JP3113171B2 - Method for producing surface-treated steel sheet with excellent press workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet having excellent press working properties for use in parts for home appliances, building materials and automobiles, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a lubricated resin-treated steel sheet having excellent workability, a lubricating property is provided by dispersing a lubricant in a coating film. Is generally known to deteriorate. It is said that this is because the base resin is particularly softened and becomes tacky, and the lubricity with the mold is impaired. As a solution to these problems, as disclosed in JP-A-1-301333 using a resin containing a high glass transition temperature,
One side of the plated steel sheet has a resin coating having a glass transition point of 70 ° C. or higher of a resin mixture or composite containing a resin having a hydroxyl group and / or a carboxyl group, silica and a solid lubricant, and has a hydroxyl group on the other side. And / or a method using a lubricated resin-treated steel sheet having a resin film containing silica and a resin having a carboxyl group and having excellent moldability and corrosion resistance, using a lubricant having a particle diameter larger than the coating thickness, or employing a high melting point lubricant And so on. However, the types of resins that can be selected for these technologies are limited, and
There are problems in that elongation characteristics cannot be sufficiently ensured and that the paint is easily separated, and that there is a problem that the optimum particle size of the lubricant changes according to the film thickness.

Accordingly, the present applicants have disclosed Japanese Patent Application Laid-Open No. Hei 6-1551.
No. 84, the first surface of the plated steel sheet
A chromate coating having a Cr adhesion of 5 to 100 mg / m ² or a chemical conversion coating of a phosphate coating having an adhesion of 0.2 to 2.0 g / m ² as a layer, a bisphenol type skeleton as a second layer,
Ether having an ester skeleton and a carboxyl group
The sum (a + b) of the ester type urethane resin (a) and the epoxy resin (b) is 50 to 85% by weight based on the total solid content;
A film obtained by applying and baking an aqueous lubricating paint containing 10 to 30% by weight of polyolefin wax (c) and 10 to 40% by weight of silica (d) having a particle size of 3 to 30 nm.
There has already been proposed a press-lubricating non-delamination type lubricated plated steel sheet provided with a coating of 2 to 5 μm.

[0004]

However, in the above-mentioned Japanese Patent Application Laid-Open No. 6-155184, as shown in FIG. 6, a plating film 2, a chromate or phosphate conversion film 3, In the film structure composed of the lubricating film 4, the lubricant 5 is dispersed in the lubricating film 4 to provide working lubricating properties. There is a problem that it cannot be obtained.

On the other hand, in order to obtain these coated steel sheets,
Since off-line processing as equipment for a coating line or equipment in a plating line requires processing on a large-scale equipment, it is a fact that the passing speed is greatly limited by the coating baking process. Therefore, a method of forming a layer having particularly high lubricating performance on the surface of the lubricating coating 4 has been proposed.

FIG. 7 is a conceptual diagram showing a conventional lubricating film forming process and a surface state. As shown in FIG. 7, when the lubricating coating 4 on the original plate 7 is a water-based emulsion paint, if baking is performed at high speed by high-temperature rapid heating, skinning 8 is generated on the surface due to rapid evaporation of water on the outermost surface. . The skin 8 on the surface is formed by gas evacuation holes 9 due to moisture evaporated from the inside.
However, particularly in a lubricated steel plate, there is a problem that the formation of a surface lubricating layer is hindered by the skinning phenomenon on the surface, and a film having high lubricating performance cannot be formed under high-speed heating conditions.

[0007] Accordingly, to solve these problems, the present inventors have intensively developed and as a result, the lubricant layer on the surface prevents direct contact between the resin and the mold, and the particles dispersed in the coating film are deep drawn. A surface-treated steel sheet with excellent workability that can be used as a lubricant supply source even when the film is severely deformed due to processing, etc. Is provided.

[0008]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems of the prior art. The gist of the invention is as follows: (1) In a high-speed plating / painting line, Cr deposited as a first layer on the surface of the plated steel sheet amount 5 to 100 mg / m ² of chromate film or coating weight 0.2 to 2.0 g / m ²
The total (a + b) of the ether / ester type urethane resin (a) and the epoxy resin (b) having a bisphenol type skeleton, an ester skeleton, and a carboxyl group as the second layer is a conversion coating with respect to the total solid content. 50 to 8
A lubricating film thickness of 0.3 to 5 μm obtained by applying and baking an aqueous lubricating paint containing 5% by weight and 10 to 40% by weight of (d).
m and the lubricant concentration in the lubricating layer is 10 to 30%.
A method for producing a surface-treated steel sheet having excellent press working characteristics, comprising dispersing and providing a surface lubricating layer thickness of 0.04 to 1 μm as a third layer on the lubricating layer. (2) In the method described in (1), the sheet temperature at the time of coating is 40
A method for producing a surface-treated steel sheet having excellent press workability, characterized in that the temperature is between 60 ° C and 60 ° C.

[0009]

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing a coating structure of a surface-treated steel sheet having excellent press workability according to the present invention. That is, a plating film 2, a conversion film 3 of a chromate or phosphate film, a lubricating film 4, and a surface lubricating coating layer 6
The lubricant 5 is present in a dispersed state in the lubricating coating 4. Each of the coatings can have a different configuration with different thicknesses on both sides, one side, or both sides, and the coating composition, depending on the application. Further, for example, the lubricating film is made of resin + silica + polyolefin wax 0.3 to 5.0.
μm, conversion coating Cr 5 to 100 mg / m ² or phosphate 0.2 to 2.0 g / m ² , plating is Zn, Zn alloy, Al, Al alloy plating, plating amount 5 to 200 g /
consisting of m ^2.

The present invention is basically applicable to all thin steel sheets, ie, aluminum-killed steel sheets, ultra-low carbon steel sheets, and high-strength steel sheets.

The plating is zinc, zinc alloy plating, multi-layered steel sheet, aluminum, aluminum alloy plating, and multi-layered steel sheet obtained by electroplating, hot-dip plating, vapor phase plating.

As the conversion coating, a chromate coating or a phosphate coating is used. The chemical conversion coating is located between the plating surface and the lubricating coating, and provides adhesion during processing, corrosion resistance, and the like. Chromate is a post-washing type electrolytic reduction chromate containing trivalent chromium hydrated oxide as the main component. A post-washing type etching chromate liquid mainly containing trivalent chromium and hexavalent chromium hydrated oxide is applied and dried. An anhydrous washing type chromate coating can be adopted. The adhesion amount is 5 to 100 mg / m ² in terms of Cr. If it is less than 5 mg / m ² , corrosion resistance cannot be obtained, which is not preferable. If it exceeds 100 mg / m ² , the cohesive failure of the chromate itself is likely to occur, and the adhesion cannot be obtained. It is desirable that the chromate film hardly dissolves in an aqueous lubricating paint having a high trivalent chromium / hexavalent chromium ratio.

The phosphate coating is formed of a phosphate such as zinc, iron, nickel, manganese and calcium. The amount of adhesion is preferably in the range of 0.3 to 2.0 g / m ² for reasons of corrosion resistance and adhesion. If it is less than 0.3 g / m ² , corrosion resistance cannot be obtained. At 2.0 g / m ² , adhesion cannot be obtained by severe processing due to cohesive failure of the phosphate coating.

The lubricating coating of the present invention will be described below.
The resin according to the present invention is to mix a resin of an appropriate type as a base resin at a constant weight ratio. This resin has adhesion, elongation, shear strength, corrosion resistance, abrasion resistance,
It is necessary that the components have a well-balanced chemical resistance. In order to satisfy these performances, it is preferable to use a combination of the resins of the present invention. The present inventors have already obtained a strong workability and corrosion resistance by blending a urethane resin and an epoxy resin and blending a specific polyolefin wax, but as a result of further intensive research, the urethane resin By specifying the structure, it was found that particularly excellent performance was exhibited.

In order to achieve high workability and high corrosion resistance,
It is premised that the coating film is uniform and has excellent adhesion, and it is important that the strength and the elongation are balanced. By using a urethane resin with a high molecular weight and an epoxy resin in combination, it is easier to control the basic physical properties than a film formed by cross-linking low molecular weight resins, and even a thin film with a coating amount of 0.3 to 5 μm. It was found that uniform physical properties could be easily obtained. It should be noted that the low molecular weight urethane resin is of a type that includes various isocyanate-based crosslinking agents. As a resin, a combination of a urethane resin with a molecular weight of 3,000 or more and excellent abrasion resistance and an epoxy resin with excellent adhesion or film strength is particularly effective in exhibiting various properties such as high workability and corrosion resistance. Base resin suitable for

The urethane resin of the present invention has a molecular weight of 300
A water-dispersible ether / ester type urethane resin (a) having a bisphenol type skeleton and an ester skeleton and having a carboxyl group of 0 or more, and the epoxy resin (b) having a glycol skeleton or a bisphenol skeleton; , (A) in a ratio that causes 20 to 100% of the carboxyl groups to react. By using the polymer urethane resin of the present invention, uniform film formability in a thin film can be obtained and the object of the present invention can be achieved, but more preferably, the elongation of the coating film is 100% or more and the tensile strength is 100 kg /
The highest workability can be obtained by applying a resin having a size of ² cm ² or more.

Examples of the polyether polyol having a urethane resin skeleton used in the present invention include polyols obtained by adding ethylene oxide and propylene oxide to low molecular weight glycols such as ethylene glycol, propylene glycol and bisphenol A, and polyoxytetramethylene glycol. Among them, a polyether polyol having a bisphenol A skeleton is particularly preferable.
Examples of the polyester polyol include a polyester obtained by a dehydration condensation reaction of a low molecular glycol and a dibasic acid, and a lactam polyol obtained by ring-opening polymerization of a lactam such as ε-caprolactam in the presence of a low molecular glycol.

Examples of the isocyanate group for bonding the ester skeleton and the ether skeleton of the urethane resin include monomers, dimers and trimers of aromatic diisocyanates such as tolylene diisocyanate, diphenyl metadiisocyanate, and xylylene diisocyanate; Reaction products with polyether polyols and polyester polyols, and their hydrogenated derivatives, alicyclic isocyanates, isophorone diisocyanate, alicyclic such as hexamethylene diisocyanate, and monomers of aliphatic isocyanates, dimers, A reaction product of a trimer with a polyether polyol or a polyester polyol, or a mixture thereof can also be used. The compounding amount depends on the ratio to the molecular weight of the polyester polyol, polyether polyol and the carboxyl group-introducing component to be used, but 5 to 20% by weight of the urethane resin in terms of NCO is:
Optimum processing characteristics can be obtained as resin properties.

The carboxyl group is a functional group for self-emulsification and exerts a great contribution to the adhesion to the metal surface. The carboxyl group-introducing component is a compound containing two or more hydroxyl groups or an amino group and one or more carboxyl groups, 2,2-dimethylolpropionacetic acid, 2,2-dimethylolpropionic acid,
Examples thereof include dihydroxycarboxylic acids such as 2,2-dimethylolbutyric acid and 2,2-dimethylolpentanoic acid, and diaminocarboxylic acids such as lysine and arginine. A carboxyl group compound selected from these is polymerized with an isocyanate compound in combination with the polyester polyol and the polyether polyol. According to this method, an ether / ester type urethane resin having a carboxyl group having a molecular weight of 3000 or more used in the present invention can be obtained.

Examples of the method of dispersing the urethane resin in water include a method of neutralizing a carboxyl group with an alkali such as ammonia or trimethylamine and self-emulsifying, or a method of emulsifying and dispersing using an emulsifier.
As a work environment countermeasure, it is most preferable to recover the solvent contained in the urethane production step before the aqueous system is used and finally obtain a solvent-free type aqueous dispersion. The amount of the carboxyl group is suitably from 10 to 50 in terms of acid value per urethane solid content. If it is less than 10, the adhesion is insufficient and the workability and the corrosion resistance are poor. If it exceeds 50, the water resistance and the alkali resistance are inferior, so that the corrosion resistance is reduced.

The amount of the epoxy resin having a reactive functional group (hydroxyl group, epoxy group, etc.) is preferably set at a ratio at which 20 to 100% of the carboxyl groups of the urethane resin react. If the amount is less than 20%, the compounding effect is poor, and if the amount exceeds 100%, the workability of hardness is reduced because the epoxy resin plays a role of a plasticizer.
The epoxy resin has a large effect of improving chemical resistance and corrosion resistance. When a structure having a bisphenol A-type skeleton is used for the epoxy resin, the effect of improving adhesion and corrosion resistance is particularly large. When a solvent-free type or an emulsifier-free type is required as an environmental measure to prevent a decrease in coating film performance, a water-soluble epoxy resin can be obtained by imparting hydrophilicity with a glycol skeleton.

It is necessary to determine the compounding amount of the epoxy resin according to the acid value of the urethane resin, and the calculation method is as follows. Assuming that the carboxyl group of the urethane resin reacts with the epoxy group of the epoxy resin in an equivalent amount, the equation for calculating the required amount of the epoxy resin to react 100% with the urethane resin having a predetermined acid value (AV) is as follows. (1)
It is.

Epoxy solid content weight (g) = AV value of urethane resin × (1/56) / 1000 × epoxy equivalent × weight of urethane resin blended (g) (1) The epoxy group blended in the present invention is a carboxyl group The carboxyl group contributing to the adhesion is eliminated by the reaction, but the OH group is generated by ring opening of the epoxy group, thereby ensuring the adhesion. In addition, the corrosion resistance is greatly improved by blending the epoxy resin. In the combination of the urethane resin having a molecular weight of less than 3000 and the epoxy resin,
High workability is not stably achieved. In addition, molecular weight 300
High film formability and corrosion resistance cannot be obtained by film formation of a urethane resin of 0 or more alone.

The total weight of the urethane resin (a) and the epoxy resin (b) in the water-based lubricating coating composition of the present invention is suitably from 50 to 85% in terms of a solid content ratio based on the total solid content. 50%
If it is less than or more than 85%, the corrosion resistance and workability are insufficient. However, the desired workability cannot be achieved only by using these resin-based coatings, and therefore, a combined use of a lubricating additive is required.

Examples of the lubricating additive include known lubricants such as fluorine-based, hydrocarbon-based, fatty acid amide-based, ester-based, alcohol-based, metal soap-based, and inorganic lubricants. As a criterion for selecting a lubricating additive for improving processability, it is necessary to select a substance in which the added lubricant is present on the surface of the resin film rather than being dispersed in the formed resin film. It is necessary in order to reduce the friction between the surface of the mold and the mold and maximize the lubrication effect. That is, when the lubricant is dispersed in the formed resin film, the surface friction coefficient is high and the resin film is easily broken, and the powdery substance is separated and deposited, resulting in poor appearance and reduced workability called a powdering phenomenon. . As the substance existing on the surface of the resin film, a substance which is not compatible with the resin and has a small surface energy is selected.

As a result of investigations by the present inventors, it has been found that the use of polyolefin wax greatly improves processability and also improves performance such as corrosion resistance and chemical resistance after processing. Examples of the wax include hydrocarbon waxes such as paraffin, microcrystalline or polyethylene. During processing, the melting point of the wax is 7 because the coating temperature rises due to the heat of deformation and frictional heat of the material.
A temperature of 0 to 160 ° C. is appropriate, and if it is lower than 70 ° C., it softens and melts during processing and does not exhibit excellent properties as a solid lubricating additive. On the other hand, if the melting point exceeds 160 ° C., hard particles are present on the surface and the frictional characteristics are reduced, so that high moldability cannot be obtained.

Preferably, the polyolefin wax has a saponification value of 30 or less or 0 and has a branched structure. Those having a saponification value of more than 30 have a high polarity and are easily compatible with the resin, so that they are unlikely to be present on the resin surface at the time of film formation. Therefore, they cannot be said to be appropriate when a high processing performance level is required.
Particularly preferred is a wax having a saponification value of 0 and having no ester bond having a lower compatibility with the resin.

The particle size of these waxes is 0.1-7.
0 μm is appropriate. If it exceeds 7.0 μm, the distribution of the solidified wax is not uniform, which is not preferable. If it is less than 0.1 μm, workability is insufficient. The amount of the lubricating additive is 3 to 30% in terms of a solid content based on the total solid weight of the lubricating paint. If it is less than 3%, the processability improvement effect is small, and if it exceeds 30%,
Workability and corrosion resistance decrease.

As other additives, SiO ₂ is added in an amount of 10 to 40% based on the total solid content to improve corrosion resistance. The addition of SiO ₂ has the effect of significantly improving corrosion resistance and processability. If it is less than 10%, the effect of improving the corrosion resistance and workability is small, and if it exceeds 40%, the binder effect of the resin becomes small, the corrosion resistance is reduced, and the elongation and strength of the resin are reduced, so that the workability is reduced. Si
As for the particle diameter of O ₂ , 3 to 30 μm is appropriate. 3
If it exceeds 0 μm or less than 3 μm, higher workability and corrosion resistance cannot be obtained. Types of silica include liquid-phase colloidal silica and gas-phase silica,
The present invention is not particularly limited. In addition, a conductive material for improving weldability or a coloring pigment for improving design may be added. Further, various additives such as an anti-settling agent, a leveling agent, and a thickener may be added.

The lubricating coating of the present invention has a thickness range of 0.3 to 0.3.
It is 5.0 μm. The optimum film thickness depends on the type of press and is difficult to limit.
Thin films are advantageous for bending. If it is less than 0.3 μm, the lubrication performance is unstable. If the length is 5.0 μm, a large amount of blocking and press debris of the coil is generated, which is not preferable.

FIG. 2 is a view showing a process of forming a film on a lubricated steel sheet according to the present invention. Immediately after the coating, a convection motion in the coating film is generated by securing a plate temperature of 40 ° C. or more, and the lubricant particles are exposed and fixed on the coating film surface, and then baked in a furnace. Therefore, even if skinning occurs due to rapid heating in the furnace, the lubricant is already fixed on the coating surface, so it is baked at a temperature equal to or higher than the melting point of the lubricant and melts on the coating surface to form a lubricant layer. Form.

FIG. 3 shows the relationship between the sheet temperature during painting and the thickness of the surface lubricating coating layer according to the present invention. According to this figure, by setting the plate temperature at the time of coating to 40 ° C. or higher, the lubricating coating layer thickness of the present invention of 0.04 μm can be secured. 45 ° C
As described above, the thickness of the lubricating coating layer is almost saturated, and it is not possible to obtain a film thickness larger than that. Further, the sheet temperature at the time of coating is 6 in order to suppress the deterioration of the paint and the wear of the coater roll.
0 ° C. or less is desirable.

FIG. 4 is a diagram showing the relationship between the plate temperature and the lubrication characteristics during coating in the method of the present invention. As shown in this figure,
It can be seen that under the production conditions according to the present invention, extremely good lubrication performance is exhibited.

Similarly, FIG. 5 is a diagram showing the relationship between the sheet temperature at the time of coating and the processing characteristics in the method of the present invention. As shown in this figure, under the manufacturing conditions according to the present invention, a very good processing performance of a processing score of 5 is shown.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to embodiments applied to galvanized steel sheets. An electroester galvanized steel sheet having a Cr adhesion amount of 40 mg / m ² was subjected to electrolytic chromate treatment at a line speed of 100 rpm using a paint baking equipment of a plating line, and an ether ester urethane resin having a molecular weight of 5,000 (bisphenol A ether: oxidation 18, ether / ester) Ratio 30/70, isocyanate content 8) and epoxy resin (epoxy equivalent 2)
20) is coated with a lubricating paint containing 25% silica sol having an average particle diameter of 8 nm and 13% of polyethylene wax having a particle diameter of 0.6 μm (specific gravity 0.93, softening point 115 ° C.). a) 40 ° C, (b) 50 ° C and (c) 6
0 ° C., baking plate temperature 140 ° C., baking time 4 seconds, film thickness 3 μm, surface lubricating layer thickness (a) 0.0
Lubricated steel plates of 5 μm, (b) 0.7 μm and (c) 0.9 μm were prepared. The coefficient of friction, which is the lubrication property of the obtained lubricated steel sheet, is (a) 0.07, (b) and (c) are 0.05.
Good lubrication characteristics were obtained. In addition, the workability was evaluated to be 5 and extremely good workability was obtained.

[0036]

As described above, according to the present invention, the lubricating layer on the surface prevents direct contact between the resin and the mold, and the lubricant particles dispersed in the film cause the film to be severely deformed as in deep drawing. When lubricating, it is possible to supply a lubricant and maintain good lubrication workability, and to produce a surface-treated steel sheet having excellent versatility and excellent press working characteristics with little deterioration of a film due to processing. . This makes it possible to perform a baking process at a high temperature and in a short time, and it is extremely effective industrially that a simple paint baking facility in a plating line enables a high productivity and a facility for shortening the furnace tone.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a coating structure of a surface-treated steel sheet having excellent press workability according to the present invention.

FIG. 2 is a view showing a process of forming a film on a lubricated steel sheet according to the present invention.

FIG. 3 is a view showing the relationship between the temperature of a lubricated steel sheet according to the present invention at the time of painting and the thickness of a surface lubricating coating layer.

FIG. 4 is a diagram showing the relationship between the lubricating properties and the temperature of a lubricated steel sheet according to the present invention during painting.

FIG. 5 is a diagram showing the relationship between the sheet temperature and the processing characteristics at the time of painting the lubricating steel sheet according to the present invention.

FIG. 6 is a conceptual diagram showing a coating structure of a conventional surface-treated steel sheet for press working.

FIG. 7 is a conceptual diagram showing a surface state of a conventional lubricating film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thin steel plate 2 Plating coating 3 Chemical conversion coating 4 Lubrication coating 5 Lubricant 6 Surface lubricant coating layer 7 Original plate 8 Skinning 9 Gas vent hole 10 High boiling point solvent

Continuation of front page (72) Inventor Katsutoshi Enyama 1 Kimitsu, Kimitsu-shi Nippon Steel Corporation Kimitsu Works (56) References JP-A-6-299367 (JP, A) JP-A-6-173037 ( JP, A) JP-A-5-309327 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B05D 1/00-7/26 C23C 22/07 C23C 22/24 C25D 11 / 38 305

Claims (2)

(57) [Claims] 1. In a high-speed plating / painting line, a Cr adhesion amount of 5 to 100 mg as a first layer on the surface of a plated steel sheet.
/ M ² chromate film or adhesion amount of 0.2 to 2.0
g / m ² of a phosphate conversion coating, and the total sum (a + b) of an ether / ester type urethane resin (a) and an epoxy resin (b) having a bisphenol type skeleton, an ester skeleton and a carboxyl group as the second layer is all 50 to 85% by weight based on the solid content, 1 part of polyolefin wax (c)
1 to 30% by weight of silica (d) having a particle size of 3 to 30 nm
A lubricating film obtained by applying and baking a water-based lubricating paint containing 0 to 40% by weight has a lubricating film thickness of 0.3 to 5 μm, and a lubricant having a particle concentration of 10 to 30% dispersed in the lubricating layer. A method for producing a surface-treated steel sheet having excellent press working characteristics, characterized by providing a surface lubricating layer thickness of 0.04 to 1 μm as three layers. 2. The method according to claim 1, wherein the sheet temperature at the time of coating is between 40 ° C. and 60 ° C.