JP2002225176A - Coated cold-rolled steel panel excellent in corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold-rolled coated steel panel enhanced in the corrosion resistance of an undercoating film to a steel panel, low in cost and excellent in processability. SOLUTION: An undercoating film layer containing a corrosion inhibitor (A) which is obtained by bonding corrosion suppressing calcium ions to porous silica particles by ion exchange, and a polyphosphate (B) is formed on the surface of a cold-rolled steel panel to which chemical forming treatment is applied. The undercoating film layer comprises a composition prepared by adding 2-50 pts. mass of the corrosion inhibitor (A), which is obtained by bonding corrosion suppressing calcium ions to porous silica particles by ion exchange, to 100 pts. mass of the resin component of the undercoating film layer, and adding the polyphosphate (B) to the resin component so that a ratio of the corrosion inhibitor (A) and the polyphosphate (B) is set to A/B=60/40-5/95 as a mass ratio. The addition amount of both of the corrosion inhibitor (A) and the polyphosphate (B) becomes 5-150 pts. mass with respect to 100 pts. mass of the resin component. By this constitution, the coated cold-rolled steel panel is further excellent in corrosion resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated cold-rolled steel sheet excellent in corrosion resistance and workability required for a pre-coated steel sheet used for home electric appliance parts and the like.

[0002]

2. Description of the Related Art In recent years, coated cold-rolled steel sheets applied to various home appliances and interior equipment are more economical, more productive and environmentally friendly than the post-coating method in which the steel sheets are painted after being processed. In view of this, precoated steel sheets coated by the precoat method, which has many advantages, have begun to spread widely.
Generally, as the performance required for a precoated steel sheet, importance is attached to corrosion resistance of a flat portion, a bent portion, a cut end face, a scratched portion, and the like, in addition to coating film adhesion and workability. Therefore, the pre-coated steel sheet satisfies the required performance by performing a chemical conversion treatment such as coating type chromate treatment on a zinc-based plated steel sheet and providing an undercoat coating layer containing a rust-preventive pigment on it. ing.

[0003] In recent years, the demand for cost reduction of these pre-coated steel sheets has been increasing more than before. On the other hand, up to now, there has been a change to a less expensive paint system, a thinner coating film, an improvement in production efficiency, etc. Various cost reduction measures have been taken, but many of them have already been implemented, and it is difficult to further reduce costs further. Therefore, if a cold-rolled steel sheet that does not pass through the plating process is used as a substrate, it is possible to significantly reduce costs. It was inferior.
In particular, red rust generated at the time of corrosion, unlike white rust observed in the case of a galvanized steel sheet, has a remarkable influence on the appearance of a product, particularly a home appliance called "white thing".

[0004]

On the other hand, in order to improve corrosion resistance, there is a paint in which a chromium-based rust-preventive pigment is added to an undercoat paint. The rust prevention effect on the steel sheet was not sufficient. It is also conceivable to use a paint in which zinc powder is added to the undercoat paint. However, since it is necessary to add a large amount of zinc powder, the elongation of the coating film becomes low, and the workability cannot be maintained.

[0005] The present invention has been devised to solve such a problem, and it is an object of the present invention to use a cold-rolled steel sheet as a substrate, improve the corrosion resistance of an undercoat coating on the cold-rolled steel sheet, and improve the pretreatment for coating. Accordingly, an object of the present invention is to provide a coated steel sheet having excellent corrosion resistance, low cost, and excellent workability to the market.

[0006]

The coated cold rolled steel sheet having excellent corrosion resistance according to the present invention is, for example, a cold rolled steel sheet which has been subjected to a chemical conversion treatment such as a conventional phosphate treatment or chromate treatment in order to achieve its object. An undercoat layer containing a corrosion inhibitor (A) and a polyphosphate (B) in which calcium ions for corrosion inhibition are bonded to porous silica particles by ion exchange is formed on the surface of the substrate. Things.

The undercoating layer is formed by adding 2 to 50 parts by weight of the above-mentioned corrosion inhibitor (A) and polyphosphate (B) to 100 parts by weight of the resin component of the coating film. The ratio of (A) and polyphosphate (B) is expressed by mass ratio of A
/ B = 60/40 to 5/95, and the total amount of the corrosion inhibitor (A) and the polyphosphate (B) to be 5 to 150 parts by mass with respect to 100 parts by mass of the resin component. Is preferably added.

Further, as a pretreatment of the steel sheet surface, aluminum dihydrogen phosphate is 100 to 350 g in terms of P ₂ O _5.
/ L containing an inorganic aqueous solution and a synthetic resin aqueous emulsion such that the nonvolatile content of the latter is 5 to 70% by mass with respect to the total amount of both non-volatile materials, and then applied and baked to form a chemical conversion treatment layer. By providing, the corrosion resistance is further improved.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Action) The corrosion inhibitor (A) in which calcium ions for corrosion inhibition are bonded to porous silica particles by ion exchange, captures corrosive ions such as hydrogen ions by ion exchange. Rust prevention effect is exhibited by releasing the cations bonded to. In particular, those in which the cation is calcium ion exhibit excellent corrosion resistance, and 2 to 50 parts by mass per 100 parts by mass of the resin component of the coating film
It is contained by mass. This is because if the amount is less than 2 parts by mass, the corrosion resistance is insufficient, and if the amount is more than 50 parts by mass, the effect is saturated. However, the rust-preventive effect of only the corrosion inhibitor (A) in which calcium ions for corrosion inhibition are bonded to porous silica particles by ion exchange is inferior to that of a conventional coating film containing a chromium compound rust-preventive pigment. As a result of pursuing the cause, it has been found that calcium ions bound to the silica particles are easily eluted by the water that has entered the coating film, and thus the elution is not persistent.

Therefore, as a result of studying a method for suppressing the elution of calcium ions, it was found that a polyphosphate may be added to the resin film. As a method of suppressing the elution of calcium ions, a method of coating the corrosion inhibitor with a hydrophobic film such as a silane coupling agent or silicone oil to increase the water resistance of the corrosion inhibitor can be considered. Since the pores of the porous silica particles are blocked and calcium ions are hardly eluted, the corrosion resistance is reduced.

On the other hand, in the case of polyphosphoric acid, the elution of calcium ions is considered to be suppressed by forming an ionic bond such as a chelate bond on the surface of the silica particles. Therefore, the elution of calcium ions is completely suppressed. do not do. In addition, since polyphosphate has a pH buffering action, acidification by corrosive ions such as hydrogen ions is weakened, and elution of calcium ions may be reduced.

Furthermore, polyphosphate alone is widely known as a rust-preventive pigment. Phosphate ions released from the polyphosphate react with iron as a substrate, and the surface of the cold-rolled steel sheet becomes water-resistant. A synergistic effect such as forming an excellent rust prevention film is also conceivable. As the polyphosphate, aluminum polyphosphates such as aluminum pyrophosphate, aluminum metaphosphate, and aluminum dihydrogen triphosphate are preferable because they exhibit an excellent calcium ion elution suppressing effect. In particular, polyphosphates are zinc, magnesium, titanium, calcium and other compounds, or silane coupling agents, silicon oil, etc., added to improve corrosion resistance and storage stability, or those that have been treated such as coating. good.

The amount of the polyphosphate to be added to the resin coating is determined by the ratio of the corrosion inhibitor (A) to the polyphosphate (B) in mass ratio of A
/ B = 60/40 to 5/95, and the total amount of the corrosion inhibitor (A) and the polyphosphate (B) is 5 to 150 parts by mass based on 100 parts by mass of the resin component of the coating film. The ratio A / B of the corrosion inhibitor (A) to the polyphosphate (B) is 60
When the ratio is more than / 40, the effect of suppressing the dissolution of calcium ions is reduced, and wet blisters are easily generated in the coating film.
If the ratio is less than / 95, the corrosion resistance of the coating film will be reduced due to the shortage of the corrosion inhibitor. The amount of calcium ions bound to the corrosion inhibitor is generally 3-4%. In order to use a corrosion inhibitor having a large calcium ion binding amount, the ratio of addition of the polyphosphate may be appropriately adjusted, for example, by increasing the ratio of addition of the polyphosphate and, in the opposite case, by decreasing the ratio. When the total amount of the corrosion inhibitor (A) and the polyphosphate (B) is less than 5 parts by mass with respect to 100 parts by mass of the resin component of the coating, the corrosion resistance of the coating decreases and exceeds 150 parts by weight. In addition, since the pigment concentration is too high, the processability and adhesion of the coating film decrease.

(Chemical conversion treatment) If a conventional phosphate treatment or coating type chromate treatment is applied as a surface pretreatment, a cold-rolled steel sheet having excellent corrosion resistance and workability can be obtained by forming an undercoating film having the above-mentioned pigment. be able to. Further, as a chemical conversion treatment, aluminum dihydrogen phosphate is converted to a P ₂ O ₅ conversion amount of 100.
An aqueous solution obtained by mixing an inorganic aqueous solution containing ３５０350 g / l and a synthetic resin aqueous emulsion such that the latter has a nonvolatile content of 5 to 70% by mass with respect to 100 parts by mass of the former P ₂ O ₅ component is applied. When applied and baked, the corrosion resistance is dramatically improved.

The mixed aqueous solution of the aluminum dihydrogen phosphate and the synthetic resin aqueous emulsion is described in, for example,
No. 78855, which was developed as a composition for forming an electromagnetic steel sheet insulating film, but was applied as a pretreatment for coating of the present invention by utilizing the good water resistance of aluminum dihydrogen phosphate, Corrosion resistance was significantly improved.
Aluminum dihydrogen phosphate in aqueous solution is Al ₂ O ₃ .3P
Having a composition of ₂ O ₅ · 6H ₂ O, and dried by heating Al ₂
Stabilizes as O ₃ · 3P ₂ O ₅ and binds firmly to the base steel to form a film. However, since Al ₂ O ₃ .3P ₂ O ₅ alone has a hard and brittle film, a resin was added to impart workability. This also has the effect of improving the wettability of the treatment liquid.

Examples of the synthetic resin aqueous emulsion mixed with the inorganic aqueous solution include a homopolymer of acrylic, styrene, alkyd, phenol, vinyl acetate, and epoxy monomers and an aqueous emulsion of a copolymer thereof. Etc. may be used. The addition amount of the synthetic resin emulsion mixed with the inorganic aqueous solution is such that the nonvolatile content of the synthetic resin emulsion is 5 to 70 with respect to the total non-volatile content of both.
% By mass. If the amount is less than 5% by mass, a sufficient effect on workability cannot be obtained, and if it exceeds 70% by mass, a film of aluminum dihydrogen phosphate is hardly formed. In addition, outside the above range, the storage stability of the mixed aqueous solution also deteriorates.

(Cold Rolled Steel Sheet) The cold rolled steel sheet serving as the substrate is not particularly limited as long as it is not subjected to a plating treatment and is a degreased or descaled rolled steel sheet.

(Undercoating film) The resin system used for the undercoating film is known, such as polyester, polymer polyester, epoxy, epoxy-modified polyester, epoxy-modified polymer polyester, and polyethersulfone. It is good. In addition to these rust preventives, various additives such as pigments such as titanium oxide, calcium carbonate, and silica can be added to these undercoats. The coating resin may be appropriately adjusted in molecular weight, glass transition temperature, pigment addition amount, and the like according to the use of the coated steel sheet. For example, in order to enhance workability, it is preferable to use an undercoat resin having a high elongation (about 50%) or a low glass transition temperature (about 40 ° C. or less).

(Overcoating film) Like the undercoating film, the overcoating film has a resin type, molecular weight,
The glass transition temperature, the amount of the pigment added, and the like may be appropriately adjusted, and there is no particular limitation. As the resin type, known types including polyester type, urethane type, PVC type, acrylic type, polyethersulfone type resin obtained by adding PTFE, silicon type and fluorine type can be used. 3 with intermediate coating layer
It may be a coat or one coat. The coating and baking method may be performed by a known method such as roll coating in a continuous coating facility and heating with hot air.

In the case of a coated steel sheet in which a corrosion inhibitor is added to a coating film, the appearance of the steel sheet surface is a one-coat coated steel sheet, since the corrosion inhibitor is added in the one-coat coating film. , A polyphosphate is added to the coating. In the case of a steel sheet having two or more coats on the surface side of the steel sheet, the polyphosphate is added to the coating layer to which the corrosion inhibitor is added, and is not added to a different coating layer. For example,
Since the corrosion inhibitor is usually added to the lowermost coating film on the steel sheet side, the polyphosphate is added to the lowermost coating film. However, when a corrosion inhibitor is added to the intermediate coating film or the top coating film, it can be added to those coating films. Further, when a corrosion inhibitor is also added to the back coating film when the back coating is performed, it can be added at the same time. The coating thickness is 3
Preferably, the thickness of the lowermost coating film is 1 to 15 μm as described above.

In addition, chemical conversion treatments other than chromate treatment such as a conventional phosphate treatment and a mixed aqueous solution of aluminum dihydrogen phosphate and a synthetic resin aqueous emulsion in this case are performed.
In recent years, the product configuration in the case of providing an undercoating film containing a corrosion inhibitor (A) in which calcium ions for corrosion inhibition are bonded to porous silica particles by ion exchange and a polyphosphate (B) is provided. It does not contain any chromium whose reduction is desired, and it can be said that it is an environmentally friendly product configuration.

[0022]

EXAMPLES The effects of the present invention will be specifically described below based on examples. Alkaline degreased plate thickness 0.5mm
A cold-rolled steel sheet is subjected to a chromate treatment, and a thermosetting epoxy-modified high-molecular polyester resin paint obtained by adding aluminum dihydrogen tripolyphosphate as a rust inhibitor to calcium ion-exchanged silica, which is one of the present invention, As a comparative example, a paint containing a conventional chromium-based rust preventive pigment and a commercially available zinc powder paint were applied to a dry film thickness of 5 μm,
Baked. Furthermore, a high-molecular polyester-based top coat layer was applied thereon so as to have a dry film thickness of 15 μm,
Baked. With respect to the prepared coated steel sheet, in addition to the corrosion resistance, the workability, adhesion, and boiling water resistance of the coating film performance were investigated. Further, a coated steel sheet produced by applying a mixed aqueous solution of an aqueous solution of aluminum dihydrogen phosphate synthetic resin to the chemical conversion treatment was also similarly investigated.

First, the preparation method of each sample is shown in Table 1. In Table 1, the coating type chromate and the phosphate treatment were performed by a usual method. Aluminum dihydrogen phosphate + acrylic water-based resin emulsion is made of aluminum phosphate binder (P ₂ O ₅ ; 31%, Al ₂ O ₃ ; 8.95%, B ₂
O ₃ ; 1.55%) in pure water at 250 g / l (asP
₂ O ₅ ), and a self-crosslinking acrylic soapless emulsion was added to 100 parts by mass of the former P ₂ O ₅ component so that the latter had a non-volatile content of 50 parts by mass, followed by stirring and mixing. The prepared aqueous solution was applied and baked at 250 ° C. Further, a paint obtained by adding calcium ion-exchanged silica and aluminum trihydrogen dihydrogen phosphate to 100 parts by mass of a thermosetting epoxy-modified high molecular weight polyester resin, and then baking was applied.

[0024]

Next, each of the test materials was evaluated for each of the above characteristics. Hereinafter, each evaluation method will be described. (1) Corrosion Resistance After a cross cut reaching the steel base was put in the test piece, a salt spray test in accordance with JISZ2371 was performed for 24 hours as a corrosion resistance test. After each test, the flat portion and the processed portion were observed, and the maximum red rust coating width on the lower burr end face and one side of the cross cut was measured, and these were evaluated according to the following criteria.

[Appearance of coating film] A: No abnormality. Δ: The occurrence of coating blisters or red rust is observed. X: Significant coating blisters or red rust are observed. [Maximum red rust coating width] ；; Red rust coating width 0.5 mm or less ；; Red rust coating width 0.5 mm to 1 mm or less △; Red rust coating width 1.0 mm to 1.5 mm or less ×; Red rust coating 1.5mm width

(2) Workability A 180 ° bending process was performed at 20 ° C. with a spacer having a pressure of 0.5 mm therebetween, and the processed portion was observed with a 30-fold loupe. The number of spacers was changed, and the evaluation was made based on the number of spacers at the time when cracks did not occur in the coating film. The evaluation was 0T when there was no spacer and 1T when there was no spacer.

(3) Coating Film Adhesion A taping (processing adhesion) test was conducted in which a tape was once applied to the processed portion subjected to 0T processing and peeled, and the state of coating film peeling after the tape was peeled was evaluated. The evaluation criteria were as follows. [Taping (working adhesion) test] ○: No abnormality. Δ: Partial peeling of the coating film was observed. ×: Peeling of the coating film is observed on the entire surface.

(3) Boiling Water Resistance After the test piece was immersed in boiling water for 2 hours and taken out, first, the appearance of the coating film was observed, and then a tape was once attached to the processed portion subjected to 0T processing. A taping (working adhesion) test for peeling was performed, and the peeling state of the coating film after the tape was peeled was evaluated. [Appearance of coating film] ○: No abnormality. Δ: Coating swelling or gloss finish is observed. ×: Marked coating blister or gloss finish is observed. [Taping (working adhesion) test] ○: No abnormality. Δ: Partial peeling of the coating film was observed. ×: Peeling of the coating film is observed on the entire surface.

[0030]

The above results are summarized in Table 2. When the conventional strontium chromate listed in Comparative Example 1 is used, the corrosion resistance is insufficient. In addition, in the zinc powder paint of Comparative Example 2, even when the workability was maintained by the top coat, water was inferior to the boiling water resistance of the processed part, and water penetrated from cracks generated in the undercoat, resulting in poor coat performance. There is a problem. On the other hand, in the examples of the present invention, it can be seen that all the coating film performances are maintained in a well-balanced manner. Test Nos. 5 and 6 in which a mixed aqueous solution of aluminum dihydrogen phosphate and an aqueous synthetic resin emulsion was applied to the chemical conversion treatment.
Thus, it can be confirmed that the corrosion resistance has been dramatically improved.

[0032]

As described above, according to the present invention, the undercoating layer contains a corrosion inhibitor and a polyphosphate in which calcium ions for corrosion inhibition are bonded to porous silica particles by ion exchange. By doing so, the elution of calcium ions can be suppressed, and excellent corrosion resistance can be maintained, and a cold-rolled coated steel sheet with good workability can be provided at low cost.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09D 5/00 C09D 5/00 D 5/02 5/02 5/08 5/08 7/12 7/12 201/00 201/00 C23C 22/07 C23C 22/07 F term (reference) 4D075 AE03 BB73X CA33 DB02 DC18 EA13 EB22 EB33 EB35 EB36 EB56 EC03 EC25 EC54 4F100 AA04B AA04C AA04H AA18B AA18H AA20BA AA02BAA03A BA10B CA14B DJ00B DJ00H EJ68C GB08 GB48 GB51 JB01 JB07 JJ03 JK06 JM01C YY00B 4J037 AA18 CA11 CB22 DD06 DD30 EE08 EE17 FF24 4J038 CC031 CF021 CG141 DA041 DB001 DB471 DD13 DD03 DD01 01201 DA03 EA06 EB11

Claims (3)

[Claims] Claims: 1. On the surface of a cold-rolled steel sheet subjected to a chemical conversion treatment,
Coating excellent in corrosion resistance characterized by forming an undercoating film layer containing a corrosion inhibitor (A) and a polyphosphate (B) in which calcium ions for corrosion inhibition are bonded to porous silica particles by ion exchange. Cold rolled steel sheet. 2. An undercoating film layer comprising a resin component 100
2 to 50 parts by mass of a corrosion inhibitor (A) obtained by binding calcium ions for corrosion inhibition to porous silica particles by ion exchange with respect to parts by mass, and polyphosphate (B) with a corrosion inhibitor (A) The ratio of polyphosphate (B) is expressed by mass ratio of A
/ B = 60/40 to 5/95, and the combined amount of the corrosion inhibitor (A) and the polyphosphate (B) is 5 to 150 parts by mass with respect to 100 parts by mass of the coating resin component. The coated cold-rolled steel sheet having excellent corrosion resistance according to claim 1, wherein the cold-rolled steel sheet is excellent in corrosion resistance. 3. An inorganic aqueous solution containing 100 to 350 g / l in terms of P ₂ O _{5 of} aluminum dihydrogen phosphate and a synthetic resin aqueous emulsion on the surface of a cold-rolled steel sheet, and the total amount of both non-volatile substances The coated cold-rolled steel sheet having excellent corrosion resistance according to claim 1 or 2, further comprising a chemical conversion treatment layer obtained by applying and baking an aqueous solution mixed such that the latter has a nonvolatile content of 5 to 70% by mass.