JPH08156174A - Highly lubricant organic resin-coated steel panel excellent in weldability - Google Patents

Abstract

PURPOSE: To obtain a steel panel excellent in lubricity, corrosion resistance and weldability by providing a chromate film on a zinc or zinc alloy plated steel panel in a specific chromium adhesion amt. and supplying a specific amt. of water dispersible org. resin emulsion particles or org. resin dispersion particles to the chromate film. CONSTITUTION: A chromate film is provided on a zinc or zinc alloy plated steel panel in a chromium adhesion amt. of 200mg/m<2> or less in terms of metal chromium and the following org. resin compsn. is applied to the upper surface of the chromate film to obtain a highly lubricant org. resin coated steel panel having a continuous and non-uniform org. resin film in an org. resin adhesion amt. of 0.05-2.0μm and excellent in weldability. The org. resin compsn. consists of water dispersible org. resin emulsion particles or org. resin dispersion particles of which the average particle size is 1.2 times or more the average thickness of the org. resin film, 3-40 pts.wt. of a solid lubricant per 100 pts.wt. of an org. resin and 5-50 pts.wt. of an inorg. filler per 100 pts.wt. of the org. resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly lubricious organic resin-coated steel sheet having an organic resin film, which is suitable for materials such as automobiles, home electric appliances and building materials.

[0002]

2. Description of the Related Art In recent years, various surface-treated steel sheets have been used in many industrial fields such as automobiles, home electric appliances, and building materials. Among them, zinc or zinc-based alloy plated steel sheets have a chromate film layer and a thin film A thin film organic resin coated steel sheet with an organic resin coating layer has overwhelmingly superior corrosion resistance among various rust-preventive steel sheets due to the anticorrosive action of the chromate film and the corrosive environment blocking effect of the organic resin film. ing. However, since it is coated with an insulating organic resin film, the weldability is not sufficient.

On the other hand, in the press forming process of a steel sheet, it is generally necessary to apply a lubricating oil, and therefore, it is necessary to degrease the lubricating oil after forming, but in recent years, improvement of working environment and atmospheric environment is further required. Due to the fact that there is a strong demand for cost reduction by omitting the degreasing process, user needs for steel sheets that can be press-formed without using lubricating oil are increasing day by day.

Under such a background, JP-A-4-44840
Japanese Patent Publication No. 4-94771 and Japanese Patent Publication No. 4-94771 disclose that a solid lubricant having a particle size of 3 to 100 μm (of which 10 wt% or more has a melting point of 120 ° C. or more and a particle size of 20 μm or more) is applied to an organic resin in an organic resin film. 2-40% by weight and, if necessary, 5-100% by weight of silica with respect to the organic resin, a lubricating thin film resin steel sheet excellent in lubricity, corrosion resistance and weldability is disclosed in JP-A-4-237449.
According to Japanese Patent Laid-Open Publication No. 10-90, a resin having a hydroxyl group and / or a carboxyl group is used in an amount of 10 to 80 parts by weight of silica, 5:95 to 95: 5 of a large particle size polyolefin wax and a small particle size polyolefin wax. Disclosed is a lubricated resin-treated steel sheet having a press coatability and a corrosion resistance in the processed portion, which has a resin film (0.3 to 3.0 g / m ^{2 in} terms of dry weight) containing 1 to 20 parts by weight of the polyolefin wax mixture contained in the following ratio. , Continuous press molding is possible without lubrication oil,
A steel sheet having excellent lubricity was obtained. However, the weldability is not yet sufficient, and further improvement is required.

Therefore, in JP-A-2-243333, a resin film amount containing 0.5 to 30% of a fluororesin is 0.1 to 2.0 g / m ²
The highly-lubricated surface-treated steel sheet having excellent conductivity, which has a discontinuous film, forms a discontinuous organic resin film in which a granular resin film having a particle size of 80 μm or less is dispersed in JP-A-4-56783. An organic resin-coated steel sheet for automobiles having a coating rate of 65 to 95% with an organic resin coating is disclosed in Japanese Patent Laid-Open No. 5-237451 in which an island-shaped organic resin coating having a particle size of 80 μm or less has a coating rate of 15 to 90%.
Disclosed is a steel sheet in which a lubricant is contained in the island-shaped organic resin coating film in an amount of 0.5 to 30%.

All of these are aimed at improving the spot weldability by securing a current-carrying point during welding by forming a discontinuous organic resin film. In order to obtain such a steel sheet, , It is necessary to spray the organic resin liquid using an electrostatic atomizer, which cannot be obtained by an ordinary simple roll coating method. Furthermore, since there is a portion of the steel sheet that is not covered with the organic resin film (the portion where the chromate film is directly exposed to the corrosive environment), compared to other organic resin-coated steel sheets.
A large amount of Cr was eluted, and sufficient corrosion resistance was not obtained.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a steel sheet excellent in lubricity, corrosion resistance and weldability.

[0008]

In view of the above circumstances, the inventors of the present invention have earnestly studied a method for improving the lubricity, corrosion resistance and weldability of an organic resin-coated steel sheet, and as a result, have found that an organic resin forming an organic resin film is formed. The present invention has been completed, knowing that it is effective to supply in the form of emulsion particles or dispersion particles, instead of being supplied in the form of solution.

Here, the gist of the present invention is that a chromium or zinc-based alloy-plated steel sheet has a chromate film having a chromium deposition amount of 200 mg / m ² or less in terms of metallic chromium,
It has the following composition in the upper layer, and the organic resin adhesion amount is 0.05 to 2.
It is a highly lubricious organic resin-coated steel sheet with excellent weldability, which is provided with a continuous and non-uniform organic oil coating of 0 μm.

For the average film thickness ^{* of the} organic resin film, 1.
Water-dispersible organic resin emulsion particles having an average particle size of 2 times or more, or organic resin dispersion particles having the above particle size, and 3 to 40 parts by weight of a solid lubricant per 100 parts by weight of the organic resin, and further, if desired. 5 to 50 parts by weight of inorganic filler per 100 parts by weight of organic resin.

Here, the average film thickness of the organic resin film was calculated by the following equation.

[0012]

[Equation 1]

[0013]

The structure and operation of the present invention will be described in detail below. Base material plated steel sheet The plated steel sheet used in the present invention is a zinc or zinc alloy plated steel sheet, and the manufacturing method thereof may be a conventional method such as electroplating or hot dipping, and is not particularly limited. The coating amount is not particularly limited, but it is preferably in the range of 5 to 100 g / m ² per surface in view of balance between workability and corrosion resistance. It is more preferably within the range of 10 to 60 g / m ² .

Chromate film layer The method of forming the chromate film may be any of coating type, reaction type and electrolytic type treatments, and any of them may be carried out by a conventional method. The chromate solution to be used may contain various known additives (acids such as hydrofluoric acid and phosphoric acid, fluorides, colloidal silica, etc.) in addition to the chromium solution or chromate salt.

The amount of the chromate film deposited is 2 in terms of metallic Cr.
The range below 00 mg / m ² is good. When it exceeds 200 mg / m ² , chromium elution is observed, the spot weldability is deteriorated, and the effect of improving the corrosion resistance is reduced, resulting in almost saturation. If the amount of chromate adhered is too small, the adhesion and corrosion resistance at the steel plate / resin interface may be deteriorated. Therefore, the range of ^{2 to} 200 mg / m ² is preferable. More preferably 2
It is ~100 mg / m ^2.

Organic resin film layer On the first layer chromate film formed as described above,
An organic resin film having the following composition is provided within the range of 0.05 to 2.0 μm in the amount of organic resin attached when dried.

Water-dispersible organic resin emulsion particles having a particle size 1.2 times or more that of the dried organic resin film, or organic resin dispersion particles having the same particle size as those, and 3 to 40 parts by weight per 100 parts by weight of the organic resin. Parts by weight of solid lubricant and optionally 5 to 50 parts by weight of inorganic filler per 100 parts by weight of organic resin.

Aqueous organic resin paint containing each of these components is applied, and the average film thickness of the organic resin film when dried is from 0.05 to
It is provided within the range of 2 μm. If necessary, it may be used as an oil paint.

The thickness of the organic resin film at this time is 0.05 μm
If it is less than the above range, direct contact between the die and the plated surface tends to occur during pressing, and the corrosion resistance becomes insufficient. On the other hand, if it exceeds 2 μm, the corrosion resistance performance is saturated and the weldability deteriorates.
More preferably, it is 0.1 to 1.0 μm.

In order to obtain this organic resin film, a thermosetting film which is simple in equipment and fast in film formation is industrially preferable, but an ultraviolet or electron beam curing film or a room temperature drying film can be used.

The organic resin liquid is applied by a usual roll coater method. Also, existing methods such as air knife coater and electrostatic coating can be adopted. Further, both water-based and solvent-based paints may be used and are not limited.

Base organic resin: The base resin type is a carboxyl group in order to improve the adhesiveness with the base steel plate and the adhesiveness with the coating film when the organic resin film is further coated.
It is desirable to have a polar functional group such as a hydroxyl group, a sulfone group, or a nitro group. As such resins, acrylic resins, epoxy resins, urethane resins, vinyl resins, etc. are generally used.

The organic resin particles forming the base resin must be adjusted to have an average particle diameter of 1.2 times or more the thickness of the dried organic resin coating film. In this case, the organic resin particles are not agglomerated but sufficiently dispersed. Then, in the process of forming the coating film, when the organic resin particles in the immediate vicinity are welded, the coating film surface is not sufficiently leveled to form a film. That is, it is considered that an organic resin film having a locally nonuniform thickness is formed. As a result, the spot where the film thickness is locally thin becomes an energizing point, and the spot weldability is improved.

However, if the average particle size of the organic resin particles is less than 1.2 times the dry coating film thickness, a plurality of organic resin particles agglomerate in the organic resin layer during film formation, resulting in a uniform surface-leveled film thickness. An organic resin film is formed and weldability cannot be improved sufficiently.

The glass transition temperature (Tg) of the resin film after solidification of the base resin is preferably 20 ° C. or higher, more preferably 80 ° C. or higher.
During continuous press molding, the temperature of the mold rises to about 120 ° C, so if the glass transition temperature of the resin film is less than 20 ° C, the resin film will easily peel off, and the peeled resin will adhere to the mold or press-formed product. Problems occur. On the other hand, Tg is 120
If the temperature exceeds ℃, the resin film will be very hard, and the internal stress of the film will be high, causing a poor appearance due to rubbing with the mold during molding, and cracks in the resin film to deteriorate corrosion resistance. There are problems such as.

Solid Lubricant: The solid lubricant contained in the organic resin-coated steel sheet of the present invention is preferably paraffin wax, polyolefin wax, or fluororesin.

The solid lubricant is preferably added in an amount of 3 to 40 parts by weight, more preferably 10 to 30 parts by weight, based on 100 parts by weight of the organic resin. If it is less than 3 parts by weight, the absolute amount of the solid lubricant is insufficient, and sufficient lubricity cannot be obtained. If the amount exceeds 40 parts by weight, the film formation of the base resin is hindered, the resin film strength is reduced, and the lubricity is reduced.

The solid lubricant may have the same particle size, but when continuous press molding is performed in multiple stages, it is necessary to include two kinds of solid lubricants having different particle sizes. Is more effective. In other words, the large particle size solid lubricant on the organic resin film, which has a high exposed rate, reduces the friction between the steel plate and the die at the initial stage of press forming, and the small particle size embedded in the film. The solid lubricant is preferable because it is exposed on the organic resin film in the latter stage of press molding and contributes to the reduction of the friction coefficient.

The particle size of the large particle size solid lubricant is preferably in the range of 0.5 to 10 times the thickness of the organic resin film. If the particle size is less than 0.5 times the thickness of the organic resin film, it is difficult to act as a lubricant in the initial stage of press molding, but rather as a solid lubricant of small particle size in the latter stage of press molding. On the other hand, if it exceeds 10 times, powdering resistance and corrosion resistance deteriorate. If the particle size of the small particle size solid lubricant is less than 0.05 times the thickness of the organic resin film, it is difficult to act as a lubricant even in the later stage of press molding. Are preferred.

The mold temperature is 10 at the time of continuous press molding.
Since the temperature rises to about 0 ° C., it is necessary that the solid lubricant does not melt at a temperature lower than that in order to maintain the good lubricity of the organic resin film even at such a high temperature. When a large amount of a low-melting solid lubricant is used, when the die temperature becomes higher than the melting point, the solid lubricant may melt and adhere to the mold, degrading continuous press formability. Therefore, the melting point of the solid lubricant is preferably 100 ° C. or higher, and particularly the large particle size solid lubricant having a high proportion exposed from the organic resin film preferably has the melting point of 100 ° C. or higher. The content of the large particle size solid lubricant is preferably 3 to 50 parts by weight based on 100 parts by weight of the total amount of the solid lubricant.

Inorganic filler: If desired, an inorganic filler may be added to the resin liquid for the purpose of improving the corrosion resistance of the resin film. Examples of useful inorganic fillers include dry silica, colloidal silica, organosilicasol and the like. The amount of inorganic filler added is 5 per 100 parts by weight of resin solids.
To 50 parts by weight, more preferably 10 to 25 parts by weight. If the amount of the inorganic filler added is less than 5 parts by weight, the above effect cannot be sufficiently obtained, and if it exceeds 50 parts by weight, the resin film becomes extremely hard and brittle, and the resin film cracks during press molding, or finally peels off. Corrosion resistance and lubricity may be deteriorated due to such problems. The average primary particle size for uniformly dispersing the inorganic lubricant in the resin is 1 to 100 nm, preferably 1 to 50 nm.

Other compounding agents: A silane coupling agent may be added to enhance the reactivity between the organic resin and the inorganic filler. Silane coupling agents include, but are not limited to, γ-aminopropyltriethoxysilane, vinyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and the like. Further, a crosslinking agent such as melamine and amine, a silane coupling agent, and a pigment can be added to the organic resin coating material used in the present invention, if necessary.

Next, the working effects of the present invention will be described in more detail with reference to Examples, but it is understood that these are merely examples and the present invention is not unduly limited thereby. Will be done.

[0034]

[Example] Pure zinc electroplating with a coating amount of 20 g / m ² and zinc-nickel electroplating on both surfaces of a cold rolled steel sheet defined by JIS SPCC with a plate thickness of 0.8 mm under the plating bath composition and plating conditions shown in Table 1. It was plated.

The obtained plated steel sheet is dipped in a reactive chromate treatment solution (containing chromic acid, phosphoric acid, and sulfurous acid), washed with water, and dried to give a pure zinc plating film with a metal chromium content of 2 to 250 mg / m 2. A chromate film of ² was formed.

Then, a resin solution in which a resin having the composition shown in Tables 2 and 3, a lubricant, and an inorganic filler (silica) is uniformly dispersed is coated on the chromate film by a roll coater, and the coating is carried out at 130 ° C.
It was baked for 20 seconds and dried to obtain an organic resin-coated steel sheet.
The organic resin-coated steel sheet thus obtained was tested by the following method to evaluate the performance. The results are shown in Tables 4 and 5.

[Lubricity] Bowden tester (tip terminal: steel ball)
Was used to measure the dynamic friction coefficient values when the test piece temperature was 20 ° C., 60 ° C. and 120 ° C. without oil coating. The load applied at this time is
The number of sliding was 10 times at 500 g. ◎: Dynamic friction coefficient is less than 0.10 ○: Dynamic friction coefficient is 0.10 or more and less than 0.15 △: Dynamic friction coefficient is 0.15 or more and less than 0.20 ×: Dynamic friction coefficient is 0.20 or more.

[Appearance after processing] A non-oiled test piece was cylindrically drawn under the following test conditions, and the appearance after processing at that time was evaluated. Cylindrical drawing conditions Appearance evaluation Wrinkle suppression pressure: 1 ton Punch diameter: 40mm ◎: No galling Die diameter: 42mm ○: Slight galling Squeeze ratio: 2.0 △: Slight galling Specimen temperature: 100 ° C ×: Large galling

[Plate Corrosion Resistance] A test piece is subjected to a salt spray test with a flat plate.
It was subjected to (JIS Z 2371) and the white rust generation time was observed. ◎: White rust occurrence time of 200 hr or more ○: White rust occurrence time of 150 hr or more and less than 200 hr △: White rust occurrence time of 100 hr or more and less than 150 hr ×: White rust occurrence time of less than 100 hr.

[Spot Weldability] Under the following test conditions, continuous spot welding was carried out without exchanging the electrodes, and evaluation was made by the number of continuous dots until shear fracture. Test condition Evaluation point Electrode: CF type 4.5mmφ ◎: 1000 dots or more Energizing time: 12 cycles ○: 700 dots or more and less than 1000 dots Pressure: 200 kgf △: 400 dots or more and less than 700 dots ×: Less than 400 dots

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

[Table 4]

[0045]

[Table 5]

[0046]

INDUSTRIAL APPLICABILITY The lubricious organic coated steel sheet of the present invention has both high lubricity and weldability that conventional surface-treated steel sheets do not have, and is useful for automobiles, home electric appliances and building materials.

Claims (2)

[Claims] 1. A zinc or zinc-based alloy plated steel sheet,
Chromium coating has a chromate film of 200 mg / m ² or less in terms of metallic chromium, and the average film thickness of the following composition is 0.05 in the upper layer.
Characterized by having an organic resin film of ~ 2.0 μm,
Highly lubricative organic resin coated steel sheet with excellent weldability. Water-dispersible organic resin emulsion particles having an average particle size of 1.2 times or more of the average film thickness of the organic resin film or organic resin dispersion particles having the above particle size, and 3 to 40 parts by weight per 100 parts by weight of the organic resin. Parts by weight of solid lubricant. 2. Further, 5 parts by weight with respect to 100 parts by weight of the organic resin.
The highly lubricious organic resin-coated steel sheet having excellent weldability according to claim 1, which contains ˜50 parts by weight of an inorganic filler.