JP2010243179A - Cover glass for timepiece, and method for manufacturing the cover glass - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive cover glass for a timepiece which is excellent in light transmission properties, mechanical strength, abrasion resistance, and also corrosion resistance, and to provide a method for manufacturing the cover glass. <P>SOLUTION: In the cover glass for the timepiece made of spinel, comprising a spinel sintered body, the maximum diameter of pores included in the spinel sintered body is 100 μm or less, and the number of pores whose maximum diameter is 10 μm or more is not more than 2 per volume of 1 cm3 of the spinel sintered body. The method for manufacturing the cover glass for the timepiece made of spinel, wherein a relative density of a spinel molded body after a primary sintering process is 95-96%, and the relative density of the spinel-molded body after a secondary sintering process is over 99.9%, includes a process for manufacturing the spinel-molded body; a primary sintering process for sintering the spinel molded body at 1,500-1,900°C under a normal pressure or in vacuum; and a secondary sintering process for sintering the spinel molded body at 1,500-2,000°C in the pressured state. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a cover glass for a watch, which is made of a spinel sintered body, does not generate birefringence, has high light transmittance, and has excellent mechanical strength, and a method for manufacturing the same.

  A watch cover glass, particularly a watch cover glass, is required to be able to clearly see a dial and a pointer, hardly break, have a scratched surface, and be difficult to get dirty. For this reason, materials for watch cover glass that do not generate birefringence, have high light transmittance over almost the entire visible light range, have excellent mechanical strength and wear resistance, and have good corrosion resistance are required. Is done.

  And since normal glass does not have sufficient mechanical strength and wear resistance, surface-crystallized high-strength glass (Patent Document 1), sapphire (sapphire glass), or surface that has been crystallized instead of normal glass is used. An inorganic glass or the like joined with a sapphire plate is used (Patent Document 2).

Japanese Patent No. 3829338 Japanese Patent No. 2777041

  However, user requirements for performance and price of watch cover glasses in recent years have become increasingly severe. For this reason, the above-mentioned materials do not always satisfy the strict requirements of users. That is, high-strength glass having a crystallized surface does not have sufficient light transmittance and cannot be said to have good productivity. In addition, sapphire and inorganic glass with a sapphire plate bonded to the surface have a problem that birefringence occurs. In addition, since the material is expensive, and it is difficult to process due to its high hardness, the price is further increased.

  In view of the problems of the above-described conventional watch cover glass, the present invention has an excellent light transmission without birefringence, excellent mechanical strength and wear resistance, and an inexpensive watch cover glass. It is an object to provide a manufacturing method.

  As a result of intensive studies, the inventor has used a spinel sintered body as a material, and further has a pore size and density (the number of pores contained in a certain volume) contained in the spinel sintered body within a predetermined range. As a result, it was found that excellent light transmittance, mechanical strength and abrasion resistance were obtained, and the present invention having the following constitution was completed.

The invention described in claim 1
It consists of a spinel sintered body, the maximum diameter of the pores contained in the spinel sintered body is 100 μm or less, and the number of pores having a maximum diameter of 10 μm or more is 2.0 or less per 1 cm ^{3 of the} spinel sintered body. A spinel watch cover glass made of spinel.

  Since the watch cover glass of the present invention is made of a spinel sintered body, it is polycrystalline and does not generate birefringence and has excellent light transmittance. In addition, since the spinel sintered body is excellent in mechanical strength and wear resistance, it is difficult to crack and the surface is hardly damaged. Furthermore, the corrosion resistance is also good.

Further, the maximum diameter of pores contained in the spinel sintered body is 100 μm or less, and the number of pores having a maximum diameter of 10 μm or more is 2.0 or less per 1 cm ^{3 in the} spinel sintered body. Since the light scattering factor is reduced as compared with glass, scattering of light passing through the watch cover glass is suppressed, and the light transmittance is further improved.

  Furthermore, the watch cover glass of the present invention also improves the Weibull coefficient, which is an index of variation in mechanical strength, and provides a stable product. This excellent mechanical property seems to have been brought about by the low number of pores.

  Moreover, since it can manufacture using powder metallurgy technology in addition to being inexpensive, it can manufacture at low cost. The shape is not limited. Furthermore, it is easier to process than sapphire.

  The maximum diameter of the pores in the watch cover glass of the present invention is measured by observing a certain range of the watch cover glass with a microscope using transmitted light. Usually, a watch cover glass is cut into a fixed volume (preferably 10 to 15 mm in thickness, 20 mm in length and 20 mm in width), the upper and lower surfaces are polished, and the obtained sample is observed with a micrograph. It can be obtained by measuring the diameter of the pores contained therein. If the pores are not spherical, the diameters in each direction in the pores are different, but the largest one is the maximum diameter.

  The watch cover glass of the present invention is characterized in that it does not include pores having a maximum diameter exceeding 100 μm, but not including means that it does not substantially include and does not impair the spirit of the present invention. That is, pores having a maximum diameter exceeding 100 μm may be contained in a trace amount within a range that does not increase the light scattering factor. A maximum pore diameter of 50 μm or less is preferable because the light scattering factor is further reduced.

Usually, when the above measurement is performed on 10 samples having a thickness of 15 mm, a length of 20 mm, and a width of 20 mm, and the upper and lower surfaces are polished, and pores exceeding the maximum diameter of 100 μm are not observed for 8 or more samples, It is assumed that pores having a maximum diameter exceeding 100 μm are not substantially included. Alternatively, the above measurement is performed on an area of 40 cm ² or more of a sample (which may be plural or singular) having a thickness of 15 mm and whose upper and lower surfaces have been polished, and the maximum diameter exceeds 80 μm for a portion having a volume of 80% or more. Even when no pores are observed, the pores having a maximum diameter exceeding 100 μm are not substantially included.

The number of pores having a maximum diameter of 10 μm or more per 1 cm ^{3 of} the spinel sintered body is also measured by observing a certain volume of the spinel sintered body with a microscope using transmitted light. Usually, the spinel sintered body is cut into a thickness of 10 to 15 mm, a length of 20 mm, and a width of 20 mm (or a plurality of spinel sintered bodies so that the total volume becomes the same size as above), and the upper and lower surfaces are cut. The sample obtained after polishing is observed with a micrograph, and whether or not the number of pores having a maximum diameter of 10 μm or more exceeds 8 is determined as being within the scope of the present invention.

The spinel forming the spinel sintered body is a compound whose molecular formula is represented by MgO.nAl ₂ O ₃ (n = 1 to 6). In the present invention, the value of n is preferably 1.05 to 1.30, more preferably 1.07 to 1.125, and particularly preferably 1.08 to 1.09.

  Elements other than the spinel constituent elements contained in the spinel sintered body, that is, impurities, also form internal defects such as pores and increase the light scattering factor, thereby reducing the light transmittance of the watch cover glass. It also affects the refractive index and the like. Since these impurities are derived from the raw material powder and mixed in the production of the sintered body and are contained in the spinel sintered body, the raw material powder has a high purity (preferably a component that is not removed by sintering). It is desirable to use a spinel having a purity of 99.9% by mass or more) and to control so that no impurities are mixed even in the sintering step described later.

  Specific examples of impurities that are likely to be contained in the raw material powder and impurities that are likely to be mixed when the sintered body is produced include W, Co, Fe, C, Cu, Sn, Zn, and Ni. In the sintering process, these impurities coalesce or precipitate to form impurity particles with a size that adversely affects the optical properties, increase the light scattering factor, and affect the transmission. . Preferably, the purity of the raw material powder and the sintering process are controlled so that the content of these impurities in the spinel sintered body is less than 10 ppm, more preferably less than 5 ppm.

The spinel watch cover glass is
Forming a spinel powder and producing a spinel compact,
A primary sintering step in which the spinel molded body is sintered at an atmospheric pressure or below in an atmosphere or vacuum at a temperature range of 1500 to 1900 ° C., and a spinel molded body after the primary sintering step is subjected to an atmospheric pressure of 5 to 300 MPa. And a secondary sintering step of sintering at a temperature range of 1500 to 2000 ° C.,
Manufactured by a method characterized in that the relative density of the spinel compact after the primary sintering step is 95 to 96% and the relative density of the spinel compact after the secondary sintering step is 99.9% or more. can do. The invention of claim 2 corresponds to the method of manufacturing the spinel watch cover glass.

  The step of forming a spinel powder by forming a spinel powder includes, for example, preparing a slurry by dispersing spinel powder in a dispersion medium, and then granulating the slurry by spray drying or the like, and then forming the granule into a mold. It is possible to carry out by pressing into a predetermined shape. As a dispersion medium for dispersing the spinel powder, water or various organic solvents can be used.

  Polyacrylic acid ammonium salt (when the dispersion medium is water), ethyl oleate, sorbitan monooleate, sorbitan trioleate, polycarboxylic acid (when the dispersion medium is an organic solvent), etc., to enable uniform dispersion To facilitate the formation of dispersants and granules, organic binders such as polyvinyl alcohol, polyvinyl acetal, various acrylic polymers, methyl cellulose, polyvinyl acetate, polyvinyl butyral, various waxes, various polysaccharides, etc. may be added to the slurry. Good.

  As described above, high-purity spinel powder is desirable as the raw material, but organic matter, halogen and water contained in the raw material are removed from the raw material in the primary sintering step, and the characteristics of the spinel sintered body are impaired. Therefore, mixing in the stage before the primary sintering is allowed.

  An example of the pressing method is cold isostatic pressing (CIP). The pressure of the press is preferably selected from the range in which the relative density of the spinel compact after the primary sintering step is in the range of 95 to 96%, but is usually 100 to 300 MPa.

  After molding into a predetermined shape, the molded body is primarily sintered. The primary sintering is a step of heating and sintering the molded body at 1500 to 1900 ° C. in a predetermined normal pressure or reduced pressure (vacuum) atmosphere. Preferred examples of the normal pressure or reduced pressure (vacuum) atmosphere include a reducing atmosphere such as hydrogen and an inert gas atmosphere such as Ar. The pressure of the atmosphere is preferably reduced pressure (vacuum), specifically, about 1 to 200 Pa is preferable. The primary sintering time is preferably about 1 to 5 hours.

The production method of the present invention is characterized in that the relative density of the spinel molded body (spinel primary sintered body) after the primary sintering step is in the range of 95 to 96%. Here, the relative density represents the ratio of the actual density to the theoretical density of spinel (3.60 g / cm ³ at 25 ° C.) (theoretical density ratio, expressed in%). The density (25 ° C.) is 3.42 g / cm ³ .

When this relative density is less than 95%, sintering in the secondary sintering process is difficult to proceed, and it is difficult to obtain a transparent spinel sintered body. On the other hand, when the relative density exceeds 96%, the coalescence of pores already existing in the spinel molded body is likely to proceed in the secondary sintering step, and pores having a maximum diameter exceeding 100 μm are easily generated. In addition, the number of pores increases, and it becomes difficult to obtain a spinel sintered body having 2.0 or less pores having a maximum diameter of 10 μm or more per 1 cm ³ of the spinel sintered body.

  The relative density of the spinel molded body after the primary sintering step varies depending on the density of the molded body before the primary sintering, the temperature and time of the primary sintering. Further, the density of the molded body before the primary sintering varies depending on the pressure of the press at the time of molding. Therefore, a relative density in the range of 95 to 96% can be obtained by adjusting the pressure of the press during molding and the temperature and time of primary sintering.

  The spinel primary sintered body obtained by the primary sintering step is secondarily sintered. The secondary sintering is a step in which the compact is heated and sintered at 1500 to 2000 ° C., preferably 1600 to 1900 ° C. under pressure. The pressurizing pressure is in the range of 5 to 300 MPa, preferably about 50 to 250 MPa, and more preferably about 100 to 200 MPa. The secondary sintering time is preferably about 1 to 5 hours. As an atmosphere for secondary sintering, an atmosphere of an inert gas such as Ar is preferable.

  The production method of the present invention is further characterized in that the relative density of the spinel molded body (spinel sintered body) after the secondary sintering step is 99.9% or more. The relative density after the secondary sintering process varies depending on the pressure and temperature in the secondary sintering process and the time of the secondary sintering. Accordingly, a relative density of 99.9% or more can be obtained by adjusting the pressure and temperature in the secondary sintering step and the time of secondary sintering.

  As described above, by adjusting the relative density of the spinel sintered body after the secondary sintering process to be 99.9% or more, the grain growth of the spinel during the sintering process is controlled, and the spinel The coalescence of fine pores accompanying grain growth can be suppressed. As a result, it is possible to obtain a spinel sintered body that suppresses the generation of pores having a maximum diameter exceeding 100 μm and the number of pores to form the watch cover glass of the present invention.

  The spinel sintered body thus obtained is processed into a watch cover glass through steps such as cutting into a predetermined shape and polishing. The size and thickness of the watch cover glass are not particularly limited as long as they are determined according to the size and design of the dial of the watch to be applied. Further, it may be formed in a convex shape, or a lens for enlarging and displaying a calendar display or the like on the dial may be formed.

  Further, if necessary, an antireflection coating layer or an optically acting layer can be formed on the surface of a watch cover glass made of a spinel sintered body. For example, the light transmission function can be further improved by forming an antireflection coating layer on one side or both sides of a spinel sintered body used as a watch cover glass.

  The antireflection coating layer is, for example, a metal oxide or metal fluoride layer, and the formation method thereof is a conventionally known PVD method (physical vapor deposition method), specifically, a sputtering method, an ion plating method, a vacuum. An evaporation method or the like can be used.

  Since the watch cover glass of the present invention is formed of a spinel sintered body in which pores are suppressed, birefringence does not occur and light transmittance is high over the entire visible light region. And it is excellent in mechanical strength, abrasion resistance, etc., and also has good corrosion resistance.

  ADVANTAGE OF THE INVENTION According to this invention, birefringence does not generate | occur | produce, it has the outstanding light transmittance, it is excellent in mechanical strength and abrasion resistance, and also the inexpensive cover glass for watches can be provided. And the watch cover glass of this invention can be easily obtained with the manufacturing method of the spinel-made watch cover glass of this invention.

  Hereinafter, the form for implementing this invention is demonstrated based on one Example of the manufacturing method of a spinel sintered compact. The present invention is not limited to the following examples. The following various modifications can be made within the same and equivalent scope as the present invention.

(Example)
1. Molded body production process In the production of the spinel sintered body of this example, first, a slurry in which spinel powder (raw material powder) is dispersed is produced. The slurry can be prepared by blending appropriate amounts of high-purity spinel powder, dispersion medium, dispersant, etc., and mechanically stirring and mixing.

I. Production of slurry Examples of the mechanical stirring and mixing method include a method of mixing by a ball mill, a method of irradiating ultrasonic waves from the outside using an ultrasonic bath, and a method of irradiating ultrasonic waves by an ultrasonic homogenizer. Since spinel powder is easily dispersed in a dispersion medium and easily becomes a uniform slurry, and a dispersion method using a ceramic ball or the like is considered to easily contain oxides or salts as impurities, ultrasonic waves are used. The method used is preferred.

  After stirring and mixing, the concentration of spinel in the slurry can be increased by performing static sedimentation, centrifugation, vacuum concentration using a rotary evaporator, or the like.

  In this example, 4750 g of high-purity (purity 99.9% or more) spinel powder, 3100 g of water (dispersion medium), and 40 g of ammonium polycarboxylate 40% by mass aqueous solution (dispersant, manufactured by San Nopco: trade name SN-D5468) 125 g The mixture was stirred and mixed for 30 minutes while irradiating ultrasonic waves. Thereafter, 1000 g of a 10 mass% solution of polyvinyl alcohol (trade name PVA-205C, manufactured by Kuraray Co., Ltd.) as an organic binder and 10 g of polyethylene glycol # 400 (reagent special grade) as a plasticizer are added, and the slurry is stirred and mixed for 60 minutes. Prepared.

  A tank having a capacity of 40 liters was used as the ultrasonic tank. The stirring and mixing time should be adjusted as appropriate according to the amount of slurry and the amount of ultrasonic irradiation. For example, when using an ultrasonic tank with a slurry amount of 10 liters and an irradiation capacity of about 25 kilohertz, it should be performed for 30 minutes or longer. Is desirable.

B. Molding Next, the slurry is granulated by spray drying, and the moisture content of the granules is adjusted to 0.5% by mass, then filled in a mold, and primary molded with a press at a pressure of 196 MPa. Secondary forming was performed by a cold isostatic press (CIP) under pressure to obtain a spinel molded body.

2.1 Primary Sintering Step The molded body was put in a graphite container and subjected to primary sintering in vacuum (5 Pa or less) at 1650 ° C. for 4 hours. When the relative density was measured by the Archimedes method, it was 95.8% (that is, in the range of 95 to 96%).

3. Secondary Sintering Step The primary sintered body is heated and pressurized by hot isostatic pressing (HIP) at a temperature of 1650 ° C. for 2 hours under conditions of Ar atmosphere and atmospheric pressure of 196 MPa. A secondary sintered body was obtained. When the relative density was measured by the Archimedes method, it was 99.95% (that is, 99.9% or more).

4). Production of watch cover glass The spinel secondary sintered body obtained by the above method was cut into a plate having a thickness of about 1.2 mm to produce a watch cover glass made of a spinel sintered body. Both surfaces of the obtained watch cover glass were mirror-finished to obtain a watch cover glass having a square of 100 mm on a side and a thickness of 1 mm (volume: 1.0 cm ³ ).

5). Physical property evaluation a. Evaluation of light transmittance When the light transmittance at a wavelength of 550 nm of the obtained watch cover glass was measured, it was 85% (thickness: 1.0 mm).

B. Observation of pores The surface of the watch cover glass obtained at a magnification of 50 times was observed using an optical microscope (Nikon T-300), and the pore diameter and the number of pores having a maximum diameter of 10 µm or more were measured. As a result, the maximum pore diameter is 13 μm or less, no pore having a maximum diameter exceeding 100 μm is observed, and the number of pores observed is one, 1.25 per cm ³ , ie, 2 or less. Met.

C. Measurement of mechanical strength Three-point bending measurement based on JIS1601R was performed using a sample of a spinel secondary sintered body obtained by the above method (n = 15). As a result, the strength was 426 MPa and the Weibull coefficient was 9.

As shown in the above results, according to the manufacturing method of the present invention, a watch cover glass made of a spinel sintered body, the maximum diameter of pores contained in the spinel sintered body is 100 μm or less, and A spinel sintered body characterized in that the number of pores (the number of pores having a maximum diameter of 10 μm or more) was 2.0 or less per 1 cm ^{3 of} the spinel sintered body was obtained. It was confirmed that the timepiece cover glass formed from this spinel sintered body has excellent light transmittance and mechanical strength, and also has a high Weibull coefficient.

(Comparative Examples 1-3)
It consists of a spinel sintered body in the same manner as in the above-described example (specific example) except that the relative density after the primary sintering step and the relative density after the secondary sintering step are the values shown in Table 1. A watch cover glass was prepared, and the pores were observed and the mechanical strength was measured. The results are shown in Table 1 together with the results of the above examples (specific examples). (The primary sintering density and secondary sintering density in the table represent the relative density (%) after the primary sintering step and the relative density (%) after the secondary sintering step, respectively.)

  As is clear from the results in Table 1, in the examples according to the production method of the present invention, the spinel watch cover glass of the present invention is obtained, but the relative density after the primary sintering step is in the range of 95 to 96%. In Comparative Examples 1 to 3, which are outside and the relative density after the secondary sintering step is less than 99.9%, pores having a maximum diameter of more than 100 μm are generated, and the number of pores having a maximum diameter of 10 μm or more is also included. Many spinel watch cover glasses of the present invention have not been obtained. Also, the results of Table 1 show that the mechanical strength and the Weibull coefficient are low.

Claims (2)

It consists of a spinel sintered body, the maximum diameter of the pores contained in the spinel sintered body is 100 μm or less, and the number of pores having a maximum diameter of 10 μm or more is 2.0 or less per 1 cm ^{3 of the} spinel sintered body. A spinel watch cover glass characterized by being. Forming a spinel powder and producing a spinel compact,
A primary sintering step in which the spinel molded body is sintered at an atmospheric pressure or below in an atmosphere or vacuum at a temperature range of 1500 to 1900 ° C., and a spinel molded body after the primary sintering step is subjected to an atmospheric pressure of 5 to 300 MPa. And a secondary sintering step of sintering at a temperature range of 1500 to 2000 ° C.,
The relative density of the spinel compact after the primary sintering step is 95 to 96%, and the relative density of the spinel compact after the secondary sintering step is 99.9% or more. A method for producing a watch cover glass.