Infrared transmissive member, and housing, railway vehicle, transformer, and engine using same

Abstract

An infrared transmissive member 100 comprises a base material and a surface layer provided on the base material. A surface layer (2) contains silicon dioxide as a main component. The infrared transmissive member 100 has higher transmittance of infrared light than the base material 1. As a result, it is possible to provide an infrared transmissive member that suppresses reflection and promotes transmission of infrared light and promotes removal of heat from a heat-generating body. The surface layer (2) may contain silicon dioxide particles. The average thickness of the surface layer (2) is preferably 200-800 nm.

Description

Infrared-transmitting member, and housing, railway vehicle, transformer, and engine using the same

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

[0002] Equipment such as inverters, computers, servers, and transformers 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 heat inside, or 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 made of a layer of silver and an aluminum layer stacked together, 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.

[0007] International Application No. 2019 / 142876 Japanese Patent Application Laid-Open No. 2015-99333

[0008] When devices such as inverters, computers, servers, and transformers generate heat, the temperature can reach approximately 100 to 150°C. This heat is transmitted by three phenomena: conduction through contact with a solid, convection due to the flow of gas or liquid, and radiation due to 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 means of increasing 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.

[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.

[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.

[0015] 1 is a schematic cross-sectional view showing an example of an infrared transparent member according to an embodiment; FIG. 2 is a schematic cross-sectional view showing another example of an infrared transparent member according to an embodiment; FIG. 3 is a schematic cross-sectional view showing the behavior of incident light, reflected light, and transmitted light in the case of only a substrate; FIG. 4 is a schematic cross-sectional view showing the behavior of incident light, reflected light, and transmitted light in an infrared transparent member according to an embodiment; FIG. 5 is a cross-sectional SEM image showing an example of a film containing silicon dioxide particles; FIG. 6 is a graph showing the relationship between the particle content and refractive index of a film according to the present disclosure; FIG. 7 is a cross-sectional view showing a housing according to an embodiment; FIG. 8 is a schematic cross-sectional view showing an example of an infrared transparent member according to an embodiment; FIG. 9 is a schematic cross-sectional view showing another example of an infrared transparent member according to an embodiment; FIG. 10 is a cross-sectional view showing an experimental device for sending heat to a remote location; FIG. 11 is a cross-sectional view showing an experimental device for sending heat to a remote location; FIG. 12 is a schematic cross-sectional view showing a railway vehicle according to the present disclosure; FIG. 13 is a schematic cross-sectional view showing a housing that stores an inverter for a railway vehicle according to the present disclosure; FIG. 14 is a schematic cross-sectional view showing a transformer according to the present disclosure; FIG. 15 is a schematic cross-sectional view showing a power-related portion of a vehicle equipped with an engine according to the present disclosure; FIG. 16 is a cross-sectional view showing an experimental device for evaluating the performance of an infrared transparent member according to an embodiment; 14 is a graph showing the IR spectra of a styrene resin and an acrylic resin. 15 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. 16 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. 17 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.

[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 heat sources at 100 to 150°C also emit infrared light with wavelengths longer than 7500 nm, this light actually originates from infrared light of 2500 to 7500 nm colliding with air molecules at room temperature (15 to 25°C according to the Japanese Pharmacopoeia), resulting in air molecules that are slightly warmer than room temperature. Therefore, even if light with wavelengths longer than 7500 nm is radiated to the outside, the high temperature heat inside is not released. Therefore, in this specification, a component that improves the transmittance of infrared light of 2500 to 7500 nm 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, or the like, 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 transmits 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, and 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 antireflection film is ideally T=λ / 4, where λ is the wavelength at which the antireflection function is most effectively exhibited.

[0023] When an antireflection film is applied to the visible region of 400 to 700 nm, the ideal film thickness T of the single-layer antireflection film 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 on 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 wavelength, and therefore, as described above, the ideal value is to adjust the length of the optical 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 films using silicon dioxide are intended for use in 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 film formed is lower than that of the substrate. If the surface of the product to which the film is applied is quite 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 the 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-Transmitting Member FIG. 1A is a schematic cross-sectional view showing an example of an infrared-transmitting member according to an embodiment.

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

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

[0032] The infrared transparent 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 higher 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 the 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 the incident light 5, excluding the 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 the infrared-transmitting member according to the embodiment.

[0039] In the infrared-transmitting member 100 shown in this 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. Iron, SUS steel, and other materials commonly used as substrates have refractive indices so high that they are 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 added to the film thickness of the anti-reflection film as a low refractive index film.

[0045] (2) Films Mainly Containing Silicon Dioxide Next, among films mainly containing silicon dioxide, the structure of FIG. 1A having no particles and the structure of FIG. 1B having particles will be described.

[0046] (A) Cases without Particles (i) Film Materials One film material for a film primarily composed of silicon dioxide is silica sol, which is obtained by polymerizing tetraalkoxysilane, specifically tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, or the like, until the average molecular weight reaches approximately 10,000. It can be formed by applying the silica sol and then thermally curing it. While tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, or the like may be directly applied to a substrate and then thermally cured, due to their low boiling points, 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 when a high-boiling alcohol is used, the solvent is less likely to volatilize from the silicon dioxide film, and film formation takes longer. Furthermore, alcohols having 5 or more carbon atoms are highly hydrophobic, making it difficult to dissolve highly hydrophilic compounds such as silica sol and the alkoxysilane compound. 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 among the above solvents.

[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 in the Film Formation When a film is formed 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, and almost no voids are generated inside. However, Si-O-Si bonds are rigid, so volume shrinkage is not possible and voids are generated. In other words, by using an alkoxysilane compound such as silica sol used in the present disclosure, a porous film can be formed.

[0056] Measurements using a refractometer (Kalnew Precision Spectrometer GM-1D) revealed that the refractive index of bulk silicon dioxide was 1.46, and 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 is also 1.0, the voids are estimated to account for 15% of the volume of the entire film.

[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 around 1.42 to 1.6. For this reason, while some glass substrates have a refractive index lower than the 1.46 refractive index of silicon dioxide, the porous silicon dioxide film of the present disclosure has a low refractive index of 1.39, making it applicable to almost all glass substrates, including these.

[0058] (B) When Particles Are Included (i) Film Material When particles are included, the film material is a mixture containing silicon dioxide particles and a binder containing silicon dioxide as a main component.

[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) A ​​film containing porous silicon dioxide as a main component can be 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 concave and convex portions. Specifically, when the arithmetic mean roughness Ra of the substrate before film formation is Ra0 and the 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 has almost the same unevenness as the substrate.

[0064] However, when the particle size used is 70 nm or larger, the concave portions of the substrate may be filled in, and when the arithmetic surface roughness of the substrate is 1000 nm or larger, the film thickness may approach 0 in the thin portions and may exceed 1000 nm in the thick portions. 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 for weighing, etc., and therefore it has been 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-forming method Silicon dioxide particles are mixed with silica sol and the above-mentioned alkoxysilane compound, and the mixture 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, as in the case of (A) above, 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 the silicon dioxide film becomes porous in the film formation process: By adding silicon dioxide particles, the overlapping portions of the particles in the film after film formation become gaps, making it possible to further lower the refractive index. This occurs because the binder does not completely penetrate 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 greater 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] Since voids 10 are formed between the silicon dioxide particles 9 in this way, the refractive index of the film 4 having particles (B) is further reduced compared to the film not having particles (A).

[0076] 4 is a graph showing the relationship between 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, when no silicon dioxide particles are added, i.e., 0 wt%, the refractive index is 1.39. 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%, the refractive index drops to 1.30. At this level, the anti-reflection function against organic materials such as acrylic resin (1.49), polycarbonate resin (1.56), and tetrafluoroethylene resin (1.35) is also significantly enhanced. Furthermore, at a silicon dioxide content of 90 wt%, the refractive index drops to 1.23. Note that when the silicon dioxide content is 100%, the absence of a binder component prevents the silicon dioxide particles from being retained on the substrate, making film formation impossible. Therefore, experiments were conducted up to a silicon dioxide content of 90%.

[0078] (iv) Proportion of silicon dioxide particles added Among the components excluding the solvent in the coating liquid, i.e., the components that become the solid content of the film, the higher the proportion of silicon dioxide particles, the more thixotropic the coating liquid becomes, and therefore a thicker film can be formed compared to a coating liquid to which silicon dioxide is not added.

[0079] For example, when forming a silicon dioxide film with a thickness of 300 nm by dip coating, if the solid content is 2 wt% and the substrate is pulled up from the coating solution at a speed of 1 mm / sec, the film thickness will be about 70 nm if no silicon dioxide particles are added. In contrast, if the film contains 70 wt% silicon dioxide particles in its solid content, the film thickness will be 310 nm, more than four times as thick. Therefore, if the required film thickness is 350 nm or more, a coating solution that does not contain silicon dioxide particles will need to be recoated five times, while a coating solution that contains 70 wt% silicon dioxide particles will only need to be recoated twice. 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 is a binder for maintaining 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 the hand. Therefore, from the perspective of practical use, the proportion of silicon dioxide is preferably 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, a polyethylene glycol monoalkyl ester, or the like, is added. The addition rate is preferably about 0.1 to 1.0 wt % of the silicon dioxide particles.

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

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

[0084] Based on the above-mentioned concept, the thickness tr of a single-layer antireflection coating that reduces the reflectance in the infrared wavelength region of 2500 to 7500 nm is adjusted so as to minimize the 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) in the same way as 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) Substrate (i) Types of Substrate The essential condition for the substrate material used in this disclosure is that it has a refractive index higher than that of the film primarily composed of silicon dioxide, which is approximately 1.3 to 1.4. In this regard, metal materials used as housings for 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 the irregularities and the higher the frequency of the irregularities, the larger 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 high a frequency 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, plate materials such as iron, aluminum, SUS steel, and titanium have rolling marks formed by rolling with an Ra of about 50 to 300 nm, but the anti-reflection function tends to be stronger as the Ra of the rolling marks increases, and the amount of heat radiated tends to increase.

[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 substrate constituting the infrared-transmitting member are filled and the surface is made flatter than the substrate, 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 approximately equal to that of the substrate.

[0095] (4) Substrate Having a Film Containing a Black Pigment Formed on One Side FIG. 5 is a cross-sectional view showing a housing according to an 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 having high transmittance to infrared light, the presence of the film 2 suppresses reflection of the infrared light that has passed through the base material 1. Therefore, the infrared light that has passed through the base material 1 is likely to pass through the film 2 and be emitted to the outside of the 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 have conjugated double bonds. As a result, the length of the conjugated system is longer than that of dyes, and black pigments 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 or more, 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 black pigment added decreases, so the maximum size is preferably 1000 nm or less.

[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. Of 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 10,000 nm. This makes it suitable as a binder. Many organic materials have CH stretching around 3000 nm and CO stretching 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 intensity than CH stretching absorption.

[0105] Furthermore, if the thickness of 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 that time, the amount of heat leaking from the edges of the film increases; therefore, a film as thin as possible is preferable. We used a black pigment with an average particle size of 1,000 nm (1 μm) and found that 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, a film 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 stack 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 illustrating 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 transparent 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 Figure 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) Infrared-transmitting member having a film mainly composed of silicon dioxide formed on a portion of the surface of a substrate By using an infrared-transmitting member having a film mainly composed of silicon dioxide formed on a portion of the surface of a substrate, it becomes possible to send heat to a location far from the heat source. Also, 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 device 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. In addition, a 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, a film 2 is provided on the surface of the substrate 1 facing the outside of the box 18, 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 outside the area 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 1200 W 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 over 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 device for delivering heat to a remote location.

[0123] 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 FIG. 7. The other conditions are the same as those in FIG.

[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 of this substrate is as a heat conduction jig for heating flammable materials. A long substrate is prepared, and similar to the substrate in Figure 7, a silicon dioxide-based film is formed on the lower left and upper right. When the heat source is an open flame such as a gas burner, the silicon dioxide-based film on the lower left of substrate 1 is heated with the open flame. In addition, a small bottle containing acetone solution, a type of flammable material, is placed on top of the silicon dioxide-based film on the upper right of substrate 1. Note that substrate 1 is prepared to be long enough to ensure a distance that will prevent the acetone from igniting due to the open flame.

[0126] When the silicon dioxide-based film 2 at the bottom left of the substrate 1 is heated with a dryer, the silicon dioxide-based film 2 at 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 member There are numerous needs for heat dissipation from heat-generating objects, and the present disclosure can be applied to these to increase the efficiency of heat external release. Examples include railway vehicles, transformers, and engines, but other applications include application to the substrate of a pipe with fins on the outer surface to promote cooling while passing high-temperature gas or liquid through it, application to components of compressors to release heat generated by friction inside the compressor during compression, and application to components of the heat-dissipating parts of various heating appliances.

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

[0130] As shown in the figure, a railway vehicle 31 takes in current flowing through an overhead line 32 via a 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 in a housing 34. The inverter sends current at an appropriate voltage to a power unit 35 containing a motor, controlling the running of the railway vehicle 31. During deceleration, the motor in the 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 a storage battery unit 36. The stored electricity is mainly used when accelerating the railway vehicle 31, thereby reducing the amount of power consumed by the overhead line. 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 services.

[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 trains and 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 voltage. As a result, the inverter 37 generates heat, causing the internal temperature of the housing 34 to rise. If the inside of the housing 34 is not cooled, the inverter 37 may malfunction 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) Transformer 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 by 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 a 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 an engine 44 that burns gasoline or diesel 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 a power mechanism including 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 operates by receiving power from a battery 47. When braking to decelerate or stop the vehicle, the motor 45 generates electricity as a regenerative brake, and the generated power 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, which burns fuel, generates the most heat when starting and traveling. 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, a 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 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.

[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 steel and a film mainly made 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 Liquid (Preparation of Coating Liquid A) The method for preparing coating liquid 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 a colorless, transparent coating liquid A.

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

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

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

[0154] (2) Film Formation (Film Formation with Coating Solution A) As a substrate, a SUS304 steel sheet measuring 100 mm square, 0.5 mm thick, and having an arithmetic surface roughness (Ra) of 100 nm is prepared. A dipping tank is also prepared for dip coating the substrate. Coating solution A is poured into the dipping tank.

[0155] Next, the substrate is immersed in a dipping tank to a depth of 90 mm and then pulled up at a speed of 1 mm / sec. The pulled-up substrate is heated at 180°C for 5 minutes. In this way, a film mainly composed of silicon dioxide and having a thickness of approximately 70 nm is formed 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] (Film formation using coating liquid B) As in the film formation using coating liquid A, a substrate having a size of 100 mm square and a thickness of 0.5 mm is prepared as the substrate. Also, a dipping tank for dip-coating this substrate is prepared. Coating liquid B is poured into the dipping tank.

[0159] Next, the prepared substrate is immersed in a dipping tank to a depth of 90 mm, and then pulled out at a speed of 1 mm / sec. The pulled-out substrate is 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. Another hole with a diameter of 55 mm is also provided between two of the holes 63 and 64, and a dryer 17 is inserted into the hole. The dryer 17 is inserted into the hole so that its outlet faces into the 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 and 70 are installed on the exterior side of the box 65 to measure the temperatures near the surfaces of the substrates 67 and 68. Display devices 71 and 72 for displaying the temperatures of the thermocouples 69 and 70, respectively, are also installed. A 10 mm thick cardboard fence 73 is installed between the two thermocouples 69 and 70 to prevent the air near the thermocouples 69 and 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 an infrared transmittance function by forming the film 66 thereon.

[0168] Furthermore, a similar evaluation 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 a film mainly composed of silicon dioxide containing silicon dioxide particles rose to 48° C. This result also confirmed that the substrate on which a film mainly composed of silicon dioxide was formed exhibits infrared transparency.

[0169] An infrared-transmitting member was prepared by the following process, in which a film mainly composed of silicon dioxide was formed on one side of a substrate made of SUS304 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 Liquid (Preparation of Coating Liquid 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 with the carbon black dispersed in it. Coating solution A (100 g) was added to this solution, and the mixture was further stirred for approximately 30 seconds with an overhead stirrer to prepare coating solution C.

[0172] (2) Film Formation In the infrared-transmitting member of this example, one side of the substrate is a film primarily composed of silicon dioxide, and the other side of the substrate is a film containing a black pigment. 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 primarily 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. A 10 wt % aqueous solution of polyethylene glycol (approximately 1 g) is applied almost uniformly to one side of this substrate 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 Liquid A) The substrate is dip-coated with the above-mentioned coating liquid A in the same manner as in Example 1 to form a film having a thickness of about 280 nm on the surface, the film being mainly composed of silicon dioxide.

[0176] (Masking Removal) When the 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 removed from the hot water, and 80°C hot water is sprayed onto the substrate with a dropper to remove the remaining polyethylene glycol.

[0177] (Film formation with coating liquid C) 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 procedure was repeated four times to form a film containing a 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] 13 is that a film 74 containing a black pigment is formed on a substrate 75 of the sample infrared-transmitting member placed in the hole 62. Other than that, it is the same as FIG.

[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) Coating solutions D, E, and F were prepared in amounts of approximately 900 g each in the same manner as in the preparation of 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 the display device 72 displaying the temperature of the thermocouple 70 rose to 40° C. Furthermore, 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 the display device 72 displaying the temperature of the 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, whereas 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, thereby reducing Ra. As a result, the actual surface area of ​​the substrate becomes smaller, and the area of ​​the substrate that exhibits the anti-reflection function becomes smaller, which is thought to result in a decrease in the amount of infrared light transmitted, i.e., the amount of heat transmitted.

[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 Arithmetic Mean Roughness Ra of 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 Liquids 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 in the vicinity of a substrate not having a film mainly 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 being evaluated together with a substrate having 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 in an infrared transparent member on which a film containing silicon dioxide particles with an average particle size of 50 nm was formed rose to 44° C. Furthermore, the displayed temperature of the display device 72 displaying the temperature of the thermocouple 70 in an infrared transparent member on which a film containing silicon dioxide particles with an average particle size of 70 nm was formed rose to 39° C. Furthermore, the displayed temperature of the display device 72 displaying the temperature of the thermocouple 70 in an infrared transparent member on which a film containing silicon dioxide particles with an average particle size of 90 nm was formed rose to 35° C.

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

[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 base material 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 as low as 20 nm.Furthermore, when a film was formed on a base material 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 Ra of the films containing silicon dioxide particles with average particle diameters of 70 nm and 90 nm both had a low value of 20 nm.

[0196] Up to an average particle size of 50 nm, the Ra of the infrared-transmitting member is not reduced. However, if the average particle size is larger than this, the Ra of the infrared-transmitting member decreases and the actual surface area of ​​the infrared-transmitting member becomes smaller. As a result, the area of ​​the infrared-transmitting 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 having 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, when the Ra of the substrate itself is less than 50 nm, the Ra also becomes less than 50 nm, and the temperature rise also decreases 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 of film containing black pigment) As described above, an infrared-transmitting member was prepared by the following process, in which a film mainly composed of silicon dioxide was formed on one side of a substrate made of SUS304 steel and a film containing black pigment was formed on the other side, and the infrared transmittance was evaluated. In this case, 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 of the black pigment-containing film instead of silica sol.

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

[0201] Carbon black (6 g) having an average particle size of 50 nm and polyvinylpyrrolidone K-30 (1 g) manufactured by Nippon Shokubai Co., Ltd. were added to dichloromethane (53 g) and stirred with an overhead stirrer for about 1 minute to prepare dichloromethane suspension G1 in which the carbon black was dispersed.

[0202] An acrylic resin (2 g) having a weight-average molecular weight of 10,000 is added to dichloromethane (98 g) and stirred with an overhead stirrer to dissolve the acrylic resin, thus preparing 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, thus preparing 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 about 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 about 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, using 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 power dryer in the same manner as above, the temperature near the substrate that did not have a film primarily composed of silicon oxide and a film containing a black pigment rose slightly above room temperature to 25°C, but the temperature near the substrate on which a film primarily composed of silicon oxide and a film containing a black pigment were formed using Coating Liquid G rose to 42°C. Furthermore, the temperature near the substrate on which a film containing a black pigment was 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 the black pigment, the temperature of the thermocouple rose only to 33°C, which indicates 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 CH stretching of aromatic rings around 3400 nm and absorption due to CH stretching of alkyl chains and methyl groups around 3500 nm, while acrylic resin has absorption due to CH stretching of alkyl chains and methyl groups around 3500 nm and absorption due to 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 light with greater energy than absorption due to CO stretching, resulting in a decrease in the amount of heat transmitted.

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

[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 Liquid (Preparation of Coating Liquid I) Methyltriethoxysilane (53 g) is dissolved in 2-propanol (947 g) to prepare 1000 g of a colorless and transparent coating liquid I. The solid content concentration of coating liquid 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, transparent coating solution J. The solids concentration of coating solution J after thermal curing is also about 2 wt %.

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

[0220] (2) Film formation A film containing silicon dioxide as a 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 Solution I, Coating Solution J, or Coating Solution K was used instead of Coating Solution 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 the 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 a 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 a 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 the result for 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.

[0224] An aluminum substrate having a silicon dioxide film was produced by 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 manner as a SUS304 steel substrate.

[0229] Instead of a substrate having a size of 100 mm square, a thickness of 0.5 mm, and an arithmetic surface roughness (Ra) of 100 nm, an acrylic resin substrate having a size of 100 mm square, a thickness of 1 mm, and an arithmetic surface roughness (Ra) of 5 nm was used. The heating conditions after dip coating with coating liquids 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 liquid A was changed from 4 to 8, and the number of dip coating and heating processes when using coating liquid B was changed from 1 to 2. An acrylic resin substrate having a film mainly composed of silicon dioxide containing silicon dioxide particles was produced using the same process as in Example 1. The thicknesses of the films formed using coating liquids 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 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 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 manner as the SUS304 steel substrate.

[0234] The same evaluation as in Example 1 was carried out using the experimental apparatus of FIG. 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 above 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 near the substrate without a silicon dioxide-based film, but remained almost the same when the film thickness exceeded 800 nm.

[0238] The temperature near the substrate using Coating Liquid B also showed almost the same results as the sample using Coating Liquid A. When the film thickness was about 310 nm, the temperature near the substrate rose to a maximum value of 48°C. The substrate with a film thickness of about 930 nm showed almost the same value as the vicinity of the substrate on which no film containing silicon dioxide as a main component was 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.

[0240] 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 polycarbonate resin having a size of 100 mm square, a thickness of 1 mm, and an arithmetic surface roughness (Ra) of 5 nm was used. Furthermore, an infrared-transmitting member was produced 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 produced 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] 17, the temperature near the polycarbonate resin 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 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 beyond that, reaching 36°C when the film thickness was approximately 770 nm. When the film thickness was approximately 840 nm or more, the temperature became almost the same as the temperature near the substrate on which a silicon dioxide-based film was not formed.

[0243] The temperature near the polycarbonate resin substrate using Coating Liquid B also showed results similar to those of the sample using Coating Liquid A, with the temperature near the substrate rising to a maximum value of 44°C when the film thickness was approximately 620 nm. When the film thickness was approximately 930 nm, the temperature near the substrate showed approximately the same value as that near the substrate on which no film containing silicon dioxide as a main component was 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.

[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 produced by the same film formation process as in Example 6. The produced 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] 18, the temperature near the silicon wafer 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 exceeded 35°C when the film thickness was about 210 nm, and exceeded 50°C when the film thickness was about 280 nm. The temperature reached a maximum of 57°C when the film thickness was about 350 nm, and gradually decreased as the film thickness increased beyond that, reaching 32°C when the film thickness was about 770 nm. When the film thickness was about 840 nm or more, the temperature became almost the same as the temperature near the substrate on which a silicon dioxide-based film was not formed.

[0249] The temperature near the polycarbonate resin substrate using Coating Liquid B also showed results similar to those of the sample using Coating Liquid A, with the temperature near the substrate rising to a maximum value of 60°C when the film thickness was approximately 310 nm. When the film thickness was approximately 930 nm, the temperature near the substrate showed approximately the same value 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]

[0253] Table 2 shows the compositions of the coating solutions used in the above examples to form films containing black pigment oil.

[0254]

[0255] In the above examples, infrared-transmitting members using a substrate formed of metal such as SUS steel or aluminum are described, but infrared-transmitting members using a substrate formed of 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 of a silicon wafer, resin, or the like is applied to a housing or the like that houses a heat-generating element, it is easy to transmit 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] When the average thickness of the surface layer is Tav, the thickness is in the range of 0<T≦2Tav.

[0259] The average thickness of the surface layer is 200 to 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 the refractive index of the substrate.

[0265] The silicon dioxide particles have an average particle size of 10 to 50 nm.

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

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

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

[0269] The average particle size of the black pigment is 10 to 1000 nm.

[0270] The black layer further includes a binder.

[0271] The binder contained in the black layer includes 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 absorption rate.

[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 reduce the size of cooling equipment inside the housing, or in some cases even eliminating the need for such equipment.

[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-transparent member comprising a substrate and a surface layer provided on the substrate, wherein the surface layer contains silicon dioxide as a main component, and the infrared-transparent member has a higher transmittance of infrared light than the substrate.

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

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

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

5. The infrared-transmitting member according to claim 1, wherein the following inequality holds: Ra1≧0.9Ra0, where Ra0 is the arithmetic mean roughness of the substrate and Ra1 is the arithmetic mean roughness of the surface of the surface layer.

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 said surface layer is smaller than the refractive index of said substrate.

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

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

10. The infrared-transmitting member according to claim 9, wherein the average particle size of the black pigment is 10 to 1,000 nm.

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

12. The infrared-transmitting member according to claim 11, wherein the binder contained in the black layer is a resin having 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 absorption rate of the infrared light.

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 formed of resin or silicone.

15. The infrared-transparent 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 of claim 1.

17. A railway vehicle having the housing of claim 16.

18. A transformer having the housing of claim 16.

19. An engine having the housing of claim 16.

Images