JPH0465918B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to an organic composite plated steel sheet for use in automobiles, home appliances, building materials, etc., which has excellent corrosion resistance, particularly corrosion resistance in processed parts. (Prior Art) It is well known that electrogalvanized steel sheets are widely used as surface-treated steel sheets that can be mass-produced without impairing the workability or strength of cold-rolled steel sheets. In recent years, attempts have been made to use galvanized steel sheets as anti-corrosive steel sheets for automobiles in response to salt sprayed to prevent roads from freezing during the winter in cold regions, and there is an increasing trend in the demand for corrosion resistance in harsh corrosive environments. In response to these demands for improving the corrosion resistance of galvanized steel sheets, it is known that the corrosion resistance can be improved by increasing the amount of zinc plating (adhesion amount). Many alloy plating methods have been proposed. Many of these are
It contains iron group elements such as Fe, Ni, and Co as alloying components. These zinc-iron group electroplated steel sheets are characterized by excellent corrosion resistance either unpainted or after painting, and are industrially produced and put to practical use, but it is strongly desired to further improve their corrosion resistance. In response to this demand, organic composite plated steel sheets have been developed for automotive applications, in which a zinc-based plated steel sheet is subjected to chromate treatment and an organic film is coated on top of the chromate treatment. For such organic composite plated steel sheets, progress has been made mainly in improving the coating composition that forms the top layer organic film, but it has not yet fully satisfied the required qualities in terms of corrosion resistance, press workability, spot weldability, etc. Nakatsuta. In other words, those coated with zinc-rich paint have poor press workability, and have insufficient corrosion resistance and weldability, while those coated with conductive pigment-containing paint have improved press workability and weldability, but are still insufficient. It wasn't. (Problem to be solved by the invention) This is a relatively thick organic composite steel sheet with an organic coating thickness of more than 5μ, but recently there has been an increasing trend toward thinner coatings from the viewpoint of press workability and weldability. , a thin film type organic composite plated steel sheet with a film thickness of 5 μm or less is disclosed. In the case of such a thin film type, attempts are being made to improve the corrosion resistance by disposing a rust preventive pigment in the organic film. For example, JP-A-59-162278 discloses an organic film containing a water-dispersible emulsion resin containing a chromium compound as a rust-preventing pigment, while JP-A-60-50181 discloses an organic film containing silica as a rust-preventive pigment. is used, but its corrosion resistance is not sufficient. Corrosion resistance of organic composite plated steel sheets originally depended largely on the organic coating, but as the films became thinner as described above from the viewpoint of press workability and weldability, it became possible to improve the corrosion resistance of the plating layer. It becomes necessary. That is, Zn plating, Zn-Ni, Zn-Fe alloy plating, etc. have been disclosed as the base plating for the above-mentioned organic composite plated steel sheet, but in the thin film type, when press working is performed, the organic film layer As the steel becomes thinner, and if there is a flaw or crack, the plating layer or steel base is partially exposed, so the corrosion resistance of the plating layer becomes more important, but conventional base plating does not have sufficient corrosion resistance. In particular, the corrosion resistance after processing is unreliable. The present invention solves the above problems and provides an organic composite plated steel sheet with improved corrosion resistance, particularly corrosion resistance after working. (Means for Solving the Problems) The present invention provides a Zn-Cr-iron group metal composite electrolyte that can form a corrosion product having an excellent protective effect when a defective part of a coating film or a processed part corrodes. By using the plating layer as the base plating layer and forming an appropriate amount of chromate film and organic film on the upper layer, corrosion resistance, especially corrosion resistance of processed parts, is dramatically improved, and the organic composite material has excellent workability and weldability. We provide steel plates with attached parts. The gist of the present invention is that 1 to 30% by weight of Cr and 1 to 30% of iron group metals are added to the surface of the steel plate.
Form a composite electroplated layer consisting of 10% by weight, 0.1 to 10% by weight of oxide fine particles, 0.001 to 5% by weight of cationic polymer, and the balance Zn, and a chromate film on the top layer with a total Cr content of 10 to 150mg/m ² An organic composite plated steel sheet with excellent corrosion resistance characterized by forming an organic film of 0.3 to 3 μm on the upper layer.
The above-mentioned organic composite plated steel sheet with excellent corrosion resistance consisting of one or more types of oxides of W, wherein the cationic polymer in the composite electroplated layer is 4
This organic composite plated steel sheet is made of grade amine polymer and has excellent corrosion resistance. (Function) First, the Zn-Cr-iron group metal composite electroplated layer for base plating will be described. Cr is not passivated by eutectoid with Zn,
It maintains an active state and, together with Zn, participates in the sacrificial anticorrosion effect on the steel substrate. Furthermore, since the corrosion products of Cr are poorly soluble and deposit a protective film in localized areas where corrosion is progressing, corrosion resistance is extremely high. When applied as the base plating layer of an organic composite plated steel sheet, the formation of this protective film exhibits extremely high corrosion resistance due to the synergistic effect with the organic film. That is, when exposed to a corrosive environment, the underlying plating layer first undergoes corrosion through defects such as pinholes in the organic film. Cracks occur in the plating layer due to corrosion, and as these cracks propagate, corrosion spreads beneath the organic film, and eventually the steel base is corroded and red rust occurs. Corrosion products of Cr fill the cracks by the so-called rust clogging effect.
Since it prevents the entry of corrosive factors such as water, oxygen, and chlorine ions, it acts as a barrier together with the organic film to prevent the progress of corrosion. Molded products processed by pressing, etc. not only have thinner coatings in the processed areas, but also have flaws and cracks that partially expose the base plated layer and steel base, making it difficult to use conventional methods. A fatal flaw in organic composite plated steel sheets is that the barrier effect of the organic film is diminished. The Zn-Cr-iron group metal composite plating layer has the effect of depositing a protective film and stopping corrosion even in such processed parts. This effect is due to the Zn, Zn-
This cannot be expected with Ni and Ze-Fe plated layers. especially,
When the organic film is thin, it inherently has many coating defects such as pinholes, and in processed areas, the film becomes even thinner, reducing its barrier effect, and if it becomes scratched or cracked, it can easily cause a plated layer or rust. Since the base material is exposed, the action of the Zn-Cr-iron group metal composite plating layer is extremely effective in improving the corrosion resistance not only of the processed parts but also of the unprocessed parts. The Cr content of the Zn-Cr-iron group metal composite plating layer is 1 to 30% by weight. If it is less than 1% by weight, it is not effective in improving corrosion resistance. When the amount exceeds 5% by weight, the occurrence of red rust is greatly suppressed in salt spray tests, etc., and an epoch-making effect appears. In addition, the Cr content
If it exceeds 30% by weight, corrosion resistance is good, but even with the eutectoid effect of the cationic polymer described below, it is difficult to prevent the deterioration of so-called powdering properties in which the plating layer peels off during processing such as press processing. I don't get it,
It is difficult to apply in practice. In addition, from the viewpoint of corrosion resistance and processability, the Cr content is more preferably 5 to 20% by weight. Iron group metals refer to Ni, Fe, and Co. By containing iron group metals, iron group metal ions such as Ni ²⁺ , Fe ²⁺ , and Co ²⁺ are eutectoid in the plating layer, thereby improving corrosion resistance and weldability. The corrosion resistance is presumed to be due to the incorporation of iron group metals into the corrosion products of Cr, thereby further densifying and stabilizing the corrosion products. In terms of weldability, Zn-Cr-iron group metal composite plating layers have iron group metals that increase the electrical resistance of the plating layer, making it easier to generate heat, and because the plating layer becomes hard, it is less likely to be heated due to the pressure of the electrode tip. The deformation of the attached layer becomes smaller,
It is thought that the current tends to concentrate in the welded part. In this case, the content of iron group metals is 1 to 10% by weight. If the content of iron group metals is less than 1% by weight, the effect of adding iron group metals will not be noticeable, and if it exceeds 10% by weight, the properties of iron group metals will become stronger and red rust will easily occur in processed parts. Iron group metals have the advantage that these ions are adsorbed to oxide fine particles in a plating bath, facilitating eutectoid deposition of oxide fine particles. However, as the total amount of Cr and iron group metals increases, the workability deteriorates.
The total amount of Cr and iron group metal is preferably 30% by weight or less. One kind of iron group metal may be used, or two or more kinds thereof may be contained at the same time, but the inclusion of Ni is particularly effective in improving corrosion resistance. The oxide particles penetrate into the corrosion products,
By strongly bonding with oxygen, it further improves the stabilization of corrosion products of Zn-Cr-iron group metals, which have a protective effect, and the oxide fine particles themselves exert a barrier effect against corrosion factors. It is effective in improving the corrosion resistance of organic composite plated steel sheets, especially in processed parts. The content of oxide fine particles is 0.1 to 10% by weight. If it is less than 0.1% by weight, it is not effective in improving corrosion resistance, and if it exceeds 10% by weight, workability deteriorates. From the viewpoint of corrosion resistance and processability, 0.1 to 5% by weight is more preferable. There are various types of oxide fine particles, such as metal and metalloid oxides, but they include Si, Al, Zr, Ti, Cr,
Oxides of Mo and W are particularly preferred, and these may be used alone or in combination of two or more. The average particle size is preferably 1 μm or less, and if the particle size exceeds 1 μm, it is difficult to eutectoid in the plating layer. Cationic polymer is a precipitation accelerator for Cr,
In addition, by eutectoiding a small amount of Cr in the plating layer, it improves powdering resistance during press working. This eutectoid effect of cationic polymers is
It is presumed that the purpose is to prevent Cr ions from inhibiting uniform electrodeposition growth of Zn and resulting in a flecked structure lacking uniformity and smoothness. That is, through the eutectoid cationic polymer,
It is thought that a dense plating layer is formed in which Zn, Cr, and iron group metals are uniformly mixed or alloyed.
The content of the cationic polymer is 0.001 to 5% by weight. If the content is less than 0.001% by weight, the effect on the above-mentioned powdering resistance is poor, and if the content exceeds 5% by weight, it is not only difficult to obtain even if the concentration of the cationic polymer in the plating bath is increased, but also if a large amount is eutectoid. This causes a decrease in plating adhesion. From the viewpoint of powdering resistance, it is desirable to eutectoid the cationic polymer at a content of 1/1000 or more of the Cr content. As the water-soluble cationic polymer used in the present invention, a quaternary amine polymer is effective, and the molecular weight is preferably 10 ³ to 10 ⁶ in this case.
Among the following amine polymers, polyamine sulfone (PAS) and polyamine (PA) are the most effective as Cr precipitation promoters. It is thought that the adsorption effect by the amine group and the bond between the sulfone group and the metal ion or metal contribute. Basically, the following quaternary amine salts (ammonium salts) Or it is composed of a copolymer. Some compounds will be specifically listed below. Examples include polymers obtained from diallylamine. R ¹ and R ² represent an alkyl group, X is Cl ^- ,
It represents ^an anion _{of HSO4-} ^, _H2PO4- ^, R- _SO3- (R is a _C1 - _C4 alkyl group), ^and _NO3- . Another example is a polymer synthesized from vinylbenzyl. R ₁ , R ₂ , R ₃ represent hydrocarbons,
X represents an anion of Cl ^- , HSO ₄ ^- , H ₂ PO ₄ ^- , R-SO ₃ ^- , NO ₃ ^- . Alternatively, allylamine polymer can be mentioned.
R ₁ , R ₂ , R ₃ represent hydrocarbons, X is Cl ^- ,
It represents an anion of HSO ₄ ^- , H ₂ PO ₄ ^- , R-SO ₃ ^- , NO ₃ ^- . In addition, polymers of primary, secondary, and tertiary amines are also effective as Cr precipitation promoters, although they are not as effective as the above-mentioned quaternary amine polymers. The amount of plating deposited is 5 to 50 g/m ² to ensure sufficient corrosion resistance. In addition to Zn, Cr, iron group metals, oxide fine particles, and cationic polymers, Pb, Sn,
Even if a small amount of Ag, In, Bi, Cu, Sb, As, Na, P, S, etc. inevitably eutectoid, the effect of the base plating layer does not essentially change. Next, there is a method for producing a Zn-Cr-iron group metal composite electroplated layer, in which Zn ²⁺ ions, Cr ³⁺ ions,
Iron group metal ions such as Ni ²⁺ , Fe ²⁺ , Co ²⁺ ,
Oxide fine particles such as SiO ₂ , TiO ₂ , Al ₂ O ₃ and
PH0.5-3 containing 0.01-20g/water-soluble cationic polymer such as a polymer of quaternary amine such as PAS,
20A/dm ² using an acidic plating bath with a bath temperature of 40 to 70℃
All you need to do is electroplating. During the pampering bath,
Furthermore, it is effective to add salts such as Na ⁺ , K ⁺ , NH ₄ ⁺ ions, etc. to increase the conductivity of the bath. The chromate layer applied on the plating layer has the effect of ensuring adhesion with the organic film. Since the Zn-Cr-iron group metal composite plating layer has good reactivity with acidic treatment solutions consisting of Cr ⁺⁶ and/or Cr ⁺³ , it has been widely used in conventional coating-type chromate treatment, reactive chromate treatment, and electrolytic treatment. Any type chromate treatment etc. can be applied. For coating type and reactive chromate treatment,
In addition to Cr ⁺⁶ and Cr ⁺³ , inorganic colloids, acids such as phosphoric acid, and fluorides may be added, or water-soluble or emulsion type organic resins may be added. For example, as a treatment liquid containing phosphoric acid and fluoride, chromic acid 30g/, phosphoric acid 10g/, titanium potassium fluoride 4g/, sodium fluoride 0.5g/
, as a treatment liquid containing silica, chromic acid 50
g/(trivalent chromium 40%), SiO ₂ 100g/
There is. Examples of inorganic colloids include
Phosphoric acid that reacts with colloids such as SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , oxygen acids such as molybtic acid, tungstic acid, vanadate and their salts, or zinc in plating to form poorly soluble salts. , phosphoric acids such as polyphosphoric acid, or silicides, titanium fluorides, phosphates, etc. that form poorly soluble salts through reactions such as hydrolysis.
These colloids are effective in fixing small amounts of hexavalent chromium in the chromate film. In addition, phosphoric acids such as phosphoric acid and fluorides are particularly effective in promoting the reaction between the plating layer and chromate. The amount of these inorganic colloids added varies depending on the type at the time of addition, but is, for example, 1 to 200 g/for phosphoric acids and 1 to 800 g/ for SiO ₂ . In some cases, an organic resin that can be stably mixed with chromate such as acrylic resin may be added. Electrolytic chromate treatments include those that add sulfuric acid, phosphoric acid, halogen ions, etc. in addition to chromic acid, those that add inorganic colloids such as SiO ₂ and Al ₂ O ₃ , and those that add cations such as Co and Mg. Additives can also be applied. Usually, cathodic electrolysis is applied, but anodic electrolysis and alternating current electrolysis can also be added. The amount of chromate film deposited is 10 to 10% as the total Cr amount.
150mg/ ^m2 . If it is less than 10 mg/m ² , the adhesion of the organic film is insufficient, and if it exceeds 150 mg/m ² , weldability and press workability deteriorate, which is not preferred in practice. A more preferable range is 20 to 100 as the total Cr content.
mg/ ^m2 . In addition, in order to avoid contamination of chemical conversion treatment liquids, etc. by chromium eluted from the chromate film and the associated complication of work such as wastewater treatment, it is necessary to use a poorly soluble chromate film with a water-soluble content of 5% or less. Electrolytic chromate treatment is suitable for this purpose. An organic film is applied on top of this chromate film. The thickness of the organic film is 0.3 to 3μ. If it is less than 0.3μ, corrosion resistance will not be sufficient, and if it exceeds 3μ, weldability and press workability may deteriorate. A more preferable range is 0.5 to 2μ. The organic coating may be either solvent-based or water-soluble, and may be made of, for example, epoxy, acrylic, polyester, urethane, acrylic olefin, or copolymer derivatives thereof. In addition, various additives such as rust-preventing pigments such as SiO ₂ and BaCrO ₄ , a hardening agent in the case of a bake-curable film, or a lubricant to further improve press workability may be added. An example of the most preferable organic coating that can be applied in the present invention is listed below. Main resin: Bisphenol type epoxy resin (average molecular weight: 300 to 100,000) Content in film: 30% by weight or more Curing agent: Block polyisocyanate compound Weight ratio of 1/10 to 20/10 to the main resin Rust preventive pigment: Dry Silica (average primary particle size 1~
100mμ) Content in film 5-50% by weight Lubricant: Polyethylene wax content in film 0.1
~10% by weight Solvent: Ketone organic solvent The coating method may be any known method such as roll coating, spray coating, curtain flow coating, etc. The structure of the present invention does not necessarily have to be used on both sides of a steel plate, but can be applied to only one side depending on the application, and the other side may be left as a rust plate surface or Zn-Cr-
Only an iron group metal composite plating layer may be used. The base steel sheet to which the present invention is applied is usually a mild steel sheet that has been subjected to dull finish rolling, but it can also be a mild steel sheet that has been brightly rolled, a high tensile strength steel sheet that contains a large amount of Mn, S, P, etc. as steel components, Cr, Cu, Ni, etc. It is also applicable to highly corrosion-resistant steel plates that contain a large amount of phosphorus, phosphorus, etc. and have a low corrosion rate. (Example) The processing conditions of the example will be described below. [1] Plating conditions A cold-rolled steel sheet with a thickness of 0.8 mm was degreased with alkaline, and
After pickling with % sulfuric acid, washing with water, electroplating was performed under the following conditions. The liquid flow rate was 90 m/min by pump stirring, the distance between poles was 10 mm, and the bath temperature was 60°C.
A sulfuric acid acid bath of pH 2 was used. The composition of the plating bath is
Zn ²⁺ ion 70g/, Cr ³⁺ ion 1~30g/
, 5 to 50 g of divalent ions of iron group metals, oxide fine particles (SiO ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ have an average particle size of 0.02 to 0.05 μm, Cr ₂ O ₃ , WO ₃ have an average particle size of 10 to 100 g of particle size 0.1 to 0.5 μ), 0.01 to 20 g of cationic polymer (polyamine polymer (PA) with a molecular weight of 50,000, or polyamine sulfone polymer (PAS) with a molecular weight of 100,000), Na ⁺
The content of Cr, iron group metal, oxide fine particles, and cationic polymer was controlled by the respective additive amounts and current density, and the plating amount was 20 g/m ² . [2] Chromate treatment Electrolytic chromate Chromic acid 30g/, sulfuric acid 0.2g/, bath temperature
Current density 10A/dm ² using treatment solution at 40℃
A plated plate was subjected to cathode electrolysis, washed with water, and dried.
The amount of chromate deposited was adjusted by the amount of coulombs. Coating type chromate Chromic acid 50g/(including Cr ³⁺ 40%), SiO ₂
After immersing the plated plate in a treatment solution containing 100 g of colloid and a bath temperature of 40°C and performing air wiping,
It was dried at 100°C for 1 minute. The amount of chromate deposited was adjusted by the dilution rate of the treatment solution and the pressure of the air wipe. Reactive chromate chromic acid 50g/, phosphoric acid 10g/,
NaF0.5g/, K ₂ TiF ₆ 4g/, bath temperature 60℃
Spray the treatment solution on the plating board, wash it with water, and then
Dry at °C. The amount of chromate deposited was adjusted by the dilution rate of the treatment solution and the spray time. [3] Organic film coating conditions Only the main resin systems are listed in Table 1, but for each resin system, rust preventive pigments such as SiO ₂ , curing agents, catalysts, lubricants, water leakage modifiers, etc. A paint made by blending the following was used. It was applied to a chromate-treated taming plate using a roll coater and baked to dry. Baking conditions depended on the resin system, but the final board temperature was 100 to 200°C. The structure and corrosion resistance, workability, and weldability evaluation results of the organic composite plated steel sheet manufactured in this way were evaluated in the first
Shown in the table. The evaluation method is as follows. (a) Flat plate corrosion resistance

[Table] The above cycle was considered as one cycle, and evaluation was made based on the amount of plate thickness reduction after 3000 cycles. 0.1mm or less: ◎ More than 0.1mm to 0.2mm or less: ○ More than 0.2mm to 0.3mm or less: △ More than 0.3mm: × (b) Corrosion resistance of processed parts Salt water spray test (JIS Z2371) after cylindrical press forming of 50mmφ x 25mmH The test was carried out for 3,000 hours and evaluated based on the area of red rust on the processed parts. 1% or less: ◎ More than 1% to less than 5%: ○ More than 5% to less than 10%: △ More than 10%: × (c) Press workability After performing cylindrical press forming of 50φ x 25H, tape the processed surface. Peeling was performed and the amount of weight loss was evaluated. 2 mg or less: ◎ More than 2 mg to 5 mg or less: ○ More than 5 mg to 8 mg: △ More than 8 mg: × (d) Spot weldability The welding conditions are as follows. Current: 8KA Number of cycles: 10 cycles Pressure force: 200Kg Welding tip shape: As shown in Figure 1 (A is 12mmφ,
B is 6mmφ and θ is 30°). Continuous score of 5,000 points or more: ◎ 4,000 points or more to less than 5,000 points: ○ 3,000 points or more to less than 4,000 points: △ Less than 3,000 points: × First, regarding the comparative example, No. 17 is a ferrous metal during base plating. (Ni) content is too high, so No.
No. 18 contains no oxide fine particles in the base plating, No. 20 has too thin an organic film, and No. 21 does not contain Cr in the base plating, so the corrosion resistance is poor. Moreover, since the amount of chromate film in No. 19 was too small, the press workability was poor, and the corrosion resistance of the processed parts was also reduced accordingly. In contrast, all of the invention examples No. 1 to No. 16 had good corrosion resistance, workability, and weldability.

[Table] (Effects of the Invention) As explained above, the organic composite plated steel sheet of the present invention uses Zn containing oxide fine particles as the base plating.
- By using a Cr-ferrous metal composite electroplated layer, the corrosion resistance, which was a problem with conventional thin film type organic composite plated steel sheets, has been greatly improved, especially the corrosion resistance of processed parts, Because it has excellent press workability and spot weldability, it can be widely used in automobiles, home appliances, building materials, etc. that require a high level of quality.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the shape of a welding tip used to evaluate spot weldability in Examples.

Claims (1)

[Claims] 1. On the surface of the steel plate, 1 to 30% by weight of Cr, iron group metal 1
~10% by weight, 0.1 to 10% by weight of oxide fine particles, 0.001 to 5% by weight of cationic polymer, and the balance Zn. A chromate film is formed on top of this layer with a total Cr content of 10 to 150mg/m. ² , and an organic composite plated steel sheet with excellent corrosion resistance, which is characterized by forming an organic film of 0.3 to 3 μm on the upper layer. 2 Oxide fine particles include Si, Al, Zr, Ti, Cr,
An organic composite plated steel sheet with excellent corrosion resistance as claimed in claim 1, comprising one or more of Mo and W oxides. 3 The cationic polymer in the composite electroplating layer is
An organic composite plated steel sheet with excellent corrosion resistance according to claim 1, which is a quaternary amine polymer.