JPH11129387A - High corrosion resistant steel plate for fuel tank - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide excellent corrosion resistance (inside corrosion resistance) to alcohol itself or gasoline mixed with alcohol and formic acid, and to corrosion resistance (outside corrosion resistance) to the atmospheric environment in which snow-melting salt or sea salt particles fly. Provide a steel plate for fuel tanks that has excellent press workability and resistance weldability. SOLUTION: Zn or Z is formed as a lowermost layer on both surfaces of a steel sheet.
n has a metal plating layer as a main component, has a chromate layer on both upper layers, and further has an amine-modified epoxy resin, a flaky Al powder, and a granular Ni on an upper layer on one surface thereof.
Powder as a main component, and flaky Al powder, granular Ni
At least one of the powders has a metal powder-containing organic resin layer surface-treated with an aminosilane coupling agent and / or an epoxysilane coupling agent, and a hydroxyl group, an isocyanate group, a carboxyl group, a glycidyl group and At least one resin having at least one functional group selected from amino groups, a lubricant,
A highly corrosion-resistant steel plate for a fuel tank, comprising a lubricating organic resin layer containing silica as a main component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel plate for a fuel tank, and more particularly to a steel plate having excellent corrosion resistance to alcohol itself or gasoline in which alcohol and formic acid are mixed (hereinafter referred to as "inner corrosion resistance"). The present invention relates to a steel plate for a fuel tank having excellent corrosion resistance to the air environment in which sea salt particles fly (hereinafter referred to as “outside corrosion resistance”), and having excellent press workability and resistance weldability.

[0002]

2. Description of the Related Art Conventionally, gasoline has been mainly used as a fuel for automobiles. However, in recent years, studies have been made on alcohol or a mixture of alcohol and gasoline from the viewpoints of air environment protection and price. I have.

Therefore, the corrosion resistance (internal corrosion resistance) to alcohol alone or to gasoline mixed with alcohol, particularly gasoline mixed with highly corrosive alcohol and formic acid.
Proposals to achieve both corrosion resistance to the outside environment (external corrosion resistance) are disclosed in Japanese Patent Publication No. 2-19881 and Japanese Patent Publication No. 2-1.
No. 8982 and Japanese Patent Publication No. 3-25349.

That is, Japanese Patent Publication No. Hei 2-18981 discloses that
A steel plate having a metal plating layer containing a Pb / Sn alloy or Sn as a main component and an organic resin film containing a metal powder as an upper layer is disclosed in JP-B-2-18982 and JP-B-3-25349.
No., Zn or a metal plating layer containing Zn as a main component,
A steel sheet having an organic resin film containing a metal powder as an upper layer is described.

[0005]

The metal powder-containing organic resin films described in the above three publications have a phenoxy resin that accounts for 40 to 90% of the organic resin.
Although the phenoxy resin itself is excellent in acid resistance and solvent resistance, it has a low affinity for metal powder, so that the metal powder is peeled off during press working, and the inner surface corrosion resistance of the damaged portion deteriorates. Also, the parts that are not damaged,
The fuel easily stays between the resin and the metal powder, and the inner surface corrosion resistance deteriorates. Corrosion resistance is also deteriorated on the outer surface side of the fuel tank due to insufficient affinity between the phenoxy resin and the metal powder.

Further, in any of the steel sheets, since the resin film contains a hardening agent as an essential component, when the degree of hardening is high, it is difficult to thermally decompose, it is difficult to remove the film during the nugget formation process, and the resistance weldability is reduced. I do. In other words, even if the energization point is secured by the metal powder, the base material around the remaining film causes poor welding, so that sufficient wrap between nuggets cannot be obtained and fuel leakage occurs. In some cases, sufficient welding strength cannot be obtained and peeling occurs. In addition, when the curing degree is low and an unreacted curing agent is contained, corrosion factors (acids, chloride ions, etc.) are likely to enter due to the low cohesive strength and hydrophilicity of the portion, and the corrosion resistance is reduced.

As described above, various types of performance defects remain, and have not yet been put to practical use. Thus, the present invention overcomes these shortcomings of current fuel tank materials,
In particular, it has excellent internal corrosion resistance against gasoline mixed with methanol itself or formic acid generated by the oxidation of methanol, and has excellent external corrosion resistance against the atmospheric environment in which snow-melting salt or sea salt particles fly, and excellent press working in the fuel tank manufacturing process. An object of the present invention is to provide a steel plate for a fuel tank exhibiting resistance and resistance weldability.

[0008]

Means for Solving the Problems The present inventors mainly have an affinity between an organic resin and a metal powder, an acid resistance of the organic resin itself,
As a result of intensive studies on resistance weldability and lubricity,
One surface has a resin layer mainly composed of flaky Al powder and granular Ni powder and a surface of an amine-modified epoxy resin treated with a specific silane coupling agent, and the other surface has a hydroxyl group, an isocyanate group, and a carboxyl group. The above problem can be solved at once by using at least one resin having at least one kind of functional group selected from a group, a glycidyl group and an amino group, and a resin layer mainly composed of silica and a lubricant. Thus, the present invention has been completed based on a completely new finding.

That is, the present invention provides a steel plate having Zn or a metal plating layer containing Zn as a main component as a lowermost layer on both surfaces of the steel sheet, a chromate layer on both upper layers, and an upper layer on one of the surfaces. And an amine-modified epoxy resin, flaky Al powder, and granular Ni powder as main components, and at least one of the flaky Al powder and the granular Ni powder is surface-coated with an aminosilane coupling agent and / or an epoxysilane coupling agent. At least one having a treated metal powder-containing organic resin layer and having at least one functional group selected from a hydroxyl group, an isocyanate group, a carboxyl group, a glycidyl group and an amino group as an upper layer on the other surface.
An object of the present invention is to provide a highly corrosion-resistant steel plate for a fuel tank, which has a lubricating organic resin layer mainly composed of a kind of resin, a lubricant and silica.

[0010] The metal powder-containing organic resin layer is coated with scaly A based on 100 parts by weight of the amine-modified epoxy resin.
1 powder and granular Ni powder are 20 to 400 parts by weight, and flaky Al powder / granular Ni powder = 5/95 to 80 /
It is preferably 20 (weight ratio). In addition, the amine-modified epoxy resin is 0.3 equivalent to 1 equivalent of epoxy group.
A composite resin obtained by adding an amine compound having a weight average molecular weight of 5,000 to 50,000 and an average major axis of 8 to 25 μm.
m, average minor axis is 1 to 10 μm, and average thickness is 1.0 to 5.
0 μm, and the granular Ni powder has an average particle size of 1 to 9 μm.
It is preferred that In addition, the lubricating organic resin layer has at least one functional group selected from a hydroxyl group, an isocyanate group, a carboxyl group, a glycidyl group, and an amino group, based on 100 parts by weight of at least one resin.
It is preferred that the lubricant be 1 to 40 parts by weight and the silica be 5 to 80 parts by weight.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below.
The steel sheet of the present invention is formed of a coating layer composed of three layers on both sides. Lowermost layer (first layer) and upper layer (second layer) of steel sheet
Is the same on both sides, and the third coating layer on the surface of the steel plate is different between one surface used on the inner surface side of the fuel tank and the other surface used on the outer surface side.

(Metal Plating Layer) The steel sheet for a highly corrosion resistant fuel tank of the present invention has a metal plating layer containing Zn or Zn as a main component as the lowermost layer (first layer) on the surface of the steel sheet. Since the metal plating layer is a metal layer showing a lower potential than the iron base material in alcohol and alcohol mixed fuel, red rust and perforation are suppressed by the sacrificial corrosion prevention effect of Zn even in the pressed part where the plating layer is damaged. And has the effect of improving corrosion resistance.

In particular, Zn-Ni alloy plating, Zn-Co
Alloy plating, Zn-Fe alloy plating, Zn-Al alloy plating, Zn-Ni-Cr alloy plating, Zn-Ni-Co
The metal plating layer mainly composed of Zn, such as alloy plating,
Since the corrosion resistance of the plating layer itself is high while maintaining the sacrificial anticorrosion performance, it is possible to further improve the perforation resistance. These plating layers are formed by a known electroplating method or hot-dip plating method.

The basis weight of Zn or a metal plating layer containing Zn as a main component is preferably from 10 to ²⁰⁰ g / m ² . More preferably, it is 20 to 100 g / m ² . When the basis weight of plating is less than 10 g / m ² , the effect of hiding the steel sheet surface becomes insufficient, and the corrosion resistance required for the lower layer becomes insufficient.
If it exceeds 200 g / m ² , the corrosion resistance required for the lower layer is saturated. The basis weight of the plating layer may be the same on the side used for the inner surface and the side used for the outer surface of the fuel tank, but the plating thickness on the outer surface may be larger than that on the inner surface for the purpose of improving the outer corrosion resistance.

(Chromate layer) Next, a chromate layer is formed on both front and back surfaces as a second layer (upper layer of metal plating). The chromate layer is formed to improve the adhesion between Zn or a metal plating layer containing Zn as a main component and the uppermost resin layer. The chromate layer is a coating composed of trivalent chromium and hexavalent chromium containing chromium hydrated oxide as a main component.

The amount of the chromate layer deposited is preferably 5 to 200 mg / m ² per one surface in terms of chromium metal. More preferably, it is 10 to 100 mg / m ² . 5 mg / m ²
If it is less than 30, the adhesion to the upper organic film is insufficient, so that the film on the sliding portion is peeled off during press working, and in some cases, the plating layer is peeled off. Further, since the amount of adhesion is small, the hexavalent chromium component to be used for self-healing is insufficient, and the corrosion resistance of the processed portion on the inner and outer surfaces is insufficient due to the peeling of the plating layer. If it exceeds 200 mg / m ² ,
The chromate layer itself becomes very brittle, the chromate layer peels off at the processed part, and the accompanying organic film peels off. For this reason, the corrosion resistance of the processed portions on the inner and outer surfaces is insufficient. The attachment amount of the chromate layer may be the same or different between the side used for the inner surface and the side used for the outer surface of the fuel tank.

As an uppermost layer (third layer), one surface is coated with a metal powder surface-treated with a specific silane coupling agent, and a metal powder-containing organic resin layer mainly containing an amine-modified epoxy, and Is covered with a lubricating organic resin layer composed of a resin, silica and a lubricant. The metal powder-containing organic resin layer is excellent in corrosion resistance, weldability, etc., and is preferably used as the inner surface side of the fuel tank (that is, the side in contact with gasoline). The lubricating organic resin layer has excellent corrosion resistance and lubricity. Is preferably used as the outer surface side.

(Metal Powder-Containing Organic Resin Layer) The metal powder-containing organic resin layer is composed of a metal powder and a resin component having excellent corrosion resistance to alcohol, particularly methanol itself, or gasoline mixed with formic acid generated by oxidization of methanol. And serves as an anticorrosion layer for preventing direct contact between the metal plating layer and the chromate layer and the alcohol-based fuel.

(Amine-Modified Epoxy Resin) Needless to say, the resin component used in the present invention has excellent corrosion resistance to gasoline and alcohol-based fuels, and has excellent coating film adhesion to a chromate layer and press workability. It exhibits excellent characteristics. That is, by using the amine-modified epoxy resin, excellent press workability, corrosion resistance to alcohol-based fuel, and coating film adhesion to the chromate layer are ensured.

The amine-modified epoxy resin is obtained by modifying an epoxy resin with an amine compound, and is preferably a resin obtained by modifying the terminal of an epoxy resin with an amine compound.
More preferably, both terminals are modified with an amine compound. Here, examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, cycloaliphatic epoxy resin, hydantoin type epoxy resin, novolak type epoxy resin, and glycidyl ester type epoxy resin. The epoxy equivalent of these epoxy resins is preferably from 180 to 5,000. Specific examples are Epicoat 1010, 1009, 1007, 100
4, 1001 (both manufactured by Yuka Shell Epoxy Co., Ltd.)
And the like. These may be used alone or in combination of two or more. Further, a reaction product obtained by reacting a bisphenol type epoxy resin such as a bisphenol A type epoxy resin or a bisphenol F type epoxy resin with bisphenol A or bisphenol F may be used. Among these, bisphenol A type epoxy resin, bisphenol F type epoxy resin and bisphenol type epoxy resin and bisphenol A or bisphenol A from the wide range of manufacturing conditions for stably obtaining paint stability, press workability, and inner surface corrosion resistance What reacted with bisphenol F is preferable.

The amine compound is n-propylamine, i
so-propylamine, n-butylamine, sec-butylamine, tert-butylamine, diethylamine, ethylenediamine, diethylenetriamine, triethylenediamine, tetraethylenediamine, propylenediamine, N-methylpiperazine, ethanolamine,
Diethanolamine, N-methylethanolamine, i
Examples thereof include so-propanolamine, diisopropanolamine, n-propanolamine, ethylethanolamine, and 3-methanolpiperidine. Of these, alkanolamine and dialkanolamine are particularly preferred.

The number of moles of the amine compound added to one equivalent of the epoxy group of the epoxy resin is preferably from 0.3 to 1.0 mol, more preferably from 0.5 to 0.8 mol. When the number of moles of the amine compound is less than 0.3, the degree of amine modification is insufficient, so that the affinity between the metal powder and the epoxy resin is reduced, and the metal powder is detached from the film during press working. If the degree is severe, peeling of the plating layer occurs, resulting in poor press workability. For the same reason, the corrosive liquid easily stays between the resin and the metal powder in the film, and the sufficient hydrophobicity cannot be obtained, and the formic acid aqueous solution is easily attracted into the film. Insufficient internal corrosion resistance to system fuel. If the number of moles of the amine compound exceeds 1.0 mole, the excess is not economical because it is not added to the epoxy group, and the excess amine increases water absorption and lowers inner corrosion resistance.

The weight average molecular weight of the amine-modified epoxy resin is preferably from 5,000 to 50,000, more preferably from 10,000 to 40,000. When the molecular weight is less than 5,000, the molecular weight of the resin is too low, so that the intermolecular distance is insufficient and the toughness of the film is reduced. For this reason, the film is shaved during the press working, and the press workability is reduced. Molecular weight 5
If it is more than 0000, the amount of amine added to the epoxy group is small, so that the affinity between the resin and the metal powder is insufficient, the metal powder is detached from the film at the time of press working, and the inner surface has corrosion resistance. Run out.

(Metal Powder) The purpose of adding metal powder is to improve resistance weldability and corrosion resistance. That is, the organic resin film generally has high electrical insulation properties, and the thickness of the resin film is about 0.5 to 9 μm. Therefore, it is impossible to expect the projection of the steel sheet to be exposed, and it is difficult to perform resistance welding. Therefore, the present invention disperses a required amount of metal powder in the organic resin film on the inner surface side of the gasoline tank, and enhances the conductivity of the film.

A metal powder having a higher specific resistance generates a larger amount of heat and is useful for resistance welding. Ni is most useful because of its excellent corrosion resistance and high specific resistance to methanol. Al has a lower specific resistance and a lower melting point than Ni, and is not necessarily optimal for welding. However, a scaly shape is useful for suppressing permeation of a formic acid aqueous solution in an organic film. The above-mentioned object is achieved by combining scaly Al and granular Ni and adding them in an appropriate ratio to the organic resin film.

The dimensions of the flaky Al powder are as follows:
25 μm, average minor axis is 1 to 10 μm, average thickness is 1.0
５5.0 μm. More preferably, the average major axis is 10
２０20 μm, average minor axis is 5-8 μm, average thickness is 2-4
μm. When at least one of the average major axis and the average minor axis is smaller than the above range, the shielding property against gasoline, alcohol, formic acid, etc. is reduced, and the inner surface corrosion resistance is reduced. On the other hand, when at least one of the average major axis and the average minor axis is larger than the above range, the strength of the coating decreases, powdering occurs, and the inner surface corrosion resistance of the pressed portion decreases. The average thickness is 1
When the thickness is less than μm, the inner surface corrosion resistance decreases, and when the thickness exceeds 5 μm, the proportion of Al powder exposed on the surface of the coating film increases, so that the moldability decreases.

The size of the granular Ni powder is 1 to 9 μm in average particle size.
Are preferred. More preferably, it is 2 to 7 μm. If the average particle size is less than 1 μm, the number of current-carrying points is insufficient. When the average particle size is more than 9 μm, the current-carrying point is sufficient, so that the addition of a small amount improves the resistance weldability. However, since the coating is porous, the corrosion resistance on the inner surface is deteriorated, and powdering of the coating at the time of press working also poses a problem.

The total amount of the flaky Al powder and the granular Ni powder is 20 to 400 parts by weight, preferably 30 to 100 parts by weight, based on 100 parts by weight of the amine-modified epoxy resin. If the amount is less than 20 parts by weight, the current-carrying point is insufficient and the conductivity is poor, so that the resistance weldability is reduced. If the amount exceeds 400 parts by weight, the organic film itself becomes brittle, powdering resistance during pressing decreases, and inner surface corrosion resistance decreases.

The ratio between the scale-like Al powder and the granular Ni powder is as follows:
Scale-like Al powder / granular Ni powder = 5 / 95-80 / 20
(Weight ratio) is preferred. More preferably, 10/90 to 5
0/50. Scale-like Al powder / granular Ni powder ratio is 5
If the ratio is less than / 95, the amount of flaky Al having a function of suppressing fuel penetration is reduced, so that the internal corrosion resistance is reduced. 80 /
If it exceeds 20, the amount of granular Ni having a high specific resistance is insufficient, and the resistance weldability is poor.

In the present invention, scaly Al powder and granular N
i powder at least one, more preferably both,
It is necessary to perform a surface treatment with an aminosilane coupling agent and / or an epoxysilane coupling agent.
When surface treatment is performed with these silane coupling agents, affinity and reactivity with the amine-modified epoxy resin are increased, and the bond between the two is strengthened. Therefore, penetration of alcohol, formic acid, and the like is prevented, and corrosion resistance is improved. Further, the powdering property at the time of press working is also improved.

As the aminosilane coupling agent, N
-Β (aminoethyl) -γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N
-Phenyl-γ-aminopropyltrimethoxysilane and the like are preferred. As the epoxysilane coupling agent, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, and the like are preferable.

The surface treatment of the silane coupling agent can be performed by a known method. Further, as other additives, additives such as a pigment, a thixotropic agent, a dispersant, a thixotropic agent, a precipitation inhibitor, a lubricant and the like can be added to the film.

The average thickness of the metal powder-containing lubricating resin is preferably 0.5 to 9 μm after drying. If it is less than 0.5 μm, the internal corrosion resistance is insufficient. If it exceeds 9 μm, the corrosion resistance is saturated, and the press workability and the resistance weldability are reduced.

An example of a method for forming this film will be described. The amine-modified epoxy resin is prepared by dissolving the epoxy resin in various organic solvents (such as hydrocarbons, esters, ketones, alcohols, and ethers), and then adding an amine compound.
It is obtained by reacting at room temperature to 100 ° C for 4 to 5 hours. Next, a metal powder and other additives are added to the resulting amine-modified epoxy resin solution, and these are dispersed with a sand mill, an attritor, or the like, to prepare a metal powder-containing lubricating organic resin paint. The paint is applied by a known method such as a roll coater or a bar coater, and dried at 150 to 300 ° C.

(Lubricating Organic Resin Layer) Next, the lubricating organic resin layer will be described. (Organic resin) The lubricating organic resin layer is a lubricating resin layer in which silica is composited. The organic resin used here may be at least one resin having at least one functional group selected from a hydroxyl group, an isocyanate group, a carboxyl group, a glycidyl group and an amino group. Specifically, epoxy resin, alkyd resin, acrylic resin, urethane resin, polyvinyl butyral resin, phenol resin, melamine resin and the like can be used. Among them, polyvinyl butyral resin is preferable from the viewpoint of corrosion resistance and the like.

(Lubricant) A lubricant is added to impart self-lubricating property to the organic resin film on the outer surface. In the present invention,
By projecting the lubricant onto the surface of the organic film, friction between the steel plate and the mold during press working is reduced, and damage to the resin film is prevented. As such a lubricant, polyethylene-based,
Polyolefin waxes such as polypropylene and polybutene and polytetrafluoroethylene are preferred. These may be used alone or as a mixture of two or more. These are preferred because they have excellent lubricity and excellent chemical resistance such as lubricating oil. The average particle size of the lubricant is preferably from 1 to 7 μm, more preferably from 2 to 6 μm
It is. When the average particle size is less than 1 μm, the amount of the lubricant projecting from the organic film is small, and the press workability is reduced. 7
When it exceeds μm, it is easy to detach from the film during press working.

The softening point of the lubricant is preferably from 70 to 150 ° C. Those having different softening points may be mixed. When the softening point is less than 70 ° C., under severe pressing conditions involving heat generation, the elastic modulus of the lubricant is significantly reduced, and press workability is poor. When the softening point is higher than 150 ° C., the softening of the lubricant is insufficient, and the press workability is poor. The amount of lubricant added is
100 parts by weight of at least one resin having at least one kind of functional group selected from isocyanate group, carboxyl group, glycidyl group and amino group is 1 to 4 parts by weight.
0 parts by weight, more preferably 5 to 20 parts by weight. If the amount is less than 1 part by weight, the lubricity is insufficient, and the film is damaged at the time of press working, so that the corrosion resistance is reduced. If the amount exceeds 40 parts by weight, desorption of the lubricant is likely to occur during press working, and the corrosion resistance deteriorates.

(Silica) The addition of silica causes the silanol groups on the silica surface to react with the chromate layer and other components in the organic coating, thereby improving the adhesion of the coating and improving the corrosion resistance. Silica is colloidal silica (for example,
Snowtex-O and Snowtex-N manufactured by Nissan Chemical Co., Ltd., and organosilica sol (for example, Nissan Chemical Co., Ltd.)
Ethyl cellosolve silica sol), silica powder (for example, a gas-phase silica powder manufactured by Aerosil Co., Ltd.) or an organic silicate (for example,
Ethyl silicate or the like is used in combination with an acid catalyst). The particle size of the silica powder is preferably from 5 to 70 nm in order to uniformly disperse the silica.

The amount of silica added is 5 to 80 parts by weight based on 100 parts by weight of at least one resin having at least one functional group selected from a hydroxyl group, an isocyanate group, a carboxyl group, a glycidyl group and an amino group. Parts by weight, more preferably 20 to 60 parts by weight. 5
If the amount is less than 10 parts by weight, the corrosion resistance is not improved. In addition, since silica has poor thermal decomposability, resistance weldability decreases.

The glass transition temperature (Tg) of the above lubricating organic resin is preferably from 0 to 90 ° C., more preferably from 0 to 85 ° C. Outside this range, the press workability is poor, and the corrosion resistance of the pressed portion is also poor. Organic coatings that require press workability are generally required to have a high Tg (for example, 90 ° C. or higher), but the coating of the present invention has a structure in which a lubricant is projected from the coating. There is no need to increase the Tg of the coating so much. Further, as other additives, additives such as a pigment, a thixotropic agent, a dispersant, a thixotropic agent and a precipitation inhibitor can be added to the film. The average thickness of the lubricating organic resin film after drying is preferably 0.5 μm to 1.5 μm. If the film thickness is less than 0.5 μm, the irregularities on the surface of the steel sheet cannot be filled, and the corrosion resistance decreases. If it exceeds 1.5 μm, the corrosion resistance is improved, but the resistance weldability is significantly reduced. Further, the wettability of the metal brazing is remarkably poor, and the brazing property is also remarkably reduced.

When the steel sheet for a high corrosion resistant fuel tank of the present invention is pressed, there is no problem at all even if lubricating oil is applied according to the difficulty of pressing without applying lubricating oil. From the viewpoint of prevention, application of lubricating oil is effective. An example of a method for forming this film will be described. After dissolving the organic resin in the organic solvent, silica is added and the mixture is heated at 50 to 150 ° C. for 30 minutes.
Allow to react for minutes to 6 hours. A lubricant and other additives are added to this solution to obtain a paint. The paint is applied by a known method such as a roll coater or a bar coater, and dried at 150 to 300 ° C.

(Embodiment) The embodiment will be specifically described below. After electrolytic degreasing and electrolytic pickling of a cold-rolled steel plate (SPCC) having a thickness of 0.8 mm, both surfaces were subjected to galvannealing (10% by weight of Fe in the plating) (the adhesion amount was 45 g / m ^{2 on} both surfaces). ). A chromate treatment solution was applied to both sides of the plated steel sheet and dried to obtain a chromate layer (the amount of adhesion was 40 mg / m ^{2 on} both sides in terms of metallic chromium). The coating was roll-coated on both sides and baked. As a comparative material, a resin paint described in JP-B-3-25349 was also applied and baked. The method for preparing the paint and the method for evaluating the film properties are shown below. Tables 1 and 2 show the composition of the resin layer and the evaluation results.

(Method for Preparing Various Coatings) (1) Method for Preparing Amine-Modified Epoxy Resin Solution (1) and Metallic Powder-Containing Resin Coating To 1,000 g of bisphenol A type epoxy resin (epoxy equivalent = 2000), add 1000 g of toluene, and replace with nitrogen. After that, the temperature was raised to 80 ° C. to obtain a uniform solution. Next, 52.5 g of diethanolamine was added dropwise to this solution over 30 minutes, and the mixture was reacted for 1 hour to obtain an amine-modified epoxy solution (1).
I got (Weight average molecular weight of amine-modified epoxy resin 1
3000, amine addition amount 0.5 mol) The metal powder, organic bentonite (benton 34, precipitation inhibitor), and cyclohexane (for dilution adjustment) shown in Table 1 described later are added to the amine-modified epoxy resin solution thus obtained. In addition, a metal powder-containing resin paint was prepared.

(2) Amine-modified epoxy resin solution (2)
And Method for Preparing Metal Powder-Containing Resin Paint To 680 g of propylene glycol monomethyl ether acetate was added and dissolved in 1000 g of a bisphenol A type epoxy resin (epoxy equivalent = 3000). Next, 25 g of bisphenol F and 1 g of lithium chloride were added, and
The mixture was reacted at 0 ° C. for 1 hour to obtain a homogeneous solution. This solution 1167
7.5 g of N-methylethanolamine was added dropwise to the resulting mixture over 2 hours, and the mixture was further reacted at 70 ° C. for 3 hours to obtain an amine-modified epoxy resin solution (2). (Weight average molecular weight of the amine-modified epoxy resin: 20,000, amine addition: 0.6
Mol) The metal powder, organic bentonite (benton 34, sedimentation inhibitor) and cyclohexane (for dilution adjustment) shown in Table 1 described below were added to the amine-modified epoxy resin solution thus obtained, and a metal powder lubricating resin paint was added. Was prepared.

(3) Preparation of Lubricant Organic Resin Coating (1) Various silicas shown in Table 1 are added dropwise to 200 g of a 30% solids cellosolve solution of polyvinyl butyral resin (average degree of polymerization = 300). Then, 30 g of an orthophosphoric acid aqueous solution was gradually added dropwise, and then the mixture was heated to 90 ° C.
The reaction was performed under reflux for 4 hours. Next, various lubricants shown in Table 1 were added to prepare a lubricating organic resin paint (1).

(4) Preparation of paint of comparative example In the same manner as in the above (1) to (3), but using a resin of the type shown in Table 1 in an amount shown in Table 1. The following paint was used for Comparative Example 8.

(Comparative Example 8) As the outermost organic resin film, those having the following composition were used for the inner surface (12 μm) and the outer surface (12 μm).
μm). The organic resin film is composed of 45% by weight of Al powder (flake, 3 μm in thickness), a rubber-modified epoxy resin and a phenoxy resin (30% by weight, 7% by weight, respectively).
0% by weight) and 1% by weight of a nonionic fluorinated surfactant. Here, the rubber-modified epoxy resin is a butadiene acrylonitrile copolymer rubber 2
It is a mixture of 5% by weight and 75% by weight of a novolak type epoxy resin.

(Evaluation Method of Film Properties) The press-workability, resistance weldability, outer surface corrosion resistance, and inner surface corrosion resistance of the prototype coated steel sheet were evaluated.

(1) Evaluation of press workability (a) Evaluation of lubricity by cylindrical molding test Press conditions: 1 g / m ^{2 of} rust preventive oil Z5 manufactured by Idemitsu Oil Co., Ltd.
・ Punch diameter and shape: 33mmφ flat bottom cylinder ・ Clearance: 1mm ・ Planck size: various changes ・ Wrinkle holding load: 2t ・ Drawing speed: 60mm / sec Under the above conditions, the outer surface of the steel sheet Is set on the die side, the inner side is set on the punch side, and the cylinder is formed. The limit drawing ratio of each sample (the maximum value of the die diameter / punch diameter of the sample that has been drawn out) is determined. Was evaluated. The larger the value, the better the press working. (B) Evaluation of powdering resistance of the film by a cylindrical molding test Press condition: 1 g / m ^{2 of} rust preventive oil Z5 manufactured by Idemitsu Oil Co., Ltd.
Lubricate and evaluate ・ Punch diameter and shape: 33mmφ flat bottom cylinder ・ Clearance: 1mm ・ Planck size: 66mm ・ Wrinkle holding load: 2t ・ Drawing speed: 60mm / sec The outer surface of the steel sheet is placed on the die side. The inner surface side was set on the punch side, and the degree of powdering of the film on the inner surface side after cup molding was visually observed and evaluated. The evaluation criteria are: ◎ level without powdering in the peeling test with cellophane tape, there is a little powdering in peeling with cellophane tape,
The level not visually observable was rated as ○, the level with slight powdering was rated as Δ, and the case where the amount of powdering was extremely large was rated as ×.

(2) Resistance Weldability Evaluation Method Seam Welding Conditions Electrode: Chromium-copper alloy, trapezoidal electrode (tip R: 15 m)
mφ) ・ Welding method ・ ・ ・ Double cap, lap seam welding ・ Pressure force ・ ・ ・ ・ ・ ・ 400kg ・ Electrification time ・ ・ ・ ・ ・ ・ 2 cycles on, 1 cycle off (2
・ Cooling: Internal / external water cooling ・ Welding speed: 2.5 m / min ・ Welding current: Various changes Weld the inner surfaces under the above conditions and T peel. An appropriate range of welding current (kA) was determined from the presence or absence of base material breakage in the tensile test and the degree of nugget wrap, and seam weldability was evaluated.

(3) Evaluation method of outer surface corrosion resistance A top coat Emaron manufactured by Dainippon Paint Co., Ltd. was applied to the outer surface so as to have a dry film thickness of 10 μm, and the coating was applied in an oven at 120 ° C. for 20 minutes.
After baking for minutes, JASO (salt spray 2 hours, 60 hours)
℃, 20-30RH% drying 4 hours ・ 50 ℃, 98RH%
2 hours) 300 cycles for the flat part and 1 for the others
It was subjected to a CCT test of 00 cycles, and evaluated by the residual plate amount (mm) of the flat portion, the cross cut portion of the flat portion, and the side wall portion of the pressed product formed under the conditions (1) and (b). The thickness before the test was 1.0 mm.

(4) Evaluation Method for Inner Surface Corrosion Resistance The flat surface and the inner surface of a flat-bottomed cylindrical cup formed under the conditions of 1 (b) were evaluated. 20 mm x 1 when evaluating a flat part
Prepare a test piece of 00mm and use unleaded gasoline / 500pp
The test piece was immersed in a fuel of an aqueous solution of formic acid = 1/1 (weight) by 80 mm and subjected to a one month immersion test at room temperature.
The degree of rusting was evaluated in terms of area ratio (%). When evaluating the inner surface of the flat-bottomed cylindrical cup, it was molded into a test piece having a diameter of 33 mm and a height of 30 mm. The above-mentioned fuel was charged at 80% of the inner volume of the cup, immersed for one month at room temperature, and then the inner surface of the cup was released. The degree of rust was evaluated in terms of area ratio (%). Since the fuel is separated from the formic acid aqueous solution in the lower layer and the unleaded gasoline in the upper layer from the order of the specific gravity, the rust generation area ratio at each site was evaluated.

[0053]

[Table 1]

[0054]

[Table 2]

Table 1-1 Note) A: Scale-like Al powder Average major axis 13 μm, average minor axis 5
μm, average thickness 2 μm A: scale-like Al powder average major axis 20 μm, average minor axis 7
F123: Granular Ni powder, average particle size 5 μm (Fukuda metal foil powder, Carbonyl Ni123) F287: Granular Ni powder, average particle size 2 μm (Fukuda metal foil powder, Carbonyl Ni287) a: γ-glycidoxypropyl Surface treatment with trimethoxysilane b: Surface treatment with N-β (aminoethyl) -γ-aminopropyltrimethoxysilane PE: Polyethylene wax Average particle size 5 μm, softening point 120 ° C. S: Colloidal silica S: Organosilica sol Average primary particle Diameter 10 nm PTFE: polytetrafluoroethylene wax Average particle size 2 μm, softening point 125 ° C. Epoxy: weight average molecular weight 13,000, epoxy equivalent 2
000, without amine compound modification

[0056]

[0057]

[0058]

The steel sheet of the present invention has a different organic coating composition on the front and back sides, and has one surface formed of an amine-modified epoxy resin, Ni powder of a specific shape treated with a silane coupling agent, and A
(1) a resin layer containing powder, on the other surface, at least one resin having at least one functional group selected from a hydroxyl group, an isocyanate group, a carboxyl group, a glycidyl group and an amino group, silica and a lubricant; By using a resin layer containing (A) as a main component, it has excellent inner surface corrosion resistance, outer surface corrosion resistance, press workability, and resistance weldability. Therefore, the steel sheet of the present invention is particularly useful as a steel sheet for alcohol and alcohol-mixed gasoline tanks.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a steel plate for a highly corrosion-resistant fuel tank according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Metal plating layer 3 Chromate layer 4 Metal powder containing organic resin layer 5 Lubricity organic resin layer

Continuation of the front page (51) Int.Cl. ⁶ Identification code FI B05D 7/24 302 B05D 7/24 302U 303 303C B60K 15/03 B60K 15/02 Z (72) Inventor Sachiko Suzuki Kawasaki, Chuo-ku, Chiba-shi, Chiba No. 1, Kawasaki Steel Engineering Co., Ltd. (72) Kazuo Mochizuki, Inventor Kazuo Mochizuki 1, Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture, Kawasaki Steel Co., Ltd. (72) Inventor, Hiroyuki Tanabe Nishinasuno, Nasu County, Tochigi 8-15 Asahi-cho, Tokyo (72) Inventor Osamu Ogawa 690-109 Kamiatsuzaki, Kuroiso City, Tochigi Prefecture

Claims (5)

[Claims] (1) Zn or Z as a lowermost layer on both surfaces of a steel sheet.
It has a metal plating layer containing n as a main component, has a chromate layer on both upper layers, and further has an amine-modified epoxy resin, flaky Al powder, and granular Ni powder on the upper layer on one side. Ingredients
And flaky Al powder and at least one of the granular Ni powder has a metal powder-containing organic resin layer surface-treated with an aminosilane coupling agent and / or an epoxysilane coupling agent, and a hydroxyl group on the other surface, Having at least one resin having at least one functional group selected from isocyanate groups, carboxyl groups, glycidyl groups and amino groups, a lubricant, and a lubricating organic resin layer containing silica as a main component; Highly corrosion-resistant steel plate for fuel tanks. 2. The metal powder-containing organic resin layer, wherein the total of flaky Al powder and granular Ni powder is 20 to 400 parts by weight based on 100 parts by weight of amine-modified epoxy resin, Ni powder = 5 / 95-80 / 20
The steel plate for a highly corrosion-resistant fuel tank according to claim 1, wherein the weight ratio is (weight ratio). 3. The amine-modified epoxy resin is a composite resin obtained by adding 0.3 to 1.0 mol of an amine compound to 1 equivalent of an epoxy group, and has a weight average molecular weight of 5,000 to 50,000. The scale-like Al powder has an average major axis of 8 to 25 μm, an average minor axis of 1 to 10 μm, an average thickness of 1.0 to 5.0 μm, and the granular Ni powder has an average particle diameter of 1 to 9 μm. The steel plate for a highly corrosion-resistant fuel tank according to claim 1 or 2, wherein: 4. The lubricating organic resin layer is lubricated with respect to 100 parts by weight of at least one resin having at least one functional group selected from a hydroxyl group, an isocyanate group, a carboxyl group, a glycidyl group and an amino group. Agents 1-4
The steel sheet for a highly corrosion-resistant fuel tank according to any one of claims 1 to 3, wherein 0 parts by weight and silica are 5 to 80 parts by weight. 5. The lubricant is a polyolefin wax and / or polytetrafluoroethylene, the lubricant has a softening point of 70 to 150 ° C. and an average particle size of 1 to 7 μm.
m, and the glass transition temperature (Tg) of the lubricating organic resin layer is from 0 to 9
The steel plate for a highly corrosion-resistant fuel tank according to any one of claims 1 to 4, wherein the temperature is 0 ° C.