JPS6050179A - Production of steel plate coated with highly corrosion- resistant film on one side - Google Patents

Abstract

PURPOSE:To produce a steel plate coated with a highly corrosion-resistant film having excellent appearance on one side by plating a zinc alloy on one surface of the steel plate, subjecting the plated surface to a chromate treatment and forming further an org. composite silicate film thereon then subjecting the plate to a heat treatment at a relatively low temp. CONSTITUTION:A zinc alloy plating film of >=1g/m<2>, more preferably, about 5- 40g/m<2> coating weight is formed by electroplating, etc. on the one surface of a steel plate. The plated surface is subjected to an electrolysis or coating type chromate treatment to form a chromate film of about <=1,000mg/m<2>, more preferably, about 10-200mg/m<2> coating weight thereon. The plated surface is successively treated with an org. composite silicate soln. to form an org. composite silicate film of about 0.5-4.0g/m<2>, more preferably about 1.0-3.0g/m<2> coating weight and thereafter the steel plate is subjected to a heating treatment at 50-250 deg.C to improve the corrosion resistance of each layer. The generation of a temper color is thus prevented and the steel plate coated with the highly corrosion-resistant film having good appearance on one side is thus obtd.

Description

[Detailed description of the invention] The present invention relates to a method for producing a coated steel plate with high corrosion resistance on one side.

In recent years, there has been an increasing demand for steel sheets with excellent corrosion resistance as steel sheets for automobile bodies.Therefore, there is a strong tendency to use surface-treated steel sheets with high corrosion resistance in place of the conventionally used cold-rolled steel sheets. ing.

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 adhering in order to improve corrosion resistance. , there is a problem that weldability deteriorates.

To improve such problems, Ni, Fe, M
n.

Zinc alloy plated steel sheets and multilayer plated steel sheets to which one or more elements such as Mo, Co, At, and Cr are added have been researched and developed, and these steel sheets have better weldability and better weldability than the above-mentioned galvanized steel sheets. Corrosion resistance can be improved without deteriorating workability. However, when a steel plate is applied to the bag structure or curved part (hemming part) of an automobile body plate, the surface thereof is required to have a high degree of surface corrosion resistance. A problem with multilayer plated steel sheets is that their corrosion resistance is still insufficient. As a steel plate with high corrosion resistance,
Rust-proof steel plates with zinc-rich coatings, such as those seen in No. 5-24230 and Japanese Patent Publication No. 47-6882, have been researched and developed, and the representative one is known as Synchrometal. . However, even with this anti-corrosion coated steel sheet, peeling of the film may occur in the processed parts such as press forming, so it is still fully satisfactory as a highly corrosion-resistant and anti-rust coated steel sheet that meets the requirements for materials for automobile bodies. It's hard to call it a thing.

In addition, the non-corrosion painted surface (steel plate surface) of Synchro Metal,
When a zinc-rich paint film is baked at a high temperature of approximately 270°C, a poorly soluble oxide film called temper color is formed, which reduces the reactivity of the phosphate treatment carried out by customers such as automobile manufacturers. A uniform phosphoric acid film is formed.
, quality performance will deteriorate after painting. In particular, in the case of high-strength copper plates containing more Si, Mn, etc. in the steel components than ordinary mild steel plates, a selective oxidation film is formed by the Si, Mn, etc., and this tendency becomes noticeable. For this reason, for example, Japanese Patent Application Laid-Open No. 56-152768 proposes a method in which a specific elemental compound is applied to a non-corrosive painted surface before the paint baking treatment to prevent temper color.
Adoption of such a method not only complicates the manufacturing process, but also causes problems such as the specific elements applied actually inhibiting chemical conversion treatment, so it is no longer possible to use a complete temper color solution. hard. The non-corrosion coated surface of copper plates is used on the exterior of automobile bodies.The surface appearance and coating quality after 3-coat, 3-bake painting are required to be at a high level, and in this sense, the above-mentioned anti-corrosion measures are indispensable. It can be said that it is a thing.

The present invention has been researched and developed in view of the drawbacks of the prior art.
An object of the present invention is to provide a method for producing a coated steel sheet with high corrosion resistance on one side and having excellent corrosion resistance on one side without producing a temper color on the non-traversing surface.

For this reason, the present invention involves applying zinc alloy plating to one side of a steel sheet to form a zinc alloy plating film with an adhesion amount of xy/m or more, and then applying electrolytic or coating chromate treatment to only the plated surface. A chromate film with an adhesion amount of 1000 lp/- or less is formed, and then treated with an organic composite silicate solution to form an organic composite silicate film with an adhesion amount of 0.5 to 4,00 m2 on the chromate film. This method allows the steel plate to be formed and then heat-treated at 50 to 250°C.This allows a film structure with excellent corrosion resistance to be obtained on one side, and since the heat treatment is performed at 250°C or less, high-temperature heating is possible. It is possible to appropriately prevent the occurrence of temper color on the uncoated surface of the steel plate.

The applicant previously applied two coatings, a chromate film and an organic composite silicate film, to the surface of an alloy-plated steel sheet with a zinc-based metal.
Patent application 1821-1987 for composite coated steel sheet with layered coating
This composite coated steel sheet has excellent corrosion resistance. The present invention focuses on this overcoating, and by applying it to one side of a copper plate and combining it with appropriate heat treatment, a high degree of corrosion resistance can be obtained on the coated side, and excellent corrosion resistance can be obtained on the uncoated side. This is a product that uses keratinization to produce steel sheets that have good chemical conversion treatment properties and paintability.

In the present invention, only the bottom surface of the copper plate is subjected to (1) zinc alloy plating, (2) subsequent chromate treatment, (3) further treatment with an organic composite silicate solution, and (4) ) Thereafter, heat treatment is performed at 50 to 250°C to obtain a finished product.

In the present invention, first, zinc alloy plating is applied to only one side of a steel plate (cold-rolled steel plate)! Sign. In this way, the reason why we apply alloy plating that uses zinc as a base metal is that this type of plating is less prone to corrosion than normal zinc plating, and it also prevents the chromate film and organic composite silicate film formed on it from progressing. This is because high corrosion resistance can be exhibited due to the synergistic effect of.

The coating weight of this zinc alloy plating must be 1 tA" or more; if it is less than this, the corrosion resistance will deteriorate. Also, even if the coating weight exceeds 30017 m", no significant improvement in corrosion resistance can be expected, and it will cost more. Becomes high. The amount of plating deposited is usually 1~6017m'', preferably 5~40m''.
Selected within the range of /7n2.

This zinc alloy plating includes zinc-iron alloy plating, zinc-nickel alloy plating, zinc-manganese alloy plating,
Zinc-aluminum alloy plating, zinc-cobalt-chromium alloy plating, and any of these plating components include Ni,
Fe, Mn, Mo, Co, A7. It is possible to use one or more elements added such as Cr,
Furthermore, it may be a composite plating in which two or more layers of the same type or different types of the above-mentioned platings are applied.

As the plating method for these zinc-based alloy platings, any practicable method such as electrolytic method, melting method, vapor phase method, etc. can be adopted, but in general, electroplating is advantageous due to the ease of single-sided plating. . The plating components in various alloy platings include N1 amount of 5 to 2 in N1-zn alloy plating.
0wt%, Fe-Zn alloy plating with FiFe content 5-35
wt%, Mll amount for Mn-Zn alloy plating is 30-8
5wt%, At amount 2-60 for Zn-A7 alloy plating
wt%, Co3 in Zn-Co-Cr alloy Metsu-r
10. Ol~15 wt%, Crko, 01~1wt
It is about %. Outside this range, corrosion resistance deteriorates, which is not preferable. In addition, even in the case of plating of two or more layers, the plating components of each layer are selected within the ranges described above.

In the present invention, the above plated surface is subjected to chromate treatment to form a chromate film.

This chromate film needs to have a chromium deposition amount (dry) of 100100O or less, and 1000 m9
If it exceeds 7 m2, the chromate film itself will peel off, resulting in film peeling during pressing, resulting in poor workability.
Furthermore, weldability also deteriorates. However, the amount of chromium attached is 1
If it is less than yng/m2, the film will become non-uniform, which is not preferable. The preferred amount of chromate film is 10 to 200□r
IL2 (the above is converted into metallic chromium).

There are three types of methods for forming such a chromate film: a coating type, an electrolytic type, and a reaction type. In the present invention, it is necessary to form a chromate film by a coating type or an electrolytic type chromate treatment. In reactive chromate treatment, it is difficult to treat one side of a steel plate, and this method cannot be applied to the present invention. The coating-type chromate treatment liquid is mainly composed of a partially cyclized chromic acid solution, and is optionally treated with an organic resin such as a water-dispersible or water-soluble acrylic resin and/or several dozen or more.
Thousands of silica particles (silica sol, humid silica)
It is made to contain. In this case Cr3 n cr rl
The ratio of i) is 1/1 to 1/3, and the pH is 1.5 to 4. Q(
2 to 3) are particularly preferred. Cr3-Cr6+
The ratio is adjusted to a predetermined ratio using a general organic reducing agent (eg, sugar, alcohol, etc.) or an inorganic reducing agent. In addition, as coating type chromate treatment, roll coater method,
Any conventional method such as a dipping method or a spray method may be used, but the roll coke method is advantageous since it is necessary to perform the chromate treatment on only one side.

In 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, so the Cr3+/Cr6+ ratio is maintained stably as it is, and the organic composite silicate solution is used in the next step. This is for processing and sealing.

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 acid,
Wash with water and dry to form a film.

Comparing the chromate films produced by the above two treatment methods, the coating-type chromate film contains more hexavalent chromium than the electrolytic chromate film, so it has superior corrosion resistance. When heat-treated at a relatively high temperature, the film becomes dense and strong, resulting in better corrosion resistance. On the other hand, electrolytic chromate forms a dense romium hydrated oxide layer mainly composed of insoluble trivalent chromium due to the electrolytic reduction reaction of chromic acid. This electrolytic chromate has the advantage of being able to form a highly complete film at a low heating temperature (50 to 100°C), but if the heating temperature is low (1'00°C or less) when performing the above heat treatment, It can be said that applied chromate coatings are also advantageous. Furthermore, the electrolytic type has the advantage that it is easy to control the amount of film deposited.

In any of the above methods, it is important to perform the chromate treatment on only one side and to avoid adhering chromium to the shredded pieces. If even a small amount of chromium adheres to this other surface, the reactivity of the chemical conversion treatment will be poor and the quality of the coating will deteriorate.

One side of the surface is treated with an organic composite silicate solution to form an organic composite silicate film on the chromate film. The amount of film attached (d) of this organic composite silicate
ry) must be selected in the range of o, s Vm" to 4.Ot/m2, preferably 1-Of/"
2-3.0 f/IIL2 range Fv)' Appropriate.

If the adhesion amount is less than 0.527'771Z, sufficient corrosion resistance cannot be obtained, and if it is more than 4.0OS'/m'', spot weldability deteriorates, which is not preferable.

The organic composite silicate has water-dispersible silica as an essential component, and a water-soluble or water-dispersible organic polymer resin is mixed therein in the presence of a silane compound, and the mixture is heated at 10°C or higher and below the boiling point, preferably 50 to 90°C. It is obtained by reacting at a temperature range of . Water-dispersible silica is so-called silica sol or colloidal silica, and has a particle diameter of several tens of amps to several thousand. Examples of the water-soluble or water-dispersible organic polymer resin include polyvinyl alcohol, hydroxyethyl cellulose, polyester, alkyd, epoxy, and acrylic copolymers, but any resin may be used as long as it reacts with silica. However, if the adhesion of cationic electrodeposition paint (epoxy resin base), which is an automotive undercoat paint, is important, the epoxy resin is good and the organic resin content is 100.
It is preferable to contain at least 30 parts per part. Further, the silane compound is used as a reaction accelerator when silica and organic resin are combined. As this silane compound, commercially available silane coupling agents may be used, such as t
Havinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, vinyltris(β-methoxyethoxy)silane, γ-crisitooxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, N=β(aminoethyl ] -r-Aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and other trialkoxysilane compounds.

The blending ratio of water-dispersible silica and water-soluble or water-dispersible organic resin in the organic composite silicate is 5=95 to 95:5, preferably 10:90 to 60 in terms of weight percentage of solid content.
:40. The addition ratio of the silane compound is 0.5-15wt based on the total solid weight of silica and organic resin.
%.

The organic composite silicate obtained in the above manner is xal
Alternatively, 2 g or more may be used in combination. Also in history,
Molybdenum, tungsten, or vanadium oxygen acids or salts thereof, or titanium or zirconium alkoxide chelate compounds may be added. , and n et al. at least ls or 2a, 14 wt% or less based on the total solid shadow content of the silica sol and organic resin, preferably 0.2 to 8
Corrosion resistance can be improved by adding wt%. Furthermore, adding a curing agent such as melamine to the organic composite silicate solution has a much greater effect.

After forming the chromate film and the organic composite silicate film as described above, in the present invention, the surface plate temperature is
Heat treatment is performed at 250°C. In the present invention, the corrosion resistance of the coated surface is further improved by heating in such a temperature range, and since the effect of improving corrosion resistance by such heating can be achieved in a temperature range of 250°C or less, temper coloring on the uncoated surface is possible. can be appropriately prevented from occurring. If the heating temperature exceeds 250°C, there is a risk that the chromate film may crack or soluble Cr8+, which has a passivating effect, may decrease, resulting in deterioration of corrosion resistance.Therefore, 250°C is the upper limit of the heating temperature. be done.

It is generally preferable to carry out heat treatment at a temperature of 100°C or higher in terms of corrosion resistance, but as mentioned above, when performing electrolytic chromate treatment, even low-temperature heating of 50 to 00°C has the effect of improving corrosion resistance. Yes, it is advantageous in practical terms. The heating method may be any method that can obtain a predetermined temperature, such as hot air drying, infrared heating, or induction heater. Further, the heating holding time is about several seconds to several minutes, and holding for a long time is not only economically disadvantageous but also undesirable because there is a risk that the film performance will deteriorate.

The purpose of this heat treatment is first to thermally harden the skin M by the combination of silica sol/silica sol, silica sol/organic polymer, and organic polymer/organic polymer in the organic composite silicate component. For example, silica sol has the property of forming a dry film as water evaporates even at room temperature, but heat treatment causes a condensation reaction between the silanol groups (-8i-0H) of the silica sol and the hydroxyl groups of the siloxane binder resin component. To,! : It is estimated that the film becomes even more dense.

The second purpose of the heat treatment is to remove Cr6 from the surface layer of the chromate film.
+ reacts with polar groups such as hydroxyl groups and carboxyl groups in the organic composite silicate film to strengthen the bond between the two layers. Furthermore, the third purpose of the heat treatment is to improve the corrosion resistance by densifying the underlying chromate film.

As described above, the steel sheet manufactured by the method of the present invention has a zinc alloy plating as a base material to prevent corrosion of the material itself as much as possible, and a chromate film is formed thereon as a base. In particular, by improving corrosion resistance and sealing with an organic composite silicate film as a top layer, the elution of CR8+, which has a passivating effect, in a corrosive environment can be suppressed to the lowest level. It can exhibit excellent corrosion resistance, and the organic composite silicate film itself has excellent corrosion resistance due to its excellent barrier effect and paint adhesion due to its organic components. Provides corrosion resistance and appropriate paint adhesion.

On the other hand, the non-coated surface (steel plate surface) uses coating type or electrolytic chromate, which is easy to treat on one side, so there is almost no chromium adhesion, and the heat treatment temperature is 25°C.
Since the temperature is 0° C. or lower, there is no occurrence of temper color, and it is possible to obtain a steel sheet surface with good phosphate treatment properties and paintability.

Next, the present invention will be explained in detail.

[Example 1. ] Corrosion resistance tests were conducted on the materials of the present invention with different plating components, coating amounts, and heat treatment temperatures as shown in Table 1 as steel sheets for use in automobile bodies. Similar tests were also conducted on each of the steel plates shown in Table 2 as comparison materials.

The plating components of each steel plate are as follows. For each steel plate shown in Table 1 and each steel plate with a chromate film and an organic composite silicate film in Table 2, the plated steel plate is degreased with alkaline, washed with water, After drying, apply a coating type chromate treatment solution using a roll coater or electrolytic chromate treatment.
An electrode chromate film was formed by cathodic electrolysis by immersion in a mate treatment bath, and after drying, an organic composite silicate treatment solution was applied as a second layer by mouth-coating. Further, after drying, heat treatment was performed, and a corrosion resistance test was conducted after being left for 10 days.

Ni-Zn alloy electroplating...Ni content 12
%Fe-Zn alloy electroplating...Fe content 2
5% Mn-Zn alloy electroplating...Mn-containing J
i ao% The details of the coating type chromate treatment solution, electrolytic chromate conditions, organic composite silicate treatment solution, and corrosion resistance test are as follows.

Coating-type chromate treatment conditions A chromate treatment solution of Cr8-Cr22/3, pH=2.5 (pIrid adjusted with KOH), and solid content of 2 ov/l was applied with a roll coater at room temperature and then dried.

0 electrolytic chromate treatment conditions CrO3: 50 f/l, H2SO4: 0.5
t/mu bath temperature 50℃, current density 0.1-20A
/dJ1 A cathodic electrolytic treatment was performed for an electrolysis time of 05 to 30 seconds, followed by washing with water and drying to obtain a film.

[Conditions] Current density Electrolysis time Chromium deposition amount O, 1,
k/□rr? 2.0 sec 0.5 m9/m24
．． 9 tt O, 5tt 10. Q tt4,9 A/
dm 2.0 sec 40 m9761ノ29.6
// 4.0 // 150 p20, Ott 30.
Ott 1500 ttAlthough some comparative examples were subjected to reactive chromate treatment, the treatment was performed using CrO3: 15
Y/l, Cr6+/'Cr": 3, Zn": 3
y/l, H2SO,: 9'//l reactive chromate treatment solution, 50°C, 5 seconds, spray 1 a
The treatment was carried out under the same conditions as 1 and +n.

0 Organic composite silicate treatment liquid Acrylic composite silicate and epoxy composite silicate synthesized as follows (each organic tree content: silica solution = 60
240) in a ratio of 70:30 and organic V1. −
@Silicate treatment solution (pH: 9s, solid content: 2o) Synthesis of A acrylic composite silicate Temperature: 1゛, stirrer, condenser, dropper - 1 ton Add isopropyle to a 4th flask of 1 ton, complete with 1. alcohol 180
After replacing the room with nitrogen, the temperature inside the flask was adjusted to about 85°C, and 140 parts of ethyl acrylate, 68 parts of methylnuccrylate, 15 parts of styrene, 15 parts of N-n-butoxymethylacrylamide, and 2-hydroxyethyl were added. A monomer mixture consisting of 38 parts of acrylate and 24 parts of acrylic acid was added dropwise in about 2 hours together with a catalyst of 6 parts of l-2,2-azobis(2,4-dimethylclero-tolyl). After the dropwise addition was completed, the reaction was continued for another 5 hours at the same temperature to obtain a colorless and transparent resin solution with a solid content of 63% and an acid value of 67. 45 parts were mixed, water was added, and the mixture was sufficiently stirred to obtain an aqueous dispersion of an acrylic copolymer with a solid content of 20% 1.H9,5. 300 parts of this aqueous dispersion was placed in a flask. While thoroughly stirring at room temperature, a quantitative amount of colloidal silica (manufactured by Nissan Chemical Co., Ltd., trade name [Stotex NJ)] was added, and then γ-methacryloxyglobyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name [Stotex NJ]) was added.
1 part of product name rKBM503J) was added dropwise and mixed under stirring,
The mixture was then heated to 85° C. and kept at the same temperature for 2 hours to react, yielding a milky white, water-dispersible acrylic V-coated silicate.

Bisphenol A type epoxy resin with 950 epoxy equivalent of B epoxy composite silicate (manufactured by Shell Kagaku Tuwa, trade name [Ebico])
1004 J) 310 parts, 95 parts of linseed oil fatty acid, 95 parts of tung oil fatty acid, and 15 parts of xylene were put into a flask, and gradually heated while passing nitrogen, and raised to 240 °C / After that, cooled and lowered to 70 °C. At the same time, 200 parts of ethylene glycol monoethyl ether was added to obtain an oil-modified epoxy rosin solution with a solid content of 70% and an oxidation value of 54%.

From this oil-modified epoxy tung fat solution, epoxy composite silicate is prepared in the same manner as in A above.

○A cycle test was conducted in which the corrosion resistance test and above were performed in one cycle, and 250
, 500, and 1000 cycles, the red rust occurrence area of each sample material was evaluated.

The results of the corrosion resistance test are shown in the right column of each table. As is clear from these tables, the single-sided coating structure of the material of the present invention has superior corrosion resistance compared to conventional zinc metal or alloy plating. In Table 2, Tables 5 and 6 indicate the range of the amount of organic composite silicate film deposited, Nα7
and N [L8 is the range of the amount of chromate film deposited.
3 and N[L4 are the ranges of heating temperatures, and 13 are the chromate treatment methods. As is clear from the comparative materials 3 to 9 in Table 2 above and Na13, within the range that deviates from the conditions of the present invention, any one of corrosion resistance, spot weldability, and formability (film peeling during pressing, etc.) Due to the above-mentioned problems, it can be said that it is unsuitable as a rust-preventing steel plate for automobile bodies.

* Dacromet (chromium U coating amount: 300 m9/In) was applied as the first layer on the cold-rolled steel plate, and the temperature was 170°C.
After heating, Zinchromet (film thickness 2μ) was applied as a second layer and baked at 270°C.

[Example 2] In this example, the surface properties of the non-coated surface (steel plate surface) were investigated, and the plated surfaces of various single-sided zinc alloy plated steel sheets were subjected to chromate treatment and organic composite silicate treatment, and then heat treated. The occurrence of temper color on the uncoated surface and chemical conversion treatment properties were investigated for the test materials manufactured by A2.

The results are shown in Table 3 together with comparative materials.

In addition, the investigation of chemical conversion treatment properties regarding phosphate treatment was carried out according to the following table procedure. Test material → Degreasing (rFc4357 J2 sy/l, s 5~ manufactured by Nippon Vercalizing Co., Ltd.
60℃, 120 see diP) ・→Water washing→'Surface adjustment (r-PL4031 manufactured by Nippon Parriki Rising Co., Ltd.)
J 1 r/z, 10sec 5play) → Phosphate treatment (Japan Parriki Rising Co., Ltd. “Bt 3 (104J
TPA22 points, FAIL points, AC1.5~
20°48-52°C, 120 Bec dip)→Water washing→Washing with pure water→Drying→Crystal appearance was examined using a scanning electron microscope (X
Observe at magnification of 1000-2000 times.

As is clear from Table 3, it can be seen that the uncoated surface of the steel sheet obtained by the method of the present invention exhibits a surface quality that is the same as that of a normal cold-rolled steel sheet. On the other hand, other steel plates such as Synchrometal that are heat-treated at temperatures exceeding the upper limit of the heating temperature of the present invention have problems such as the occurrence of Denver color and deterioration of phosphate treatability.

Claims (1)

[Claims] After applying zinc alloy plating to one side of a steel plate to form a zinc alloy plating film with a coating weight of 1 f/m or more, electrolytic or coating chromate treatment is applied to only the plated surface, resulting in a coating weight of 1000m97m. 'The following chromate film is formed, and then treated with an organic composite silicate solution to form a coating amount of 0.5 to 4.09 on the chromate film.
A method for producing a coated steel sheet with high corrosion resistance on one side, which is characterized by forming a 7 m'' organic composite silicate film and then heat-treating the steel sheet at 50 to 250°C.