JPH03215376A - Zircon-based coating composition and production of molded graphite article coated with zircon-based oxide - Google Patents

Abstract

PURPOSE:To provide the subject composition containing a zirconium tetraalkoxide, tetraalkoxysilane, an amine compound, an organic solvent and water at specific molar ratios, easily applicable to a substrate and giving a coating film having excellent stability. CONSTITUTION:A zircon-based composition is produced from (a) a zirconium tetraalkoxide (e.g. zirconium tetramethoxide), (b) a tetraalkoxysilane (e.g. tetramethoxysilane), (c) an amine compound expressed by formula I, II or III, (d) an organic solvent and (e) water. The molar ratios of the components in the composition are: b/a is 0.25-2.5, c/a is 0.5-6, d/(a+b) is 0.05-500 and e/(a+b) is 0.02-2. The amine compound is e.g. ethanolamine, diethanolamine or triethanolamine. In addition to the above characteristics, the above composition is storable over a long period.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention can be stored for a long time, can be easily coated,
This invention relates to a dinorecon coating composition that provides a coating film with excellent stability. The present invention also has excellent stability! ! ! "Relating to a method for easily producing a zircon-based oxide-coated graphite molded body having a film."

(Conventional technology) Conventionally, coatings have been used to form coatings on materials such as metal, plastic, wood, paper, cement, and graphite in order to improve their corrosion resistance, heat resistance, abrasion resistance, insulation, etc. Among them, zircon-based compositions have excellent corrosion resistance, heat resistance, abrasion resistance, insulation properties, etc.
Due to its low coefficient of thermal expansion, it is useful as a coating composition for the above materials. Zircon-based compositions are disclosed, for example, in JP-A No. 61-25006.
No. 3 describes a composition formed by mixing a zirconium compound represented by the formula Zr(OCsH+ +)a, ethyl silicate and isopropyl alcohol, and JP-A-63-190175 describes a composition comprising a mixture of a zirconium compound represented by the formula Zr(OCsH+ +)a, and JP-A-63-190175 Compositions consisting of an acid salt, a silicon alkoxide or a derivative thereof, water and an organic solvent are described. However, the above-mentioned composition had the disadvantage that it had poor long-term storage stability, and the coating film obtained by coating it on a substrate was prone to cracking and peeling. On the other hand, among the above materials, graphite in particular is known as a material with a low coefficient of thermal expansion and excellent thermal shock resistance, and is used as a material for jigs used at high temperatures. but,
Graphite has the disadvantage of poor oxidation resistance at high temperatures. In addition, when using a graphite jig for powder metallurgy, it is necessary to sprinkle alumina powder on the graphite surface, or use alumina-based
It is necessary to apply a silica-based adhesive to prevent the molten metal from wetting or reacting with the graphite, but the former method
In addition to being a complicated process, it has the disadvantage of deteriorating the working environment due to the fine alumina powder.The latter method has the disadvantage that the caking agent is removed from the graphite surface due to the difference in thermal expansion coefficient between the caking agent and the graphite. In addition to being easy to peel off, under a hydrogen atmosphere, the silica in the binder reacts with hydrogen at high temperatures to generate water vapor, which hinders the sintering of the metal.

In order to solve the above-mentioned drawbacks, it has been proposed to form a coating of a zircon-based composition on the surface of a graphite molded body. Methods for forming this coating include vapor deposition, sputtering, and CVD.
method, thermal spraying method, paste sintering method, coating film pyrolysis method, etc., but with these methods, it is difficult to form a thick film of 0.1 μm or more, and the oxidative deterioration of graphite etc. This was insufficient to prevent it. Furthermore, JP-A-1-122982 discloses that a solution of tetraalkoxysilane, its hydrolyzate and/or partial condensate, and zirconium tetraalkoxide, its hydrolyzate and/or partial condensate, etc. is applied to a graphite molded body. A method of coating or impregnating and drying is described, and the coating film obtained by the above method has a coefficient of thermal expansion approximately equal to that of graphite, and for this coating film, molten metal shows no wettability or reactivity, and the coating film does not react with hydrogen. However, the above method has the disadvantage that the coating solution cannot be stored for a long time because it is easily hydrolyzed. Moreover, the stability of the resulting 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 its purpose is to provide a zircon-based coating that can be easily coated, provides a coating film with excellent stability, and can be stored for a long time. 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 tRM) Zirconium tetraalkoxide used in the present invention (
a) is a compound represented by the general formula Zr (OR), where Rl 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 should be 1 to 5, since long-term storage properties will be poor.

As the zirconium tetraalkoxide (a),
Examples include zirconium tetramethoxide, zirconium tetraethoxide, zirconium tetra iso-proboxide, zirconium tetra n-poxide, zirconium tetra see-poxide, zirconium tetra ter t-butoxide, and especially zirconium tetra n-butoxide. Butoxide and zirconium tetraiso-propoxide are preferred. These may be used alone or in combination of two or more.

The tetraalkoxysilane used in the present invention is a compound represented by the general formula Si(OR"), in which:
R2 represents an aliphatic hydrocarbon group, and if the number of carbon atoms increases, the stability of the zircon-based coating composition decreases and the long-term storage property deteriorates, so the number of carbon atoms is 1 to 5.

Examples of the above tetraalkoxysilane (b) include:
Tetramethoxysilane, tetraethoxysilane, tetran-propoxysilane, tetraisopropoxysilane, tetran-butoxysilane, tetrasee-
Proxysilane, tetra-tert-ptoxysilane, etc. are mentioned, and tetraethoxysilane and tetramethoxysilane are particularly preferred. These may be used alone or in combination of two or more.

If the amount of the above-mentioned tetraalkoxysilane, etc. added to the zirconium tetraalkoxide (a) is too small, the stability of the zircon-based coating composition will decrease, resulting in poor long-term storage stability, and if it is too large, cracks will easily occur in the resulting coating film. Therefore, the molar ratio of tetraalkoxysilane (a)/zirconium tetraalkoxide (a) is 0.2
5 to 2.5. Amine compounds used in the present invention (
c) is a compound represented by the following one-shell formula (I), (n) or (]II). HO R3NHz ”(I) (HO-R'hN
H”(II)(HO-R3)IN...(I[[
) In the formula, R3 represents an aliphatic hydrocarbon group, but even if the number of carbon atoms decreases or increases, the stability of the zircon-based coating composition will decrease and the long-term storage property will deteriorate. It is 2 to 5. Examples of the compound represented by the above formula (I) include ethanolamine, propanolamine, isopropanolamine, etc., and examples of the compound represented by the formula (It) include diethanolamine, diisopropanolamine, etc. Examples of the compound represented by the formula (I[[) include triethanolamine and triisopropanolamine, with diethanolamine and triethanolamine being particularly preferred. These may be used alone or in combination of two or more. If the amount of the amine compound (c) added to the zirconium tetraalkoxide (a) is too small, the stability of the zircon-based coating composition will decrease, resulting in poor long-term storage stability, and if it is too large, the resulting coating film will be prone to cracking. Therefore, the amine compound (c)/zirconium tetraalkoxide (a) (molar ratio) is from 0.5 to
It is 6.

The organic solvent (b) used in the present invention is not particularly limited as long as it is compatible with the zirconium tetraalkoxide (a) and tetraalkoxysilane (b) (hereinafter referred to as total alkoxide). Examples 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.

If the amount of the organic solvent (d) added to the total alkoxide is small, the stability of the zircon-based coating composition will be reduced and the long-term storage stability will be poor, and if it is too large, pinholes will easily occur in the resulting coating film. Organic solvent《Mountain/
The total alkoxide (molar ratio) is 0.05 to 500,
Preferably it is 0.2-300. If the amount of water (e) added to the total alkoxide used in the present invention is small, the hydrolysis of all the alkoxides will be insufficient, and the resulting coating film will tend to crack, and if it is too large, the zircon-based coating composition will The water (e)/total alkoxide (molar ratio) is 0.02 to 2, since the stability of the water (e) and the long-term storage properties will be poor. It is preferable that an acid or a base be added to the water (e) as a catalyst to promote hydrolysis of all alkoxides. Examples of the above acids include inorganic acids such as hydrochloric acid, hydrofluoric acid, and nitric acid, and organic acids such as acetic acid and formic acid. Examples of the base include:
Examples include ammonia, sodium hydroxide, potassium hydroxide, etc., and hydrochloric acid is particularly preferred. If the amount of the acid or base added is too small, it will not have the effect of promoting hydrolysis, and if it is too large, the stability of the zircon-based coating composition will decrease, resulting in poor long-term storage stability. ~15 mol 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. After mixing and stirring the organic solvent (6), it is preferable to add the tetraalkoxysilane, etc.) and water (e), and then mix and stir.

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

When the average particle size of the zircon powder becomes small, it becomes difficult to disperse it into the zircon-based coating composition, and when it becomes large, cranks are likely to occur in the resulting coating film.
0.01-100 am is preferable, 0.02-2
μm is particularly preferred.

If the amount of the above-mentioned zircon powder added to the zircon-based coating composition is small, the degree of improvement in the stability of the resulting coating film will be low, and if it is too large, the stability of the zircon-based coating composition will decrease and the long-term shelf life will be affected. Therefore, it is preferably 1 to 60% by weight of the total zircon-based oxide (total amount of the oxide formed from zirconium tetraalkoxide (a) and tetraalkoxysilane (b), and zircon powder). Incidentally, the addition of zircon powder is preferably carried out after mixing and stirring the constituent materials of the zircon-based coating composition. In the method for manufacturing 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 onto a graphite molded body, and the graphite molded body is dried to be coated with a zircon-based oxide.

Any method may be used to produce the graphite molded body, such as a method of molding natural graphite, artificial graphite, etc. as a starting material by extrusion molding, cast molding, etc., and then firing it, anthracite, coal coke, etc. Examples include a method of forming an amorphous carbonaceous material such as petroleum coke, pitch coke, carbon plaque, etc. as a starting material by extrusion molding, casting molding, etc., followed by firing and graphitization. In addition,
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 prong shape, a roll shape, a crucible shape, and the like.

The above-mentioned coating method is not particularly limited, and examples thereof include coating methods such as brush coating, spray coating, dip coating, spin coating, and roll coating.

The above-mentioned impregnation method is not particularly limited, and includes, for example, a method of impregnation by immersion under normal pressure, a method of impregnation by immersion under reduced pressure, etc. It is preferable to impregnate by immersion under reduced pressure, and the degree of vacuum is: When the value is low, it becomes difficult for the zircon-based coating composition to be impregnated inside the pores of the graphite molded body, and when it is high, the zircon-based coating composition becomes more volatile, increasing the solution viscosity, and zircon is impregnated inside the pores of the graphite molded body. IX10-3 to 100 Torr is preferable because it makes it difficult for the system coating composition to be impregnated.

The above drying method is not particularly limited, and includes, for example, a method of naturally drying at room temperature, a method of naturally drying at room temperature and then heating drying, a method of naturally drying at room temperature and then high temperature heat treatment, Examples include a method of air drying at room temperature, heat drying, and then further high temperature heat treatment.

Conditions at each stage in the above drying method are determined as appropriate depending on the type of zircon-based coating composition and graphite molded object, but - Air drying at room temperature is preferably carried out for 2 to 48 hours, and heating drying is 30 minutes at 60-300°C
It is preferable to carry out the heat treatment for 48 hours, and the high temperature heat treatment is preferably carried out at 450 to 1700''C for 30 minutes to 10 hours in a non-oxidizing atmosphere.

(Example) Examples of the present invention will be described below.

The methods for evaluating each physical property of the zircon-based coating composition and zircon-based oxide-coated graphite molded body shown in the results are as follows. ■． Physical properties related to zircon-based coating composition (I) Initial adhesion A slide glass (manufactured by Matsunami Co., Ltd.) that had been ultrasonically cleaned with acetone was immersed in the obtained zircon-based coating composition and pulled up at a speed of 300 mm/min. An evaluation sample was prepared by drying under the following conditions to form a zircon-based oxide coating layer, and a cross-cut tape peeling test was conducted in accordance with JIS D 0202. Evaluation was made by measuring the ratio of squares of the peeled zircon-based oxide layer (peeling rate).

(Drying conditions) Initial drying: 25°C, 224 hours Final drying: 500"C (temperature raised from 25°C at 50°C/hr), 2 hours (2) Boiling water resistance (crank resistance and adhesion durability) obtained After immersing an evaluation sample in boiling water for 8 hours using the zircon-based coating composition prepared in the same manner as in the above initial adhesion evaluation, the surface condition was sensory tested and evaluated according to the following criteria. Crack resistance was evaluated.

(Judgment criteria) ○: No crank on the surface ×: Cracks on the surface After performing the above sensory test, a cross force tape peeling test was performed in the same manner as the above initial adhesion evaluation, 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, evaluation samples were prepared in the same manner as in the above initial adhesion evaluation.
After being immersed in wt% hydrochloric acid for 75 hours, the surface condition was subjected to a sensory test and the crack resistance was evaluated according to the following criteria.

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

(4) Long-term storage The sealed container containing the obtained zircon-based coating composition was left in an atmosphere of 50°C and 65% RH for 6 months, and then evaluated in the same manner as in the above initial adhesion evaluation. A cross-cut tape peeling test was conducted, and long-term storage stability was evaluated according to the following criteria.

(Judgment criteria) ○: Peeling rate is 20% or less Δ: Peeling rate is 21-50% X: Peeling rate is over 50% 2. Physical properties regarding zircon-based oxide-coated graphite molded body [Heat resistance] After the obtained zircon-based oxide-coated graphite molded body was left in the air at 600”C for 10 hours, the zircon-based oxide-coated graphite molded body was The heat resistance was evaluated by measuring the weight reduction rate with respect to the initial weight.

Example 1 J02 Σ [{ Predetermined amounts of zirconium tetraalkoxide, amine compound, and isopropyl alcohol shown in Table 1 were supplied to a separable flask, and stirred at room temperature for 15 hours to a stirring degree of 8.
A stabilized alcoholic solution of zirconium tetraalkoxide was obtained by stirring at 0 Q rpm. 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 at a stirring speed of 8.
After stirring at 00 rpm, a hydrochloric acid aqueous solution consisting of predetermined amounts of water and hydrochloric acid shown in Table 1 was added, and the mixture was stirred at room temperature for 1 hour at a stirring speed of 800 rpm to obtain a zircon-based coating composition.

Using the obtained zircon-based coating composition, various physical properties were measured based on the measurement method described above, 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 m, height: 20 cm) that had been ultrasonically cleaned with acetone was immersed in the zircon-based coating composition. After that, the inside of the vacuum container is
The zircon-based coating composition was impregnated into the graphite molded body under reduced pressure. Next, the pressure inside the vacuum container was returned to normal pressure, and the graphite molded body was taken out to obtain a graphite molded body impregnated with a zircon-based coating composition. The obtained graphite molded body impregnated with the zircon-based coating composition was naturally dried at room temperature for 24 hours, and then heated in a heating container for 1 hour.
Dry at 00℃ for 24 hours, and then dry at 150℃ under nitrogen atmosphere.
After treatment at 0°C for 1 hour, a zircon-based oxide-coated graphite molded body was obtained. Using the obtained zircon-based oxide-coated graphite molded body, the weight loss rate was measured based on the measurement method described above, and the results are shown in Table 1. Pig 15,16- 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 added was changed.

Adding a predetermined amount of zircon powder (average particle size 1 μm) shown in Table 1 to the obtained zircon-based coating composition,
A zircon-based coating composition containing zircon powder was obtained by stirring at room temperature for 1 hour at a stirring degree of 1000 rpII+.

Using the obtained zircon powder-containing zircon-based coating composition, various physical properties were measured based on the measurement method described above, and the results are shown in Table 1. A zircon-based oxide-coated graphite molded body was obtained in the same manner as in Example 1 using the above-mentioned 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 measurement method described above, and the results are shown in Table 1. (The following is a blank space) As shown in Table 2, a zircon-based coating composition was obtained in the same manner as in Example 1, except that the amounts of the constituent materials in the composition were changed.

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

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

Using the obtained zircon-based oxide-coated graphite molded body, the weight loss rate was measured based on the measurement method described above, and the results are shown in Table 2. Comparison 5E As shown in Table 2, a zircon-based coating composition containing zircon powder 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-based coating composition, each physical property was measured based on the measurement method described above, and the results are shown in Table 2.

A zircon-based oxide-coated graphite molded body was obtained in the same manner as in Example 1 using the above-mentioned 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 measurement method described above, and the results are shown in Table 2. (The following is a blank space) 为l■LL1 Using the same graphite molded body as used in Example 1, the weight loss rate was measured based on the measurement method described above, and the result was 3.
It was 5wt%. ．． A zircon-based coating composition with an alumina concentration of 7% by weight
An alumina colloid-impregnated graphite molded body was obtained in the same manner as in Example 1, except that the aqueous dispersion of alumina colloid (manufactured by Catalyst Kasei Co., Ltd., trade name: Cataloid AS-3) was used.

The obtained alumina colloid-impregnated graphite molded body was heated at room temperature for 2
After air drying for 4 hours, heat in a heating container at 150"C, 1
After drying for several hours, an alumina-coated graphite compact was obtained. Using the obtained alumina-coated graphite molded body, the weight loss rate was measured based on the measurement method described above, and it was found to be 3.1 wt%.
Met.

Comparison group ↓I Zircon-based coating composition with silica concentration of 30% by weight
Alcohol dispersion of silica colloid (manufactured by Catalyst Kasei Co., Ltd.,
Product name. A silica colloid-impregnated graphite molded body was obtained in the same manner as in Example 1, except that the mixture was changed to silica colloid (OSCAL).

The obtained silica colloid-impregnated graphite molded body was heated 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 a silica-coated graphite molded body.

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

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

The above-mentioned 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 according to the second invention, since the above-mentioned zircon-based coating composition is used, a graphite molded body coated with a zircon-based oxide can be easily obtained. Zircon-based oxide-coated graphite molded bodies have excellent heat resistance.

Claims (1)

[Claims] 1. (a) General formula Zr(OR^1)_4 (wherein R^1
represents an aliphatic hydrocarbon group having 1 to 5 carbon atoms), (b) General formula Si(OR^2)_4 (wherein R^2 is an aliphatic hydrocarbon group having 1 to 5 carbon atoms HO-R^3-NH_2... (I )▲Mathematical formula, chemical formula,
There are tables, etc. ▼... (II) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼... (III) (In the formula, R^3 represents an aliphatic hydrocarbon group having 2 to 5 carbon atoms) (d) A zircon-based coating composition containing an organic solvent and (e) water, wherein the molar ratio of each component in the composition is (b)/(a) = 0.2.
5-2.5, (c)/(a)=0.5-6, (d)/(
(a)+(b))=0.05~500 and (e)/(
A zircon-based coating composition in which (a)+(b))=0.02-2. 2. A method for producing a zircon-based oxide-coated graphite molded body, which comprises applying or impregnating the zircon-based coating composition according to claim 1 onto a graphite molded body, and drying it.