JP2014037324A - Ceramics sintered compact for reflector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dense ceramics sintered compact for a reflector capable of being reflected at high efficiency to light from a near-ultraviolet region to a near-infrared region with transmission and absorption loss reduced, and also having reduced open pores.SOLUTION: Disclosed is a ceramics sintered compact for a reflector in which the dispersion particles made of alumina and either or both of zirconia and yttria are dispersed into a glass as a matrix at a ratio of 60 vol.% or higher in total, regarding the diameter of the dispersion particles, the ratio lying in the range of 1 μm is 50 vol.% or higher to all the dispersion particles, and water absorption percentage is 1 mass% or lower.

Description

  The present invention relates to a sintered ceramic body used for a reflector for an LED, a reflector for a laser oscillator, or the like.

  With the recent trend of energy saving, the invention of LED and the realization of white LED, it is considered that the future lighting will move to LED lighting along with the cost reduction of LED. Until now, there was intense development competition for LED chips, but the surrounding technology, packaging and modularization technology, will continue to develop and compete in the future.

  As this peripheral technology, development of a reflector material that efficiently reflects light emitted from the element in the light projecting direction must also progress. For example, when a silver film is used as a reflector material, there is a drawback that the reflectance in the near ultraviolet region with a wavelength of 450 nm or less is drastically reduced. However, the appearance of a reflector material that efficiently reflects light from the near ultraviolet to the near infrared region is desired.

  On the other hand, although it is said that LEDs have high light conversion efficiency, they also generate heat, and heat generated from surrounding power supply modules cannot be ignored. The more heat-resistant LEDs are required, the more heat resistance is required. Further, in some cases, a specification capable of glass bonding at the time of LED production is also required, and in this respect, ceramics are suitable as a heat-resistant reflector material. Of course, considering the market intention, that is, low price orientation, most of them will be made of resin or metal, but ceramics will be an indispensable material for reflectors for high-performance LEDs.

  Recently, LED reflectors made of ceramics have been developed and adopted. As of 2011, Japan's share in this field is over 90%, which is a relatively new field unique to Japan (Non-Patent Document 1).

  As a preparation example, when alumina is a main component, it is known that the reflectivity is remarkably superior to dense alumina by appropriately inserting voids (Patent Document 1).

  However, in the process of packaging or modularizing the LED, a wet process such as plating may be performed or an organic substance may be touched. In this case, the impurities in the voids are likely to be discolored, and even if washed, the porous body having voids is generally difficult to wash and tends to be uneven in color. For this reason, as the ceramic, a dense body with few open pores is desirable, and since it is a dense body, the thermal conductivity is increased, and the effect of having the feature of easily radiating heat can be obtained.

  As another example of a ceramic sintered body for a reflector, a ceramic sintered body made of alumina and a glassy component is also known (Patent Document 2).

  In Patent Documents 1 and 2, a ceramic sintered body that exhibits a higher reflectance is desired, although the reflectance is improved.

JP 2006-108180 A Japanese Patent No. 4747067

“Toward Japan's LED Advanced Countries Leading by Western Japan” The Development Bank of Japan

  The problem to be solved by the present invention is a dense reflector ceramic that can reflect light in the near-ultraviolet to near-infrared region with low transmission and absorption loss and high efficiency, and with few open pores. The object is to provide a sintered body.

  In the ceramic sintered body for a reflector of the present invention, dispersed particles composed of alumina and one or both of zirconia and yttria are dispersed in a glass as a matrix at a ratio of 60% by volume or more in total. The diameter of the dispersed particles is 50% by volume or more with respect to the total dispersed particles and the water absorption is 1% by mass or less with respect to the total dispersed particles.

  That is, the present invention forms a ceramic sintered body for a reflector by adding one or both of zirconia and yttria together with alumina as a scatterer (dispersed particles) to a transparent glass phase. Alumina, zirconia, and yttria are all transparent materials that do not absorb in the target wavelength region (near ultraviolet to near infrared region), and alumina, zirconia, and yttria have different refractive indexes. Therefore, a higher reflectance than the case where only alumina is dispersed in the glass phase as in Patent Document 2 can be obtained.

  Furthermore, in the present invention, glass exists as a matrix in the gaps of the dispersed particles, so that unlike the above-mentioned Patent Document 1, a dense ceramic sintered body with few open pores is obtained. In the present invention, “dense” means that there are few open pores, so the degree of denseness is evaluated by the water absorption rate. Specifically, the present invention requires that the water absorption is 1% by mass or less. When the water absorption rate exceeds 1% by mass, the probability that the closed pores and the open pores are connected increases, and contaminants that enter the voids (open pores) in the wet process such as plating described above are likely to cause discoloration and color unevenness.

  In the present invention, the larger the amount of dispersed particles added to the glass phase, the better. However, if a dense body is prepared using a material containing 100% dispersed particles, the crystal particles develop up to several μm and transparency is obtained. On the other hand, when the composition is such that the amount of dispersed particles is less than 60% by volume, the amount of glass phase becomes excessive, and transparency appears and becomes defective. Therefore, in the present invention, the dispersed particles are dispersed in the glass phase, and the amount is required to be 60% by volume or more. The upper limit of the amount of dispersed particles is naturally less than 100% by volume, but is preferably 75 to 85% by volume from the viewpoint of obtaining high reflectivity and denseness.

  The above description leads to the fact that the dispersed particles must be a certain size (diameter) or less. However, in the experiment (see Examples described later), the proportion of the dispersed particles in the range of 1 μm or less is the total dispersed particles. If it is 50 volume% with respect to this, there is no problem, and it is preferable that it is 55 volume% or more from a viewpoint of light scattering.

  As described above, the present invention adds one or both of zirconia and yttria together with alumina as dispersed particles for the glass phase. For example, when zirconia is added, the reflectance increases, but the thermal conductivity decreases. Alumina has a price of 1/10 or less compared to zirconia and yttria, and alumina is very cheap. In practice, the composition is determined in consideration of physical properties other than these prices and reflectivity. That is, zirconia and yttria are added as reflectivity improvers and adjusters.

  A preferable blending ratio of these dispersed particles is a ratio of 100% by volume of the ceramic sintered body in consideration of the above-mentioned circumstances, and 70 to 85% by volume of alumina, one of or both of zirconia and yttria is a total. 3 to 10% by volume.

  In the present invention, α-alumina particles having a primary particle diameter of 0.2 μm or less are preferably used as the alumina raw material. In Patent Document 2, the use of transition alumina is recommended. However, if transition alumina is used, shrinkage during sintering is too large, and it is difficult to pass the product dimensions as it is. For this reason, by using alumina fired to a high temperature, that is, α-alumina, shrinkage during sintering is suppressed, and a ceramic sintered body for a reflector that is favorable in terms of dimensions can be obtained.

  According to the ceramic sintered body of the present invention, since one or both of zirconia and yttria are dispersed as dispersed particles in the glass matrix together with alumina, it is suitable for light in the near ultraviolet to near infrared region. Therefore, it is possible to reflect with high efficiency by reducing transmission and absorption loss.

  Further, since glass exists as a matrix in the gaps between the dispersed particles, a dense ceramic sintered body with few open pores is obtained. Therefore, even if a wet process such as plating is performed in the manufacturing process of the reflector or an organic substance is touched, impurities and the like are not easily invaded and color unevenness hardly occurs, and a good reflector can be provided. Furthermore, since it is dense, the thermal conductivity is increased, and an effect of having the characteristics of easily radiating heat can be obtained.

The measurement result of the reflectance of the Example of the ceramic sintered compact for reflectors of this invention and a comparative example is shown. An example is shown in the structure | tissue (scanning electron micrograph) of the ceramic sintered compact for reflectors of this invention.

  In the ceramic sintered body for a reflector of the present invention, dispersed particles composed of alumina and one or both of zirconia and yttria are dispersed in a glass as a matrix at a ratio of 60% by volume or more in total. Become. Moreover, the ratio of the diameter of the dispersed particles in the range of 1 μm or less is 50% by volume or more with respect to the total dispersed particles, and the water absorption is 1% by mass or less.

  The ceramic sintered body for reflector according to the present invention can be obtained by mixing, molding and firing glass and dispersed particles (alumina, zirconia, yttria). As these raw materials, those having a fine particle size and high purity (having few impurities that absorb light) are preferable, and any of the commercially available products can be used.

  These raw material particles are mixed as, for example, a suspension, dried, and then formed into a predetermined size. The molded product is fired at about 1200 to 1500 ° C. Here, the range of 1200 to 1500 ° C. in the firing temperature means that the optimum firing temperature varies depending on the blending of raw materials. Specifically, the firing temperature at which the diameter of the dispersed particles of the obtained ceramic sintered body is in the range of 1 μm or less is 50% by volume or more with respect to the total dispersed particles and the water absorption is 1% by mass or less. Is the optimum firing temperature.

  Examples of the present invention are shown below together with comparative examples.

<Example 1>
As raw materials for dispersed particles, 74% by mass of α-alumina having a primary particle size of 0.2 μm or less, 11% by mass of zirconia sol having a primary particle size of 0.1 μm or less as zirconium oxide, and silica sol as a raw material for silica-based glass 10% by mass and 5% by mass of calcium carbonate as calcia. A normal dispersion material, binder, and release material were added thereto to prepare a suspension having a concentration of about 30%. This suspension was supplied to a spray dryer apparatus at a tower top temperature of about 140 ° C. and a tower bottom temperature of about 80 ° C. to obtain granules. The granules were molded with a hand press molding machine under a pressure of 1.0 ton / cm ² to obtain a molded product having a diameter of 20 mm and a thickness of about 2 mm. This was fired in the atmosphere at a temperature of 1200 to 1500 ° C. for 2 hours, and the reflectance was measured using a sample having a water absorption rate of 1% by mass or less as a sample.

  That is, as described above, in the present invention, the firing temperature at which the water absorption rate is 1% by mass or less is the optimum firing temperature without overcalcination, and in this example and the following examples, the water absorption rate is 1% by mass or less. Each is fired at an optimum firing temperature, and the temperature range is 1200 to 1500 ° C.

  Here, the water absorption was measured by the Archimedes method of vacuum defoaming. The reflectance was measured with a spectroscopic color difference meter based on a double beam method and a simultaneous compensation method for all wavelengths. In the measurement of the reflectance, the sample was ground to a thickness of 0.8 mm, the organic content was removed by oxidation at 1000 ° C. to remove the grinding liquid, and then the reflectance was measured. Note that the actual product is assumed to have a burned surface, but this is a preliminary experiment in which the burned surface is prepared by accurately examining the weighing and shrinkage rate and compared with the ground product. And it has been confirmed that the 1000 ° C. treatment does not affect the reflectance or is within the error range.

  The reflectance of the sample of this example is shown in FIG. High reflectivity is obtained from the near ultraviolet to the near infrared region.

  Moreover, the scanning electron micrograph of the sample of a present Example is shown in FIG. Although alumina particles and zirconia particles of approximately 1 μm or less are observed, alumina particles of 3 μm or more are also present. When the dispersed particles (alumina particles and zirconia particles) were image-analyzed, among the dispersed particles, those having a particle size of 1 μm or less were 53% by volume.

  The water absorption of the sample of this example was 0.0% by mass. Furthermore, when 20 samples were produced and the variation in diameter after shrinkage was confirmed, the variation was within 0.5% of the average diameter. In addition, when the raw material of alumina was changed from α-alumina to transition alumina, and the variation in diameter after shrinkage was confirmed in the same manner, the variation was 0.76%.

  The volume ratio of the dispersed particles (alumina particles and zirconia particles) of the sample of this example was 78% by volume (71% by volume of alumina particles and 7% by volume of zirconia particles) with respect to the entire sintered body as a result of image analysis. Met.

<Example 2>
Only 70% by mass of alumina and 15% by mass of zirconia differed only in their blending amounts. Thereafter, samples were prepared under the same conditions as in Example 1. The reflectance is shown in FIG. The reflectance was the same as in Example 1. From this, it can be said that sufficient reflectance can be obtained if the blending amount of zirconia is up to 15% by mass. When the amount of zirconia is excessive, the thermal conductivity is lowered as described above, and the cost is also increased.

  The water absorption of the sample of this example is 0.0% by mass. Further, as a result of image analysis, 58% by volume of the dispersed particles having a particle size of 1 μm or less is obtained, and the volume ratio of the dispersed particles is the sintered body It was 78 volume% (68 volume% of alumina particles, 10 volume% of zirconia particles) with respect to the whole.

<Example 3>
In Example 1, a sample was produced in the same manner as in Example 1 except that zirconia was replaced with yttria. As a yttria raw material, one previously ground to 0.7 μm or less by a bead mill was used. The reflectance is shown in FIG. The reflectance was the same as in Examples 1 and 2.

The water absorption of the sample of this example is 0.0% by mass. Further, as a result of image analysis, 55% by volume of the particles having a particle size of 1 μm or less among the whole dispersed particles is obtained, and the volume ratio of the dispersed particles is the sintered body. For the whole
78% by volume (70% by volume of alumina particles and 8% by volume of yttria particles).

<Comparative Example 1>
A commercially available silver reflective film was purchased and the reflectance was measured. The result is shown in FIG. It can be seen that the reflectance in the near-ultraviolet region with a wavelength of 450 nm or less rapidly decreases.

<Comparative example 2>
The reflectance of a conventional alumina sintered body is shown in FIG. This is the result of investigating a commercially available alumina material for reflectors, preparing a sintered body close to its component, and measuring the reflectance. The reflectivity was lower than that of the example of the present invention. This can be said to be the effect of the present invention.

<Comparative Example 3>
The blending was 62% by mass of alumina, 10% by mass of zirconia, 21% by mass of silica, and 7% by mass of calcia, and the same operation as in Example 1 was performed to prepare a sample. As a result of image analysis, the volume ratio of the dispersed particles of the sample was 59.5% by volume with respect to the entire sintered body.

  The reflectance of the sample of Comparative Example 3 is shown in FIG. In Comparative Example 3 in which the glass component was increased, the reflectance decreased.

Claims (3)

  In the glass as a matrix, dispersed particles composed of alumina and one or both of zirconia and yttria are dispersed in a ratio of 60% by volume or more in total, and the diameter of the dispersed particles is 1 μm or less. The ceramic sintered body for reflectors, wherein the proportion in the range of 50% by volume or more with respect to the total dispersed particles and the water absorption is 1% by mass or less.   2. The ceramic sintered for reflector according to claim 1, wherein the alumina is dispersed at a ratio of 70 to 85 volume%, and one or both of the zirconia and yttria are dispersed at a ratio of 3 to 10 volume% in total. body.   The ceramic sintered body for a reflector according to claim 1 or 2, wherein the alumina raw material is α-alumina particles having a primary particle diameter of 0.2 µm or less.