JP2008189965A - Painted steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-treated steel sheet which remarkably inhibits red rust from initiating from the portion at which basis steel in a cut end face is exposed in an outdoor environment, by a chrome-free surface treatment technique. <P>SOLUTION: The painted steel sheet has a paint film formed thereon which contains particles of an alkaline earth metal compound, particles of a zinc compound, particles of a phosphate particle, and particles of an organic carboxylate as needed. The paint film contains each particle so that when the painted steel sheet sample is immersed in pure water of atmospheric temperature, the molar ratio of the eluted quantities per hour of components which elute from the paint film can satisfy the following expressions (1): 0.95≤([alkaline earth metal element]+Zn)/P, and (2): 0.1≤[alkaline earth metal element]/Zn≤10, and so that the quantity of eluted P can be in a range of 0.5 to 30 mmol in terms of a value per square meter of the paint film area. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a coated steel sheet having good corrosion resistance at a cut end face, and particularly to a coated steel sheet suitable for applications exposed to an outdoor environment in a state where a steel substrate is exposed on the cut end face.

  A surface-treated steel sheet used in various fields such as building materials, automobiles, and home appliances is cut into a size corresponding to the application and then formed into a predetermined shape. Although the initial rust prevention function is maintained in the flat part and the processed part, the steel base (underlying steel) is exposed at the cut end face, and red rust is likely to occur. Even when a plated steel plate such as a galvanized steel plate or an aluminum plated steel plate is used as a raw material, the steel substrate is exposed at the cut end surface without the plating layer, and becomes a starting point of red rust. The generated red rust becomes a red rust flow from the cut end face toward the center of the plate, and the appearance is remarkably deteriorated.

  In order to suppress the occurrence of such red rust on the cut end face, conventionally, a method of coating the cut end face using a spray or a brush or a method of applying a rust preventive oil to the cut end face has been adopted. However, the method of coating the surface including the cut end surface of the surface-treated steel sheet cut into a predetermined size is inferior in workability and productivity and increases in cost. Moreover, since it is difficult to apply | coat a coating material uniformly depending on the shape of a steel plate, it is easy to generate | occur | produce a coating film in a cut end surface, and red rust may generate | occur | produce from the part. There is a similar problem in the method of applying the rust preventive oil, and there is also a problem that the steel plate becomes sticky due to the application of the rust preventive oil and the handling is hindered.

  On the other hand, attempts have been made to improve the corrosion resistance at the cut end face by using a surface treatment film formed on the steel sheet surface. For example, Patent Document 1 discloses a method of providing an organic resin film containing a basic alkali metal salt on the surface of a steel plate after chromate treatment. Patent Document 2 discloses a technique in which strontium chromate having low water solubility and strontium chromate having further low water solubility are contained in a primer.

JP-A-8-13156 Japanese Patent Application Laid-Open No. 8-17684

  According to the surface treatment methods disclosed in Patent Documents 1 and 2, a substance dissolved from the surface treatment film in an outdoor use environment acts on the cut end face, and the occurrence of red rust on the end face is suppressed. However, these techniques require chromate treatment. Chromate treatment has become difficult to adopt as a recent surface treatment method that places importance on environmental protection.

  The present invention is a so-called chromium-free surface treatment technique that does not cause harmful substances such as hexavalent chromium, and the steel base of the cut end face is exposed in an outdoor environment by a technique that does not impair workability and productivity. It is intended to provide a surface-treated steel sheet in which the occurrence of red rust from a certain location is significantly suppressed.

  As a result of intensive studies, the inventors have made it possible to have a plurality of substances in the form of "particles" in the coating film as a source of substances for forming a film covering the cut end face in an outdoor use environment. It has been found that it is extremely effective in achieving the above object.

That is, in the present invention, it is a coated steel sheet in which a coating film containing alkaline earth metal compound particles, zinc compound particles, phosphate particles, and, if necessary, further organic carboxylate particles is formed, When immersed in pure water at room temperature, the elution amount molar ratio of the components eluted per hour from the coating film satisfies the following formulas (1) and (2), and P is eluted per hour. There is provided a coated steel sheet in which the above-mentioned particles are blended in the coating film so as to be in a range satisfying 0.5 to 30 mmol in terms of a converted value per 1 m ² of coating film area.
0.95 ≦ ([Alkaline earth metal element] + Zn) / P (1)
0.1 ≦ [Alkaline earth metal element] / Zn ≦ 10 (2)
For “normal temperature”, the standard temperature state in JIS Z8703 is set to 23 ° C., and a temperature of 23 ± 2 ° C. may be adopted. Ion exchange water may be used as pure water.

  Examples of the alkaline earth metal include one or more elements among Ca, Mg and Sr. As the alkaline earth metal compound, one or more substances selected from oxides, hydroxides and salts of alkaline earth metals can be employed. The phosphate is a salt of orthophosphoric acid, phosphorous acid, polyphosphoric acid or the like. When organic carboxylate particles are blended in the coating film, the metal constituting the organic carboxylate is one or more elements selected from alkaline earth metals and Zn.

  When two or more kinds of substances are employed as the alkaline earth metal compound, the individual particles made of the alkaline earth metal compound may be made of a single compound or a combination of two or more kinds of compounds. It may be made. The same applies to individual particles made of a zinc compound, individual particles made of a phosphate, and individual particles made of an organic carboxylate.

Among the alkaline earth metal compound particles, zinc compound particles, phosphate particles and organic carboxylate particles, the average particle diameter of all kinds of particles mixed in the coating film is D (μm), When the average film thickness is T (μm), it is desirable to satisfy the following formula (3).
0.15 ≦ T / D (3)
Here, the average particle diameter D of the particles was obtained by averaging the individual particle diameters obtained by measuring the longest part (major axis) of the particles in the particle image observed when the cross section of the coating film was observed with an SEM. Value can be adopted. What is necessary is just to employ | adopt the average value about a total of 20 or more particle | grains observed in a fixed area | region. The average film thickness T is the thickness of the dry coating film, and may be measured by observing the cross section of the coating film (in this case, the portion of particles protruding from the surface of the organic film is excluded from the measurement), but was used. Usually, it is obtained by calculation from the mass of the paint (excluding the added particles) and the coating area.

  A zinc-based plated steel plate or an aluminum-based plated steel plate may be used as the coating original plate. Here, the coating original plate is a substrate for forming a coating film, and a surface treatment layer or a base coating layer may be provided between the coating original plate and the coating film. “Zinc-based plating” is plating in which Zn occupies at least 50 mass% of the elements constituting the plating layer, and “aluminum-based plating” is plating in which Al occupies at least 50 mass% of the elements constituting the plating layer. It is. These plating can employ various plating methods such as hot dipping, electroplating, and vapor deposition plating.

  According to this invention, the surface treatment steel plate which can suppress generation | occurrence | production of the red rust flow from the location where the steel base of a cut end surface is exposed in the outdoor environment by the chromium-free surface treatment was implement | achieved. The means is a relatively simple method of incorporating particles made of a substance that exhibits an antirust effect on the cut end face into the coating film, and mass production is possible using existing coated steel sheet manufacturing equipment. The complicated rust prevention treatment for the cut end face can be omitted. Accordingly, the present invention contributes to the reduction of manufacturing costs and the promotion of environmental protection through the use of chromium-free, particularly in the use of surface-treated steel sheets exposed to the outdoor environment such as exterior building materials and automobile members.

  The surface-treated steel sheet of the present invention is a coated steel sheet in which alkaline earth metal compound particles, zinc compound particles, and phosphate particles are dispersed and blended in a coating film. There are many unclear parts about the mechanism that prevents the occurrence of red rust on the cut end face, but the following are considered at this time.

[Stage 1]: In an outdoor environment, zinc and phosphoric acid components contained in the paint film (organic resin film) are dissolved during rainfall and flow into the cut end surface, where zinc phosphate is exposed to the exposed part of the steel substrate. Form a film. Zinc phosphate has excellent adhesion to the steel substrate. However, since the formed zinc phosphate film has many voids, only zinc phosphate has a low barrier effect against corrosion factors.

[Second stage]: Alkaline earth metal components such as calcium are filled in the voids of zinc phosphate formed in the first stage as poorly soluble oxides and hydroxides to form a film with an excellent environmental barrier function. To do. At this time, if the amount of alkaline earth metal or zinc is too small, the formation of oxides and hydroxides filling the gaps in the zinc phosphate becomes insufficient, and a dense film is not formed. In the elution component, by increasing the ratio of the total amount of metal ions (alkaline earth metal ions and zinc ions) and the total amount of phosphate ions to a certain extent, it becomes easier to form hardly soluble oxides and hydroxides. The denseness of the film increases. As a result of various studies, this point is defined by the following equation (1).

Hereinafter, matters for specifying the present invention will be described.
[Alkaline earth metal compound particles]
Alkaline earth metal compound particles serve as a source of alkaline earth metal ions in an outdoor environment by being dispersed and blended in the coating film. Alkaline earth metal ions eluted during rainfall form oxides and hydroxides, filling the voids of the zinc phosphate film formed on the cut end faces, and densifying them. Thereby, generation | occurrence | production of red rust is suppressed notably in the steel base exposed part of a cut end surface. Suitable alkaline earth metals are Ca, Mg, and Sr. The alkaline earth metal compound may be an oxide, a hydroxide, or a salt as long as it is a substance that is a source of alkaline earth metal ions in an outdoor environment. For example, calcium hydroxide, magnesium hydroxide, strontium hydroxide, calcium oxide, magnesium oxide, strontium oxide, calcium phosphate, magnesium phosphate, strontium phosphate, calcium nitrate, magnesium nitrate, strontium nitrate, and the like can be used.

[Zinc compound particles]
The zinc compound particles serve as a supply source of zinc ions in an outdoor environment by being dispersed and blended in the coating film. Zinc ions eluted during rainfall react with phosphate ions eluted from phosphate particles to form a zinc phosphate film on the cut end face. The zinc phosphate coating is excellent in adhesion to the steel substrate, and covers the steel substrate on the cut end face, thereby improving the corrosion resistance of the portion. The zinc compound may be an oxide, hydroxide, or salt as long as it is a substance that is a source of zinc ions in an outdoor environment. For example, zinc hydroxide, zinc oxide, zinc phosphate, zinc nitrate, or the like can be used.

[Phosphate particles]
Phosphate particles serve as a source of phosphate ions in an outdoor environment by being dispersed and blended in the coating film. The phosphate ion here refers to a negative ion made of a phosphorus-containing substance eluted from orthophosphate, phosphite, or polyphosphate. The phosphate ions eluted during rainfall react with the zinc ions eluted from the zinc compound particles as described above to form a zinc phosphate film on the cut end face, and cover the steel substrate of the cut end face, Responsible for improving corrosion resistance. The phosphate needs to be a substance that serves as a source of phosphate ions in an outdoor environment, and salts of orthophosphoric acid, phosphorous acid, and polyphosphoric acid can be used.

[Organic carboxylate particles]
In addition to the above alkaline earth metal compound particles, zinc compound particles, and phosphate particles, organic carboxylate particles can be dispersed and blended in the coating film. The organic carboxylic acid which is the subject of the present invention is one in which the metal constituting the organic carboxylate, that is, the metal substituting the H portion of the carboxyl group is composed of an alkaline earth metal or zinc. One or more of such organic carboxylates can be employed. The organic carboxylate has an action of improving the denseness of the zinc phosphate film formed on the cut end face by the chelate effect, and contributes to the formation of a stronger film. Thereby, the long-term corrosion resistance of the cut end face is further improved. When the organic carboxylate particles are contained in the coating film, the blending amount may be within a range of 50 mmol (mmol) or less as the molar amount of the organic carboxylate per 1 m ² of the coating area, and usually 10 to 40 mmol. If it is about, it is effective. Examples of organic carboxylates include calcium tartrate, magnesium tartrate, strontium tartrate, zinc tartrate, calcium acetate, magnesium acetate, strontium acetate, zinc acetate, calcium citrate, magnesium citrate, strontium citrate, and zinc citrate. Can be mentioned.

[(1) Formula]
It is important that the alkaline earth metal compound particles, zinc compound particles, and phosphate particles have an appropriate blending ratio in the coating film so as to sufficiently exhibit the above-described action. As a result of various studies, the inventors have filled the gaps of zinc phosphate with an alkaline earth metal oxide or hydroxide as described above in order to densify the zinc phosphate film formed on the cut end face. Has been found to be extremely effective. In this case, it is necessary to ensure a sufficient amount of alkaline earth metal ions and zinc ions eluted with respect to the amount of phosphate ions eluted in the outdoor environment. According to the detailed examination by the inventors, when the coated steel sheet sample is subjected to an “immersion test” in which the coated steel sheet sample is immersed in pure water at room temperature, the molar ratio of components eluted from the coating film per hour is It was found that a dense zinc phosphate film was constructed when the properties satisfying the following formula (1) were satisfied, and the occurrence of red rust on the cut end face could be suppressed.
0.95 ≦ ([Alkaline earth metal element] + Zn) / P (1)

  This “immersion test” can be performed, for example, by a method in which a test piece is immersed in 100 mL of pure water at 50 mm × 50 mm. The test piece is exposed to the coating surface to be evaluated, and the opposite surface is not touched by the liquid by attaching a resin film or the like. The cut end surface of the test piece may remain exposed. When evaluating a coated steel sheet in which the same kind of coating film is formed on both surfaces of the steel sheet, the evaluation is performed for each side in the above-described manner. (1) The [alkaline earth metal element], Zn, and P in the formula have a molar amount of each element eluted in water by the above immersion test (a value of mol% of each element present in water or proportional thereto). Value to be substituted) (the same applies to equation (2) described later). When two or more kinds of alkaline earth metal elements are used, the total value of the molar amount of each alkaline earth element eluted is substituted for [alkaline earth metal element] (the same applies to the formula (2) described later) ).

If the total elution amount of [alkaline earth metal element] + Zn becomes excessive, the corrosion resistance of the flat portion may be lowered. When emphasizing the corrosion resistance at the flat portion, it is more preferable to adopt the following formula (1) ′ instead of the formula (1).
0.95 ≦ ([Alkaline earth metal element] + Zn) / P ≦ 5 (1) ′

[Formula (2)]
The quantitative relationship between the alkaline earth metal ions eluted in the outdoor environment and the Zn ions also needs to be appropriately controlled. As a result of various studies, when the elution amount molar ratio of the component eluted from the coating film satisfies the following formula (2) when subjected to the above-mentioned “immersion test”, red rust occurs on the cut end face It can be deterred.
0.1 ≦ [Alkaline earth metal element] / Zn ≦ 10 (2)
When the elution amount molar ratio [alkaline earth metal element] / Zn is less than 0.1, the amount of alkaline earth metal oxides and hydroxides generated is insufficient, and the zinc phosphate coating is not sufficiently densified. Cheap. On the other hand, even if it exceeds 10, the effect of suppressing the occurrence of red rust on the cut end face is saturated, and in some cases, the corrosion resistance at the flat part may be lowered.

[Elution amount of P]
In order to achieve the object of the present invention, in an outdoor environment, an amount of phosphate ions sufficient to form a zinc phosphate film covering the steel base exposed portion of the cut end face is supplied from the coating film around the cut end face. There is a need. According to the detailed examination by the inventors, the amount of P eluting from the coating film per hour when subjected to the above-mentioned “immersion test” is 0.5 mmol (as converted value per 1 m ^{2 of the} coating area). In the case of having the property of being greater than or equal to millimoles, the occurrence of red rust at the cut end face can be suppressed. However, if the coating amount is such that the amount of elution of P is too large, the effect of preventing red rust generation is saturated and uneconomical. Therefore, the phosphate particles are blended in such a range that the amount of P eluting from the coating film per hour when subjected to the “immersion test” is 30 mmol or less as a converted value per 1 m ^{2 of the} coating film area. It is desirable that

[Formula (3)]
The size of the alkaline earth metal compound particles, zinc compound particles, phosphate particles, and in some cases, the organic carboxylate particles that are present in the coating film may be optimized in relation to the coating thickness. desirable. Specifically, the average particle diameter of alkaline earth metal compound particles, zinc compound particles and phosphate particles blended in the coating film is D (μm), and the average film thickness of the coating film is T (μm). , It is preferable that the relationship between D and T satisfies the following expression (3). However, when organic carboxylate particles are blended in the coating film, the average particle diameter of alkaline earth metal compound particles, zinc compound particles, phosphate particles and organic carboxylate particles is defined as D (μm). To do.
0.15 ≦ T / D (3)

When the value of T / D is less than 0.15, most of the particles are present in a form protruding from the surface of the coating film. In this case, depending on how to handle the coated steel sheet, the number of particles that are detached from the coating film before the construction as the final member increases. If it becomes so, the red rust prevention effect in the cut end surface planned will not be fully exhibited. Note that it is more preferable to adopt the following expression (3) ′ instead of the above expression (3). The upper limit of the T / D value is usually not particularly limited, but when considering the handleability of the powder, for example, the formula (3) '' can be employed.
0.2 ≦ T / D (3) ′
0.2 ≦ T / D ≦ 10 (3) ''

[Painted original plate]
In addition to conventional coated steel sheets, zinc-plated steel sheets or aluminum-plated steel sheets, which are highly effective in improving coating film adhesion and corrosion resistance, can be used as the coating original sheet. Depending on the application, copper-plated steel sheets and tin-plated steel sheets can be used. May be used. Cold-rolled steel sheets or cold-rolled annealed pickled steel sheets that have not been plated can also be used. Examples of the zinc plating include Zn plating, Zn-2 to 22 mass% Al-2 to 10% Mg plating, Zn-0.5 to 40 mass% Mg plating, Zn-3 to 30 mass% Ni plating, and the like. . Examples of the aluminum plating include Al plating, Al-5 to 13 mass% Si plating, and 50 to 60 mass% Al-Zn plating. As these plating methods, various plating methods such as hot dipping using a continuous plating line, hot dipping hot dipping, electroplating, and vapor deposition plating can be adopted. In the case of hot dip galvanizing, in the plating bath, for example, one or more of Si: 2% by mass or less, Ti: 0.02% by mass or less, B: 0.01% by mass or less, Fe: 2% by mass or less It does not matter if elements are mixed. Moreover, you may have one or more base coating films as a base of the coating film which mix | blends alkaline-earth metal compound particle | grains, zinc compound particle | grains, phosphate particle | grains, and organic carboxylate particle | grains depending on the case. Absent.

As the steel type, various steel types that are conventionally used in outdoor environments as building materials and automobile members can be applied. Typical examples include the following.
(I) By mass%, C: 0.15% or less, Mn: 0.80% or less, P: 0.05% or less, S: 0.05% or less, the balance being substantially Fe
(Ii)% by mass, C: 0.12% or less, Mn: 0.60% or less, P: 0.04% or less, 0.04% or less, the balance being substantially Fe
(Iii) By mass%, C: 0.25% or less, Mn: 1.70% or less, P: 0.20% or less, 0.05% or less, the balance being substantially Fe
Here, “the balance is substantially Fe” means that mixing of elements other than those described above is allowed within a range not impairing the object of the present invention. For example, Si: 1% or less, Ti: 0.1% or less, Nb: 0.1% or less, B: 0.01% or less, Cu: 1% or less, Ni: 1% or less, Cr: 1% or less, Mo: 1% or less, Zr: 1% or less, V: 1% or less of one or more elements are allowed to be mixed, and the total content of these mixed elements is more preferably limited to 3% or less It becomes. “The balance is substantially Fe” includes a case where “the balance is made of Fe and inevitable impurities”.

[Production method]
When a steel plate is manufactured by a conventional general method and plated, the plating process is performed on a continuous plating line while the steel strip is used, or the cut plate is used for the plating process to obtain a coating original plate. If necessary, a chromium-free surface treatment may be performed thereafter, and a base coating may be applied as necessary. The coating material for constructing the coating film (the outermost layer coating film if it has a base coating film) can be prepared based on various coating materials conventionally used for outdoor use. For example, adding alkaline earth metal compound particles, zinc compound particles, phosphate particles and, if necessary, organic carboxylate particles to a paint mainly composed of polyester-based, acrylic-based resin, and stirring. To disperse and mix these particles. The blending ratio of each particle may be, for example, the “example of the present invention” shown in the below-described examples. However, when preparing a paint having a new blending composition, for example, the blending composition with reference to the following examples. It is possible to design the components of the paint relatively easily by performing the “immersion test” described above in the laboratory experiment and confirming the evaluation result. As a coating method, a method in which a coating is applied to the surface of the original plate by an appropriate means such as a roll coater method or a bar coater method according to the application, the type of resin, and the coating thickness, and a baking process can be employed.

Using steel sheets of steel type A (plate thickness 0.8 mm) and steel type B (plate thickness 0.8 mm) in the following component ranges, both of the plating adhesion amount on one side in a continuous molten aluminum plating line: 150 g / m ^Two hot-dip aluminized steel sheets were produced.
[Steel A]% by mass, C: 0.05% or less, Mn: 0.1 to 0.2%, P: 0.02% or less, S: 0.01% or less, remaining Fe and inevitable impurities [Steel Type B] By mass%, C: 0.12 to 0.15%, Mn: 0.5 to 1.0%, P: 0.03% or less, S: 0.03% or less, remaining Fe and inevitable impurities

On the other hand, a polyester-based resin coating is prepared, and alkaline earth metal compound particles, zinc compound particles, phosphate particles, and in some cases, organic carboxylates in the mixing ratios shown in Tables 1A and 2A. Particles were added and stirred to prepare a paint in which these particles were dispersed. For some comparative examples, paints with metal particles added instead of alkaline earth metal compound particles were also prepared. The “addition amount” of each particle in Table 1A and Table 2A is the amount per 1 m ² of the coating film area of the substance constituting each particle.

  By using a hot-dip aluminum-plated steel sheet of either steel type A or B as a coating original sheet, degreasing and washing it, applying the above-mentioned paint on one side with a bar coater, and heating and drying (baking) at a final plate temperature of 215 ° C A coated steel sheet sample having a dry film thickness of 5 to 10 μm was obtained.

Ten immersed test pieces of 50 mm × 50 mm were cut out from each coated steel sheet sample. Each immersion test piece was affixed with a resin film on the surface opposite to the painted surface, and the cut end surface was exposed. 100 mL of ion exchange water was put into a glass beaker and kept at 23 ° C. ± 2 ° C., and each immersion test piece was immersed therein. It was immersed with an inclination angle (angle formed with a horizontal plane) of 0 ° so that the painted surface was on top. The water in each beaker after immersion for 10 hours was analyzed with a light absorbance meter, and the amounts of alkaline earth metal elements, Zn, and P eluted in the water were measured. By summing the 10 analysis values of each coated steel sheet sample and dividing this by the total surface area of the coating film (0.05 m × 0.05 m × 10), the coating area per 1 m ² to 1 hour The amount of alkaline earth metal element (metal element in some examples), Zn, and P to be eluted was determined. Here, the alkaline earth metal element or the metal element replacing it was expressed as M, and the elution amount molar ratios (M + Zn) / P and M / Zn were calculated. These results are shown in Table 1B and Table 2B.

  A cross-section observation specimen was cut out from each coated steel sheet sample, and a sample capable of observing the cross section of the coating film was prepared. Observe the cross section of the coating film with SEM, measure the major axis of each particle image for all particles (however, the number of measurements is 20 or more) in a certain region, and average the average value. The particle diameter was D (μm). Further, the dry film thickness of the coating film was determined by calculation based on data obtained in advance from the mass of the paint used (part excluding added particles) and the coating area, and this was defined as the average film thickness T (μm). . And T / D value was calculated | required. These values are shown in Tables 1B and 2B.

A 70 mm × 100 mm exposure test piece was cut out from each coated steel sheet sample, and an outdoor exposure test was performed in an industrial area of Sakai City, Osaka Prefecture. The exposure test piece was placed in a place where it was exposed to direct sunlight and directly exposed to rain water so that the inclination angle (angle formed with the horizontal plane) was 35 ° and the coated surface was up. The cut end surface of the exposed specimen was left in a state where the steel substrate was exposed. With respect to the test pieces having an outdoor exposure period of 3 months and 6 months, the surface of the cut end surface was observed and evaluated as follows.
◎: No occurrence of red rust on the cut end face ○: Red rust occurrence area ratio on the cut end face is 10% or less and no red rust flow is found △: Red rust occurrence area ratio on the cut end face exceeds 10%, No red rust flow was observed. ×: Red rust flow from the cut end face was not recognized even during an exposure period of 6 months where the red rust flow from the end face was recognized (△ evaluation or higher), and the others were judged as rejected. . The results are shown in Table 1B and Table 2B.

  In the coated steel sheet of the present invention, each particle was appropriately dispersed and blended in the coating film, so that the red rust flow at the cut end face was prevented even after 6 months of outdoor exposure. On the other hand, No. 51-53 which is a comparative example has a small elution amount molar ratio (M + Zn) / P in the immersion test that deviates from the equation (1). Nos. 54 to 57 use metal particles in place of the alkaline earth metal compound particles in the coating film. No. 58 was obtained by not incorporating alkaline earth metal compound particles in the coating film, No. 59 was obtained by not incorporating zinc compound particles, and No. 60 was obtained by not incorporating phosphate particles. is there. In these comparative examples, the flow of red rust had already occurred from the cut end face after exposure to the atmosphere for 3 months.

Claims (7)

A coated steel sheet in which a coating containing alkaline earth metal compound particles, zinc compound particles, and phosphate particles is formed, and when the coated steel sheet sample is immersed in pure water at room temperature, The elution amount molar ratio of the components eluted per hour satisfies the following formulas (1) and (2), and the elution amount per hour of P is 0.5 to 5 in terms of the converted value per 1 m ^{2 of the} coating area. A coated steel sheet in which the particles are blended in the coating so as to be in a range satisfying 30 mmol.
0.95 ≦ ([Alkaline earth metal element] + Zn) / P (1)
0.1 ≦ [Alkaline earth metal element] / Zn ≦ 10 (2)   The coated steel sheet according to claim 1, wherein the alkaline earth metal is one or more elements of Ca, Mg, and Sr.   The coated alkaline steel sheet according to claim 1 or 2, wherein the alkaline earth metal compound is one or more substances selected from oxides, hydroxides and salts of alkaline earth metals.   The coated steel sheet according to any one of claims 1 to 3, wherein the zinc compound is one or more substances selected from zinc oxides, hydroxides and salts.   Organic carboxylate particles are further blended in the coating film, and the metal constituting the organic carboxylate is one or more elements selected from alkaline earth metals and Zn. The coated steel sheet described in 1. Among the alkaline earth metal compound particles, zinc compound particles, phosphate particles and organic carboxylate particles, the average particle diameter of all kinds of particles mixed in the coating film is D (μm), The coated steel sheet according to any one of claims 1 to 5, which satisfies the following expression (3) when the average film thickness is T (µm).
0.15 ≦ T / D (3)   The coated steel sheet according to any one of claims 1 to 6, wherein a zinc-based plated steel sheet or an aluminum-based plated steel sheet is used as the coating original sheet.