JP6545641B2 - Reflective material - Google Patents

Description

  The present invention relates to a reflective material made of porous ceramic.

  Substances with high light reflectance have a wide range of applications as optical reflectors as reflectors because they have little light loss due to absorption, but such substances can be used, for example, in the visible to near UV range. Barium sulfate and fluorocarbon resin porous bodies having high reflectance in a wavelength range are known.

  However, from the viewpoint of heat resistance, barium sulfate is about 80 ° C. and fluorine resin is about 360 ° C., respectively, and the upper limit of the usage temperature is, and these materials are stable in a high temperature environment exceeding 360 ° C. It is difficult to evaluate the characteristics. Further, barium sulfate has a wavelength of 1200 nm or more, and the fluorocarbon resin porous body has a wavelength of 2000 nm or more, and a decrease in total reflectance is observed, so that it is not suitable for use in the near infrared region.

  Therefore, as a material for a reflective material having higher heat resistance than the above-mentioned barium sulfate and the porous fluorocarbon resin, for example, alumina ceramics described in Patent Document 1 can be mentioned. Here, when the pore diameter of the alumina ceramic is 0.10 to 1.25 μm, the reflectance is very high in the visible region and is also high in the ultraviolet region.

  On the other hand, there are disclosures of porous ceramics described in Patent Documents 2 to 4 and heat insulating materials using the same as materials having more excellent heat conduction properties. According to these thermal insulation materials, the thermal conductivity can be suppressed low even at high temperatures by appropriately adjusting the pore volume ratio having a predetermined pore diameter.

JP, 2006-287132, A JP 2012-229139 A JP, 2013-209278, A JP, 2015-000838, A

  According to the invention described in Patent Document 1, the reflectance exceeding 95% is obtained in the region from the ultraviolet region to the wavelength near 600 nm, but the reflectance is near 90% in the near infrared region of 700 nm or more and 2500 nm or less Down to. Therefore, it can not always be said that it is appropriate as a reflector which has high reflectance in a wide wavelength range including the near-infrared range.

  On the other hand, the porous ceramics described in Patent Documents 2 to 4 are heat insulating materials having a radiation suppressing effect, and the reflector manufactured using this has heat resistance of 1500 ° C. or higher, and also use at high temperatures It was considered possible to expect high total reflectance from visible to near infrared region.

  However, the porous ceramics described in Patent Documents 2 to 4 have pores with a pore diameter of 0.5 μm or less existing with a pore volume of more than 0.1 ml / g in order to secure the excellent thermal insulation. There is. When a large number of small pores are present, the amount of adsorbed water is increased by the increase of the specific surface area. Water has absorption at wavelengths of 1400 nm, 1900 nm, and 2500 nm, respectively, and reduces the reflectance in the vicinity of this wavelength range, so that there is a problem that it is not suitable for use as a reflector in the near infrared range. .

  An object of the present invention is, in view of the above, to provide a reflective material made of porous ceramic having high reflectance from visible region to near infrared region.

  The reflective material according to the present invention has a pore volume of not less than 0.5 μm and not more than 10 μm and not less than 0.2 ml / g and not more than 2 ml / g, and a pore volume of less than 0.5 μm and not more than 0.1 ml / g, It is characterized in that it is made of a porous ceramic having an absorptivity of 5% or less at a wavelength range of 500 nm to 2500 nm.

  By having such composition, it can be considered as a reflective material which consists of porous ceramics which have high reflectance from visible region to near-infrared region.

  The reflector according to the present invention can have a high reflectance from the visible region to the near infrared region, specifically, the total reflectance of the wavelength region of 500 nm or more and 2500 nm or less can be 94% or more.

A porous ceramic suitable as such a reflector is made of MgAl ₂ O ₄ or LaAl ₁₁ O ₁₈ .

  An integrating sphere according to the present invention is characterized by using the above-mentioned reflecting material.

  The reflective material according to the present invention can obtain high heat resistance by porous ceramics fired at a high temperature at the time of production, so that it may be used even in a temperature range of 500 ° C. or higher, for example. , Have high reflectance over a wide light wavelength range stably. Therefore, it can be suitably used as a reflector of an optical measuring instrument assumed to be used in a high temperature environment, or as a reflector in ceramics, glass, steel, non-ferrous furnaces and the like.

  Since the reflector according to the present invention has high heat resistance, the integrating sphere of which the reflecting surface is made of the reflector is preferably a conventional integral in the evaluation of a light emitting element accompanied by heat generation or the high temperature evaluation by external heating. It enables accurate and stable evaluation of optical characteristics at high temperature, which was difficult with spheres.

It is the graph which showed the light reflectivity about the porous ceramics of Examples 1 and 3, the fluororesin porous body of comparative example 1, the porous ceramics of comparative example 2, and the MgAl ₂ O ₄ dense body of comparative example 3. Arrows in FIG. 1 indicate that, in the fluorocarbon resin porous body of Comparative Example 2, total reflection decreases at wavelengths of 1400 nm, 1900 nm, and 2500 nm, respectively. It is the photograph which observed the surface of the porous ceramics of Examples 1 and 3, the porous body ceramics of comparative example 2, and the MgAl ₂ O ₄ dense body of comparative example 3 with a scanning electron microscope (SEM), respectively.

  Hereinafter, the present invention will be described in more detail. The reflective material according to the present invention has a pore volume of not less than 0.5 μm and not more than 10 μm and not less than 0.2 ml / g and not more than 2 ml / g, and a pore volume of less than 0.5 μm and not more than 0.1 ml / g, It consists of porous ceramics whose absorptivity in a wavelength range of 500 nm or more and 2500 nm or less is 5% or less.

  First, in the porous ceramic according to the present invention, the pore volume of the pore diameter of 0.5 μm or more and 10 μm or less is 0.2 ml / g or more and 2 ml / g or less. That is, pores with a diameter of 0.5 μm or more and 10 μm or less having a volume of 0.2 ml / g or more and 2 ml / g or less contained in the porous ceramic scatter light with a wavelength of 500 nm or more and 2500 nm or less with high probability.

  Here, the pore volume is calculated from the measurement value obtained by JIS R 1655: 2003 “Test method for pore size distribution of molded body by mercury intrusion method for fine ceramics”.

  The light has a large scattering coefficient when the size of the scatterer is about the same as the wavelength. Mie scattering occurs when the wavelength and size of the scatterer are comparable. Since Mie scattering has less wavelength dependence and less directivity of light, materials in which Mie scattering mainly occurs are suitable as a reflector.

The reflective material according to the present invention is produced by Mie scattering by having relatively large amounts of pores with a pore diameter of 0.5 μm or more and 10 μm or less in the porous ceramic of 0.2 ml / g or more and 2 ml / g or less. A large amount of light of 500 nm or more and 2500 nm or less, which has a wavelength similar to that of the pore diameter, can be scattered.
In addition, the reflective material which consists of a barium sulfate and a fluororesin porous body is also based on Mie scattering, and the point that the directivity of light is small is similar. Therefore, when barium sulfate or a fluorocarbon resin porous body is replaced with the porous ceramic of the present invention, it can be applied as a reflector having improved heat resistance and near infrared reflection characteristics.

  If the pore volume is less than 0.2 ml / g, the amount of pores that scatter light is small, and the reflection characteristics tend to be degraded. On the other hand, when the pore volume is more than 2 ml / g, the number of pores is increased, which may make it fragile, which may make it difficult to produce a reflector and handle it.

  In addition, when the pore volume of the pore diameter of less than 0.5 μm is 0.1 ml / g or less, the adsorption of water to the inner wall surface of the pore is reduced, and the absorption of each of the wavelengths 1400 nm, 1900 nm and 2500 nm is suppressed. Ru. As a result, it is possible to suppress a decrease in the total reflectance at a wavelength of 780 nm or more and 2500 nm or less.

  When the pore volume of the pore diameter of less than 0.5 μm exceeds 0.1 ml / g, the specific surface area tends to be large, and the amount of adsorbed water in the atmosphere tends to be large. The lower limit is preferably lower, but in practice, it is set at the lower limit of detection of a known method, preferably the above-mentioned test method.

  As described above, the porous ceramic according to the present invention has high probability that light with a wavelength of 500 nm or more and 2500 nm or less due to the pore volume of 0.5 μm or more and 10 μm or less being 0.2 ml / g or more and 2 ml / g or less. The effect of scattering and the effect of suppressing the decrease in total reflectance at a wavelength of 780 nm or more and 2500 nm or less due to the pore volume of a pore diameter of less than 0.5 μm being 0.1 ml / g or less are exhibited synergistically As a result, it is possible to further increase the light reflectance in the wavelength range of 500 nm to 2500 nm.

  In the present invention, the pore size distribution in the range of the pore size of 0.5 μm or more and 10 μm or less is not particularly limited. For example, although there may be one peak of the pore size distribution in the relevant range, there may be two or more. The pore size distribution is also measured by the above-mentioned JIS R 1655: 2003 “Test method for pore size distribution of molded body by mercury intrusion method for fine ceramics”.

  More preferably, the porosity of the porous ceramic of the reflective material according to the present invention is 45 vol% to 65 vol%. Within this range, in particular, pores having a pore diameter of more than 10 μm are not excessively present, and there is little concern that the effect of the present invention is impaired. The porosity is calculated in accordance with JIS R 2614 "Method of Measuring Specific Gravity and True Porosity of Fireproof Insulating Brick".

  In addition, when the size of each particle constituting the porous ceramic is from 1 μm to 10 μm, which is the same size as the pore diameter of the pores, the particles also function as a scatterer, so the absolute number of scatterers Can reflect light more efficiently.

  Here, the porous sintered bodies according to the inventions described in Patent Documents 2 to 4 each have a pore volume of not less than 0.5 μm and not more than 10 μm and not less than 0.2 ml / g and not more than 2 ml / g, Since the pore volume of 0.5 μm or less exceeds 0.1 ml / g, the specific surface area is large. Therefore, there exist absorptions at wavelengths of 1400 nm, 1900 nm and 2500 nm, which are not suitable for use in the near infrared region.

  That is, the porous ceramics disclosed in Patent Documents 2 to 4 have a relatively large number of pores per unit volume due to the relatively large number of pores with a pore diameter of 0.5 μm or more and 10 μm or less. The scattering effect is enhanced, and it is effective for reflection of radiation that has a large effect on the thermal conductivity in high temperature areas, that is, suppression of radiation heat transfer, but on the other hand, the pore volume less than 0.5 μm is also relatively large. Due to the presence, the amount of adsorption of water increases as the specific surface area increases, and a sufficient reflection effect is not obtained in the near infrared region.

  On the other hand, in the porous ceramic according to the present invention, the pore volume of the pore diameter of less than 0.5 μm is 0.1 ml / g or less, and preferably, the porosity is 45 vol% to 65 vol%. Therefore, the heat transfer is high, and the heat insulation effect may be inferior to Patent Documents 2 to 4, but since the adsorption of water is suppressed, it can be said that high reflectance can be obtained in a wide wavelength range. .

  Moreover, the porous ceramics which comprise the reflective material which concerns on this invention are 5% or less in absorptivity in a wavelength range of 500 nm or more and 2500 nm or less. In order to obtain high reflectivity, the material itself needs to have no absorption.

In the present invention, as such a material, a material having no absorption in the visible to near infrared region is used, for example, X ₁ Al ₁₁ O ₁₈ (X ₁ = La, Ce, Pr, Nd, Sm, Eu and Examples include hexaaluminate-based ceramics consisting of any of Gd, and spinel ceramics represented by X ₂ Al ₂ O ₄ (X ₂ = any of Mg, Zn, Fe, Ni and Mn) Be

Among the above-mentioned materials, specifically, materials such as MgAl ₂ O ₄ and LaAl ₁₁ O ₁₈ which do not have absorption in the wavelength range of 500 nm to 2500 nm, that is, in the visible to near infrared region are used.

  The reflector according to the present invention is not limited to a single composition as long as the material has the characteristics as described above, and may be a mixture of two or more kinds of materials. In addition, a structure in which a plurality of kinds of materials are stacked, or a structure in which the composition ratio of materials or the pore volume ratio is inclined in the thickness direction or the main surface direction may be used.

  In addition, using the above materials, the pore volume of pore size 0.5 μm or more and 10 μm or less is 0.2 ml / g or more and 2 ml / g or less, and the pore volume of pore size less than 0.5 μm is 0.1 ml / g or less Reflective materials made of porous ceramics and produced using them exhibit the respective functions and effects as a whole, and as a result, it is possible to make the reflectance 94% or more in the wavelength range of 500 nm or more and 2500 nm or less It is

A material such as MgAl ₂ O ₄ or LaAl ₁₁ O ₁₈ described above can be produced by firing, for example, at a high temperature of 1500 ° C. or more, and in this case, it has heat resistance up to the firing temperature and In the wavelength range of 500 nm or more and 2500 nm or less, a remarkable effect of reflectivity of 94% or more is exhibited.

  The method for producing porous ceramics according to the present invention is not particularly limited, and any known method for producing porous ceramics can be applied. For example, adjustment of pore volume can be carried out using a pore former or foam The addition can be carried out as appropriate depending on the addition of the agent, the baking temperature and the like.

  In addition, although one aspect of the manufacturing method of porous ceramics concerning the present invention is similar to one embodiment of a method of obtaining porous ceramics indicated by patent documents 2-4, baking temperature of a forming object is mentioned By making the higher, the grain growth of the ceramic particles can be promoted, many of the pores having a pore diameter of 0.5 μm or less can be crushed, and as a result, the pore volume of a pore diameter of less than 0.5 μm can be lowered. In terms of point, it can be said that it is one of the preferable manufacturing conditions. And while making the calcination temperature of a molded object higher, and adding a pore making material to a ceramic particle timely, the pore volume of 0.5 micrometer or more and 10 micrometers or less of pore diameter, and the pore volume of 0.5 micrometer or less of pore diameters Can be adjusted.

  As described above, since the reflector according to the present invention can obtain high reflectance in a wide wavelength range of visible to near infrared even at high temperatures of 1000 ° C. to 1500 ° C., for example, high temperature range of 1000 ° C. to 1500 ° C. The effect as a heat insulating material which reflects radiation light is obtained.

  Further, the reflector according to the present invention is a diffuse reflector whose scattering mechanism has no directivity in the scattering direction of light similar to the current barium sulfate or fluororesin porous body, so the barium sulfate or fluororesin porous body is a reflector It is possible to use it alternatively for the place where it is being used and to increase the heat resistance much more than these materials.

  As the heat resistance increases, it becomes possible to measure the reflectance at high temperatures. For example, characteristics due to temperature change can be measured, such as light emission accompanied by heat generation (quantity efficiency measurement of LED phosphors, etc.). The integrating sphere in which the reflecting surface is formed by applying the paste made by mixing the porous ceramic according to the present invention and the binder to form a reflecting surface has the conventional integrating method in which the reflecting surface is the above-mentioned barium sulfate or fluorocarbon resin porous material etc. It enables accurate and stable evaluation of a light emitting element accompanied by heat generation, which is difficult with a sphere, or high temperature evaluation by external heating.

  In addition, although the form which contains the said porous ceramics in a part of reflective surface is inferior to the form formed with 100% porous ceramics, the effect of this invention is exhibited significantly. In addition, when a paste-like material is applied to form a reflective surface, heat treatment may be performed before use to remove the binder and dispersion medium used for the paste formation.

  In addition to visible light, the total reflectance in the near infrared region is also high, so that sunlight can be reflected efficiently. Therefore, it can be extremely suitably used also for the insulation of sunlight and the accumulation of sunlight in the space environment.

  In addition, by using the reflector according to the present invention for the innermost layer of the high-temperature furnace, the radiant light in the furnace can be efficiently reflected in the furnace, so the amount of radiant light irradiated to the fired material and the muffle material is increased. Can be fired efficiently. At this time, when the fired product and the muffle material have high emissivity, it is possible to efficiently convert the emitted light into heat, and the efficiency is further improved. Furthermore, because of the heat resistance, when the reflection efficiency is reduced due to the adhesion of the organic matter, the adhered matter can be removed by heating.

  Hereinafter, the present invention will be more specifically described based on examples, but the present invention is not limited by the following examples.

Example 1
11 mol of hydraulic alumina powder (BK-112: manufactured by Sumitomo Chemical Co., Ltd.) and 9 mol of magnesium oxide powder (MGO11PB: manufactured by High Purity Chemical Laboratory Co., Ltd.) are mixed, and pure water having the same weight as the mixture is added. The slurry was prepared. An acrylic resin with a diameter of 10 μm was added to this as a pore former at 50 vol% to the above slurry and mixed, and then it was molded by hydraulic method to obtain a molded body of 60 mm × 70 mm × 20 mm. The molded body was fired in the air at 1850 ° C. for 3 hours to obtain a porous ceramic made of MgAl ₂ O ₄ .

(Example 2)
MgAl ₂ O was prepared under the same conditions as in Example 1 except that the amount of pure water added was 1.2 times the weight of the above mixture, and 60 vol% of acrylic resin was added to the above slurry, followed by firing at 1700 ° C. _A porous ceramic consisting of ₄ was obtained.

(Example 3)
100 g of hydraulic Al ₂ O ₃ powder (BK-112; made by Sumitomo Chemical Co., Ltd.), 29 g of La ₂ O ₃ powder (LAO02PB; made by High Purity Chemical Laboratory Co., Ltd.) and 100 g of pure water are mixed, and acrylic A slurry was prepared by adding 4 g of the emulsion dispersant. The slurry was cast and formed to obtain a 60 mm × 70 mm × 20 mm molded body. This molded body was fired at 1700 ° C. for 3 hours in the air atmosphere to obtain porous ceramics composed of LaAl ₁₁ O ₁₈ .

(Example 4)
120 g of pure water, 5 g of an acrylic emulsion dispersant, and a firing temperature of 1,800 ° C. The other conditions were the same as in Example 3 to obtain a porous ceramic made of LaAl ₁₁ O ₁₈ .

(Example 5)
140 g of pure water, 6 g of an acrylic emulsion dispersant, and a firing temperature of 1850 ° C. The other conditions were the same as in Example 3 to obtain a porous ceramic made of LaAl ₁₁ O ₁₈ .

(Comparative example 1)
The fluoroplastics porous body which is a standard sample of UV-VIS-NIR spectrophotometer (Lambda950 from PerkinElmer) was used.

(Comparative example 2)
The porous ceramic described in Example 1 of Patent Document 3 was used as the porous ceramic formed of MgAl ₂ O ₄ of Comparative Example 2. The preparation method is shown below.
9 mol of magnesium oxide powder (MGO11PB; High Purity Chemical Laboratory Co., Ltd.) is mixed with 11 mol of hydraulic alumina powder (BK-112; manufactured by Sumitomo Chemical Co., Ltd.), and pure water is added to prepare a slurry did. To this, 50 vol% of acrylic resin with a diameter of 10 μm was added as a pore forming material to the slurry and mixed, and the mixture was molded by hydraulic method to obtain a plate-like molded body of 75 mm × 105 mm × 30 mm thickness. This molded body was fired at 1500 ° C. for 3 hours in the air to obtain porous ceramic made of MgAl ₂ O ₄ .

(Comparative example 3)
Using a commercially available MgAl ₂ O ₄ (Bicarox: manufactured by Baikouski Japan Co., Ltd.), a MgAl ₂ O ₄ dense body produced by firing at 1850 ° C. was used.

With regard to the porous ceramics of Examples 1 to 5, the porous ceramics of Comparative Example 2, and the MgAl ₂ O ₄ dense body of Comparative Example 3, JIS R 1655: 2003 “Pore diameter distribution of compacts of fine ceramics by mercury intrusion method” The pore volume was measured and calculated according to “Test method”. In addition, with respect to the materials of Examples 1 to 5 and Comparative Examples 1 to 3 described above, a wavelength of 500 nm is obtained using a UV-VIS-NIR spectrophotometer (Lambda 950 made by PerkinElmer) and an integrating sphere of 150 mm in diameter attached thereto. And the total reflectance at a wavelength of 2500 nm was measured. These results are summarized in Table 1.

  Furthermore, the reflectance in the wavelength range of 250 nm to 2500 nm is shown in FIG. 1 for Examples 1 and 3 and Comparative Examples 1 to 3. As described above, Comparative Example 1 represents the spectrum of the standard sample of the UV-VIS-NIR spectrophotometer, and in Examples 1 and 3 and Comparative Examples 2 and 3, the values obtained from Comparative Example 1 are used. Represents a calibrated spectrum.

  As is clear from Table 1, in each of Examples 1 to 5, the reflectance at a wavelength of 500 nm and a wavelength of 2500 nm exceeded 94%. It can be said that this is comparable to the fluorocarbon resin porous body (Comparative Example 1) used as a standard sample of the UV-VIS-NIR spectrophotometer. Furthermore, as shown in FIG. 1, in Examples 1 and 3, in particular, the reflectance from around the wavelength of 2100 nm to the wavelength range of 2500 nm is substantially higher than that of Comparative Example 1.

  In particular, in the porous ceramics of Examples 2 to 4 having a pore volume of 0.5 ml / g or more in the pore diameter of 0.5 μm to 10 μm, a high reflectance of 96% or more at a wavelength of 500 nm is shown. This is because even when compared to the porous ceramics of Example 1 or Example 5 having a pore volume of less than 0.5 ml / g in the pore diameter of 0.5 μm to 10 μm, higher reflectance can be obtained on the short wavelength side. It is particularly preferable in terms of

  The porous ceramic of Comparative Example 2 is a spinel that does not have a large absorption in the wavelength range of 250 nm to 2500 nm, and as in the embodiment of the present invention, the pore volume of 0.5 μm to 10 μm is 0.2 ml. It is more than / g and less than 2 ml / g. However, since the pore volume of the pore diameter of less than 0.5 μm is larger than 0.1 ml / g, the moisture in the air is trapped in the pores of the pore diameter of less than 0.5 μm, and as shown by the arrow in FIG. It is considered that there is a decrease in total reflection at 1900 nm and 2500 nm, respectively.

  In Comparative Example 3, although grain boundaries are present, the pore volume of pore sizes of 0.5 μm to 10 μm is zero. Therefore, since there are no pores for scattering light, the total reflectance decreases as the wavelength increases. It can be seen from FIG. 1 that the reflectance is significantly lower than 94%, particularly in the wavelength range of 1000 nm or more.

The photograph which carried out SEM observation by 5000 times of the surface of the porous ceramics of Example 1 and 3 and the porous-body ceramics of Comparative example 2 and the MgAl ₂ O ₄ -based dense body of Comparative Example 3 is shown in FIG. As is clear from FIG. 2, in Examples 1 and 3, it can be confirmed that there is a single micron-order particle. On the other hand, in Comparative Example 2, although there is a particle of single micron order and the particle is also considered to be a scatterer of light, since there is a pore of submicron order, the specific surface area becomes large, and the water in the atmosphere is It is estimated that the amount of adsorbing is increasing. However, since there are submicron-order particles, it can be said that the total reflectance of 500 nm or less is large. In Comparative Example 3, it is understood that no pore exists.

Claims (4)

  The pore volume of pore diameter 0.5 μm or more and 10 μm or less is 0.2 ml / g or more and 2 ml / g or less, the pore volume of pore diameter less than 0.5 μm is 0.1 ml / g or less, and in the wavelength range of 500 nm or more and 2500 nm or less A reflector characterized in that it is made of porous ceramic having an absorptivity of 5% or less.   The total reflectance in a wavelength range of 500 nm or more and 2500 nm or less is 94% or more, The reflector according to claim 1. The reflective material according to claim 1, wherein the porous ceramic is made of MgAl ₂ O ₄ or LaAl ₁₁ O ₁₈ .   An integrating sphere using the reflector according to any one of claims 1 to 3.