JPH0551763A - Manufacturing method of steel sheet with lubrication and excellent paint adhesion - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention relates to a method for producing a lubricated surface-treated steel sheet having excellent surface characteristics. Provided is a method for producing a low-cost surface-treated steel sheet which is capable of deep drawing without using press oil, has excellent surface characteristics, and saves user's process, which is environmentally friendly and low cost. [Composition] A lubricating coating containing a zinc-plated steel plate surface chromate-treated to contain an aqueous resin, silica sol, a polar group-added molecular weight of 1000 to 4000, an acid value of 1 to 20 and a polyolefin wax dispersion having a particle size of 3 μm or less. 0.5 to 5 g / m ² applied, reaching plate temperature 90
Rapidly bake to ~ 200 ° C and cool.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is excellent in high-speed machining lubricity,
Further, it is an invention relating to a method for producing a lubricity plated steel sheet which is used without removing the coating film after pressing, which is excellent in surface characteristics such as paint adhesion.

[0002]

2. Description of the Related Art Surface-treated steel sheets coated with a thin organic film are used in place of post-painted products which have been conventionally coated after processing. This steel sheet has a zinc-based plating film as an underlayer and is coated with an organic film, and can be welded, and has good characteristics in adhesion workability and corrosion resistance.

JP-A-3-39485 discloses a resin coating in which a zinc-based plated steel sheet is subjected to a chromate film treatment, and silica and a wax having a glass transition point (Tg point) of 40 ° C. or higher are dispersed in an aqueous resin. 0.3 to 3g in dry film thickness
/ M ² coating is disclosed. In addition, JP-A-3
JP-A-28380 discloses that a paint comprising a carboxylated polyethylene resin and a Teflon lubricant is chromated on an electrogalvanized steel sheet in a dry film thickness of 0.
A lubricated steel sheet obtained by coating with 5 to 4.0 g / m ² is disclosed. These surface-treated steel sheets provide lubricity, corrosion resistance, weldability, and paint adhesion by the combined effect of plating, chromate, and organic coating, and are still under active development for the purpose of improving productivity and quality. There is.

[0004]

The prior art is widely applied to shallow drawn products. However, in order to thoroughly reduce costs, save labor, and solve environmental problems in recent years, it has lubricating characteristics that can be applied to the field of high-speed deep drawing without applying press oil, and without degreasing after pressing. It cannot be said that it is sufficient for use as it is as a precoated steel sheet. To meet this demand, the product must have a good performance balance, high quality and low cost. The prior art has improved lubricity. However, other performances such as adhesion of top coating, corrosion resistance and weldability need further improvement. In addition, there is a problem in the stability of the paint in terms of manufacturing. That is, the aqueous resin, the lubricant and the silica sol that compose the coating are all dispersions, and are stable by themselves,
When mixed, there is a problem in that it easily aggregates. In addition, the cost of coating will increase if new equipment is installed, so it is necessary to use a coating that can be produced in the existing plating line under simple manufacturing conditions. A manufacturing method that solves all of these problems has not yet been established.

[0005]

The gist of the present invention is to subject the surface of a plated steel sheet to a chromate treatment of 5 to 100 mg / m ^{2 in} terms of Cr, and then add silica to the upper layer as an aqueous resin 1.
0.5 to 5.0 g / m ² as a dry adhesion amount of a lubricating coating containing 10 to 70 parts by weight of solids based on 00 parts by weight and 2 to 30 parts by weight of the following polyolefin wax dispersion as a wax. It is a method for producing a lubricated plated steel sheet having excellent paint adhesion, which comprises coating and immediately baking at an ultimate plate temperature of 90 to 200 ° C. and cooling. [Polyolefin Wax Dispersion] A polyolefin wax having a polar group containing an ethylenically unsaturated carboxylic acid or its anhydride or a carboxyl group-containing derivative as a binding component has a molecular weight of 1000 to 4000 and an acid value of 1 to 20% or less. A spherical polyolefin dispersion having a diameter of 3 μm or less dispersed in water or an aqueous solution with an emulsifier.

[0006]

The plated steel sheet targeted by the present invention includes a galvanized steel sheet manufactured by electroplating, hot dipping, and vapor deposition plating, a zinc alloy plated steel sheet, a dispersion plated steel sheet, a laminated plated steel sheet, aluminum and an aluminum alloy plated steel sheet. To do. The plating amount is not particularly limited, but in the present invention, it is preferably 5 to 100 g / m ² . After the cold-rolled steel sheet is plated by the above existing method, chromate treatment is performed. Chromate adhesion amount is 5 to 1 in terms of Cr
It is 00 mg / m ² . As the type of chromate treatment, any of electrolytic chromate, etching chromate, and coating chromate can be applied to the present invention, but electrochromic or etching chromate having a low plate temperature in which a chromate film is difficult to dissolve at the time of applying an aqueous paint is desirable. The reason why the amount of deposited Cr is limited is that if Cr is less than 5 mg / m ^2, it is difficult to obtain corrosion resistance, and if it exceeds 100 mg / m ² , cohesive failure of chromate itself occurs and adhesion cannot be obtained.

The present invention is characterized by a lubricating film, which will be described in detail below.

The present invention is a method for producing a plated steel sheet having excellent lubricity and surface characteristics (corrosion resistance, paint adhesion). Conventionally, it has been known to apply wax to a lubricating film, but unfortunately, the chemically inactive property of wax does not provide surface properties, and a paint dispersed with a high concentration of emulsifier is used. Because of this, the emulsifier remains in the coating film, resulting in the drawback that a coating film with good surface characteristics cannot be obtained. The present invention solves this difficult problem.

The lubricating coating composition used in the present invention comprises an aqueous resin containing no volatile solvent, silica sol, and a highly reactive polyolefin wax dispersion as components. As the water-based resin, olefin acrylic resin, polyolefin ionomer, epoxy resin, urethane epoxy resin, polyester resin, acrylic resin,
Vinyl acetate resin can be used. In particular, olefin acrylic resin, polyolefin ionomer, urethane epoxy resin, and polyester resin are preferable.

The composition weight ratio is such that silica sol is 10 to 70 and wax is 2 to 30 parts by weight with respect to 100 parts of the aqueous resin. The role of the silica sol is to improve the corrosion resistance and film strength of the film, and to improve the heat resistance of the resin against heat generated during press working. Silica sol resin 100
If the weight ratio to 10 is less than 10, corrosion resistance cannot be obtained and 70
If it exceeds the above value, the coating will be hard and will not stretch, so it will not be able to follow the processing, and the pressability will deteriorate. The preferred weight ratio range of silica sol to resin 100 is 30 to 50. The shape of the silica sol is preferably fine particles having a diameter of 5 to 50.
nm spherical silica sol or linear silica chemically bonded with a diameter / length of 5 to 50 nm and a length / thickness ratio of 1 to 5 is used. If the diameter of the silica sol is less than 5 nm, the stability of the coating exceeds the practical range, which is not preferable, and if it exceeds 50 nm, galling tends to occur during press working. The polyolefin wax is for imparting lubricity. The concentration of the polyolefin wax varies depending on the degree of pressing, and it is difficult to limit the concentration, but for high-speed crank press applications, the concentration ratio described above is used. That is, if the polyolefin wax is less than 2 with respect to the resin 100, it is difficult to obtain sufficient characteristics for high-speed deep drawing, and if the polyolefin wax is more than 30, the surface characteristics, particularly the adhesion of the top coat, deteriorates. A preferable weight ratio range of the polyolefin wax to the resin 100 is 5 to 20.

In the present invention, unlike the conventional wax, a polyolefin wax dispersion having excellent surface properties and being easily dispersed uniformly in the aqueous resin liquid is used as the polyolefin wax. This polyolefin wax dispersion has an acid value of 1 to 20 and a molecular weight of 1 having a polar group containing an ethylenically unsaturated carboxylic acid or its anhydride or a carboxyl group-containing derivative as a binding component.
000-4000 almost spherical polyolefin wax such as polyethylene wax, polypropylene wax, polybutylene wax with an emulsifier concentration of 5% or less,
A spherical polyolefin dispersion having a diameter of 3 μm or less, which is obtained by dispersing in water or an aqueous solution without using an emulsifier, is preferable.

That is, a lubricant having a characteristic of having a high melting point in a shape close to a true sphere by ensuring chemical reactivity with a polyolefin to which a polar group is added and dispersing it in an aqueous solution without lowering the slipperiness of the polyolefin. is there.

The polar group is an oxidized polyolefin wax obtained by oxidizing a polyolefin wax with an oxidizing agent such as oxygen, ozone or nitric acid in the presence of a catalyst, or acrylic acid, methacrylic acid, crotonic acid, maleic acid. , Ethylenically unsaturated carboxylic acid monomers such as fumaric acid and itaconic acid, and polyolefin wax are dissolved with benzol and the like, and heated with a polymerization initiator (peroxide, redox, heavy metal catalyst, etc.) in a nitrogen stream for grafting. obtain.

The limiting reason for the molecular weight is the lubricating properties and melting point of the wax. Ideally, it is 2000 to 4000.
The acid value of the modified polyolefin is limited in terms of surface characteristics and dispersibility. If the acid value is less than 1, paint adhesion cannot be obtained, and if the acid value exceeds 20, frictional resistance is large and pressability deteriorates. The preferable acid value range of the polyolefin is 5 to 10. The reason why the diameter of the dispersed particles is limited is that if the diameter exceeds 3 μm, the surface becomes rough and build-up on the roll easily occurs on the production side. The preferred average diameter is 0.
It is 1 to 1.0 μm. If it is too small, the surface characteristics tend to deteriorate.

The coating and baking methods will be described below.

After the chromate treatment, a dry coating amount of 0.5 to 5.0 g / m ^{2 is} applied to the lubricating coating, and the coating is immediately baked to reach an ultimate plate temperature of 90 to 200 ° C. The dry adhesion amount is limited because both the lubricity and the corrosion resistance are improved in proportion to the dry adhesion amount, and the dry adhesion amount is 0.5 g / m.
^If it is less than ² , lubricity and corrosion resistance cannot be obtained, and if the dry adhesion amount exceeds 5.0 g / m ² , welding is not possible, and build-up on the roll in production and foaming due to rapid heating are likely to occur, which is not practical. Because. The most preferable dry adhesion amount is 1 to 3 g / m ² . As a coating method, an existing method such as a roll coater, an air knife coater or electrostatic coating can be adopted.

After coating, it is baked immediately. In the present invention, good results can be obtained by the rapid heating method in which baking is performed in the shortest possible time. That is, it is preferable to put in a baking furnace within a few seconds after coating and bake to a final plate temperature of 90 to 200 ° C. within 10 seconds. The reason is that, as described above, the surface concentration of the wax is suppressed in order to obtain the lubricating film having the excellent surface characteristics which is the object of the present invention. In the conventional wax-containing paint, the inert wax floats on the surface and occupies the surface, and the adhesion of the topcoat paint cannot be obtained. As the baking method, known methods such as hot air, infrared rays, induction heating, gas direct-fired furnace, electric furnace and the like can be adopted, but the rapid heating baking method is preferable as described above.

The aqueous resin used in the present invention may optionally contain a crosslinking agent such as melamine or amine, a silane coupling agent,
Pigments and the like can be added.

[0019]

EXAMPLES Bath components in the examples are concentration ratios as non-volatile components. The symbols and contents of the examples are shown in Table 1.

[0020]

[Table 1]

Example 1 Electrogalvanized steel sheet having a plating amount of 20 g / m ² (sheet thickness: 0.
(8 mm) surface is subjected to a commercially available etching chromate treatment, washed with water and coated with a lubricating coating shown in Table 2 by a roll coater.
It was baked at 50 ° C. and cooled with water to prepare a lubricity plated steel sheet.

The resulting lubricated plated steel sheet was evaluated for dynamic friction coefficient and "galling" by a square cylinder crank press. The dynamic friction coefficient is 10 for a steel ball with a diameter of 10 mm.
It was loaded with 0 g, moved at 100 mm / min, the tension (g) was measured with a load cell, and calculated by the tension / load.
The conditions of the crank press are 65 x 115 mm for a rough plate (0.8 x 220 x 180 mm) with wrinkle suppression pressure of 6 tons,
Molded to a height of 50 mm, the side was peeled off with adhesive tape (Nichiban Cello Tape), and the lightness (L) was measured with a color difference meter on an imitation paper. ₂ ) and the difference (L ₂ −L) are shown as ΔL values. Corrosion resistance is the time when white rust occurs in a salt spray test in an area ratio of 5%, and paint adhesion is a commercially available melamine alkyd resin paint applied at 20 g / m ^{2 in} dry adhesion amount and hot air 120 ° C.
After baking for 20 minutes and squeezing it by an Erichsen tester for 9 mm, it was peeled off with an adhesive tape (Nichiban Cello Tape) and visually evaluated (peeling area ratio). Further, the continuous spot weldability is such that the current of 9 kA, the applied pressure of 250 kgf, and the electrode tip diameter of 4.5 m at intervals of 20 mm when two test plates of 200 × 300 mm are combined.
spot welding under the conditions of m, energizing time 12 cycles,
Evaluation was made based on the number of weldable points. The results are shown in Table 2.

[0023]

[Table 2]

No. Nos. 1 to 4 have a lubricant coating amount of 0.
In Examples of the present invention changed to ⁵ , 1.0, 2.0, and 3.0 g / m ² , the thicker the film, the lower the coefficient of friction, and almost no galling of the crank press, indicating good lubricity. Corrosion resistance is excellent in proportion to the film thickness. However, in terms of weldability, no.
Nos. 1 and 2 obtained good results, but No. 1 having a large film thickness. Three and four
Is hard to weld.

No. Nos. 5 and 6 are examples of the present invention in which the amount of chromate deposition was changed. No. 5 has a slightly lower corrosion resistance and has a high adhesion amount. Sample No. 6 had a paint adhesion property and was slightly peeled off, but good results were obtained in all cases. No. 1 having a low silica content. No. 7 has a slightly low corrosion resistance and a high silica content. No. 8 had a slightly high friction coefficient and press galling was recognized, but both are at a practical level.

No. Nos. 9 to 11 are examples of the present invention in which the content of the olefin wax with respect to the resin was changed. In No. 9, galling occurred in pressability.
When the wax content is increased, the galling of the pressability is improved, and No. No. 11 gave good pressing results. No. 1
Sample No. 1 had a slight adhesiveness to the paint and had a tendency to peel off.

No. Reference numeral 12 is a comparative example using a conventional polyolefin wax to which no polar group is added, and paint adhesion cannot be obtained at all.

No. 13 to 15 are examples of the present invention in which the acid value of the polyolefin wax lubricant is changed. When the acid value is high, the coating adhesion is improved, but it becomes easy to bite by pressing. No. Nos. 13 and 14 are practical levels, but Nos. No. 16 is too biting. No. No. 15 is an example in which the particle size of the wax is 3 μm, and although the corrosion resistance and the adhesion are slightly lowered, the pressability is good and it is practical. N
o. 17 is a comparative example of a high molecular weight polyolefin resin,
Pressability cannot be obtained. No. On the contrary, 18 is a comparative example of a low molecular weight olefin, and the performance is generally poor.

Example 2 A cold-rolled steel plate having a plate thickness of 0.8 mm was plated with an existing method to a plating amount of 20.
Electrogalvanization of g / m ² was performed, and the surface thereof was subjected to chromic acid / sulfuric acid = 30 / 0.3 g / l bath with current density of 10 A / d.
m ² , electrolyzed for 2 seconds, washed with water, Cr adhesion amount 60 mg / m ²
Lubricating coatings with different water-based resins shown in Table 3 were coated with a roll coater, immediately baked at a plate temperature of 120 to 170 ° C. depending on the resin in a gas direct-fired furnace, and water-cooled to prepare a lubricated plated steel sheet. The evaluation was performed according to Example 1, and the obtained results are shown in Table 3.

[0030]

[Table 3]

No. 19 is an olefin acrylic resin, N
o. No. 20 is a polyethylene ionomer of the present invention, which shows a good balanced performance. No. Reference numeral 21 is an example of the present invention of styrene-acrylic resin, and some galling occurred due to pressability. No. No. 22 is a polyester resin of the present invention, and good results were obtained. No. No. 23 is an example of the present invention in which the water-based resin is vinyl acetate, which is in a practicable range but generally low in performance. No. 24-26 uses epoxy resin,
In the examples of the present invention in which the baking plate temperature was changed, good pressability, corrosion resistance, and paint adhesion were obtained, but No. No. 24, which has a low corrosion resistance and a high plate temperature. No. 26 has excellent corrosion resistance, but on the other hand, galling is likely to occur due to pressability. No. Two
Nos. 7 and 28 are examples of the present invention in which the type of silica is changed, and No. 7 having a large silica particle size. 28 is paint adhesion and easy to peel off,
I got almost balanced performance.

Example 3 12% Ni-Zn electrogalvanized steel sheet (plating amount 2
0 g / m ²⁾ to electrolytic chromating conducted at Cr deposition amount 50 mg / m ² Aim commercial coating chromate on the surface of the galvanized steel sheet (coating weight 4020 g / m ^2), No. shown in Table 2 Lubrication-plated steel sheet was prepared under the condition of 2 (N
o. 29, 30).

No. No. 29 has a coefficient of friction of 0.07, almost no galling on the crank press (ΔL = 0), and corrosion resistance of 1
Good paint adhesion was obtained for 000 hours. No. Three
0 is a friction coefficient of 0.08, and press galling is ΔL = −0.
9, the corrosion resistance was 500 hours, and the paint adhesion was 2%, which were substantially good results.

[0034]

The plated steel sheet produced by the method of the present invention is
Since deep drawing can be done without applying pressing oil, and it can be used as it is as a corrosion-resistant coating or coated steel sheet without coating without removing the coating, the degreasing process can be omitted, the environmental destruction due to evaporation of the degreasing solvent can be prevented, and the work environment can be improved. It is a high-quality surface-treated steel sheet that has the merits of improvement and can minimize the total cost.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazo Shibata 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Kimitsu Works

Claims (3)

[Claims] 1. The surface of a plated steel sheet is 5 to 10 in terms of Cr.
After a chromate treatment of 0 mg / m ² was performed, silica was added to the upper layer in an amount of 10 parts by weight based on 100 parts by weight of the aqueous resin.
˜70 parts by weight, and a dry coating amount of a lubricating coating material containing the following polyolefin wax dispersion in a proportion of 2 to 30 parts by weight as a wax: 0.5 to 5.0 g / m
^{2. A} method for producing a lubricated plated steel sheet having excellent paint adhesion, which comprises coating, immediately baking at an ultimate plate temperature of 90 to 200 ° C. and cooling. [Polyolefin Wax Dispersion] A polyolefin wax having a polar group containing an ethylenically unsaturated carboxylic acid or its anhydride or a carboxyl group-containing derivative as a binding component has a molecular weight of 1000 to 4000 and an acid value of 1 to 20% or less. A spherical polyolefin dispersion having a diameter of 3 μm or less dispersed in water or an aqueous solution with an emulsifier. 2. An olefin acrylic resin containing no volatile solvent as the aqueous resin, a polyolefin ionomer,
The method according to claim 1, wherein an epoxy resin, a urethane epoxy resin, a polyester resin, an acrylic resin, or a vinyl acetate resin is used. 3. The method according to claim 1, wherein a spherical silica sol having a diameter of 5 to 50 nm or a linear silica sol is used as silica.