Patent Grant
9580346
Field of the Invention
The present invention relates to a method for manufacturing an optical element and particularly relates to a method for manufacturing an optical element for use in an optical apparatus, such as cameras and videos, by press-molding.
Description of the Related Art
Heretofore, a method for obtaining an optical element by press-molding glass which is heated and softened is known. However, in recent years, a technique of molding a glass material having a special optical constant has been required with an enhancement of performance of a lens unit.
The composition of the glass material of a special optical constant sometimes become a thermally unstable composition. When the glass material of the composition is heated to a molding temperature, the generation amount of volatile constituents increases. When a lens is hot-molded using such a glass material, a foggy lens in which air bubbles are generated due to the generation of volatile constituents is molded, so that the appearance becomes poor. Therefore, when molding the glass material of a special optical constant, a technique of suppressing the generation of volatile constituents is required.
As a former technique of suppressing the generation of volatile constituents, a method for pressurizing the atmosphere in a chamber to be equal to or higher than the vapor pressure is disclosed (Japanese Patent Laid-Open No. 2004-107145).
However, in the former technique described in Japanese Patent Laid-Open No. 2004-107145, the pressure from the atmosphere does not act on the surface where a mold and glass contact each other, and the pressurization force to the glass decreases, so that air bubbles due to volatilization are generated in the molded surface. Furthermore, although the standard of “equal to or higher than the vapor pressure” is described, the material of a special optical constant, particularly a phosphate-based glass containing Bi2O3 in a proportion of 10 mass % or higher and 30 mass % or lower, has had a problem to be solved such that the effect of suppressing volatilization is not obtained even when pressurization exceeding the vapor pressure of metallic elements is performed.
The present invention provides a method for manufacturing an optical element whose pressed surface is good even when hot press-molding is performed using a phosphate-based glass material.
The method for manufacturing an optical element which solves the above-described problems includes, in a method for manufacturing an optical element by pressing a phosphate-based glass containing Bi2O3 in a proportion of 10 mass % or higher and 30 mass % or lower with a hot mold, and then cooling the same, continuously applying pressure equal to or higher than the critical pressure of oxygen and equal to or lower than a strength of glass to the glass from the time of bringing the glass into contact with a pressing surface of the mold at a glass viscosity of log η=9 [dPa·sec] or higher and 10 [dPa·sec] or lower until the glass viscosity log η increases to 12 [dPa·sec] by cooling.
The present invention can provide a method for manufacturing an optical element whose pressed surface is good even when hot press-molding is performed using a phosphate-based glass material.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
A method for manufacturing an optical element of the invention includes, in a method for manufacturing an optical element by pressing a phosphate-based glass containing Bi2O3 in a proportion of 10 mass % or higher and 30 mass % or lower with a hot mold, and then cooling the same, continuously applying pressure equal to or higher than the critical pressure of oxygen and equal to or lower than the strength of glass to the glass from the time of bringing the glass into contact with a pressing surface of the mold at a glass viscosity of log η=9 [dPa·sec] or higher and 10 [dPa·sec] or lower until the glass viscosity log η increases to 12 [dPa·sec] by cooling.
It is suitable that pressure equal to or higher than the critical pressure of oxygen and equal to or lower than the strength of glass is continuously applied to the glass from the time bringing the glass into contact with the pressing surface of the mold, and then heating to adjust the glass viscosity to log η=9 [dPa·sec] or higher and 10 [dPa·sec] or lower until, after pressing, the glass viscosity log η increases to 12 [dPa·sec] by cooling.
Hereinafter, a first embodiment of the invention is specifically described with reference to the drawings.
The material of the glass preform denoted by 5 is a phosphate-based glass containing Bi2O3 in a proportion of 10 mass % or higher and 30 mass % or lower. The Tg (glass transition point) of the phosphate-based glass is 454° C. or higher and 483° C. or lower.
The explanation of each process is described below.
In the heating process of A of
The value of the glass viscosity in the invention is a measured value obtained by penetration type viscosity measurement in the viscosity range of log η=7.5 [dPa·sec] or higher and 10 [dPa·sec] or lower or a measured value obtained by a beam bending method in the viscosity range of log η=11 [dPa·sec] or higher and 14 [dPa·sec] or lower.
In the pressing process of B of
In the middle of the pressure holding process of C of
In the cooling and pressing process of D of
In the extraction process of E of
The appearance of the lens obtained through the processes described above is good. This is considered to be because, when the pressure equal to or higher than the critical pressure is applied to oxygen which forms a covalent bond with Bi which is an easily-volatilizable component, Bi2O3 is not decomposed into Bi and O, and the bond can be maintained. By this action, the deposition of Bi onto the front surface of the pressed surface or the generation of air bubbles by oxygen in the glass surface can be prevented.
The method for manufacturing an optical element of the invention is suitably used for a method for manufacturing an optical element using a phosphate-based glass containing Bi2O3 in a proportion of 10 mass % or higher and 30 mass % or lower and suitably 20 mass % or higher and 30 mass % or lower as the material. Even when the glass containing Bi2O3 in a proportion of 10 mass % or higher and 30 mass % or lower is hot press-molded, air bubbles or the like due to volatilization are not formed in the pressed surface, so that a lens excellent in the appearance quality can be molded. In glass containing Bi2O3 in a proportion lower than 10 mass %, the generation amount of volatile constituents from the glass is small, so that the appearance quality is good, even when the molding is not performed under the molding process conditions of the invention. In glass containing Bi2O3 in a proportion higher than 30 mass %, the generation amount of volatile constituents in the heating process is large, so that the appearance quality does not become good even when the molding is performed under the molding process conditions of the invention.
Next, a second embodiment of the invention is specifically described with reference to the drawings. In contrast to the first embodiment in which molding is performed by up-and-down operation of only the upper mold, a method for certainly continuously applying a predetermined pressure to glass while controlling the pressure and the temperature of upper and lower molds by a molding machine having upper and lower biaxial press shaft is described in the second embodiment.
The explanation of each process is described below.
In the heating process of A of
In the upper mold pressing process of B of
In the lower mold pressure holding process of C of
In the upper mold/blow mold striking process of D of
On the other hand, as a comparison, when the conditions are changed to conditions where the load P2 is not made to act on the mold in the process C, the load P1 does not act on the glass by the striking, so that the pressure in the glass becomes almost 0 with time. In this case, since a large amount of easily-volatilizable components are generated, so that the appearance of a lens becomes poor. Therefore, the timing at which the load P2 is applied to the glass is required to be set before the striking.
The necessary time until the stress in the glass by P1 becomes 0 can be calculated by comparing with the thickness of a molded article in which the molding temperature is sufficiently increased and the position coordinate of the upper mold positioned by the striking. This adjusts the timing at which cooling is started in the following process. The stress in the glass by P1 is made as small as possible when starting the cooling, whereby the surface accuracy can be stabilized.
In the lower mold cooling and pressing process of E of
In the lens extraction process of F of
The extracted lens is evaluated for the appearance quality, such as fogging and air bubbles, by a visual inspection under an optical microscope. Moreover, the form quality is evaluated by variation measurement of the center thickness with a height gauge. In the lens obtained through the above-described molding processes, poor appearance is not observed and, in spite of the fact that the pressure is continuously applied to the glass, the variation in the center thickness can be controlled to ±10 μm or lower.
The manufacturing method of the invention can be used for manufacturing of optical elements, such as a lens and a prism, for example.
In this example, molding was performed under various kinds of conditions described below, and the appearance quality of lenses was confirmed. The molding method is based on the processes of
First, the conditions of glass materials for use in molding are described. As glass materials, five kinds of glass materials of A-1, A-2, A-3, B-1, and B-2 were prepared. All the glasses are phosphate-based glasses, the content of Bi2O3 which is an easily-volatilizable component is 5, 10, 20, 30, and 40 mass % in A-1, A-2, A-3, B-1, and B-2, respectively. The composition ratio of each of the glass materials of A-1, A-2, A-3, B-1, and B-2 is shown in Table 1.
Next, molding process conditions are described.
In the heating process of
In the pressure holding process of
In the cooling and pressing process of
Even when the glass viscosity η during the upper mold pressing in the upper mold pressing process of
It was able to be confirmed from these results that, under the conditions of log η=9.0 [dPa·sec] or higher and 10.0 [dPa·sec] or lower, the generation of fogging was suppressed, cracking did not occur, and press deformation was able to be performed to a predetermined thickness at a standard pressing pressure value of 50 MPa or higher and 100 MPa or lower. In the upper mold pressing process of
It was able to be confirmed that, also in the pressure holding process of
In this comparative example, the following conditions were changed from those of Example 1, and then molding was performed. Then, it was able to be confirmed whether or not the appearance quality deteriorated. In the upper mold pressing process of
As a result, when the conditions were set in such a manner that the glass viscosity η during the upper mold pressing in the upper mold pressing process of
In this comparative example, the following conditions were changed from the conditions of Example 1 in which the appearance was good, and then molding was performed. Then, it was able to be confirmed whether or not the appearance quality deteriorated.
In the pressure holding process of
As a result, in the pressure holding process of
In this comparative example, the glass viscosity η at which the pressure holding ended in the pressure holding process of
As a result, fogging generated, so that the appearance quality became poor. It was able to be confirmed that when the glass viscosity at which the pressure holding ended was made lower than log η=12.0 [dPa·sec], the appearance quality deteriorated.
In this comparative example, the appearance quality of an optical element molded under the same molding process conditions as those of Example 1 using the glass material B-2 described in Example 1 was confirmed.
As a result, since Bi2O3 was contained in a proportion as high as 40 mass % in the glass material B-2, the generation amount of volatile constituents in the heating process of
In this reference example, the appearance quality of an optical element molded under the same molding process conditions as those of Example 1 using the glass material A-1 described in Example 1 was confirmed.
As a result, since Bi2O3 was contained in a proportion of only 5 mass % in the glass material A-1, the generation amount of volatile constituents from the glass is small, so that the appearance quality was good under all the molding process conditions except the molding process conditions under which cracking occurs.
In the case of a phosphate-based glass containing Bi2O3 in a proportion lower than 10 mass %, the appearance quality was good even when molding was not performed under the molding process conditions of the invention.
In this example, the pressure of each of P1 to P3 illustrated in
As a result, with respect to the appearance quality, the same result as that of Example 1 was obtained. In the case where the pressure pattern applied to glass was the same, even when the structure was the upper and lower biaxial molding mold structure, good appearance quality was obtained.
On the other hand, with respect to the form quality, the center thickness accuracy improved under the conditions where the deformation rate of the lens was low in the lower mold pressure holding process of
In the case where the process for striking the upper mold and the blow mold was performed with the upper and lower biaxial molding mold structure and the lens deformation rate during pressure holding was set to 1 μm/sec or lower, even when the molding conditions were conditions where pressure was continuously applied, the center thickness accuracy was within ±10 μm, so that good form quality was obtained.
According to the manufacturing method of the invention, the pressed surface is good even when hot press-molding is performed using a phosphate-based glass material. Therefore, the manufacturing method of the invention can be used for methods for manufacturing optical elements, such as a lens and a prism.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2012-130082 filed Jun. 7, 2012, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-130082 | Jun 2012 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6629435 | Tomisaka | Oct 2003 | B2 |
| 7336424 | Yoneda | Feb 2008 | B2 |
| 7930901 | Fujiwara et al. | Apr 2011 | B2 |
| 20050011227 | Sakai et al. | Jan 2005 | A1 |
| 20050054511 | Fujiwara et al. | Mar 2005 | A1 |
| 20100004112 | Ohkawa et al. | Jan 2010 | A1 |
| Number | Date | Country |
|---|---|---|
| 2004-107145 | Apr 2004 | JP |
| 2005-154248 | Jun 2005 | JP |
| 2005-255499 | Sep 2005 | JP |
| 2006-111499 | Apr 2006 | JP |
| 2012-041195 | Mar 2012 | JP |
| Entry |
|---|
| Kazuo Tachiwana, “Optical Glass”, Glass Engineering Handbook, first edition, pp. 525-539, ISBN: 4-254-25238-2 (1999). |
| Number | Date | Country | |
|---|---|---|---|
| 20130327094 A1 | Dec 2013 | US |
