Structure with silica thermal spray coating and method for manufacturing the same

Abstract

In a structure in which a silica thermal spray coating is formed on a substrate, both the insulating properties of the silica thermal spray coating and adhesion to the substrate are achieved. [Solution] The structure 1 comprises a base material 2, a silica thermal spray coating 3 provided directly on the base material 2 or on an intermediate layer on the base material, and an epoxy resin contained within the pores 31 of the silica thermal spray coating 3, wherein the epoxy resin is present in pores 31a located at least at the boundary 4a between the base material 2 or intermediate layer and the silica thermal spray coating 3.

Description

Technical Field

[0001] The present invention relates to a structure provided with a silica sprayed film and a method for manufacturing the same.

Background Art

[0002] Insulating materials are widely used as means for blocking current, and are applied to, for example, bearings, semiconductor devices, and liquid crystal devices, and are also used as protective films in various devices. Silica is known as a material having a low relative permittivity and high insulation properties.

[0003] Patent Document 1 discloses a sprayed film in which metal silicon and silica are mixed as a sprayed film that is less likely to generate particles by plasma etching and has insulating properties. According to Patent Document 1, the molten splats of silica have high viscosity and are difficult to spread on a low-temperature substrate, so they do not adhere to the substrate, and it was not easy to form a silica sprayed film. However, according to this sprayed film, it is said that metal silicon in the vicinity of the substrate adheres to both the substrate and silica, making it possible to manufacture a sprayed film mainly composed of silica at low temperature.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the thermal spray coating described in Patent Document 1, if the metallic silicon content is high, the dielectric constant of the thermal spray coating becomes high, making it difficult to ensure sufficient insulation. Conversely, if the metallic silicon content in the thermal spray coating is low, the adhesion between the thermal spray coating and the substrate becomes poor, making it difficult to achieve both insulation and adhesion. Furthermore, Patent Document 1 also proposes sealing open pores in the thermal spray coating with a sealing agent made of organosilicon compounds, but it has been found that a silica-based thermal spray coating sealed with an organosilicon compound does not have sufficient dielectric strength. [Means for solving the problem]

[0006] To solve the above problems, the structure of the present invention comprises a substrate, a silica thermal spray coating provided directly on the substrate or between the substrate and the substrate with an intermediate layer in between, and an epoxy resin contained within the pores of the silica thermal spray coating. The epoxy resin is present in pores located at least at the boundary between the substrate or the intermediate layer and the silica thermal spray coating.

[0007] Examples of more detailed features of the structure include (1) to (4) below. (1) The structure comprises an oxide ceramic coating made of an oxide other than silica on the silica thermal spray coating. (2) The structure comprises the oxide ceramic film as its outermost layer. (3) The structure comprises an oxide ceramic film made of an oxide other than silica as the intermediate layer. (4) The oxide ceramic film as the intermediate layer includes at least one of alumina, zirconia, titania, chromia, yttria, cordierite, mullite, gray alumina, zircon, forsterite, and steatite. (5) The structure further comprises a silica thermal spray coating on the oxide ceramic coating.

[0008] To solve the above problems, the method for manufacturing the structure of the present invention comprises the steps of forming a silica thermal spray coating directly on a substrate or on an intermediate layer on the substrate, and impregnating the pores of the silica thermal spray coating with epoxy resin so as to reach the pores located at the boundary between the substrate or the intermediate layer and the silica thermal spray coating.

[0009] As an example of a more detailed characteristic of the manufacturing method, the viscosity of the epoxy resin is 5 to 1000 mPa·s. [Effects of the Invention]

[0010] According to the structure of the present invention, or the method for manufacturing the structure of the present invention, a structure can be obtained that has excellent insulating properties and excellent adhesion, as well as a silica thermal spray coating capable of suppressing dielectric breakdown. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a cross-sectional view showing a schematic configuration of an example of the structure of the present invention. [Figure 2] Figure 2 is a schematic cross-sectional view showing the configuration of another example of the structure of the present invention. [Figure 3] Figure 3 is a cross-sectional photograph of the silica thermal spray coating of Example 1 after the PT test. [Figure 4] Figure 4 is a cross-sectional photograph of the silica thermal spray coating of Comparative Example 1 after the PT test. [Modes for carrying out the invention]

[0012] <Structure> The structure of this embodiment comprises a substrate and a silica thermal spray coating. The silica thermal spray coating has pores and is either applied directly to the substrate or with an intermediate layer in between. The structure also comprises epoxy resin contained within the pores of the silica thermal spray coating, and the epoxy resin is present in pores located at least at the boundary between the substrate or intermediate layer and the silica thermal spray coating. The presence of the epoxy resin in pores located at the boundary between the substrate or intermediate layer and the silica thermal spray coating enhances the adhesion between the substrate or intermediate layer and the silica thermal spray coating.

[0013] For example, in the structure 1 shown in Figure 1, a silica thermal spray coating 3 is directly applied to a substrate 2. The silica thermal spray coating 3 contains pores 31 inside. Some of the pores 31 exist between the substrate 2 and the boundary 4a between the substrate 2 and the silica thermal spray coating 3. The pores located at this boundary 4a are denoted as "31a". Of the pores 31, epoxy resin is present in at least the pores 31a located at the boundary 4a. Epoxy resin may also be present in pores 31 other than those located at the boundary 4a.

[0014] Furthermore, in the structure 11 shown in Figure 2, an intermediate layer 5 is provided on the substrate 2, and a silica thermal spray coating 3 is provided on top of that. The explanation in Figure 1 applies to the silica thermal spray coating 3. In addition, among the pores 31 in the silica thermal spray coating 3, pores located at the boundary 4b between the intermediate layer 5 and the silica thermal spray coating 3 are denoted as "31b". Of the pores 31, epoxy resin is present in at least the pores 31b located at the boundary 4b. Epoxy resin may also be present in pores 31 other than the pores 31b located at the boundary 4b.

[0015] The statement that epoxy resin "exists within pores located at the boundary between the substrate or intermediate layer and the silica thermal spray coating" means that a portion of the epoxy resin is in contact with the substrate or intermediate layer. In other words, if we consider the substrate side as "bottom" and the silica thermal spray coating side as "top" in the structure, then it can be said that the epoxy resin exists within pores located at least on the lower end surface of the silica thermal spray coating.

[0016] In addition, since the relative permittivity of the epoxy resin is lower than that of other resin materials, the relative permittivity of the layer composed of the silica spray coating film and the epoxy resin (hereinafter referred to as the "coating layer") can be kept low. That is, sufficient insulation can be obtained even if the coating layer is thin.

[0017] Moreover, since the epoxy resin is contained in the pores of the silica spray coating film, the breakdown voltage characteristics of the entire coating layer are improved, and the occurrence of dielectric breakdown can be suppressed.

[0018] Note that the epoxy resin may be present in all the pores located at the boundary between the base material or the intermediate layer and the silica spray coating film, or may be present only in some of the pores. However, it is preferable that the ratio of the pores in which the epoxy resin is present to the total pores located at the boundary between the base material or the intermediate layer and the silica spray coating film is higher, as higher adhesion can be obtained. Also, the epoxy resin may be present in all the pores of the silica spray coating film in the thickness direction, or may be present only in the pores located at the boundary. It is preferable that the distribution range of the epoxy resin in the thickness direction of the silica spray coating film is wider, as the breakdown voltage characteristics of the coating layer become higher and the intrusion of water into the pores is also suppressed.

[0019] The presence of the epoxy resin can be confirmed by confirming that the pores of the silica spray coating film are blocked (i.e., sealed). Specifically, it can be confirmed by a penetrant inspection test. The penetrant inspection test is carried out as follows. First, the structure is cut along its thickness direction, and a dye solution is applied to the cross-section. When the dye solution on the cross-section is wiped off, only the dye solution that has penetrated into the voids such as pores remains. By applying a developer thereto, the portion where the dye solution remains becomes colored, and the presence of the voids can be recognized. That is, it can be said that the epoxy resin has not penetrated into the colored portion, and the non-colored portion is sealed by the epoxy resin.

[0020] Examples of the epoxy resin include bisphenol F type epoxy resin, bisphenol A type epoxy resin, and polyglycidyl acrylate. Examples of the curing agent for the epoxy resin include tetrahydromethyl phthalic anhydride, diethylenetriamine, etc. Examples of the method for specifying that the substance present in the pores is an epoxy resin include Fourier transform infrared spectroscopy (FT-IR).

[0021] The silica sprayed film is a sprayed film substantially composed of only silica and may contain inevitable impurities. Specifically, the content rate of silica in the silica sprayed film is 95% by mass or more, and may exceed 99% by mass.

[0022] The film thickness of the silica sprayed film is preferably 5 to 150 μm. When the film thickness of the silica sprayed film is 5 μm or more, sufficient insulation can be ensured. When it is 150 μm or less, the occurrence of cracks and peeling due to internal stress in the silica sprayed film immediately after film formation can be suppressed. A more preferable film thickness of the silica sprayed film is 5 to 100 μm.

[0023] The porosity of the silica sprayed film is preferably 2 to 40%. When the porosity is 2% or more, the epoxy resin easily penetrates into the pores located at the boundary between the base material or the intermediate layer and the silica sprayed film, so the adhesion between the base material or the intermediate layer and the silica sprayed film is likely to be improved. When the porosity is 40% or less, the adhesion between the silica particles in the silica sprayed film becomes high, and the strength of the silica sprayed film increases. The porosity of the silica sprayed film can be calculated by regarding the black portions in the film in the cross-sectional film photograph (SEM-BEI image) of the scanning electron microscope as pores, subjecting the black portions to binarization processing to calculate the total area of the pores, and dividing the total area of the pores by the total area of the film within the observation range.

[0024] The structure may further comprise an oxide ceramic coating made of an oxide other than silica (hereinafter sometimes simply referred to as "oxide ceramic coating"). An "oxide ceramic coating made of an oxide other than silica" is a coating made substantially only of oxides other than silica, and may contain unavoidable impurities. Specifically, the content of oxides other than silica in the oxide ceramic coating is 95% by mass or more, and may exceed 99% by mass. Examples of oxides other than silica include alumina, zirconia, titania, chromia, yttria, cordierite, mullite, gray alumina, zircon, forsterite, and steatite.

[0025] It is preferable that the oxide ceramic coating be positioned in contact with the silica thermal spray coating. Since oxides have a higher affinity for silica compared to other ceramics, the oxide ceramic coating exhibits excellent adhesion to the silica thermal spray coating. The oxide ceramic coating may be positioned either on top of the silica thermal spray coating (opposite side from the substrate) or below it (substrate side).

[0026] For example, the oxide ceramic coating may be applied to the outermost layer of the structure. By applying the oxide ceramic coating to the outermost layer, the surface of the structure can be given the desired properties, or the layers provided beneath it can be protected.

[0027] Furthermore, the oxide ceramic coating may be provided as an intermediate layer between the substrate and the silica thermal spray coating. It is preferable that the oxide ceramic coating as an intermediate layer is positioned so as to be in contact with both the substrate and the silica thermal spray coating.

[0028] More specifically, the structure may have a metal substrate and an oxide ceramic coating as an intermediate layer. As mentioned above, oxide ceramics have good affinity with silica, so excellent adhesion can be obtained between the silica thermal spray coating and the oxide ceramic intermediate layer. Here, since there is a large difference in the coefficient of thermal expansion (CTE) between metal and silica, if a silica thermal spray coating is applied directly to a metal substrate, cracking and peeling of the silica thermal spray coating may occur due to the CTE difference. By providing an intermediate layer between the metal substrate and the silica thermal spray coating, cracking and peeling of the silica thermal spray coating due to the CTE difference between metal and silica are suppressed.

[0029] In particular, by providing an oxide ceramic coating as an intermediate layer having a CTE intermediate between that of the metal substrate and that of the silica thermal spray coating, cracking and peeling of the silica thermal spray coating caused by the CTE difference can be effectively suppressed. Examples of oxide ceramics having a CTE intermediate between that of the metal substrate and that of the silica thermal spray coating include alumina, zirconia, titania, chromia, yttria, cordierite, mullite, gray alumina, zircon, forsterite, and steatite. Therefore, it is preferable that the oxide ceramic intermediate layer contains at least one of alumina, zirconia, titania, chromia, yttria, cordierite, mullite, gray alumina, zircon, forsterite, and steatite.

[0030] The oxide ceramic coating is preferably an oxide ceramic thermal spray coating formed by thermal spraying. Oxide ceramic thermal spray coatings tend to contain numerous pores, which suppresses cracking and delamination compared to coatings formed by other film formation methods. Furthermore, similar to the silica thermal spray coating described above, sealing the oxide ceramic thermal spray coating with epoxy resin can improve adhesion to the substrate and enhance dielectric strength.

[0031] The base material consists of a single material, such as a metal bulk body, and forms the basic structural integrity of the structure. The shape of the base material is not particularly limited and may be plate-shaped, columnar, tubular, disc-shaped, annular, or even a three-dimensional shape with steps in some parts. Furthermore, the base material is not limited to metal and may be composed of other materials such as ceramics.

[0032] The structure may comprise multiple silica thermal spray coatings and multiple oxide ceramic thermal spray coatings. In this case, the silica thermal spray coatings and oxide ceramic thermal spray coatings may be arranged alternately on top of each other. While there are limitations to the film thickness when using a single coating, the overall thickness of the coating composed of silica thermal spray coatings and oxide ceramic thermal spray coatings can be increased by alternately layering the silica thermal spray coatings and oxide ceramic thermal spray coatings. As a result, the insulation performance of the entire coating can be improved.

[0033] When multiple silica spray coatings and multiple oxide ceramic spray coatings are alternately laminated, the epoxy resin only needs to be present in the pores located at the boundary between the silica spray coating closest to the substrate and the substrate or intermediate layer. The epoxy resin may be present throughout the multiple silica spray coatings and multiple oxide ceramic spray coatings, and may be present in the pores of the multiple silica spray coatings, the pores of the multiple oxide ceramic spray coatings, and in the pores located at the boundary between the silica spray coatings and the oxide ceramic spray coatings.

[0034] <Method for manufacturing the structure> The following describes an embodiment of the manufacturing method for the above-mentioned structure. Note that the matters described regarding the structure can also be applied to the manufacturing method. The manufacturing method of this embodiment is: (a) A step of forming a silica thermal spray coating directly on a substrate or on an intermediate layer on the substrate, (b) A step of impregnating the pores of the silica thermal spray coating with epoxy resin so that it reaches the pores located at the boundary between the substrate or the intermediate layer and the silica thermal spray coating, It is equipped with.

[0035] In step (a) above, atmospheric pressure plasma spraying is used, for example, to form the silica spray coating.

[0036] In step (b) above, the viscosity of the epoxy resin is preferably 5 to 1000 mPa·S, and more preferably 30 to 200 mPa·S. When the viscosity is 1000 mPa·S or less, the epoxy resin easily penetrates the pores contained in the silica thermal spray coating, making it easy to reach the pores located at the boundary between the silica thermal spray coating and the substrate or intermediate layer. The above-mentioned curing agent may be mixed with the epoxy resin.

[0037] After impregnation with epoxy resin, a curing process is carried out. This curing process involves heat treatment, specifically heating to 100°C or higher.

[0038] Furthermore, the manufacturing method may further include a step of forming an intermediate layer before forming the silica thermal spray coating. Similarly, a thermal spraying method such as atmospheric pressure plasma spraying can be used to form the intermediate layer.

[0039] Furthermore, the manufacturing method may further include a step of forming the oxide ceramic thermal spray coating after forming the silica thermal spray coating. The oxide ceramic coating may also be the outermost layer. In this case, step (b) may be performed after forming the silica thermal spray coating or after laminating the oxide ceramic thermal spray coating.

[0040] Alternatively, the process of forming a silica thermal spray coating and the process of forming an oxide ceramic thermal spray coating may be repeated alternately. In this case, step (b) may be performed each time a silica thermal spray coating is formed, or it may be performed after the silica thermal spray coating and the oxide ceramic thermal spray coating have been alternately laminated. [Examples]

[0041] <Structure formation> (1) Film formation A 5mm thick SS400 steel material was used as the base material, and a coating was formed on the base material by atmospheric pressure plasma spraying. The coating materials are shown in Table 1. When different materials are listed as "Layer 1," "Layer 2," etc., each layer was formed by layering coatings of each material. When only one material is listed, the coating was formed using only that material.

[0042] (2) Resin coating On the film formed in step (1) above, a mixture of 100 parts by mass of bisphenol F type epoxy resin (epoxy equivalent approximately 180; number average molecular weight approximately 370) and 55 parts by mass of tetrahydromethyl anhydride, or a silicone resin (average molecular weight 130), was applied by brush to allow the resin to penetrate the film. In both cases, the film was baked at 120°C for 2 hours after application.

[0043] <Measuring film thickness> The thickness of the coating formed on the substrate was measured based on cross-sectional SEM images of the structure.

[0044] <Relative permittivity> A simple parallel-plate capacitor was created by forming measuring electrodes on the surface of the film, and the capacitance and loss coefficient of the simple capacitor were measured at a measurement frequency of 1 MHz using an LCR meter (HIOKI IM3536). The relative permittivity was calculated from these values.

[0045] <Evaluation of voltage withstand characteristics> A high-voltage insulation resistance meter (HIOKI IR3455A960) was used to apply voltage to an Al foil attached to the surface of the coating, and the dielectric breakdown strength of the coating was measured at room temperature in an atmospheric environment.

[0046] <Penetrant testing> As described above, the formed structure was cut in the thickness direction and polished to obtain a test specimen.

[0047] The following procedure was performed using a PT (solvent-removable dye penetrant testing) test kit manufactured by Eika Chemical Co., Ltd., consisting of a cleaning agent (R-1M(NT)), a dyeing solution (R-1A(NT)), and a developer (R-1S(NT)). First, the test specimen was degreased with the cleaning agent using a CK wiper. The dyeing solution was applied to the cross-section of the test specimen with a cloth sprayed with the dyeing solution. The test specimen was left for about 15 minutes until the dyeing solution dried. The cross-section of the test specimen was wiped with a cloth sprayed with the cleaning agent. The developer was sprayed onto the cross-section. The cross-section after the above procedure was observed using a microscope to confirm whether the resin had reached the pores located at the boundary between the substrate or intermediate layer and the silica thermal spray coating.

[0048] The results are shown in the "Resin Reaching" column of Table 2. Here, Figure 3 shows a cross-sectional photograph of Example 1 as an example where the resin reached, and Figure 4 shows a cross-sectional photograph of Comparative Example 1 as an example where the resin did not reach. Comparing Figure 3 and Figure 4, it can be seen that the silica thermal spray coating in Figure 4 is stained black throughout, and the area near the silica thermal spray coating on the substrate is also stained gray. These black and gray areas are the colored areas. When resin is present in the pores, the dyeing solution cannot enter the pores, and no coloring occurs around those pores. In other words, by checking for coloring around pores located at the boundary between the substrate and the silica thermal spray coating, the presence or absence of resin in those pores can be confirmed.

[0049] <Peeling> For each test specimen, the presence or absence of delamination of the thermal spray coating from the substrate was visually confirmed.

[0050] [Table 1]

[0051] [Table 2]

[0052] [result] In Comparative Example 1, only a silica thermal spray coating was applied to the substrate. No sealing treatment was performed on the silica thermal spray coating. In the structure of Comparative Example 1, although the relative permittivity of the coating was low at 2.2, the dielectric breakdown strength was low and delamination was observed.

[0053] In Comparative Example 2, only a silica thermal spray coating was applied to the substrate, and the silica thermal spray coating was sealed with a silicone resin. The silicone resin reached the pores at the boundary between the silica thermal spray coating and the substrate. In the structure of Comparative Example 2, no delamination of the coating was observed, and although the dielectric constant was low at 2.4, the dielectric breakdown strength was low.

[0054] In Comparative Example 3, a first layer, an alumina thermal spray coating, and a second layer, a silica thermal spray coating, were applied to the substrate. No sealing treatment was performed on these coatings. In the structure of Comparative Example 3, no delamination of the coating was observed, but the dielectric breakdown strength was low.

[0055] In Example 1, only a silica thermal spray coating was applied to the substrate, and the silica thermal spray coating was sealed with epoxy resin. The epoxy resin reached the pores present at the boundary between the silica thermal spray coating and the substrate. Unlike Comparative Example 1, which was not sealed with epoxy resin, no delamination of the coating was observed in the structure of Example 1, and high dielectric breakdown strength was obtained. Furthermore, the silica thermal spray coating of Example 1, which was sealed with epoxy resin, showed even higher dielectric breakdown strength than the silica thermal spray coating of Comparative Example 2, which was sealed with silicone resin. In addition, the relative permittivity of the silica thermal spray coating of Example 1 was 2.7, which was similar to that of the silica thermal spray coating of Comparative Example 1, which was not sealed with resin.

[0056] In Examples 2, 5, and 6, a first layer consisting of an alumina thermal spray coating, a cordierite thermal spray coating, or a mullite thermal spray coating, and a second layer consisting of a silica thermal spray coating on top of it, were applied to the substrate. In these examples, the entire first and second layers were sealed with epoxy resin, and the epoxy resin reached the pores present at the boundary between the first and second layers. No delamination of the coating was observed in these structures, and the dielectric constant of the coating was lower and the dielectric breakdown strength was higher compared to Comparative Example 3 (i.e., a structure with a two-layer coating consisting of an alumina thermal spray coating and a silica thermal spray coating, but without sealing treatment).

[0057] In Examples 3 and 4, alumina thermal spray coatings and silica thermal spray coatings were alternately laminated on a substrate two and three times, respectively. In these examples, each layer was sealed with epoxy resin, and the epoxy resin reached the pores at the boundary between the first layer (alumina thermal spray coating) and the second layer (silica thermal spray coating). Furthermore, these structures showed no delamination of the coatings and exhibited higher dielectric breakdown strength compared to Comparative Example 3, which had a similar thickness as a whole but was not sealed. [Industrial applicability]

[0058] This invention can be used in various equipment components such as industrial machinery parts like bearings, semiconductor devices, and liquid crystal devices. [Explanation of Symbols]

[0059] 1, 11 structure 2 Base material 3. Silica thermal spray coating 31 Stomata 31a Pores located at the boundary between the silica thermal spray coating and the substrate 31b Pores located at the boundary between the silica thermal spray coating and the intermediate layer 4a Boundary between silica thermal spray coating and substrate 4b Boundary between silica thermal spray coating and intermediate layer 5. Middle Class

Claims

1. Substrate and A silica thermal spray coating provided directly on the substrate or on an intermediate layer on the substrate, The silica thermal spray coating comprises an epoxy resin contained within the pores of the aforementioned silica thermal spray coating, The epoxy resin is present in pores located at least at the boundary between the substrate or the intermediate layer and the silica thermal spray coating. structure.

2. The silica thermal spray coating is provided with an oxide ceramic coating made of an oxide other than silica. The structure according to claim 1.

3. The oxide ceramic film is provided as the outermost layer, The structure according to claim 2.

4. The structure according to any one of claims 1 to 3, comprising an oxide ceramic film made of an oxide other than silica as the intermediate layer.

5. The oxide ceramic film as the intermediate layer includes at least one of alumina, zirconia, titania, chromia, yttria, cordierite, mullite, gray alumina, zircon, forsterite, and steatite. The structure according to claim 4.

6. The oxide ceramic film is further provided with a silica thermal spray coating. The structure according to claim 2.

7. A step of forming a silica thermal spray coating directly on a substrate or on an intermediate layer on the substrate, A step of impregnating the pores of the silica thermal spray coating with epoxy resin so that it reaches the pores located at the boundary between the substrate or the intermediate layer and the silica thermal spray coating, A method for manufacturing a structure that includes the above.

8. The viscosity of the epoxy resin is 5 to 1000 mPa·s. A method for manufacturing the structure described in claim 7.

Images