JP2950611B2 - Method for producing zircon-based coating composition and zircon-based oxide-coated graphite molded article - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a zircon-based coating composition which can be stored for a long time, can be easily coated, and can provide a coating film having excellent stability. The present invention further relates to a method for easily producing a zircon oxide-coated graphite molded article 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, and graphite to improve its corrosion resistance, heat resistance, abrasion resistance, insulation, and the like. In particular, zircon-based compositions are excellent in corrosion resistance, heat resistance, abrasion resistance, insulation, etc., and have a low coefficient of thermal expansion. Useful as

As a zircon-based composition, for example, JP-A-61-250063 describes a composition obtained by mixing a zirconium compound represented by the formula Zr (OC ₅ H ₁₁ ) ₄ , ethyl silicate and isopropyl alcohol. JP-A-63-190175 describes a composition comprising a zirconium oxyacid salt, a silicon alkoxide or a derivative thereof, water and an organic solvent. However, the above composition has poor long-term storage stability, and a coating film obtained by applying the composition on a substrate has a defect that cracks and peeling are liable to occur.

On the other hand, among the above materials, graphite is particularly 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. However, graphite has a disadvantage that it has poor oxidation resistance at high temperatures. When a graphite jig is used for powder metallurgy, alumina powder is sprayed on the graphite surface, or an alumina-based or silica-based binder is applied to prevent the molten metal from wetting or reacting with the graphite. Although it is necessary to prevent this, the former method has the drawback that the process is complicated and the working environment is deteriorated by alumina fine powder. Due to the difference in expansion coefficient, the binder easily separates from the graphite surface, and in a hydrogen atmosphere, the silica and hydrogen in the binder react at high temperatures to generate water vapor, which hinders metal sintering. Had.

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 molded body.
The method for forming the coating includes a vapor deposition method, a sputtering method, a CVD method, and the like.
Method, thermal spraying method, paste sintering method, coating film pyrolysis method, etc. are known, but it is difficult to form a thick film of 0.1 μm or more by these methods, and it prevents oxidative deterioration of graphite etc. Was not enough.

Japanese Patent Application Laid-Open No. 1-122982 discloses that a solution of a tetraalkoxysilane, a hydrolyzate and / or a partial condensate thereof, and a solution of a zirconium tetraalkoxide, a hydrolyzate and / or a partial condensate thereof is formed into a graphite molded body. A method of coating or impregnating, drying and coating is described, and the coating obtained by the above method has a thermal expansion coefficient substantially equal to that of graphite. Does not show wettability or reactivity, and the coating film does not react with hydrogen. However, the above method has a disadvantage that the coating solution cannot be stored for a long time because the coating solution is easily hydrolyzed. In addition, there is a disadvantage that the stability of the obtained coating film is poor, and cracks and peeling are likely to occur.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to provide a zircon-based material that can be easily coated and has a long-term storage that can provide a coating film having excellent stability. An object of the present invention is to provide a coating composition and a method for producing zircon-based 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 number of carbon atoms increases, the stability of the zircon-based coating composition decreases and the long-term storage property deteriorates, so that the number of carbon atoms is limited to 1 to 5.

Examples of the zirconium tetraalkoxide (a) include zirconium tetramethoxide, zirconium tetraethoxide, zirconium tetra-iso-propoxide, zirconium tetra-n-butoxide, zirconium tetra-sec-butoxide, and zirconium tetra-tert-butoxide. And zirconium tetra-n-butoxide and zirconium tetra-
Iso-propoxide is preferred. These may be used alone or in combination of two or more.

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

Examples of the tetraalkoxysilane (b) include, for example, tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetra-iso-propoxysilane, tetra-n-butoxysilane, tetra-sec
-Butoxysilane, tetra-tert-butoxysilane and the like, and particularly preferred are tetraethoxysilane and tetramethoxysilane. These may be used alone or in combination of two or more.

When the addition amount of the above tetraalkoxysilane (b) to the zirconium tetraalkoxide (a) is small, the stability of the zircon-based coating composition is reduced and the long-term storage property is deteriorated. Because it becomes easier, tetraalkoxysilane (b)
/ Zirconium tetraalkoxide (a) (molar ratio)
It is limited to 0.2 to 9, preferably 0.25 to 2.5.

The pyridine compound (c) used in the present invention includes 2-oxy alcohol, 2-oxo alcohol, 3-oxy alcohol, 3-oxo alcohol, α-diol, β-
It is a compound selected from the group consisting of diols and triols.

Examples of the 2-oxyalcohol include 2-methoxyethanol, 2-ethoxyethanol,
(1-methylethoxy) ethanol, 1-methoxy-2
-Propanol, diethylene glycol, tetrahydrofurfuryl alcohol and the like; 2-oxo alcohols include, for example, 2-oxo-1-propanol and ethyl lactate; 3-oxy alcohols include, for example, 3-methoxy Propanol, 2- (2
-Hydroxyethyl) furan and the like, and 3-oxo alcohols include, for example, 2-oxo-1-butanol, ethyl 3-hydroxybutyrate, and the like, and α-diols include, for example, ethylene glycol and propylene glycol. And the like, and as the β-diol,
For example, 1,3-propanediol, 1,3-butanediol, 2,4-pentanediol and the like can be mentioned, and as the triol, for example, glycerin can be mentioned. These may be used alone or in combination of two or more.

When the amount of the alcohol compound (c) added to the zirconium tetraalkoxide (a) is small, the stability of the zircon-based coating composition is reduced and the long-term storage property is deteriorated. Therefore, the alcohol compound (c) / zirconium tetraalkoxide (a) (molar ratio) is limited to 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, all alkoxides). Examples thereof include alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol and butyl alcohol, ketones such as acetone and methyl ethyl ketone, benzene and toluene, and isopropyl alcohol is particularly preferred. These may be used alone or in combination of two or more.

When the amount of the organic solvent (d) added to all alkoxides decreases, the stability of the zircon-based coating composition decreases and the long-term storage property deteriorates, and when the amount increases, pinholes easily occur in the obtained coating film. Organic solvent (d) / total alkoxide (molar ratio) is limited to 0.05 to 500, preferably 0.2 to 300.

When the addition amount of water (e) to the total alkoxide used in the present invention is small, cracks are likely to occur in the obtained coating film, and when it is large, the stability of the zircon-based coating composition is lowered and the long-term storage stability is poor. Therefore, water (e) / total alkoxide (molar ratio) is limited to 0.02 to 2.

It is preferable that an acid or a base is added to the water (e) as a catalyst for promoting the hydrolysis of all alkoxides.

Examples of the acid include hydrochloric acid, hydrofluoric acid, inorganic acids such as nitric acid, acetic acid, and organic acids such as formic acid. Examples of the base include, for example, ammonia, sodium hydroxide, potassium hydroxide, and the like. Hydrochloric acid is preferred.

Since the amount of the acid or base added is less effective for promoting hydrolysis when it is small, and the stability of the zircon-based coating composition is reduced when it is increased, and the long-term storage property is deteriorated.
It is preferably 0.01 to 15 mol per 1 water.

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

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

The average particle size of the zircon powder is difficult to disperse in the zircon-based coating composition when the size is small, and cracks are easily generated in the obtained coating film when the size is large, so 0.01 to 100 μm is preferable, and 0.02 to 2 μm is preferable. Particularly preferred.

In the case where zircon powder is added to the zircon-based coating composition, the amount of the zircon powder added to the zircon-based coating composition is reduced, and the degree of improvement in stability of the obtained coating film is reduced. If this is the case, the stability of the zircon-based coating composition will decrease and the long-term storage stability will deteriorate, so that all zircon-based oxides (oxides formed from zirconium tetraalkoxide (a) and tetraalkoxysilane (b), and zircon powders) 1 to 60% by weight. The addition of the zircon powder is preferably performed after mixing and stirring each constituent material of the zircon-based coating composition.

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

An arbitrary method may be adopted as a method for producing the graphite molded body.For example, natural graphite, artificial graphite or the like as a starting material, extrusion molding, molding by casting, etc., followed by firing, anthracite, coal coke, Extrusion molding using amorphous carbonaceous materials such as petroleum coke, pitch coke, and carbon black as starting materials, and molding by cast molding, etc.
Firing, and further graphitizing. The graphite molded body may contain other kinds of materials such as clay and metal.

The shape of the graphite molded body is not particularly limited, for example, a rod shape, a plate shape, a block shape, a roll shape,
A crucible shape and the like are given.

The application method is not particularly limited,
For example, a coating method using a brush, a spray coat, a dip coat, a spin coat, a roll coat and the like can be mentioned.

The impregnation method is not particularly limited,
For example, a method of immersion and impregnation under normal pressure, a method of immersion and impregnation under reduced pressure, and the like are preferable.It is preferable to perform immersion and impregnation under reduced pressure. Since the composition is less likely to be impregnated, the higher the viscosity, the more volatile the zircon-based coating composition and the higher the solution viscosity, and the more difficult it is to impregnate the zircon-based coating composition inside the pores of the graphite molded article. ^{-3 to} 100 Torr is preferred.

The drying method is not particularly limited,
For example, a method of naturally drying at room temperature, a method of drying by heating after natural drying at room temperature, and a method of naturally drying at room temperature,
Examples of the method include a high-temperature heat treatment, and a method of performing natural drying at room temperature, heating and drying, and then performing a high-temperature heat treatment.

The conditions at each stage in the drying method are appropriately determined depending on the types of the zircon-based coating composition and the graphite molded body, but the natural drying at room temperature is preferably performed for 2 to 48 hours, and the heating drying is performed at 60. The heat treatment is preferably performed at a temperature of 300 ° C. for 30 minutes to 48 hours.
It is preferably carried out at 〜1700 ° C. for 30 minutes to 10 hours.

(Example) Hereinafter, an example of the present invention will be described.

In addition, the evaluation method of each physical property regarding the zircon-based coating composition and the zircon-based oxide-coated graphite molded article shown in the results is as follows.

1. Physical properties of zircon-based coating composition (1) Initial adhesion A slide glass (Matsunami) ultrasonically cleaned with acetone is immersed in the obtained zircon-based coating composition and pulled up at a speed of 300 mm / min. After that, dried under the following conditions to form a zircon-based oxide coating layer to prepare an evaluation sample, a cross-cut tape peeling test according to JIS D0202, 100 zircon-based oxide coating layer Ratio of peeled zircon-based oxide layer to mesh (measuring rate)
Was measured and evaluated.

(Drying conditions) Initial drying: 25 ° C, 24 hours Final drying: 500 ° C (heating from 50 ° C / hr from 25 ° C), 2 hours (2) Boiling resistance (crack resistance and adhesion durability) Using a zircon-based coating composition, an evaluation sample prepared in the same manner as in the evaluation of the initial adhesion was immersed in boiling water for 8 hours, and the surface condition was subjected to a sensory test, and crack resistance was determined according to the following criteria. The sex was evaluated.

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

(3) Acid resistance (crack resistance and adhesion durability) Using the obtained zircon-based coating composition, an evaluation sample prepared in the same manner as in the evaluation of the initial adhesion described above was put in 20 wt% hydrochloric acid in 75% by weight. After immersion for a period of time, the surface condition was subjected to a sensory test to evaluate the crack resistance according to the following criteria.

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

(4) Long-term storage property After leaving the sealed container enclosing the obtained zircon-based coating composition in an atmosphere of 50 ° C. and 65% RH for 6 months, a cloth was prepared in the same manner as in the evaluation of the initial adhesion described above. A cut tape peeling test was performed, and the long-term storage property was evaluated according to the following criteria.

(Judgment criteria) ○: Peeling rate of 20% or less △: Peeling rate of 21 to 50% ×: Peeling rate of more than 50% 2. Physical properties of zircon oxide-coated graphite molded article [Heat resistance] obtained After the zircon-based oxide-coated graphite molded body was allowed to stand at 600 ° C. for 10 hours in an air atmosphere, the heat resistance was evaluated by measuring the weight loss rate with respect to the initial weight of the zircon-based oxide-coated graphite molded body.

Examples 1 to 15 A predetermined amount of zirconium tetraalkoxide, an alcohol compound and isopropyl alcohol shown in Table 1 were supplied to a separable flask, and the mixture was stirred at room temperature for 15 hours at a stirring speed of 800 rpm to stabilize zirconium tetraalkoxide. Was obtained.

A predetermined amount of tetraalkoxysilane shown in Table 1 was added to the obtained alcohol solution, and the mixture was stirred at room temperature for 1 hour.
After stirring at 800 rpm, a predetermined amount of water shown in Table 1 and a hydrochloric acid aqueous solution composed of hydrochloric acid were added, and the stirring speed was 1 hour at room temperature.
The mixture was stirred at 800 rpm to obtain a zircon-based coating composition.

Using the obtained zircon-based coating composition, various physical properties were measured based on the above-mentioned measurement methods, and the results are shown in Table 1.

Next, the obtained zircon-based coating composition was supplied into a vacuum container, and a cylindrical graphite molded body (diameter: 20 mm, height: 20 mm) ultrasonically washed with acetone was immersed in the zircon-based coating composition. After that, 5 Torr
The graphite compact was impregnated with the zircon-based coating composition. Next, the interior of the vacuum container was returned to normal pressure, and the graphite molded body was taken out to obtain a zircon-based coating composition-impregnated graphite molded body.

After naturally drying the obtained zircon-based coating composition impregnated graphite molded body at room temperature for 24 hours, 10 minutes in a heating vessel
Dry at 0 ° C for 24 hours.
After a time treatment, a zircon-based oxide-coated graphite molded body was obtained.

Using the obtained zircon-based oxide-coated graphite molded body,
Based on the above measuring method, the weight loss rate was measured, and the
It is shown in the table.

Example 16 As shown in Table 1, a zircon-based coating composition was obtained in the same manner as in Example 1 except that the amount of isopropyl alcohol was changed.

A predetermined amount of zircon powder (average particle size: 1 μm) shown in Table 1 was added to the obtained zircon-based coating composition, and the mixture was stirred at room temperature for 1 hour at a stirring speed of 1,000 rpm, and the zircon-containing zircon-based coating composition was added. I got

Using the obtained zircon powder-containing zircon-based coating composition, based on the above measurement method, to measure each physical property,
The results are shown in Table 1.

A zircon-based oxide-coated graphite molded article was obtained in the same manner as in Example 1 using the zircon-based coating composition containing zircon powder.

Using the obtained zircon-based oxide-coated graphite molded body,
Based on the above measuring method, the weight loss rate was measured, and the
It is shown in the table.

Comparative Examples 1 to 8 As shown in Table 2, a zircon-based coating composition was obtained in the same manner as in Example 1 except that the amount of the constituent material in the composition was changed.

Using the obtained zircon-based coating composition, various physical properties were measured based on the above-mentioned measurement methods, and the results are shown in Table 2.

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

Using the obtained zircon-based oxide-coated graphite molded body,
The weight loss rate was measured based on the above measurement method, and the
It is shown in the table.

Comparative Example 9 As shown in Table 2, a zircon powder-containing zircon-based coating composition was obtained in the same manner as in Example 16 except that the amount of zircon powder was changed.

Using the obtained zircon powder-containing zircon-based coating composition, based on the above measurement method, to measure each physical property,
The results are shown in Table 2.

A zircon-based oxide-coated graphite molded article was obtained in the same manner as in Example 1 using the zircon-based coating composition containing zircon powder.

Using the obtained zircon-based oxide-coated graphite molded body,
The weight loss rate was measured based on the above measurement method, and the
It is shown in the table.

Comparative Example 10 Using the same graphite molded body as used in Example 1,
Based on the measurement method, the weight loss rate was measured,
3.5 wt%.

Comparative Example 11 Alumina colloid was impregnated in the same manner as in Example 1 except that the zircon-based coating composition was changed to an aqueous dispersion of alumina colloid having an alumina concentration of 7% by weight (trade name: Cataroid AS-3, manufactured by Catalyst Kasei Co., Ltd.). A graphite molded body was obtained.

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

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

Comparative Example 12 A zircon-based coating composition having a silica concentration of 30% by weight
Silica colloid alcohol dispersion (manufactured by Catalyst Kasei Co., Ltd.
A silica colloid-impregnated graphite molded body was obtained in the same manner as in Example 1 except that the product name was changed to OSCAL).

The obtained silica colloid-impregnated graphite molded body is allowed to stand at room temperature for 24 hours.
After air drying for a period of time, it was dried in a heating vessel at 150 ° C. for 1 hour to obtain a silica-coated graphite molded body.

Using the obtained silica-coated graphite molded body, the weight loss rate was measured based on the above-mentioned measurement method, and it 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, alcohol compound,
Since it is composed of an organic solvent and water, it can be easily coated, can be stored for a long period of time, and the coating film obtained from the zircon-based coating composition has excellent initial adhesion, boiling water resistance and acid resistance.

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

In the method for producing a zircon-based oxide-coated graphite molded body of the second aspect of the present invention, since the above-described zircon-based coating composition is used, a graphite molded body coated with a zircon-based oxide can be easily obtained. The zircon-based oxide-coated graphite molded body has excellent heat resistance.

The zircon-based oxide-coated graphite molded body is suitably used for crucibles for melting metals, jigs for firing, and the like.

Claims (2)

(57) [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); Tetraalkoxysilane represented by Si (OR ² ) ₄ (wherein R ² represents an aliphatic hydrocarbon group having 1 to 5 carbon atoms), (c) 2-oxy alcohol, 2-oxo alcohol,
A zircon-based coating composition containing an alcohol compound selected from the group consisting of 3-oxyalcohol, 3-oxoalcohol, α-diol, β-diol and triol, (d) an organic solvent and (e) water; The molar ratio of each component in the composition is (b) / (a) = 0.2 to
9, (c) / (a) = 0.5-6, (d) / ((a) +
(B)) = 0.05-500 and (e) / ((a) +
(B)) a zircon-based coating composition in which 0.02 to 2 or zircon powder is added to the zircon-based coating composition, and all zircon-based oxides of the zircon powder (zirconium tetraalkoxide (a) and tetra A zircon-based coating composition in an amount of 1 to 60% by weight of the total amount of the oxide formed from the alkoxysilane (b) and the zircon powder. 2. A graphite molded article is coated or impregnated with the zircon-based coating composition according to claim 1,
A method for producing a zircon-based oxide-coated graphite molded body, characterized by drying.