JPH0280598A - Organic composite plated steel sheet having superior corrosion resistance - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance of the worked part of a plated steel sheet by forming a composite plating layer consisting of specified weight percentages of Cr, fine oxide particles and a cationic polymer and the balance Zn on the surface of a steel sheet by electroplating, incorporating an Fe family element into the plating layer, forming a chromate coating layer on the plating layer by a specified amt. (expressed in terms of Cr) and further forming a specified org. coating film. CONSTITUTION:A composite plating layer consisting of 1-30wt.% Cr, 0.1-10wt.% fine oxide particles, 0.001-5wt.% cationic polymer and the balance Zn is formed on the surface of a steel sheet by electroplating. A chromate coating film is formed on the plating layer by 10-150mg/m<2> (expressed in terms of Cr) and an org. coating film of 0.3-3mum thickness is further formed. 1-10% Fe family element may be incorporated into the plating layer. Particles of one or more kinds of oxides selected among the oxides of Si, Al, Zr, Ti, Cr, Mo and W are used as the oxide particles and a quat. amine polymer is used as the cationic polymer. The corrosion resistance of the worked part of the plated steel sheet can be improved.

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 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-corrosion 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 are Fe.

It contains iron group elements such as 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 fully satisfy the required quality in terms of spot weldability, etc.

In other words, those coated with zinc-rich paint have poor press workability and are insufficient in corrosion resistance and weldability, while those coated with paint containing conductive pigments have improved press workability and weldability. But it still 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.

The corrosion resistance of organic composite coated steel sheets was originally largely due to the organic coating, but as the films become thinner as described above for press workability and weldability, improvements in the coating layer are also required in terms of corrosion resistance. It's coming.

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. Since the layers and the steel base are exposed, the corrosion resistance of the plating layer becomes more important, 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 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 electroplating 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. The Company provides organic composite plated steel sheets.

The gist of the present invention is that 1 to 30% by weight of Cr is added to the surface of the steel plate.
, a composite electroplated layer containing 0.1 to 10% by weight of oxide fine particles, 0.001 to 5% by weight of Kanaon polymer, and the balance Zn is formed, and a chromate film is formed on the top layer with a total Cr content of 1%.
0-150mg/rr? An organic composite plated steel sheet with excellent corrosion resistance, characterized in that an organic coating of 0.3 to 3 μm is formed on top of the organic coating.

1 to 30% by weight of Cr and 0.0% of oxide fine particles are applied to the surface of the steel plate.
1 to 10% by weight of a cationic polymer, 0.001 to 5% by weight of a cationic polymer, 1 to 10% of an iron group metal, and the balance Zn.
An organic composite plated steel sheet having excellent corrosion resistance, characterized in that the organic coating is formed in an amount of 10 to 150 mg/m, and further has an organic coating of 0.3 to 3 μm formed on the upper layer.

Oxide fine particles are + si, AI, Zr, Ti,
The above-mentioned organic composite plated steel sheet having excellent corrosion resistance and comprising one or more oxides of Cr, Mo, and W.

This organic composite plated steel sheet has excellent corrosion resistance, in which the cationic polymer in the composite electroplated layer is a quaternary amine polymer.

(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.

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, the corrosion spreads beneath the organic coating, and eventually the steel base is corroded and red rust occurs. Corrosion products of Cr are caused by the so-called rust clogging action that fills cracks, causing water to evaporate.

It prevents the entry of corrosive factors such as oxygen and chlorine ions,
Together with the organic film, it acts as a barrier and prevents corrosion from progressing.

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 can be seen in Zn, Zn-Ni, and Zn-, which have been conventionally used as the base plating layer of organic composite plated steel sheets.
This cannot be expected with the Fe plating layer. In particular, when the organic film is a thin film, 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 action 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. 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. Furthermore, if the Cr content exceeds 30% by weight, although the corrosion resistance is good, even with the eutectoid effect of the cationic polymer described below, the plating layer peels off during processing such as pressing, which causes deterioration of so-called powdering property. This cannot be prevented and is difficult to apply in practice.

In addition, from the viewpoint of corrosion resistance and workability, the Cr content is 5.
-20% by weight is more preferred.

Oxide particles penetrate into corrosion products.

By strongly bonding with oxygen bonds, the stability of Zn-Cr corrosion products, which have a protective effect, is further improved, and the oxide fine particles themselves exert a barrier effect against corrosion factors, so As such, it is effective in improving the corrosion resistance of organic composite plated steel sheets.

The content of oxide fine particles is 0.1 to 10% by weight.

0.1. If it is less than i@%, 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 many types of oxide fine particles, including metal and metalloid oxides, including Si, AI, Zr, Ti, Cr,
Mo.

W oxides are particularly preferred, and these may be used alone or in a mixture of two or more.The average grain size is preferably 1 μm or less, and if it exceeds 1Pm, it is difficult to eutectoid in the plating layer. .

Cationic polymers are Cr precipitation promoters, and Cr
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 is increased, but also a large amount of eutectoid This causes a decrease in plating adhesion. From the viewpoint of powdering resistance, the Cr content is 1
It is desirable to eutectoid the cationic polymer at a content of /1000 or more.

As the water-soluble cationic polymer used in the present invention, a quaternary amine polymer is effective, and its molecular weight is:
In this case, 103 to 106 is desirable.

Among the following amine polymers, polyamine sulfone (P
AS) and polyamines (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, it is composed of the following quaternary amine salts (ammonium salts) or copolymers.

Some compounds will be specifically listed below.

Examples of polymers obtained from diallylamine include R
,, R2 represents 7) L/kyl group, X is C1~, H3O
4-1H2PO, -1R-3O3- (R is an alkyl group of C□ to C4), and NO3- are anions.

Another example is a polymer synthesized from vinylbenzyl. R□tR111R3 represents a hydrocarbon, and X is Cr
, l5O4-1H, PO4-1R-8O, -, No, -
indicates the anion of

Alternatively, allylamine polymer can be mentioned.

R1, R,, R, represents a hydrocarbon, and X is C1-1H3
It shows anions of O4-1H, PO, -1R-9O, -1NO3-.

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 base plating layer contains Zn, Cr, and oxide fine particles.

In addition to the cationic polymer, an iron group metal may be contained.

Here, the iron group metals refer to Ni, Fe, and Go. Corrosion resistance and weldability can be improved by containing iron group metals. Regarding corrosion resistance, the inclusion of iron group metals in the Cr corrosion products further densifies the corrosion products.
It is presumed that this is due to stabilization. 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 deformed by the pressure of the electrode tip. It is thought that the current becomes smaller and 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.

When containing iron group metals, there is an advantage that these ions are adsorbed to the oxide fine particles in the plating bath, facilitating eutectoid deposition of the oxide fine particles. However, if the total amount of Cr and iron group metal increases, workability deteriorates, so the total amount of Cr and iron group metal is preferably 30% by weight or less.

One type of iron group metal may be used, or two or more types may be contained at the same time, but the inclusion of Ni is particularly effective in improving corrosion resistance.

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

Even if a small amount of Bi, Cu, Sb, As, Na, P, S, etc. inevitably eutectoid, the effect of the base plating layer does not essentially change.

Next, regarding the manufacturing method of a Zn-Cr based composite electroplating layer, Zn2+ ion, Cr3+ ion, Sin□
, Tie, .

A water-soluble cationic polymer such as a polymer of oxide fine particles such as Al2O3 and a quaternary amine such as PAS is
20g/Q including p+to, s~3, bath temperature 40~70℃
Electroplating may be performed using an acidic plating bath of 20 A/dm2 or more.

Iron group metal ions such as Ni", Fe", and Co"+ may be added to the plating bath, and these may be eutectoided within the plating layer. Salts such as Na", K", and NH4+ ions may also be added. The addition is effective 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 good reactivity with an acidic treatment solution consisting of cr+G and/or Cr+3.

Any of the conventionally known coating-type chromate treatments, 9-aggressive chromate treatments, electrolytic chromate treatments, etc. can be applied.

As a coating type 9 reaction type chromate treatment, Cr″6Cr
In addition to +3, it is also possible to add inorganic colloids, acids such as phosphoric acid, fluorides, or water-soluble or emulsion type organic resins.

For example, as a treatment liquid containing phosphoric acid and fluoride, chromic acid 30g/Q, phosphoric acid 10g/Q, titanium potassium fluoride 4g/Q + sodium fluoride 0.5g/Q
.

As a treatment liquid containing silica, chromic acid 50 g/
Q (including 40% trivalent chromium), SiO□100 g
/ There is a Q.

Examples of inorganic colloids include 5in2. Al□0
31Tie, 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 a dissolvable salt. , or one or more types of silica fluorides, titanium fluorides, phosphates, etc., which 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 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 for example, for phosphoric acids, it is 1 to 200 g/n, and for Sun
, Teha.

1 to 800 g/Q.

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, or 5in2. It can also be used to add inorganic colloids such as Al, O, etc., and to add cations such as Co, Mg, etc.6 Although cathodic electrolysis is usually applied.

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.
mg/rd. If it is less than 10mg/rd, the adhesion of the organic film is insufficient, and if it is less than 150+mg/rd.
Weldability exceeds .

Press workability deteriorates, which is not practical. A more preferable range is 20 to 100 mg/rrl as the total Cr amount.
'is.

In addition, in order to avoid contamination of chemical conversion treatment solutions due to 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. is preferably formed, and 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 is not sufficient, and if it exceeds 3μ, it is difficult to weld.

Press workability may deteriorate. A more preferable range is 0.5 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.

Also, Sin, BaCr0. Various additives such as anticorrosive pigments, curing agents for bake-hardening films, and lubricants 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:
300-100000) 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: rate 5-5
0% by weight Lubricant: Content in polyethylene wax film 0.1-10% by weight Solvent: Diketone 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 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 subjected to bright finish rolling, a high tensile strength steel plate that contains a large amount of Mn, S, P, etc. as steel components, Cr, Cu, Ni+. Highly corrosion resistant steel plates containing a large amount of P etc. and having a low corrosion rate can also be used.

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

(1) Plating conditions A cold-rolled steel plate with a thickness of 0 and 8 mm was degreased with alkali, pickled with 5% sulfuric acid, washed with water, and electroplated under the following conditions. Liquid flow a 90 m/min by pump stirring
, the distance between poles was 1910 mm, and a sulfuric acid acidic bath @60'C, pl+2 was used. The plating bath composition is Zn” + ion 7
0gIQ, Cr''+ ions 1-30g/(1, oxide fine particles (sio21A120., ZrO2, Tie□, average particle size 0.02-0.05 μm.

Cr2O, l wo3 has an average particle size of 0.1 to 0.5 μ)
10~long/Q, divalent ion of iron group metal O~50
gIQ, cationic polymer (polyamine polymer (PA) with a molecular weight of 50,000 or polyamine sulfone polymer (PAS) with a molecular weight of 100,000) 0.01-20g/Q
, , Na + ion was set at 16 g/Q, the contents of Cr, oxide fine particles, iron group metals, and cationic polymers were controlled by the respective addition amounts and current density, and the plating deposition amount was 20 g/rr! And so.

(2) Chromate treatment■ Electrolytic chromate chromic acid 30g1. Using a treatment solution containing 0.2 g/Q sulfuric acid and a bath temperature of 40° C., the plated plate was subjected to cathodic electrolysis at a current density of 10 A/dm 2 , washed with water, and dried. The amount of chromate deposited was adjusted by the amount of coulombs.

■ Coating type chromate chromic acid 50g/+2 (including Cr” 40%L 5
102 colloid 100 g
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 50g IQ, phosphoric acid 10g/Q, NaF
0.5g/Q.

K, TiF, 4 gIQ l A treatment solution with a bath temperature of 60°C was sprayed onto the plated plate, washed with water, and then dried at 60°C. The adhesion amount of Chrome-1 was adjusted by the dilution rate of the treatment liquid 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 SiO□, curing agents, and catalysts are added.

A paint containing lubricant, water leak modifier, etc. was used. 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 was set at 100 to 200°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) Corrosion resistance of flat plate The above cycle was regarded as one cycle, and the plate thickness was evaluated by the amount of decrease in plate thickness after 3000 cycles.

0.1mm or less: ◎ More than 0.1mm to 0.2mm or less: O 0.2mo+ to 0,3 +n +n or less: Δ0.3
More than mm:

1% or less: ◎ More than 1% to less than 5%: 0 More than 5% to less than 10%: Δ More than 10%: The weight was evaluated based on the amount of decrease by 1 weight.

2mg or less: ◎ More than 2g to less than 5mg 20 More than 5 mg to less than 8 mg: Δ More than 8mg: × (d) Spot weldability The welding conditions are as follows.

Current: 8KA Number of cycles: 10 cycles Pressurized crab 200kg Welding tip shape: Shown in Figure 1 (A is 12mmφ.

B is 6 mmφ and θ is 30'').

Number of continuous points: 5000 points or more: ◎ 4000 points or more - less than 5000 points: 0 3000 points or more - less than 4000 points: 6 Less than 3000 points: Therefore, since Na26 has too much iron group metal (Ni) content in the base plating, Na27
(128 does not contain oxide fine particles in the base plating, Nα32 has too thin an organic film, and Na34 does not contain Cr in the base plating, so its corrosion resistance is poor. Because the Cr content of Nα29 is too high, Nα29 does not contain a cationic polymer in the base plating, and Nn30 has too little chromate film, the press workability is poor, and the corrosion resistance of processed parts is also reduced accordingly. In addition, Nα31 has too much chromate film, so Nn3
Sample No. 3 had poor press workability and spot weldability, respectively, because the organic film was too thick.

On the other hand, all of the inventive examples Nα1 to Isao 23 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 a Zn-Cr based composite electroplating layer containing oxide fine particles as the base plating, thereby making it possible to improve the organic composite plated steel sheet of the conventional thin film type. This product greatly improves the corrosion resistance, which had been a problem, especially the corrosion resistance of processed parts, and has excellent press workability and spot weldability, so it is used in automobiles, home appliances, and building materials that require high quality. It can be widely used for.

[Brief explanation of the drawing]

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

Claims (4)

[Claims] (1) On the surface of the steel plate, 1 to 30% by weight of Cr, 0.1 to 10% by weight of oxide fine particles, and 0.001 to 0.001% of cationic polymer.
Forming a composite electroplated layer with 5% by weight and the balance being Zn,
On top of that is a chromate film with a total Cr content of 10 to 150 m.
g/m^2, and then an organic film of 0.3~2 on top.
An organic composite plated steel sheet with excellent corrosion resistance characterized by a 3μ coating. (2) On the surface of the steel plate, 1 to 30% by weight of Cr, 0.1 to 10% by weight of oxide fine particles, and 0.001 to 0.001% of cationic polymer.
A composite electroplated layer containing 5% by weight of iron group metal, 1-10% by weight of iron group metal, and the balance Zn is formed, and a chromate film with a total amount of Cr of 10-150mg/m^2 is formed on the top layer, and an organic An organic composite plated steel sheet with excellent corrosion resistance, characterized by forming a film of 0.3 to 3μ. (3) Oxide fine particles are Si, Al, Zr, Ti, Cr
An organic composite plated steel sheet with excellent corrosion resistance according to claims 1 and 2, which comprises one or more oxides of , Mo, and W. (4) The organic composite plated steel sheet with excellent corrosion resistance according to claims 1 and 2, wherein the cationic polymer in the composite electroplated layer is a quaternary amine polymer.