Method for manufacturing near-infrared solar reflectors

Abstract

This invention provides a manufacturing method for a material that is highly flame-retardant, has low density, and is easy to crush or pulverize, while also exhibiting high solar reflectance in the near-infrared wavelength range. [Solution] Rice husks are heated in the presence of air at any temperature in the range of 250°C to 400°C, and then heated again at 500°C.

Description

Technical Field

[0001] The present invention relates to reflection of light in the near-infrared region, and to a material that efficiently reflects wavelengths in the near-infrared region.

Background Art

[0002] In recent years, global warming has been progressing. The high-temperature environment caused by being irradiated with sunlight, especially in summer, not only affects daily life but also industrial activities and crops, and may even endanger life. Therefore, various countermeasures against solar radiation for outdoor buildings and structures have been implemented.

[0003] The near-infrared region, which is the wavelength range of sunlight from 780 nm to 2500 nm, occupies nearly 50% of the radiant energy of sunlight and has a heat effect. Therefore, a reflective material with a wavelength in the near-infrared region is used as a countermeasure for suppressing temperature rise.

[0004] Examples of reflective materials include organic, metal, and ceramic types. However, in order to be widely used outdoors, conditions such as high reflectivity, high flame retardancy, light weight, and ease of manufacture are required. Organic materials are inferior in terms of flammability and reflectivity, while metal and ceramic materials are excellent in terms of reflectivity and flame retardancy, and various methods have been proposed. For example, metal-based white pigments such as titanium oxide and zinc oxide are well-known, and a method using titanium oxide has been proposed (Patent Document 1). As another method, a method of arranging glass beads on the surface irradiated with sunlight has been proposed (Patent Documents 2 and 3).

[0005] However, metal-based white pigments represented by titanium oxide in Patent Document 1 have a problem of weight during use because of their high density. In addition, since the minerals used as raw materials are hard, strong physical forces are required for crushing and pulverization, and there is a drawback that the manufacture is not easy. The method using glass beads in Patent Documents 2 and 3 also has a problem of weight during use because glass beads have a high density, similar to the metal-based white pigments in Patent Document 1. Furthermore, there is a drawback that crushing and pulverization of glass are not easy.

Prior Art Documents

[0006] [Patent Document 1] Patent No. 4546834 [Patent Document 2] Japanese Patent Publication No. 2009-127325 [Patent Document 3] Japanese Patent Publication No. 2009-127326 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In view of the above issues, the present invention aims to provide a novel manufacturing method for a material that is highly flame-retardant, has low density, is easy to crush and pulverize, and has a high solar reflectance in the near-infrared wavelength range. [Means for solving the problem]

[0008] As a result of diligent research to solve the aforementioned problems, the present inventors have found that they can be solved by the following invention.

[0009] One aspect of the present invention, which solves the above problems, is a method for producing a near-infrared solar radiation reflector, comprising heating rice husks in the presence of air at an arbitrary temperature in the range of 250°C to 400°C, and then heating them again at 500°C.

[0010] Another aspect of the present invention for solving the above problems is a method for producing a near-infrared solar radiation reflector, comprising heating rice husks in the presence of air at an arbitrary temperature in the range of 300°C to 400°C, and then heating them again at an arbitrary temperature in the range of 500°C to 650°C. [Effects of the Invention]

[0011] According to the present invention, a novel manufacturing method is available for a material that is highly flame-retardant, has low density, and is easy to crush or pulverize, while also having a high solar reflectance in the near-infrared wavelength range. [Modes for carrying out the invention]

[0012] The embodiments will be described in more detail below. These are examples of methods for realizing the technical concept of the present invention, and the technical concept of the present invention is not limited to those described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims described in the patent claims.

[0013] The near-infrared solar radiation reflector of the present invention refers to a material that reflects electromagnetic waves with wavelengths of 780 nm to 2500 nm. The rice husk of the present invention refers to the outer layer of rice husks. One embodiment of the method for manufacturing the near-infrared solar radiation reflector of the present invention is to first heat the rice husks in the presence of air at any temperature in the range of 250°C to 400°C. The rice husks may be heated multiple times at different temperatures in the range of 250°C to 400°C. Next, the rice husks are heated in the presence of air at 500°C. After this, the material is cooled to complete the process.

[0014] Another method of production involves first heating the rice husks in the presence of air to any temperature in the range of 300°C to 400°C. This heating may be repeated multiple times at different temperatures within the range of 300°C to 400°C. Next, the husks are heated in the presence of air to any temperature in the range of 500°C to 650°C. After this, they are cooled to complete the process.

[0015] The heating times for temperatures within the 250°C to 400°C range, any temperature within the 300°C to 400°C range, and any temperature within the 500°C or 500°C to 650°C range vary depending on the amount of rice husks, heat conduction, and degree of contact with air. A larger amount of rice husks results in longer heating times. To shorten the heating time, it is best to ensure that heat is easily transferred to the rice husks and that they are exposed to air. Thinner layers of rice husks during heating result in shorter heating times. Heating of rice husks is carried out in a heating furnace, and both batch and continuous furnaces are possible. Heat sources include electric, gas, heavy oil, and fossil fuels such as kerosene; either method is acceptable as long as temperature control is possible.

[0016] The end of heating in the range of 250°C to 400°C and the range of 300°C to 400°C is determined by the disappearance of brown rice husks. Also, the end of heating in the range of 500°C or the range of 500°C to 650°C is determined by the disappearance of black ash. Dry rice husks are used. Also, when heating the rice husks, stems and the like mixed in the rice husks remain as black ash when fired, so it is preferable to remove them before or after heating. Also, it may be in the presence of oxygen instead of air.

[0017] All the calcined ashes produced by the method of the present invention have a high near-infrared solar reflectance of 70% or more. The reflectance indicating the degree of effectiveness of near-infrared solar reflection is determined as follows according to JIS K5602:2008. The spectral reflectance of a standard white plate is set to 100% at wavelengths of 780 nm to 2500 nm. Based on this, the spectral reflectance of each sample at each wavelength is obtained, multiplied by the weighting coefficient indicating the distribution of the spectral irradiance of standard sunlight, and weighted-averaged over wavelengths of 780 nm to 2500 nm. The weighting coefficient is the spectral irradiance of standard sunlight defined in Table 1 column 8 of ISO9845-1:1992, integrated over wavelengths of 780 nm to 2500 nm.

[0018] Also, the calcined ash produced by the method of the present invention has very high flame retardancy and a small density. When used as a near-infrared solar reflective material, it is easier to handle when powdered, and has excellent moldability, coating properties, etc. The ash is brittle and can be easily crushed or pulverized to several hundred μm or less using a mortar and a light force such as a pestle or an air current.

[0019] The near-infrared solar reflective material produced in the present invention can be used alone, but there is no problem in mixing and using it with other materials.

[0020] Examples are shown below to specifically explain the present invention, but these are merely for illustrative purposes and the present invention is not limited to these examples.

Example

[0021] (Manufacture of Near-Infrared Solar Reflective Material 1) Two crucibles (outer diameter 72 mm × height 59 mm, internal volume 155 mL) were each added with 10 g of dried rice husks and placed in a muffler furnace (HPM-1N, manufactured by AS ONE Corporation). As the initial heating, they were heated at 200 °C, 250 °C, 300 °C, 350 °C, and 400 °C for 4 hours respectively. The temperature was raised from room temperature to the heating temperature at a rate of 20 °C / min. Next, each was heated to 500 °C at a rate of 20 °C / min and heated at 500 °C for 4 hours. All temperature increases and isothermal heating were carried out in the presence of air. Thereafter, they were naturally cooled to room temperature.

[0022] The rice husks had no black parts on the surface or deep inside, and all were white and ashed. When the ash from the two crucibles was collected and weighed, it was 5 g for all initial heating temperatures from 200 °C to 400 °C. Each ash was ground manually with a light force for about 5 minutes using a mortar and pestle.

[0023] (Measurement of near-infrared solar reflectance) The near-infrared solar reflectance of these calcined ashes was measured by the following method. The spectrophotometer was an ultraviolet-visible-near-infrared spectrophotometer (V-770, manufactured by JASCO Corporation) attached with an integrating sphere unit for the light receiver (ISN-923 type, manufactured by JASCO Corporation). Using a standard white plate (registered trademark: Spectralon, manufactured by Labsphere Inc.) as the baseline, the sample was filled into a powder cell (PSH-002, manufactured by JASCO Corporation) to a thickness of 3 mm or more, and the reflectance at wavelengths from 200 nm to 2500 nm was measured with a light incident angle of 1° and a D65 lamp as the light source.

[0024] The calculation of the near-infrared solar reflectance was carried out in accordance with JIS K5602:2008 using a solar transmittance / reflectance measurement program (manufactured by JASCO Corporation) introduced into a personal computer that controls the ultraviolet-visible-near-infrared spectrophotometer, and was obtained by the sum of the products of the spectral reflectance and the weighting coefficient at each wavelength from 780 nm to 2500 nm. The higher the solar reflectance, the higher the effect of reflecting near-infrared light.

[0025] As a result, the near-infrared solar reflectance of the calcined ash was 71% at an initial heating temperature of 200°C, 74% at 250°C, 77% at 300°C, 76% at 350°C, and 77% at 400°C. The near-infrared solar reflectance was higher when the initial heating temperature was 250°C or higher. [Examples]

[0026] (Manufacturing of near-infrared solar radiation reflecting materials 2) Two crucibles (72mm outer diameter x 59mm height, 155mL capacity) were each filled with 10g of dried rice husks and placed in a muffle furnace (HPM-1N, manufactured by AS ONE Corporation). For the initial heating, each crucible was heated at 250°C, 300°C, 350°C, 400°C, and 450°C for 4 hours. The temperature was increased from room temperature to the heating temperature at a rate of 20°C / min. Next, each crucible was heated to 550°C at a rate of 20°C / min and heated at 550°C for 4 hours. All heating and constant temperature heating were performed in the presence of air. Afterwards, the crucibles were allowed to cool naturally to room temperature.

[0027] The rice husks had no black parts on the surface or inside, and were all white and ash-like. The ash from two crucibles was collected and weighed, and all of them weighed 5g, depending on the initial heating temperature of 250°C to 450°C. Each batch of ash was then ground manually with a mortar and pestle using light force for about 5 minutes.

[0028] The near-infrared solar reflectance of these calcined ashes was measured. The measurement method was the same as that described in Example 1. As a result, the near-infrared solar reflectance of the calcined ash was 69% at an initial heating temperature of 250°C, 75% at 300°C, 76% at 350°C, 76% at 400°C, and 74% at 450°C. The near-infrared solar reflectance was higher when the initial heating temperature was 300°C or higher. [Examples]

[0029] (Manufacturing of near-infrared solar radiation reflecting materials 3) Two crucibles (72mm outer diameter x 59mm height, 155mL capacity) were each filled with 10g of dried rice husks and placed in a muffle furnace (HPM-1N, AS ONE Corporation). For the initial heating, each crucible was heated at 250°C, 300°C, 350°C, 400°C, and 500°C for 4 hours. The temperature was increased from room temperature to the initial heating temperature at a rate of 20°C / min. Next, each crucible was heated to 625°C at a rate of 20°C / min and heated at 625°C for 4 hours. All heating and constant temperature heating were performed in the presence of air. Afterwards, the crucibles were allowed to cool naturally to room temperature.

[0030] The rice husks had no black parts on the surface or inside, and were all white and ash-like. The ash from two crucibles was collected and weighed, and all of them weighed 5g, depending on the initial heating temperature of 250°C to 500°C. Each batch of ash was then ground using a mortar and pestle with light manual force for about 5 minutes.

[0031] The near-infrared solar reflectance of these calcined ashes was measured. The measurement method was the same as that described in Example 1. As a result, the near-infrared solar reflectance of the calcined ashes was 67% at an initial heating temperature of 250°C, 73% at 300°C, 77% at 350°C, 75% at 400°C, and 71% at 500°C. The near-infrared solar reflectance of the calcined ashes was high when the initial heating temperature was in the range of 300°C to 400°C. [Examples]

[0032] (Manufacturing of near-infrared solar radiation reflecting materials 4) Two crucibles (72mm outer diameter x 59mm height, 155mL capacity) were each filled with 10g of dried rice husks and placed in a muffle furnace (HPM-1N, manufactured by AS ONE Corporation). For the initial heating, the mixture was heated to 350°C for 4 hours. The temperature was increased from room temperature to 350°C at a rate of 20°C / min. Next, the temperature was increased to 650°C at a rate of 20°C / min and heated at 650°C for 4 hours. All heating and constant temperature heating were performed in the presence of air. Afterwards, the mixture was allowed to cool naturally to room temperature.

[0033] The rice husks had no black parts on the surface or inside, and were white and ash-like. The ash was collected from two crucibles and weighed, and it was 5g. This ash was then ground using a mortar and pestle with light manual force for about 5 minutes.

[0034] The near-infrared solar reflectance of this calcined ash was measured. The measurement method was the same as that described in Example 1. As a result, the near-infrared solar reflectance was 76%. [Examples]

[0035] (Manufacturing of near-infrared solar radiation reflecting materials 5) Two crucibles (72mm outer diameter x 59mm height, 155mL capacity) were each filled with 10g of dried rice husks and placed in a muffle furnace (HPM-1N, manufactured by AS ONE Corporation). The first heating was performed at 300°C for 4 hours. The second heating was performed at 400°C for 4 hours, and finally at 500°C for 4 hours. The temperature was increased from room temperature to 300°C, and then to 400°C and 500°C at a rate of 20°C / min. All heating and constant temperature heating were performed in the presence of air. Afterwards, the mixture was allowed to cool naturally to room temperature.

[0036] The rice husks had no black parts on the surface or inside, and were white and ash-like. The ash was collected from two crucibles and weighed, and it was 5g. This ash was then ground using a mortar and pestle with light manual force for about 5 minutes.

[0037] The near-infrared solar reflectance of this calcined ash was measured. The measurement method was the same as that described in Example 1. As a result, the near-infrared solar reflectance was 78%. [Examples]

[0038] (Manufacturing of near-infrared solar radiation reflecting materials 6) Three porcelain evaporating dishes (150mm outer diameter x 42mm height, 400mL capacity) were each filled with 40g of dried rice husks and placed in an electric furnace (F0610, manufactured by Yamato Scientific Co., Ltd.). For the initial heating, the furnace was heated to 350°C for 6 hours. The temperature was increased from room temperature to 350°C at a rate of 20°C / min. Subsequently, the temperature was increased to 600°C at a rate of 20°C / min and heated at 600°C for 6 hours. All heating and constant temperature heating were carried out in the presence of air. Afterwards, the furnace was allowed to cool naturally to room temperature.

[0039] The rice husks had no black parts on the surface or inside, and were white and ash-like. The ash collected from three evaporation dishes was weighed and found to be 30g. This ash was ground using a mortar and pestle with light manual force for about 15 minutes. The manufacturing process described here was repeated twice to obtain a total of 60g of ash.

[0040] (Near infrared solar reflectance) The near-infrared solar reflectance of this calcined ash was measured. The measurement method was the same as that described in Example 1. As a result, the near-infrared solar reflectance was 76%.

[0041] (Color evaluation) The above color evaluation of calcined ash is based on the color system L. * a * b * The value was determined by measuring the reflectance using a spectrophotometer. The spectrophotometer was an ultraviolet-visible-near-infrared spectrophotometer (V-770, manufactured by JASCO Corporation) with an integrating sphere unit for the light receiver (ISN-923, manufactured by JASCO Corporation). The reflection of a standard whiteboard (registered trademark: Spectralon, manufactured by Labsphere Corporation) was used as the baseline, and the sample was packed into a powder cell (PSH-002, manufactured by JASCO Corporation) to a thickness of 3 mm or more. The reflectance at wavelengths of 360 nm to 830 nm was measured with a light incidence angle of 1° and a D65 lamp as the light source. The Lab value was calculated in accordance with JIS Z8730:2002, using a color evaluation program (manufactured by JASCO Corporation) installed on a personal computer controlling the ultraviolet-visible-near-infrared spectrophotometer. As a result, L * ga 79, a * 3.1, b * The value was 1.7.

[0042] (Specific heat capacity) The specific heat capacity of the calcined ash described above was determined by differential scanning calorimetry (DSC). A Rigaku DSC8230 differential scanning calorimeter was used, and Rigaku Thermo Plus2 series software was used for data processing. Approximately 10 mg of calcined ash was accurately weighed into a 5 mm diameter aluminum container, an aluminum lid was placed over it, and it was compressed tightly using a special jig. An empty container was placed in one of the two container holders as a control, and the temperature was increased from room temperature to 30°C at a rate of 5°C / min, held at 30°C for 5 minutes, and then increased to 90°C at a rate of 5°C / min, and the heat flux value (mW) was measured. The empty container was measured in the same manner, and this value was used as the baseline. Approximately 10 mg of α-alumina (Rigaku Corporation) was accurately weighed as a standard substance and measured in the same manner. The specific heat capacity of the calcined ash was calculated by multiplying the ratio of the difference in heat flux values ​​between the calcined ash, the standard substance, and the baseline at 86.9°C by the specific heat capacity value of α-alumina at 86.9°C, which is 0.887 J / g·°C. As a result, the specific heat capacity of the calcined ash at 86.9°C was 1.3 J / g·°C.

[0043] (Sifting) When the above calcined ash was sorted by size using stainless steel test sieves with mesh openings of 250 μm and 106 μm, ash larger than 250 μm accounted for 13% by weight, ash between 106 μm and 250 μm accounted for 24% by weight, and ash smaller than 106 μm accounted for 63% by weight.

[0044] (Bulk density) 20 g of the sieved ash, with a size of 106 μm or less, was accurately weighed, placed in a glass graduated cylinder, and tapped. The volume was measured, and the bulk density was calculated to be 0.67 g / mL. [Examples]

[0045] (Comparative study 1) As a comparative sample, dried rice husks were ground in a continuous mill (MF10 Basic, IKA Corporation) without calcination, and powder smaller than 500 μm was collected using a sieve. As another comparative sample, 5 g of dried rice husks was added to one crucible (outer diameter 72 mm x height 59 mm, internal volume 155 mL) and placed in a muffle furnace (HPM-1N, AS ONE Corporation). The temperature was raised from room temperature at a rate of 20 °C / min to 300 °C, and then heated at 300 °C for 2 hours. The temperature increase from room temperature to 300 °C and the heating at 300 °C for 2 hours were performed in the presence of air. After that, it was allowed to cool naturally to room temperature. The surface of the rice husks was entirely black. This ash was ground in a mortar.

[0046] The near-infrared solar reflectance of these two comparative samples was measured. The measurement method was the same as that described in Example 1. As a result, the near-infrared solar reflectance of uncalcined rice husks was 52%, while that of calcined ash heated at 300°C was 33%. [Examples]

[0047] (Comparative study 2) As a separate comparative test, 5g of dried rice husks was added to each of four crucibles (outer diameter 72mm x height 59mm, capacity 155mL) and placed in a muffle furnace (HPM-1N, manufactured by AS ONE Corporation). The temperature was increased from room temperature at a rate of 20°C / min to 500°C, 550°C, 600°C, and 650°C, and each temperature was heated for 2 hours. The temperature increase from room temperature and the 2-hour constant temperature heating were performed in the presence of air. Afterwards, the mixture was allowed to cool naturally to room temperature. The rice husks had no black parts on the surface or in the depths, and were all white and ash-like. Each ash was then ground manually with light force using a mortar and pestle for about 5 minutes.

[0048] The near-infrared solar reflectance of these calcined ashes was measured. The measurement method was the same as that described in Example 1. As a result, the near-infrared solar reflectance of the calcined ashes was 72% at 500°C, 66% at 550°C, 64% at 600°C, and 57% at 650°C. [Industrial applicability]

[0049] The present invention is useful, for example, in the field of materials for providing heat-shielding properties to buildings and structures.

Claims

1. A method for producing a near-infrared solar radiation reflector, comprising heating rice husks in the presence of air at an arbitrary temperature in the range of 250°C to 400°C, and then heating them again at 500°C.

2. A method for producing a near-infrared solar radiation reflector, comprising heating rice husks in the presence of air at an arbitrary temperature in the range of 300°C to 400°C, and then heating them again at an arbitrary temperature in the range of 500°C to 650°C.