JPH0517703A - Anticorrosion pigment and method for producing the same - Google Patents

Abstract

(57) [Summary] [Purpose] The solubility of Cr ⁶⁺ under acidic conditions is suppressed, it is used for electric composite plating of steel sheets and has good dispersibility in a plating solution, and it is easily codeposited in the plating layer. And an anticorrosion pigment exhibiting excellent corrosion resistance and a method for producing the same. A rust preventive pigment having a first coating layer made of fine particles of barium sulfate and a second coating layer made of fine particles of sparingly soluble chromate or / and chromium hydroxide on the surface of barium chromate particles. The production method is as follows. An aqueous slurry of barium chromate is added and reacted with an aqueous solution of sulfuric acid or a sulfate to form a first coating layer, and a salt or reducing agent selected from soluble salts of Ni, Cr, Fe and Pb is added. The process comprises adding and reacting an aqueous solution to form a second coating layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rust preventive pigment, particularly to a rust preventive pigment useful for electric composite plating of steel sheets and a method for producing the same.

[0002]

2. Description of the Related Art Recently, there has been a strong demand for a zinc-based alloy-plated steel sheet such as a steel sheet for automobiles, which is more excellent in corrosion resistance, and has been actively developed. As such a plated steel sheet, a dispersion-type plated steel sheet is known in which fine insoluble particles such as chromia, alumina, silica, or titania are suspended during electroplating to disperse the fine particles in a plating layer. (JP 60-211094 A, JP
60-211095, JP-A-60-211096).

Further, a sparingly soluble chromate is added to a zinc-based alloy plating bath, and an alumina sol and a Ni ion are added.
There is also known a method of forming a plating layer containing them by using a plating bath in which two or more kinds are mixed (JP-A-63-11695).
Japanese Patent Laid-Open No. 63-11696). In this case, the chromate dispersed and codeposited in the zinc or zinc alloy-based plating layer acts as one kind of rust preventive pigment, and remarkably improves the corrosion resistance of the steel sheet.

Chromates of metals such as Sr, Ba, Zn, and Pb are known as rust-preventive pigments for electric composite plating of steel sheets of this type, but their solubility in water, coating property of plating film, etc. From this point of view, barium chromate is mainly attracting attention.

[0005]

However, since barium chromate has a high solubility under acidic conditions, hexavalent chromium (hereinafter referred to as "Cr ⁶⁺ ") eluted from barium chromate in an acidic plating solution is used. However, there is a serious problem that the accumulation of metal gradually makes the plating operation unstable and causes the loss of metallic luster on the plated surface.

As a measure to improve this problem, a method of contacting a plating solution with metal particles having a high ionization tendency to reduce Cr ⁶⁺ to Cr ³⁺ and removing it from the system (Japanese Patent Laid-Open No. 63-255399).
Japanese Patent Laid-Open No. 246399) and a method of depositing and coating fine insoluble metal oxide, silicate or amorphous silica on the surface of barium chromate particles (Japanese Patent Laid-Open No. 1-246399).

Of these, the method of reducing and removing Cr ⁶⁺ has the drawback that it requires the addition of a special reducing agent and equipment for removing Cr ³⁺ after reduction, and the surface of barium chromate particles is not The method of coating with oxide or silica is effective for controlling the solubility of barium chromate under acidic conditions, but it is likely to cause coarsening due to agglomeration of particles during the coating treatment, and the plating solution There is a drawback that the dispersibility of particles in the plating layer is reduced.

[0008]

The inventors of the present invention have suppressed the solubility of Cr ⁶⁺ under acidic conditions, and have good dispersibility in a plating solution when used for electric composite plating of steel sheets. As a result of various experimental studies on the realization of an excellent rust preventive pigment that easily co-deposits in the plating layer and exhibits an excellent anticorrosion effect, it was found that certain oxyacid salts and other The present invention has been completed by finding that the desired effect can be achieved very appropriately by forming the coating of 2) in two steps.

That is, the rust preventive pigment according to the present invention comprises a first coating layer composed of fine particles of barium sulfate on the surface of barium chromate particles, and a first coating layer composed of fine particles of sparingly soluble chromate or / and chromium hydroxide. It is a structural feature to have two coating layers.

In the rust preventive pigment according to the present invention, the barium sulfate particles forming the first coating layer directly on the barium chromate particle surfaces must be at least finer than the core barium chromate particles. Is. Meanwhile, the second
The poorly soluble chromate forming the coating layer of at least has a solubility lower than that of the core material barium chromate, and refers to chromate particles having a fine particle size, which may be amorphous or crystalline. Good.

Examples of such chromates include one or two or more of nickel chromate, chromium chromate, iron chromate, lead chromate and the like produced by precipitation reaction, and particularly chromium chromate and chromium. Nickel acid salts are preferred. The barium chromate as the core material is, of course, a normal barium chromate, but a part of CrO ₄ ²⁻ is SO.
_It may be a solid solution of ₄ ²⁻ , MoO ₄ ²⁻ , PO ₄ ³⁻ , F ^−, or the like.

Further, barium chromate is desirable to have fine primary particles as well as good dispersibility in view of the properties of the rust preventive pigment, and in many cases, the average particle diameter is 0.1 to 2.
The range of μm is good. If the average particle size is less than 0.1 μm, the coating efficiency with the oxyacid salt is low, the formation of a large amount of oxyacid salt is required, the effective chromate content becomes extremely low, and it is difficult to manufacture. Become. On the other hand, 2μ
If it is more than m, it is not suitable as a rust preventive pigment, and especially when it is used for steel plate plating, not only the deposition rate in the plating layer is low, but also the dispersion in the plating solution and the plating layer is unsatisfactory. Will be enough.

The rust preventive pigment according to the present invention comprises, as a core material, barium chromate as described above, a first coating layer composed of fine particles of barium sulfate uniformly formed on the surface of the core, and further thereon. The second coating layer is composed of fine particles of poorly soluble chromate or / and chromium hydroxide formed in the above. The coating state of the second coating layer can be easily observed by an electron microscope or the like. You can judge. That is, the particle states before and after coating were almost the same, the elution of Cr ⁶⁺ from the core material barium chromate was suppressed more reliably than before coating, and the zeta potential in the sulfuric acid acid solution was The condition of the coating can be determined based on whether or not it is positive.

The amount of barium sulfate in the first coating layer formed on the surface of the barium chromate particles varies depending on the purpose of use of the rust preventive pigment, but is 1 to 20% by weight, preferably 5 to 50% by weight based on the total weight of the rust preventive pigment. It is in the range of 15% by weight. This amount is 1
If the content is less than 10% by weight, the second coating layer formed on the core material lacks in adhesion and uniformity, resulting in C from the core material barium chromate.
The effect of suppressing r ⁶⁺ dissolution becomes insufficient and uncertain, while
If it exceeds 20% by weight, the content of the barium chromate component that exerts the rust-preventing effect is so low that it does not hinder the formation of the second coating layer, and the practicality is lowered.

The second coating formed on the first coating layer
The amount of chromate and / or chromium hydroxide in the coating layer also varies depending on the purpose of use of the anticorrosion pigment, but is in the range of 0.5 to 20% by weight, preferably 3 to 15% by weight, based on the total weight of the antirust pigment. If this amount is less than 0.5% by weight, the effect of suppressing the elution of Cr ⁶⁺ from the core material barium chromate becomes insufficient,
On the other hand, if it exceeds 20% by weight, the content of the barium chromate component becomes lower, and the practicality is lowered. However,
The sum of the two coating amounts is in the range 1.5 to 40, preferably 8 to 30% by weight, based on the total weight.

The rust preventive pigment according to the present invention can be industrially advantageously produced by the following method. That is, an aqueous solution of sulfuric acid or a sulfate is added to an aqueous slurry of barium chromate and reacted to form barium sulfate having a first coating layer of fine particles on the surface of barium chromate particles, and then nickel, An aqueous solution of one or more salts selected from soluble salts of chromium, iron and lead, or an aqueous solution of a reducing agent is added and reacted to form a chromic acid of those metals on the first coating layer on the particle surface. Salt or
And forming a second coating layer consisting of fine particles of chromium hydroxide.

In the above step, the formation of the first coating layer is carried out by adding to the aqueous slurry of barium chromate an aqueous solution of sulfuric acid or a sulphate in an amount necessary for producing a desired amount of barium sulphate and allowing them to react. However, it is desirable that the barium chromate particles are well dispersed so as to be as close to the primary particles as possible. For this purpose, it is preferable to disperse the slurry by high-speed stirring or deagglomerate using a desired disperser having a strong shearing force such as a colloid mill or a homogenizer.

At this time, examples of the reaction carried out on the surface of the barium chromate particles are represented by the equations (1) and (2). BaCrO ₄ + H ₂ SO ₄ → BaSO ₄ + H ₂ CrO ₄ (1) BaCrO ₄ + Na ₂ SO ₄ → BaSO ₄ + Na ₂ SO ₄ (2) Of the above equations, the reaction of the equation (1) is prompt even at room temperature. Although the reaction proceeds, in the case of the formula (2), the reaction is slow, so it is desirable to accelerate it by heating. Each of these reactions is a kind of ion substitution reaction carried out on the surface of barium chromate particles, and is a uniform first reaction consisting of fine barium chromate particles.
While the coating layer is formed, the chromic acid component such as chromic acid or chromate eluted by the reaction is dissolved in the slurry after the reaction.

On the other hand, the formation of the second coating layer is carried out by adding the required amount of chromic acid component to the slurry after the formation of the first coating layer, if necessary, and then adding the desired amount of nickel, chromium or iron. , One or more salts selected from soluble salts of lead, or a reducing agent, and the pH value is appropriately adjusted to react with the chromic acid component. As metal salts of nickel, chromium, iron, lead, etc.,
Water-soluble salts such as sulfates, chlorides, and nitrates of these metals can be used, and as the reducing agent, the chromic acid component (Cr ⁶⁺ ) dissolved in the slurry is converted to trivalent chromium (Cr ^{3 +} ). ⁺ ) Can be used, and sulfite, sulfite, thiosulfate, etc. are practical.

Examples of the chromate-forming reaction carried out in the slurry by adding the above-mentioned respective metal salts are described in the following (3)-
It is shown by the equation (6). H ₂ CrO ₄ + NiSO ₄ + 2NaOH → NiCrO ₄ + Na ₂ SO ₄ + 2H ₂ O (3) 3H ₂ CrO ₄ + 2Cr (OH) SO ₄ + 4NaOH → Cr ₂ (CrO ₄ ) ₃ + 2Na ₂ SO ₄ + 6H ₂ O (4) ) 3H ₂ CrO ₄ + Fe ₂ (SO ₄ ) ₃ + 6NaOH → Fe ₂ (CrO ₄ ) ₃ + 3Na ₂ SO ₄ + 6H ₂ O (5) H ₂ CrO ₄ + Pb (NO ₃ ) ₂ + 2NaOH → PbCrO ₄ + 2NaNO ₃ + 2H ₂ O… (6)

The above reactions (3) to (6) proceed by adjusting the pH value of the slurry to about 3 to 4.5 to form a refractory chromate in the form of fine particles.
Is efficiently deposited on the above coating layer to form a dense and uniform second coating layer.

On the other hand, trivalent chromium (C
An example of the r ³⁺ ) formation reaction is represented by the formula (7). 2H ₂ CrO ₄ + 3H ₂ SO ₃ → Cr ₂ (SO ₄ ) ₃ + 5H ₂ O (7) If the pH of the slurry containing trivalent chromium is adjusted to 4.5 or higher, fine particles of chromium hydroxide will precipitate, To form a dense second coating layer. In any case, after completion of the reaction, aging is continued for a while, solid-liquid separation is then carried out by a conventional method, and if necessary, washing with water is carried out, followed by drying and crushing to obtain a product.

[0023]

The role of the first coating layer in the rust preventive pigment of the present invention is to form a coating of barium sulfate in the form of extremely fine and uniform particles on the surface of the particles of the barium chromate core material. To facilitate the deposition and fixation of fine particles of poorly soluble chromate or / and chromium hydroxide, which are the material of the formed second coating layer, and contribute to the formation of a dense and uniform second coating layer. Conceivable.

On the other hand, the role of the second coating layer is such that the fine particles forming the second coating layer fill the particle gaps of barium sulfate in the first coating layer and coat the entire surface of the barium chromate particles. Depending on the amount of the coating material, the elution of Cr ⁶⁺ from the core material barium chromate in an acidic liquid can be controlled to an arbitrary degree, and the zeta potential of the particles as a whole can be made positive to disperse in the plating layer. It is considered to exert the effect of facilitating precipitation in the state.

The zeta potential (one type of surface charge) in the acidic sulfuric acid solution was negative when the barium chromate core material and barium sulfate in the first coating layer were negative.
Chromate and chromium hydroxide in the coating layer are positive.

[0026]

EXAMPLES The present invention will be described below based on examples. In each example, the elution of Cr ^{6+ in} the acidic region of the rust preventive pigment was evaluated by the following test method. That is, 5 g of a sample of an anticorrosive pigment was put in 100 ml of a sulfuric acid aqueous solution having a pH of 2 ± 0.1, stirred and mixed with a magnetic stirrer at 20 ° C. for 1 hour, and then the solid-liquid was separated by filtration to obtain hexavalent chromium (CrO 3) in the filtrate. (As ₃ ) was measured by a colorimetric method (mg / l).

Example 1 After thoroughly dispersing 500 parts of an aqueous slurry containing 100 parts of barium chromate having an average particle size of 0.5 μm, 14.9 parts of an aqueous sulfuric acid solution (H ₂ SO ₄ 48%) was added to the slurry, The mixture was reacted for 30 minutes at room temperature with stirring to form a first coating layer. Subsequently, the reaction product slurry was added to a nickel sulfate aqueous solution (NiS
After adding 58.7 parts of O ₄ 20%) and adjusting the pH to 4.0, the mixture was reacted at 60 ° C. for 1 hour to form a second coating layer. The reaction product was filtered, washed with water, dried and pulverized by a conventional method to obtain 106 parts of a rust preventive pigment.

This rust preventive pigment has a barium sulfate first coating layer and a nickel chromate second coating layer on the surface of the core barium chromate particles, and the average particle size in Table 1 is Cr ^6+. Although it showed elution properties, it did not show the tendency of particles to aggregate under the observation under an electron microscope, and it was confirmed that the particles had the same particle state as the original barium chromate.

Example 2 After thoroughly dispersing 600 parts of an aqueous slurry containing 100 parts of barium chromate having an average particle size of 0.5 μm, 9 parts of a sulfuric acid aqueous solution (H ₂ SO ₄ 48%) was added to the slurry, The mixture was stirred and reacted at room temperature for 1 hour. Next, 16.5 parts of an aqueous solution of basic chromium sulfate [Cr (OH) SO ₄ 20%] was added to the reaction product slurry, the pH was further adjusted to 4.0, and the reaction was carried out at 50 ° C. for 1 hour. The reaction product is filtered by a conventional method, washed with water,
By drying and pulverizing, 102 parts of an anticorrosive pigment was obtained.

The rust preventive pigment has a barium sulfate first coating layer and a chromium chromate second coating layer on the surface of barium chromate particles, and the average particle size and Cr ⁶⁺ elution property in Table 1 are shown. And the zeta potential in the sulfuric acid acid solution was positive.

Example 3 The reaction and finishing treatment were carried out in the same manner as in Example 2 except that the amount of the basic chromium sulfate aqueous solution added was 33 parts to obtain 104 parts of a rust preventive pigment. The average particle size, Cr ⁶⁺ elution property, zeta potential, etc. of this rust preventive pigment are shown in Table 1.

Example 4 After thoroughly dispersing 600 parts of an aqueous slurry containing 100 parts of barium chromate having an average particle size of 0.5 μm, 13 parts of a sulfuric acid aqueous solution (H ₂ SO ₄ 48%) was added to the slurry, While stirring, the reaction was carried out at room temperature for 1 hour to form a first coating layer. Then, the reaction product slurry was added to an aqueous solution of sodium sulfite (Na ₂ SO ₃
After adding 120 parts of 10%) and adjusting the pH to 3 to reduce the chromic acid component, the pH was further adjusted to 5 and reacted at 50 ° C. for 1 hour to form a second coating layer. The reaction product was filtered, washed with water, dried and pulverized by a conventional method to obtain 104 parts of a rust preventive pigment.

The rust preventive pigment had a first coating layer of barium sulfate and a second coating layer of chromium hydroxide, and exhibited the average particle size, Cr ⁶⁺ elution property, zeta potential and the like shown in Table 1. .

Example 5 A rust preventive pigment was prepared in the same manner as in Example 2 except that the amount of the aqueous sulfuric acid solution added was 7.4 parts, and 25.8 parts of an aqueous iron sulfate solution (FeSO ₄ 10%) was added instead of the basic chromium sulfate aqueous solution. I got 104 copies. This rust preventive pigment has a first coating layer of barium sulfate and a second coating layer of iron chromate and chromium chromate,
Table 1 shows the average particle size, Cr ⁶⁺ elution property, zeta potential and the like.

Example 6 Instead of the basic chromium sulfate aqueous solution, an aqueous lead nitrate solution (Pb (NO
₃ ) ₂ 20%) In the same manner as in Example 2 except that 71 parts were used, 105 parts of a rust preventive pigment was obtained. This rust preventive pigment has a first coating layer of barium sulfate and a second coating layer of lead chromate,
Table 1 shows the average particle size, Cr ⁶⁺ elution property, zeta potential and the like.

Comparative Example 1 Barium chromate itself before coating was used as Comparative Example 1.
As shown in Table 1, this rust preventive pigment having no coating layer had a large Cr ⁶⁺ elution property and a negative zeta potential.

Comparative Example 2 After thoroughly dispersing 500 parts of an aqueous slurry containing 100 parts of barium chromate having an average particle diameter of 0.5 μm, 8.8 parts of a sulfuric acid aqueous solution (H ₂ SO ₄ 48%) was added to the slurry, The mixture was reacted for 1 hour at room temperature with stirring. The reaction product was filtered, washed with water, dried and pulverized by a conventional method to obtain 98 parts of a rust preventive pigment having only the first coating layer of barium sulfate. The anticorrosion pigment of the comparative example showed a value in which the Cr ⁶⁺ elution property was slightly suppressed as compared with the comparative example 1 as shown in Table 1, but the zeta potential was obviously negative.

[0038]

[Table 1]

[0039]

The rust preventive pigment according to the present invention comprises a first coating layer made of barium sulfate on the surface of barium chromate particles, and a sparingly soluble chromate or / and chromium hydroxide formed thereon. By the second coating layer, the elution of Cr ⁶⁺ can be effectively suppressed, and the release of Cr ⁶⁺ exhibiting a rust preventive effect on the metal can be arbitrarily controlled.

Therefore, the rust-preventive pigment according to the present invention is not only suitable as a rust-preventive pigment for electric composite plating for improving the corrosion resistance of a steel sheet, but also used for zinc chromate and strontium chromate which have been conventionally used. Instead, it can be used relatively safely as a rust preventive paint or a rust preventive pigment for electrodeposition coating. In addition, this rust preventive pigment can be designed by the manufacturing method according to the present invention so that the type and thickness of the coating or the surface potential can be arbitrarily designed to set the elution property of Cr ⁶⁺ and the particle characteristics. This can be obtained advantageously.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Teruaki Izaki             No. 1-1 Tobatacho, Tobata-ku, Kitakyushu City, Fukuoka Prefecture New             Nippon Steel Co., Ltd., Yawata Works (72) Inventor Kazuhiko Sano             1-2, Harumi-cho, Tokuyama City, Yamaguchi Prefecture             Gaku Kogyo Co., Ltd. Tokuyama Factory (72) Inventor Makoto Yoshida             No. 1-1 Tobatacho, Tobata-ku, Kitakyushu City, Fukuoka Prefecture New             Nippon Steel Co., Ltd., Yawata Works (72) Inventor Nobuo Takagi             9-15 Kameido, Koto-ku, Tokyo Japanization             Gaku Kogyo Co., Ltd. (72) Inventor Kazunori Nagai             No. 1-1 Tobatacho, Tobata-ku, Kitakyushu City, Fukuoka Prefecture New             Nippon Steel Co., Ltd., Yawata Works (72) Minoru Yokoyama, inventor             3-36-5 Sakashita, Itabashi-ku, Tokyo Toho face             Research Co., Ltd. (72) Inventor Seiji Sugiyama             No. 1-1 Tobatacho, Tobata-ku, Kitakyushu City, Fukuoka Prefecture New             Nippon Steel Co., Ltd., Yawata Works

Claims (5)

[Claims] 1. A first coating layer comprising barium sulfate fine particles on the surface of barium chromate particles and a second coating layer comprising fine particles of sparingly soluble chromate or / and chromium hydroxide.
A rust preventive pigment having a coating layer of 2. Barium sulfate is 1 per total weight of the rust preventive pigment.
The anticorrosive pigment according to claim 1, wherein the anticorrosive pigment is coated in an amount of 0.5 to 20% by weight, and a poorly soluble chromate or / and chromium hydroxide in an amount of 0.5 to 20% by weight. 3. The rust preventive pigment according to claim 1, wherein the poorly soluble chromate is one or more selected from nickel chromate, chromium chromate, iron chromate, and lead chromate. 4. The rust preventive pigment according to claim 1, which has an average particle size in the range of 0.1 to 2 μm. 5. An aqueous slurry of barium chromate is added with an aqueous solution of sulfuric acid or a sulfate to react with each other to form a first coating layer composed of fine particles of barium sulfate on the surface of barium chromate particles, Furthermore, an aqueous solution of one or more salts or reducing agents selected from soluble salts of nickel, chromium, iron, and lead is added and reacted, and those metals are further deposited on the first coating layer on the particle surface. 2. A method for producing a rust preventive pigment, which comprises forming a second coating layer comprising fine particles of chromate or / and chromium hydroxide.