Vacuum heat insulation material

Abstract

To provide an environmentally-friendly vacuum heat insulation material that enables an initial value of heat insulation performance to be satisfactory and has excellent long-term reliability.SOLUTION: A vacuum heat insulation material 1 includes a core material 10 and a gas barrier film covering the core material 10. The core material 10 is decompressed and encapsulated in an outer bag 12 formed of the gas barrier film. The core material 10 includes a biomass-derived powder body, fumed silica, a radiation suppression constituent and inorganic fiber. The content of the biomass-derived powder body is 25-45 mass% of a total amount of the core material, the content of the fumed silica is 25-45 mass% of the total amount of the core material, the content of the radiation suppression constituent is 3-30 mass% of the total amount of the core material, and the content of the inorganic fiber is 2-30 mass% of the total amount of the core material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a vacuum insulation material.

Background Art

[0002] Vacuum insulation materials are used in various fields such as refrigerators and water heaters. For example, Patent Document 1 proposes a vacuum insulation material in which a core material, which is a sheet-like cellulose fiber aggregate, is vacuum-sealed in an outer bag.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to obtain an environmentally friendly vacuum insulation material, the present inventor has studied blending a biomass-derived material into the core material that is vacuum-sealed in the outer bag. Biomass-derived materials have great advantages because they may be able to suppress CO2 emissions at the time of acquisition or production as compared with industrially produced fumed silica.

[0005] In the vacuum insulation material of Patent Document 1, since a cellulose fiber aggregate, which is a biomass-derived material, is used, it is environmentally friendly. However, when a core material of a cellulose fiber aggregate is vacuum-sealed in an outer bag, the core material is likely to be crushed in the thickness direction. And the present inventor has found that there is a problem that, in addition to the changes in thickness and density associated with crushing, the internal pressure of the vacuum insulation material increases, resulting in deterioration of the initial value of the heat insulation performance. Furthermore, since cellulose fibers are hygroscopic, there is also a possibility that the long-term heat insulation performance gradually decreases as the internal pressure increases. Thus, there is still room for improvement in the long-term reliability of the heat insulation performance.

[0006] The present invention provides an environmentally friendly vacuum insulation material that has a good initial heat insulation performance and excellent long-term reliability.

Means for Solving the Problems

[0007] The present invention has the following aspects. [1] A vacuum insulation material comprising a core material and a gas barrier film covering the core material, wherein the core material is vacuum-encapsulated in an outer bag formed of the gas barrier film, the core material contains biomass-derived powder, fumed silica, a radiation suppression component, and inorganic fibers, the content ratio of the biomass-derived powder is 25 to 45% by mass of the total amount of the core material, the content ratio of the fumed silica is 25 to 45% by mass of the total amount of the core material, the content ratio of the radiation suppression component is 3 to 30% by mass of the total amount of the core material, and the content ratio of the inorganic fibers is 2 to 30% by mass of the total amount of the core material. [2] The vacuum insulation material according to [1], wherein the biomass-derived powder is at least one selected from the group consisting of biomass-derived silica, rice husk, rice straw, bagasse, wheat straw, and sawdust. [3] The vacuum insulation material according to [2], wherein the biomass-derived silica is at least one selected from the group consisting of rice husk ash silica and rice straw ash silica. [4] The vacuum insulation material according to [3], wherein at least one selected from the group consisting of the rice husk ash silica and the rice straw ash silica is amorphous silica, and the content of crystalline silica is less than 0.1% by mass. [5] The vacuum insulation material according to [3] or [4], wherein the silica content of at least one selected from the group consisting of the rice husk ash silica and the rice straw ash silica is 90% by mass or more. [6] The vacuum insulation material according to any one of [3] to [5], wherein the silica content of the biomass-derived powder is 70% by mass or more. [7] The silica content of the biomass-derived powder is 30% by mass or less, the vacuum insulation material according to [1] or [2]. [8] The bulk density of the biomass-derived powder is 0.25 g / cm 3 or less, the vacuum insulation material according to any one of [1] to [7]. [9] The particle size distribution of the biomass-derived powder has a peak in the range of 1 to 300 μm, the vacuum insulation material according to any one of [1] to [8].

[10] The bulk density of the fumed silica is 0.1 g / cm 3 or less, the vacuum insulation material according to any one of [1] to [9].

[11] The radiation suppression component is at least one selected from the group consisting of graphite, silicon carbide, titanium oxide, tin oxide, and potassium titanate, the vacuum insulation material according to any one of [1] to

[10] .

[12] The inorganic fiber is at least one selected from the group consisting of alumina fiber, glass fiber, silica fiber, glass wool, rock wool, carbon fiber, and silica-alumina fiber, the vacuum insulation material according to any one of [1] to

[11] .

[13] At least a part of the inorganic fiber is glass fiber, The ratio of the total mass of Na2O and K2O in the glass fiber to the total mass of the glass fiber is 11% by mass or less, the vacuum insulation material according to any one of [1] to

[12] .

[14] The fiber length of the inorganic fiber is 0.1 to 10 mm, and The fiber length distribution Lw / Ln represented by the ratio of the number average fiber length Ln to the weight average fiber length Lw of the inorganic fiber is 1.05 or more, the vacuum insulation material according to any one of [1] to

[13] .

[15] The thickness reduction rate when the core material is vacuum-sealed in the outer bag is 20% or less, the vacuum insulation material according to any one of [1] to

[14] .

Advantages of the Invention

[0008] According to the present invention, there is provided an environmentally friendly vacuum insulation material having a good initial value of heat insulation performance and excellent long-term reliability.

Brief Description of the Drawings

[0009]

Figure 1

Embodiments for Carrying Out the Invention

[0010] The meanings of the terms are as follows. The "core material" means a molded body composed of a raw material mixture in a vacuum insulating material, which has been formed into a desired shape by molding. "Fumed silica" means amorphous and spherical silica fine particles composed of primary particles without pores. Fumed silica can be obtained, for example, by vaporizing silicon tetrachloride and performing a gas-phase reaction in a high-temperature hydrogen flame. The "radiation suppression component" means particles that suppress radiative heat transfer by reflecting or scattering infrared light, or by once absorbing infrared light and radiating isotropically when re-radiating the temperature rise due to the absorption, thereby disturbing the directionality of the infrared light.

[0011] The "average aggregate particle size D50" is the volume-based cumulative 50% diameter determined by the laser diffraction scattering method. In the volume-based frequency particle size distribution by the laser diffraction scattering method, the cumulative curve is obtained with the total volume of the particle population as 100%, and the particle size at the point where the cumulative volume becomes 50% on the cumulative curve is defined as D50.

[0012] The "particle size distribution of the biomass-derived powder" is determined by the laser diffraction scattering method. The "bulk density of the biomass-derived powder" is determined by the constant mass measurement method of JIS R1628 1997. The "specific surface area of fumed silica" is measured by the nitrogen adsorption method (BET method). The "bulk density of fumed silica" is determined by the constant mass measurement method of JIS R1628 1997.

[0013] The coefficient of thermal expansion of the inorganic fiber is measured using a thermomechanical analyzer (TMA) in the temperature range of 50 to 400 °C at a heating rate of 5 °C / min. The Young's modulus of the inorganic fiber is measured by the tensile test method. The ratios of Na2O and K2O in the glass fiber are determined from various compositional analyses performed on the glass fiber. The alkali elution amount of the glass fiber is measured according to the method described in JIS R3503-1994.

[0014] "Fiber length D10" means the fiber length at the point where the cumulative number is 10% in the cumulative number distribution curve with the total number of the fiber length distribution determined on a number basis taken as 100%. "Fiber length D50" means the fiber length at the point where the cumulative number is 50% in the cumulative number distribution curve with the total number of the fiber length distribution determined on a number basis taken as 100%. "Fiber length D90" means the fiber length at the point where the cumulative number is 90% in the cumulative number distribution curve with the total number of the fiber length distribution determined on a number basis taken as 100%. The fiber length distribution is determined from the frequency distribution and the cumulative number distribution curve obtained by randomly measuring the lengths of 50 or more fibers in a photograph observed with an optical microscope.

[0015] "Density of the core material" means the average density of the entire core material. Three samples of 30 mm × 150 mm are cut out from arbitrary locations of the core material, each sample is quartered in the thickness direction to make test pieces, the density of each test piece is measured, and the average of these values is taken as the density of the core material.

[0016] "Density of the core material encapsulated under reduced pressure" means the average density of the entire core material in the state of being encapsulated under reduced pressure in the outer bag, and is a value measured by the following measurement method. Measurement method: Put the core material into the outer bag, place it in a vacuum chamber with a heat-sealing function, heat-seal and seal the opening of the outer bag while reducing the pressure in the chamber to 5 Pa, and return the outside of the outer bag to atmospheric pressure conditions to obtain a vacuum insulation material. Calculate the weight of the core material encapsulated under reduced pressure from the weight of the vacuum insulation material and the weight of the outer packaging material. Calculate the volume from the average value of the side lengths and thicknesses at five locations. Calculate the density from the obtained core material weight and volume. This value is taken as the density of the core material encapsulated under reduced pressure.

[0017] The "thickness of the core material" means the average thickness of the entire core material. Measure the thickness at any five locations in the core material and average them to obtain the thickness of the core material. The "total thickness of the vacuum insulation material" refers to the thickness of the portion excluding the ear-folded part (folded-back part) at the end of the gas-barrier film. The "thickness reduction rate" is determined by the method described in the examples.

[0018] The "~" indicating a numerical range means including the numerical values described before and after ~ as the lower limit value and the upper limit value. The numerical ranges disclosed in this specification can be combined arbitrarily with their lower limit values and upper limit values to form new numerical ranges.

[0019] Hereinafter, several embodiments will be described with appropriate reference to the drawings as needed. The following description relates to representative examples of embodiments of the invention, and the invention is not limited to the following description. Also, the dimensional ratios in each drawing may be different from the actual ones for convenience of explanation.

[0020] The vacuum insulation material according to the embodiment includes a core material and a gas-barrier film covering the core material. The core material is encapsulated under reduced pressure in an outer bag formed of the gas-barrier film.

[0021] FIG. 1 is a cross-sectional view showing an example of a vacuum insulation material. The vacuum insulation material 1 includes a core material 10 and an outer bag 12. The core material 10 is encapsulated under reduced pressure in the outer bag 12. For example, the core material 10 is housed in an outer bag 12 formed by making a gas-barrier film into a bag shape, and the vacuum insulation material 1 is obtained by sealing the opening of the outer bag 12 under reduced pressure conditions.

[0022] [Core material] Examples of the shape of the core material include, but are not limited to, a flat plate shape. The shape of the core material viewed from the thickness direction can also be appropriately designed according to the application. For example, a square, a rectangle, or a circle can be mentioned.

[0023] The core material contains a biomass-derived powder, fumed silica, a radiation suppression component, and inorganic fibers. In one example, within a range that does not impair the effects of the invention, the core material may further contain other materials other than the biomass-derived powder, fumed silica, the radiation suppression component, and inorganic fibers.

[0024] (Biomass-derived powder) Phosphorus oxides such as phosphorus pentoxide may be detected from the biomass-derived powder. The detected amount of the phosphorus oxide may be, for example, 0.01 to 3.0% by mass of the total amount of the biomass-derived powder, 0.03 to 2.0% by mass, or 0.05 to 1.0% by mass. Further, the detected amount of the phosphorus oxide may be 0.0025 to 1.35% by mass of the total amount of the core material, 0.0075 to 0.9% by mass, or 0.0125 to 0.45% by mass.

[0025] Examples of the biomass-derived powder include biomass-derived silica, rice husks, rice straw, bagasse, wheat straw, and sawdust. However, the biomass-derived powder is not limited to those exemplified here. The biomass-derived powder may be used alone or in combination of two or more.

[0026] Examples of the biomass-derived silica include rice husk ash silica and rice straw ash silica. The biomass-derived silica may be used alone or in combination of two or more.

[0027] Rice husk ash silica and rice straw ash silica are obtained by combustion treatment. By controlling the combustion conditions of rice husks and rice straw, substantially amorphous silica can be obtained, and the generation of undesirable crystalline silica can be suppressed. Therefore, in one example, it is preferable that rice husk ash silica and rice straw ash silica are amorphous silica. Substantially being amorphous silica can be confirmed by being less than 0.1% which is the detection limit of X-ray diffraction analysis method. Thus, in a preferred example, the content of crystalline silica in rice husk ash silica and rice straw ash silica is less than 0.1% by mass.

[0028] In one example, the silica content of rice husk ash silica and rice straw ash silica is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 97% by mass or more. Generally, the calcined ash obtained by burning rice husks or rice straw contains many impurities such as metals. In order to obtain highly pure silica as the core material of a vacuum insulation material, it is preferable to wash with an acid. By washing with an acid, highly pure silica with a silica content of 90% or more can be obtained. As the acid used for washing, for example, citric acid and oxalic acid are suitable.

[0029] When the biomass-derived powder is, for example, a powder before burning such as biomass-derived silica, rice husks, rice straw, bagasse, wheat straw, and sawdust, the silica content of the biomass-derived powder may be, for example, 30% by mass or less, 25% by mass or less, or 20% by mass or less. In this case, the lower limit of the silica content of the biomass-derived powder is not particularly limited, but may be, for example, 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, or even a trace amount so small that it cannot be detected.

[0030] On the one hand, when the biomass-derived powder is a powder after combustion such as rice husk ash silica or rice straw ash silica, the silica content of the biomass-derived powder may be, for example, 70% by mass or more, 80% by mass or more, or 90% by mass or more. In this case, the upper limit of the silica content of the biomass-derived powder is not particularly limited, but may be, for example, 95% by mass or less, 97% by mass or less, 99.9% by mass or less, or 100% by mass.

[0031] The average agglomerated particle size D50 of the biomass-derived powder is preferably 10 to 100 μm, more preferably 20 to 90 μm, and even more preferably 30 to 80 μm. When the average agglomerated particle size D50 of the biomass-derived powder is equal to or greater than the lower limit value within the above numerical range, it is easy to suppress scattering when the core material is evacuated and encapsulated. When the average agglomerated particle size D50 of the biomass-derived powder is equal to or less than the upper limit value within the above numerical range, it is easy to suppress solid heat transfer. Therefore, excellent heat insulation performance is easily obtained.

[0032] The bulk density of the biomass-derived powder is not particularly limited, but may be, for example, 0.25 g / cm 3 or less, 0.20 g / cm 3 or less, 0.18 g / cm 3 or less. When the bulk density of the biomass-derived powder is equal to or less than the above upper limit value, it is easy to mold the core material into a desired shape. The lower limit of the bulk density of the biomass-derived powder is not particularly limited, but may be, for example, 0.04 g / cm 3 or more, 0.05 g / cm 3 or more, 0.08 g / cm 3 or more.

[0033] The particle size distribution of the biomass-derived powder may have a peak in the range of, for example, 1 to 300 μm, may have a peak in the range of 10 to 300 μm, or may have a peak in the range of 15 to 280 μm. When the peak position of the particle size distribution of the biomass-derived powder is equal to or higher than the lower limit value within the above numerical range, it is easy to form the core material into a desired shape even if the amount of the biomass-derived powder used is increased. As a result, an environmentally friendly vacuum insulation material can be easily obtained. When the peak position of the particle size distribution of the biomass-derived powder is equal to or lower than the upper limit value within the above numerical range, it is easy to suppress solid heat conduction. Therefore, excellent heat insulation performance can be easily obtained.

[0034] (Fumed silica) The average agglomerated particle diameter D50 of fumed silica is preferably 5 to 50 μm, more preferably 5 to 30 μm, and even more preferably 5 to 20 μm. When the average agglomerated particle diameter D50 of fumed silica is equal to or higher than the lower limit value within the above numerical range, it is easy to suppress scattering when the core material is encapsulated under reduced pressure. When the average agglomerated particle diameter D50 of fumed silica is equal to or lower than the upper limit value within the above numerical range, it is easy to suppress solid heat conduction. Therefore, excellent heat insulation performance can be easily obtained.

[0035] The specific surface area of fumed silica is preferably 50 to 400 m 2 / g, more preferably 100 to 350 m 2 / g, and even more preferably 200 to 300 m 2 / g. When the specific surface area of fumed silica is within the above numerical range, excellent heat insulation performance can be easily obtained.

[0036] Fumed silica may be a commercially available product. Examples of commercially available fumed silica include Aerosil 200 (specific surface area 200 m 2 / g, manufactured by Nippon Aerosil Co., Ltd.), Aerosil 300 (specific surface area 300 m 2 / g, manufactured by Nippon Aerosil Co., Ltd.), CAB-O-SIL M-5 (specific surface area 200 m 2 / g, manufactured by Cabot Japan Ltd.), CAB-O-SIL H-300 (specific surface area 300 m 2 / g, manufactured by Cabot Japan Ltd.), Rheolosil QS30 (specific surface area 300 m 2Examples include fumed silica manufactured by Tokuyama Corporation. However, fumed silica is not limited to those exemplified herein. Fumed silica may be used alone or in combination of two or more.

[0037] The bulk density of fumed silica is not particularly limited. For example, it may be 0.1 g / cm 3 or less, or may be 0.05 g / cm 3 or less, or may be 0.04 g / cm 3 or less. When the bulk density of fumed silica is at or below the above upper limit value, it is easy to mold the core material into a desired shape. The lower limit of the bulk density of fumed silica is not particularly limited. For example, it may be 0.01 g / cm 3 or more, or may be 0.02 g / cm 3 or more, or may be 0.03 g / cm 3 or more.

[0038] (Radiation suppression component) Examples of the radiation suppression component include metal particles such as aluminum particles, silver particles, and gold particles, graphite, carbon black, silicon carbide, titanium oxide, tin oxide, and potassium titanate. However, the radiation suppression component is not limited to those exemplified herein. The radiation suppression component may be used alone or in combination of two or more.

[0039] From the viewpoints of thermal conductivity and workability, as the radiation suppression component, one or more selected from graphite, silicon carbide, titanium oxide, tin oxide, and potassium titanate are preferable, one or more selected from the group consisting of graphite and silicon carbide are more preferable, and graphite is even more preferable.

[0040] (Inorganic fiber) Examples of the inorganic fibers include, for example, alumina fibers, glass fibers, mullite fibers, silica fibers, glass wool, rock wool, carbon fibers, slag wool, silicon carbide fibers, silica-alumina fibers, silica-alumina-magnesia fibers, silica-alumina-zirconia fibers, and silica-magnesia-calcia fibers. However, the inorganic fibers are not limited to those exemplified herein. The inorganic fibers may be used alone or in combination of two or more.

[0041] As the inorganic fibers, one or more selected from alumina fibers, glass fibers, silica fibers, glass wool, rock wool, carbon fibers, and silica-alumina fibers are preferable, one or more selected from the group consisting of glass fibers, silica-alumina fibers, and glass wool are more preferable, and glass fibers are even more preferable. These inorganic fibers are preferable in that they have little volatilization of gas components under vacuum, are likely to suppress a decrease in heat insulation performance due to a decrease in vacuum degree, have excellent heat resistance, can increase the strength of the core material, are low in price, and are easy to handle.

[0042] When the core material contains glass fibers in at least a part thereof as the inorganic fibers, the ratio of the total mass of Na2O and K2O in the glass fibers to the total mass of the glass fibers (hereinafter also referred to as "ratio A") is preferably 11% by mass or less. In the case of glass fibers with a ratio A of 11% by mass or less, it is easy to suppress the gradual increase in thermal conductivity caused by moisture infiltrating into the vacuum insulation material. Therefore, the long-term reliability is likely to be improved. The mechanism by which such an effect is obtained is not necessarily clear, but it is considered as follows.

[0043] In a vacuum insulation material in which a core material is vacuum-sealed in an outer bag, moisture may gradually penetrate from the outer surface of the outer bag and the heat-sealed portion. In the case of glass fibers with a proportion A exceeding 11% by mass, the affinity between the glass fibers and water is high. Therefore, since the core material tends to retain moisture, silanol groups may be generated. For example, in the vacuum insulation material disclosed in Japanese Patent Application Laid-Open No. 2008-215538, in order to enable molding at a lower temperature, an alkali-containing glass with a high content of sodium and potassium components is used for the glass fibers, so there is a risk that the long-term heat insulation performance may deteriorate. On the other hand, if glass fibers with a proportion A of 11% by mass or less are used, it becomes difficult for the core material to retain moisture. As a result, since it is suppressed that the thermal conductivity of the core material gradually increases due to the moisture that has penetrated into the vacuum insulation material, it is considered that the long-term reliability of the heat insulation performance of the vacuum insulation material is improved.

[0044] From the point of further improving the long-term reliability of the vacuum insulation material, the proportion A is preferably 11% by mass or less, more preferably 6% by mass or less, and even more preferably 3% by mass or less. Glass fibers imparted with meltability by using boric acid or the like instead of the alkali component may be used. As in this example, an alkali-free glass substantially free of Na2O and K2O can also be preferably used.

[0045] In one example, when glass fibers with a proportion A not exceeding the above upper limit are used as inorganic fibers, the glass constituting the glass fibers is not particularly limited, but examples include aluminoborosilicate glass, borosilicate glass, and aluminosilicate glass. The glass constituting the glass fibers may be used alone or in combination of two or more. Among them, one or more selected from aluminoborosilicate glass, borosilicate glass, and aluminosilicate glass are preferred. Also, as the glass fibers, E glass fibers are particularly preferred.

[0046] In one example, the alkali elution amount of the glass fiber is preferably 1.9 mL / g or less, more preferably 1 mL / g or less, and even more preferably 0.5 mL / g or less. When the alkali elution amount of the glass fiber is equal to or less than the above upper limit value, it is easy to suppress the increase in the thermal conductivity due to the moisture that has penetrated into the vacuum insulation material.

[0047] In one example, the range of the fiber length of the inorganic fiber in the core material is 0.1 to 10 mm, and the fiber length distribution Lw / Ln is preferably 1.05 or more. In this case, the fiber length distribution of the inorganic fiber becomes wider. By using inorganic fibers with a wide fiber length distribution, the compressive strength of the core material increases. Therefore, when the core material is vacuum-encapsulated in the outer bag, it is difficult to be crushed. As a result, since the low density of the core material after vacuum encapsulation is maintained, the thermal conductivity becomes low. Therefore, excellent heat insulation performance can be easily obtained.

[0048] The reason why the compressive strength of the core material increases by using inorganic fibers with a wide fiber length distribution is not necessarily clear, but it is considered that because the fiber length distribution is wide, the orientation of the inorganic fibers is likely to vary, and thus the compressive strength tends to increase isotropically.

[0049] Here, Ln is the number average fiber length of the inorganic fiber. Ln is obtained by the following formula 1 from the frequency distribution based on the number obtained by measuring the lengths of 50 or more inorganic fibers randomly in a photograph observed with an optical microscope. Lw is the weight average fiber length of the inorganic fiber. Lw is obtained by the following formula 2 from the frequency distribution based on the weight obtained by measuring the lengths of 50 or more inorganic fibers randomly in a photograph observed with an optical microscope.

[0050]

Number

[0051] In formulas 1 and 2, Ni is the number of fibers in each histogram of the average length Li.

[0052] The fiber length of the inorganic fiber may be, for example, 0.1 to 10 mm, may be 1 to 8 mm, or may be 2 to 6 mm. When the fiber length of the inorganic fiber is equal to or greater than the lower limit value within the above numerical range, a high-strength vacuum heat insulating material can be easily obtained. Also, the compressive strength of the core material is likely to be improved. When the fiber length of the inorganic fiber is equal to or less than the upper limit value within the above numerical range, the influence of solid heat conduction of the fiber can be easily reduced. Therefore, a vacuum heat insulating material with good thermal conductivity can be easily obtained.

[0053] Lw / Ln is represented by the ratio of the number average fiber length Ln to the weight average fiber length Lw of the inorganic fiber. Lw / Ln indicates the fiber length distribution of the inorganic fiber. Lw / Ln is preferably 1.05 or more, more preferably 1.10 or more, and even more preferably 1.20 or more. The upper limit of Lw / Ln is not particularly limited, but may be, for example, 2.00 or less, may be 1.80 or less, or may be 1.60 or less. The larger Lw / Ln is, the wider the fiber length distribution of the inorganic fiber means.

[0054] The spread index of the fiber length of the inorganic fiber is represented by (D90 - D10) / D50 using the fiber length D10 of the inorganic fiber, the fiber length D50 of the inorganic fiber, and the fiber length D90 of the inorganic fiber. The larger (D90 - D10) / D50 is, the wider the fiber length distribution of the inorganic fiber indicates. (D90 - D10) / D50 is preferably 0.21 or more, more preferably 0.4 or more, and even more preferably 0.6 or more. When (D90 - D10) / D50 is equal to or greater than the above lower limit value, the compressive strength of the core material is likely to be high. Also, a vacuum heat insulating material with excellent heat insulating performance can be easily obtained. The upper limit of (D90 - D10) / D50 is not particularly limited, but may be, for example, 2.0 or less, may be 1.9 or less, or may be 1.8 or less.

[0055] The fiber length D10 of the inorganic fiber may be, for example, 2.4 mm or less, may be 2.0 mm or less, or may be 1.8 mm or less. The fiber length D50 of the inorganic fiber may be, for example, 2.0 to 5.0 mm, may be 2.1 to 4.8 mm, or may be 2.15 to 4.6 mm. The fiber length D90 of the inorganic fiber may be, for example, 4.0 to 7.0 mm, 3.5 to 6.7 mm, or 3.2 to 6.5 mm.

[0056] In one example, the coefficient of thermal expansion of the inorganic fiber is 90×10 -7 / °C or less is preferable, 80×10 -7 / °C or less is more preferable, and 50×10 -7 / °C or less is even more preferable. When the coefficient of thermal expansion of the inorganic fiber is at or below the above upper limit value, the initial thermal conductivity becomes low. Therefore, a vacuum heat insulating material excellent in heat insulating performance can be easily obtained. The mechanism by which the initial thermal conductivity becomes low is not necessarily clear, but when the coefficient of thermal expansion of the inorganic fiber is at or below the above upper limit value, the inorganic fiber is less likely to change its shape when dried after the core material is formed. Also, voids are less likely to occur around the inorganic fiber. As a result, it is considered that the deterioration of the initial thermal conductivity is suppressed. The lower limit of the coefficient of thermal expansion of the inorganic fiber is not particularly limited.

[0057] In one example, the Young's modulus of the inorganic fiber is preferably 50 GPa or more, more preferably 60 GPa or more, and even more preferably 70 GPa or more. When the Young's modulus of the inorganic fiber is at or above the above lower limit value, the strength of the core material is likely to be improved. The upper limit of the Young's modulus of the inorganic fiber is not particularly limited, but may be, for example, 95 GPa or less, or 90 GPa or less.

[0058] (Other materials) As long as the effects of the present invention are not impaired, powders derived from biomass, fumed silica, radiation suppressing components, and other materials other than the inorganic fiber may be blended in the core material. Examples of other materials include binders and porous silica. The other materials may be used alone or in combination of two or more.

[0059] Examples of the binder include inorganic binders such as sodium silicate, aluminum phosphate, magnesium sulfate, and magnesium chloride. However, the binder is not limited to inorganic binders and may be an organic binder.

[0060] (Composition of the core material) The content ratio of the biomass-derived powder is 25 to 45% by mass of the total amount of the core material. The content ratio of the biomass-derived powder is preferably 26 to 43% by mass, more preferably 27 to 41% by mass, and even more preferably 28 to 40% by mass of the total amount of the core material. When the content ratio of the biomass-derived powder is equal to or higher than the lower limit value within the above numerical range, an environmentally friendly vacuum insulation material can be obtained. When the content ratio of the biomass-derived powder is equal to or lower than the upper limit value within the above numerical range, it is easy to mold the core material into a desired shape.

[0061] The content ratio of fumed silica is 25 to 45% by mass of the total amount of the core material. The content ratio of fumed silica is preferably 27 to 43% by mass, more preferably 30 to 41% by mass, and even more preferably 35 to 40% by mass of the total amount of the core material. When the content ratio of fumed silica is equal to or higher than the lower limit value within the above numerical range, it is easy to obtain a core material with high strength. Also, it is easy to mold the core material into a desired shape. When the content ratio of fumed silica is equal to or lower than the upper limit value within the above numerical range, an environmentally friendly vacuum insulation material can be obtained.

[0062] The content ratio of the radiation suppression component is 3 to 30% by mass of the total amount of the core material. The content ratio of the radiation suppression component is preferably 5 to 27% by mass, more preferably 8 to 25% by mass, and even more preferably 10 to 20% by mass of the total amount of the core material. When the content ratio of the radiation suppression component is equal to or higher than the lower limit value within the above numerical range, the deterioration of the thermal conductivity of the vacuum insulation material due to radiation within the core material can be suppressed. When the content ratio of the radiation suppression component is equal to or lower than the upper limit value within the above numerical range, the increase effect of solid heat transfer by the radiation suppression component can be suppressed. Therefore, excellent heat insulation performance can be easily obtained.

[0063] The content ratio of the inorganic fiber is 2 to 30% by mass of the total amount of the core material. The content ratio of the inorganic fiber is preferably 0.5 to 25% by mass, more preferably 1.0 to 20% by mass, and even more preferably 2.0 to 10% by mass of the total amount of the core material. When the content ratio of the inorganic fiber is equal to or higher than the lower limit value within the above numerical range, it is easy to obtain a core material with high strength. When the content ratio of the inorganic fiber is equal to or lower than the upper limit value within the above numerical range, the increase in solid heat transfer due to the fiber can be suppressed. Therefore, it is easy to suppress the deterioration of the heat insulation performance.

[0064] When the core material further contains other materials in addition to the powder derived from biomass, fumed silica, radiation suppression component, and inorganic fiber, the content ratio of the other materials may be 0.5 to 20% by mass of the total amount of the core material, may be 1.0 to 15% by mass, or may be 1.5 to 10% by mass. When the content ratio of the other materials is equal to or higher than the lower limit value within the above numerical range, it is easy to impart the characteristics of the other materials to the core material. When the content ratio of the other materials is equal to or lower than the upper limit value within the above numerical range, the effects of the present invention are less likely to be impaired.

[0065] (Physical properties of the core material) The thickness of the core material is preferably 2 mm or more, more preferably 5 mm or more, and even more preferably 8 mm or more. When the thickness of the core material is equal to or greater than the lower limit value, it is easy to exhibit heat insulation performance in consideration of the influence of heat bridges generated at the ends of the vacuum insulation material. The upper limit of the thickness of the core material is not particularly limited, and for example, it may be 50 mm or less, 40 mm or less, or 30 mm or less.

[0066] The density of the core material is preferably 0.15 to 0.25 g / cm 3 and more preferably 0.15 to 0.20 g / cm 3 and even more preferably 0.15 to 0.18 g / cm 3 When the density of the core material is equal to or higher than the lower limit value within the above numerical range, the handling of the core material is easy. Also, when pressure-reducing encapsulation is performed, the powder derived from biomass, fumed silica, and radiation suppression component are less likely to scatter from the core material. When the density of the core material is equal to or lower than the upper limit value within the above numerical range, it is easy to obtain a vacuum insulation material having excellent heat insulation performance.

[0067] The density of the pressure-reducing encapsulated core material is preferably 0.30 g / cm 3 or less, more preferably 0.20 g / cm 3 or less, and even more preferably 0.18 g / cm 3The following is more preferable. When the density of the core material encapsulated under reduced pressure is equal to or less than the upper limit value, a vacuum heat insulating material with low thermal conductivity and excellent heat insulation performance can be easily obtained. In terms of easy handling of the core material and the fact that powders derived from biomass, fumed silica, and radiation suppressing components are less likely to scatter from the core material during encapsulation under reduced pressure, the density of the core material encapsulated under reduced pressure is 0.11 g / cm 3 or more is preferable, and 0.12 g / cm 3 or more is preferable, and 0.13 g / cm 3 or more is more preferable. These lower limit values and upper limit values can also be arbitrarily combined. For example, the density of the core material encapsulated under reduced pressure is preferably 0.11 to 0.30 g / cm 3 and more preferably 0.13 to 0.20 g / cm 3 .

[0068] [Outer bag] The size and shape of the outer bag are not particularly limited and can be set according to the size and shape of the target vacuum heat insulating material. The gas barrier film used for the outer bag is a film having airtightness. For example, a laminated film provided with a sealant layer and a barrier layer can be mentioned. However, the gas barrier film is not limited to this example. The gas barrier film may further have other layers such as an adhesive layer and a protective layer in addition to the sealant layer and the barrier layer.

[0069] The sealant layer is provided as the innermost layer of the gas barrier film. The material forming the sealant layer is not particularly limited. For example, polyolefin resins such as low density polyethylene, medium density polyethylene, linear low density polyethylene (LLDPE), and polypropylene can be mentioned. The constituent material of the sealant layer may be one type or two or more types. The sealant layer may have a single-layer structure or a multi-layer structure.

[0070] Examples of the barrier layer include an aluminum vapor deposition layer, an aluminum foil layer, and a metal oxide vapor deposition layer made of alumina, silica, or the like. The aluminum vapor deposition layer and the metal oxide vapor deposition layer can be formed by vapor-depositing aluminum or a metal oxide on a vapor deposition substrate. Examples of the vapor deposition substrate include resin films such as polyethylene terephthalate (PET) films and ethylene-vinyl alcohol copolymer (EVOH) films. However, the resin film is not limited to this example. In the gas barrier film, the number of barrier layers is preferably 2 or more, more preferably 2 to 6 layers, and even more preferably 2 to 4 layers.

[0071] As the adhesive used for the adhesive layer, an adhesive suitable for dry lamination such as a two-component curable polyurethane-based adhesive, an acrylic-based adhesive, or an epoxy-based adhesive is preferable, and a two-component curable polyester-based adhesive is particularly preferable.

[0072] The protective layer is preferably provided on the outermost layer, but is not limited thereto. The protective layer may be provided between the barrier layer and the sealant layer, or may be provided between two barrier layers. When the gas barrier film has a protective layer, the protective layer may be one layer or two or more layers.

[0073] Examples of the material for forming the protective layer include polyamide resins such as nylon 6, nylon 66, and a copolymer of nylon 66 and nylon 6, and polyester resins such as PET and polyethylene naphthalate. However, the material of the protective layer is not limited to this example.

[0074] The thickness of the gas barrier film is preferably 40 to 65 μm, more preferably 45 to 65 μm, and even more preferably 47 to 62 μm. When the thickness of the gas barrier film is equal to or greater than the lower limit value within the above numerical range, the film has excellent strength. When the thickness of the gas barrier film is equal to or less than the upper limit value within the above numerical range, the weight of the vacuum insulation material can be reduced.

[0075] [Properties of Vacuum Insulation Material] In a vacuum insulation material, the thickness reduction rate when the core material is vacuum-encapsulated in the outer bag is preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. When the thickness reduction rate is below the above upper limit value, the change in thickness due to crushing when the core material is vacuum-encapsulated in the outer bag is small. Therefore, it is easy to suppress the change in the density of the core material before and after encapsulation and the increase in the internal pressure of the vacuum insulation material. As a result, it is easy to obtain a vacuum insulation material excellent in both the initial value of the heat insulation performance and the long-term reliability.

[0076] The degree of vacuum inside the outer bag of the vacuum insulation material is preferably 1×10 3 Pa or less, more preferably 5×10 2 Pa or less, and even more preferably 3×10 2 Pa or less. When the degree of vacuum inside the outer bag of the vacuum insulation material is below the above upper limit value, excellent heat insulation performance can be obtained, and the life of the vacuum insulation material is prolonged. In terms of ease of depressurization inside the outer bag, the degree of vacuum inside the outer bag is preferably 1 Pa or more, more preferably 10 Pa or more. These lower limit values and upper limit values can also be arbitrarily combined.

[0077] The total thickness of the vacuum insulation material may be, for example, 3 mm or more, 5 mm or more, or 10 mm or more. Also, the total thickness of the vacuum insulation material may be 40 mm or less, 30 mm or less. These lower limit values and upper limit values can also be arbitrarily combined.

[0078] [Method for manufacturing a vacuum insulation material] The method for manufacturing the vacuum insulation material according to the embodiment is not particularly limited. For example, a method including press-molding a raw material mixture containing biomass-derived powder, fumed silica, a radiation suppression component, and inorganic fibers within the range of the above-described composition to obtain a core material, and vacuum-encapsulating the core material in an outer bag formed of a gas barrier film can be mentioned.

[0079] The method for obtaining a raw material mixture containing biomass-derived powder, fumed silica, a radiation suppression component, and inorganic fibers is not particularly limited. For example, methods using a V-type mixer, a blender with a stirrer, etc. can be mentioned, but it is not limited thereto, and various methods can be used.

[0080] When using inorganic fibers with a fiber length range of 0.1 to 10 mm and a fiber length distribution Lw / Ln of 1.05 or more, for example, the desired inorganic fibers can be prepared in advance by the following Method 1, Method 2, or Method 3. Method 1: A method of widening the fiber length distribution by pulverizing a part of inorganic fibers with a fiber length of 1.5 to 10 mm using a pulverizing device such as a ball mill. Method 2: A method of obtaining a fiber mixture with a wide fiber length distribution by mixing two or more inorganic fibers with different fiber lengths in the range of 0.1 to 10 mm. Method 3: A method of pulverizing a part of the fiber mixture using a pulverizing device.

[0081] In Method 1, Method 2, and Method 3, while pulverizing the inorganic fibers using a pulverizing device, inorganic fibers of the same fiber length may be sequentially introduced into the pulverizing device. When using a ball mill, the pulverization treatment time is preferably 1 to 10 hours, more preferably 2 to 5 hours.

[0082] For the press molding of the raw material mixture, for example, the manufacturing apparatus for a heat insulating plate described in paragraphs 0013 to 0028 of JP-A-2016-102511 can be used. The manufacturing apparatus includes an upper mold having a convex portion with a reduced-pressure chamber formed therein and a lower mold having a concave portion, and a plurality of exhaust holes are formed in the surface of the convex portion on the concave portion side. With the raw material mixture being put into the concave portion of the lower mold, the upper mold is lowered by a cylinder, the convex portion of the upper mold is fitted into the concave portion of the lower mold, and the reduced-pressure chamber of the upper mold is depressurized by a vacuum pump, thereby performing press molding while exhausting the air in the raw material mixture. By adjusting the amount of the raw material mixture put into the concave portion of the lower mold and the press pressure, the thickness and density of the core material can be controlled.

[0083] By using an apparatus having such an exhaust mechanism, even when manufacturing a thick-film core material at a low press pressure, it is easy to suppress the generation of voids in the core material. Also, in the thickness direction of the obtained core material, the density of the central portion tends to be lower than that of the surface layer portions on both sides. Since this low-density portion has a lower thermal conductivity, it works advantageously for heat insulation.

[0084] After press forming, it is preferable to heat-treat and dry the core material. This can sufficiently remove the moisture contained in the raw material, further reducing the thermal conductivity of the core material. The method of heat-treating the core material is not particularly limited. For example, it can be heated in a constant-temperature dryer, an electric furnace, or the like. The heat treatment temperature is preferably 80 to 400 °C, more preferably 100 to 300 °C. The heat treatment time is preferably 0.1 to 120 hours, more preferably 0.1 to 60 hours.

[0085] The method of vacuum-sealing the core material inside the outer bag is not particularly limited, and the core material can be vacuum-sealed inside the outer bag by various methods. For example, there is a method in which the core material is stored inside the outer bag, the opening of the outer bag is sealed under reduced pressure conditions, and then the outside of the outer bag is returned to atmospheric pressure conditions.

[0086] In one example, the core material is stored in an outer bag formed by overlapping two gas-barrier films and sealing three sides, placed inside a vacuum chamber equipped with a heat-sealing function, and the inside of the vacuum chamber is decompressed. After the inside of the vacuum chamber is decompressed to a predetermined pressure, the remaining one open side of the outer bag is heat-sealed and sealed, and the inside of the vacuum chamber is returned to atmospheric pressure conditions. In another example, after the core material is stored inside the outer bag, the air inside the outer bag can be sucked out to decompress the inside of the outer bag, and then the outer bag can be sealed by heat-sealing or the like.

[0087] The core material may be vacuum-sealed inside the outer bag in a state where it is stored in a breathable inner bag. The inner bag may be any material that has breathability and can prevent the raw material from leaking out when the core material is vacuum-sealed. Examples of the material of the inner bag include paper materials and non-woven fabrics. However, the material of the inner bag is not limited to those exemplified here.

[0088] [Function mechanism] In the vacuum insulating material according to some of the embodiments described above, the core material contains biomass-derived powder as a biomass raw material. When the biomass raw material is in the form of powder in this way, compared with the case where the biomass raw material is cellulose fiber as in Patent Document 1, the core material is less likely to be crushed in the thickness direction when the core material is vacuum-encapsulated in the outer bag. Therefore, the changes in thickness and density due to crushing are reduced. Also, the internal pressure of the vacuum insulating material is less likely to rise. Thus, the initial value of the heat insulation performance is improved. Furthermore, if it is a powder biomass raw material, even if the internal pressure rises, it is less likely to absorb moisture like cellulose fiber. As a result, the long-term reliability of the heat insulation performance is also improved. In addition, regarding the composition of the core material, since the content ratios of each component of the biomass-derived powder, fumed silica, radiation suppression component, and inorganic fiber are within a predetermined range, a vacuum insulating material with excellent heat insulation performance and environmentally friendly can be obtained, and the core material can be formed into a desired shape.

[0089] As described above, some embodiments have been explained, but the present invention is not limited to the embodiment examples disclosed in this specification, and can be appropriately modified and implemented without changing the gist thereof. The embodiments disclosed in this specification can be implemented in various other forms, and various omissions, substitutions, and changes are possible without departing from the gist of the invention.

Examples

[0090] Hereinafter, the embodiments will be described in more detail with examples. However, the present invention is not limited to the following description. Examples 1 and 2 are comparative examples, and Examples 3 to 5 are examples.

[0091] [Measurement method] (Bulk density) The bulk density of the biomass-derived powder was measured by the constant mass measurement method of JIS R1628 1997. The bulk density of fumed silica was measured by the constant mass measurement method of JIS R1628 1997.

[0092] (Fiber lengths D10, D50, D90) In a photograph of inorganic fibers observed with an optical microscope, the lengths of 50 or more randomly extracted fibers were measured, and a cumulative number distribution curve was obtained with the total number of the fiber length distribution determined on a number basis taken as 100%. Thereafter, the fiber lengths at the points where the cumulative numbers were 10%, 50%, and 90% were defined as D10, D50, and D90, respectively.

[0093] (Average fiber length) In a photograph of inorganic fibers observed with an optical microscope, the lengths of 50 or more randomly extracted fibers were measured, and the average value of these lengths was defined as the average fiber length of the fibers.

[0094] (Ln and Lw) In a photograph of inorganic fibers observed with an optical microscope, the lengths of 50 or more randomly extracted fibers were measured, and Ln was determined by Equation 1 from the frequency distribution on a number basis. Also, Lw was determined by Equation 2 from the frequency distribution on a weight basis. In Equations 1 and 2, Ni is the number of fibers in each histogram of the average length Li.

[0095] [Number]

[0096] (Volume-based frequency particle size distribution) The volume-based frequency particle size distributions of the biomass-derived powder and fumed silica were measured by the laser diffraction scattering method using a scattering-type particle size distribution measuring device LA-920V (manufactured by HORIBA). In the particle size distribution measurement, 0.4 g of the sample was put into 40 g of a dispersion liquid (0.1 mass% sodium hexametaphosphate) and dispersed by ultrasonic waves for 1 minute. The refractive index condition was set to 1.46 for both the measurement of the biomass-derived powder and the measurement of fumed silica.

[0097] (Rate of thickness reduction) In each case, the thickness was measured before putting the flat core material into the outer bag. The thicknesses at five locations, namely the four corners and the center of the flat core material, were measured, and the average value of these five points was taken as the thickness D0 before encapsulation. Next, after the core material was encapsulated under reduced pressure in the outer bag, the thicknesses at five locations, namely the four corners and the center of the flat vacuum insulation material, were measured. The average value of these five points was taken as the thickness D1 after encapsulation. In calculating D1, the values at five points were measured including the thickness of the outer bag in addition to the thickness of the core material. From the following formula, the thickness reduction rate during reduced-pressure encapsulation was calculated. (Thickness reduction rate [%]) = ((D0 - D1) / D0) × 100

[0098] (Internal pressure) The vacuum insulation materials produced in each case were installed in the chamber. Then, the pressure was gradually reduced so that the inside of the chamber became a vacuum state. In the process of this pressure reduction, the pressure inside the chamber when the surface of the outer bag of the vacuum insulation material began to bulge was taken as the internal pressure of the vacuum insulation material. The values described in Table 1 are the values when this measurement was carried out only once.

[0099] (Thermal conductivity) The thermal conductivity of the vacuum insulation material was measured using a thermal conductivity measuring device HFM-436 (NETZSCH). Three samples were prepared for measurement, and the average value was taken as the thermal conductivity of the vacuum insulation material. The measurement conditions were a central temperature of 25°C and a temperature difference of 20°C. The thermal conductivity measured for the vacuum insulation material before conducting the long-term reliability test described later was taken as the "initial thermal conductivity".

[0100] (Long-term reliability test 1) In the long-term reliability test 1, the reliability of the vacuum insulation materials obtained in each case was tested by leaving them standing in an environment of 70°C and 90% RH for 7 days. The thermal conductivities of the vacuum insulation materials before and after the test were measured respectively, and the increase amount (△λ1) was calculated. Also, the internal pressures of the vacuum insulation materials before and after the test were measured respectively, and the increase amount (△Pa1) was calculated.

[0101] (Long-term reliability test 2) In the long-term reliability test 2, the reliability of the vacuum insulation material obtained in each case was tested by leaving it still in an environment of 70°C and 90% RH for 28 days. Similar to the long-term reliability test 1, the increases in thermal conductivity and internal pressure (Δλ2, ΔPa2) were calculated respectively.

[0102] [Raw material of the core material] · Cellulose fiber 1 (diameter of single fiber: within the range of 10 to 30 μm) · Polyester fiber 1 (diameter of single fiber: within the range of 20 to 50 μm) · Biomass-derived powder 1: Rice husk ash silica (average agglomerated particle diameter D50: 67 μm, bulk density: 0.17 g / cm 3 , peak position of particle size distribution: 77 μm) · Fumed silica 1 (average agglomerated particle diameter D50: 13.5 μm, bulk density: 0.035 g / cm 3 , specific surface area: 300 m 2 / g) · Inorganic fiber 1: Fibers obtained by pulverizing glass fibers with a fiber length of 3 mm for 10 minutes using a blender with a stirrer (range of fiber length: 0.3 to 3 mm) · Radiation suppression component 1: Graphite

[0103] The fiber diameter of inorganic fiber 1 was 6 μm, the fiber length was 3 mm, the ratio A was 0.8 mass%, the alkali elution amount was 0.2 mL / g, the thermal expansion coefficient was 45×10 -7 / °C, and the Young's modulus was 68 GPa. Also, D10 of inorganic fiber 1 was 1.29 mm, D50 was 2.55 mm, D90 was 3.00 mm, (D90 - D10) / D50 was 0.68, the average fiber length was 2.47 mm, Ln was 2.35, Lw was 2.53, and Lw / Ln was 1.08.

[0104] [Example 1] A non-woven fabric formed of 100 parts by mass of cellulose fiber 1 with a single fiber diameter of 10 to 30 μm was used to produce a flat plate-shaped core material with a length of 200 mm × width of 200 mm × thickness of 15 mm. Next, three sides of two gas-barrier films each measuring 300 mm × 300 mm were heat-sealed to produce a three-sided sealed outer bag. After placing the core material inside the outer bag, it was installed in a vacuum chamber equipped with a heat-sealing function. Then, the inside of the chamber was evacuated to 5 Pa. In this state, the opening of the outer bag was heat-sealed and sealed. Then, the outside of the outer bag was returned to atmospheric pressure conditions to obtain a vacuum insulation material.

[0105] [Example 2] A vacuum insulation material was obtained under the same conditions as in Example 1, except that a nonwoven fabric formed from a mixture of 50 parts by mass of Cellulose Fiber 1 and 50 parts by mass of Polyester Fiber 1 was used instead of 100 parts by mass of Cellulose Fiber 1.

[0106] [Example 3] A raw material mixture was obtained by mixing 40 parts by mass of Biomass-derived Powder 1, 40 parts by mass of Fumed Silica 1, 16 parts by mass of Radiation Suppression Component 1, and 4 parts by mass of Inorganic Fiber 1. The raw material mixture was press-molded and heat-treated at 200 °C for 1 hour to produce a flat core material measuring 200 mm in length × 200 mm in width × 15 mm in thickness. Next, three sides of two gas-barrier films each measuring 300 mm × 300 mm were heat-sealed to produce a three-sided sealed outer bag. After placing the core material inside the outer bag, it was installed in a vacuum chamber equipped with a heat-sealing function. Then, the inside of the chamber was evacuated to 5 Pa. In this state, the opening of the outer bag was heat-sealed and sealed. Then, the outside of the outer bag was returned to atmospheric pressure conditions to obtain a vacuum insulation material.

[0107] [Example 4] A vacuum insulation material was obtained under the same conditions as in Example 3, except that the mass ratio of Biomass-derived Powder 1 to Fumed Silica 1 was changed to 40:60.

[0108] [Example 5] A vacuum insulation material was obtained under the same conditions as in Example 3, except that the mass ratio of Biomass-derived Powder 1 to Fumed Silica 1 was changed to 30:70.

[0109] For each example of the vacuum insulation material, Table 1 shows the thickness reduction rate during vacuum encapsulation, the internal pressure of the vacuum insulation material, the measurement results of the initial thermal conductivity, and the evaluation results of the long-term reliability. The evaluation results of the long-term reliability show the results after 7 days and after 28 days respectively.

[0110]

Table 1

[0111] In each of the vacuum insulation materials of Examples 3 - 5, the initial thermal conductivity is lower than that of the vacuum insulation materials of Examples 1 and 2. Also, in each of the vacuum insulation materials of Examples 3 - 5, the variation in thermal conductivity (△λ) and the variation in internal pressure (△Pa) after the long-term reliability test are smaller than those of the vacuum insulation materials of Examples 1 and 2. Each of the vacuum insulation materials of Examples 3 - 5 has a better initial value of heat insulation performance and also excellent long-term reliability compared to the vacuum insulation materials of Examples 1 and 2.

[0112] In each of the vacuum insulation materials of Examples 3 - 5, the thickness reduction rate during vacuum encapsulation is lower compared to the vacuum insulation materials of Examples 1 and 2 that use cellulose fiber 1. It is considered that by suppressing the crushing in the thickness direction of the core material during vacuum encapsulation, both the initial value of the heat insulation performance and the long-term reliability have been improved.

Industrial Applicability

[0113] According to the present invention, an environmentally friendly vacuum insulation material with a good initial value of heat insulation performance and excellent long-term reliability is provided.

Explanation of Reference Numerals

[0114] 1 Vacuum insulation material 10 Core material 12 Outer bag

Claims

1. A vacuum insulation material comprising a core material and a gas barrier film covering the core material, wherein the core material is vacuum-encapsulated in an outer bag formed of the gas barrier film, the core material contains biomass-derived powder, fumed silica, a radiation suppression component, and inorganic fibers, the content ratio of the biomass-derived powder is 25 to 45% by mass of the total amount of the core material, the content ratio of the fumed silica is 25 to 45% by mass of the total amount of the core material, the content ratio of the radiation suppression component is 3 to 30% by mass of the total amount of the core material, and the content ratio of the inorganic fibers is 2 to 30% by mass of the total amount of the core material.

2. The vacuum insulation material according to claim 1, wherein the biomass-derived powder is at least one selected from the group consisting of biomass-derived silica, rice husk, rice straw, bagasse, wheat straw, and sawdust.

3. The vacuum insulation material according to claim 2, wherein the biomass-derived silica is at least one selected from the group consisting of rice husk ash silica and rice straw ash silica.

4. At least one selected from the group consisting of the rice husk ash silica and the rice straw ash silica is amorphous silica, and the content of crystalline silica is less than 0.1% by mass.

5. The vacuum insulation material according to claim 3, wherein the silica content of at least one selected from the group consisting of the rice husk ash silica and the rice straw ash silica is 90% by mass or more.

6. The vacuum insulation material according to claim 3, wherein the silica content of the biomass-derived powder is 70% by mass or more.

7. The vacuum insulation material according to claim 1, wherein the silica content of the biomass-derived powder is 30% by mass or less.

8. The bulk density of the powder derived from biomass is 0.25 g / cm ３ The vacuum insulating material according to claim 1, wherein the bulk density is 0.25 g / cm or less.

9. The vacuum insulation material according to claim 1, wherein the particle size distribution of the biomass-derived powder has a peak in the range of 1 to 300 μm.

10. The bulk density of the fumed silica is 0.1 g / cm ３ The vacuum insulating material according to claim 1, wherein the bulk density is 0.1 g / cm or less.

11. The vacuum insulation material according to claim 1, wherein the radiation suppression component is at least one selected from the group consisting of graphite, silicon carbide, titanium oxide, tin oxide, and potassium titanate.

12. The vacuum insulation material according to claim 1, wherein the inorganic fibers are at least one selected from the group consisting of alumina fibers, glass fibers, silica fibers, glass wool, rock wool, carbon fibers, and silica-alumina fibers.

13. At least a part of the inorganic fibers is glass fibers, Na in the glass fiber ２ The total mass of O and K ２ The ratio of the total mass of the glass fiber to the total mass of the glass fiber is 11% by mass or less. The vacuum heat insulating material according to claim 1.

14. The fiber length of the inorganic fiber is 0.1 to 10 mm, and the fiber length distribution Lw / Ln represented by the ratio of the number average fiber length Ln to the weight average fiber length Lw of the inorganic fiber is 1.05 or more. The vacuum insulation material according to Claim 1.

15. The thickness reduction rate when the core material is vacuum-encapsulated in the outer bag is 20% or less. The vacuum insulation material according to Claim 1.

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