JP2965112B2 - Optical element molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding an optical element used for forming a high-precision optical element such as an aspherical lens by press molding.

[0002]

2. Description of the Related Art In recent years, attention has been paid to a method of directly press-forming a heat-softened glass material in a molding die instead of a method of processing an optical element by grinding and polishing.

[0003] Usually, in this type of molding, a molding die member composed of an upper and lower die that slides on the trunk die is used in the trunk die.
Pressing a glass material in a softened state, forming an optical function surface corresponding to the molding surface of the mold member on the glass material,
Thereafter, cooling is performed, a molded product is taken out from the mold member, and an optical element is obtained.

Japanese Unexamined Patent Publication (Kokai) No. 62-21720 discloses that a glass material is heated to a temperature corresponding to a glass viscosity of 10 ⁸ to 10 ⁶ poise, and a glass mold having a temperature corresponding to 10 ^14.5 to 10 ^13.5 poise. A method of forming an optical element by a reheat multi-stage press in which the pre-forming is performed and the main press-forming is performed again has been proposed.

Japanese Patent Publication No. 36-18982 discloses a method of molding an optical element by a multi-stage press. The inner dimensions of an outer cylinder whose peripheral dimensions are to be determined in molding are increased in the order of a first press and a second press. A method of setting and molding has been proposed.

[0006]

However, in the conventional example of the reheating described above, a method of multistage pressing from a crow having a very low viscosity, such as molten glass, which is easily deformed by its own weight has been proposed. Thus, the problem of molding from low-viscosity glass described below has not been solved.

That is, since the glass has a low viscosity, the glass easily penetrates into the gap between the body mold and the upper and lower molds, and burrs are likely to be generated. When it comes around, it becomes a serious flaw. Optical elements cannot be used with defects caused by only a few burrs. Therefore, when burrs occur, continuous production becomes impossible.

However, when glass having low viscosity is molded under conditions where there is no restriction on the outer periphery such as a barrel mold, not only is the outer diameter of the glass molded product distorted, but the outer diameter and the optical center are displaced. In press molding, it becomes difficult to align the intermediate molded product with the mold, which causes a transfer failure and a shape failure of the optical function surface. In addition, in this press molding, which is the final step of the multi-stage press, in order to transfer the optical functional surface reliably, it is necessary to secure a slight press allowance in the deformation for imitating the glass to the mold. It is necessary to secure an appropriate shape of the mold in the preforming to prevent the remainder.

[0009]

SUMMARY OF THE INVENTION Accordingly, the present invention is intended to prevent the occurrence of burrs even from low-viscosity glass such as molten glass, thereby not causing surface defects of the glass optical element, and ultimately, the present invention. Another object of the present invention is to provide a method for molding an optical element, which can provide an optical element with good transfer of an optical functional surface and good accuracy in outer diameter.

[0010]

For this reason, the inventors of the present invention have developed a method for producing a glass block having a certain capacity obtained from a melting furnace or the like.
It was preliminarily press-molded into a soft shape that caused deformation by its own weight, with a weak pressure such that glass did not enter the gap between the barrel mold and the upper and lower molds, and into a shape that was easy to obtain the desired product shape. Later, it was found that the above-mentioned problems could be avoided by the molding method of the present press molding.

[0011] As one of the methods, an upper and lower mold having a desired product shape from the beginning and a body mold for forming a wall thickness of 0.1 mm or more larger than the desired product thickness are used. When the viscosity is between 10 ^{2 and} 10 ⁸ Pa · s, at a pressure of, for example, 20 MPa or less such that glass is not filled in the connection between the body mold and the upper mold, and the body mold and the lower mold. The first press molding is performed, and then the second press molding is performed in a state where the body die is removed, to thereby obtain a molded product having a desired thickness. Here, good quality optical elements can be molded directly from molten glass.

Further, as another method, a glass block having a predetermined capacity is once pre-pressed by a pre-forming mold having a capacity larger than the capacity, for example, larger by 1 to 20%. Combination of the upper mold, lower mold, and body mold that constitutes a middle hit shape that is thicker than the final product and that the glass is deformed from the center of the upper and lower molds during this press molding. After the pre-press, there is a method for forming an optical element, wherein the main press-forming is performed so that the outer periphery of the glass molded product is not restricted so as to have a predetermined thickness. Here, similarly to the above, a good quality optical element can be directly formed from molten glass.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. Here, FIG. 1 to FIG. 4 are diagrams showing devices used in one embodiment of the present invention and their operation procedures, and FIGS. 5 to 9 are similarly used in other embodiments of the present invention. FIG. 1 is a diagram showing devices to be operated and their operation procedures.

1 to 4, reference numeral 1 denotes a lower mold, and an upper surface 1a of the lower mold 1 is finished to a precision molding surface corresponding to an optical function surface of a molded product. Reference numeral 2 denotes an upper die, which has a precise molding surface 2a, like the lower die 1. Reference numeral 3 denotes a body mold divided into two, a forming surface 3a forming a side surface of the preformed product 10b, and a forming surface 2
a, 1a, contact surfaces 3b, 3c for determining the thickness of the preform 10b, and abut against the outer peripheral portion 2b of the upper die 2 and the outer peripheral portion 1b of the lower die 1. The contact surfaces 3e, 3f for regulating the positions of the dies 1, 2, 3 and the contact surface 3d for determining the thickness of the molded article 10c by abutting against the lower surface 2c of the flange portion of the upper mold 2. It has.

A cylinder 6 for opening and closing the body mold 3 is attached to the body mold 3. Reference numeral 4 denotes a guide member attached to the bottom plate 5, which has a cavity 4a for accommodating the flange portion 1c of the lower die 1, performs positioning of the lower die 1 and guides the upper die in a vertical direction. The mold 3 is supported in the vertical direction. Reference numeral 7 denotes an upper press shaft, and a hook 8 for hooking a flange portion 2d of the upper die 2 and lifting the flange portion 2d is attached to a lower end thereof. Reference numeral 9 denotes a lower press shaft, and a lower die 1
Can be pressed upward from below to perform press molding.

[0016] In the embodiment of FIGS. 5 through 9, reference numeral 2
Reference numeral 1 denotes a lower mold for preforming, which is fixed to a bottom plate 24. Reference numeral 22 denotes an upper mold for preforming, which is abutted against an upper edge portion of a barrel mold 23 by a press device (not shown) to perform preforming. Body type 2
Numeral 3 is a structure that can be divided into two, and has a molding surface 23a that forms the side surface of the preform 40b, and a portion below the molding surface 23a is abutted against the side surface 21b of the lower mold 21. Thereby, the positioning at the time of closing can be performed. The bottom plate 24
A cylinder 25 for opening and closing above is attached.

Reference numerals 26 and 27 denote a lower mold and an upper mold, respectively, for main molding, each of which is a molded product (optical element).
Molding surfaces 26a and 27a corresponding to the optical function surfaces of the above. Reference numeral 28 denotes a lower mold 2 fixed to a bottom plate 29.
A guide member for aligning the axis of the upper die 6 with the upper die 27, and has a through hole for guiding the lower die 26 and the upper die 27 in the vertical direction. In the lower part of the through hole, a gap 28a is provided for accommodating the flange portion 26b of the lower die 26 and allowing the lower die 26 to slide up and down. A window 28b for insertion and removal is provided. The window 28b has a sufficient size so that the side surface of the molded product 40c does not touch the guide member 28 before and after molding.
The upper die 27 has a mold opening flange portion 27 b, and the hook 3 attached to the upper press shaft 30.
1 allows it to be suspended. In this embodiment, reference numeral 32 denotes a lower press shaft for pushing up the lower die 26 from below. Although the body dies 3 and 23 are divided into two parts here, the body dies may be divided into smaller parts and the body dies may be opened and closed by using a corresponding number of drive mechanisms.

Next, the steps of the molding method of the present invention for molding an optical element molded product using the above-described apparatus will be specifically described with reference to the drawings. Example 1 Using the apparatus shown in FIGS. 1 to 4, the curvature of both surfaces of the lens was R 40 mm and R 60 mm, the outer diameter was about 20 mm, and the center thickness was 5.6 mm. A step of forming a biconcave lens used in a camera or a video camera will be specifically described. At the time of this molding, the glass viscosity was 10 ¹ Pa ·
to s, the 10 ^8.2 Pa · s when the 580 ° C., in 10 ^{1 1} Pa · s when the 515 ° C., 10 when 46 5 ℃ ¹⁴ Pa · s
A glass material having a viscous property was used.
The molding operation was performed in an N ₂ atmosphere to prevent oxidation of the mold.

First, each mold was processed and prepared as follows. That is, processing was performed so that the molding surface 1a had a curvature of R = 60 mm and the molding surface 2a had a curvature of R = 40 mm, and mirror polishing was performed. When the body die 3 is closed, the molding surface 3a has an inner diameter of 18 mm, and the distance between the center portions of the molding surfaces 1a and 2a is 7.
5mm, the cavity formed by each mold 1, 2, 3
So that 2.125Cm ^3, also when the body mold 3 is opened, the molding surface 1a, the distance between the center portion of 2a and processed so that 5.6 mm.

Next, a molten glass lump 10a having a capacity of 2 cm ³ is received on a molding surface 1a as shown in FIG. 2 from a molten glass material having a viscosity of 10 ¹ Pa · s and having the above viscosity characteristics. While the glass block 10a has a viscosity of 10 ⁴ to 10 ⁵ Pa · s, the upper press shaft 7 is operated to
Then, pressure was applied so as to obtain the state shown in FIG. 3 to obtain a preform 10b. Thereafter, as shown in FIG. 4, the upper press shaft 7 is slightly raised, and the pressurization of the preform 10b is interrupted.
The cylinder 6 was operated, and the drum mold 3 was opened. When the viscosity of the preform 10b becomes 10 ^8.5 Pa · s,
Activate the upper press shaft 7 and add 23M to the preformed product 10b.
A pressure of Pa was applied to bring the state of FIG.

As shown in FIG. 1, the lower surface 2 of the flange portion of the upper die 2
When the molded product 10c has a viscosity of 10 ¹⁰ Pa · s, the lower press shaft 9 is operated, and the lower mold 1 is moved to the molded product 10c by 20 MPa.
To maintain the transfer of the molded surface. When the molded product 10c reaches 10 ¹² Pa · s, the lower press shaft 9
, The pressurization of the molded product 10c was interrupted, the cylinder 7 was raised, the flange 2d was hooked by the hook 8, the mold was opened up and down, and the molded product 10c was taken out. The molded article 10c taken out was observed in detail using a microscope. Defects caused by burrs and defects such as residual gas generated due to confining an atmosphere gas during molding between the molded article and the mold were found. Was not observed at all, and the outer diameter with respect to the center was within a range of variation of ± 0.1 mm.

As a comparative embodiment, when the molding was performed under the same conditions as above without using the body mold 3, the center and the outer diameter were greatly deviated in the first pressing stage, and the second pressing was performed. There were many situations where it was not possible. Similarly, when the volume of the glass gob was increased and the molding was performed in the same manner, burrs were generated at the corners of the molded product, and the fragments went around the lens surface, and as a result, a good product was not obtained. Glass powder adhered to the molding surfaces 1a and 2a, and it was not in a state where the next molding could be performed continuously.

[Embodiment 2] Using the same glass material and the same apparatus as in Embodiment 1, the curvatures of both surfaces of the lens are R =
A biconvex lens having 24 mm and R = 49 mm, an outer diameter of about 20 mm, and a center thickness of 3.85 mm was molded. Here, the molding surface 1a of the lower mold 1 corresponding to the lens surface is R = 4
9 mm, the molding surface 2a of the upper die 2 is processed into a spherical surface of R = 24 mm, and further, the molding surface is mirror-polished so that the surface transferred from the molding surface to the molded product functions as an optical element. Was done. When the body mold 3 is closed, the inner diameter is Φ
19 mm, the center thickness is 4.0 mm, the volume of the cavity formed by each mold 1, 2, ³ is 0.729 cm ³ , and the center thickness is 3.85 mm when the body mold 3 is opened. Processed as follows.

Next, as in Example 1, 10 ¹ Pa ·
s viscosity of 0.7c from molten glass material
receiving the molten glass lump 10a of m ³ on the molding surface 1a,
While the glass lump 10a had a viscosity of 10 ² to 10 ⁴ Pa · s, the upper press shaft 7 was operated and pressurized at a pressure of 5 MPa to obtain a preform 10b. Thereafter, the upper press shaft 7 was slightly raised, the pressurization of the preform 10b was interrupted, and the cylinder 6 was operated to open the barrel die 3. Preform 1
When the viscosity of Ob becomes ^108.2 Pa · s, the upper press shaft 7 is operated again to apply 25 MPa to the preformed product 10b.
Was applied to obtain the state shown in FIG. As shown in FIG.
Cooling is started with the flange lower surface 2c of the upper die 2 abutting against the contact surface 3d, and when the molded product 10c has a viscosity of 10 ¹⁰ Pa · s, the lower press shaft 9 is operated and the lower die 1 Was pressed against the molded product 10c at a pressure of 15 MPa to maintain the transfer of the molded surface. When the molded product 10c reaches 10 ¹³ Pa · s, the lower press shaft 9 is lowered to interrupt the pressurization of the molded product 10c, and the upper press shaft 7 is raised and the hook 8
By hooking the flange 2d, the mold is opened up and down,
The molded product 10c was taken out. The molded article 10c taken out was observed in detail using a microscope, but no defects such as defects due to burrs or residual gas were observed at all, and the outer diameter dimension with respect to the center was within a range of variation of ± 0.1 mm. The fit and appearance were very good as in Example-1.

Example 3 The same glass material as in Example 1 was used.
Using the apparatus shown in FIGS. 5 to 9, a biconcave lens having a curvature of both sides of the lens of R = 35 mm and R = 55 mm, an outer diameter of about 21 mm, and a center thickness of 5.0 mm was formed. Here, the molding surface 21a of the lower mold 21 is R = 50
mm, the forming surface 22a of the upper mold 22 is mirror-polished to a curvature of R = 90 mm, processed into a spherical surface, and when the body mold 23 is closed, the inner diameter is Φ20 mm and the center thickness is 7.2 mm. Processing was performed so that the capacity of the cavity formed by 21, 22, and 23 became 2.508 cm ³ . In addition, lower mold 2
6, the molding surface 26a is R = 35 mm, and the molding surface 2 of the upper mold 27
7a was processed into a spherical surface with a curvature of R = 55 mm, and then the formed surface was mirror-polished so that the transfer surface could function as an optical element. In FIG. 8,
The lower mold 26 is in contact with the bottom plate 29, and when the lower surface of the flange of the upper mold 27 abuts against the upper surface of the guide member 28, the thickness of the center of each mold 27 is 5.0 mm.
The dimensions of 26 and the guide member 28 were matched.

Next, a molten glass lump 40a having a capacity of 2.3 cm ³ is received on a molding surface 21a from a molten glass material having a viscosity of 8 Pa · s (see FIG. 5).
While the upper die 22 has a viscosity of 10 ⁵ to 10 ⁷ Pa · s.
Was slowly pressed under a pressure of 18 MPa to obtain a preform 40b (see FIG. 6). Thereafter, the upper mold 22 is raised, the cylinder 25 is operated, the barrel mold 23 is opened (see FIG. 7), and a hand with a positioning mechanism (not shown) is used.
The preform 40b is taken out of the preform. A heating mechanism (not shown) is used to place the lower mold 26 at the center on the molding surface 26a of the lower mold 26 maintained at a temperature corresponding to 10 ^8.5 Pa · s in glass viscosity, and lower the upper mold 27 to the state shown in FIG. I made it. Thereafter, a pressure of 30 MPa was applied to the upper mold 27, and when the lower surface of the flange of the upper mold 27 hit the upper surface of the guide member 28, cooling of the mold and the molded product was started, as shown in FIG. After the start of cooling, when the viscosity of the molded product becomes 10 ^9.5 Pa · s, the lower press shaft 32 is operated, and the lower die 26 is pushed up from below, thereby applying a pressure of 24 MPa to the molded product 40 c to form the molded product. The mold is made to follow the shrinkage accompanying the cooling of the article 40c, and when the pressure reaches 10 ¹¹ Pa · s, the pressure is released,
Raise the upper press shaft 30 and use the hook 31 to
7b was hooked, the mold was opened up and down, and the molded product 40c was taken out of the mold with a hand (not shown). The removed molded article 40c was observed in detail using a microscope, but no defect such as a defect due to a burr or a gas residue was observed at all, and the outer diameter dimension with respect to the center was within a range of variation of ± 0.2 mm. And the appearance was very good as in Example-1.

[Embodiment 4] Similarly to the embodiment 3, and using the same glass material as that of the embodiment 1 and the apparatus shown in FIGS. 50
A biconvex lens having mm and R = 60 mm, an outer diameter of about 18 mm, and a center thickness of 2.7 mm was formed. Here, the molding surface 21a of the lower mold 21 is mirror-polished with a curvature of R = 49.5 mm and the molding surface 22a of the upper mold 22 with a curvature of R = 59.5 mm, processed into a concave surface, and the body mold 23 is closed. When the inner diameter is Φ1
7.2 mm, center thickness 2.9 mm, each mold 21, 2
The volume of the cavity formed by 2, 23 is 0.514
was processed in such a way that cm ^3. The molding surface 26a of the lower mold 26 is R = 50 mm, and the molding surface 27a of the upper mold 27 is R = 50 mm.
After processing to a concave surface of 60 mm, the molding surface was further mirror-polished so that the transfer surface could function as an optical element. 8, when the lower mold 26 is in contact with the bottom plate 29 and the lower surface of the flange of the upper mold 27 abuts against the upper surface of the guide member 28, the center thickness is 2.7 m.
The dimensions of the dies 27 and 26 and the guide member 28 were adjusted to be m.

Next, a molten glass mass 4 having a capacity of 0.49 cm ³ was prepared from a molten glass material having a viscosity of 12 Pa · s.
0a is received on the molding surface 21a (see FIG. 5), and while the glass lump 40a has a viscosity of 10 ³ to 10 ⁵ Pa · s, a pressure of 4 MPa is applied to the upper mold 22 to slowly pressurize, and A molded product 40b was obtained (see FIG. 6). Then, the upper mold 22
Is raised, the cylinder 25 is operated, and the barrel mold 23 is opened (see FIG. 7), and a hand with a positioning mechanism (not shown)
Then, the preform 40b is taken out of the preform. Then, with a heating mechanism (not shown), the glass viscosity is ^108.2 P
The preform was placed at the center of the molding surface 26a of the molding die 26 held between a and s, and the upper die 27 was lowered to the state shown in FIG. Thereafter, a pressure of 20 MPa was applied to the upper mold 27, and when the lower surface of the flange of the upper mold 27 hit the upper surface of the guide member 28, cooling of the mold and the molded product was started, as shown in FIG. After the start of cooling, the viscosity of the molded product becomes 1
When the pressure reaches 0 ¹⁰ Pa · s, the lower press shaft 32 is actuated, and the lower mold 26 is pushed up from below, thereby forming the molded product 4.
Applying a pressure of 12MPa in 0c, the shrinkage due to the cooling, to follow the mold, where it becomes 10 ^12.5 Pa · s, the pressure was released, raising the upper press shaft 30, the flange portion 27b with the hook 31 And the mold was opened up and down, and the molded product 40c was taken out of the mold with a hand (not shown).

The molded article 40c taken out was observed in detail using a microscope, but no defects such as burrs and defects such as residual gas were observed at all, and the outer diameter with respect to the center varied by ± 0.15 mm. Within the range, the appearance,
As in Example 1, a very good product was obtained.

[0030]

According to the present invention, as described above,
Using a mold with a wall thickness larger than the final shape, press softly so that glass does not enter between the upper and lower molds and the mold, and then, without restraining the outer periphery of the molded product, By molding, even from low-viscosity glass such as molten glass, there is no surface defect due to burrs, etc. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing an apparatus used in one embodiment of the present invention.

FIG. 2 is a diagram showing an operation procedure of one embodiment of the present invention.

FIG. 3 is a diagram showing an operation procedure of one embodiment of the present invention.

FIG. 4 is a diagram showing an operation procedure of one embodiment of the present invention.

FIG. 5 is a diagram showing devices used in another embodiment of the present invention and their operation procedures.

FIG. 6 is a diagram showing the above procedure.

FIG. 7 is a diagram showing the above procedure.

FIG. 8 is a diagram showing the above procedure.

FIG. 9 is a diagram showing the above procedure.

[Explanation of symbols]

 Reference Signs List 1 lower die 2 upper die 3,23 trunk die 10a, 40a glass lump 10b, 40b preformed product 10c, 40c formed product 21 preformed lower die 22 preformed upper die 26 formed lower die 27 formed upper die 28 guide member

Continuation of the front page (72) Inventor Masayuki Tomita 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-3-265528 (JP, A) JP-A-63-162539 ( JP, A) JP-A-62-1720 (JP, A) JP-B-36-18982 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) C03B 11/00 C03B 11/08

Claims (5)

(57) [Claims] 1. An optical element is formed by using an upper and lower mold having a desired surface shape and a barrel mold for forming a wall thickness larger than a desired product thickness, and having a glass viscosity of 10 ² to 1.
The first press molding is performed on the glass block between 0 ⁸ Pa · s so that the glass mold and the upper mold and the connection between the mold and the lower mold are not filled with glass. A method for forming an optical element, wherein a second press forming is performed in a state where a mold is removed to form a product to a desired product thickness. 2. The barrel mold used in the first press molding,
2. A structure which can be divided.
3. The method for molding an optical element according to 1. 3. In molding an optical element, a glass block having a predetermined capacity is once pre-pressed by a pre-forming mold having a capacity larger than that capacity, and then an upper mold and a lower mold constituting the pre-forming mold are formed. , Combination of barrel molds, thicker than the thickness of the final product, and at the time of the main press forming a middle hit shape such that the glass deforms from the center of the upper and lower molds, after the preliminary press, A method for molding an optical element, comprising: performing a main press molding in a state where the outer periphery of a glass molded product is not restricted so as to have a predetermined thickness. 4. The pre-press molding is performed when the viscosity of the glass is 10
4. The molding method according to claim 3, wherein when the pressure is between ^{2 and} 10 < ⁸ > Pa.s, the connection between the body mold and the upper mold and between the body mold and the lower mold are not filled with glass. Optical element molding method. 5. The method of molding an optical element according to claim 3, wherein the body mold used in the preforming has a structure that can be divided.