JPH11183647A - Watch and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart an improve strength and a gloss of high-class feeling by forming a dial mode of alumina ceramic that has a crystal diameter in a specified range and a specified void diameter. SOLUTION: The average grain diameter of an alumina raw material powder is set to approximately 0.1-0.5μm, and a grain size distribution is set to shape range. Water is added to a raw material power to form a slurry, which is injected into a forming mold in a specific shaped. The then forming mold is rotated and a raw material powder is formed by a centrifugal force of approximately 3,000 G or higher, and the forming body is backed at a relatively low temperature of approximately 1,200-1,300 deg.C. A sintered body thus obtained becomes a fine crystal with a crystal particle diameter of approximately 1.0 μm or less, thus reducing an average void diameter to approximately 0.5 μm or less and hence achieving a bending resistance of approximately 700 MPa or higher and a glass with high-class feeling. As a result, crackes due to a shock when the watch is dropped or hit against a hard object can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a timepiece having a timepiece dial made of alumina ceramics and a method of manufacturing the timepiece.

[0002]

2. Description of the Related Art Conventionally, in a timepiece using a solar cell as a driving source, since the solar cell absorbs light to generate power, it is used in a structure that can be seen from the outside on a dial face under a windshield. Generally, however, in this configuration, the solar cell has a unique dark purple color, and the color and design of the dial are greatly restricted.

Therefore, it has been proposed to dispose a covering member and a dial on the light receiving surface side of the solar cell so that the solar cell is not visible from the outside. However, in order to secure the electromotive force of the solar cell, it has been proposed. In addition, it is necessary to increase the light transmittance of the cover and the dial. The light transmittance of the cover member and the dial is related to the thickness, and the transmittance increases as the thickness decreases.

[0004]

However, when the cover member and the dial are made of ordinary alumina ceramics, if the thickness is reduced to increase the transmittance,
There are problems such as cracking due to low mechanical strength. Moreover,
Due to the presence of many voids, gloss was not obtained, and luxury was not obtained.

Further, regarding the above-mentioned covering member and dial,
It is desired that the material be excellent in light transmittance and be capable of obtaining a desired color by adding a pigment, since it is very decorative.

In view of the above circumstances, the present inventor has made intensive studies, and as a result, conventional alumina ceramics have a sintering temperature of 1
Since the temperature is as high as 500 to 1750 ° C, the crystal grain size is 2
１５15 μm, which is very large, and the diameter and number of the voids are large, and as a result, the strength is a low value of 200 to 400 MPa. As a result of investigation, it was found that alumina ceramics with very few voids and high strength were obtained, and with this alumina ceramics, excellent light transmittance and color could be achieved, and furthermore, by specifying the void diameter and crystal grain size, a watch We found that it was most suitable for a clock face.

Accordingly, the present invention has been accomplished based on the above findings, and an object of the present invention is to provide a timepiece having a timepiece dial that achieves excellent strength and has a high-grade gloss. .

Another object of the present invention is to provide a timepiece having a timepiece dial arranged on the light receiving surface side of a solar cell with improved light transmittance.

Still another object of the present invention is to provide a timepiece provided with a timepiece dial that can be colored as required to obtain various colors.

It is a further object of the present invention to provide a method for manufacturing such a timepiece dial used in the timepiece of the present invention.

[0011]

A timepiece according to the present invention is characterized by using a dial made of alumina ceramics having a void diameter of 0.5 μm or less and a crystal grain size of 1 μm or less.

Another timepiece according to the present invention is characterized in that the alumina ceramic contains metal oxides such as Cr, Co, and Ni in an amount of 0.01 to 0.01%.
It is characterized by being added in a range of 3% by weight to obtain a colored ceramic.

[0013] Still another timepiece of the present invention is that the above-mentioned alumina ceramic or colored ceramic is HIPed,
It is characterized in that grains are grown to a crystal grain size of 3 to 5 μm.

Further, in the method of manufacturing a timepiece according to the present invention, a slurry in which alumina raw material powder is dispersed is poured into a mold having a predetermined shape, and the raw material powder is formed by centrifugal force generated by rotating the mold. And firing the obtained molded body.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The timepiece of the present invention uses a general timepiece dial or a timepiece dial equipped with a solar cell. FIG. 1 shows an example of a timepiece 1 according to the present invention, in which a movement 4 is arranged inside an exterior 3 having a windshield 2, and a solar cell 5 and a dial 6 are provided on the movement 4. Reference numeral 7 denotes a pointer driven by the movement 4.

In the present invention, the dial 6 is made of alumina ceramics as described above. That is, in order to reduce the crystal grain size of the sintered body, the sintering temperature is reduced as much as possible. For this purpose, the alumina raw material powder is made finer to increase the packing density of the compact. In practice, the raw material powder has an average particle size of 0.1 to 0.5 μm (measured by a microtrack), and its particle size distribution is also in a sharp range. Outside this range, the particle size distribution becomes broad,
In the next molding step, the difference in the sedimentation speed of the particles due to the centrifugal force increases, and as a result, the particles are oriented, and a good sintered body cannot be obtained.

In the next molding step, water is added to the alumina raw material powder to form a slurry, and then the slurry is poured into a molding die having a predetermined shape, and the raw material powder is subjected to centrifugal force generated by rotating the molding die. Is molded. When the centrifugal force is set to 3000 G or more, preferably 5000 G or more, an extremely high-density molded article can be obtained.
(Sintering under normal pressure).

The sintered body obtained by the sintering becomes fine crystals having a crystal grain size of 1.0 μm or less, preferably 0.5 to 1.0 μm, and further has an average void diameter of 0.5 μm.
It is possible to obtain a very high strength with a transverse rupture strength of 700 MPa or more and a luxurious luster, and as a result, to prevent cracking due to impact when the watch is dropped or hit. I was able to.

In the alumina ceramics of the present invention, Cr and C are used as pigments in order to enhance decorativeness.
Metal oxides such as o and Ni are added alone or in combination in a total amount of 0.01 to 3% by weight, whereby coloring can be performed as desired. If the amount is less than 0.01% by weight, good coloring is not obtained due to insufficient coloring, and if it exceeds 3% by weight, the strength is deteriorated.

Further, the above-mentioned alumina ceramics or the above-mentioned colored alumina ceramics may be HIP-coated.
By performing the above, excellent translucency can be achieved.

That is, 1200 to 1 with respect to the sintered body
When HIP is performed at 500 ° C., the crystal grain size is 3 to 5 μm.
However, the void diameter becomes 0.1 μm or less, whereby the strength is increased and the translucency is obtained. As a result, the watch can be sufficiently used as a clock face provided with a solar cell.

Then, upon commercialization, by polishing the alumina ceramic having such a small amount of voids, it was possible to obtain excellent surface smoothness having a surface roughness Ra of 10 nm or less and a high-grade gloss.

Thus, according to the present invention, the watch face can be made of alumina ceramics having a void diameter of 0.5 μm or less and a crystal grain diameter of 1 μm or less by devising the raw materials, molding, firing and the like in production. Thereby, bending strength 7
High strength of 00 MPa or more could be achieved, and the thickness could be reduced to a certain extent, and further excellent gloss was obtained. In addition, it can be colored or made transparent, thereby giving an excellent decorative and luxurious feeling. In addition, such a timepiece dial could be used as both a covering member and a dial to be disposed on the light receiving surface side of the solar cell.

[0024]

EXAMPLE Alumina powder 100 having an average particle size of 0.2 μm and a sharp particle size distribution (in the range of 0.15 to 0.3 μm)
%, 30% of ion-exchanged water and 1% of a dispersant were added, and the mixture was blended in a pot mill for 24 hours to prepare a slurry. Further, a material to which a suitable amount of chromium oxide was added as a coloring agent was produced. As a comparative material for this,
The average particle size is 0.7 μm and the particle size distribution is broad (0.1 to
(A range of 2.6 μm) was prepared.

Next, the alumina slurry is poured into a mold, the mold is set on a rotor in a centrifuge, and a centrifugal acceleration of 15000 G is applied by rotating the rotor. Accumulates on the bottom of the mold by the centrifugal action, and the deposit becomes a compact. According to this method, the air in the slurry was effectively discharged to the outside, and the alumina particles were closest packed by the action of the centrifugal force to obtain a very high-density compact.

In order to obtain a compact that is most closely packed in this way, the centrifugal acceleration is most closely related and requires at least 3000 G. If it is less than 3000 G, the compact is not sufficiently densified by centrifugation, and therefore, it is not possible to achieve the reduction in the size of crystals and the reduction in voids due to the lowering of the firing temperature as in the present invention.

The present inventor shows in Table 1 the relationship between the sintering temperature at which the relative density is 99% or more and the required centrifugal acceleration.

[0028]

[Table 1]

As is clear from the table, the centrifugal acceleration was 3
At 000 G, the firing temperature could be reduced to 1270 ° C. The magnitude of the centrifugal force is related to the time required for centrifugal separation, and a high centrifugal force is desirable in consideration of production efficiency.

The thus obtained molded body was fired at a temperature of 1200 to 1300 ° C. using a Kanthal super furnace. No. 1 to No. 1 8 was obtained. In addition, the sample No. 11 to sample no. Sample No. 16 shows a case where chromium oxide as a coloring agent was added in an amount shown in the table. In 9, 10, 15, 16
HIP is performed according to the firing temperature indicated in the table. However, by changing the firing temperature in various ways, sintered bodies having various crystal grain sizes were obtained.

[0031]

[Table 2]

Then, the strength and transmittance of each of the above sintered bodies were measured.

For the measurement of strength, a bending piece of 3 × 4 × 40 mm was cut out, and a three-point bending strength was measured in accordance with JISR1601.

For the transmittance, the sample No. 9,
Each sintered body as in 10, 15, 16 is 1200 to 150
After HIP treatment at a temperature of 0 ° C., both surfaces were mirror-finished and finished to a thickness of 0.5 mm, and it was determined whether or not it was sufficient to obtain an electromotive force of the solar cell by the following method. That is, the current value obtained when the solar cell is irradiated with 500 lux of neutral white light is defined as I _0, and is obtained from the solar cell when the sintered body is set between the solar white cell and the light source of the neutral white light. The current value is defined as I ₁ and this ratio [I ₁ /
If I ₀ ] is 30% or more, a sufficient electromotive force can be obtained. In the alumina ceramics of the present invention, the sample No. As shown in FIG. 4, a transmittance of 30% or more could be obtained without performing the HIP treatment.

Thus, in the sample of the present invention, 700 to 12
The strength of 60 MPa was obtained, but the reason for the wide range of strength was the difference in crystal grain size caused by the difference in sintering temperature. Had increased and the strength had decreased.

According to the present invention, the crystal grain size of the sintered body achieving the strength of 700 MPa is about 1.0 μm, and the crystal grain size of the sintered body having the strength exceeding 1000 MPa is 0.5 to 0. The range was about 0.8 μm. When HIP is performed at 1200 to 1500 ° C. in order to improve light transmission, the crystal grain size grows to 3 to 5 μm, but the void size is very small, 0.1 μm or less. In addition, a strength of 700 MPa or more was still obtained, whereby an alumina ceramic having both strength and light-transmitting properties was obtained, and as a result, it could be used as a clock face provided with a solar cell.

In addition, the easily sintered alumina, which is a comparative material, was sintered at 1450 to 1600 ° C., and the inner peripheral side was sintered in the direction of the centrifugal force. Therefore, sintering was not sufficient, and the outermost peripheral portion was unsintered, and a good sintered body could not be obtained.
The reason is that when the molded body is calcined and the particles of the powder are observed, the particles are coarser at the outermost periphery and finer at the innermost periphery, and the particle orientation due to such centrifugal force is occurring. That's why.

Next, a sample No. of the invention was prepared. 3 and the easily sinterable alumina produced by the conventional pressure press are each polished, and furthermore, using a scanning electron microscope (SEM: 1500 ×, 10000 ×) at an arbitrary number of places over a measurement area of 540 μm ^2. When the number of voids was counted, the results shown in Table 3 were obtained.

[0039]

[Table 3]

As is clear from the table, in the ceramics of the present invention, no void exceeding 0.5 μm was found due to void defects, and the surface roughness was measured by AFM (atomic force microscope). 9 nm, and had a high-grade gloss.
3 nm, many voids, and surface roughness was deteriorated.

[0041]

As described above, in the timepiece of the present invention, the timepiece dial is made of alumina ceramic having a void diameter of 0.5 μm or less and a crystal grain size of 1 μm or less, and can have a bending strength of 700 MPa or more. , To a certain extent, and further excellent gloss was obtained.

Further, according to the present invention, a metal oxide such as Cr, Co, Ni or the like is added to the alumina ceramics in an amount of 0.01%.
~ 3% by weight to obtain various colors
Furthermore, the decorativeness could be improved.

Furthermore, by using HIP of alumina ceramics or colored ceramics, it is possible to provide a timepiece dial that can be disposed on the light receiving surface side of the solar cell with increased light transmittance.

[Brief description of the drawings]

FIG. 1 is a sectional view of a timepiece according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Watch 2 Windshield 3 Exterior 4 Movement 5 Solar cell 6 Dial 7 Pointer

Claims (4)

[Claims] 1. A void diameter of 0.5 μm or less and a crystal grain diameter of 1 μm.
A watch using a dial made of the following alumina ceramics. 2. The method according to claim 2, wherein the alumina ceramic is Cr, Co,
The timepiece according to claim 1, wherein a colored ceramic is obtained by adding a metal oxide such as Ni in a range of 0.01 to 3% by weight. 3. The timepiece according to claim 1, wherein the alumina ceramic or the colored ceramic is HIP-grown to a grain size of 3 to 5 μm. 4. A slurry in which alumina raw material powder is dispersed is poured into a molding die having a predetermined shape, and the raw material powder is molded by centrifugal force generated by rotating the molding die. Watch manufacturing method comprising the steps of: