JPH10193507A - Fuel tank rust-prevention steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve press workability and corrosion resistance of worked part by forming a dry coating film of an organic resin in a specified thickness on one side of an Al-based-plating processed steel plate with a specific treatment liquid in which silica sol of a specified amount and a chromate of a specified amount are added. SOLUTION: Urethane-resin film is applied on at least one side of an Al- based-plating processed steel plate by a known application method such as a roll-coating method, by using a dispersion of an aqueous urethane resin in which silica sol and a chromate are added, in this case, amount of silica sol/(aqueous urethane resin non-volatilable content + amount of silica sol) = 0.10-0.14, and amount of chromate/(aqueous urethane resin non-volatilable content + amount of silica sol) = 0.001-0.10, and the film thickness is set to be 0.5-2.0μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel tank which does not rust even when used for storage of fuel containing degraded gasoline or alcohol and has resistance weldability and press workability in tank production. It relates to a rust-proof steel plate.

[0002]

2. Description of the Related Art Fuel tank materials for automobiles and the like are excellent in resistance weldability and press workability, and the fuel tank corrodes the inner surface of the tank while being mounted on the automobile, causing perforations, and a fuel circulation system filter. It is necessary that clogging does not occur. As a fuel tank material having such properties, a hot-dip Pb-Sn alloy plated steel sheet (Japanese Patent Publication No.
No. 6133) and galvanized steel sheet (JP-B-53-19).
No. 981), which has been widely used in the manufacture of fuel tanks.

[0003] However, a hot-dip Pb-Sn alloy-plated steel sheet exhibits excellent corrosion resistance if the fuel is plain gasoline, but the fuel is an alcohol fuel such as methanol or ethanol or other fuel. If it is a fuel mixture of gasoline,
Corroded by alcohol. In the case of hot-dip galvanized steel sheets, if poor gasoline is used as fuel and left in a high-temperature and high-humidity environment for a long time, highly corrosive formic acid and acetic acid are generated due to oxidative deterioration of gasoline, and white rust is generated. Would.

[0004] Therefore, as a fuel tank material which does not have such a problem, an Al-based plated steel sheet (Japanese Patent Publication No. 4-68399) coated with Al or an Al-Si alloy, or a fuel tank coated with an epoxy resin. Rusted steel plate (Japanese
No. -306638). However, although these fuel tank materials are excellent in corrosion resistance, when manufacturing tank members by press working, if the shape is severe, the material will break due to poor lubrication or the corrosion resistance of the pressed part will decrease. There was a problem that

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a rust-preventive steel plate for a fuel tank having improved press workability and corrosion resistance in a processed portion.

[0006]

Means for Solving the Problems The first invention of the present invention is the A
In a rust-preventive steel sheet in which an organic resin film is formed on a l-plated steel sheet, the organic resin film is treated with a water-based urethane resin dispersion to which silica sol and chromate are added, and the silica sol is calculated as silica sol amount / (water-based urethane resin nonvolatile). Amount + silica sol) = 0.10 to 0.40, chromate amount / (aqueous urethane resin non-volatile content + silica sol amount) = 0.001 to 0.10, At least one side has a dry coating thickness of 0.5 to 2.0 μm
It is a rust-proof steel plate for a fuel tank, characterized in that it is formed with m.

According to a second aspect of the present invention, an antioxidant for gasoline is added to the treatment liquid of the first aspect of the present invention, and the amount of the antioxidant is divided by the amount of the antioxidant / (amount of aqueous urethane resin nonvolatile content + amount of silica sol).
= 5 × 10 ^{−2 to} 5 × 10 ⁻⁵ .

According to a third aspect of the invention, a solid polymer lubricant is added to the treatment liquid of the first invention, and the solid polymer lubricant is added to the solid polymer lubricant amount / (aqueous urethane resin nonvolatile content + silica sol amount) = 0. It is characterized by being a rust-preventive steel plate for a fuel tank set to 0.01 to 0.10.

In a fourth aspect, the processing liquid of the third aspect is gasoline.
Antioxidant, add antioxidant to antioxidant amount /
(Aqueous urethane resin nonvolatile content + silica sol content) = 5 x
10 ^-2~ 5 × 10^-FiveCorrosion-resistant steel plate for fuel tanks
It is characterized by:

[0010]

The present inventors have conducted various studies to improve the press workability of an organic resin-coated Al-based plated steel sheet. As a result, it was found that the organic resin film should be a urethane resin film and that the corrosion resistance should be improved. They have found that silica sol and chromate can be added to the organic resin coating. In other words, the urethane resin film has gasoline resistance, which is an essential condition as a fuel tank material, and is less likely to seize or break when pressed, and contains chromate at the stage of the processing solution. Even if it does, the treatment liquid does not increase in viscosity, gelling, precipitation, etc., so that a uniform thin film can be formed on the surface of the Al-based plated steel sheet.

The urethane resin film is formed by adding silica sol and chromate using a dispersion of an aqueous urethane resin and, if necessary, using a polymer solid lubricant and an antioxidant for gasoline as described later. After the addition, it is formed by applying to at least one surface of an Al-based plated steel sheet by a known coating method such as a roll coating method and heating. Water-based urethane resin dispersion is A
Since the leveling property with respect to the 1-based plated steel sheet is very good, a uniform film can be formed even in a thin film, and even if a chromate having a large oxidizing effect is added, the treatment solution does not thicken or precipitate. An important point in stabilizing the treatment liquid is to make the pH of the added silica sol approximately the same as that of the aqueous urethane resin dispersion.

The urethane resin includes aliphatic, alicyclic,
Although there are aromatic compounds and the like, alicyclic compounds are particularly preferable because they have excellent gasoline resistance. This alicyclic urethane resin includes hydrogenated 2,4-toluylene diisocyanate.
, Hydrogenated 1,6-toluylene diisocyanate, dicyclohexylmethane-p, p'-diisocyanate, dicyclohexyldimethylmethane-p, p'-diisocyanate and the like. Polio
And those polymerized with a polymer.

[0013] Even if the organic resin film of the fuel tank material is a urethane resin film, it is difficult to eliminate the occurrence of galling during press working. However, if silica sol and chromate are added to the urethane resin film, the galling occurs because of corrosion resistance, so that the aluminum-plated steel sheet of the base material does not corrode. The silica sol may be a general commercial product, but preferably has a particle size of 10 to 50 μm, and the chromate may be sodium chromate, ammonium chromate, barium chromate, strontium chromate, or the like.

The amount of silica sol to be added is expressed as silica sol amount /
(Aqueous urethane resin nonvolatile content + silica sol content) = 0.
10 to 0.40, preferably 0.15 to 0.3
5, more preferably 0.20 to 0.30. If the silica sol ratio in the coating is less than 0.10, the corrosion resistance of the processed portion is not improved, and if it is more than 0.40, the silica sol is inferior in lubricity, so that the press workability is reduced.

The amount of chromate to be added is as follows: chromate amount / (aqueous urethane resin non-volatile content + silica sol content) =
0.001 to 0.10. However, the preferred range is 0.005 to 0.05, more preferably 0.01 to 0.03.
It is. If the chromate ratio in the coating is less than 0.001, the corrosion resistance of the processed portion is not improved, and if it is greater than 0.10, the stability of the treatment liquid is reduced and gelation is likely to occur.

When silica sol is added to the urethane resin film, the silica sol lowers the lubricity as described above. Therefore, if the amount of silica sol is increased to improve the corrosion resistance and severe pressing is performed, galling of the film occurs. Increase. However, in such a case, the press workability can be improved by adding a polymer solid lubricant of the resin powder. As the polymer solid lubricant, fine powders of polyethylene, polypropylene, polystyrene, and fluororesin may be used and dispersed in the coating. When the pressing is not severe, it is not necessary to add a solid polymer lubricant.

The amount of the polymer solid lubricant to be added is such that the amount of the polymer solid lubricant / (the amount of the aqueous urethane resin nonvolatile content + the amount of the silica sol) = 0.01 to 0.10. If it is smaller than 0.01, the effect of addition is small, so that severe press working becomes difficult. If it is larger than 0.10, the adhesion of vinyl chloride paint or the like applied to the outer surface of the tank as a measure against chipping after assembly in the fuel tank is reduced. Resulting in.

Further, when an antioxidant for gasoline is added to the urethane resin coating, gasoline oxidation and corrosion of the fuel tank when water is mixed into gasoline in the fuel tank can be suppressed. That is, when gasoline is deteriorated, highly corrosive formic acid and acetic acid are generated. Therefore, depending on gasoline, the generation of formic acid and acetic acid is prevented by adding an antioxidant. However, when water is mixed into gasoline, formic acid and acetic acid are generated despite the addition of an antioxidant. This is presumed to be due to the fact that the antioxidant in the gasoline migrates to the water phase and the stability of the gasoline decreases.

However, if an antioxidant is added to the urethane resin film, the antioxidant is eluted to prevent the gasoline from being oxidized and deteriorated. Further, since the antioxidant is also eluted into the aqueous phase, the concentration of the antioxidant in the aqueous phase increases, and the corrosiveness decreases. For this reason, the antioxidant exerts one type of inhibitory effect and suppresses corrosion of the inner surface of the fuel tank.

As the antioxidant, amine-based ones such as N, N'-diisopropyl-p-phenylenediamine and N, N'-di-sec-butyl-p-phenylenediamine are most preferred. Also, phenolic compounds such as 2,6-di-tert-butyl-4
-Methylphenol, 2,4-dimethyl-6-tert
-Butylphenol and the like can also be used. These compounds may be used in combination. Addition amount is antioxidant amount /
(Aqueous urethane resin nonvolatile content + silica sol content) = 5 x
10 ^{−2 to} 5 × 10 ⁻⁵ , preferably 1 × 10 ⁻³ to 1 × 10
^It is desirable to set it to ^-4 . If it is smaller than 5 × 10 ⁻⁵ , the inhibitor effect is small, and if it is larger than 5 × 10 ⁻² , the effect is not changed.

When the coating thickness is less than 0.5 μm, the corrosion resistance of the processed portion is not improved. When the coating thickness is more than 2.0 μm, the coating becomes an insulator and resistance welding becomes difficult. .0
μm.

As the Al-based plated steel sheet, pure Al-plated steel sheet, Al-3 to 13% Si alloy-plated steel sheet, Al-Z
n alloy plated steel sheet, Al-Zn-Si alloy plated steel sheet,
Al-Mg alloy plated steel sheet, Al-Mn alloy plated steel sheet and the like can be mentioned. As a method for producing an Al-based plated steel sheet, there are a hot-dip plating method, a vapor deposition plating method, a molten salt plating method, and the like. When a pure Al-coated steel sheet is produced by the hot-dip plating method, a Fe-Al alloy layer having poor ductility at a plating interface is provided. It is preferable to use an Al-plated steel sheet manufactured by a vapor deposition plating method or a hot-dip salt plating method.
On the other hand, in the case of an Al alloy-plated steel sheet, since it can be manufactured at low cost by the hot-dip plating method, it is preferable to use one manufactured by the hot-dip plating method. In order to enhance the adhesion of the coating to the Al-based plated steel sheet, as a pretreatment, 5 to 100 m in terms of metal Cr
It is preferable to form a g / m ² chromate film.

[0023]

【Example】

Example 1 A cold-rolled steel sheet prepared by adding a silica sol and a chromate to each of a resin dispersion of an aqueous urethane resin, an acrylic resin, an ionomer resin, and an epoxy resin, and adding them to an ultra-low carbon Ti. A 9% Si-9% Si alloy coated steel sheet (sheet thickness 0.8 mm, coating weight 60 g / m ² ) was applied by a bar coating method so that the dry coating thickness became μm, and 200 ° C. For 1 minute to harden the coating and produce a rustproof steel plate. The silica sol of the treatment liquid was silica sol amount / (resin dispersion nonvolatile content + silica sol content) = 0.2, and chromate was chromate content / (resin dispersion nonvolatile content + silica sol content) = 0.01. Chromate was not added to the treatment solution using the epoxy resin.

Next, these rustproof steel sheets were subjected to flat bottom cylindrical drawing (drawing ratio 2.1, blank diameter φ84 mm).
They were immersed in unleaded gasoline (50 ° C.) for 24 hours, and the gasoline resistance of the coating was visually observed and examined with an infrared spectrophotometer.
, A slight change (loss of the film and a change in the infrared spectrum of less than 5%) was evaluated with a symbol ○, and a film with peeling was evaluated with a symbol x. Table 1 shows the results.

[0025]

[Table 1] (Note) The aliphatic system of the urethane resin is hexamethylene diisocyanate-base urethane, the alicyclic system is dicyclohexylmethane-p, p'-diisocyanate-base urethane, and the aromatic system is toluene diisocyanate-base. The urethane and acrylic resins are copolymers of methyl methacrylate and butyl acrylate, the ionomer resin is polyethylene ionomer, and the epoxy resin is bisphenol A type epoxy.

Example 2 In Example 1, silica sol and chromate were dispersed in an aqueous dicyclohexylmethane-p, p'-diisocyanate-base urethane resin (alicyclic urethane resin) dispersion as a treatment liquid. The corrosion resistance test A of the processed part was carried out on the obtained rustproof steel sheet using
And press workability test A. Table 2 shows the coating composition and the coating thickness of the rustproof steel sheet, and Table 3 shows the performance test results.

(1) Corrosion resistance test A for processed part Flat-bottom cylindrical drawing (drawing ratio 2.1, blank diameter φ84m)
m), immersed in the following test solution, and immersed in the test solution for 10 weeks while changing the test solution every week. Those with the symbol ○, those with 5% or more and less than 20% with the symbol 、 ２
Those with 0% or more were evaluated with the symbol x. Test solution A A mixture of 50% gasoline and 50% water (containing 350 ppm formic acid) Test solution B 85% methanol, 15% gasoline and 350p formic acid
pm mixed solution (2) Press workability test A: Flat bottom cylindrical drawing (punch diameter: 40 mm) with a limit drawing ratio of 2.15 or more, symbol ◎; less than 2.15, 2.1 or more symbol In the case of ○, those less than 2.1 were evaluated with the symbol x.

[0028]

[Table 2] (Note 1) Silica sol amount = Silica sol amount / (aqueous urethane resin nonvolatile content + silica sol amount) (Note 2) Chromate addition amount = chromate salt / (aqueous urethane resin nonvolatile content + silica sol amount)

[0029]

[Table 3]

Example 3 Various treatment liquids were prepared by adding silica sol, chromate and polyethylene resin powder to an aqueous dicyclohexylmethane-p, p'-diisocyanate-base urethane resin (alicyclic urethane resin) dispersion. Then, they were converted to the Al-
A 9% Si alloy plated steel sheet (0.8 mm thick, 80 g / m ² plating weight, 20 mg / m ² chromium coating weight) is applied by bar coating and heated at 200 ° C. for 1 minute. The coating was cured to produce a rustproof steel plate. Next, the following corrosion test B and press formability test B were performed on the obtained rust-preventive steel sheet. Table 4 shows the coating composition and coating thickness of the rust-proof steel plate, and Table 5 shows the performance test results.

(1) Corrosion resistance test B for processed part Flat-bottom cylindrical drawing (drawing ratio 2.3, blank diameter φ84m)
m), immersed in the following test solution, and immersed in the test solution for 10 weeks while changing the test solution every week. Those with the symbol ○, those with 5% or more and less than 20% with the symbol 、 ２
Those with 0% or more were evaluated with the symbol x. Test solution A A mixture of 50% gasoline and 50% water (containing 350 ppm formic acid) Test solution B 85% methanol, 15% gasoline and 350p formic acid
mixture test solution C gasoline 50% and water pm ^(Cl - 50 ppm content) 50% mixture (2) press-formability test B flat bottom cylindrical drawing limit drawing ratio (punch diameter 40 mm) is 2.3 or more Those with the symbol ○ and those with less than 2.3 with the symbol ×
Was evaluated.

[0032]

[Table 4] (Note 1) The method of calculating the amount of silica sol and the amount of chromate added is the same as in Table 2 of Example 2. (Note 3) Amount of polyethylene resin powder = Amount of polyethylene resin powder / (amount of non-volatile content of aqueous urethane resin + amount of silica sol)

[0033]

[Table 5] (Note) No. 11 and 15 of the comparative examples could not be processed at a draw ratio of 2.3, and thus the corrosion resistance test of the processed portion was not performed.

Example 4 In Example 3, an Al-low-cold Ti-added cold-rolled steel sheet was used.
Instead of a 9% Si alloy plated steel sheet, a Zn-55% Al alloy plated steel sheet (thickness 0.8) of an ultra-low carbon Ti-added cold rolled steel sheet
mm, the coating weight and the coating weight are 80 g / m ² ), and the coating composition and the coating thickness are the same as those of Examples Nos. 11 to 20 and Comparative Example N.
o. Corrosion-resistant steel sheets corresponding to Nos. 11 to 14 were manufactured and subjected to the same corrosion resistance test B and press workability test B as in Example 3. Table 6 shows the results.

[0035]

[Table 6] (Note) No. 21 of the comparative example could not be processed at a draw ratio of 2.3, and thus the corrosion resistance test of the processed portion was not performed.

Example 5 Various treatment liquids prepared by adding silica sol, chromate and an antioxidant for gasoline to an aqueous dicyclohexylmethane-p, p'-diisocyanate-to-urethane resin (alicyclic urethane resin) dispersion. And applying them to a low-carbon Ti-added cold-rolled steel sheet of an Al-9% Si alloy-plated steel sheet (sheet thickness 0.8 mm, coating weight 60 g / m ² ) by a bar coating method. The coating was cured by heating at 200 ° C. for 1 minute to produce a rust-proof steel plate. Next, the obtained corrosion-resistant steel sheet was subjected to the following corrosion resistance test C for a processed portion and the press workability test A in Example 2 as described below. Table 7 shows the coating composition and coating thickness of the rust-preventive steel sheet, and Table 8 shows the performance test results.

(1) Corrosion resistance test of processed part C Flat bottom cylindrical drawing (drawing ratio 2.1, blank diameter φ84m)
m), immersed in the following test solution, and immersed in the test solution for 10 weeks while changing the test solution every week. Those with the symbol ○, those with 5% or more and less than 20% with the symbol 、 ２
Those with 0% or more were evaluated with the symbol x. Test liquid D 50% gasoline and 50% water (containing 3500 ppm formic acid)
Test solution E 85% methanol, 15% gasoline and 3500 formic acid
ppm mixture

[0038]

[Table 7] (Note 1) The method of calculating the amount of silica sol and the amount of chromate added is the same as in Table 2 of Example 2. (Note 2) Amount of antioxidant = amount of antioxidant / (amount of non-volatile content of aqueous urethane resin + amount of silica sol) (Note 3) A of antioxidant is N, N'-diisopropyl-
p-phenylenediamine, B is N, N'-di-sec-
Butyl-p-phenylenediamine, C is 2,6-di-t
tert-butyl-4-methylphenol, D is 2,4-
Dimethyl-6-tert-butylphenol, E is A
(50 mass%) + C (50 mass%)

[0039]

[Table 8]

Example 6 In Example 3, an antioxidant for gasoline was added to the treatment liquid, and a corrosion resistance test C in the processed part in Example 5 and a press workability test B in Example 3 were performed. Table 9 shows the coating composition and the coating thickness of the rust-proof steel sheet, and Table 10 shows the performance test results.

[0041]

[Table 9] (Note 1) The method of calculating the amount of silica sol and the amount of chromate added is the case of Table 2 in Example 2, and the method of calculating the amount of polyethylene resin powder is the case of Table 4 of Example 3; The method of calculating the agent is the same as in Table 7 of Example 5. (Note 2) The antioxidants A, B, C, D and E are the same as in Table 7 of Example 5.

[0042]

[Table 10] (Note) No. 41 of the comparative example could not be processed at a draw ratio of 2.3, so that the corrosion resistance test of the processed portion was not performed.

[0043]

As described above, in a rust-preventive steel sheet in which an organic resin film is formed on an Al-based plated steel sheet, the organic resin film is formed into a urethane resin film, and silica sol and chromate are added to the urethane resin film. Excellent workability,
It also has excellent corrosion resistance to deteriorated gasoline and fuels containing alcohol. In particular, when the coating is made of an alicyclic urethane resin, the gasoline resistance is improved and becomes equivalent to the epoxy resin coating. Further, when a polymer solid lubricant is added to the urethane resin film, a decrease in press workability can be prevented even if the amount of silica sol added is increased to improve corrosion resistance. Further, when an antioxidant for gasoline is added, the corrosion resistance to water-containing gasoline can be improved.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] February 18, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

[0023]

Example 1 A treatment solution was prepared by adding silica sol and chromate to each resin dispersion of an aqueous urethane resin, an acrylic resin, an ionomer resin, and an epoxy resin. Addition of cold-rolled steel sheet to Al-9% Si alloy coated steel sheet (sheet thickness 0.8 mm, coating weight 60 g / m ² ) by bar coating method so that the dry coating thickness becomes 1.0 μm. And heated at 200 ° C. for 1 minute to cure the coating, thereby producing a rust-proof steel plate. The silica sol of the treatment liquid was silica sol amount / (resin dispersion nonvolatile content + silica sol content) = 0.2, and chromate was chromate content / (resin dispersion nonvolatile content + silica sol content) = 0.01. Chromate was not added to the treatment solution using the epoxy resin.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuji Tomizuka 5 Ishizu Nishimachi, Sakai-shi, Osaka Nisshin Steel Co., Ltd.

Claims (8)

[Claims] 1. An anti-rust steel sheet having an organic resin film formed on an Al-based plated steel sheet, the organic resin film is treated with a water-based urethane resin dispersion containing silica sol and chromate. (Aqueous urethane resin nonvolatile content + silica sol content) = 0.10 to 0.1.
40, the chromate amount is set to the amount of chromate / (amount of aqueous urethane resin nonvolatile content + amount of silica sol) = 0.001 to 0.10, and at least one side of the Al-based plated steel sheet has a dry coating thickness of 0.5 to 2 A rust-preventive steel plate for a fuel tank, which is formed to have a thickness of 0.0 μm. 2. An antioxidant for gasoline is further added to the treatment liquid according to claim 1 to reduce the amount of the antioxidant by the amount of the antioxidant /
(Aqueous urethane resin nonvolatile content + silica sol content) = 5 x
A rust-preventive steel plate for a fuel tank, wherein the steel plate has a thickness of 10 ^{-2 to} 5 × 10 ^-5 . 3. The rustproof steel sheet for a fuel tank according to claim 1, wherein the aqueous urethane resin is an alicyclic resin. 4. The rustproof steel plate for a fuel tank according to claim 2, wherein the gasoline antioxidant is an amine-based or phenol-based antioxidant. 5. A rust-preventive steel sheet in which an organic resin film is formed on an Al-based plated steel sheet, the organic resin film is treated with a treatment liquid obtained by adding a silica sol, a chromate and a polymer solid lubricant to an aqueous urethane resin dispersion. The silica sol is silica sol amount / (aqueous urethane resin nonvolatile content + silica sol amount) = 0.10 to 0.40, and the chromate is chromate content / (aqueous urethane resin nonvolatile content + silica sol amount) =
0.001 to 0.10, wherein the solid polymer lubricant is the amount of the solid polymer lubricant / (the amount of the aqueous urethane resin nonvolatile content + the amount of the silica sol) = 0.01 to 0.10, and at least one surface of the Al-based plated steel sheet A rust-preventive steel sheet for a fuel tank, wherein the rust-proof steel sheet is formed to have a dry coating thickness of 0.5 to 2.0 μm. 6. An antioxidant for gasoline is further added to the treatment liquid of claim 5, and the amount of the antioxidant is
(Aqueous urethane resin nonvolatile content + silica sol content) = 5 x
A rust-preventive steel plate for a fuel tank, characterized in that the thickness is 10 ^{-2 to} 5 × 10 ^-5 . 7. The rustproof steel sheet for a fuel tank according to claim 5, wherein the aqueous urethane resin is an alicyclic resin. 8. The rustproof steel sheet for a fuel tank according to claim 6, wherein the gasoline antioxidant is an amine-based or phenol-based antioxidant.