JPS6399938A - High corrosion-resistant surface-treated steel plate - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a highly corrosion-resistant surface-treated steel sheet suitable for use in automobile bodies and the like.

[Conventional technology]

In recent years, steel plates used for automobile bodies are required to have excellent corrosion resistance, and instead of the conventionally used cold-rolled steel plates,
There is a growing trend to use surface-treated steel sheets with high corrosion resistance.

The first example of such surface-treated steel sheets is galvanized steel sheets, but with this type of steel sheet it is necessary to increase the amount of zinc deposited in order to improve corrosion resistance.
There is a problem that workability and weldability deteriorate with ζ.

To improve such problems, Ni, Fe, Mn
One or two elements such as %MO1co, kt, Cr, etc.
Research and development has been carried out on zinc alloy-plated steel sheets and multilayer-plated steel sheets with the addition of at least a certain amount of zinc, and these steel sheets can improve corrosion resistance without deteriorating weldability and workability compared to the above-mentioned galvanized steel sheets. However, when steel plates are applied to the bag structure and bent parts (hemming parts) of automobile body panels, the surfaces must have a high degree of corrosion resistance, so zinc alloy plated steel plates and multilayered steel plates such as those mentioned above are required. A problem with plated steel sheets is that their corrosion resistance is still insufficient. As a steel plate with a high degree of corrosion resistance,
Rust-preventive coated steel sheets with zinc-rich coatings, such as those seen in No. 24230 and Japanese Patent Publication No. 47-6882, have been researched and developed, and the representative one is known under the name of Synchrometal. However, even with this anti-corrosion coated steel sheet, the coating may peel off in the processed parts such as press forming, and the corrosion resistance may deteriorate. is still far from being fully satisfactory.

For these reasons, the present inventors have developed a thin film (approximately several microns or less) that does not use metal powder such as Zn powder at all, from the viewpoint that there is a limit to the performance improvement of anti-corrosion coated steel sheets with zinc-rich coating films. We have newly developed a steel plate with a lumbar coating of 1988-224174, 60-50179, 60-50180 and 60-5018.
It was proposed as No. 1. This steel sheet is based on a zinc or zinc alloy plated steel sheet, and is coated with a chromate film and an organic composite silicate film as the top layer, and has excellent workability and corrosion resistance.

Furthermore, in some parts of the inner surface of the automobile body (trunk lid, hood, etc.), a top coat is applied to the film during cationic electrodeposition.
There are cases where more than one coat of paint is applied, and there are concerns about the adhesion of the steel sheet proposed above with such a multilayer Ik film, so we improved the steel sheet and improved the adhesion of the multilayer Ik film. Unexamined Japanese Patent Publication No. 60-1 on the manufacturing method of excellent anti-corrosion steel plate for multi-layer coating
It was proposed as No. 74879.

This invention sufficiently crosslinks the organic polymer film by baking at a high temperature of 250 to 350°C to ensure excellent paint adhesion for multi-layer coating.If the polymer film is insufficiently crosslinked, This problem is solved by crosslinking by high-temperature baking, which causes the film to swell softly due to the alkali generated at the interface during cationic electrodeposition and deteriorates paint adhesion.

[Problems that the invention attempts to resolve]

However, as a result of subsequent research by the present inventors, the above-mentioned steel plate can ensure extremely excellent paint adhesion (multilayer paint adhesion of two or more coats) by baking at a high temperature of 250° C. or higher.

If there is a problem with so-called bare corrosion resistance (no-paint corrosion resistance), which is assumed to be difficult to form an electrodeposition coating, and the surface treatment film is damaged, for example, cross-cuts that reach the iron substrate, etc.
Deep drawing molding.

It has been found that when subjected to drawbead processing, etc., the bare corrosion resistance tends to be slightly inferior to that of the steel sheets disclosed in JP-A-58-224174 and the like mentioned above.

Highly corrosion-resistant surface-treated steel sheets for automobiles have excellent workability and weldability.

1) Corrosion resistance in areas where a one-coat coating is difficult to form, such as the bag structure and hemming areas, that is, a high degree of bare corrosion resistance.

2) Paintability for multi-layer coating of 2 coats or more (cationic electrodeposition + top coat) such as trunk lids and hood inner surfaces (
paint adhesion, paint corrosion resistance).

In recent years, there has been a growing demand for anti-corrosion properties for automobile bodies, and the above-mentioned steel sheets cannot be said to have sufficient properties.

The present invention was made in view of such conventional problems,
The object of the present invention is to provide a highly corrosion-resistant surface-treated steel sheet that has not only workability and weldability but also excellent bare corrosion resistance, paint adhesion to two-coat paint, and paint corrosion resistance.

[Means to solve the problem]

Therefore, the basic feature of the present invention is to have a chromate film on the surface of a galvanized or zinc alloy plated steel sheet, and on the top of the chromate film, at least one basic nitrogen atom is attached to the end of the epoxy resin. and at least 2
The base resin is made by adding 1 or more primary hydroxyl groups,
One or two of silica and aluminum phosphomolybdate are blended, and the weight ratio of base resin:additive is 99:1.
The present invention has a coating structure having a resin composition coating with a coating temperature of 0 to 30 nia.

Another basic feature of the present invention is that the surface of the galvanized or zinc alloy plated steel sheet has a chromate film, and on the top of the chromate film, at least one basic nitrogen atom is added to the end of the epoxy resin. atoms and at least two
The base resin is made by adding 1 or more primary hydroxyl groups,
An additive consisting of one or two of silica and aluminum phosphomolybdate and a poorly soluble CR compound are blended,
And the weight ratio of base resin:additive is 99:1 to 30:
70, base resin: weight ratio of poorly soluble Cr compound is 99=1
The present invention has a film structure having a resin composition skin PA of ~60:40.

The present invention will be explained in detail below.

The present invention uses a zinc-plated or zinc-alloy plated steel sheet as a starting material, and has a chromate film on its surface and a basic epoxy resin film containing predetermined additives on top of the chromate film.

The starting materials, zinc-coated steel sheets, include galvanized steel sheets, zinc-iron alloy-plated steel sheets, zinc-nickel alloy-plated steel sheets, zinc-manganese alloy-plated steel sheets, zinc-aluminum alloy-plated steel sheets, and zinc-cobalt-chromium alloy-plated steel sheets. , Furthermore, Nl is added to the plating components of these arbitrary steel sheets.
, Fe, Mn%MO% 00% ALs Cr, etc. can be added to one or more elements, and furthermore, a composite in which two or more of the same or different types of plating as described above are applied. May be plated steel plate0
For example, the plated film may be formed by applying two or more layers of F.-Zn alloy plating with different Fe contents.

Among these, zinc-nickel alloy plated steel sheets and zinc-manganese alloy plated steel sheets are particularly preferred from the viewpoint of corrosion resistance. When these steel sheets are used, the zinc-nickel alloy plated steel sheets have a nickel content in the plating film of 5 to 5. The zinc-manganese alloy plated steel sheet preferably has a manganese content in the range of 30 to 85 wt%.

As a plating method for these zinc-based plated steel sheets, any practicable method among the electric folding method, melting method, vapor phase method, etc. can be adopted. However, the rust-proof steel sheets that are the object of the present invention are mainly used for automobile bodies.

In such applications, it is important not to damage the material of the cold-rolled steel sheet to be plated, so electroplating, which does not generate heat, is advantageous.

A chromate film is formed on the surface of the above material plated steel sheet by chromate treatment.

This chromate film has a chromium deposition amount (dry) of 1 to 100 Q'97m2. Preferably 10-2o.

'97 m'', more preferably about 30 to 8 oq/mW (the above is calculated as metal chromium).

When the amount of chromium deposited exceeds 200 q/m", workability and weldability tend to deteriorate, and this tendency
It becomes especially noticeable when it exceeds /-. Furthermore, if the amount of chromium deposited is less than 10"P/-", the coating may become non-uniform and the corrosion resistance may be deteriorated, and such deterioration of corrosion resistance is particularly significant when the amount is less than 1lIIP/-. Also, it is preferable that hexavalent Cr exists in the chromate film, C? + has a repair effect and works to suppress corrosion if the steel plate is scratched.

The chromate treatment for such a base film may be performed by any known method such as reaction type, coating type, electrolytic type, etc.

The main component of the coating type chromate treatment solution is a partially reduced chromic acid solution, and if necessary, water is added to this solution. - [Group or organic resin such as water-soluble acrylic resin and/or particle size of several meters]
It contains silica (colloidal silica, fumed silica) of μ to several hundred μm. In this case Cr:q
/+ ratio is 1:1 to 1:3, pH is 1.5 to 4.0 (
2 to 3) are more preferred.

The ratio of Cr3+:Cr' is adjusted to a predetermined ratio using a general organic reducing agent (eg, sugar, alcohol, etc.) or an inorganic reducing agent. Further, as the coating type chromate treatment, any method such as a roll coater method, a dipping method, a spray method, etc. may be used. In the coating type chromate treatment, a film is obtained by drying without washing with water after the chromate treatment. The reason for drying without washing with water is that Cr6+ is removed by normal washing with water, and Cr, Cr
The basic epoxy resin film formed on the top allows cP to remain stable in corrosive environments.
It is possible to suppress excessive outflow of , effectively maintain the passivation effect over a long period of time, and obtain high corrosion resistance.

On the other hand, in electrolytic chromate treatment, cathodic electrolysis treatment is performed in a bath containing chromic anhydride and one or more of anions such as sulfuric acid, phosphoric acid fluoride, or halogen oxygen acid, followed by washing and drying to form a film. Comparing the chromate films produced by one or more two treatment methods that form When heat treated as described below, the film becomes dense and strong, resulting in better corrosion resistance than electrolytic chromate. On the other hand, electrolytic Chromate Co., Ltd. has the advantage that the film is highly complete regardless of the presence or absence of heat treatment.
It has the advantage of being easy to control the amount of film deposited.

In consideration of corrosion resistance, coated chromate is the most desirable.

Further, rust-preventing steel sheets for automobiles are often single-sided treated steel sheets, and from this point of view, coating type and electrolytic type are preferable.

A basic epoxy resin film is formed on the chromate film.

This resin lacrimal is made by adding at least one basic nitrogen atom and at least two or more primary hydroxyl groups to the end of an epoxy resin, and adding it to a base resin dissolved in an organic solvent.
This film is formed by drying a resin composition treatment solution containing one or two of silica and aluminum phosphomolybdate as additives and, if necessary, a poorly soluble Cr compound.

Preferably, the epoxy resin is mainly composed of a condensate obtained by condensing bisphenol A and shrimp chlorohydrin. Epoxy resins include epoxidized oil,
Epoxy resins such as polybutadiene that consist only of aliphatic structures or alicyclic structures are available.In order to obtain excellent corrosion resistance, it is preferable to use epoxy resins mainly composed of the above condensates. For example, Epicoat 828°1001.1004.100? , 1009
．． 1010 (both manufactured by Shell Chemical Co., Ltd.), etc. can be used. This epoxy resin desirably has a number average molecular weight of 1500 or more, especially when curing at low temperatures is required. Incidentally, the above Epicoat can be used alone or in a mixture of different types. In order to introduce a basic nitrogen atom and a primary hydroxyl group into an epoxy resin, for example, a method can be adopted in which an alkanolamine and/or an alkylalkanolamine is added to an oxirane group of the epoxy resin. Examples of these amines include monoethanolamine and jetanolamine.

dimethylaminoethanol, monopropanolamine,
Dibrobanolamine, jetanolamine, etc. are used, and these amines are used alone or in combination.

Alternatively, the epoxy resin may be partially modified with other compounds. However, in this case, it is necessary to contain an average of 2 moles or more of primary hydroxyl groups in one molecule of the epoxy resin.

Methods for partial modification of epoxy resins include: (1) Esterification with monocarboxylic acids (monocarboxylic acids include, for example, coconut oil fatty acids).

Saturated or unsaturated fatty acids such as soybean oil fatty acids and castor oil fatty acids, low molecular weight aliphatic monocarboxylic acids such as acetic acid, propionic acid, butyric acid.

(2) Modification with aliphatic or aromatic amines (aliphatic or aromatic amines include aliphatic amines such as monomethylamine, dimethylamine, monoethylamine, diethylamine, and isopropylamine) , aromatic amines such as aniline, etc.) (3) Modification with oxyacids (oxyacids include lactic acid, r-oxypropionic acid, etc.).

Note that dicarboxylic acids (e.g. adipic acid).

There is also a modification method using cepatic acid, etc.), but this method
It is difficult to obtain the film of the present invention due to the following reasons: the molecular weight of the epoxy resin is too high than necessary, it is difficult to control the molecular weight distribution at a constant level in terms of reaction control, and no improvement in corrosion resistance is observed. is an inappropriate method.

The epoxy resin that is the base resin of the film-forming composition is
Although it is possible to neutralize the base with a low molecular acid and use it as a water dispersion or water-soluble composition, the present invention
Since it requires low-temperature drying of 0°C or lower, especially extremely low-temperature drying of 170°C or lower, H@@ skin and abdominal membrane materials are targeted for this purpose.For this reason, the base resin must be neutralized as described above. First, it is used as a composition dissolved in an organic solvent.

That is, when using water-dispersed or water-soluble compositions, it is not possible to obtain a sufficiently strong film under low-temperature drying conditions, and salts are formed in the film with acidic compounds required for water solubilization.
@Easy to draw moisture into and under the film in a humid environment.
As the organic solvent type, 11s of organic solvents commonly used in the paint industry or a mixed solvent of two or more types can be used, but for this purpose, it is preferable to avoid high boiling point alcoholic solvents.

These include, for example, ethylene glycol or diethylene glycol, monoalkyl ethers, and alcohols having more than one primary hydroxyl group. Such solvents inhibit the curing reaction of the film. Recommended solvents include hydrogenated, ketone, ester, and ether solvents, and alcohols with a low molecular weight of C or less, or alcohols having secondary or tertiary hydroxyl groups are also suitable.

In the present invention, the following points can be mentioned as aims of providing the resin composition film as described above. In other words, in order to obtain a high degree of corrosion resistance and multilayer stoichiometric adhesion of two or more coats, we adopted an epoxy resin as the base and expected to obtain high adhesion and corrosion resistance with the substrate and cationic electrodeposition. ,
In addition, (1) By making the resin basic in polarity, deterioration of the resin structure due to alkali generated at the interface during cationic electrodeposition is eliminated. To explain this in detail,
First, by using an epoxy resin made from a condensation reaction of bisphenol A and shrimp chlorohydrin as the base resin, excellent adhesion with cationic electrodeposition paints commonly used for rust prevention of automobile bodies can be expected. In addition, by introducing basic nitrogen atoms and primary hydroxyl groups into the resin structure, (1) the film is prevented from being destroyed by the alkali generated during cationic electrodeposition, and the adhesion with the base chromate and cationic electrodeposited am is stabilized; , (2) Furthermore, by introducing 2 or more moles of hydroxyl groups into one epoxy molecule, a film with a sufficiently dense structure can be obtained. If the amount is less than 2 moles, a sufficiently stable film cannot be obtained.

In addition, as an additive, a monohydric alcohol having 1 to 5 carbon atoms is reacted with part or all of a methylol compound obtained by reacting formaldehyde with one or more selected from isocyanate compounds, melamine, urea, and benzoguanamine. An alkyl etherified amine resin or the like may be used in combination.

In the present invention, corrosion resistance is obtained by containing one or more of silica and aluminum phosphomolybdate as additives in the resin composition film. The additive has a base resin:additive weight ratio of 99:1 to 30:70.
, preferably in the range of 90:10 to 50:50.

Here, the blending amount of the above additive is base resin:additive=99
If the ratio is less than 1, no improvement in corrosion resistance can be expected due to the combination, while if the ratio exceeds 30:70, the adhesion of the two coats will deteriorate.

The mechanism by which silica improves corrosion resistance is not necessarily clear, but Zn'' and silica eluted in a corrosive environment react with each other, producing stable corrosion products and inhibiting pitting corrosion. It is estimated that the effect of improving corrosion resistance can be obtained.

Furthermore, the details of the anticorrosion effect of aluminum phosphomolybdate are not necessarily clear, but in a corrosive environment, a small amount of phosphoric acid is eluted from aluminum phosphomolybdate.
It is thought that it reacts with zinc ions to form insoluble phosphates, and as a result, the progress of corrosion is suppressed.

Hydrophobic silica, hydrophilic silica, and aluminum phosphomolybdate have the best anticorrosion effect as additives. The reason for this is not clear, but it is because the compatibility with the basic epoxy resin, which is the base resin of the present invention, during film formation is good, resulting in the formation of a uniform and strong film. It is estimated that

As described above, by blending appropriately selected additive components, that is, silica and aluminum phosphomolybdate or 2fi, into the resin composition, excellent corrosion resistance and excellent paintability for multilayer coating can be obtained. Can be done.

The present invention further provides the above-mentioned silica and/or in the resin composition film.
In addition to aluminum phosphomolybdate, nu contains sparingly soluble Cr.
A compound can be contained, thereby further improving anticorrosion properties. In a corrosive environment, a small amount of soluble Cr compound (Cr) in the film is eluted, and this exerts a passivation effect over a long period of time, improving corrosion resistance. The poorly soluble Cr compound has a base tree a' and a poorly soluble Cr compound.
The weight ratio of the r compound is 99:1 to 60:40, preferably 95:5 to 75:25. The blending amount of the poorly soluble Cr compound is base resin: poorly soluble Cr compound 29
If the ratio is less than 921, no improvement in corrosion resistance can be expected from the combination, while if the ratio exceeds 60:40, the adhesion and corrosion resistance of a large amount of MA of 2 or more parts will be affected due to the water absorption effect of the poorly soluble Cr compound. will decrease.

Here, the anticorrosion effect is most improved when silica and a sparingly soluble Cr compound are added together in a predetermined ratio in the above composition.

As mentioned above, when Zn or the like is eluted from the base plating, silica is presumed to react with the Zn, form stable corrosion products over the entire surface of the sample, and exhibit a corrosion-preventing effect. - The slightly soluble Cr compound elutes a trace amount of Cr and exerts an anticorrosive effect by passivating this Cr'+.

This is particularly effective in corrosive environments such as SST where dissolution progresses continuously.

When a poorly soluble Cr compound is incorporated into a resin film as an anti-corrosion additive, it can be used as an O
In accelerated corrosion tests, such as CT, in which wet and dry conditions are alternately repeated, no significant corrosion protection effect can be expected.

In fact, using silica as a rust preventive additive is more effective in such tests.

However, if the product has been subjected to strong processing or has undergone an accelerated test with extremely strong cuts.

If only silica is included in the resin as a rust-preventing additive, the effect of repairing damaged areas is insufficient.

The present inventors have discovered that by incorporating silica and a sparsely soluble Cr compound, which have different anti-corrosion mechanisms, into a resin in a specific ratio, excellent corrosion resistance can be obtained through the synergistic effect of their respective anti-corrosion effects.

Next, the corrosion resistance (Example (3) The results of the cycle test [100 cycles of strong cutting] described in Section 2 are shown below. In this test, electrolytic zinc-nickel alloy plating (12% Ni-Zn) with single-sided adhesion ji[2Of/rn'' was used as the test material.The chromate treatment was performed under the coating-type chromate treatment conditions described in the examples below. The amount of adhesion was 50q7m'' in terms of Cr on one side, and the coating was applied using a roll coater and dried. Further, as the base resin, a solvent-type cationic epoxy resin (resin listed in Table 3, Nat) was used. The silica was fumed silica R811, manufactured by Nippon Aerosil, and the 11-soluble Cr compound used was BaCrO4 manufactured by Kikuchi Shikoku.

In Figure 1, the weight ratio of silica:releasable Cr compound is 37:
Corrosion resistance test in which the weight ratio of base resin and [silica + LA-soluble Cr compound] was kept constant at 3 and varied from 100:0 to O:100 by weight ratio of base resin: (silica + sparingly soluble Cr compound). Figure 2 shows the results when the weight ratio of silica:releasable Cr compound was 30:
Corrosion resistance test where the weight ratio of base resin and [silica + poorly soluble Cr compound] was kept constant at 10 and the weight ratio of base resin = (silica + poorly soluble Cr compound) was varied from 100:0 to 0:100. The results are shown below.

Figure 3 shows a weight ratio of silica:S-soluble cr compound of 20:
20, and the blending ratio of the base resin and [silica-S* Cr compound] is Zo, where the weight ratio of base resin = (silica + sparingly soluble Cr compound).

Figure 4 shows the results of a corrosion resistance test conducted with varying the ratio from 0 to 100 O:0. The results of corrosion resistance tests conducted while varying the weight ratio of the compounds from 40:0 to O:40 are shown.

Figure 5 shows that the weight ratio of the base resin (silica + poorly soluble Cr compound) was kept constant at 60:40, and the weight ratio of silica: poorly soluble Cr compound was varied from 4020 to 0:40. The results of the corrosion resistance test are shown.

Figure 6 shows that the weight ratio of base resin = (silica + poorly soluble Cr compound) is constant at 50:50, and silica, poorly soluble Cr compound
The results of corrosion resistance tests conducted while varying the weight ratio of the compounds from 4020 to 0:40 are shown.

As is clear from FIGS. 1 to 6, excellent corrosion resistance can be obtained by controlling each component within a specific region. That is, the optimal region of each component is as follows.

■Base resin: weight ratio of (silica + poorly soluble Cr compound)→
75: 25 to 50:50 Preferably 7G: 30 to 55:45 ■ Weight ratio of silica to sparingly soluble Cr compound → 37: 3 to 20:20 Preferably 35:5 to 25:15 Weight ratio of silica to sparingly soluble Cr compound If the weight ratio of base resin: (silica + poorly soluble Cr compound) is less than 75:25, the corrosion resistance will not be sufficient (if it is 70:30 or more, a film with the best corrosion resistance can be obtained.On the other hand, Even if the blending ratio of the above additive exceeds 50:50, corrosion resistance problems will occur;
5 or less shows good corrosion resistance, therefore the base resin: (
The optimal weight ratio of silica + poorly soluble Cr compound is 75:25.
~50:50, preferably less than 37:3, there is a problem that the repair effect of Cra+ is not sufficient and the corrosion resistance is insufficient, and when it is 35:5 or more, a skin M with the best corrosion resistance is obtained. be able to.

On the other hand, if the weight ratio of silica is less than 20:20, the formation of stable corrosion products by silica and Zn" will be insufficient, resulting in a disadvantage in terms of corrosion resistance. Therefore, the silica contained in the resin : The optimum weight ratio of poorly soluble Cr compound is 37:3 to 20:20, preferably 35:5 to 2.
It will be 5:15.

The silica used in the present invention includes hydrophilic silica and hydrophobic silica, which are called colloidal silica and fumed silica. Among these silicas, water-dispersible silica can also be expected to improve corrosion resistance, but as will be described later, hydrophobic silica significantly improves corrosion resistance. The suitable particle size of silica is 1 mμ to 50 omp, especially 5 mp-
100 mμ is preferable. Hydrophilic silica known as colloidal silica (silica gel) or fumed silica has a surface containing hydroxyl fi (silanol group)
-OH) and exhibits hydrophilicity.

Since this silanol group is highly reactive, it easily reacts with various organic compounds (and can make the silica surface organic).

Hydrophobic silica is obtained by subjecting some or most of the silanol groups on the surface of such water-dispersible silica to a substitution reaction with methyl groups, alkyl groups, etc. to make the silica surface hydrophobic.

There are many different methods for producing hydrophobic silica, and typical examples include reactions with organic solvents such as alcohols, ketones, and esters, silanes, silazane, and polysiloxanes. Examples include a reaction pressurization method in an organic solvent and a catalyst heating method.

Silica has an excellent anticorrosion effect, and hydrophobic silica is particularly effective in improving corrosion resistance. For example, in the above-mentioned JP-A-58-22T174, it is disclosed that hydrophilic colloidal silica is added to an organic resin. However, due to its strong hydrophilicity, hydrophilic silica has poor compatibility with solvents, and due to its strong hydrophilicity, it easily invites water penetration, which causes a decrease in corrosion resistance. It is estimated that it is likely to cause initial rust.

Therefore, when manufacturing the steel sheet of the present invention, it is preferable to blend silica with a hydrophobic surface (hydrophobic silica) into the basic resin to increase the compatibility with the basic epoxy resin and obtain high corrosion resistance.

Examples of such hydrophobic silica include ■ methyl alcohol, ethyl alcohol, n-propyl alcohol,
Organic solvent-dispersed colloidal silica dispersed in a solvent such as isopropyl alcohol, n-butyl alcohol, ethyl cellosolve, or ethylene glycol (for example, 08CAL 1132.1232.1332 manufactured by Catalysts Kasei Kogyo Co., Ltd.)
1432. 1332, 1622, 1722°172
4 etc.), silica whose surface has been made hydrophobic with an organic solvent or a reactive silane compound, i.e. hydrophobic ultrafine particle silica (
For example, 1 Nippon Aerosil Co., Ltd. R974, R811, R8
12, R805, T2Ori, R202, RY200.
RX200, etc.).

The hydrophobic silica described above is stably dispersed in the basic epoxy resin. Examples of poorly soluble Cr compounds include barium chromate (BaCr04), strontium chromate (
5rCrO+) - Lead chromate (PbCr0+) - Zinc chromate (ZnCrO4.4 Zn (OH%), Calcium chromate (CaCr No. 0), Zinc potassium chromate (Kgo4Zn0.4 cros-aHto),
Each powder of silver chromate (AgCr04) can be used.

One or more of these are dispersed in the base resin.

Chromium compounds other than these may have poor compatibility with the base resin, or may have an anticorrosion effect but are soluble Cr.
Since it contains a large amount of , it has problems such as poor adhesion of two coats of paint, and is not suitable for the purpose of the present invention.

However, in terms of corrosion resistance when subjected to strong processing (for example, drawbead test) or when cut (approximately 1 ■ It @), BaCrO4,5rCrO
It is preferable to use +.

In addition, when the surface-treated steel sheets obtained by the present invention are actually used by consumers, they are often painted, and when they are installed in parallel at automobile manufacturers, etc., they are degreased, surface conditioned, and treated with phosphate. Pre-treatments such as the following are performed as necessary. Since the surface-treated steel sheet obtained according to the present invention contains soluble Cr in the base chromate film and resin film, a small amount of Cr is eluted in the pre-painting process. When wastewater generated in each of these pretreatment steps is released into the environment, the Cr concentration in the wastewater is limited by environmental standards, and therefore automobile manufacturers and the like treat the wastewater. However, there is a limit to the capacity of wastewater saturation facility 1, and the leached C
It is preferable to have less rfk.

Of the poorly soluble chromium compounds blended into the base resin, Ba
CrO4 has a lower Cr elution property than other chromium compounds in the pretreatment process, and therefore, from the viewpoint of such Cr11 release property, it is preferable to use BaCrO4.

In addition, in the corrosion resistance test conducted to limit the weight ratio of base resin: (silica + sparingly soluble Cr compound) and the weight ratio of silica: pyramidal soluble Cr compound, hydrophobic fumed silica R811 manufactured by Nippon Aerosil was used. , the weight ratio of base resin: (silica + Cr compound) is 75:25 to 50:50
And the weight ratio of silica:ll-soluble Cr compound is 37=
3 to 20:20, similar results were obtained even when other hydrophobic silicas mentioned above were used.

In addition, although BaCr0a was used as the poorly soluble Cr compound, other compounds 1 such as 5rCrO+, AgCrO
4.

PbCrO4, CaCrO4, K104Zn0・4Cr
03.3H10, Zrcr04.4Zn(01)! Even when used alone or in combination of two or more types, the weight ratio of base resin: (silica + hardly soluble @ Cr compound) is 75:25 to 50.
:50 and the weight ratio of silica:Cr compound is 37:3~
Similar results were obtained at 20:20.

Note that the present invention uses the above-mentioned additive components silica and poorly soluble Cr.
In addition to the compounds, other known additives (for example, surfactants, etc.), anti-rust pigments, such as chromium-based, non-chromium-based anti-rust pigments, and extender pigments.

Coloring pigments etc. can be blended.

The resin composition film as described above is coated on the chromate film.
．． 2~3.997m", preferably 0.5~15?/
It is desirable to form the film with a coating weight of -0.2f/-.If the film coating weight is less than 0.2f/-, sufficient corrosion resistance cannot be obtained;
On the other hand, if it exceeds 3.9 f/-, the weldability (continuous multi-point weldability to I!#) will deteriorate;
/Fll'' is particularly suitable as a highly corrosion-resistant surface-treated steel sheet for automobiles.

The above resin composition is applied to a predetermined thickness by a method such as roll drawing, roll coater 1 or air knife, and then
If hot air drying is carried out to a board temperature of room temperature to 250°C (preferably room temperature to 170°C), a dry film can be obtained within several seconds to several minutes.

The method for drying the film is not particularly limited to hot air.

The steel sheet of the present invention has the great feature that it can be obtained by such low-temperature drying.

When baking at a high temperature exceeding 250℃,
Similar to No. 0-174879, the corrosion resistance deteriorates. This is due to the volatilization of moisture that forms in the chromate film components and the formation of hydroxyl groups (-Cr-OH) during high-temperature baking over 250°C.
Due to the rapid progress of the dehydration condensation reaction between the two, the destruction of the chromate film due to the occurrence of cracks in the chromate film progresses, and the reduction of Cr progresses, reducing the passivation effect of Cr. Presumed.

Furthermore, although cationic X-coated paint is applied to automobile bodies,
The wet electrical resistance of the chromate coating resin composition coating is 20
0Kn/rrr? If the resistance exceeds 200Kn/at?, there is a problem that the cationic electrodeposited film cannot be formed efficiently.For this reason, in the steel sheet of the present invention, which is mainly used for automobile bodies, the wet resistance of the chromate film and the resin composition film is set to 200 Kn/at? It is preferable to form both films so as to suppress the amount below.

The present invention has the above-described film structure +→iL! l
] Contains a steel plate on one side or one side.

Examples of the embodiments of the steel sheet of the present invention include the following.

(1) One side...Plated film - Chromate film - Resin composition film One side... Fe side (2) One side... Plated film - Chromate film - Resin composition film One side... Plated film ( 3) Both sides: Plating film - Chromate film - Resin composition film The highly corrosion resistant surface-treated steel sheet of the present invention can be used not only for automobiles but also for home appliances, building materials, etc.

〔Example〕

Example 16 Adhesion tests and corrosion resistance tests were conducted on the materials of the present invention having different plating components and coating amounts as shown in Table 1 as Q plates suitable for the inner surface of automobile bodies. Similar tests were also conducted on each steel plate shown in Table 2 as comparative materials.

The plating components of each steel plate are as follows. For each steel plate in the table with a chromate film and a basic epoxy resin film, the plated steel plate is degreased with alkaline, washed with water, dried, and then coated with a coating-type chromate treatment solution. An electrolytic chromate film was formed by coating with a roll coater or by dipping in an electrolytic chromate treatment bath, and after drying, a basic epoxy resin liquid was applied as a second layer with a roll coater. After further drying, it was heat-treated and air-cooled.

Ni-Zn alloy electroplating...Ni content 12chiFe-Zn alloy electroplating...Fe content f 25
4Mn-Zn alloy electroplating...Mn content 6
The details of the coating type chromate treatment, electrolytic chromate treatment, and basic epoxy resin liquid are as follows.

・Coating type chromate treatment conditions Cr”/Cr”==2/3, pH=2. ．． 5
(pH adjusted with KOH) A chromate treatment solution with a solid content of 20 l/l was applied with a roll coater at room temperature and then dried. Electrolytic chromate treatment conditions CrO3: 50 f/l, H! 804: 0.5
$'/l, current density f 4.9 due to bath temperature of 50°C
A/dm”.

It was subjected to cathodic electrolysis treatment for an electrolysis time of 2.0 seconds, washed with water, and dried.

・Resin composition (1) Epikote 1004 (epoxy resin, manufactured by Shell Chemical Co., Ltd., 2 molecular weight approximately 1600) was added to a reaction apparatus equipped with a reflux condenser, a stirring device, a thermometer, and a nitrogen gas blowing device. ) 57f, xylene 8
02 was added thereto, and the reaction was allowed to proceed at 170° C. until the acid value of the reactant became approximately O. Thereafter, xylene was removed under reduced pressure to obtain a reaction intermediate [:A'lK].

(It) A reaction apparatus equipped with a stirring device, a reflux condenser, a hygrometer, and a liquid dripping device Epicor) 1009 (Shell Chemical Co., Ltd. epoxy resin bimolecular weight a7
50) After adding 10002 mixed solvent of xs50r (o, s mol) and methyl-isobutylketone/xylene=171 (weight ratio), stirring and heating were performed to uniformly dissolve the mixture at the boiling point of the solvent. Then cooled to 70℃,
Di(n-propatool)amine fractionated into a liquid dropping device? Of was added dropwise over a period of 30 minutes. During this time, the reaction temperature was maintained at 70°C.

After the dropwise addition was completed, the temperature was maintained at 120°C for 2 hours to complete the reaction. The obtained reaction product is used as a resin. The active ingredient in resin is 66%.

(Blood Into the same reaction apparatus as in (n) above, put the reaction intermediate (A) 1650F obtained in (1) and xylene xoo.

f was weighed out and heated to 10°O.C., and then jetanolamine 65F and monoethanolamine 30t, which had been separated into a liquid dropping device, were added dropwise thereto over 30 minutes.

Thereafter, the temperature was maintained at 120°C for 2 hours to complete the reaction. The obtained reaction product is referred to as resin B. The active ingredient of Resin B was found to be 63%.

In addition, in the adhesion test, the sample material after phosphoric acid treatment was electrocoated with a cationic electrodeposition paint M9210 (manufactured by Kansai Paint Co., Ltd.) to a thickness of 20 μm, and then Amirac 002 (manufactured by Kansai Paint Co., Ltd.) was electrocoated with a film thickness of 20 μm.
was spray-painted to a thickness of 40μ and tested for primary adhesion and secondary adhesion. The primary adhesion test was carried out by cutting 100 gongs at 1 inch intervals on the membrane-lined surface of each sample material, and applying and peeling the adhesive tape to these goblets. After painting, each test material was soaked in warm water (pure water) at 40°C for 24 hours.
After being immersed for 0 hours, the sample was taken out, and within 30 minutes thereafter, grids were cut at intervals of 1 inch in the same manner as described above, and adhesive tape was applied to and peeled off from the grids.

In addition, the corrosion resistance test was conducted as a cycle test with the above as one cycle.
Evaluation was performed using the prescribed cycles shown in Table and Table 2.

Regarding corrosion resistance after unpainted processing, bead shape Tip angle 60 Tip RO15 Bead height 5■ Sample size 25■300mm Pulling speed
The test material processed by the drawbead test at 200 m/min and 500 Kf was tested in 50 cycles.

Regarding the corrosion resistance after painting, cross-cutting was performed after electrodeposition painting, a test was conducted for 100 cycles, the maximum blistering width was measured, and evaluation was performed using half of the maximum blistering width. The evaluation criteria for each test result are as follows.

(1) Corrosion resistance after unpainted processing ◎: No red rust ○+: Less than 5 inches of red rust ○: l 5 inches or more and less than 10 inches ○-: #10, 20 inches, l Δ: 120, 150, IX: #5050 Ch (2) Corrosion resistance after painting ◎ : Blistering @ less than 0.5 layer ○ 10 : 70.50 or more 1.0 IO: I
1. Owa#2. Og #〇-: '
2.0ml 3.0m I△:
I 3. Ow# 5bOsai zX
: #5,0 ■ 1 (3) 2-coat adhesion ◎ : Peeling area 0% 0+: # Less than 5 inches ○ : # 5% or more 10 inches IO-:
l 10 inches I 20 inches I△: Peeling area 2Q section or more less than 50 inches X:
n 5Q section" Sohi (*1)...Amount of solids added to 100 parts of total solid content of cationic base resin and additives (*2)...See Table 3 (*3)...・See Table 4 Table 3 (*1) Example of mixing by solid content ratio λ As a steel plate for the inner surface of an automobile body, the material of the present invention with different plating components and coating amounts as shown in Table 5 adheres closely. A durability test and a corrosion resistance test were conducted. Similar tests were also conducted on each steel plate shown in Table 6 as comparative materials.

In addition, the preparation method of the test material and base resin, each test method, evaluation method, etc. are all the same as Example 1.

As is clear from this example, excellent corrosion resistance can be obtained under severe corrosion conditions by forming a resin composition film in which a specified chromium compound is added together with silica and/or aluminum phosphomolybdate to the base resin. can.

*1 Total solid content of cationic base resin and additive (1) 1
Amount of solid content added to 00 parts *2 Total solid content of cationic base resin and additive (2) 1
Amount of solid content added to 00 parts *3 See Table 3 of Example 1 *4 See Table 4 of Example 1 *5 See Table 7 Example 3 Same as Example 1, steel plate for inner surface of automobile body As shown in Tables 8-a and 8-b, the materials of the present invention having different plating components and coating amounts were tested for adhesion and corrosion resistance.

Similar tests were also conducted on each steel plate shown in Table 9 as comparative materials.

The plating components of each steel plate are as shown in Table 10. For each steel plate in the table that has a chromate film and a basic epoxy resin film, the plated steel plate is degreased with alkaline, washed with water, dried, and then subjected to coating-type chromate treatment. Roll coater the liquid
An electrolytic chromate film was formed by coating or dipping in an electrolytic chromate treatment bath, and after drying, a basic epoxy resin solution was applied as a second layer using a roll coater. After further drying, it was heat-treated and air-cooled.

The details of the coating type chromate treatment, electrolytic chromate treatment, and basic epoxy resin liquid are as follows: 0 Coating type chromate treatment conditions Cr3+/Cr''=273, pH=2.5 (
KOHtepl' adjustment) Solid content 20? /L of chromate treatment liquid was applied at room temperature using a roll coater and then dried.

・Electrolytic chromate treatment conditions cro: 501/L, HgSO4: 0.5
t/l, current density 4.9 A/l with bath temperature 50°C.
dm'', and cathodic electrolysis treatment was performed by changing the electrolysis time depending on the target amount of Cr deposited, followed by washing and drying.

・Resin composition Same as Example 1 Each test was conducted as follows.

・Adhesion test Same as Example 1 e Corrosion resistance test Cycle test with the above as one cycle The following tests were conducted using the

Flat plate cc'1' Tested up to 300 cycles using the flat plate sample as is.

Strong cut OCT A strong cut (approximately 1 ml @ cross cut) is made on the entire surface of a flat sample, and this is tested for up to 100 cycles.

OCT after processing (edible after unpainted processing) Same as in Example 1 @ Cr @ OCT test material was treated with degreasing agent Fc-4410 manufactured by Nippon Parkerizing Co., Ltd. under standard conditions, and 1 ton of degreasing liquid was subjected to 0. 6 was degreased, and CrfK in the liquid was measured by atomic absorption.

The evaluation criteria for each test result are as follows.

(1) Corrosion resistance (common to flat plates, after processing, and strong cuts) ◎:
No red rust ○+: Red rust less than 5 inches ○: 〃 5% or more and less than 10 inches △: 110% / F 50 inches I →-: l Less than 5 inches 0: #5 or more 10 inches 〃 ○-: I 10 inches 〃 2o person 〃△:
1 20%l150%pX: I
5Q Section 〃(31Cr elution ◎: Cr in the degreasing solution is less than 2 pprn○'
2ppm or more, less than 6ppm△:
z 6ppm W 12ppm i
tX: Cr in the degreasing solution is 12 ppm or more (*1)
See Table 3 of Example 1 (*2) See Table 4 of Example 1 (*3) See Table 11 (*4) Weight ratio of base resin and [silica + sparingly soluble Cr compound] Base resin/( silica + poorly soluble Cr compound).

(*5) Represents the weight ratio of silica and poorly soluble Cr compound dispersed in the base resin, silica/W@soluble Cr compound.

(*6) See Table 10; 1 As can be seen from the above examples, the steel sheet of the present invention has an alkali-resistant film with a basic epoxy resin as the base layer on the top layer, and the resin Since it is a low temperature drying type, it is possible to ensure good corrosion resistance of the chromate film itself without causing deterioration of the chromate film or reduction of cr.

Regarding corrosion resistance after painting, steel plates coated with conventional organic composite silicate that are baked at a low temperature (150℃) tend to cause alkali blisters due to the poor alkali resistance of the coating, and steel plates that are baked at a high temperature (260℃) In contrast, in the example of the present invention, the alkali resistance of the film is improved and Since the chromate film maintains good corrosion resistance, good corrosion resistance after painting is obtained. By the way, the width of the blisters on Synchro Metal is due to the occurrence of red rust.

Regarding corrosion resistance after processing, conventional organic composite silicate low-temperature baking type (150C) does not have sufficient cross-linking of the film and is also poor in alkalinity, so if the film is partially damaged during processing, phosphate treatment is required. The coating deteriorates due to alkaline degreasing, resulting in poor corrosion resistance.

Furthermore, even high-temperature types have poor corrosion resistance due to deterioration of the corrosion resistance of chromate and damage to the film.

On the other hand, in the examples of the present invention, the strength and alkali resistance of the film are improved, and the corrosion resistance of chromate is maintained, so that the film exhibits good corrosion resistance even after processing.

In particular, they used hydrophobic silica and poorly soluble Cr compound in a weight ratio of silica:slightly soluble Cr compound of 35:5 to 35:5.
It is preferable to mix in the range of 25:15, with a-soluble cr
A good compound is BaCroasSrCrO.

In addition, surface forces of scr elution) are used as JmWl Cr compounds such as BaCrO4, ZnCrO4・4zn(on
)2. cacro.

is good. Therefore, in order to obtain the best overall quality performance (especially corrosion resistance and Cr elution property) in the present invention, hydrophobic silica and BaCrO4 are replaced with hydrophobic silica: B
The aCrO4 may be dispersed in the base resin at a weight ratio of 35:5 to 25:15.

〔Effect of the invention〕

According to the present invention described above, by forming a strong resin film with excellent alkali resistance on the top layer, excellent paint adhesion can be achieved.

Corrosion resistance can be obtained. In particular, the steel sheet of the present invention can dry the resin composition film at a low temperature (250°C or less), so there is no deterioration of the chromate film or reduction of Cr due to high temperature baking unlike in conventional steel sheets, and the chromate film itself Good corrosion resistance is maintained. In addition, since the steel sheet of the present invention can be manufactured by drying at low temperatures, it is possible to improve productivity and reduce energy consumption. By doing so, it is possible to manufacture a highly corrosion-resistant surface-treated steel sheet made from a so-called BH steel sheet having bake hardenability.

[Brief explanation of the drawing]

Figures 1 to 3 show base resin/(silica + Jl-soluble C
This figure shows the relationship between (r compound) and corrosion resistance. Figures 4 to 6 show the relationship between silica/1m-soluble Cr compounds and corrosion resistance. Patent applicant: Nippon Kokan Co., Ltd. Kansai Paint Co., Ltd. Inventor: Yasutani Takeshioka Tadashi Yamashita Kirikai Kubo 1) Takashi Hiroma
Natsu Kouma Nori Nikaido Yudo Yoshiaki Miyosawa Momoji Tato at CCT (100”J Ita 1)
〉 ○ ◎ Sea Vine CCT (100 Sai 9 Lu) No. 9) [× 〉 ○
◎ Appearance at 逼蒲OCT (100 rhino '71) × 〉
○ ◎ 1 Sea Appearance at CCT (100 cycles) × 〉 ○ ◎ Appearance at CCT (100 cycles) τ × 〉 ○ ◎ Straddle the sea

Claims (5)

[Claims] (1) A chromate film is formed on the surface of a galvanized or zinc alloy plated steel sheet, and on the top of the chromate film, at least one basic nitrogen atom and at least two primary hydroxyl groups are formed at the end of the epoxy resin. An additive consisting of one or two of silica and aluminum phosphomolybdate is blended into the base resin, and the weight ratio of base resin:additive is 99:1 to 30:70.
A highly corrosion-resistant surface-treated steel sheet comprising a resin composition film. (2) A chromate film is formed on the surface of a galvanized or zinc alloy plated steel sheet, and on the top of the chromate film, at least one basic nitrogen atom and at least two primary hydroxyl groups are formed at the end of the epoxy resin. An additive consisting of one or two of silica and aluminum phosphomolybdate and a sparingly soluble Cr compound are blended into the base resin, and the weight ratio of base resin:additive is 99:
1 to 30:70, and a highly corrosion-resistant surface-treated steel sheet comprising a resin composition film having a weight ratio of base resin: hardly soluble Cr compound of 99:1 to 60:40. (3) The weight ratio of base resin: (silica + poorly soluble Cr compound) is 75:25 to 50:50, and silica: poorly soluble C
The highly corrosion-resistant surface-treated steel sheet according to claim (2), wherein the weight ratio of the r compound is 37:3 to 20:20. (4) The weight ratio of base resin: (silica + poorly soluble Cr compound) is from 70:30 to 55:45 (3)
) Highly corrosion-resistant surface-treated steel sheet. (5) The weight ratio of silica: poorly soluble Cr compound is 35:5 or more
The highly corrosion-resistant surface-treated steel sheet according to claim (3) or (4), wherein the ratio is 25:15.