Method for manufacturing near-infrared solar radiation 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 to any temperature in the range of 300°C to 550°C or more and 650°C or less at a heating rate of 150°C / hour or less, and then heated to the final temperature of the heating process.

Description

Technical Field

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

Background Art

[0002] In recent years, global warming has advanced, and the high-temperature environment caused by being irradiated with sunlight, especially in summer, has a great impact not only on daily life but also on industrial activities and crops, and there is a risk of endangering 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 measure to suppress temperature rise.

[0004] Examples of the reflective material include organic, metal, and ceramic types. In order to be widely used outdoors, conditions such as high reflectivity, high flame retardancy, light weight, and easy manufacturing are required. Organic types are inferior in terms of flammability and reflectivity, while metal and ceramic types 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, the metal-based white pigments represented by titanium oxide in Patent Document 1 have a problem of weight when used 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 manufacturing is not easy. The method using glass beads in Patent Documents 2 and 3 also has a problem of weight when used 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 to any temperature in the range of 300°C to 550°C or more and 650°C or less at a heating rate of 150°C / hour or less, and then heating at the final heating temperature.

[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 from 300°C to 500°C at a heating rate of 150°C / hour or less, and then heating them to an arbitrary temperature in the range of 550°C to 650°C.

[0011] 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 from 350°C to 550°C at a heating rate of 150°C / hour or less, and then heating them to an arbitrary temperature in the range of 550°C to 650°C. [Effects of the Invention]

[0012] 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]

[0013] 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.

[0014] 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 heat the material to any temperature in the range of 300°C to 550°C or more and 650°C or less at a heating rate of 150°C / hour or less. In this case, a slower heating rate generally results in a higher near-infrared solar radiation reflectance. The heating rate from 300°C or less to 300°C is not specified. Next, the material is heated to the endpoint temperature in the range of 550°C to 650°C. After this, it is cooled to complete the process.

[0015] Another method of manufacturing involves heating rice husks in the presence of air from 300°C to 500°C at a heating rate of 150°C / hour or less. In this case, a slower heating rate generally results in a higher near-infrared solar reflectance. The heating rate from below 300°C to 300°C is not specified. Next, the husks are heated to any temperature in the range of 550°C to 650°C. The heating rate from 500°C to the desired temperature is not specified. After this, the husks are cooled to complete the process.

[0016] Another method of manufacturing involves heating rice husks in the presence of air from 350°C to 550°C at a heating rate of 150°C / hour or less. The heating rate from below 350°C to 350°C is not specified. Generally, a slower heating rate results in a higher near-infrared solar reflectance. Next, the husks are heated to any temperature in the range of 550°C to 650°C. The heating rate from 550°C to the desired temperature is not specified. After this, the husks are cooled to complete the process.

[0017] In the manufacturing methods of the three embodiments described above, oxygen may be present instead of air. The heating rate of the present invention is the average heating rate. Heating of the rice husks is carried out in a heating furnace, and both batch furnaces and continuous furnaces are possible. Heat sources include electric and combustion types using fossil fuels such as gas, heavy oil, and kerosene, but electric is preferred because temperature control is easier. Also, the heating time at any temperature in the range of 550°C to 650°C varies depending on the amount of rice husks, heat conduction, and degree of contact with air, and the heating time increases as the amount of rice husks increases. To shorten the heating time, it is better to make it easier for heat to be transferred to the rice husks and for them to come into contact with air. The thinner the thickness of the stacked rice husks during heating, the shorter the heating time. The end of heating is indicated by the disappearance of black ash. Dry rice husks should be used. Also, when heating the rice husks, stems and other parts mixed in with the rice husks will remain as black ash when burned, so it is preferable to remove them before or after heating.

[0018] The calcined ash produced by the method of the present invention all have a high near-infrared solar reflectance of 70% or more. The reflectance, which indicates the degree of effectiveness of near-infrared solar reflectance, is determined according to JIS K5602:2008, by setting the spectral reflectance of a standard white plate to 100% at wavelengths of 780 nm to 2500 nm, using this as a reference, determining the spectral reflectance of each sample at each wavelength, multiplying it by a weighting coefficient that shows the distribution of spectral irradiance of standard sunlight, and taking a weighted average over wavelengths of 780 nm to 2500 nm. The weighting coefficient is the irradiance obtained by integrating the spectral irradiance of standard sunlight, as defined in Table 1, Column 8 of ISO9845-1:1992, over wavelengths of 780 nm to 2500 nm.

[0019] In addition, it has very high flame retardancy and low density. When used as a near-infrared solar radiation reflector, it is easier to handle when powdered, and has excellent formability, coating properties, etc. The ash is brittle and can be easily crushed or pulverized to less than several hundred μm using a mortar and a pestle with a light force such as a pestle or an air current.

[0020] The near-infrared solar radiation reflector produced by the present invention can be used alone, but there is no problem even when mixed with other materials and used.

[0021] Examples are shown below to specifically describe the present invention, but this is merely for illustrative purposes and the present invention is not limited to these examples.

Examples

[0022] (Manufacture 1 of near-infrared solar radiation reflector) Four crucibles (outer diameter 72 mm × height 59 mm, internal volume 155 mL) were each filled with 5 g of dried rice husks and placed in a muffler furnace (HPM-1N, manufactured by AS ONE Corporation). The temperature was raised from 300 °C to 550 °C at rates of 100 °C / h, 150 °C / h, and 200 °C / h, and heated at 550 °C for 2 hours. Separately, the temperature was raised from 300 °C to 600 °C at rates of 100 °C / h, 150 °C / h, and 200 °C / h, and heated at 600 °C for 2 hours. Separately, the temperature was raised from 300 °C to 625 °C at rates of 100 °C / h, 150 °C / h, and 200 °C / h, and heated at 625 °C for 2 hours. Separately, the temperature was raised from 300 °C to 650 °C at rates of 100 °C / h, 150 °C / h, and 200 °C / h, and heated at 650 °C for 2 hours. In all cases, the temperature was raised from room temperature to 300 °C at 20 °C / min, and the temperature increase from room temperature and the 2-hour constant temperature heating were carried out in the presence of air. Then, it was naturally cooled to room temperature.

[0023] The rice husks had no black parts on the surface or in the deep part, and all were whitened and ashed. When the ash from the four crucibles was collected and weighed, it was 5 g for all the above manufacturing methods. Each ash was ground manually with a light force for about 5 minutes using a mortar and a pestle.

[0024] (Measurement of near-infrared solar reflectance) The near-infrared solar reflectance of these calcined ashes was measured using the following method. The spectrophotometer used 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 white plate (registered trademark: Spectralon, manufactured by Labsphere Corporation) was used as the baseline. The sample was packed into a powder cell (PSH-002, manufactured by JASCO Corporation) to a thickness of 3 mm or more, and the reflectance at wavelengths of 200 nm to 2500 nm was measured with a light incidence angle of 1° and a D65 lamp as the light source.

[0025] The solar reflectance in the near-infrared region was calculated in accordance with JIS K5602:2008, using a solar transmittance / reflectance measurement program (manufactured by JASCO Corporation) installed on a personal computer controlling the ultraviolet-visible-near-infrared spectrophotometer. The calculation was performed by summing the products of the spectral reflectance and weight coefficient at each wavelength from 780 nm to 2500 nm. A higher solar reflectance indicates a greater effect in reflecting near-infrared light.

[0026] As a result, the near-infrared solar reflectance of the calcined ash was 73% at a heating temperature of 550°C and a heating rate of 100°C / hour, 73% at 150°C / hour, and 69% at 200°C / hour. At a heating temperature of 600°C, the reflectance was 74% at a heating rate of 100°C / hour, 74% at 150°C / hour, and 69% at 200°C / hour. At a heating temperature of 625°C, the reflectance was 76% at a heating rate of 100°C / hour, 73% at 150°C / hour, and 66% at 200°C / hour. At a heating temperature of 650°C, the reflectance was 74% at a heating rate of 100°C / hour, 74% at 150°C / hour, and 68% at 200°C / hour. At all heating temperatures, the near-infrared solar reflectance was high when the heating rate was 150°C / hour or less. [Examples]

[0027] (Manufacturing of near-infrared solar radiation reflecting materials 2) Four crucibles (72mm outer diameter x 59mm height, 155mL capacity) were each filled with 5g of dried rice husks and placed in a muffle furnace (HPM-1N, manufactured by AS ONE Corporation). The temperature was increased from 300°C to 400°C, 450°C, 500°C, and 550°C at a rate of 100°C / hour, and then heated to 625°C for 2 hours. The temperature was increased from room temperature to 300°C and from 100°C / hour to 625°C at a rate of 20°C / minute, and the temperature increase from room temperature and the heating to 625°C were performed in the presence of air. After that, it was allowed to cool naturally to room temperature.

[0028] The rice husks had no black parts on the surface or inside, and were all white and ash-like. The ash from four crucibles was collected and weighed, and all of the above-mentioned manufacturing methods yielded 5g. Each batch of ash was then ground using a mortar and pestle with light manual force for about 5 minutes.

[0029] 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 71% when heated from 300°C to 400°C at a heating rate of 100°C / hour, 69% up to 450°C, 74% up to 500°C, and 74% up to 550°C. When heated at a heating rate of 100°C / hour, the near-infrared solar reflectance was high when the heating range from 300°C to 500°C or higher. [Examples]

[0030] (Manufacturing of near-infrared solar radiation reflecting materials 3) Four crucibles (72mm outer diameter x 59mm height, 155mL capacity) were each filled with 5g of dried rice husks and placed in a muffle furnace (HPM-1N, manufactured by AS ONE Corporation). The temperature was increased from 300°C to 500°C at rates of 100°C / hour, 150°C / hour, and 200°C / hour, and then heated to 550°C for 2 hours. The temperature was increased from room temperature to 300°C and from 500°C to 550°C at a rate of 20°C / minute. The temperature increase from room temperature and the heating to 550°C were performed in the presence of air. Afterwards, the mixture was allowed to cool naturally to room temperature.

[0031] The rice husks had no black parts on the surface or inside, and were all white and ash-like. The ash from four crucibles was collected and weighed, and it was 5g at all heating rates. Each batch of ash was then ground using a mortar and pestle with light manual force for about 5 minutes.

[0032] 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 77% when heated from 300°C to 500°C at a heating rate of 100°C / hour, 73% at 150°C / hour, and 69% at 200°C / hour. The near-infrared solar reflectance was higher when the heating rate was 150°C / hour or less. [Examples]

[0033] (Manufacturing of near-infrared solar radiation reflecting materials 4) Four crucibles (72mm outer diameter x 59mm height, 155mL capacity) were each filled with 5g of dried rice husks and placed in a muffle furnace (HPM-1N, manufactured by AS ONE Corporation). The temperature was increased from 350°C to 450°C, 500°C, and 550°C at a rate of 100°C / hour, and then heated to 625°C for 2 hours. The temperature was also increased from 400°C to 550°C at a rate of 100°C / hour, and then heated to 625°C for 2 hours. In all cases, the temperature was increased from room temperature to 300°C and from 100°C / hour to 625°C at a rate of 20°C / minute, and the temperature increase from room temperature and the heating to 625°C were performed in the presence of air. After that, the mixture was allowed to cool naturally to room temperature.

[0034] The rice husks had no black parts on the surface or inside, and were all white and ash-like. The ash from four crucibles was collected and weighed, and all of the above-mentioned manufacturing methods yielded 5g. Each batch of ash was then ground using a mortar and pestle with light manual force for about 5 minutes.

[0035] 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 65% when heated from 350°C to 450°C at a heating rate of 100°C / hour, 71% up to 500°C, 74% up to 550°C, and 71% when heated from 400°C to 550°C at a heating rate of 100°C / hour. The near-infrared solar reflectance was high when the heating range from 350°C to 550°C was at a heating rate of 100°C / hour. [Examples]

[0036] (Manufacturing of near-infrared solar radiation reflecting materials 5) 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.). The temperature was raised from room temperature to 300°C at a rate of 20°C / min, and then from 300°C to 625°C at a rate of 100°C / hour. Next, the mixture was heated at 625°C for 6 hours. The temperature increase from room temperature to 625°C and the heating at 625°C for 6 hours were performed in the presence of air. Afterwards, the mixture was allowed to cool naturally to room temperature.

[0037] The rice husks had no black parts on the surface or inside, and were all 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.

[0038] (Measurement of solar reflectance in the near-infrared region) 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%.

[0039] (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 80, a * 2.6, b * The value was 2.7.

[0040] (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 1.4 J / g·°C.

[0041] (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.

[0042] (Bulk density) 20 g of the sieved ash, with particles smaller than 106 μm, was accurately weighed, placed in a glass graduated cylinder, and tapped. The volume was measured, and the bulk density was calculated to be 0.68 g / mL. [Examples]

[0043] (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 to 300 °C at a rate of 20 °C / min, 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 rice husks were entirely black. This ash was ground in a mortar.

[0044] 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]

[0045] (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.

[0046] 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]

[0047] 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 to any temperature in the range of 300°C to 550°C or more and 650°C or less at a heating rate of 150°C / hour or less, and then heating to the final temperature of the heating process.

2. A method for producing a near-infrared solar radiation reflector, comprising heating rice husks in the presence of air from 300°C to 500°C at a heating rate of 150°C / hour or less, and then heating them to an arbitrary temperature in the range of 550°C to 650°C.

3. A method for producing a near-infrared solar radiation reflector, comprising heating rice husks in the presence of air from 350°C to 550°C at a heating rate of 150°C / hour or less, and then heating them to an arbitrary temperature in the range of 550°C to 650°C.