JPH1044307A - Weldable type organic composite plated steel sheet with excellent corrosion resistance and press moldability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a weldable type organic composite plated steel sheet having excellent corrosion resistances and press moldabilities of a general surface and a cut surface and excellent operability. SOLUTION: A Zn-plated layer having an adhesion amount corresponding to 30 to 130 = plating adhesion amount (g/m)/thickness of steel sheet (mm), a chromate film having a total Cr adhesion amount of 10 to 150mg/m<2> , and an organic film having a thickness of 1 to 20μm are sequentially formed from the sheet side on one side surface or both side surfaces of the sheet. In this case, a conductive inorganic pigment ratio of the organic film is 1 to 40vol.%, non-chromium rustpreventive pigment ratio is 5 to 40vol.%, lubricant is 1 to 40vol.%, and its total sum is 7 to 65Vol.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a weldable organic composite plated steel sheet having excellent weldability, corrosion resistance and workability and suitable as a rustproof steel sheet for automobiles.

[0002]

2. Description of the Related Art It is well known that an electro-galvanized steel sheet is already widely used as a surface-treated steel sheet which can be mass-produced without impairing the corrosion resistance of a cold-rolled steel sheet, the corrosion resistance after painting, and the workability. In recent years, the use of Zn-plated steel sheets has been attempted as an anti-rust measure for automobiles against scattered rock salt for preventing road freezing in winter in cold regions, and the demand for corrosion resistance in severe corrosive environments tends to increase.

In order to improve the corrosion resistance of these Zn-plated steel sheets, it is known to improve the corrosion resistance by the amount of Zn plating (the amount of adhesion). However, as a method other than increasing the amount of plating, an alloy for suppressing the dissolution of Zn itself is used. Many platings have been proposed. Most of them contain iron group elements such as Fe, Ni, and Co as alloy components. These Zn-iron group electroplated steel sheets are characterized by having excellent corrosion resistance after unpainting or after painting, and are industrially produced and put to practical use. However, it is desired to further improve the corrosion resistance. In response to this requirement, an organic composite plated steel sheet has been developed in which, for automotive applications and the like, a Zn-based plated steel sheet is subjected to a chromate treatment, and an upper layer is coated with an organic film.

On the other hand, there is a growing need to omit the assembling process mainly in the home electric appliance industry, and the pre-coating of post-coating is being promoted. Also for automotive outer panels, there is a growing need for steel sheets for automobiles, which are pre-coated with electrodeposition coating, or without electrodeposition coating and intermediate coating. When a precoated steel sheet is used for an automobile, its weldability is a problem, but Japanese Patent Application Laid-Open Nos. 62-73938 and 63-27.
JP-A-0131 discloses an organic composite plated steel sheet provided with conductivity by containing a conductive pigment.

[0005]

However, the above-mentioned organic composite plated steel sheet is premised on the existence of electrodeposition coating in the automobile manufacturing process, and when the electrodeposition coating or the electrodeposition coating or the intermediate coating is omitted. However, the corrosion resistance of the cut surface where the iron surface is exposed was not considered, and the corrosion resistance of the cut surface did not have sufficient performance. Originally, the purpose of organic composite steel sheets is to increase the corrosion resistance of the general surface, and improvements in coating compositions that mainly form the uppermost organic film, such as the inclusion of a rust preventive pigment in the organic film, have been promoted. . However, the corrosion resistance of the cut surface depends more on the sacrificial corrosion protection ability of the plating layer than on the anticorrosion performance of the organic coating, and a sufficient study of the plating layer is required.

[0006] Further, in the organic composite plated steel sheet using Zn plating, since the plating layer is soft, the problem of galling or peeling of the organic film often occurs at the time of pressing, and a technique for improving the lubricity of the organic film is required. Was. Further, in the case of an automobile body outer panel, there is a step called polishing, in which the undercoating surface is polished with a fine sandpaper soaked before the overcoating. In the absence of electrodeposition coating, the coating film of the organic composite plated steel sheet is directly water-polished. However, the organic composite plated steel sheet disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 62-73938 is not suitable for coating. Contains a chromium-based rust-preventive pigment, and it is necessary to treat coating film fine powder generated during water sharpening.
The present invention solves the above problems, and provides an organic composite plated steel sheet which has improved corrosion resistance, particularly corrosion resistance of a cut surface and press workability, and is excellent in workability.

[0007]

According to the present invention, there is provided an electro-Zn plating layer or a hot-dip Zn plating layer having excellent sacrificial anti-corrosion ability when a cut surface is corroded, and a chromate film and an organic film are appropriately formed. The present invention provides an organic composite plated steel sheet in which the corrosion resistance, especially the corrosion resistance of the cut surface, is dramatically improved by forming the layer in the upper layer. Further, by using a non-chromium pigment as a rust preventive pigment in an organic coating film, an organic composite plated steel sheet excellent in workability is provided.

The gist of the present invention is as follows: (1) The coating weight (g / m ² ) / the thickness of the steel sheet (mm) = 30 to 1 on one or both sides of the steel sheet in order from the steel sheet side.
A Zn plating layer having an adhesion amount corresponding to 30; a chromate film having a total Cr adhesion amount of 10 to 150 mg / m ² ;
An organic film having a thickness of 20 μm is formed, the organic film contains 1 to 40 vol% of a conductive inorganic pigment, 5 to 40 vol% of a chromium-free rust preventive pigment, and 1 to 40 v of a lubricant.
ol%, a total of which is 7 to 65 vol%. (2) The Zn plating layer is made of electric Zn plating or hot-dip Z
The weldable organic composite plated steel sheet according to the above (1), which is n-plated.

(3) The weldable organic composite plated steel sheet according to (1), wherein the chromate film is a poorly soluble chromate film having a water-soluble content of 30% or less. (4) The chromium-free rust-preventive pigment is a basic zinc phosphite or a basic phosphite-based rust-preventive pigment, which is basic calcium zinc phosphite, alone or as a main component, and At least one of hypophosphite, phosphite, phosphate, borate, molybdate or oxycarboxylate of zinc, nickel or cobalt as a component;
A weldable organic composite-plated steel sheet according to the above (1), wherein the steel sheet contains a type.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a base plating layer will be described. To enhance the corrosion resistance of the cut portion, electric Zn plating or hot-dip Zn plating is effective. Regarding the corrosion resistance of the general surface, various Zn-based alloy platings have been developed, but in such Zn-based alloy plating, preferential dissolution of Zn occurs at the time of corrosion, and the iron surface is exposed like a cut surface. In some cases, sacrificial corrosion protection is weak. In that regard, the electric Zn plating and the hot-dip Zn plating have a high sacrificial anticorrosion ability against steel because of a single phase of Zn, which is advantageous. In the hot-dip Zn plating, trace amounts of Al, Pb, Cd, Sb, Ti, Mg and the like may be contained.

The adhesion amount of Zn plating is as follows: adhesion amount of plating (g / m ² ) / thickness of steel sheet (mm) = 30
To 130. If it is less than 30, sufficient corrosion resistance of the cut surface cannot be obtained. Further, even if it exceeds 130, its effect is saturated, so the upper limit is set to 130 in consideration of economy.
The chromate layer provided on the plating layer has an effect of securing adhesion to the organic film. Since the Zn plating layer has good reactivity with the pickling treatment solution composed of Cr ⁶⁺ and / or Cr ^3+, any of conventionally known coating-type chromate treatment, reaction-type chromate treatment, and electrolytic-type chromate treatment can be applied.

The amount of the chromate film adhered is 10 to 150 mg / m ² as the total amount of Cr. At 10 mg / m ² , the adhesion of the organic film is insufficient, and the corrosion resistance deteriorates. 1
If it exceeds 50 mg / m ² , the weldability and the press workability will deteriorate, which is not practically preferable. A more preferred range is 20 to 100 mg / m ² as the total amount of Cr. The water-soluble content of the chromate film is preferably 30% or less, more preferably 20% or less. If the water-soluble content exceeds 30%, soluble Cr ⁶⁺
, The chromium elution resistance or water swelling resistance is reduced, and it is difficult to obtain a lower secondary adhesion of the upper layer coating film or a high corrosion resistance as an organic composite plated steel sheet.
An organic film is applied to the upper layer of the chromate film. The thickness of the organic coating is 0.5 to 20 μm. If the thickness is 0.5 μm or less, the corrosion resistance is not sufficient, and if it exceeds 20 μm, the press workability may deteriorate, and the upper limit is set to 20 μm. Preferably, it is 2 to 10 μm.

The organic coating may be of a solvent type or a water-soluble type. For example, epoxy resin, alkyd resin, oil-free polyester resin, acrylic resin, acrylic ethylene resin, melamine resin, urethane resin, phenol resin, polycarbonate resin and the like can be used. . If necessary, various additives such as a curing agent, a coloring pigment, or a lubricant for further improving press workability may be added. The coating method may be any known method such as roll coating, spray coating, curtain flow coating and the like.

The purpose of the conductive pigment is to impart conductivity to the coating film, and one or a combination of two or more of SUS powder, ferrosilicon, iron phosphide, Zn powder, Ni powder, and conductive carbon is used. It is possible to use it. The average particle size is 1 to 15 μm, preferably 4 to 12 μm.
μm is good. If the average particle size is less than 1 μm, it is not preferable because secondary aggregation occurs in the coating material and the particles are coarsened to cause generation of particles, and the processing strength of the coating film is lowered. If the average particle size exceeds 15 μm, the appearance of the coating film becomes rough and rough, and the appearance is likely to be uneven between the processed portion and the non-processed portion of the mold or pressed product, which is not preferable in quality.

The mixing ratio of the conductive pigment is an important factor in quality. The mixing ratio in the present invention is preferably 1 to 40 vol%. If the compounding ratio is less than 1 vol%, the contact resistance of the coating film is high and the conductive function is not sufficient, so that the appropriate current range is narrow, and there are difficulties in spot weldability such as poor continuous spotting due to adhesion of the organic film burning residue to the electrode. is there. If the content exceeds 40 vol%, the function as a resin binder is exceeded, which hinders uniform coating techniques such as roll coating. Even if the coating is solidified, it has poor adhesion and deteriorates corrosion resistance.

The rust-preventive pigment can impart high rust-preventive ability to the coating film, and is effective in suppressing the corrosion of the plating layer or the steel sheet. The effect is particularly large on the general surface (flat portion), and when the electrodeposition coating is omitted, it is particularly effective for maintaining the corrosion resistance on the back side where the intermediate coating and the top coating are not applied.
For rust preventive pigments, taking into account the treatment of coating film fine powder during water sharpening,
Use a non-chromium rust preventive pigment. As the non-chromium rust preventive pigment, a basic zinc phosphite or a basic phosphite rust preventive pigment which is a basic zinc calcium phosphite is used.

One of zinc, nickel or cobalt hypophosphite, phosphite, phosphate, borate, molybdate or oxycarboxylate as an auxiliary component.
More than one kind may be contained. The content in the organic coating film is 5
40 vol%. If it is less than 5 vol%, the rust-preventive effect is thin, and if it exceeds 40 vol%, it exceeds the function as a resin binder. It is difficult to commercialize.

The purpose of the lubricant is to impart high slidability to the coating film, and polyolefin compounds and carboxylic esters can be used. Mixing ratio is 1-40v
ol% is good. If the compounding ratio is less than 1 vol%, the sliding resistance of the coating film is high, and galling and peeling of the coating film occur during press molding. If the content exceeds 40 vol%, the function of the resin as a binder is exceeded, which hinders uniform coating techniques such as roll coating, and even if it is solidified as a coating film, it has poor adhesion and is difficult to commercialize. In addition, the total content of the conductive pigment, the chromium-free rust preventive pigment, and the lubricant is set to 65 vol% or less because it is necessary to secure the binder force of the organic resin. Therefore, the total of the conductive pigment and the non-chromium rust preventive pigment is 7 to
Defined as 65 vol%.

[0019]

EXAMPLES Examples of the present invention are shown in Table 1. A low carbon steel sheet having a thickness of 0.8 mm was subjected to Zn plating by a Zenzimer hot-dip plating or an electroplating method, and a chromate layer and an organic coating layer shown in Table 1 were sequentially applied. The corrosion resistance of the cut portion was evaluated by the following method. (1) Salt spray (JIS Z2371) 1 hour (2) Drying (60 ° C.) 3.5 hours (3) Wetting (50 ° C., RH 95%) 3.5 hours The above (1) to (3) are defined as one cycle. After 20 cycles, the end face was evaluated for the occurrence of red rust. It can be seen that Nos. 1 to 108 shown in the corrosion resistance evaluation results of the cut surface in Tables 1 to 4 show the excellent corrosion resistance of the cut surface of the product of the present invention. In contrast,
Nos. 109, 110 and 112 in the comparative examples shown in Table 4 have insufficient corrosion resistance of the cut surface due to insufficient plating adhesion amount, chromate adhesion amount, or organic film thickness. 1
No. 15 is an example in which the corrosion resistance of the cut surface is deteriorated because the amount of the conductive pigment in the organic film is too large and the binder power as the organic film is insufficient. No. 119 is an example in which the corrosion resistance of the cut surface is deteriorated due to too much lubricant in the organic film. Nos. 121 and 122 are examples in which the total of the conductive pigment, the rust-preventive pigment and the lubricant is too large, and the binder strength as an organic film is insufficient, so that the corrosion resistance is deteriorated.

[0020] The general surface corrosion resistance is determined by performing a phosphate test (PB3020 / manufactured by Nippon Parkerizing Co., Ltd.) on a Zn-plated steel sheet having the same amount of Zn plating when a corrosion test is performed in the above cycle, and then applying a cationic electrodeposition coating power top U. -10
0 (manufactured by Nippon Paint Co., Ltd.) was evaluated as x when the generation of white rust on the flat plate portion was faster than that of the sample subjected to 20 μm, and evaluated as Δ when it was equal to or more than that. The results are shown in Tables 1 to 4, and it can be seen that Nos. 1 to 108 in the examples of the present invention show excellent general surface corrosion resistance. On the other hand, No. 112, which is a comparative example, is insufficient in the corrosion resistance of the general surface because No. 116 is insufficient in the thickness of the organic coating, and No. 116 is low in the ratio of the chromium-based rust preventive pigment. Nos. 115, 117, 120, and 121 do not function as an organic coating because the conductive pigment and the chromium-based rust-preventive pigment or each of them is too large.
This is an example in which the corrosion resistance has deteriorated.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

[Table 4]

The weldability was evaluated by a continuous weldability test by spot welding. An appropriate welding current range was determined, and the number of critical continuous welding points at a predetermined welding current value obtained from the result was determined. The appropriate current range was determined by the following procedure. Plate set: 2-piece set of the same type of surface-treated steel sheet shown in Examples Welding electrode: T-16D, Obara Co., Ltd. (Material code: DH
OM) Pressure between electrodes: 200 kgf Welding pattern: Start pressurization → Hold for 0.5 seconds → Apply predetermined current (0.2 seconds) → Release pressurization Appropriate current range measurement:
Upper and lower current values were measured, with the lowest current value that can secure a nugget diameter of 4 mm or more as the lower current value, and the lowest current value at which strong welding occurs between the sample piece and the electrode as the upper current value.

The limit number of continuous welding points is the upper limit of the number of continuous welding points at which a required nugget diameter can be secured, and was determined by the following procedure. Plate set: 2-piece set of the same type of surface-treated steel sheet shown in Examples Welding electrode: T-16D, Obara Co., Ltd. (Material code: DH
OM) Inter-electrode pressure: 200 kgf Welding pattern: Start of pressurization → Hold for 0.5 seconds → Apply predetermined current (0.2 seconds) → Pressurize Welding current value: Intermediate value of the appropriate welding current range previously obtained ( (Lower limit current value + upper limit current value) / 2 Limit continuous welding spot number: Under the welding conditions of 打, the hitting speed is set to 1 point / 3 seconds, and the maximum continuous welding point where the diameter of the nugget formed on the test piece does not become less than 4 mm. Measure.

The weldability was evaluated as Δ when the number of continuous hit points measured was 500 points or more, and as × when the number was less than 500 points. It can be seen that Examples Nos. 1 to 108 whose evaluation results are shown in Tables 1 to 4 show excellent weldability with the product of the present invention. On the other hand, in Comparative Examples 111 and 113,
In the case of No. 114, the weldability cannot be sufficiently ensured because the organic pigment is too thick and the conductive pigment in the organic film is too small.

The press formability was evaluated according to the following procedure. The steel sheet was sandwiched by a mold imitating a press-forming bead, and was pulled out at a constant speed while applying a load, and the damage state of the coating film was investigated.・ Sample pulling width: 30mm ・ Pressing load: φ4mm cylinder on one side, flat plate on the other side ・ Pressing load: 1000kg ・ Pulling speed: 200mm / min ・ Coating oil: Low viscosity oil coating Evaluation: △: No galling, no peeling of coating film X: The test was performed with galling or peeling of the coating film. It can be seen that Examples Nos. 1 to 108 whose evaluation results are shown in Tables 1 to 4 have excellent press workability with the product of the present invention. In contrast, Comparative Example 11
No. 8 is poor in press formability due to lack of lubricant.

[0029]

As described above, the organic composite plated steel sheet of the present invention is excellent in corrosion resistance and press workability, and can be used as a steel sheet for automobiles even when electrodeposition coating is omitted. In addition, workability is high because a chromium-free pigment is used as the rust preventive pigment in the organic coating.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location C25D 5/26 C25D 5/26 C

Claims (4)

[Claims] 1. Coating weight (g / m ² ) / plate thickness (mm) of one side or both sides of a steel sheet in order from the steel sheet side =
A Zn plating layer having an adhesion amount corresponding to 30 to 130, a chromate film having a total Cr adhesion amount of 10 to 150 mg / m ² ,
An organic film having a film thickness of 1 to 20 μm is formed, the organic film contains 1 to 40 vol% of a conductive inorganic pigment, 5 to 40 vol% of a chromium-free rust preventive pigment, and 1 lubricant.
A weldable type organic composite plated steel sheet characterized by being 40 to 40% by volume, the total of which is 7 to 65% by volume. 2. The weldable type organic composite plated steel sheet according to claim 1, wherein the Zn plating layer is one of electric Zn plating and hot-dip Zn plating. 3. The weldable organic composite plated steel sheet according to claim 1, wherein the chromate film is a poorly soluble chromate film having a water-soluble content of 30% or less. 4. The chromium-free rust preventive pigment comprises a basic zinc phosphite or a basic phosphite-based rust preventive pigment which is basic zinc calcium phosphite, or contains any one of them as a main component. , Zinc, nickel or cobalt hypophosphites, phosphites, phosphates, borates as auxiliary ingredients,
The weldable organic composite plated steel sheet according to claim 1, which contains at least one of molybdate and oxycarboxylate.