JPH06104799B2 - Resin coated steel sheet with excellent press formability, paintability and corrosion resistance - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-coated steel sheet having excellent press formability, paintability and corrosion resistance, which are used in automobiles, household electric appliances, building materials and the like.

[0002]

2. Description of the Related Art Generally, when pressing a steel plate,
Press oil is applied to the surface of the steel sheet to improve its workability. However, for this purpose, a press oil application process and a degreasing process are required before and after the press working of the steel plate, and further, the press oil is scattered during the press working, which deteriorates the work environment or causes a pollution problem. There are problems such as causing it.

Therefore, various surface treatment methods for steel sheets have been proposed in order to obtain good press workability without using press oil. For example, a mill bond coating or a wax coating is formed on the surface of the steel sheet, or a resin emulsion or resin aqueous solution containing an inorganic or organic solid lubricant is used as a surface treatment agent, and this is applied to the surface of the steel sheet.
A method of forming a resin film by drying is known.
In particular, the latter method is preferably used as a surface treatment method in the case of a product that is subjected to strong processing, or in the case where degreasing is omitted after processing and the product is required to have paintability.

In this method, graphite or molybdenum disulfide is conventionally used as the solid lubricant in the inorganic system, and metallic soap such as calcium stearate or paraffin is used in the organic system. There is. Thus, the method of using an inorganic solid lubricant, for example,
JP-A-61-227178, JP-A-61-227
179, JP 61-231177 A, JP 61-279687 A and the like.

However, when graphite or molybdenum disulfide is used as the solid lubricant, it is generally difficult to adjust the color tone of the surface of the steel sheet and, in addition, to provide a lubricating performance capable of withstanding the heavy working of the steel sheet, When a large amount of a lubricant is added to the surface treatment agent, the adhesiveness of the resin coating obtained is extremely poor and the corrosion resistance of the steel sheet after processing deteriorates. Furthermore, since graphite and molybdenum disulfide have a large specific gravity, it is difficult to disperse them uniformly in the surface treatment agent, and they easily settle in the surface treatment agent not only during storage, but also during storage, so storage stability and workability are improved. There are also difficulties.

On the other hand, when metal soap is used as a solid lubricant, the resin coating formed on the surface of the steel sheet has high hygroscopicity, which causes stickiness and has a problem in corrosion resistance. In addition, when a surface treatment agent such as a resin emulsion containing a large amount of wax is used, when the steel sheet is coated and then dried, the wax comes out on the surface of the resin coating, so that the surface slipperiness is not good. However, when the temperature of the mold is increased by continuous pressing, the wax on the surface is liquefied and flows, its lubricating performance is deteriorated, the resin film is peeled off, and the corrosion resistance after processing is also deteriorated.

Therefore, the inventors of the present invention have already disclosed in JP-A-3-
As described in Japanese Patent No. 17189, a resin-coated steel sheet having a water-based urethane modified polyolefin-based resin as a main component and a resin coating formed by containing a predetermined amount of fluorine-based resin particles and silica particles on a steel sheet surface. is suggesting. However, such a resin-coated steel sheet has good press formability in light processing, and is excellent in corrosion resistance and paintability, but in strong press forming such as draw forming, the sliding surface is rubbed by die scuffing. Defects and blackening may occur and the appearance of the molded product may be significantly deteriorated.

[0008]

Therefore, the inventors of the present invention investigated the influence of various properties of the resin on press formability in obtaining a resin-coated steel sheet having excellent press formability. As a result, it has been found that the characteristics of the resin coating formed on the surface of the steel sheet have a great influence on the appearance of a molded product that has undergone strong processing such as press molding. Further, they have found that in order to obtain good press formability, it is necessary that the resin coating film has two characteristics, that is, the protective property of the steel sheet surface by the resin and the slip property on the resin surface.

In general, during strong working such as press forming, phenomena such as shrinkage, bending, sliding, and elongation occur in the steel sheet. If the steel sheet cannot withstand these phenomena, cracks may occur, or die galling of the steel sheet may occur. Among these, it is believed that the sliding phenomenon has a large influence on the surface condition of the steel sheet. Therefore, as long as the surface coating that can withstand a certain amount of sliding is formed on the steel sheet and the surface coating can reduce the frictional force due to sliding, the mold used for sliding during press molding It seems that it is possible to prevent galling.

In order to solve the above-mentioned problems in the conventional resin-coated steel sheet, the present inventors have made various studies in consideration of the above, and as a result, as a resin coating in the resin-coated steel sheet excellent in press formability, a steel sheet is used. In order to protect the surface, it is effective that the main resin has a glass transition temperature in the range of 60 to 90 ° C. and has good film-forming property. It was found that the addition of a trace amount of polyethylene wax is effective for reducing the amount. Furthermore, the present inventors have found that the addition of a cross-linking agent is effective in improving corrosion resistance and paintability, and have reached the present invention.

That is, the present invention has excellent lubricity, can sufficiently withstand extreme pressure during strong working and temperature rise of the mold, and is also excellent in paintability and corrosion resistance after working. The purpose is to provide a resin-coated steel sheet.

[0012]

A resin-coated steel sheet having excellent press formability, coatability and corrosion resistance according to the present invention comprises a polyester resin as a main component, a crosslinking agent in an amount of 1 to 20% by weight, and an average molecular weight of 2000 as a lubricant. It is characterized in that a resin coating containing 0.2 to 10% by weight of polyethylene wax of 8000 to 8000 is formed on the surface of the steel sheet with an adhesion amount of 0.2 to 5 g / m ² .

In the present invention, the polyester resin is
It mainly forms the resin coating on resin-coated steel sheets. Such a polyester resin is obtained from an organic acid and a diol, but in the present invention, its glass transition temperature needs to be in the range of 60 to 90 ° C. Also,
When such a polyester-based resin is used as an aqueous dispersion containing an emulsifier, a dispersant, etc., the film-forming property of the main polyester-based resin is not sufficient, and the resulting resin-coated steel sheet is inferior in corrosion resistance. In the invention, the polyester resin is preferably used as a solvent-type resin dissolved in an organic solvent such as toluene or xylene.

For example, in the present invention, the Byron 23
CS, Byron 29CS, Byron 20SS, Byron 29SS (manufactured by Toyobo Co., Ltd.) and the like are preferably used. In the present invention, examples of the crosslinking agent include melamine-based compounds, aziridine-based compounds, epoxy-based compounds, and isocyanate-based compounds. Such a cross-linking agent has an effect of reacting with a hydroxyl group or a carboxyl group in the polyester resin to three-dimensionally cross-link the resin and cure the resin. In the present invention, as the cross-linking agent, a melamine-based or isocyanate-based compound is particularly preferably used because it has good compatibility with the polyester-based resin that is the main constituent of the resin coating and has excellent liquid stability. As such a cross-linking agent, for example, Millionate MT, Millionate M
R, Coronate N, Coronate T, Coronate HL, Coronate L, Coronate HK, Coronate EH, Coronate 2030, Coronate 2067, Suprasec 32
40, Sprasec 3340, Daltsec 1350,
Examples thereof include Dartsec 2170, Daltsec 2280 (manufactured by Nippon Polyurethane Industry Co., Ltd.), and Cymel 25 (manufactured by Mitsui Cyanamid Co., Ltd.).

In the present invention, such a crosslinking agent is used in the range of 1 to 20% by weight based on the weight of the resin coating. When the compounding amount of the cross-linking agent is less than 1% by weight, the resulting resin film has a low cross-linking density, so that the corrosion resistance and paintability are poor. On the other hand, when it exceeds 20% by weight,
The obtained resin film has no problem in terms of lubrication performance, but since the density of polar groups in the resin film becomes excessively large, it has poor corrosion resistance.

Generally, the glass transition temperature of the polyester resin is changed by the cross-linking agent, but the lubricating performance of the resin coating largely depends on the properties of the resin which is the main component of the resin coating, particularly on the glass transition temperature thereof. Therefore, in the present invention, when the glass transition temperature of the polyester resin is lower than 60 ° C., the strength of the coating film is so small that the resin coating film is broken and peeled off in the case of strong working such as press working. However, the appearance of the molded product is remarkably impaired by becoming blackened. On the other hand, when the glass transition temperature of the polyester resin is higher than 90 ° C., the resin coating obtained becomes brittle, and the resin coating may be damaged by cracking or the like in the case of strong working such as press working, resulting in poor corrosion resistance. become.

In the present invention, the polyethylene wax has the effect of reducing the friction coefficient on the surface of the resin coating. However, when the average molecular weight is less than 2000, the wax penetrates into the resin coating and reduces the strength of the resin coating, and as a result, the coating is destroyed during strong working such as press molding, resulting in blackening (blackening). ), Which impairs the appearance of the molded product. On the other hand, when the average molecular weight exceeds 8,000, the slipperiness of the surface is poor and the processability is poor.
Therefore, the polyethylene wax used in the present invention preferably has an average molecular weight of 2000 to 8000.

As such polyethylene wax,
For example, Disparlon SE 210-15T, Disparlon SE 480-10T (manufactured by Kusumoto Kasei Co., Ltd.) and the like are preferably used. Further, in the present invention, the amount of the polyethylene wax added is preferably in the range of 0.2 to 10% by weight. If less than 0.2% by weight,
The resulting resin coating has still low lubricity, while 10% by weight
When it exceeds, the adhesiveness of the obtained resin coating is deteriorated and the coating peels off during processing, resulting in poor corrosion resistance after processing. Further, with respect to paintability as well, the adhesion between the coating film and the paint is reduced.

In the resin-coated steel sheet according to the present invention, the above-mentioned resin coating film is formed on the surface of the steel sheet with an adhesion amount of 0.2 to 5 g / m ² . The amount of resin coating adhered to the steel plate is 0.2 g /
When it is less than m ² , the required lubrication effect and the corrosion resistance after working cannot be obtained in strong working. But,
When the adhesion amount exceeds 5 g / m ² , the peeling amount of the coating film increases during press working of the steel sheet, and for example, in press molding, a peeling coating film accumulates in the mold, which causes trouble in press molding.

In the present invention, the steel sheet material is not particularly limited, but for example, zinc or zinc alloy plated steel sheet, those obtained by subjecting these steel sheets to chemical conversion treatment such as chromate treatment or phosphate treatment, and the like. It is preferably used.

[0021]

As described above, according to the present invention, a resin coating solution comprising a polyester resin containing a cross-linking agent and a polyethylene wax is applied to a steel sheet and dried to obtain a press oil. It is possible to perform strong working without coating, and to form a resin film having excellent coatability and corrosion resistance after working.

The treated steel sheet having the resin film with high lubricity and high corrosion resistance can be used not only as a coated steel sheet but also as a bare sheet after press working.

[0023]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples. Example 1 A chromate-treated electrogalvanized steel plate (zinc adhesion amount 20 g / m ² , chromium adhesion amount 20 mg / m ² ) was used as a material steel plate.

Polyester resin having a glass transition temperature of 40 to 95 ° C., an isocyanate-based crosslinking agent of 8% by weight in terms of total solid content after film formation and an average molecular weight of 2 as a lubricant.
000 polyethylene wax 2% by weight was dispersed to prepare a surface treatment agent. This surface-treating agent was applied to the surface of the steel sheet by a bar coater so that the dry weight was 1.5 g / m ^2, and dried to form a resin film to obtain a resin-coated steel sheet.

The resin coated steel sheet thus obtained was subjected to a sliding test, a cylindrical deep drawing test, a press test, a salt spray test and a coating test to obtain a dynamic friction coefficient, a limiting drawing ratio, a mold galling resistance, a corrosion resistance and a coating film. The adhesion was examined. The dynamic friction coefficient is
It was determined from the load due to sliding at a load of 500 g using a surface property tester (Model 14-D manufactured by Haydon). The limiting drawing ratio was determined by the single blank method with a blank diameter of 110 mm and a punch diameter of 50 mm. The mold gall resistance was determined by visually observing the mold gall on the sliding surface of the molded product after press molding using a single-shot press tester. For the corrosion resistance, a salt spray test was carried out according to the method described in JIS Z-2371. Regarding the coating film adhesion, after coating with acrylic and melamine alkyd coatings, the adhesion of the coating film with cross-cut and cross-cut Erichsen was examined. The results are shown in Table 1.

[0026]

[Table 1]

Example 2 A polyester resin having a glass transition temperature of 72 ° C. was converted into a total solid content after coating of 0 to 0.
30% by weight of an isocyanate crosslinking agent and 1% by weight of a polyethylene wax having an average molecular weight of 2000 as a lubricant
And were dispersed to prepare a surface treatment agent.

This surface treatment agent was applied to the surface of the steel sheet by a bar coater so that the dry weight was 1.5 g / m ^2, and dried to form a resin film, thereby obtaining a resin-coated steel sheet. The properties of the treated steel sheet were examined in the same manner as in Example 1.
The results are shown in Table 2.

[0029]

[Table 2]

Example 3 In the same polyester resin as in Example 2, 0 to 12% by weight of a polyethylene wax having an average molecular weight of 2000 as a lubricant and 5% by weight of a cross-linking agent are dispersed in terms of total solids after film formation. Then, the surface treatment agent was prepared. This surface-treating agent was applied to the surface of the steel sheet by a bar coater so that the dry weight was 1.5 g / m ^2, and dried to form a resin film to obtain a resin-coated steel sheet. The properties of the treated steel sheet were examined in the same manner as in Example 1. The results are shown in Table 3.

[0031]

[Table 3]

Comparative Example 1 Using a resin mainly containing an epoxy resin, a polyethylene resin or a urethane-modified polyethylene resin, 10% by weight of an epoxy or aziridine crosslinking agent was added, and 1% by weight of polyethylene wax having an average molecular weight of 2000 was added. A surface treatment agent was prepared by adding.

The surface treatment agent was applied to the surface of the steel sheet with a bar coater so that the dry weight was 1 g / m ² .
It was dried to form a resin film and a resin-coated steel plate was obtained.
The properties of the treated steel sheet were examined in the same manner as in Example 1. The results are shown in Tables 4 and 5.

[0034]

[Table 4]

[0035]

[Table 5]

Example 4 In the same polyester resin as in Example 2, 8% by weight of an isocyanate-based crosslinking agent and 2% by weight of a polyethylene wax having an average molecular weight of 1000 to 9000 as a lubricant are calculated in terms of total solid content after forming a film. Was dispersed to prepare a surface treatment agent. This surface-treating agent was applied to the surface of the steel sheet by a bar coater so that the dry weight was 1.5 g / m ^2, and dried to form a resin film to obtain a resin-coated steel sheet. The properties of the treated steel sheet were examined in the same manner as in Example 1. The results are shown in Table 6.

[0037]

[Table 6]

Example 5 2 wt% of a polyethylene wax having an average molecular weight of 2000 as a lubricant and 5 wt% of a cross-linking agent were dispersed in the same polyester resin as in Example 2 in terms of the total solid content after film formation. A surface treating agent was prepared. This surface treatment agent was applied to the surface of the steel sheet by a bar coater so that the dry weight was 0.1 to 6.0 g / m ^2, and dried to form a resin coating film to obtain a resin-coated steel sheet. The properties of the treated steel sheet were examined in the same manner as in Example 1. The results are shown in Table 7.

[0039]

[Table 7]

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Claims (3)

[Claims] 1. A polyester resin as a main component, a crosslinking agent as 1 to 20% by weight, and a lubricant having an average molecular weight of 2000 to
0.2 to 10% by weight of 8000 polyethylene wax
Press formability, characterized in that a resin film containing is formed on the surface of the steel sheet with an adhesion amount of 0.2 to 5 g / m ² .
Resin coated steel sheet with excellent paintability and corrosion resistance. 2. The resin-coated steel sheet according to claim 1, wherein the crosslinking agent is an isocyanate compound or a melamine compound. 3. The resin-coated steel sheet according to claim 1, wherein the polyester resin has a glass transition temperature in the range of 60 to 90 ° C.