JPH10137681A - Steel plate of superior molding properties for highly corrosion-resistant fuel tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel plate of superior corrosion resistance, press processing properties and seam welding properties for a highly corrosion- resistant fuel tank used as a tank material durable particularly for alcohol itself or gasoline mixed with alcohol and formic acid. SOLUTION: A steel plate for a fuel tank is provided with a metal plated layer composed of Zn or Zn as a main component as lowest layers on both surfaces of a steel plate, chromate films on both faces of an upper layer on the metal plated layers, a metal powder containing organic resin film composed of Al and Ni metal powder amine modified epoxy resin and a curing agent as main components formed on a layer on one of the chromate films and a silica containing organic resin film composed of at least one kind of resin having at least one kind of functional group selected from among hydroxyl, isocyanate, carboxyl, glycidyl and amino, and silica and polyolefin wax as main components formed on a layer on the other of the chromate films.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly corrosion-resistant steel plate for a fuel tank having excellent formability, and more particularly to a tank material capable of withstanding alcohol itself or gasoline in which alcohol and formic acid are mixed, and having excellent corrosion resistance and press workability. The present invention relates to a highly corrosion-resistant steel plate for a fuel tank having seam weldability.

[0002]

2. Description of the Related Art In North America, Central and South America, and Europe, many countries have adopted national policies to reduce the dependence on petroleum as an energy policy, and alcohol (methanol, ethanol) has been used as a new fuel for vehicles.
The introduction ratio of so-called gasohol, which is itself or a mixture of these with gasoline in an amount of 5 to 20%, is increasing year by year.

[0003] However, these alcohol fuels (a) are apt to contain water, (b) undergo layer separation due to an increase in the amount of water mixed in and decrease in temperature, and (c) oxidatively degrade alcohol to produce organic acids. (E.g., formic acid in the case of methanol and acetic acid in the case of ethanol), which gives rise to a separation layer mainly composed of alcohol and / or an organic acid and water in the lower layer.
The turn (Pb-Sn alloy) -plated steel sheet, which is the current mainstream tank material, has much higher corrosiveness to the above-mentioned alcohol and gasoline mixture than normal gasoline fuel, such as the plating layer dissolving. .

However, the fuel tank of an automobile is positioned as the most important part from the viewpoint of ensuring safety. The material is free from defects in seam welds, does not cause pitting due to corrosion on both the inside and outside surfaces of the tank, and In the fuel circulation system, it is required that no floating corrosion products that cause clogging of the filter be generated.

[0005]

By the way, the material of a fuel tank for an ordinary automobile at present is, for example, Japanese Patent Publication No. Sho 57-6l833.
JP-A-53-1998l discloses a Pb-Sn alloy hot-dip coated steel sheet and a Zn-plated steel sheet which has been subjected to a thick chromate treatment. Looking at the corrosion resistance of these materials to gasoline, alcohol, or alcohol-mixed gasoline (hereinafter referred to as inner corrosion resistance), the Pb-Sn alloy has a disadvantage that it is very easily dissolved in methanol. Practical use is considered difficult.

On the other hand, the inner corrosion resistance of a material obtained by subjecting an electro-zinc plated steel sheet to a thick chromate treatment suppresses the occurrence of slight red rust and perforation due to the sacrificial corrosion prevention effect of Zn. However, the elution rate of Zn is large, a large amount of floating white precipitate is generated, and clogging of the filter occurs in the fuel circulation system. After the elution of Zn, the base steel has a disadvantage that red rust and perforation are apt to occur, and it is insufficient as a steel plate for a fuel tank.

[0007] Instead of the above-mentioned electro-zinc plated steel sheet, Zn
Alloy-plated steel sheet whose main component is, for example, JP-A-55-ll
No. 079l, a Zn-Ni alloy-plated steel sheet disclosed in Japanese Patent Publication No. 57-33347, a Zn-Fe alloy-plated steel sheet described in Japanese Patent Publication No. 57-61831, No. 33222 discloses Zn-
Al alloy-plated steel sheet, Zn-Ni-Cr alloy-plated steel sheet disclosed in JP-A-57-70288, JP-B-57-33347
In the case of using a Zn—Co—Ni alloy-plated steel sheet disclosed in Japanese Patent Application Laid-Open No. H11-284, since the elution rate of each of the alloy plating layers is considerably suppressed as compared with the Zn plating layer, corrosion is suppressed on both the inner and outer surfaces. However, it still cannot solve the problem of filter clogging and hole corrosion due to perforated corrosion on the outer surface of the tank or floating white precipitate on the inner surface of the tank.

[0008] In order to solve the above-mentioned drawbacks, excellent internal corrosion resistance is exhibited with respect to alcohol alone or alcohol-mixed gasoline, particularly gasoline in which highly corrosive alcohol and formic acid are mixed, and the outer surface of the tank is exposed to the external environment. A steel plate for fuel tanks that exhibits excellent corrosion resistance (hereinafter referred to as “corrosion resistance to the external environment is referred to as external corrosion resistance”) and has excellent press workability and resistance weldability in the tank manufacturing process. No. 2-18
No. 982 and Japanese Patent Publication No. 3-25349. Japanese Patent Publication No. 2-18981 describes 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. Tokuhei 2-
No. 18982 and Japanese Patent Publication No. 3-25349 include Zn or Z
A steel plate having a metal plating layer containing n as a main component and an organic resin film containing a metal powder as an upper layer is described.

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. For this reason, when used as a gasoline tank, the properties of the outer surface side are due to the lack of affinity between the hydroxyl group of the phenoxy resin and the metal powder,
The metal powder detaches from the film during the press working. For this reason, peeling of the plating occurs on the outer surface side, and the press formability deteriorates.

On the inner surface side when used as a gasoline tank, the inner surface has poor corrosion resistance at the portion damaged by the desorption of the metal powder and the peeling of the plating layer. Even in a flat part that has not been damaged, the corrosive liquid tends to stay between the resin and the metal powder in the film, and the inner surface corrosion resistance is poor.

In any steel sheet, since the resin film on the inner and outer surfaces of the tank is thermosetting, it is difficult to be thermally decomposed, and it is difficult to remove the film during the nugget formation process, thereby deteriorating the seam weldability. In other words, even if the energization point is secured by the metal powder, the remaining base metal around the coating causes poor welding,
Lack of sufficient nugget wrap is not obtained and fuel leakage occurs. In some cases, sufficient welding strength cannot be obtained and peeling occurs. As described above, various performance defects are left, but have not yet been put to practical use.

Accordingly, the present invention solves such disadvantages of the current tank material and exhibits excellent internal corrosion resistance to alcohol, particularly methanol itself, or gasoline mixed with formic acid generated by oxidizing methanol. Another object of the present invention is to provide a steel plate for a fuel tank having high corrosion resistance, which exhibits excellent press workability, seam weldability, and outer corrosion resistance in a tank manufacturing process.

[0013]

As a result, Zn or a metal plating layer containing Zn as a main component is provided as a lower layer on the surface of the steel sheet, a chromate film is provided thereon, and an organic film is provided as an upper layer on one of the surfaces. A metal powder-containing organic resin film is provided (hereinafter, this surface is referred to as an inner surface), and a silica-containing organic film containing polyethylene wax and silica is provided as an organic film on the other surface (hereinafter, this surface is referred to as an outer surface). Accordingly, the present invention has been completed by obtaining a completely new finding that these problems can be solved at once.

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 film on both surfaces of the upper layer, and an upper layer on one of the surfaces. The film is a metal powder-containing organic resin film containing Al and Ni metal powder, an amine-modified epoxy resin and a curing agent as main components, and the film is a hydroxyl group, isocyanate group, carboxyl group, glycidyl group and A highly corrosion-resistant fuel tank with excellent moldability, characterized in that the resin is at least one resin having at least one functional group selected from amino groups and a silica-containing organic resin containing silica and a polyolefin wax as main components. Provide steel sheet.

More preferably, the metal powder in the metal powder-containing organic resin film is 3 parts by weight based on 100 parts by weight of the organic resin.
0 to 110 parts by weight, and the composition of the metal powder is Ni / Al
= 80/20 to 30/70 (weight ratio), and the shape of the Al powder is such that the major axis is 8 to 18 μm, the minor axis is 1 to 10 μm, and the thickness is 1.
~ 5μm scale, Ni powder shape is particle size 1 ~ 9
μm, and the amine-modified epoxy resin is used in an amount of 0.2 to 1.0 with respect to 1 equivalent of epoxy group in the epoxy resin.
100 mole parts of a curing agent which is a composite resin obtained by adding moles of alkanolamine, and wherein the weight average molecular weight of the amine-modified epoxy resin is in the range of 5,000 to 50,000, and a curing agent capable of performing a curing reaction with the amine-modified epoxy resin. To a 10 mm × 5 mm felt impregnated with methyl ethyl ketone.
g under a load, and the number of reciprocations until the underlayer was exposed was measured. The degree of cure defined by the following formula was 80% or more, and the thickness of the metal powder-containing organic resin film was Is 2 to 10 μm. Curing degree = number of reciprocations until the base is exposed / 100 × 10
0%

Further, 100 parts by weight of at least one resin having at least one kind of functional group selected from a hydroxyl group, an isocyanate group, a carboxyl group, a glycidyl group and an amino group is added to the silica-containing organic resin film. 80 parts by weight, 1 to 40 parts by weight of a polyolefin wax having a softening point of 70 to 150 ° C. and an average particle size of 1 to 7 μm, and the glass transition temperature (Tg) of the silica-containing organic resin is 0 to 90 ° C. The thickness of the silica-containing organic resin film is preferably 0.5 to 1.5 μm.

The metal plating layer containing Zn as a main component,
Zn-Ni alloy plating, Zn-Co alloy plating, Zn-
Fe alloy plating, Zn-Ni-Cr alloy plating, Zn-
Ni—Co alloy plating or Zn—Al alloy plating, the basis weight of the metal plating layer containing Zn or Zn as a main component is 10 to 200 g / m ² , and the adhesion amount of the chromate film is: 5 per side in terms of metal chrome
Preferably, it is 200 mg / m ² .

[0018]

Hereinafter, the present invention will be described in more detail.
First, the steel plate for a highly corrosion resistant fuel tank of the present invention has Zn or a metal plating layer containing Zn as a main component as a lowermost layer on the surface of the steel plate. Since the metal plating layer is a metal layer exhibiting a lower potential than the iron base in alcohol and alcohol-mixed fuel, the occurrence of red rust and perforation is suppressed by the sacrificial anticorrosive action of Zn even in the pressed part where the plating layer is damaged. And improve the corrosion resistance of the outer surface of the fuel tank. On the other hand, the inner surface prevents the formic acid aqueous solution from penetrating due to the barrier effect of the organic film, and suppresses the elution of Zn, which is weak against acids, and the formation of a floating white precipitate accompanying the elution.

When the metal plating layer is made of an alloy plating layer containing Zn as a main component, the elution rate of the plating layer during the sacrificial anticorrosion action is slowed down. The amount can extend the perforated life of the fuel tank. Further, the corrosion resistance when combined with an upper chromate layer or an organic resin film containing a metal powder described later is further improved. Examples of such a metal plating layer containing Zn as a main component include Zn-Ni alloy plating, Zn-Co
Alloy plating, Zn-Fe alloy plating, Zn-Al alloy plating, Zn-Ni-Cr alloy plating, Zn-Ni-Co
Any of the alloy platings is suitable.

The basis weight of such 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 above-described Zn or a metal plating layer containing Zn as a main component can be formed by a known electroplating method or hot-dip plating method.

[0021] For example Zn plating layer, ZnSO ₄ · 7
H ₂ O 410 g / l, AlCl ₃ 20 g / l, Na ₂
It can be formed by electroplating using a mixed solution of 75 g / l of SO _{4 at a} pH of 3 to 5, a temperature of 20 to 30 ° C., and a current density of 1 to 10 A / dm ² . The metal plating layer containing Zn as a main component is ZnSO _{4 in} the case of Zn-Ni alloy plating.
・ 7H ₂ O 300g / l, NiSO ₄・ 6H ₂ O 2
200 g / mixed solution of l, Zn-Co case of alloy plating _{ZnSO 4 · 7H 2 O 200g /} l, CoSO 4 · 7
Mixed solution of _{H 2 O 200g / l, Na} 2 SO 4 45g / l, in the case of Zn-Fe alloy plating, ZnSO ₄ ·
_{7H 2 O 110g / l, FeSO} 4 · 7H 2 O 10
0 g / l, (NH ₄ ) ₂ SO ₄ 20 g / l, KCl
20 g / l, a mixed solution of second antimony citrate 60 g / l, and Zn-Ni-Cr alloy plating, ZnS
_{O 4 · 7H 2 O 160g /} l, NiSO 4 · 6H 2 O
240 g / l, 2 g / l CrO ₃ mixed solution, Zn-
For Ni-Co alloy plating, ZnSO ₄ · 7H ₂ O
100 g / l, NiSO ₄ .6H ₂ O 60 g / l,
_{CoSO 4 · 7H 2 O 60g /} l, (NH 4) 2 SO
₄ 5 g / l, using a mixed solution of H ₂ SO ₄ 10g / l, and adjust the respective PH2.0～4.5, current density 5~50A / dm ^2, temperature, electroplating at room temperature to 60 ° C. Can be formed. In the case of Zn-Al alloy plating, a hot-dip plating bath composed of 4 to 5% of Al and 95 to 96% of Zn, or 50 to 60% of Al, and 50 to 4% of Zn.
It can be formed by a 0% hot-dip plating bath.

Next, in the present invention, a chromate film is formed on the plating layer. Chromate coating weight per one side 5 to 200 mg / m ² reckoned as metal chromium, more preferably 10-100 mg / m ^2. Chromate film is provided on both sides. If the amount is less than 5 mg / m ² , the adhesiveness with the organic film on the upper layer is insufficient, so that the film on the sliding portion peels off during press working, and in some cases, even the plating layer peels 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 in combination with the peeling of the plating layer. If it exceeds 200 mg / m ² , the chromate film itself becomes very brittle and peeling of the chromate film occurs in the processed sliding portion, and accompanying this, peeling of the upper organic film also occurs. Therefore, the corrosion resistance of the processed portion on the inner and outer surfaces is insufficient.

As the uppermost layer, the inner surface side is a metal powder,
The resin is coated with an organic resin containing a metal powder containing a terminal amine-modified epoxy and a curing agent as main components, and the outer surface is coated with a silica-containing organic resin composed of a resin, silica, and a polyolefin wax. Because the inner surface is excellent in weldability, gasoline resistance, etc.,
It is preferably used as the inner side of the gasoline tank (that is, the side in contact with gasoline). Since the outer surface is excellent in corrosion resistance and lubricity, it is preferably used as the outer surface of a gasoline tank.

First, the metal powder-containing organic resin film on the inner surface will be described. The metal powder-containing organic resin film on the inner surface is made of a metal powder and a resin component having excellent corrosion resistance and durability against alcohol, particularly methanol itself or gasoline mixed with formic acid generated by oxidization of methanol, and the metal component. The anticorrosion layer serves to prevent direct contact between the plating layer and the chromate layer and the alcohol fuel.

The purpose of adding the metal powder is to secure resistance weldability. That is, the organic resin film generally has a high electric insulation property, and furthermore, since the film thickness of the resin film is 2 to 10 μm, exposure of the projections of the steel sheet cannot be expected at all, and resistance welding is difficult. Therefore, in the present invention, a required amount of metal powder is dispersed in the organic resin film on the inner surface side of the gasoline tank to enhance the conductivity of the film.

The higher the specific resistance of the metal powder, the larger the calorific value and the more useful it is. Specifically, Ni, Al, Fe,
Cu and the like are conceivable. 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 object is achieved by combining Al and Ni and adding them in an appropriate ratio to the organic resin film. Fe and Cu have poor corrosion resistance to methanol and are not useful.

As the shape of the metal powder, any of a granular shape and a flake shape can be applied, but as described above, the inner surface corrosion resistance and the resistance weldability slightly change depending on the shape. Ni powder has a particle size of 1
Particles having a particle size of about 9 μm are preferred. More preferably, 2
７7 μm. When the particle size is less than 1 μm, the energization point is insufficient. When the particle size is more than 9 μm, the current-carrying point is sufficiently provided, so that the resistance weldability is improved by adding a small amount. However, since the film becomes porous, the inner surface corrosion resistance is deteriorated, and powdering of the coating film at the time of press working also poses a problem.

The shape of the Al powder is a scale having a major axis of 8 to 18 μm, a minor axis of 1 to 10 μm, and a thickness of 1 to 5 μm.
More preferably, the major axis of the Al powder is 10 to 15 μm, the minor axis is 5 to 8 μm, and the thickness is 2 to 4 μm. Long diameter,
If the minor axis is less than 8, 1 μm, the scale area is too small, and the ability to suppress the permeation of an aqueous solution of formic acid or the like is reduced, and the inner surface corrosion resistance is reduced. This problem also occurs when only the major axis or the minor axis is short. On the other hand, when the major axis and the minor axis are more than 18, 10 μm, respectively, the film becomes too porous, so that the strength of the film is insufficient and the film becomes brittle. For this reason, powdering occurs and the inner surface corrosion resistance of the pressed portion is reduced. When the thickness is less than 1 μm, the life of the inner surface corrosion resistance is shortened. If the thickness is more than 5 μm, the proportion of Al powder exposed on the coating film surface is too large,
Resistance weldability decreases.

The reason why the amount of the metal powder added is limited will be described. The amount of the metal powder added is 30 to 110 parts by weight, preferably 45 to 1 part by weight, per 100 parts by weight of the resin in the organic resin film.
00 parts by weight. If the amount is less than 30 parts by weight, the current-carrying point is insufficient and the conductivity is poor, so that the resistance weldability is reduced. If the amount is more than 110 parts by weight, the organic film itself becomes fragile, the powdering resistance at the time of pressing decreases, and the inner surface corrosion resistance decreases.

In the case of the above-mentioned appropriate amount of metal powder addition, Ni
/ Al ratio (weight ratio) needs to be 80/20 to 30/70. That is, when the Ni / Al ratio is less than 30/70, the amount of Ni having a high specific resistance is insufficient, resulting in poor resistance weldability. On the other hand, when the ratio exceeds 80/20, the amount of Al having a function of suppressing the penetration of fuel decreases, so that the internal corrosion resistance decreases. Preferably it is 70/30 to 40/60.

Next, needless to say, the resin component on the inner surface side used in the present invention has excellent corrosion resistance and durability against gasoline, alcohol, and formic acid-based fuels, It exhibits excellent properties in press formability. That is, the amine-modified epoxy resin ensures excellent press moldability, corrosion resistance to alcohol-based fuel, and adhesion of the coating film to the base material. The amine-modified epoxy resin is preferably an epoxy resin having a molecular weight of 5,000 to 50,000, preferably 10,000 to 40,000, in order to ensure excellent press moldability.

The raw material of the epoxy resin is bisphenol A
Epoxy resin, bisphenol F epoxy resin, cycloaliphatic epoxy resin, hydantoin epoxy resin,
Novolak type epoxy resins, glycidyl ester type epoxy resins and the like can be mentioned. Of these, bisphenol A type epoxy resins and bisphenol F type epoxy resins are preferred from the viewpoint of a wide range of production conditions for stably obtaining stability, pressability, and inner surface corrosion resistance as a paint.

In this embodiment, the epicoats 1010, 100
9, 1007, 1004, and 1001 (all manufactured by Yuka Shell Epoxy Co., Ltd.), and phenoxy resins obtained by polymerizing these epoxy resins (manufactured by UCC). These may be used alone or an epoxy ester resin obtained by reacting a dicarboxylic acid such as adipic acid, azelaic acid, sebacic acid, phthalic acid or dimer acid may be used.
Further, it may be used in combination with polyalkylene glycol diglycidyl ether.

Here, the reason why the molecular weight must be in the range of 5,000 to 50,000 will be described. Molecular weight 5000
If it is less than 1, the molecular weight of the resin is too low, so that the intermolecular force is insufficient and the toughness of the film is insufficient. For this reason, a film is shaved at the time of press working, and pressability is insufficient. When the molecular weight is more than 50,000, the amount of alkanolamine added to the epoxy group is reduced, so that the affinity between the resin and the metal powder is insufficient, and the metal powder is detached from the film during press working. Or the internal corrosion resistance is insufficient.

Examples of the amine to be added to the epoxy group of the epoxy resin include monoalkanolamines such as ethylethanolamine and ethanolamine, and dialkanolamines such as diethanolamine, dipropanolamine and dibutanolamine. In order to further enhance the low-temperature reactivity with a curing agent described later, dialkanolamine which can introduce more primary hydroxyl groups is preferable.

The number of moles of the alkanolamine added to one equivalent of the epoxy group of the epoxy resin must be 0.2 to 1.0 mole. When the epoxy equivalent is 500 to 1000, the mole number of the alkanolamine is 0.2 to 0.6 mole, and when the epoxy equivalent is 1000 to 5000, the mole number of the alkanolamine is particularly preferably 0.6 to 1.0 mole. . When the number of moles of the alkanolamine is less than 0.2, 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 pressability. 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 alkanolamine 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.

In the present invention, a curing agent is blended. As such a curing agent, an isocyanate-based curing agent, an amine-based curing agent,
Melamine-based curing agents, dicyandiamide-based curing agents, hydrazide-based curing agents, phenol-based curing agents, boron-based curing agents,
An imidazole-based curing agent can be used. Such a curing agent is blended so as to react with the composite resin.

The curing agent is used in an amount of 2 to 20 parts by weight, preferably 4 to 10 parts by weight, based on 100 parts by weight of the amine-modified epoxy resin (solid content). If the compounding ratio of the curing agent is less than 2 parts by weight, the curing degree is too low,
The ability to suppress formic acid permeation is insufficient, and the internal corrosion resistance is reduced. In addition, since the toughness of the film is insufficient, pressability is reduced.
On the other hand, if it exceeds 20 parts by weight, the unreacted curing agent makes the resin film brittle, so that the pressability is reduced, and the water absorption is increased, so that the inner surface corrosion resistance is reduced.

The degree of cure of the film is important. The degree of cure is defined by the following formula by rubbing the surface of the film with a load of 500 g applied to a 10 mm × 5 mm felt impregnated with methyl ethyl ketone and measuring the number of reciprocations until the base is exposed. Curing degree = number of reciprocations until the base is exposed / 100 × 10
0% In this test, if the number of times until the underlayer is exposed is 100 or more times, it can be used for normal use. The degree of cure is preferably 80% or more. If the degree of cure is less than 80%, the degree of cure is too low, so that the ability to suppress formic acid permeation is insufficient and the internal corrosion resistance is reduced. In addition, since the toughness of the film is insufficient, pressability is reduced.

As described above, in the present invention, an organic resin film containing the above-mentioned metal powder and the above-mentioned amine-modified epoxy resin component is provided as an upper layer on the inner surface side.
The thickness of this film is preferably 2 to 10 μm. If it is less than 2 μm, the internal corrosion resistance required for the outer layer is insufficient.
If it exceeds 10 μm, the corrosion resistance is saturated, the press workability,
Seam weldability decreases.

As additives to the resin film on the inner surface side, lubricants, coupling agents, pigments, thixotropic agents,
An additive such as a dispersant may be added to the film.

An example of a method for preparing this paint will be described. The amine-modified epoxy resin is obtained by adding an alkanolamine to an epoxy resin having an epoxy equivalent of 500 to 5,000 and reacting at room temperature to 100 ° C. for 4 to 5 hours. Next, in the present invention, a metal powder and a curing agent are added to the resin by a sand mill or an attritor to prepare a predetermined ratio of a metal powder-containing organic resin paint.

Next, the silica-containing organic resin film on the outer surface will be described. The silica-containing organic resin film on the outer surface side is preferably a lubricating resin in which silica is compounded. The base resin used for the silica-containing organic resin 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,
Examples thereof include those modified using an alkyd resin, an acrylic resin, a urethane resin, a polyvinyl butyral resin, a phenol resin, a melamine resin, or the like as a curing agent. The usefulness of these resins in the present invention is that the hydroxyl group on the silica surface reacts with these resins to form an inorganic material having high corrosion resistance.
The purpose is to form an organic composite film and improve the corrosion resistance of the outer surface of the tank.

As described above, silica is blended to impart corrosion resistance to the organic resin film on the outer surface side. Examples of silica include colloidal silica (for example, Snowtex-O and Snowtex-N manufactured by Nissan Chemical Co., Ltd.), organosilica sol (for example, ethyl cellosolve silica sol manufactured by Nissan Chemical Co., Ltd.), and silica powder (for example, Aerosil Co., Ltd.) )
Gas-phase silica powder) or an organic silicate (for example, ethyl silicate or the like is used in combination with an acid catalyst) which becomes silica by condensation by itself. The particle size of the silica powder is preferably from 5 to 70 nm in order to uniformly disperse the silica.

A silane coupling agent may be used as a reaction accelerator between the base resin and silica. Examples of the silane coupling agent include γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and the like. General additives such as a reaction accelerator, a stabilizer, and a dispersant may be appropriately added to the base resin within a range that does not impair the gist of the present invention.

Next, the lubricity imparting agent will be described. Generally, organic dry lubricants such as polyolefin wax and fluorine wax and inorganic dry lubricants such as molybdenum disulfide, organic molybdenum, graphite, carbon fluoride, metal soap, and boron nitride are used as bearing lubricants. .
These lubricants are added to plastics, oils, greases, and the like, and are used to improve lubricity. The lubricity was examined using these lubricants. In order to obtain a resin-treated steel sheet having a high degree of lubricity that can be continuously formed, it does not cause film peeling under severe press forming conditions involving heat generation of the sliding part called high-speed press forming as in the present invention. The glass transition temperature of the resin must be as high as about 70 ° C. or higher. When a lubricant having a small coefficient of friction and protruding from the surface of the resin film is used, the lubricant absorbs the frictional impact with the mold and has the same effect as lowering the glass transition temperature of the base resin. When a steel sheet treated with such a film is used, the lubricant on the surface of the resin film reduces friction with the mold, prevents damage to the resin film, and improves continuous formability during industrial production. By using a protruding lubricant, the glass transition temperature of the base resin can be reduced to about 40 ° C.

The present inventors have studied diligently for such a purpose. As a result, it was found that a polyolefin wax having an average particle size of 1 to 7 μm was effective. That 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. If it exceeds 7 μm, the organic film becomes too brittle and the powdering resistance of the film is reduced, so that the pressability is poor. The polyolefin wax may be any wax composed of a polymer of an olefinic hydrocarbon such as polyethylene, polypropylene and polybutene, or may be used in combination.

Also, polyolefin waxes having various melting points are known. Any material may be used as long as the melting point is in the range of 70 to 150 ° C. A combination of a low melting point and a high melting point may be used, whereby the press workability is further improved. 70 ° C melting point
If it is less than 1, under severe pressing conditions involving heat generation, the elasticity of the wax layer is significantly reduced, so that the lubricity is reduced and the pressability is inferior. When the melting point exceeds 150 ° C., the softening of the wax is insufficient, and the wax layer is too tough, so that the lubricity is reduced and the pressability is poor.

It is preferable that the compounding amounts of silica and polyolefin wax in the silica-containing organic resin are contained in the following proportions. Silica for improving corrosion resistance is 5 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.
It is preferable to add ~ 80 parts by weight. If the amount is less than 5 parts by weight, the corrosion resistance is reduced. If the amount is more than 80 parts by weight, the film becomes brittle, and the mold is seized at the time of molding to deteriorate the pressability. In addition, since silica has poor thermal decomposability, resistance weldability decreases. More preferably, it is 20 to 60 parts by weight.

The amount of the lubricity-imparting agent added is 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, based on 100 parts by weight of a polyolefin wax. Is preferably 1 to 40 parts by weight or less. If the amount exceeds 40 parts by weight, the strength of the resin film decreases, and the lubricity decreases.
If the amount is less than 1 part by weight, lubricity is insufficient. More preferably 5
-30 parts by weight.

It is preferable that the above-mentioned components are contained in the above-described ratios, and that essential components such as a base resin and other additives are combined. The glass transition temperature (Tg) of such a silica-containing organic resin is from 0 to 90 ° C.
Outside this range, the press workability is poor, and the corrosion resistance of the pressed portion is also poor.

The thickness of the silica-containing organic resin film is preferably 0.5 μm to 1.5 μm in dry thickness on one side. 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.

The steel plate for a highly corrosion-resistant fuel tank of the present invention has the above-described structure. Even if lubricating oil is applied according to the difficulty of pressing, there is no problem at all, and it is rather effective from the viewpoint of preventing damage to the coating film.

An example of a specific method for forming the above-mentioned resin film will be described. The resin film on the inner surface is mainly composed of the above-mentioned amine-modified epoxy resin, and is coated and dried as a coating composition containing an appropriate amount of an organic solvent or a curing agent, a metal powder, and other commonly used additives. Can be formed. An example relating to the formation of the metal powder-containing organic resin film on the inner surface side is shown below. First, Epicoat 1007 (epoxy equivalent of epoxy resin manufactured by Yuka Shell Epoxy Co., Ltd. = 2000) was added to a reactor equipped with a reflux condenser, a stirrer, a thermometer, and a nitrogen gas blower.
1000 g of toluene was added to 00 g (1 equivalent of epoxy group), and after replacing with nitrogen, the temperature was raised to 80 ° C. to obtain a uniform solution. Next, 52.5 g of diethanolamine was added to this solution.
The reaction was allowed to proceed for 1 hour after dropping over 0 minutes. A metal powder, a surfactant, an organic solvent, a curing agent, and other additives are added to the composite thus obtained, and the mixture is kneaded to prepare a suspension. The amount of the organic solvent used is preferably from 60 to 85 parts by weight based on the whole suspension. Next, this is applied to a required thickness by roll coating, dried, and baked at a sheet temperature of 150 to 300 ° C.

An example of the formation of the organic resin film on the outer surface will be described below. First, a solid content 30 of denkabutyral # 2000-L (polyvinyl butyral resin manufactured by Denki Kagaku Kogyo Co., Ltd .: average degree of polymerization = 300) was added to a reactor equipped with a reflux condenser, a stirrer, a thermometer, and a nitrogen gas injection device.
100 g of an ethyl polysilicate (ethyl silicate 40, manufactured by Nippon Colcoat Chemical Co., Ltd., z: degree of polymerization = 4-6, SiO ₂ content 40%) through a dropping funnel with sufficient stirring after nitrogen substitution and 200 g of a 100% cellosolve solution. Is dropped. Then, 30 g of an orthophosphoric acid aqueous solution was gradually added dropwise, and then the mixture was heated to 90 ° C., reacted under reflux for 4 hours, and a polyolefin wax was added.
A colorless and transparent resin mixture or composite was obtained. This resin mixture or composite is applied to a predetermined thickness by a known ordinary method such as roll coating, spray coating, or dip coating, and dried at 50 to 180 ° C. for 3 to 90 seconds.

[0056]

The configuration of the present invention has been described above, and the effect of the present invention will be specifically described with reference to examples. (Example) A steel plate for a high corrosion resistant fuel tank of the present invention and various comparative materials were obtained using a cold rolled steel plate (SPCC) having a plate thickness of 0.8 mm as an original plate. In manufacturing, Zn or Zn in the lower layer
After performing pretreatment (electrolytic degreasing, electrolytic pickling) on the metal plating layer containing as a main component, several types of plating were applied. The abbreviations of the plated steel sheets used are shown below. GA ... alloyed hot-dip galvanized steel sheet / in plating F
e% = 10 ZnNi: electro-galvanized steel sheet (nickel content: 12 wt%) GI: hot-dip galvanized steel sheet GF: 5% aluminum-95% galvanized steel sheet GL:・ 55% aluminum-45% galvanized steel sheet EG ・ ・ ・ ・ ・ Electro-galvanized steel sheet Zn-Co ・ ・ 13% cobalt-containing, zinc-cobalt alloy plated steel sheet Zn-Ni-Co ・ ・ ・ 12% nickel, 5% Cobalt-containing, zinc-nickel-cobalt alloy-plated steel sheet Zn-Ni-Cr: 12% nickel, 5% chromium-containing, zinc-nickel-chromium alloy-plated steel sheet Roll coat the resin film on
It was obtained by drying and baking. As a comparison material,
Various types of zinc-coated steel sheets, turn-coated steel sheets, and hot-dip aluminum-coated steel sheets were used in which a resin film described in Japanese Patent Application Publication No. 3-25349 was applied on various types of plated steel sheets. The alkanolamine addition amount (mol) is an amount based on 1 equivalent of epoxy group in the epoxy resin.

The above-mentioned steel sheet for a high corrosion resistant gasoline tank of the present invention and a comparative example were evaluated for press workability, resistance weldability, outer shochu, inner corrosion resistance, and brazing properties by the following evaluation methods. (A) Evaluation of press workability (1) Evaluation of lubricity by cylindrical molding test Press conditions: 1 g / m ^{2 of} rust preventive oil Z5 manufactured by Idemitsu Oil Co., Ltd.
Oiling and evaluation ・ 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 and the inner surface is set on the punch side, and the cylinder is formed into a cylinder. The limit drawing ratio of each sample (the maximum value of the die diameter / punch diameter of the sample that has been drawn out) ) Was obtained, and the lubricity was evaluated using this value. A larger value indicates better moldability.

(2) Evaluation of Powdering Resistance of Film by Cylindrical Molding Test Press conditions: 1 g / m ^{2 of} rust preventive oil Z5 manufactured by Idemitsu Oil Co., Ltd.
Oiling and evaluation ・ Punch diameter and shape ・ ・ ・ 33mmφ flat bottom cylinder ・ Clearance ・ ・ ・ ・ 1mm ・ Planck size ・ ・ ・ 66mm ・ Wrinkle holding load ・ ・ ・ ・ 2t ・ Drawing speed ・ ・ ・ ・ ・ ・ 60mm / sec The degree of powdering of the film on the outer surface after cup formation was visually observed and evaluated. The evaluation criteria were as follows: the level at which powdering of the coating was not visually observable, x when the amount of powdering was extremely large, and Δ between the two.

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

(C) Evaluation method of outer surface corrosion resistance Top coat paint: Emaron manufactured by Dainippon Paint Co., Ltd. was applied to the outer surface side so as to have a dry film thickness of 10 μm.
After baking for minutes, JASO (salt spray 2 hours $ 60
℃, 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 was evaluated by the residual plate thickness (mm) of the flat portion, the cross cut of the flat portion, and the side wall portion of the pressed product formed under the conditions of (A) and (2). The thickness before the test was 1.0 mm.

(D) Evaluation Method for Corrosion Resistance of Inner Surface The flat portion and the inner surface of the flat-bottomed cylindrical cup formed under the conditions of (A) (2) were evaluated. 20mm when investigating a flat part
A test piece of × 100 mm was prepared, and unleaded gasoline / 500
The test piece was immersed in a fuel having a ppm formic acid aqueous solution = 1/1 (weight) by 80 mm, and subjected to a one-month immersion test at room temperature. Then, the rusting degree 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 mmφ and a height of 30 mm. The above-mentioned fuel was charged at 80% of the inner volume of the cup, immersed at room temperature for one month, 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 area ratio of red rust generation in each part was evaluated.

(E) Brazing properties Two samples of 15 mm × 200 mm size were prepared.
The outer surfaces are wrapped with 15 mm × 15 mm, and between them, IS-344 (JIS standard name: King solder # 101) manufactured by Ishifuku Metal Industry Co., Ltd. and Ishifuku Flux # 6 manufactured by Ishifuku Metal Industry Co., Ltd. are used. The gas was heated with a constant heating time of 10 seconds. Thereafter, a shear tensile test was performed, and the case where the base material was broken was evaluated as ○, the case where the base material / wax was peeled off was evaluated as x, and the middle between the two was evaluated as Δ.

(F) Method of Measuring Degree of Curing The surface of the film was rubbed with a load of 500 g applied to a 10 mm × 5 mm felt impregnated with methyl ethyl ketone, and the number of reciprocations until the substrate was exposed was measured. The degree of cure defined by the following equation was calculated. Curing degree = number of reciprocations until exposure / 100 × 100
(%)

[0064]

[Table 1]

[0065]

[Table 2]

[0066]

[Table 3]

[0067]

[Table 4]

[0068]

[Table 5]

[0069]

[Table 6]

[0070]

[Table 7]

[0071]

[Table 8]

[0072]

[Table 9]

[0073]

[Table 10]

[0074]

[Table 11]

[0075]

[Table 12]

[0076]

[Table 13]

[0077]

[Table 14]

[0078]

[Table 15]

[0079]

[Table 16]

[0080]

[Table 17]

[0081]

[Table 18]

[0082]

[Table 19]

[0083]

[Table 20]

[0084]

[Table 21]

[0085]

[Table 22]

[0086]

[Table 23]

[0087]

[Table 24]

[0088]

[Table 25]

[0089]

[Table 26]

[0090]

[Table 27]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096]

[0097]

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

The steel sheet for gasoline tank of the present invention has excellent corrosion resistance, press workability, resistance welding property and brazing property, and is particularly useful as a steel sheet for alcohol and alcohol mixed gasoline.

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 film on both surfaces of the upper layer, and further has Al and Ni metal powder, an amine-modified epoxy resin, and a curing agent as the main components on one surface. Having a metal powder-containing organic resin film,
And 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 in the upper layer of the other surface, and a silica-containing organic material containing silica and a polyolefin wax as main components. A highly corrosion-resistant steel plate for fuel tanks having a resin film and excellent moldability. 2. The metal powder in the metal powder-containing organic resin film is 30 to 110 parts by weight based on 100 parts by weight of the organic resin, and the composition of the metal powder is Ni / Al = 80/20 to 30/70.
(Weight ratio), and among the metal powders, the shape of the Al powder is scale-like with a major axis of 8 to 18 μm, a minor axis of 1 to 10 μm, and a thickness of 1 to 5 μm.
A composite resin in which the shape of the powder is granular having a particle size of 1 to 9 μm, and the amine-modified epoxy resin is obtained by adding 0.2 to 1.0 mol of alkanolamine to 1 equivalent of epoxy group in the epoxy resin. And the weight average molecular weight of the amine-modified epoxy resin is 5,000 to 5,000.
0, a curing agent capable of curing with the amine-modified epoxy resin is contained in an amount of 2 to 20 parts by weight based on 100 parts by weight of the resin, and a load of 500 g is applied to a 10 mm × 5 mm felt impregnated with methyl ethyl ketone. The coating surface was rubbed in the applied state, and the number of reciprocations until the base was exposed was measured. The degree of curing defined by the following formula was 80% or more, and the thickness of the metal powder-containing organic resin film was 2 to 10 μm. The steel plate for a highly corrosion-resistant fuel tank according to claim 1, which is excellent in formability. Curing degree = number of reciprocations until the base is exposed / 100 × 10
0% 3. The method according to claim 1, wherein the silica-containing organic resin film has a hydroxyl group,
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, and silica 5 to 80
Weight part and softening point are 70-150 ° C and average particle size is 1-7μ
m comprising 1 to 40 parts by weight of a polyolefin wax,
The moldability according to claim 1 or 2, wherein the silica-containing organic resin has a glass transition temperature (Tg) of 0 to 90 ° C, and the thickness of the silica-containing organic resin film is 0.5 to 1.5 µm. Excellent high corrosion resistance steel plate for fuel tanks. 4. The metal plating layer containing Zn as a main component,
Zn-Ni alloy plating, Zn-Co alloy plating, Zn-
Fe alloy plating, Zn-Ni-Cr alloy plating, Zn-
The basis weight of the metal plating layer which is either Ni-Co alloy plating or Zn-Al alloy plating, and has Zn or Zn as a main component is 10-200 g / m < ² >.
A highly corrosion-resistant steel sheet for a fuel tank having excellent formability according to any one of the above. 5. The steel plate for a highly corrosion-resistant fuel tank according to claim 1, wherein the amount of the chromate film adhered is 5 to 200 mg / m ² per one surface in terms of chromium metal.