JP2016160138A - Alumina material, translucent alumina porcelain, and led illumination - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alumina material for restraining transmission of blue light, translucent alumina porcelain, and an LED illumination.SOLUTION: The alumina material contains 99.7 mass% or more of AlO, 0.1-10 ppm of Cr in terms of the oxide thereof (CrO), and 0.1-10 ppm of Ni in terms of the oxide thereof (NiO) and has 25% or higher of an average value A1 of spectral absorptivities at 380-500 nm wavelength. The translucent alumina porcelain has the same composition as that of the alumina material and alumina crystal grains and grain boundaries and 0.5% or smaller porosity. When the average value of the spectral transmissivities at 380-500 nm wavelength is defined as T1 and that of the spectral transmissivities at 500-780 nm wavelength is defined as T2, T2 is 25% or higher and T1 is 65% or lower of T2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to alumina materials, translucent alumina porcelain, and LED lighting.

  Alumina material is excellent in heat resistance and thermal conductivity. For example, a material that requires heat dissipation such as a lighting cover, such as a resin or glass in which an alumina filler is dispersed, translucent alumina porcelain, etc. are used. (For example, see Patent Documents 1 and 2).

  With the practical use of blue LEDs, it is possible to use a white LED in which a yellow phosphor is combined with a blue LED as a light source for a display or illumination. Such an LED light source is rapidly spreading as an energy saving measure.

  The light emitted from the LED light source contains a lot of light called blue light having a wavelength of 380 to 500 nm, which is likely to adversely affect human eyes. Blue light has a large energy in visible light, so light is likely to scatter behind the eyes, causing glare and flickering.

In order to reduce blue light, it is known to add a coloring compound (organic compound) having blue light absorption ability and a coloring component such as Se, Ag, CeO ₂ , TiO ₂ , and Fe ₂ O _{3 to} resin and glass. It has been.

JP 2012-119313 A JP-A-8-293204

  However, the translucent alumina described in Patent Documents 1 and 2 transmits blue light as well as visible light.

  This invention is made | formed in view of said subject, and it aims at providing the alumina material which suppresses permeation | transmission of blue light, a translucent alumina porcelain, and LED illumination.

The alumina material of the present invention contains 99.7% by mass or more of Al ₂ O ₃ and Cr and Ni in an oxide equivalent (Cr ₂ O ₃ , NiO) of 0.1 ppm or more and 10 ppm or less, and has a wavelength of 380 to 500 nm. The average value A1 of the spectral absorptance is 25% or more.

The translucent alumina ceramic of the present invention has alumina crystal particles and grain boundaries, has a porosity of 0.5% or less, Al ₂ O ₃ is 99.7% by mass or more, and Cr and Ni are respectively While containing 0.1 ppm or more and 10 ppm or less in terms of oxide (Cr ₂ O ₃ , NiO), the average value of spectral transmittance at a wavelength of 380 to 500 nm is T1, and the average value of spectral transmittance at a wavelength of 500 to 780 nm is T2. The T2 is 25% or more and the T1 is 65% or less of the T2.

  The LED illumination according to the present invention includes a light source including one or more LED light-emitting elements and a circuit board on which the light-emitting elements are mounted, and a translucent cover that covers at least a part of the light source, and the translucency The cover is characterized by including the above-mentioned alumina material or being composed of the above-described translucent alumina porcelain.

  ADVANTAGE OF THE INVENTION According to this invention, the alumina material which suppresses permeation | transmission of blue light, a translucent alumina porcelain, and LED illumination can be provided.

An example of LED illumination is shown, (a) is a plan view, (b) is a cross-sectional view taken along the line A-A 'of (a). An example of LED illumination is shown, (a) is a plan view, (b) is a cross-sectional view taken along line B-B 'of (a).

One embodiment of the alumina material of the present invention will be described. The alumina material of this embodiment contains 99.7% by mass or more of Al ₂ O ₃ , and contains Cr and Ni in an oxide equivalent (Cr ₂ O ₃ , NiO) of 0.1 ppm or more and 10 ppm or less, respectively, and a wavelength of 380 The average value A1 of the spectral absorptance of ˜500 nm is 25% or more. In the alumina material of the present embodiment, although not certain, Cr contained in the material is considered to be a state in which Cr ²⁺ and Cr ³⁺ coexist, and Ni is considered to be in a state in which Ni ¹⁺ and Ni ²⁺ coexist. It is done. As a result, the alumina material of the present embodiment is considered to have the blue light absorbing ability as described above.

In the present embodiment, Cr and Ni are contained in an amount of 0.1 ppm to 10 ppm in terms of oxides (Cr ₂ O ₃ , NiO), respectively. Alumina (corundum) containing Cr is red and alumina (corundum) containing Ni is known to exhibit yellow to green. However, this content does not usually cause coloration (coloring), and white ( Colorless). In this embodiment, although not certain, Cr ²⁺ and Cr ³⁺ , and Ni ¹⁺ and Ni ²⁺ coexist in the alumina, so that blue light is absorbed by both Cr and Ni, and influence on other visible light. Are considered to offset each other.

Further, by containing 99.7% by mass or more of Al ₂ O ₃ in the alumina material, the blue light as described above is maintained while maintaining the excellent thermal characteristics, weather resistance, and moisture resistance inherent in high-purity alumina. Can be given.

In the alumina material of the present embodiment, it is further preferable that the minimum value of the spectral absorptance at a wavelength of 380 to 500 nm is 10% or more. By setting the minimum value of the spectral absorptance at a wavelength of 380 to 500 nm to 10% or more, the transmission of blue light can be further suppressed. The minimum value of the spectral absorption at a wavelength of 380~500nm to 10% or more, the ratio of the content of Cr and Ni, and the ratio of _{Cr 2 O 3 (Cr 2 O} 3 / NiO) for NiO 0. What is necessary is just to set it as 5-3.0.

The shape of the alumina material in the present embodiment is such that particles (powder) and a film are formed as long as Cr ²⁺ and Cr ³⁺ coexist and Ni ¹⁺ and Ni ²⁺ coexist and have the blue light absorbing ability as described above. Any of the shapes may be used. In the case of a film, it is preferably a polycrystalline film or a polycrystalline body.

In both cases of particles and films, Cr is preferably dissolved in the alumina crystal particles. A part of Ni may be dissolved in alumina crystal particles, or may be present as non-stoichiometric nickel oxide or nickel spinel.

  The particulate alumina material can be used as a coating material or the like by being dispersed in a solvent, or can be used as a glass or resin film that is dispersed in glass or resin and imparted with a blue light absorbing function. Such coatings and resin films can be applied to eyeglass lens coatings, display cover films, and the like. Moreover, you may use the glass and resin itself which disperse | distributed the alumina material of this embodiment as a lens or a cover glass. The average particle diameter of the particulate alumina material is preferably 0.01 to 10 μm from the viewpoint of dispersibility and applicability.

  The LED light source includes many blue lights in the wavelength range of 380 to 500 nm, and the alumina material of the present embodiment is applied to a cover that covers the LED light source in, for example, LED illumination as shown in FIGS. As a result, it is possible to absorb blue light and reduce adverse effects of the blue light on the human body.

  The LED illumination shown in FIG. 1 includes an LED light source in which a plurality of LED light emitting elements 2 are mounted on a circuit board 3, and a translucent cover 1 that covers the LED light source. A power cord 5 is connected to the base 4 on which the LED light source is installed. The power supply to the LED light emitting element 2 is not limited to the power cord 5 and may be a battery.

  The LED illumination shown in FIG. 2 is a wireless power feeding type that further includes a power feeding unit 6 and the base 4 also serves as a power receiving unit. The power cord 5 is connected to the power supply unit 6, and the base 4, which is a power reception unit, supplies the received power to the LED light emitting element 2 via the wiring provided in the column 7. The translucent cover 1 is installed on the column 7.

  As the translucent cover 1 for these LED illuminations, for example, a resin in which the alumina material of the present embodiment is dispersed in a resin is used. In such LED illumination, the alumina material in the translucent cover 1 absorbs the blue light emitted from the LED light source and suppresses the transmission thereof, thereby reducing the adverse effects of the blue light on the human body. The translucent cover 1 may include the alumina material of the present embodiment as a whole, or may use the alumina material of the present embodiment for only a part thereof.

  It is desirable that the alumina material of this embodiment is substantially composed of Al, Cr, Ni, and O as constituent elements. Thereby, an alumina material having blue light absorption ability can be obtained with the minimum constituent elements. Here, substantially consisting of Al, Cr, Ni, and O means that elements other than Al, Cr, Ni, and O are not actively added to the raw material, but Si, Mg, Ca, The total amount of Na, Fe, Mn, Cu, and C in terms of oxides may be contained in an amount of 0.2% by mass or less.

  In addition, it is good also as a colored alumina material which controlled content of the element used as these impurities to such an extent that the above-mentioned spectral absorptance is not impaired. In addition to the blue light absorbing ability, the colored alumina material can be suitably used as a decoration material for LED light sources.

  The type and content of the constituent elements and impurities of the alumina material may be confirmed by elemental analysis such as high frequency inductively coupled plasma (ICP) emission spectroscopy. The valence of Cr and Ni contained in the alumina material can be determined by measuring the spectral transmittance in the wavelength range of 380 to 780 nm as described above. It can also be determined by checking the X-ray absorption fine structure (XAFS).

Such an alumina material can be produced, for example, as follows. As raw material powder,
For example, high-purity Al ₂ O ₃ powder, Cr ₂ O ₃ powder, and NiO powder (each having a purity of 99.8% by mass or more) having an average particle size of 0.1 to 0.8 μm are weighed at a predetermined ratio to obtain high purity. Wet mixing is performed using alumina balls.

The obtained mixture is dried and granulated, and the first heat treatment is performed at 1600 ° C. or higher for 2 to 7 hours in a vacuum. The degree of vacuum in the first heat treatment may be, for example, 1 × 10 ⁻¹ to 1 × 10 ⁻³ Pa. Thereafter, a second heat treatment is further performed in the atmosphere at 1600 to 1680 ° C. for 2 to 5 hours. By performing such a heat treatment, a part of Cr reduced to Cr ²⁺ by the first heat treatment is oxidized again to Cr ³⁺ by the second heat treatment, and Cr ²⁺ and Cr ³⁺ coexist. It is done. Further, it is considered that a part of Ni reduced to Ni ¹⁺ by the first heat treatment is oxidized again to Ni ²⁺ by the second heat treatment, and Ni ¹⁺ and Ni ²⁺ coexist. Incidentally, Cr ₂ O ₃ is considered to dissolved alumina in the crystal particles from the taking corundum structure.

  The alumina powder thus obtained has an improved spectral absorptance at a wavelength of 380 to 500 nm and has a blue light absorptivity, and an average value A1 of a spectral absorptance at a wavelength of 380 to 500 nm is 25% or more. Become. The obtained alumina powder may be further pulverized to adjust the particle size. Further, a translucent alumina porcelain described later may be pulverized to form a particulate (powdered) alumina material.

  The film-like alumina material can be produced by, for example, introducing a predetermined amount of Cr and Ni into aluminum alkoxide as a raw material and using a sol-gel method. When the sol-gel method is used, the temperature of the first and second heat treatments may be lower than that in the case of using the raw material powder as described above, and may be appropriately adjusted according to the raw material to be used.

One embodiment of the translucent alumina porcelain of the present invention will be described. The translucent alumina porcelain of the present embodiment has alumina crystal particles and grain boundaries, has a porosity of 0.5% or less, Al ₂ O ₃ is 99.7% by mass or more, Cr and Ni are contained. Each of them is contained in an amount of 0.1 ppm to 10 ppm in terms of oxide (Cr ₂ O ₃ , NiO). When the average value of spectral transmittance at wavelengths of 380 to 500 nm is T1, and the average value of spectral transmittance at wavelengths of 500 to 780 nm is T2, T2 is 25% or more and the ratio of T1 to T2 (T1 / T2) is 0.65 or less.

  In the present embodiment, since the porosity is 0.5% or less, the influence (reflection) of light scattering due to the difference in refractive index between the pores and the alumina crystal particles constituting the alumina porcelain is reduced, and visible. The spectral transmittance T2 in the light region is 25% or more, and it has a light-transmitting property to transmit visible light appropriately.

Further, Cr contained in the porcelain is considered to be in a state where Cr ²⁺ and Cr ³⁺ coexist, and Ni is considered to be in a state where Ni ¹⁺ and Ni ²⁺ coexist. As a result, the translucent alumina porcelain of the present embodiment has a ratio of T1 to T2 (T1 / T2) of 0.65 or less as described above, and it is considered that transmission of blue light can be suppressed. T1 / T2 is further preferably 0.55 or less.

  The translucent alumina porcelain of this embodiment showing such behavior of spectral transmittance exhibits an ivory color tone. The ivory color tone is in the range of (255, 255, 170) to (255, 255, 210) in the RGB color model.

In this embodiment, Cr and Ni are each contained in an amount of 0.1 ppm to 10 ppm in terms of oxide (Cr ₂ O ₃ , NiO). Alumina (corundum) containing Cr is red and alumina (corundum) containing Ni is known to exhibit yellow to green. However, this content does not usually cause coloration (coloring), and white ( Colorless). In this embodiment, although not certain, Cr ²⁺ and Cr ³⁺ , and Ni ¹⁺ and Ni ²⁺ coexist in the alumina, so that blue light is absorbed by both Cr and Ni, and influence on other visible light. Are considered to offset each other. Thus, in the translucent alumina porcelain of this embodiment, blue light is absorbed by the contained Cr and Ni, and transmission of blue light is suppressed.

Moreover, in the translucent alumina porcelain of this embodiment, by containing 99.7% by mass or more of Al ₂ O ₃ , the excellent thermal characteristics, weather resistance, and moisture resistance inherent in high-purity alumina are maintained. The blue light permeation suppressing ability as described above can be imparted.

  In the translucent alumina ceramic of the present embodiment, it is further preferable that the maximum value of the spectral transmittance at a wavelength of 380 to 500 nm is 30% or less. By setting the maximum value of the spectral transmittance at a wavelength of 380 to 500 nm to 30% or less, it is possible to more reliably suppress blue light transmission.

Incidentally, the maximum value of the spectral transmittance of the wavelength 380~500nm to 30% or less, the ratio of the content of Cr and Ni, and the ratio of _{Cr 2 O 3 (Cr 2 O} 3 / NiO) for NiO What is necessary is just to set it as 0.5-3.0.

  The average pore diameter of pores present in the porcelain is preferably 3 μm or less. In order to further suppress the influence of light scattering by the pores, the average pore diameter is preferably 2 μm or less, and the porosity is preferably 0.4% or less.

  The average particle diameter of the alumina crystal particles constituting the translucent alumina porcelain of this embodiment is preferably 10 μm or less. When the average particle diameter of the alumina crystal particles exceeds 10 μm, the mechanical strength of the porcelain decreases. In view of maintaining high mechanical strength, the average particle diameter of the alumina crystal particles is more preferably 1 to 5 μm.

  The porosity, the average pore diameter, and the average particle diameter of the alumina crystal particles can be determined by, for example, mirror-polishing the porcelain cross section and performing thermal etching or chemical etching as necessary, and then using an optical microscope or scanning electron microscope (SEM). A cross-sectional photograph of the porcelain may be taken and calculated by image analysis.

  Moreover, in this embodiment, it is preferable that 300 ppm or more of Mg is contained in translucent alumina ceramics in terms of MgO. Mg functions as a sintering aid when firing alumina porcelain and has an effect of suppressing grain growth of alumina crystal particles. By containing Mg at 300 ppm or more in terms of MgO, the porosity is small and dense, A translucent alumina ceramic having a small average particle diameter of alumina crystal particles can be obtained. In addition, when Mg is less than 300 ppm in terms of MgO, the sinterability tends to decrease, the pore diameter and porosity increase, and the mechanical strength of the porcelain tends to decrease. The content of MgO is preferably 600 ppm or less.

  The LED light source contains a lot of blue light in the wavelength range of 380 to 500 nm, and the translucent alumina porcelain of the present embodiment is used to cover the LED light source in the LED illumination as shown in FIGS. By applying it to the light cover 1, it is possible to absorb blue light and reduce the adverse effects of the blue light on the human body. The whole of the translucent cover 1 may be made of the translucent alumina porcelain of the present embodiment, or may be a portion using the translucent alumina porcelain of the present embodiment only for a part thereof. The thickness of the translucent alumina porcelain used for the translucent cover 1 is preferably 1.0 to 6.0 mm from the viewpoints of visible light transmissivity, blue light permeation suppression, and durability.

  It is desirable that the translucent alumina porcelain of this embodiment is substantially composed of Al, Cr, Ni, Mg, and O as constituent elements. Thereby, a translucent alumina porcelain that suppresses the transmission of blue light can be obtained with the minimum constituent elements. Here, substantially consisting of Al, Cr, Ni, Mg, and O means that other than Al, Cr, Ni, Mg, and O are not actively added to the raw material, but Si, The total amount of Ca, Na, Fe, Mn, Cu, and C in terms of oxides may be contained in an amount of 0.2% by mass or less.

  In addition, it is good also as colored translucent alumina porcelain by controlling content of the element used as these impurities to the extent which does not impair the above-mentioned spectral transmittance. The colored translucent alumina porcelain can be suitably used especially for decoration of LED lighting while having appropriate visible light transmissivity and blue light permeation suppressing ability.

  The type and content of the constituent elements and impurities of the translucent alumina ceramic may be confirmed by elemental analysis such as high frequency inductively coupled plasma (ICP) emission spectroscopy. The valence of Cr and Ni contained in the translucent alumina ceramic can be determined by measuring the spectral transmittance in the wavelength range of 380 to 780 nm as described above. It can also be determined by checking the X-ray absorption fine structure (XAFS).

What is necessary is just to produce such a translucent alumina ceramic as follows. As the raw material powder, for example, Al ₂ O ₃ powder having a particle diameter of 0.1 to 0.8 μm, Cr ₂ O ₃ powder, NiO powder, and optionally MgO powder (purity of 99.8% or more). Weigh at a predetermined ratio and perform wet mixing using high-purity alumina balls.

  An appropriate amount of binder is added to the obtained slurry to form a desired shape. As the molding method, a known molding method may be applied according to a desired shape, such as sheet molding or die press molding. The molded body thus formed is temporarily fired at 600 to 1000 ° C. for 0.5 to 2 hours in an air atmosphere.

Then, the 1st baking is performed at 1600-1800 degreeC in a vacuum for 2 to 7 hours. The degree of vacuum in the first heat treatment may be, for example, 1 × 10 ⁻¹ to 1 × 10 ⁻³ Pa. By this first firing (vacuum firing), the porosity of the alumina porcelain is densified to 0.5% or less. Thereafter, the second baking is further performed at 1600 to 1680 ° C. for 2 to 5 hours in the air. By performing such two-stage firing, a part of Cr reduced to Cr ²⁺ by the first firing is oxidized again to Cr ³⁺ by the second firing, so that Cr ²⁺ and Cr ³⁺ coexist. It is considered to be. Further, it is considered that a part of Ni reduced to Ni ¹⁺ by the first firing is oxidized again to Ni ²⁺ by the second firing, and Ni ¹⁺ and Ni ²⁺ coexist. Incidentally, Cr ₂ O ₃ is considered to dissolved alumina in the crystal particles from the taking corundum structure.

  In this way, T2 is 25% or more and has a suitable visible light transmissivity, and the ratio of T1 to T2 (T1 / T2) is 0.65 or less and has the ability to suppress the transmission of blue light. Porcelain is obtained.

  In addition, although the alumina porcelain obtained after the first firing (vacuum firing) is densified to a porosity of 0.5% or less, it has a white color due to the presence of many oxygen defects, and has a spectral reflectance of visible light. It is high and has a low spectral absorptivity and low spectral transmittance. Next, by performing second baking (atmospheric baking), oxygen defects are reduced, the spectral reflectance of visible light is reduced, and the spectral transmittance in the wavelength range of 500 to 780 nm is improved.

At the same time, a part of Cr reduced to Cr ²⁺ by the first firing and a part of Ni reduced to Ni ¹⁺ are oxidized again to Cr ³⁺ and Ni ²⁺ by the second firing, and Cr ²⁺ and Cr ³⁺ In addition, Ni ¹⁺ and Ni ²⁺ coexist, the blue light absorption ability is expressed and its transmission is suppressed, and the spectral transmittance at a wavelength of 380 to 500 is lowered. Thus, the alumina ceramics that have undergone the first and second firings are transmissive alumina ceramics that exhibit an ivory color tone, moderately have visible light transmittance, and have blue light transmission suppressing ability.

  In the case of only air firing or vacuum firing after air firing, there are many pores, and the spectral transmittance decreases in the entire visible light wavelength range of 380 to 780 nm. A light alumina porcelain cannot be obtained.

  As a raw material powder containing metal elements of Al, Cr, Ni, and Mg, any powder can be used as long as it is formed as an oxide by firing, such as inorganic compounds such as carbonates and acetates in addition to oxides. May be used. Alternatively, an organic compound such as a metal alkoxide or a metal complex that becomes an oxide by firing may be used as a raw material.

  Further, after performing the first firing (vacuum firing), for example, a hot isostatic pressing (HIP) is performed under the conditions of a pressure of 100 to 200 MPa and a temperature of 1300 to 1650 ° C., and then Second baking (atmospheric baking) may be performed.

  The translucent alumina porcelain obtained as described above has the above-mentioned translucency of visible light and the ability to suppress the transmission of blue light, and at the same time, has bending strength (JIS R 1601-2008, three-point bending strength). It is possible to have excellent mechanical and thermal properties such that the thermal conductivity is 380 MPa or more and the thermal conductivity is 30 W / (m · K) or more. That is, since the bending strength is high, the durability is high, and since the thermal conductivity is high, the heat can be efficiently released and the heat resistance is excellent.

  Hereinafter, the alumina material and translucent alumina ceramic of the present invention will be described in detail based on examples.

(Powdered alumina material)
White alumina raw material powder (Al ₂ O ₃ purity 99.99%) containing 0.5 μm in average particle diameter, 10 ppm in terms of Cr oxide (Cr ₂ O ₃ ) and 10 ppm in terms of Ni oxide (NiO) Prepared. This powder was subjected to heat treatment at 1600 ° C. for 2 hours in a vacuum of 1 × 10 ⁻² Pa as a first heat treatment and for 2 hours in air at 1580 ° C. as a second heat treatment. The obtained alumina powder was crushed and subjected to elemental analysis by inductively coupled plasma (ICP) emission spectroscopy. As a result, the contents of Cr and Ni in the alumina powder were both 10 ppm in terms of oxide as before heat treatment. there were.

  The spectral absorptance of the obtained alumina powder was determined as follows. A sample for evaluation was obtained by press-molding only the obtained alumina powder into a size of 20 mm × 20 mm and a thickness of 2 mm. Using a UV-visible near-infrared spectrophotometer (V-670, manufactured by JASCO Corporation), diffuse reflection measurement was performed in the wavelength range of 200 to 2000 nm, and the spectral absorptance was determined from the result. The average value (A1) of the spectral absorptance at a wavelength of 380 to 500 nm of the alumina powder was 25%, and the minimum value was 10%.

(Translucent alumina porcelain)
An alumina raw material powder containing Cr and Ni, having an average particle size of 0.5 μm, and an Al ₂ O ₃ purity of 99.8 to 99.99% by mass was prepared. A predetermined amount of MgO powder (purity 99.9%) was added to 100% by mass of these alumina raw material powders, and primary mixing was performed for 24 hours in a mill using high-purity alumina balls. Thereafter, a binder was additionally added to perform secondary mixing for 1 hour. The obtained mixed powder was dried and granulated, and then a molded body was produced by mold molding at a pressure of 1 ton / cm ² .

  The produced compact was treated to remove the binder and then fired at the atmosphere and temperature shown in Table 1 to produce various alumina porcelains.

The obtained alumina ceramic was subjected to elemental analysis by inductively coupled plasma (ICP) emission spectroscopy, and the contents of Cr, Ni and Mg in the alumina ceramic were calculated as Cr ₂ O ₃ , NiO and MgO equivalent values. The results are shown in Table 1. In addition, Al ₂ O ₃ content of the obtained alumina porcelain was 99.7% by mass or more.

  The spectral transmittance was evaluated as follows. The obtained alumina porcelain was processed into a size of 20 mm × 20 mm and a thickness of 2 mm, and both sides of the 20 mm × 20 mm were mirror-polished to obtain an evaluation sample. Spectral transmittance and spectral reflectance are measured using a UV-Vis near-infrared spectrophotometer (V-670, manufactured by JASCO Corporation) with a total wavelength of 200 to 2000 nm and an irradiation diameter of 4 mm × 8 mm. Was measured. Table 2 shows the average value (T1) and the maximum value of spectral transmittance at wavelengths of 380 to 500 nm, and the average value (T2) of spectral transmittance at 500 to 780 nm.

  For the evaluation of the structure of the alumina porcelain, the above-mentioned sample for evaluation was thermally etched. Using the optical microscope image (magnification 100 times) of the mirror surface portion after the thermal etching, the pore distribution state was analyzed by an image analyzer (Win ROOF manufactured by Mitani Corporation), and the average pore diameter and porosity were quantified. The average particle diameter of the alumina crystal particles was similarly quantified using an optical microscope image with a magnification of 200 times. Table 2 shows the average pore diameter and porosity of the alumina porcelain and the average particle diameter of the alumina crystal particles.

  The bending strength was obtained by processing an alumina porcelain into a 4 mm × 3 mm × 40 mm test piece and measuring the three-point bending strength at room temperature (conforming to JIS R 1601-2008). The thermal conductivity was measured by a laser flash method (TC-7000 manufactured by Vacuum Riko Co., Ltd.) after processing an alumina porcelain into a test piece having a diameter of 10 mm and a thickness of 2 mm (conforming to JIS R 1611-1997). Each of the produced samples had a bending strength of 380 MPa or more and a thermal conductivity of 30 W / (m · K) or more.

From the above results, the porosity is 0.5% or less, Al ₂ O ₃ is 99.7% by mass or more, and Cr and Ni are each 0.1 to 10 ppm in terms of oxide (Cr ₂ O ₃ , NiO). Sample No. contained 1-4, 7-9 are the ratio (T1 / T2) with respect to T2 of the average value (T1) of the spectral transmittance of wavelength 500-780nm and 25% or more and the average value (T1) of the spectral transmittance of 380-500 nm. ) Is 0.65 or less, indicating that the transmission of blue light can be effectively suppressed.

On the other hand, Sample No. with a porosity exceeding 0.5%. Nos. 5, 6, and 13 to 17 had T2 smaller than 25% and inferior in visible light transmissivity. This is considered because visible light is scattered by many pores. In addition, sample No. 1 which was subjected only to the first firing in vacuum and not subjected to the second firing in the air. In 10-13, there was no difference in the spectral transmittance of T1 and T2, and it became inferior to the transmission suppression function of blue light. Sample No. containing no Cr or Ni Similarly, Nos. 18 and 19 have no difference in spectral transmittance between T1 and T2, and are inferior in the blue light transmission suppressing function.

DESCRIPTION OF SYMBOLS 1 Translucent cover 2 LED light emitting element 3 Circuit board 4 Base 5 Power cord 6 Feeding part 7 Prop

Claims (10)

99.7% by mass or more of Al ₂ O ₃ ,
In addition to containing Cr and Ni in an oxide equivalent (Cr ₂ O ₃ , NiO) of 0.1 ppm or more and 10 ppm or less,
An alumina material, wherein an average value A1 of spectral absorptance at a wavelength of 380 to 500 nm is 25% or more.   2. The alumina material according to claim 1, wherein the minimum value of spectral absorptance at a wavelength of 380 to 500 nm is 10% or more. Having alumina crystal grains and grain boundaries, with a porosity of 0.5% or less,
99.7 mass% or more of Al ₂ O ₃ and 0.1 ppm to 10 ppm of Cr and Ni in terms of oxides (Cr ₂ O ₃ , NiO),
When the average value of the spectral transmittance at a wavelength of 380 to 500 nm is T1, and the average value of the spectral transmittance at a wavelength of 500 to 780 nm is T2,
The translucent alumina porcelain, wherein the T2 is 25% or more and the T1 is 65% or less of the T2.   4. The translucent alumina porcelain according to claim 3, wherein the maximum value of spectral transmittance at a wavelength of 380 to 500 nm is 30% or less.   The translucent alumina porcelain according to claim 3 or 4, wherein an average pore diameter is 3 µm or less.   The translucent alumina porcelain according to any one of claims 3 to 5, wherein an average particle diameter of the alumina crystal particles is 10 µm or less.   The translucent alumina ceramic according to any one of claims 3 to 6, wherein Mg is contained in an amount of 300 ppm or more in terms of oxide (MgO). A light source comprising one or more LED light emitting elements and a circuit board on which the light emitting elements are mounted;
A translucent cover covering at least a part of the light source,
LED lighting characterized by the translucent cover containing the alumina material of Claim 1 or 2. A light source comprising one or more LED light emitting elements and a circuit board on which the light emitting elements are mounted;
A translucent cover covering at least a part of the light source,
The translucent cover is composed of the translucent alumina porcelain according to any one of claims 3 to 7.   The LED illumination according to claim 9, wherein the translucent alumina porcelain has an average thickness of 1.0 to 6.0 mm.

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