KR20030010052A - The manufacturing methods of automobile fuel tanks using the resin coated steel sheets - Google Patents

Abstract

PURPOSE: A method for manufacturing a resin covered steel sheet by covering a chromate solution for automobile fuel tanks on a Zn-Ni alloy plated steel sheet, and a method for obtaining fuel tanks with improved corrosion resistance by high temperature baking after applying an external coating on the resin covered steel sheet are provided. CONSTITUTION: The chromate solution for automobile fuel tanks having superior corrosion resistance and fuel resistance during high temperature baking comprises a base compound solution containing an aqueous chromium solution in which composition of trivalent chromium in 7 to 50 g/L of chromium constituent is 0.4 to 0.8, 1000 weight parts of colloidal silica, 25 weight parts of hydrofluoric acid and 60 weight parts of phosphoric acid for 100 weight parts of chromium constituent in the aqueous solution; and a curing agent solution which is prepared into 5 to 50 wt.% of an aqueous solution by mixing titanium and zirconium having alkoxy groups in a ratio of 1:1 so that pH of the solution is adjusted to 2 to 3, wherein the chromate solution comprises 100 weight parts of the base compound solution and 20 to 50 weight parts of the curing agent solution. The method for manufacturing a Zn-Ni alloy plated steel sheet treated with the chromate solution for automobile fuel tanks having superior corrosion resistance and fuel resistance during high temperature baking comprises the process of baking the chromate solution coated steel sheet at a steel sheet temperature of 180 to 250 deg.C after coating the chromate solution on a Zn-Ni alloy electrolytic plated steel sheet in the amount of 30 to 200 mg/m¬2 on the basis of adhesion amount of dried coating film.

Description

The manufacturing methods of automobile fuel tanks using the resin coated steel sheets}

The present invention relates to a method for manufacturing a fuel tank using a resin coated steel sheet for automotive fuel tanks having excellent high temperature corrosion resistance and fuel resistance, and more particularly, an oven for curing a chromate, a resin film, and an outer coating film. ) Chromate solution for automobile fuel tank that can maintain excellent corrosion resistance and fuel resistance even after high temperature drying in the inside, and coating on zinc-nickel alloy plated steel sheet using the same, and such a resin coated steel sheet for automobile fuel tank It is about a manufacturing method that can obtain a fuel tank product that is improved in corrosion resistance by high temperature calcination after coating during the external coating (black powder coating and PVC coating) processing to ensure the corrosion resistance to the outer surface of the fuel tank when making the .

Materials used in fuel tanks, which are one of the main parts of automobiles, require various properties such as workability and weldability as well as excellent corrosion resistance and fuel resistance. Conventionally, as a fuel tank material, electric and hot-dip galvanized steel sheets, which are lead-tin alloy plated steel sheets, have been widely used, but in recent years, there is a need for materials that have less influence on the global environment and easy to recycle resources. There is a need for development of alternative materials that do not use harmful lead. In Japan, as regulations on lead in dust generated from automobile scrapping are tightened, the need for lead-free steel sheets that can replace the molten Terne steel sheets in use has been increased. There is a technical development, and there is a special chromate-treated zinc-nickel plated steel sheet disclosed in Korean Patent Application No. 97-703448 and Japanese Patent Publication No. 9-59783. However, the chromate treatment causes a crack in the surface of the zinc-nickel alloy plating film in order to prevent the corrosion resistance after processing, resulting in a process load and deterioration of fuel resistance due to chromium elution by moisture contained in the fuel. Has the disadvantage.

Accordingly, the present inventors have studied the improvement of the fuel tank manufacturing conditions to solve this problem and have excellent corrosion resistance and fuel resistance even at high temperature drying of the steel sheet. In addition, it belongs to the development of environmentally friendly lead-free plated steel sheets containing no lead, and studied to replace them with automotive fuel tank steel sheets using resin-treated steel sheets on Zn-based alloy plated steel sheets.

Therefore, the present invention is excellent in corrosion resistance and fuel resistance by using a chromate solution capable of high-temperature drying by adding a curing agent with high thermal stability at high temperature to improve the corrosion resistance deterioration during high temperature drying of the fuel tank chromate solution The present invention is to provide a plated steel sheet for fuel tank, and to provide a good quality lead-free fuel tank product by improving the adhesion between the chromate coating and the resin coating at high temperature for a long time during thick film coating in the fuel tank manufacturing process.

1 is a schematic side view of a resin coated steel sheet for an automobile fuel tank.

2 is a schematic side view of a resin coated steel sheet for an automobile fuel tank.

The present invention is a chromium solution of 0.4 to 0.8 in the chromium component of 7 to 50 g / l chromium solution, 1000 parts by weight of colloidal silica, 25 parts by weight of hydrofluoric acid, 60 parts by weight based on 100 parts by weight of chromium Based on the main solution sufficiently stirred by administration of negative phosphoric acid, titanium and zirconium having an alkoxy group as 1: 1, and prepared in 5 to 50 parts by weight of an aqueous solution, consisting of a curing agent solution adjusted to pH 2-3, Characterized by the coated chromate solution, characterized in that the curing agent solution is made by mixing 20 to 50 parts by weight with respect to 100 parts by weight of the main solution.

In addition, the present invention is a chromate treatment method and fuel formed by applying the coating type chromate solution to the zinc-nickel alloy electroplated steel sheet at 30 to 200 mg / ㎡ on the basis of the dry film adhesion amount and then baked at a steel plate temperature of 180 ~ 250 ℃ Powder coating and thick film PVC coating for securing corrosion resistance outside the fuel tank while seam welding the upper and lower plates and joining various pipes and brakes after press machining chromate-treated resin coated steel sheet for fuel tank in tank manufacturing method. Another method is to manufacture a fuel tank product using a lead-free plated steel sheet which is baked at 130 to 280 ° C. to improve the adhesion, corrosion resistance, and fuel resistance of the chromate coating and the resin coating of the resin coated steel sheet at high temperature for a long time. do.

Referring to the present invention in more detail as follows.

The chromate solution of the present invention uses titanium-based and zirconium-based curing agents having an alkoxy group having excellent thermal stability, and exhibits excellent corrosion resistance even after high temperature drying by preventing crosslinking with sufficient crosslinking even at high temperature drying. It is characterized by the excellent fuel resistance by reducing the dissolution of soluble hexavalent chromium by increasing the hydrophobicity of.

The chromate solution is composed mainly of the main solution and the hardener solution. The main solution is phosphoric acid, hydrofluoric acid and colloidal silica in the chromium solution, and the hardener solution is an aqueous titanium and zirconium solution having an alkoxy group.

The hexavalent chromium is reduced to a trivalent chromium compound so that the ratio of trivalent chromium to total chromium is 0.4 to 0.8. When the reduction ratio is lower than 0.4, it is difficult to achieve the effect of improving the corrosion resistance by trivalent chromium. Chromium elution resistance is deteriorated due to the increase of, whereas when the reduction ratio is higher than 0.8, solution storage property is deteriorated due to the gelation of the solution.

The concentration of the chromium component in which the component ratio of trivalent chromium is adjusted is preferably 7 to 50 g / l. In the case of the coated chromate treatment by the roll coating method, when the chromium concentration is lower than 7 g / l or less, the target adhesion amount of chromium is lowered. On the contrary, when the chromium concentration is higher than 50 g / l, the spreadability of the solution deteriorates. This results in a decrease in surface stability due to the deterioration of solution stability.

An additive is added to the chromium solution to improve the physical properties of the chromate solution, and the additives include phosphoric acid, hydrofluoric acid, and colloidal silica.

The role of the curing agent is to promote the crosslinking reaction of the chromate to form the chromium film and to maintain the bonding force between the chromate film and the material metal. For this, it is important to select an appropriate curing agent. In addition, when drying is performed at a high temperature as in the present invention, it is excellent in thermal stability so that cracking does not occur during processing due to breakage of connective tissue.

Therefore, in the present invention, in order to prevent such a phenomenon, a curing agent in which titanium and zirconium having an alkoxy group is 1: 1 is used in order to effectively crosslink the chromate film while having excellent thermal properties.

When the amount of the curing agent is less than 5 parts by weight, the amount of the curing agent administered when mixed with the main ingredient is increased to form chromate crosslinks at an appropriate temperature and time range, so that the total amount of chromium in the overall chromate solution is reduced to reach the target adhesion amount It is difficult, and when it exceeds 50 parts by weight, the solution storage property is lowered, and stability such as precipitation occurrence in the solution is lowered when the curing agent solution for mixing with the main solution alone. In addition, titanium and zirconium-based curing agents having an alkoxy functional group should be used to maintain the bonding strength with the zinc-nickel alloy electroplated steel sheet, which has many effects depending on the functional group type and the effective crosslinking of the chromate coating. Because you receive.

It is preferable to administer the curing agent solution in an amount of 20 to 50 parts by weight based on the main solution, and when the curing agent solution is less than 20 parts by weight, the crosslinking reaction of chromate does not occur sufficiently when forming a film, and when the amount exceeds 50 parts by weight, solution stability is lowered. Because it becomes.

The chromate solution of the present invention described above is applied to a steel sheet, and the coating at this time may use a method such as a three-stage roll coater. The coating amount is applied to the steel sheet in the range of 30 ~ 200 mg / ㎡ based on the adhesion amount of the dry coating, which is less than 30 mg / ㎡ less than the effect of improving the corrosion resistance by the chromate coating, more than 200 mg / ㎡ If high, the cost of the solution and chromium elution is worsened.

After coating as described above, it is baked at a steel plate temperature of 180 ~ 250 ℃, which is because the reaction of the curing agent of the present invention at a high temperature and should be heated to 180 ℃ or more for sufficient curing reaction, if the heat is higher than 250 ℃ This is because the production cost due to increase.

As the resin to be applied to the top, the most preferred phenoxy resin is excellent in corrosion resistance and fuel resistance. Unlike other resins, phenoxy resins exhibit a high glass transition temperature (Tg), and resins with a high glass transition temperature shield the underlying metal against corrosion factors (moisture, gasoline, etc.) of external molecules. The effect is great.

In the fuel tank manufacturing method of automobiles, after press-processing the chromate-treated resin coated steel sheet, the upper and lower plates are seam welded, and various pipes and brakes are joined (spot, projection and brazing welding methods). Black powder coating (15 to 80 ㎛) and thick film PVC coating (300 to 1200 ㎛) to secure the corrosion resistance from external corrosive environment on the outer surface of the fuel tank and to mitigate impacts when colliding with stones and collisions during road driving. Will be processed. Drying of the coating film after such coating can also be normally processed at high temperature for a long time (usually about 30 minutes). In the case where the resin coated steel sheet is treated by such a coating method, the physical properties of the chromate coating may change due to high temperature baking. Accordingly, in the case of the resin coated steel sheet composed of the chromate solution and the treatment method of the present invention, when the baking condition generated in the thick film coating process during the fuel tank manufacturing of the automobile manufacturing process is treated at 130 to 280 ° C., the adhesion between the chromate film and the resin film is This improved production of fuel tanks using lead-free plated steel sheets with improved corrosion resistance on the outer surface of the fuel tank and improved fuel resistance on the inner surface of the fuel tank. If the baking temperature is less than 130 ℃ after powder coating, the outer coating film is insufficient to dry and the adhesion of the coating film is poor. If the baking temperature exceeds 280 ℃, corrosion and fuel resistance are lowered due to cracks in the chromate film due to high temperature. There is a problem.

Hereinafter, the present invention will be described in more detail based on the following examples, but the present invention is not limited thereto.

Test Example

To a Zn-Ni alloy plated steel sheet having a plating adhesion of 30 g / m ² , a chromium aqueous solution having a trivalent chromium content of 0.5 g of a chromium component of 20 g / l in a chromate treatment solution, and 100 parts by weight of chromium in the aqueous solution. Based on the main solution sufficiently stirred by administering 1000 parts by weight of colloidal silica, 25 parts by weight of hydrofluoric acid, and 60 parts by weight of phosphoric acid, as shown in Table 1 below, the solution was chromated with a solution prepared by changing the curing agent. The resin coated steel sheet for the fuel tank was manufactured by the standard manufacturing method in the resin solution composition, and the baking condition after the powder coating was changed in the fuel tank manufacturing.

At this time, the basic composition of the resin solution was added 5 parts by weight of melamine resin as a curing agent to 100 parts by weight of a phenoxy resin having a number average molecular weight of 50,000 in a form dispersed in water, and then 15 parts by weight of colloidal silica having a particle diameter of 20 nm, A resin solution having a solution base composition of 2 parts by weight of wax was prepared. Unless otherwise specified, the resin solution prepared by the above mixing ratio is referred to as standard solution composition, and the resin solution prepared by the above composition is applied by a roll coating method, and then the steel sheet temperature is baked at 190 ° C. The method for producing a resin coated steel sheet having a dry resin coating thickness of 3 µm by water cooling is referred to as a standard steel sheet manufacturing method.

After processing, the film adhesion evaluation was taken in two modes: first, the plate was cut to 95 mmφ, and then cups 50 mm in diameter and 25 mm in height were made. The area where the resin was peeled off was obtained, and the secondary mode was washed by applying ultrasonic waves to 50 ° C. and 10% caustic soda solution for 3 minutes, and then evaluated in the same manner as in the first step.

◎: 0% exfoliated area ○: 1-10% exfoliated area

(Triangle | delta): The peeled area is 10 to 20% X: The peeled area is 20% or more

Corrosion resistance evaluation of the seam processing part was evaluated only by the salt spray tester. In the specimen preparation, the flat plate was cut into 95 mmφ, the cup of 50 mm diameter and 30 mm high was made, and after 600 hours, After removal, washing with pure water, drying and evaluating as follows according to the percentage of rust generated.

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

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

(Triangle | delta): 30-100% or less of white rust generated area with respect to the whole sample area.

×: Red blue

In addition, the fuel resistance evaluation was made by cutting the plate of the contact area of the fuel to 95 mmφ, and then made a cup 50 mm in diameter and 30 mm high, and 30 ml of the solution was put therein. Two types of solutions were used for the evaluation of fuelability. In case of Type A, a mixture of 5% salt was mixed with unleaded gasoline, and type B was mixed gasoline containing methanol and additives. It is in a 20ppm containing 1% ^pure-gas 85% methanol + 14% formic acid + 60ppm and Cl. In addition, in order to reproduce the running situation of the car was used a shaker made in advance to receive the fuel shake in the container made of cups, the evaluation was carried out after 6 hours as the above method, washed with pure water and dried after According to the ratio of rust was evaluated as follows.

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

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

(Triangle | delta): 30-100% or less of white rust generated area with respect to the whole sample area.

×: Red blue

As shown in Table 1, in Examples 1 to 5, corrosion resistance and fuel resistance were superior to Comparative Examples 4 to 7 at a baking temperature of 250 ° C., which is a high temperature. Excellent results were obtained compared to Comparative Example 1, which is a raw material, Comparative Example 2, which was not treated with the chromate solution of the present invention, and Comparative Example 3, which had no resin layer of the resin coated steel sheet. However, in the case of the comparative example 8 in which chromate adhesion amount is lower than the conditions of this invention, corrosion resistance and fuel resistance were shown to fall.

In Comparative Examples 9 and 10, when the fuel tank was manufactured using the resin coated steel sheet, the baking temperature during powder coating was treated out of the conditions specified in the present invention, and the corrosion resistance and the fuel resistance were lower than those of the examples.

Steel plate for automobile fuel tank by applying chromate solution mixed with a hardening agent solution prepared by administering alkoxy-titanium and zirconium-based cuffing agent to the coated chromate solution in an appropriate ratio on the surface of zinc-nickel alloy plated steel sheet. In the case of manufacturing, it is possible to secure corrosion resistance and fuel resistance even at several high-temperature small loads, so that it is possible to supply fuel tank products of high quality.

In addition, the present invention can be expected to have a significant effect on the environmental level compared to the existing Pb-Sn plated steel sheet by the development of a new plated fuel tank steel, which uses no lead at all, and significantly improves the safety and environmental regulation of automobile customers by improving the quality of the steel sheet. There is an advantage to contribute.

Claims (3)

Among the chromium components of 7 to 50 g / l, a chromium aqueous solution having a trivalent chromium component of 0.4 to 0.8 and 1000 parts by weight of colloidal silica, 25 parts by weight of hydrofluoric acid, and 60 parts by weight of phosphoric acid based on 100 parts by weight of the chromium component of the aqueous solution. Main solution containing; Based on the above, titanium and zirconium having an alkoxy group is 1: 1, and is prepared as an aqueous solution of 5 to 50% by weight, and is composed of a curing agent solution adjusted to pH 2-3, and the curing agent solution is 100 parts by weight of the main solution. A chromate solution for automobile fuel tanks having excellent corrosion resistance and fuel resistance at high temperature firing, characterized by mixing at 20 to 50 parts by weight. High-temperature baking resistance, characterized in that the zinc-nickel alloy electroplated steel sheet is coated by the chromate solution of claim 1 at 30 to 200 mg / ㎡ on the basis of the dry film adhesion amount and then baked at a steel plate temperature of 180 ~ 250 ℃ Method for producing chromate-treated zinc-nickel alloy plated steel sheet for automobile fuel tank with excellent fuel resistance. After press-processing the resin coated steel plate treated with the chromate for fuel tank composed of claim 1, 2, powder coating for securing corrosion resistance outside the fuel tank while seam welding the upper and lower plates and joining various pipes and brakes. A method for producing an automotive fuel tank having excellent corrosion resistance and fuel resistance at high temperature firing, wherein the thick film type PVC coating is baked at 130 to 280 ° C.