JP5442420B2 - Thickness determination method and manufacturing method of glass material for precision press molding, and manufacturing method of glass optical element - Google Patents

Description

  The present invention relates to a method for determining the thickness of a glass material for precision press molding that can be used to obtain a glass optical element by precision press molding, a method for manufacturing a glass material for precision press molding, and a precision press obtained by the above manufacturing method. The present invention relates to a method for producing a glass optical element using a molding glass material.

  As a method of manufacturing an optical element such as a glass lens, a method of press molding a molding material (hereinafter referred to as “glass material for press molding” or “glass preform”) using an upper mold and a lower mold having opposed molding surfaces (Referred to as “precision press molding method”, “precision mold press method”, etc.). This method is a method of obtaining a glass optical element by putting optical glass solidified into a predetermined shape from a molten state or optical glass polished into a predetermined shape into a mold and hot press molding. The precision press molding method does not require post-processing such as polishing after press molding by using a precisely machined mold, so that a high-performance lens can be obtained at low cost.

  When an optical element is molded by the precision press molding method, the amount of deformation is reduced and the press molding can be performed in a short time as the shape and volume of the glass preform are approximated to the shape and volume of the target optical element. Therefore, it is desirable from the viewpoint of improving production efficiency.

  As a method of approximating the shape of an optical element for molding a glass preform, there is known a method of dropping a molten glass and pressing it with a mold to approximate the glass preform (Patent Documents 1 to 3). 3).

  In addition, as a measure of approximate shaping of the glass preform, the curvature is defined (see Patent Document 4), the surface roughness is defined (see Patent Document 5), and the outer diameter is defined (see Patent Document 6). ) Has been proposed.

JP-A-9-52720 JP-A-7-165431 Japanese Patent No. 2790547 Japanese Patent No. 3130619 JP-A-5-286728 Japanese Patent Publication No. 7-055838

As described above, the closer the glass preform is to the approximate shape, the more it contributes to the improvement of production efficiency.However, if the thickness of the glass preform is too close to the thickness of the optical element to be molded, transfer defects occur due to insufficient deformation. As a result, poor performance of the optical function surface occurs.
However, conventionally, regarding the approximate shape standard, it has not been specified to define the thickness of the approximated glass preform. Even if there is a description relating to the thickness of an approximately shaped glass preform (Patent Document 6), it is only described that the thickness of the glass preform is a little thicker than the lens. Therefore, conventionally, the thickness in the approximate shaping of the glass preform has only been determined as a rough guide by trial and error.

  SUMMARY OF THE INVENTION An object of the present invention is to provide means for determining the thickness of a precision press-molded glass preform having an approximate shape without trial and error.

As a result of intensive studies to achieve the above object, the present inventors have established a correlation between the deformation amount and the deformation speed of the glass during press molding, and by utilizing this correlation, It has been newly found that the thickness of the glass material for precision press molding that has been approximated can be set within a range that does not cause transfer failure due to insufficient deformation.
The present invention has been completed based on the above findings.

That is, the above object was achieved by the following means.
[1] A method for determining the thickness of a glass material for precision press molding,
The thickness of the glass molding to be obtained is the same glass material as the glass molding to be obtained by precision press molding, has the same volume, and is thicker than the glass molding. Performing test press molding to press-mold,
Creating an approximate line indicating the correlation between the thickness deformation amount and the deformation speed in the test press molding,
Is performed with at least two different press loads of 300 kg or less, thereby creating at least two types of the approximate lines and obtaining the value of the thickness deformation at the intersection of the created approximate lines. The said thickness determining method characterized by determining the thickness of the said glass material for precision press molding more than the value added to the thickness of the molded object.
[2] In a method for producing a glass material for precision press molding by molding raw glass,
The thickness of the glass material for precision press molding is determined by the method described in [1],
A method for producing a precision press-molding glass material, which comprises producing a precision press-molding glass material having a determined thickness in the molding.
[3] producing a glass material for precision press molding by the production method according to [2],
A method for producing a glass optical element, comprising: heating a produced glass material for precision press molding and obtaining a glass molded body by precision press molding the softened glass material.
[4] The method for producing a glass optical element according to [3], comprising removing an outer peripheral portion of the obtained glass molded body by grinding.

  According to the present invention, it is possible to approximate the glass preform in a range that does not cause transfer failure without trial and error. Thereby, the improvement of the production efficiency in precision press molding can be achieved.

It is sectional drawing which shows one form of the glass material for precision press molding. It is sectional drawing of the glass molded object obtained by carrying out precision press molding of the glass raw material shown in FIG. It is sectional drawing of the glass optical element obtained from the glass molded object shown in FIG. It is explanatory drawing showing one form of the precision press molding method. It is a graph which shows the correlation with the thickness deformation amount at the time of press molding (press load: 240 kg, 180 kg) and the average deformation speed of center thickness. It is a graph which shows the correlation with the thickness deformation amount at the time of press molding (press load: 240 kg, 210 kg) and the average deformation speed of center thickness. It is a graph which shows the correlation with the thickness deformation amount at the time of press molding (press load: 210 kg, 180 kg) and the average deformation speed of center thickness.

[Thickness determination method of glass material for precision press molding]
The thickness determination method of the precision press-molding glass material of the present invention (hereinafter also simply referred to as “thickness determination method”)
The thickness of the glass molding to be obtained is the same glass material as the glass molding to be obtained by precision press molding, has the same volume, and is thicker than the glass molding. Performing test press molding to press-mold,
Creating an approximate line indicating the correlation between the thickness deformation amount and the deformation speed in the test press molding,
Is performed with at least two different press loads of 300 kg or less, thereby creating at least two types of the approximate lines and obtaining the value of the thickness deformation at the intersection of the created approximate lines. The thickness of the glass material for precision press molding is determined to be equal to or greater than the value added to the thickness of the molded body. In the thickness determination method of the present invention, the value obtained by adding the above is the lower limit value of the approximate press-molded glass material for precision press molding, and is deformed by setting the thickness to be equal to or greater than the lower limit value. As a result of the present inventors' finding that good precision press molding is possible without causing transfer failure due to insufficient amount, the present inventors have completed.
Hereinafter, the validity of adopting the above value as the wall thickness lower limit will be described.

FIG. 1 is a sectional view showing an embodiment of a precision press-molding glass material, and FIG. 2 is a sectional view of a glass molded body obtained by precision press-molding the glass material shown in FIG. The glass molded body shown in FIG. 2 can be used as a glass optical element as it is, but the outer peripheral portion can be removed by grinding (centering) to obtain a glass optical element. A cross-sectional view of such a glass optical element is shown in FIG.
The outer diameter d1 and the center thickness t1 of the glass material 1 for press molding for obtaining the glass molded body 2 (outer diameter d2, center thickness t2) shown in FIG. 2 are in a relationship of t2 <t1 and d1 <d2. . The center thickness of the glass optical element 3 after the centering process is the same as the center thickness t2 of the glass molded body 2, and the outer diameter is d3 <d2.
Here, the central thickness of the glass material 1 for press molding for obtaining a glass lens having a lens diameter d2 = 12 mm and a center thickness t2 = 1.7 mm as a convex meniscus glass lens (glass molding) shown in FIG. In order to determine t1, as a convex meniscus-shaped glass material (test glass material) made of the same glass material as the glass lens and having the same volume, a plurality of different center wall thickness t0 (1.7 mm <center wall thickness t0) A glass material for test was prepared. These glass materials for test consist of glass materials (phosphate glass) shown in the examples described later, and were produced by the method shown in the examples.
As shown in FIG. 4, the plurality of test glass materials are supplied into a molding die 7 including an upper die 4, a lower die 5 and a barrel die 6, and 10 phosphoric acid glasses constituting the test glass material are provided. After raising the temperature to a temperature equivalent to ^7.2 dPa · s, a predetermined press load was applied by lowering the press head 8, and press molding was performed until the center thickness of the glass molded body 2 became 1.7 mm. The specific process of press molding was as described in Examples described later.
Table 1 below shows the thickness deformation amount (t0-t2) and the average deformation speed of the center thickness when press-molding is performed at a press load of 240 kg and 180 kg. A graph plotting the data shown in Table 1 is shown in FIG. The average deformation speed is a value obtained by dividing the thickness deformation amount by the time required for the glass material to reach the lens thickness. FIG. 5 shows an approximate expression and a correlation coefficient when each plot is approximated to a straight line. The approximate straight line and the approximate expression were obtained by fitting by the least square method.

Statistically, a correlation coefficient is generally used as an index indicating the strength of relevance between two variables, and the strength of correlation with respect to the range of the correlation coefficient is shown as follows.
0 to 0.2 Almost no correlation 0.2 to 0.4 Somewhat correlated 0.4 to 0.7 Significantly correlated 0.7 to 1 Strongly correlated It can be said that they are related. As shown in FIG. 5, the correlation coefficients of the approximate expressions of the thickness deformation amount and the deformation speed are both 0.4 or more, and it can be seen that there is a correlation between the wall thickness deformation amount and the deformation speed. Further, it can be seen from FIG. 5 that the deformation speed varies depending on the deformation amount. This is because the glass material having the same volume is used, so that the glass material having a larger deformation amount has a smaller contact area at the initial stage of deformation, and as a result, a higher surface pressure is applied even at the same press load. On the other hand, it can be seen that the deformation speed increases as the press load increases. This indicates that if the press is performed with a high load, it can be deformed quickly.

Furthermore, it can be seen from FIG. 5 that the approximate expression of the thickness deformation amount and the deformation speed differs depending on the press load. Here, the intersection of the two approximate straight lines is where the difference in the deformation speed due to the load is reversed. That is, the intersection of the approximate straight lines indicates a boundary where the deformation speed decreases as the press load increases. This can be said to be a boundary where the deformation by the press is insufficient and the glass material does not have sufficient transferability with respect to the mold. Accordingly, the value of x at the intersection of the two approximate straight lines is the lower limit value of the thickness deformation amount at which sufficient transferability can be obtained. In the embodiment shown in FIG. 5, the two approximate expressions are as follows, as described in FIG.
y ₁ = 16.46x-2.7
y ₂ = 12.5x-0.8
Here, the value of x at the intersection of the two approximate lines can be obtained as x = about 0.5 mm by setting y ₁ = y ₂ . A value obtained by adding the lens thickness to the lower limit value of the thickness deformation amount is the lower limit of the thickness when the glass material for press molding is approximated in the precision press molding of the glass molded body. Therefore, in the above aspect, since the lens thickness is 1.7 mm, the lower limit of the thickness of the glass material for press molding that provides sufficient transferability to the mold is lower than the lower limit of deformation amount 0 above the lens thickness of 1.7 mm. It becomes 2.2mm which added .5mm.
FIG. 5 shows a graph plotting data of the thickness deformation amount and the average deformation speed of the center wall thickness when press-molding with a press load of 240 kg and 180 kg. A graph is prepared in the same manner as described above by setting the press load to 210 kg, and an approximate curve is obtained. The graph shown together with the approximate curve in the case of the press load of 240 kg is FIG. 6A, and the approximate curve in the case of the press load of 180 kg The combined graph is shown in FIG. In the graphs shown in FIGS. 6A and 6B, x = about 0.5 mm at the intersection of the approximate curves. Therefore, it can be seen that a constant value can be obtained regardless of the press load.

Then, next, the validity of the calculation method in the present invention was confirmed by press-molding a plurality of press-molding glass materials made of the same glass material as described above, having the same volume as the lens, and having different center thicknesses. The press load was 210 kg. The obtained glass molded body (glass lens) was evaluated using a spherical interferometer according to the following criteria. The results are shown in Table 2 below.
○: Both curvature and surface shape are good △: Spherical curvature is non-uniform ×: Spherical curvature step due to insufficient transfer

From the results shown in Table 2, when the center thickness of the glass material for press molding is 2.1 mm, that is, when the thickness deformation amount is 0.4 mm or less, sufficient transferability cannot be obtained with respect to the mold, so the shape of the molding surface It turns out that has become defective. On the other hand, if the thickness of the glass material for press molding was 2.2 mm or more, a good shape of the molding surface was obtained.
From the above results, in precision press molding of glass lenses, it is proved that it is appropriate to calculate the lower limit of wall thickness when approximating the glass material for press molding from the deformation amount and deformation speed of the glass material during press molding. It was done.

In general, the inventors of the present application have found a phenomenon in which the deformation speed is higher when the press load is higher in general, and the press speed is lower when the press load is higher than a certain deformation region. It was derived for the first time.
Hereinafter, the thickness determination method of the present invention will be described in more detail. The wall thickness determined by the wall thickness determining method of the present invention is preferably the center wall thickness.

  The glass material whose thickness is determined by the thickness determining method of the present invention is subjected to precision press molding. The precision press molding method is also called a mold optics molding method, and is already well known in the technical field to which the present invention belongs. A surface that transmits, refracts, diffracts, or reflects light rays of the optical element is called an optical functional surface. For example, taking a lens as an example, a lens surface such as an aspherical surface of an aspherical lens or a spherical surface of a spherical lens corresponds to an optical function surface. The precision press molding method is a method of forming an optical functional surface by press molding by precisely transferring a molding surface of a press mold to glass. That is, it is not necessary to add machining such as grinding or polishing to finish the optical functional surface. Therefore, the transfer failure at the time of press molding causes a performance failure in the optical element as the final product. According to the glass material for press molding whose thickness is determined by the thickness determining method of the present invention, it is possible to avoid a transfer failure due to insufficient deformation during press molding, so high-performance optical elements can be obtained by precision press molding. Can be produced.

  The glass material for test used in the thickness determination method of the present invention is the same glass material as the glass molded body to be obtained by precision press molding, has the same volume, and is thicker than the glass molded body. It is. Applicable glass types are not particularly limited, and the present invention can be applied to various glasses such as phosphate glass and borate glass, but the present invention can be applied to phosphate glass. preferable.

  The glass material for press molding that determines the wall thickness has the same volume as the glass molded body obtained by precision press molding and has a shape approximate to the glass molded body. 1 and 2, it is preferable that d2 / d1 ≦ 1.5 and 1.2 ≦ t1 / t2 ≦ 3.0 from the viewpoint of improving production efficiency and reducing waste, Is more preferably 1.25 ≦ t1 / t2 ≦ 2.0. From the viewpoint of calculating the wall thickness lower limit value with higher reliability, the specific value range of d2 is preferably about 3 mm to 19 mm, and the specific value of t2 is about 0.6 mm to 2.7 mm. Is preferred. As for the curvature ratio, 0.6 ≦ each surface curvature of the glass material for press molding / each surface curvature of the glass molded body ≦ 1.0 is preferable. Therefore, it is preferable to prepare a test glass material having a shape within the above range. The glass material for test can be produced by the same method as the glass material for press molding described later.

  The test press molding for press-molding the test glass material is not necessarily performed by a press molding machine used for actual molding, but is preferably performed by the same press molding machine in consideration of errors between devices. Test press molding is performed with two or more different press loads in order to obtain at least two types of approximate straight lines. It is also possible to perform test press molding with three or more different loads, and in this case, three or more types of approximate straight lines can be obtained. It is of course possible to obtain the wall thickness lower limit value from the intersection of three or more types of approximate lines, but the number of steps for obtaining the wall thickness lower limit value will be increased. Therefore, in the present invention, it is preferable to perform test press molding with two different press loads.

  The press load applied in the test press molding is not particularly limited, and can be set, for example, in the range of about 100 to 300 kg. In order to obtain an approximate straight line, at least two test glass materials having different thicknesses with the same press load are press-molded. From the viewpoint of fitting accuracy, three or more are preferably press-molded, and five or more are press-molded. More preferably. As the number of test glass materials to be press-molded for the same press load increases, the fitting accuracy increases and is preferable. However, the number of test press moldings increases accordingly. From the viewpoint of achieving both fitting accuracy and workability, the number is preferably 10 or less.

  Next, an approximate straight line showing the correlation between the thickness deformation amount and the deformation speed in the test press molding is created. Details of this step are as specifically described above.

  By performing the above steps with at least two different press loads, at least two types of approximate straight lines can be created. The thickness that can be press-molded without causing improper transfer, as described above, is the value obtained by adding the thickness of the glass molding to be molded to the value of the thickness deformation at the intersection of the created approximate lines. Lower limit value. Therefore, by determining the thickness of the precision press-molding glass material beyond the required thickness lower limit value, it is possible to produce a high-quality optical element without causing transfer defects in precision press molding. Can be obtained. The upper limit value of the thickness of the glass material for press molding is a value equal to or higher than the lower limit value, and is within 3 times, preferably within 2 times the center thickness of the glass molded body to be obtained. Desirable in terms of production efficiency.

[Manufacturing method of glass material for precision press molding]
The method for producing a glass material for precision press molding according to the present invention is a method for producing a glass material for precision press molding by molding a raw glass, and the glass for precision press molding to be produced by the method for determining a wall thickness of the present invention. The thickness of the material is determined, and a precision press-molding glass material having the determined thickness is produced. According to the glass material for press molding produced in this way, a high-performance optical element can be obtained without causing a transfer failure due to insufficient deformation.
The determination of the thickness is as described above. Hereinafter, other steps will be described.

  As the raw glass, a glass made of the same glass material as the glass molded body to be obtained by precision press molding is used. For example, a glass material for precision press-molding can be obtained by molding a material glass cut out from a block-shaped optical glass into a predetermined volume and a predetermined shape by grinding or polishing. Alternatively, the molten optical glass can be dropped or dropped from the pipe and separated into a predetermined amount of glass lump, and the glass lump can be molded during cooling. Here, it is also possible to adopt a method in which the molten glass is received by a receiving mold that ejects gas from the bottom, and is preformed while being cooled in a substantially floated state. This method is preferable because the production efficiency is high and a glass material having a smooth surface can be obtained.

[Glass optical element manufacturing method]
The method for producing a glass optical element of the present invention is to produce a glass material for precision press molding by the method for producing a glass material for precision press molding of the present invention, and heat and soften the produced glass material for precision press molding. This includes obtaining a glass molded body by precision press-molding the glass material.
The production of the glass material for precision press molding is as described above. Hereinafter, other steps will be described.

  As a mold used for precision press molding, a precision material made of a dense material having sufficient heat resistance and rigidity can be used. Examples include metals such as silicon carbide, silicon nitride, tungsten carbide, aluminum oxide, titanium carbide, and stainless steel, or those whose surfaces are coated with a film of carbon, refractory metal, noble metal alloy, carbide, nitride, boride, etc. be able to.

  As a shaping | molding die, what has coating films, such as a carbon containing film | membrane, can also be used for the shaping | molding surface used as a contact surface with the glass material for press molding. As the carbon-containing film, it is preferable to use an amorphous and / or crystalline film composed of a single component layer or a composite layer of graphite and / or diamond. This carbon film can be formed by means such as sputtering, plasma CVD, CVD, or ion plating. For example, a film can be formed by sputtering using an inert gas such as Ar as a sputtering gas and graphite as a sputtering target. Or you may form into a film using methane gas and hydrogen gas as source gas by a microwave plasma CVD method. When forming by an ion plating method, it can be ionized using benzene gas. These carbon films include those having C—H bonds. By providing a carbon-containing film on the molding surface of the molding die, it becomes possible to prevent the press-molding glass material and the molding die from being fused at the time of press molding. In order to prevent carbon oxidation during molding, it is preferable to perform pressing in a non-oxidizing atmosphere.

  On the surface of the precision press-molding glass material, a coating for preventing fusion between the glass material and the mold and for improving the mold release property can be formed. Such a film is not particularly limited as long as it has a desired effect, and examples thereof include a film containing carbon. When the glass material is supplied to the mold prior to pressing, the carbon-containing film provides sufficient slipperiness with the mold and allows the glass material to move smoothly to a predetermined position (center position) of the mold. In addition, when the glass material is softened and deformed by the press, the glass material can be stretched according to the glass deformation on the surface of the glass material to help spread the glass material on the mold surface. Furthermore, it is useful in that the glass is easily separated from the surface of the mold when the molded body is cooled to a predetermined temperature after pressing, thereby assisting the mold release.

  The carbon-containing film is preferably one containing carbon as a main component, and may contain a component other than carbon, such as a hydrocarbon film. As a film forming method, a known film forming method such as vacuum vapor deposition using a carbon raw material, sputtering, ion plating method, plasma treatment, ion gun treatment or the like can be used. Alternatively, the film may be formed by thermal decomposition of a carbon-containing material such as hydrocarbon.

Specifically, the precision press molding can be performed by the following method, for example.
In press molding, as shown in FIG. 4, the glass material 1 for press molding is supplied into a molding die 7 including an upper die 4, a lower die 5 and a body die 6, and the temperature is raised to a temperature range suitable for pressing. . For example, the heating temperature is appropriately set depending on the optical glass constituting the press-molding glass material 1, but the press-molding glass material 1 and the mold 7 have a viscosity of 10 ⁵ to 10 ¹⁰ dPa. -It is preferable to perform press molding when the temperature is in the temperature range. The pressing temperature is preferably, for example, a temperature at which the optical glass constituting the glass material 1 for press molding is approximately equivalent to 10 ^7.2 dPa · s. The higher the temperature at the time of press molding, the lower the mold life. Therefore, considering the mold life, the temperature at which the viscosity is around 10 ^7.2 dPa · s is 800 ° C. or lower, preferably 750 ° C. or lower, more preferably 650 It is desirable to select a glass that will be at or below ° C. Press molding can be performed by lowering the press head 8 and applying a predetermined load.

The press-molding glass material 1 may be introduced into the mold 7 and the press-molding glass material 1 and the mold 7 may be heated together to the press molding temperature for press molding, or the preheated mold 7 is heated. Press molding may be performed by introducing the glass material 1 for press molding. When the latter method is employed, the glass material 1 for press molding is heated to a temperature corresponding to 10 ⁵ to 10 ⁹ dPa · s viscosity, and the mold 7 is heated to a temperature corresponding to a glass viscosity of 10 ⁹ to 10 ¹² dPa · s. Alternatively, a method may be adopted in which the press-molding glass material 1 is placed in the mold 7 and immediately press-molded. This method is preferable in that the temperature of the molding die can be relatively lowered, so that the temperature rise / cooling cycle time of the molding apparatus can be shortened and the deterioration of the molding die 7 due to heat can be suppressed. In either case, cooling is started at or after the start of press molding, and the temperature is lowered while applying an appropriate load application schedule and maintaining close contact between the molding surface and the glass element. Then, it molds and takes out a molded object. The mold release temperature is preferably a temperature corresponding to a glass viscosity of 10 ^12.5 to 10 ^13.5 dPa · s.

The obtained glass molded body can be shipped as an optical element as a final product as it is, or a centering process for removing the outer peripheral portion by grinding is performed to obtain an optical element as a final product. Furthermore, the final product may be formed after an optical functional film such as an antireflection film is formed on the surface. In this case, a desired antireflection film is formed on the glass molded body by appropriately forming a film such as Al ₂ O ₃ , ZrO ₂ —TiO ₂ , MgF _2, etc. in a single layer or in a laminated manner. Can do. The antireflection film can be formed by a known method such as vapor deposition, ion-assisted vapor deposition, ion plating, or sputtering. For example, in the case of the vapor deposition method, the vapor deposition material is heated by an electron beam, direct energization or arc in a vacuum atmosphere of about 10 ⁻⁴ Torr using a vapor deposition apparatus, and the material generated by evaporation and sublimation from the material is used. The antireflection film can be formed by transporting the vapor onto the substrate and condensing / depositing it. The substrate heating temperature can be about room temperature to about 400 ° C. However, when the glass transition temperature (Tg) of a base material is 450 degrees C or less, it is preferable that the upper limit temperature of base-material heating shall be Tg-50 degreeC.

  The glass optical element obtained by the present invention is a small-diameter, thin-weight lens, for example, a small imaging lens, a communication lens, an optical pickup objective lens, a collimator lens, etc. mounted on a portable imaging device. Can do. The lens shape is not particularly limited, and various shapes such as a convex meniscus lens, a concave meniscus lens, a biconvex lens, and a biconcave lens can be taken.

  The present invention will be further described below with reference to examples. However, this invention is not limited to the aspect shown in the Example.

A. 1. Production of 1.45 mm thick glass lens by precision press molding Production of glass material for test To obtain a convex meniscus glass lens (glass molded body; lens diameter d2 = 11 mm, center thickness t2 = 1.45 mm) made of optical glass shown in Table 3 below. In order to determine the lower limit value of the center wall thickness t1 of the glass material 1 for press molding, a glass material for test was prepared by the following method.
The optical glass shown in Table 3 below was dropped from a molten state onto a receiving mold and cooled to preliminarily mold a glass lump having a convex surface on one side and a concave surface on the other side as shown in FIG. This preforming was repeated to produce a plurality of test glass materials made of the same glass material, having the same volume but different center thickness.

2. Test press molding and calculation of wall thickness lower limit value 1. Test press molding of the test glass material produced in the above was performed with a press load of 240 kg and 180 kg. Specific steps are shown below.
A glass material for test was press-molded in a nitrogen gas atmosphere by a mold press molding apparatus. In other words, a SiC upper and lower mold in which a carbon-containing release film is formed on the molding surface by a sputtering method, and a molding mold comprising a barrel mold, and the atmosphere in the chamber of the molding apparatus is filled with non-oxidizing N ₂ gas. Then, the glass material for test was heated to a temperature at which the viscosity became 10 ^7.2 dPa · s, and supplied to a mold heated to a temperature equivalent to 10 ^8.5 dPa · s as the viscosity of the glass material for test. Immediately after the supply, the glass material is pressed between the upper and lower molds until the center thickness becomes 1.45 mm, and the glass material is cooled to a temperature lower than the annealing temperature of the glass material for pressing while maintaining the adhesion between the glass and the upper and lower molds. The molded body (glass lens) was taken out from the mold.
For the press loads of 240 kg and 180 kg, an approximate straight line showing a correlation was obtained from the wall thickness deformation amount and the average deformation speed of the center wall thickness as in FIG. 5, and the value of the wall thickness deformation amount at the intersection was found to be 0.48 mm. Met. Therefore, the wall thickness lower limit value was calculated as 0.48 mm + 1.45 mm = 1.93 mm.

3. Production of glass lens by precision press molding A plurality of press-molding glass materials made of the same glass material as the glass lens to be obtained and having the same volume and different center wall thickness were produced by the same method. Except for the point that the press load was 210 kg using the produced glass material, the above 2. The same process was performed to obtain a molded body (glass lens). The shape of the obtained molded body was evaluated by the method described above. The results are shown in Table 4 below.

  From the results shown in Table 4, if the center thickness of the glass material for press molding is 1.93 mm, that is, if the amount of deformation of the wall thickness is 0.48 mm or more, the surface shape is good because sufficient transferability is obtained during press molding. It can be seen that a simple molded body can be obtained.

B. Production of glass lens having a thickness of 1.64 mm by precision press molding The glass material 1 for press molding for obtaining a glass lens having a lens diameter d2 = 9 mm and a center thickness t2 = 1.64 mm as a convex meniscus glass lens (glass molded body) shown in FIG. When the lower limit of the center wall thickness t1 was determined, it was calculated to be about 2.20 mm. A. above. In the same manner as above, precision press molding of glass materials for press molding having different center thicknesses was performed, and the shape of the obtained molded body was evaluated by the method described above. The results are shown in Table 5 below.

  From the results shown in Table 5, it can be seen that if the center thickness of the glass material for press molding is about 2.20 mm or more, a molded body having a good surface shape can be obtained because sufficient transferability can be obtained during press molding. .

  From the above results, it was shown that a high-quality glass optical element can be obtained by precision press molding according to the glass material for press molding having a thickness determined by the thickness determining method of the present invention. . As the wall thickness is set to a value closer to the determined lower wall thickness limit, the wall thickness can be reduced within a range that does not cause transfer defects, so the amount of deformation during pressing decreases, and as a result, the pressing time is reduced. It can be shortened. The above A. , B. The glass molded body obtained in (1) can be made into a convex meniscus aspherical glass lens by removing the outer periphery by grinding.

  The present invention is useful in the field of manufacturing glass optical elements.

Claims (4)

A method for determining the thickness of a glass material for precision press molding,
The thickness of the glass molding to be obtained is the same glass material as the glass molding to be obtained by precision press molding, has the same volume, and is thicker than the glass molding. Performing test press molding to press-mold,
Creating an approximate line indicating the correlation between the thickness deformation amount and the deformation speed in the test press molding,
Is performed with at least two different press loads of 300 kg or less, thereby creating at least two types of the approximate lines and obtaining the value of the thickness deformation at the intersection of the created approximate lines. The said thickness determining method characterized by determining the thickness of the said glass material for precision press molding more than the value added to the thickness of the molded object. In the method of manufacturing a glass material for precision press molding by molding raw glass,
The thickness of the precision press-molding glass material is determined by the method according to claim 1,
A method for producing a precision press-molding glass material, which comprises producing a precision press-molding glass material having a determined thickness in the molding. Producing a glass material for precision press molding by the manufacturing method according to claim 2;
A method for producing a glass optical element, comprising: heating a produced glass material for precision press molding and obtaining a glass molded body by precision press molding the softened glass material. The manufacturing method of the glass optical element of Claim 3 including removing the outer peripheral part of the obtained glass molded object by grinding process.

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