JP2015098625A - Sn-BASED PLATED STEEL SHEET, AND AQUEOUS PROCESSING SOLUTION - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Sn-based plated steel sheet that remarkably reduces a load against the environment, has excellent corrosion resistance and paint adhesion, and is subjected to hexavalent-chromium-free surface treatment to be used as a material for an automobile fuel tank, and to provide an aqueous processing solution.SOLUTION: An Sn-based plated steel sheet having an Sn ratio of 50% or more in plating is coated with a film composed of at least trivalent chromium, a sulfate ion, and silica, the film having a mass ratio of the Cr and the sulfate ion of SO/Cr=1/10-1000/1 and SiO/Cr=0.5/1-20/1. The amount of coating is 3-100 mg/mon a single face in terms of metallic chromium. An aqueous processing solution contains a water-soluble chromium compound, a sulfuric acid compound, water dispersible silica, and water, and no hexavalent chromium, and has a mass ratio of the Cr, the sulfate ion, and the water dispersible silica in the processing solution of SO/Cr=1/10-1000/1 and SiO/Cr=0.5/1-20/1, and a pH of 0.8-2.0.

Description

  The present invention relates to an Sn-based plated steel sheet and a water-based treatment liquid thereof, which have excellent corrosion resistance and paint adhesion, and are subjected to a surface treatment that does not contain hexavalent chromium as an automobile fuel tank material.

  Conventionally, Pb-Sn-based plated steel sheets with excellent corrosion resistance, workability, solderability (weldability), etc. have long been used as automotive fuel tank materials, but their use has become difficult due to recent strengthening of environmental regulations for Pb. ing. Various steel plates have been proposed as alternatives, but the application of Sn—Zn-plated steel plates is expanding because they are excellent in corrosion resistance, workability, and economy. However, recently, improvement of the inner surface corrosion resistance of the fuel tank has been demanded against the background of strengthening quality control. Corrosion on the inner surface of the fuel tank is corrosion in a weak acid aqueous solution caused by extraction of organic acids such as formic acid and acetic acid generated by oxidative degradation of gasoline, which is fuel, into condensed water generated by the temperature difference between day and night. . In order to prevent engine stop due to clogging of the fuel supply pipe due to the internal corrosion of the fuel tank, which is a market defect, it is necessary that the corrosion of the railway is not recognized in a mild corrosive environment (200 ppm acetic acid aqueous solution). It has become. Furthermore, powder coatings have recently been used to reduce environmental impact. Since the coating material has weaker coating film adhesion than conventional solvent-based and water-based coatings, it requires higher coating adhesion than ever before.

  In the prior art, a method for obtaining a treatment liquid having good liquid stability by a combination of trivalent chromium and an organic acid is disclosed in Patent Document 1 below. However,

  The inventions shown in the following Patent Documents 2, 3, 4, and 5 all relate to a technique for forming a protective film for protecting a metal on a metal surface different from the metal of interest in the present invention. is there. Although the techniques described in these documents are component systems (trivalent chromium, silica, sulfate ions) close to the present invention, as described later, the actions are different from the present invention.

International Publication No. 08/029953 JP 2003-171778 A Japanese Patent Laid-Open No. 2003-166075 JP 2000-282255 A JP 2000-017451 A

  However, even if the method described in Patent Document 1 is used to suppress the occurrence of red rust in the fuel tank inner surface corrosion resistance evaluation, it cannot always be said to be sufficient.

  Moreover, although the technique described in the said patent document 2,3,4,5 is a component system (trivalent chromium, a silica, a sulfate ion) close | similar to this invention, as it mentions later, this invention has an effect | action. Different.

  The present invention is intended to solve the above-mentioned problems of the prior art, a hexavalent Cr-free rust-prevented galvanized steel sheet excellent in corrosion resistance and paint adhesion on the inner surface of the fuel tank, and its hexavalent Cr-free water system. It aims at providing a processing liquid.

  As a result of intensive studies in order to solve the problems of the prior art, the present inventors have provided Sn-plated steel sheets coated with a treatment film whose composition is controlled by financing trivalent chromium, silica and sulfate ions. It was found that can be achieved. The cause of rusting in the fuel tank inner surface corrosive environment of the Sn-based plated steel sheet is because the exposed portion of the ground iron such as a plating scratch is electrochemically lower than Sn during plating, but is sacrificed and dissolved. Part of the sulfate ion elutes in the chromium and silica film to form a strong precipitate film on the exposed part of the iron core, thereby suppressing the dissolution of the iron alloy, and the sulfate ion is adsorbed on the tin surface to treat the solution. It has been found that the wettability to the plating surface is improved at the time of coating, and the insulation of the coating is enhanced along with the coating coverage.

In order to solve the above problems, the present invention has a coating containing at least trivalent chromium, sulfate ions, and silica provided on a Sn-based plated steel sheet having a Sn ratio of 50 mass% or more during plating, The mass ratio of Cr and sulfate ions in the film is SO ₄ / Cr = 1/10 to 1000/1, and the mass ratio of Cr and silica in the film is SiO ₂ /Cr=0.5/ Provided is a Sn-based plated steel sheet that is 1 to 20/1 and has a film adhesion amount of 3 to 100 mg / m ² in terms of metallic chromium per one side.

Then, the coating, as an additional component, containing phosphoric acid and / or phosphoric acid compound, the mass ratio of the PO ₄ of Cr and phosphoric acid and / or phosphoric acid compound in the coating, PO 4 _/ Cr = 1 / 1-3 / 1 is desirable.

  The film contains at least one metal selected from the group consisting of Ba, Sr, Co, Ni, and Zr as an additional component, and the mass ratio of the metal to Cr in the film is metal / The range of Cr = 0.01 / 1 to 0.5 / 1 is desirable.

  The Sn-plated steel sheet having a Sn ratio of 50% by mass or more in the plating is formed with a Sn—Zn plating layer composed of 1 to 8.8% by mass of Zn and Sn: 91.2 to 99.0% by mass. It is desirable that the steel plate be made.

Furthermore, in order to solve the said subject, this invention is a water-system processing liquid used for Sn type plating steel plate whose Sn ratio during plating is 50 mass% or more, and is a water-soluble chromium compound (A) and a sulfuric acid compound (B). And water-dispersible silica (C) and water, the mass ratio of Cr and sulfate ions in the aqueous treatment liquid is SO ₄ / Cr = 1/10 to 1000/1, and the treatment The mass ratio of Cr in the liquid to water-dispersible silica (C) is SiO ₂ /Cr=0.5/1 to 20/1, and the water-soluble chromium compound (A) does not contain hexavalent chromium. A water-based treatment liquid having a pH of 0.8 to 2.0 is provided.

The water-dispersible silica (C) is composed of at least two types of spherical silica and chain silica, and the SiO ₂ mass ratio is chain silica / spherical silica = 2/8 to 8/2. desirable.

Then, the aqueous treatment liquid, as an additional component, containing phosphoric acid and / or phosphoric acid compound (D), PO ₄ of the aqueous Cr and phosphoric acid in the treatment solution and / or phosphoric acid compound (D) The mass ratio is preferably in the range of PO ₄ / Cr = 1/1 to 3/1.

  The aqueous processing solution contains a metal nitrate (E) as an additional component, and the metal of the metal nitrate (E) is at least selected from the group consisting of Ba, Sr, Co, Ni, and Zr. It is one kind of metal, and it is desirable that the mass ratio of the metal and Cr in the aqueous treatment liquid is in the range of metal / Cr = 0.01 / 1 to 0.5 / 1.

  As described above, the water-based treatment liquid of the present invention does not substantially contain hexavalent chromium harmful to the human body and the environment, and is a molten Sn-Zn plated steel sheet produced by applying and drying the water-based treatment liquid of the present invention. Is excellent in both corrosion resistance and paint adhesion, and has a much greater effect on the environment and industrial use than for automotive fuel tank materials.

  The preferred embodiment of the present invention will be described in detail below with respect to the Sn-plated steel sheet to which the anticorrosive film of the present invention has been applied and its aqueous treatment liquid.

  The film which concerns on embodiment of this invention is related with Sn type plated steel plate whose Sn ratio during plating is 50 mass% or more. Sn is a metal that is electrochemically noble with respect to the base iron in a corrosive environment, and protection-type anticorrosion can be expected by covering the surface of the base iron.

  In the embodiment of the present invention, the corrosion cathode reaction is continuously suppressed by forming a film on Sn during plating. Therefore, if the Sn ratio is less than 50% by mass, the effect cannot be exhibited. Therefore, the Sn ratio during plating needs to be 50% by mass or more.

A film containing trivalent chromium, sulfate ions, and silica is formed on the plated layer of the Sn-based plated steel sheet according to the embodiment of the present invention. The mass ratio of Cr and sulfate ions in this film is SO ₄ / Cr = 1/10 to 1000/1. When the mass ratio is less than 1/10, the uniformity of the film becomes poor, and the corrosion resistance deteriorates because the amount of leaching as chromium sulfate is small. On the other hand, when the mass ratio is more than 1000/1, the amount of leaching as chromium sulfate from the film increases, so that the paint adhesion deteriorates. The mass ratio is preferably 1/1 to 500/1, and more preferably 5/1 to 100/1. The method for measuring trivalent chromium and sulfate ions is not particularly limited, but the film can be dissolved in an aqueous nitric acid solution, and ion chromatograph and trivalent chromium can be measured by the diphenylcarbazide method.

The composition of the silica component of the film according to the embodiment of the present invention is required to be SiO ₂ /Cr=0.5/1 to 20/1 in terms of mass ratio with respect to metal Cr in trivalent chromium. When the mass ratio is 0.5 or less, the effect is not exhibited, and thus the corrosion resistance and paint adhesion deteriorate, and when it exceeds 20/1, the elution amount of the mixed ions composed of trivalent chromium-silica-sulfate ions described later Decreases, corrosion resistance deteriorates. The method for measuring the SiO ₂ adhesion amount is not particularly limited, but the presence form of Si can be measured by a wide angle X-ray analysis method, and the existence amount can be measured by a fluorescent X-ray analysis method.

The coating amount according to the embodiment of the present invention needs to be ³ to 100 mg / m ² in terms of the mass of Cr per one side. Coating amount is more preferably 4~80mg / ^{m 2} by weight in terms of Cr, and further preferably from 5 to 40 mg / ^{m 2.} When the coating amount is less than 3 mg / m ² , the effect of improving the corrosion resistance is poor, and when the coating amount exceeds 100 mg / m ² , cracks or the like are likely to occur in the coating itself, resulting in a decrease in coating adhesion.

The coating according to the embodiment of the present invention preferably contains phosphoric acid and / or a phosphoric acid compound as an additional component. By including phosphoric acid and / or a phosphoric acid compound in the film according to the embodiment of the present invention, the corrosion resistance of the fuel tank inner surface is improved. Phosphoric acid and / or phosphate ions are preferably in a range of PO ₄ / Cr = 1/1 to 3/1 in terms of mass ratio with respect to metal Cr in trivalent chromium. Such a mass ratio is more preferably in a range of PO ₄ / Cr = 1/1 to 2/1. When the mass ratio is less than 1/1, there is no effect of improving the corrosion resistance. When the mass ratio is more than 3/1, the paint adhesion is lowered. The method for measuring the amount of phosphoric acid and / or phosphate ions attached is not particularly limited, but the presence form of P can be measured by wide-angle X-ray analysis, and the amount of P can be measured by fluorescent X-ray analysis. it can.

  The film according to the embodiment of the present invention contains at least one metal ion selected from the group consisting of Sr, Ba, Co, Ni, and Zr as a further additional component for the purpose of further improving the corrosion resistance. preferable. More preferably, the film according to the embodiment of the present invention contains Ni and / or Co in a metal-converted mass ratio of metal / Cr = 0.01 / 1 to 0.5 / 1, more preferably metal / Cr =. It is contained at 0.05 / 1 to 0.4 / 1. When the mass ratio is less than 0.01 / 1, there is no effect of improving the corrosion resistance, and when the mass ratio exceeds 0.5 / 1, the effect is saturated. Although the measurement method of the said metal ion is not specifically limited, A membrane | film | coat can be melt | dissolved in nitric acid aqueous solution and it can measure by ICP-MS (Inductively Coupled Plasma-Mass Spectrometry: ICP mass spectrometry) method.

  In addition, examples of the Sn-based plated steel sheet according to the embodiment of the present invention include Sn and Sn alloy plating such as an tin-plated steel sheet, an electric Sn—Zn plated steel sheet, and a molten Sn—Zn plated steel sheet. The Sn-based plated steel sheet according to the embodiment of the present invention is more preferably a steel sheet in which a Sn—Zn plated layer composed of 1 to 8.8 mass% Zn and Sn: 91.2 to 99.0 mass% is formed. is there. The purpose of adding Zn is to give sacrificial anticorrosive action to the plating layer. Tin-zinc alloy plating is mainly based on protection of a steel sheet by tin (standard potential: E0 = −0.14 V) coating, which is an electrochemically noble metal, and zinc (standard potential: E0 = −). 1. The sacrificial anticorrosive ability by 1.245V) was provided. If Zn is less than 1% by mass, the sacrificial anticorrosive action cannot be obtained. On the other hand, when the amount of Zn increases, white rusting of Zn increases. When Zn exceeds 8.8%, which is the eutectic point, white rust is prominent, so this point is defined as the upper limit. The impurity element may be a trace amount of Fe, Ni, Co, Pb, or the like. Moreover, the effect of improving corrosion resistance can also be obtained by adding Mg. Further, if necessary, Al, misch metal, Sb, etc. may be added.

  The manufacturing method of the Sn-based plated steel sheet is not particularly defined, but the hot dipping method is preferable from the viewpoint of easily obtaining thickening. As the hot dipping process, there are a Sendzimer method and a flux method, but a manufacturing method is not particularly limited.

  Further, in order to obtain a good appearance with Sn-based plating having a high Sn composition, it is preferable to perform Ni and Co-based pre-plating. This facilitates good plating without unplating. In particular, when Ni—Fe pre-plating is performed, a Sn dendrite structure is formed in which Zn concentration in the Sn—Zn plating spangle boundary is suppressed, and thus excellent corrosion resistance is obtained. At this time, a Ni, Co, Fe plating layer, an intermetallic compound layer containing Sn, Zn, Mg containing these, or a composite of both is formed at the interface between the Sn—Zn plating layer and the substrate. To do. The thickness of this layer is not particularly limited, but is usually 1 μm or less.

The adhesion amount of Sn-based plating affects characteristics and manufacturing costs. Of course, a larger amount of adhesion is preferable for corrosion resistance, and a smaller amount of adhesion is preferable for cost. The amount of adhesion to balance is about 10 to 100 g / m ² per side, and this range is preferable.

The plated steel sheet is excellent in corrosion resistance with respect to the zinc-based plated steel sheet due to the coating of tin excellent in corrosion resistance, but on the other hand, tin oxide formed on the Sn surface that occupies most of the plated surface at the time of production or natural standing ( Since SnO, SnO ₂ ) is brittle and has poor wettability, the adhesion between the plating and the paint may be insufficient depending on the type of paint. However, the sulfate ion in the treatment liquid according to the embodiment of the present invention creates a new plated metal surface by appropriately etching the surface tin oxide, and is directly bonded to the plated metal after coating and drying. Since a composite film made of plated metal is formed, a surface-treated Sn-based plated steel sheet having good corrosion resistance and excellent paint adhesion can be provided.

  The aqueous treatment liquid according to the embodiment of the present invention contains a water-soluble chromium compound (A), a sulfuric acid compound (B), water-dispersible silica (C), and water. It contains no valent chromium and has a pH of 0.8 to 2.0. Moreover, in the aqueous processing liquid which concerns on embodiment of this invention, mass ratio of Cr in a processing liquid and a sulfate ion is 1 / 10-1000 / 1. When the mass ratio is less than 1/10, the uniformity of the film becomes poor, and the corrosion resistance deteriorates because the amount of leaching as chromium sulfate is small. On the other hand, if the mass ratio is more than 1000/1, the amount of leaching out as chromium sulfate from the film increases, so that the paint adhesion deteriorates. The mass ratio is preferably 1/1 to 500/1, and more preferably 5/1 to 100/1.

  The sulfuric acid compound (B) of the aqueous treatment liquid used in the embodiment of the present invention is a water-soluble sulfuric acid compound, and is not particularly limited. For example, chromium sulfate, ammonium sulfate, potassium aluminum sulfate, sodium aluminum sulfate, Ammonium hydrogen sulfate, ammonium thiosulfate, barium sulfate, barium thiosulfate, calcium sulfate, tetraammonium cerium sulfate, cerium sulfate, cesium sulfate, cobalt sulfate, copper sulfate, dimethyl sulfate, guanidine sulfate, lithium sulfate, magnesium sulfate, manganese sulfate, Silver sulfate, nickel sulfate, potassium sulfate, sodium sulfate, tin sulfate, strontium sulfate, sulfuric acid and the like can be mentioned, and some of them may be selected and used.

  The component (A) of the aqueous treatment liquid used in the embodiment of the present invention is a water-soluble chromium compound and does not substantially contain hexavalent chromium. The phrase “substantially free of hexavalent chromium” as used herein means that hexavalent chromium is not detected by a colorimetric method using diphenylcarbazide, which is generally known as a quantitative method for hexavalent chromium. . The aqueous processing liquid which concerns on embodiment of this invention contains chromium compounds other than hexavalent chromium, and the liquid is colored by these. In order to reduce the influence of the coloring, the liquid was adjusted to 200 ppm with the total chromium concentration, and in the analysis result at this time, 0.1 ppm was regarded as the reliability limit, and less than 0.1 ppm did not contain hexavalent chromium. .

  The water-soluble chromium compound (A) may be any chromium compound that does not substantially contain hexavalent chromium as described above, and is not particularly limited. For example, chromium phosphate, chromium biphosphate, fluorine And trivalent chromium compounds such as chromium fluoride, chromium nitrate, and chromium sulfate. Moreover, starch, saccharides, alcohols, hydroxycarboxylic acids, or hydrogen peroxide, hydrazine, phosphorous acid, hypophosphorous acid, ferrous sulfate are added to an aqueous solution containing hexavalent chromium ions in which chromic anhydride is dissolved in water. A compound obtained by adding a compound having a reducing action as described above and reducing hexavalent chromium ions may be used.

  The component (C) of the aqueous treatment liquid according to the embodiment of the present invention is water-dispersible silica. Such water-dispersible silica can improve the corrosion resistance. Such water-dispersible silica is not particularly limited. For example, as spherical silica, SNOWTEX C, SNOWTEX CS, SNOWTEX CM, SNOWTEX O, SNOWTEX OS, SNOWTEX OM, SNOWTEX NS, SNOWTEX N, SNOWTEX NM, SNOWTEX S, SNOWTEX 20, SNOWTEX 30, SNOWTEX 40, etc., for example, as chain silica, SNOWTEX UP, SNOWTEX OUP, SNOWTEX PS-S, SNOWTEX PS- SO, Snowtex PS-M, Snowtex PS-MO, Snowtex PS-L, Snowtex PS-LO, and the like. Dispersed vapor phase silica is not preferred because it tends to cause precipitation in the treatment liquid.

The composition of the component (C) of the aqueous processing liquid according to the embodiment of the present invention is a mass ratio with respect to metal Cr in the water-soluble chromium compound of (A), and SiO ₂ /Cr=0.5/1 to ₂₀ / 1 is preferable. When the mass ratio is 0.5 or less, the contribution to the corrosion resistance and paint adhesion is small, and when the mass ratio exceeds 20/1, the effect is saturated.

Since the water-dispersible silica used in the aqueous treatment liquid according to the embodiment of the present invention has different effects on the film depending on the spherical and chain forms, one or more of chain silica and spherical silica are mixed and used. More preferably. Specifically, when a film is formed on the surface of a steel sheet using chain silica, the structural irregularities of the chain silica are reflected in the film, which is very effective in improving paint adhesion. However, a decrease in alkali resistance was observed during the study of the present invention. The decrease in alkali resistance means that when the steel sheet of the present invention was washed with an alkaline solution (alkali degreasing), chromium as a film component was easily eluted. This phenomenon was discovered during the examination process of the present invention. On the other hand, spherical silica forms a dense film with few surface irregularities and has good alkali resistance, but has a low anchoring effect and therefore has lower paint adhesion than chain silica. Therefore, in the embodiment of the present invention, it is more preferable to combine at least one of chain silica and spherical silica from the viewpoint of compatibility between paint adhesion and alkali resistance, and the chain silica / spherical silica ratio is SiO _2. In terms of a converted mass ratio, chain silica / spherical silica = 8/2 to 2/8 is preferable, and 6/4 to 4/6 is more preferable. When the chain silica / spherical silica mass ratio is 10/0 to 8/2, the alkali resistance tends to deteriorate, and when 2/8 to 0/10, the paint adhesion may not be sufficiently obtained.

  The pH of the aqueous treatment liquid according to the embodiment of the present invention is preferably in the range of 0.2 to 6.0, more preferably 0.8 to 2.0, and even more preferably 1.0 to 1.8. The acid added for adjusting the pH is not particularly limited, but a strong acid capable of adjusting the pH with a small amount of addition is preferable, and examples thereof include nitric acid, sulfuric acid, and phosphoric acid. Examples of the alkali that raises the pH include ammonium salts such as ammonia and ammonium carbonate, amine compounds such as ethylenediamine and triethylamine, and guanidyl compounds such as guanidine carbonate. The aqueous treatment liquid according to the embodiment of the present invention has an inferior processability because the etching action on the plating becomes intense when the pH is below 0.2, and hydrogen is generated on the plating surface, and the pH exceeds 6.0. In addition, the removal of the oxide film on the surface of the plated Sn is insufficient and the liquid stability is lowered.

The aqueous treatment liquid according to the embodiment of the present invention preferably contains phosphoric acid and / or a phosphoric acid compound as the additional component (D). Examples of these phosphoric acids and phosphoric acid compounds include orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, and ammonium salts, amine salts, and chromium biphosphate. Corrosion resistance is improved by including phosphoric acid and / or a phosphoric acid compound in the aqueous treatment liquid according to the embodiment of the present invention. The phosphoric acid and / or phosphoric acid compound (D) is preferably in the range of PO ₄ / Cr = 1/1 to 3/1 in terms of mass ratio relative to metal Cr in the water-soluble chromium compound (B). Such a mass ratio is more preferably in a range of PO ₄ / Cr = 1/1 to 2/1. When the mass ratio is less than 1/1, there is no effect of improving the corrosion resistance, and when the mass ratio exceeds 3/1, the paint adhesion is reduced.

  In order to further improve the corrosion resistance, the aqueous processing liquid according to the embodiment of the present invention preferably further contains a metal nitrate (E) as an additional component, and is composed of Sr, Ba, Co, Ni, Zr. It is preferable to contain a nitrate containing at least one metal selected from the group. More preferably, as the nitrate metal salt (E), Ni and / or Co nitrate is contained in a metal-converted mass ratio in the range of metal / Cr = 0.01 / 1 to 0.5 / 1, more preferably. It is contained in the range of metal / Cr = 0.05 / 1 to 0.4 / 1. When the mass ratio is less than 0.01 / 1, there is no effect of improving corrosion resistance, and when the mass ratio exceeds 0.5 / 1, the effect is saturated.

  In addition, phosphonic acid or a phosphonic acid compound can be added to the treatment liquid according to the embodiment of the present invention in order to further improve the adhesion between the plating surface and the film. The phosphonic acid compound is not particularly limited, but, for example, methyl diphosphonate, methylene phosphonate, ethylidene diphosphonate, etc., or ammonium salts, alkali metal salts thereof, etc. Or a chelating agent having at least one salt thereof, and as oxidants thereof, those phosphonic acid chelating agents having a nitrogen atom in the molecule thereof are oxidized to form an N-oxide form. Things.

  Moreover, a water-soluble resin can be mix | blended with the process liquid which concerns on embodiment of this invention as an additional component in order to improve corrosion resistance and coating property. Such a water-soluble resin is not particularly limited, but it is desirable to use a water-soluble acrylic resin or copolymer generally used for this purpose within a range not affecting the liquid stability.

  About the processing method using the aqueous processing liquid which concerns on embodiment of this invention, after apply | coating the aqueous processing liquid which concerns on embodiment of this invention to the surface of plating steel materials, it should just heat-dry, an application method, a drying method, etc. There are no particular restrictions on. Usually, roll coating method in which the treatment liquid is roll-transferred onto the material surface, or the material surface is wetted by showering or dipping, and then the excess treatment liquid is removed with a roll squeeze or air knife to adjust the coating amount. A method is mentioned. At this time, the temperature of the aqueous treatment liquid is not particularly limited, but the treatment temperature is preferably 5 to 60 ° C.

  The drying temperature after applying the aqueous treatment liquid according to the embodiment of the present invention is desirably 50 to 200 ° C. as the maximum plate temperature. The heating method is not particularly limited, and any method such as hot air, direct fire, induction heating, infrared, near infrared, and electric furnace may be used.

  Although it does not specifically limit about the steel component of the base material used for Sn system plating steel materials concerning the present invention, As steel grade, for example, IF steel which added Ti, Nb, B, etc., Al-k steel, Cr addition steel, Stainless steel, high-tensile (high-tensile steel), electromagnetic steel plate and the like can be mentioned. In particular, for steel tanks and other applications that require deep drawability and secondary work cracking resistance, it is desirable to apply IF steel or B additive.

(Function)
Next, the effect | action is demonstrated about the film | membrane component of this invention.
A particularly important aspect in the present invention is the addition of sulfate ions. The combination of a trivalent chromium compound and water-dispersible silica has been known so far. In addition, since sulfate ions are anions, they are attracted to the corrosion anode sites to maintain electrical neutrality with Fe ²⁺ ions, which are cations generated at the corrosion anode reaction sites in a corrosive environment. Since it is known as a compound that forms a pH environment and promotes corrosion, it has not been selected as a chemical conversion treatment agent. In the present invention, a combination of a trivalent chromium compound and silica is used to form a mixed ion composed of soluble trivalent chromium-silica-sulfate ions in the film, although the structure is not clear. It has been found that the mixed ions start to dissolve from the film in a corrosive environment as in the case of hexavalent chromium, and form a precipitate film at the corrosive anode site to suppress corrosion. Furthermore, it discovered that a sulfate ion adsorb | sucks to a tin surface first, the wettability on tin can be improved, and the uniform coating property of a film | membrane can be improved.

  Since the phosphoric acid or phosphate compound of the film according to the present invention forms a three-dimensional insoluble salt with trivalent chromium, it is considered effective for improving the corrosion resistance.

  Ba, Sr, Co, Ni, and Zr of the film according to the present invention are effective in improving corrosion resistance when combined with silica. In particular, on the plating surface containing Zn, since the production of basic zinc chloride or basic zinc carbonate that suppresses corrosion is promoted, zinc wear due to corrosion can be reduced.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In addition, these Examples are described for description of this invention, and do not limit this invention at all.

<Creation of test plate>
(1) Specimen ○ Preparation of Molten Sn-Zn Plated Steel Sheet Steels having the components shown in Table 1 below were melted by ordinary converter-vacuum degassing treatment to form a steel slab, and then heated under normal conditions. Cold rolling, cold rolling, and a continuous annealing process were performed to obtain an annealed steel sheet (plate thickness 0.8 mm). After applying 0.2 g / m ² of Fe—Ni plating to a part of this steel plate, Sn—Zn plating was performed by a flux method. The Fe—Ni alloy plating bath used was a solution obtained by adding 30 to 200 g / L of iron sulfate to the Ni plating watt bath. The flux was used by applying a ZnCl ₂ aqueous solution in a roll, and the Zn composition in the plating bath was changed from 0 to 20% by mass. The bath temperature was 280 ° C., and the amount of plating was adjusted by gas wiping after plating. The plated steel sheet thus manufactured was temper-rolled with rolls having various roughnesses to adjust the surface roughness. Several types of post-treatments were applied to this steel plate. The types and compositions of post treatment are shown in Table 2 below. In addition, all the post-processing films were the same on both sides.

(2) Degreasing treatment Each test material prepared above was degreased (concentration 20 g / L, temperature 60 ° C, 20 ° C) with a fine cleaner 4336 (registered trademark: manufactured by Nihon Parkerizing Co., Ltd.), a silicate alkaline degreasing agent. Sprayed for 2 seconds) and then washed with tap water.

(3) Preparation of surface treatment liquid Table 2 shows water-soluble chromium compounds, Table 3 shows sulfuric acid compounds, Table 4 shows water-dispersible silica, Table 5 shows phosphoric acid and its compounds, 6 shows a nitrate metal salt. It has been confirmed that the treatment liquids of Examples 1 to 31 and Comparative Examples 1 to 7 (excluding Comparative Examples 5 to 6) shown in Tables 7 and 8 are substantially free of hexavalent chromium. 30% reduced chromium is obtained by dissolving chromic anhydride in pure water and adding methanol to reduce 30% of hexavalent chromium. 100% reduced chromium is added to 30% reduced chromium so as to have the composition shown in Table 7 (water-dispersible silica is added later), and the pH is adjusted with nitric acid and aqueous ammonia. Hydrazine monohydrate (NH ₂ NH ₂ .H ₂ O) is added until hexavalent chromium is not detected.

  Each was mixed and dissolved so as to have the compositions shown in Tables 7 and 8, and the pH was adjusted using nitric acid and aqueous ammonia. Water-dispersible silica was added after adjusting the pH, and adjusted with pure water so that the Cr concentration was 1% by mass to obtain an aqueous treatment liquid. In Tables 7 and 8 below, the relative concentration of the sulfuric acid compound (B) when the metal Cr equivalent concentration of the water-soluble chromium compound (A) is 1 is shown as “relative concentration with respect to metal Cr”. .

(4) Application of surface treatment liquid Each of the surface treatment liquids prepared above was applied onto each of the test materials with a bar coater and dried at an ambient temperature of 240 ° C. The amount of adhesion is adjusted by appropriately adjusting the solid content concentration of the surface treatment liquid, and the amount of Cr deposited on one side (mg / m ² ) is measured by the average value in the Φ30 mm area by fluorescent X-ray analysis. Adopted.

<Performance evaluation items and evaluation methods>
(1) Coating adhesion A polyester powder coating was applied to the obtained test piece with an electrostatic powder coating apparatus, and dried by heating at 180 ° C. for 10 minutes to obtain a baked coating film having a thickness of 60 μm. Then, the obtained test piece with a coating film was immersed in boiling water for 60 minutes, taken out, and allowed to stand naturally for 24 hours. Thereafter, a grid pattern of 1 mm and 100 squares was applied using a cutter knife, and the number of remaining coating films was determined by a tape peeling test. The evaluation criteria for paint adhesion are shown below. The number of individuals in the test was 2. ○ and ◎ were accepted.

[Evaluation criteria]
◎: Remaining number 100 ○: Remaining number 98 to less than 100 △: Remaining number 50 to less than 98 ×: Remaining number less than 50

(2) Fuel tank inner surface corrosion resistance A cup with a brim was prepared by cylindrical deep drawing with a 50 mmφ punch using the obtained test piece. A total of 50 ml of 200 ppm acetic acid and 165 ppm NaCl was sealed in a cup with gasoline and a 10 mass% aqueous solution, and left in a constant temperature bath at 45 ° C. for 1000 hours.
After the test, the sample was visually observed to confirm the occurrence of red rust from the bottom of the cup.

[Evaluation criteria]
○: No rust ×: Rust is generated

  As apparent from Tables 7 and 9, the molten Sn-Zn plated steel sheet coated with the coating of the present invention had excellent paint adhesion and fuel tank inner surface corrosion resistance. On the other hand, as shown in Tables 8 and 10, the comparative example could not obtain them in a well-balanced manner.

  As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to this example. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

Claims (8)

Having a coating containing at least trivalent chromium, sulfate ions, and silica provided on a Sn-based plated steel sheet having a Sn ratio of 50 mass% or more during plating;
The mass ratio of Cr and sulfate ions in the film is SO ₄ / Cr = 1/10 to 1000/1,
The mass ratio of Cr and silica in the film is SiO ₂ /Cr=0.5/1 to 20/1,
The Sn-based plated steel sheet, wherein the film adhesion amount is 3 to 100 mg / m ² in terms of metal chromium per side. The film contains phosphoric acid and / or a phosphoric acid compound as an additional component,
The mass ratio of Cr in the film and PO _{4 in} phosphoric acid and / or phosphoric acid compound is in the range of PO ₄ / Cr = 1/1 to 3/1. The Sn-based plated steel sheet described. The film contains at least one metal selected from the group consisting of Ba, Sr, Co, Ni, and Zr as an additional component,
3. The Sn-based plating according to claim 1, wherein a mass ratio of the metal to Cr in the coating is in a range of metal / Cr = 0.01 / 1 to 0.5 / 1. steel sheet.   The Sn-plated steel sheet having a Sn ratio of 50% by mass or more in the plating was formed with a Sn—Zn plating layer composed of 1 to 8.8% by mass of Zn and Sn: 91.2 to 99.0% by mass. The Sn-based plated steel sheet according to any one of claims 1 to 3, which is a steel sheet. It is an aqueous treatment liquid used for Sn-based plated steel sheets having a Sn ratio of 50% by mass or more during plating.
Water-soluble chromium compound (A), sulfuric acid compound (B) and water-dispersible silica (C) and water,
The mass ratio of Cr and sulfate ions in the aqueous treatment liquid is SO ₄ / Cr = 1/10 to 1000/1, and the mass ratio of Cr and water-dispersible silica (C) in the treatment liquid Is SiO ₂ /Cr=0.5/1 to 20/1,
The water-soluble chromium compound (A) does not contain hexavalent chromium,
An aqueous treatment liquid, characterized in that the pH is 0.8 to 2.0. The water-dispersible silica (C) consists of at least two kinds of spherical silica and chain silica,
The aqueous processing liquid according to claim 5, wherein the SiO ₂ mass ratio is chain silica / spherical silica = 2/8 to 8/2. The aqueous treatment liquid contains phosphoric acid and / or a phosphoric acid compound (D) as an additional component,
The mass ratio of Cr in the aqueous treatment liquid and PO _{4 in} phosphoric acid and / or phosphoric acid compound (D) is in the range of PO ₄ / Cr = 1/1 to 3/1. The aqueous processing solution according to claim 5 or 6. The aqueous processing liquid contains a nitrate metal salt (E) as an additional component, and the metal of the nitrate metal salt (E) is at least one selected from the group consisting of Ba, Sr, Co, Ni, and Zr. The metal of
8. The mass ratio of the metal to Cr in the aqueous treatment liquid is in a range of metal / Cr = 0.01 / 1 to 0.5 / 1. The aqueous processing liquid according to item.