JP2019143005A - Coating composition, heat-resistant coating, and formation method thereof - Google Patents

Abstract

To provide a heat-resistant coating excellent in ash deposition preventing performance and adhesion to a substrate surface even under a high temperature environment at or above 500°C, and a coating composition that can be used in formation of such a heat-resistant coating.SOLUTION: A coating composition contains alkali metal silicate, fly ash, and boron nitride.SELECTED DRAWING: None

Description

  The present disclosure relates to coating compositions, heat resistant coatings and methods for forming the same.

  Boron nitride is known to have lubricity and low wettability. Ceramic coating in which boron nitride particles are mixed with inorganic binder is used for applications that require heat resistance or durability, for example, to prevent ash from adhering to structures such as coal boiler inner walls and steam pipes. Has been.

  Patent Document 1 (Japanese Patent Publication No. 2005-534478) discloses “in a method of producing a ceramic coating of a metal and / or ceramic surface and a product ceramic coating in a reactor, a process plant, and a combustion plant. Applying at least one medium particle size inorganic binder in the nanometer range and at least one solvent and / or water mixture onto the metal and / or ceramic surface or product; The method is characterized in that the coating is performed by baking the resulting mixture by heating.

  Patent Document 2 (Japanese Patent Application Laid-Open No. 2012-251228) states that “a film formed on the surface of a substrate, and the pores of the porous film formed by including hexagonal boron nitride particles and silica particles are hexagonal. “A film formed by sealing with a resin material having permeability and curability mixed with boron nitride particles”.

Patent Document 3 (Japanese Patent Publication No. 2006-527090) is a sizing agent for producing a release layer having long-term stability, and A) silicon oxide, zirconium oxide, aluminum oxide, boehmite, or a mixture thereof. Inorganic forming agent containing colloidal inorganic particles based on Si, SiO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ , AlOOH, Y ₂ O ₃ , CeO ₂ , SnO ₂ , iron oxide, carbon In the case of using an inorganic filler selected from the above, an additive, and B) the molding agent (i) containing silicon oxide, a suspension of boron nitride particles in an organic solvent, the molding not containing silicon oxide When the agent (ii) is used, a suspension of boron nitride particles in water, and C) when using the molding agent (i), an organic solvent, when using the molding agent (ii) Water, and the molding agent (i) comprises one or more specific silanes, a substoichiometric amount of water based on a hydrolyzable group of the silane component, and optional And the molding agent (ii) optionally further contains water as a solvent, and forms a nanocomposite sol when hydrolysis and condensation are required under the sol-gel process conditions A sizing agent for producing a release layer having long-term stability is described.

JP 2005-534478 A JP 2012-251228 A JP 2006-527090 Gazette

  The present disclosure relates to a heat-resistant coating excellent in adhesion to a substrate surface and anti-ash adhesion performance even in a high-temperature environment of 500 ° C. or higher, and a coating composition that can be used to form such a heat-resistant coating I will provide a.

  According to one embodiment of the present disclosure, a coating composition comprising an alkali metal silicate, fly ash, and boron nitride is provided.

  According to another embodiment of the present disclosure, there is provided a method for forming a heat resistant coating comprising spraying the coating composition onto a metal or ceramic surface.

  According to yet another embodiment of the present disclosure, a heat resistant coating comprising an alkali metal silicate matrix, fly ash, and boron nitride is provided.

  By using the coating composition of the present disclosure, it is possible to form a heat resistant coating excellent in adhesion to the substrate surface and ash adhesion preventing performance even in a high temperature environment of 500 ° C. or higher.

  The above description should not be construed as disclosing all embodiments of the present invention and all advantages related to the present invention.

It is a photograph which shows the contact angle after putting spherical soda-lime glass on Examples 1-4 and a control sample, and heating to 800 degreeC or 900 degreeC.

  Hereinafter, the present invention will be described in more detail for the purpose of illustrating representative embodiments of the present invention, but the present invention is not limited to these embodiments.

  The coating composition of one embodiment includes alkali metal silicate, fly ash, and boron nitride.

  Alkali metal silicate functions as a binder for bringing boron nitride into close contact with the substrate surface. Alkali metal silicate is a siloxane bond (Si-O-Si) when forming a coating, a bond through a metal ion present in the system (Si-O-M-O-Si, M is a metal), etc. Is formed to retain the boron nitride in the heat resistant coating. The matrix is generally amorphous.

  Examples of the alkali metal silicate include lithium silicate, sodium silicate, and potassium silicate. Since it is stable in the coating composition at the time of preparation and storage of the coating composition, and has a suitable strength and cohesive force, a coating having high adhesion to the substrate can be obtained. It is advantageous to use potassium acid.

  In some embodiments, the amount of alkali metal silicate is about 25 parts by weight or more, about 30 parts by weight or more, or about 35 parts by weight, based on 100 parts by weight solids of the coating composition. The amount is about 60 parts by mass or less, about 55 parts by mass or less, or about 50 parts by mass or less.

  In some embodiments, the alkali metal silicate content in the coating composition is about 10% or more, about 12% or more, or about 15% or more, about 50% or less, about 40%. % Or less, or about 30% by mass or less.

  The alkali metal silicate may be provided, for example, in the form of an aqueous solution (water glass), and the concentration of the alkali metal silicate is about 10% by mass or more, about 20% by mass or more, or about 30% by mass or more, It can be about 90% by weight or less, about 80% by weight or less, or about 70% by weight or less. In this embodiment, water in the aqueous solution also functions as a solvent for the coating composition.

  Fly ash is a kind of coal ash containing silica and alumina as main components, and the ash particles melted by combustion float in the high-temperature combustion gas and become spherical when the temperature drops at the boiler outlet. It is a fine particle. Fly ash functions as a filler that interacts with the alkali metal silicate to increase the cohesive strength of the coating, and also serves as a source of metal ions for use in forming the alkali metal silicate matrix. Yes. By increasing the cohesive strength of the coating, peeling from the substrate can be suppressed or prevented. Moreover, the fluidity | liquidity of a coating composition can be improved by including a fly ash in a coating composition.

  The silica content of fly ash is generally about 20% or more, about 30% or more, or about 40% or more, about 90% or less, about 80% or less, or about 70% or less.

  The alumina content of fly ash is generally about 10% or more, about 15% or more, or about 20% or more, about 50% or less, about 45% or less, or about 40% or less.

Other components of fly ash include transition metal oxides such as Fe ₂ O ₃ , alkali metal oxides such as Na ₂ O and K ₂ O, alkaline earth metal oxides such as MgO and CaO, and sulfur such as SO _3. Minutes may be included. The total content of these components is generally about 2% or more, about 4% or more, or about 6% or more, about 22% or less, about 20% or less, or about 18% or less. .

  In some embodiments, the fly ash has an average particle size of about 1 μm or more, about 10 μm or more, or about 20 μm or more, about 100 μm or less, about 90 μm or less, or about 80 μm or less. When the average particle diameter is in the above range, the fluidity of the coating composition can be increased, and for example, when the spray composition is formed, excellent spray characteristics can be obtained. Surface tension and thixotropy can be mentioned as elements of the spray characteristics.

Fly ash is graded into types I to IV according to JIS A 6201: 1999, and types I to IV differ, for example, in fineness (specific surface area). In some embodiments, the specific surface area of the fly ash, JIS A 6201: when measured in accordance with 1999, about 1000 cm ² / g or more, about 1200 cm ² / g or more, or about 1500 cm ² / g or more, About 5500 cm ² / g or less, about 5200 cm ² / g or less, or about 5000 cm ² / g or less. In one embodiment, the fly ash is type II.

  In some embodiments, the fly ash content is about 40 parts by weight or more, about 45 parts by weight or more, or about 50 parts by weight or more, based on 100 parts by weight solids of the coating composition. 65 parts by mass or less, about 60 parts by mass or less, or about 55 parts by mass or less.

  In some embodiments, the fly ash content in the coating composition is about 10% or more, about 15% or more, or about 20% or more, about 40% or less, about 35% or less, Or about 30 mass% or less.

  Boron nitride has releasability and imparts ash adhesion prevention performance to the heat resistant coating. The adhesion prevention performance of ash can be evaluated by a contact angle between the molten ash and the heat resistant coating surface. The anti-ash adhesion performance of the heat resistant coating is exhibited even at a high temperature of, for example, 500 ° C to 900 ° C. Hexagonal (hcp) boron nitride has a layered structure similar to that of graphite, and exhibits high releasability due to the layered structure, so that it can be advantageously used.

  Without being bound by any theory, a coating composition comprising boron nitride tends to contain bubbles due to mixing or homogenization during its preparation, or stirring or shaking during use. When the coating composition is an aqueous composition, boron nitride is more hydrophobic and therefore more likely to contain bubbles. When a coating composition containing bubbles is applied to the substrate surface and cured, a porous region is formed on the surface or inside the heat resistant coating. When spray coating is used, bubbles are mixed during the application of the coating composition to form a porous region. This porous region is considered to compensate for thermal stress due to the difference in thermal expansion coefficient between the heat resistant coating and the substrate, and to prevent or suppress the peeling of the heat resistant coating from the substrate. . Boron nitride also contributes to the slurry stability of the coating composition, and precipitation and aggregation are less likely to occur than an equivalent composition except that it does not contain boron nitride.

  The particle shape of boron nitride may be a flat plate shape, a scale shape, an aggregate shape, or the like.

  In some embodiments, the boron nitride particle size is about 1 μm or more, about 2 μm or more, or about 3 μm or more, about 300 μm or less, about 290 μm or less, or about 280 μm or less. By setting the particle size of boron nitride within the above range, the fluidity of the coating composition at the time of spray coating can be increased, and a more uniform film can be formed. The particle size of boron nitride is defined as the median diameter determined by laser diffraction / scattering particle size distribution measurement.

In some embodiments, the specific surface area of boron nitride is about 3 m ² / g or more, about 3.2 m ² / g or more, or about 3.5 m ² / g or more, about 25 m, as measured by the BET method. ² / g or less, about 23 m ² / g or less, or about 20 m ² / g or less.

In some embodiments, the bulk density of the boron nitride is about 0.01 g / cm ³ or more, about 0.03 g / cm ³ or more, or about 0.05 g / cm ³ or more, about 0.65 g / cm ³ or less , About 0.63 g / cm ³ or less, or about 0.6 g / cm ³ or less.

  Boron nitride may include impurities or additives in an amount up to about 10% by weight. Examples of impurities or additives include boric acid, boron trioxide, carbon, alkali metal and alkaline earth metal borates. The purity of boron nitride is desirably about 90% by mass or more, or about 95% by mass or more.

  In some embodiments, the boron nitride loading is about 1 part by weight or more, about 1.5 parts by weight or more, or about 2 parts by weight or more, based on 100 parts by weight of the solid content of the coating composition. , About 20 parts by mass or less, about 18 parts by mass or less, or about 15 parts by mass or less. By setting the blending amount of boron nitride within the above range, a heat resistant coating having excellent ash adhesion prevention performance can be formed.

  In some embodiments, the boron nitride content in the coating composition is about 1 wt% or more, about 1.3 wt% or more, or about 2.5 wt% or more, about 5 wt% or less, about 4 wt%. 4 mass% or less, or about 4 mass% or less. By setting the boron nitride content in the coating composition within the above range, a heat-resistant coating excellent in ash adhesion prevention performance can be formed, and the viscosity and surface tension of the coating composition can be applied to the substrate surface. It can be suitable for spray application.

  In some embodiments, the mass ratio of fly ash to alkali metal silicate (mass of fly ash / mass of alkali metal silicate) is about 0.6 or more, about 0.7 or more, or about 0.00. It is 8 or more, about 1.6 or less, about 1.5 or less, or about 1.4 or less. By setting the mass ratio of fly ash and alkali metal silicate to about 1.6 or less, an excessive increase in the viscosity of the coating composition can be effectively suppressed and desired fluidity can be ensured. By setting the mass ratio of fly ash and alkali metal silicate to about 0.6 or more, the thermal stability of the heat resistant coating can be enhanced.

  The coating composition may contain a viscosity modifier as an optional component. By using a viscosity modifier, the surface tension of the coating composition can be reduced, and fluidity suitable for the intended use, for example, spray characteristics can be imparted to the coating composition. The viscosity modifier can impart a suitable thixotropy to the coating composition depending on the application method. As the viscosity modifier, polyurethane and modified products thereof (for example, urea-modified polyurethane), polymer-based viscosity modifiers such as acrylic resin, silicone resin, acrylic-modified silicone resin, polyethylene glycol, and polypropylene glycol can be used.

  In some embodiments, the blending amount of the viscosity modifier is about 0.1 parts by weight or more, about 0.3 parts by weight or more, or about 0.1 parts by weight or more based on a total of 100 parts by weight of fly ash and boron nitride. 0.5 parts by mass or more, about 1.5 parts by mass or less, about 1.3 parts by mass or less, or about 1.0 parts by mass or less.

  The coating composition generally includes a solvent. Solvents include water, alcohol such as methanol, ethanol, n-propanol, isopropanol, butanol, ethylene glycol, ethers such as diethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, ketones such as acetone and methyl ethyl ketone, ethyl acetate, butyl acetate, etc. These esters, mixed solvents thereof and the like can be used. In one embodiment, the coating composition is an aqueous composition that includes water as a solvent. The aqueous coating composition is easy to handle, has excellent spray characteristics, and can form a heat-resistant coating having excellent adhesion to the substrate surface.

  The coating composition includes fly ash such as titanium oxide, zirconium oxide, aluminum oxide, yttrium oxide, cesium oxide, tin oxide, iron oxide, mullite, boehmite, silicon nitride, silicon carbide, aluminum nitride as other optional components. And inorganic fillers other than boron nitride, curing accelerators such as metal salts and metal alkoxides, molding agents such as polyvinyl butyral, polyethylene glycol, polyethyleneimine, polyvinyl alcohol and polyvinylpyrrolidone, pigments, pH adjusters, dispersants, etc. But you can.

  The coating composition can be prepared by mixing alkali metal silicate, fly ash, boron nitride, and other optional ingredients such as viscosity modifiers. For example, the coating composition can be prepared by the following procedure. A binder composition is prepared by mixing fly ash and alkali metal silicate. The alkali metal silicate is mixed, for example, in the form of a 50% by weight aqueous solution. Components such as boron nitride and a viscosity modifier are added to the binder composition, and a solvent is added as necessary to obtain a desired solid content, and the mixture is mixed for about 10 minutes to about 1 hour. In order to avoid unnecessary reaction during mixing, components other than alkali metal silicate may be mixed, and finally alkali metal silicate may be added and mixed without preparing a binder composition. . For mixing, a paint shaker and beads such as zirconia beads, alumina beads, silica beads and the like can be used.

  In some embodiments, the solids content of the coating composition is about 30% or more, about 35% or more, or about 40% or more, about 70% or less, about 65% or less, or about 60% by weight. % Or less. By making solid content of a coating composition into the said range, it can be set as the composition in which the component was disperse | distributed uniformly, and the spraying characteristic of a coating composition can be improved.

  In some embodiments, the viscosity of the coating composition is about 10 mPa · s or more, about 15 mPa · s or more, or about 18 mPa · s or more, about 50 mPa · s or less, about 40 mPa · s or less, or about 30 mPa · s. It is as follows. By setting the viscosity of the coating composition within the above range, the spray characteristics of the coating composition can be enhanced. The viscosity of the coating composition is measured with a Meiji V-1 viscosity cup (Meiji Machinery Co., Ltd., Osaka, Osaka, Japan).

  In some embodiments, the surface tension of the coating composition is about 10 mN / m or more, about 12 mN / m or more, or about 15 mN / m or more, about 40 mN / m or less, about 36 mN / m or less, or about 34 mN / m. m or less. A coating composition having a surface tension in the above range is particularly suitable for spray application to the surface of metal or ceramics.

  When the coating composition is an aqueous composition, the pH of the coating composition can be, for example, about 7 or more and about 14 or less. By setting the pH of the aqueous coating composition within the above range, the stability of the components in the composition can be increased and the storage stability of the coating composition can be increased.

  The coating composition can be applied to the substrate surface by spraying, dipping, casting, spin coating, knife coating, brush coating, and the like. In one embodiment, the coating composition is sprayed onto the substrate surface. In one embodiment, the substrate is a metal such as iron, chromium, copper, nickel, aluminum, titanium, tin, zinc, and alloys thereof, or a ceramic such as alumina, silica. The substrate surface may have a primer treatment.

  The thickness (wet thickness) when the coating composition is applied can be about 30 μm or more, about 50 μm or more, or about 80 μm or more, about 1000 μm or less, about 900 μm or less, or about 800 μm or less. By making the thickness at the time of application of a coating composition into the said range, peeling from the base-material surface can be prevented or suppressed more effectively.

  The applied coating composition is cured at room temperature or by heating to form a heat resistant coating. The curing temperature can be about 50 ° C. or higher, about 100 ° C. or higher, or about 200 ° C. or higher. Curing of the coating composition may be performed in an environment where the substrate is actually used. For example, the coating composition may be cured in situ by applying the coating composition to the surface of a steam pipe in the coal boiler and operating the coal boiler.

  In some embodiments, the thickness of the heat resistant coating (dry thickness) is about 25 μm or more, about 35 μm or more, or about 50 μm or more, about 300 μm or less, about 280 μm or less, or about 250 μm or less. By setting the thickness of the heat resistant coating within the above range, peeling from the substrate surface can be more effectively prevented or suppressed.

  The coating composition of the present disclosure can be used in various applications where heat resistance and ash adhesion prevention performance are required. For example, the coating composition can be used to form a heat resistant coating on the surface of a steel steam pipe that reaches a temperature of 500-600 ° C. in a coal boiler.

  In the following examples, specific embodiments of the present disclosure are illustrated, but the present invention is not limited thereto. All parts and percentages are by weight unless otherwise specified.

  Table 1 shows the raw materials used in the preparation of the coating composition of this example.

Examples 1-13
A binder composition was prepared in which fly ash and No. 1 potassium silicate were in a mass ratio of 1: 1.2 (mass of fly ash / 50 mass% potassium silicate aqueous solution = 0.6). Tabular grain boron nitride P003 in an amount of 1.3 wt%, 2.5 wt%, 3.4 wt%, 4.4 wt% in the coating composition, and in some cases nitriding A viscosity modifier BYK-425 in an amount of 0.5 parts by mass or 1 part by mass based on 100 parts by mass of the total mass of boron and fly ash is added to the binder composition, and the water content of the coating composition is 40. Water was added and mixed so that it might become mass%-60 mass%. An appropriate amount of zirconia balls having a diameter of 1.5 mm was added to the obtained mixture, and the mixture was stirred for 30 minutes with a paint shaker, and the zirconia balls were removed to obtain a coating composition. Table 2 shows the composition of the coating composition.

Examples 14-15
A coating composition was prepared in the same procedure as in Example 1 except that flaky boron nitride F70 / 500 or agglomerated particles of boron nitride A50 were used instead of boron nitride P003. The content of boron nitride in the coating composition is 2.5% by mass, the water content of the coating composition is about 50% by mass, and the blending amount of the viscosity modifier is based on a total mass of 100 parts by mass of boron nitride and fly ash. As 0.5 mass part. Table 2 shows the composition of the coating composition.

Example 16
A coating composition was prepared in the same manner as in Example 1 except that sodium silicate was used instead of potassium silicate. The content of boron nitride in the coating composition is 2.5% by mass, the water content of the coating composition is about 50% by mass, and the blending amount of the viscosity modifier is based on a total mass of 100 parts by mass of boron nitride and fly ash. As 0.5 mass part. Table 2 shows the composition of the coating composition.

Comparative Example 1
A coating composition was prepared by the same procedure as in Example 1 except that sodium silicate was not used. The content of boron nitride in the coating composition is 2.5% by mass, the water content of the coating composition is about 50% by mass, and the blending amount of the viscosity modifier is based on a total mass of 100 parts by mass of boron nitride and fly ash. As 0.5 mass part. Table 2 shows the composition of the coating composition.

Comparative Example 2
A coating composition was prepared in the same procedure as in Example 1 except that boron nitride was not used. The water content of the coating composition was about 50% by mass, and the blending amount of the viscosity modifier was 0.5 parts by mass based on 100 parts by mass of fly ash. Table 2 shows the composition of the coating composition.

  The coating composition was evaluated for the following items.

Contact angle Using a SUS304 test piece (0.8 × 25 × 50 mm) as a base material, the coating composition was applied in a wet thickness of 200 μm and an area of 15 × 15 mm, and dried at room temperature for about 1 hour. A spherical soda lime glass having a diameter of 1 mm was placed on the coating surface, and heated to 800 or 900 ° C. in the air using an electric furnace. Since soda lime glass has a low melting point suitable for observing wet resistance, it was used as a substitute for ash. The mixture was heated from room temperature to a predetermined temperature at a heating rate of 13 ° C./min, held at that temperature for 1 hour, and then naturally cooled. The appearance of the heated sample was observed, and the contact angle between the glass and the coating surface was determined from the photographic image. As a control sample, an uncoated test piece was similarly evaluated.

  Table 3 shows the contact angle evaluation results, and FIG. 1 shows photographs of contact angles of Examples 5 to 8 and the control sample.

Viscosity The coating composition was placed in a viscosity cup, and the viscosity (mPa · s) was evaluated from the time when the coating composition fell from the viscosity cup. For the purpose of observing the state of the coating composition over time, the viscosity after the coating composition was prepared and left at room temperature for 1 week was similarly evaluated.

  The viscosity of the coating composition is shown in Table 4.

Adhesiveness Using a SUS304 test piece (0.8 × 25 × 50 mm) as a base material, the coating composition was applied in an area of 15 × 15 mm and dried at 60 ° C. for about 1 hour. The thickness of the coating was set to two levels: thin coating (wet thickness 200 μm) and thick coating (wet thickness 400 μm). Then, it heated at 500-900 degreeC under air | atmosphere using the electric furnace. The mixture was heated from room temperature to a predetermined temperature at a heating rate of 13 ° C./min, held at that temperature for 1 hour, and then naturally cooled. The appearance of the heated sample was observed, and even if the coating surface was rubbed, “A” was adhered, “B” was partially peeled, and “C” was entirely peeled.

  Table 5 shows the evaluation results of the adhesion of the coating composition.

  It will be apparent to those skilled in the art that various modifications can be made to the embodiments and examples described above without departing from the basic principles of the invention. It will also be apparent to those skilled in the art that various modifications and variations of the present invention can be made without departing from the spirit and scope of the invention.

Claims (10)

  A coating composition comprising an alkali metal silicate, fly ash, and boron nitride.   The coating composition according to claim 1, which is an aqueous composition.   The coating composition according to claim 1, further comprising a viscosity modifier.   Viscosity is 10-50 mPa * s, The coating composition as described in any one of Claims 1-3.   The coating composition according to any one of claims 1 to 4, wherein the solid content is 40 to 60% by mass and the boron nitride is included in an amount of 1.3 to 4.4% by mass.   The coating composition according to any one of claims 1 to 5, wherein the alkali metal silicate is potassium silicate.   The coating composition as described in any one of Claims 1-6 applied to the surface of a metal or ceramics.   A method for forming a heat resistant coating, comprising spraying the coating composition according to any one of claims 1 to 7 onto a surface of a metal or ceramic.   A heat resistant coating comprising an alkali metal silicate matrix, fly ash, and boron nitride.   The heat resistant coating according to claim 9, wherein the thickness is 25 to 200 μm.