JP2011236093A - Red translucent alumina sintered compact and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a red translucent alumina sintered compact which has a sharp red color tone with excellent esthetics, and has translucency with moderate shielding properties, and a method for producing the same.SOLUTION: The red alumina sintered compact comprises manganese dioxide (MnO) of 0.06 to 1.5 mol% as a coloring agent. In the Labcolor system, Lvalue is ≥10, avalue is ≥20 and bvalue is ≥-5. In the alumina sintered compact, contrast ratio in a sample thickness of 1 mm and a measurement wavelength of 600 nm is preferably 20 to 85%. The alumina sintered compact can be suitably used for the external members and ornaments of various parts.

Description

  The present invention relates to a red light-transmitting alumina sintered body, a method for producing the same, a decorative member using the same, and an exterior member.

  Ruby and sapphire, which are single crystals of alumina, are widely used in jewelry applications as red to reddish purple translucent alumina. However, alumina single crystals are difficult to shape and cannot be used for exterior parts such as watches and portable electronic devices having complicated shapes. Furthermore, since the alumina single crystal is too light-transmitting and inferior in shielding properties, it is not suitable for applications such as decorative parts and exterior parts that need to hide the base. Therefore, there is a demand for an alumina sintered body that is colored in red and has translucency in a polycrystalline alumina sintered body that is easy to impart shape.

  Patent Document 1 discloses an alumina sintered body containing chromium oxide, magnesium oxide, lanthanum oxide, and yttrium oxide. However, the disclosed sintered body is reddish purple and has a color tone different from the bright red color exhibited by the alumina single crystal. Further, since the sintering temperature was as high as 1650 ° C. or higher, the crystal grains were large and the strength was low.

  Patent Document 2 proposes a red alumina sintered body using Au nanoparticles coated with silica as a pigment. However, the disclosed alumina sintered body had a red color with metallic luster and was different from a bright red color. Furthermore, since very special Au nanoparticles are used as a pigment, they are very expensive.

  Patent Document 3 discloses a translucent alumina sintered body containing manganese oxide. However, the sintered body had a pink color and was not a bright red alumina sintered body.

  Thus, although a translucent alumina sintered body having a color tone close to red has been proposed, a colored translucent alumina sintered body exhibiting a clear red color and having an appropriate shielding property is provided. No ligation was obtained.

JP 56-140071 JP2008-031039 JP2007-182348

  The present invention provides a colored light-transmitting alumina sintered body that exhibits a clear red color and has an appropriate shielding property that can hide the base.

  As a result of diligent research by the present inventors, a red translucent alumina sintered body having vivid red and translucency and having an appropriate shielding property by containing manganese dioxide as a colorant. The inventors have found that the present invention can be obtained and have completed the present invention.

That is, the present invention contains 0.06 mol% or more and 1.5 mol% or less of manganese dioxide (MnO ₂ ) as a colorant, the L ^* value in the L ^* a ^* b ^* color system is 10 or more, and the a ^* value is It is a red alumina sintered body having 20 or more and b ^* value of −5 or more.

  Hereinafter, the alumina sintered body of the present invention will be described.

The alumina sintered body of the present invention contains manganese dioxide (MnO ₂ ). By containing manganese dioxide, the alumina sintered body exhibits a clear red color.

  The content of manganese dioxide is 0.06 mol% or more, preferably 0.1 mol% or more, and more preferably 0.2 mol% or more. When the manganese dioxide content is less than 0.06 mol%, the sintered body has a pink color tone different from red, and a bright red alumina sintered body cannot be obtained. On the other hand, if the content of manganese dioxide is too large, the density of the sintered body is lowered and the aesthetics are lowered. Therefore, the content of manganese dioxide is 1.5 mol% or less and 1.0 mol% or less. Is preferred.

Although the detailed reason why the alumina sintered body of the present invention exhibits a clear red color is unknown, it is considered that Mn ^{4+ in} manganese dioxide exhibits a red color by containing manganese dioxide having the above content.

Note that manganese oxide (MnO) easily forms spinel (MnAl ₂ O ₄ ) in the alumina sintered body, and does not generate Mn ⁴⁺ . Therefore, when manganese oxide (MnO) is contained, the sintered body exhibits a pink color and does not become a bright red alumina sintered body.

The alumina sintered body of the present invention preferably further contains chromium oxide (Cr ₂ O ₃ ) as a colorant. By containing manganese dioxide and chromium oxide (Cr ₂ O ₃ ), a deep red color is easily obtained. The content ratio of chromium oxide (Cr ₂ O ₃ ) is preferably 50% or more in terms of molar ratio of Mn / Cr, more preferably 60% or more, and further preferably 75% or more. When the Mn / Cr ratio is 50% or more in terms of molar ratio, a clearer red color tends to be obtained. Further, (2 _{O 3 Cr)} content chromium oxide, meets the above Mn / Cr ratio, and is preferably at least 0.04 mol%.

  The alumina sintered body of the present invention preferably has a total content of colorants of 1.5 mol% or less, more preferably 1.0 mol% or less. When the total content of the colorant is within this range, the sintered body exhibits a clear red color and has an appropriate shielding property.

  The alumina sintered body of the present invention can contain other oxides as long as the shielding properties and color tone are not affected. However, since magnesium oxide acts as a grain growth inhibitor, it is preferable not to include it.

Alumina sintered body of the present ^{invention, L * a * b * L} * value of 10 or more at a color system, ^{a *} value is 20 or more, ^{b *} value is -5 or more. Furthermore, the L ^* value is preferably 15 or more. Further, the a ^* value is preferably 25 or more, and more preferably 30 or more. When the values of L ^* , a ^* and b ^* are within this range, a bright red color is exhibited.

Furthermore, the alumina sintered body of the present invention preferably has a lightness L ^* of 10 ≦ L ^* ≦ 60, a hue a ^* of 20 ≦ a ^* ≦ 60, and a b ^* of −5 ≦ b ^* ≦ 30. More preferably, L ^* is 15 ≦ L ^* ≦ 50, hue a ^* is 25 ≦ a ^* ≦ 50, b ^* is −5 ≦ b ^* ≦ 20, and lightness L ^* is 15 ≦ L ^* ≦ 50, hue. More preferably, a ^* is 30 ≦ a ^* ≦ 50 and b ^* is −5 ≦ b ^* ≦ 20. By making the color tone (L ^* , a ^* , b ^* ) within this range, the alumina sintered body tends to become a brighter red.

Here, the lightness L ^* varies from 0 to 100. When L ^* = 100, white is indicated, and when L ^* = 0, black is indicated. Therefore, when L ^* is 10 or more and 60 or less, it becomes easy to exhibit a color tone other than white and black. In addition, hue a ^* represents redness when a ^* > 0, greenness when a ^* <0, hue b ^* represents yellowness when b ^* > 0, and blueness when b ^* <0. Large especially impact on b ^* values gives color, b ^* but can exhibit red by in the range of these, b ^* value tends to be intense red yellowish if 30 or less When the value of b ^* is −5 or more, it tends to be red with a strong blue taste.

Furthermore, as light red, the color tone (L ^* , a ^* , b ^* ) has a lightness L ^* of 20 ≦ L ^* ≦ 45, a hue a ^* of 30 ≦ a ^* ≦ 40, and b ^* of −2 ≦ b ^* ≦. 6 is particularly preferable. Furthermore, the lightness L ^* is preferably 30 ≦ L ^* ≦ 35, the hue a ^* is preferably 30 ≦ a ^* ≦ 35, and the b ^* is preferably −1 ≦ b ^* ≦ 1.

On the other hand, as deep red, the color tone (L ^* , a ^* , b ^* ) has a lightness L ^* of 15 ≦ L ^* ≦ 40, a hue a ^* of 25 ≦ a ^* ≦ 50, and a b ^* of 10 ≦ b ^* ≦ 20. Is particularly preferable, and lightness L ^* is preferably 15 ≦ L ^* ≦ 35, hue a ^* is preferably 25 ≦ a ^* ≦ 50, and b ^* is preferably 12 ≦ b ^* ≦ 18.

  The alumina sintered body of the present invention preferably has a concealment rate of 20% to 85% at a sample thickness of 1 mm and a measurement wavelength of 600 nm, more preferably 25% to 85%, and further 25% to 65%. It is preferable that The concealment rate is an index indicating the shielding property. When the concealing rate is 20% or more, the concealment rate has an appropriate shielding property, and when used for an application such as an exterior member, the base is easily concealed. On the other hand, if the concealment rate is 85% or less, it tends to be a shielding property with aesthetics.

  Further, the total light transmittance can be used as an index representing the shielding properties of the alumina sintered body of the present invention. As the total light transmittance increases, the shielding property tends to decrease. Therefore, the total light transmittance and the concealment ratio tend to be approximately inversely proportional.

  The alumina sintered body of the present invention preferably has a total light transmittance of 15% or more at a sample thickness of 1 mm and a measurement wavelength of 600 nm, more preferably 20% or more, and further preferably 40% or more. When the total light transmittance is 15% or more, aesthetics are likely to be improved. On the other hand, when the total light transmittance is increased, the shielding properties are likely to be lowered. Therefore, the upper limit of the total light transmittance is preferably 70% or less, and more preferably 60% or less.

  For the same reason, the alumina sintered body of the present invention preferably has a linear transmittance at a sample thickness of 1 mm and a measurement wavelength of 600 nm of 10% or less, more preferably 8% or less, and more preferably 6% or less. Preferably there is.

  The total light transmittance and the linear transmittance are parameters having a relational expression of the following formula (1).

Tt = Ti + Td (1)
Tt: Total light transmittance (%)
Td: diffuse transmittance (%)
Ti: Linear transmittance (%)

  Since total light transmittance and linear transmittance follow Lambert-Beer's law, they increase as the sample becomes thinner, while they decrease as the sample becomes thicker.

  The alumina sintered body of the present invention preferably has a relative density of 99.5% or more, and preferably 99.9% or more.

  The alumina sintered body of the present invention preferably has an average crystal grain size of 20 μm or less, and more preferably 15 μm or less. When the average crystal grain size is 20 μm or less, the strength of the sintered body tends to increase. On the other hand, the smaller the average grain size, the higher the strength. However, if the lower limit is 1 μm or more, more preferably 2 μm or more, sufficient strength can be obtained for the intended use of the present invention.

  Next, the manufacturing method of the alumina sintered compact of this invention is demonstrated.

In the production method of the present invention, an alumina powder containing 0.06 mol% or more and 1.5 mol% or less of manganese dioxide (MnO ₂ ) is molded, subjected to primary sintering under normal pressure, and then further subjected to hot isostatic pressing (HIP ) A process for producing an alumina sintered body to be processed, wherein the HIP treatment temperature is not higher than the primary sintering temperature.

  Alumina powder is used in the production method of the present invention. The alumina powder is not particularly limited, but is preferably a high-purity alumina powder, and particularly preferably 99.9% or more in purity. By using high-purity alumina powder, the density of the resulting alumina sintered body tends to increase.

The production method of the present invention uses manganese dioxide (MnO ₂ ) as a colorant that develops red color. Although manganese dioxide will not be specifically limited if it contains Mn ^<4+> , Electrolytic manganese dioxide (EMD), chemical manganese dioxide (CMD), etc. can be illustrated.

In the production method of the present invention, it is preferable to further use chromium oxide (Cr ₂ O ₃ ) as a colorant. When using chromium oxide (Cr ₂ O ₃ ), the Mn / Cr ratio is preferably 50% or more in terms of molar ratio.

Manganese dioxide (MnO ₂ ) and chromium oxide (Cr ₂ O ₃ ) do not necessarily use oxides, and precursors that become oxides by firing can also be used. When using a precursor, it is preferable to use it so that the usage-amount may contain in the above-mentioned range in oxide conversion after sintering.

When manganese oxide (MnO) is used, it is preferable to use manganese oxide as a precursor of manganese dioxide because manganese oxide forms MnAl ₂ O ₄ and the sintered body becomes pink and red is not obtained. Absent.

  In the production method of the present invention, a colorant and alumina powder are mixed. The mixing is not particularly limited as long as the alumina powder and the colorant can be uniformly mixed, but it can be exemplified by dispersing and mixing using a mixing and pulverizing apparatus such as a wet pulverization by a ball mill.

  In the production method of the present invention, the mixed raw material powder is molded to obtain a molded body.

  There is no restriction | limiting in particular in a shaping | molding method, It is preferable to shape | mold a raw material powder into a defined shape using a cold isostatic press (CIP) or a powder press method. Moreover, it is preferable to apply an injection molding method, a casting molding method, etc. according to the objective.

  In the production method of the present invention, the obtained molded body is sintered to obtain a primary sintered body. In the primary sintering, the relative density of the primary sintered body obtained is preferably 95% or more, particularly preferably 97% or more.

  In order to obtain such a primary sintered body, the primary sintering temperature is preferably 1250 ° C. or higher and 1500 ° C. or lower, more preferably 1250 ° C. or higher and 1450 ° C. or lower, and further 1300 ° C. or higher and 1450 ° C. or lower. It is preferable that When the primary sintering temperature is 1250 ° C. or higher, the density of the alumina sintered body is likely to increase even after the subsequent HIP treatment. On the other hand, when the primary sintering temperature is 1500 ° C. or lower, the primary sintered body hardly contains intragranular pores. Become.

In the range where the primary sintering temperature is 1250 ° C. or higher and 1500 ° C. or lower, the higher the primary sintering temperature, the deeper the color exhibited by the alumina sintered body obtained after the HIP treatment becomes (red hue of the sintered body b). ^{* Tends to} be large). The color exhibited by the alumina sintered body varies depending on the type and content of the colorant, but the primary sintering temperature for obtaining a light red sintered body is 1250 ° C. or more and less than 1350 ° C., and a deep red sintered body is used. Examples of the primary sintering temperature in the case of obtaining can be 1350 ° C. or higher and 1500 ° C. or lower.

  Primary sintering is preferably performed in an atmosphere such as air, oxygen, or vacuum, and is most preferably performed in the air because it is the simplest.

  In the production method of the present invention, the obtained primary sintered body is subjected to HIP treatment to obtain an alumina sintered body. Residual pores in the primary sintered body are eliminated and densified by the HIP treatment, and an alumina sintered body having translucency with appropriate shielding properties and a clear red color can be obtained.

  The HIP processing temperature is not higher than the primary sintering temperature. By setting the HIP processing temperature to be equal to or lower than the primary sintering temperature, the color tone of the obtained alumina sintered body becomes a clear red color.

  The HIP treatment temperature is particularly preferably not higher than the primary sintering temperature and not lower than 1200 ° C and not higher than 1500 ° C, and more preferably not lower than 1250 ° C and not higher than 1400 ° C. When the HIP treatment temperature is 1200 ° C. or higher, sintering is promoted and densification is likely to proceed. On the other hand, when the temperature is 1500 ° C. or lower, a red color tone is easily exhibited.

  The HIP processing pressure is preferably 50 MPa or more, and more preferably 100 MPa or more. When the HIP processing pressure is 50 MPa or more, densification of the alumina sintered body easily proceeds. On the other hand, if the HIP processing pressure is 200 MPa or less, densification of the alumina sintered body proceeds, so that it is not necessary to set the HIP processing pressure higher than this. The pressure medium for the HIP treatment is preferably nitrogen, oxygen, or argon gas, and particularly preferably argon gas.

  The obtained alumina sintered body is preferably subjected to surface polishing in order to obtain gloss and aesthetics according to the purpose.

  The alumina sintered body of the present invention has a clear red color tone and moderate shielding properties.

Total light transmittance of Example 1 Total light transmittance of Example 2 Total light transmittance of Comparative Example 1 SEM photograph of Example 5 (scale in the figure is 3 μm) SEM photograph of Comparative Example 2 (scale in the figure is 3 μm)

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these Examples.

(Measurement of concealment rate)
The concealment rate was measured as an indicator of shielding properties. The concealment ratio was measured using a color analyzer TC-1800MK-II by a method according to the test methods of JIS K 5400-5-2 and JIS Z 8722. The measurement sample was processed to have a sintered body thickness of 1 mm and polished on both surfaces. This is irradiated with visible light having a wavelength of 600 nm, a spectral reflectance (R1) when measured by placing a black plate with a visible light reflectance of 0% on the back of the sample, and a visible light reflectance of 100% on the back of the sample. Spectral reflectance (R2) when measured by placing a white plate was determined, and the ratio (R1 / R2) was determined as the concealment rate.

(Total light transmittance)
The total light transmittance is based on JIS K 7105 (Plastics optical property test method) and JIS K 7361-1 (Test method for total light transmittance of plastics and transparent materials), a double beam spectrophotometer (V-650). The light emitted from the light source (deuterium lamp and halogen lamp) was transmitted and scattered through the sample, and the total light transmission was measured using an integrating sphere.The measurement wavelength range was 200 to 800 nm. The transmittance at a wavelength of 600 nm in the visible light region was defined as the total light transmittance, and a sample subjected to the same treatment as the measurement of the concealment rate was used.

(Measurement of color tone (lightness, hue))
The color tone (lightness L ^* , hue a ^* , b ^* ) conforms to JIS Z 8722, and a color difference meter (Color Analyzer TC-1800MK-II, manufactured by Tokyo Denshoku Co., Ltd.) is used under the conditions of a D65 light source and a 10 ° viewing angle. And measured. As the measurement sample, a sample treated in the same manner as the measurement of the concealment rate was used.

Examples 1-7
High-purity alumina powder (manufactured by Daimei Chemical Co., Ltd., purity 99.99% or more) and 0.1 mol% to 1.0 mol% of manganese dioxide (manufactured by high-purity chemical) are mixed and placed in a ball mill for wet grinding. went. The pulverized powder was dried to obtain a raw material powder.

  The obtained raw material powder was applied with a pressure of 50 MPa using a uniaxial press device and a mold, and then put into a rubber mold and molded at a pressure of 200 MPa using a cold isostatic press (CIP) device to obtain a molded body. . The obtained molded body was primarily sintered at 1300 ° C. or 1450 ° C. for 2 hours in the air to obtain a primary sintered body. The results are shown in Table 1.

  The obtained primary sintered body was subjected to HIP treatment in an argon gas at a temperature of 1300 ° C. and a pressure of 150 MPa for 1 hour to obtain an alumina sintered body. The results are shown in Table 2.

Each of the obtained alumina sintered bodies had the same manganese dioxide content as the charged composition, and the relative density was 100% or more. In addition, any alumina sintered body exhibited a clear red color and had an appropriate shielding property.
Example 8
An alumina sintered body was obtained in the same manner as in Example 1 except that 0.06 mol% MnO ₂ and 0.04 mol% Cr ₂ O ₃ were used as colorants. The results are shown in Table 3.

  The obtained alumina sintered body exhibited a light red color, and had an appropriate shielding property. The colorant content was the same as the charged composition, and the Mn / Cr ratio was 75%.

Comparative Examples 1-2
An alumina sintered body was obtained by the same method as in Examples 1 to 7, except that the amount of MnO ₂ added was 0.05 mol%. The results are shown in Table 4.

All of the obtained alumina sintered bodies had a low b ^* and exhibited a pink color.

Comparative Examples 3-6
Except that the colorant was only 0.1 mol% or 1.0 mol% of _Cr 2 _{O 3,} thereby obtaining the alumina sintered body in the same manner as in Examples 1-7. The results are shown in Table 5.

The obtained alumina sintered body had a low b ^* value, a purple color, and a color tone different from red.

  Since the alumina sintered body of the present invention has an appropriate shielding property and is excellent in aesthetics, it is used as a cover for accessories such as ornaments, watches and housings, and exteriors of portable electronic devices such as mobile phones. It can be used as various members such as members.

Claims (10)

Containing more than 0.06 mol% 1.5 mol% or less of manganese dioxide (MnO ₂₎ as a ^{colorant, L * a * b * L} * values in the color system is 10 or more, ^{a *} value is 20 or more, ^{b *} A red alumina sintered body having a value of -5 or more.   The alumina sintered body according to claim 1, wherein the concealment ratio at a sample thickness of 1 mm and a measurement wavelength of 600 nm is 20% or more and 85% or less. 3. The alumina sintered product according to claim 1, wherein brightness L ^* is 10 ≦ L ^* ≦ 60, hue a ^* is 20 ≦ a ^* ≦ 60, and b ^* is −5 ≦ b ^* ≦ 30. body.   The alumina sintered body according to any one of claims 1 to 3, wherein the total light transmittance at a sample thickness of 1 mm and a measurement wavelength of 600 nm is 15% to 70%. The alumina sintered body according to any one of claims 1 to 4, further comprising chromium oxide (Cr ₂ O ₃ ) as a colorant. The alumina sintered body according to claim 5, wherein the content ratio of chromium oxide (Cr ₂ O ₃ ) is a molar ratio of Mn / Cr of 50% or more. Alumina sintered body formed by molding alumina powder containing manganese dioxide (MnO ₂ ) in an amount of 0.06 mol% to 1.5 mol%, followed by primary sintering under normal pressure, followed by hot isostatic pressing (HIP) treatment The method for producing an alumina sintered body according to any one of claims 1 to 6, wherein the HIP treatment temperature is not higher than the primary sintering temperature.   The method for producing an alumina sintered body according to claim 7, wherein the primary sintering temperature is 1250 ° C or higher and 1500 ° C or lower.   A decorative member using the alumina sintered body according to any one of claims 1 to 6.   An exterior member comprising the alumina sintered body according to any one of claims 1 to 6.

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