Near-infrared solar radiation reflecting material

Abstract

The present invention provides a material that has high solar reflectance in the near-infrared wavelength range, excellent flame retardancy, low density, and is easy to crush or pulverize during manufacturing. [Solution] Use calcined ash produced by heating rice husks.

Description

[Technical Field]

[0001] This invention relates to reflection in the near-infrared region, and more specifically to a material that efficiently reflects wavelengths in the near-infrared region. [Background technology]

[0002] In recent years, global warming has progressed, and the high temperatures caused by sunlight, especially during the summer, are having a significant impact not only on daily life but also on industrial activities and agricultural crops, potentially endangering lives. Therefore, various measures are being implemented to mitigate the effects of sunlight on outdoor buildings and structures.

[0003] Near-infrared light, which corresponds to the wavelength range of 780nm to 2500nm in sunlight, accounts for nearly 50% of the sun's radiant energy and has a thermal effect. Therefore, reflective materials with wavelengths in the near-infrared region are used as a measure to suppress temperature rise.

[0004] As reflective materials, metallic white pigments such as titanium dioxide and zinc oxide are well-known, and a method using titanium dioxide has been proposed (Patent Document 1). Another method using hollow silica has been proposed (Patent Document 2). Alternatively, organic materials such as azomethine azo pigments, perylene pigments, isoindolino pigments, disazo pigments, polyazo pigments, quinacridone pigments, and phthalocyanine pigments have been used (Patent Documents 3 and 4).

[0005] However, metallic white pigments, such as titanium dioxide described in Patent Document 1, have high density, which poses a weight problem when used. Furthermore, the minerals used as raw materials for these metals are hard, requiring strong physical force for crushing and pulverizing, making manufacturing difficult. The method using hollow silica described in Patent Document 2 requires the silica shell to have mesopores, limiting the raw material silica to tetramethoxysilane and tetraethoxysilane, among other problems. Additionally, the organic materials described in Patent Documents 3 and 4 have low reflectivity and problematic flame retardancy. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent No. 4546834 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2011-122096 [Patent Document 3] Japanese Unexamined Patent Application Publication No. 4-255769 [Patent Document 4] Japanese Unexamined Patent Application Publication No. 2000-129172 [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] In view of the above problems, an object of the present invention is to provide a material that has a high solar reflectance at wavelengths in the near-infrared region, excellent flame retardancy, a low density, and is easy to crush or pulverize during production. [Means for Solving the Problems]

[0008] As a result of intensive research to solve the above problems, the present inventors have found that the following invention can solve the problems.

[0009] To solve the above problems, one aspect of the present invention is summarized as a near-infrared solar reflective material containing calcined ash of rice husk as an active ingredient.

[0010] Another aspect of the present invention is summarized as a near-infrared solar reflective material containing, as an active ingredient, calcined ash produced by heating rice husk at an arbitrary temperature within the range of 500°C or higher and 525°C or lower in the presence of air.

[0011] Still another aspect of the present invention is summarized as a paint characterized by containing 1% by weight or more of a near-infrared solar reflective material containing calcined ash of rice husk as an active ingredient.

[0012] A further aspect of the present invention is a paint characterized by containing 3% by weight or more of calcined rice husk ash, which is a near-infrared solar radiation reflecting material with calcined rice husk ash as an active ingredient, and having a size of 106 μm or less. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a material that has a high solar reflectance in the near-infrared wavelength range, excellent flame retardancy, low density, and is easy to crush or pulverize during manufacturing. [Modes for carrying out the invention]

[0014] 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.

[0015] 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 husks of the present invention refer to the outer layer of rice husks. The near-infrared solar radiation reflector of the present invention is calcined ash produced by heating rice husks. It has been found that this calcined ash possesses near-infrared solar radiation reflectivity and can be used as a near-infrared solar radiation reflector. The calcined ash of the present invention is produced by heating in a range of approximately 500°C to 800°C. During production, heating the rice husks in the presence of air results in a higher near-infrared solar radiation reflectance of 55% or more, making it more effective as a reflector. The calcined ash produced in this case conforms to the L standard specified in the CIE standard. * a * b * L in the color system * The value is 70 or higher, and it exhibits a white color. Oxygen may be present instead of air.

[0016] The reflectance, which indicates the degree of effectiveness of near-infrared solar radiation reflection, is determined 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. Using this as a reference, the spectral reflectance of each sample at each wavelength is determined, multiplied by a weighting coefficient representing the distribution of spectral irradiance of the reference sunlight, and then weighted and averaged over wavelengths of 780 nm to 2500 nm. The weighting coefficient is the irradiance obtained by integrating the spectral irradiance of the reference sunlight, as defined in Table 1, Column 8 of ISO 9845-1:1992, over wavelengths of 780 nm to 2500 nm.

[0017] Furthermore, the calcined ash produced by heating rice husks in the presence of air at any temperature within the range of 500°C to 525°C in this invention has particularly high reflectivity and is an effective component suitable for use as a near-infrared solar radiation reflector. Heating of rice husks within the range of 500°C to 525°C is carried out in a heating furnace, and both batch furnaces and continuous furnaces are possible. Heat sources include electric, gas, heavy oil, and combustion types using fossil fuels such as kerosene, but electric is preferred because temperature control is easier. The heating time within the range of 500°C to 525°C varies depending on the amount of rice husks, heat conduction, and degree of contact with air, with the heating time increasing 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 stack of rice husks during heating, the shorter the heating time. The end of heating is indicated by the disappearance of black ash.

[0018] Use dried rice husks. When heating the rice husks, it is preferable to remove any stems or other parts mixed in with the husks before or after heating, as these will remain as black ash when burned.

[0019] When used as a near-infrared solar radiation reflector, powdering it makes handling easier and improves moldability and coating properties. The calcined ash is brittle and can be easily pulverized to a size of several hundred micrometers or less using a mortar and pestle with light force or airflow.

[0020] Furthermore, when using the calcined ash of the present invention as a near-infrared solar radiation reflector, there is no problem in mixing it with other reflectors or materials.

[0021] The type of paint used in this invention is not particularly limited as long as the desired effect is achieved, but it can be used in various types of paints, such as water-based and oil-based paints. The solar reflector of this invention is preferably added to the paint in a crushed or powdered form for more uniform dispersion. Dispersants and binders may also be added as appropriate. The content of the near-infrared solar reflector used in the paint is 1% by weight or more from the viewpoint of near-infrared solar reflectance effect. On the other hand, when the reflector of this invention, which consists of particles of 106 μm or less after crushing, is added to the paint, the content is 3% by weight or more from the viewpoint of adhesion. The size of 106 μm or less in this invention refers to calcined ash that is small enough to pass through a sieve with a mesh size of 106 μm. Painting methods include brushes, rollers, and sprays. It can also be used in combination with other near-infrared solar reflectors and various components commonly used in paints.

[0022] The present invention can be used on structures such as houses, factories, and agricultural greenhouses that are exposed to sunlight outdoors, as well as on roofs, exterior walls, and interior walls of outdoor refrigerators and freezers, air conditioning outdoor units, storage tanks, and various other structures.

[0023] The present invention will be specifically described below with reference to examples, but these are merely illustrative and the present invention is not limited to these examples. [Examples]

[0024] (Manufacturing of near-infrared solar radiation reflecting material 1) 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 room temperature at a rate of 20°C / min to 500°C, 525°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.

[0025] 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 temperatures. Each batch of ash was then ground using a mortar and pestle with light, manual force for about 5 minutes.

[0026] (Measurement of solar reflectance in the near-infrared region) 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.

[0027] 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.

[0028] As a result, the near-infrared solar reflectance of the calcined ash was 72% at a heating temperature of 500°C, 71% at 525°C, 66% at 550°C, 64% at 600°C, and 57% at 650°C. At heating temperatures of 500°C and 525°C, the near-infrared solar reflectance was high, exceeding 70%.

[0029] (Color evaluation) The above color evaluation of each type of calcined ash is based on the color system L. * a * b *The value was determined by measuring the reflectance with a spectrophotometer. 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 the reflection of 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 360 nm to 830 nm was measured with an incident light angle of 1° and a D65 lamp as the light source. L * a * b * The calculation of the value was performed according to JIS Z8730:2002 using a color evaluation program (manufactured by JASCO Corporation) introduced into a personal computer that controls the ultraviolet-visible-near-infrared spectrophotometer.

[0030] As a result, the calcined ash at a heating temperature of 500 °C had L * of 78, a * of 1.9, b * of 3.8, and at 525 °C, L * was 77, a * was 1.5, b * was 3.5, and at 550 °C, L * was 76, a * was 1.7, b * was 2.4, and at 600 °C, L * was 75, a * was 1.5, b * was 2.0, and at 650 °C, L * was 73, a * was 1.4, b * was 0.6.

Example

[0031] (Comparative Test) 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 heated at 300 °C for 2 hours. The temperature increase from room temperature to 300 °C and the heating at 300 °C were performed in the presence of air. Afterwards, it was allowed to cool naturally to room temperature. The rice husks were entirely black. This ash was ground in a mortar.

[0032] The near-infrared solar reflectance and color system L of these two comparative samples * a * b * The values ​​were 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%, L * ga 64, a * 1.3, b * The value is 11, and the near-infrared solar reflectance of the calcined ash at a heating temperature of 300°C is 33%, L * 34, a * 0.8, b * The value was 1.0. [Examples]

[0033] (Manufacturing of near-infrared solar radiation reflecting materials 2) 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 500°C at a rate of 20°C / min, and then heated at 500°C for 6 hours. The temperature increase from room temperature to 500°C and the heating at 500°C were performed in the presence of air. Afterwards, the furnace 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 was collected from three evaporation dishes and weighed 30g. This ash was placed in a mortar and ground with a pestle using light manual force for about 15 minutes. The manufacturing process described here was repeated twice to obtain a total of 60g of ash.

[0035] (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 72%.

[0036] (Color evaluation) Color system L of the above calcined ash * a * b * The value was measured. The measurement method was the same as the method described in Example 1. As a result, L * ga 77, a * 1.9, b * The value was 3.8.

[0037] (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 and sealed 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.

[0038] (Sifting) When the above calcined ash was separated by size using stainless steel test sieves with mesh openings of 250 μm and 106 μm, ash larger than 250 μm accounted for 5% by weight, ash between 106 μm and 250 μm accounted for 16% by weight, and ash smaller than 106 μm accounted for 79% by weight.

[0039] (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]

[0040] (Paint containing near-infrared solar radiation reflector 1) 20g of water-based wood protective paint (product name: synthetic resin paint, color: transparent, manufactured by Kanpe Hapio Co., Ltd.) was mixed with the calcined ash prepared in Example 3 in amounts of 1%, 2.5%, and 5% by weight, and thoroughly stirred with chopsticks. Each of these paints was applied once to a cedar board with a brush and allowed to air dry at room temperature overnight.

[0041] At all concentrations, the surface of the board was white, the color of the calcined ash, and an amount exhibiting near-infrared solar reflection was present. When the painted board was tapped on a table, the calcined ash did not peel off at any concentration. Furthermore, when cool air from a hairdryer was applied to the same board surface from a distance of 10 cm for 3 minutes, the calcined ash did not peel off. [Examples]

[0042] (Paint containing near-infrared solar radiation reflector 2) To 20g of water-based wood protective coating (product name: synthetic resin coating, color: transparent, manufactured by Kanpe Hapio Co., Ltd.), calcined ash prepared in Example 3 above and passed through a sieve with a mesh size of 106 μm was added in amounts of 1%, 2%, 3%, 5%, 10%, and 20% by weight, and the mixture was thoroughly stirred with chopsticks. This coating was applied once to each cedar board with a brush and allowed to air dry at room temperature overnight.

[0043] When calcined ash was added to the surface of the board at a thickness of 1% and 2% by weight, the thickness of the calcined ash was very thin and insufficient to exhibit near-infrared solar radiation reflection. With paint containing 3% or more by weight of calcined ash, a sufficient amount of calcined ash adhered to the surface of the board to exhibit near-infrared solar radiation reflection. When boards coated with paint containing 3% or more by weight of calcined ash were tapped on a table, the calcined ash did not peel off at any concentration. Furthermore, when cold air from a hairdryer was applied to the surface of the same board from a distance of 10 cm for 3 minutes, the calcined ash did not peel off. [Industrial applicability]

[0044] The present invention is useful, for example, in the field of materials for providing heat-shielding properties to buildings and structures.

Claims

1. A near-infrared solar radiation reflector that uses the ash from burnt rice husks as an active ingredient.

2. A near-infrared solar radiation reflector whose active ingredient is calcined ash produced by heating rice husks in the presence of air at any temperature within the range of 500°C to 525°C.

3. A paint characterized by containing 1% by weight or more of the near-infrared solar radiation reflecting material described in claim 1.

4. A paint characterized by containing 3% by weight or more of calcined ash having a size of 106 μm or less among the near-infrared solar radiation reflecting material described in claim 1.