JPH0243398A - Organic composite plated steel sheet having excellent corrosion resistance - Google Patents

Abstract

PURPOSE:To remarkably improve the corrosion resistance of especially the worked part by forming a chromate film on a substrate plating layer contg. specified amts. of Cr, cationic polymer, and Zn, and further forming a specified amt. of org. film thereon. CONSTITUTION:A substrate plating layer is formed on a steel sheet, a chromate film is formed at 10-150mg/m<2> (based on total Cr) on the layer, and further an org. film is formed thereon in 0.3-3mu thickness to form the title org. composite plated steel sheet. The substrate plating layer is an electroplating layer contg., by weight, 1-30% Cr, 0.001-5% cationic polymer, and the balance Zn. The plated steel sheet has excellent corrosion resistance of especially the worked part.

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-corrosion steel sheets for automobiles in response to the salt sprayed on roads in winter to prevent roads from freezing in cold regions, and there is a trend towards increasing demands for corrosion resistance in harsh corrosive environments.

In response to these demands for improving the corrosion resistance of galvanized steel sheets, is it known that the corrosion resistance can be improved by the amount of zinc plating (adhesion amount)?Also, as a method other than increasing the amount of plating, alloy plating is used to suppress the dissolution of zinc itself. Many have been proposed.

Many of these contain iron group elements such as Fe, Ni, and Co 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.

For such organic composite plated steel sheets, progress has been made mainly in improving the coating composition that forms the top organic film, but it has not been possible to sufficiently meet the required qualities in terms of corrosion resistance, press workability, spot weldability, etc. It wasn't.

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

(Problem to be solved by the invention) These are relatively thick organic composite steel sheets with an organic coating thickness exceeding 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 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, in JP-A-59-162278, etc., an organic film is prepared by blending a chromium compound as a rust-preventive pigment into a water-dispersible emulsion resin, and in JP-A-60-50181, an organic film is prepared by blending silica as a rust-preventive pigment. Either a film is used or the corrosion resistance is not sufficient.

The corrosion resistance of organic composite plated steel sheets was originally dependent on the organic coating, but as films become thinner as described above for press workability and weldability, it is necessary to improve the coating layer in terms of corrosion resistance. It becomes.

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 there are flaws or cracks, it may partially break. Because the mesh layer and steel base are exposed,
Much of this depends on the corrosion resistance of the plating layer, but conventional undercoatings do not have sufficient corrosion resistance, and especially their 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 processing.

(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, has been dramatically improved, and workability,
To provide an organic composite plated steel sheet with excellent weldability.

The gist of the present invention is to form a composite electroplating layer on the surface of a steel sheet, which contains 1 to 30% by weight of Cr, 0001 to 5% by weight of a cationic polymer, and the balance Zn, and a chromate film on the top layer with a total Cr of 10 to 150 mg/ An organic composite plated steel sheet with excellent corrosion resistance characterized by forming I+12 and further forming an organic film of 0.3 to 3μ on the upper layer, and a total of 30% by weight or less of Cr and iron group metals on the surface of the steel sheet. , and Cr is 1% by weight or more, and iron group metal is 1/1 of the Cr content.
Contains in the range of 0 to l/2, cationic polymer 0.00
A composite electroplated layer containing 1 to 5% by weight of Zn and the balance being Zn is formed, and a chromate film is formed on the top layer with a total Cr content of 10 to 15% by weight.
0 mg/m2 and further an organic film on top of it.
This is an organic composite plated steel sheet with excellent corrosion resistance, characterized by having a thickness of 3 to 3μ.

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

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

As a base plating layer for organic composite plated steel sheets, the formation of this protective film works synergistically with the organic film.
C: It shows high corrosion resistance. 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 the 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 base plating layer and steel base are partially exposed due to scratches and cracks.
A fatal flaw in conventional organic composite plated steel sheets is that the barrier effect of the organic film is diminished. Zn-Cr
The system composite plating layer has the effect of depositing a protective film and stopping corrosion even in such processed parts.

This effect is similar to Zn, Zn-Ni, and Zn-F, which have traditionally been used as the base plated layer of organic composite plated steel sheets.
You can't expect much from the e-plated layer. In particular, when the organic film is thin, there are inherently many coating film defects such as pinholes.
In processed areas, the film becomes even thinner and the barrier effect becomes smaller, and if flaws or cracks occur, the plating layer and steel base are easily exposed, so the effect of the zn-Cr composite plating layer is limited to the processed areas only. It is also extremely effective in improving the corrosion resistance of 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. Although it can be prevented, it is difficult to apply it 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 this cationic polymer eutectoid effect is due to the fact that Cr ions inhibit the uniform electrodeposition growth of Zn and prevent a plating 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. This will cause 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 71,000 or more.

As the water-soluble cationic polymer used in the present invention, a quaternary amine polymer is effective, and the molecular weight is:
In this case, 103 to 108 is desirable. Among the amine polymers shown below, 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 specific compounds are listed below.

Examples include polymers obtained from diallylamine. R,
, R2 represents a lower alkyl group or an alkyl group, and X is C
l3-, +1504-, ll2PO4-1R-5
03- (R is a C-C4 alkyl group) represents an anion of No3-.

H3O4 , H2PO4-1R-503-1 Claw the anion of NO3- vinegar.

-(-CH2-CII 10) or a polymer synthesized from vinylbenzyl. R1, R2, R3 represent a hydrocarbon, and X is Cu
-, H3O4-, +(2PO4-1R-503-1NO
Indicates the anion of 3-.

Alternatively, allylamine polymer can be mentioned. R1,R
2, R8 represents a hydrocarbon, X is CIl, and 1,2.
Tertiary amine polymers are also effective as Cr precipitation promoters, although they are not as effective as the above-mentioned quaternary amine polymers.

The base plating layer may contain an iron group metal in addition to Zn, Cr, and a cationic polymer. Here, iron group metals refer to the former, Fe, and Go. Inclusion of iron group metals can improve corrosion resistance and weldability. The corrosion resistance is presumed to be due to the iron group metal entering into the Cr corrosion product, thereby further densifying and stabilizing the corrosion product. Regarding weldability, when a Zn-Cr based composite plating layer contains an iron group metal, the electrical resistance of the plating layer increases and heat generation becomes easier, and since the plating layer becomes hard, the plating layer may be damaged by the pressure of the electrode tip. It is thought that the deformation of the weld becomes smaller and the current becomes more concentrated in the weld.

In this case, the content of iron group metals is 1/10 to 1/10 of the Cr content.
The total amount including l/2 and Cr content is 30% by weight or less. If the content of iron group metals is less than the Cr content of 171O, the effect of adding iron group metals will not be noticeable, and if it exceeds 1/2, the properties of iron group metals will become stronger and red rust will easily occur in processed parts. Become. Moreover, when the total content of Cr and iron group metal exceeds 30% by weight, press workability deteriorates. Iron group metals are 1
Although it may be a species or two or more types may be contained at the same time, the inclusion of Ni is particularly effective in improving corrosion resistance.

A coating weight of 5 to 50 g/m2 can ensure sufficient corrosion resistance. In addition to Zn, Cr, iron group metals, and cationic polymers, Pb, Sn, Ag, In, Bi,
Cu.

Sb, As, 842. Ti, Na, P, S
Even if there is unavoidably a small amount of eutectoid, the effect of the base plating layer will not change in terms of wood quality.

Next, regarding a method for manufacturing a Zn-Cr based composite electroplating layer, a water-soluble cationic polymer such as a polymer of Zn'' ions, Cr3+ ions, divalent ions of iron group metals, and quaternary amines such as PAS is used. .01-20g/J2 containing pho
, s ~ 3, using an acidic plating bath with a bath temperature of 40 to 70°C.
Electroplating may be performed at 0 A/dm2 or higher. In the plating bath, 5j02. Tie28JI! 2
Oxide particles such as 03 may be added. Furthermore, it is effective to add salts such as Na, Ni, NH, + 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.

The Zn-Cr based composite plating layer has Cr+6 and or C
Since it has good reactivity with an acidic treatment liquid consisting of S', any of the conventionally known coating type chromate treatment, adaptive type chromate treatment, electrolytic type chromate treatment, etc. can be applied.

The coating type 1-reaction type chromate treatment includes Cr“6,
Addition of inorganic colloids in addition to Cr”3,
Applicable materials include those to which acids such as phosphoric acid, compounds, or water-soluble or emulsion-type organic resins are added.

For example, a treatment solution containing phosphoric acid and a compound includes chromic acid 30g/β, phosphoric acid 10g/ρ, and potassium titanium fluoride 4g/j2. Examples of processing liquids containing sodium fluoride (05 g/It) and silica include chromic acid (50 g/Il (of which trivalent chromium 40%)) and 5402100 g/fl. Examples of inorganic colloids include 5i02. A
n 203. Tf02. Colloids such as 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 hydrolysis. It contains one or more types of silicides, titanium silicides, phosphates, etc. that produce poorly soluble salts through reactions such as these. 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 of additive, but for example, for phosphoric acids, it is 1 to 200 g/J2,5i.
02 is 1 to 800 g/It.

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,
It is also possible to add phosphoric acid, halogen ions, etc., or add inorganic colloids such as 5j02.71112 (h), or add cations such as Co or Mg. Usually cathodic electrolysis is applied, but anode electrolysis Electrolysis and AC electrolysis can also be added.

The amount of chromate film deposited is 10 to 150 as total Cri.
mg/m'. If it is less than 10 mg/m2, the sealability of the organic film is insufficient, and if it exceeds 150 mg/m', 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 the chemical conversion treatment solution due to chromium eluted from the chromate film and the associated complication of work such as wastewater treatment, it is necessary to use an Ilt-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~
It is 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 conductors thereof.

In addition, 5i02 and BaCr0. Various additives such as rust-preventing pigments such as +, 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/block polyisocyanate compound Weight ratio to the main resin: l/lO to 20/10 Rust preventive 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: Two-ketone organic solvent The coating method may be any known method such as roll coating, spray coating, or curtain flow coating. Good too.

The structure of the present invention does not necessarily have 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 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 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. Liquid flow rate 90 m/min by pump stirring, 1iflo between poles
A sulfuric acid acid bath with a bath temperature of 60° C. and p) 12 was used. The plating bath composition was Zn2+ ion 70g/j2. II:
r”+ ion 1 to 30 g/j2, divalent iron group metal ion O to 30 g/it, cationic polymer (polyamine polymer (PA) with a molecular weight of 50,000 or polyamine sulfone polymer (PAS) with a molecular weight of 100,000) 0.01~
20 g/11, Na + ion 16 g/j2, the contents of Cr, iron group metal, and cationic polymer were controlled by their respective addition amounts and current density, and the coating weight was 20 g/m2.

(2) Chromate treatment ■ Electrolytic chromate Using a treatment solution containing 30 g of chromic acid, 0.2 g of sulfuric acid, and a bath temperature of 40°C, the plated plate was electrolyzed cathodically at a current density of 10 A/dm2, washed with water, and dried. . The amount of chromate deposited was adjusted by the amount of coulombs.

■ Coating type chromate chromic acid 50g/J2 (including 40% Cr), 5i
The plated plate was immersed in a treatment solution containing 100 g/u of n2 colloid and a bath temperature of 40°C, air wiped, and then heated at 100°C for 1
Dried in minutes. 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 s o g/u-phosphoric acid 10g/u, NaFO
15g/It, )hTiFs 4g/It
fl, spray a treatment solution with a bath temperature of 60°C onto the plating plate,
After washing with water, it was 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, rust preventive pigments such as 5in2, hardeners, catalyst lubricants, water wettability modifiers, etc. are added. The material was made into a paint. It was applied to a chromate-treated plated plate using a roll coater and baked and dried. Although the baking conditions depended on the resin system, the final plate temperature was set at 100 to 200°C.

Table 1 shows the structure and evaluation results of corrosion resistance, workability, and weldability of the organic composite smoothed steel sheet produced in this manner. 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.

Q, 1 mm or less: ◎ More than 0.1 mm - 0.2 mm or less; 0 More than 0.2 mm - 0.3 mm or less: △ More than 0.3 mm: (JIS Z2371) for 2000 hours, and evaluation was made based on the area where red rust occurred in the processed parts.

1% or less: ◎ More than 1% to less than 5% 205% to less than 10%: △ More than 10% ・× (C) Press workability After performing cylindrical press forming of 50φ x 25H, tape peeling is performed on the processed surface. and evaluated based on the amount of weight loss.

2mg or less: ◎ More than 2mg to less than 5mg 0 More than 5mg to less than 8mg △ More than 8mg: × (d) Spot weldability The welding conditions are as follows.

Current: 8HA Number of cycles: 10 cycles Pressure Crab 200kg Welding tip shape - Shown in Figure 1 (A is 12mmφ, B is 6mmφ, 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: △ Less than 3000 points: X First, regarding the comparative example, No. 21 contains Cr in the base plating. No. 24 was selected because the iron group metal (Ni) content in the base plating was too low.
No. 8 has a too thin organic film, and No. 30 does not contain Cr in the base plating, so the corrosion resistance is poor. In addition, No. 22 has too high a Cr content in the base plating, No. 23 does not contain a cationic polymer in the base plating, and No. 25 has a combination of Cr and iron group metal (Ni) in the base plating. No, because the total content is too high.
In No. 26, the amount of chromate film was too small, so the press workability was poor, and the corrosion resistance of the processed part was accordingly reduced. In addition, No. 27 has a large amount of chromate film, and No. 29 has an organic film that is too thick, resulting in poor spot weldability.

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 the drawing]

FIG. 1 is a diagram showing a welding tip shape used to evaluate spot weldability in Examples. 7i1 illustration agent Patent attorney Masamitsu Akisawa and 1 other person

Claims (3)

[Claims] (1) Form a composite electroplated layer on the surface of the steel plate containing 1 to 30% by weight of Cr, 0.001 to 5% by weight of a cationic polymer, and the balance Zn, and add a chromate film on the top layer with a total amount of Cr of 10 to 150 mg/ An organic composite plated steel sheet having excellent corrosion resistance, characterized in that a 0.3 to 3 μm organic film is formed on the upper layer. (2) A total of 30% by weight of Cr and iron group metals on the surface of the steel plate
A composite electroplated layer containing 1% by weight or more of Cr, 1/10 to 1/2 of the iron group metal content, 0.001 to 5% by weight of a cationic polymer, and the balance Zn. A chromate film with a total Cr content of 1 is formed on top of the chromate film.
An organic composite plated steel sheet with excellent corrosion resistance, characterized by forming an organic film of 0 to 150 mg/m^2 and further forming an organic film of 0.3 to 3 μm on the upper layer. (3) The organic composite plated steel sheet with excellent corrosion resistance according to claim 1 or 2, wherein the cationic polymer in the composite electroplated layer is a quaternary amine polymer.