JPH0387399A - Organic composite plated steel sheet excellent in corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain an organic composite plated steel sheet for rust prevention excellent in corrosion resistance by forming a plating layer having a specific composition consisting of Cr, cation polymer, and Zn on the surface of a steel sheet and then forming a chromate film and an organic film on the above. CONSTITUTION:A composite electroplating layer having a composition consisting of, by weight, 1-30% Cr, 0.001-5% cation polymer, and the balance Zn is formed on the surface of a steel sheet. At this time, quaternary amine polymer, particularly polyamine sulfone and sulfone, can be suitably used as the above cation polymer, and about 10<3>-10<6> molecular weight is preferred. Further, as the coating weight of the above plating layer, about 5-50g/m<2> suffices. Subsequently, a chromate film is formed on the above by 10-150mg/m<2> total Cr content, and further, an organic film is formed on the above to 0.3-3mu thickness. As the above organic film, films of epoxy, acryl, polyester, urethane, acryl olefin, etc., can be used. By this method, the organic composite plated steel sheet excellent in corrosion resistance, particularly in corrosion resistance in a worked part, and also having superior workability and weldability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rust-preventing organic composite plated steel sheet that is used in automobiles, home appliances, building materials, etc. and has excellent corrosion resistance, particularly in processed parts.

(Prior Art) It is well known that electrogalvanized steel sheets are already widely used as surface-treated steel sheets that can be mass-produced without impairing the corrosion resistance of cold-rolled steel sheets, the corrosion resistance after painting, and workability.

However, in recent years, attempts have been made to use galvanized steel sheets as anti-corrosive steel sheets for automobiles in response to the salt sprayed on roads in winter to prevent roads from freezing in cold regions, and the demand for corrosion resistance in harsh corrosive environments is increasing.

In response to these demands for improving the corrosion resistance of galvanized steel sheets, it is known that corrosion resistance can be improved by increasing the amount of zinc plating (adhesion amount). Many have been proposed.

Many of these contain iron group elements such as Fe, Ni, and Go as alloy 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 into 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.

In such organic composite plated steel sheets, improvements have been made mainly to the coating composition that forms the top organic film, but corrosion resistance and press workability have not been improved.

It did not sufficiently meet the required quality in terms of spot weldability, etc.

In other words, those coated with zinc-rich paint have poor press workability, and have insufficient corrosion resistance and weldability, while those coated with paint containing conductive pigments have improved press workability and weldability, but still have poor press workability. It wasn't enough.

(Problem to be solved by the invention) These are relatively thick organic composite steel sheets with an organic coating thickness of more than 5μ, but recently there has been a growing 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 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-preventing pigment. is used, but its corrosion resistance is not sufficient.

In organic composite coated steel sheets, their corrosion resistance was originally largely due to 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 by improving the coating layer. It becomes necessary.

That is, as the base plating for the above-mentioned organic composite plated steel sheet,
Zn plating, Zn-Ni, Zn-Fe alloy plating, etc. are disclosed, but in the thin film type, the organic film layer becomes even thinner when pressed, and if flaws or cracks occur, the plating may be partially removed. Because the layers and steel substrate are exposed,
This depends largely on the corrosion resistance of the plating layer, but conventional base plating does not have sufficient corrosion resistance, and especially 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 is directed to Z, which is capable of forming corrosion products having an excellent protective effect when a coating film defect or a processed part corrodes.
By using the n-Cr composite 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 the corrosion resistance of processed parts, is dramatically improved, and it also has excellent workability and weldability. Provides organic composite plated steel sheets.

The gist of the present invention is to add 1 to 30% by weight of Cr on the surface of the steel plate.

A composite electroplated layer is formed with a cationic polymer o, ooi ~ 5% by weight and the balance is Zn, a chromate film with a total Cr content of 10 to 150 cm/bo is formed on the top layer, and an organic film is further formed on the top layer. This is an organic composite plated steel sheet with excellent corrosion resistance, characterized by a 0.3 to 3 μm diameter.

(Function) First, the Zn-Cr based composite electroplating layer as the base plating will be described.

Cr does not become passivated by eutectoiding with Zn, but maintains an active state and participates in the sacrificial anticorrosion effect on the steel base together with Zn. Furthermore, the corrosion products of Cr are poorly soluble;
A protective film is deposited on the areas where corrosion is progressing, resulting in extremely high corrosion resistance.

As a 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, the corrosion spreads beneath the organic coating, and eventually the steel base is corroded and red rust occurs. Corrosion products of Cr fill cracks and prevent corrosion factors such as water, oxygen, and chlorine ions from entering through a so-called rust-filling action, and thus act as a barrier together with the organic film to prevent the progress of corrosion.

In molded products that have been processed by pressing, etc., not only the thickness of the processed part becomes thinner, but also the underlying plating layer and steel base are partially exposed due to scratches and scratches.
A fatal flaw in conventional organic composite plated steel sheets is that the barrier effect of the organic film is diminished. Zn-C
The r-based composite plating layer has the effect of depositing a protective film and stopping corrosion even in such processed parts. This effect occurs when Zn, Zn Ni, and Zn, which have been conventionally used as the base plating layer of organic composite plated steel sheets,
-Cannot be expected with Fe plating layer. In particular, when the organic film is thin, there are inherently many paint film defects such as pinholes, and the film becomes even thinner in processed areas, reducing the barrier effect, and when scratches and cracks occur, the plating layer is easily damaged. Since the steel base is exposed, the effect of the Zn-Cr 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 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. In addition, when the Cr content exceeds 30% by weight, although corrosion resistance is good, even with the effect of the eutectoid of the cationic polymer described below, the so-called powdering property deteriorates, in which the plating layer peels off during processing such as press working. can be prevented,
It is difficult to apply in practice.

In addition, from the viewpoint of corrosion resistance, the Cr content is more preferably 5 to 30% by weight.

The cationic polymer is a precipitation accelerator for Cr, and
At the same time, by eutectoiding in a small amount within the plating layer, powdering resistance during press working is improved.

It is presumed that the eutectoid effect of the cationic polymer is that Cr ions inhibit the uniform electrodeposition growth of Zn and prevent a plated structure lacking in uniformity and smoothness. . That is, it is thought that a dense plating layer in which Zn and Cr are uniformly mixed or alloyed is formed through the eutectoid cationic polymer. 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 cationic polymer in the plating bath is increased, but also a large amount of powdering resistance is obtained. Analysis causes a decrease in plating adhesion. From the viewpoint of powdering resistance, the Cr content is 1
It is sufficient that the cationic polymer is eutectoid at a content of /1000 or more.

As the water-soluble cationic polymer used in the present invention, a quaternary agon polymer is effective, and the molecular weight is:
In this case, 10' to 106 is desirable.

Among the following amine polymers, polyamine sulfone (P
AS) and polyamine (1'A) 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 copolymers.

Some compounds will be specifically listed below.

One example is a polymer derived from diaryl.

R,, R2 represents a lower alkyl group or an alkyl group, and X is C1-11504-, II□+'04-, R-5O1
-(R is 01-C4 alkyl, 49) represents an anion of NO, -.

R.

2 Or polymers synthesized from vinylbenzyl. R1, R2, Ri represent hydrocarbons, X is l-1
11SO, -1l12PO4-, R-3O+-, NO:
Indicates the anion of l-.

→C1l□-C11-)7- +C.

1(2 1 (3 Alternatively, allylamine polymer can be mentioned.

R+, Rz, R3 represent hydrocarbon, X is CZ-1
IISO411□ Shows the anions of PO4-, R-SO3-, and NO3-.

1011□-C11-+- In addition, polymers of 1, 2, and 3-class amines are also effective as Cr precipitation promoters, although they are not as effective as the above-mentioned quaternary amine polymers.

A coating weight of 5 to 50 g/nT can ensure sufficient corrosion resistance. In addition, Zn, Cr, cationic polymers also include Pb, Sn, 8g, In,
Bi, Cu, Sb, 8S, 8L.

Even if Ti, Na, P, S, etc. inevitably eutectoid in amounts, the effect of the base plating layer remains essentially the same.

Next, regarding a method for producing a Zn-Cr composite electroplating layer, a water-soluble cationic polymer such as a polymer of Zn'' ions, Cr'' ions, and a quaternary amine such as PAS is mixed with 0.00% of a water-soluble cationic polymer such as a polymer of Zn" ions, Cr" ions, and a quaternary amine such as PAS.
01-20 g/f including pllo, 5-3, bath temperature 4
20A/dnf using acidic plating bath at 0-70°C
Electroplating can be performed using the above steps. Oxide particles such as SiO□, TiOz, AN 203, etc. may be added to the plating bath as necessary. Furthermore, Na″″, ni′″,
Adding salts such as NH4'' ions is effective in increasing the conductivity of the bath.

The chromate layer applied on the plating layer has the effect of ensuring adhesion with the organic film.

The Zn-Cr based composite plating layer contains Cr” and or C
Since the reactivity with the acidic treatment liquid consisting of r+'' is good, any of the conventionally known coating type chromate treatment, reaction type chromate treatment, electrolytic type chromate treatment, etc. can be applied.

As a coating type 1 reaction type chromate treatment, Cr"6.
In addition to Cr+:l, it is possible to add inorganic colloids, acids such as phosphoric acid, fluorides, or water-soluble or emulsion type organic resins.

For example, a treatment solution containing phosphoric acid and a compound includes 30 g/l of chromic acid, 10 g/f of phosphoric acid, 4 g/l of potassium titanium fluoride, and 0.5 g/l of sodium fluoride.
As a treatment liquid containing g/11 silica, chromic acid 50
g/l (including 40% trivalent chromium), Si0□1
00g/j! There is. Examples of inorganic colloids include SiO□.

A N 203. Colloids such as TtOz and ZrO, oxygen acids and their salts such as molybdic acid, tungstic acid, and vanadate, or phosphoric acids such as phosphoric acid and polyphosphoric acid that react with zinc in plating to form poorly soluble salts, or It contains one or more types of silicides, titanium oxides, phosphates, etc. that produce 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 accelerating the reaction between the plating layer and chromate. The amount of these inorganic colloids added varies depending on the type of additive, but for example, for phosphoric acids, it is 1 to 200 g/
1~800g/jl for 5ift! It is.

In some cases, an organic resin that can be stably mixed with chromate such as acrylic resin may be added.

For electrolytic chromate treatment, in addition to chromic acid, sulfuric acid,
Those to which phosphoric acid, halogen ions, etc. are added, those to which inorganic colloids such as 5tOz and AfzOz are added, and those to which cations such as Co and Mg are added are also applicable. 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 150 as the total Cr amount.
■/rrf. If it is less than 1O 2 /bo, the adhesion of the organic film will be insufficient, and if it exceeds 150 /bo, weldability and press workability will deteriorate, which is not preferred in practice. A more preferable range is 20 to 100 .mu./bo as total Cr1i.

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
．． It is 5 to 2μ.

The organic film 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 anticorrosion pigments such as 5iOz and BaCrO4, curing agents for bake-hardening films, and lubricants to further improve press workability may be added. An example of an organic film that can be applied in the present invention is given below.

Main resin: Bisphenol type epoxy resin (average molecular weight =
300 to 100,000) Content in the film: 30% by weight or more Curing agent: Niblock polyisocyanate compound Weight ratio to the main resin: 1/10 to 20/10 Antirust pigment: Nidry silica (average primary particle size: 1 to 100 mμ) Contained in the film: Lubricant: Content in polyethylene wax film 0.1 to 10% by weight Solvent: Ketone diameter Organic solvent The coating method may be any known method such as roll coating, spray coating, curtain flow coating, etc. Good too.

The structure of the present invention does not necessarily need to be applied to both sides of a steel plate, but may be applied to only one side depending on the application, and the other side may be left as a steel plate surface or only a Zn-Cr composite plating layer may be used.

The base steel plate to which the present invention is applied is usually a mild steel plate that has been subjected to dull finish rolling, but it may also be a mild steel plate that has been bright finish rolled, a high tensile strength steel plate that contains a large amount of Mn, S, P, etc. as steel components, Cr, Cu, Ni. It can also be applied to highly corrosion-resistant steel plates that contain a large amount of P, etc. and have a low corrosion rate.

(Example) The processing conditions of the examples are described below.

(1) Plating conditions Cold rolled steel sheets were degreased with alkali, pickled with 5% sulfuric acid, washed with water, and electroplated under the following conditions. A sulfuric acid acid bath with a bath temperature of 60"C and PO2 was used, with a liquid flow rate of 90 m/n + in and a distance between poles of 10 mm by stirring with a pump. The plating bath composition was 70 g of Zn"+ ions/42, Cr"
Ion l~30g/l, cationic polymer (polyamine polymer (PA) with a molecular weight of 50,000, or polyamine sulfone polymer (PAS) with a molecular weight of 1.1 million) 0.0
1-20 g/1, Na” ion 16 g/l
The Cr and cationic polymer 〇 contents were controlled by the respective additive amounts and current density, and the plating deposition amount was 20 g/rrr.

(2) Chromate treatment■ Electrolytic chromate Chromic acid 30 g/ffi, sulfuric acid 0.2 g/C using a treatment solution with a bath temperature of 40"C, current density 10A/dr
The plated plate was subjected to cathodic electrolysis using rr, washed with water, and dried.

The amount of chromate deposited was adjusted by the amount of coulombs.

■ Sprayed chromate Chromic acid 50g/ff1 (of which Cr"4Q%).

After immersing the plated plate in a treatment solution containing 100 g/f of Si0g colloid and having 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 50 g/i! ,, Phosphoric acid Log//
! , NaFO, 5g/l, KzTiF6
A treatment solution of 4 g/l and a bath temperature of 60°C was sprayed onto the plated plate, washed with water, and then dried at 60''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 Table 1 lists only the main resin systems, but for each resin system, apply rust preventive pigments such as Sin, curing agents, catalysts, lubricants, water wettability modifiers, etc. A mixture of the two was used as a paint. It was applied to a chromate-treated plated plate using a roll coater and baked and dried.

Baking conditions depend on the resin system, but the final plate temperature is 100-2.
The temperature was 00°C.

Table 1 shows the structure of the organic composite plated steel sheet produced in this way and the evaluation results of corrosion resistance, workability, and weldability. The evaluation method is as follows.

(a) Raw corrosion resistance The above cycle was taken as one cycle, and evaluation was made based on the amount of plate thickness reduction after 200 cycles.

0.1mm or less: ◎ More than 0.1nu ~ 0.2- or less More than 200.2mm ~ 0.31m11 or less: Δ More than 0.3mm: × (b) Processed part corrosion resistance After cylindrical press molding of 50mmφX25nnnH, salt water A spray test (JIS Z2371) was conducted for 2000 hours, and evaluation was made based on the area of red rust on the processed parts.

1% or less: ◎ More than 1% to less than 5%: 0 More than 5% to less than 10%: Δ 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 ■ or less: ◎ More than 2mg ~ 5■ or less 20 More than 5■~8■ or less: Δ 8 ■ Super: × (d) Spot weldability The welding conditions are as follows.

Current: 8KA Number of cycles: 1O cycle Pressure crab 200kg Welding tip shape: As shown in Figure 1 (A is 12 order φ, B is 6
IITfflφ, θ is 30″).

Number of consecutive points: 5000 points or more: ◎ 4000 points or more - less than 5000 points 203000 points or more - less than 4000 points: Δ Less than 3000 points: × First, regarding the comparative example, Nα7 is C in the base plating
Since the r content is too low, corrosion resistance is poor. Also,
Nα8 has too high a Cr content in the base plating, so Nl
], 9 does not contain a cationic polymer in the base plating, and NolO has too little chromate film, so
The press workability is poor in each case, and the corrosion resistance of the processed parts is also reduced accordingly. In addition, No. 11 has an excessive amount of chromate film, so the spot weldability is poor.

In contrast, all the examples of the present invention had good corrosion resistance, workability, and weldability.

(Effects of the Invention) As explained above, the organic composite plated steel sheet of the present invention has greatly improved the corrosion resistance, particularly the corrosion resistance of processed parts, which was a problem with conventional thin film type organic composite plated steel sheets. ,
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 a welding tip shape used to evaluate spot weldability in Examples.

Claims (2)

[Claims] (1) Form a composite electroplated layer on the surface of the steel plate with 1 to 30% by weight of Cr, 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 150 mg/m An organic composite plated steel sheet with excellent corrosion resistance, characterized by forming an organic coating of 0.3 to 3 μm on the top layer. (2) The organic composite plated steel sheet with excellent corrosion resistance according to claim 1, wherein the cationic polymer in the composite electroplated layer is a quaternary amine polymer.