Infrared transmitting member, housing using the same, railroad vehicle, voltage transformer, and engine

Abstract

To provide an infrared transmitting member which suppresses reflection and facilitates transmission of infrared light, and also facilitates removal of heat from heat generators.SOLUTION: An infrared transmitting member 100 is provided, comprising a substrate and a surface layer provided on the substrate, the surface layer (2) principally containing silicon dioxide. The infrared transmitting member 100 has an infrared transmittance greater than that of the substrate 1. The surface layer (2) may contain silicon dioxide particles. The surface layer (2) may preferably have an average thickness in a range of 200-800 nm.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present disclosure relates to an infrared-transparent member, and a housing, a railway vehicle, a transformer, and an engine using the same. [Background technology]

[0002] Inverters, computers, servers, transformers, and other equipment installed under the floor of railway cars generate heat continuously throughout the year. For this reason, these devices need to be cooled not only in summer but also in winter. These devices are usually housed in enclosures such as boxes or rooms.

[0003] Inverters for railway vehicles are becoming larger due to factors such as increased speeds, and the amount of heat they generate is increasing. Furthermore, the total amount of heat generated is also increasing with the global spread of railways. Furthermore, the number of computers, servers, and other devices has been rapidly increasing in recent years due to the increase in the number of digital devices, such as personal computers and smartphones, and the increase in the amount of data they handle.

[0004] To remove the heat generated by these devices, measures are taken, such as installing ventilation fans in the housings to release the internal heat, installing air conditioning devices to cool the inside, etc. As a result, the amount of electricity used for these measures is increasing year by year.

[0005] Patent Document 1 discloses a radiative cooling device in which an infrared radiation layer made of a specified glass and a light-reflecting layer located on the opposite side of the infrared radiation layer from the side where the radiation surface is present are stacked, and the light-reflecting layer is a stack of a silver layer and an aluminum layer, with the silver layer being located on the side closer to the infrared radiation layer.

[0006] Patent Document 2 discloses an anti-reflection coating provided on at least one surface of a substrate, the coating including a binder containing 50 mass % or more of silica, silica particles, and air pockets, the binder being formed from a condensate having a main skeleton of Si-O repeating units obtained by a hydrolysis-condensation reaction of an alkoxide compound having a predetermined non-hydrolyzable group and an alkyl group, and the coating being heat-treated after being formed on the substrate. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Application No. 2019 / 142876 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-99333 Summary of the Invention [Problem to be solved by the invention]

[0008] When devices such as inverters, computers, servers, and transformers generate heat, it can reach a temperature range of approximately 100 to 150°C. This heat is transmitted through three phenomena: conduction through contact with solids, convection through the flow of gas or liquid, and radiation through irradiation with infrared light with a wavelength of approximately 2500 to 7500 nm emitted by the heat source.

[0009] When the heat generated by the above-mentioned devices is transmitted by radiation, it is irradiated as infrared light onto the inner surface of the box, the inner surface of the room, etc.

[0010] When infrared light is irradiated onto a component, some of the light is reflected as reflected light, some is absorbed as absorbed light, and the remainder is emitted outside the component as transmitted light. If the proportion of transmitted light can be increased, it will be easier to release heat from inside the box or room to the outside, contributing to the cooling of the above-mentioned equipment. This is thought to lead to improved cooling efficiency and reduced increases in the amount of power required for cooling, thereby saving energy.

[0011] We considered reducing the proportion of reflected light from components as a way to increase the proportion of transmitted light. To reduce reflected light, if a thin film with an anti-reflection function against infrared light is formed on the surface of the base material that makes up the component, this will inevitably increase transmitted light and promote heat release from the component.

[0012] An object of the present disclosure is to provide an infrared-transparent member that suppresses reflection of infrared light and promotes transmission of infrared light, thereby promoting removal of heat from a heat-generating body. [Means for solving the problem]

[0013] The infrared-transparent member of the present disclosure comprises a substrate and a surface layer provided on the substrate, the surface layer containing silicon dioxide as a main component, and the infrared-transparent member has a higher transmittance of infrared light than the substrate. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide an infrared-transmitting member that suppresses reflection of infrared light and promotes transmission thereof, thereby promoting removal of heat from a heat-generating body. [Brief explanation of the drawings]

[0015] [Figure 1A] FIG. 2 is a schematic cross-sectional view illustrating an example of an infrared-transparent member according to an embodiment. [Figure 1B] FIG. 10 is a schematic cross-sectional view showing another example of an infrared-transparent member according to the embodiment. [Figure 2A] FIG. 2 is a schematic cross-sectional view showing the behavior of incident light, reflected light, and transmitted light in the case of only a substrate. [Figure 2B] 3A to 3C are schematic cross-sectional views showing the behavior of incident light, reflected light, and transmitted light in an infrared-transmitting member according to an embodiment. [Figure 3] 1 is a cross-sectional SEM image showing an example of a film containing silicon dioxide particles. [Figure 4] 1 is a graph showing the relationship between particle content and refractive index of a film according to the present disclosure. [Figure 5] FIG. 2 is a cross-sectional view showing a housing according to the embodiment. [Figure 6A] FIG. 2 is a schematic cross-sectional view illustrating an example of an infrared-transparent member according to an embodiment. [Figure 6B] FIG. 10 is a schematic cross-sectional view showing another example of an infrared-transparent member according to the embodiment. [Figure 7] FIG. 1 is a cross-sectional view showing an experimental device for delivering heat to a remote location. [Figure 8] FIG. 1 is a cross-sectional view showing an experimental device for delivering heat to a remote location. [Figure 9] 1 is a schematic diagram showing a railway vehicle according to the present disclosure. FIG. [Figure 10] 1 is a schematic cross-sectional view showing a housing that houses an inverter of a railway vehicle according to the present disclosure. FIG. [Figure 11] FIG. 1 is a schematic cross-sectional view showing a transformer according to the present disclosure. [Figure 12] 1 is a schematic cross-sectional view showing a power-related portion of an automobile equipped with an engine of the present disclosure. [Figure 13] FIG. 2 is a cross-sectional view showing an experimental device for evaluating the performance of the infrared-transparent member of the example. [Figure 14] FIG. 2 is a cross-sectional view showing an experimental device for evaluating the performance of the infrared-transparent member of the example. [Figure 15] 1 is a graph showing IR spectra of a styrene resin and an acrylic resin. [Figure 16] 14 is a graph showing the relationship between the thickness of a film constituting the infrared-transmitting member of the present disclosure and the temperature in the vicinity of the infrared-transmitting member in an evaluation using the experimental apparatus of FIG. 13. [Figure 17] 14 is a graph showing the relationship between the thickness of a film constituting the infrared-transmitting member of the present disclosure and the temperature in the vicinity of the infrared-transmitting member in an evaluation using the experimental apparatus of FIG. 13. [Figure 18] 14 is a graph showing the relationship between the thickness of a film constituting the infrared-transmitting member of the present disclosure and the temperature in the vicinity of the infrared-transmitting member in an evaluation using the experimental apparatus of FIG. 13. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present disclosure relates to an infrared-transmitting member, and more particularly to a member having a silicon dioxide film formed on the surface of a substrate made of metal, resin, or the like, that improves infrared transmittance.

[0017] Although a heat source at 100 to 150°C also emits infrared light with wavelengths longer than 7500 nm, this light is actually derived from air molecules at room temperature (15 to 25°C according to the Japanese Pharmacopoeia) when infrared light with wavelengths of 2500 to 7500 nm collides with them, resulting in a temperature that is slightly higher than room temperature. Therefore, even if light with wavelengths longer than 7500 nm is emitted to the outside, the internal high-temperature heat is not released. Therefore, in this specification, a component that improves the transmittance of infrared light in the 2500 to 7500 nm range is defined as an infrared-transparent component.

[0018] As a result of extensive research, we have found that a component having a layer containing silicon dioxide particles and a binder containing silicon dioxide that fixes the silicon dioxide particles on the outermost surface of a base material made of iron, stainless steel (SUS steel), aluminum, titanium, etc., which are widely used as general-purpose housing materials, can reduce the reflectance of infrared light in the 2500 to 7500 nm range, increase the amount of infrared light that passes through the component, and promote heat dissipation from the outer surface of the component.

[0019] In the case of the surfaces of metal materials such as iron, SUS steel, aluminum, and titanium, as well as other inorganic materials, Ra is at least 30 nm or more.

[0020] Furthermore, while anti-reflection films are generally used to reduce the reflectance of visible light in the wavelength range of about 400 to 800 nm, the purpose of the present disclosure is to achieve an anti-reflection effect in the wavelength range of 2500 nm or more.

[0021] It was also confirmed that the above-mentioned effects could be obtained even when the film was made of only a binder containing silicon dioxide without adding silicon dioxide particles.It was also confirmed that the above-mentioned effects could be obtained when the main component of the silicon dioxide film was silicon dioxide and the silicon dioxide film had a substituent such as an amino group, a methyl group, an ethyl group, or a glycidyl group.

[0022] The thickness T of the anti-reflection coating ideally satisfies the equation T=λ / 4, where λ is the wavelength at which the anti-reflection function is most effective.

[0023] When an antireflection coating is applied to the visible region of 400 to 700 nm, the ideal film thickness T of a single-layer antireflection coating is 137.5 nm, which is obtained by dividing 550 nm, the median value between 400 and 700 nm, by 4.

[0024] The principle of anti-reflection coating is to reduce reflected light by overlapping the peaks and valleys of the amplitude of the wavelength of light reflected by the surface of the substrate and the surface of the anti-reflection coating on the substrate. Therefore, it is necessary to shift the reflected light from the two surfaces by 1 / 4 of the wavelength, and therefore, as mentioned above, the ideal value is to adjust the length of the light path in the anti-reflection coating, i.e., the film thickness, to 1 / 4 of the wavelength.

[0025] If λ is 2500 to 7500 nm, the ideal value for T is 1250 nm, which is the value obtained by dividing 5000 nm, the median value of that wavelength range, by 4.

[0026] Anti-reflective coatings using silicon dioxide are intended for use on products where visibility is reduced by light reflection, such as show windows and showcases, and exhibit anti-reflective properties when the refractive index of the coating formed is lower than that of the substrate. If the surface of the product to which the coating is applied is fairly flat, specifically if the arithmetic mean roughness (Ra) is 10 nm or less, visibility will be reduced due to reflection.

[0027] However, if the surface is roughened to a certain extent, specifically if Ra is 30 nm or more, the anti-glare effect will eliminate the problem of reduced visibility due to reflection.

[0028] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings and the like.

[0029] (1) Overview of infrared-transparent materials FIG. 1A is a schematic cross-sectional view showing an example of an infrared-transparent member according to an embodiment.

[0030] In this figure, the infrared-transmitting member 100 has a configuration in which a film 2 (surface layer) mainly composed of silicon dioxide is formed on the surface of a substrate 1. With this configuration, the film 2 exhibits an anti-reflection effect against infrared light of 2500 to 7500 nm, improving the transmittance of the surface of the substrate 1 for infrared light of 2500 to 7500 nm.

[0031] FIG. 1B is a schematic cross-sectional view showing another example of an infrared-transparent member according to an embodiment.

[0032] The infrared-transmitting member 100 shown in this figure has a configuration in which a film 4 (surface layer) is formed on a substrate 1. The film 4 contains silicon dioxide particles 3 and has a configuration in which porous silicon dioxide is the main component.

[0033] 1A and 1B show a state in which a film is formed on both sides of the substrate 1. Reflection occurs on both the light incident surface and the light exit surface of the substrate 1, so forming a film on both sides of the substrate 1 provides a greater anti-reflection effect.

[0034] Due to the structure, it may be possible to form only one side, but even if only one side is used, the anti-reflection function for that surface is exerted, so in total, about half of the infrared transmission function can be exerted.

[0035] Next, the anti-reflection effect will be described.

[0036] FIG. 2A is a schematic cross-sectional view showing the behavior of incident light, reflected light, and transmitted light in the case of only a substrate, i.e., in the case of no film.

[0037] As shown in the figure, when incident light 5 is irradiated onto substrate 1, part of the incident light 5 is reflected from the irradiated surface, generating surface reflected light 6. The part of incident light 5 that is not reflected is absorbed by the irradiated surface, but the light that is neither reflected nor absorbed travels inside substrate 1, where some is absorbed inside substrate 1 and the remainder passes through the interior of substrate 1 and reaches the surface opposite the irradiated surface. Reflection also occurs on this surface, and reflected light 7 heads toward the irradiated surface. Ultimately, the light of incident light 5 excluding light absorbed by substrate 1, surface reflected light 6, and reflected light 7 is emitted as transmitted light 8 from the surface of substrate 1 opposite the irradiated surface.

[0038] FIG. 2B is a schematic cross-sectional view showing the behavior of incident light, reflected light, and transmitted light in an infrared-transmitting member according to an embodiment.

[0039] In the infrared-transmitting member 100 shown in the figure, by providing a film 2 (silicon dioxide film) whose main component is silicon dioxide on the surface of the substrate 1, it is possible to reduce the surface reflected light 6 and the reflected light 7. This makes it possible to increase the transmitted light 8, and as a result, it is possible to increase the transmittance of the substrate 1 for infrared light in the 2500 to 7500 nm range. This makes it possible to promote transmission of incident light 5, which is radiant heat (infrared light) that reaches the substrate 1 from a heating element (heat source), through the substrate 1.

[0040] Therefore, it can be said that the film 2 provided on the infrared-transmitting member 100 functions as an anti-reflection film against infrared light.

[0041] Next, the function as an anti-reflection film will be quantitatively examined.

[0042] To function as an anti-reflective coating, the refractive index of a film whose main component is silicon dioxide must be lower than that of the substrate. Silicon dioxide has a refractive index of approximately 1.46. The refractive index of materials commonly used as substrates, such as iron and SUS steel, is so high that it is difficult to measure. Aluminum also has a refractive index of 3.1 at a wavelength of 2500 nm, which is significantly higher than that of silicon dioxide. Therefore, films whose main component is silicon dioxide usually have a lower refractive index than the substrate.

[0043] Furthermore, as will be described later, the refractive index can be further reduced by using a film with a porous structure in which voids are provided inside. Due to this porous structure, the film exhibits anti-reflection properties even when applied to a substrate made of an organic material such as an acrylic resin, which has a refractive index close to that of silicon dioxide.

[0044] Furthermore, although the film thickness varies depending on the substrate, it was found that controlling it to roughly 200 to 800 nm promoted the infrared transmission function. As mentioned above, it was initially estimated that if the wavelength targeted for anti-reflection was 2500 to 7500 nm, the ideal film thickness would be 1250 nm, calculated by dividing 5000 nm, the median value of that wavelength range, by 4. However, it was found that a thinner thickness of 200 to 800 nm was actually preferable. The reason for this is unclear, but it is assumed that the thickness of the uneven portion of the substrate surface acts as a low-refractive-index film and is added to the film thickness of the anti-reflection coating.

[0045] (2) A film mainly composed of silicon dioxide Next, the structure of the film containing silicon dioxide as the main component, shown in FIG. 1A, which does not contain particles, and the structure of the film containing particles, shown in FIG. 1B, will be described.

[0046] (A) No particles (i) Membrane material One film material for a silicon dioxide-based film is silica sol, which is formed by polymerizing tetraalkoxysilanes, specifically tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, etc., to an average molecular weight of approximately 10,000. It can be formed by applying the silica sol and then thermally curing it. While tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, etc., can be directly applied to a substrate and then thermally cured, their low boiling points mean that some of them may volatilize from the substrate surface before polymerizing to form a film. Therefore, it is preferable to add acetic acid or hydrochloric acid, heat to approximately 50°C, and polymerize the material to a certain molecular weight before use.

[0047] As the film material, in addition to silica sol, alkoxysilane compounds having various substituents can be used, or they can be used in combination with silica sol. Specific examples of the alkoxysilane compound include vinyltrimethoxysilane, vinyltriethoxysilane, 3-isocyanatepropyltriethoxysilane, 3-ureidopropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 4-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2- (aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, n-propyltrimethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, 1,6-bis(trimethoxysilyl)hexane, trifluoropropyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, n-propyltriethoxysilane, hexyltriethoxysilane, octyltriethoxysilane, and the like.

[0048] In summary, the silicon dioxide-based film may be one whose main component is inorganic silicon dioxide, or one that contains a silicon compound having a hydrolyzable residue. The silicon compound having a hydrolyzable residue functions as a binder for the film.

[0049] (ii) Film formation method The silica sol and the alkoxysilane compound are diluted in a low-boiling alcohol having a carbon number of approximately 1 to 4 and a boiling point of 120°C or less to prepare a coating liquid to be applied to a substrate. This is because using a high-boiling alcohol makes it difficult for the solvent to volatilize from the silicon dioxide film, resulting in a long film formation time. Furthermore, alcohols having 5 or more carbon atoms are highly hydrophobic, making it difficult for highly hydrophilic compounds such as silica sol and the alkoxysilane compound to dissolve. Therefore, suitable solvents include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and 3-butanol. When forming a film in a high-humidity environment, it is preferable to use 1-butanol, 2-butanol, or 1-propanol, which have high boiling points.

[0050] After preparing the coating solution, the substrate is coated with the solution and then heated to form a film. The coating method is not particularly limited, and may be spray coating, dip coating, spin coating, or the like. However, spray coating is generally preferred when the substrate has a large surface area, while dip coating is preferred to improve the uniformity of the film thickness. Furthermore, spin coating is preferred when the substrate is flat and small.

[0051] Note that some substrates repel the coating liquid, and a portion of the substrate surface may not be coated. Specifically, the phenomenon of coating liquid repellency is relatively common in resin substrates such as polytetrafluoroethylene and polyethylene. Even in the case of iron or aluminum that has just been rolled, coating liquid may be repelled if a small amount of rolling oil used during rolling remains on the surface. Therefore, when coating such substrates, a pretreatment is performed to enhance wettability with the coating liquid before coating.

[0052] Specifically, wettability is improved by oxidizing the substrate surface by irradiating it with oxygen plasma, exposing it to ozone gas, or roasting it with a flame before coating, or by decomposing and removing oily components on the substrate surface.

[0053] In addition, during the rainy season and summer, humidity levels are high, and moisture in the air may penetrate the coating solution immediately after application, causing the film to become cloudy. In such cases, by preheating the substrate before coating, condensation is less likely to occur as the coating surface cools due to the evaporation of alcohol in the coating solution, and clouding of the film can be suppressed. However, when heating, the temperature must be adjusted to a level that does not deform the substrate.

[0054] In addition, by changing the solvent to a high-boiling alcohol as described above, it is possible to reduce condensation that occurs when the substrate cools as the solvent evaporates.

[0055] (iii) Porosity during film formation When forming a film using silica sol or an alkoxysilane compound, a dealcoholization reaction occurs and Si-O-Si bonds are formed. The formation of Si-O-Si bonds during thermal curing reduces the distance between molecules. Resins formed by polymerization of organic substances have flexible bonds, so polymerization is completed while shrinking in volume, with almost no internal voids. However, Si-O-Si bonds are rigid, so they cannot shrink in volume and voids are generated. In other words, by using alkoxysilane compounds such as silica sol used in the present disclosure, it is possible to form porous films.

[0056] Measurements using a refractometer (Kalnew Precision Spectrometer GM-1D) showed that the refractive index of bulk silicon dioxide was 1.46, while that of the porous silicon dioxide film was 1.39. Since the refractive index of air is 1.0, if we assume that the refractive index of the voids mentioned above is also 1.0, the voids are estimated to account for 15% of the film's total volume.

[0057] As mentioned above, the anti-reflection film must have a lower refractive index than the substrate. In the case of glass, the refractive index varies depending on the element type contained, but is generally about 1.42 to 1.6. Therefore, while some glass substrates have a refractive index lower than that of silicon dioxide, 1.46, the porous silicon dioxide film of the present disclosure has a refractive index as low as 1.39, making it applicable to almost all glass substrates, including these.

[0058] (B) When particles are present (i) Membrane material When particles are present, the film material is a mixture containing silicon dioxide particles and a binder whose main component is silicon dioxide.

[0059] Of these, the binder is a material that constitutes the film (A) above, and therefore a description thereof will be omitted. Here, only silicon dioxide particles will be described.

[0060] (silicon dioxide particles) The film, whose main component is porous silicon dioxide, is formed along the irregularities of the substrate, thereby achieving a uniform film thickness.

[0061] Furthermore, the substrate surface and the silicon dioxide film surface have large irregularities and the higher the frequency of these irregularities, the larger the surface area, and therefore the greater the contribution of the anti-reflection function of the silicon dioxide film, i.e., the greater the amount of infrared light emitted from the substrate, which is preferable.

[0062] When the particle size used is 50 nm or less, the concave portions of the substrate are hardly filled, and the film is formed while maintaining the unevenness. Specifically, when the arithmetic mean roughness Ra of the substrate before film formation is Ra0 and Ra after film formation is Ra1, the following formula (1) holds:

[0063] Ra1>0.9Ra0 …(1) Therefore, it was found that the surface of the film was almost the same as the unevenness of the substrate.

[0064] However, if the particle size used is 70 nm or larger, the concave portions of the substrate may be filled in, and if the arithmetic surface roughness of the substrate is 1000 nm or larger, the film thickness may approach 0 in thin areas and exceed 1000 nm in thick areas. In this case, the amount of infrared light emitted is suppressed due to the increase in surface area caused by the unevenness of the substrate.

[0065] Particles with a particle size greater than 50 nm and less than 70 nm were not available, and it is unclear what part of this range can be used, but it was determined that it is possible to maintain the roughness of the substrate at least up to 50 nm.

[0066] On the other hand, if the silicon dioxide particles are too small, they are likely to scatter due to air currents or static electricity when handled during weighing, etc., so it was found that an average particle size of 10 nm or more is desirable.

[0067] From the above, the average particle size of the silicon dioxide particles is preferably 10 to 50 nm.

[0068] Although silicon dioxide particles are usually spherical, particles formed by bonding several to a dozen spherical particles together can also be used in the same manner as spherical particles. In this case, the size of the bonded particles is preferably 10 to 50 nm for the same reasons as for the spherical particles.

[0069] (ii) Film formation method Silicon dioxide particles are mixed with silica sol and the above alkoxysilane compound, and as in the case of (A) above, this is diluted with a low-boiling alcohol having a carbon number of approximately 1 to 4 and a boiling point of 120°C or less to prepare a coating liquid to be applied to a substrate.

[0070] The coating method and pretreatment method are the same as those in (A) above.

[0071] (iii) Why does the silicon dioxide film become porous during the above film formation? By adding silicon dioxide particles, the overlapping areas of the particles in the formed film become gaps, which allows for an even lower refractive index. This occurs because the binder does not completely fill the spaces between the particles.

[0072] Next, the state of the porous film will be described.

[0073] FIG. 3 is a cross-sectional SEM image showing an example of a film containing silicon dioxide particles.

[0074] As shown in the figure, a film 4 is formed on the surface of a substrate 1. The film 4 is configured to contain silicon dioxide particles 9. Voids 10 having dimensions larger than the diameter of the silicon dioxide particles 9 can be seen between the silicon dioxide particles 9. The thickness of the film 4 is approximately 100 nm.

[0075] In this way, voids 10 are formed between the silicon dioxide particles 9, and therefore the refractive index of the film 4 having particles (B) is further reduced compared to the film (A) having no particles.

[0076] 4 is a graph showing the relationship between the particle content and refractive index of a film according to the present disclosure. The horizontal axis represents the percentage of silicon dioxide particles contained in the film (unit: wt% (weight %)), and the vertical axis represents the refractive index of the film. The film thickness was adjusted to 300 nm ± 30 nm.

[0077] As shown in this figure, the refractive index is 1.39 when no silicon dioxide particles are added (i.e., 0 wt%). As the silicon dioxide particle content increases, the refractive index gradually decreases. At a silicon dioxide content of 50 wt%, the refractive index drops to 1.34, and at 70 wt%, it drops to 1.30. At this level, the anti-reflection properties are significantly enhanced against organic materials such as acrylic resin (1.49), polycarbonate resin (1.56), and tetrafluoroethylene resin (1.35). Furthermore, at a silicon dioxide particle content of 90 wt%, the refractive index drops to 1.23. Note that with a silicon dioxide particle content of 100%, the absence of a binder component means that the silicon dioxide particles cannot be held to the substrate, making film formation impossible. For this reason, experiments were conducted up to a silicon dioxide particle content of 90%.

[0078] (iv) Addition ratio of silicon dioxide particles The higher the proportion of silicon dioxide particles in the components excluding the solvent in the coating solution, i.e., the components that make up the solid content of the film, the more thixotropic the coating solution becomes, and therefore a thicker film can be formed compared to a coating solution that does not contain silicon dioxide.

[0079] For example, when forming a 300-nm-thick silicon dioxide film by dip coating, if the solids concentration is 2 wt% and the substrate is pulled out of the coating solution at a speed of 1 mm / s, the film thickness will be approximately 70 nm if no silicon dioxide particles are added. In contrast, if the film contains 70 wt% silicon dioxide particles, the film thickness will be more than four times as thick (310 nm). Therefore, if the required film thickness is 350 nm or thicker, five coats of a coating solution without silicon dioxide particles would be required, but only two coats would be required if the coating solution contains 70 wt% silicon dioxide particles. This has the advantage of significantly improving throughput during mass production.

[0080] However, the higher the proportion of silicon dioxide particles, the lower the physical strength, such as abrasion resistance. This is because the proportion of silica sol, which serves as a binder for retaining the silicon dioxide particles in the film and ensuring physical strength, or silicon dioxide derived from an alkoxysilane compound, decreases. In particular, if the proportion of silicon dioxide particles in the coating solution exceeds 70 wt%, there is a high possibility that the film will peel off along with the particles even when lightly rubbed with a hand. Therefore, from a practical standpoint, it is desirable for the proportion of silicon dioxide to be 70 wt% or less.

[0081] (v) Dispersant Silicon dioxide particles have a small specific gravity of approximately 2.2, so they may disperse without the addition of a dispersant. However, if the particle diameter exceeds 100 nm, a nonionic surfactant, specifically a polyethylene glycol dialkyl ether, a polyethylene glycol dialkyl ester, a polyethylene glycol monoalkyl ether, or a polyethylene glycol monoalkyl ester, should be added. The addition rate is preferably about 0.1 to 1.0 wt% of the silicon dioxide particles.

[0082] (vi) Film thickness As mentioned above, in the case of a single-layer antireflection coating that reduces reflectance in the visible wavelength range of 400 to 700 nm, the film thickness is adjusted so as to minimize reflectance at 550 nm, the median value of the 400 to 700 nm wavelength range. If the film thickness is t, t can be calculated using the following formula (2):

[0083] t=550 / 4=137.5 …(2) That is, the ideal film thickness t is 137.5 nm.

[0084] Following the above concept, the thickness tr of a single-layer antireflection coating that reduces reflectance in the infrared wavelength range of 2500 to 7500 nm is adjusted so as to minimize reflectance at 5000 nm, the median value of the 2500 to 7500 nm wavelength range. Specifically, this can be calculated using the following formula (3), similar to the above formula (2).

[0085] tr=5000 / 4=1250 …(3) That is, the ideal film thickness tr is 1250 nm.

[0086] However, our research has shown that the film thickness varies depending on the substrate used, but is generally between 200 and 800 nm. For metals such as iron, SUS steel, and aluminum, a thickness of 200 to 300 nm is suitable. For inorganic materials such as glass and silicon wafers, a thickness of 400 to 600 nm is suitable. For organic materials such as polyethylene resin, polycarbonate resin, and acrylic resin, a thickness of 300 to 800 nm is suitable.

[0087] From the above results, it was found that the preferred thickness of the silicon dioxide film in the present disclosure is 200 to 800 nm, which is thinner than the thickness considered when designing conventional antireflection films. Thus, the reason for the difference between the ideal film thickness of a conventional single-layer antireflection film and the preferred film thickness of the antireflection film in the present disclosure is not yet understood.

[0088] (3) Base material (i) Type of substrate The essential requirement for the substrate material used in this disclosure is that it has a refractive index higher than that of the film whose main component is silicon dioxide, which is approximately 1.3 to 1.4. In this regard, metal materials used for the housing of structures, such as iron, aluminum, various SUS steels, and titanium, are suitable because they have a refractive index of 3 or more. Other examples include organic materials such as polyethylene resin, polycarbonate resin, and acrylic resin, which have a refractive index of approximately 1.5. Other examples include inorganic materials such as silicon wafers, which have a refractive index of 3.4, and glass, which have a refractive index of approximately 1.5.

[0089] (ii) Surface roughness of the substrate The larger the actual surface area relative to the projected surface area of ​​the substrate, that is, the larger and more frequent the irregularities, the greater the surface area of ​​the substrate, and the greater the area through which infrared light passes, making it possible to efficiently release heat. Therefore, it is desirable for the substrate to have as large a surface roughness and as frequent a surface roughness as possible, within the range that does not impair the original function of the substrate.

[0090] The original function referred to here will be explained next.

[0091] Substrates are typically used in parts that make up the housing of some device or component, or as a substrate to which multiple components are joined. Their shape is basically a flat plate, or a flat plate with an intentional curvature. It is desirable for these substrates to have a high frequency of irregularities per unit area, as long as it does not impair their intended function, as this allows for highly efficient heat dissipation.

[0092] For example, among base materials, the Ra of rolling marks formed by rolling on plate materials such as iron, aluminum, SUS steel, and titanium is about 50 to 300 nm, but the larger the Ra of the rolling marks, the greater the anti-reflection function and the greater the amount of heat radiated.

[0093] (iii) Surface roughness of the infrared-transmitting member after forming the silicon dioxide film As mentioned above, the greater the surface roughness, the greater the amount of heat dissipation. However, if the valleys of the unevenness of the base material constituting the infrared-transmitting member are filled in and the surface is made flatter than the base material, the heat dissipation effect will be reduced.

[0094] Our investigation has revealed that when the particle diameter is 50 nm or less as described above, the irregularities in the substrate are hardly filled in, and the infrared-transmitting member exhibits an Ra that is almost the same as that of the substrate.

[0095] (4) A substrate having a film containing a black pigment formed on one side FIG. 5 is a cross-sectional view showing a housing according to the embodiment.

[0096] In this figure, a heat-generating device 11 is housed and stored in a housing 12 made of an infrared-transparent material.

[0097] In the housing 12, a film 13 containing a black pigment is formed on the inner surface of the substrate 1. A film 2 containing silicon dioxide as a main component is formed on the outer surface of the substrate 1.

[0098] Because the film 13 contains a black pigment, the infrared light emitted from the device 11 is efficiently absorbed by the black pigment, and the heat generated in the film 13 is thereby conducted within the base material 1 and easily released to the outside of the housing 12.

[0099] In particular, in the case of a resin material with high transmittance to infrared light, the presence of film 2 suppresses reflection of infrared light that has passed through substrate 1. Therefore, infrared light that has passed through substrate 1 is likely to pass through film 2 and be released to the outside of housing 12.

[0100] Therefore, if such a housing 12 is used, heat from the device 11 is quickly released to the outside of the housing 12.

[0101] Heat can be efficiently dissipated to the outside of the housing 12 in the form of infrared light from the outer surface of the housing 12, where reflection by the film 2 is suppressed. Substrates suitable for forming a film containing a black pigment on one side rather than a silicon dioxide film are mirror-polished iron, aluminum, and other substrates with high surface reflection. Iron, in particular, reflects a significant proportion of the infrared light that free electrons attempt to enter the substrate, so the film containing the black pigment absorbs the infrared light in the form of heat. This heat diffuses through the substrate and is released on the opposite surface as transmitted light in the infrared range. The amount of transmitted light is increased by suppressing reflection with the silicon dioxide film.

[0102] The main component of black pigments is a structure in which many carbon atoms are conjugated with double bonds. As a result, the length of the conjugated system is longer than that of dyes, and they absorb a wide range of light from ultraviolet to infrared. This makes them desirable as materials for absorbing energy such as infrared light emitted from the device 11.

[0103] The average particle size of the black pigment used is preferably at least 10 nm, since if the particles are too small, handling such as weighing becomes difficult. On the other hand, if the particles are too large, the hiding power per unit volume of the added black pigment decreases, so a maximum of 1000 nm or less is desirable.

[0104] The film 13 preferably contains a binder to hold the black pigment. Examples of binders include organic materials, silica sol used in forming silicon dioxide films, and various alkoxysilane compounds. Among these, silica sol acts as a binder for silicon dioxide. Silicon dioxide has no absorption band due to its chemical structure from 2500 to 7500 nm, and only absorption due to Si-O stretching vibrations around 7500 to 10000 nm. This makes it suitable as a binder. Most organic materials have a CH stretching band around 3000 nm and a CO stretching band around 5500 to 6300 nm. Of these, stronger CO stretching absorption, which has a lower photon energy per photon, than CH stretching absorption at 3000 nm, which has a higher photon energy per photon, increases the efficiency of heat transfer from the black pigment-containing film 13 to the substrate 1. Therefore, it is preferable for the organic material to have a stronger CO stretching absorption than CH stretching absorption.

[0105] Furthermore, if the black pigment-containing film 13 is too thick, it takes a long time for heat to be conducted to the substrate 1, and during this time, the amount of heat leaking from the edges of the film increases; therefore, a thin film is preferable. We used a black pigment with an average particle size of 1000 nm (1 μm) to absorb almost 100% of the infrared light emitted from the heat source, i.e., to block almost 100% of the reflection from the substrate 1, and we found that a film 13 thickness of at least 10 μm was required. This means that to block almost 100% of the reflection from the substrate 1, it is necessary to layer 10 black pigment particles in the thickness direction. Therefore, if the average particle size of the black pigment used is 1 μm or less, it is thought that the required film thickness will be 10 μm or less.

[0106] The film 2 constituting the housing 12 in FIG. 5 may or may not contain silicon dioxide particles.

[0107] FIG. 6A is a schematic cross-sectional view showing an example of an infrared-transparent member according to an embodiment.

[0108] In this figure, the infrared-transmitting member 200 has a configuration in which a film 2 containing silicon dioxide as a main component is formed on one surface (the surface on the right side in the figure) of a substrate 1. This is a case in which silicon dioxide particles are not included. A film 13 containing a black pigment is formed on the other surface (the surface on the left side in the figure) of the substrate 1.

[0109] FIG. 6B is a schematic cross-sectional view showing another example of the infrared transparent member according to the embodiment.

[0110] The infrared-transmitting member 200 shown in this figure has a configuration in which a film 4 is formed on one surface (the surface on the right in the figure) of a substrate 1. The film 4 contains silicon dioxide particles 3 and has a configuration in which porous silicon dioxide is the main component. As in FIG. 6A, a film 13 containing a black pigment is formed on the other surface (the surface on the left in the figure) of the substrate 1.

[0111] (5) An infrared-transmitting member in which a film mainly composed of silicon dioxide is formed on a portion of the surface of the substrate. By using an infrared-transmitting member in which a film mainly composed of silicon dioxide is formed on a portion of the surface of the base material, it becomes possible to transmit heat to a location far from the heat source, and it becomes possible to radiate heat significantly only from the portion where the film mainly composed of silicon dioxide is formed.

[0112] FIG. 7 is a cross-sectional view showing an experimental setup for delivering heat to a remote location.

[0113] In the experimental apparatus shown in this figure, holes 14, 15, and 16 are made in a cardboard box 18. Another hole is made between the two holes 15 and 16, and a dryer 17 (HD-1301 manufactured by Hitachi, Ltd.) is inserted into this hole. Hole 14 is made on the surface opposite to the surface where holes 15 and 16 are made. The dimensions of box 18 are 300 mm in length, 400 mm in width, and 150 mm in height. The dimensions of holes 14, 15, and 16 are 80 mm square. The dimension of the hole into which dryer 17 is inserted is 55 mm in diameter.

[0114] Dryer 17 is inserted into the hole so that its outlet faces the inside of box 18. Holes 15 and 16 are exhaust ports for discharging hot air to the outside of box 18 when dryer 17 is operating.

[0115] An infrared-transmitting member made up of a substrate 1 and a film 2 is placed so as to cover the hole 14. At a position on the substrate 1 corresponding to the hole 14, a film 2 is provided facing the inside of the box 18. Furthermore, on the surface of the substrate 1 facing the outside of the box 18, a film 2 is provided at a position separated from the film 2 facing the inside of the box 18. The main component of the film 2 is silicon dioxide.

[0116] Fences 25 (shields) are provided on both sides of the membrane 2 facing the outside of the box 18. The fences 25 are made of cardboard with a thickness of 10 mm.

[0117] A thermocouple 20 is installed 5 mm from the membrane 2 facing the outside of the box 18. Thermocouples 19 and 21 are installed on the outside separated by a fence 25, 5 mm from the substrate 1. The temperatures of the thermocouples 19, 20, and 21 are displayed on display devices 22, 23, and 24, respectively. The provision of the fence 25 makes it difficult for the air near the membrane 2 to mix with the air outside it.

[0118] The thermocouple 20 can detect the effect of radiation from the surface of the film 2 by comparing it with the temperatures measured by the thermocouples 19 and 21 .

[0119] When the dryer 17 is operated at a power consumption of 1200W and hot air is released into the inside of the box 18, the substrate 1 and film 2 are heated at the position of the hole 14, and the heat is conducted inside the substrate 1 and transferred to the film 2 toward the outside of the box 18.

[0120] When the room temperature was 20°C and hot air was emitted from the dryer 17 for 30 seconds, the display device 22 displayed 28°C and the display device 24 displayed 25°C, which were slightly higher than room temperature. In contrast, the display device 23 displayed 45°C, which was clearly higher than the displays 22 and 24. This shows that by forming the film 2 partially rather than on the entire surface, it is possible to locally heat the desired portion of the infrared-transmitting member (the portion where the film 2 is provided).

[0121] Next, a case where a film containing a black pigment is provided at the position of the hole 14 instead of the film 2 in FIG. 7 will be described.

[0122] FIG. 8 is a cross-sectional view showing an experimental setup for delivering heat to a remote location.

[0123] The difference between this figure and Figure 7 is that a film 13 containing a black pigment is provided at the position of the hole 14 instead of the film 2 in Figure 7. The other conditions are the same as in Figure 7.

[0124] In the experiment shown in Fig. 8, display device 22 showed 30°C, display device 24 showed 27°C, and display device 23 showed 48°C. That is, display devices 22, 23, and 24 all showed temperatures higher than the experimental results shown in Fig. 7. This is because film 13 has a higher absorptance of infrared light than film 2, is more likely to absorb radiant heat, and is more likely to transfer heat inside box 18 in Fig. 7 to substrate 1.

[0125] One use for this substrate is as a heat transfer jig for heating flammable materials. A long substrate is prepared, and like the substrate in Figure 7, a film made primarily of silicon dioxide is formed on the bottom left and top right. If the heat source is an open flame such as a gas burner, the open flame is used to heat the silicon dioxide-based film on the bottom left of substrate 1. A small bottle containing a solution of acetone, a type of flammable material, is placed on top of the silicon dioxide-based film on the top right of substrate 1. Note that substrate 1 should be long enough to ensure that the open flame does not ignite the acetone.

[0126] When the silicon dioxide-based film 2 on the bottom left of the substrate 1 is heated with a hair dryer, the silicon dioxide-based film 2 on the top right of the substrate 1 releases heat preferentially, making it possible to safely heat the acetone.

[0127] Another example is a griddle used to grill food at a barbecue. When grilling meat or vegetables on a griddle, thinly sliced ​​meat that is cooked at a low temperature or for a short time is placed on an area that does not have a silicon dioxide film. On the other hand, vegetables such as onions and pumpkins that are cooked at a high temperature or for a long time are placed on an area that has a silicon dioxide film. This allows for a greater amount of heat to be imparted to the food from the griddle compared to areas that do not have a silicon dioxide film, thereby minimizing the difference in cooking time between ingredients and allowing all the cooked food to be eaten at roughly the same time.

[0128] (6) Products using the above infrared-transmitting materials There are many needs for heat dissipation from heat-generating objects, and the application of the present disclosure to these applications has the effect of increasing the efficiency of heat external release. Below, railway vehicles, transformers, and engines are given as examples, but other applications include application to the base material of pipes with fins on the outer surface to promote cooling in order to cool them while passing high-temperature gas or liquid through them, application to components of compressors to release heat generated by friction inside the compressor during compression to the outside, and application to components of the heat-dissipating parts of various heating appliances.

[0129] (i) Railway vehicles FIG. 9 is a schematic diagram showing a railway vehicle according to the present disclosure.

[0130] As shown in the figure, railway vehicle 31 takes in the current flowing through overhead wires 32 via pantograph 33. The taken-in current passes through current control means, such as a transformer and various rectifying elements, inside the vehicle and then flows to an inverter inside housing 34. The inverter sends current at an appropriate voltage to power unit 35, which houses the motor, to control the running of railway vehicle 31. During deceleration, the motor in power unit 35 generates electricity while functioning as a regenerative brake. The obtained electricity is adjusted to an appropriate voltage by the inverter and then sent to and stored in battery unit 36. The stored electricity is mainly used when accelerating railway vehicle 31, thereby reducing the amount of power consumed from the overhead wires. It is also used as part of the power required for purposes other than running, such as heating and cooling and lighting inside the vehicle. The inverter also controls the voltage to be appropriate when supplying these.

[0131] FIG. 10 is a schematic cross-sectional view showing a housing that houses an inverter of a railway vehicle according to the present disclosure.

[0132] As shown in the figure, the housing 34 is installed on the outside of the bottom surface 31a of the railway vehicle. An inverter 37 is installed inside the housing 34. In the case of railways or subways in densely populated areas, where stations are located every few hundred meters, the vehicle frequently accelerates and decelerates. This forces the inverter 37 to frequently control the voltage. As a result, the inverter 37 generates heat, causing the temperature inside the housing 34 to rise. If the inside of the housing 34 is not cooled, the inverter 37 may break down due to the heat, so the inside of the housing 34 is cooled by a cooling unit 38.

[0133] In this figure, the inner surface of the housing 34 is covered with a film 13 containing a black pigment, and the outer surface is covered with a silicon dioxide film 2. With this configuration, heat inside the housing 34 is efficiently released to the outside, reducing the load on the cooling unit and the amount of electricity required for cooling.

[0134] (ii) Transformers FIG. 11 is a schematic cross-sectional view showing a transformer of the present disclosure.

[0135] The transformer 39 shown in this figure is an oil-filled type in which the inside is cooled with insulating oil 42.

[0136] The transformer 39 includes an iron core 40 and a copper or aluminum winding 41 wound around the iron core 40. The iron core 40 and the winding 41 are immersed in insulating oil 42 injected inside a housing. The housing includes a substrate 1 and a silicon dioxide film 2. The transformer 39 has the function of stepping up and stepping down AC voltage. The transformer 39 generates heat when current is applied, so it is cooled by the insulating oil 42.

[0137] Since the silicon dioxide film 2 is formed on the outer surface of the transformer 39, heat dissipation to the outside of the transformer 39 proceeds efficiently.

[0138] In the oil-filled type, insulating oil 42 is cooled by air cooling, water cooling, etc., but forming a silicon dioxide film 2 on the outer surface of the transformer 39 simplifies the cooling mechanism. It also suppresses thermal degradation of the insulating oil 42. In this specification, the component of the transformer 39 on which the film 2 is provided is referred to as the "casing."

[0139] Furthermore, even in the case of a dry type that does not use oil rather than an oil-filled type, the inside of the transformer 39 generates heat, so by forming a silicon dioxide film 2 on the inside and outside surfaces of the transformer 39, heat dissipation is more efficient than before and thermal deterioration of the internal components is suppressed.

[0140] (iii) Engine FIG. 12 is a schematic cross-sectional view showing the power-related portion of an automobile equipped with the engine of the present disclosure.

[0141] The automobile 43 shown in this figure is a hybrid type front-wheel drive vehicle powered by a gasoline or diesel-burning engine 44 and a motor 45. Note that an automobile with only an engine 44 does not have the motor 45, power control unit 46, or hybrid vehicle battery 47.

[0142] The automobile 43 includes, as its power mechanism, an engine 44, a motor 45, and a power control unit 46 that appropriately controls the power energy output from these power mechanisms. The engine 44 is supplied with fuel from a fuel tank 48. The motor 45 is powered by electricity received from a battery 47. When braking to decelerate or stop the vehicle, the motor 45 generates electricity as a regenerative brake, and the generated electricity is used to charge the battery 47. Acceleration and deceleration of the automobile 43 are controlled by a cruise control unit 49. Of the power mechanisms of the automobile 43, the engine 44 that burns fuel generates the most heat when starting and driving. To cool the engine 44, cooling water is circulated around the engine 44. The cooling water is cooled by a radiator 50. The cooling water is also cooled by a fan 51.

[0143] A silicon dioxide film 2 is formed on the surface of the engine 44. That is, the silicon dioxide film 2 is formed on the surface of the cylinder, housing, etc. (in this specification, these are referred to as the "casing") of the engine 44. This allows for efficient transmission and release of heat from the inside of the engine 44 to the outside, making it possible to reduce the size of the radiator 50 and the fan 51, leading to a reduction in the number of components.

[0144] In this figure, it is shown as being formed only on the outer surface of the engine 44, but by forming it on the inner surface as well, the amount of heat transmitted and released to the outside will be further increased, improving the cooling efficiency of the engine 44.

[0145] In addition, by reducing the size of the radiator 50 and the fan 51, new space can be obtained inside the engine room, making it easier to add safety equipment and the like that will be required in the future.

[0146] Hereinafter, examples of the present disclosure will be described. [Example]

[0147] First, the preparation of the coating liquid, the formation of the film on the substrate, and the evaluation will be described.

[0148] Infrared-transmitting members each having a substrate made of SUS304 stainless steel and a film mainly composed of silicon dioxide formed on both sides thereof were prepared by the following process, and their infrared transmittance was evaluated.

[0149] (1) Preparation of coating solution (Preparation of Coating Solution A) The method for preparing coating solution A for forming a silicon dioxide film is as follows.

[0150] Tetraethoxysilane (70 g) was dissolved in 2-propanol (920 g), 0.01 N hydrochloric acid (10 g) was added, and the mixture was heated at 50°C for 1 hour with stirring to prepare approximately 1000 g of colorless, transparent coating liquid A.

[0151] The silicon dioxide concentration of Coating Solution A after thermal curing is approximately 2% by weight. Coating Solution A is generally called a silica sol solution.

[0152] (Preparation of Coating Solution B) The coating liquid B containing silicon dioxide particles was prepared as follows.

[0153] 225 g of a dispersion (solvent: isopropanol) containing 6% by weight of silicon dioxide particles with an average particle size of 10 nm is mixed with 675 g of the above coating solution A. This mixture is thoroughly stirred with an ultrasonic homogenizer to improve dispersibility, and approximately 900 g of a translucent coating solution B is prepared.

[0154] (2) Film formation (Film formation with coating solution A) The substrate is a 100mm square SUS304 steel sheet with a thickness of 0.5mm and an arithmetic surface roughness (Ra) of 100nm. A dip tank is also prepared for dip coating the substrate. Coating liquid A is poured into the dip tank.

[0155] Next, the substrate is immersed 90 mm deep into the dipping tank and then pulled out at a speed of 1 mm / sec. The pulled-out substrate is heated at 180°C for 5 minutes. This forms a film of silicon dioxide with a thickness of approximately 70 nm on the surface of the substrate.

[0156] The process of immersion in the dipping bath, removal, and heating at 180°C was repeated four times. In this way, a film containing silicon dioxide as its main component and having a thickness of approximately 280 nm was formed on the surface of the substrate. The substrate having the film formed thereon in this way was used as a sample of an infrared-transmitting member.

[0157] The Ra of the infrared transmitting member after the film formation was 100 nm, which was the same as that of the substrate before the film formation.

[0158] (Coating solution B film formation) As with the film formation using Coating Liquid A, a substrate measuring 100 mm square and 0.5 mm thick is prepared. A dip tank is also prepared for dip coating this substrate. Coating Liquid B is poured into the dip tank.

[0159] Next, the prepared substrate is immersed in a dipping tank to a depth of 90 mm, then pulled out at a speed of 1 mm / sec, and heated at 180°C for 5 minutes.

[0160] In this way, a film containing silicon dioxide as a main component and containing silicon dioxide particles with a thickness of about 310 nm is formed on the surface of the substrate.

[0161] The Ra after the film formation was 90 nm, which was 0.9 times the Ra of the substrate before the film formation.

[0162] (3) Evaluation FIG. 13 is a cross-sectional view showing an experimental device for evaluating the performance of the infrared-transmitting member produced as described above.

[0163] In this figure, a cardboard box 65 measuring 600 mm in length, 400 mm in width, 150 mm in height, and 10 mm in thickness is prepared. Box 65 has 80 mm square holes 61, 62, 63, and 64. In addition, between the two holes 63 and 64, another hole with a diameter of 55 mm is provided, and dryer 17 is inserted into it. Dryer 17 is inserted into the hole so that its outlet faces into box 65. Holes 63 and 64 are exhaust ports for discharging hot air to the outside of box 65 when dryer 17 is operating.

[0164] A substrate 67 (infrared-transmitting member) on which a film 66 containing silicon dioxide as a main component is formed using coating liquid A is fixed so as to cover the hole 62. Next, a substrate 68 to which neither coating liquid A nor B has been applied is fixed so as to cover the hole 61.

[0165] Two thermocouples 69, 70 are installed on the exterior of the box 65 to measure the temperatures near the surfaces of the substrates 67, 68. Display devices 71, 72 that display the temperatures of the thermocouples 69, 70, respectively, are also installed. A 10 mm thick cardboard fence 73 is installed between the two thermocouples 69, 70 to prevent the air near the thermocouples 69, 70 from mixing with each other. The room temperature is 20°C.

[0166] Here, dryer 17 was operated at a power consumption of 1200 W and hot air was released into box 65, heating substrates 67 and 68. After 30 seconds, the temperature near substrate 68, which did not have film 66 mainly composed of silicon dioxide, rose slightly above room temperature to 25°C. In contrast, the temperature near substrate 67, which had film 66 mainly composed of silicon dioxide, rose to 45°C. This confirmed that the substrate on which film 66 mainly composed of silicon dioxide was formed, functioned as an infrared-transmitting member.

[0167] Therefore, it was confirmed that the substrate 67 exhibits the infrared transmittance function by forming the film 66 thereon.

[0168] Furthermore, the same evaluation as above was carried out using a substrate on which a film mainly composed of silicon dioxide containing silicon dioxide particles was formed using Coating Liquid B instead of Coating Liquid A. When hot air was emitted from Dryer 17 for 30 seconds, the temperature near the substrate not having Film 66 mainly composed of silicon dioxide rose slightly above room temperature to 25°C. In contrast, the temperature near the substrate having Film mainly composed of silicon dioxide containing silicon dioxide particles rose to 48°C. This result also confirmed that the substrate on which Film mainly composed of silicon dioxide was formed exhibits infrared transparency. [Example]

[0169] An infrared-transmitting member was prepared using the following process, in which a film primarily composed of silicon dioxide was formed on one side of a substrate made of SUS304 stainless steel and a film containing a black pigment was formed on the other side, and the infrared transmittance was evaluated.

[0170] (1) Preparation of coating solution (Preparation of Coating Solution C) The method for preparing coating liquid C for forming a film containing a black pigment is as follows.

[0171] Carbon black (0.6 g) with an average particle size of 50 nm and polyvinylpyrrolidone K-30 (0.1 g) manufactured by Nippon Shokubai Co., Ltd. were added to ethanol (5.3 g) and stirred for approximately 1 minute with an overhead stirrer to prepare an ethanol suspension containing dispersed carbon black. Coating solution A (100 g) was added to this solution and further stirred for approximately 30 seconds with an overhead stirrer to prepare coating solution C.

[0172] (2) Film formation The infrared-transmitting member of this example has a substrate with a film mainly composed of silicon dioxide on one side and a film containing a black pigment on the other side. When forming a film on this substrate, in addition to the method of Example 1, it is necessary to add a step of masking one side with polyethylene glycol and then peeling off this film. Specifically, a polyethylene glycol film is formed on one side, forming a film mainly composed of silicon dioxide. Then, the polyethylene glycol film is removed, and a film containing a black pigment is formed.

[0173] (masking) First, polyethylene glycol (1 g) having an average molecular weight of 1,000,000 is added to water (9 g), and the mixture is heated to about 80°C while stirring with an overhead stirrer for about 10 minutes to dissolve the polyethylene glycol, thereby preparing a 10 wt% aqueous solution of polyethylene glycol (10 g).

[0174] Next, as in Example 1, a substrate made of SUS304 steel, measuring 100 mm square, 0.5 mm thick, and having an Ra of 100 nm, is prepared. One side of this substrate is uniformly coated with a 10 wt % aqueous solution of polyethylene glycol (approximately 1 g) using a brush. The substrate is then placed in a thermostatic chamber at an internal temperature of 100°C and dried for approximately 2 hours. This results in a polyethylene glycol film with an average thickness of 10 μm being formed on one side.

[0175] (Film formation with coating solution A) The substrate is dip-coated with the above-mentioned coating solution A in the same manner as in Example 1 to form a film having a thickness of about 280 nm and containing silicon dioxide as the main component on the surface.

[0176] (Masking removal) When this substrate is immersed in 80°C hot water stirred with an overhead stirrer, the polyethylene glycol film gradually dissolves. After replacing the hot water, the substrate is immersed again. The substrate is then removed from the hot water and 80°C hot water is sprayed onto the substrate with a dropper to remove any remaining polyethylene glycol.

[0177] (Coating solution C film formation) Coating liquid C (approximately 1 g) was applied almost uniformly with a brush to the surface from which the polyethylene glycol had been removed. The sample was then placed in a thermostatic chamber at 100°C and heated for approximately 10 minutes. This process was repeated four times to form a film containing black pigment with an average thickness of approximately 10 μm. The Ra of this film was 100 nm.

[0178] (3) Evaluation FIG. 14 is a cross-sectional view showing an experimental device for evaluating the performance of the infrared-transmitting member produced as described above.

[0179] The difference between this figure and Figure 13 is that a film 74 containing a black pigment is formed on a substrate 75 of the sample of the infrared transparent member placed in the hole 62. Other than that, it is the same as Figure 13.

[0180] As a result of heating with the dryer 17 in the same manner as in Fig. 13, the temperature displayed on the display device 72, which displays the temperature of the thermocouple 70, rose to 50°C. This result confirmed that the substrate 75 on which the film 74 containing the black pigment was formed functions as an infrared-transmitting member.

[0181] When coating liquid B was used instead of coating liquid A, the temperature displayed on the display device 72 that displays the temperature of the thermocouple 70 also rose to 50°C.

[0182] (Relationship with particle size of silicon dioxide particles) Approximately 900 g of each of coating solutions D, E, and F were prepared in the same manner as for preparing coating solution B in Example 1, except that the silicon dioxide particles used were changed to those with average particle sizes of 50 nm, 70 nm, and 90 nm.

[0183] These coating solutions D, E, and F are used to form films on substrates of the same size and Ra as in Example 1 in the same manner as in Example 1.

[0184] When the substrate on which the film was formed was evaluated using the experimental apparatus used in Example 1, in the case of a film containing silicon dioxide particles with an average particle diameter of 50 nm formed using coating liquid D, the displayed temperature of display device 72, which displays the temperature of thermocouple 70, rose to 45°C.

[0185] In contrast, in the case of a film containing silicon dioxide particles with an average particle size of 70 nm formed using Coating Liquid E, the displayed temperature of display device 72 displaying the temperature of thermocouple 70 rose to 40°C. In addition, in the case of a film containing silicon dioxide particles with an average particle size of 90 nm formed using Coating Liquid F, the displayed temperature of display device 72 displaying the temperature of thermocouple 70 rose to 35°C.

[0186] From these results, it was confirmed that all the substrates functioned as infrared-transmitting members, although there were differences in their effectiveness.

[0187] When the Ra of the film-formed surface of the infrared-transmitting member was measured, the film containing silicon dioxide particles with an average particle size of 50 nm had an Ra of 90 nm, while the film containing silicon dioxide particles with an average particle size of 70 nm had an Ra of 50 nm and the film containing silicon dioxide particles with an average particle size of 90 nm had an Ra of 30 nm, both of which were low values.

[0188] The reason why Ra becomes smaller is thought to be that large particles get into the recesses of the unevenness of the substrate, reducing Ra. As the actual surface area of ​​the substrate becomes smaller, the area of ​​the substrate that exhibits anti-reflection function becomes smaller, and as a result, the amount of infrared light transmitted, i.e., the amount of heat transmitted, is thought to decrease.

[0189] Therefore, it is believed that when large silicon dioxide particles with an average particle size exceeding 50 nm are used, the amount of heat transmitted through the infrared-transmitting member decreases, and the temperature rise in the vicinity of the infrared-transmitting member also decreases.

[0190] (Relationship with the arithmetic mean roughness Ra of the substrate surface) Infrared-transmitting members were produced by forming films containing silicon dioxide particles with average particle sizes of 50 nm, 70 nm, and 90 nm on substrates having the same size and thickness as in Example 1 using coating solutions D, E, and F in the same manner as in Example 1, except that the arithmetic mean roughness Ra of the substrate surface was set to 50 nm or 40 nm.

[0191] When evaluated using the experimental equipment used in Example 1, the temperature near a substrate that did not have a film primarily composed of silicon dioxide was 23°C for a substrate with an Ra of 50 nm and 22°C for a substrate with an Ra of 40 nm, regardless of the average particle size of the substrate or substrates that had a film using silicon dioxide particles.

[0192] In contrast, when a base material with an Ra of 50 nm was used, the displayed temperature of the display device 72 displaying the temperature of the thermocouple 70 rose to 44°C in an infrared-transparent member on which a film containing silicon dioxide particles with an average particle size of 50 nm was formed. Also, the displayed temperature of the display device 72 displaying the temperature of the thermocouple 70 rose to 39°C in an infrared-transparent member on which a film containing silicon dioxide particles with an average particle size of 70 nm was formed. Furthermore, the displayed temperature of the display device 72 displaying the temperature of the thermocouple 70 rose to 35°C in an infrared-transparent member on which a film containing silicon dioxide particles with an average particle size of 90 nm was formed.

[0193] When a substrate with Ra of 40 nm was used, the display temperature of the display device 72 displaying the temperature of the thermocouple 70 rose to 40°C in an infrared-transparent member on which a film containing silicon dioxide particles with an average particle size of 50 nm was formed. Furthermore, the display temperature of the display device 72 displaying the temperature of the thermocouple 70 rose to 35°C in an infrared-transparent member on which a film containing silicon dioxide particles with an average particle size of 70 nm was formed. Furthermore, the display temperature of the display device 72 displaying the temperature of the thermocouple 70 rose to 32°C in an infrared-transparent member on which a film containing silicon dioxide particles with an average particle size of 90 nm was formed.

[0194] Therefore, it was confirmed that all the substrates functioned as infrared-transmitting members.

[0195] When the Ra of the film-forming surface of the substrate was measured, when a film was formed on a substrate with an Ra of 50 nm, the film containing silicon dioxide particles with an average particle diameter of 50 nm had an Ra of 50 nm. In contrast, the film containing silicon dioxide particles with an average particle diameter of 70 nm had an Ra of 30 nm. Furthermore, the film containing silicon dioxide particles with an average particle diameter of 90 nm had an Ra of 20 nm, which is a low value. Furthermore, when a film was formed on a substrate with an Ra of 40 nm, the film containing silicon dioxide particles with an average particle diameter of 50 nm had an Ra of 40 nm, and the films containing silicon dioxide particles with average particle diameters of 70 nm and 90 nm both had an Ra of 20 nm, which is a low value.

[0196] Up to an average particle size of 50 nm, silicon dioxide particles do not reduce the Ra of the infrared-transparent member. However, if the average particle size becomes larger than this, the Ra of the infrared-transparent member decreases and the actual surface area of ​​the infrared-transparent member becomes smaller. As a result, the area of ​​the infrared-transparent member that exhibits the anti-reflection function becomes smaller, and it is thought that as a result, the amount of infrared light transmitted, i.e., the amount of heat transmitted, decreases.

[0197] Therefore, it was found that when large silicon dioxide particles with an average particle size exceeding 50 nm are used, the amount of heat transmitted through the infrared-transmitting member decreases, and the temperature rise in the vicinity of the infrared-transmitting member also becomes slight.

[0198] Furthermore, even if the average particle size of the silicon dioxide particles used is 50 nm, if the Ra of the substrate itself is less than 50 nm, Ra will also be less than 50 nm, and the temperature rise will be reduced by 5°C from 45°C to 40°C. Therefore, it was found that the Ra of the substrate is also preferably 50 nm or more.

[0199] (Effect of binder on film containing black pigment) As described above, an infrared-transmitting member was prepared using the following process: a substrate made of SUS304 steel, with a film primarily made of silicon dioxide formed on one side and a film containing a black pigment formed on the other side. The infrared transmittance was evaluated. Instead of silica sol, an acrylic resin with a weight-average molecular weight of 10,000 or a styrene resin with a weight-average molecular weight of 40,000 was used as the binder for the black pigment-containing film.

[0200] (1) Preparation of coating solution (Preparation of Coating Solutions G and H) The method for preparing the coating liquid G for forming a film containing a black pigment oil is as follows.

[0201] Add 6 g of carbon black with an average particle size of 50 nm and 1 g of Nippon Shokubai Polyvinylpyrrolidone K-30 (manufactured by Nippon Shokubai Co., Ltd.) to 53 g of dichloromethane and stir with an overhead stirrer for approximately 1 minute to prepare dichloromethane suspension G1 in which the carbon black is dispersed.

[0202] Add 2 g of acrylic resin with a weight-average molecular weight of 10,000 to 98 g of dichloromethane and stir with an overhead stirrer to dissolve the acrylic resin. This gives a 2 wt % acrylic resin dichloromethane solution G2.

[0203] Add 2 g of styrene resin with a weight-average molecular weight of 40,000 to 98 g of dichloromethane and stir with an overhead stirrer to dissolve the acrylic resin. This prepares a 2 wt % polystyrene resin dichloromethane solution H2.

[0204] 6 g of Liquid G1 is added to Liquid G2, and the mixture is further stirred with an overhead stirrer for approximately 30 seconds to prepare Coating Liquid G.

[0205] 6 g of liquid G1 is added to liquid H2, and the mixture is further stirred with an overhead stirrer for approximately 30 seconds to prepare coating liquid H.

[0206] (2) Film formation As in the above, a substrate having a size of 100 mm square, a thickness of 0.5 mm, and an arithmetic surface roughness (Ra) of 100 nm is prepared.

[0207] An infrared-transmitting member having a film mainly composed of silicon dioxide and a film containing a black pigment is prepared in the same manner as above, except that coating solution G or coating solution H is used instead of coating solution C.

[0208] (3) Evaluation Evaluation was carried out using the same method as above with the experimental apparatus shown in FIG.

[0209] In this experiment, a substrate coated with coating liquid G or coating liquid H was fixed to the experimental apparatus instead of the substrate coated with coating liquid C. The room temperature was 20°C.

[0210] As a result, when hot air was released for 30 seconds from a 1200W dryer in the same manner as above, the temperature near the substrate that did not have a film primarily composed of silicon oxide or a film containing black pigment rose slightly above room temperature to 25°C, but the temperature near the substrate that had a film primarily composed of silicon oxide and a film containing black pigment formed using Coating Liquid G rose to 42°C. Furthermore, the temperature near the substrate that had a film containing black pigment formed using Coating Liquid H rose to 33°C. Therefore, it was confirmed that these substrates functioned as infrared-transmitting members.

[0211] However, when polystyrene resin was used as the film binder containing black pigment, the temperature of the thermocouple rose only to 33°C, indicating that the film has low thermal permeability compared to when acrylic resin was used.

[0212] FIG. 15 is a graph showing the absorption spectra of styrene resin and acrylic resin in the range of 2500 to 7500 nm.

[0213] As shown in this figure, styrene resin has absorption due to the CH stretching of aromatic rings around 3400 nm and absorption due to the CH stretching of alkyl chains and methyl groups around 3500 nm.Acrylic resin also has absorption due to the CH stretching of alkyl chains and methyl groups around 3500 nm and absorption due to the CO stretching of esters around 5800 nm.

[0214] Here, the shorter the wavelength of the observed absorption, the greater the amount of infrared light with greater thermal energy is absorbed. Absorption due to CH stretching absorbs more energy than absorption due to CO stretching, resulting in a decrease in the amount of heat transmitted.

[0215] Therefore, when using an organic material as a binder for black pigment, it was found that thermal transmittance can be improved by using acrylic resin, which has a greater absorption strength for CO stretching, rather than styrene resin, which has a greater absorption strength for CH stretching. [Example]

[0216] In this example, a film containing silicon dioxide as the main component is formed using a material other than silica sol, and the heat permeability is evaluated.

[0217] (1) Preparation of coating solution (Preparation of Coating Solution I) Methyltriethoxysilane (53 g) is dissolved in 2-propanol (947 g) to prepare 1000 g of a colorless and transparent coating solution I. The solid content concentration of coating solution I after thermal curing is approximately 2 wt %.

[0218] (Preparation of Coating Solution J) Phenyltrimethoxysilane (31 g) is dissolved in 2-propanol (969 g) to prepare 1000 g of a colorless and transparent coating solution J. The solids concentration of coating solution J after thermal curing is also approximately 2 wt %.

[0219] (Preparation of Coating Solution K) 3-Aminopropyltriethoxysilane (40 g) is dissolved in 2-propanol (960 g) to prepare 1000 g of colorless and transparent coating solution J. The solid concentration of coating solution J after thermal curing is also approximately 2 wt %.

[0220] (2) Film formation A film containing silicon dioxide as its main component and having a thickness of approximately 280 nm was formed on the surface of a substrate made of SUS304 steel by the same process as in Example 1, except that Coating Liquid I, Coating Liquid J, or Coating Liquid K was used instead of Coating Liquid A. The Ra after film formation was 100 nm, which was the same as the Ra of the substrate before the film was formed.

[0221] (3) Evaluation Instead of a substrate on which a silicon dioxide film was formed using Coating Liquid A, a substrate made of SUS304 steel on which a film containing silicon dioxide as the main component was formed using Coating Liquid I, Coating Liquid J, or Coating Liquid K was evaluated using the same experimental equipment as in Example 1.

[0222] As a result of evaluation using the experimental apparatus shown in Figure 13, when heated for 30 seconds with the same dryer as in Example 1, the temperature in the vicinity of the uncoated substrate was 25°C. The substrates on which a film containing silicon dioxide as the main component was formed using Coating Liquid I, Coating Liquid J, or Coating Liquid K all showed a temperature of 45°C. This result was the same as that of the SUS304 substrate coated with Coating Liquid A.

[0223] Therefore, it was confirmed that even if the coating liquid was changed, the substrate on which the film containing silicon dioxide as the main component was formed could function as an infrared-transmitting member. [Example]

[0224] An aluminum substrate having a silicon dioxide film was produced using the same process as in Example 1, except that an aluminum substrate having a size of 100 mm square, a thickness of 0.5 mm, and an arithmetic surface roughness (Ra) of 100 nm was used as the substrate instead of a SUS304 steel substrate having a size of 100 mm square, a thickness of 0.5 mm, and an arithmetic surface roughness (Ra) of 100 nm.

[0225] Whether or not this substrate functions as an infrared-transmitting member was evaluated in the same manner as in Example 1. The room temperature during the evaluation was 20°C.

[0226] As in Example 1, when heated for 30 seconds with a dryer with a power consumption of 1200 W, the temperature near the substrate that did not have a film primarily composed of silicon dioxide rose slightly above room temperature to 27°C, but the temperature near the substrate that had a film primarily composed of silicon dioxide formed with Coating Liquid A rose to 48°C.

[0227] Furthermore, the temperature in the vicinity of the substrate having the film mainly composed of silicon dioxide containing silicon dioxide particles formed with Coating Liquid B rose to 50°C.

[0228] Therefore, it was confirmed that by forming a film containing silicon dioxide as the main component, an aluminum substrate can function as a heat-transmitting substrate in the same way as a substrate made of SUS304 steel. [Example]

[0229] Instead of a substrate measuring 100 mm square, 0.5 mm thick, and with an arithmetic surface roughness (Ra) of 100 nm, an acrylic resin substrate measuring 100 mm square, 1 mm thick, and with an arithmetic surface roughness (Ra) of 5 nm was used. The heating conditions after dip coating with coating solutions A and B during film formation were changed from 180 ° C. for 5 minutes to 70 ° C. for 20 minutes. Furthermore, the number of dip coating and heating processes when using coating solution A was increased from four to eight times, and the number of dip coating and heating processes when using coating solution B was increased from one to two times. An acrylic resin substrate having a silicon dioxide-based film containing silicon dioxide particles was produced using the same process as in Example 1. The thicknesses of the films formed using coating solutions A and B were 560 nm and 620 nm, respectively.

[0230] Whether or not this substrate functions as an infrared-transmitting member was evaluated in the same manner as in Example 1. The room temperature during the evaluation was 20°C.

[0231] As in Example 1, when heated for 30 seconds with a 1200W dryer, the temperature near the substrate that did not have a film primarily composed of silicon dioxide rose very slightly above room temperature to 22°C, but the temperature near the substrate that had a film primarily composed of silicon dioxide formed with Coating Liquid A rose to 42°C.

[0232] Furthermore, the temperature in the vicinity of the substrate having the film mainly composed of silicon dioxide containing silicon dioxide particles formed with Coating Liquid B rose to 44°C.

[0233] Therefore, it was confirmed that by forming a film containing silicon dioxide as the main component, the acrylic resin substrate can function as an infrared-transmitting member in the same way as the SUS304 steel substrate. [Example]

[0234] The same evaluation as in Example 1 was carried out using the experimental apparatus shown in Figure 13, except that 13 types of SUS304 steel substrates were subjected to the dip coating and heating process using Coating Liquid A not only four times but also once, twice, three times, five to thirteen times, and three types of SUS304 steel substrates were subjected to the dip coating and heating process using Coating Liquid B not only once but also twice or three times.

[0235] Coating liquid A formed a film of approximately 70 nm thick, primarily composed of silicon dioxide containing silicon dioxide particles, through a single application and heat-curing process, while coating liquid B formed a film of approximately 310 nm thick, primarily composed of silicon dioxide containing silicon dioxide particles, through a single application and heat-curing process.

[0236] FIG. 16 is a graph showing the relationship between the thickness of the film constituting the infrared-transmitting member and the temperature in the vicinity of the infrared-transmitting member in an evaluation using the experimental apparatus of FIG.

[0237] As shown in Figure 16, the temperature near the substrate using Coating Liquid A was in the 20°C range when the thickness of the silicon dioxide-based film was less than 200 nm, but rose to over 40°C when the film thickness was approximately 210 nm. It then reached a maximum of 45°C at a film thickness of approximately 280 nm, and gradually decreased as the film thickness increased beyond that. Up to a film thickness of approximately 500 nm, the temperature remained above 40°C. Up to a film thickness of approximately 770 nm, the temperature was higher than that near the substrate without a silicon dioxide-based film, but remained almost the same once the film thickness exceeded 800 nm.

[0238] The temperature near the substrate using Coating Liquid B also showed results similar to those of the sample using Coating Liquid A. When the film thickness was approximately 310 nm, the temperature near the substrate rose to a maximum value of 48°C. The temperature near the substrate with a film thickness of approximately 930 nm showed approximately the same value as the temperature near the substrate on which a film mainly made of silicon dioxide was not formed.

[0239] From the above results, it was found that when a substrate made of SUS304 stainless steel is used as the infrared-transmitting member, the thickness of the film containing silicon dioxide as the main component is preferably 200 to 800 nm. [Example]

[0240] Instead of a SUS304 steel substrate measuring 100 mm square, 0.5 mm thick, and having an arithmetic surface roughness (Ra) of 100 nm, a polycarbonate resin substrate measuring 100 mm square, 1 mm thick, and having an arithmetic surface roughness (Ra) of 5 nm was used. An infrared-transmitting member was fabricated using the same film-forming process as in Example 6, except that the heating conditions after dip coating using coating solutions A and B during film formation were changed from 180°C for 5 minutes to 90°C for 10 minutes. The fabricated infrared-transmitting member was evaluated in the same manner as in Example 6 using the experimental apparatus shown in FIG. 13.

[0241] FIG. 17 is a graph showing the relationship between the thickness of the film constituting the infrared-transmitting member and the temperature in the vicinity of the infrared-transmitting member in an evaluation using the experimental apparatus of FIG.

[0242] As shown in Figure 17, the temperature near the polycarbonate resin substrate coated with Coating Liquid A was in the 20°C range when the thickness of the silicon dioxide-based film was less than 200 nm, but exceeded 30°C when the film thickness was approximately 210 nm, and exceeded 40°C when the film thickness was approximately 420 nm.The temperature reached a maximum of 42°C when the film thickness was approximately 560 to 630 nm, and gradually decreased as the film thickness increased, reaching 36°C when the film thickness was approximately 770 nm.When the film thickness was approximately 840 nm or more, the temperature was almost the same as the temperature near the substrate without the silicon dioxide-based film.

[0243] The temperature near the polycarbonate resin substrate using Coating Liquid B showed similar results to the sample using Coating Liquid A, with the temperature near the substrate rising to a maximum of 44°C when the film thickness was approximately 620 nm. When the film thickness was approximately 930 nm, the temperature near the substrate was approximately the same as that near the substrate on which a film mainly made of silicon dioxide was not formed.

[0244] From the above results, it was found that when polycarbonate resin is used as the substrate, the thickness of the film containing silicon dioxide as the main component is preferably 200 to 800 nm.

[0245] The results of Examples 6 and 7 show that when used as an infrared-transmitting member, the thickness of the film containing silicon dioxide as the main component is preferably 200 to 800 nm. [Example]

[0246] Instead of a substrate made of SUS304 steel having a size of 100 mm square, a thickness of 0.5 mm, and an arithmetic surface roughness (Ra) of 100 nm, a substrate made of a double-side polished silicon wafer having a size of 100 mm square, a thickness of 1 mm, and an arithmetic surface roughness (Ra) of 1 nm was used as the substrate, and an infrared-transmitting member was fabricated using the same film formation process as in Example 6. The fabricated infrared-transmitting member was evaluated in the same manner as in Example 6 using the experimental apparatus shown in FIG.

[0247] FIG. 18 is a graph showing the relationship between the thickness of the film constituting the infrared-transmitting member and the temperature in the vicinity of the infrared-transmitting member in an evaluation using the experimental apparatus of FIG.

[0248] As shown in Figure 18, the temperature near the silicon wafer substrate coated with Coating Solution A was in the 20°C range when the thickness of the silicon dioxide-based film was less than 200 nm, but exceeded 35°C when the film thickness was approximately 210 nm, and exceeded 50°C when the film thickness was approximately 280 nm.The temperature reached a maximum of 57°C when the film thickness was approximately 350 nm, and gradually decreased as the film thickness increased, reaching 32°C when the film thickness was approximately 770 nm.When the film thickness was approximately 840 nm or more, the temperature was almost the same as the temperature near the substrate without a silicon dioxide-based film.

[0249] The temperature near the polycarbonate resin substrate using Coating Liquid B showed similar results to the sample using Coating Liquid A, with the temperature near the substrate rising to a maximum of 60°C when the film thickness was approximately 310 nm. When the film thickness was approximately 930 nm, the temperature near the substrate was approximately the same as that near the substrate on which a film mainly made of silicon dioxide was not formed.

[0250] From the above results, it was found that, similarly to Examples 6 and 7, when a silicon wafer was used as the substrate, the thickness of the film containing silicon dioxide as the main component was preferably 200 to 800 nm.

[0251] Table 1 shows the compositions of the coating solutions used in the above examples to form films containing silicon dioxide as the main component.

[0252] [Table 1]

[0253] Table 2 shows the composition of the coating liquid used in the above examples to form a film containing a black pigment.

[0254] [Table 2]

[0255] In the above examples, infrared-transmitting members using a substrate formed from a metal such as SUS steel or aluminum are described, but infrared-transmitting members using a substrate formed from a silicon wafer, resin, or the like, which has a higher infrared light transmittance than metal (transmittance in the infrared region is several tens of percent), allow incident infrared light to pass through the substrate and suppress reflection of the transmitted infrared light. Therefore, when an infrared-transmitting member using a substrate formed from a silicon wafer, resin, or the like is applied to a housing or the like that houses a heat-generating element, it easily transmits infrared light, thereby promoting heat dissipation from the heat-generating element.

[0256] Preferred embodiments of the present disclosure will be described below.

[0257] In the infrared-transmitting member, the substrate may have a plate-like structure.

[0258] The surface layer is within the range of 0 < T ≤ 2Tav in terms of its average thickness Tav.

[0259] The average thickness of the surface layer is 200 - 800 nm.

[0260] The surface layer is porous.

[0261] The arithmetic mean roughness of the surface of the substrate is 50 nm or more.

[0262] When the arithmetic mean roughness of the substrate is Ra0 and the arithmetic mean roughness of the surface of the surface layer is Ra1, the following inequality holds.

[0263] Ra1 ≥ 0.9Ra0 The surface layer contains a binder containing silicon dioxide and silicon dioxide particles.

[0264] The refractive index of the surface layer is smaller than that of the substrate.

[0265] The average particle diameter of the silicon dioxide particles is 10 - 50 nm.

[0266] The infrared transmissive member further includes a black layer containing a black pigment.

[0267] The surface layer is provided on one surface of the substrate, and the black layer is provided on the other surface of the substrate.

[0268] The substrate is sandwiched between the surface layer and the black layer.

[0269] The average particle diameter of the black pigment is 10 - 1000 nm.

[0270] The black layer further contains a binder.

[0271] The binder contained in the black layer contains silicon dioxide.

[0272] The binder contained in the black layer is a resin that has an absorption band derived from CH stretching and an absorption band derived from CO stretching, and the absorption band derived from CO stretching has a higher infrared light absorptance.

[0273] The substrate is formed of an iron alloy or an aluminum alloy.

[0274] The substrate is made of resin or silicon.

[0275] The surface layer comprises a silicon compound having a hydrolyzable residue.

[0276] The housing includes an infrared-transparent member.

[0277] The railcar has a housing.

[0278] The transformer has a housing.

[0279] The engine has a housing.

[0280] The infrared-transmitting member is used in a housing that houses a heating element.

[0281] The infrared-transparent member is a part of the constituent members of the housing.

[0282] The heating element is an inverter device that converts DC power supplied from a DC power source into three-phase AC power to drive an AC motor.

[0283] An inverter device, which is an example of a heating element, is provided in a railway vehicle having a control device that controls the operation of a DC power supply.

[0284] The heating element is a transformer that steps up and down AC voltage.

[0285] The heating element is an engine that burns gasoline or diesel to generate kinetic energy.

[0286] According to the present disclosure, by forming a film made of silicon dioxide, which has a lower refractive index than the substrate, on the surface of a substrate such as iron, SUS steel, or aluminum, which are widely used as general-purpose housing materials, the material becomes an infrared-transparent member that promotes heat dissipation from the surface, thereby reducing the energy required to cool the inside of the housing, contributing to significant energy savings, and making it possible to miniaturize cooling equipment inside the housing, or in some cases even eliminating the need for such equipment. [Explanation of symbols]

[0287] 1: substrate, 2, 4, 13: film, 3, 9: silicon dioxide particles, 5: incident light, 6: surface reflected light, 7: reflected light, 8: transmitted light, 10: gap, 11: equipment, 12: housing, 14, 15, 16: hole, 17: dryer, 18: box, 19, 20, 21: thermocouple, 22, 23, 24: display device, 25: fence, 31: railway vehicle, 32: overhead wire, 33: pantograph, 34: housing, 35: power unit, 36: storage battery unit, 37: inverter, 38: cooling unit, 39: transformer , 40: iron core, 41: winding, 42: insulating oil, 43: automobile, 44: engine, 45: motor, 46: power control unit, 47: battery, 48: fuel tank, 49: driving control unit, 50: radiator, 51: fan, 61, 62, 63, 64: hole, 65: box, 66: film, 67, 68: substrate, 69, 70: thermocouple, 71, 72: display device, 73: fence, 74: film containing black pigment, 75: substrate, 100, 200: infrared-transparent member.

Claims

1. An infrared-transmitting member comprising a substrate and a surface layer provided on the substrate, the surface layer contains silicon dioxide as a main component, The infrared-transmitting member has a higher transmittance of infrared light than the base material.

2. 2. The infrared-transmitting member according to claim 1, wherein the surface layer has an average thickness of 200 to 800 nm.

3. The infrared-transmitting member according to claim 1 , wherein the surface layer is porous.

4. The infrared-transmitting member according to claim 1 , wherein the arithmetic mean roughness of the surface of the substrate is 50 nm or more.

5. 2. The infrared transmitting member according to claim 1, wherein the following inequality holds when the arithmetic mean roughness of the base material is Ra0 and the arithmetic mean roughness of the surface of the surface layer is Ra1. Ra1≧0.9Ra0

6. The infrared-transparent member of claim 1 , wherein the surface layer comprises a silicon dioxide binder and silicon dioxide particles.

7. The infrared-transmitting member according to claim 1 , wherein the refractive index of the surface layer is smaller than the refractive index of the substrate.

8. 7. The infrared-transmitting member according to claim 6, wherein the silicon dioxide particles have an average particle size of 10 to 50 nm.

9. Further comprising a black layer containing a black pigment, The infrared-transmitting member according to claim 1 , wherein the substrate is sandwiched between the surface layer and the black layer.

10. 10. The infrared transmitting member according to claim 9, wherein the black pigment has an average particle size of 10 to 1000 nm.

11. the black layer further comprises a binder; The infrared-transparent member of claim 9 , wherein the binder comprises silicon dioxide.

12. The binder contained in the black layer has an absorption band derived from CH stretching and an absorption band derived from CO stretching, and the absorption band derived from CO stretching is a resin having a higher absorption rate of the infrared light. The infrared transparent member according to claim 11.

13. The infrared-transmitting member according to claim 1 , wherein the substrate is formed of an iron alloy or an aluminum alloy.

14. The infrared-transmitting member according to claim 1 , wherein the substrate is made of resin or silicone.

15. The infrared-transmitting member according to claim 1 , wherein the surface layer comprises a silicon compound having a hydrolyzable residue.

16. A housing comprising the infrared-transparent member according to claim 1.

17. A rail vehicle comprising the housing of claim 16.

18. A transformer comprising the housing of claim 16.

19. An engine comprising the housing of claim 16.

Images