reducing agent can be removed.

Since the oily substance thus obtained contains the solvent used in the reaction such as water, methanol and ethanol having high solubility in water and high volatility and toluene that can be azeotroped with water are used. After the addition, the sol-like metal nanoparticles and the high molecular weight pigment dispersant are first obtained by drying. Subsequently, a bismuth metal nanoparticle dispersion liquid can be obtained by adding and dissolving a nonpolar solvent to this.

The bismuth metal dispersion containing the non-polar high molecular weight pigment dispersant thus obtained was mixed with various shapes such as tetrahedron, hexahedron, ellipse, sphere, rod and the like having a size of 2 to 15 nm. It contains amorphous bismuth metal nanoparticles.
The bismuth metal nanoparticle dispersion produced by the above method can measure the bismuth content by TG-DTA or XRF, and can observe the particle shape and the like by TEM analysis.

The concentration of the bismuth metal nanoparticle dispersion to be used is preferably 0.1 to 10% by mass. If it is less than 0.1% by mass, the area of the anode part becomes excessive, and the balance may be lost to cause corrosion. If it exceeds 10% by mass, it may be difficult to apply uniformly.

The method for applying the bismuth metal nanoparticle dispersion is not particularly limited as long as it can be applied uniformly. Examples of preferable coating methods include spin coating, air spraying, and dipping.

The coating amount of the bismuth metal nanoparticles on the steel sheet surface is preferably 100 mg / m ² or more in terms of metal bismuth. This is because excellent corrosion resistance and adhesion between the steel sheet and the film can be imparted. If it is less than 100 mg / m ² , adhesion and anticorrosion may be reduced. Moreover, it is preferable that the said coating amount is 2000 mg / m < ² > or less in conversion with the metal which comprises a metal nanoparticle. This is because even if it exceeds 2000 mg / m ² , the effect is not improved, and there is a risk of becoming uneconomical. The coating amount is more preferably 1000 mg / m ² or less.

After the application of the bismuth metal nanoparticle dispersion, it is preferable to perform a step of drying at 80 to 100 ° C. for 10 to 30 minutes. Thereby, the metal nanoparticles of bismuth can be well dispersed and bonded on the steel plate surface.

The metal pretreatment method is applied to a steel plate. The steel sheet may be a structure used for a specific application, such as an automobile body. The structure is formed by forming the metal material into a concavo-convex shape so as to be used for automobiles or other applications.

The surface of the steel sheet is preferably subjected to degreasing treatment and post-degreasing water washing treatment before performing the step of applying the bismuth metal nanoparticle dispersion.
The degreasing treatment is performed to remove oil and dirt adhering to the surface of the base material, and usually with a degreasing agent such as phosphorus-free and nitrogen-free degreasing cleaning liquid at about 30 to 55 ° C. for about several minutes. Immersion treatment is performed. If desired, a preliminary degreasing process can be performed before the degreasing process. The post-degreasing rinsing treatment is performed by spraying once or more with a large amount of rinsing water in order to wash the degreasing agent after the degreasing treatment.

In the method for forming a composite film of the present invention, an organic resin film is formed on the surface of the steel sheet that has been subjected to the above-described pretreatment, thereby forming a composite film as shown in the conceptual diagram of FIG. 1 (bismuth metal nanoparticles and This is a method for forming an organic resin film. The composite coating formed on the steel sheet has excellent adhesion and corrosion resistance.

In the conventional film formation on steel plates, it is excellent by performing degreasing treatment, water washing treatment after degreasing, surface conditioning treatment, zinc phosphate chemical treatment, water washing treatment after chemical conversion, drying and electrodeposition coating in this order. Adhesion and corrosion resistance are obtained. On the other hand, in the composite film forming method of the present invention, excellent adhesion and anticorrosion properties can be obtained simply by performing degreasing treatment, post-degreasing water washing treatment, application of bismuth metal nanoparticle dispersion, drying, and electrodeposition coating in this order. Can be obtained. Accordingly, the number of steps can be reduced as compared with the conventional method, and desired performance can be expressed by a simple method. Moreover, it is not necessary to collect sludge which is necessary when performing the zinc phosphate chemical conversion treatment.

The said composite film formation method includes the process of forming an organic resin film on the surface of the steel plate which gave the pretreatment obtained by using the metal pretreatment method mentioned above. The organic resin film can be formed by, for example, electrodeposition coating using a conventionally known cationic electrodeposition coating composition, but a cationic electrodeposition coating composition containing an amine-added epoxy resin and a curing agent is used. It is preferable that it is formed using. Thereby, the outstanding adhesiveness and corrosion resistance can be obtained.

The amine-added epoxy resin is a cation-modified epoxy resin obtained by modifying an oxirane ring in a resin skeleton with an organic amine compound. In general, a cation-modified epoxy resin is produced by ring-opening an oxirane ring in a starting material resin skeleton by a reaction with an organic amine compound such as a primary amine, secondary amine, or tertiary amine acid salt. A typical example of the starting material resin (epoxy resin) is a polyphenol polyglycidyl ether type epoxy resin which is a reaction product of a polycyclic phenol compound such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, cresol novolak and epichlorohydrin. Can be mentioned. Examples of other starting material resins include oxazolidone ring-containing epoxy resins described in JP-A-5-306327. The oxazolidone ring-containing epoxy resin is obtained by reacting a diisocyanate compound or a bisurethane compound obtained by blocking an NCO group of a diisocyanate compound with a lower alcohol such as methanol or ethanol, and epichlorohydrin.

The starting material resin can be used by extending the chain with a bifunctional polyester polyol, polyether polyol, bisphenol, dibasic carboxylic acid or the like before the oxirane ring-opening reaction with the organic amine compound.
Similarly, before the oxirane ring-opening reaction with an organic amine compound, 2-ethylhexanol, nonylphenol, ethylene glycol may be added to some oxirane rings for the purpose of adjusting molecular weight or amine equivalent and improving heat flow. Monohydroxy compounds such as mono-2-ethylhexyl ether and propylene glycol mono-2-ethylhexyl ether can also be added and used.

Examples of organic amine compounds that can be used for opening an oxirane ring and introducing an amino group include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, There may be mentioned primary, secondary or tertiary amine salts such as triethylamine salt and N, N-dimethylethanolamine salt. A ketimine block primary amino group-containing secondary amine such as aminoethylethanolamine methyl isobutyl ketimine can also be used. These organic amine compounds are preferably reacted at least in an equivalent amount with respect to the oxirane ring in order to open all the oxirane rings.

The number average molecular weight of the cation-modified epoxy resin is preferably 1500 to 5000, and more preferably 1600 to 3000. If it is less than 1500, physical properties such as solvent resistance and corrosion resistance of the cured coating film may be inferior. If it exceeds 5000, the viscosity of the resin solution is difficult to control and synthesis is difficult, and handling such as emulsification and dispersion of the resulting resin may be difficult to handle. Furthermore, because of the high viscosity, the flowability during heating and curing is poor, and the appearance of the coating film may be significantly impaired.

The cation-modified epoxy resin is preferably molecularly designed so that the hydroxyl value is in the range of 50 to 250. When the hydroxyl value is less than 50, the coating film is poorly cured. When the hydroxyl value exceeds 250, water resistance may decrease as a result of excess hydroxyl groups remaining in the coated film after curing.

The cation-modified epoxy resin is preferably molecularly designed so that the amine value is in the range of 40 to 150. If it is less than 40, emulsification and dispersion failure in an aqueous medium due to acid neutralization is caused. If it exceeds 150, water resistance may be deteriorated as a result of excessive amino groups remaining in the coating film after curing.

The curing agent may be of any type as long as each resin component can be cured at the time of heating. Among them, a block polyisocyanate suitable as a curing agent for an electrodeposition resin is recommended.
Examples of the polyisocyanate that is a raw material of the block polyisocyanate include aliphatic diisocyanates such as hexamethylene diisocyanate (including trimer), tetramethylene diisocyanate, and trimethylhexamethylene diisocyanate, isophorone diisocyanate, 4,4′- Examples thereof include alicyclic polyisocyanates such as methylene bis (cyclohexyl isocyanate), and aromatic diisocyanates such as 4,4′-diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate. The blocked polyisocyanate can be obtained by blocking these with an appropriate sealant.

Examples of the sealant include monovalent alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbinol, methylphenyl carbinol; ethylene glycol Cellosolves such as monohexyl ether and ethylene glycol mono-2-ethylhexyl ether; polyether-type double-end diols such as polyethylene glycol, polypropylene glycol and polytetramethylene ether glycol phenol; ethylene glycol, propylene glycol, 1,4-butanediol and the like Polyester-type double-ended polyols obtained from diols of the above and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid and sebacic acid; para-t-butylphenol, Phenols such as tetrazole; dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, oximes such as cyclohexanone oxime; .epsilon.-caprolactam, lactams typified by γ- butyrolactam is preferably used. In particular, since oximes and lactams are dissociated at low temperatures, they are suitable from the viewpoint of resin curability when co-baking with an intermediate coating film in a subsequent step.

The block polyisocyanate is preferably blocked in advance by using a single or a plurality of sealants. The blocking rate is preferably set to 100% in order to ensure the storage stability of the paint unless there is a purpose of denaturing reaction with each of the above resin components. In addition, block polyisocyanate may be used in combination of a plurality of types for convenience of coating film properties, degree of curing, and adjustment of curing temperature.

The blending amount of the block polyisocyanate with respect to 100% by mass (solid content) of the amine-added epoxy resin varies depending on the degree of crosslinking required for the purpose of use of the cured coating film, etc. Considering the properties, the solid content is preferably in the range of 15 to 40% by mass. If it is less than 15% by mass, the resulting coating film may be poorly cured. As a result, the physical properties of the coating film such as mechanical strength may be lowered. There is a case. On the other hand, if it exceeds 40% by mass, excessive curing may result, resulting in poor coating properties such as impact resistance.

The amine-added epoxy resin neutralizes the amino group in the resin with an appropriate amount of an inorganic acid such as hydrochloric acid, nitric acid, hypophosphorous acid, or an organic acid such as formic acid, acetic acid, lactic acid, sulfamic acid, and acetylglycine acid. It is prepared by treating and emulsifying and dispersing in water as a cationized emulsion. Moreover, when emulsifying and dispersing, usually, emulsion particles containing a curing agent (block polyisocyanate) as a core and an amine-added epoxy resin as a shell are formed.

The average particle diameter of the emulsion particles is 0.01 to 0.5 μm, preferably 0.02 to 0.3 μm, more preferably 0.05 to 0.2 μm. If the average particle size is less than 0.01 μm, the neutralizing agent necessary for water-dispersing the resin component becomes excessive, and the electrodeposition efficiency per a certain amount of electricity decreases. If it exceeds 0.5 μm, the dispersibility of the particles is lowered, so that the storage stability of the electrodeposition paint is lowered, which is not preferable.

If necessary, the cationic electrodeposition coating composition may further contain a pigment. As said pigment, what is normally used for a coating material can be used. Specifically, coloring pigments such as carbon black, titanium dioxide, and graphite; extender pigments such as kaolin, aluminum silicate (clay), talc, calcium carbonate, and inorganic colloids (silica sol, alumina sol, titanium sol, zirconia sol, etc.); phosphorus Heavy metal-free rust preventive pigments such as acid pigments (aluminum phosphomolybdate, (poly) zinc phosphate, calcium phosphate, etc.) and molybdate pigments (aluminum phosphomolybdate, zinc phosphomolybdate, etc.) can be mentioned. Of these, titanium dioxide and carbon black are most suitable for electrodeposition coatings because they have high concealability as color pigments and are inexpensive. These may be used alone or in combination of two or more.

The mass ratio {P / (P + V)} of the pigment to the total mass (P + V) of the pigment (P) and the resin solid content (V) contained in the cationic electrodeposition coating composition (hereinafter referred to as PWC) is , Preferably in the range of 5 to 30% by mass. If it is less than 5% by mass, the barrier properties against corrosion such as water and oxygen with respect to the coating film are excessively lowered due to insufficient pigment, and weather resistance and corrosion resistance at a practical level may not be exhibited. However, when such inconvenience does not occur, the pigment concentration may be set to zero as much as possible, and a clear or nearly clear electrodeposition coating composition may be formed and supplied to the present invention. If it exceeds 30% by mass, an excess of pigment will cause an increase in viscosity at the time of curing, and the flow property will be lowered and the appearance of the coating film may be remarkably deteriorated. However, the resin solid content (V) constitutes an electrodeposition coating film including a pigment-dispersed resin in addition to the amine-added epoxy resin and the curing agent (block polyisocyanate) which are the main resins of the coating composition. The total solid content of all resin binders is shown.

The cationic electrodeposition coating composition is adjusted so that the total solid concentration is in the range of 5 to 40% by mass, preferably 10 to 25% by mass. An aqueous medium (water alone or a mixture of water and a hydrophilic organic solvent) is used to adjust the total solid concentration. The pH of the cationic electrodeposition coating composition is preferably 5 to 7, and more preferably 5.5 to 6.5. If the pH is less than 5, the electrodeposition coating efficiency and the film appearance may decrease. If it exceeds 7, the stability of the base resin emulsion in the coating composition tends to decrease. Chemicals used for pH adjustment are inorganic acids such as nitric acid and sulfuric acid when high, or organic acids such as formic acid and acetic acid, and organic bases such as amine when low, or inorganic bases such as ammonia and sodium hydroxide. It is sufficient to add, and the additive chemicals are not limited.

Furthermore, a small amount of additives may be introduced into the cationic electrodeposition coating composition. Examples of additives include UV absorbers, antioxidants, surfactants, coating surface smoothers, curing catalysts (dibutyltin oxide, dioctyltin dilaurate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin Organic tin compounds such as dibenzoate and dioctyltin dibenzoate) and curing accelerators (zinc acetate).

The organic resin film is most preferably formed by cationic electrodeposition coating in order to improve the uniformity of the paint film and reduce film defects such as film thickness, pins, and repellency. If defects are conspicuous in the organic resin film obtained by a coating method other than the electrodeposition coating method, the defective portion becomes the base point of the anode portion and corrosion proceeds, which is not preferable for the application of the present invention.

After the cationic electrodeposition coating, an electrodeposition-cured coating film having a high degree of crosslinking can be obtained by performing a curing reaction at 120 to 200 ° C., preferably 140 to 180 ° C. If it exceeds 200 ° C., the coating film becomes excessively hard and brittle, and if it is less than 120 ° C., curing is not sufficient, and film properties such as solvent resistance and film strength are unfavorable.

The composite coating coated steel sheet of the present invention has a composite coating obtained by using the above-described composite coating forming method. Therefore, this coated steel sheet is excellent in adhesion and corrosion resistance. The composite coating formed on the composite-coated steel plate preferably contains bismuth metal nanoparticles and an organic resin coating bonded to the surface of the steel plate as shown in FIG. By having the composite film having such a configuration, it is possible to improve adhesion and corrosion resistance.

The surface-treated metal substrate of the present invention has an iron substrate and bismuth metal nanoparticles of 100 mg / m ² or more in terms of bismuth fixed so as to be in contact with the surface of the iron substrate. Moreover, the composite film-coated metal substrate of the present invention has the above-mentioned surface-treated metal substrate and an organic resin film formed on the surface. The composite film-coated metal substrate has adhesion and corrosion resistance comparable to those obtained when a pretreatment consisting of a conventional zinc phosphate chemical conversion treatment is performed.
The metal pretreatment method of the present invention is a method including a step of applying a bismuth metal nanoparticle dispersion liquid of 100 mg / m ² or more in terms of metal bismuth on the surface of a steel plate. For this reason, by forming an organic resin film on the steel sheet after the pretreatment, adhesion and corrosion resistance comparable to those obtained when a pretreatment consisting of a conventional zinc phosphate conversion treatment is performed. Further, according to the metal pretreatment method and the composite film forming method of the present invention, a composite film-coated steel sheet having desired performance can be produced in a simpler process than the conventional method.

Examples The present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In the examples, “parts” means “parts by mass” unless otherwise specified.

Production Example 1 Production of Metal Bismuth Metal Nanoparticle Dispersion Liquid 500 ml Kolben was charged with 300 g of 1N hydrochloric acid and 9.46 g of bismuth chloride, and stirred and dissolved in a 50 ° C. hot water bath. After dissolution of bismuth chloride, the hot water bath was removed, and then 5.37 g of EFKA-4550 (manufactured by Fuka Additive Co., Ltd., 50% by mass of active ingredient) was added with stirring to obtain a colorless and transparent mixed solution. Next, apart from the above Kolben, 23.11 g of sodium formaldehyde sulfoxylate dihydrate and 36.89 g of deionized water were stirred and dissolved in a 50 ° C. hot water bath, and the temperature of the resulting solution was obtained. Was added to Kolben instantaneously while stirring. The liquid turned black in an instant. Stirring was continued for 2 hours while maintaining the liquid temperature at 25 ° C., and a black bismuth metal nanoparticle dispersion liquid was obtained.

Next, ultrafiltration module AHP1010 (manufactured by Asahi Kasei Co., Ltd .; molecular weight cut off 50000, number of membranes used 400), magnet pump, and 3 l stainless steel cup with tube connection port at the bottom are connected by a silicon tube, and ultrafiltration is performed. The device. The previous bismuth metal nanoparticle dispersion was placed in a stainless steel cup, and 2 liters of water was further added, and then ultrafiltration was performed by operating the pump. When the filtrate from the module became 2 liters after about 20 minutes, 2 liters of water was added to the stainless steel cup. Thereafter, the filtrate was confirmed to have a conductivity of 7 μS / cm or less, and concentrated until the amount of the mother liquor was 500 ml.

Subsequently, an ultrafiltration device comprising a 500 ml stainless cup, an ultrafiltration module AHP0013 (manufactured by Asahi Kasei Co., Ltd .; fractional molecular weight 50000, number of membranes used 100), a tube pump, and an aspirator was assembled. The mother liquor obtained previously was put into this stainless steel cup and concentrated to increase the solid content concentration. When the mother liquor reached about 100 ml, the pump was stopped and the concentration was terminated to obtain a bismuth metal nanoparticle dispersion having a solid content of 24.1%. In observation using a transmission electron microscope, the average particle diameter of the bismuth metal nanoparticles present in the dispersion was 20 nm. Moreover, the composition of each component of the obtained bismuth metal nanoparticle dispersion was 20.0% bismuth content, 4.1% EFKA-4550, and 75.9% deionized water. In addition, the said composition was calculated and calculated | required from the measurement result obtained with the differential thermal balance "TG-DTA" (made by Seiko Instruments Inc.).

Production Example 2 Production of Cationic Electrodeposition Coating Composition Into a flask equipped with a stirrer, a cooling tube, a nitrogen introduction tube, a thermometer and a dropping funnel, 940 parts of liquid epoxy, methyl isobutyl ketone (hereinafter abbreviated as MIBK) 61.4 Part and 24.4 parts of methanol were charged. The reaction mixture was heated from room temperature to 40 ° C. with stirring, and then 0.01 part of dibutyltin laurate and 21.75 parts of tolylene diisocyanate (hereinafter abbreviated as TDI) were added. The reaction was continued for 30 minutes at 40-45 ° C. The reaction was continued until the absorption based on the isocyanate group disappeared in the measurement of IR spectrum. To the reaction product, 82.0 parts of polyoxyethylene bisphenol A ether and 125.0 parts of diphenylmethane-4,4′-diisocyanate were added. The reaction was performed at 55 ° C. to 60 ° C. and continued until absorption based on the isocyanate group disappeared in the measurement of IR spectrum. Subsequently, the temperature was raised, and 2.0 parts of N, N-dimethylbenzylamine was added at 100 ° C. and maintained at 130 ° C. When methanol was fractionated using a fractionating tube and reacted, the epoxy equivalent was 284. became. Thereafter, the reaction mixture was diluted with MIBK until the nonvolatile content was 95%, cooled, and 268.1 parts of bisphenol A and 93.6 parts of 2-ethylhexanoic acid were added. The reaction was performed at 120 ° C. to 125 ° C., and when the epoxy equivalent reached 1320, the reaction mixture was diluted with MIBK until the nonvolatile content was 85%, and the reaction mixture was cooled. 93.6 parts of MIBK-blocked primary amine of diethylenetriamine and 65.2 parts of N-methylethanolamine were added and reacted at 120 ° C. for 1 hour. Thereafter, an oxazolidone ring-containing modified epoxy resin having a cationic group (resin solid content: 85%) was obtained.

After charging 1330 parts of crude MDI and 585.6 parts of MIBK into a reaction vessel and heating it to 85 to 95 ° C., 486 parts of diethylene glycol monobutyl ether (molecular weight 162) was added dropwise over 2.5 hours. After completion of dropping, the mixture was kept warm for 1 hour. Thereafter, 194.8 parts of MIBK was added and cooled to 50 ° C., and 532 parts of propylene glycol (molecular weight 76) was added dropwise. After completion of dropping, the mixture was heated to 60 ° C. and kept for 1 hour. After adding 0.4 parts of dibutyltin laurate, the temperature was raised and the temperature was kept at 70 ° C. for 1 hour, and in the IR spectrum measurement, it was confirmed that absorption based on the isocyanate group disappeared, and the glass transition temperature was 8 ° C. The block polyisocyanate curing agent was obtained.

The obtained oxazolidone ring-containing modified epoxy resin having a cationic group and a block polyisocyanate curing agent were mixed so as to be uniform at a solid content ratio of 70/30. Further, the mixture was neutralized with glacial acetic acid so that the milligram equivalent of acid per 100 g of resin solid content was 27% with 2-ethylhexyl glycol added to 3% of the resin solid content, and further ion-exchanged water was slowly added for dilution. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained. 1730 parts of this emulsion, 1970 parts of ion exchange water and 10 parts of dibutyltin oxide were mixed to obtain a cationic electrodeposition coating composition having a solid content of 20% by mass. The amount of solvent in the paint of this cationic electrodeposition coating composition was 0.5%, and the milligram equivalent of acid per 100 g of resin solids was 25.1. The 20 μm coating voltage at a bath temperature of 30 ° C. was 220 V, and the coating film resistance value calculated from the residual current at the end of electrodeposition was 1100 KΩ · cm ² .

Production Example 3 Production of Bismuth Metal Nanoparticle-Containing Cationic Electrodeposition Coating Composition The bismuth metal nanoparticle dispersion obtained in Production Example 1 is applied to the resin solid content of the cationic electrodeposition coating composition obtained in Production Example 2. The bismuth metal nanoparticle-containing cationic electrodeposition coating composition was obtained by gradually adding 1.0% by mass in terms of bismuth metal.

Example 1
Bismuth metal nanoparticle dispersion of Production Example 1 diluted with deionized water to a concentration of 0.5% by mass on an untreated cold-rolled steel sheet not subjected to zinc phosphate treatment having a length of 7 cm, a width of 7 cm, and a thickness of 0.8 mm After being spin-coated, it was immersed in a bath of the cationic electrodeposition coating composition composition of Production Example 2 as a cathode, electrodeposited, and thoroughly washed with deionized water. This coated plate was baked at 160 ° C. for 10 minutes to obtain a cured coating film having a dry film thickness of 20 μm. The amount of bismuth applied by spin coating was 150 mg / m ² in terms of bismuth metal.

Example 2
Spin the bismuth metal nanoparticle dispersion of Production Example 1 diluted with deionized water to a concentration of 5% by mass on an untreated cold-rolled steel sheet that is 7 cm long, 7 cm wide, and 0.8 mm thick and not treated with zinc phosphate. After coating, it was immersed in a bath of the cationic electrodeposition coating composition composition of Production Example 2 as a cathode, electrodeposited, and thoroughly washed with deionized water. This coated plate was baked at 160 ° C. for 10 minutes to obtain a cured coating film having a dry film thickness of 20 μm. The amount of bismuth applied by spin coating was 850 mg / m ² in terms of bismuth metal.

Example 3
Spin the bismuth metal nanoparticle dispersion of Production Example 1 diluted with deionized water to a concentration of 20% by mass on an untreated cold-rolled steel sheet that is 7 cm long, 7 cm wide, and 0.8 mm thick and not treated with zinc phosphate. After coating, it was immersed in a bath of the cationic electrodeposition coating composition composition of Production Example 2 as a cathode, electrodeposited, and thoroughly washed with deionized water. This coated plate was baked at 160 ° C. for 10 minutes to obtain a cured coating film having a dry film thickness of 20 μm. The amount of bismuth applied by spin coating was 1500 mg / m ² in terms of bismuth metal.

Comparative Example 1
An untreated cold-rolled steel sheet having a length of 7 cm, a width of 7 cm, and a thickness of 0.8 mm, which has not been subjected to zinc phosphate treatment, is immersed in a bath of the cationic electrodeposition coating composition of Production Example 2 and electrodeposition-coated. Wash thoroughly with ionic water. This coated plate was baked at 160 ° C. for 10 minutes to obtain a cured coating film having a dry film thickness of 20 μm.

Comparative Example 2
Bismuth metal nanoparticle dispersion of Production Example 1 diluted with deionized water to a concentration of 0.05% by mass on an untreated cold-rolled steel sheet not subjected to zinc phosphate treatment having a length of 7 cm, a width of 7 cm, and a thickness of 0.8 mm After being spin-coated, it was immersed in a bath of the cationic electrodeposition coating composition of Production Example 2 as a cathode, electrodeposited, and thoroughly washed with deionized water. This coated plate was baked at 160 ° C. for 10 minutes to obtain a cured coating film having a dry film thickness of 20 μm. The amount of bismuth applied by spin coating was 20 mg / m ² in terms of bismuth metal.

Comparative Example 3
An untreated cold-rolled steel sheet having a length of 7 cm, a width of 7 cm, and a thickness of 0.8 mm, which has not been subjected to zinc phosphate treatment, was immersed in a bismuth metal nanoparticle-containing cationic electrodeposition coating composition bath of Production Example 3 It was applied and washed thoroughly with deionized water. This coated plate was baked at 160 ° C. for 10 minutes to obtain a cured coating film having a dry film thickness of 20 μm.

Comparative Example 4
Cold-rolled steel sheets 7 cm long, 7 cm wide and 0.8 mm thick pretreated with a surface conditioner (“Surffine 5N-10” manufactured by Nippon Paint Co., Ltd.) were obtained. Immerse in a chemical conversion treatment agent containing zinc phosphate dissolved in ion-exchanged water and adjusted to 600 mg / L, SiF ₆ 1000 mg / L, NO ₃ 6000 mg / L, PO ₄ 15000 mg / L at 40 ° C. for 2 minutes. Wash thoroughly with deionized water. Next, the material taken out and dried was used as a cathode, immersed in a bath of the cationic electrodeposition coating composition composition of Production Example 2, electrodepositioned, and thoroughly washed with deionized water. This coated plate was baked at 160 ° C. for 10 minutes to obtain a cured coating film having a dry film thickness of 20 μm.

The coated steel plates obtained in Examples and Comparative Examples were evaluated by the following methods. The results are shown in Table 1.
[Corrosion resistance evaluation 1 Salt water immersion test]
The obtained test piece having a cured coating film having a predetermined film thickness was immersed in a 5% sodium chloride aqueous solution at 55 ° C. for 240 hours, then the test piece was washed with water and allowed to stand at room temperature for 2 hours, and then evaluated by the following method. Nichiban Co., Ltd. “Cellotape (registered trademark)” (cellophane adhesive tape, width 24 mm) was pressure-bonded to the surface of the coating film with a finger and peeled vigorously. The area peeled by the tape was measured. The criteria for evaluation are as follows.
○: 10% or less Δ: 10 to 33%
X: 33% or more

[Corrosion Resistance Evaluation 2 Salt Spray Test]
The test piece having a cured coating film having a predetermined film thickness was subjected to a salt spray resistance test according to JIS K 5400 9.1. The test piece after 840 hours passed was washed with water, allowed to stand at room temperature for 2 hours, and then evaluated by the following method. Nichiban Co., Ltd. “Cellotape (registered trademark)” (cellophane adhesive tape, width 24 mm) was pressure-bonded to the surface of the coating film with a finger and peeled vigorously. The width at which the coating film peeled from the cut part (maximum on one side) was measured with a tape. The criteria for evaluation are as follows.
A: 0 mm ≦ peeling width <3.0 mm
Δ: 3.0 mm ≦ peeling width <6.0 mm
X: Peel width ≧ 6.0 mm

From Table 1, the cured coating films obtained by Examples 1 to 3 have good corrosion resistance equivalent to that of Comparative Example 4 that does not appear in Comparative Examples 1 to 3 even if the zinc phosphate treatment as in Comparative Example 4 is not performed. It was confirmed to have

The composite film-coated metal substrate of the present invention can be suitably used for automobile bodies and the like. Moreover, the metal pretreatment method of the present invention can be suitably applied to steel plates used in automobile bodies and the like.

The conceptual diagram of the composite film coating metal base material of this invention. The conceptual diagram (estimated figure) of the anticorrosion mechanism in this invention.

Claims (15)

An iron substrate;
A surface-treated metal substrate comprising bismuth metal nanoparticles of 100 mg / m ² or more in terms of bismuth, which is fixed so as to be in contact with the surface of the iron substrate. The surface-treated metal substrate according to claim 1, wherein the average particle diameter of the bismuth metal nanoparticles is 1 to 50 nm. The surface-treated metal substrate according to claim 1 or 2, wherein the iron substrate is not subjected to chemical conversion treatment. The surface-treated metal substrate according to any one of claims 1 to 3, wherein the iron substrate is a steel plate. The surface-treated metal substrate according to any one of claims 1 to 4,
It has an organic resin film formed on the surface of the said surface treatment metal base material, The composite film coating metal base material characterized by the above-mentioned. A metal pretreatment method comprising a step of applying a dispersion of bismuth metal nanoparticles on a surface of a steel plate in an amount of 100 mg / m ² or more in terms of bismuth. The metal pretreatment method according to claim 6, wherein the steel sheet is not subjected to chemical conversion treatment. The metal pretreatment method according to claim 6 or 7, wherein the coating amount of the dispersion liquid of bismuth metal nanoparticles is 2000 mg / m ² or less in terms of bismuth. The metal pretreatment method according to any one of claims 6 to 8, wherein the average particle diameter of the bismuth metal nanoparticles in the dispersion is 1 to 50 nm. 10. The metal pretreatment method according to claim 6, wherein the bismuth metal nanoparticle dispersion contains bismuth metal nanoparticles having an average particle diameter of 1 to 50 nm, a high molecular weight pigment dispersant, and a solvent. A composite film formation comprising a step of forming an organic resin film on the surface of a pretreated steel sheet obtained by using the metal pretreatment method according to any one of claims 6 to 10. Method. 12. The method of forming a composite film according to claim 11, wherein the organic resin film is formed using a cationic electrodeposition coating composition containing an amine-added epoxy resin and a blocked polyisocyanate. The method for forming a composite film according to claim 12, wherein the amine-added epoxy resin is a cation-modified epoxy resin obtained by modifying an oxirane ring in a resin skeleton with an organic amine compound. A composite film-coated steel sheet comprising a composite film obtained by using the composite film forming method according to claim 11. The composite film-coated steel sheet according to claim 14, wherein the composite film includes bismuth metal nanoparticles and an organic resin film bonded to the surface of the steel sheet.

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