JP2008138254A - Surface-treated metal sheet, surface treatment agent for metal, and method for manufacturing surface-treated metal sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-treated metal sheet which does not contain chromium and has superior adhesiveness to a paint film, superior corrosion resistance, and further, superior weldability, and to provide a manufacturing method therefor. <P>SOLUTION: The surface-treated metal sheet comprises a metal layer (A) of which the metal excludes chromium, and a layer (B) formed of a hydroxide or an oxide of a metal (b) which excludes chromium and a metal (a), or a mixture of the hydroxide and the oxide, on the metal layer (A). The layer (B) also includes the metal (a) which is the same type as the metal layer (A). The surface treatment agent for the metal and the method for manufacturing the surface-treated metal sheet are disclosed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface-treated metal plate and a metal surface treatment agent that do not use hexavalent chromium. Moreover, it is related with the manufacturing method of the surface treatment metal plate which uses the said metal surface treating agent.

  Plated metal plates and metal plates used in various applications such as containers, automobiles, home appliances, and building materials are subjected to treatments such as painting and laminating for the purpose of developing various properties such as design properties, corrosion resistance, and insulation. Is done.

  The surface of these metal plates may be subjected to a precipitation treatment of chromium metal and chromium hydrated oxide or a chromate treatment as a base treatment. The former is so-called tin-free steel, which satisfies the required performance of cans such as coating adhesion, corrosion resistance, and post-coating corrosion resistance in a well-balanced manner, and is used in a wide range of beverage cans and the like. The latter has been used in a wide range of fields and applications because coating adhesion and corrosion resistance are improved by immersing or electrolyzing a metal plate in a dichromic acid solution to form a chromium oxide film.

  However, in recent years, interest in global environmental issues has increased, and it has become desirable not to use hexavalent chromium, with the aim of achieving performance equivalent to a film using hexavalent chromium in a film that does not use hexavalent chromium. Various treatments have been developed, but sufficient characteristics have not been obtained. Here, the use of hexavalent chromium means that hexavalent chromium is used in the production process and that the film contains hexavalent chromium.

  For example, in Patent Document 1, as a chromium-free technique that can replace tin-free steel, tannic acid, which uses a cold-rolled steel sheet as a base material, reacts with an iron base to form a passive film, and contributes to improved paint adhesion. A technique for improving a coating adhesion and corrosion resistance by immersing or spraying a base material in a chemical conversion treatment solution containing a ring agent to form a composite film is disclosed. However, the composite coating formed on the cold-rolled steel sheet cannot be said to have sufficient performance as compared with the coating formed using conventional hexavalent chromium.

  Patent Document 2 discloses an anticorrosive treatment agent containing a crosslinkable resin and a hydrophilic resin that are reactive with zirconium in at least one of zirconium oxide, oxyacid salt, organic acid salt, and fluoro complex salt for aluminum. It is disclosed. In the case of this treatment agent, a crosslinkable resin is an essential component to make up for the lack of water resistance of the hydrophilic resin, thereby forming a very strong resin film by imparting a film-forming property, while an inorganic component Therefore, the corrosion resistance is not sufficient.

  In contrast to these technologies, metal oxides and metals not containing chromium, which are formed by immersing or electrolyzing a metal material in a solution containing complex ions of metal ions and fluorine ions, disclosed in Patent Document 3. Inorganic coatings such as hydroxides are excellent in corrosion resistance and excellent in adhesion to the resin applied to the upper layer.

JP 2002-275641 A JP 2000-282267 A WO2003 / 048416

  As described above, a metal plate coated with a metal oxide or metal hydroxide inorganic coating formed from a complex ion of metal ions and fluorine ions is excellent in corrosion resistance and adhesion to a resin. Metal oxides and metal hydroxides have high electrical insulating properties, so that the weldability of metal plates coated with inorganic coatings of metal oxides and metal hydroxides is low.

  Conventional metal plates such as tin-free steel, which have chromium hydrated oxide as the upper layer, are generally poor in weldability due to their large electrical resistance, and mechanically and chemically hydrated chromium oxides when welding. It was necessary to remove the layer. In order to improve the weldability, it is conceivable to make the inorganic coating thin, but sufficient corrosion resistance cannot be obtained. Of course, when the inorganic coating is thickened, the corrosion resistance is excellent, but the weldability is lowered.

  That is, a metal plate coated with a metal oxide or metal hydroxide inorganic coating formed from a complex ion of fluorine ions and metal ions not using hexavalent chromium has a corrosion resistance and a resin layer formed on the upper layer. An inorganic coating with excellent adhesion but also excellent weldability has not been developed, and an immediate solution has been desired.

  The present invention has been made in view of such a situation, and is an inorganic coating that does not use hexavalent chromium, has excellent coating adhesion and corrosion resistance, and has a surface treatment having a coating with excellent weldability. It aims at providing a metal plate and a metal surface treating agent, and also aims at providing the manufacturing method of the said surface treatment metal plate.

  As a result of intensive studies on means for solving the above problems, the present inventors have found that a metal layer A of metal a excluding chromium and a hydroxide, oxide of metal b excluding chromium and metal a on the upper layer thereof, or the water It has a layer B made of a mixture of an oxide and the oxide, and the layer B contains the same kind of metal a as the metal layer A, which has high paint adhesion and high corrosion resistance, and further has excellent weldability. As a result, the present invention has been found.

The gist of the present invention is as follows.
(1) From the metal layer A of the metal a excluding chromium on the metal surface, and further from the hydroxide or oxide of the metal b excluding chromium and the metal a on the upper layer, or a mixture of the hydroxide and the oxide. A metal plate comprising: a layer B comprising: a metal B of the same kind as that of the metal layer A.
(2) The metal plate according to (1), wherein the average thickness of the metal layer A is 1 nm or more and 1 μm or less.
(3) The metal plate according to (1) or (2), wherein the metal a of the metal layer A is one or more selected from cobalt, nickel, copper, and tin.
(4) The metal plate according to any one of (1) to (3), wherein the average thickness of the layer B is 1 nm or more and 1 μm or less.
(5) In any one of (1) to (4), the metal a contained in the layer B is contained in an amount of 0.1 at% or more and less than 50 at% relative to the total metal elements in the layer B. Metal plate of description.
(6) The metal plate according to any one of (1) to (5), wherein the metal b of the layer B is at least one selected from silicon, titanium, and zirconium.

(7) a metal b excluding chromium and a complex ion containing fluorine at a molar ratio of at least 6 times the metal b, and a metal ion of metal a excluding chromium and different from the metal b, A metal surface treatment agent comprising a metal ion having a molar ratio of 2 to 10 times the metal b.
(8) The metal surface treating agent according to (7), wherein the pH is 2 or more and 4 or less.
(9) The metal surface treatment agent according to (7) or (8), wherein the fluorine-containing complex ion metal b is at least one selected from silicon, titanium, and zirconium.
(10) The metal surface treatment agent according to any one of (7) to (9), wherein the metal a of the metal ion is one or more selected from cobalt, nickel, copper, and tin.

(11) A method for producing a surface-treated metal sheet, comprising forming a film by cathodic electrolysis of a metal substrate in the metal surface treatment agent according to any one of (7) to (10).

  ADVANTAGE OF THE INVENTION According to this invention, the surface treatment metal plate which is a film with a low environmental load which does not use hexavalent chromium, is excellent in coating adhesiveness and corrosion resistance, and also has the film excellent in weldability can be provided. In addition, according to the metal surface treatment agent of the present invention and the method for producing the surface-treated metal plate using the treatment agent, a two-layer coating film of a metal layer A and a layer B of metal oxide or metal hydroxide is provided. A layer B containing the same kind of metal a as that of the metal layer A can be formed.

  The present invention is described in detail below.

  As a result of intensive studies, the present inventors have found that a surface-treated metal plate having a metal layer A on the surface of the metal plate and a layer B containing the same kind of metal a as the metal layer A reduces paint adhesion and corrosion resistance. The present inventors have found that excellent weldability can be obtained without causing them to occur. This mechanism is estimated as follows.

  When the same kind of metal a as that of the lower metal layer A is contained in the layer B made of hydroxide, oxide, or a mixture of hydroxide and oxide, the following remarkable effects are produced. By containing conductive metal in the insulating inorganic layer B in a dispersed manner, the electrical resistance of the layer B is lowered and weldability is improved as compared with the case where no metal is present in the layer B. .

  As long as the electric resistance of the layer B is simply lowered, any metal can be dispersed. However, when a metal different from the metal layer A is dispersed in the upper layer B, a local cell is formed and the corrosion resistance is lowered. That is, when the metal contained in the layer B is the same type of metal a as that of the metal layer A, the formation of local cells can be prevented and high corrosion resistance is exhibited. Furthermore, in addition to the corrosion resistance by prevention of local cell formation, the presence of the metal layer A on the metal surface shows excellent corrosion resistance.

  In addition, the layer B made of hydroxide, oxide, or a mixture of hydroxide and oxide on the upper layer is formed by chemical bonds, hydrogen bonds, or the like with the organic resin layer formed thereon, if necessary. Because it can form a strong bond, it exhibits excellent paint adhesion. Furthermore, since the layer B is an oxide or hydroxide inorganic film having a high barrier property, it also contributes to an improvement in corrosion resistance. Although depending on the layer thickness, the reason that the corrosion resistance, weldability, and adhesion are expressed in a balanced manner is that the metal a is finely dispersed in the inorganic layer B with a size of 1/10 or less of the average thickness of the inorganic layer B. Is the case.

  The average thickness of the metal layer A is preferably 1 nm or more and 1 μm or less. If it is 1 nm or less, the coverage may be less than 100% and the corrosion resistance may be insufficient. On the other hand, if it exceeds 1 μm, the corrosion resistance is saturated and it is not economical. Here, the average thickness means an average value of film thicknesses measured in arbitrary 10 fields of view in cross-sectional SEM observation or cross-sectional TEM observation of about 1000 to 200,000 times.

  The metal a constituting the metal layer A is preferably a metal that can be electrodeposited from an aqueous system, more preferably cobalt, nickel, copper, zinc, and tin that are easily electrodeposited, more preferably cobalt having a high standard electrode potential, Nickel, copper and tin. The metal layer A may contain compounds such as oxides and fluorides.

  The average thickness of the layer B made of hydroxide, oxide, or a mixture of hydroxide and oxide is preferably 1 nm or more and 1 μm or less. If it is 1 nm or less, the coverage may be less than 100%, and the paint adhesion may be insufficient. On the other hand, if it exceeds 1 μm, the coating adhesion is saturated, which is not economical and may decrease. The paint adhesion means the adhesion with an organic resin layer formed by painting or laminating.

  The metal a contained in the layer B is preferably 0.1 at% to 50 at% with respect to the total metal elements in the layer B. If it is less than 0.1 at%, weldability may be insufficient, and if it exceeds 50 at%, paint adhesion may be reduced.

  The metal species of the hydroxide and oxide constituting the layer B are not particularly limited, and examples thereof include iron, magnesium, niobium, tantalum, aluminum, nickel, cobalt, titanium, zirconium, silicon and the like. Moreover, you may be comprised with 1 type of metal and 2 or more types of composite type | system | groups, mixed systems, and lamination | stacking may be sufficient. Suitable metals are silicon, titanium and zirconium. These have excellent corrosion resistance and are presumed to be due to high barrier properties, but the detailed mechanism is unknown.

Next, the metal surface treating agent of the present invention for forming the layers A and B on the surface of the metal plate will be described.
A complex ion containing fluorine at a molar ratio of at least 6 times with respect to the metal b and the metal b forms an equilibrium reaction with the metal oxide, and forms a layer B due to the deviation of the equilibrium. If the fluorine is less than 6 times, the pH buffering action of complex ions forming the layer B described later does not work effectively, and the layer A may not be formed properly by reduction of the metal a ions. Furthermore, metal oxide and metal hydroxide may not be appropriately deposited on the upper layer. If the fluorine is 6 times or more, a suitable metal oxide or metal hydroxide film can be formed due to the pH buffering action for film formation, the effect on the fluorine ion concentration in the liquid that activates the substrate surface, etc. At the same time, the layer A is formed by reduction of the ions of the coexisting metal a.

  As the complex ion, for example, hexafluorotitanic acid, hexafluoroniobic acid, hexafluorotantalic acid, hexafluorozirconic acid, etc., or salts thereof such as ammonium salt, potassium salt, sodium salt, etc. can be used. There are no particular restrictions on these. Furthermore, elements other than metal and fluorine may be contained in the complex ions. The concentration range may be set as appropriate.

  Further, the metal ion a of the metal a forming the metal layer A is preferably 2 times or more and 10 times or less in molar ratio as compared with the metal b. If it is less than 2 times, the layer B may not contain the metal a. When it is larger than 10 times, the formation of the layer B may be inhibited.

  The pH of the metal surface treatment agent is preferably 2 or more and 4 or less. When the treatment solution pH is less than 2, hydrogen generation reaction occurs actively, and the film formation amount may not be stable. On the other hand, when it is larger than 4, it becomes difficult for the metal ions a and complex ions to coexist, and the solution may be unstable and aggregated. The pH adjustment may be performed by a known method such as using ammonia water or hydrofluoric acid, and there is no particular limitation.

When the metal plate is immersed in the above-described metal surface treatment agent for electrolysis, the electrolysis conditions are not particularly limited, and various conditions such as reaction temperature and reaction time may be set as appropriate. For example, the current density at the time of ^{electrolysis, 0.1A / dm 2 ~50A / dm} 2 is preferred. The reaction temperature during electrolysis is preferably from room temperature to 80 ° C. The reaction time for electrolysis may be set according to the target film formation amount, but is preferably 1 second to 60 minutes in consideration of productivity. Moreover, although there is no restriction | limiting in particular about the pretreatment of a metal plate, etc., the surface from which the degreased surface and the scale were removed is preferable.

  The film formation mechanism of layer A and layer B is estimated but is as follows. First, the pH buffer action of the complex ions forming the layer B works effectively, and the layer A is formed by reduction of the metal a ions. Thereafter, while reduction of ions of metal a occurs, layer B is formed from complex ions, and metal a is taken into layer B. As a result, a metal layer A of the metal a is formed on the metal surface, and a hydroxide or oxide layer B of the metal b is formed thereon, and the layer B contains the same metal a as the metal layer A. A covered film structure is formed. Therefore, in the metal surface treatment agent and the production method using the treatment agent of the present invention, a metal film and a metal oxide or metal hydroxide film can be produced on the metal surface in one step.

  The metal plate applicable to the present invention is, for example, a cold-rolled steel plate, a stainless steel plate, an aluminum or aluminum alloy plate, a galvanized steel plate or the like, for example, various metals / alloys, various metal surface treatment materials, etc., and is not particularly limited.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Tables 1 and 2 show the conditions. As the metal plate, a cold-rolled steel plate subjected to ultrasonic degreasing treatment in acetone was used. The metal surface treatment agent uses a salt of nickel, copper, zinc, tin, tin-cobalt as the metal a contained in the metal layer A and the layer B, and titanium, zirconium, silicon, niobium as the metal b of the layer B. Using a hexafluoro complex salt aqueous solution and a tantalum heptafluoro complex salt aqueous solution, a treatment agent whose pH was adjusted with ammonium water or hydrofluoric acid as necessary was used. The metal plate was subjected to cathodic electrolysis for 1 to 100 seconds while controlling the current density at 0.1 to 10 A / dm ² in the above treatment agent, washed with water and dried after film formation.

  Experiment No. No. 1 was formed by immersing the base material in a 0.1 mol / L ammonium hexafluorosilicate aqueous solution and performing electrolysis using a copper plate as a counter electrode.

  Experiment No. In Nos. 2 to 12, copper sulfate was added to a 0.1 mol / L ammonium hexafluorosilicate aqueous solution so as to be 0 to 1 mol / L, the substrate was immersed, and electrolysis was performed using a copper plate as a counter electrode to form a film.

  Experiment No. 13 to 24 were added nickel sulfate and nickel chloride to a 0.1 mol / L ammonium hexafluorozirconate aqueous solution so that the molar concentration of nickel was 0.11 to 1.1 mol / L, and adjusted to pH 2 to 4, The substrate was immersed and electrolysis was performed using a nickel plate as a counter electrode to form a film.

  Experiment No. Nos. 25 to 33 were prepared by adding nickel sulfate and nickel chloride to a 0.1 mol / L ammonium hexafluoroniobate aqueous solution so that the molar concentration of nickel was 0.11 mol / L, adjusting the pH to 2 to 4, and then immersing the substrate. Then, electrolysis was performed using a nickel plate as a counter electrode to form a film.

  Experiment No. For 34 to 42, nickel sulfate and nickel chloride were added to 0.01 mol / L ammonium heptafluorotantalate aqueous solution so that the molar concentration of nickel was 0.011 mol / L, and after adjusting to pH 2 to 4, the substrate was immersed Then, electrolysis was performed using a nickel plate as a counter electrode to form a film. The molar ratio of nickel sulfate to nickel chloride was 10: 1.

  Experiment No. 43, after adding zinc sulfate to 0.001 mol / L ammonium hexafluorozirconate aqueous solution to adjust the pH to 2, the substrate is immersed, and electrolysis is performed using the zinc plate as a counter electrode. A film was formed.

  Experiment No. After adding zinc sulfate to 0.01 mol / L ammonium hexafluorozirconate aqueous solution to adjust the pH to 2, the substrate was immersed, and electrolysis was performed using the zinc plate as a counter electrode. A film was formed.

  Experiment No. 45 was adjusted to pH 2 by adding zinc sulfate to a 0.1 mol / L ammonium hexafluorozirconate aqueous solution to adjust the pH to 2, and then the substrate was immersed, and electrolysis was performed using the zinc plate as a counter electrode. A film was formed.

  Experiment No. After adding zinc sulfate to 0.001 mol / L ammonium hexafluorozirconate aqueous solution to adjust its pH to 2, 46 was immersed in the base material and electrolyzed using the zinc plate as a counter electrode, A film was formed.

  Experiment No. 47 was added zinc sulfate to 0.01 mol / L ammonium hexafluorozirconate aqueous solution to adjust the pH to 2 and adjusted to pH 2, and then the substrate was immersed, and electrolysis was performed using the zinc plate as a counter electrode. A film was formed.

  Experiment No. 48 was adjusted to pH 2 by adding zinc sulfate to a 0.1 mol / L ammonium hexafluorozirconate aqueous solution to adjust the pH to 2, and then the substrate was immersed and electrolyzed using the zinc plate as a counter electrode, A film was formed.

  Experiment No. 49 was added to the 0.001 mol / L ammonium hexafluorozirconate aqueous solution to adjust the pH to 2 by adding zinc sulfate to 0.1 mol / L, and then the substrate was immersed and electrolyzed using the zinc plate as a counter electrode, A film was formed.

  Experiment No. 50, after adding zinc sulfate to 0.01 mol / L ammonium hexafluorozirconate aqueous solution to adjust the pH to 2 and adjusting the pH to 2, the substrate is immersed, and the zinc plate is used as a counter electrode for electrolysis. A film was formed.

  Experiment No. 51 was adjusted to pH 2 by adding zinc sulfate to a 0.1 mol / L ammonium hexafluorozirconate aqueous solution to adjust the pH to 2, and then the substrate was immersed, and electrolysis was performed using the zinc plate as a counter electrode. A film was formed.

  Experiment No. In 52 to 54, tin sulfate was added to a 0.1 mol / L ammonium hexafluorotitanate aqueous solution so as to have a concentration of 0.1 mol / L, the substrate was immersed, and electrolysis was performed using a tin plate as a counter electrode to form a film.

  Experiment No. 55-57 add 0.3 mol / L cobalt chloride and 0.3 mol / L tin fluoride to 0.1 mol / L ammonium hexafluorotitanate aqueous solution, immerse the base material and perform electrolysis using the tin plate as the counter electrode. The film was formed.

  The film thickness of these films was controlled by the film formation time. The cross-sectional TEM (high resolution transmission electron microscope) observation and EDS (energy dispersive X-ray analysis) measurement confirmed the laminated structure of the A and B layers and the metal a. Experiment No. About 55-57, it confirmed that A layer and the metal a consisted of two types, cobalt and tin. The contained elements in the film were quantified by X-ray photoelectron spectroscopy.

  In the cross-sectional TEM observation, the average size of the metal a contained in the B layer is determined according to Example No. 2 to 12 are sizes of 1/20 to 1/40 of the thickness of the B layer in the range of 5 to 50 nm. Nos. 13 to 33 are sizes of 1/10 to 1/30 of the thickness of the B layer in the range of 10 to 60 nm. In 34 to 42, the size was 1/10 to 1/20 of the thickness of the B layer in the range of 1 to 5 nm. In addition, Example No. 43 to 51, the average size of the metal a contained in the B layer is in the range of 0.5 to 50 nm. In 52 to 57, the average size of the metal a contained in the B layer was in the range of 5 to 50 nm.

As a comparative example, no. In No. 58, a coating type chromate treatment agent was applied and dried so that the chromium adhesion amount was 20 mg / m ² . Furthermore, as a comparative example, no. 59 and 60 are tin-free steel and cold-rolled steel, respectively.

The corrosion resistance test of the flat plate portion was evaluated under the following conditions. A 5 mass% NaCl aqueous solution was sprayed at 35 ° C., and the white rust occurrence rate after 72 hours was measured and evaluated in four stages.
A: Rust occurrence rate 0%
○: Rust occurrence rate less than 5% △: Rust occurrence rate 5% or more, less than 20% ×: Rust occurrence rate 20% or more

Weldability was evaluated in four stages by measuring the surface resistance 10 times using a Loresta surface resistance measuring machine on a 100 mm × 100 mm surface, and by the number of times of 1 mΩ or less.
◎: 10 times ○: 8-9 times △: 5-7 times ×: 0-4 times

  The organic resin layer was formed as follows. No. 1-13, 16, 19, 22-25, 28, 31, 34, 37, 40, 43-60 were coated with an acrylic emulsion and dried to form an acrylic resin layer. No. Nos. 14, 17, 20, 26, 29, 32, 35, 38, and 41 were coated with an epoxy resin emulsion and dried to form an epoxy resin layer. No. 15, 18, 21, 27, 30, 33, 36, 39, and 42 were formed by thermocompression bonding of a polyethylene terephthalate resin film. The organic resin layer was formed so that the thickness after formation was 15 μm.

  The adhesion with the resin layer was evaluated under the following conditions. After dipping in boiling water for 60 minutes, a grid pattern was applied according to the grid pattern test method described in JIS K5400, and an Eriksen process of 7 mm was further performed. Adhesive tape (cellophane (registered trademark) tape, manufactured by Nichiban Co., Ltd.) was applied to the processed part, and the tape was peeled off by pulling it in an oblique direction of 45 ° and peeling off within 100 grids. I counted the number of. The evaluation was made in four stages depending on the degree of peeling.

The score of adhesion with the resin layer is as follows.
◎: Peeling area rate less than 25% ○: Peeling area rate of 25% or more and less than 50% Δ: Peeling area rate of 50% or more and less than 75% ×: Peeling area rate of 75% or more

  Tables 1 and 2 show the results obtained. Experiment No. 1 does not contain metal a, the weldability is insufficient. When the metal a was present in the 2 to 57 layers B, good weldability was exhibited. In addition, the metal plate of the present invention was confirmed to have an excellent performance balance as compared with the non-treated, coated chromate and TFS. Further, since the metal plate of the present invention does not contain hexavalent chromium, it is clear that the environmental load is smaller than that of the chromate treatment.

Claims (11)

  A metal layer A of metal a excluding chromium on the surface of the metal plate, and a layer made of a hydroxide or oxide of metal b excluding chromium and metal a on the upper layer, or a mixture of the hydroxide and the oxide. A surface-treated metal plate comprising B, wherein the layer B contains the same metal a as the metal layer A.   2. The surface-treated metal plate according to claim 1, wherein the average thickness of the metal layer A is 1 nm or more and 1 μm or less.   The metal a of the said metal layer A is 1 or more types chosen from cobalt, nickel, copper, and tin, The surface treatment metal plate of Claim 1 or 2 characterized by the above-mentioned.   The average thickness of the said layer B is 1 nm or more and 1 micrometer or less, The surface treatment metal plate of any one of Claims 1-3 characterized by the above-mentioned.   5. The metal a contained in the layer B is 0.1 at% or more and less than 50 at% with respect to the total metal elements in the layer B. 5. Surface treatment metal plate.   The surface-treated metal plate according to any one of claims 1 to 5, wherein the metal b of the layer B is at least one selected from silicon, titanium, and zirconium.   A metal ion excluding chromium and a complex ion containing fluorine in a molar ratio of at least 6 times that of the metal b, and a metal ion of a metal a excluding chromium and different from the metal b, the metal b A metal surface treatment agent comprising a metal ion having a molar ratio of 2 to 10 times.   The metal surface treating agent according to claim 7, wherein the pH is 2 or more and 4 or less.   The metal surface treating agent according to claim 7 or 8, wherein the metal b of the complex ion containing fluorine is at least one selected from silicon, titanium, and zirconium.   The metal surface treatment agent according to any one of claims 7 to 9, wherein the metal a of the metal ion is at least one selected from cobalt, nickel, copper, and tin.   A method for producing a surface-treated metal plate, comprising cathodic electrolyzing a metal plate in the metal surface treatment agent according to any one of claims 7 to 10 to form a film on the surface of the metal plate.