JPH0812905A - Anticorrosion agent for electrodeposition paint - Google Patents

Abstract

PURPOSE:To obtain a rust preventive for a cationic electrodeposition coating material which is a white powder excellent in rust-preventive function and contg. no toxic substance by mixing a fine silica powder with specified amts. of zinc carbonate and orthophosphoric acid and baking and grinding the resulting mixture. CONSTITUTION:This rust preventive has a ratio of three components (in terms of oxide), P2O5:ZnO:SiO2, of 4-22mol%: 25-65mol%: 13-71mol%, at least exhibits peaks of crystals of zinc phosphate tetrahydrate, zinc silicate, and zinc pyrrophosphate by X-ray diffraction, and has a median diameter of 1-3mum according to particle size distribution measurement with laser, an oil absorption of 40-65ml/100g, according to JISK 5101, a bulk specific gravity of 0.3-0.5g/ml by the Ishiyama specific vol. test method, and a pH of the aq. dispersion thereof of 5.5-9 at 25 deg.C. The preventive enables the production of an electrodeposition coating compsn. exibiting almost the same coating film stability and rust- preventive function as those attained with a lead-base rust-preventive pigment without using it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pollution-free rust preventive agent for electrodeposition paints, and more specifically, a white rust preventive agent for cationic electrodeposition paints comprising three components of silica, zinc oxide and phosphoric acid. Regarding pigments.

[0002]

2. Description of the Related Art Electrodeposition paints have been widely used for coating automobiles and home electric appliances since they can form coating films excellent in durability, corrosion resistance and gloss. For electrodeposition paints, pigments composed of lead and chromium compounds such as lead chromate, lead silicate, zinc chromate, and strontium chromate have been conventionally used as rust preventives as rust preventives. Since these pigments contain harmful substances such as lead and chromium, their use has been regarded as a problem from the standpoint of pollution control, and in recent years, they have become particularly severe in terms of social environment, and legal regulations have been imposed. Is about to be banned by.

Therefore, as a non-toxic or low-toxic rust preventive pigment which replaces the lead compound, zinc phosphate, titanium phosphate, silicon phosphate, aluminum phosphate, calcium phosphate, zinc oxide, aluminum phosphomolybdate, phosphomolybdenum is conventionally used. Although the use of zinc acid has been investigated, these compounds are not practically satisfactory because they do not have the rust-preventing ability and film-forming ability of the above-mentioned lead compounds and chromium compounds.

[0004]

Phosphates such as zinc and silicon, which have been studied so far, have a pH value of an aqueous suspension and have a large amount of elution components, and particularly a strong coating film as an electrodeposition coating composition is obtained. Not formed. Therefore, the main object of the present invention is a white fine powder pigment composed of three components of silica, zinc oxide and phosphoric acid, which is capable of forming a coating film having a rust preventive ability comparable to the above rust preventive agent. It is to provide anticorrosion pigments for coating materials.

[0005]

According to the present invention, the three-component composition ratio expressed on the oxide basis is 4 to 22 mol% as P ₂ O ₅ , 25 to 65 mol% as ZnO, and 13 to 71 mol as SiO _2. % By X-ray diffraction and shows a peak due to crystals of at least zinc phosphate tetrahydrate, zinc silicate and zinc pyrophosphate, and has a median diameter of 1 by a laser particle size distribution measurement method. 0.0 to 3.0 μm, J
Oil absorption by ISK5101 method is 40 to 65ml / 1
00 g, the bulk specific gravity by the Ishiyama specific volume test method is 0.3 to 0.5, and the pH of the aqueous suspension at 25 ° C. is 5.
5 to 9.0, and the water-soluble phosphorus content is P ₂ O.
There is provided a rust preventive pigment for a cationic electrodeposition coating, which is characterized by having an amount of 0.001 to 0.1 g / 100 ml based on ₅ oxides.

[0006]

The rust-preventive pigment used in the present invention does not contain highly toxic components such as lead and chromium, and is 4 to 22 mol% as P ₂ O ₅ , 25 to 65 mol% as ZnO, and Si based on the oxide.
It is characterized in that it is in the range of 13 to 71 mol% as O ₂ and is a composite having clear crystal peaks of at least zinc phosphate tetrahydrate, zinc silicate and zinc pyrophosphate according to X-ray diffraction. is there. This is advantageous in that it can be easily made into a paint because it tends to have a smaller oil absorption amount and a smaller bulk than the conventional X-ray amorphous phosphate-based rust preventive pigments. .

When the rust preventive pigment is used as an electrodeposition coating composition, it is compatible with the electrodeposition resin in the coating system, and in particular, the resin must not be gelled. It is extremely important that the pH of the liquid is 5.5 to 9.0, preferably 6.5 to 8.0. Especially when the pH is 5.
If the acidity is 5 or less, not only does the resin gel, but the antirust ability tends to decrease. On the other hand, when the pH is 9.0 or higher, there is no particular advantage, and in view of the water-soluble component of the present pigment, the pH is preferably 8.0 or lower.

Further, in the present invention, the details of its rust preventive action are unknown, but since it is basically a phosphate-based rust preventive pigment, the water-soluble phosphoric acid component does not exist on the iron surface. It is considered that it forms a dynamic state and prevents the generation of rust. In the rust preventive agent of the present invention, the phosphoric acid content is eluted in the range of 0.001 to 0.1 g / 100 ml based on P ₂ O ₅ oxide. have.

If the amount of this elution is 0.001 g / 100 ml or less, the rust preventive ability tends to decrease, and 0.1 g / 1
If it is more than 00 ml, the adhesion of the coating film may be deteriorated and the coating film may be blistered. Therefore, as described above, the rust preventive pigment according to the present invention is a phosphate-based pigment,
It is characterized in that the pH of the aqueous suspension is neutral or weakly alkaline, and that the water-soluble phosphorus content is at a lower level than that of conventional phosphate-based rust preventive pigments. (See FIG. 1 described later.)

Further, the oil absorption of this rust preventive pigment is at a low level of 40 to 65 ml / 100 g, and if it is high, the volume concentration of the pigment becomes low, and a large amount is added to impart a predetermined fluidity to the pigment. The vehicle has to be used, which has the disadvantage that the coating must be thick in order to obtain the required rust protection. Further, it is important that the median system of this rust preventive pigment measured by the laser particle size distribution is in the range of 1.0 to 3.0 μm,
This is because if the particle size is too large, it becomes a factor that reduces the storage and dispersion stability of the paint and the adhesion of the coating film.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the resin for electrodeposition coating is used in a neutral or weakly acidic condition, but the pH of the rust preventive agent of the present invention is weakly acidic or weakly alkaline as described above. is important. From the above viewpoint,
This rust inhibitor has a three-component composition ratio of P ₂ O ₅ expressed on an oxide basis.
Of 4 to 22 mol%, ZnO of 25 to 65 mol%, SiO ₂ of 13 to 71 mol%, and pH of 5.5 to 9.0 and water-soluble phosphorus content of P 0.001 to 0.1g based on ₂ O ₅ oxide
It is manufactured so that it will be in the range of / 100 ml.

As a raw material, the silica component has a particle size of 10
Amorphous silica or crystalline silica may be used as long as it is not more than μm, zinc white may be used as zinc oxide, but zinc carbonate is preferable, and an orthophosphoric acid solution is used as a phosphorus component. First, commercially available zinc carbonate is uniformly mixed with the amorphous silica fine powder, and then an orthophosphoric acid solution is added, and the heat generated mainly by the reaction between phosphoric acid and zinc carbonate subsides. 1.0 to 10 obtained by thoroughly mixing with a double screw type kneader
The granules having a particle diameter of mm are fired in an electric furnace at 700 to 1000 ° C. for about 0.5 to 10 hours. In the present invention, among the obtained rust preventives, the above-mentioned pH range is satisfied, but depending on the blending ratio of the three components, there are some that vitrify, and these may also be the rust preventives of the present invention. the vitrification avoid areas preferably pH5.5 to 9.0, and Mizuka溶phosphorus content also preferably in P ₂ O ₅ oxide basis 0.
It is better to synthesize them at a compounding ratio of 001 to 0.1 g / 100 ml.

Then, after dry-milling with an atomizer or the like,
The present rust preventive pigment having an average particle size of 1.0 to 3.0 is obtained by performing wet pulverization with a pot mill or the like and filtering, drying and pulverizing the obtained slurry. In forming an electrodeposition coating composition using the rust-preventive pigment and the electrodeposition resin obtained by the present invention, the type of the coating may be either anionic type or cationic type, but in general, corrosion resistance From the viewpoint of, a cation type resin is preferable, and as the base resin, any of epoxy resin, acrylic resin, polybutadiene resin, alkyd resin and polyester resin can be used. Among them, for example, amine-added epoxy resin is representative. Preferred are polyamine resins.

Examples of the amine-added epoxy resin include (i) an adduct of a polyepoxide compound with a primary mono- and polyamine, a secondary mono- and polyamine or a primary and secondary mixed polyamine, and (ii) a polyepoxide compound. Secondary mono-containing ketiminated primary amino group
And an adduct with a polyamine, (iii) a reaction product obtained by etherification of a polyepoxide compound and a ketiminated hydroxy compound having a primary amino group, and the like.

The polyepoxide compound used for producing the amine-added epoxy resin is a compound having two or more epoxy groups in one molecule, and generally has at least 20.
Those having a number average molecular weight of 0, preferably in the range of 400 to 4000 are suitable. Further, as long as it does not impair the stability of the coating as an inorganic pigment that can be used in addition to the rust preventive agent of the present invention, any pigment can be used without particular limitation as long as it is a pigment usually used in electrodeposition coating, for example, oxidation. Coloring pigments such as titanium, carbon black and red iron oxide, extenders such as clay, mica, barita, talc, calcium carbonate and silica, and rust preventive pigments such as aluminum phosphomolybdate and aluminum tripolyphosphate.

Further, the electrodeposition coating composition using the rust preventive pigment according to the present invention may be mixed with coating additives such as an organic compound, a pigment dispersant and a coating surface adjusting agent, if necessary. The electrodeposition coating composition of the present invention can be applied to a desired substrate surface by electrodeposition coating. The electrodeposition coating is generally carried out by diluting it with deionized water or the like so that the solid content concentration becomes about 5 to 40% by weight, and adjusting the pH within the range of 5.5 to 9.0. The electrodeposition bath composed of the coating composition is usually adjusted to a bath temperature of 15 to 35 ° C. and a load voltage of 100.
It can be performed under the condition of 400 V. The film thickness of the electrodeposition coating film that can be formed using the composition of the present invention is not particularly limited, but generally 10 to 10 based on the cured coating film.
It is preferably within the range of 40 μm. In addition, the baking and curing temperature of the coating film is generally suitable in the range of 100 to 200 ° C.

[0017]

The present invention will be described in the following examples. The measurement of each item in the present invention was carried out by the following methods.

1. Elution amount of phosphorus 10.0 g of a sample was weighed in a 200 ml beaker, 100 ml of ion-exchanged water was added, and the mixture was stirred for 1 hour while maintaining the temperature at 25 ° C. The supernatant was collected by a centrifuge (10000 rpm × 30 minutes) and concentrated. Add 1 ml of nitric acid-concentrated sulfuric acid mixed acid 9
After boiling for 0 minutes, molybdenum blue (ascorbic acid)
It was quantified by absorptiometry. 2. Weigh 10.0 g of PH sample into a 200 ml beaker, add 100 ml of deionized water and stir for 5 minutes, then at 25 ° C.
The pH of the supernatant was measured for 3 hours. 3. Median diameter Laser particle size measuring device (Coulter LS-13
0 type). 4. Oil absorption amount Measured by the method described in JISK-5101-19. 5. Ishiyama-type specific volume test method Weigh 5.0 g of sample into a 20 ml graduated test tube, drop impact with a specific volume tester manufactured by Ishiyama Scientific Instruments Co., Ltd. for 20 minutes, and read the volume up to 0.1 ml, The bulk specific gravity was calculated by the formula. Bulk specific gravity (g / ml) = sample weight (g) / volume after drop impact (ml)

(Example 1) 73 g of amorphous silica [Mizucasil (94% as SiO ₂ ) manufactured by Mizusawa Chemical Industry Co., Ltd.]
And 320 g of industrial zinc carbonate (69% as ZnO),
Mix with a mixer, and then use industrial phosphoric acid (85%) 23
Mixing was continued while dropping 0 g to obtain a granular product. This product was placed in an electric furnace, fired at 850 ° C. for 2 hours, and dry-ground with a small sample mill. 40% porcelain balls were filled in a porcelain pot mill having an internal volume of 5 L, and the dry pulverized product 3
00 g and 2 L of water were added, wet pulverization was performed for 20 hours, the obtained slurry was suction filtered, and dried at 105 ° C. for 15 hours. The dried product was pulverized with a small sample mill to obtain a white rust preventive pigment having a median diameter of 1.5 μm.

(Example 2) 42 g of crystalline silica [high silica (manufactured by Nihon Nihon KK) (99% as SiO ₂ )] having a particle size of 10 μm or less and industrial zinc carbonate (6 as ZnO)
9%) (350 g) was mixed with a mixer, and further 230 g of industrial phosphoric acid (85%) was added dropwise to continue mixing to obtain a granular product. This product was placed in an electric furnace and fired at 950 ° C. for 3 hours, and then the same procedure as in Example 1 was carried out to obtain a white rust preventive pigment having a median diameter of 2.0 μm.

(Example 3) Amorphous silica [Mizukasil (94% as SiO ₂ ) manufactured by Mizusawa Chemical Industry Co., Ltd.] 780
g and Zinhua [Ginrei A manufactured by Toho Zinc Co., Ltd. (9 as ZnO
9%)] 486 g was mixed with a mixer, and further 230 g of industrial phosphoric acid (85%) was added dropwise to continue mixing to obtain a granular product. This product was placed in an electric furnace and fired at 750 ° C. for 5 hours, and then the same procedure as in Example 1 was performed to obtain a median diameter of 1.0 μm.
To obtain a white rust preventive pigment.

Comparative Example 1 Amorphous silica [Mizukasil (94% as SiO ₂ ) manufactured by Mizusawa Chemical Industry Co., Ltd.] 190
345 g of industrial phosphoric acid (85%)
The mixture was continuously added while dropping to obtain a granular product. This was placed in an electric furnace and calcined at 800 ° C. for 2 hours, and then the same procedure as in Example 1 was carried out to obtain a white powder having a median diameter of 1.5 μm.

Comparative Example 2 410 g of industrial zinc carbonate (69% as ZnO) was placed in a mixer, and 230 g of industrial phosphoric acid (85%) was added dropwise to continue mixing to obtain a granular product. Thereafter, the same procedure as in Comparative Example 1 is performed and the median diameter is 1.5 μm.
A white powder of m was obtained.

Comparative Example 3 Reagent Zinc phosphate tetrahydrate was used.

(Comparative Example 4) Basic lead silicate powder (Valus S manufactured by Mizusawa Chemical Industry Co., Ltd.) was used. Table 1 shows the powder physical properties of the above Examples and Comparative Examples.

(Application Example) Tungren oil as a soft component, an amine-added epoxy resin added with polyethylene glycol is used as a base, and tolylene diisocyanate of ethyl cellosolve half block is reacted, and after solubilization with acetic acid, deionized water is added. The resin compositions were mixed in the formulations shown in Table 2 to obtain a cationic electrodeposition coating composition having a solid content of 20%. This electrodeposition coating composition is applied to an object to be coated (cold-rolled untreated steel sheet) by electrodeposition coating under conditions of 30 ° C. and 250 V for about 3 minutes using the object to be coated as a cathode so that the dry film thickness is 20 μm.
After washing with deionized water and baking at 170 ° C. for 30 minutes, a salt spray cycle test was conducted under the following conditions according to JIS K-5400. (Salt Water Spray Cycle Test) Salt water spray 35 ° C. 7 hours Thermal normal drying 50 ° C. 2 hours Wet 50 ° C. 2 hours Test results are shown in Table 3.

[0027]

According to the present invention, the rust preventive pigment of the present invention comprising three components of phosphoric acid component, zinc oxide component, and silica component is a mixed crystal substance having a clear crystal peak in X-ray diffraction. Therefore, the pH of the aqueous suspension is weakly acidic to weakly alkaline, and the water-soluble phosphorus content is also low, so that almost the same coating film stability can be achieved without using lead compound-based rust preventive pigments. It has become possible to provide an electrodeposition coating composition having good properties and rust prevention ability.

[Brief description of drawings]

FIG. 1 shows the water-soluble phosphorus content (P ₂
The relation between O ₅ oxide standard) and pH is shown.

[Table 1]

[Table 2]

[Table 3]

Claims (2)

[Claims] 1. A composition having a three-component composition ratio expressed on an oxide basis in the range of 4 to 22 mol% as P ₂ O ₅ , 25 to 65 mol% as ZnO, and 13 to 71 mol% as SiO ₂ . Further, according to X-ray diffraction, at least a peak due to crystals of zinc phosphate tetrahydrate, zinc silicate and zinc pyrophosphate is shown, and a median diameter by a laser particle size distribution measurement method is 1.0 to 3.0 μm,
Oil absorption by JISK5101 method is 40 to 65 ml /
At 100 g, the bulk specific gravity is 0.3 according to the Ishiyama specific volume test method.
To 0.5 g / ml and the pH of the aqueous suspension at 25 ° C. is in the range of 5.5 to 9.0, which is a white fine powder rust preventive agent for cationic electrodeposition coatings. 2. The rust preventive agent for cationic electrodeposition coating composition according to claim 1, wherein the water-soluble phosphorus content of the rust preventive agent is 0.00 to 0.1 g / 100 ml based on P ₂ O ₅ oxide.