JP2001316839A - Production method for surface treated steel sheet having high corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method for a surface treated steel sheet that has a high corrosion resistance, remarkably suppresses a process of corrosion from a machined part, also has a great suppressive effect against blackening of the surface under the environment of high temperature and high humidity and is excellent in workability. SOLUTION: The surface of a zinc plating steel sheet containing zinc of 30 wt.% or above, is subjected to a chromate treating, is coated with a treatment agent containing an organic resin and a complex compound having Ca-PO4- SiO2 as a main component further and is dried at a sheet temperature of 60 deg.C or above and 250 deg.C or below to form a film. In the above film, the coating weight of the organic resin is 50 mg/m2 or above and 5000 mg/m2 or below, the coating weight of Cr is 1 mg/m2 or above and 100 mg/m2 or below, (Ca+ SiO2+PO4)/the organic resin is 0.01-0.5 in a wt.ratio and (Ca+SiO2)/PO4 is 0.05-0.8 in a wt.ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides excellent corrosion resistance even without painting, and does not cause blackening of the plating surface even in a high-temperature and high-humidity environment. The present invention relates to a method for producing a surface-treated steel sheet that can be maintained.

[0002]

2. Description of the Related Art In recent years, in the fields of home electric appliances and building materials, in order to improve the durability of members having severe corrosive environment especially outdoors,
There is a strong demand for a high corrosion-resistant material that is superior to conventionally used surface-treated steel sheets. In these applications, since a bending process or the like is performed, a galvanized steel sheet excellent in sacrificial corrosion resistance has been used to prevent the progress of iron corrosion even if a crack occurs in plating. Recently, in addition to this, Al
From 1 to 10% (hereinafter referred to as "5% Al-based") or Al
Al-Zn-based alloy-coated steel sheets containing 40 to 70% (hereinafter referred to as "so-called 55% Al-based") and having excellent corrosion resistance have been widely used. Each of these three types of plated steel sheet has the following features.

[0003] Although galvanized steel sheet is excellent in sacrificial corrosion resistance, it has an active plated surface, so that zinc rust, which is a zinc oxide, is easily formed in the presence of moisture and oxygen, and the appearance quality is deteriorated. Since zinc oxide cannot be expected to have high corrosion resistance, there is a limit in long-term durability. So-called
5% Al-based alloys have a lower surface activity than galvanized steel sheets due to the effect of Al, so they are less susceptible to white rust and more durable than zinc-coated steel sheets. As a result, there is a problem that the surface turns black and the appearance quality is remarkably deteriorated. In a so-called 55% Al-based material, since the surface is more stable, white rust hardly occurs and blackening hardly occurs. However, since the plating film is hard, cracks occur in the plating due to severe processing, and corrosion from that part progresses.
There is a disadvantage that black rust mainly composed of the Al component is generated, and the appearance quality of the processed portion is greatly reduced.

Conventionally, steel sheets having improved corrosion resistance by subjecting the surface of zinc plating or zinc-based alloy plating to chromate treatment have been used. However, the corrosion resistance or blackening resistance of a processed portion where a defect occurs in a plating film has been used. A chromate film that can be improved to the level required for the final product has not yet been found.

[0005] As a means for improving the corrosion resistance of a worked portion of zinc plating or zinc-based alloy plating, many methods using an organic resin for a chromate film have been proposed. According to this method, although an improvement effect is recognized because damage to the chromate film due to processing or the like is reduced, particularly, the so-called 55
In the case of the% Al-based alloy, a sufficient plating crack is generated by processing, so that a sufficient effect has not been obtained. Also, so-called 5% Al
No effect has been obtained on blackening resistance, which is a problem of the system.

[0006] The addition of silica, phosphoric acid, or the like to the chromate film has an effect of improving corrosion resistance and is generally used for increasing corrosion resistance. It cannot be obtained, and it has been recognized that the so-called 5% Al system even tends to further reduce blackening resistance by addition.

Further, although simply increasing the amount of chromate film is effective in improving corrosion resistance, it is not only economically disadvantageous but also increases the amount of chromium eluted from the film, which has an adverse effect on the environment. It should be avoided because of its potential effects.

[0008] In the manufacturing method, it is most desirable that the device can be manufactured by simple processing steps because it does not require a huge amount of equipment and is easy to manufacture. Therefore, there is no need for a special pretreatment for attaching Ni, Co, Fe, etc. before chromate treatment, which has been performed mainly as a blackening resistance or painting pretreatment, and conventionally used methods, especially coating It is most preferred to form a film by a chromate treatment method of a mold.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has high corrosion resistance, remarkably suppresses the progress of corrosion from a processed portion, and has a high surface and high temperature and high humidity environment. It is an object of the present invention to provide a method for producing a surface-treated steel sheet that exhibits a large effect of suppressing black change and has excellent workability.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, by forming a Ca-containing film as a new additive, Zn has been reduced to 30%.
The corrosion resistance including the processed part of the zinc-based plated steel sheet including the above can be improved. Further, the so-called 5% Al-based steel can form a film excellent in blackening resistance. Because of the severe processing, cracks are generated in the plating, and corrosion is promoted from that part in a corrosive environment. Was completed. The gist of the present invention for solving the above problems is as follows.

(1) Zinc-based plating containing 30% by weight or more of zinc
The surface of the steel plate is subjected to chromate treatment,
And Ca-PO_Four-SiO_TwoContaining complex compounds whose main component is
Apply a physical solution and dry at a plate temperature of 60 ° C or more and 250 ° C or less.
The film has an organic resin adhesion amount of 50 mg.
/ m^TwoMore than 5000mg / m^TwoBelow, the amount of Cr attached is 1 mg / m^TwoMore than 100mg / m^Two
Below, and by weight ratio, (Ca + SiO_Two+ PO_Four) /0.0% organic resin
1-0.5, (Ca + SiO_Two) / PO _FourIs between 0.05 and 0.8
A method for producing a highly corrosion-resistant surface-treated steel sheet (first invention).

(2) The highly corrosion-resistant surface-treated steel sheet according to (1), wherein the galvanized steel sheet containing 30% by weight or more of zinc is a Zn-Al alloy coated steel sheet containing 1 to 10% by weight of Al. (Second invention).

(3) The highly corrosion-resistant surface-treated steel sheet according to (1), wherein the galvanized steel sheet containing 30% by weight or more of zinc is a Zn-Al alloy-plated steel sheet containing 40 to 70% by weight of Al. (Third invention). In this specification, all the percentages indicating the components of the plating film are wt%.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. (Type of Steel Plate) In the present invention, the types of target steel plates are limited for the following reasons. That is, Zn is 30%
In the case of a plated steel sheet containing less than less than 10, since the sacrificial corrosion resistance of Zn is inferior, even if a minute defect occurs in the plating film, red rust which is a corrosion product of Fe is easily generated. Therefore, it is necessary to contain Zn in an amount of 30% or more from the viewpoint of the corrosion resistance of the steel sheet. On the other hand, since Zn is an active metal, the plating film itself is likely to be corroded, and from the viewpoint of long-term durability, There is a limit.

As means for improving the durability of Zn-plated steel sheets, alloy plating with Al has been studied and has already been put to practical use. Above all, it contains 1 to 8% of Al
Plated steel sheet to which Mg, MM, etc. are added (hereinafter referred to as 5% Al type),
Al containing 40-70% and 1-3% Si, and optionally further Ti
Alloy-plated steel sheet (hereinafter referred to as 55% Al-based steel) to which the addition is also made. In the present invention, such Zn
The purpose of the present invention is to improve the corrosion resistance of a galvanized steel sheet containing 30% or more. The galvanized steel sheet currently used in the market that corresponds to this is galvanized steel sheet, hot-dip galvanized steel sheet, 5% Al-based steel sheet, 55% A
l-plated steel sheet.

Although the durability is improved by using 5% Al as compared with zinc plating, there is a problem that the surface is blackened in a high-temperature and high-humidity environment and the commercial value is significantly reduced. The present invention improves the 5% Al-based blackening resistance and solves such a problem.

In the case of the 55% Al-based alloy, although the corrosion resistance of the plating is further improved, the plating film is hard, so that cracks are caused by the processing, and the corrosion from the processed portion progresses.
, There is a problem that much black rust is generated and the appearance quality is greatly reduced. The present invention improves the black rust resistance of a 55% Al-based processed portion to solve such a problem.

In the present invention, each of the above-mentioned plated steel sheets is subjected to a pretreatment for washing with hot water or alkali degreasing, and in some cases, for attaching Ni, Co, Fe, etc. to the surface, if necessary. Is also good.

(Applying chromate treatment to the surface of a plated steel sheet) By subjecting the surface of a plated steel sheet to a chromate treatment, the surface is passivated and the corrosion resistance can be significantly improved. The conditions of the chromate treatment are not particularly specified, but usually, a chromic acid having a Cr reduction ratio of 10 to 40% to which a fluoride, an anion or the like is added as a reaction accelerator, if necessary, is used. As a result, a film is formed. The effect is exhibited when the amount of adhesion is 1 mg / m ² or more. However, if the amount is more than 100 mg / m ² , no further effect is observed and the appearance quality is deteriorated by coloring, which is not preferable.

(Organic film adhesion amount: 50 mg / m ² or more and 5000 mg / m ²
Below) The coating of the plated surface, an organic resin is 50 mg / m ² or more 5
It must be contained within the range of 000 mg / m ² or less.
The organic resin is required because it has the effect of improving the corrosion resistance of the chromate film and also has the effect of preventing the occurrence of surface scratches due to processing. The effect is dependent on the coating weight, not recognized corrosion resistance improving effect is 50 mg / m of less than ² as the organic resin amount, when depositing conversely exceed 5000 mg / m ^2, peeling of the film occurs during working, peel An object is not preferable because it may cause new surface scratches. Therefore, the organic resin coating weight, 50 mg / m ² or more 5000 mg / m ² or less, preferably
Should be between 200 mg / m ^{2 and} 2500 mg / m ² .

As the organic resin, a water-soluble or water-dispersible organic resin is used. The type of organic resin is acrylic,
Acrylic-styrene-based, urethane-based, or polyester-based ones can be used, but it is desirable to use a resin containing a nonionic component as the treatment liquid in order to stably disperse it with other components. From the viewpoint of corrosion resistance, it is desirable to use a water-dispersible resin (emulsion resin) rather than a water-soluble resin. Among these organic resins, acrylic-based resins which can be produced by an emulsion polymerization method, which is advantageous in terms of cost, and are excellent in corrosion resistance and processability, are used.
There is a styrene resin. If the proportion of styrene in the acrylic-styrene resin is less than 10%, the corrosion resistance is reduced,
If it exceeds 70%, the workability is reduced. Therefore, the styrene / organic resin ratio (weight ratio) is 0.1-0.7 acrylic-
By using a styrene-based resin, it is possible to form a film that is inexpensive and has excellent corrosion resistance and potential. Also,
If the acid value is less than 1, the stability of the liquid is inferior, and if it exceeds 50, the corrosion resistance decreases.If the acid value is 1 to 50, it is possible to achieve both liquid stability and high corrosion resistance. .

In addition, the film properties (film adhesion, corrosion resistance, blackening resistance, water resistance, paint adhesion, slip resistance, tape adhesion, pef adhesion, etc.) can be controlled by the addition of a dispersion stabilizer or an antifoaming agent. , Adhesion to urethane foam), mixing stability of the liquid, or mechanical stability is greatly affected, but it is important to select one that is more suitable for the purpose according to other required characteristics and usage conditions. It is.

(Composite compound containing Ca-PO ₄ -SiO ₂ as a main component) The most important feature of the present invention is that a film containing a composite compound containing Ca-PO ₄ -SiO ₂ as a main component is formed. is there. The composite compound is, for example, a phosphate compound (zinc phosphate,
A precipitate obtained by appropriately adding Na silicate and Ca nitrate in a state where zinc polyphosphate, aluminum tripolyphosphate and the like are dispersed in water is washed with water, and a residue obtained by removing soluble components can be used. Further, those having an average particle diameter of about 3 μm to 0.1 μm can be used. However, the present invention does not specify the method for producing the composite compound and the particle size thereof. This compound contains Ca-
The feature is that each component of PO ₄ —SiO ₂ is dispersed in the same position. However, it is also possible to add phosphoric acid for the purpose of, for example, making the coating uncolored, in which case it will be distributed at a position different from other components, so that most of the Ca and SiO ₂ will be distributed in the vicinity. The feature is that PO ₄ is distributed.

((Ca + SiO ₂ + PO ₄ ) / organic resin: 0.01-0.
5) The composite compound has an effect of remarkably improving corrosion resistance and blackening resistance, but excessive addition thereof not only lowers workability but also lowers corrosion resistance. If the ratio of (Ca + SiO ₂ + PO ₄ ) / organic resin is less than 0.01, a sufficient effect on the improvement of corrosion resistance and blackening resistance cannot be obtained. Therefore, (Ca + SiO ₂ + PO ₄ ) / organic resin (weight ratio) needs to be 0.01 to 0.5, and more desirably 0.05 to 0.3.

((Ca + SiO ₂ ) / PO ₄ : 0.05-0.8) The composition of the composite compound has a significant effect on the effects on corrosion resistance and blackening resistance. If (Ca + SiO ₂ ) / PO ₄ is less than 0.05, a remarkable effect of improving corrosion resistance and blackening resistance cannot be obtained. Conversely, (Ca + SiO
₂ ) When / PO ₄ is 0.8, the corrosion resistance tends to decrease. Therefore, (Ca + SiO ₂ ) / PO ₄ (weight ratio) needs to be 0.05 to 0.8, and more preferably 0.1 to 0.5.

(Drying temperature) An aqueous treatment liquid containing the above components is applied using a roll coater or the like, and is dried by heating or hot air to form a film. The film formation temperature must be 60 ° C. or higher, and if it is lower than that, a film having poor corrosion resistance and adhesion due to the influence of moisture remaining in the film is obtained. Further, even if the maximum temperature exceeds 250 ° C., there is no improvement effect on the properties, and conversely, a film having poor corrosion resistance tends to be formed. Therefore, the drying plate temperature for forming a film should be 60 ° C or higher and 250 ° C or lower.

[0027]

Embodiments will be described below. As shown in Table 1-2, the chromate treatment applied to the surfaces of various plated steel sheet, an organic resin and Ca-PO ₄ was further adjusted to a predetermined composition
Applying a treatment liquid containing a composite compound mainly composed of -SiO _2, and heated and dried at peak metal temperature shown in Table 1-2, test one which formed coating weight of the film shown in Table 1-2 Material. Symbols in the plating column in the table and similar symbols in the following description represent the following plated steel sheets. GI; hot-dip galvanized steel sheet (coating amount: Z27, sheet thickness 0.5 mm) 5Al; 5% Al-Zn alloy coated steel sheet (coating amount: Y22, sheet thickness 0.
5mm) 55Al; 55% Al-Zn alloy plated steel sheet (coating amount: AZ-150,
Al; Hot-dip Al-plated steel sheet (Coating amount: 200g / m ² , Sheet thickness 0.5m)
m)

The composite salts shown in Tables 1 and 2 are zinc phosphate (Zn ₃ (PO ₄ ) ₂ .4H ₂ O) used as a rust preventive.
Was dispersed in water, Ca nitrate and Na silicate were added and reacted, and the resulting precipitate was washed with water to remove soluble components. The ratio of Ca + SiO ₂ to PO ₄ was adjusted by the addition amounts of Ca nitrate and Na silicate. Further, Ca / SiO ₂ of the compound obtained as described above was approximately 1: 2. Further, a powder whose average particle diameter was adjusted to 0.7 μm was used.

In order to evaluate the corrosion resistance of the flat part of the test material, a composite corrosion test (CCT; salt spray test (30 minutes) → wetting test (90 minutes)
Min) → natural drying (120 minutes) as one cycle), and the evaluation was performed by the number of cycles at which the white rust generation area became 10% or more. In addition, in order to evaluate the corrosion resistance of the processed portion, a CCT 50 cycle was performed on a sample subjected to 3T bending, and the degree of rust generation at the bent portion was evaluated based on the following criteria.

Bending portion corrosion resistance evaluation criteria: 10; white rust area less than 10%, black rust area less than 10%,
8; White rust area 10% or more and less than 50%, black rust area 10%
Less than, 6: White rust occurrence area 50% or more, black rust occurrence area less than 10%, 4: Black rust occurrence area 10% or more, less than 50%, 2: Black rust occurrence area 50% or more, 1: Red rust occurrence

The blackening resistance was evaluated based on the following criteria for the degree of blackening after storage in a stacked state under an environment of 50 ° C. and 98% RH for 480 hours.

Evaluation criteria for blackening resistance: 5; no change, 4; blackening part observable and obliquely observable
Less than 25%, 3; black discoloration part 25 observable and obliquely observable
%; 2; there is a blackened portion that can be observed and confirmed from the front (less than 25%); 1; 25% or more of the blackened portion that can be observed and confirmed from the front

In order to evaluate the workability, the tip is 1 mm × 10 m
A plate having a width of 30 mm was pulled out at a constant speed while a bead having a flat surface of m was pressed against the surface of the test material with a constant load, and flat plate sliding was performed. The test was performed by changing the level of the pressing load, and the evaluation was performed based on the limit pressing load at which galling occurs on the plating surface. Table 3 shows the evaluation results.

[0034]

【table 1】

[0035]

[Table 2]

[0036]

[Table 3]

Nos. 1-4 are GI, Nos. 5-8 are 5Al, Nos. 9-1
No. 2 is an example in which a film was formed on 55Al, and No. 13 is an example in which a film was formed on Al. No.4, No.8, No.12 which formed a film within the scope of the present invention
GI, 5Al, and 55Al containing Zn at 30% or more have the effect of improving the flat plate corrosion resistance, blackening resistance, and processed portion corrosion resistance, which are issues of plating, to levels that cannot be achieved with conventional chromate films. It also has excellent workability. On the other hand, in No. 13 containing no zinc, red rust is generated from the processed portion, and a film having poor corrosion resistance is formed on the processed portion.

Nos. 14 to 17 show the effect of the amount of organic resin adhered, No. 18
No. 20 is the effect of the amount of Cr attached, Nos. 21 to 24 are the effects of additives / resins, and Nos. 25 to 28 are the effects of (Ca + SiO ₂ ) / PO _{4 in} the additives with 55Al as the base. This is an example studied. If the amount of resin adhered is out of the range of the present invention, workability is particularly deteriorated, and if the amount of Cr is small, all properties are deteriorated. Further, when Cr is excessively adhered, a film having good characteristics with respect to corrosion resistance, blackening resistance and workability is obtained, but coloring is remarkable and a problem arises in appearance quality. Further, the addition amounts of Ca, PO ₄ , and SiO ₂ greatly affect the corrosion resistance of the flat portion and the processed portion, and if any of them is out of the range of the present invention, it is difficult to achieve both.

Nos. 29 to 32 are examples of examination of the drying temperature. When the drying temperature is out of the range of the present invention, the corrosion resistance and blackening resistance tend to be inferior outside the range of the present invention.

[0040]

As described above, the coating of the present invention is made of Zn.
By forming the surface of a plated steel sheet containing 30% or more, a surface-treated steel sheet that can exhibit high corrosion resistance even when used without painting can be obtained.

By forming the coating of the present invention on the surface of a galvanized steel sheet containing 1 to 10% of Al, the corrosion resistance is further improved and the blackening resistance, which has been a problem in the conventional plating, is dramatically improved. It is possible to do.

Further, by forming the coating of the present invention on the surface of a galvanized steel sheet containing 40 to 70% of Al, a higher level of corrosion resistance can be obtained, and the corrosion resistance of the processed portion, which has been a conventional problem, is also increased. High corrosion resistance is possible.

Further, according to the present invention, a high-performance coating of the steel sheet can be stably manufactured.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 22/24 C23C 22/24 28/00 28/00 C // C22C 18/04 C22C 18/04 21 / 10 21/10 (72) Inventor Etsuo Hamada 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Masaaki Yamashita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Stock In-house F term (reference) 4K026 AA02 AA07 AA09 AA12 AA13 AA22 BA03 BA04 BA06 BB08 BB09 CA16 CA18 CA22 CA24 CA26 CA27 CA39 CA41 DA02 DA11 DA16 4K027 AA05 AA22 AB05 AB42 AB48 AC82 4K044 BA15 BA17 BB04

Claims (3)

[Claims] 1. A surface of a galvanized steel sheet containing 30% by weight or more of zinc is subjected to a chromate treatment, and a treatment liquid containing an organic resin and a composite compound mainly composed of Ca—PO ₄ —SiO ₂ is applied. And drying at a plate temperature of 60 ° C. or more and 250 ° C. or less to form a film, and the film has an organic resin adhesion amount of 50 mg / m ²
5,000 mg / m ² or less, Cr adhesion amount 1 mg / m ² or more and 100 mg / m ² or less, and (Ca + SiO ₂ + PO ₄ ) / organic resin is 0.01% by weight.
_{~0.5, (Ca + SiO 2)} / method of producing a high corrosion resistant surface-treated steel sheet, wherein the PO ₄ is 0.05 to 0.8. 2. The highly corrosion-resistant surface-treated steel sheet according to claim 1, wherein the galvanized steel sheet containing 30% by weight or more of zinc is a Zn-Al alloy coated steel sheet containing 1 to 10% by weight of Al. Method. 3. The method according to claim 1, wherein the galvanized steel sheet containing 30% by weight or more of zinc is a Zn-Al alloy coated steel sheet containing 40 to 70% by weight of Al. .