Heat insulating material and its manufacturing method

Abstract

To provide a heat insulating material that has excellent heat insulation by compositing silica aerogel and thermoplastic resin, and a method for manufacturing the heat insulating material.SOLUTION: A heat insulating material has silica aerogel and non-olefin thermoplastic resin. A DBA adsorption amount of silica aerogel is 300 mmol / kg or less, and the content of silica aerogel is 5 mass% or more and 25 mass% or less when the total mass of the heat insulating material is 100 mass%. A method for manufacturing a heat insulation material has a kneading step of adding and kneading silica aerogel with a DBA adsorption amount of 300 mmol / kg or less to a molten non-olefin thermoplastic resin, and a molding step of molding the obtained kneaded material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a thermal insulation material using silica aerogel. [Background technology]

[0002] Silica aerogel is a material made up of multiple silica particles linked together to form a skeleton, with pores between the skeletons smaller than the mean free path of air. This microporous structure gives it low thermal conductivity, making it useful as a component material for thermal insulation. While silica aerogel can be used alone as a thermal insulation material, its nanometer-sized skeleton and numerous pores make it brittle and prone to breakage, with more than 90% of its volume being voids. For this reason, silica aerogel is often used by supporting it on a substrate such as fiber, binding it together with a binder, or compounding it with a resin.

[0003] Typically, the surface of silica aerogel is hydrophobic, typically through a hydrophobic treatment. Therefore, when silica aerogel is compounded with a hydrophobic thermoplastic resin such as polypropylene, the two materials are compatible and intimately blended, but the thermoplastic resin may penetrate the pores of the silica aerogel and crush them. Furthermore, the porous structure of the silica aerogel may be damaged by shear forces during mixing with the resin. This prevents the silica aerogel from achieving its unique insulating effect of suppressing heat transfer through convection.

[0004] Known methods for preventing resin penetration into pores include forming a coating on the surface of silica aerogel or modifying the surface. For example, Patent Document 1 describes a composite material containing a polymer and an aerogel coated with a coating. Patent Document 1 lists polypropylene and other polymers and describes how coating the aerogel surface with a coating prevents the polymer from penetrating into pores. Patent Document 2 describes a resin composition containing an aerogel powder containing aerogel components and silica particles, and a resin. Patent Document 2 also describes how adding silica particles as a component constituting the three-dimensional network skeleton of the aerogel powder prevents resin penetration into pores and provides flexibility that prevents breakage even when stress such as compression is applied. Patent Document 3 also describes a process for producing composite pellets by melt-kneading a thermoplastic resin and aerogel particles as one step in a method for producing a porous membrane for membrane distillation. Paragraph

[0022] of the same document lists polypropylene and the like as resins that can form hydrophobic porous membranes, and paragraph

[0024] describes that when the melt viscosity of the thermoplastic resin is 100 Pa·s or more, the penetration of aerogel particles into the pores tends to be reduced. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2009-512764 [Patent Document 2] Japanese Patent Application Publication No. 2018-145332 [Patent Document 3] International Publication No. 2021 / 166088 Summary of the Invention [Problem to be solved by the invention]

[0006] However, methods such as those described in Patent Document 1, which involve forming a coating on the surface of silica aerogel or modifying the surface, require special treatment of the silica aerogel before compounding with a resin, which increases production costs. Furthermore, as described in Patent Document 2, reinforcing the silica aerogel skeleton with another component increases the solid content, which increases heat transfer by conduction and may reduce thermal insulation. Furthermore, as described in Patent Document 3, simply adjusting the melt viscosity of the thermoplastic resin makes it difficult to prevent the resin from penetrating into the pores during kneading.

[0007] The present disclosure has been made in view of the above circumstances, and aims to provide a thermal insulating material having excellent thermal insulation properties by compounding silica aerogel with a thermoplastic resin, and also to provide a method for manufacturing the thermal insulating material. [Means for solving the problem]

[0008] (1) In order to solve the above-mentioned problems, the present disclosure provides a thermal insulating material comprising silica aerogel and a non-olefin thermoplastic resin, wherein the DBA adsorption amount of the silica aerogel is 300 mmol / kg or less, and the content of the silica aerogel is 5% by mass or more and 25% by mass or less, where the total mass of the thermal insulating material is 100% by mass.

[0009] (2) The method for producing a heat insulating material according to the present disclosure is the method for producing a heat insulating material according to (1) above, characterized in that it comprises a kneading step of adding the silica aerogel having a DBA adsorption amount of 300 mmol / kg or less to the molten non-olefin thermoplastic resin and kneading the resin, and a molding step of molding the resulting kneaded mixture. [Effects of the Invention]

[0010] (1) Olefin-based thermoplastic resins, such as polypropylene, are highly hydrophobic because their main chains consist of carbon-carbon (CC) bonds and lack hydrophilic groups. In contrast, the thermal insulation material disclosed herein uses a non-olefin-based thermoplastic resin that is less hydrophobic than the olefin-based thermoplastic resin, i.e., more hydrophilic. Furthermore, the silica aerogel to be composited with the non-olefin-based thermoplastic resin is limited to one with a DBA adsorption of 300 mmol / kg or less. Untreated silica typically possesses hydrophilic properties due to the presence of a large number of silanol groups on its surface. DBA (di-n-butylamine) bonds to the silanol groups present on the silica surface. Therefore, a lower DBA adsorption indicates fewer silanol groups, i.e., higher hydrophobicity. Thus, the thermal insulation material disclosed herein combines a highly hydrophobic silica aerogel with a nearly hydrophilic thermoplastic resin. Therefore, the two materials are less compatible with each other, and the thermoplastic resin is less likely to penetrate the pores of the silica aerogel. Therefore, even when the two materials are composited, the pores of the silica aerogel are less likely to be crushed by the thermoplastic resin, and the porous structure is less likely to be damaged. Therefore, according to the heat insulating material of the present disclosure, the heat insulating effect of silica aerogel can be exhibited when composited with a thermoplastic resin, without the need for special treatment such as coating of silica aerogel. Furthermore, the content of silica aerogel is limited to 5% by mass or more and 25% by mass or less, assuming the total mass of the heat insulating material to be 100% by mass. This makes it possible to achieve both the desired heat insulating properties and maintain mechanical strength by suppressing the shedding of silica aerogel (so-called powder shedding).

[0011] (2) According to the manufacturing method of the present disclosure, in the kneading step, silica aerogel having a DBA adsorption amount of 300 mmol / kg or less is added to and kneaded with a molten non-olefin thermoplastic resin. As described above, since a highly hydrophobic silica aerogel having a DBA adsorption amount of 300 mmol / kg or less and a relatively hydrophilic non-olefin thermoplastic resin are used, the two are less likely to be miscible with each other during kneading, and the molten non-olefin thermoplastic resin is less likely to penetrate the pores of the silica aerogel. As a result, the pores of the silica aerogel are less likely to be crushed by the thermoplastic resin, and the porous structure is less likely to be damaged. In this way, according to the manufacturing method of the present disclosure, the above-mentioned insulating material of the present disclosure can be manufactured relatively easily and at low cost without performing special processing steps such as coating formation. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the heat insulating material and the method for manufacturing the same of the present disclosure will be described. Note that the heat insulating material and the method for manufacturing the same of the present disclosure are not limited to the following embodiments, and can be embodied in various forms including modifications and improvements that can be made by those skilled in the art within the scope of the present disclosure.

[0013] <Insulation material> The heat insulating material of the present disclosure includes silica aerogel and a non-olefin thermoplastic resin.

[0014] [Silica aerogel] Silica aerogel is a structure in which multiple silica particles are linked together to form a skeleton, with pores inside. The diameter of the silica particles (primary particles) that form the skeleton is preferably approximately 2 to 5 nm, and the size of the pores formed between the skeletons is preferably approximately 10 to 50 nm. Most of the pores are so-called mesopores, with a size of 50 nm or less. Because mesopores are smaller than the mean free path of air, they restrict air convection and hinder heat transfer. The shape of silica aerogel is not particularly limited, and may be spherical or irregularly shaped blocks. For example, spherical silica aerogels are easier to pack closely, allowing for a larger amount to be incorporated, which enhances their thermal insulation properties.

[0015] The average particle size of silica aerogel is preferably about 1 to 200 μm. The larger the particle size of silica aerogel, the smaller the surface area and the larger the pore volume, resulting in a greater effect in improving heat insulation. For example, an average particle size of 10 μm or more is preferable. Furthermore, when two or more types of silica aerogel with different particle sizes are used in combination, the smaller-diameter silica aerogel penetrates into the gaps between the larger-diameter silica aerogel, allowing for a larger filling amount and a greater effect in improving heat insulation. The average particle size is determined by the median diameter (D 50 For commercially available products, the catalog value may be used.

[0016] The DBA adsorption amount of silica aerogel is 300 mmol / kg or less. The lower the DBA adsorption amount, the fewer silanol groups there are, and the more hydrophobic the silica aerogel is. More preferable DBA adsorption amounts are 280 mmol / kg or less, 250 mmol / kg or less, and even 200 mmol / kg or less. It is desirable for silica aerogel to be hydrophobic not only on the surface but also inside the pores. If the pores are hydrophobic, the hydrophobicity can be maintained even if the pores crack and the inside is exposed during kneading with a non-olefin thermoplastic resin. The DBA adsorption amount of silica aerogel can be measured as follows.

[0017] First, weigh 250 mg of dried silica aerogel sample, add 50 mL of N / 500 di-n-butylamine solution (petroleum benzine solvent), and let stand at room temperature for approximately 1 hour. Next, take 25 mL of this supernatant, add 10 mL of ethanol, and then determine the titration value (A mL) at the neutralization point by potentiometric measurement using N / 100 perchloric acid solution (acetic anhydride solvent). A blank measurement was separately performed using N / 500 di-n-butylamine solution, and the titration value was designated as B mL. The DBA adsorption amount was then calculated using the following formula (I). Titration was performed twice, and the average values ​​were used as the titration values ​​A and B in formula (I). In formula (I), f is the titration value of the N / 100 perchloric acid solution. DBA adsorption amount (mmol / kg) = 80(BA)f (I)

[0018] Silica aerogel can be produced by hydrophobizing the silica aerogel during the production process, such as by adding hydrophobic groups. The method for producing silica aerogel is not particularly limited, and the drying process can be performed at normal pressure or supercritical pressure. For example, if the hydrophobizing process is performed before the drying process, supercritical drying is not required, i.e., drying at normal pressure is sufficient, making production easier and less costly. Depending on the drying method used in producing silica aerogel, silica aerogel dried at normal pressure is sometimes called a "xerogel" and silica aerogel dried at supercritical pressure is sometimes called an "aerogel." However, in this specification, both are referred to as "aerogel."

[0019] The content of silica aerogel is 5% by mass or more and 25% by mass or less, when the total mass of the heat insulating material is 100% by mass. If it is less than 5% by mass, the desired heat insulating effect cannot be obtained. A suitable content is 7% by mass or more. On the other hand, if it is more than 25% by mass, the heat insulating material becomes brittle, the mechanical strength decreases, and the silica aerogel easily falls off. A suitable content is 23% by mass or less.

[0020] [Non-olefin thermoplastic resin] The non-olefin thermoplastic resin may be appropriately selected depending on the application, taking into consideration the melting point, viscosity when melted, etc. For example, from the viewpoint of melting at a practical temperature and excellent processability, it is desirable to select from polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), polymethyl methacrylate (PMMA), polyamide (PA), and polyurethane (PU). One selected from these may be used alone, or two or more may be mixed and used. Among these, polyamide is preferred because of its high surface energy.

[0021] If the viscosity of the non-olefin thermoplastic resin when melted is too low, it may penetrate the pores of the silica aerogel. Conversely, if the viscosity is too high, it becomes difficult to knead, and a large shear stress is applied to the silica aerogel, which may lead to damage to the silica aerogel. Considering these balances, it is desirable that the melt flow rate (MFR) at the melting point of the non-olefin thermoplastic resin be 10 g / 10 min or more under a load of 2.16 kg. The MFR can be measured using a measuring device such as a melt indexer manufactured by Toyo Seiki Seisakusho Co., Ltd. An example of a non-olefin thermoplastic resin with an MFR of 10 g / 10 min or more is nylon 6.

[0022] [Other ingredients] The thermal insulation material of the present disclosure may contain other components such as reinforcing components in addition to the silica aerogel and non-olefin thermoplastic resin. For example, adding reinforcing fibers to the thermal insulation material improves the mechanical strength of the thermal insulation material by physically entangling the fibers around the silica aerogel, thereby preventing the silica aerogel from falling off. The type of reinforcing fiber is not particularly limited, but glass fiber, ceramic fiber, etc. are preferred in terms of heat resistance, etc.

[0023] <Insulating material manufacturing method> The method for producing a thermal insulating material according to the present disclosure includes a kneading step and a molding step. Each step will be described below.

[0024] [Mixing process] This step involves adding silica aerogel with a DBA adsorption of 300 mmol / kg or less to a molten non-olefin thermoplastic resin and kneading it. The non-olefin thermoplastic resin and silica aerogel have been described above. Therefore, further explanation will be omitted here. The silica aerogel may be added so that its content is 5% by mass or more and 25% by mass or less, assuming the total mass of the insulating material to be manufactured to be 100% by mass. Furthermore, if other components such as reinforcing fibers are to be blended, they may be added and kneaded in this step. For kneading, commonly used equipment such as a Banbury mixer, kneader, twin-screw kneader, or twin-screw extruder may be used. Kneading is preferably performed at a temperature above the melting point of the non-olefin thermoplastic resin, preferably at least 10°C higher than the melting point.

[0025] [Molding process] This step is to mold the kneaded material obtained in the previous step. The shape can be determined depending on the application of the heat insulating material. As a molding machine, a press, an extrusion machine, an injection molding machine, etc. can be used. [Example]

[0026] Next, the present disclosure will be described more specifically with reference to examples.

[0027] <Production of insulation samples> [Example 1] First, 36.5 g of nylon 6 was melted at 250°C using a kneading and extrusion evaluation tester (Labo Plastomill®) manufactured by Toyo Seiki Seisakusho Co., Ltd., and 10.2 g of silica aerogel B (DBA adsorption capacity: 280 mmol / kg) was added and kneaded at the same temperature for 15 minutes (kneading step). Next, the kneaded mixture was pressed into a sheet with a thickness of 2 mm (molding step). The resulting sheet-like molded product is referred to as the sample of Example 1. The silica aerogel content in the sample of Example 1 was 21.8% by mass, where the mass of the entire sample is taken as 100% by mass. The MFR of nylon 6 at 220°C (melting point), measured under a load of 2.16 kg, was 15.5 g / 10 min.

[0028] [Example 2] Except for changing the type of silica aerogel to silica aerogel C (DBA adsorption amount 160 mmol / kg), a sheet-like molded body was produced in the same manner as in Example 1. The obtained molded body is referred to as a sample of Example 2.

[0029] [Example 3] Except for changing the type of silica aerogel to silica aerogel D (DBA adsorption amount 50 mmol / kg), a sheet-like molded body was produced in the same manner as in Example 1. The obtained molded body is referred to as a sample of Example 3.

[0030] [Example 4] A sheet-shaped molded body was produced in the same manner as in Example 1, except that the type of silica aerogel was changed to silica aerogel C, the same as in Example 2, the blended amount was changed to 7.5 g, and the blended amount of nylon 6 was changed to 57.0 g. The obtained molded body is referred to as the sample of Example 4. The content of silica aerogel in the sample of Example 4 was 11.6 mass% when the mass of the entire sample was 100 mass%. The samples of Examples 1 to 4 are included in the concept of the heat insulating material of the present disclosure.

[0031] [Comparative Example 1] 114.0 g of nylon 6 was melted at 250°C using a Labo Plastomill (same as above) and then pressed into a 2 mm thick sheet. The resulting nylon 6 sheet is referred to as the sample of Comparative Example 1. Note that the samples of Comparative Examples 2 and 3 below also all have a thickness of 2 mm.

[0032] Comparative Example 2 50.0 g of polypropylene was melted at 200°C using a Labo Plastomill (same as above), and 10.2 g of silica aerogel C, the same as in Example 2, was added and kneaded for 15 minutes at the same temperature. The kneaded product was then pressed into a sheet. The resulting sheet-like sample is referred to as the sample of Comparative Example 2. The silica aerogel content in the sample of Comparative Example 2 was 16.9% by mass, with the total mass of the sample being 100% by mass.

[0033] Comparative Example 3 50.0 g of polypropylene was melted at 200° C. using a Labo Plastomill (same as above) and then pressed into a sheet. The resulting polypropylene sheet is referred to as the sample of Comparative Example 3.

[0034] [Reference example 1] Except for changing the type of silica aerogel to silica aerogel A (DBA adsorption amount 350 mmol / kg), a sheet-like molded body was produced in the same manner as in Example 1. The obtained molded body is referred to as a sample of Reference Example 1.

[0035] [Reference example 2] A sheet-like molded body was produced in the same manner as in Example 1, except that the type of silica aerogel was changed to silica aerogel C, the same as in Example 2, the blended amount was changed to 3.8 g, and the blended amount of nylon 6 was changed to 85.5 g. The obtained molded body is referred to as the sample of Reference Example 2. The content of silica aerogel in the sample of Reference Example 2 was 4.2 mass% when the mass of the entire sample was 100 mass%.

[0036] <Evaluation> The thermal conductivity and density of the produced samples were measured, and the breakage rate of the silica aerogel was calculated.

[0037] [Thermal Conductivity] The thermal conductivity of the samples was measured using a thermal conductivity measuring device, "HC-074" or "HC-110" manufactured by Eiko Seiki Co., Ltd. These two devices have different measurement ranges for thermal conductivity. Therefore, the appropriate device was selected depending on the thermal conductivity of the sample.

[0038] [density] The density of the sample was measured using a submerged displacement density and specific gravity meter "DSG-1" manufactured by Toyo Seiki Seisakusho Co., Ltd.

[0039] [Silica aerogel damage rate] The breakage rate Rb (%), which is an index showing the degree to which the silica aerogel contained in the sample was broken by kneading, was calculated based on the following formula (II): In formula (II), (Va × Rb) means the volume of broken silica aerogel, and (Va × Rb × Da / Ds) means the volume of broken and silicified silica aerogel. Di=(Wa+Wr) / {(Va-Va×Rb)+(Va×Rb×Da / Ds)+Vr}...(II) [Di: Density of the insulation sample (measured value, g / cm 3 ), Wa: mass of silica aerogel (g), Wr: mass of thermoplastic resin (g), Va: volume of silica aerogel (cm 3 ), Vr: volume of thermoplastic resin (cm 3 ), Da: density of silica aerogel (g / cm 3 ), Ds: density of silica (g / cm 3 )]

[0040] Table 1 shows the measurement results for the sample materials, silica aerogel content, kneading temperature, thermal conductivity, etc. [Table 1]

[0041] As shown in Table 1, the samples of Examples 1 to 4, which were manufactured using the non-olefin thermoplastic resin nylon 6 and silica aerogel with a DBA adsorption amount of 300 mmol / kg or less, had a low thermal conductivity of 0.120 W / m·K or less, confirming excellent thermal insulation. Furthermore, comparing the samples of Examples 1 to 3, when manufactured under the same conditions, the lower the DBA adsorption amount of the silica aerogel, the better the thermal insulation. A similar trend was observed in the sample density and the silica aerogel breakage rate. That is, the lower the DBA adsorption amount of the silica aerogel, the lower the silica aerogel breakage rate and the lower the sample density (approaching the density of the silica aerogel alone). The higher the silica aerogel breakage rate, the higher the density of the sample due to the destruction and silicification of the porous structure. For example, it is desirable for the silica aerogel breakage rate to be 70% or less. In the samples of Examples 1 to 4, the density of the silica aerogel is low, which prevents nylon 6 from penetrating into the pores of the silica aerogel and prevents damage to the silica aerogel, thereby maintaining the porous structure.

[0042] On the other hand, the sample of Comparative Example 2, which used the same silica aerogel as the sample of Example 2, had a high thermal conductivity and poor thermal insulation. Furthermore, the silica aerogel breakage rate was high, and the sample density was also high. The sample of Comparative Example 2 was manufactured using polypropylene, an olefin-based thermoplastic resin. Therefore, it is believed that molten polypropylene penetrated the pores of the silica aerogel, causing the breakage to progress. When silica is generated due to breakage of the silica aerogel, heat transfer by conduction through the silica increases. As a result, it is believed that the sample of Comparative Example 2 had a higher thermal conductivity than the sample of Comparative Example 3, which was made solely of polypropylene.

[0043] Furthermore, the sample of Reference Example 1 was produced using silica aerogel with a DBA adsorption capacity of 350 mmol / kg. Therefore, it is believed that the hydrophobicity of the silica aerogel was low, and the penetration of nylon 6 into the pores was not sufficiently suppressed. As a result, the thermal conductivity was higher than that of the samples of Examples 1 to 4. Furthermore, the sample of Reference Example 2 contained a small amount of silica aerogel. Therefore, the insulating effect of the silica aerogel was not sufficiently obtained, and the thermal conductivity was higher than that of the samples of Examples 1 to 4.

Claims

1. A heat insulating material comprising silica aerogel and a non-olefin thermoplastic resin having a lower hydrophobicity than an olefin thermoplastic resin having no hydrophilic group, the DBA adsorption amount of the silica aerogel is 300 mmol / kg or less; The heat insulating material is characterized in that the content of the silica aerogel is 5% by mass or more and 25% by mass or less, when the total mass of the heat insulating material is 100% by mass.

2. A thermal insulation material comprising silica aerogel and a non-olefin thermoplastic resin, the DBA adsorption amount of the silica aerogel is 300 mmol / kg or less; The content of the silica aerogel is 5% by mass or more and 25% by mass or less, when the total mass of the thermal insulation material is 100% by mass, The heat insulating material is characterized in that the non-olefin thermoplastic resin is at least one selected from polyamide and polyurethane.

3. 3. The heat insulating material according to claim 1, wherein the non-olefin thermoplastic resin has a melt flow rate of 10 g / 10 min or more at the melting point under a load of 2.16 kg.

4. A method for producing the heat insulating material according to claim 1 or claim 2, a kneading step of adding the silica aerogel having a DBA adsorption amount of 300 mmol / kg or less to the molten non-olefin thermoplastic resin and kneading the resin; a molding step of molding the obtained kneaded product; A method for producing a heat insulating material, comprising:

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