Coating film formation method and coating film formation device

Abstract

To provide a coating film formation method and a coating film formation device of a heat-shielding material which can obtain a coating film having both high durability and excellent heat-shielding performance.SOLUTION: A coating film formation method is a method for coating a heat-shielding material containing particles and a resin material onto the surface of a coated object and forming a coating film, and includes: a temperature adjustment step of adjusting the surface temperature of the coated object to an initial temperature which is higher than the temperature before coating of the heat-shielding material and is 35°C or higher and 52°C or lower; and a coating step of coating the heat-shielding material onto the surface of the coated object.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a coating film forming method and a coating film forming apparatus for a thermal barrier material. [Background technology]

[0002] It is common to provide a heat-shielding layer with low specific heat and low thermal conductivity on the wall surfaces (the crown surface of the piston, the underside of the cylinder head, etc.) that form the combustion chamber of an engine to reduce the cooling loss of the engine and improve fuel efficiency. For example, Patent Document 1 describes a method in which a liquid heat-shielding material made of a mixture of hollow particles and a binder is applied to the crown surface of a piston with a spray gun to form a heat-shielding layer, and then the heat-shielding layer is fired. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-177693 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the volume ratio of particles such as hollow particles contained in the heat shielding material is high, when the heat shielding material is applied to the surface of the object to be coated, the solvent is difficult to diffuse, which tends to generate air bubbles (voids) inside the coating film, and there is a risk of this leading to a decrease in durability. On the other hand, in order to improve the smoothness of the coating film and ensure excellent heat shielding performance, it is necessary to leave a sufficient amount of solvent on the coating film surface when the coating film is formed so that the applied particles, which are droplets of the applied heat shielding material, can flow sufficiently, and it has been difficult to simultaneously suppress the generation of voids and ensure sufficient surface smoothness.

[0005] Therefore, an object of the present disclosure is to provide a coating film forming method and coating film forming device for a thermal insulation material, which can obtain a coating film that combines high durability and excellent thermal insulation performance. [Means for solving the problem]

[0006] In order to solve the above problems, one embodiment of a coating film forming method disclosed herein comprises the steps of: A method for forming a coating film by applying a heat shielding material containing particles and a resin material to a surface of an object to be coated, comprising the steps of: a temperature adjusting step of adjusting the surface temperature of the object to an initial temperature of 35° C. or more and 52° C. or less before applying the heat-shielding material; A coating process for coating the heat shielding material on a surface of the object to be coated. It is characterized by:

[0007] Further, one embodiment of the coating film forming apparatus disclosed herein is An apparatus for applying a heat insulating material containing particles and a resin material to a surface of an object to form a coating film, comprising: A temperature adjusting device for adjusting the surface temperature of the object to be coated; a coating device that coats the heat shielding material on a surface of the object to be coated, The temperature adjustment device adjusts the surface temperature of the object to be coated before the heat shielding material is coated to an initial temperature that is higher than the surface temperature of the object before the heat shielding material is coated and is 35° C. or higher and 52° C. or lower. It is characterized by:

[0008] When the thermal barrier material is applied to the surface of the object to be coated, the solvent gradually evaporates from the surface of the coating during the drying and baking process. As the solvent evaporates, the coating shrinks, and finally a coating containing particles and a resin binder is formed.

[0009] When the particle content in the thermal barrier material increases, the presence of many particles reduces the diffusion rate of the solvent inside the thermal barrier material. This makes it difficult for the diffusion rate of the solvent inside the coating to keep up with the evaporation rate of the solvent. As a result, although the solvent evaporates on the surface of the coating, a large amount of solvent remains inside the coating. Then, during the drying and baking process, the solvent remaining inside the coating is rapidly gasified, causing the generation of voids.

[0010] On the other hand, if there is not enough solvent when the heat shielding material is applied to the surface of the object, the flow of the applied particles will be insufficient, and the solid components of the heat shielding material will remain unevenly distributed when dried and baked. This will reduce the surface roughness of the coating film and lead to a decrease in heat shielding performance.

[0011] According to this configuration, before the heat-shielding material is applied, the surface temperature of the workpiece is adjusted to the above-mentioned initial temperature, which is higher than the temperature before the heat-shielding material is applied (the temperature of the heat-shielding material before it is applied to the surface of the workpiece), thereby promoting the diffusion of the solvent inside the coating film. This reduces the amount of solvent remaining inside the coating film, thereby suppressing the generation of voids. In addition, excessive temperature rise is suppressed on the coating film surface, and a state in which there is a large amount of solvent can be maintained. This ensures sufficient flowability of the applied particles of the heat-shielding material, and allows the coating film surface to have sufficient smoothness. This makes it possible to obtain a coating film that combines high durability with excellent heat-shielding performance.

[0012] Preferably, the surface temperature of the object is adjusted to the initial temperature by a temperature adjusting device arranged on the back side of the object.

[0013] According to this configuration, it is easy to adjust the surface temperature of the object to be coated, and the temperature of the surface side of the coating film of the object to be coated can be appropriately increased. Note that the temperature adjustment device is preferably a heating device that heats the object to be coated.

[0014] The particles are preferably at least one of hollow particles and nanoparticles.

[0015] According to this configuration, the heat insulating performance and / or strength of the coating film can be improved.

[0016] The coating is preferably a spray coating.

[0017] According to this configuration, the heat shielding material can be efficiently applied to the entire surface of the object.

[0018] The coating film is preferably formed by applying two or more coats.

[0019] According to this configuration, the amount of coating per application can be reduced, and the diffusion and volatilization of the solvent inside the coating film can be promoted, thereby effectively suppressing the occurrence of voids.

[0020] Preferably, the surface temperature of the object is continuously maintained at a temperature higher than the temperature of the heat shielding material before the application, from the temperature adjusting step until after the final spray application in the application step is completed.

[0021] According to this configuration, it is possible to more effectively suppress the occurrence of voids while ensuring the smoothness of the coating surface.

[0022] Preferably, the object to be coated is a piston, The piston is rotated to apply the heat insulating material to the top surface of the piston, thereby forming the coating on the top surface.

[0023] According to this configuration, the heat insulating material can be sprayed uniformly over the entire piston top surface.

[0024] The temperature of the heat shielding material before application is preferably room temperature.

[0025] According to this configuration, it is possible to appropriately set the temperature difference between the temperature before the heat shield material is applied and the surface temperature of the object to be applied before the heat shield material is applied. Effect of the Invention

[0026] As described above, according to the present disclosure, a coating film having both high durability and excellent heat-shielding performance can be obtained. [Brief description of the drawings]

[0027] [Figure 1] 1 is a cross-sectional view of an engine which is an application example of the present disclosure. [Diagram 2] FIG. 2 is a cross-sectional view showing a heat shield layer on a piston top surface of the engine of FIG. 1, and also shows an example of the configuration of a coating film forming apparatus according to the present disclosure. [Diagram 3]FIG. 3 is an enlarged cross-sectional view of a portion of the thermal barrier layer in FIG. 2. [Figure 4] FIG. 2 is a diagram for explaining the mechanism of void generation in a conventional coating film forming method. [Diagram 5] FIG. 2 is a diagram for explaining the mechanism of void generation suppression in the coating film forming method of the present disclosure. [Figure 6] FIG. 4 is a diagram showing an example of a trajectory of the relative position of a spray gun with respect to a piston. [Figure 7] FIG. 4 is a diagram for explaining an experimental method of the examples and comparative examples. [Figure 8] 1 is a graph showing the change over time in surface temperature of a test piece of an example during a coating process. [Figure 9] 1 is a graph showing the relationship between the initial temperature and the C* value in the test pieces of the examples and the comparative examples. [Figure 10] 1 is a graph showing the relationship between the initial temperature and the surface roughness Ra in the test pieces of the examples and the comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely illustrative in nature and is not intended to limit the present disclosure, its application, or its uses.

[0029] <Coating film> The coating film according to this embodiment is a heat-shielding coating film (also referred to as a "heat-shielding layer" in this specification) formed on the surface of a substrate such as a general industrial product, building material, or automobile part.

[0030] The coating film contains particles for the purpose of imparting various functions such as durability, design, rust prevention, heat resistance, etc. in addition to heat insulation properties. The coating film also contains a resin binder that holds the particles on the surface of the substrate on which the coating film is formed and fills the spaces between the particles to form the base material (matrix) of the coating film.

[0031] [particle] The particles are not particularly limited, and may be any particulate component contained in a typical heat insulating coating film, such as hollow particles, nanoparticles, and core-shell polymer particles.

[0032] In addition, when the coating film is a heat shielding layer formed on a portion of an engine part facing a combustion chamber, which will be described later, it is preferable that the particles contain at least one of hollow particles and nanoparticles, and it is more preferable that the particles contain both hollow particles and nanoparticles. By containing hollow particles, the heat shielding performance of the heat shielding material is improved. Furthermore, by containing nanoparticles, the strength of the coating film is improved. Details of hollow particles and nanoparticles will be described later.

[0033] The coating may further contain other particles such as fillers, reinforcing fibers, pigments, metal flakes, and the like.

[0034] The filler is added to impart strength to the coating film, etc. There are no particular limitations on the filler, and common fillers such as talc, kaolin, and mica can be used.

[0035] The reinforcing fibers are added to impart strength to the coating film. There are no particular limitations on the reinforcing fibers, and general reinforcing fibers such as glass fibers, carbon fibers, metal fibers, natural fibers, and synthetic fibers can be used.

[0036] The pigment is added to impart color to the coating film. There are no particular limitations on the pigment, and general pigments such as red pigments, black pigments, yellow pigments, blue pigments, green pigments, and purple pigments can be used.

[0037] Metal flakes are added to impart design properties such as metallic luster to the coating film. There are no particular limitations on the metal flakes, and general metal flakes such as aluminum flakes, copper flakes, and stainless steel flakes can be used.

[0038] The particles may be of a single type, or a mixture of multiple types.

[0039] The average particle size of the particles (in this specification, "average particle size" means "number average particle size") is not particularly limited and can be any generally known average particle size, and is appropriately determined depending on the application of the coating film. The average particle size of the particles can be obtained, for example, by determining D50, which is the 50% value of the particle size distribution measured by a laser diffraction particle size distribution measuring device.

[0040] The content of particles in the coating film is preferably more than 30% by volume. When the coating film contains multiple types of particles, the content is the total content of all particles. The content is not intended to be limited, but is, for example, 40% by volume or more and 80% by volume or less, preferably 45% by volume or more and 75% by volume or less, more preferably 50% by volume or more and 70% by volume or less.

[0041] [Resin binder] The resin binder is not particularly limited, and may be any resin binder that is generally used in heat-shielding coating films. Although there is no intention to limit the resin binder, for example, silicone-based resin binders, epoxy-based resin binders, acrylic-based resin binders, polyester-based resin binders, urethane-based resin binders, melamine-based resin binders, etc. may be used alone or in combination.

[0042] When the coating film is a heat shield layer formed on a portion of a component that constitutes a combustion chamber of an engine, which will be described later, that faces the combustion chamber, the resin binder is preferably a silicone-based resin binder. Silicone-based resin binders have excellent heat resistance, and therefore can ensure excellent heat shielding performance in a heat shield layer used in an environment exposed to high temperatures, such as 300°C or higher.

[0043] [Other ingredients] The coating film may contain additives such as dyes, ultraviolet shielding materials, viscosity agents, thickeners, pigment dispersants, surface conditioners, etc., either alone or in combination, as necessary. The type and content of the additives are not particularly limited, and known conditions can be appropriately adopted depending on the application of the coating film, etc.

[0044] [Liquid permeability] The occurrence of voids inside a coating film can be confirmed by evaluating the liquid permeability of the coating film. That is, when many voids are generated, the liquid permeability is high. When the occurrence of voids is suppressed, the liquid permeability is low.

[0045] The liquid permeability is evaluated by, for example, comparing the color of the coating film after the liquid permeability evaluation with C, as described below. * This can be done by expressing it as a value, etc.

[0046] C * From the viewpoint of obtaining a coating film having excellent durability, the value can be set to, for example, 5.3 or less.

[0047] As described later, when the coating film is a thermal barrier layer formed on a part of a component that constitutes the combustion chamber of an engine, which faces the combustion chamber, the C of the thermal barrier layer * A value of 2.0 or less is preferred.

[0048] [Surface roughness] Increasing the surface roughness of the coating film leads to a decrease in the heat-shielding performance of the coating film. From the viewpoint of ensuring excellent heat-shielding performance, the surface roughness Ra of the coating film is, for example, 8 or less, preferably 7.8 or less, more preferably 7 or less, and particularly preferably 6 or less.

[0049] In particular, when the coating is a thermal barrier layer formed on a portion of a component that constitutes an engine combustion chamber, facing the combustion chamber, as described below, the surface roughness of the thermal barrier layer is preferably 3.2 or less. For controlling fuel combustion in an engine, it is important to transport fuel to the combustion point as intended, and sufficient smoothness is required for the thermal barrier layer. By setting the surface roughness of the thermal barrier layer to the above range, it is possible to suppress an extension of the fuel transport period or slowing down of combustion, thereby improving fuel efficiency.

[0050] [Engine parts] Hereinafter, without intending to limit the present disclosure, a thermal barrier layer formed on a portion of an engine part that constitutes a combustion chamber of the engine and faces the combustion chamber will be described as an example of a coating film.

[0051] FIG. 1 shows an example of an engine part according to the present embodiment. In FIG. 1, 1 is an aluminum alloy piston of an engine as a coating object on which a thermal barrier layer is formed, 2 is a cylinder block, 3 is a cylinder head, 4 is an intake valve that opens and closes an intake port 5 of the cylinder head 3, 6 is an exhaust valve that opens and closes an exhaust port 7, and 8 is a fuel injection valve. The parts that constitute the combustion chamber of the engine are a top surface 9 of the piston 1, the cylinder block 2, the cylinder head 3, and the front faces of the heads of the intake and exhaust valves 4 and 6 (surfaces facing the combustion chamber), and a thermal barrier layer 11, which will be described later, is provided on the surfaces of these parts. A cavity is formed in the top surface 9 of the piston 1. Note that an ignition plug is not shown in the figure.

[0052] 2 and 3 show the heat insulating layer 11 formed on the top surface 9 of the piston 1.

[0053] As shown in Fig. 3, the thermal barrier layer 11 contains a large number of hollow particles 12 made of inorganic oxide or ceramic, nanoparticles 14, and a resin binder 13. The hollow particles 12 and nanoparticles 14 are dispersed in the resin binder 13 (in Fig. 3, the nanoparticles 14 are represented by dots). In other words, the resin binder 13 holds the hollow particles 12 and the nanoparticles 14 in the piston 1 and fills the spaces between these particles to form the base material (matrix) of the thermal barrier layer 11.

[0054] The thickness of the heat shield layer 11 (hereinafter referred to as "film thickness") is, for example, from 20 μm to 150 μm, preferably from 25 μm to 125 μm, more preferably from 25 μm to 100 μm, even more preferably from 30 μm to 100 μm, and particularly preferably from 40 μm to 100 μm. The hollow particles 12 used have a particle size on the order of μm, which is smaller than the film thickness of the heat shield layer 11. The average particle size is preferably, for example, 30 μm or less. For example, hollow particles having an average particle size of 10 μm or less can be preferably used.

[0055] However, the above numerical ranges are preferred from the viewpoint of ensuring excellent heat shielding performance when the heat shielding layer 11 is provided on the surface forming the combustion chamber of the engine, and are not limiting. Furthermore, when the heat shielding layer is provided on equipment other than the surface forming the combustion chamber, the particle diameter of the hollow particles 12 and the film thickness of the heat shielding layer 11 can be further smaller or larger.

[0056] It is preferable to adopt inorganic hollow particles as the hollow particles 12, for example, ceramic hollow particles containing a Si-based oxide component (e.g., silica) or an Al-based oxide component (e.g., alumina), such as glass balloons, glass bubbles, fly ash balloons, shirasu balloons, silica balloons, aluminosilicate balloons, etc. The hollow ratio of the hollow particles is preferably 60% by volume or more, and more preferably 70% by volume or more.

[0057] The content of hollow particles 12 (the content of hollow particles 12 in heat shield layer 11 after firing; the same applies below) can be adjusted according to the heat shield performance required of the heat shield layer. The content of hollow particles 12 is not intended to be limited, but can be, for example, 30 volume % or more and 60 volume % or less, and preferably 40 volume % or more and 55 volume % or less.

[0058] The average particle size of the hollow particles 12 is not intended to be limited and can be changed depending on the application of the heat shield layer, etc., but from the viewpoint of ensuring excellent heat shielding performance of the heat shield layer, it can be, for example, 1 μm or more and 30 μm or less, and preferably 1 μm or more and 10 μm or less.

[0059] The surfaces of the hollow particles 12 may be subjected to a hydrophobic treatment or a hydrophilic treatment. The hydrophobic treatment or hydrophilic treatment is not particularly limited, and known methods such as a chemical modification treatment using an organic compound and a surface modification treatment using fluorine plasma can be used.

[0060] As the nanoparticles 14, inorganic nanoparticles made of inorganic compounds such as zirconia, alumina, silica, titania, etc., metal nanoparticles such as Ti, Zr, Al, etc. can be used. The nanoparticles may be hollow or solid.

[0061] The nanoparticles 14 are preferably inorganic nanoparticles. In particular, it is preferable to adopt at least one selected from silica nanoparticles, alumina nanoparticles, and zirconia nanoparticles as the nanoparticles 14, and it is more preferable to adopt silica nanoparticles. It is believed that the thermal deterioration of the resin binder 13 occurs when oxygen radicals are generated in the resin binder and diffuse. In contrast, inorganic nanoparticles suppress the thermal deterioration by lowering the diffusion rate of the oxygen radicals. In addition, inorganic nanoparticles suppress the molecular motion of the resin binder, thereby suppressing the thermal deterioration. Furthermore, inorganic nanoparticles, especially silica nanoparticles, have low thermal conductivity, which is advantageous for improving the thermal insulation performance of the heat shielding layer.

[0062] The ratio of the nanoparticles 14 (the ratio of the nanoparticles 14 to the total amount of the resin binder 13 and the nanoparticles 14 after firing. The same applies below.) is preferably 10% by volume or more and 55% by volume or less, and more preferably 20% by volume or more and 55% by volume or less. The effect of suppressing thermal deterioration as described above becomes more pronounced by setting the ratio of the inorganic nanoparticles to the total amount of the resin binder and the inorganic nanoparticles to the above lower limit value or more. The higher the ratio of the nanoparticles 14, the more advantageous it is for improving the strength of the heat shield layer according to the composite rule. In addition, with a high content of the nanoparticles 14, the content of the resin binder, which is a cause of thermal deterioration of the heat shield layer, relatively decreases, which is advantageous for improving the heat resistance of the heat shield layer. And, by the suppression of thermal deterioration of the resin binder due to the high content of the nanoparticles 14 and the insulating effect of the hollow particles, it is possible to improve the durability of the heat shield layer while ensuring excellent heat shielding performance. However, if the ratio of the nanoparticles 14 is excessively high, the moldability of the heat shield layer decreases, so the ratio is preferably set to the above upper limit value or less.

[0063] The average particle size of the nanoparticles 14 is not intended to be limited, and can be changed depending on the application of the heat shield layer, but can be, for example, about 1 / 1000 to 1 / 10 of the average particle size of the hollow particles 12, preferably 1 / 100 to 1 / 10. Specifically, the average particle size of the nanoparticles 14 can be, for example, 3 μm or less, preferably 500 nm or less, more preferably 1 nm to 200 nm, and even more preferably 1 nm to 120 nm. Setting the average particle size of the nanoparticles in the above range is advantageous for suppressing thermal deterioration of the resin binder in the heat shield material, and is advantageous for improving the heat shielding performance of the heat shield material.

[0064] The surface of the nanoparticles 14 may be hydrophobized or hydrophilized, and is preferably hydrophobized. The hydrophobization or hydrophilization is not particularly limited, and known methods such as chemical modification with an organic compound and surface modification with fluorine plasma can be adopted. When a silicone-based resin binder is used as the resin binder and silica nanoparticles are used as the nanoparticles 14, the nanoparticles 14 are preferably modified silica nanoparticles whose surfaces are modified with phenyl groups. This increases the hydrophobicity of the silica nanoparticles, thereby increasing the dispersibility of the silica nanoparticles in the silicone-based resin binder, which is advantageous for suppressing thermal deterioration of the heat shielding layer. In particular, the phenyl group is compatible with the silicone-based resin, which is advantageous for dispersing the silica nanoparticles. In addition, the phenyl group itself has high heat resistance, and as described above, the phenyl group modification makes it difficult for defects such as voids that are the starting points of cracks to occur in the silicone-based resin. In this way, the thermal deterioration of the heat shielding layer can be effectively suppressed.

[0065] The resin binder 13 is made of a three-dimensional polymer having a high degree of branching, such as a silicone-based resin binder, an epoxy-based resin binder, etc., and is preferably a silicone-based resin binder having excellent heat resistance as described above. A specific example of the silicone-based resin binder is organopolysiloxane.

[0066] When the heat shield layer 11 is composed of hollow particles 12, nanoparticles 14, and resin binder 13, the content of resin binder 13 (the content of resin binder 13 in the heat shield layer 11 after firing; the same applies below) is the remainder other than the hollow particles 12 and nanoparticles 14. The resin binder 13 may contain, for example, residual components derived from components contained in the raw materials of the resin binder 13 described below, as unavoidable components.

[0067] <Coating film formation method> An example of a method for forming a coating film on the surface of an object to be coated will be described below.

[0068] The coating film forming method includes, in this order, a preparation step of preparing a heat-shielding material for forming the coating film, a temperature adjustment step of adjusting the surface temperature of the object to be coated to an initial temperature, a coating step of coating the heat-shielding material onto the surface of the object to be coated, and a drying and firing step of drying and firing the applied heat-shielding material to obtain the coating film.

[0069] [Preparation process] In the preparation step, the raw material resin of the resin binder, the particles, a dilution solvent, and other additives as required are mixed together to obtain a heat shielding material.

[0070] The method for mixing the above components is not particularly limited, and can be any known method, such as stirring with a mixer, etc. The stirring conditions, such as the number of rotations during stirring and the stirring time, are not particularly limited, and can be any known condition.

[0071] The obtained heat shielding material is subjected to post-treatment such as filtration as necessary, and then stored or subjected to a coating step. If necessary, a catalyst is added to the heat shielding material immediately before the material is subjected to the coating step.

[0072] -Heat shielding materials- The heat-shielding material is a paint for forming the coating film. In particular, when the coating film is a heat-shielding layer formed on a portion of a component that constitutes a combustion chamber of an engine, the portion facing the combustion chamber, as described above, the heat-shielding material is a paint for a heat-shielding layer that is applied to the portion.

[0073] -Raw resin for resin binder- The raw resin of the resin binder is a resin component before curing, and is usually prepared or available as a raw resin solution containing the resin component, a crosslinking agent, a filler, an accelerator, a solvent, etc. The raw resin solution may be hydrophobic or hydrophilic.

[0074] In the case where the resin binder is the above-mentioned silicone-based resin binder, the raw resin solution is specifically, for example, a reactive silicone-based resin solution. The reactive silicone-based resin solution as the raw resin solution contains a reactive silicone-based resin as a resin component. The reactive silicone-based resin solution may be a one-part addition curing type or a dehydration condensation curing type, and is preferably a one-part addition curing type.

[0075] -Dilution solvent- The dilution solvent is used for the purpose of adjusting the viscosity of the heat shielding material, etc. It is desirable that the dilution solvent has high compatibility with the raw resin solution. The dilution solvent may be a single-component solvent or a mixed solvent consisting of multiple components. When the raw resin solution is hydrophobic, it is preferable that the dilution solvent also contains a hydrophobic component, and when the raw resin solution is hydrophilic, it is preferable that the dilution solvent also contains a hydrophilic component.

[0076] Examples of hydrophobic dilution solvents include organic solvents. The organic solvent is not particularly limited, and generally known organic solvents can be used. Specific examples include aliphatic solvents, hydrocarbon solvents such as aromatic solvents, ester solvents, ketone solvents such as acetone, and ether solvents. The organic solvent is preferably an aromatic solvent. Specific examples of aromatic solvents include toluene, xylene, 1,2,4-trimethylbenzene, dilution thinner, and high-boiling aromatic solvents. The aromatic solvent is preferably at least one selected from the group consisting of toluene, xylene, and 1,2,4-trimethylbenzene. In particular, when a reactive silicone resin is used as the raw resin solution, it is preferable to use toluene, which dissolves the reactive silicone resin well.

[0077] Examples of hydrophilic dilution solvents include alcohol solvents such as 2-ethylhexanol, butanol, ethanol, propanol, and ethylene glycol, and preferably at least one selected from the group consisting of 2-ethylhexanol, 1-butanol, and 1-propanol.

[0078] In this specification, the term "solvent contained in the heat shielding material" refers to the liquid components in the heat shielding material, including the liquid components such as the solvent contained in the raw resin solution and the dilution solvent. The liquid components contained in the raw resin solution are not particularly limited, and may be, for example, the same components as the dilution solvent described above.

[0079] The viscosity of the heat shielding material is not particularly limited and is appropriately determined depending on the application of the heat shielding material. Specifically, the viscosity is, for example, 1×10 -3 Pa·s or more 1×10 5 Pa s or less, preferably 1×10 -2 Pa·s or more 1×10 5 It is less than Pa·s.

[0080] The content of solid components (particles and raw material resin) contained in the heat shielding material can be, but is not intended to be limited to, for example, 5 vol.% or more and 99.5 vol.% or less, preferably 6 vol.% or more and 99 vol.% or less, more preferably 9 vol.% or more and 95 vol.% or less, even more preferably more than 40 vol.% and 95 vol.% or less, and particularly preferably 41 vol.% or more and 95 vol.% or less.

[0081] [Temperature adjustment process] In the temperature adjustment step, the surface temperature of the object to be coated is adjusted to an initial temperature before the heat-shielding material is applied. In this specification, the "initial temperature" refers to a specific temperature that is higher than the temperature before the heat-shielding material is applied and is 35°C to 52°C, preferably 35°C to 50°C. If the initial temperature is below the lower limit, the diffusion of the solvent inside the coating film in the coating step is not sufficiently promoted, making it difficult to suppress the generation of voids, and the durability of the coating film may decrease. If the initial temperature exceeds the upper limit, the coating film surface may not have sufficient smoothness, and the heat-shielding performance of the coating film may decrease.

[0082] The method of adjusting the surface temperature of the object to be coated is not particularly limited, and may be adjusted by arranging a heating device (temperature adjustment device) on the back side of the object to be coated and heating the object from the back side, or by arranging a heating device in a non-coating area of ​​the surface of the object to be coated and heating the object from the front side. Specific examples of the heating device include a heater, a rubber heater, a hot plate, a Peltier element, etc.

[0083] The temperature before application of the heat-shielding material is not limited as long as it is lower than the initial temperature, but is preferably room temperature, more preferably 5° C. or higher and 25° C. or lower, and even more preferably 10° C. or higher and 20° C. or lower. This allows the temperature difference between the temperature before application of the heat-shielding material and the surface temperature of the object to be coated before the heat-shielding material is applied to be appropriately set. The temperature before application of the heat-shielding material may be measured by measuring the temperature of the heat-shielding material itself, or room temperature may be used as the temperature before application if the heat-shielding material has been left at room temperature for a sufficiently long time (e.g., one day or more).

[0084] [Coating process] In the coating step, the heat shield material is coated on the surface of the object whose surface temperature has been adjusted to the initial temperature in the temperature adjustment step.

[0085] The method for applying the heat shielding material is not particularly limited, and for example, known methods such as spray application, application with a brush or spatula, etc., can be used, but spray application is preferred, as the heat shielding material can be efficiently applied to the entire surface of the object to be applied.

[0086] In the coating process, it is preferable to form a coating film by applying two or more coats. In other words, it is preferable to apply the heat shielding material in multiple coats and repeatedly apply the coats to form the final coating film. This makes it possible to reduce the amount of coating per coat, which is advantageous in suppressing the generation of voids.

[0087] In particular, in the case of spray coating using reciprocating parallel movement, which will be described later, if one trajectory from the start to the end of the reciprocating parallel movement (from the upper left end to the lower left end of the trajectory indicated by the solid arrow in Figure 6) is considered to be one pass, it is preferable to form a coating film by repeating spray coating using reciprocating parallel movement for two or more passes.

[0088] In addition, since excessively increasing the number of recoats is disadvantageous in terms of costs, it is preferable to recoat the film four times or less, and more preferably two times.

[0089] [Drying and baking process] When the heat shielding material is applied to the surface of the workpiece, a film of heat shielding material is formed. In the firing process, the workpiece is dried and fired to obtain a coating film.

[0090] By drying and baking, the solvent in the film-like heat shielding material volatilizes and the resin component hardens to form a resin binder, resulting in a coating film in which particles are dispersed in the resin binder.

[0091] The drying and firing conditions are not particularly limited, and known conditions can be appropriately adopted.

[0092] Specific examples of drying and firing conditions include, for example, when the coating film is the above-mentioned heat-shielding layer, drying can be performed by leaving the workpiece in the air at room temperature for several minutes to several hours, while firing can be performed by heating the dried workpiece at a temperature of, for example, about 100 to 200°C for several minutes to several hours.

[0093] [Features and Effects] Here, the coating film forming method according to the present disclosure is characterized by including a temperature adjustment step prior to the coating step.

[0094] Fig. 4 is a diagram for explaining the mechanism of void generation in a conventional coating film formation method. Here, an example is explained in which a coating film is formed by two overcoats (two passes) using spray coating.

[0095] As shown in Fig. 4(a), when the first pass starts, the heat shielding material 31 is sprayed from the spray gun 25, and the spray particles, which are fine droplets, are applied to the surface of the workpiece 1a to form a coating film. Then, as shown in Fig. 4(b), between the first and second passes, the solvent 33 volatilizes from the surface of the coating film, and the solvent 33 diffuses inside the coating film.

[0096] As described above, when the content of particles in the thermal insulation material is large, the presence of many particles reduces the diffusion rate of the solvent inside the coating film. As a result, it becomes difficult for the diffusion rate of the solvent inside the coating film to keep up with the evaporation rate of the solvent. As a result, although the evaporation of the solvent progresses on the surface of the coating film, a large amount of the solvent remains inside the coating film.

[0097] Next, while a large amount of solvent 33 remains inside the coating (FIG. 4(c)), a second pass of coating is performed (FIG. 4(d)). As shown in the enlarged view in FIG. 4(d), the coating particles flow sufficiently on the coating surface because there is a sufficient amount of solvent on the surface of the coating film formed in a wet state by the second pass of coating. This makes the coating surface smooth.

[0098] After the second pass, the solvent 33 evaporates from the coating surface and diffuses into the coating, just as it does between passes (Fig. 4(e)). However, even at this stage, the diffusion inside the coating is insufficient, and the coating dries with a large amount of solvent 33 remaining inside the coating (Fig. 4(f)).

[0099] The coating film is then subjected to firing with a large amount of solvent 33 remaining inside. During firing, the solvent 33 remaining inside the coating film is rapidly gasified due to a sudden rise in temperature caused by convection heat transfer, and voids are generated inside the coating film.

[0100] As described above, in the conventional coating film forming methods, although surface smoothness can be ensured, it is difficult to prevent the occurrence of voids.

[0101] On the other hand, as shown in FIG. 5, in the coating film forming method according to the present disclosure, before starting to apply the heat-shielding material 31, the surface temperature of the object 1a to be coated is adjusted to an initial temperature by heating the object 1a to be coated using a heater 21 arranged on the back side of the object 1a to be coated.

[0102] In this state, when the heat shielding material 31, which has a pre-application temperature lower than the above-mentioned initial temperature, is applied to the surface of the workpiece 1a to form a coating (FIG. 5(a)), a temperature difference occurs between the inner side and the surface side of the coating film. That is, since the inner side of the coating film is closer to the surface of the workpiece 1a, which has an initial temperature higher than the temperature before application of the heat shielding material 31, the temperature of the inner side of the coating film is higher, and the temperature of the surface side of the coating film is lower.

[0103] As a result, between passes, the diffusion of the solvent inside the coating film is promoted, and the amount of solvent remaining inside the coating film decreases due to evaporation from the coating film surface (Figures 5(b) and (c)).

[0104] Then, as shown in Figure 5(d), the second pass is applied with only a small amount of solvent remaining inside the coating. The initial temperature mentioned above is only slightly higher than the temperature before the application of the thermal barrier material, so excessive temperature rise is suppressed on the coating surface, and a state of high solvent content can be maintained. This ensures sufficient flowability of the applied particles of the thermal barrier material, and a sufficient smoothness of the coating surface can be obtained.

[0105] When the second pass is completed, the solvent 33 volatilizes from the coating surface and diffuses inside the coating, just as it does between passes (Fig. 5(e)). Even at this stage, diffusion inside the coating is promoted, and the amount of solvent remaining inside the coating is reduced due to evaporation from the coating surface, and the coating dries in this state (Fig. 5(f)).

[0106] Thus, the coating film is subjected to baking in a state where almost no solvent 33 remains inside the coating film or the amount of remaining solvent is very small. Therefore, even if a sudden temperature rise occurs during baking due to convection heat transfer, the amount of solvent remaining inside the coating film is small, so the generation of voids inside the coating film is suppressed.

[0107] In this way, the coating film forming method of the present disclosure can effectively suppress the generation of voids while ensuring sufficient smoothness of the coating film surface, thereby making it possible to obtain a coating film that combines high durability with excellent heat-shielding performance.

[0108] In addition, when the application of the heat-shielding material is started, the surface temperature of the object to be applied may drop from the initial temperature adjusted before application due to the application of the heat-shielding material to the surface of the object to be applied. Therefore, it is preferable that the surface temperature of the object to be applied is continuously maintained at a temperature higher than the temperature before application of the heat-shielding material from the temperature adjustment step until the final application in the application step is completed, preferably from the temperature adjustment step until the coating film is dried (before baking). This effectively promotes the diffusion of the solvent inside the coating film, effectively suppressing the generation of voids, and ensures sufficient flowability of the applied particles during application, thereby ensuring sufficient smoothness of the coating film surface.

[0109] <Coating film forming equipment> As shown in FIG. 2, FIG. 5(a) and the like, a configuration example of a film forming apparatus 20 according to the present disclosure includes a spray gun 25 (applicator) and a heater 21 (warmer).

[0110] Referring to FIG. 2, spray gun 25 is a device that is arranged on the top surface 9 side of piston 1 and is used to spray heat shielding material 31 onto top surface 9 before heat shielding layer 11 is formed.

[0111] Heater 21 is disposed on the rear side of the top portion including top surface 9 of piston 1, and adjusts the temperature of top surface 9 of piston 1 to an initial temperature before heat shielding material 31 is applied. Note that heater 21 only needs to be able to adjust the surface temperature of top surface 9, and may or may not be in contact with piston 1.

[0112] In addition to the above configuration, the coating film forming apparatus 20 may include configurations such as a support section that supports the object to be coated so that its surface is directed toward the spray gun 25, a moving device that moves at least one of the spray gun 25 and the object to be coated, and a supply device that supplies the heat shielding material to the spray gun 25. In addition to these configurations, the coating film forming apparatus 20 may further include other configurations. Specifically, for example, it may include a device that adjusts the temperature of the heat shielding material before coating, a device that transports the object to be coated before and after coating, etc.

[0113] [Relative position of the spray gun to the workpiece] When spray coating is used as the coating method, it is preferable to coat the heat shielding material 31 while changing the relative position of the spray gun 25 with respect to the object to be coated. That is, when the object to be coated is a piston 1, it is preferable to change the relative position of the spray gun 25 with respect to the piston 1. This allows the heat shielding material 31 to be coated over the entire surface of the object to be coated.

[0114] The relative position may be changed by fixing the object to be coated and moving the spray gun 25, or by fixing the spray gun 25 and moving the object to be coated. A preferable method is to fix the spray gun 25 and move the object to be coated. Fixing the spray gun 25 ensures that the droplets sprayed from the spray gun 25 travel in a straight line. Moving the object to be coated can suppress, for example, the adhesion of spray dust to a wall surface other than the surface of the object to be coated, and improve the efficiency of application of the heat shielding material to the surface.

[0115] The moving path, i.e., the trajectory, of the object to be coated or spray gun 25 is not particularly limited, but from the viewpoint of efficiently coating the heat shielding material on top surface 9, it is preferable that the moving path be a trajectory of linear reciprocating parallel movement in a fixed direction at a fixed distance between the lines, as shown by the solid line arrows in Fig. 6. In Fig. 6, the object to be coated is represented by piston 1.

[0116] [Rotary coating] Furthermore, the coating film forming apparatus 20 may include a rotation device (not shown) that rotates the object to be coated. Specifically, for example, as shown by the dashed line arrow in Fig. 6, the rotation device rotates the piston 1, which is the object to be coated, around the center O. That is, by coating the top surface 9 with the heat shielding material 31 while rotating the piston 1, the heat shielding material can be sprayed evenly over the entire top surface, and a coating film of uniform thickness can be obtained.

[0117] It is preferable to combine the above-mentioned reciprocating parallel movement of the object 1a (piston 1) and the rotational coating.

[0118] Furthermore, in terms of improving the uniformity of the coating film, it is effective to perform the above-mentioned reciprocating translation and rotation coating not only on the piston 1 but also on various other objects to be coated.

[0119] Regardless of whether rotation is performed or not, if the amount of heat shielding material applied is the same, the average thickness of the coating will be roughly the same. EXAMPLES

[0120] Next, specific examples will be described.

[0121] <Examples 1 to 3 and Comparative Examples 1 to 3> Using the same heat insulating material, the initial surface temperature of the disk-shaped test piece as the substrate was changed to form coating films in Examples 1 to 3 and Comparative Examples 1 to 3. The liquid permeability (durability) and surface roughness (heat insulating properties) of the finally obtained coating films were evaluated. The results are shown in Table 1.

[0122] [Table 1]

[0123] [Heat shielding materials] A precursor solution was prepared by adding xylene and butanol as dilution solvents to an addition-curing silicone resin solution containing the raw resin of the resin binder (organopolysiloxane) and stirring the mixture by hand.

[0124] Next, hollow particles and nanoparticles were added to the precursor solution and stirred with a rotation / revolution mixer to obtain a resin material. Note that aluminosilicate fine balloons with an average particle size of 5 μm were used as the hollow particles, and phenyl-modified silica nanoparticles with an average particle size of 100 nm were used as the nanoparticles. The rotation speed of the rotation / revolution mixer was 2000 rpm (rotation) and 1000 rpm (revolution), and the stirring time was 5 minutes.

[0125] The content of solid components (hollow particles, nanoparticles, and raw resin of the resin binder) in the obtained resin material was 42% by volume.

[0126] The heat shield material was subjected to a coating process with the catalyst added immediately before coating.

[0127] The temperature before the application of the heat shielding material was 16.6°C to 19.7°C, as shown in Table 1. It has been experimentally confirmed that if the heat shielding material is stored at room temperature for a sufficiently long period of time (e.g., one day or more), the temperature of the heat shielding material becomes the same as room temperature. Therefore, the outside air temperature (room temperature) during the experiment is used as the temperature before the application of the heat shielding material.

[0128] [Coating and baking heat shielding material] As shown in Figure 7, a disk-shaped test piece and a dummy test piece of the same shape and size as the disk-shaped test piece were arranged side by side. A thermocouple was attached to the surface of the dummy test piece. A heater was placed on the back side of the test piece and the dummy test piece, and the test piece and the dummy test piece were heated from the back side to adjust the surface temperatures of both to the initial temperatures shown in Table 1.

[0129] Next, the thermal barrier material was sprayed onto the surfaces of the test specimen and the dummy specimen (including the surface of the thermocouple) within the application range shown in Figure 7. The spray application was performed by moving the spray gun back and forth parallel to the test specimen within the application range. The thermal barrier material was applied twice.

[0130] After coating, the coating film was dried in the air and then baked in an oven to obtain the final coating film (thermal barrier layer).

[0131] The conditions for coating, drying and firing are as follows. Spray gun speed: 0.15m / s Between passes: 20 seconds Drying: 30℃ x 2 hours Firing: After heating at 3℃ / min, bake at 120℃ for 3 hours FIG. 8 shows the change over time in surface temperature of the test pieces of Examples 1 to 3 from the start of spray coating to the initial stage of drying (about 1 minute from the start of spray coating (about 50 seconds in Example 1)). The heater temperature setting was maintained for 2 minutes from the start of spray coating, at the temperature setting used when adjusting the surface temperature before coating to the initial temperature. Thereafter, the test pieces were subjected to drying.

[0132] In addition, the content of hollow particles in the fired coating film was 50% by volume, the content of nanoparticles was 20% by volume, and the content of resin binder was 30% by volume.

[0133] [Liquid permeability evaluation (durability evaluation)] The liquid permeability evaluation was performed in accordance with JIS Z 2343. The color of the coating film after the liquid permeability evaluation was quantified using a multi-angle spectrophotometer (evaluation was performed at a light receiving angle of 15° in this case). The quantification was performed using the representative color value L * a * b * In color space, a * value and b * Chroma C, a composite of values * Value = √(a *2 +b *2 The results are shown in Table 1 and FIG.

[0134] C * If the value is 2.0 or less, the coating film has low liquid permeability, i.e., little generation of voids, and is excellent in durability.

[0135] [Surface roughness evaluation] The surface roughness of the coating film was measured in accordance with JIS B 0633 (for the roughness parameter Ra, see JIS B 0601). The results are shown in Table 1 and FIG.

[0136] When the surface roughness Ra is 3.2 or less, it can be said that the coating film has sufficient surface smoothness and excellent heat insulating performance.

[0137] [Consideration] As shown in FIG. 9, in the coating films of Comparative Examples 1 and 2, whose initial temperatures were less than 35° C., * The value exceeded 2.0, indicating that the coating film had many voids inside the coating film and was insufficient in durability. On the other hand, in the coating films of Examples 1 to 3 and Comparative Example 3, in which the initial temperature was 35° C. or higher, the C * The value was below 2.0, indicating that the coating had few voids inside and was excellent in durability.

[0138] As shown in Fig. 10, in Comparative Example 3 where the initial temperature was over 52°C, the surface roughness Ra exceeded 3.2, indicating that the coating film had insufficient smoothness and poor heat-shielding performance. On the other hand, in Examples 1 to 3 and Comparative Examples 1 and 2 where the initial temperature was 52°C or less, the surface roughness Ra was 3.2 or less, indicating that sufficient smoothness was obtained and the coating film had excellent heat-shielding performance.

[0139] As shown in FIG. 8, the surface temperatures of the test pieces of Examples 1 to 3 tended to gradually decrease after application (up to a maximum of about 10°C), but by maintaining the heater temperature setting, the surface temperatures were maintained higher than the temperatures before the heat-shielding material was applied. [Industrial Applicability]

[0140] INDUSTRIAL APPLICABILITY The present disclosure is extremely useful since it can provide a coating film forming method and coating film forming apparatus for a heat shielding material, which can obtain a coating film having both high durability and excellent heat shielding performance. [Explanation of symbols]

[0141] 1 Piston (subject to be coated, engine part) 1a Object to be coated 11 Heat-shielding layer (coating) 12 Hollow particles (particles) 13 Resin binder (resin material) 14 Nanoparticles (particles) 20 Paint film forming equipment 21 Heater (temperature control device, heating device) 25 Spray gun (applying device) 31 Heat shielding materials 33 Solvents

Claims

1. A method for forming a coating film by applying a heat shielding material containing particles and a resin material to a surface of an object to be coated, comprising the steps of: a temperature adjusting step of adjusting a surface temperature of the object to an initial temperature of 35° C. or more and 52° C. or less before applying the heat-shielding material; A coating process for coating the heat shielding material on a surface of the object to be coated. A method for forming a coating film comprising the steps of:

2. In claim 1, The surface temperature of the object to be coated is adjusted to the initial temperature by a temperature adjusting device arranged on the back side of the object to be coated. A method for forming a coating film comprising the steps of:

3. In claim 1 or 2, The particles are at least one of hollow particles and nanoparticles. A method for forming a coating film comprising the steps of:

4. In claim 1 or 2, The coating is a spray coating. A method for forming a coating film comprising the steps of:

5. In claim 4, The coating film is formed by applying two or more coats. A method for forming a coating film comprising the steps of:

6. In claim 5, The surface temperature of the object to be coated is continuously maintained at a temperature higher than the temperature of the heat shielding material before coating from the temperature adjustment step until the completion of the final spray coating in the coating step. A method for forming a coating film comprising the steps of:

7. In claim 1 or 2, The object to be coated is a piston, The piston is rotated to apply the heat insulating material to the top surface of the piston, thereby forming the coating on the top surface. A method for forming a coating film comprising the steps of:

8. In claim 1 or 2, The temperature of the heat shielding material before application is room temperature. A method for forming a coating film comprising the steps of:

9. An apparatus for applying a heat insulating material containing particles and a resin material to a surface of an object to form a coating film, comprising: A temperature adjusting device for adjusting the surface temperature of the object to be coated; a coating device that coats the heat shielding material on a surface of the object to be coated, The temperature adjustment device adjusts the surface temperature of the object to be coated before the heat shielding material is coated to an initial temperature that is higher than the surface temperature of the object before the heat shielding material is coated and is 35° C. or higher and 52° C. or lower. A coating film forming apparatus comprising:

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