JPH11138096A - Organic coated steel sheet for fuel tank - Google Patents

Abstract

(57) [Problem] To provide an organic-coated steel sheet for a fuel tank containing no Pb. SOLUTION: An organic coated steel sheet in which a coating containing an aqueous urethane resin having a glass transition temperature of 100 to 150 ° C as an essential component is formed on at least one surface of a plated steel sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic-coated steel sheet having excellent corrosion resistance, especially corrosion resistance to degraded gasoline.

[0002]

2. Description of the Related Art Pb is used as a surface-treated steel sheet for a fuel tank.
-Sn alloy plated steel sheets have been used for many years. However, in recent years, due to the toxicity problem of Pb, a material containing no Pb has been demanded. As a substitute material, a plastic fuel tank has been put to practical use, but its safety is not always sufficient, and a steel plate material is required. As a material for steel sheets, resins mainly composed of epoxy resin,
An organic-coated steel sheet coated with a paint containing flaky Al on a plated steel sheet and baked is used. However, the corrosion resistance to degraded gasoline is not sufficient, and improvement is required.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an organically coated steel sheet which has good corrosion resistance to degraded gasoline, and is excellent in weldability and press formability.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its gist is as follows. (1) At least one surface of a plated steel sheet has a glass transition temperature of 100%.
An organic coated steel sheet for a fuel tank, characterized in that a coating containing an aqueous urethane resin at a temperature of up to 150 ° C. as an essential component is formed,
(2) The tensile strength of the aqueous urethane resin film is 400 kg / c
The organic coated steel sheet according to (1), characterized in that in m ² or more, and is elongation of 5% or more, (3) a urethane resin, ether-esters having a bisphenol skeleton, an ester backbone and a carboxyl group The organic-coated steel sheet according to the above (1) or (2), wherein the organic-coated steel sheet is a urethane resin of a mold type.

(4) The organic coated steel sheet according to any one of (1) to (3), wherein the coating contains polyethylene wax, and (5) the plating layer is made of N
any one or more of Ni, Cr and Fe through a metal or metal oxide or metal hydroxide or a mixture thereof consisting of at least one of i, Co, Cr and Fe The organic-coated steel sheet according to any one of the above (1) to (4), which is a zinc-based alloy plating layer containing:

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The resin used for the organic coating in the present invention is a resin containing an aqueous urethane resin as a main component and having a glass transition temperature in the range of 100 to 150 ° C. The glass transition temperature is measured by measuring the viscoelasticity of the cured film,
Was the maximum temperature. Create a free film by baking the paint at a predetermined temperature and set the frequency to 1 in the tensile mode.
It was measured under the conditions of 1 Hz, an amplitude of 1 μm, and a heating rate of 5 ° C./min.

[0007] A film having a glass transition temperature of less than 100 ° C has insufficient corrosion resistance to deteriorated gasoline, and a film having a glass transition temperature of more than 150 ° C tends to cause cracking of the film during processing, and the processed portion has insufficient corrosion resistance. The tensile strength of the filey film is 400 kg / cm ² or more and the elongation is 5%.
The above film is particularly excellent in the balance between corrosion resistance and moldability. When the tensile strength is less than 400 kg / m ² ,
Poor corrosion resistance. If the elongation is less than 5%, the coating tends to crack and peel at the processed part, and the corrosion resistance of the processed part is also reduced. Tensile strength and elongation
The free film is stretched at a temperature of 25 ° C. at a pulling speed of 10
It was determined by testing at a speed of mm / min.

Further, a urethane resin containing a bisphenol skeleton and an ester skeleton in the structure and having a carboxyl group is preferred. For this urethane resin, there is a method of neutralizing a carboxyl group with an alkali compound such as ammonia or trimethylamine and self-emulsifying, or a method of emulsion dispersion using an emulsifier, and either method may be used. The molecular weight of the aqueous urethane resin is 8000 or more, and a resin having a urea bond in the molecule is preferable. When a polyethylene wax is contained in the coating, an organically coated steel sheet having more excellent corrosion resistance and formability can be obtained. The urethane resin may be an emulsion or water-soluble. The average particle size of the wax is desirably 1 to 6 μm. If it is less than 1 μm, the effect of improving corrosion resistance and moldability is small, and if it exceeds 6 μm, the corrosion resistance decreases.

Further, the urethane resin and the other resin can be mixed and used under the condition that the ratio of the solid content of the other resin to the whole resin is 40% or less. As other resin types, olefin resins, polyester resins, polycarbonate resins, epoxy resins, and the like, and mixtures and copolymers thereof can be used. For these resins, one or more of a melamine resin and an isocyanate resin (compound) serving as a crosslinking agent can be used. The content of the resin in the film is not particularly limited, but is preferably 40% by weight or more in terms of solid content. If it is less than 40%, it cannot sufficiently serve as a binder, causing problems such as poor film formability, poor adhesion and insufficient workability.

[0010] In order to improve corrosion resistance, a rust preventive pigment can be contained in the film. Known pigments can be used as the rust preventive pigment. For example, strontium chromate, potassium chromate, zinc chromate, barium chromate, ammonium chromate, ammonium dichromate, etc. can be used as the chromate-based rust preventive pigment. In addition, a metal lower than iron, such as zinc powder, can also be used.

It is also possible to use rust-preventive pigments which do not use chromium, such as those which release vanadium ions, those which release phosphate ions, molybdenum compounds, phosphate compounds, zinc phosphite and the like. Phosphite,
Basic zinc cyanamide, colloidal silica, silica and the like. Among them, colloidal silica improves corrosion resistance,
This is effective in improving the weldability and imparting an appropriate hardness to the film. The amount of the rust preventive pigment to be added is not particularly limited, but is preferably about 1 to 40% in terms of the solid content in the film after drying. If it is 1% or less, the rust-preventing effect is hardly exhibited, and if it is 40% or more, the film-forming property is poor and the effect of improving the corrosion resistance is reduced.
The above-mentioned film is formed on a plated steel sheet. The coating amount of the film is not particularly limited, but is preferably 0.4 to 5 g / m ² . If it is less than 0.4 g / m ² , there is no effect of improving corrosion resistance, and if it is 5 g / m ² or more, the weldability will be poor.

The method for forming the film is as follows: a coating containing a predetermined organic resin, a conductive material, and a rust-preventive pigment is applied to a roll coater,
What is necessary is just to apply | coat on a plating steel plate by well-known methods, such as a curtain coater, an air knife, electrostatic spray, air spray, and an airless spray method, and to dry-harden by a well-known method. ,
As a method of drying and curing, a method of applying heat such as a hot air drying furnace, an induction heating furnace, a near-infrared heating furnace, a far-infrared heating furnace, and the like, and curing by radiation depending on the type of paint can also be employed.

The drying conditions can be appropriately selected depending on the type of the paint. For example, in the case of a paint containing an epoxy resin, a modified epoxy resin, or a phenoxy resin and a phenol resin, baking is performed at a temperature of about 180 to 260 ° C. as the ultimate plate temperature. Can be When crosslinking with a melamine resin or an isocyanate resin, for example, 140 to 240 ° C.
It is baked at the temperature of the plate. In the case of a thermoplastic water-based olefin resin, a baking temperature of about 80 to 140 ° C. is sufficient. Thus, the baking temperature is selected according to the type of the contained resin.

Before forming the film, a pretreatment film for enhancing the adhesion of the film may be formed on the plated steel sheet. Pre-coating treatments include chromate treatment, zinc phosphate treatment, iron phosphate treatment, composite oxide film treatment of Ni and Co,
There are non-chrome treatments. Also, degreasing, water washing, hot water washing,
It is also possible to perform pretreatments such as brushing and grinding. As the pretreatment, electrolytic chromate treatment is particularly suitable for weldability,
Suitable for balance of corrosion resistance. Further, by performing the electrolytic chromate treatment on both surfaces of the plated steel sheet, the slidability of the surface on which the organic coating is not formed is improved, and the press formability is also improved.

Of course, even when organic coating is applied to both surfaces, electrolytic chromate treatment is suitable in terms of balance between weldability and corrosion resistance. The adhesion amount of the electrolytic chromate treatment layer is not particularly limited, but is 5 to 50 mg / m as Cr.
^{About 2} is desirable. When using the coating type chromate treatment, the treatment containing no silica is excellent in terms of weldability. The pretreatment layer can be formed on one side or both sides of the steel sheet as necessary.

Although the organic film is coated on the side in contact with the fuel, it can be formed on the outer surface not in contact with the fuel.
The same film as the inner surface side may be formed, or another type of film may be formed. Forming an organic film on the outer surface within a range that does not impair weldability is advantageous from the viewpoint of press moldability. This is because the organic coating can ensure lubricity during press molding. In particular, when the organic coating contains wax, the slidability may be particularly improved. Coloring pigments, extender pigments, lubricants, other additives, and the like can be added to the paint, if necessary, in addition to the essential components described above. However, it is desirable that the content of the essential component be 80% by volume or more in the film. When the content of the essential component is less than 80% by volume, there is a possibility that adhesion, moldability, corrosion resistance, and weldability are reduced.

Although the type of plating is not particularly limited, Zn alloy plating or galvannealing is preferred from the viewpoint of ensuring the corrosion resistance to deteriorated gasoline and the corrosion resistance of the tank outer surface. More preferably,
First, a metal or a metal oxide or a metal hydroxide of at least one of Ni, Co, Cr, and Fe, or an alloy layer or a mixture layer thereof is formed on a steel plate (hereinafter, referred to as a pre-plated layer). It is preferable that a zinc-based alloy plating layer containing at least one of Ni, Cr and Fe as an alloy component is further formed thereon.

Ni, Co, Cr, Fe to be formed first
The metal or metal oxide or metal hydroxide of at least one of the above, or an alloy layer or a mixture layer (pre-plated layer) thereof can be formed by an electroplating method. For example, Ni, Co, C
r, Fe sulfate in an ion concentration of 10 g / l to 100 g / l and a current density of 1 A / dm ² to 100 A
/ Dm ² , a sulfuric acid concentration of 0.1 g / l to 10 g / l, a high sulfuric acid concentration for metal plating, and a low sulfuric acid concentration for co-depositing oxides or hydroxides. Good to lower.

In order to promote the precipitation of metal ions in the electroplating bath, additives or supporting salts include dextrin, vanillin, phenolsulfonic acid, cationic polymers, aromatic aldehydes and the like in the former case. In this case, sodium sulfate, aluminum sulfate, ammonium sulfate, boric acid, borate and the like can be mentioned, and these can be added. The amount of the metal or metal oxide or metal hydroxide composed of at least one of Ni, Co, Cr and Fe obtained in this way or the amount of the alloy layer or mixture layer thereof is not particularly limited. Is 0.01 g / m ^{2 to} 10 g / m
A range of ² is desirable. If it is less than 0.01 g / m ² , the effect of improving the corrosion resistance to deteriorated gasoline is hardly obtained, and
If it exceeds 0 g / m ² , the effect is substantially saturated, and a further increase in the amount of adhesion only increases the cost, which is not preferable.

I would like to apply the following plating on these layers
Form a film of so-called plated steel sheet. As mentioned above, Z
n alloy plating or galvannealing is preferred
However, other platings can be used. Ie zinc
Galvanized steel sheet (electrogalvanized, hot-dip galvanized steel sheet),
At least one of Ni, Cr and Fe
Galvanized steel sheet containing alloy components, galvannealed steel
Steel sheet, aluminum-zinc alloy plated steel sheet, nickel plating
Steel, chrome-plated steel, tin-plated steel,
Steel sheet (for example, zinc-nickel or zinc-iron
And SiO _Two, TiO_Two, ZrO_Two, BaCrO
_FourZinc dispersion by uniformly dispersing and depositing metal oxides such as
Steel plate).

As described above, the adhesion amount of the plating film is 10
g / m^Two90 g / m or more^TwoThe following ranges are desirable. Me
Electroplating method or displacement plating method
(Sulfuric acid bath, hydrochloric acid bath, alkali bath) or molten metal
Hot-dip plating method (flux method, Sendzimer
Known methods such as molten salt electrolysis, vapor deposition, etc.
Can be used.
Layered steel sheets are also included in this patent. Plating weight
Is not particularly limited, but required corrosion resistance and weldability
Selected according to level. In terms of corrosion resistance,
1g / m ^TwoIt is desirable that this is the case. welding
From the viewpoint of the property, the plating adhesion amount is 90 g / m^TwoIs below
It is desirable. Plating thickness varies on both sides of steel plate
May be. When the corrosive environment of the tank outer surface is severe
May be plated thicker on the outer surface than on the inner surface.
If the required level of corrosion resistance on the side is higher, the inner side
It may be plated thick.

[0022]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples.
I do. Pre-plated and plated as shown in Table 1
The coating was performed by a vapor plating method or a hot-dip plating method. Ni
Pre-plating and Co pre-plating are Ni or Co plating.
ON concentration: 60 g / l, current density: 35 A / dm^Two,
Electrodeposition was performed under the conditions of a sulfuric acid concentration of 2 g / l and a bath temperature of 60 ° C. Z
For the n-Ni plating, a Zn ion concentration of 65 g / l,
ON concentration 45 g / l, sulfuric acid concentration 10 g / l, current density 7
0A / dm^TwoContains 11% of Ni at a bath temperature of 55 ° C.
The Zn—Ni alloy plating was electrodeposited. Zn-Fe alloy
The galvanized steel sheet was plated so as to contain 15% of Fe.
Zn plating was performed at a Zn ion concentration of 65 g / l and a sulfuric acid concentration of 1
0 g / l, current density 70 A / dm ^TwoAt a bath temperature of 55 ° C
For electrodeposition. Alloying hot-dip galvanizing is a method of
After immersing the steel sheet in the n-bath, the Fe
It heated so that% might be 11%.

[0023]

[Table 1]

Next, the plated steel sheet was spray-degreased with FC364S (concentration 2%, temperature 60 ° C.), washed well with water, washed with hot water and dried, and then subjected to a chromate treatment. As the chromate treatment, an electrolytic chromate treatment and a coating type chromate treatment (LN4545K, manufactured by Nippon Parkerizing Co., Ltd., a silica-free chromate treatment agent) were performed. The amount of chromium was 30 mg / m ² . After the electrolytic chromate treatment, it was washed with water and dried. After the coating chromate treatment, drying was performed so that the reached plate temperature was 100 ° C.

Next, a predetermined paint was applied by a roll coater so as to have a predetermined dry adhesion amount, and baked in a hot air drying oven. Aqueous urethane resin used (symbol U1 in the table)
Has an average molecular weight of 30,000 and a nitrogen content of 7.6 in the resin.
%, The amount of nitrogen involved in the urea bond in the nitrogen is 50%
%, An acid value of 16 (all as solids), and a solids concentration of 35%. This urethane resin contains a bisphenol skeleton and an ester skeleton, and has a carboxyl group. Hitec S-7024 (manufactured by Toho Chemical Co., Ltd.) was used as an acrylic olefin resin to be mixed with the resin (symbol A1 in the table). Furthermore, as a comparative resin,
Solvent-based urethane resins U2 and A1 were used, and the glass transition temperature (Tg) of the acrylic olefin resin A1 was increased by increasing the composition ratio of the acrylic resin. The Tg, tensile strength and elongation of the resin were measured by the methods described in the specification. Colloidal silica (Snowtex N, manufactured by Nissan Chemical Industries, Ltd.) was used as a rust preventive. As the wax, Chemipearl W4
00 (average particle size: 4 μm, manufactured by Mitsui Chemicals, Inc.).

Table 1 also shows the structure of the front and back sides. The specifications on the inner side of the tank are shown in detail, and the specifications on the outer side are indicated as follows. Those indicated as "same" in the plating column indicate that the specifications are exactly the same as those of the pre-plating and plating on the inner surface side. Those indicated as "differential thickness plating" indicate that the pre-plating is exactly the same and the plating type is the same, but that the amount of plating applied is different on the front and back. 20g / m plating weight on inner surface
In the case of ^2, the outer surface side 40 g / m ^2, when the coating weight of the inner surface side of 40 g / m ^2, the outer surface 20 g / m
² The same applies to the column of pre-treatment, and what is indicated as “same” means that the specification of the pre-treatment is the same as that of the inner side (even if there is no coating on the outer side, the pre-coating layer is provided. In some cases). In the film column, those indicated as "same" indicate that the film type and the amount of adhesion are exactly the same as those on the inner surface side. Those indicated as "none" indicate that no organic film was formed.

The evaluation method is as follows. The adhesion of the organic film is 1 m as specified in 8.5 of JIS K 5400.
7. The grids at m intervals were put into the organic coating, extruded 7 mm with an Erichsen tester specified in 8.2 so that the organic coating surface became convex, and tape-peeled by the method specified in 8.5.
5 (5) was referred to to give a rating. Moldability is
A cylindrical drawing test was performed under the conditions of a drawing ratio of 2.2, a holding pressure of 2 tons, and a shoulder radius of 3 mm, and the possibility of forming and the state of the steel sheet surface were observed. When the specifications were different between the front and back sides, two types of molding were performed so that each of the front and back sides became a convex portion.

The rating was 5: Formable and good surface condition after molding 4: Formable and slight flaws occurred on surface after molding 3: Formable and flaws on surface after molding 2: Moldable, but galling or peeling of the film by the press was remarkable.

The corrosion resistance of the organic-coated steel sheet was determined by cylindrical drawing under the conditions of a shoulder R of 5 mm, a holding pressure of 1 ton, and a drawing ratio of 2.2 (blank diameter: 110 mm) such that the “tank inner surface side” in Table 1 became the inner surface. Then, a cross-cut was made at the bottom of the cylinder, degraded gasoline was put into the cylinder, and the cylinder was hermetically sealed and left for 7 weeks in an environment at 25 ° C. for examination. The deteriorated gasoline was prepared by a method according to JIS K2287, mixed with new gasoline so that the formic acid concentration became 1000 mg / l, and further used pure water of 10% by volume. 1
When 0% by volume of pure water is added, the deteriorated gasoline is separated into two layers, and the formic acid concentration increases in the aqueous layer. Therefore, corrosion in a place in contact with the aqueous layer tends to be accelerated. After seven weeks, the appearance of the organic-coated steel sheet and the corrosion products in the deteriorated gasoline sealed therein were visually evaluated and scored.

The rating was: 5: Rust and swelling of the coating film hardly occurred even in the area where the aqueous layer was present. 4: Rust and swelling of the coating film were slightly observed in the area where the aqueous layer was present. The coating film was clearly swollen at the existing position. 2: The coating film was peeled off at the position where the aqueous layer was present. 1: It was determined that rust and the coating film were swollen even at the position where no aqueous layer was present.

For the weldability, an appropriate current range for spot welding and seam welding was examined. The inner surfaces of the coated steel sheets were overlapped (so that the organic coatings were joined together), and the spot weldability was 220 kgf for 12 cycles of energizing time. The OBARA alumina dispersed copper electrode (φ6R4
0), the seam weldability was 400 k
gf, energization pattern 2on-2off, electrode is R4.5
(Continuous grinding). Nugget diameter 4√t
The current range larger than (t: plate thickness mm) and free of dust and welding was regarded as an appropriate current range, and it was judged that the wider the appropriate current range, the better the weldability.

Table 1 shows the evaluation results. The organic coated steel sheet according to the present invention is excellent in film adhesion, formability, and corrosion resistance to deteriorated gasoline. The organic coated steel sheet is excellent in corrosion resistance, formability, and weldability within the range of the present invention even if the plating type of the base sheet is different. For the same coating weight, the smaller the weight, the better the weldability. Regarding the plating type, zinc-based alloy plating containing at least one of Ni, Cr, and Fe as an alloy component was particularly excellent in corrosion resistance. Regarding weldability, galvannealed steel sheets are
When the adhesion amount was the same, the weldability was superior to other plated steel sheets.

In Comparative Example No. 6, in which the amount of the applied film exceeded 5 g / m ² , no welding was possible. In Comparative Example No. 5 in which the coating amount of the coating was less than 0.2 g / m ² , the corrosion resistance was poor. Comparative Example No. 1 in which Tg of the film is less than 100 ° C.
In No. 4, the corrosion resistance is poor. Comparative Example No. 15 in which the tensile strength of the film is insufficient also has poor corrosion resistance. Comparative Example No. whose resin type is not urethane resin and Tg is less than 100 ° C.
No. 18 has poor corrosion resistance. In Comparative Examples Nos. 20 and 21 in which the resin type was not an aqueous urethane resin, the corrosion resistance was poor.

Among the examples, Example No. 1 having an upper limit of the amount of coating film tends to have slightly poor weldability. Example No. 4 in which the coating amount is close to the lower limit is slightly inferior in corrosion resistance. Examples Nos. 29, 30 and 30 having a film on both sides are excellent in moldability. Example No19 without flash plating is slightly inferior in corrosion resistance and moldability. Ni, Cr, F
The zinc-based alloy plating containing at least one of e as an alloy component was particularly excellent in corrosion resistance. Regarding the weldability, when the amount of adhesion was the same, the alloyed hot-dip galvanized steel sheet was superior in weldability to other galvanized steel sheets (comparison between Examples Nos. 29 and 30 and Example No. 7). Example No. 3 in which the electrolytic chromate film is formed on the outer surface side is Example N3 in which the electrolytic chromate film is not formed on the outer surface side.
It has better moldability than o8.

[0035]

As described above, the organic coated steel sheet according to the present invention, in which a coating containing an aqueous urethane resin having a glass transition temperature of 100 to 150 ° C. as an essential component is formed on at least one surface of the plated steel sheet, has a high corrosion resistance to degraded gasoline. Excellent in formability and weldability. That is, it is suitable as a material for a fuel tank containing no Pb.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Kanai 1 Kimitsu, Kimitsu City, Chiba Prefecture Inside Kimitsu Works, Nippon Steel Corporation

Claims (5)

[Claims] 1. An organic coated steel sheet for a fuel tank, wherein a coating containing an aqueous urethane resin having a glass transition temperature of 100 to 150 ° C. as an essential component is formed on at least one surface of the plated steel sheet. 2. The aqueous urethane resin film has a tensile strength of 400.
^2. The organic-coated steel sheet according to claim 1, wherein the steel sheet has an elongation of 5% or more at a rate of 5 kg / cm ² or more. 3. The urethane resin has a bisphenol skeleton,
Ether having an ester skeleton and a carboxyl group
The organic coated steel sheet according to claim 1 or 2, wherein the organic coated steel sheet is an ester type urethane resin. 4. The organic coated steel sheet according to claim 1, wherein the coating contains polyethylene wax. 5. The method according to claim 1, wherein the plating layer is formed of at least one of Ni, Co, Cr, and Fe through a metal or metal oxide or metal hydroxide or a mixture thereof. The organic coated steel sheet according to any one of claims 1 to 4, which is a zinc-based alloy plating layer containing at least one of Fe as an alloy component.