This invention relates to a glass shaping method capable of performing precision machining, such as grinding and/or polishing, of molded glass; and a glass shaped article formed by this method.
When machining (i.e., mechanical processing), such as grinding and/or polishing, is applied to glass per se which is a brittle material, there have been limitations on the size of the material to be processed, or on the miniaturization of the material, owing to the brittleness of the material. For a complicated shape, moreover, processing itself has faced limitations.
To form such a fine glass product, a technology for forming fine glass by chemical processing is available. According to Patent Document 1, for example, a spring shaped like a power spring (or spiral spring), which is used for a clock or watch, is disclosed as a glass shaped article. Such a spring is produced in the following manner: Glass is ground and/or polished to form a glass sheet with a predetermined thickness. Then, the surface of the glass sheet is covered with a power spring-shaped mask. A glass portion of the glass surface, which has not been covered with the mask, is modified by UV irradiation and, after modification, is removed by selective etching. In this manner, a glass shaped article in the shape of a power spring is formed by chemical processing.
There is a technology for forming a fine ceramic shaped article from a ceramic, a brittle material like glass, with the use of a mold. Patent Document 2, for example, makes the following disclosure: To form a piezoelectric ceramic into a predetermined shape, a silicon mold is formed by providing a plurality of apertures on a silicon substrate by use of reactive ion etching. Then, a slurry containing a powder of a piezoelectric ceramic and a binder is coated on a surface of the silicon mold including the interior of the apertures, and the coating is dried. Then, the binder is removed, and the remaining product is pressurized at the sintering temperature of the piezoelectric ceramic to calcine the piezoelectric ceramic powder. After calcination, the silicon mold is etched away to form the fine-shaped piezoelectric ceramic into a predetermined shape.
Patent Document 1: Japanese Patent No. 5061117
Patent Document 2: Japanese Patent No. 4065049
As described above, the technology of forming fine glass by UV irradiation is disclosed in Patent Document 1, and the technology of shaping a fine ceramic, a brittle material like glass, using a silicon mold is disclosed in Patent Document 2.
However, there is a case where the glass product formed by UV irradiation needs to be further ground and/or polished after UV irradiation, as in Patent Document 1. If an object to be ground and/or polished is fine like a glass spring for a wristwatch, the shaped article is apt to be damaged or scarred during a grinding and/or polishing operation, and its processing is difficult.
There is also a case where the ceramic shaped material formed from a calcined ceramic in Patent Document 2 needs grinding and/or polishing in order to be further formed into a shape different from the shape of the mold. In such a case as well, processing is difficult, particularly when the shaped article is fine, because the ceramic is a brittle material.
The present invention has been accomplished in the light of these circumstances. Its object is to provide a glass shaping method capable of grinding and/or polishing a fine brittle material more stably than conventional methods; and a glass shaped article formed by this method.
To attain the above object, the glass shaping method of the present invention includes a mold forming step of forming a mold having a concavity by use of a base material which does not deform at a higher temperature than the softening point of glass; a glass molding step of heating a glass substrate at a temperature equal to or higher than the softening point of glass, sealing softened glass or molten glass into the concavity of the mold, and cooling and solidifying the softened glass to mold the glass substrate; a glass processing step of performing machining, such as grinding and/or polishing, of the glass substrate together with the mold, or only the glass substrate, with the glass substrate being sealed in the concavity of the mold, to form a glass shaped article; and a mold elimination step of eliminating the remaining base material of the mold after the glass processing step to remove the glass shaped article from the mold.
In the glass molding step of the above glass shaping method, a surface of the glass substrate alone or together with the mold, the surface intersecting the depth direction of the concavity of the mold, is ground and/or polished, whereby the glass shaped article having the same planar shape as that of the surface intersecting the concavity can be formed.
According to the glass shaping method, the base material is preferably silicon and, in the mold elimination step, the mold is preferably eliminated by etching.
It is preferred that the base material of the glass shaping method be carbon and, in the mold elimination step, the mold be eliminated by burning.
The glass shaping method can include an additional glass molding step of grinding and/or polishing the glass substrate within the cavity, together with the remaining mold of the mold, after forming the cutting surface. Herein, the term “softening point of glass” refers to a temperature at which glass softens and deforms under its own weight, and its viscosity reaches 107.65 dpa•s. The expression “eliminating the base material of the mold” does not include removal by mere release of the molded product from the mold, but means that a part or all of the mold disappears physically or chemically. The term “softened glass” refers to glass in a state ranging from a state in which it has a softening point to a state before it melts 100%. The term “molten glass” refers to glass in a 100% molten state.
The glass shaping method of the present invention, as described above, includes the mold forming step of forming a mold having a concavity by use of a base material which does not deform at a higher temperature than the softening point of glass; the glass molding step of heating a glass substrate at a temperature equal to or higher than the softening point of glass, sealing softened glass or molten glass into the concavity of the mold, and cooling and solidifying the softened glass or molten glass to mold the glass substrate; the glass processing step of performing machining, such as grinding and/or polishing, of the glass substrate together with the mold, or only the glass substrate, with the glass substrate being sealed in the concavity of the mold, to form a glass shaped article; and the mold elimination step of eliminating the remaining base material of the mold after the glass processing step to remove the glass shaped article from the mold. Hence, the mold holds the glass substrate, thus enabling the fine glass or glass portion to be ground and/or polished with accurate precision. Consequently, cracking of or damage to the glass can be prevented.
By reducing the difference in thermal expansion between the glass and the mold of the base material, glass shaping with high dimensional accuracy can be performed.
Hereinbelow, glass shaping in the first embodiment of the present invention will be described by reference to the accompanying drawings.
To form the film groove 13, the resist film 12 is coated on the surface of the silicon plate 11. Then, a mask 14 is disposed above the resist film 12. The mask 14 is in a shape in which a chromium film 14b, for example, has been vapor-deposited on a transparent quartz substrate 14a, and portions where the chromium film 14b is absent are in conformity with the planar (cross-sectional) shape of the spring 1. From above the mask 14, the resist film 12 is exposed, for example, to ultraviolet radiation (UV), thereby forming a resist pattern. The resist film 12 is exposed to far ultraviolet radiation, electron beam, X-rays or the like, aside from ultraviolet radiation.
Upon exposure of the resist film 12, the exposed silicon plate 11 is dipped in a developing solution to remove the resist film in the exposed portions, as shown in
Starting with the state shown in
After formation of the mold 10, glass is sealed onto the surface of the spring groove 15 of the mold 10, as shown in
If the softened glass enters the spring groove 15 with difficulty, the softened glass may be pressurized. The mold 10 is formed with the spring groove 15, but may be provided with a through-hole instead of the groove. However, a closing member (or a closing means) is needed so that the softened glass will not flow out of the through-hole. After the softened glass is sealed into the spring groove 15, the softened glass is cooled and solidified. (Glass molding step)
Upon cooling and solidification of the softened glass or molten glass, the mold 10 holding the glass is set unchanged in a grinding machine and/or a polishing machine (not shown), without the release of the glass and the mold 10 from each other.
Then, a glass substrate 17 on the surface of the mold 10 shown in
As is well known, glass is a hard material and easily breakable, and is not an easy material when grinding and/or polishing a micro-component as a single body for the purpose of shaping. However, the glass alone is not ground and/or polished, but the glass, together with the mold 10, is ground and/or polished. Thus, the glass is held integrally with the silicon and, even if a shearing force is applied during grinding and/or polishing, damage to the glass material having brittleness can be prevented. Higher precision grinding and/or polishing as well as cutting of glass can be achieved.
A hairspring for a watch has been prepared as above, but the present invention is also applicable to the manufacture of gears for watches or precision components of other products.
Next, glass shaping in the second embodiment of the present invention will be described by reference to the accompanying drawings.
After formation of the mold 20, glass is sealed onto the surface of the mold 20, as shown in
Upon cooling and solidification of the softened glass, the mold 20 holding a glass substrate 24 is set unchanged in a grinding machine and/or a polishing machine (not shown), without releasing the glass and the mold 20 from each other. Then, as shown in
Next, glass shaping in the third embodiment of the present invention will be described by reference to the accompanying drawings.
To form the fine round hole 31, a diamond drill can be operated on the silicon wafer, thereby forming the round hole. In the same manner as in the aforementioned first embodiment, a resist film is formed, and the round hole can be formed, using photolithography.
If only one of the prisms 3 is to be formed, it is sufficient to form one of the round holes. (Mold forming step)
After formation of the mold 30, glass is sealed onto the surface of the mold 30, as shown in
Upon cooling and solidification of the softened glass on the mold 30, the mold 30 holding the glass is set unchanged in a fixing part of a grinding machine and/or a polishing machine (not shown), without releasing the glass and the mold 30 from each other.
Then, as shown in
Then, the positioning portion 6 of the prism 3 is formed by grinding. During grinding for formation of the positioning portion 6, the outer peripheral surface of the body 4 of the prism 3 is axially ground, together with the remaining silicon 34, to form a flat surface. (Additional glass processing step)
The relationship between the mold and the glass holds under conditions such that the mold does not soften (deform) or melt at a temperature equal to or higher than the softening point of the glass. Preferably, the mold is made of a material having a coefficient of linear expansion close to that of the glass, the material to be shaped.
The softening point of heat-resistant glass is 820° C., and high-melting metals, such as Ti, Mo, W and Pt, can be used in addition to silicon and carbon, as materials for the mold having a higher melting temperature than the softening point of glass. A metal mold, in particular, is advantageous in that a glass shaped article can be easily taken out as a single body, since the mold is eliminated by selective etching. The melting temperature of the material for the mold differs according to type, and is 1414° C. for Si, 3370° C. for carbon, 1668° C. for Ti, 2623° C. for Mo, 3387° C. for W, and 1772° C. for Pt.
The coefficient of linear expansion of glass usable as a base material is 3.3×10−6/° C. for non-alkali glass (Tempax, a registered trademark of Schott AG), 9.0×10−6/° C. for soda-lime glass, and 7.2×10−6/° C. for D263 (produced by Schott AG).
The coefficient of linear expansion of the material usable as the mold is 3.9×10−6/° C. for Si, 3.3×10−6/° C. for carbon, 8.8×10−6/° C. for Ti, 5.1×10−6/° C. for Mo, 4.5×10−6/° C. for W, and 9.0×10−6/° C. for Pt.
The present invention can heat glass to a temperature equal to or higher than the softening point of glass, pour the softened glass into the mold, and machine the so molded fine glass to form a glass shaped article.
However, the difference in the coefficient of thermal expansion between the glass and the base material should preferably be minimal from the viewpoint of precision. A combination of the glass and the mold similar in the coefficient of thermal expansion brings the effect of performing glass shaping with high dimensional accuracy, and the effect of preventing damage to glass due to the difference in thermal expansion.
According to the foregoing first to third embodiments, glass is heated to a temperature equal to or higher than the softening point, and the softened glass is sealed into the spring groove 15, the reticulated grooves 21, or the round hole 31. Even when molten glass is sealed into the spring groove 15, reticulated grooves 21, or round hole 31, however, the spring 1, reticulated glass 2, or prism 3 can be produced in the same manner as for the softened glass. In this case, the glass needs to be molded at a temperature equal to or lower than a temperature at which the mold does not deform. In the case of the molten glass, the difference in thermal expansion between the glass and the mold becomes greater than when the softened glass is sealed in.
The present invention has been described in detail above based on the embodiments by reference to the accompanying drawings. However, the present invention is not limited to these embodiments, but other changes or modifications can be made without departing from the scope of the present invention.
In the third embodiment, for example, the mold 30 is formed from silicon. However, a prism of the same configuration as above can be formed, even if the mold is carbon instead of silicon. In the second embodiment, the mold 20 is formed from carbon. However, reticulated glass of the same configuration as above can be formed, even if the mold is silicon instead of carbon.
The above embodiments exemplify grinding and/or polishing as the machining of the glass substrates 17, 24, 32 contained in the remaining molds 16, 23, 34. However, other processing technologies such as cutting are also included in the machining. As machine tools for performing such processing technologies, there can be used, for example, a lathe, a drilling machine, a boring machine, a milling machine, a grinding machine, a gear cutting machine, a numerically controlled machine tool, and a dicing saw.
In the glass processing step, the glass substrate is processed together with the mold 10, 20 or 30. However, only the glass substrate can be processed.
Number | Date | Country | Kind |
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2017-139192 | Jul 2017 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2018/022963 | 6/15/2018 | WO | 00 |