JPH09170089A - Rust preventive steel sheet excellent in bare corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel sheet free from deterioration in corrosion resistance in the part in which the steel sheet is exposed in a bare state to corrosive environment in construction of automobile body, e.g. an uncoated part such as weld zone between a floor and members, and capable of improving the rust- preventing property of a car body. SOLUTION: This steel sheet has a rust-preventive film formed by applying a rust preventive oil, containing at least one kind selected from among perfluoroalkylcarboxylates, perfluoroalkyltrimethyl ammonium salts, and perfluoroalkylsulfonates, to the surface of a steel sheet, to which acid cleaning is previously applied as pretreatment, and then holding the steel sheet at 50-100 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anticorrosion steel plate having excellent corrosion resistance, which is used for inner and outer plates of automobiles, suspension structural members and the like.

[0002]

2. Description of the Related Art Conventionally, zinc-based plated steel sheets have been widely used as anticorrosion steel sheets in automobiles, home electric appliances and the like which are required to have corrosion resistance. As such a rustproof steel plate,
Electrogalvanized steel sheet, hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet, electrogalvanized iron alloy plated steel sheet, electrogalvanized nickel alloy plated steel sheet, oxide-dispersed zinc-based electroplated steel sheet (JP-A-60-125395, special feature) Examples include zinc-based plated steel sheets such as Kai 611-130498.

Further, it has been attempted to subject the zinc-based plated steel sheet to a chromate treatment and an organic thin film coating in order to impart more excellent corrosion resistance, and various types of rust-preventive steel sheets are known. As mentioned above, in the automobile industry, various rust preventive steel sheets are used to extend the rust preventive life of the car body, but since welding is often performed in the automobile manufacturing process, in order to improve the weldability of the rust preventive steel sheets. Although there is a demand to secure corrosion resistance by light weight coating, sufficient corrosion resistance is not always obtained, and there is an urgent need to develop a light weight high corrosion resistant rust-preventive steel sheet and a cold rolled steel sheet with improved corrosion resistance of the steel material itself.

On the other hand, in the welded joints such as the suspension member and the hem structure such as the hood and the door, there is inevitably a portion where there is no paint wraparound in the electrodeposition coating that is usually performed on automobile body materials. The steel sheet is exposed to the corrosive environment in a bare state. The corrosive environment of such a part is severe, and it becomes a perforated corrosion, which is an important problem for rust prevention of the vehicle body, but a rust preventive steel plate showing sufficient performance has not yet been obtained.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and in the structure of an automobile body, a portion where a steel sheet is exposed to a corrosive environment in a bare state, for example, a weld between a floor and members. We provide steel plates that can improve vehicle body rust prevention without deterioration of corrosion resistance at the joints, welded joints of inner and outer reinforcements, hood hem, door hem, etc. where paint does not adhere. The purpose is to do.

[0006]

The present invention provides a rust preventive oil containing at least one selected from perfluoroalkylcarboxylic acid salts, perfluoroalkyltrimethylammonium salts and perfluoroalkylsulfonic acid salts.
After applying to the surface of the steel sheet that has been subjected to acid cleaning as a pretreatment,
A rust-preventive steel sheet having excellent bare corrosion resistance, which is characterized by having a rust-preventive film formed by holding it at 50 to 100 ° C.

Further, in the present invention, it is preferable that the steel sheet is a cold rolled steel sheet.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
As a result of repeated intensive studies to solve the problems of the above-mentioned conventional techniques, the present inventors made a steel plate surface such as a cold-rolled steel plate into a surface active state by performing a pretreatment by acid cleaning, and then extremely. Achieving the intended purpose by applying anti-corrosion oil to which a specific perfluoroalkyl compound has been added among a wide variety of perfluoroalkyl compounds, and maintaining it in a heated state to form a hydrophobic adsorption monolayer It was done.

According to the present invention, by adding a specific perfluoroalkyl compound to the rust preventive oil applied in the final step of steel sheet production, the surface tension of the rust preventive oil is lowered and the additive (perfluoroalkyl compound) is added. Since the critical surface tension of the adsorbed monolayer is lower than that of the rust preventive oil, the adsorbed monolayer is formed on the surface of the steel sheet. Further, as a preliminary treatment, acid cleaning of a steel sheet such as a cold rolled steel sheet brings the surface of the steel sheet into an active state, so that the adhesive force of the adsorbed monomolecular film is improved.

Examples of the acid cleaning in the present invention include acid cleaning using a hydrochloric acid aqueous solution, a sulfuric acid aqueous solution, or a mixed acid aqueous solution. After coating, apply a drying oven etc. to 50
By keeping the temperature within the range of up to 100 ° C, the viscosity of the rust preventive oil is lowered, the perfluoroalkyl compound is easily transferred and adsorbed to the surface of the steel sheet, and a film having a strong adhesive force is formed in a short time.

The adsorbed monomolecular film formed on the surface of the steel sheet is hydrophobic and water repellent due to the action of the perfluoroalkyl group, so that the adsorption of water molecules which is a corrosion factor on the surface of the steel sheet is prevented and the corrosion resistance is improved. It becomes possible. Furthermore, in a perfluoroalkyl compound, a hydrogen atom of a carboxyl group is replaced with a metal such as an alkali metal, an ammonium group, an amine or the like, a terminal group having a halogen atom, a trimethylammonium group having a halogen atom, or a hydrogen atom of a sulfone group is treated with an alkali metal or an alkali. By introducing a functional group such as a metal such as an earth metal or the like, an ammonium group, or a terminal group substituted with an amine or the like, the adhesion of the adsorbed monomolecular film to the steel sheet is enhanced.

That is, according to the present invention,
As the perfluoroalkyl compound corresponding to and, perfluoroalkylcarboxylic acid salt, perfluoroalkyltrimethylammonium salt, perfluoroalkylsulfonic acid salt, or a mixture thereof is used. According to the present invention, since the perfluoroalkyl compound is a salt having a metal such as an alkali metal or an alkaline earth metal, an ammonium group, an amine, or a halogen atom, the dispersibility in rust preventive oil becomes good, and The rust-preventive film formed on the surface of the steel sheet after applying rust oil and holding it in a heated state becomes uniform, and an excellent rust-preventing effect is obtained.

As described above, according to the present invention, a rust preventive oil is used to prevent rusting in the process of steel plate production and before degreasing before coating, and the structure of an automobile body is free from spillage of paint after degreasing and painting. Thus, it becomes possible to extremely effectively improve the bare corrosion resistance of the portion where the steel sheet is to be used bare, by the film of the perfluoroalkyl compound having uniform and strong adhesion formed by the present invention.

The perfluoroalkylcarboxylic acid salt used in the present invention has a perfluoroalkyl group (C _n F _{2n + 1} ) at the terminal of the compound and a hydrogen atom of the carboxyl group such as a metal such as an alkali metal, an ammonium group, an amine and the like. It has a terminal group (COOM) substituted with. [Here, M represents a metal such as an alkali metal such as Na, K, or Li, an ammonium group, an amine, or the like. Examples of preferable perfluoroalkylcarboxylic acid salts include those shown in Table 1.

[0015]

[Table 1]

Perfluoroalkyl trimethyl ammonium
The um salt is the above-mentioned perfluoroamine at the end of the compound.
Alkyl group and trimethylammonium group [N
⁺(CH _Three)_ThreeX^-]. [Where X is B
Indicates a halogen such as r, I or Cl. ] Perfluoroalkyltrimethylammonium salt is preferred
As specific examples, those shown in Table 2 are exemplified.
You.

[0017]

[Table 2]

The perfluoroalkyl sulfonate is a terminal group obtained by substituting the hydrogen atom of the above-mentioned perfluoroalkyl group and sulfone group with a metal such as an alkali metal or an alkaline earth metal, an ammonium group or an amine at the terminal of the compound. (SO ₃ M). [Where M is N
Examples of the metal include alkali metals such as a, K and Li, metals such as alkaline earth metals such as Mg and Ca, ammonium groups and amines. ] As a preferable specific example of the perfluoroalkyl sulfonate, those shown in Table 3 are exemplified.

[0019]

[Table 3]

The number of n in the perfluoroalkyl group of the perfluoroalkylcarboxylic acid salt, perfluoroalkyltrimethylammonium salt and perfluoroalkylsulfonic acid salt used in the present invention is preferably an integer of 2 to 16, more preferably 6 to 6. An integer of 10 is preferred. Examples of the rust preventive oil used in the present invention include light, medium and heavy mineral oils such as petroleum base oils, or rust preventive oils obtained by adding various rust preventive additives to vegetable oils.

Examples of the various anticorrosive additives include carboxylic acids such as stearic acid and dimer acid, carboxylic acid salts such as metal soaps, sulfonic acid salts such as Na sulfonate and Ca sulfonate, ethyl stearate, sorbitan monooleate and the like. Carboxylic acid ester, monododecylamine,
Examples include, but are not limited to, primary to tertiary amines such as dioctadecylamine, phosphoric acid esters such as alkyl phosphates, and mixtures thereof.

The rust preventive oil preferably has a viscosity of 1 to 20 cst at a temperature of 40 ° C. For the amount of rust preventive oil applied, as the total amount of rust preventive oil and the perfluoroalkyl compound, per one side of the steel sheet, 0.
The range of 5 to 5.0 g / m ² is preferable. If it is less than 0.5 g / m ² , the rust preventive oil does not spread over the entire surface of the steel sheet, and the temporary rust preventive effect after the steel sheet is manufactured and before degreasing deteriorates. On the other hand, when it exceeds 5.0 g / m ² , the temporary rust preventive effect is not further improved and it is not economical.

The perfluoroalkyl compound is preferably added in an amount of 0.01 to 1.0 part by weight with respect to 100 parts by weight of the rust preventive oil. If the amount is less than 0.01 part by weight, the effect of lowering the surface tension is not observed and the corrosion resistance deteriorates. On the contrary,
If it exceeds 1.0 part by weight, the corrosion resistance is not further improved and it is not economical. Further, in the present invention, the amount of the perfluoroalkyl compound attached to the steel sheet surface during rust preventive oil application is preferably 0.1 mg / m ^{2 to} 0.04 g / m ² , and more preferably 0.003 to 0.02 g / m ² . It is preferably in the range.

If it is less than 0.1 mg / m ² , corrosion resistance deteriorates, and conversely
If it exceeds 0.04 g / m ² , corrosion resistance is not further improved and it is not economical. The adsorbed monomolecular film of the perfluoroalkyl compound obtained in the present invention does not deteriorate the weldability because it has a film thickness of about several tens of liters. In the present invention, in order to impart surface lubricity during press molding, waxes such as graphite, natural wax, polyolefin wax, fluorocarbons exemplified by polytetrafluoroethylene wax are appropriately added to rust preventive oil in combination. It is possible.

The method for applying the above-mentioned rust preventive oil containing a perfluoroalkyl compound to a steel sheet is a spray method, a dipping method,
Any method such as a roll coater method and a curtain flow coater method can be used. The steel plate after applying the perfluoroalkyl compound-containing rust preventive oil has a temperature of 50 to 100 ° C, and more preferably 80
It is preferable to maintain at -100 ° C. If less than 50 ° C,
It takes time to form a film with strong adhesion, and if the temperature exceeds 100 ° C, the rust preventive oil will be oxidized or decomposed.

When the rust-preventing steel sheet according to the present invention is used, the corrosion resistance is greatly improved in the conventional structure where the steel sheet is used bare.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. Example 1 A cold rolled steel plate (SPCD) having a plate thickness of 0.8 mm was degreased and then washed with a 5% hydrochloric acid solution for 20 seconds. After applying rust preventive oil of the following composition to the obtained steel plate, heat treatment was performed for 30 seconds at the temperature shown in Table 4 using a drying furnace, and the amount of rust preventive oil applied per one side of the steel plate was 0.3 to 8.0 g / m 2. A treated steel sheet of No. ² was obtained (Invention Example 1)
~ 5, Comparative Examples 1 to 3).

Further, treated steel sheets were prepared by carrying out the same treatments as described above except that the rust preventive oil coating, the acid cleaning treatment or the heating and holding after the rust preventive oil coating was not carried out (Comparative Examples 4 to 7). [Rust preventive oil composition] Rust preventive oil: Oil coat Z5 [; trade name, Idemitsu Kosan Co., Ltd.
Co., Ltd.] 100 parts by weight Perfluoroalkyl compound: Perfluoroalkylcarboxylic acid salt [manufactured by Mitsubishi Materials Corp., trade name F-top EF-700] 0.001 to 0.6 parts by weight Next, for the obtained treated steel sheet, the following The performance test shown in FIG. The test results are also shown in Table 4.

[Performance test method] (1) Test piece shape: treated steel sheet A: width 70 mm, length 150 mm
And B: Cut into two sizes of width 50mm and length 100mm,
These were overlapped and spot-welded to produce a test piece (hereinafter referred to as a test piece for a laminated material).

(2) Corrosion resistance evaluation method: A test piece for a composite material was subjected to a normal zinc phosphate chemical conversion treatment (including a washing step with an alkaline aqueous solution), and then cationic electrodeposition coating [manufactured by Nippon Paint Co., Ltd., U-600; 20 μm], intermediate coating [Kansai Paint Co., Ltd., KPX-36; 30 μm], top coating [Kansai Paint Co., Ltd., B531; 30 μm]. A cycle corrosion test was performed under the conditions to evaluate the corrosion resistance of the joint part.

Cycle corrosion test conditions: 5% NaCl solution sprayed at 35 ° C. for 3 hours → dried at 60 ° C. for 2 hours → left at 50 ° C., 95% RH (wet) atmosphere for 3 hours →
After 100 cycles, the test piece for the composite material was removed and the corrosion depth inside the composite material was evaluated according to the following criteria. The corrosion depth was measured with a micrometer after removing rust with an iron brush and citric acid.

[0032]

[0033]

[Table 4]

Example 2 The same as Example 1 except that the perfluoroalkyl compounds added to the rust preventive oil were the compounds shown in Table 5 and the rust preventive oil coating amount and the perfluoroalkyl compound addition amount were the following amounts. A treated steel sheet was produced by using the same, and the obtained treated steel sheet was evaluated for corrosion resistance in the same manner as in Example 1. The test results are also shown in Table 5.

Amount of anti-rust oil applied (anti-rust oil + perfluorocarbon compound): 1 g / m ² Anti-rust oil: 100 parts by weight Perfluoroalkyl compound addition amount: 0.1 parts by weight

[0036]

[Table 5]

[0037]

EFFECTS OF THE INVENTION When conventional cold-rolled steel sheets and various anticorrosion steel sheets are used, the corrosion resistance of the anticorrosion steel sheet according to the present invention is improved in a portion where the steel sheet is used naked and the corrosion resistance deteriorates due to the structure of an automobile body. Is possible.

Claims (1)

[Claims] 1. A rust preventive oil containing at least one selected from a perfluoroalkylcarboxylic acid salt, a perfluoroalkyltrimethylammonium salt and a perfluoroalkylsulfonic acid salt is applied to a steel sheet surface which has been subjected to acid cleaning as a pretreatment. A rust-preventing steel plate with excellent bare corrosion resistance, which has a rust-preventing film formed by holding it at 50 to 100 ° C later.