Single-face electrogalvanized, chromium-free surface treated steel plate for fuel tank and surface treatment agent

Abstract

The invention relates to an inorganic aqueous surface treatment agent for a single-face electrogalvanized, chromium free surface treated steel plate, a single-face electrogalvanized, chromium-free surface treated steel plate used for fuel tanks and a process of making the same. The inorganic aqueous surface treatment agent for a single-face electrogalvanized, chromium free surface treated steel plate comprises the following components: one or more metallic ion compounds comprising at least one of Zn.sup.2+, Mn.sup.2+, Mg.sup.2+, Ni.sup.2+, Al.sup.3+ and Ca.sup.2+; one or more vanadium compounds comprising at least one of V.sup.4+ and V.sup.5+; one or more compounds comprising at least one of phosphoric acid, pyrophosphoric acid, metaphosphoric acid, organic phosphoric acid and the ammonium salts thereof; one or more fluoric acid compounds comprising at least one of Zr, Ti, Si and Ha; one or more silane coupling agents comprising at least one of vinyl silane coupling agent, amino silane coupling agent, epoxy silane coupling agent and acryloxy silane coupling agent; a silica sol having a particle diameter less than 100 nm; one or more surfactants comprising at least one of carboxylate, sulfuric acid ester salt, sulfonate and phosphoric acid ester salt; wherein the total solid content in the inorganic aqueous surface treatment agent is 2 wt %-20 wt % of the surface treatment agent. The process for preparing the single-face electrogalvanized chromium-free surface treated steel plate used for fuel tanks comprises the steps of coating the plated surface of the single-face electrogalvanized steel plate with the above surface treatment agent, solidifying at a temperature of 70-100 C., and finally oil finishing on the surface to produce a skin film resulting from the surface treatment with a weight of 100-600 mg/m.sup.2.

Claims

1. A chromium free aqueous surface treatment agent for the surface treatment of a single-face electrogalvanized steel plate, formulated by dissolving or dispersing each component in an aqueous medium, wherein the aqueous solution comprises the following components: (A) one or more metallic ion compounds comprising at least one of the ions of Zn.sup.2+, Mn.sup.2+, Mg.sup.2+, Ni.sup.2+, Al.sup.3+ and Ca.sup.2+, wherein the molar concentration of the metallic ion in the surface treatment agent is 0.01-0.3 mol/L; (B) one or more vanadium compounds selected from the group consisting of a compound comprising V.sup.4+, a compound comprising V.sup.5+ and a combination thereof, wherein the molar concentration of V element in the surface treatment agent is 0.005-0.08 mol/L; (C) one or more compounds comprising at least one of phosphoric acid, pyrophosphoric acid, metaphosphoric acid, organic phosphonic acid compound or organic phosphoric acid compound and the ammonium salts thereof, wherein P element of (C) has a molar concentration of 0.05-1 mol/L in the surface treatment agent; (D) one or more hexafluoric acid compounds comprising at least one of Zr, Ti, Si and Hf, wherein the hexafluoric acid compound comprises 6 fluorine atoms, and F element in (D) has a molar concentration in the surface treatment agent of 0.01-0.2 mol/L; (E) one or more silane coupling agents comprising at least one of vinyl silane coupling agent, amino silane coupling agent, epoxy silane coupling agent and acryloxy silane coupling agent, wherein the molar concentration of the silane coupling agent in the surface treatment agent is 0.1-0.5 mol/L; (F) a silica sol comprising particles having a particle diameter less than 100 nm, wherein the molar concentration of its Si element in the surface treatment agent is 0.01-0.2 mol/L; and (G) one or more surfactant comprising at least one of carboxylate, sulfuric acid ester salt, sulfonate and phosphoric acid ester salt, wherein the molar concentration of the surfactant in the surface treatment agent is 0.0001-0.003 mol/L; wherein the total solid content in the aqueous surface treatment agent is 2 wt %-20 wt % of the surface treatment agent.

2. The chromium free aqueous surface treatment agent for the surface treatment of a single-face electrogalvanized steel plate according to claim 1, wherein the molar concentration of the metallic ions in the surface treatment agent is 0.07-0.2 mol/L; the molar concentration of V element in the surface treatment agent is 0.005-0.03 mol/L; P element of (C) has a molar concentration of 0.08-0.4 mol/L in the surface treatment agent; F element in (D) has a molar concentration in the surface treatment agent of 0.04-0.1 mol/L; the molar concentration of the silane coupling agent in the surface treatment agent is 0.1-0.4 mol/L; the molar concentration of Si element in the surface treatment agent is 0.06-0.12 mol/L; the molar concentration of the surfactant in the surface treatment agent is 0.0005-0.0015 mol/L; and the total solid content in the aqueous surface treatment agent is 4 wt %-15 wt % of the surface treatment agent.

3. The chromium free aqueous surface treatment agent for the surface treatment of a single-face electrogalvanized steel plate according to claim 1, wherein the metallic ion compound is dihydrogen phosphate, hydrogen phosphate or phosphate of the metallic ion.

4. The chromium free aqueous surface treatment agent for the surface treatment of a single-face electrogalvanized steel plate according to claim 1, wherein the vanadium containing compound is selected from at least one of vanadium pentoxide, vanadium tetroxide, sodium metavanadate, ammonium metavanadate, sodium pyrovanadate, vanadyl sulfate and vanadyl oxalate.

5. The chromium free aqueous surface treatment agent for the surface treatment of a single-face electrogalvanized steel plate according to claim 1, wherein the organic phosphonic acid compound or organic phosphoric acid compound is selected from at least one of nitrilotris(methylene phosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid and sodium ethylenediamine tetramethylene phosphate.

6. The chromium free aqueous surface treatment agent for the surface treatment of a single-face electrogalvanized steel plate according to claim 1, wherein the hexafluoric acid compound comprising Ti is selected from ammonium fluorotitanate; and the hexafluoric acid compound comprising Zr is selected from ammonium fluorozirconate.

7. The chromium free aqueous surface treatment agent for the surface treatment of a single-face electrogalvanized steel plate according to claim 1, wherein the surfactant is selected from at least one of fluorinated carboxylic acid, sodium fatty alcohol polyoxyethylene ether carboxylate, ternary polycarboxylic acid, sodium dodecyl sulfate and sodium dodecyl sulfonate.

8. A method of treating a surface of a single-face electrogalvanized steel plate used for fuel tanks, comprising: coating a plated surface of a single-face electrogalvanized steel plate with the chromium free aqueous surface treatment agent of claim 1, and then solidifying at 70-100 C. to obtain the single-face electrogalvanized steel plate having a skin film of 100-600 mg/m.sup.2 resulting from the surface treatment.

9. A single-face electrogalvanized steel plate used for fuel tanks with the single-face plated surface of the steel plate being coated with a chromium free skin film resulting from surface treatment, wherein the chromium free skin film resulting from surface treatment comprises the following components: one or more metallic ion compounds comprising at least one of the ions of Zn.sup.2+, Mn.sup.2+, Mg.sup.2+, Ni.sup.2+, Al.sup.3+ and Ca.sup.2+, and the metallic ion compound comprises 1%-10% of the skin film resulting from surface treatment based on metallic elements; one or more vanadium-containing compounds selected from the group consisting of a compound comprising V.sup.4+, a compound comprising V.sup.5+, and a combination thereof, and the vanadium-containing compound comprises 0.1%-5% by weight of the skin film resulting from surface treatment based on vanadium element; one or more phosphorus containing compounds, which comprise 1%-10% by weight of the skin film resulting from surface treatment based on phosphorus element; one or more fluorine containing compounds, which comprise 1%-10% by weight of the skin film resulting from surface treatment based on fluorine element; one or more silicon containing compounds, which comprise 1%-10% by weight of the skin film resulting from surface treatment based on silicon element; one or more surfactants, which comprise 0.1%-1% by weight of the skin film resulting from surface treatment; wherein the skin film resulting from the surface treatment covering the plated layer surface of the single-face electrogalvanized steel plate is a monolayer structure and has a film weight of 100-600 mg/m.sup.2.

10. The single-face electrogalvanized steel plate used for fuel tanks according to claim 9, wherein the metallic ion compound is dihydrogen phosphate, hydrogen phosphate or phosphate of the metallic ion; the vanadium containing compound is selected from a group consisting of a compound comprising V.sup.4+, a compound comprising V.sup.5+ and a combination thereof; the phosphorus containing compound is selected from at least one of phosphoric acid, pyrophosphoric acid, metaphosphoric acid, organic phosphoric acid and the ammonium salts thereof; the fluorine containing compound is a fluoric acid compound comprising at least one of Zr, Ti, Si and Hf, wherein the fluoric acid compound comprises 6 fluorine atoms; the silicon containing compound consists of a silane coupling agent and a silica sol comprising particles having a particle diameter of less than 100 nm, wherein the silane coupling agent is selected from at least one of vinyl silane coupling agent, amino silane coupling agent, epoxy silane coupling agent and acryloxy silane coupling agent; and the surfactant is selected from at least one of carboxylate salt, sulfuric acid ester salt, sulfonate salt, and phosphoric acid ester salt.

11. A process of making a single-face electrogalvanized steel plate used for fuel tanks, wherein the steel plate has been subjected to surface treatment, comprising the steps of single-pass roll coating, low-temperature solidification and medium oil finishing, wherein a plated surface of the single-face electrogalvanized steel plate is coated with the chromium free aqueous surface treatment agent of claim 1, then solidified at a low temperature of 70-100 C. to form a skin film, and finally oil finished on the surface at an oiling amount of 1.0-1.9 g/m.sup.2 to obtain the single-face electrogalvanized, steel plate for fuel tanks which has the skin film with an amount of 100-600 mg/m.sup.2.

12. The process of making a single-face electrogalvanized, steel plate used for fuel tanks according to claim 11, wherein the weight of the skin film resulting from the surface treatment of the single-face electrogalvanized, steel plate is 250-450 mg/m.sup.2.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a typical process chart of processing a material for a fuel tank;

(2) FIG. 2 is a picture of a test sample after impact molding;

(3) FIG. 3 is a schematic view showing a degraded gasoline soaking test, wherein A. seal clip; B. test sample; C. seal gasket; D. degraded gasoline; E. seal glass.

DETAILED DESCRIPTION OF THE INVENTION

(4) The technical solution of the invention will be further described in detail with reference to the following specific Examples.

(5) The following Examples 1-7 and Comparative Examples 1-5 describe specifically the single-face electrogalvanized steel plate material used and the method of cleaning its surface; the inorganic aqueous surface treatment agents for the single-face electrogalvanized, chromium free surface treated steel plate (shown in Table 1); the method of treating the single-face electrogalvanized, chromium free surface treated steel plates; and the property evaluation of the resulting single-face electrogalvanized, chromium free surface treated steel plates (shown in Table 3).

(6) 1. Sample Plate for Test

(7) Single-face electrogalvanized steel plate having a thickness of 0.8 mm and a zinc layer weight of 30/0 g/m.sup.2.

(8) 2. Method of Cleaning the Single-Face Electrogalvanized Steel Plate:

(9) The surface of the single-face electrogalvanized steel plate was spray cleaned with a degreaser having medium basicity (pH=11-12) to remove the smudge and oil adhered to the surface; then rinsed with pure water to remove the residual alkaline components from the surface; and dried by purging with cool air for later use.

(10) 3. The Compositions of the Surface Treatment Agents for Examples 1-7 and Comparative Examples 1-5 are Shown in Table 1.

(11) TABLE-US-00001 TABLE 1 The compositions of the surface treatment agents for the Examples and Comparative Examples Metallic ion Phosphoric Fluoric compound (A), Vanadium acid-type acid-type based on compound (B), compound (C), compound (D), metallic element based on V based on P based on F content element content element content element content mol/L mol/L mol/L mol/L No. Type Content Type Content Type Content Type Content Example Zinc 0.07 Ammonium 0.01 Phosphoric acid 0.12 Ammonium 0.06 1 dihydrogen metavanadate fluorotitanate phosphate Example Manganese 0.09 Vanadyl 0.01 Phosphoric acid 0.12 Ammonium 0.06 2 dihydrogen oxalate fluorozirconate phosphate Example Magnesium 0.09 Vanadyl 0.006 Organic 0.1 Ammonium 0.1 3 dihydrogen oxalate phosphoricacid fluorotitanate phosphate Example Manganese 0.09 Vanadyl sulfate 0.01 Phosphoric acid 0.03 Ammonium 0.06 4 dihydrogen fluorotitanate phosphate Example Manganese 0.2 Vanadyl 0.01 Phosphoric acid 0.12 Ammonium 0.06 5 dihydrogen oxalate fluorotitanate phosphate Example Manganese 0.09 Vanadyl 0.02 Phosphoric acid 0.12 Ammonium 0.06 6 dihydrogen oxalate fluorotitanate phosphate Example Manganese 0.09 Vanadyl 0.01 Phosphoric acid 0.35 Ammonium 0.08 7 dihydrogen oxalate fluorotitanate phosphate Example Manganese 0.09 Vanadyl 0.01 Phosphoric acid 0.12 Ammonium 0.04 8 dihydrogen oxalate fluorotitanate phosphate Comp. Manganese 0.4 Vanadyl 0.01 Phosphoric acid 0.12 Ammonium 0.06 Ex. 1 dihydrogen oxalate fluorotitanate phosphate Comp. Vanadyl sulfate 0.01 Phosphoric acid 0.12 Ammonium 0.06 Ex. 2 fluorotitanate Comp. Manganese 0.09 Vanadyl 0.01 Phosphoric acid 0.16 Ex. 3 dihydrogen oxalate phosphate Comp. Zinc 0.09 Vanadyl 0.01 Phosphoric acid 0.12 Ammonium 0.06 Ex. 4 dihydrogen oxalate fluorozirconate phosphate Comp. Manganese 0.07 Vanadyl 0.01 Phosphoric acid 0.12 Ammonium 0.06 Ex. 5 dihydrogen oxalate fluorotitanate phosphate Comp. Manganese 0.09 Vanadyl 0.01 Phosphoric acid 0.12 Ammonium 0.06 Ex. 6 dihydrogen oxalate fluorozirconate phosphate Silane coupling agent (E), Silica sol (F), based on Si based on Si element content element content Surfactant (G), mol/L mol/L mol/L PMT No. Type Content Type Content Type Content C. Example Silane coupling 0.16 Silica sol 0.07 Sulfonic acid 0.0005 85 1 agent (20 nm) ester salt Example Silane coupling 0.16 Silica sol 0.07 Sulfuric acid 0.0005 75 2 agent (20 nm) ester salt Example Silane coupling 0.16 Silica sol 0.07 Sulfonic acid 0.0007 85 3 agent (40 nm) ester salt Example Silane coupling 0.16 Silica sol 0.07 Sulfuric acid 0.0007 75 4 agent (40 nm) ester salt Example Silane coupling 0.16 Silica sol 0.05 Sulfuric acid 0.0007 85 5 agent (20 nm) ester salt Example Silane coupling 0.16 Silica sol 0.07 Sulfonic acid 0.0007 85 6 agent (60 nm) ester salt Example Silane coupling 0.1 Silica sol 0.03 Sulfuric acid 0.0007 90 7 agent (20 nm) ester salt Example Silane coupling 0.3 Silica sol 0.1 Sulfuric acid 0.0015 85 8 agent (20 nm) ester salt Comp. Silane coupling 0.16 Silica sol 0.07 Sulfuric acid 0.0005 85 Ex. 1 agent (20 nm) ester salt Comp. Silane coupling 0.16 Silica sol 0.07 Sulfuric acid 0.0005 85 Ex. 2 agent (20 nm) ester salt Comp. Silane coupling 0.16 Silica sol 0.07 Sulfuric acid 0.0007 75 Ex. 3 agent (20 nm) ester salt Comp. Silane coupling 0.05 Silica sol 0.07 Sulfonic acid 0.0007 85 Ex. 4 agent (40 nm) ester salt Comp. Silane coupling 0.16 Silica sol 0.07 Sulfuric acid 0.0005 140 Ex. 5 agent (20 nm) ester salt Comp. Silane coupling 0.55 Silica sol 0.07 Sulfuric acid 0.0007 85 Ex. 6 agent (20 nm) ester salt Note: 1. In Phosphoric acid-type compound (C), the organic phosphoric acid in Example 3 is 1-hydroxyethylidene-1,1- diphosphonic acid (HEDP); 2. In Silane coupling agent (E), vinyl silane coupling agent is used in Examples 3, 4, and the silane coupling agent for the rest is a mixture of amino silane coupling agent and epoxy silane coupling agent mixed at a ratio of 1:2; 3. In Surfactant (G), the surfactant (G) used in Examples 1, 3, 7 and Comparative Example 4 is sodium dodecyl sulfonate, and the surfactant for the rest is sodium dodecyl sulfate.

(12) 4. Method of Treating the Single-Face Eletrogalvanized, Chromium Free Steel Plates with the Inorganic Aqueous Surface Treatment Agents:

(13) The surface treatment agents of the Examples and Comparative Examples listed in Table 1 were used to coat the plated surface of the single-face electrogalvanized steel plates respectively. A roll coating process was used for coating. In the roll coating process, the following procedure was used to control the coating thickness: the surface of the coating roll was wrapped with polyurethane resin; reverse coating was used in the coating process, i.e. the coating process was conducted in such a manner where the surface of the coating roll and the strip steel moved in contrary directions; in the coating process, the ratio between the rotation rate of the coating roll and that of the strip steel was 0.5-1.5, and the ratio between the rotation speed of the pick-up roll and that of the strip steel was 0.5-1.5; the pressure of the pick-up roll and the coating roll was 50-240 kg; then, solidification was conducted at 70-100 C. (see Table 1 for the specific solidifying temperatures), so that single-face eletrogalvanized, chromium free surface treated steel plates were obtained wherein the amount of the skin film resulting from surface treatment was 250-450 mg/m.sup.2 (see Table 2).

(14) TABLE-US-00002 TABLE 2 Amount of skin film (g/m.sup.2) Example 1 0.4 Example 2 0.3 Example 3 0.4 Example 4 0.4 Example 5 0.4 Example 6 0.4 Example 7 0.3 Example 8 0.5 Comp. Ex. 1 0.4 Comp. Ex. 2 0.4 Comp. Ex. 3 0.4 Comp. Ex. 4 0.4 Comp. Ex. 5 0.4 Comp. Ex. 6 0.4

(15) 5. Property Assessment

(16) The properties of the single-face electrogalvanized surface treated steel plate samples obtained in the above Examples and Comparative Examples were assessed using the following experimental methods, and the results are shown in FIG. 3.

(17) (1) Gasoline Degradation Liquid Resistance

(18) The acidic product produced by the degradation of gasoline during storage and use concentrates in condensed water coexisting with gasoline, and forms a highly corrosive medium having relatively high acidity which corrodes fuel tanks. A simulated gasoline degradation liquid was used as a corrosive medium in this test, and the soaking test was conducted to assess corrosion resistance. With such factors as machining deformation, cleansing, coating (baking) of a typical fuel tank taken into account, the following test procedure was developed:

(19) Assessment of corrosion resistance of a steel plate for fuel tank in the condition of ultimate service: first, an impact molded part (shown in FIG. 2) was spray cleaned with a degreaser having medium basicity (pH=11-12) to remove the smudge and oil adhered to the surface thereof; then the part was rinsed with pure water to remove the residual alkaline components on the surface and dried by purging with cool air; subsequently, the sample was placed in an oven, baked at 18 C. for 20 minutes, and air cooled to room temperature; then, 20 ml gasoline degradation liquid and 5 ml gasoline were infused into the cup, the assembly was sealed (shown in FIG. 3) and placed in an environment at a constant temperature of 40 C.

(20) 120 h later, the rusting level of the cup bottom was observed: : The area ratio of white rust was less than 1%; : The area ratio of white rust was more than 1% and less than 10%; : The area ratio of white rust was more than 10% and less than 50%; x: The area ratio of white rust was more than 50% and red rust appeared.
(2) Salt Fog Corrosion Resistance

(21) The samples were machined into 150 mm75 mm sample plates, and the edges thereof were sealed. The fixed-time salt fog resistance test was conducted with reference to ASTMB 117. : The area of white rust was less than 3%; : The area of white rust was 3%-10%; : The area of white rust was more than 30%; x: The area of white rust was more than 90%, or red rust appeared.
(3) Adhesion Property of the Coatings

(22) The samples were machined into 150 mm75 mm sample plates without forming any scratches on the surfaces thereof. An Erichsen tester was used to test the sample plates until the Erichsenvalue was 7 mm; then 3M Scotch tape was used for peeling; and the state of the surface coating was observed. : No change in appearance; : The surface whitened slightly; : The surface whitened apparently, and the coating peeled off slightly; x: The coating peeled off in large scale.
(4) Weldability

(23) Galvanized plates having identical steel plate thickness and plated layer thickness were used as substrates for surface treatment with the same process, and the weldability of the material was characterized by test results of spot welding and seam welding in a range of weldable electrical current. : The appearance at the welding position was good, and the performance was superior; : The appearance at the welding position was good, and the performance basically satisfied the requirements; : The performance at the welding position was poor; x: Not weldable.
(5) Alkali Resistance

(24) Flat plate samples were spray cleaned in a degreasing agent having medium basicity (pH=11-12) at 50 C. for 3 minutes to remove the smudge and oil adhered to the surface; then rinsed with pure water to remove the residual alkaline components on the surface and dried by purging with cool air; and the state of the surface coatings was observed. : No change in appearance; : The appearance whitened slightly; : The appearance whitened and a portion of the skin film dissolved or peeled off; x: The skin film dissolved or peeled off completely.
(6) Humidity-Heat Resistance

(25) A stack of laminated flat plate samples was clamped tightly with a clip and placed in a humid heat box at a temperature of 48 C. and a relative humidity of 98% for 120 hours; and the change of the appearance was observed. : No change in appearance; : The appearance blackened slightly; : The appearance blackened and local white rust appeared; x: Large area rusting appeared.

(26) As seen from the assessment results of the performances of the various Examples and Comparative Examples (shown in FIG. 3), the single-face electrogalvanized surface treated steel plates of Examples 1-8 exhibited good comprehensive performances in terms of the various assessment items. Particularly, the single-face electrogalvanized surface treated steel plates of Examples 1, 2, 3 and 5 showed excellent comprehensive performances. In Example 4, the reduction of the relative addition amount of component C in the surface treatment agent affected the protective function of the phosphate reactant on the surface, leading to decreased salt fog corrosion resistance of the skin film resulting from surface treatment. In Example 6, the particle diameter of component F in the surface treatment agent was relatively large, and had some influence on the gasoline degradation liquid resistance of the skin film. Excessive addition of component A in the surface treatment agent of Comparative Example 1 resulted in incomplete reaction of component A during film formation and its physical deposit which affected the alkali resistance, humidity-heat resistance of the surface and the adhesion of the coating. The absence of component A in the surface treatment agent of Comparative Example 2 rendered poor resistance of the skin film structure to acidic medium corrosion, i.e. poor gasoline degradation liquid resistance, and insufficient wear resistance of the skin film. The absence of component D in the surface treatment agent of Comparative Example 3 affected the alkali cleansing resistance of the skin film. The amount of component E in the surface treatment agent of Comparative Example 4 was so low that the salt fog corrosion resistance of the skin film decreased remarkably. The amount of component E in the surface treatment agent of Comparative Example 6 was rather high, such that the condensate of the silane coupling agent was the main component in the surface skin film structure. This skin film structure possessed excellent salt fog corrosion resistance, but the gasoline degradation liquid resistance was lowered obviously. Low-temperature solidification at 75 C. was employed in Example 2, and high-temperature solidification at 140 C. was adopted in Comparative Example 5. These two ways of solidification provided skin films resulting from surface treatment which showed superior comprehensive performances, indicating that solidification via film forming reaction may be completed with these surface treatment agents at relatively low temperatures (PMT=70-100 C.). Unduly high temperature not only increases energy consumption, but also barely contributes to the improvement of the comprehensive resistance of the skin film resulting from surface treatment.

(27) TABLE-US-00003 TABLE 3 Performances of Various Examples and Comparative Examples Gasoline Salt fog Alkali Humid- degradation corro- cleans- ity- liquid sion ing heat corrosion resis- Weld- resis- resis- Coating No. resistance tance ability tance tance adhesion Exam- ple 1 Exam- ple 2 Exam- ple 3 Exam- ple 4 Exam- ple 5 Exam- ple 6 Exam- ple 7 Exam- ple 8 Comp. X Ex. 1 Comp. X Ex. 2 Comp. X Ex. 3 Comp. X Ex. 4 Comp. Ex. 5 Comp. X Ex. 6