JP2521462B2 - High corrosion resistance multi-layer coated steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a highly corrosion-resistant multi-layer coated steel sheet suitable for automobile bodies and the like.

[Conventional technology]

In recent years, steel sheets used for automobile bodies are required to have excellent corrosion resistance, and there is an increasing tendency to use surface-treated steel sheets having high corrosion resistance in place of cold-rolled steel sheets that have been conventionally used.

As such a surface-treated steel sheet, a galvanized steel sheet can be mentioned first, but in this type of steel sheet, it is necessary to increase the amount of zinc to increase the corrosion resistance. Is deteriorated.
In order to solve such problems, zinc alloy plated steel sheets and multi-layer plated steel sheets to which one or more elements such as Ni, Fe, Mn, Mo, Co, Al and Cr are added have been researched and developed. In a steel sheet, corrosion resistance can be improved without deteriorating weldability and workability as compared with the galvanized steel sheet.
However, when a steel sheet is applied to a bag structure portion or a bent portion (hemming portion) of an inner plate of an automobile body, the surface thereof is required to have high corrosion resistance, and the zinc alloy plated steel plate or the multilayer There is a problem that the corrosion resistance of a plated steel sheet is not enough. As a steel sheet with a high degree of corrosion resistance, a rust-preventive coated steel sheet with a zinc-rich coating film such as those found in Japanese Patent Publication Nos. 45-24230 and 47-6882 has been researched and developed, and its representative Is known by the name of zinc metal. However, even in this rust-prevention coated steel sheet, in the processing part such as press forming, the coating is peeled off, and the corrosion resistance may be deteriorated, and as a high corrosion-resistant rust-proof coated steel sheet that should meet the requirements of automotive body materials etc. Is still not fully satisfactory.

From this, the present inventors have a limit to improving the performance of the rust-preventive coated steel sheet in the zinc-rich coating film, a thin film that does not use any metal powder such as Zn powder (about several μ or less) A steel sheet having a protective film has been newly developed, and is disclosed in JP-A-58-224174, JP-A-60-50179, and JP-A-60-50180.
And JP-A-60-50181. This steel sheet is based on a zinc or zinc alloy plated steel sheet, on which a chromate film and an uppermost organic composite silicate film are applied, and has excellent workability and corrosion resistance.

[Problems to be solved by the invention]

However, as a result of subsequent research conducted by the present inventors, the treated steel sheet as described above is a zinc-rich coated steel sheet (eg, Japanese Patent Publication No.
45-24230), it was found that the corrosion resistance in a humid environment tends to be slightly inferior.

Further, steel sheets for automobiles tend to be thinner in order to reduce the weight of the vehicle body, and as a steel sheet suitable for this, they have ductility at an environmental temperature of 120 ° C or lower and have toughness at 120 ° C or higher, So-called bake-hardening steel plates (bake hardenable steel plates) have been widely used. For this reason,
A film forming material suitable for such a steel plate is required to complete the film at a low temperature of 150 ° C. or lower, and further, a film durability sufficient to maintain the corrosion resistance of the metal is required. However, it is hard to say that the coated steel sheet according to the above-mentioned proposals made by the inventors of the present invention has sufficient properties in this respect.

The present invention has been made in view of such conventional problems, and has a high corrosion resistance multi-layer coated steel sheet having excellent bare corrosion resistance, workability and weldability, coating adhesion to two-coat coating, coating corrosion resistance, and low temperature curing property. Is intended to be provided.

[Means for solving the problem]

The present invention uses the following means in order to solve such a problem.

(1) In order to obtain corrosion resistance in a humid environment, the resin film that constitutes the uppermost layer of the multi-layer coated steel sheet is a film that suppresses oxygen and moisture permeability, which is considered as a metal corrosion factor. It is necessary to have a structure. The coating film has a significant increase in oxygen and water permeability on the high temperature side with the glass transition temperature (Tg) as a boundary, and the glass transition temperature of the coating film under moisture absorption is that of the coating film under drying. It is known to show even lower values. Therefore, in order to obtain the corrosion inhibiting action, it is necessary that the film has a glass transition temperature higher than the environment in which the steel sheet is used. Therefore, an organic polymer resin having a glass transition temperature in a predetermined range is used as a base resin. did. Further, the organic resin needs to have a resin composition having a small number of hydrophilic functional groups, and therefore, a hydrophobic organic solvent-soluble resin is used instead of the water-soluble resin.

(2) Silica is added to the resin film, and the metal passivation effect of the hexavalent chromium compound is also used in order to maintain the corrosion resistance. Then, as the chromium compound, a compound which is sparingly soluble in water is selected to suppress excessive water absorption, and hexavalent chromium is gradually eluted,
It was decided to continue the corrosion inhibition effect.

Furthermore, it was found that the corrosion resistance is significantly improved by adding silica and sparingly soluble chromium compounds having different corrosion effects in a specific ratio, and the ratio of silica and sparingly soluble chromium compound to the base resin, silica and sparingly soluble It was decided to specify the proportion of the soluble chromium compound.

Further, the silica component tends to adsorb water because the surface of the silica particle is composed of a hydrophilic silanol group as an inherent property of silica, and when the corrosion resistance is important, the silanol group is alkylated. The so-called hydrophobic silica was used to suppress the absorption of water in the film.

(3) Using a di- or trialkoxysilane compound (so-called silane coupling agent) that plays a cross-linking role between an organic compound and an inorganic compound in order to obtain a low-temperature hardening type coating required for application to baking and hardening steel materials. , The organic resin-silica-chromium compound is promoted.

That is, the basic features of the present invention are as follows.

(1) An organic solvent-soluble organic polymer resin [A] having a chromate film on the surface of a zinc-plated or zinc-alloy-plated steel sheet and a glass transition temperature of 343 to 423K is added on top of the chromate film. Silica [B] in which the weight ratio of molecular resin [A]: silica [B] is 99: 1 to 30:70.
And 1 to 30 parts by weight of the sparingly soluble Cr compound [C] per 100 parts by weight of the organic polymer resin [A], and the organic polymer resin [A]: (silica [B] + difficulty A resin composition film having a weight ratio of soluble Cr compound [C]) of 80:20 to 44:56 and a weight ratio of silica [B]: hardly soluble Cr compound [C] of 37: 3 to 25:15 is 0.3. Highly corrosion-resistant multi-layer coated steel sheet formed with a deposit of ~ 3.0 g / m ² .

(2) An organic solvent-soluble organic polymer resin [A] having a glass transition temperature of 343 to 423 K has a chromate film on the surface of a zinc-plated or zinc alloy-plated steel sheet Silica [B] in which the weight ratio of molecular resin [A]: silica [B] is 99: 1 to 30:70.
And 1 to 30 parts by weight of the insoluble Cr compound [C] per 100 parts by weight of the organic polymer resin [A], (organic polymer resin [A] + silica [B] + insoluble Cr compound [ C]) 0.5 to 15 parts by weight with respect to 100 parts by weight of a di- or trialkoxysilane compound [D], and an organic polymer resin [A]: (silica [B] + sparingly soluble Cr compound [ C])
Of the resin composition film having a weight ratio of 80:20 to 44:56 and a weight ratio of silica [B]: sparingly soluble Cr compound [C] of 37: 3 to 25:15 of 0.3 to 3.0 g / m ² . Highly corrosion-resistant multi-layer coated steel sheet formed by the amount of adhesion.

 The details of the present invention will be described below.

The present invention uses a galvanized or zinc alloy-plated steel sheet as a starting material, and has a chromate film on its surface and a resin film on the upper part of which a predetermined additive is mixed.

The starting material zinc-based plated steel sheet is a zinc-plated steel sheet, a zinc-iron alloy-plated steel sheet, a zinc-nickel alloy-plated steel sheet, a zinc-manganese alloy-plated steel sheet, a zinc-aluminum alloy-plated steel sheet, a zinc-cobalt-chrome alloy-plated steel sheet. In addition, Ni, F
It is possible to use one or two or more kinds of elements such as e, Mn, Mo, Co, Al, Cr, etc. added, and a composite in which two or more layers of the same kind or different kind of plating as described above are applied. It may be a plated steel plate. For example, Fe-Zn with different Fe contents
It is possible to form a plating film as if two or more layers of alloy plating were applied.

Among them, zinc-nickel alloy-plated steel sheet and zinc-manganese alloy-plated steel sheet are preferable from the viewpoint of corrosion resistance, and when these steel sheets are used, the zinc-nickel alloy-plated steel sheet has a nickel content in the plating film of 5 to 5. 20
wt%, and 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 of practicable methods such as an electrolytic method, a melting method, and a gas phase method can be adopted. However, the rust-preventive steel sheet as the object of the present invention is mainly used for an automobile body, and in such an application, it is important not to impair the material of the cold-rolled steel sheet to be plated. Therefore, it can be said that electroplating that does not generate heat is advantageous.

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

It is appropriate that the chromate film has a chromium adhesion amount (dry) of 1 to 1000 mg / m ² , preferably 10 to 200 mg / m ² , and more preferably 30 to 80 mg / m ² (above, converted to metallic chromium). Is.

When the amount of deposited chromium exceeds 200 mg / m ² , workability and weldability tend to deteriorate, and this tendency becomes particularly remarkable when it exceeds 1000 mg / m ² . Further, when the amount of deposited chromium is less than 10 mg / m ² , the coating may be non-uniform and the corrosion resistance may be deteriorated. Such deterioration of corrosion resistance is particularly remarkable at less than 1 mg / m ² . Further, it is preferable that hexavalent Cr is present in the chromate film. Cr ⁶⁺ has a repairing action and, when the steel sheet is damaged, acts to suppress corrosion therefrom.

Such a chromate treatment for the undercoat may be performed by any known method such as a reaction type, a coating type, and an electrolytic type.

The coating type chromate treatment liquid contains a partially reduced chromic acid solution as a main component, and if necessary, a water-dispersible or water-soluble organic resin such as an acrylic resin and / or a particle size of several mμ.
~ Several hundreds of mμ of silica (colloidal silica, fumed silica). In this case Cr ³⁺ / Cr ⁶⁺
The ratio is 1/1 to 1/3, and the pH is 1.5 to 4.0 (more preferably 2 to
3) is preferable. The ratio of Cr ³⁺ / Cr ⁶⁺ is adjusted to a predetermined ratio by using a general organic reducing agent (eg sugar, alcohol, etc.) or an inorganic reducing agent. As the coating type chromate treatment, any method such as a roll coater method, a dipping method or a spray method may be used. In the coating type chromate treatment, a film is obtained after the chromate treatment by drying without washing with water. The reason for drying without washing in this way is that Cr ⁶⁺ is removed by the usual washing,
The ratio of Cr ³⁺ / Cr ⁶⁺ is kept stable as it is, and the basic epoxy resin film formed on the top suppresses the excessive outflow of Cr ^{6+ in} a corrosive environment and is effective for a long period of time. It is possible to maintain high passivation effect and obtain high corrosion resistance.

On the other hand, in the electrolytic chromate treatment, with chromic anhydride,
Cathodic electrolytic treatment is performed in a bath containing one or more anions such as sulfuric acid, phosphoric acid fluoride, and halogen oxyacid, and the film is washed and dried to form a film. Comparing the chromate films obtained by the above two treatment methods, the coating type chromate is superior in corrosion resistance because it contains a larger amount of hexavalent chromium in the film than the electrolytic type chromate. When subjected to heat treatment, the film becomes dense and strong, so that the corrosion resistance becomes better than that of electrolytic chromate. On the other hand, the electrolytic chromate has an advantage that the degree of completion of the film is high regardless of the presence or absence of heat treatment, and has an advantage that it is easy to control the amount of film adhesion. From the viewpoint of corrosion resistance, coating type chromate is most preferable. In many cases, rust-preventive steel sheets for automobiles are treated on one side, and from this point of view, a coating type and an electrolytic type are desirable.

On the chromate film, a resin composition film in which an inorganic compound is added to an organic polymer resin as a base resin is formed.

The glass transition temperature of the organic polymer, which is the base resin of the resin composition film, needs to be in the range of 343 to 423K.

If the glass transition temperature is less than 343K, the corrosion resistance in the environment of use is not sufficient, while if it exceeds 423K, the cohesive force of the coating becomes significantly high, so bending, overhanging, drawing, etc. Cracks may occur in the film, coating film peeling may occur, and the corrosion resistance may decrease.

Examples of organic polymers include acrylic copolymer resins, alkyd resins, epoxy resins, polybutadiene resins, phenol resins, polyurethane resins, polyamine resins, polyphenylene resins, and mixtures or addition condensates of two or more of these resins. Is mentioned. Among these, acrylic copolymer resins, alkyd resins, epoxy resins and the like are preferable.

The acrylic copolymer is a resin synthesized by a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, or the like, using a normal unsaturated ethylenic monomer, and is a methacrylate-based, acrylonitrile, styrene, Obtained by using a hard monomer such as acrylic acid, acrylamide or vinyltoluene as an essential component and appropriately blending an unsaturated vinyl monomer for the purpose of imparting hardness, flexibility and crosslinkability of the resin. . Further, this resin may be a resin modified with other alkyd resin, epoxy resin, phenol resin, or the like.

Further, the alkyd resin may be a known one obtained by a usual synthetic method, for example, an oil-modified alkyd resin, a rosin-modified alkyd resin, a phenol-modified alkyd resin, a styrenated alkyd resin, a silicone-modified alkyd resin, Examples thereof include acrylic modified alkyd resin and oil-free alkyd resin (polyester resin).

The epoxy resin, epichlorohydrin type, straight epoxy resin such as glycidyl ether type, fatty acid modified epoxy resin, polybasic acid modified epoxy resin, acrylic resin modified epoxy resin, alkyd (or polyester) modified epoxy resin, polybutadiene modified epoxy resin, Phenol-modified epoxy resin, amine- or polyamine-modified epoxy resin, urethane-modified epoxy resin and the like are used.

In the present invention, silica is contained as an additive in the resin composition film to obtain high corrosion resistance.

Although the mechanism of the improvement of anticorrosion property due to such silica blending is not always clear, Zn eluted under corrosive environment
It is presumed that ²⁺ and silica react with each other to form a stable corrosion product and prevent pitting corrosion, thereby providing a long-term anticorrosion improving effect.

Generally, silica includes colloidal silica, hydrophilic silica called fumed silica, and hydrophobic silica,
Either can be used. These silicas have an excellent anticorrosion effect, but hydrophobic silicas are particularly effective in improving the corrosion resistance. For example, the above-mentioned JP-A-58-2
No. 24174 and the like show that hydrophilic colloidal silica is added to an organic resin. However, since hydrophilic silica has a strong hydrophilicity, it has poor compatibility with a solvent, and due to its strong hydrophilicity, it easily causes water penetration,
This causes the corrosion resistance to decrease, and it is presumed that initial rust is likely to occur particularly in a humid environment. On the other hand, the reason why hydrophobic silica has an excellent anticorrosion effect is that the compatibility (familiarity) with the resin during film formation is good, and as a result, a uniform and strong film is formed. To be

The steel sheet of the present invention is one in which silica is blended with the base resin to enhance the compatibility with the base resin and obtain high corrosion resistance.

This silica has a weight ratio of base resin: silica of 99: 1 to 3
It is mixed in the range of 0:70, preferably 90:10 to 50:50.

Here, the compounding amount of the above silica is base resin: silica = 9
If it is 9: 1 or less, the anticorrosive property-improving effect due to the compounding cannot be expected. On the other hand, if it is 30:70 or more, the adhesion of the two-coat coating film is deteriorated. Also, the particle size of silica is 1 m
μ to 500 mμ is suitable, and particularly preferably 5 to 100 mμ.

Hydrophilic silica known as colloidal silica (silica gel) or fumed silica has a surface covered with a hydroxyl group (silanol group Si—OH) and exhibits hydrophilicity. Hydrophobic silica is obtained by substituting a silanol group on the surface of such water-dispersible silica for a part or most of the silanol group with a methyl group, an alkyl group, or the like to make the silica surface hydrophobic.

There are various methods for producing hydrophobic silica, and the representative ones are reaction of organic solvents such as alcohols, ketones and esters, silanes, silazanes, polysiloxanes, etc. Includes a reaction pressurization method in an organic solvent, a catalyst heating method, and the like.

Examples of such silica include organic solvent-dispersed colloidal silica dispersed in a solvent such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, ethyl cellosolve, and ethylene glycol (for example, Catalyst Chemical Industry). OSCAL 1132,1232,1332,1432,1532,1622,1722,172
4 etc.), silica whose surface has been hydrophobized with an organic solvent or a reactive silane compound, that is, hydrophobic ultrafine particle silica (for example, R974, R811, R812, R805, manufactured by Nippon Aerosil Co., Ltd.
T805, R202, RY200, RX200, etc.), hydrophilic silica (for example, Aerosil 130,200,300,380, manufactured by Nippon Aerosil Co., Ltd.)
Fuji DeVison Chemical Co., Ltd. Syloid 72,244 etc.).

 The silica as described above is stably dispersed in the base resin.

The present invention is a composite addition of a sparingly soluble Cr compound together with the silica in the resin composition film, as will be described later, by the composite addition of this silica and a sparingly soluble Cr compound, remarkably excellent corrosion resistance is obtained. . In a corrosive environment, a trace amount of Cr ⁶⁺ is eluted from the above-mentioned sparingly soluble Cr compound in the film, which exerts a passivation action for a long period of time and improves the corrosion resistance.

The sparingly soluble Cr compound is a base resin (organic polymer resin) 100
It is added in an amount of 1 to 30 parts by weight, preferably 5 to 20 parts by weight, based on parts. The amount of the sparingly soluble Cr compound is 10
If it is less than 1 part by weight with respect to 0 parts by weight, the anticorrosion-improving effect due to the compounding cannot be expected, while if it exceeds 30 parts by weight, the adhesion of the two or more multi-layer coating film due to the water-absorbing action of the poorly soluble Cr compound. Here, the anticorrosion effect is most improved when the silica and the sparingly soluble Cr compound are added together in a predetermined ratio as described above.

As described above, when Zn ²⁺ or the like is eluted from the underlying plating, silica reacts with this Zn ²⁺ to form a stable corrosion product over the entire surface of the sample, and it is presumed that the silica exhibits an anticorrosion effect. On the other hand, a sparingly soluble Cr compound elutes a small amount of Cr ⁶⁺ and exerts an anticorrosion effect by immobilizing this Cr ^6+.
It is very effective in corrosive environments such as SST where dissolution progresses continuously.

When a sparingly soluble Cr compound is included in the resin film as a rust preventive additive, it is a CC that simulates the actual corrosion environment.
In the accelerated corrosion test in which Wet and Dry conditions such as T are repeated alternately, the anticorrosion effect cannot be expected so much. Rather, in such a test, it is more effective to use silica as a rust preventive additive. However, in cases such as when subjected to strong processing or when performing an accelerated test with an extremely strong cut, the effect of repairing the damaged part is not sufficient if only silica is included in the resin as a rust preventive additive. Is.

The present inventors have found that by including silica and a sparingly soluble Cr compound having different anticorrosion mechanisms in a resin at a specific ratio, excellent corrosion resistance can be obtained by the synergistic action of each anticorrosion effect. .

Next, the corrosion resistance (in Example (2)) was changed by variously changing the compounding ratio of the base resin and [silica + refractory Cr compound] and the compounding ratio of silica and the refractory Cr compound dispersed in the base resin. The result of having tested about the described cycle test [strong cut 75 cycles] is shown. In this test, electrolytic zinc-nickel alloy plating (12% Ni-Zn) with a coating amount of 20 g / m ^{2 on} one side was used as the test material. The chromate treatment was carried out under the coating type chromate treatment conditions described in the below-mentioned examples, and the adhesion amount was 50 mg / m ^{2 in} terms of Cr on one side, and the coating was performed using a roll coater and dried. A solvent type cationic epoxy resin (resin of No. 4 in Table 4) was used as the base resin. Silica is fumed silica R8 manufactured by Nippon Aerosil Co., Ltd.
11. As the sparingly soluble Cr compound, BaCrO ₄ manufactured by Kikuchi Dye was used.

In Fig. 1, the weight ratio of silica: sparingly soluble Cr compound is kept constant at 37: 3, and the mixing ratio of the base resin and [silica + sparingly soluble Cr compound] is shown as follows. The results of the corrosion resistance test performed by changing the weight ratio from 100: 0 to 0: 100 are shown.

In Fig. 2, the weight ratio of silica: sparingly soluble Cr compound is 30:10.
Of the base resin and [silica + sparingly soluble Cr compound] in a weight ratio of base resin: [silica + sparingly soluble Cr compound] from 100: 0 to 0: 100. The results are shown.

In Fig. 3, the weight ratio of silica: sparingly soluble Cr compound is 25:15.
Of the base resin and [silica + sparingly soluble Cr compound] in a weight ratio of base resin: [silica + sparingly soluble Cr compound] from 100: 0 to 0: 100. The results are shown.

In Fig. 4, the weight ratio of the base resin: [silica + sparingly soluble Cr compound] was kept constant at 80:20, and the weight ratio of silica: sparingly soluble Cr compound was variously changed from 40: 0 to 0:40. The results of the corrosion resistance test are shown below.

Fig. 5 shows that the weight ratio of the base resin: [silica + sparingly soluble Cr compound] was kept constant at 60:40, and the weight ratio of silica + sparingly soluble Cr compound was variously changed from 40: 0 to 0:40. The results of the corrosion resistance test are shown below.

Fig. 6 shows that the weight ratio of base resin: [silica + sparingly soluble Cr compound] was kept constant at 56:44, and the weight ratio of silica + sparingly soluble Cr compound was variously changed from 40: 0 to 0:40. The results of the corrosion resistance test are shown below.

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

Base resin: [silica + sparingly soluble Cr compound] weight ratio → 80:20 to 44:56 preferably 70:30 to 44:56 Silica: sparingly soluble Cr compound weight ratio → 37: 3 to 25:15 35: 5 to 25:15 If the compounding amount of silica and sparingly soluble Cr compound is less than 80:20 in the weight ratio of base resin: [silica + sparingly soluble Cr compound], the corrosion resistance is not sufficient. A film with good corrosion resistance can be obtained. On the other hand, the compounding amount of the above additive is 44: 5
Even if it exceeds 6, corrosion resistance problems occur, and at 44:56 or less, good corrosion resistance is exhibited. Therefore, the optimum weight ratio of the base resin: [silica + sparingly soluble Cr compound] is 80:20 to 44:56, preferably 70:30.
~ 44: 56.

There is a problem that the amount of the sparingly soluble Cr compound to be dispersed in the resin is less than 37: 3 by weight ratio of silica: sparingly soluble Cr compound and the corrosion resistance is not sufficient because the repair effect of Cr ⁶⁺ is insufficient. When it is 35: 5 or more, the film having the best corrosion resistance can be obtained.

On the other hand, if the blending amount of silica is less than 25:15 in the above weight ratio, the formation of stable corrosion products by silica and Zn ²⁺ becomes insufficient, which is disadvantageous in terms of corrosion resistance. Therefore, the optimum weight ratio of silica: sparingly soluble Cr compound contained in the resin is 37: 3 to 25:15, preferably 35: 5 to 25:15.

Barium chromate (BaCr
O ₄ ), strontium chromate (SrCrO ₄ ), lead chromate (PbCrO ₄ ), zinc chromate (ZnCrO ₄・ 4Zn (OH) ₂ ), calcium chromate (CaCrO ₄ ), zinc potassium chromate (K _{2
O · 4ZnO · 4CrO 3 · 3H} 2 O), can be used powders of silver chromate (AgCrO _4), one or two or more of these are dispersed in the base resin.

Chromium compounds other than these have poor compatibility with the base resin or have an anticorrosive effect, but plastic Cr
^Since it contains a large amount of ⁶⁺ , it has problems such as poor adhesion of two-coat coating, and is not suitable for the purpose of the present invention.

However, BaCrO ₄ and SrCrO ₄ are preferably used from the viewpoint of corrosion resistance when subjected to strong processing (for example, a draw bead test) or when an extremely strong cut (width of about 1 mm) is put.

In addition, the surface-treated steel sheet obtained by the present invention is often painted when actually used by customers, and when it is painted by an automobile manufacturer, etc., degreasing surface adjustment, phosphate treatment, etc. Is pre-treated as required. Since the surface-treated steel sheet obtained by the present invention contains soluble Cr ^{6+ in} the underlying chromate film and the resin film, a small amount of Cr is eluted in the pretreatment process of coating. When discharging the wastewater generated in each of these pretreatment steps into the environment, the Cr concentration in the wastewater is suppressed according to environmental standards, and therefore automobile manufacturers and the like treat wastewater. However, there is a limit to the capacity of the wastewater treatment facility, and it is preferable that the amount of eluted Cr is small. Of the sparingly soluble Cr compounds that are compounded in the base resin, BaCrO ₄ has a smaller elution rate of Cr in the pretreatment process than other chromium compounds.
From the viewpoint of elution property, it is preferable to use BaCrO ₄ .

In a corrosion resistance test conducted when limiting the weight ratio of the base resin: [silica + hardly soluble Cr compound] and the weight ratio of silica: hardly soluble Cr compound, hydrophobic fumed silica R811 manufactured by Nippon Aerosil Co., Ltd. was used. If the weight ratio of the base resin: [silica + hardly soluble Cr compound] is 80:20 to 44:56 and the weight ratio of silica: hardly soluble Cr compound is 37: 3 to 25:15, Similar results were obtained with the other silicas mentioned above.

Although BaCrO ₄ was used as the sparingly soluble Cr compound, other compounds such as SrCrO ₄ , AgCrO ₄ , PbCrO ₄ , CaCrO ₄ , and K _{2 were used.}
Even if O ・ 4ZnO ・ 4CrO ₃・ 3H ₂ O and ZnCrO ₄・ 4Zn (OH) ₂ are used alone or in combination of two or more, the weight ratio of base resin: [silica + sparingly soluble Cr compound] is 80:20 ~ 44:56 and silica:
Similar results were obtained when the weight ratio of the poorly soluble Cr compound was 37: 3 to 25:15.

Furthermore, in the present invention, a crosslinking reaction can be promoted by adding a di- or trialkoxysilane compound to the composition of the above-mentioned base resin, silica and sparingly soluble Cr compound.
As a silane compound that exhibits such a function and effect,
For example, divinyldimethoxysilane, divinyl-β-methoxyethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, β- (3 , 4-Epoxycyclohexyl) ethyltrimethoxysilane, N-P
(Aminoethyl) γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane and the like can be mentioned.

The addition ratio of the silane compound is 0.5 based on 100 parts by weight of the total solid content of the base resin, silica, and the component of the insoluble Cr compound.
-15 parts by weight, preferably 1-10 parts by weight. Addition amount
If it is less than 0.5 parts by weight, the crosslinking effect due to addition is not clear,
On the other hand, even if it is added in excess of 15 parts by weight, an effect commensurate with the amount added cannot be expected.

The present invention is based on the above-mentioned additional components such as silica and refractory Cr.
In addition to the compounds and silane compounds, other known additives (for example, surfactants) and rust-preventive pigments such as chromium-based and non-chromium-based rust-preventive pigments, extender pigments, and coloring pigments can be added.

The resin composition film as described above is on the chromate film.
It is formed with a deposition amount of 0.3 to 3.0 g / m ² , preferably 0.5 to 2.0 g / m ² . If the coating amount is 0.3 g / m ² , sufficient corrosion resistance cannot be obtained, while if it exceeds 3.0 g / m ² , weldability (particularly continuous multi-point weldability) and electrodeposition coatability deteriorate. I will end up.

Although the car body is subjected to cationic electrodeposition coating, the wet electrical resistance of the chromate film + resin composition film
If it exceeds 200 KΩ / cm ² , there is a problem that the cationic electrodeposition coating film will not be formed properly. Therefore, when using it for automobile bodies, the wetting resistance of the chromate film + resin composition film should be 200 KΩ / cm ² or less. It is preferable to form both films so as to suppress.

The present invention includes a steel sheet having the film structure as described above on both sides or one side.

The present invention is also effective as a highly corrosion-resistant surface-treated steel sheet for home electric appliances, building materials, etc., in addition to automobile bodies.

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

(1) One side: plating film-chromate film-resin composition film One surface: Fe surface (2) One side: plating film-chromate film-resin composition film One surface: plating film (3) Both sides ... plating film-chromate film-resin Composition coating [Example] Example 1 An adhesion test and a corrosion resistance test were performed on the materials of the present invention and comparative materials having different plating components and coating amounts as shown in Tables 1 and 2.

For each steel sheet, after degreasing the plated steel sheet with alkali, washing with water and drying, apply a coating type chromate treatment liquid to this with a roll coater or dip it in an electrolytic chromate treatment bath to form an electrolytic chromate film, and after drying, the second layer Then, the resin liquid was applied by a roll coater. After further drying, it was heat-treated and air-cooled. The conditions of the coating type chromate treatment and electrolytic chromate treatment are as follows.

● Coating Chromate Treatment Conditions A chromate treatment liquid of Cr ³⁺ / Cr ⁶⁺ = 2/3, pH = 2.5 was applied at room temperature with a roll coater and then dried.

Electrolytic chromate treatment conditions CrO ₃ : 50g / l, H ₂ SO ₄ : 0.5g / l, bath temperature 50 ° C, cathodic electrolysis treatment with current density 4.9A / dm ² , electrolysis time 2.0 seconds, and washing with water. Dried.

In addition, Table 3 shows the composition for forming the second layer coating used in this Example. The contents of the composition of each Example in Tables 1 and 2 are shown in Table 3. It is indicated by a number. Further, Tables 4 to 7 show the base resin, silica, chromium compound and silane compound used in the composition of Table 3, and the above components constituting each composition in Table 3 are shown. The contents are shown by the numbers in Tables 4 to 7.

In addition, in this example, the composition of the second surface coating and each component constituting the same were prepared as follows.

-Synthesis of organic polymer <Example 1. Synthesis of acrylic copolymer resin> 180 parts of isopropyl alcohol was placed in a four-necked flask equipped with a thermometer, a stirrer, a condenser, and a dropping funnel, and after nitrogen substitution, The temperature inside the flask was adjusted to about 85 ° C, 180 parts of methyl methacrylate, 15 parts of ethyl methacrylate, 30 parts of n-butyl methacrylate, 30 parts of styrene.
2, 2-azobis (2,4-dimethylvaleronitrile) 6 was added to a monomer mixture consisting of 30 parts of N-n-butoxymethyl acrylamide and 15 parts of hydroxyethyl methacrylate.
It takes about 2 hours to add dropwise with a catalyst consisting of 10 parts. After completion of dropping, if the reaction is continued for another 5 hours at the same temperature, solid content will be about
A 63% colorless and transparent resin solution was obtained.

<Example 2. Synthesis of acrylic copolymer resin> Acrylic monomer was used as methyl methacrylate 30 parts, isobutyl acrylate 198 parts, Nn-butoxymethyl acrylamide 30 parts, and hydroxyethyl methacrylate 15
Parts and acrylic acid 27 parts were synthesized under the same conditions as in Example 1 to obtain a colorless and transparent resin solution having a solid content of 61%.

<Example 3. Synthesis of oil-free polyester> 15 parts of adipic acid, 15 parts of phthalic anhydride and isophthalic acid were placed in a four-necked flask equipped with a thermometer, a stirrer and a condenser.
125 parts, 87 parts of trimethylolpropane, 31 parts of neopentyl glycol, 6 parts of 1,6-hexanediol and 0.02 parts of monobutyltin hydroxide were added, and it took about 2 hours to stir to 160 ° C under a nitrogen stream. Raise the temperature. Then, the nitrogen gas flow is stopped and the temperature is raised to 240 ° C. for another 4 hours. During this time, the reaction proceeds while separating condensed water from the reaction. After further reacting at a temperature of 240 ° C. for 2 hours, 8.4 parts of xylene was added, a condensation reaction was carried out under reflux at the same temperature for 2 hours, 160 parts of dimethyl ester solvent and 110 parts of cyclohexanone solvent were added and cooled, A colorless transparent resin solution having a solid content of about 50% was obtained.

<Example 4. Synthesis of Epoxy Resin> Epicoat 1004 (Shell Chemical Co., Ltd.) was placed in a four-necked flask equipped with a thermometer, a stirrer, a condenser, and a dropping funnel.
Made, epoxy resin, molecular weight: about 1500) 225 parts, methyl isobutyl ketone 100 parts, xylene 100 parts, and dissolve evenly under a nitrogen stream at a temperature of 180 ° C, then at 70 ° C
It is cooled to room temperature, and then 21 parts of di (n-propanol) amine is added dropwise over 30 minutes. After the dropping was completed, the reaction was continued for 2 hours at 120 ° C. to obtain a colorless and transparent resin solution having a solid content of about 51%.

・ Curing agent (synthesis of blocked isophorone diisocyanate) Take 222 parts of isophorone diisocyanate in a reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser with a dropping funnel, and add 100 parts of methyl isobutyl ketone to dissolve it uniformly. After that, 88 parts of 50% trimethylolpropane in methyl isobutyl ketone was added to the dropping funnel at 70%.
It dripped in the isocyanate solution of the stirring state hold | maintained at degree C over 1 hour. After that, the temperature was further held at 70 ° C. for 1 hour and then at 90 ° C. for 1 hour. Then, 230 parts of n-butyl alcohol was added and reacted at 90 ° C. for 3 hours to obtain a blocked isocyanate. The active ingredient of this curing agent is 76
%Met.

-Resin composition The organic polymer resin synthesized as described above and a commercially available resin were added with a curing agent, if necessary, and used in the examples.
Table 4 shows the composition and the glass transition temperature of the cured film.

-Film-forming composition To the above resin composition, silica shown in Table 5, a chromium compound shown in Table 6, and an alkoxysilane compound shown in Table 7 were added to prepare respective compositions, It provided for each Example. The composition is shown in Table 3.

Further, the corrosion resistance and adhesion tests were conducted as follows.

First, in the post-processing corrosion resistance test, draw bead processing (bead shape tip angle 60 °, tip R0.5, bead height 5 mm, sample size 25 mm × 300 mm, drawing speed 200 mm / min, pressing force 250 Kg) was performed, and then salt water was applied. Spray (5% saline solution, 35
℃, 3 hours) -Dry (60 ℃, 2 hours) -Wet (95% RH,
It was carried out by carrying out 50 cycles of 50 ° C. for 3 hours.

For adhesion, cationic electro-deposition paint (Kansai Paint Co., Ltd., Electron No.9450) was applied by 20 micron electrodeposition, and further amino alkyd paint (Kansai Paint Co., Ltd.,
Amilac No.002) is spray-coated with 30 micron and 1
Secondary adhesion and secondary adhesion were tested. The primary adhesion test is carried out by engraving 100 gobangs at 1 mm intervals on the surface of each test material coating, and sticking and peeling the adhesive tape on the gobangs. After painting each test material
After soaking in warm water (pure water) at 40 ℃ for 240 hours, take it out and
After a lapse of time, it was carried out by scoring 2 mm intervals of gobang like the above and adhering / peeling an adhesive tape to the gobang.

Regarding the corrosion resistance after coating, a cross cut was put after electrodeposition coating, and a test was conducted at 100 cycles. The evaluation criteria for each test result are as follows.

(1) Corrosion resistance after unpainted processing ◎: Red rust does not occur ○ +: Red rust less than 5% ○: Red rust 5% or more and less than 10% ○-: Red rust 10% or more and less than 20% △: Red rust 20% or more and less than 50% ×: Red rust 50% or more (2) Corrosion resistance after painting ◎: Blistering width less than 0.5 mm ○ +: Blistering width 0.5 mm to less than 1.0 mm ○: Blistering width 1.0 mm to less than 2.0 mm ○-: Blistering width 2.0 mm to less than 3.0 mm △ : Blistering width 3.0 mm or more and less than 5.0 mm ×: Blistering width 5.0 mm or more (3) Adhesion between two coats ◎: Peeling area 0% ○ +: Peeling area less than 5% ○: Peeling area 5% or more but less than 10% ○-: Peeling area 10% or more and less than 20% △: Peeling area 20% or more and less than 50% ×: Peeling area 50% or more Example 2 An adhesion test and a corrosion resistance test were performed on the materials of the present invention having different plating components and coating amounts as shown in Tables 8-a and 8-b. Further, the same test was performed for each steel sheet shown in Table 9 as a comparative material.

For each steel sheet, after degreasing the plated steel sheet with alkali, washing with water and drying, apply a coating type chromate treatment liquid to this with a roll coater or dip it in an electrolytic chromate treatment bath to form an electrolytic chromate film, and after drying, the second layer Then, the resin liquid was applied by a roll coater. After further drying, it was heat-treated and air-cooled. The conditions of the coating type chromate treatment and electrolytic chromate treatment are as follows.

● Coating Chromate Treatment Conditions Same as in Example 1 ● Electrolytic Chromate Treatment Conditions CrO ₄ : 50g / l, H ₂ SO ₄ : 0.5g / l, bath temperature 50 ℃ Target current density of 4.9A / dm ² The cathodic electrolysis treatment was performed by changing the electrolysis time according to the amount of Cr deposited on the plate, followed by washing with water and drying.

In this example, the composition of the second layer coating and each component constituting the same are the same as in Example 1.

Further, the corrosion resistance and adhesion tests were conducted as follows.

● Corrosion resistance 5% NaCl spray 35 ° C 4.5 hours ↓ Dry 60 ° C 2.0 hours ↓ 95% RH wet 1.5 hours The following tests were conducted by a cycle test with one cycle above.

After processing CCT draw bead processing (bead shape tip angle 60 °, tip R0.
5, after conducting bead height 5mm, sample size 25mm × 300mm, drawing speed 200mm / min, pressing force 250Kg), test up to 100 cycles.

Flat plate CCT Using a flat plate sample as is, tests up to 250 cycles.

Strong cut CCT A strong cut (cross cut of about 1 mm width) is put on the entire surface of the flat plate sample, and this is tested up to 75 cycles.

● Adhesiveness Same as in Example 1 ● Cr elution test The test material was a degreasing agent FC-L 441 manufactured by Nippon Parkerizing Co.
Using 0 as a standard condition, 0.6 m ² was degreased in an effective test area for the degreasing solution of 1, and the amount of Cr in the solution was measured by atomic absorption.

 The evaluation criteria for each test result are as follows.

(1) Unpainted corrosion resistance (CCT after processing, flat plate CCT, strong cut CC
T common) ◎: Red rust does not occur ○ +: Red rust less than 5% ○: Red rust 5% or more and less than 10% ○-: Red rust 10% or more and less than 20% △: Red rust 20% or more and less than 50% ×: Red rust 50% or more ( 2) Two-coat adhesiveness Same as in Example 1 (3) Cr elution property ◎: Cr amount in degreasing liquid less than 2ppm ○: Cr amount in degreasing liquid 2ppm or more and less than 6ppm △: Cr amount in degreasing liquid 6ppm or more and 12ppm Less than ×: Cr content in the degreasing liquid is 12 ppm or more (* 1) See Table 10 (* 2) See Table 4 (* 3) See Table 5 (* 4) See Table 6 (* 5) Weight ratio of base resin and (silica + sparingly soluble Cr compound) Base resin / (silica / refractory Cr compound)

(* 6) Weight ratio of silica and sparingly soluble Cr compound dispersed in the base resin: Silica / poorly soluble Cr compound.

(* 7) See Table 7 (* 8) Represents parts by weight of di- or trialkoxysilane compound per 100 parts by weight of (organic polymer resin + silica + refractory Cr compound).

(* 9) Represents parts by weight of a sparingly soluble Cr compound with respect to 100 parts by weight of the base resin.

According to the above examples, the organic solvent-soluble organic polymer resin having a glass transition temperature of 343 to 423 K is used as the base resin of the resin composition film, and silica and the sparingly soluble chromium compound are contained in the resin composition film. It can be seen that the combined addition under the conditions of the present invention provides excellent corrosion resistance even in a severe corrosive environment. On the other hand, even if silica and a sparingly soluble chromium compound are added in the resin composition film,
If the added amount does not satisfy the conditions of the present invention, sufficient corrosion resistance cannot be obtained in a severe corrosive environment.

Further, as can be seen from the examples, BaCrO ₄ and SrCrO ₄ are preferable as the sparingly soluble Cr compound to be dispersed together with silica in the resin, particularly from the viewpoint of corrosion resistance.

From the aspect of Cr elution, BaCrO ₄ , ZnCrO ₄・ Zn (O
H) ₂ and CaCrO ₄ are good. Therefore, the most comprehensive quality performance of the present invention (especially corrosion resistance and Cr elution)
To obtain the above, silica and BaCrO ₄ may be dispersed in the base resin in a predetermined range.

〔The invention's effect〕

According to the present invention described above, excellent corrosion resistance and a high degree of coating adhesion can be obtained, and since it can be manufactured by low temperature baking, it is possible to improve productivity and reduce the energy consumption rate, and By setting the baking temperature to 150 ° C. or less, it becomes possible to manufacture a highly corrosion-resistant surface-treated steel sheet using a so-called BH steel sheet having bake hardenability as a raw material.

[Brief description of drawings]

1 to 3 show the relationship between the base resin / (silica + refractory Cr compound) and the corrosion resistance. 4 to 6 show the relationship between silica / refractory Cr compound and corrosion resistance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takahiro Kubota 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Tube Co., Ltd. Co., Ltd. (72) Inventor Yoshiaki Sandaizawa 4-17-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Kansai Paint Co., Ltd. (72) Inventor Tadashi Nishimoto 4-1-1, Higashi-Hachiman, Hiratsuka, Kanagawa Prefecture Kansai Paint Co., Ltd. (72) Inventor Kazuhiko Ozawa 4-17-1, Higashi-Hachiman, Hiratsuka City, Kanagawa Kansai Paint Co., Ltd. (56) Reference JP-A-59-222275 (JP, A) JP-A-60-110444 (JP, A) JP-A-60-141549 (JP, A) JP-A-60-204320 (JP, A)

Claims (8)

(57) [Claims] 1. An organic solvent-soluble organic polymer resin [A] having a chromate film on the surface of a zinc-plated or zinc alloy-plated steel sheet and having a glass transition temperature of 343 to 423 K on the chromate film. The weight ratio of organic polymer resin [A]: silica [B] is 99: 1 to 30:70, and silica [B] is 1 to 3 per 100 parts by weight of organic polymer resin [A].
0 parts by weight of a poorly soluble Cr compound [C] is blended,
And organic polymer resin [A]: (silica [B] + sparingly soluble Cr
The weight ratio of compound [C]) is 80:20 to 44:56, and the weight ratio of silica [B]: sparingly soluble Cr compound [C] is 37: 3 to 25:15.
A high corrosion-resistant multi-layer coated steel sheet having a resin composition coating film of 0.3 to 3.0 g / m ² formed thereon. 2. Organic polymer resin [A]: (silica [B] +
The highly corrosion-resistant multi-layer coated steel sheet according to claim 1, wherein the weight ratio of the refractory Cr compound [C]) is 70:30 to 44:56. 3. A highly corrosion-resistant multi-layer coated steel sheet according to claim 1, wherein the weight ratio of silica [B]: sparingly soluble Cr compound [C] is 35: 5 to 25:15. . 4. The highly corrosion-resistant multi-layer coated steel sheet according to claim 1, wherein silica [B] in the resin composition film is hydrophobic silica. 5. An organic solvent-soluble organic polymer resin [A] having a chromate film on the surface of a zinc-plated or zinc alloy-plated steel sheet and having a glass transition temperature of 343 to 423K on the chromate film, The weight ratio of organic polymer resin [A]: silica [B] is 99: 1 to 30:70, and silica [B] is 1 to 3 per 100 parts by weight of organic polymer resin [A].
0 parts by weight of the sparingly soluble Cr compound [C] and (organic polymer resin [A] + silica [B] + sparingly soluble Cr compound [C])
0.5 to 15 parts by weight of di- or trialkoxysilane compound [D] is mixed with 100 parts by weight, and organic polymer resin [A]: (silica [B] + sparingly soluble Cr compound [C]) Of the resin composition film having a weight ratio of 80:20 to 44:56 and a weight ratio of silica [B]: sparingly soluble Cr compound [C] of 37: 3 to 25:15 of 0.3 to 3.0 g / m ² . Highly corrosion-resistant multi-layer coated steel sheet formed by the amount of adhesion. 6. An organic polymer resin [A]: (silica [B] +
The high corrosion-resistant multi-layer coated steel sheet according to claim (5), wherein the weight ratio of the sparingly soluble Cr compound [C]) is 70:30 to 44:56. 7. A highly corrosion-resistant multi-layer coated steel sheet according to claim 5 or 6, wherein the weight ratio of silica [B]: sparingly soluble Cr compound [C] is 35: 5 to 25:15. . 8. The highly corrosion-resistant multi-layer coated steel sheet according to claim 5, wherein the silica [B] in the resin composition film is hydrophobic silica.