JP6699027B2 - Heat resistant gas barrier coating - Google Patents

Description

The present invention relates to a heat-resistant gas barrier coating, and more specifically, it has anisotropy (a) a ratio of diagonal length to thickness of a surface having the largest area of 20 or more and 1000 or less, (b). A plate-like member satisfying all the requirements that the diagonal length of the surface having the largest area is 100 nm or more and 5000 nm or less, (c) the thickness is 1 nm or more and 20 nm or less, and (d) the surface of the alumina particles is coated with silica. The present invention relates to a gas barrier coating coated with alumina particles, which is excellent in high-temperature stability and has a gas barrier that exceeds conventional ones, and a method for imparting the heat resistant gas barrier.

Since metal members typified by stainless steel have moldability and high heat resistance, they are widely adopted as members used at high temperatures such as catalyst supports. However, at high temperatures, oxidation and corrosion are likely to proceed, and research and development aimed at improving environmental resistance is being carried out.
For example, an attempt has been made to improve oxidation resistance and corrosion resistance by hydrolyzing a metal alkoxide and preparing a metal oxide sol solution through a polycondensation reaction and coating it on a stainless steel substrate to form a protective film. .. Compared to PVD, CVD, thermal spraying, etc. as a ceramic coating, this sol-gel method can be applied uniformly to a substrate with a large area and a complicated shape, the composition can be controlled at the molecular level, and the initial capital investment is required. It is low and inexpensive and can be formed into a film.
In addition, in the field of electronic materials, many efforts have been made to improve durability by covering the surface with a member having a gas barrier property that does not permeate air in order to prevent deterioration of function and corrosion from progressing due to exposure to air. There is.

For example, in Non-Patent Document 1, alumina gel obtained by hydrolyzing and polycondensing aluminum alkoxide under acidic conditions of nitric acid is applied to a stainless (SUS304) plate and baked to improve oxidation resistance at high temperature. Have been described.
However, the alumina gel obtained as a coating solution contains a large number of hydroxyl groups, which is one kind of aluminum hydroxide (Akdalaite), and the alumina film formed by coating this alumina gel on a stainless steel substrate is heat treated. Sometimes the shrinkage of the film is very large due to the dehydration reaction of the hydroxyl groups, and there are problems such as cracks and peeling due to the difference in thermal expansion from the substrate, and there are many problems to be solved for industrial use. is there.

Patent Document 1 proposes a method of forming an α-Al2O3 film having an average pore diameter of 2 to 50 nm and a porosity of 30 to 40% from a mixture of α-Al2O3 fine particles of 10 to 100 nm and γ-Al2O3 or boehmite. There is. However, the above-mentioned method forms a porous film and has fine pores, so that it does not have an oxygen barrier property and is difficult to be used as a coating film that particularly improves the heat resistance of the substrate.

Patent Document 2 proposes a catalyst in which a specific stainless steel is heat-treated to deposit a metal oxide on the surface, and amorphous alumina is fixed on the surface. It is necessary to add an amount of molybdenum to make an alloy, and to heat-treat before alumina coating to deposit a porous metal oxide film. There is no effect unless a specific amount of molybdenum is added and heat treatment is performed. Therefore, there are many problems in widespread application.

As described above, in order to realize industrially applicable adhesion, strength, and gas barrier property by coating with a metal oxide, there are many problems to be solved by known methods, and high oxidation resistance and acid resistance are required. There is a demand for members capable of imparting chemical corrosion properties.

In such a situation, the inventors of the present invention, in view of the above technique, have conducted intensive studies with the goal of developing a surface treatment that imparts the above-mentioned high environmental resistance, and as a result, have a specific shape of silica. By sintering a high-density, high-barrier film using plate-shaped alumina particles whose surface is coated with, on the surface of the base material, it was found that the member has high heat-resistant gas barrier properties and transparency, The present invention has been completed.

JP, 2005-305342, A JP-A-11-156194

Journal of the Japan Institute of Metals, Vol. 55, No. 12 (1991) 1345-1352

Provided is a heat resistant gas barrier coating that has never been seen before.

Means for solving the above problems,
(1) A heat-resistant gas barrier coating, wherein the surface is coated with alumina particles having anisotropy and having a plate-like shape that satisfies all of the following (a) to (d).
(A) The ratio of the diagonal length to the thickness of the surface having the largest area is 20 or more and 1000 or less (b) The diagonal length of the surface having the largest area is 100 nm or more and 5000 nm or less (c) The thickness is 1 nm or more 20 nm or less (d) The surface of the heat resistant gas barrier coating according to (2) or (1) in which the alumina particles are coated with silica on one or more surfaces of metal, silicon carbide, titanium nitride and carbon, A coated article, which is a coated article.
(3) The coating described in (1) includes all of a step of preparing a dispersion liquid in which alumina particles are coated with silica, a step of applying the dispersion liquid to the surface, and a step of sintering at 100° C. or higher and 1400° C. or lower. A method for producing a heat resistant gas barrier coating, comprising:
(4) A heat resistant gas barrier coating which is characterized in that the alumina described in (1) comprises at least one of boehmite, gibbsite, bayerite, γ, θ and δ type alumina.
(5) A method for imparting a heat resistant gas barrier property, which comprises coating the surface with alumina particles having anisotropy and having a plate-like shape satisfying all of the following (a) to (d).
(A) The ratio of the diagonal length to the thickness of the surface having the largest area is 20 or more and 1000 or less (b) The diagonal length of the surface having the largest area is 100 nm or more and 5000 nm or less (c) The thickness is 1 nm or more 20 nm or less (d) The surface of alumina particles is coated with silica

In the heat resistant gas barrier coating, by coating the surface with metal oxide particles having anisotropy and having a plate-like shape satisfying all of the following (a) to (d), the adhesion to the substrate is high. In addition, due to its high gas barrier property, it is possible to provide a highly heat-resistant coating material that has never been seen before.
(A) The ratio of the diagonal length to the thickness of the surface having the largest area is 20 or more and 1000 or less (b) The diagonal length of the surface having the largest area is 100 nm or more and 5000 nm or less (c) The thickness is 1 nm or more 20 nm or less (d) Alumina particles whose surface is covered with silica. A transparent gas barrier which has never been obtained by coating one or more surfaces of metal, silicon carbide, titanium nitride and carbon with the alumina particles. It is possible to simply provide a heat resistant coating having a conductive coating. Since the coating includes all of the steps of preparing a dispersion in which alumina particles are coated with silica, coating the dispersion on the surface, and sintering at 100°C or more and 1400°C or less, heat resistance is simplified. Gas barrier coatings can be produced. When the alumina is composed of at least one of boehmite, gibbsite, bayerite, γ, θ, and δ-type alumina, it is possible to impart marked heat resistance. It is possible to provide a method of imparting an unprecedentedly high gas barrier property by coating the surface with alumina particles having anisotropy and having a shape satisfying all of the following (a) to (d).
(A) The ratio of the diagonal length to the thickness of the surface having the largest area is 20 or more and 1000 or less (b) The diagonal length of the surface having the largest area is 100 nm or more and 5000 nm or less (c) The thickness is 1 nm or more The present invention in which the alumina particles having a diameter of 20 nm or less (d) are coated with silica is covered by coating the substrate with a dense and highly gas-barrier coating of alumina particles having a specific shape. Not only can it be used in a temperature range that could not be used until now, but it can also contribute to widespread industrial development by greatly improving the service life time. Specifically, by coating the surface of metal, it is possible to suppress thermal deterioration due to oxidation of the base material and prevent surface changes such as discoloration.By coating the surface of carbide, weight loss due to oxidation can be reduced. Can be suppressed, and the durability of these base materials in a high temperature environment can be significantly improved.

FIG. 1 is a SEM photograph in which the heat-resistant coating particles of Example 1 are magnified 30,000 times, and one scale of the photograph shows 100 nm.

In the plate-like alumina particles constituting the present invention, most of the crystals as primary particles (about 80% or more) have hexagonal plate-like anisotropy, and in the dispersion liquid, the alumina particles are dispersed. The average diagonal length (also referred to as long side) and average thickness of the surface having the largest area can be formed by aggregating a part of the primary particles to form secondary particles within the range where the state of maintaining The ratio (also referred to as the short side) (also referred to as the aspect ratio) is 20 to 1000, and the preferable average aspect ratio is 30 to 900. When the average aspect ratio of the alumina particles is less than 20, the orientation due to self-organization of the particles is low, a dense film exhibiting gas barrier properties cannot be obtained, and when the average aspect ratio of the particles exceeds 1000, transparency is improved. It is not preferable because it does not have such a structure and cracks easily occur in the film, and a dense film cannot be obtained. In addition, since alumina particles having a non-anisotropic shape do not have orientation, cracks easily occur in the film and a dense and high-strength film cannot be obtained, and a film with high gas barrier properties cannot be obtained. Not preferable. Having anisotropy as used in the present invention means that the average diagonal length and thickness of the surface of the particle having the largest area are different, such as a spherical shape having no sides or the length of all sides. Shapes such as equilateral triangular pyramids and squares are not included. Further, having orientation in the present invention means a state in which most of particles having anisotropy are arranged on a base material with the same specific surface oriented in a certain direction, and the orientation of particles is It does not include the state of being randomly arranged on the substrate. Having anisotropy and orientation can be observed by enlarging the surface of the heat resistant gas barrier coating or the dispersion used for coating with a known scanning electron microscope (also referred to as SEM) about 30,000 times. This can be confirmed.

The thickness of the plate-like alumina particles constituting the present invention is, as primary particles, 1 to 20 nm, preferably 3 to 10 nm. When it is less than 1 nm, it is not preferable because it is difficult to form a uniform coating because the dispersibility in the sol state in which alumina particles are dispersed in the medium is low, and when it exceeds 20 nm, the adhesiveness to the substrate is deteriorated and it is practically useable. In some cases, it may not be possible to obtain precise compactness, which is not preferable. The average diagonal length of the surface of the alumina particles constituting the present invention having the largest area is 100 to 5000 nm as primary particles, and preferably 200 to 3000 nm. If it is less than 100 nm, it may not show sufficient heat resistance in some cases, and if it exceeds 5000 nm, the flexibility of the coating film may decrease and peeling may occur due to thermal expansion of the substrate, which is not preferable. It can be confirmed that the particles have the above-described shape and size by observing the particles with a known scanning electron microscope (also referred to as SEM) magnified about 30,000 times.

By coating with the alumina particles having the above-mentioned specific shape, a dense, transparent film having a high gas barrier property and a high heat resistance can be formed.

The heat-resistant gas barrier coating constituting the present invention comprises a step of preparing a dispersion liquid in which alumina particles having a specific shape are coated with silica, a step of applying the dispersion liquid to the surface, and sintering at 100° C. or higher and 1400° C. or lower. By including all of the steps, the heat resistant gas barrier coating can be easily produced, preferably 120°C or higher and 600°C or lower, and particularly preferably 120°C or higher and 400°C or lower. A uniform coating can be formed by using a dispersion in which alumina particles are coated with silica. The coating is applied by a known method and then sintered at 100° C. or more and 1400° C. or less to have high heat resistance and adhesion. A good coating can be formed. If silica coating is performed after applying an alumina dispersion having a specific shape, only the surface is coated and the adhesion does not improve, and sufficient strength cannot be obtained at a sintering temperature of 100°C or lower, and 1400°C. The above is not preferable because the transition of alumina crystals to α-alumina proceeds and a dense coating cannot be obtained.

The crystal system of the alumina particles constituting the present invention is at least one selected from gibbsite, boehmite, γ, δ and θ, and preferably at least one selected from gibbsite and boehmite. The heat treatment of the alumina hydrate causes the crystal system to transition to boehmite, γ, δ, θ or the like.

The base material constituting the present invention is selected from one or more of metal, silicon carbide, titanium nitride, and carbon, and the surface of stainless steel, aluminum, or copper is coated as the metal to impart heat resistance due to high gas barrier properties. The base material may contain additives and other kinds of metals for the purpose of improving workability and strength. The base material constituting the present invention can be applied only by performing usual treatments such as cleaning and degreasing to remove dirt and foreign substances on the surface of the base material that are generally performed, and a special heat treatment or the like can be performed. Can be used without doing. The surface of the base material used in the present invention is preferably flat and has few irregularities. Since the surface is flat and there are few irregularities, it becomes possible to form a dense and uniform coating film on the surface of the base material, and the gas barrier property can be further improved. On the other hand, when the base material is a porous body such as activated carbon, alumina does not stay in the fine pores on the surface to form a uniform film thickness, or the gas in the internal pores expands during firing. The denseness of the coating may be lost and the gas barrier property may not be exhibited.

Next, the method for producing the heat resistant coating of the present invention will be described. A known method can be applied to the method for producing the heat resistant gas barrier coating of the present invention, and the following method can be mentioned as a typical example although it is not particularly limited.

Plate-like alumina hydrate particles having a thickness of 1 to 20 nm, an average diagonal length of a surface having the largest area of 100 to 5000 nm, and an aspect ratio of 20 to 1000, the surface of which is coated with silica. A method of applying an aqueous alumina sol in which is dispersed to a base material, removing an excessive dispersion liquid, drying it if necessary, and performing a sintering treatment will be described.
The above-mentioned aqueous alumina sol can be produced by hydrolyzing a hydrolyzable aluminum compound and deflocculating under acidic conditions in which an organic acid or an inorganic acid is added. By properly selecting the type of hydrolyzable aluminum compound and the conditions of hydrolysis and peptization by a known method (for example, Ceramic Industry Kyokai Vol.76 No.875 P207), bayerite or gibbsite having a specific shape is selected. Aqueous alumina sol composed of alumina hydrate particles which are boehmite, boehmite, or pseudo-boehmite can be produced. As the crystal system of the alumina hydrate particles, gibbsite, boehmite, or pseudo-boehmite is preferable because it can form a film with high heat resistance.

The hydrolyzable aluminum compound includes various inorganic aluminum compounds and organic group-containing aluminum compounds. Examples of the inorganic aluminum compound include salts of inorganic acids such as aluminum chloride, aluminum sulfate and aluminum nitrate.

Examples of the aluminum compound having an organic group include ammonium ammonium carbonate, carboxylates such as aluminum acetate, aluminum ethoxide, aluminum isopropoxide, aluminum n-butoxide, aluminum alkoxides such as aluminum sec-butoxide, and cyclic aluminum oligomers. Examples thereof include aluminum chelates such as diisopropoxy(ethylacetoacetato)aluminum and tris(ethylacetoacetato)aluminum, and organic aluminum compounds such as alkylaluminum.
Among these compounds, aluminum alkoxides are preferable, and those having an alkoxyl group having 2 to 5 carbon atoms are particularly preferable because they have appropriate hydrolyzability and can easily remove by-products. The amount of water required for the hydrolysis is not particularly limited, but at least 3 mol is required for 1 mol of aluminum atom, and it may be added at once or stepwise. If the amount of water added is less than 3 mol, the hydrolysis reaction is not completed and it is difficult to obtain alumina particles having a certain shape, which is not preferable. The amount of boehmite or pseudo-boehmite particles in the aqueous boehmite sol is preferably adjusted to 0.1 to 30 parts by weight, and more preferably adjusted to 0.5 to 20 parts by weight.
When the concentration of the alumina particles in the aqueous alumina sol is 0.1 part by weight or less, the coating-drying operation needs to be repeated to create an appropriate film thickness, which is not preferable because the operation becomes complicated. In the case of more than 1 part, the viscosity of the dispersion liquid becomes high, and it is difficult to obtain a film having a uniform thickness, and the stress due to heat shrinkage increases by forming a thick film at one time, which may cause cracking or film formation. Is peeled off, which is not preferable.

In the production of the gas barrier coating of the present invention, the pH of the plate-like alumina dispersion used is preferably 1 to 7, and particularly preferably 2 to 6. Organic amines such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogen carbonate, ammonia, alkylamines, alkanolamines, tetramethylammonium hydroxide, urea and aromatic amines can be used as the pH adjusting reagent. Inorganic hydroxides, carbonates and the like have elements that remain after firing. Therefore, organic amines are preferably used for applications in which residual elements derived from inorganic salts are not desirable. Furthermore, when the substrate to be coated and/or the coating operation is not affected by pH, the addition of this type of regulator is not particularly required, and the pH adjusting additive is not particularly limited and is not particularly limited. It is not something that will be done.

Alumina particles according to the present invention can be used in a state of being dispersed in water used at the time of production, but when the dispersion medium of the alumina particles having a specific shape is water, it is difficult to apply to the substrate. In addition to a monohydric alcohol having 1 to 3 carbon atoms and a water-soluble organic solvent such as DMF to improve the coating property, ethyl acid phosphate, butyl acid phosphate, butyl pyrophosphate, butoxyethyl acid phosphate, 2- Ethylhexyl acid phosphate, oleyl acid phosphate, tetracosyl acid phosphate, phenyl acid phosphate, diphenyl acid phosphate, benzyl acid phosphate, n-octyl acid phosphate, (2-hydroxyethyl)methacrylate acid phosphate, dibutyl phosphate, bis(2-ethyl) Hexyl) phosphate, lauryl acid phosphate, stearyl acid phosphate, phosphorus compounds such as ethylene glycol monoethyl ether acid phosphate, triethylene glycol monoethyl ether acid phosphate, triethylene glycol monobutyl ether acid phosphate, methanesulfonic acid, ethanesulfonic acid, etc. Aromatic sulfonic acids such as alkyl sulfonic acids, benzene sulfonic acid, p-toluene sulfonic acid, styrene sulfonic acid, and alkyl benzene sulfonic acid, and esters with these lower alcohols, sulfonic acids such as alkali metal salts and ammonium salts, By a known method using polyhydric alcohols, carboxylic acid compounds, surfactants, etc., the surface of alumina by a known method to disperse in a water-insoluble organic solvent such as toluene, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and acetic acid ester. It can also be modified and used as an organosol.

In the alumina particles according to the present invention, the surfaces of the alumina particles having the above-mentioned specific shapes are formed by using known 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3 -Glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3- By silylating hydroxyl groups on the surface of alumina particles by a known method using a silane coupling agent such as methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-methacryloxypropyltriethoxysilane, The surface is coated with silica. By coating the surface of the alumina particles with silica, the adhesion to the base material is improved, and a gas barrier coating having a high density and a high heat resistance can be formed on the base material surface. The coating of silica on the alumina particles is not particularly limited to one that silylates a part of the hydroxyl groups on the surface of the alumina particles or one that silylates all of the hydroxyl groups. It is preferable to use 01 to 5 equivalents, particularly preferably 0.05 to 2 equivalents. When the amount is less than 0.01 equivalent, sufficient adhesion may not be exhibited, and when the amount exceeds 5 equivalents, unreacted silane coupling agent residue may be mixed in a large amount and the denseness may decrease, which is not preferable. When the surface of alumina is not covered with silica, the gas barrier property provided by the present application cannot be sufficiently shown because the adhesion to the base material is reduced, and the heat resistance is not sufficiently improved. There is.

When the viscosity of the alumina dispersion used to form a film on the surface is high, the liquid may contain bubbles, and degassing treatment is required to obtain a highly uniform and dense coating. It is preferable to carry out. Bubbles can be removed by using a depressurizing process, a centrifugal process, or the like as a degassing process method. The degassed metal oxide dispersion is applied to a substrate, the dispersion medium is removed, and the substrate is dried.

The alumina dispersion can be applied to various general base materials depending on the desired shape and size of the film. As a method for coating the substrate, for example, a method in which an alumina dispersion liquid dispersed in water is evenly applied to a support by spraying, a method in which the surface is applied by roll coating or the like, or a uniformly dispersed alumina dispersion liquid is used. Examples of the method include a dipping method in which the base material is immersed in the substrate for a certain period of time, then pulled up at a constant rate to remove excess alumina dispersion and dried.
A known evaporation method is preferable when the dispersion medium is removed as needed after the dispersion liquid is applied to the substrate.

The coating according to the present invention can cover a part of the base material or the entire surface of the base material, but when it is used for applications requiring high heat resistance and gas barrier properties, it is exposed to heat or gas. By covering the entire surface of the base material, corrosion of the base material from the uncoated portion due to oxidation can be prevented, gas permeation can be prevented, and durability can be improved.

After applying the dispersion liquid to the substrate, by sintering at a temperature in the range of 100°C to 1400°C for 1 minute to 24 hours, the heat resistant gas barrier coating of the present invention is obtained, and the sintering temperature is 120°C. As described above, 600° C. or lower is preferable, and 120° C. or higher and 400° C. or lower is particularly preferable. When the sintering temperature is 1400° C. or lower, the dispersion medium is not sufficiently removed, so that the coating may not have a strength that can withstand practical use and may be inferior in durability. There is a case where α-alumina conversion progresses and a dense coating film having a high gas barrier property is not formed, which is not preferable.

The film thickness of the heat resistant coating of the present invention can be easily adjusted by the concentration of alumina particles in the dispersion medium. When the concentration of alumina particles is low, a thin film is formed, and when the concentration is high, a thick film is formed, and the desired film thickness can be obtained by adjusting the concentration. The thickness of the film obtained by one-time coating is not particularly limited, but generally a film having a thickness of 0.01 to 100 μm can be produced, and the coating operation is repeated as necessary to obtain a desired thickness. It can also be a coating. The thickness of the coating is not limited, but generally 0.05 to 50 μm is preferable because a transparent coating having a sufficient gas barrier property can be formed. The thickness of the coating film formed on the base material is measured by using a known high-precision micrometer (for example, high-precision digimatic micrometer MDH-25M manufactured by Mitutoyo Co., Ltd.) for increasing the thickness of the coating on the base material. Alternatively, it can also be confirmed by observing the cross section at a magnification of about 10,000 times using a known scanning electron microscope (also referred to as SEM).

The fact that a film with high heat resistance and barrier properties is formed means that a heat resistant coating formed by sintering the film at 120° C. on stainless steel degreased with acetone or a surfactant after washing by a known method. It can be confirmed that the product does not peel even if it is heated in air at 800° C. for 10 hours and maintains the metallic luster of stainless steel. In the case of a film that does not use a metal oxide of a specific shape, when the barrier property is low, oxygen permeates the film and oxidation of the stainless steel surface progresses to lose the metallic luster. While the base material oxidizes due to peeling and the metallic luster of stainless steel is lost as well, the one using alumina whose surface is covered with silica of a specific shape is a dense and highly adherent coating. No peeling occurs, and the gas barrier property is high and oxygen is not transmitted, so that the surface of stainless steel is not oxidized and the metallic luster is maintained. It can be confirmed by visually observing the surface that the film is not peeled off after the heating test. Further, when the base material is a carbide, it can be confirmed that the amount of weight loss due to combustion is lower than that in the case where the non-coated material is similarly tested.

Next, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the following Examples.

(Example 1)
10 parts by weight of plate-like gibbsite particles (average thickness: 5 nm, average diagonal length of the largest flat surface: 200 nm) of a stainless steel (SUS304) substrate 50 mm×50 mm degreased with acetone, having an average aspect ratio of 40 It was immersed for 5 minutes in a mixed solution of 15 g of a dispersion liquid containing 3 g of 3-glycidoxypropyltrimethoxysilane (KBM403 manufactured by Shin-Etsu Polymer Co., Ltd.): 0.75 g. Then, the substrate was slowly pulled up, dried at 30° C. for 2 hours, and further sintered at 150° C. for 2 hours to prepare a heat resistant gas barrier coating in which a colorless and transparent coating having a thickness of 0.8 μm was coated on stainless steel. This heat resistant gas barrier coating was subjected to a heat resistance test at 800° C. for 10 hours, and as a result, it retained a metallic luster like that of the raw material stainless steel. Further, peeling of the coating from the gas barrier coating was not confirmed after the heat resistance test.

(Example 2)
As in Example 1 except that the dispersion liquid was changed to 10 parts by weight of plate-like boehmite particles having an average aspect ratio of 50 (average thickness: 3 nm, average diagonal length of the plane having the largest area: 150 nm). The operation was performed to prepare a heat resistant gas barrier coating having a transparent coating. When a heat resistance test was conducted in the same manner as in Example 1, the same metallic luster as that of the raw material stainless steel was retained. Further, peeling of the coating from the heat resistant gas barrier coating could not be confirmed after the heat resistance test.

(Example 3)
Alumina dispersion liquid was applied to the graphite substrate in the same manner as in Example 1 except that the graphite substrate degreased with acetone was changed to 100 mm×50 mm. Then, after drying at 30° C. for 2 hours, sintering treatment was further performed at 200° C. for 2 hours to prepare a graphite gas barrier coating.
The weight loss of this gas barrier coating when heated from room temperature to 800°C (holding time 0 minutes) at a heating rate of 10°C/minute was measured, and as a result, the weight was reduced by 20% compared to before heating. It was

(Comparative Example 1)
A transparent alumina coating was produced on stainless steel in the same manner as in Example 1 except that boehmite particles having an average aspect ratio of 1 (average minor axis: 20 nm, average major axis: 20 nm) were used. As a result of conducting a heat resistance test on this substrate at 800° C. for 10 hours, the alumina film was not peeled from the substrate, but the stainless steel of the substrate lost its metallic luster and changed its color to brown, and the gas barrier property of the substrate was Did not improve.

(Comparative example 2)
A colorless and transparent alumina coating was produced on stainless steel in the same manner as in Example 1 except that the amorphous alumina particles were changed to amorphous particles. As a result of conducting a heat resistance test on this substrate at 800° C. for 10 hours, a part of the alumina coating was peeled off from the substrate and the stainless steel of the substrate lost its metallic luster and turned brown, which improved the gas barrier property of the substrate. I didn't.

(Comparative example 3)
A colorless transparent alumina coating was produced on stainless steel by the same procedure as in Example 1 except that 3-glycidoxypropyltrimethoxysilane was not added. As a result of conducting a heat resistance test on this substrate at 800° C. for 10 hours, a part of the alumina coating was peeled off from the substrate and the stainless steel of the substrate lost its metallic luster and turned brown, which improved the gas barrier property of the substrate. I didn't.

(Comparative example 4)
An alumina coating of graphite was prepared in the same manner as in Example 4, except that boehmite particles having an average aspect ratio of 1 (average minor axis: 20 nm, average major axis: 20 nm) were used. As a result of measuring the weight loss when the temperature of this coated article was raised from room temperature to 800° C. (holding time 0 minute) at a rate of temperature increase of 10° C./minute, the weight loss was 40%.

(Comparative example 5)
An alumina coating of graphite was prepared in the same manner as in Example 4, except that 3-glycidoxypropyltrimethoxysilane was not added. When the heat-resistant coating was heated from room temperature to 800° C. (holding time 0 minutes) at a heating rate of 10° C./minute, the weight loss was measured and the result was 60%.

From the comparison between Examples 1 and 2 and Comparative Examples 1 to 3, when the metal surface is coated with silica-coated alumina particles having a specific shape, oxidation of the metal surface is effective due to the gas barrier property of the coating. While it is suppressed and the heat resistance is improved and the metallic luster can be maintained, when the surface of the metal is coated with alumina that does not have a specific shape, the oxidation of the metal progresses and the luster of the metallic surface In the case of using metal oxide particles without silica coating, peeling of the coating occurred due to low adhesion, so the surface of the metal was coated with alumina particles with a specific shape coated with silica. By coating, a special gas barrier effect was exhibited and the heat resistance of the substrate was improved.
From the comparison between Example 3 and Comparative Examples 4 and 5, when the graphite substrate was coated with alumina having a specific shape coated with silica, the weight loss due to oxidation was 20% due to the gas barrier property of the carbon coating. On the other hand, in the case of coating with alumina having no specific shape or alumina without silica coating, the oxidation of carbon progressed and the weight loss of 40 to 60% occurred, so that silica coating was performed. By coating the carbon surface with alumina having a specific shape, a special gas barrier effect was exhibited and the heat resistance of the substrate was improved.

Claims (4)

A heat gas barrier coating,
Alumina having a plate-like shape in which the surface of at least one of metal, silicon carbide, titanium nitride, and carbon has anisotropy , and the primary particles satisfy all of the following (a) to (d): heat gas barrier coating, characterized in that it overturned the particle.
(A) the most ratio of the mean diagonal length and the average thickness of the surface having a large area is 20 to 1,000 (b) the most average diagonal length of the surface having a large area is 100nm or more 5000nm or less (c) Average thickness Is 1 nm or more and 20 nm or less (d) The surface of the alumina particles is silylated . The heat resistant gas barrier coating according to claim 1 , wherein the alumina particles are made of at least one of boehmite, gibbsite, bayerite, and γ, θ, and δ type alumina. Preparing a dispersion liquid silylating the surface of the alumina particles, the more engineering coating the dispersion surface, and viewing including all step of sintering at 100 ° C. or higher 1400 ° C. or less,
The method for producing a heat resistant gas barrier coating, wherein the alumina particles have anisotropy and the primary particles have a plate-like shape satisfying all of the following (a) to (d) .
(A) The ratio of the average diagonal length and the average thickness of the surface having the largest area is 20 or more and 1000 or less.
(B) The average diagonal length of the surface having the largest area is 100 nm or more and 5000 nm or less.
(C) Average thickness is 1 nm or more and 20 nm or less
(D) The surface of the alumina particles has been silylated. A method for imparting a heat resistant gas barrier property, characterized in that the surface of the primary particles has anisotropy and is coated with alumina particles having a plate-like shape satisfying all of the following (a) to (d).
(A) the most ratio of the mean diagonal length and the average thickness of the surface having a large area is 20 to 1,000 (b) the most average diagonal length of the surface having a large area is 100nm or more 5000nm or less (c) Average thickness Is 1 nm or more and 20 nm or less (d) The surface of the alumina particles is silylated .