Thermal insulation layer and method for manufacturing the same, as well as a coating liquid for forming a thermal insulation layer and method for manufacturing the same.

Abstract

The present invention provides an insulating layer capable of exhibiting high thermal insulation properties and suppressing the deterioration of thermal insulation properties during long-term durability, a method for manufacturing the insulating layer, a coating liquid for forming the insulating layer, and a method for manufacturing the coating liquid for forming the insulating layer. [Solution] The heat insulating layer 1 contains a large number of aggregate substances 12 in a binder resin 11. The aggregate substances 12 have a large number of inorganic nanoprimary particles 121 having hydrophobic functional groups on their surface, and at least one pore 122 formed by being surrounded by the large number of inorganic nanoprimary particles 121. The coating liquid 2 for forming the heat insulating layer contains a large number of aggregate substances 12 and a large number of binder resin particles 111 in a solvent 21. The solvent 21 contains water and alcohol, and the proportion of alcohol in the total solvent 21 is less than 46% by volume. In the method for manufacturing the heat insulating layer, the coating liquid 2 for forming the heat insulating layer is applied in layers and dried to form the heat insulating layer 1.

Description

Technical Field

[0001] The present invention relates to a heat insulation layer, a method for manufacturing the same, a coating liquid for forming a heat insulation layer, and a method for manufacturing the same.

Background Art

[0002] Conventionally, a coating liquid for forming a heat insulation layer has been coated on the surface of a base material composed of a metal material, resin, rubber, etc. to form a heat insulation layer. In the heat insulation method by coating, generally, a coating liquid added with a filler having a hollow structure or a porous aerogel is used to form a heat insulation layer, thereby reducing the thermal conductivity of the heat insulation layer and ensuring heat insulation performance.

[0003] Prior Patent Document 1 describes a paint composition containing hollow particles made of glass or the like with a 50% particle diameter of 10 to 35 μm, and the proportion of hollow particles in the non-volatile matter is 45 to 70% by volume, and a heat-insulating coating film formed from this paint composition.

[0004] Also, Patent Document 2 describes that an aerogel, which is a super-porous substance having a porosity of about 90% to 99.9% and a pore size in the range of 1 nm to 100 nm, is a material having super heat insulation properties. Further, Patent Document 3 discloses a technology related to a composition for a heat insulation material having a silica aerogel, an aqueous binder, and a thickening agent, and a heat insulation material having a cured product of this composition for a heat insulation material.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006]

Patent Document 2

[0007] <000 [Patent Document 3] Japanese Patent Publication No. 2022-055295 [Overview of the project] [Problems that the invention aims to solve]

[0008] In recent years, the electrification of vehicles has accelerated, particularly in the automotive sector, in order to achieve carbon neutrality, and internal combustion engines, which have traditionally been a source of heat, are gradually disappearing. Therefore, from the perspective of thermal management, there is a demand for higher insulation technologies to suppress heat loss and improve thermal efficiency.

[0009] However, in insulating layers using hollow particles, there are limits to how small the hollow structure introduced into the particles can be, making it difficult to further reduce thermal conductivity.

[0010] Furthermore, because aerogel is a highly porous material, an insulating layer made of aerogel can achieve low thermal conductivity. However, aerogel has a complex manufacturing process, and not only does its insulating properties decrease due to moisture penetration into the pores during use, but the pore structure collapses due to shrinkage during the evaporation of the moisture that has penetrated the pores, resulting in a permanent loss of insulating properties. Thus, while aerogel has low initial thermal conductivity, its insulating properties deteriorate over long-term use.

[0011] This invention has been made in view of the above problems, and aims to provide an insulating layer that can exhibit high thermal insulation properties and suppress the deterioration of thermal insulation properties during long-term durability, a method for manufacturing an insulating layer, a coating liquid for forming an insulating layer, and a method for manufacturing a coating liquid for forming an insulating layer. [Means for solving the problem]

[0012] One aspect of the present invention is, The binder resin (11) contains numerous lumpy substances (12), The aforementioned lump-like substance is Numerous inorganic nanoprimary particles (121) having hydrophobic functional groups on their surface, Having at least one pore (122) formed by being surrounded by a large number of the aforementioned inorganic nanoprimary particles, It is located in the insulation layer (1).

[0013] Other aspects of the present invention include: A method for manufacturing an insulating layer, comprising applying a coating liquid (2) for forming an insulating layer in layers and drying it to form an insulating layer (1), The aforementioned coating liquid for forming the heat insulating layer is The solvent (21) contains numerous lumpy substances (12) and numerous binder resin particles (111). The aforementioned lump-like substance is Numerous inorganic nanoprimary particles (121) having hydrophobic functional groups on their surface, It has at least one pore (122) formed by being surrounded by a large number of the aforementioned inorganic nanoprimary particles, The aforementioned solvent is It contains water and alcohol. The proportion of the alcohol in the total solvent is less than 46% by volume. It lies in the manufacturing method of the insulation layer.

[0014] Further aspects of the present invention include: The solvent (21) contains numerous lumpy substances (12) and numerous binder resin particles (111). The aforementioned lump-like substance is Numerous inorganic nanoprimary particles (121) having hydrophobic functional groups on their surface, It has at least one pore (122) formed by being surrounded by a large number of the aforementioned inorganic nanoprimary particles, The aforementioned solvent is It contains water and alcohol. The proportion of the alcohol in the total solvent is less than 46% by volume. It is located in the coating liquid (2) for forming the heat insulating layer.

[0015] Further aspects of the present invention include: A first step (S1) of preparing a dispersion (31) in which a large number of inorganic nano primary particles (121) having a hydrophobic functional group on the surface are dispersed in a dispersion medium (310); A second step (S2) of mixing a flocculating liquid (32) for aggregating the dispersed inorganic nano primary particles into the dispersion liquid to generate a large number of massive substances (12) including at least one pore (122) formed by being surrounded by the large number of inorganic nano primary particles; A third step (S3) of mixing a resin aqueous solution (34) containing binder resin particles (111) into a mixed liquid (33) containing a large number of the massive substances; It is a method for producing a coating liquid for forming a heat insulating layer.

Effect of the Invention

[0016] The heat insulating layer has the above structure. Therefore, since the heat insulating layer contains a large number of massive substances having fine pores formed by being surrounded by a large number of inorganic nano primary particles in a binder resin, it is possible to lower the initial thermal conductivity and exhibit high heat insulation. Further, since the heat insulating layer has a hydrophobic functional group on the surface of the inorganic nano primary particles surrounding the pores, it is difficult for moisture to penetrate into the pores during use, and the collapse of the pores due to the penetration of moisture and the shrinkage of the pores due to the evaporation of the moisture penetrating into the pores are suppressed, and the pore structure can be maintained, and the decrease in the heat insulation during long-term durability can be suppressed.

[0017] The method for producing the heat insulating layer has the above structure. Therefore, according to the method for producing the heat insulating layer, by applying the coating liquid for forming the heat insulating layer in layers and drying it, a heat insulating layer capable of exhibiting high heat insulation and suppressing the decrease in heat insulation during long-term durability can be obtained.

[0018] The coating liquid for forming the heat insulating layer has the above structure. Therefore, according to the coating liquid for forming the heat insulating layer, by applying the coating liquid for forming the heat insulating layer in layers and drying it, a heat insulating layer capable of exhibiting high heat insulation and suppressing the decrease in heat insulation during long-term durability can be formed.

[0019] The method for manufacturing the coating liquid for forming the heat insulating layer described above has the above configuration. Therefore, according to the method for manufacturing the coating liquid for forming the heat insulating layer described above, it is possible to obtain the coating liquid for forming the heat insulating layer that can exhibit high heat insulating properties and suppress the deterioration of heat insulating properties during long-term durability.

[0020] The reference numerals in parentheses in the claims and the means for solving the problem indicate the correspondence with the specific means described in the embodiments later, and do not limit the technical scope of the present invention. [Brief explanation of the drawing]

[0021] [Figure 1] Figure 1 is a schematic diagram showing a cross-section along the thickness direction of the thermal insulation layer according to the embodiment. [Figure 2] Figure 2 is a schematic diagram showing a cross-section along the thickness direction of the heat insulating layer formed on one side of the substrate according to the embodiment. [Figure 3] Figure 3 is a schematic diagram showing the coating liquid for forming an insulating layer used in the method for manufacturing an insulating layer according to the embodiment, and the coating liquid for forming an insulating layer according to the embodiment. [Figure 4] Figure 4 is a schematic diagram showing a modified example of the coating liquid for forming the heat insulating layer shown in Figure 3. [Figure 5] Figure 5 is a diagram illustrating the method for manufacturing a coating liquid for forming an insulating layer and a method for manufacturing an insulating layer according to the embodiment. [Figure 6] Figure 6 is a diagram illustrating modified examples of the method for manufacturing the coating liquid for forming a heat insulating layer and the method for manufacturing the heat insulating layer, as shown in Figure 5. [Figure 7] Figure 7 is a scanning electron microscope (SEM) image of a cross-section along the planar direction of the insulating layer formed by the coating solution of sample 1, obtained in an experimental example. [Figure 8] Figure 8 shows the pore size distribution of the heat insulating layer formed by the coating solutions of Sample 1 and Sample 4 obtained in the experimental example. [Figure 9]Figure 9 shows optical photographs of the film surface of the insulating layer formed by the coating solutions of Sample 1 and Sample 8, as well as transmission electron microscope (TEM) images of the cross-section along the thickness direction of the insulating layer, obtained in the experimental example. [Figure 10] Figure 10 shows the pore size distribution of the heat insulating layer formed by the coating solutions of Sample 1 and Sample 8 obtained in the experimental example. [Modes for carrying out the invention]

[0022] The thermal insulation layer and its manufacturing method described herein, as well as the coating liquid for forming the thermal insulation layer and its manufacturing method, will be described in detail below with reference to the drawings.

[0023] The thermal insulation layer and its manufacturing method, as well as the coating liquid for forming the thermal insulation layer and its manufacturing method, described herein are not limited to the embodiments described below. Furthermore, the components of the thermal insulation layer and its manufacturing method, and the coating liquid for forming the thermal insulation layer and its manufacturing method, as described below, can be combined with each other as needed. Also, the lower and upper limits of the numerical ranges shown below can be combined in any way.

[0024] (Insulation layer) First, the thermal insulation layer of this embodiment will be explained using Figures 1 and 2.

[0025] As illustrated in Figures 1 and 2, the thermal insulation layer 1 of this embodiment is formed in layers. The thermal insulation layer 1 can be formed on the surface of a base material 4, for example, as illustrated in Figure 2. The thermal insulation layer 1 may be formed to cover the entire surface of the base material 4, or to cover a part of the surface of the base material 4. Specifically, the base material 4 can be exemplified by constituent materials that make up at least a part of a component, part, product, etc., for which thermal insulation is required. Examples of materials for the base material 4 include metal materials (metals include alloys, hereafter omitted), resin materials, rubber materials (including elastomer materials, hereafter omitted), and various other materials. In Figure 2, the surface of the base material 4 is shown as being flat, but the surface of the base material 4 may have an uneven shape, etc., and is not limited to being flat.

[0026] The thermal insulation layer 1 contains numerous lumpy substances 12 in the binder resin 11. Note that the lumpy substances 12 are omitted in Figure 2. In the thermal insulation layer 1, the binder resin 11 is the part that plays the role of the matrix (parent phase) of the thermal insulation layer 1. The binder resin 11 can be selected considering the material of the base material 4 that forms the thermal insulation layer 1.

[0027] The binder resin 11 is preferably anionic functional group. This is because it has good dispersibility in the solvent 22 containing water and alcohol, which constitutes the insulating layer forming coating liquid 2 (described later) used to form the insulating layer 1.

[0028] The binder resin 11 specifically includes at least one resin selected from the group consisting of epoxy resin, urethane resin, and silicone resin. Epoxy resin has an OH group as an anionic functional group. Urethane resin has an OH group and a COOH group as anionic functional groups. Silicone resin has an OH group as an anionic functional group. Thus, epoxy resin, urethane resin, and silicone resin all have anionic functional groups. Therefore, in this case, the effects described above can be reliably achieved. Furthermore, when the binder resin 11 contains epoxy resin, there are advantages such as being able to create a heat insulating layer 1 that combines chemical resistance and high strength. Similarly, when the binder resin 11 contains urethane resin, there are advantages such as being able to create a heat insulating layer 1 that has high heat resistance and abrasion resistance. When the binder resin 11 contains silicone resin, there are advantages such as being able to create a heat insulating layer 1 that has high toughness and high heat resistance.

[0029] In the thermal insulation layer 1, the aggregate material 12 has a large number of inorganic nanoprimary particles 121 and pores 122. The inorganic nanoprimary particles 121 are nano-sized primary particles composed of inorganic material. In this disclosure, nano-size (nano-order) refers to a size greater than 0 nm and less than or equal to 1000 nm (hereinafter omitted). Whether or not the inorganic nanoprimary particles 121 are nano-sized is determined by the average primary particle diameter of the inorganic nanoprimary particles 121. The average primary particle diameter of the inorganic nanoprimary particles 121 is the arithmetic mean of the primary particle diameters of 200 inorganic nanoprimary particles 121 arbitrarily extracted from a transmission electron microscope (TEM) image of a cross-section along the thickness direction of the thermal insulation layer 1.

[0030] Specifically, the inorganic nanoprimary particles 121 can be ceramic particles or the like. One or more types of inorganic nanoprimary particles 121 can be used in combination. When the inorganic nanoprimary particles 121 are ceramic particles, it is easier to lower the thermal conductivity of the inorganic nanoprimary particles 121 and they have excellent heat resistance, which is advantageous for lowering the thermal conductivity of the insulating layer 1 and improving its durability.

[0031] Examples of ceramics that make up ceramic particles include silica, glass, bentonite, and shirasu. Preferably, the ceramic constituting the ceramic particles is silica.

[0032] The average primary particle diameter of the inorganic nanoprimary particles 121 can preferably be 5 nm or more, from the viewpoint of handling and workability. Furthermore, the average primary particle diameter of the inorganic nanoprimary particles 121 can preferably be 100 nm or less, more preferably 90 nm or less, even more preferably 80 nm or less, even more preferably 70 nm or less, even more preferably 60 nm or less, and even more preferably 50 nm or less, from the viewpoint of being able to reduce the pore size of the aggregate material and making it easier to obtain a heat insulating layer with high heat insulating properties.

[0033] The inorganic nanoprimary particles 121 have hydrophobic functional groups on their surface. This makes the surface of the inorganic nanoprimary particles 121 hydrophobic. The inorganic nanoprimary particles 121 may have one type of hydrophobic functional group on their surface, or they may have two or more types.

[0034] Hydrophobic functional groups preferably have at least one of an alkyl group and an alkoxy group. In this case, the degree of hydrophobicity can be easily adjusted by changing the number of carbon atoms in the alkyl group or alkoxy group. From the viewpoint of ease of introduction and reaction efficiency, hydrophobic functional groups preferably have an alkyl group.

[0035] Examples of hydrophobic functional groups include alkylsilyl groups and alkoxysilyl groups. Examples of alkylsilyl groups include methylsilyl groups. The alkylsilyl group may be a trialkylsilyl group, a dialkylsilyl group, or a monoalkylsilyl group. Of these alkylsilyl groups, a trimethylsilyl group is preferred from the viewpoint of having a greater hydrophobic effect. Examples of alkoxysilyl groups include methoxysilyl groups. The alkoxysilyl group may be a trialkoxysilyl group, a dialkoxysilyl group, or a monoalkoxysilyl group. Of these alkoxysilyl groups, a trimethoxysilyl group is preferred from the viewpoint of having a greater hydrophobic effect. These hydrophobic functional groups can be used individually or in combination of two or more.

[0036] In the aggregate material 12, the pores 122 are formed by being surrounded by a large number of inorganic nanoprimary particles 121 having hydrophobic functional groups on their surfaces. In other words, the aggregate material 12 holds the pores 122 inside because the large number of inorganic nanoprimary particles 121 having hydrophobic functional groups on their surfaces are tightly packed together. Therefore, the outer periphery of the pores 122 is surrounded by a large number of inorganic nanoprimary particles 121 having hydrophobic functional groups on their surfaces, which suppresses the penetration of moisture from the outside of the aggregate material 12 into the pores 122. Each aggregate material 12 may contain multiple pores 122, as long as it contains at least one such pore 122. Furthermore, the heat insulating layer 1 may contain aggregate material that does not contain pores 122, as long as it contains aggregate material 12 containing pores 122. In addition, while the pores 122 in the heat insulating layer 1 are normally filled with air, they may also be filled with gases other than air (hydrocarbon gases, noble gases, etc.). Furthermore, as long as it does not hinder the effect of the heat insulating layer 1, some of the solvent 22 of the coating liquid 2 for forming the heat insulating layer may remain in some of the pores 122 due to unavoidable manufacturing reasons.

[0037] The size of the pores 122 should ideally be nano-sized from the perspective of achieving low thermal conductivity.

[0038] From the viewpoint of reducing thermal conductivity, the pore diameter of the pores 122 is preferably 200 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less. Since the pores 122 in the bulk material 12 are better as small as possible from the viewpoint of thermal conductivity, the lower limit of the pore diameter of the pores 122 is not particularly limited, but from the viewpoint of manufacturing, for example, it may be 20 nm or more. The average pore diameter of the pores 122 can be measured by the mercury intrusion method. The measurement conditions for the mercury intrusion method are an initial pressure of 4 kPa, a mercury contact angle of 130 degrees, and a mercury surface tension of 485 dynes / cm. Specifically, the pore diameter of the pores 122 described above is the most frequent value (the peak top value in the pore diameter distribution) in the pore diameter distribution (bubble diameter distribution) of the insulating layer 1.

[0039] The thickness of the heat insulating layer 1 can be preferably 300 μm or more, more preferably 500 μm or more, and even more preferably 700 μm or more, from the viewpoint of heat insulating properties, for example. Alternatively, the thickness of the heat insulating layer 1 can be preferably 1500 μm or less, more preferably 1200 μm or less, and even more preferably 1000 μm or less, from the viewpoint of shortening drying time and productivity, for example. The thickness of the heat insulating layer 1 is the arithmetic mean of 10 thickness measurements taken in a cross-section along the thickness direction of the heat insulating layer 1.

[0040] The thermal insulation layer 1 of this embodiment, as described above, contains a large number of massive substances 12 in the binder resin 11, each having fine pores 122 formed by being surrounded by a large number of inorganic nanoprimary particles 121. This makes it possible to lower the initial thermal conductivity and achieve high thermal insulation performance. Furthermore, since the thermal insulation layer 1 of this embodiment has hydrophobic functional groups on the surface of the inorganic nanoprimary particles 121 surrounding the pores 122, moisture is less likely to penetrate the pores 122 during use. This suppresses pore collapse due to moisture penetration and pore shrinkage due to evaporation of moisture that has penetrated the pores, thus maintaining the pore structure and preventing a decrease in thermal insulation performance over long-term use.

[0041] Furthermore, the descriptions of "(Method for manufacturing the heat insulating layer, coating liquid for forming the heat insulating layer)" and "(Method for manufacturing the coating liquid for forming the heat insulating layer)" described later can be referred to as needed.

[0042] (Method for manufacturing an insulating layer, coating liquid for forming an insulating layer) Next, the method for manufacturing the heat insulating layer of this embodiment and the coating liquid for forming the heat insulating layer of this embodiment will be explained with reference to Figures 3 and 4. Figures 1 and 2 mentioned above will also be referred to as appropriate.

[0043] The method for manufacturing the heat insulating layer of this embodiment (hereinafter sometimes referred to as "the method for manufacturing this heat insulating layer") comprises the step of applying the heat insulating layer forming coating liquid 2 of this embodiment (hereinafter sometimes referred to as "the coating liquid") in layers and drying it to form the heat insulating layer 1.

[0044] In this method for manufacturing the heat insulating layer, specifically, the coating liquid 2 is applied to the surface of the substrate 4 (see Figure 2) described above using various known coating methods, and the heat insulating layer 1 (see Figures 1 and 2) is formed by drying the resulting layered coating layer.

[0045] Examples of coating methods include spraying, brushing, molding by pouring into a mold, and application by dispenser. Coating may be performed only once, or multiple times under the same or different coating conditions.

[0046] The drying temperature can be preferably 23°C or higher, more preferably 40°C or higher, and even more preferably 60°C or higher, from the viewpoint of shortening the drying time, for example. Alternatively, the drying temperature can be preferably 80°C or lower, more preferably 70°C or lower, and even more preferably 60°C or lower, from the viewpoint of suppressing cracking during drying, for example. Drying may be performed only once, or it may be performed multiple times under the same or different drying conditions.

[0047] As illustrated in Figure 3, the coating liquid 2 contains a large number of lumpy substances 12 and a large number of binder resin particles 111 in a solvent 21.

[0048] In this coating liquid 2, the aggregate substance 12 has a large number of inorganic nanoprimary particles 121 having hydrophobic functional groups on their surface, and at least one pore 122 formed by being surrounded by the large number of inorganic nanoprimary particles 121. Details of the aggregate substance 12 are as described above, so a further explanation will be omitted. In this coating liquid 2, the pore 122 can be filled with a portion of the solvent 21. Specifically, the pore 122 can be filled with alcohol or the like, which is a portion of the solvent 21, due to the manufacturing method of the coating liquid for forming the heat insulating layer described later. In Figure 3, the dots drawn inside the pore 122 indicate that a portion of the solvent 21 is filling it.

[0049] In this coating liquid 2, the binder resin particles 111 constitute the binder resin 11 portion of the heat insulating layer 1 described above. Details of the binder resin 11 constituting the binder resin particles 111 are as described above and therefore will not be explained further. In this coating liquid 2, one or more types of binder resin particles 111 can be used in combination.

[0050] In this coating liquid 2, it is preferable that at least a portion of the outer surface of the lump material 12 is covered by a resin layer 112 composed of a portion of the binder resin particles 111, as illustrated in Figure 4. In this case, the resin layer 112 covering the outer surface of the lump material 12, formed by a portion of the binder resin particles 111, protects the shape of the lump material 12 and improves the retention of the pores 122. Therefore, in this case, the production of the heat insulating layer 1 having the above-described effects can be reliably achieved.

[0051] In this coating solution 2, the solvent 21 contains water and alcohol. Therefore, this coating solution 2 can be described as an aqueous coating solution.

[0052] The proportion of alcohol in the total solvent 21 (hereinafter sometimes simply referred to as the alcohol proportion of solvent 21) is set to less than 46% by volume.

[0053] If the alcohol content of the solvent 21 exceeds 46% by volume, it becomes difficult to generate a lump-like substance 12 having pores 122 surrounded by a large number of inorganic nanoprimary particles 121. From the viewpoint of ensuring the reliable generation of a lump-like substance 12 that retains the pores 122, the alcohol content of the solvent 21 is preferably 44% by volume or less, more preferably 40% by volume or less, even more preferably 38% by volume or less, even more preferably 35% by volume or less, and even more preferably 30% by volume or less.

[0054] In this coating solution 2, the alcohol constituting the solvent 21 is preferably a lower alcohol with 5 or fewer carbon atoms. In this case, it becomes easier to make the average pore diameter of the pores 122 smaller. Examples of lower alcohols with 5 or fewer carbon atoms include methanol, ethanol, isopropyl alcohol (IPA), butanol, and pentanol. These can be used individually or in combination of two or more.

[0055] Other substances may be added to the solvent 21, insofar as they can form the insulating layer 1. Examples of other substances include metal salts. In this case, the metal salt 35 cancels the surface charge (e.g., negative charge) of the binder resin particles 111 in the emulsion state of the coating liquid 2, thereby disrupting the dispersion stability of some of the binder resin particles 111, and causing some of the unstable binder resin particles 111 in the coating liquid 2 to adhere to the outer surface of the aggregate material 12. Therefore, in this case, it is easier to form a structure in which at least a portion of the outer surface of the aggregate material 12 is covered by a resin layer 112 composed of some of the binder resin particles 111, which has the advantage of promoting the retention of pores 122 within the aggregate material 12.

[0056] Examples of metal salts include calcium chloride, calcium sulfate, sodium chloride, magnesium chloride, and magnesium sulfate. These can be used individually or in combination of two or more.

[0057] Other examples of substances that can be used include pH adjusters such as acids and alkalis.

[0058] The aforementioned coating liquid 2 can be prepared, for example, using a method for manufacturing a coating liquid for forming a heat insulating layer, as described later.

[0059] The manufacturing method for this insulation layer has the above configuration. Therefore, by applying the coating liquid 2 in layers and drying it, it is possible to obtain an insulation layer 1 that exhibits high insulation performance and can suppress the decrease in insulation performance during long-term durability.

[0060] Furthermore, the coating liquid 2 has the above configuration. Therefore, by applying the coating liquid 2 in layers and drying it, it is possible to form a thermal insulation layer 1 that exhibits high thermal insulation properties and suppresses the decrease in thermal insulation properties during long-term durability.

[0061] The above-mentioned explanation of "(insulating layer)" and the description of "(method for manufacturing coating liquid for forming insulating layer)" described later can be referred to as needed.

[0062] (Method for manufacturing a coating liquid for forming an insulating layer) Next, the method for manufacturing the coating liquid for forming the heat insulating layer of this embodiment will be explained with reference to Figures 5 and 6.

[0063] The method for manufacturing the coating liquid for forming a heat insulating layer according to this embodiment (hereinafter sometimes referred to as the method for manufacturing this coating liquid) comprises a first step S1, a second step S2, and a third step S3.

[0064] The first step S1 is a step of preparing a dispersion 31 in which a large number of inorganic nanoprimary particles 121 having hydrophobic functional groups on their surface are dispersed in a dispersion medium 310, as illustrated in Figure 5.

[0065] Inorganic primary nanoparticles 121 having hydrophobic functional groups on their surface can be prepared by performing a surface treatment that introduces hydrophobic functional groups to the surface of the inorganic primary nanoparticles 121. The detailed structure of the inorganic primary nanoparticles 121 having hydrophobic functional groups on their surface is as described above in the explanation of "(thermal insulation layer)", so the explanation is omitted here.

[0066] As the dispersion medium 310, alcohols can be suitably used from the viewpoint of monodispersing inorganic nanoprimary particles 121. Specifically, lower alcohols with 5 or fewer carbon atoms are preferred. In this case, the average pore diameter of the pores 122 of the formed aggregate material 12 can be made smaller. Examples of lower alcohols with 5 or fewer carbon atoms include methanol, ethanol, isopropyl alcohol (IPA), butanol, and pentanol. These can be used individually or in combination of two or more.

[0067] The second step S2 is a step in which a coagulation liquid 32 for agglomerating dispersed inorganic nanoprimary particles 121 is mixed into the dispersion liquid 31, as illustrated in Figure 5, to generate a large number of aggregated substances 12, each containing at least one pore 122 surrounded by a large number of inorganic nanoprimary particles 121.

[0068] As the coagulation liquid 32, water or the like can be suitably used, from the viewpoint of reliably coagulating the dispersed inorganic nanoprimary particles 121. When alcohol is used as the dispersion medium 310 and water as the coagulation liquid 32, the solvent 21 of the resulting coating liquid 2 can be configured to contain both water and alcohol. The mixing of the coagulation liquid 32 into the dispersion liquid 31 can be adjusted so that the proportion of alcohol in the total solvent 21 of the resulting coating liquid 2 is less than 46% by volume.

[0069] In the second step S2, as illustrated in Figure 5, the inorganic nanoprimary particles 121 that were monodispersed in the dispersion 31 aggregate upon mixing with the coagulation liquid 32, generating a large number of clumps 12 containing pores 122 surrounded by a large number of inorganic nanoprimary particles 121. In this case, since the clumps 12 aggregate in the dispersion 31, the formed pores 122 are usually filled with the dispersion medium 310. In Figure 5, the dots drawn inside the pores 122 indicate that they are filled with the dispersion medium 310.

[0070] The third step S3 is a step of mixing a resin aqueous solution 34 containing binder resin particles 111 into a mixed liquid 33 containing a large number of lumpy substances 12, as illustrated in Figure 5.

[0071] The binder resin particles 111 contained in the resin aqueous solution 34 are for the purpose of constituting the binder resin 11 in the heat insulating layer 1 formed by the resulting coating liquid 2. Therefore, the details of the binder resin 11 constituting the binder resin particles 111 are as described above in the explanation of "(heat insulating layer)" and will be omitted here. Also, the average particle size of the binder resin particles 111, etc., are as described above in the explanation of "(method of manufacturing the heat insulating layer, coating liquid for forming the heat insulating layer)" and will be omitted here.

[0072] The coating liquid 2 obtained through the first step S1 to the third step S3 can be used to form a heat insulating layer 1 on the surface of a substrate 4 by applying the coating liquid 2 using various known coating methods, as illustrated in Figure 5, and then drying the resulting layered coating layer.

[0073] The method for producing this coating solution may further include a fourth step S4, as illustrated in Figure 6.

[0074] The fourth step S4 is the step of mixing a metal salt 35 into a mixture 33 in which an aqueous resin solution 34 is mixed. When the method for producing this coating liquid includes the fourth step S4, the metal salt 35 can cause some of the binder resin particles 111 dispersed in the mixture 33 to adhere to the outer surface of the lump-like substance 12. This is because the metal salt 35 cancels the surface charge (for example, negative charge) of the binder resin particles 111 in the mixture 33 in which the aqueous resin solution 34 in an emulsion state is mixed, thereby disrupting the dispersion stability of some of the binder resin particles 111, and some of the binder resin particles 111 that have become unstable in the mixture 33 adhere to the outer surface of the lump-like substance 12. In this case, it is easier to form a structure in which at least a part of the outer surface of the lump-like substance 12 is covered by a resin layer 112 composed of some of the binder resin particles 111, which has the advantage of promoting the retention of pores 122 within the lump-like substance 12.

[0075] Examples of metal salts include calcium chloride, calcium sulfate, sodium chloride, magnesium chloride, and magnesium sulfate. These can be used individually or in combination of two or more. Furthermore, the metal salts can be mixed as an aqueous solution containing the metal salts.

[0076] The coating liquid 2 obtained through the first step S1 to the fourth step S4 can be applied to the surface of the substrate 4 by various known coating methods, as illustrated in Figure 6, to form a heat insulating layer 1 by drying the resulting layered coating. Note that in Figures 5 and 6 described above, the lumpy material 12 in the heat insulating layer 1 is omitted.

[0077] The method for manufacturing this coating liquid has the configuration described above. Therefore, according to the method for manufacturing this coating liquid, it is possible to obtain the above-described coating liquid 2, which can form an insulating layer that exhibits high heat insulation properties and suppresses the deterioration of heat insulation properties during long-term durability.

[0078] (Example of experiment) <Preparation of Sample 1> Ethanol was added to nanosilica (manufactured by Nippon Aerosil Co., Ltd., "AEROSIL") with an average primary particle diameter of 40 nm and a surface treated with trimethylsilyl groups, and the mixture was stirred using a three-one motor until uniformly dispersed. This produced a dispersion in which numerous inorganic nanoprimary particles (nanosilica primary particles) having trimethylsilyl groups on their surface were dispersed in ethanol.

[0079] Next, deionized water was added dropwise to an ethanol aqueous solution in which inorganic nanoprimary particles were uniformly dispersed, over a period of 5 minutes or more, to achieve an ethanol concentration of 24% by volume, and the mixture was stirred for 5 minutes. This yielded a mixed solution consisting of a water / ethanol slurry containing numerous clumps formed by the aggregation of dispersed inorganic nanoprimary particles.

[0080] Next, ion-exchanged water was added to a urethane resin emulsion (Sanyo Chemical Industries, Ltd., "Permarine UA368") so that the solid content was 20 parts by mass, and the mixture was stirred to prepare a resin aqueous solution containing binder resin particles. Then, this resin aqueous solution was added dropwise to the above mixture over a period of 5 minutes or more so that the amount of binder resin was 25 parts by mass for every 100 parts by mass of inorganic nanoprimary particles, and the mixture was stirred for 5 minutes. In this way, the resin aqueous solution containing binder resin particles was mixed into the mixture containing numerous lumpy substances.

[0081] Next, ion-exchanged water was added to calcium chloride as a metal salt, and the mixture was stirred to prepare a 10% by mass aqueous solution of calcium chloride. Then, this aqueous solution of calcium chloride was added dropwise to the mixture containing the resin aqueous solution over a period of 5 minutes or more, so that the amount of calcium chloride was 1.2 parts by mass per 100 parts by mass of inorganic nanoprimary particles, and the mixture was stirred for 5 minutes. In this way, calcium chloride, which is a metal salt, was mixed into the mixture containing the resin aqueous solution.

[0082] Based on the above, a coating solution for forming the heat insulating layer of sample 1 was prepared.

[0083] Next, the prepared coating solution was poured into the mold and dried in a hot air oven at 80°C for 1 hour, then the temperature was raised to 100°C for an additional 1 hour of drying. This resulted in obtaining an insulating layer (film thickness 200 μm) of sample 1 in film form.

[0084] <Preparation of Samples 2 to 8> The coating solutions and heat insulating layers for Samples 2 to 4 were obtained in the same manner as in the preparation of Sample 1, except that the average primary particle size of the inorganic nanoprimary particles was changed as shown in Table 1.

[0085] The coating solution and heat insulating layer of Sample 5 were obtained in the same manner as in the preparation of Sample 1, except that nanosilica with a dimethylsilyl surface treatment (manufactured by Nippon Aerosil Co., Ltd., "AEROSIL") was used instead of nanosilica with a trimethylsilyl surface treatment.

[0086] The coating solution and heat insulating layer of sample 6 were obtained in the same manner as in the preparation of sample 1, except that an aqueous solution of isopropyl alcohol (IPA) was used instead of an aqueous solution of ethanol.

[0087] The coating solution and heat insulating layer of sample 7 were obtained in the same manner as in the preparation of sample 1, except that an octanol aqueous solution was used instead of an ethanol aqueous solution.

[0088] In the preparation of Sample 1, the coating solution and heat insulating layer of Sample 8 were obtained in the same manner as before, except that calcium chloride aqueous solution was not added to the mixed solution containing the resin aqueous solution.

[0089] <Preparation of Sample 1C> Referring to Example 5 described in Japanese Patent Publication No. 2022-055295 (Patent Document 3), a composition for thermal insulation material having silica aerogel was prepared and used as the coating solution for sample 1C. Furthermore, the thermal insulation layer of sample 1C was formed using this coating solution for sample 1C.

[0090] <Preparation of Sample 2C> The coating solution and heat insulating layer of sample 2C were obtained in the same manner as in the preparation of sample 1, except that nanosilica without hydrophobic functional group treatment on its surface (manufactured by Nippon Aerosil Co., Ltd., "AEROSIL") was used instead of nanosilica with a trimethylsilyl group treatment on its surface.

[0091] <Preparation of Sample 3C> In the preparation of Sample 1, ion-exchanged water was added dropwise as a coagulation solution over a period of 5 minutes or more to an ethanol aqueous solution in which inorganic nanoprimary particles were uniformly dispersed, so that the ethanol concentration reached 46% by volume, and the mixture was stirred for 5 minutes. The coating solution and insulating layer of Sample 3C were obtained in the same manner as before.

[0092] <Various evaluations> -Pore formation- The presence or absence of porosity material with fine pores, formed by being surrounded by numerous inorganic nanoparticles, was confirmed by transmission electron microscopy (TEM) observation of the cross-section along the thickness direction of the insulating layer of the sample. Furthermore, if porosity material with fine pores is confirmed in the insulating layer, it can be said that the porosity material contained in the coating liquid used to form the insulating layer also has fine pores.

[0093] Furthermore, sections were cut from the insulating layer of the sample and used as samples for pore size measurement. The pore size distribution of the measurement samples was measured using a pore distribution analyzer (Micromeristics, "Autopore V9620") by the mercury intrusion method. The measurement conditions for the mercury intrusion method were an initial pressure of 4 kPa, a mercury contact angle of 130 degrees, and a mercury surface tension of 485 dynes / cm. The most frequent value (peak top value in the pore size distribution) in the pore size distribution (bubble size distribution) of the insulating layer was defined as the pore size contained in the lumpy material.

[0094] When pore formation was confirmed in the lumpy material, cases where the pore diameter was 200 nm or less were classified as "A," and cases where the pore diameter was greater than 200 nm were classified as "B."

[0095] -Thermal insulation- The thermal conductivity of the insulating layer of the sample was measured using a NETZSCH HFM436 analyzer. The measurement conditions were at room temperature (23°C ± 3°C).

[0096] If the thermal conductivity of the insulation layer was 0.03 W / m or less, it was classified as "A" as it demonstrated higher insulation performance. If the thermal conductivity of the insulation layer was between 0.03 W / mK and 0.1 W / mK, it was classified as "B" as it demonstrated high insulation performance. On the other hand, if the thermal conductivity of the insulation layer was greater than 0.1 W / m, it was classified as "C" as it demonstrated inferior insulation performance.

[0097] -Durability- The insulation layer of the sample was placed in a constant temperature and humidity chamber and exposed to the environment at 85°C and 85%RH for 1000 hours. Subsequently, a durable insulation layer was obtained by drying it in a hot air oven at 100°C for 6 hours. Then, the thermal conductivity of the durable insulation layer was measured in the same manner as above.

[0098] The thermal conductivity of the insulation layer was compared before and after the durability treatment. If the increase in thermal conductivity was less than 20%, it was classified as "A," indicating that the decrease in insulation performance during long-term durability was suppressed. On the other hand, if the increase in thermal conductivity was 20% or more, it was classified as "C," indicating that the decrease in insulation performance during long-term durability was not suppressed. The increase in thermal conductivity was calculated using the formula 100 × |(thermal conductivity of the insulation layer after durability treatment - thermal conductivity of the insulation layer before durability treatment)| / (thermal conductivity of the insulation layer before durability treatment). || represents the absolute value.

[0099] Table 1 summarizes the detailed composition of the coating solution for each sample and the various evaluation results. Figures 7 to 10 show SEM images, optical images, TEM images, and pore size distribution of the heat insulating layer formed with the coating solution for the specified sample.

[0100] [Table 1]

[0101] Table 1 and Figures 7-10 show the following: The insulating layer of sample 1C is made of silica aerogel. Since silica aerogel is a superporous material, the insulating layer made of silica aerogel is able to achieve low thermal conductivity. However, the insulating layer of sample 1C has poor long-term durability in terms of thermal insulation. This is because the porous structure collapses due to the infiltration of water into the pores of the silica aerogel and the shrinkage that occurs when the water that has entered the pores evaporates.

[0102] Sample 2C's inorganic nanoprimary particles used in the coating solution do not have hydrophobic functional groups on their surface. Therefore, the insulating layer of Sample 2C coated with this solution has low long-term durability in terms of thermal insulation. This is because the porous structure could not be maintained due to the penetration of water into the pores formed in the mass material and the shrinkage that occurred during the evaporation of the water that had penetrated the pores.

[0103] Sample 3C has an alcohol content of 46% or more by volume in the total solvent of the coating solution. As a result, the insulating layer of Sample 2C coated with this solution had high thermal conductivity and could not exhibit high insulating properties. This is because, due to the alcohol content of 46% or more by volume in the total solvent of the coating solution, it was not possible to generate a granular material with pores surrounded by numerous inorganic nanoparticles in the coating solution.

[0104] In contrast to these, in Samples 1 to 8, a coating liquid that satisfies the requirements specified in this disclosure was prepared and used to form an insulating layer. As a result, it was confirmed that the insulating layers of Samples 1 to 8 exhibit high insulating properties and suppress the deterioration of insulating properties during long-term durability.

[0105] Furthermore, when comparing samples 1 to 8, it can be seen that when the average primary particle diameter of inorganic nanoparticles is 100 nm or less, or when a lower alcohol with 5 or fewer carbon atoms is used as the alcohol in the coating solution, the pore size in the aggregate material can be made smaller, making it easier to obtain an insulating layer with high thermal insulation properties.

[0106] The present invention is not limited to the embodiments and experimental examples described above, and various modifications are possible without departing from the spirit of the invention. Furthermore, each of the configurations shown in the embodiments and experimental examples can be combined in any way.

[0107] The features of this invention are as follows. Section 1. The binder resin (11) contains numerous lumpy substances (12), The aforementioned lump-like substance is Numerous inorganic nanoprimary particles (121) having hydrophobic functional groups on their surface, Having at least one pore (122) formed by being surrounded by a large number of the aforementioned inorganic nanoprimary particles, Insulation layer (1). Section 2. The inorganic nanoprimary particles are ceramic particles. The insulating layer described in item 1. Section 3. The average primary particle diameter of the inorganic nanoprimary particles is between 5 nm and 100 nm. The insulating layer described in item 1 or item 2. Section 4. The size of the aforementioned pores is nanoscale. The insulating layer described in any one of items 1 to 3. Section 5. The hydrophobic functional group has at least one of an alkyl group and an alkoxy group. The insulating layer described in any one of items 1 through 4. Section 6. The binder resin comprises at least one resin selected from the group consisting of epoxy resin, urethane resin, and silicone resin. The insulating layer described in any one of items 1 through 5. Section 7. A method for manufacturing an insulating layer, comprising applying a coating liquid (2) for forming an insulating layer in layers and drying it to form an insulating layer (1), The aforementioned coating liquid for forming the heat insulating layer is The solvent (21) contains numerous lumpy substances (12) and numerous binder resin particles (111). The aforementioned lump-like substance is Numerous inorganic nanoprimary particles (121) having hydrophobic functional groups on their surface, It has at least one pore (122) formed by being surrounded by a large number of the aforementioned inorganic nanoprimary particles, The aforementioned solvent is It contains water and alcohol. The proportion of the alcohol in the total solvent is less than 46% by volume. A method for manufacturing an insulating layer. Section 8. The solvent (21) contains numerous lumpy substances (12) and numerous binder resin particles (111). The aforementioned lump-like substance is Numerous inorganic nanoprimary particles (121) having hydrophobic functional groups on their surface, It has at least one pore (122) formed by being surrounded by a large number of the aforementioned inorganic nanoprimary particles, The aforementioned solvent is It contains water and alcohol. The proportion of the alcohol in the total solvent is less than 46% by volume. Coating liquid for forming an insulating layer (2). Section 9. At least a portion of the outer surface of the aforementioned bulk material is covered by a resin layer (112) composed of a portion of the binder resin particles. A coating liquid for forming an insulating layer as described in item 8. Section 10. The aforementioned alcohol is a lower alcohol having 5 or fewer carbon atoms. A coating liquid for forming an insulating layer as described in item 8 or item 9. Section 11. A first step (S1) is to prepare a dispersion (31) in which a large number of inorganic nanoprimary particles (121) having hydrophobic functional groups on their surface are dispersed in a dispersion medium (310), A second step (S2) involves mixing a coagulation liquid (32) for agglomerating the dispersed inorganic nanoprimary particles into the dispersion liquid to generate a large number of aggregated substances (12) each containing at least one pore (122) formed by being surrounded by a large number of inorganic nanoprimary particles. The method comprises a third step (S3) of mixing a resin aqueous solution (34) containing binder resin particles (111) into a mixed liquid (33) containing a large number of the aforementioned lumpy substances, A method for manufacturing a coating liquid for forming an insulating layer. Section 12. The mixture includes a fourth step (S4) of mixing a metal salt (35) into the aforementioned resin aqueous solution. A method for producing a coating liquid for forming an insulating layer as described in item 11. [Explanation of symbols]

[0108] 1. Insulation layer 11 Binder resin 12 Massive material 121 Inorganic nanoprimary particles 122 pores 2. Coating liquid for forming an insulating layer 21 Solvent S1 First process S2 Second process S3 Third Process 31 Dispersion 310 Dispersion medium 32 Flocculant 33 Mixed liquid 34 Resin aqueous solution

Claims

1. The binder resin (11) contains numerous lumpy substances (12), The aforementioned lump-like substance is Numerous inorganic nanoprimary particles (121) having hydrophobic functional groups on their surface, It has at least one pore (122) formed by being surrounded by a large number of the aforementioned inorganic nanoprimary particles, Insulation layer (1).

2. The inorganic nanoprimary particles are ceramic particles. The thermal insulation layer according to claim 1.

3. The average primary particle diameter of the inorganic nanoprimary particles is 5 nm or more and 100 nm or less. The thermal insulation layer according to claim 1 or claim 2.

4. The size of the aforementioned pores is nanoscale. The thermal insulation layer according to claim 1 or claim 2.

5. The hydrophobic functional group has at least one of an alkyl group and an alkoxy group. The thermal insulation layer according to claim 1 or claim 2.

6. The binder resin comprises at least one resin selected from the group consisting of epoxy resin, urethane resin, and silicone resin. The thermal insulation layer according to claim 1 or claim 2.

7. A method for manufacturing an insulating layer, comprising applying a coating liquid (2) for forming an insulating layer in layers and drying it to form an insulating layer (1), The aforementioned coating liquid for forming the heat insulating layer is The solvent (21) contains a large number of lumpy substances (12) and a large number of binder resin particles (111). The aforementioned lump-like substance is Numerous inorganic nanoprimary particles (121) having hydrophobic functional groups on their surface, It has at least one pore (122) formed by being surrounded by a large number of the aforementioned inorganic nanoprimary particles, The aforementioned solvent is It contains water and alcohol. The proportion of the alcohol in the total solvent is less than 46% by volume. A method for manufacturing an insulating layer.

8. The solvent (21) contains a large number of lumpy substances (12) and a large number of binder resin particles (111). The aforementioned lump-like substance is Numerous inorganic nanoprimary particles (121) having hydrophobic functional groups on their surface, It has at least one pore (122) formed by being surrounded by a large number of the aforementioned inorganic nanoprimary particles, The aforementioned solvent is It contains water and alcohol. The proportion of the alcohol in the total solvent is less than 46% by volume. Coating liquid for forming an insulating layer (2).

9. At least a portion of the outer surface of the aforementioned bulk material is covered by a resin layer (112) composed of a portion of the binder resin particles. The coating liquid for forming a heat insulating layer according to claim 8.

10. The aforementioned alcohol is a lower alcohol having 5 or fewer carbon atoms. A coating liquid for forming a heat insulating layer according to claim 8 or claim 9.

11. A first step (S1) is to prepare a dispersion (31) in which a large number of inorganic nanoprimary particles (121) having hydrophobic functional groups on their surface are dispersed in a dispersion medium (310), A second step (S2) involves mixing a coagulation liquid (32) for agglomerating the dispersed inorganic nanoprimary particles into the dispersion liquid to generate a large number of aggregated substances (12) each containing at least one pore (122) formed by being surrounded by a large number of inorganic nanoprimary particles. The method comprises a third step (S3) of mixing a resin aqueous solution (34) containing binder resin particles (111) into a mixed liquid (33) containing a large number of the aforementioned lumpy substances, A method for manufacturing a coating liquid for forming an insulating layer.

12. The mixture includes a fourth step (S4) of mixing a metal salt (35) into the aforementioned resin aqueous solution. A method for producing a coating liquid for forming a heat insulating layer according to claim 11.

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