JPH0624992B2 - Mold for press lens and molding method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a molding die for a press lens used when reheat press-molding a highly accurate press glass lens, and a molding method thereof.

2. Description of the Related Art In recent years, optical elements are in the direction of an aspherical surface that can simultaneously achieve simplification of the lens structure of an optical device and weight reduction of the lens portion (for example, Japanese Patent Laid-Open No. 57-76512).

Among them, as a method of manufacturing a high-precision glass product at a lower cost, JP-A-58-84134 proposes a method of shortening the time required for the pressurizing cycle to obtain a high-precision optical glass element. The outline is to use a glass preform with a shape close to that of the final product, and heat the mold and glass flexible foam respectively, and the glass and the mold can handle glass viscosities of 10 ⁸ poise or more and 10 ¹² poise or less. It has been proposed to start the press at a temperature that corresponds to the temperature and to terminate the press at a temperature corresponding to a glass viscosity below 10 ¹³ poise and to remove the glass.

In addition, although it is not a lens having a surface order of wavelength order, Japanese Patent Publication No. 56-378 discloses a method of molding a lens material.
Keep the temperature of the metal above the transition point and below the softening point of the glass to be molded, put fluid glass in this metal mold and press-mold, and in this state the temperature distribution of the glass becomes uniform It is said that it should be held for 20 seconds or more before being processed.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the production of the above glass lens, the optical performance of the glass lens needs to be better than that of the glass lens by the conventional polishing method, and very high surface accuracy and surface roughness are required. To be done. For example, in the case of a high-precision camera lens, the surface precision Neutring is 5 pieces, the ass is 1 piece or less, and the inner surface roughness is 0.
It is required to be within 03 μm. However, in the conventional glass lens manufacturing method, the glass and the molding die are separately heated, and then the glass is supplied into the molding die to perform the pressing, so that the temperature is likely to become very uneven during the pressing, so I had to hold the press over. Therefore, it has been impossible to manufacture an inexpensive lens that affects the cycle time.

That is, in order to shorten the cycle time, it is considered most preferable to prepare a large number of molds and heat and mold the glass while the glass is kept in the mold.

However, as shown in JP-A-61-26528, when cooling is performed using a temperature gradient type slow cooling chamber in the cooling after pressing, a huge number of molding dies are used in the cooling process. Since it is necessary, it is not a preferable molding method.

Further, the cooling rate of the press die is very important in determining the lens performance, but as described in JP-A-61-53126, a constant rate of 0.9 ° C./sec or less without pressurization. Cooling by means increasing the cycle time, so pressurizing and quenching up to 10 ^10.5 poise will reduce the number of molding dies used and will supply cheaper press lenses. Is possible.

In view of the above problems, the present invention provides a press lens molding die for rapidly manufacturing a highly accurate and inexpensive press lens, and a molding method thereof.

Means for Solving the Problems In order to solve the above-mentioned problems, a molding die for a press lens according to the present invention is arranged between a pair of heater blocks to mold a press lens, and a molding surface for defining a cavity and The first and second molding dies on the opposite side of the molding surface and having a back surface in contact with the heater block;
And a barrel die for guiding a second molding die, the first die
The rear surface of at least one of the second molding dies has a non-contact portion with the heater block in a portion near the thin portion of the press lens.

Further, another press lens forming die includes first and second forming dies each having a forming surface defining a cavity, a first barrel die and a first barrel for guiding the first and second forming dies. A second barrel mold made of a material having a lower thermal conductivity than the first barrel mold is provided outside the mold, the second barrel mold is longer than the first barrel mold, and the second barrel mold is molded. The thickness of the press lens is determined by abutting against the mold or pressing means.

Furthermore, in the method for molding a press lens of the present invention, a glass having a temperature of not higher than the glass transition point is supplied with glass having a temperature of 10 ¹² poise or higher, and heated to a temperature corresponding to a glass viscosity of 10 ⁸ to 10 ¹⁰ poise, After pressing for 3 to 90 seconds, pressurizing with pressure 10 ¹⁰ to 10 ¹¹ is 1.5.
Cooling at a cooling rate of ~ 2.5 ° C / sec, 10 ¹⁰ ~
A molding method of 10 ¹¹ poise or more is a molding method in which cooling is performed at a cooling rate of 0.2 to 1.5 ° C./sec and a press lens is taken out at a temperature not higher than the glass transition point.

Operation With the above configuration, the back surface of the molding die, which is the thin-walled portion of the press lens to be molded, has a portion that is not in contact with the heater block, so there is no contact with the pair of heater blocks in each stage, and heat transfer is suppressed. It Therefore, it has an effect of making it difficult to generate a temperature difference inside the glass. Further, when the curvatures are different, a temperature difference is likely to occur inside the glass on the side of the mold having a small curvature. Therefore, it is easier to obtain the effect more by providing the mold having a small curvature with the non-contact portion with the heater block.

Since the second barrel die made of a material having a lower thermal conductivity than that of the first barrel die is provided outside the first barrel die by another die configuration, heat is taken from the periphery of the press lens. This has the effect of preventing this and making it difficult for a temperature difference to occur inside the glass. However, the gap between the first body mold and the second body mold is 3
The effect is further enhanced by performing it within the range of mm. Further, by making the second barrel mold longer than the first barrel mold, the heater block contacts the second barrel mold, and the thickness of the press lens can be determined. At that time, the parallelism of the press lens can be determined by accurately finishing the second barrel mold. The conditions for selecting the material of the second barrel type are excellent oxidation resistance, high compressive strength, and low cost. In order to satisfy the above conditions, stainless steel is suitable, and austenitic or martensitic stainless steel is preferable. The first barrel mold guides the first molding die and the second molding die, and when the molding die having the molding surface is inserted into the first barrel mold, the first molding surface is inserted. The first cylinder inner surface and the second molding surface and the first cylinder inner surface are at right angles, and the optical axes can be aligned.

On the other hand, by the above method, it is possible to quickly manufacture a highly accurate and inexpensive press lens, but since the method for molding a press lens of the present invention is performed within the range of 10 ⁸ to ^10.75 poise, it is possible to Both the glass and the mold are cooled in order to prevent the deformation of the shape and the occurrence of distortion due to cooling. Further, if the temperature of the molding die and the temperature of the glass are made the same in the cooling process before annealing and the cooling rate is controlled under pressure, no change in surface accuracy is observed even if annealing is performed, and there is almost no residual strain. On the contrary, the press lens formed without such a cooling process does not maintain the shape obtained by the cooling process when annealed.

Further, in the method of molding a press lens, the press molding machine is a simplified press molding machine that does not have a special space for exchanging air and inert gas and does not perform vacuum evacuation.

EXAMPLES Hereinafter, a molding die for a press lens of the present invention will be described with reference to the drawings.

In FIG. 1, 1a, 1b, 1c are first molds having a first optical surface, 2a, 2b, 2c are second molds having a second optical surface, which are It forms a non-contact part.

The optical surfaces of the first and second molds are processed into spherical surfaces or aspherical surfaces. The first aspect of the present invention has 3a, 3b, 3c as a barrel die for guiding these first and second forming dies.
Although the length of the barrel die is determined by the lens size, the lens size may be determined by a press cylinder (not shown). When a lens is molded by the conventional molding die for a press lens shown in FIG. 9, the thickness of the lens center and the thickness of the outer periphery are different from each other, so that temperature nonuniformity occurs during cooling and it is difficult to obtain desired lens performance. Therefore, in order to control the cooling of the outer peripheral portion, a non-contact portion with the heater block is formed on the outer peripheral portion of the molding die.

In Fig. 1a, the lens shape has an upper surface with a radius of curvature of 45 m.
m, the lower surface has a radius of curvature of 32 mm, a diameter of 30 mm, a central wall thickness of 5 mm, and an outer peripheral wall thickness of 1.4 mm. In this case, a glass preform 4a was formed by forming a non-contact portion having a triangular cross section with a depth of 3 mm at the outer peripheral portion at 24 mm corresponding to 80% of the diameter of the lower molding die having a small curvature.

In FIG. 1b, the lens shape has a radius of curvature of 50 at the top.
mm, the lower part has a radius of curvature of 23 mm, the diameter is 30 mm, the central thickness is 7 mm, and the outer peripheral thickness is 1.1 mm. In this case, a non-contact portion having a quadrangular cross section with a depth of 8 mm is formed in the peripheral portion from 24 mm, which is 80% of the diameter of the lower mold having a small curvature,
A glass preform 4b was formed by forming a non-contact portion having a semicircular cross section with a depth of 1 mm from 21 mm corresponding to 70% of the diameter in the upper mold. 1A and 1B, the thickness of the first mold at the center of the optical surface of the first mold is the same as the thickness of the second mold at the center of the optical surface of the second mold. It is 10 mm.

Further, in FIG. 1c, the lens shape has an upper radius of curvature of 50 mm, a lower radius of curvature of 23 mm, a diameter of 30 mm, a central wall thickness of 7 mm, and a peripheral wall thickness of 1.1 mm, which is the same as in the case of b. Since the glass preform 4c to be molded is a cube, the amount of deformation increases. Therefore, the lower mold was shortened to form a non-contact portion having a triangular cross section. In any of the above cases, the wavefront aberration of the press lens obtained is RMS = 0.02.
It was very good with 3λ.

In FIG. 2, 6a, 6b and 6c are first convex molds having a first optical surface, and 7a, 7b and 7c are second convex molds having a second optical surface. . The second aspect of the present invention provides a cylinder die for guiding these first and second forming dies.
a, 8b, 8c. The thickness of the barrel die is determined by the difference in wall thickness between the center and the periphery, but normally when molding a lens with a small difference in wall thickness, it is preferable to be thin in order to shorten the cycle time.

In Fig. 2a, the lens shape has an upper surface with a radius of curvature of 90 m.
m, the lower surface has a radius of curvature of 80 mm, the diameter is 25 mm, the center wall thickness is 3.2 mm, and the outer wall thickness is 4 mm. In this case, a glass preform 9a was formed by forming a non-contact portion having a depth of 2 mm from the center of the optical surface within 40% of the diameter of the lower mold having a small curvature at a radius of 8 mm.

In FIG. 2b, the upper surface of the lens shape has a radius of curvature of 8
The thickness is 8 mm, the lower surface has a radius of curvature of 50 mm, the diameter is 15 mm, the center thickness is 1.1 mm, and the outer peripheral thickness is 3 mm. In this case, a non-contact part with a depth of 6 mm is formed inside 4.5 mm, which is 30% of the diameter of the lower mold, which has a small curvature, and inside the upper mold, which is 4.5 mm, which is 30% of the diameter. To 2
The non-contact part of mm was formed and the glass preform 9b was shape | molded. 2A and 2B, the thickness of the first mold at the center of the optical surface of the first mold is the same as the thickness of the second mold at the center of the optical surface of the second mold. It is 11 mm.

Further, in FIG. 2c, the lens shape has an upper surface with a radius of curvature of 90 mm, a lower surface with a radius of curvature of 46 mm, a diameter of 15 mm, a central wall thickness of 1 mm, and an outer peripheral wall thickness of 3.3 mm, which is 40% of the diameter.
A glass preform 9c was formed by forming a non-contact portion having a semicircular cross section inside 6 mm which is within the range. The wavefront aberration of the press lens obtained in any of the above cases is R
The accuracy was very high with MS = 0.028 λ.

In FIG. 3, 11a and 11b are first concave molds having a first optical surface, and 12a and 12b are second concave molds having a second optical surface. The press die of the third invention of the present invention has a first barrel die 13a, 13b as a barrel die for guiding the first and second molds,
Furthermore, on the outer side of the first barrel molds 13a, 13b, 14a, 14
There is a second barrel type that is b.

It is easier to maintain a uniform temperature by using the same first mold material as the mold material. Therefore, in this case, since tungsten carbide was selected as the mold material,
The same tungsten type was used for the body type. This tungsten carbide has a thermal conductivity of 43.2 kcal / mh
The temperature is ℃, and it has excellent heat permeability. So the second
Austenitic stainless steel SUS3 for maintaining cooling effect and cooling by using the body type
04 was used. SUS304 has a thermal conductivity of 13.4kcal
Since it is / mh ° C, a heat retaining effect can be obtained. The gap between the outer shape of the first barrel die and the inner diameter of the second barrel die is set to 1.20 mm. Further, the lens thickness is determined by making the second barrel mold longer than the first barrel mold. Fig. 3 a, b
The difference between the molding dies is whether the bottom surface of the molding die has a flange portion or not. In general, b is preferable for transferring the molding die, but a is preferable for improving the cycle time. As described above, unlike the first invention, the molding die does not have a non-contact portion with the heater, but by using the second barrel die, a press lens having very good lens performance can be formed. .

In the method for molding a press lens of the present invention, molding was performed using any of the molding dies shown in FIG. The glass material to be pressed is SF3, and the press lens molding device is shown in FIG. FIG. 4 is a temperature profile diagram of the method for molding a press lens of the first present invention. First, the glass preform was preheated to 200 ° C., fed into a molding die at room temperature, and heated to 480 ° C. (10 ^8.5 poise). Then, it was transferred to a press stage, the press cylinder was lowered, and pressing was performed for 30 seconds. Pressing pressure is 500 kg /
It was cm ² . After that, the first pressing pressure was released
Transferred to the cooling stage. The first cooling stage is 435 ° C
The pressure was kept constant and the pressing pressure was applied for 30 seconds after the transfer. At this time, the cooling rate was 2.5 ° C./sec in the first half and 1.6 ° C./sec in the second half, and the glass was cooled to 440 ° C. (10 ¹¹ poise). Then, it is transferred to a second cooling stage of 400 ° C. and kept in a pressurized state for 50 seconds. The cooling rate was 1.5 ° C./sec in the first half and 0.3 ° C./sec in the latter half. At this time, the temperature of the glass becomes 405 ° C. (10 ¹³ poise), whereupon the glass is rapidly cooled and the lens is taken out.

Further, another method of molding the press lens of the present invention will be described with reference to FIG. Note that FIG. 5 is a temperature profile diagram of the method for molding a press lens of the second present invention.
First, the glass preform is preheated to 400 ° C. and supplied into a molding die heated to 400 ° C.,
Heat to 480 ° C. (10 ^8.5 poise). Then transfer to the press stage and lower the press cylinder to 30
Press for seconds. The press pressure was 500 Kg / cm ² . After that, the press pressure was once released and transferred to the first cooling stage. The first cooling stage was capable of cooling at a constant rate from 480 ° C, cooled to 435 ° C (10 ^11.5 poise), and then taken out. Pressing pressure during cooling is 20 kg /
It was cm ² . Cooling time is 30 seconds, constant cooling rate is 1.
It was 5 ° C / sec. A sectional view of the press cylinder and the molding die in the first cooling stage used in the method for molding a press lens according to the first and second aspects of the present invention is shown in FIG. 7, and the method for molding a press lens according to the first aspect of the present invention. FIG. 8 shows a sectional view of the press cylinder and the molding die in the second cooling stage used in FIG.

The molding method of the first and second press lenses is 10 ⁸ to 1
Since it is performed in the range of 0 ^12.5 poise, the shape of the molded product is likely to be deformed and the distortion due to cooling is easily generated. Therefore, the glass and the molding die were both cooled to prevent the deformation. Also, in the cooling process before annealing, the molding die and glass temperature are made the same,
When the cooling rate is variably controlled under pressure, very good results can be obtained in the annealing process. That is, there was almost no residual strain in cooling, and high surface accuracy was obtained even after annealing.

EFFECT OF THE INVENTION The press lens molding die of the present invention is arranged between a pair of heater blocks to mold a press lens.
First and second molding dies each having a molding surface defining a cavity and a back surface on the side opposite to the molding surface and in contact with the heater block, and a barrel mold for guiding the first and second molding dies. And a rear surface of at least one of the first and second molding dies has a non-contact portion with the heater block in a portion close to the thin portion of the press lens. The non-contact portion does not come into contact with each other, heat conduction is suppressed, and it is possible to prevent a temperature difference from occurring inside the glass.

Further, another press lens forming die includes first and second forming dies each having a forming surface defining a cavity, a first barrel die and a first barrel for guiding the first and second forming dies. A second barrel mold made of a material having a lower thermal conductivity than the first barrel mold is provided outside the mold, the second barrel mold is longer than the first barrel mold, and the second barrel mold is molded. Since the thickness of the press lens is determined by abutting against the mold or the pressing means, it is possible to prevent heat from being taken from the periphery of the lens and prevent a temperature difference from occurring inside the glass.

Furthermore, in the method for molding a press lens of the present invention, a glass having a glass transition temperature of 10 ¹² poise or more is supplied to a molding die and heated to a temperature corresponding to a glass viscosity of 10 ⁸ to 10 ¹⁰ poises, After being pressed for 3 seconds to 90 seconds, the pressure remains 1.5 to 10 ¹⁰ to 10 ¹¹ poise.
Cooling is performed at a cooling rate of 5 ° C / sec, 10 ¹⁰ to 10 ¹¹
Cooling is performed at a cooling rate of 0.2 to 1.5 ° C / sec above Poise and the press lens is taken out below the glass transition point, so cycle time can be shortened and a highly accurate and inexpensive press lens can be molded. be able to.

[Brief description of drawings]

1, 2, and 3 are sectional views of a molding die for a press lens according to an embodiment of the present invention, and FIGS. 4 and 5 are moldings for a press lens according to an embodiment of the present invention. FIG. 6 is a glass temperature profile diagram of the method, FIG. 6 is a block diagram of a press lens molding apparatus used in the embodiment of the present invention, and FIG. 7 is a press cylinder and a molding die in the first cooling stage used in the embodiment of the present invention. FIG. 8 is a sectional view of a press cylinder and a molding die in the second cooling stage used in the embodiment of the present invention, and FIG. 9 is a sectional view of a molding die of a conventional press lens. 1a, 1b, 1c ... Upper mold, 2a, 2b, 2c ...
Lower molds 3a, 3b, 3c ... Body molds 4a, 4b, 4
c ... Glass preform, 5a, 5b, 5b ', 5c
... Non-contact part, 6a, 6b, 6c ... Upper mold, 7a,
7b, 7c ... lower mold, 8a, 8b, 8c ... barrel mold,
9a, 9b, 9c ... Glass preform, 10a, 1
0b, 10b ', 10c ... Non-contact part, 11a, 11b
...... Upper mold, 12a, 12b ...... Lower mold, 13a,
13b ... first barrel mold, 14a, 14b ... second barrel mold, 15a, 15b ... glass preform, 16 ...
Cartridge heater, 17 ... Cooling tube.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shoji Nakamura 1006, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A 63-107822 (JP, A) JP-A 63-159227 (JP, A)

Claims (16)

[Claims] 1. A mold, which is arranged between a pair of heater blocks to form a press lens, has a molding surface for defining a cavity and a back surface which is on the opposite side of the molding surface and is in contact with the heater block. 1, a second mold, and a barrel mold for guiding the first and second molds, wherein at least one of the first and second molds has a heater block on its back surface. A press lens molding die having a non-contact portion. 2. The curvature of the first molding surface of the first molding die and the second
The molding die for a press lens according to claim 1, characterized in that the second molding surface of the molding die has a curvature different from that of the second molding surface, and has a non-contact portion with the heater block on the back surface of the molding die having a small curvature. Type. 3. A mold, which is arranged between a pair of heater blocks and molds a press lens, has a molding surface that defines a cavity and a back surface that is on the opposite side of the molding surface and is in contact with the heater block. The first and second moldings, which include first and second molding dies and a barrel mold for guiding the first and second molding dies, and which are thin-walled portions of a press lens to be molded.
The molding die for a press lens, wherein the back surface of at least one of the molding dies is not in contact with the heater block. 4. The molding die is for molding a convex lens, and at least one of the first and second molding dies has a heater block and a non-contact portion at a portion whose rear surface is close to the outside. A molding die for a press lens according to item (3). 5. The molding die is for molding a concave lens, and at least one of the first and second molding dies has a heater block and a non-contact portion at a portion whose back surface is close to the center. A molding die for a press lens according to item (3). 6. A first and a second having molding surfaces defining each.
And a first guide for guiding the first and second molding dies.
And a second barrel mold provided outside the first barrel mold and made of a material having a lower thermal conductivity than that of the first barrel mold. A mold for a press lens, wherein the mold is longer than the first barrel mold, and the second barrel mold contacts the molding die or pressing means to determine the thickness of the press lens. 7. A cemented carbide containing tungsten carbide (WC) as a main component, wherein the first and second forming dies and the first body are
Or titanium nitride (TiN), titanium carbide
The molding die for a press lens according to claim 6, characterized in that a sintered material such as cermet containing (TiC) or chromium carbide (Cr ₃ C ₂ ) as a main component is used. 8. The mold for a press lens according to claim 6, wherein the second barrel mold is made of austenitic stainless steel or martensitic stainless steel. 9. The gap between the outer diameter of the first barrel die and the inner diameter of the second barrel die is 3 mm or less.
Mold for press lens described. 10. The press according to claim 6, wherein the parallelism between the back surface of the first mold and the back surface of the second mold is determined by the parallelism of the second barrel mold. Mold for lens molding. 11. The mold for a press lens according to claim 6, wherein the first barrel mold guides the first and second molds to determine the optical axis of the lens. . 12. A glass having a temperature not higher than the glass transition point is supplied with a glass having a porosity of 10 ¹² poise or more, and the temperature of the glass and the vicinity of the molding surface of the molding die has a glass viscosity of 10 ⁸ to 10 ¹⁰ poise. Heat to the corresponding temperature for 3 seconds to 90
After pressing for 10 seconds, it is cooled at a cooling rate of 1.5 to 2.5 ° C./sec up to 10 ¹⁰ to 10 ¹¹ poise while being pressurized, and 0.2 to 1.5 ° C. at 10 ¹⁰ to 10 ¹¹ poise or more. / Se
A method of molding a press lens, characterized in that cooling is performed at a cooling rate of c and the press lens is taken out below the glass transition point. 13. The method of molding a press lens according to claim 12, wherein the pressing pressure is 500 kg / cm ² or less. 14. The cooling after pressing is characterized in that at least one cooling stage maintained at a constant temperature is provided and the cooling stages are sequentially transferred to cool.
A method for molding a press lens as described above. 15. The method of molding a press lesbian according to claim 12, wherein, after the pressing, the cooling is performed until the glass transition point is reached except during the transfer to the cooling stage. 16. The method of molding a press lens according to claim 12, wherein annealing is performed after the press lens is taken out.