Spinel sintered body, method for producing the same, transparent substrate, and liquid crystal projector

Technical Field

The invention relates to the transparency and its stability is fine spinel sintered body and method of manufacturing the same. Furthermore, the invention also relates to a spinel sintered body and of the transparent substrate with the transparent base plate of the liquid crystal projector.

Background Art

Spinel sintered body that does not have crystal forms are tetragonal of aromatic polyimide film, the oxide ceramic having a relatively high heat conductivity, in which infrared region to the visible region of the display a transparency, therefore, as a liquid crystal projector or a rear projection television, various electronic equipment, and the like, such as a polarizing plate or dust-proof window transparent window or lens, the attention of the transparent substrate material.

Figure 2 represents the general structure of the liquid crystal projector. As shown in Figure 2, from the metal halide lamp or a xenon lamp such as light source 1 to the light projected by the reflector 2 reflecting, through the ultraviolet ray cut-off filter 3 after such as, is introduced into the integrator polarization conversion optical system 4 in. Furthermore, the carried out according to the wavelength of the light transmission and reflection of the dichroic mirror 5 decomposition of the red (R), green (G), blue (B) each primary color, making use of the whole reflector 6, so that the decomposition light respectively passes through a polarizer 7 and dust-proof window 8, the cross-dichroic prism 9 after synthesis in, through a projecting lens system 10 to expand, at the front of the projection on the screen of the Image 11. With this kind of structure of the liquid crystal projector, such as a polarizing plate or dust-proof window for light transmission window or transparent lens or the like material of the transparent substrate, even having a thickness of raw, also called for the stable high light transmittance.

For example, reports that Al₂ O₃ and the composition of the MgO ratio the 0.53 [...] 0.47-0.58 the [...] 0.42 scope, and the thickness is 1 mm at the wavelength of 600 nm in a linear light transmittance of 75% or more polycrystalline transparent spinel sintered body (reference Japanese opens illustriously especially 59-121158 of communiques (Patent document 1)). However, the wavelength of the spinel sintered body 600 nm of the highest linear transmittance of the light is about 84% the following, and wavelength 450 nm linear transmittance of the light of low, therefore, though can be in the infrared region, but it is difficult to the request for high transmission characteristics in the visible region.

Furthermore, the reported purity of 99.5% or more, specific surface area is 10m²/g of spinel powder more than the vacuum in the 1200-1700 the [...] after hot pressed under [...] , for HIP (Hot   Isostatic Pressing, hot isostatic processing method) of a light-transmitting spinel sintered body manufacturing method (reference Japanese extra Kaiping 02-018354 of communiques (Patent document 2)). According to the method for manufacturing a wavelength of spinel sintered body 3 the the m-5   m exhibits the highest infrared region 85% linear transmittance, however, wavelength 0.4 the the m-3   m linear transmittance of the light of an average of 75%, therefore, the spinel sintered body is also difficult to the characteristic of high light transmission can be seen by the region.

On the other hand, the reported purity is 99.9% of the spinel powder preform above, hot-pressing, to the obtained spinel sintered body of the polycrystal of transparent HIP manufacturing method (reference Japanese opens especially 2005-070734, Gazette (Patent literature 3)). The transparent crystals of wavelength 400 nm -800 nm linear transmittance of the light of an average of 84%, however, transmittance of the sintered body of the spinel a deviation exists, different linearity on the basis of the measured sample of a transmittance of 80% the following, and the like, problems in the stability of the sintered body. Furthermore, the thickness of the sintered body 10 mm the above, the central part to produce heterogeneous, the problems exist the linear transmittance is reduced.

Patent literature 1: Japanese opens illustriously especially 59-121158, the

Patent document 2: Japanese extra Kaiping 02-018354, the

Patent literature 3: Japanese opens especially 2005-070734, the

Content of the invention

The present invention is completed in view of the above current situation, the purpose is to, provide a pair of wavelength 350 nm -450 nm in the visible light can be fully used also the 80% of the linear transmittance above, and can obtain stable high transmissivity of the spinel sintered body. Furthermore, even if the thickness of the raw material for the to visible can be obtained with stable light of area of the high transmittance of a spinel sintered body and method of manufacturing the same. Furthermore, by the above-mentioned spinel provided comprised of a sintered body and the transparent base plate for liquid crystal projector having the transparent base plate of the liquid crystal projector.

Spinel sintered body of the present invention the composition is MgO·nAl₂ O₃ (1.05     n≤ 1.30), Si element is in a content of 20 PPM the following. The sintered body preferably the following shape: in a thickness of 1 mm when the wavelength of 350 nm -450 nm of the light of the linear transmittance is 80% or more.

The present invention provides a manufacturing method of the sintered spinel, the spinel sintered body is MgO·nAl₂ O₃ (1.05     n≤ 1.30), Si element is in a content of 20 PPM the following, the manufacturing method has the following processes: the content of the Si element 50 PPM the following, the purity of 99.5% of spinel powder quality more than the process of forming a molded body; the vacuum in the 1500-1700 the [...][...] sintering the shaped body, having a density of 95% of the above 1st the sintering process of the sintered body; and in the 1600-1800 the [...] the [...] pressurizing sintering of the sintered body by sintering process 2nd.

Through the 1st sintered body formed by sintering process can make the content of the Si element 20 PPM the following. Furthermore, preferably the sintering procedure 1st the following forms: in 50 Pa under the pressure, and insulating from the sintered body to the center portion of the outer side of the of the sintered body to the minimum thickness of the D (mm), from the 1000 [...] raising the temperature to the highest temperature of the heating-up time of the minute t, has the following relationship:

D=a×t^1/2

1 the   a≤ 3

The transparent substrate of the present invention by the spinel sintered body, is suitable as a transparent substrate for liquid crystal projector, particularly preferred shape of the surface has a coating. The liquid crystal projector of the present invention is characterized in that, with the transparent base plate and a light source of visible light.

The effect of this invention

The invention is capable of providing with the visible light can be fully used also the stability of the light transmittance of the sintered body of the spinel structure. Furthermore, because the light transmittance is high, therefore, the light from the light source less heat absorption caused by the, temperature to the heat of the liquid crystal. According to this characteristic, as a useful transparent base plate for liquid crystal projector.

Description of drawings

Figure 1 is diagram of said wavelength 350 nm linear transmittance of the light of the relationship of the content of Si element.

Figure 2 is diagram of the general structure of the liquid crystal projector said.

Symbol description

1 light source, 2 reflecting plate, 3 the ultraviolet cut-off filter, 4 integrator polarization conversion optical system, 5 dichroic mirror, 6 the whole reflector, 7 polarizing plate, 8 dust-proof window, 9 cross-dichroic prism, 10 projection lens system, 11 Image.

Mode of execution

(Spinel sintered body)

Spinel sintered body of the present invention the composition is MgO·nAl₂ O₃ (1.05     n≤ 1.30), Si element is in a content of 20 PPM the following. This spinel sintered body in the thickness 1 mm wavelength of 350 nm -450 nm of the linear transmission rate of the visible light rays is preferably 80% or more, more preferably 82% or more, especially preferably 84% or more, linear transmittance is sufficiently high. Furthermore, high transmittance can be stabilized, the magnitude of the deviation. And, even with a thickness of material, to the visible light can be obtained a stable high transmittance. Therefore, suitable as includes a light emitting diode, laser equipment, liquid crystal projectors, rear projection television, or digital micromirror devices, and the like for a light-emitting device such as a polarizing plate or dust-proof window transparent window, or transparent lens, the material of the transparent substrate. Therefore, with this invention the liquid crystal projector of the transparent substrate, the visible light rays from the light source the linear transmittance thereof is high, small inequality of illumination intensity.

Linear transmittance of the incident light is parallel to the optical axis of the transmitted light on the straight line relative to the intensity of the ratio of the intensity of incident light, measured CCD can be used. Therefore, for each wavelength of the higher linear transmittance of the light, the higher the light transmission, a transmission window through the lens or the less the absorbed light energy, therefore, can inhibit heating of the lens or a transmission window.

Spinel sintered body containing composition in MgO·nAl₂ O₃ (1.05     n≤ 1.30), by the MgO (magnesium oxide) and Al₂ O₃ (alumina) of the oxide. Spinel sintered body because of crystalline form for vertical tetragonal, therefore, is capable of scattering of light is not easy to occur, when the sintering high density, good light transmittance can be obtained. Through making the 1.05   n≤ 1.30, the MgO melting quantity can be reduced, reducing the deviation of the crystal lattice of micro and deformation, to improve light transmittance. From this point of view, preferably the 1.07   n≤ 1.125.

Usually, the spinel sintered body of a light transmittance of the factors reducing the mixing of the metal impurities, as the metal impurity, can be enumerated Si, Ti, Na, K, Ca, Fe, , C. These metallic impurities from the raw material powder, in the sintered body and mix. These metal in the impurity, the content of the Si element 20 PPM the following, can be stably obtain a high light transmittance. From this point of view, the elemental content of Si is more preferably 10 PPM the following, particularly preferred 5 PPM the following. By this control the content of the element Si, even in the thickness 10 mm more spinel sintered body is obtained also in the transparency to light. During the sintering and the element Si with the spinel powder reaction and produce the liquid phase. This liquid phase sintering of the powder has the effect of the spinel, but if the liquid residue on the grain boundary, become non-homogeneous, reduce the light transmittance.

The metal impurity element other than Si includes, for example, Na, K, Fe, or Ca mixing of the impurities, spinel light transmittance of the sintered body, manufacturing of the transparency to light the stability of the bias and will be adversely affected. Therefore, in the spinel powder MgO·nAl₂ O₃ set to purity of 99.5 mass % or more, preferably 99.9 mass % or more, more preferably 99.99% or more quality.

The spinel sintered body used for a transparent substrate of the liquid crystal projector, light transmittance and surface from the point of view of stability, the preferred shape of the surface has a coating. Even for the single-layer coating is also effective, however, in the normal use of the wavelength of from 400 nm -700 nm of the area the viewpoint of transmission properties, more preferably the shape of the provided with a multi-layer coating. The is provided with a plurality of coating, coating material is preferably SiO₂, TiO₂, Al₂ O₃, Y₂ O₃, Ta₂ O₅, ZrO₂ and other metal oxide or MgF₂, YF₃, LaF₃, CeF₃, BaF₂ metal fluoride. A total film thickness of this coating is preferably the 5   m the following. With such single surface of the spinel coating obtained average transmittance of the sintered body, at a wavelength of 400 nm -700 nm region preferably 90% or more, more preferably 91% or more, especially preferably 92% or more.

(Spinel sintered body manufacturing method)

Spinel of this invention manufacturing method of the sintered body with: the content of the Si element 50 PPM the following, the purity of 99.5% of spinel powder quality more than the process of forming a molded body; the vacuum in the 1500-1700 the [...][...] sintering the shaped body, having a density of 95% of the above 1st the sintering process of the sintered body; and in the 1600-1800 the [...] the [...] pressurizing sintering of the sintered body by sintering process 2nd. According to this method, a composition can be manufactured MgO·nAl₂ O₃ (1.05     n≤ 1.30), Si element is in a content of 20 PPM the following spinel sintered body, can provide a stable high light transmittance, and the deviation of the light transmittance of the lens or light-transmitting window.

First of all, by stamping or CIP (Cool   Isostatic   Pressing, cold isostatic processing method) the spinel powder molding. Furthermore, in the sintering process in the 1st, the vacuum in the 1500-1700 the [...][...] sintering the shaped body, having a density of 95% or more of the sintered body. By sintering in a vacuum atmosphere, can make the Si as an impurity in the liquid phase of the element removed by evaporation in vacuum. From this point of view, the vacuum degree is preferably 50 Pa the following, more preferably of 20 Pa the following.

1st because of the conditions of the sintering process of the amount of Si element and vary the thickness of the sintered body, but preferably the following manner: from insulating to the central part of the sintered body of the sintered body of a minimum thickness at the outer side for D (mm), from the 1000 [...] raising the temperature to the highest temperature of the heating-up time of the minute t, has the following relationship:

D=a×t^1/2

1 the   a≤ 3

By the latter embodiment 2 the results show that, within the range of the temperature in such, when the spinel powder in the elemental content of Si is 50 PPM the following, the 1st after the end of sintering process, can be reduced to the elemental content of the Si 20 PPM the following, thus can get the high-light transmittance of the spinel sintered body. In the sintered body from further reduce the content of the element Si, spinel sintered body increase the viewpoint of the light transmittance, spinel powder element content of Si is preferably in the 30 PPM the following. When the spinel powder in the elemental content of Si is 50 PPM the above, 1st through a further extension in the sintering process of the warming-up time in the vacuum atmosphere, the sintered body can be reduced in the content of Si.

Furthermore, density can be obtained from the 95% of the high-density sintered body more than the point of view, the temperature in the sintering process of 1st preferably 1500 the above [...]. The light transmittance of the sintered body from the point of view, the density of the sintered body is more preferably 95% or more. In this specification, to arab League base Mi �fa density is calculated according to the relative density. On the other hand, from the inhibiting vacuum in the evaporation of MgO, is to prevent cooling Al₂ O₃ 2nd phase precipitation as, the viewpoint of maintaining a high transparency to light, the sintering temperature is preferably the 1700 [...] the following, more preferably the 1650 [...] the following.

1st after the end of sintering process, the sintering process of the 2nd, through HIP in such as the 1600-1800 the [...] under [...] pressurizing sintering of the sintered body. The temperature the 1600-1800 the [...][...] , pressure of about 100 MPa HIP is carried out, by means of plastic deformation and diffusion mechanisms to promote the removal of the empty holes, therefore, can be more high density, light transmittance is further improved. HIP gas preferably used in gas Ar, N₂ gas to an inert gas, such as, O₂ gas or the mixed gas of these gases, mixed O₂ gas, can prevent light transmittance caused by the reducing of the deoxidation.

The surface of a transparent substrate to form a coating preferably make use of physical vapor deposition, can implement the sputtering method, ion plating method, vacuum evaporation method. The ion of the auxiliary or plasma assisted, coating film performance is improved, is thus preferred.

(Embodiment 1-7)

In this embodiment, in the 50 PPM as raw materials for the following of the spinel powder in the elemental content of the Si various alteration, after forming a spinel sintered body, research light transmittance. First of all, for the purity of 99.5 mass %, the content of impurity elements in the table 1 shown in the spinel powder, after shaping, is processed through the CIP Φ 95 mm × L95mm. Furthermore, in the 1 [...] /minutes under elevated temperature conditions, the pressure is 20 Pa in the vacuum, in 1600 the sintering process implemented under [...] 1st. The density of the resulting sintered body is 95%-97%.

1st to elevated temperature conditions of the sintering process: from the center of the sintered body of the sintered body of a minimum thickness at the outer side for D 39 mm, from the 1000 [...] raising the temperature to the highest temperature the 1600 until [...] to 1 the temperature [...] /minutes, therefore the time of heating for t 600 minutes. Therefore, under D=a×t^1/2, calculated for a 1.6, meet the 1   a≤ 3.

Furthermore, using Ar gas, in the 1700 [...] , 100 MPa HIP under, 2nd sintering process implementation. The resulting sintered body is Φ 82 mm × L78mm, by ICP emission spectral analysis (Inductively   Coupled   Plasma   Atomic   Emission   Spectometry, inductively coupled plasma atomic emission spectroscopy) as known MgO· 1.07Al₂ O₃, 1.05     n≤ 1.30. Cutting the sintered body after the median, grinding, using spectrophotometrie spectrometer (Hitachi high-tech companies U-4100) measuring thickness 1 mm wavelength of 350 nm and 450 nm of the linear transmittance of the light. Furthermore, the crushing the central part of the, by ICP emission spectral analysis for determining the elemental content of Si. Determine results are shown in table 1.

From table 1 the results show that, using the content of the Si element 50 PPM the following spinel powder, through the method of the present invention, capable of producing composition is MgO·nAl₂ O₃ (1.05     n≤ 1.30), Si element is in a content of 20 PPM the following spinel sintered body. Furthermore, the linear transmittance spinel sintered body are 80% or more, small the deviation of the light transmittance can be known.

Table 1

(Embodiment 8-10 and reference example 1)

The embodiment of the invention, changes in the sintering process of 1st t the heating-up time (a certain D), research by D=a×t^1/2 find a value of the Si element content and the relationship between the light transmittance of the sintered body.

The embodiment of the 5 the spinel powder used in, through the sintering process does not change in 1st D t change the value of the time of heating, the value like table of a 2 change shown, other conditions and embodiment 5 the same, making the spinel sintered body. With the embodiment 5 similarly to be measured, measurement by 1st sintered body formed by sintering process of the Si element content and 2nd after the end of sintering process of linear transmittance of the sintered body. Determine results are shown in table 2.

Table 2

The table 2 results shows that, in meeting the 1   a≤ 3 under the condition, when the spinel powder in the elemental content of Si is 50 PPM the following time, after the end of sintering process of 1st, can be reduced to the elemental content of the Si 20 PPM the following, and spinel sintered body for linear transmittance of 80% or more.

The embodiment 2 and 4 and reference example 1 of spinel sintered body at intervals in the direction of thickness of 5 mm for cutting, the sample processing thickness of 1 mm, the wavelength 350 nm linear transmittance of the light of the relationship between the content of Si of the elements to be measured. The result shown in Figure 1. By fig. 1 results show, the elemental content of Si of the sample, the deviation of the linear transmittance large, opposite to this, the content of the Si element 20 PPM the following sample, exhibits stable high transmission characteristics.

The embodiment of the time from any angle and embodiment should be considered as exemplary and not restrictive. The scope of the invention as shown in the claims and not limited by the above description, and comprises claim equivalent and within the scope of the meaning of all alteration.

Industrial practicability

Spinel sintered body of the present invention has stable high transparency to light, therefore, is suitable as a light-emitting diode, laser equipment, liquid crystal projectors, rear projection television, or digital micromirror device for a light-emitting device such as the light transmission window or transparent lens material.