JPH0733302B2 - Zircon coating composition and method for producing zircon oxide-coated graphite compact - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field The present invention can be stored for a long period of time, can be easily coated,
The present invention relates to a zircon-based coating composition capable of obtaining a coating film having excellent stability. The present invention further relates to a method capable of easily producing a zircon-based oxide-coated graphite molded product having a coating film having excellent stability.

(Prior Art) Conventionally, a coating film is formed on a material such as metal, plastic, wood, paper, cement, graphite, etc. by coating in order to improve its corrosion resistance, heat resistance, abrasion resistance, insulation, etc. Among them, the zircon composition is particularly useful as a coating composition for the above materials because of its excellent corrosion resistance, heat resistance, abrasion resistance, insulation properties, and low thermal expansion coefficient. Is.

The zircon composition is, for example, in JP-A-61-250063, a zirconium compound represented by the formula Zr (OC ₅ H ₁₁ ) ₄ ,
A composition comprising a mixture of ethyl silicate and isopropyl alcohol is described, and JP-A-63-190175 describes a composition comprising a zirconium oxyacid salt, a silicon alkoxide or a derivative thereof, water and an organic solvent. There is. However, the above composition is poor in long-term storage stability, and the coating film obtained by coating the composition on a substrate is
It had a defect that cracks and peeling were likely to occur.

On the other hand, among the above materials, graphite is known as a material having a low coefficient of thermal expansion and excellent thermal shock resistance, and is used as a material for a jig for use at high temperatures. But,
Graphite has the drawback of being inferior in oxidation resistance at high temperatures. When a graphite jig is used for powder metallurgy, it is possible to spray alumina powder on the graphite surface,
It is necessary to apply a binder such as silica to prevent wetting and reaction of the molten metal with respect to graphite, but the former method is:
In addition to the complicated process, it has a drawback that the working environment is deteriorated by the fine alumina powder, and the latter method causes the binder to be removed from the graphite surface due to the difference in the coefficient of thermal expansion between the binder and graphite. In addition to being easily peeled off, in a hydrogen atmosphere, there is a drawback that silica in the binder reacts with hydrogen at a high temperature to generate water vapor, which hinders sintering of the metal.

In order to solve the above drawbacks, it has been proposed to form a coating of a zircon-based composition on the surface of a graphite compact. This coating formation method includes vapor deposition, sputtering, and CVD.
Methods, thermal spraying methods, paste sintering methods, coating film pyrolysis methods, etc. are known, but it is difficult to form thick films of 0.1 μm or more by these methods, and oxidative deterioration of graphite is prevented. Was not enough to

Further, in JP-A-1-122982, a solution of tetraalkoxysilane, its hydrolyzate and / or partial condensate and zirconium tetraalkoxide, its hydrolyzate and / or partial condensate, etc. is formed into a graphite molded body. A method of coating or impregnating and drying and coating is described, and the coating film obtained by the above method has a coefficient of thermal expansion almost the same as that of graphite. Does not show wettability or reactivity, and the coating film does not react with hydrogen. However, the above method has a drawback that it cannot be stored for a long time because the coating solution is easily hydrolyzed. In addition, the obtained coating film has poor stability, and cracks and peeling easily occur.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned drawbacks, and an object thereof is a long-term storable zircon system that can be easily coated to obtain a coating film excellent in stability. It is an object of the present invention to provide a coating composition and a method for producing zircon oxide-coated graphite using the coating composition.

(Means for Solving the Problems) The zirconium tetraalkoxide (a) used in the present invention is a compound represented by the general formula Zr (OR ¹ ) ₄ , wherein R ¹ is an aliphatic hydrocarbon group. However, when the carbon number is large, the stability of the zircon-based coating composition is deteriorated and the long-term storage stability is deteriorated. Therefore, the carbon number is 1 to 5.

As the zirconium tetraalkoxide (a),
For example, zirconium tetramethoxide, zirconium tetraethoxide, zirconium tetra-iso-propoxide, zirconium tetra-n-butoxide, zirconium tetra-sec-butoxide, zirconium tetra-tert.
-Butoxide and the like, particularly zirconium tetra-n
-Butoxide and zirconium tetra-iso-propoxide are preferred. These may be used alone or in combination of two or more.

The tetraalkoxysilane (b) used in the present invention is
A compound represented by the general formula Si (OR ² ) ₄ , in which R ² represents an aliphatic hydrocarbon group, but the stability of the zircon-based coating composition decreases as the carbon number increases, and long-term storage The carbon number is 1 to 5 because the property deteriorates.

Examples of the tetraalkoxysilane (b) include:
Tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetra-iso-propoxysilane, tetra-n-butoxysilane, tetra-sec-butoxysilane, tetra-tert-butoxysilane, and the like,
Particularly, tetraethoxysilane and tetramethoxysilane are preferable. These may be used alone or in combination of two or more.

When the amount of the tetraalkoxysilane (b) added to the zirconium tetraalkoxide (a) decreases, the stability of the zircon coating composition decreases and the long-term storage stability deteriorates, and when the amount increases, cracks occur in the resulting coating film. Tetraalkoxysilane (b) /
Zirconium tetraalkoxide (a) (molar ratio) is 0.
25 to 2.5.

The amine compound (c) used in the present invention is a compound represented by the following general formula (I), (II) or (III).

_{^{HO-R 3 -NH 2 ‥ (}} I) (HO-R 3 2 NH ‥ (II) (HO-R 3 3 N ‥ (III) wherein, R ³ is an aliphatic hydrocarbon group, the number of carbon atoms The carbon number is from 2 to 5, because the stability of the zircon-based coating composition decreases and the long-term storage stability deteriorates even if the amount is small or large.

Examples of the compound represented by the above formula (I) include ethanolamine, propanolamine and isopropanolamine, and examples of the compound represented by the formula (II) include diethanolamine and diisopropanolamine. Examples of the compound represented by the formula (III) include triethanolamine and triisopropanolamine, and diethanolamine and triethanolamine are particularly preferable. These may be used alone or in combination of two or more.

When the amount of the amine compound (c) added to the zirconium tetraalkoxide (a) decreases, the stability of the zircon coating composition decreases and the long-term storage stability deteriorates, and when the amount increases, cracks easily occur in the resulting coating film. Therefore, the amine compound (c) / zirconium tetraalkoxide (a) (molar ratio) is 0.5 to 6.

The organic solvent (d) used in the present invention is not particularly limited as long as it is compatible with the zirconium tetraalkoxide (a) and the tetraalkoxysilane (b) (hereinafter referred to as all alkoxide). , For example, alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol and butyl alcohol, ketones such as acetone and methyl ethyl ketone, benzene,
Examples thereof include toluene, and isopropyl alcohol is particularly preferable. These may be used alone or in combination of two or more.

When the amount of the organic solvent (d) added to the total alkoxide is small, the stability of the zircon-based coating composition is low and the long-term storage stability is poor, and when it is large, pinholes are likely to occur in the resulting coating film. The organic solvent (d) / total alkoxide (molar ratio) is 0.05 to 500, preferably 0.2 to 300.

When the amount of water (e) used in the present invention with respect to all alkoxides is small, hydrolysis of all alkoxides is insufficient, so that the resulting coating film is prone to cracking, and when the amount is large, zircon coating composition. The water (e) / total alkoxide (molar ratio) is 0.02 to 2 because the stability of the compound is deteriorated and the long-term storage property is deteriorated.

An acid or base is preferably added to the water (e) as a catalyst for promoting the hydrolysis of all alkoxides.

Examples of the acid include inorganic acids such as hydrochloric acid, hydrofluoric acid and nitric acid, and organic acids such as acetic acid and formic acid, and examples of the base include:
Examples thereof include ammonia, sodium hydroxide, potassium hydroxide and the like, and hydrochloric acid is particularly preferable.

If the amount of the acid or base added is small, there is no effect of promoting hydrolysis, and if it is large, the stability of the zircon-based coating composition decreases and the long-term storage stability deteriorates. Is preferred.

The zircon-based coating composition of the present invention is obtained by mixing and stirring the above-mentioned constituent materials, and the mixing and stirring method is not particularly limited, but the zirconium tetraalkoxide (a) and the amine compound (c) are not particularly limited. After mixing and stirring the organic solvent (d) and the organic solvent (d), the tetraalkoxysilanes (b) and (e) are preferably added and mixed and stirred.

Zircon powder may be added to the zircon coating composition of the present invention in order to further improve the stability (crack resistance, peel resistance, etc.) of the resulting coating film.

The average particle size of the zircon powder becomes difficult to disperse in the zircon-based coating composition as it becomes smaller, and cracks easily occur in the coating film obtained when it becomes larger,
0.01 to 100 μm is preferable, and 0.02 to 2 μm is particularly preferable.

When the amount of the zircon powder added to the zircon coating composition decreases, the degree of improvement in the stability of the resulting coating film decreases, and when the amount increases, the stability of the zircon coating composition decreases and long-term storage stability increases. Therefore, 1 to 60% by weight in the total zircon oxide (the total amount of the zircon powder and the oxide formed from the zirconium tetraalkoxide (a) and the tetraalkoxysilane (b)) is preferable. The zircon powder is preferably added after the constituent materials of the zircon-based coating composition are mixed and stirred.

In the method for producing a zircon oxide-coated graphite molded body of the present invention 2, the above-described zircon coating composition is applied to or impregnated in the graphite molded body and dried to coat the zircon oxide.

Any method may be adopted as the method for producing the above graphite molded body, for example, natural graphite, artificial graphite or the like as a starting material, extrusion molding, molding by cast molding or the like, followed by firing, anthracite, coal coke, After molding by amorphous carbonaceous materials such as petroleum coke, pitch coke, carbon black as a starting material by extrusion molding, cast molding, etc.,
Examples of the method include firing and further graphitization. The graphite molded body may contain other materials such as clay and metal.

The shape of the graphite molded body is not particularly limited, and examples thereof include a rod shape, a plate shape, a block shape, a roll shape, and a crucible shape.

The coating method is not particularly limited, and examples thereof include brush, spray coating, dip coating, spin coating, and roll coating.

The impregnation method is not particularly limited, and examples thereof include a method of immersion impregnation under normal pressure, a method of immersion impregnation under reduced pressure, etc., preferably immersion impregnation under reduced pressure, and the degree of reduced pressure is When it becomes low, it becomes difficult for the zircon coating composition to be impregnated inside the pores of the graphite molded body,
When it becomes higher, the volatilization of the zircon coating composition becomes more vigorous, the solution viscosity increases, and it becomes difficult for the zircon coating composition to be impregnated into the pores of the graphite molded body, so 1 × 10 ^{−1 to} 100 Torr is preferable.

The drying method is not particularly limited, for example, a method of naturally drying at room temperature, a method of naturally drying at room temperature, then heat drying, a method of naturally drying at room temperature, then a high temperature heat treatment, Examples of the method include natural drying at room temperature, heat-drying, and further high-temperature heat treatment.

The conditions at each step in the drying method are appropriately determined depending on the type of the zircon-based coating composition and the graphite molded body, but natural drying at room temperature is preferably performed for 2 to 48 hours, and heat drying is 60 It is preferably carried out at ~ 300 ° C for 30 minutes to 48 hours, and the high temperature heat treatment is carried out under a non-oxidizing atmosphere at 450 ~ 1.
It is preferably carried out at 700 ° C. for 30 minutes to 10 hours.

(Example) Hereinafter, the Example of this invention is described.

The methods for evaluating the physical properties of the zircon-based coating composition and the zircon-based oxide-coated graphite molded product shown in the results are as follows.

1. Physical Properties of Zircon Coating Composition (1) Initial Adhesion Immersing a slide glass (manufactured by Matsunami Co., Ltd.) ultrasonically cleaned with acetone into the obtained zircon coating composition and pulling it up at a speed of 300 mm / min. After that, it was dried under the following conditions to form a zircon-based oxide coating layer to prepare an evaluation sample, and a cross-cut tape peeling test was performed according to JIS D0202, and the grid of 100 zircon-based oxide coating layers. The ratio of the squares (peeling rate) of the peeled zircon-based oxide layer was measured and evaluated.

(Drying conditions) Initial drying: 25 ° C, 24 hours Final drying: 500 ° C (temperature rising from 25 ° C to 50 ° C / hr), 2 hours (2) Boiling water resistance (crack resistance and adhesion durability) was obtained. A zircon-based coating composition was used to immerse an evaluation sample prepared in the same manner as in the case of evaluating the initial adhesion described above in boiling water for 8 hours, and then the surface state was subjected to a sensory test to evaluate crack resistance according to the following criteria. The sex was evaluated.

(Judgment Criteria) ○: No cracks on the surface ×: Cracks on the surface After performing the above-mentioned sensory test, a cross-cut tape peeling test was performed in the same manner as in the case of evaluating the above initial adhesiveness, and the adhesion durability was determined by the peeling rate. Was evaluated.

(3) Acid resistance (crack resistance and adhesion durability) An evaluation sample prepared in the same manner as the above initial adhesion was evaluated using the obtained zircon-based coating composition in 75 wt% hydrochloric acid. After immersion for a period of time, the state of the surface was subjected to a sensory test to evaluate crack resistance according to the following criteria.

(Judgment Criteria) ○: No cracks on the surface ×: Cracks on the surface After performing the above-mentioned sensory test, a cross-cut tape peeling test was performed in the same manner as in the case of evaluating the above initial adhesiveness, and the adhesion durability was determined by the peeling rate. Was evaluated.

(4) Long-term storability After leaving the sealed container containing the obtained zircon-based coating composition in an atmosphere of 50 ° C. and 65% RH for 6 months,
A cross-cut tape peeling test was conducted in the same manner as in the case of evaluating the initial adhesiveness, and the long-term storability was evaluated according to the following criteria.

(Judgment criteria) ○: Peeling rate is 20% or less △: Peeling rate is 21 to 50% ×: Peeling rate is more than 50% 2. Physical Properties of Zircon Oxide-Coated Graphite Molded Product [Heat Resistance] Obtained The zircon-based oxide-coated graphite molded body was allowed to stand at 600 ° C. for 10 hours in an air atmosphere, and then the weight reduction rate with respect to the initial weight of the zircon-based oxide-coated graphite molded body was measured to evaluate heat resistance.

Examples 1 to 14 Predetermined amounts of zirconium tetraalkoxide, amine compound and isopropyl alcohol shown in Table 1 were fed to a separable flask and stirred at room temperature for 15 hours at a stirring speed of 800r.
Stirring at pm gave a stabilized zirconium tetraalkoxide alcoholic solution.

To the resulting alcohol solution, add the specified amount of tetraalkoxysilane shown in Table 1, and stir at a room temperature for 1 hour at a stirring speed of 80.
After stirring at 0 rpm, a predetermined amount of water and a hydrochloric acid aqueous solution containing hydrochloric acid shown in Table 1 were added, and the stirring speed was 80% for 1 hour at room temperature.
The mixture was stirred at 0 rpm to obtain a zircon coating composition.

Using the obtained zircon-based coating composition, each physical property was measured based on the above-mentioned measuring method, and the results are shown in Table 1.

Then, the obtained zircon-based coating composition was supplied into a vacuum vessel, and a cylindrical graphite molded body (diameter: 20 mm, height: 20 mm) ultrasonically washed with acetone was immersed in the zircon-based coating composition. Then, the inside of the decompression container was depressurized to 5 Torr to impregnate the above-mentioned graphite molded body with the zircon-based coating composition. Next, the inside of the vacuum vessel was returned to normal pressure, and the graphite compact was taken out to obtain a zircon-based coating composition-impregnated graphite compact.

The obtained zircon-based coating composition-impregnated graphite compact was air-dried at room temperature for 24 hours, and then 100% in a heating container.
C., dried at 24.degree. C. for 24 hours, and further treated at 1500.degree. C. for 1 hour in a nitrogen atmosphere to obtain a zircon-based oxide-coated graphite compact.

Using the obtained zircon oxide-coated graphite molded body, the weight loss rate was measured based on the above-mentioned measuring method, and the results are shown in Table 1.

Examples 15 and 16 As shown in Table 1, zircon-based coating compositions were obtained in the same manner as in Example 1 except that the addition amount of isopropyl alcohol was changed.

To the obtained zircon coating composition was added a predetermined amount of zircon powder (average particle size 1 μm) shown in Table 1,
The mixture was stirred at room temperature for 1 hour at a stirring speed of 1000 rpm to obtain a zircon coating composition containing zircon powder.

Using the obtained zircon powder-containing zircon coating composition, each physical property was measured based on the above-mentioned measuring method, and the results are shown in Table 1.

Using the above zircon powder-containing zircon coating composition, a zircon oxide-coated graphite molded body was obtained in the same manner as in Example 1.

Using the obtained zircon oxide-coated graphite molded body, the weight loss rate was measured based on the above-mentioned measuring method, and the results are shown in Table 1.

Comparative Examples 1 to 8 As shown in Table 2, zircon coating compositions were obtained in the same manner as in Example 1 except that the amounts of constituent materials added to the composition were changed.

Using the obtained zircon-based coating composition, each physical property was measured based on the above-mentioned measurement method, and the results are shown in Table 2.

Using the above-mentioned zircon-based coating composition, a zircon-based oxide-coated graphite molded body was obtained in the same manner as in Example 1.

Using the obtained zircon oxide-coated graphite molded body, the weight loss rate was measured based on the above-mentioned measuring method, and the results are shown in Table 2.

Comparative Example 9 As shown in Table 2, a zircon powder-containing zircon coating composition was obtained in the same manner as in Example 15 except that the amount of zircon powder added was changed.

Using the obtained zircon powder-containing zircon coating composition, each physical property was measured based on the above-mentioned measurement method, and the results are shown in Table 2.

Using the above zircon powder-containing zircon coating composition, a zircon oxide-coated graphite molded body was obtained in the same manner as in Example 1.

Using the obtained zircon oxide-coated graphite molded body, the weight loss rate was measured based on the above-mentioned measuring method, and the results are shown in Table 2.

Comparative Example 10 Using the same graphite molded body as that used in Example 1, the weight reduction rate was measured based on the above-mentioned measurement method.
It was t%.

Comparative Example 11 A zircon coating composition having an alumina concentration of 7% by weight
An alumina colloid-impregnated graphite compact was obtained in the same manner as in Example 1 except that the aqueous dispersion of alumina colloid (trade name, manufactured by Catalyst Kasei Co., Ltd .; Cataloid AS-3) was used.

The obtained alumina colloid-impregnated graphite compact was allowed to stand at room temperature for 24 hours.
After air-drying for an hour, it was dried in a heating container at 150 ° C. for 1 hour to obtain an alumina-coated graphite compact.

Using the obtained alumina-coated graphite molded body, the weight reduction rate was measured based on the above-mentioned measurement method, and was 3.1 wt%.

Comparative Example 12 A silica colloid-impregnated graphite compact was prepared in the same manner as in Example 1 except that the zircon coating composition was changed to an alcohol dispersion of silica colloid having a silica concentration of 30% by weight (Catalyst Kasei Co., Ltd., trade name: OSCAL). Got

The obtained silica colloid-impregnated graphite molded body was naturally dried at room temperature for 24 hours and then dried in a heating container at 150 ° C. for 1 hour to obtain a silica-coated graphite molded body.

Using the obtained silica-coated graphite molded body, the weight reduction rate was measured based on the above-mentioned measurement method, and was 2.9 wt%.

(Effect of the Invention) The composition of the zircon-based coating composition of the present invention is as described above, and a specific amount of zirconium tetraalkoxide, tetraalkoxysilane, the general formula (I),
Since it is composed of the amine compound represented by (II) and (III), an organic solvent and water, it can be easily coated, can be stored for a long time, and the coating film obtained from the zircon-based coating composition has Excellent adhesion, boiling water resistance and acid resistance.

The zircon-based coating composition is suitably used for coating metal, plastic, wood, paper, cement, graphite and the like.

In the method for producing a zircon-based oxide-coated graphite compact of the present invention 2, since the above-mentioned zircon-based coating composition is used, a zircon-based oxide-coated graphite compact can be easily obtained and obtained. The zircon-based oxide-coated graphite compact has excellent heat resistance.

The zircon-based oxide-coated graphite compact is preferably used for a crucible for melting a metal, a jig for firing, and the like.

Claims (2)

[Claims] 1. A zirconium tetraalkoxide represented by (a) a general formula Zr (OR ¹ ) ₄ (wherein R ¹ represents an aliphatic hydrocarbon group having 1 to 5 carbon atoms), and (b) a general formula. A tetraalkoxysilane represented by Si (OR ² ) ₄ (wherein R ² represents an aliphatic hydrocarbon group having 1 to 5 carbon atoms), (c) the following general formula (I), (II) or ( amine compounds represented by ^{III), HO-R 3 -NH} 2 ‥ (I) (HO-R 3 2 NH ‥ (II) (HO-R 3 3 N ‥ (III) ( wherein, R ³ is carbon A zircon-based coating composition containing (d) an organic solvent and (e) water, wherein the molar ratio of each component in the composition is (b) / (A) = 0.25 ~
2.5, (c) / (a) = 0.5 to 6, (d) / ((a) +
(B)) = 0.05-500 and (e) / ((a) +
(B)) = 0.02 to 2 zircon coating composition. 2. A graphite compact is coated or impregnated with the zircon coating composition according to claim 1,
A method for producing a zircon oxide-coated graphite molded body, which comprises drying.