JP5585034B2 - Optical element manufacturing method and annealing apparatus - Google Patents

Description

  The present invention relates to a method for manufacturing an optical element in which a press-molded optical element is annealed to remove distortion and the refractive index is adjusted, and to an annealing apparatus used at that time. The present invention relates to an optical element manufacturing method and an annealing apparatus that suppress the occurrence of white burn.

  In recent years, high performance and downsizing of optical elements such as glass lenses have been demanded, and various efficient methods for producing aspherical lenses have been studied in particular. Among various manufacturing methods, a direct press molding method that can press-mold an optical element molding material and use it as it is without polishing the molding surface has attracted attention.

  In this method, an optical element molding material having desired characteristics as an optical element is set in a press mold composed of an upper mold, a lower mold, and a body mold, heated to a moldable temperature, and then pressed. Thus, an optical element is manufactured by giving a desired shape and then cooling and taking out from the press mold.

  By the way, this manufacturing method is currently most suitable for products that require small, high-performance, and inexpensive lenses such as digital cameras. However, as the required performance improves, the optical element molding material is cooled and solidified. There is a growing concern about the influence of the refractive index distribution and distortion generated in the lens on the optical performance due to variations in the refractive index of each lens.

  As a method of removing such distortion inside the optical glass element and adjusting the refractive index, it has been found that the introduction of an annealing process that heat-treats the optical element after press molding is most effective. In the production of the optical elements, they have been widely introduced and implemented (see Patent Document 1).

JP 2003-40634 A

  However, this annealing step is performed by heating the optical element, and there is a case where white burn occurs that causes the optical element to become white due to the temperature rise.

  This white discoloration mainly forms hydroxides when alkali metals and alkaline earth metals in glass react with moisture in the processing atmosphere, and then reacts with carbon dioxide in the air to form carbonates, etc. This is considered to be caused by precipitation.

  If the white discoloration is slight, it can be removed by simply wiping off the product on the surface of the optical element, but if it is severe, the reaction proceeds and the surface of the optical element is eroded to increase the roughness. As a result, the reaction product would not be able to fully function as an optical element.

  When the surface of the optical element has been eroded in this way, the white burn was removed by polishing or the like, but in the first place, it is very difficult to polish in the case of an optical glass material that is highly reactive with water. In addition, there is a problem of causing deformation due to polishing. In addition, since the number of manufacturing steps is increased by polishing, the manufacturing cost is also increased.

  In order to prevent the occurrence of this white discoloration, it is conceivable that the annealing process is performed at a lower temperature than before. However, if such a low temperature is used, the annealing process takes time and is efficient. In addition, since there is a case where the annealing process is not sufficiently performed, there is a problem in that a desired refractive index cannot be obtained.

  Therefore, the present invention provides an optical element manufacturing method and an annealing apparatus that can effectively remove distortion and adjust the refractive index by annealing, and can suppress the occurrence of white burn. For the purpose.

  The optical element manufacturing method of the present invention includes a heat softening step for heat-softening an optical element molding material, a molding step for converting the heat-softened optical element molding material into an optical element by press molding, and the molded optical element as a heat treatment furnace. In the method for manufacturing an optical element, the annealing process is performed in a dry gas atmosphere having an atmospheric pressure dew point of −5 ° C. or lower. .

  The optical element annealing apparatus of the present invention includes a heat treatment furnace having a heating means capable of heating the inside of the furnace, and a space capable of holding a dry gas in the heat treatment furnace separately from the atmospheric gas in the furnace. And a dry gas supply means for supplying a dry gas having an atmospheric pressure dew point of −5 ° C. or lower into the space, and an in-furnace container capable of accommodating an optical element obtained by press molding in the space It is characterized by having.

  According to the method for manufacturing an optical element and the annealing apparatus of the present invention, it is possible to suppress the occurrence of white burn in the optical element during the annealing process. In addition, since the occurrence of white burn can be sufficiently suppressed, it is not necessary to lower the heating temperature, so that the annealing treatment of the optical element can be sufficiently performed.

  Furthermore, since the difference in temperature distribution of the optical element to be processed can be reduced by using the furnace container, the optical element obtained by the method for manufacturing an optical element of the present invention has a variation in refractive index. Small and very good.

1 is a schematic cross-sectional view of an optical element annealing apparatus according to an embodiment of the present invention. It is the figure which showed the mounting position of the tray of the optical element made into the sample in an Example and a comparative example.

  The present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of an optical element annealing apparatus according to an embodiment of the present invention.

  Here, the optical element annealing apparatus 1 of FIG. 1 includes a heat treatment furnace 3 having a heating means 2 capable of heating the inside of the furnace in order to heat-treat the optical element, and the heat treatment furnace 3 includes a furnace. A furnace container 4 which is provided with a space capable of holding a dry gas different from the atmosphere gas inside and can store an optical element obtained by press molding in the space. 4 includes a tray 5 for accommodating optical elements therein, and a dry gas supply means 6 capable of supplying a dry gas into the furnace vessel 4.

  In addition, the annealing apparatus 1 forcibly circulates the partition plate 7 forming the circulation path and the furnace atmosphere gas so that the temperature difference can be reduced by circulating the atmosphere gas in the heat treatment furnace 3. And a stirring blade 8 to be moved.

  The heat treatment furnace 3 used in the present invention has a heating means 2 that can heat the inside of the furnace, and can heat the atmosphere gas in the furnace of the heat treatment furnace 3, This may be achieved by using a heat treatment furnace having a configuration similar to that conventionally used for annealing of optical elements.

  In the heat treatment furnace 3 of FIG. 1, a circulation path is formed in the furnace by providing the partition plate 7, and the atmospheric gas heated by the heating means 2 provided in the circulation path rises and is treated by the stirring blade 8. It is sent to the space where things are placed. The sent atmospheric gas is circulated in the heat treatment furnace 3 again through the circulation path (circulates counterclockwise in the cross section of FIG. 1).

  The heat treatment furnace 3 may have a structure other than that shown in FIG. 1, for example, a circulation path is not formed, a heating means is provided on the inner surface of the furnace, and the atmosphere gas in the furnace is stirred. And a heat treatment furnace provided with a stirring blade that can be used. This heat treatment furnace is intended to reduce the temperature difference in the furnace by forcibly stirring the atmospheric gas in the furnace with a stirring blade.

  Next, the in-furnace container 4 is provided with a space capable of holding a dry gas separately from the atmospheric gas in the furnace, and the optical element obtained by press molding is accommodated in the space. Can be done. That is, the optical element to be processed to be annealed is covered with a dry gas held in the container, and can be annealed in a dry gas atmosphere.

  The in-furnace container 4 is preferably structured to be in a semi-sealed state so that the dry gas can be effectively held. Here, the semi-sealed state is intended to prevent the atmosphere gas inside the furnace vessel 4 and the atmosphere gas inside the heating furnace 3 outside from entering and exiting easily. When flowing into the in-furnace container 4, the air that has been filling the in-furnace container 4 can be expelled out of the in-furnace container 4 and replaced with dry gas. By doing in this way, the inside of the in-furnace container 4 is filled with dry gas, and the circumference | surroundings of an optical element can be made into dry gas atmosphere.

  In this way, when the surroundings of the optical element are treated with dry gas, if the inner space of the furnace vessel 4 is semi-sealed, the treatment can be performed with a simple operation with a simple furnace vessel configuration. Further, the effect of substituting with dry gas can be sufficiently obtained, which is preferable because the manufacturing cost can be reduced.

  Even in a furnace vessel that can completely close the internal space, annealing treatment that suppresses white burn is possible, but in order to completely replace with dry gas, the vessel structure should be made leak-proof and the interior The use of vacuum means such as a pump so that the atmosphere can be completely replaced increases the cost of the apparatus itself and takes time and thus increases the manufacturing cost.

  The in-furnace container 4 transmits the heat from the heated atmosphere gas in the heat treatment furnace 3 to the dry gas in the in-furnace container 4 through the in-furnace container 4, so that the optical inside the in-furnace container 4 is accommodated. Since the element can be annealed, it is preferably formed of a material having a thermal conductivity of 10 to 450 W / (m · K), such as stainless steel, copper, or an aluminum alloy. More preferably.

  Next, the tray 5 is placed in the internal space of the in-furnace vessel 4 so that an optical element that is an object to be heat-treated can be placed so that the annealing treatment can be effectively performed. In general, optical elements may be placed side by side vertically and horizontally. A plurality of trays 5 in which such optical elements are arranged are stored in a plurality of shelves of different heights in the inner space of the furnace vessel 4, and the optical elements are stabilized during annealing in the heat treatment furnace. And hold it. The tray 5 may be the same as that conventionally used.

  In the annealing process, the dry gas is supplied to the inside of the in-furnace container 4 by the dry gas supply means 6, whereby the atmosphere around the optical element is replaced with a dry gas with very little moisture, and the inside of the container is dried with the dry gas. Can be filled with. This replacement effect is effective in suppressing the occurrence of burns that are considered to be caused by the influence of moisture on the optical element.

  The dry gas supply means 6 supplies a dry gas having an atmospheric pressure dew point temperature of −5 ° C. or less to the in-furnace container 4, and normally connects dry nitrogen piping and dry compressed air piping used in a factory through various filters. In addition, the drying gas can be supplied to the internal space of the in-furnace vessel 4 at a desired supply amount via a pressure adjustment valve, a flow rate regulator, and the like. Here, the atmospheric pressure dew point means the dew point of the dry gas under the atmospheric pressure (1 atm).

  As described above, in the annealing apparatus of the present invention, the optical element can be accommodated in the space capable of holding the dry gas, and the dry gas supply means capable of supplying the dry gas into the space. The use of the in-furnace container 4 having 6 is a characteristic configuration.

  Next, an optical element manufacturing method using the optical element annealing apparatus 1 will be described.

  First, a heat softening process for heat-softening the optical element molding material and a molding process for forming the heat-softened optical element molding material as an optical element by press molding are performed. This is the same as the operation used in the manufacture of the conventional optical element, and is not based on a special method. The optical element obtained by press molding in this way is generally subjected to heat treatment because distortion occurs in the optical element due to a rapid temperature change during molding or a predetermined refractive index cannot be obtained. It is necessary to remove distortion and adjust the refractive index.

  Therefore, the optical elements obtained by press molding as described above are placed in alignment with the tray 5, and the tray 5 is accommodated in the in-furnace container 4. The in-furnace container 4 has a shelf that can store a plurality of trays 5 in a plurality of stages.

  The molding material of the optical element to be processed at this time can be used without particular limitation as long as it requires an annealing treatment by press molding. For example, phosphoric acid-based, fluorophosphoric acid-based, bismuth-based, A lanthanum-based glass material can be used, and in particular, a lanthanum-based glass material is preferable because it can effectively prevent white burn in the annealing treatment.

  In this way, the optical elements housed in the in-furnace container 4 are housed in the heat treatment furnace 3 at the same time, so that the annealing process can be performed by the heat treatment furnace 3. However, neither the heat treatment furnace 3 nor the in-furnace container 4 has a strictly sealed structure.

  Next, the dry gas is supplied from the dry gas supply means 6 provided in the furnace container 4 into the furnace container 4. The dry gas supplied here has an atmospheric pressure dew point of −5 ° C. or lower, and if the dew point temperature is higher than that, it is not preferable because a dry state cannot be obtained. In addition, it is preferable that this atmospheric pressure dew point temperature is -10 degrees C or less.

  Examples of the dry gas include dry air and dry nitrogen. The dry air can be obtained by a refrigeration air dryer, but further, if the dry air obtained from the refrigeration air dryer is removed by using an oil mist filter or the like to remove fine particles and oil, the contamination of the optical element is prevented. Can be preferable. Moreover, what is necessary is just to use industrial nitrogen gas for dry nitrogen.

  When this dry gas is supplied to the in-furnace container 4, as described above, the in-furnace container 4 is in a semi-sealed state, so that the inner space of the in-furnace container 4 is filled with the dry gas and has existed until then. Air is pushed out and leaks out of the in-furnace container 4 and flows into the heat treatment furnace 3. In this way, the inside of the furnace vessel 4 is filled with the dry gas, and the dry gas is continuously supplied from the dry gas supply means 6 so that the inside of the furnace vessel 4 has a positive pressure. Is prevented from flowing back to the inside of the in-furnace container 4.

  Next, the atmospheric gas in the heat treatment furnace 3 is heated by the heating means 2 of the heat treatment furnace 3 so that the optical element can be annealed. When the heating means 2 is set to a predetermined temperature, first, the atmospheric gas in the heat treatment furnace 3 is heated and circulated in the heat treatment furnace 3. At this time, the atmospheric gas heated by the heating means 2 was drawn into the stirring blade 8 side through the circulation path, and was sent to the space where the furnace vessel 4 was located by the stirring blade 8, and the periphery of the furnace vessel 4 was heated. It becomes an atmosphere.

  The heated atmosphere also passes through the circulation path and circulates in the heat treatment furnace counterclockwise in FIG. At this time, the heat treatment furnace 3 is not completely sealed in the same manner as the in-furnace container 4, so that atmospheric gas flows out from the heat treatment furnace 3 to the outside. Therefore, after the dry gas supplied from the dry gas supply means 6 fills the inside of the in-furnace container 4, this time also fills the inside of the heat treatment furnace 3, and the annealing apparatus 1 of the present invention is in the annealing process. The effect of maintaining a high concentration of dry gas can be expected at the same time.

  Since this atmospheric gas does not flow into the furnace vessel 4, the dry gas in the furnace vessel 4 transfers heat from the atmospheric gas in the heat treatment furnace 3 to the drying gas through the furnace vessel 4. Then, the dry gas in the furnace container 4 is heated to a temperature suitable for the annealing process. At this time, the drying gas in the in-furnace vessel 4 is heated from the glass transition point Tg of the glass material, which is the material of the optical element to be processed, to a temperature range lower by 50 ° C. than the Tg to perform the annealing treatment. Is preferred.

  Conventionally, the annealing process is performed by storing the tray 5 in the heat treatment furnace 3 without using the furnace container 4. However, the optical element may be whited out due to the influence of moisture in the heat treatment furnace 3. There were many. However, when the in-furnace container was used as in the present invention, it was possible to suppress the occurrence of white burns on the surface of the optical element and to perform the annealing treatment sufficiently.

  Conventionally, the atmosphere gas is stirred in the heat treatment furnace 3 by the stirring blade so that the temperature distribution in the furnace does not occur. However, in the portion where the hot air from the stirring blade directly hits and in the other portions Since the processing temperature of the optical element changes considerably, a difference in quality often occurs depending on whether the annealing process is sufficiently performed due to the temperature difference. However, when the furnace vessel was used as in the present invention, the hot air from the stirring blade did not directly hit the optical element, and the difference in the processing temperature of the optical element could be reduced.

  Furthermore, in addition to the white burn, scratches caused by scattered matter in the heat treatment furnace, and adhesion of contaminants that are considered to be caused by mineral oil contained in the atmospheric gas, etc. are provided with an in-furnace container 4 to provide dry gas. It can suppress by making it supply.

  Even if the optical element manufacturing method of the present invention is used, the optical element after annealing may not be able to completely suppress white discoloration, but the degree is slight, such as hand wiping, alkali cleaning, ultrasonic cleaning, etc. Can be removed. Therefore, since it can be made into a product without polishing as in the prior art, the present invention can improve the workability in the production of the optical element and increase the production efficiency.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
An optical element was manufactured using an annealing apparatus having the configuration shown in FIG. The heat treatment furnace used at this time is a heat treatment furnace (internal dimensions: 600 mm × 600 mm × 600 mm, output specification: 200 V 9.5 kVA) using a forced hot air circulation / ventilation system, and is made of stainless steel (SUS304). ) (Inside container dimensions: 404 mm × 285 mm × 95 mm).

  Prepared a 300mm x 200mm tray with 8 x 8 (64) optical elements aligned and placed by heat-softening and press-molding optical element molding material made of barium borate glass. And housed in a furnace container. A ceramic blanket mainly composed of alumina fibers was used as a buffer material.

  The furnace vessel and the heat treatment furnace door are closed, and dry air is supplied to the inside of the furnace vessel using a dry gas supply means at a flow rate of 5 L / min while using a pressure regulating valve and a flow rate regulator. The internal space of was made positive pressure. The dry air supplied at this time is dry air having an atmospheric pressure dew point of about −20 ° C. obtained by removing fine particles and oil from a compressor with a refrigeration air dryer through an oil mist filter and an air filter. In addition, in order to prevent the temperature fall by supply of dry gas, the heat exchanger produced by bending the SUS pipe | tube of (phi) 6mm and length 20m was arrange | positioned in the furnace.

  At the same time as the supply of the dry air was started, the heater of the heat treatment furnace was also operated to heat stepwise so that the temperature of the in-furnace container reached the target temperature for each step as shown in Table 1. An optical element was obtained by annealing for 16.5 hours.

(Example 2)
300 optical element molding materials made of a lanthanum borate glass material were used, and dry nitrogen having an atmospheric pressure dew point of −60 ° C. was used as a dry gas. Moreover, the heating by the heat treatment furnace was performed stepwise as shown in Table 2. Otherwise, an optical element was obtained in the same manner as in Example 1.

(Example 3)
An optical element was manufactured using an annealing apparatus having the configuration shown in FIG. The heat treatment furnace used at this time is a heat treatment furnace (internal dimensions: 600 mm × 600 mm × 600 mm, output specification: 200 V 9.5 kVA) using a forced hot air circulation / ventilation system, and is made of stainless steel (SUS304). ) (Inside container dimensions: 448 mm × 453 mm × 428 mm).

  468 optical elements obtained by heating and softening an optical element molding material made of a lanthanum borate glass material and press molding were prepared. The optical elements were placed evenly on six trays having an outer diameter of 360 mm × 200 mm, divided into three stages, an upper stage, a middle stage, and a lower stage, and each stage had two trays stored in a furnace container. As the dry gas, dry air having an atmospheric dew point of −15 ° C. was used. Further, heating by a heat treatment furnace was performed as shown in Table 3. Otherwise, an optical element was obtained in the same manner as in Example 1.

(Comparative Example 1)
An optical element was obtained by the same operation as in Example 1 except that dry air was not supplied.

(Comparative Example 2)
An optical element was obtained by the same operation as in Example 2 except that dry nitrogen was not supplied.

(Comparative Example 3)
An optical element was obtained by the same operation as in Example 3 except that the furnace container was not provided and dry air was not supplied.

(Test Example 1)
In Example 1 and Comparative Example 1, 30 out of 64 annealed samples were randomly extracted, and the obtained optical elements were examined for the presence of white burns after annealing, and the results are shown in Table 4. Indicated. In addition, about the presence or absence of white discoloration, the presence or absence of white discoloration was determined visually.

(Test Example 2)
In Example 2 and Comparative Example 2, 30 samples were randomly extracted from 300 samples that were annealed, and the obtained optical elements were examined for the presence of white burns after annealing, and the results are shown in Table 5. It was. In addition, about the presence or absence of white discoloration, the presence or absence of white discoloration was determined visually.

  Moreover, even if white discoloration occurred after the annealing treatment, those that could be removed by wiping were counted as having no white discoloration. In Example 2, there were 3/30 optical elements with white burns, but all of them could be removed by hand wiping.

(Test Example 3)
In Example 3 and Comparative Example 3, the optical element at a location indicated by a circle in FIG. 2 from the uppermost stage of the furnace vessel was used as a sample. FIG. 2 is a plan view of the uppermost two trays as viewed from above, and when stored in the furnace vessel, the door side of the furnace vessel is in front (front), and the opposite sides are in the back, The middle (middle) was taken as the interval. Similarly, the left end when viewed from the door side is left, the right end is right, and the middle (middle) is displayed between them. In this way, the position display is divided, the left and right display is first, the depth display is later, and the kanji is combined to indicate the position.

  That is, from the uppermost stage of the reactor vessel, nine optical elements of the left front, left middle, left rear, middle front, middle middle, middle rear, right front, right middle, right rear are extracted, and the middle stage and bottom stage are removed. In the same manner, a total of 27 optical elements of 9 were extracted, and the obtained optical elements were examined for the refractive index variation width of the optical elements and the presence or absence of white burns after annealing. The results are shown in Table 6. . The variation width of the refractive index was calculated from the maximum value and the minimum value of the refractive index of the sample optical element.

  In addition, about the presence or absence of white discoloration, the presence or absence of white discoloration was determined visually. Moreover, even if white discoloration occurred after the annealing treatment, those that could be removed by wiping were counted as having no white discoloration. In Example 3, although about 1/3 of the optical elements had white burns, they could all be removed by wiping.

The refractive index was measured by using an immersion type refractive index measuring machine using a right-angle prism block. Further, the target value of a general refractive index is ± 50 × 10 ⁻⁵ , and it has been found that the annealing treatment can be sufficiently performed according to the present invention, and variation in refractive index can be suppressed.

  As described above, according to the method for manufacturing an optical element of the present invention, it is possible to sufficiently perform an annealing process while suppressing white blurring, and to efficiently remove the distortion of the optical element and adjust the refractive index. be able to. By preventing white burns, it is possible to reduce the manufacturing cost without the need for polishing treatment or the like.

  The optical element manufacturing method and annealing apparatus of the present invention can efficiently perform an annealing process for removing distortion and adjusting a refractive index of an optical element obtained by press molding, and in the field of manufacturing optical elements. Useful.

DESCRIPTION OF SYMBOLS 1 ... Optical element annealing treatment apparatus, 2 ... Heater, 3 ... Heat treatment furnace, 4 ... Furnace container, 5 ... Tray, 6 ... Dry gas supply means, 7 ... Partition plate, 8 ... Stirring blade

Claims (7)

Heat-softening step for heat-softening the optical element molding material, molding step for converting the heat-softened optical element molding material into an optical element by press molding, and annealing for storing the molded optical element in a heat treatment furnace In the method of manufacturing an optical element comprising:
The annealing treatment step is performed in a dry gas atmosphere having an atmospheric pressure dew point of −5 ° C. or less, the dry gas can be held in the heat treatment furnace separately from the atmospheric gas in the furnace, and A method for producing an optical element , comprising: providing an in-furnace container for forming a space capable of accommodating an optical element obtained by press molding, and supplying the dry gas into the space . The optical element manufacturing method according to claim 1 , wherein the annealing treatment step is performed by transferring heat from an atmospheric gas in the furnace to a dry gas inside the furnace container through the furnace container. Method. The method for manufacturing an optical element according to claim 1, wherein the space is in a semi-sealed state, and the space is always kept at a positive pressure by supplying the dry gas. A heat treatment furnace having a heating means capable of heating the inside of the furnace;
In the heat treatment furnace, there is provided a space capable of holding a dry gas separately from the atmospheric gas in the furnace, and a furnace container capable of storing an optical element obtained by press molding in the space;
A dry gas supply means for supplying a dry gas having an atmospheric pressure dew point of −5 ° C. or less into the space;
An optical element annealing treatment apparatus characterized by comprising: 5. The optical element according to claim 4 , wherein the in-furnace container can replace the air filled in the in-furnace container with the dry gas by allowing the dry gas to flow into the in-furnace container by the dry gas supply unit. Annealing equipment. 6. The optical element annealing treatment apparatus according to claim 4 , wherein the furnace container is configured to place the space in a semi-sealed state. The optical element annealing treatment apparatus according to any one of claims 4 to 6 , further comprising a stirring blade for stirring the atmosphere gas in the furnace.

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