KR100402014B1 - A resin coating solution for coated steel sheets with exellent adhesion after forming and a method for manufacturing resin coating steel sheets by using it - Google Patents

Abstract

The present invention relates to a resin coating solution for a plated steel sheet and a resin coated steel sheet using the same, which is capable of mixing a resin that only lowers the glass transition temperature without compromising other physical properties in the phenoxy resin and at the same time the phenoxy resin and the base metal. By adding an additive to improve the adhesion of the, to provide a resin coating solution for a plated steel sheet excellent in adhesion after processing, and to provide a method for producing a resin coated steel sheet using the same, and its purpose.

The present invention,

(a) a main solution of a water-soluble phenoxy resin having a number average molecular weight of 25000 to 50000;

(b) 2 to 15 phr melamine resin for the main solution;

(c) 10 to 20 phr of colloidal silica with respect to the main solution;

(d) 5 to 15 phr of a water-soluble ethylene-acrylic resin having a molecular weight of 20000 to 500,000 and containing 50 to 80% and 50 to 20% of ethylene and acrylic resin, respectively; or

Resin coating solution for plated steel sheet having excellent adhesion after processing, which comprises 0.5 to 3.0 phr of phosphoric acid-ether with respect to the main solution;

In the method of applying the resin coating solution to the chromate-treated electrogalvanized steel sheet,

After applying the resin coating solution and dried at the baking temperature of 160 ~ 250 ℃, the dry coating thickness is 2 ~ 10㎛ It relates to a method for producing a resin coated steel sheet for coated steel sheet excellent in adhesion after processing, It is a technical point.

Description

RESIN COATING SOLUTION FOR COATED STEEL SHEETS WITH EXELLENT ADHESION AFTER FORMING AND A METHOD FOR MANUFACTURING RESIN COATING STEEL SHEETS BY USING IT}

The present invention belongs to the field of development of lead-free plated steel sheet that can replace the plating system of lead-tin alloy plated steel sheet (hereinafter referred to as Terne steel sheet) applicable to automobile fuel tanks. More specifically, the present invention relates to a resin coating solution for plated steel sheet using a zinc-based alloy plated steel sheet containing no lead component and adjusting the composition and coating conditions of the resin coating solution to improve adhesion after processing, and a method for producing a resin coated steel sheet using the same. It is about.

Turn steel sheet that is currently used as a fuel tank steel plate for automobiles contains a large amount of lead in the plating component of the steel sheet, it may be a problem when processing the lead component, etc. when scrapping. In order to replace this, steel sheets which have been treated with resin using chromate-treated zinc and zinc alloy plated steel sheets which do not use lead at all have been developed.

These resin-treated steel sheets mainly exhibit various performances according to the physical properties of the resin-coated film. In the related art, a method of improving corrosion resistance and fuel resistance has been proposed by using the resin layer of the uppermost layer of the steel sheet as a phenoxy resin. However, the phenoxy resin has a high glass transition temperature that is somewhat different from general resins, and exhibits much better properties than epoxy, acrylic, and urethane resins in terms of corrosion resistance and fuel resistance in the unprocessed flat plate. In part, due to the high glass transition temperature of the resin, there is a problem showing corrosion resistance and fuel resistance inferior to the flat plate portion during deep processing.

As a conventional technique for improving this, a method of lowering the glass transition temperature of the phenoxy resin or chemically bonding the phenoxy resin and the chromate, which is the underlying layer, to exhibit excellent characteristics without peeling the coating film during deep processing, etc. have. For example, Japanese Patent Application Laid-Open No. 2-18981 proposes a method of strengthening the adhesion between the resin and the base material by lowering the glass transition temperature to modify the resin molecules into rubber. However, when the method is applied to a water-soluble resin, there is a problem in that it is difficult to accept the rubber when denatured into rubber and it is difficult to inject the rubber into the phenoxy resin.

Accordingly, the present invention enables a mixed method of resins that lower only the glass transition temperature without impairing other physical properties in the phenoxy resin, and at the same time, adds an additive which improves the adhesion between the phenoxy resin and the base metal, thereby providing adhesion after processing. It is an object of the present invention to provide a resin coating solution for a plated steel sheet which can obtain the excellent resin coated steel sheet, and also to provide a resin coated steel sheet using the same.

1 is a schematic view of a resin coated steel sheet for a fuel tank

Figure 2 is a schematic diagram of a facility for coating a resin on a steel sheet using a coating roll

Figure 3 is a schematic diagram showing the bond between the phosphate ester and the base metal

* Explanation of the main symbols in the drawing

One… Backup roll (B.U.R), 2... Lift Roll

3... Applicator roll (A.P.R), 4... Transfer Roll (T.F.R)

5... Pickup roll (P.U.R), 6... Drip pan

The present invention for achieving the above object,

(a) a main solution of a water-soluble phenoxy resin having a number average molecular weight of 25000 to 50000;

(b) 2 to 15 phr melamine resin for the main solution;

(c) 10 to 20 phr of colloidal silica with respect to the main solution;

(d) 5 to 15 phr of a water-soluble ethylene-acrylic resin having a molecular weight of 20000 to 500,000 and containing 50 to 80% and 50 to 20% of ethylene and acrylic resin, respectively; or

It relates to a resin coating solution for plating steel sheet having excellent adhesiveness after processing comprising 0.5 to 3.0 phr of phosphoric acid-ether with respect to the main solution alone or in combination.

In the present invention for achieving the above another object, in the method for applying a resin coating solution to the chromate-treated electrogalvanized steel sheet,

After coating the resin coating solution and dried at a baking temperature of 160 ~ 250 ℃, to a dry coating thickness of 2 ~ 10㎛ relates to a method for producing a resin coated steel sheet for plating steel sheet excellent in adhesion after processing.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In the resin coated steel sheet of the present invention, as shown in Fig. 1, the steel sheet subjected to zinc or zinc-nickel electroplating on a cold rolled steel sheet is chromated with an adhesion amount of 100 mg / m 2, and a resin solution having excellent fuel resistance is 2 to 10. It has a three-layer structure formed by applying about 탆.

As the plated steel sheet, zinc or zinc alloy plated steel sheet may be used, and a zinc-nickel steel sheet which is a zinc alloy plated steel sheet having excellent corrosion resistance is more preferable than a plated steel sheet composed of zinc alone.

The chromate solution applied to the zinc-nickel steel sheet has a reaction type, an electrolytic type, and an application type, and an excellent coating type in terms of corrosion resistance is good.

The coating of the chromate solution is carried out on all sides without distinction between one side and two sides of the steel sheet, and in the case of the resin solution, one side or two side modes are taken according to the customer's equity in order to give functionality. In other words, customers who frequently exchange electrodes with high current conditions that can be easily welded may use both sides.However, customers who do not frequently replace electrodes with low current conditions should use steel sheets coated with single-sided resin. good. When the fuel tank is made of steel sheet coated with single-sided resin, the resin coating surface faces toward the fuel and the surface coated with only chromate on the opposite side faces outward. Therefore, there is an advantage that the welding is much easier. In addition, since the surface to which the resin is not coated is coated with a thick top coat (about 100 μm) to reinforce the corrosion resistance of the fuel tank, it can be said that there is little effect on the corrosion resistance.

Hereinafter, the resin coating solution of the present invention will be described in detail.

The present invention is characterized in that by adding at least one ethylene-acrylic resin or phosphate-ester to phenoxy resin, melamine resin, colloidal silica, it can have excellent adhesion after processing in resin coated steel sheet for plating steel sheet.

The main component of the resin applied to the uppermost portion of the plated steel sheet is a phenoxy resin, preferably having a number average molecular weight of 25,000 to 50,000. If the number average molecular weight is 25,000 or less, the molecular weight is too small to secure the desired physical properties, and if it is 50,000 or more, the synthesis is impossible due to the limitation of the resin synthesis method.

The phenoxy resin is very excellent in corrosion resistance and fuel resistance, for the following reasons.

The phenoxy resin has a physical characteristic different from that of other resins, the biggest characteristic being that the glass transition temperature (Tg) is high. In other words, the urethane, epoxy and acrylic resins are slightly different depending on the molecular weight, but the glass transition temperature is usually around 50 ° C or lower, whereas phenoxy resin is 100 ° C. The high glass transition temperature means that the resin chain is moving at a high temperature. At temperatures below the glass transition temperature, the chains of the resin itself do not undergo micro-brown movement, and thus the external low molecular corrosion factors (moisture, gasoline, etc.) It has a primary defense against it. In other words, when the resin chains have micro brown movements, low molecules easily penetrate between the moving chains, thereby facilitating the penetration of corrosion factors. Therefore, the resin having a high glass transition temperature has such a large shielding effect on the base metal that it can exhibit a significant shielding effect in the flat state.

However, phenoxy resins have the following problems in addition to the above advantages. In other words, the resin film itself is hard, and once subjected to processing, the resin is not easily elongated compared to the soft resin, that is, the low glass transition temperature, and the adhesion of the resin film to the underlying plating layer is also weak. In the meantime, the film adhesion is weakened and the more severe processing is carried out, the film peels up to facilitate the penetration of the corrosion factor to the metal layer, so that the corrosion may be more likely to occur. Furthermore, in the case of a fuel tank of an automobile company, in the processing process, press oil is applied before processing and then pressed in order to increase formability, followed by a degreasing process for removing it. During deep processing, a resin treatment is applied to the coating film. Even if it is, the resin is hard and damage by the degreasing solution occurs at the site where the coating film adhesion is weak. Therefore, it is difficult to expect the original shielding effect of the resin treatment. Therefore, it is preferable to use another poly-alloy or poly-blend state by adding another resin having excellent film adhesion and elongation than pure phenoxy resin.

The conditions of the other resin forming the poly blend are, firstly, compatibility with the water-soluble phenoxy resin, so that no gelation or sludge occurs, and second, the corrosion resistance and fuel resistance, which are excellent properties possessed by the phenoxy resin itself. At the same time there should be no effect, and the glass transition temperature of the resin as a whole should have a complementary effect of improving the film adhesion.

The addition of the other resin has a method of chemically bonding to the phenoxy resin and the method of physically input, in this case, the physical input. The reason why the chemical bonding method is not suitable in the present invention is that the ethylene-acrylic resin to be used is synthesized in the gas phase, and it is impossible to synthesize the resin in the already hydrated state into the phenoxy resin. Because.

The ethylene-acrylic resin of the present invention has a molecular weight of 20000 to 50000, preferably 50 to 80% and 50 to 20% of ethylene and acrylic resin, respectively, because the acrylic resin is less than 20%. This is because there is a problem in that the glass transition temperature is increased when the water is not solvable and, on the contrary, when it is added more than 80%, the adhesion is deteriorated. The content of the ethylene-acrylic resin is preferably 5 ~ 15phr relative to the phenoxy resin. When the ethylene-acrylic resin content is less than 5 phr, the coating adhesion effect is less. On the contrary, when the ethylene-acrylic resin content is 15 phr or more, deterioration in fuel resistance occurs, because a hydrocarbon compound composed of carbon and hydrogen is typical for gasoline used as fuel. This is because ethylene swelling occurs because gasoline penetrates into ethylene-acrylic resin because it is similar in molecular structure to ethylene resin composed of carbon and hydrogen only.

In the resin solution of this invention, as a method of improving the coating film adhesiveness of resin, there exists a method of adding an additive other than the method of constructing said poly blend. That is, by using an additive that enhances the adhesion between the phenoxy resin and the chromate layer, which is the underlying layer, the coating film adhesion of the resin coating film can be increased during deep processing. The working principle of the phosphate-ester in the additive used in the present invention will be briefly described with reference to FIG.

In the molecular structure of FIG. 3, the hydroxyl group of the phosphate-ester forms a hydrogen bond with the hydrogen atom of the water molecule to prevent further penetration of moisture, thereby improving corrosion resistance, and the oxygen of the phosphate-ester is combined with the metal ion. Improves film adhesion.

Therefore, it can be understood that the improvement of the coating film adhesion after the phenoxy resin is due to the composite synergistic effect that the ions of the phosphate-ester are combined with the metal together with the glass transition temperature decrease of the phenoxy resin itself.

The content of the phosphate-ester is 0.5 to 3.0 phr compared to the phenoxy resin, when the content is less than 0.5 phr, the adhesion effect is lowered, if more than 3.0 phr is due to the effect of increasing the input amount.

In the phenoxy resin solvated (hereinafter, referred to as the main solution) of the present invention, melamine resin is added as 2 to 15 phr of the phenoxy resin content as a curing agent. In the case of melamine resin injected at this time, it is good to select a good reactivity. If the content is less than 2phr compared to the phenoxy resin, it is difficult to secure the desired physical properties because the curing reaction is not sufficient after the resin coating.On the contrary, if the content is more than 15phr, the curing agents react by excessive addition to adversely affect the coating properties. Because it is not desirable.

In addition, colloidal silica is added to improve the corrosion resistance, the content of which is preferably 10 ~ 20phr compared to the phenoxy resin content. If the silica content is less than 10phr, the content is too small, there is no corrosion resistance effect, on the contrary, if more than 20phr because the corrosion resistance is not improved compared to the silica input content.

Next, the manufacturing method of the resin coated steel plate using the said resin coating solution is demonstrated.

The resin coated steel sheet of the present invention is prepared by subjecting the zinc coating and the galvanized steel sheet to chromate treatment, followed by baking, and then applying the resin coating solution to baking the sheet again.

At this time, the dry thickness of the resin film to be applied is preferably set to 2.0 ~ 10.0㎛. When the film thickness is 2㎛ or less, it is difficult to ensure sufficient corrosion resistance and fuel resistance because the film thickness is thin, and when it is 10㎛ or more, the corrosion resistance and fuel resistance are not affected by the increase of the film thickness, and weldability when welding steel sheets together This is because it is degraded.

The baking temperature after coating the resin solution is preferably in the temperature range of 160 to 250 ° C based on the MT-Metal Temperature. When the baking temperature is less than 160 ° C, the curing reaction of the resin is not sufficient, which leads to corrosion resistance and fuel resistance. In other words, when the temperature falls below 250 ° C., the curing reaction no longer occurs and the calorie loss is large.

On the other hand, as a coating method of the steel sheet, there are various methods such as roll coating, spraying, and deposition method using a roll. In the present invention, it is most preferable to use a roll coating method. The roll coating equipment used for the chromate treatment and the resin solution coating of the present invention is configured as shown in FIG. 2, for example. That is, the resin in the drip pan is transferred to the transfer roll (P.U.R), transferred to the transfer roll (T.F.R) and finally buried in the steel plate in the applicator roll (A.P.R), and then dried in an oven to form a resin coating. The amount of resin adhering at this time is adjusted by the driving direction of each roll, the rotational speed, the adhesion pressure between the rolls, and the like.

In the present invention, there is an advantage that it is possible to coat on one side and both sides of the steel sheet using the roll coating method described above.

Hereinafter, the present invention will be described in detail through examples.

Example 1

5 phr of melamine resin is added to a phenoxy resin having a number average molecular weight of 50,000 as a curing agent, and a composition of a resin solution containing 15 phr of colloidal silica having a particle diameter of 20 nm and 2 phr of wax is referred to as a standard solution composition unless otherwise specified. In addition, chromate treatment was performed on electro-galvanized and alloy plated steel sheets having a plating deposition amount of 30 g / m 2, baked and cooled by baking at a steel plate temperature of 160 ° C., and then coated with a resin solution prepared in each composition. A series of processes for producing resin coated steel sheets having a dry thickness of 3 µm by baking and drying are called standard steel sheet manufacturing methods.

In the standard solution composition, an ethylene-acrylic resin in which the ratio of ethylene resin to acrylic resin is 80:20 is mixed to a content as shown in Table 1 below to prepare a resin solution, followed by plating with a zinc plating amount of 20 to 30 g / m 2. The resin solution was applied to a steel plate subjected to a chromate treatment of 100 mg / m 2 by a roll coating method, followed by baking in a steel sheet temperature of 190 ° C., followed by water cooling to prepare a resin coated steel sheet having a dry resin coating thickness of 3 μm.

Corrosion resistance evaluation of the resin coated steel sheet produced by the above method was evaluated only the processed portion using a salt spray tester. Specimens for evaluation were prepared by cutting a plate into 95mm ψ to produce a cup having a diameter of 50mm and a height of 25mm, and then, after 500 hours, taken out from a salt sprayer, washed with pure water and dried. Then, the corrosion resistance was evaluated as follows according to the ratio of rust generated in the specimen, and the results are shown in Table 1 below.

◎: Generated white rust less than 5% of the total specimen area

○: White rust generated area is less than 5 ~ 30% of the total sample area

□: White rust is less than 30 ~ 50% of the total specimen area

△: White rust generated area is less than 50-100% of the total specimen area

In addition, two modes were taken for evaluation of the film adhesion after processing. That is, the primary mode is to obtain a cup having a diameter of 50 mm and a height of 25 mm by cutting a flat plate into 95 mm ψ, and then apply scotch tape around the 25 mm high cup specimen to obtain an area where the resin is peeled off. 10% caustic soda solution is sonicated for 3 minutes, washed, and then evaluated in the same manner as the first. Then, the coating film adhesion was evaluated according to the following criteria, and the results are shown in Table 1.

◎: 0% of exfoliated area

○: 1 to 5% of the peeled area

□: 5 ~ 10% of peeled area

△: peeled area is 10-20%

×: 20% or more of exfoliated area

In the fuel resistance evaluation, a plate having a diameter of 50 mm and a height of 25 mm was made by cutting a flat plate at the point where the fuel contacted with 95 mm ψ, 25 ml of three types of solution were put therein, and then placed a "0" ring on the steel sheet A transparent glass plate was covered on the top and fixed with a clamp to prevent leakage of gasoline. Three types of solutions were used for the fuel resistance evaluation. In the case of type A, a solution containing 5% salt was mixed with a conventional unleaded gasoline, and a type B was mixed with 0.2% salt with a conventional unleaded gasoline. One solution was used, and C type was used as lead-free gasoline containing methanol and additives. The composition of the C type was 85% lead-free gasoline + 14% methanol + 1% pure water containing formic acid and Cl-20ppm. . In addition, in order to reproduce the running situation of the car, a shake device made in advance so that fuel in the cup made container is shaken. After 4 months by the above method, it was taken out, washed with pure water, dried, and evaluated for fuel resistance according to the percentage of rust generated. The results are shown in Table 1. Evaluation criteria are as follows.

◎: less than 5% of white rust generated area

○: White rust generated area is less than 5 ~ 30% of the total specimen area

□: White rust is less than 30 ~ 50% of the total specimen area

△: White rust generated area is less than 50-100% of the total specimen area

×: Red blue

division Topic solution additive Hardener Quality evaluation after processing Kinds Kinds content Kinds content Film adhesion Corrosion resistance Fuel resistance Comparative Material 1 Phenoxy resin Ethylene-Acrylic Resin 0 Melamine resin 5 □ ○ ○ Comparative Material 2 10 Comparative Material 3 15 △ □ Comparative Material 4 3 5 ○ ◎ ◎ Comparative Material 5 10 Comparative Material 6 15 Comparative Material7 20 5 ◎ □ Comparative Material 8 10 ○ Comparative Material 9 15 Invention 1 5 5 ◎ Invention 2 10 Invention 3 15 Invention 4 5 10 Invention 5 10 Invention 6 15 Invention 7 5 15 Invention Material 8 10 Invention Material 9 15

Table 1 shows the results of the quality evaluation according to the change in the content of the additives ethylene-acrylic resin and melamine resin in the curing solution. As can be seen from Table 1, when the ethylene-acrylic resin content is 20phr or more, the coating film adhesion and corrosion resistance was good, but the fuel resistance showed a tendency to decrease slightly. In addition, in the case of the comparative material having an ethylene-acrylic resin content of less than 5 phr, it can be seen that in each quality evaluation, a grain worse than the inventive material of the present invention is shown.

Example 2

After preparing a resin solution by mixing phosphoric acid-ester as an additive in the standard solution composition as shown in Table 2 below, the steel plate was plated with a zinc plating amount of 20 to 30 g / m 2 and subjected to chromate treatment of 100 mg / m 2. The resin solution was applied by a roll coating method, baked and dried at a steel plate temperature of 190 ° C., followed by water cooling to prepare a resin coated steel sheet having a dry resin coating thickness of 3 μm. Thereafter, quality evaluation was carried out under the same conditions as in Example 1, and the results are shown in Table 2.

division Topic solution additive Hardener Quality evaluation after processing Kinds Kinds content Kinds content Film adhesion Corrosion resistance Fuel resistance Comparative Material A Phenoxy resin Phosphate-ether 0.3 Melamine resin 5 □ ○ ◎ Comparative material B 10 □ Comparative Material C 15 ○ Comparative Material D 4.0 5 ◎ ◎ Comparative Material E 10 Comparative Material F 15 ○ Invention Material A 0.5 5 ◎ Invention Material B 1.0 Invention Material C 2.0 Invention Material D 3.0 Invention Material E 0.5 10 Invention Material F 1.0 Invention Material G 2.0 Invention Material H 3.0 Invention Material I 0.5 15 Invention J 1.0 Invention Material K 2.0 Invention Material L 3.0

Table 2 shows the results of the quality evaluation according to the change in the content of the phosphoric acid-ester and the melamine resin as an additive in the resin solution. As can be seen in Table 2, when the phosphate ester content is in the range of 0.5 ~ 3.0phr of the present invention, the coating film adhesion after processing is improved. However, when the phosphate ester content is more than 3.0 phr or less than 0.5 phr, it can be seen that in each quality evaluation, it is deteriorated compared to the present invention.

On the other hand, when the phosphate-ester and ethylene-acrylic resin are added as an additive to the standard solution composition according to the present invention, compared with the addition of the phosphate ester and the ethylene-acrylic resin alone as in the above-mentioned embodiment, It was found to be effective.

As described above, according to the present invention, by preparing a resin coating solution in which ethylene-acrylic resin and phosphate-ester are added to a water-soluble phenoxy resin, lead is significantly improved after coating with coating film adhesion, fuel resistance, and corrosion resistance. By providing a new plated fuel tank steel sheet that is not used at all, it can provide a significant effect on the environmental level compared to the existing Pb-Sn plated steel sheet and can improve the quality of the steel sheet, which can significantly contribute to the resolution of customer complaints.

Claims (2)

(a) a main solution of a water-soluble phenoxy resin having a number average molecular weight of 25000 to 50000; (b) 2 to 15 phr melamine resin for the main solution; (c) 10 to 20 phr of colloidal silica with respect to the main solution; (d) 5 to 15 phr of a water-soluble ethylene-acrylic resin having a molecular weight of 20000 to 500,000 and containing 50 to 80% and 50 to 20% of ethylene and acrylic resin, respectively; or A resin coating solution for plating steel sheet having excellent adhesiveness after processing, which comprises 0.5 to 3.0 phr of phosphoric acid-ether with respect to the main solution alone or in combination. In the method of applying the resin coating solution to the chromate-treated electrogalvanized steel sheet, A method for producing a resin coated steel sheet for coating steel sheet having excellent adhesion after processing, wherein the resin coating solution of claim 1 is applied and dried at a baking temperature of 160 to 250 ° C., so that the dry coating thickness is 2 to 10 μm.