JP2000086255A - Method for molding optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical element which does not give rise to chipping and cracking at a ridge line part by feeding a glass gob subjected to weight regulation into a female mold having a cavity approximate to a finished good shape, heating the glass gob to a temp. corresponding to a specific viscosity, packing the glass gob into the cavity by softening fluidization, forming the optical element having the shape approximate to the finished good shape and subjecting the optical element to press forming by forming dies. SOLUTION: The glass gob is heated to the temp. corresponding to 105 to 108.5 dpa.s in viscosity. The glass gob 3 is fed into the cavity of the female mold 1 and the male mold 2 is slidably fitted thereto and is pushed by pressure to form the glass gob to the shape approximate to the finished good shape. Pressing force below 30 KPa is loaded on the glass gob to transfer the cavity inside surface to the glass gob surface. Carbon stock is used for the female mold. The optical element is formed to a non-axisymmetrical shape and comes into contact with the inside surface of the cavity so as to form R=0.5 to 1.5 mm (radius of curvature) at the ridge line part. The optical element is press formed under vacuum by using the forming dies in such a manner that the surface roughness attains Ra=10 nm or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an optical element by pressing an optical material which has been heated and softened by an upper and lower mold member having a molding surface corresponding to the optical function surface of the optical element.

[0002]

2. Description of the Related Art In recent years, optical elements such as lenses are mainly manufactured by press molding. In particular, recently, this pressing method has been adopted for lenses that are not axially symmetric, such as f-θ lenses and prisms. For example, in the molding apparatus described in Japanese Patent Application Laid-Open No. 6-256015, various devices have been devised in order to accurately mold a non-axially symmetric optical element having a toric surface or an anamorphic surface on both surfaces or one surface. Molded molds have been proposed.

[0003] That is, here, a square cavity is formed by a square-hole body mold and a corresponding square-shaped upper and lower mold member, and a glass block (optical material) is filled therein and pressed. Thus, a required square optical element (optical element having a non-axially symmetric surface) is formed.

[0004]

However, the above-mentioned molding method has the following disadvantages. (1) When the spherical glass block is pressed and filled so as to be sufficiently distributed in the rectangular cavity, the glass enters the gap between the upper and lower molds and the body mold.
Chipping or cracking occurs in the molded product (optical element). Even if the gap is devised by some method, a sharp edge is formed at the ridge of the optical element, so that the edge of the optical element is broken and a minute chip is generated at that location. Therefore, every time molding is performed, a cleaning operation for removing glass fragments remaining in the molding die is required, which hinders automatic and continuous molding operation. (2) When the degree of filling in the mold is reduced for the purpose of preventing the glass from entering the gaps of the mold member and the formation of the edge of the molded product as described above, the spherical glass block becomes square. Due to deformation into an optical element of a mold, the degree of filling partially varies, and transfer failure occurs in the area of the optically effective portion (optically functional surface) of the molded product. (3) In order to prevent the above-mentioned variation in the degree of filling, a glass block having a shape similar to a finished product (optical material = preform)
However, if it is manufactured by a grinding / polishing method, time and cost are increased, and it is not suitable for mass production. In particular, in the case of producing an optical element having a non-axisymmetric shape, the problem appears more remarkably. In addition, if the polishing step is omitted to reduce the cost, the surface of the glass material does not have a surface roughness (mirror surface) that is effective in the subsequent molding,
Even when the optical element is molded, the roughness cannot be completely removed, the quality of the lens is reduced, and the function of the lens with the required precision is impaired.

The present invention has been made based on the above circumstances, and an object of the present invention is to form an optical element having a ridge portion, particularly, a non-axially symmetric optical element. Prior to molding, the optical material to be preformed is subjected to molding such that a small curvature or chamfer is formed at the ridge, and the optical element is formed. An object of the present invention is to provide a method for forming an optical element, which is devised so as not to cause the generation.

[0006]

Therefore, in the present invention,
In a molding method of an optical element in which a heat-softened optical material is pressed and molded with a pair of molding dies, in advance, a weight-adjusted glass lump is put into a female mold having a cavity similar to the shape of a completed optical element, The above glass lump has a viscosity of 1
0 ⁵ -10 is heated to the corresponding temperature ^8.5 dpa · s,
By holding the state, the glass lump is filled with the glass lump by the softening flow of the glass lump, and an optical material similar to the finished product shape of the optical element is formed. Press molding is performed.

In this case, the male mold is slidably fitted to the female mold, so that the glass block in the cavity is reduced by 3 mm.
By applying a pressing force of 0 KPa or less, the inner surface of the cavity can be transferred to the surface of the glass lump. In addition, by using a carbon material for the female mold, even when molding an optical material for an optical element having a complicated shape such as a non-axisymmetric shape, it is possible to easily process a cavity having a shape following the shape. is there.
Moreover, since it is a carbon material, there is no fusion between the two even if the glass material is above its softening point, and it can be easily processed in a heating furnace, etc., so it is low cost and has a shape similar to an optical element as a final molded product Is easily obtained.

[0008] However, since the inner surface of the female cavity of the carbon material cannot be made as mirror as the optically functional surface, the surface of the optical material to which the carbon material is transferred also has a glass surface roughness Ra =
The surface roughness of the optical element after molding is reduced to 0.1 nm to 1 μm, and the surface roughness of the optical element after molding is reduced to Ra = 10 nm or less (surface roughness of the molding die) by being pressed under vacuum with a pair of molding dies. Therefore, there is no problem in quality as an optical element such as a lens.

According to an embodiment of the present invention, the optical material has a non-axially symmetric shape, and R = 0.5 to 1.5 mm (radius of curvature) at a ridge portion in the cavity.
Alternatively, the optical material is brought into contact with the inner surface of the cavity so that C = 0.5 to 1.5 mm (chamfer) is formed, and the surface roughness is Ra = 0.1 to 1 μm. It is preferable that the optical material is molded by the above-mentioned female mold, and the optical material is heat-softened and pressed by using the above-mentioned mold under vacuum so that the surface roughness is Ra = 10 nm or less. Further, the optical material is a glass material having an approximate shape, and has a glass viscosity of 10 ⁹ to 10 ^11.
At dpa · s and a pressing pressure of 0.5 MPa to 2 MPa, it is preferable to press-mold with the above mold. This means that it will be molded with high viscosity and low pressure,
Even if the amount of deformation is small, it is possible to transfer the entire surface within the cavity of the molding die, and unnecessary filling pressure (causing generation of burrs, etc.) can be avoided. Moreover, since Ra = 0.5 to 1.5 (radius of curvature) or C = 0.5 to 1.5 (chamfer) is formed at the ridge line portion of the optical material,
A small curvature is left on all ridges of the optical element after molding.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, as an embodiment of the present invention, an example of forming a toric lens will be described as an example of forming a non-axisymmetric optical element with reference to the drawings. First, a molding method (preform) of an approximate optical material will be specifically described with reference to FIGS. In the figure, reference numeral 1 denotes a female mold made of isotropic carbon, in which a completed product of a toric lens is engraved (cavity). Reference numeral 2 is also a male type (push type) made of isotropic carbon.

Then, a glass lump 3 separated from the molten glass and adjusted in weight is put into the cavity of the female mold 1, and the male mold 2 is slidably fitted into the opening at the upper end of the female mold 1. Then, the required amount of the male mold 2 is pressed with a suitable pressure to form the glass lump 3 into a shape approximating the shape of the completed toric lens, and an optical material 4 having an approximate shape as shown in FIG. You get.

In the present embodiment, the glass lump 3 has an elongated ellipsoidal shape. The glass block 3 has a transition point of about 490 ° C. and a sag point of about 530.
C. and a crown-based glass having a softening point of about 620.degree. C. are used. Here, as shown in FIG. 1, with the glass lump 3 housed in the cavity, the whole is put into a vacuum heating furnace and kept at 630 ° C. As a result, the glass lump 3 has a softening point or higher, so that a softening flow occurs, and the glass lump 3 is gradually deformed according to the pressing force of the male mold 2 as shown in FIG.

Further, all the ridges formed on the inner wall of the cavity have a radius of curvature R = 0.5 to 1.5.
mm, preferably 1 mm (of course,
Its length: C = 0.5-1.5 mm, preferably 1 mm
May be chamfered). As a result, a shape corresponding to the machining of the cavity of the carbon mold (female mold), for example, a shape corresponding to the radius of curvature is obtained at the ridge 4 ′ of the glass material (optical material) 4 of the approximate shape.

In this embodiment, the male mold 2 is fitted to the female mold 1 and a required load is applied. This makes it possible to accelerate the above-mentioned softening flow rate. Here, a load (weight) corresponding to a pressure of about 8 KPa was applied. However, when the pressure was increased to about 30 KPa or more, glass entered the gap formed between the two dies 1 and 2 and burrs were generated. Become. Therefore, it was clarified in practice that the load of the male mold 2 needs to be set to less than 30 KPa.

The surface roughness of the glass lump 3 was Ra = about 0.002 μm, but the surface roughness of the approximate glass material 4 obtained in the above process was Ra = about 0.75 μm. . That is, the roughness of the inner surface of the cavity of the female mold 1 is transferred as it is.

Next, a method for forming an optical element using the optical material 4 having an approximate shape will be specifically described with reference to FIGS.

In FIG. 4, reference numeral 5 denotes an upper die, 6 denotes a lower die,
Reference numeral 7 denotes a side surface type (or a trunk type). They are,
It is set in a molding chamber (not shown) filled with an inert gas. First, the upper die 5 is lifted by a press rod (not shown), and the optical material 4 is placed in a cavity formed by the lower die 6 and the side die 7, and then the upper die 5 is lowered. Then, press pressure is applied to the upper surface of the optical element 4. The final state is shown in FIG.

In this case, since the optical material 4 previously approximates the shape of the optical element of the final product from the glass block 3, the optical material 4 is close to the inner wall of the cavity, and is pressed by the upper die 5. With only a slight deformation, the optically effective surface is transferred to the optical material 4 and the optical element 8 is formed. Also,
The ridge line portion 4 'of the optical material 4 corresponds to the ridge line portion 6' (a sharp angle) of the molding die. Have been.

In this state, using a suitable heating source (not shown), 570 ° C. (glass viscosity: about 10 ^9.5 dpa ·
s). This is about 15 ° C. lower than the conventional molding temperature. When the predetermined temperature is reached, the molding chamber is evacuated. The degree of vacuum is about 2 ×
10 ^-2 Torr. Then, the upper mold 5 is lowered to start pressing. The pressing pressure is 1 MPa. this is,
This corresponds to 1/10 or less of the conventional pressure.

The temperature setting and the pressure setting mean high-viscosity and low-pressure molding, and show that the all-optically effective surface is transferred with a small amount of deformation. In addition, as shown in FIG. 6 described above, the pressing / forming is completed with a small R remaining on the ridge line portion 8 '. Thereafter, the molding chamber is again filled with an inert gas, and cooling is started. On the way, a press rod (not shown) provided at the lower part of the lower die 6 is raised in a temperature range where the glass viscosity is equal to 10 ¹² to 10 ¹⁴ dpa · s, and pressed again. This is to prevent surface precision failure due to shrinkage of the glass during cooling. The pressing pressure at this time is 10 MPa to 15 MPa. And
When the temperature of the mold reaches 460 ° C., the molding is completed and the molded article 8
(Optical element) is taken out.

As a result, the optically effective surface of the molded article 8 had a surface roughness Ra of 10 nm or less. This corresponds to the surface roughness of the molds 5, 6, 7. In this embodiment, press molding is performed under vacuum.
If the vacuum is not applied, the surface roughness of the molded product
Ra varied from 10 nm to 100 nm depending on the location. That is, small air bubbles remained on the surface of the molded product (gas remaining).

As described above, even if the optical material according to the present invention has a poor surface roughness, it can be formed under vacuum to eliminate gas residue and provide an optical element having a desired surface accuracy without causing burrs and chips. It can be achieved.

[0023]

As described above, according to the present invention,
Even when molding an optical element that has ridges,
A glass material having an approximate shape can be manufactured in advance at low cost, and an optical element free from chipping at the ridge and no cracking can be obtained by only slightly deforming the glass material. In addition, by molding under vacuum, it is possible to mold even an optical material having poor surface roughness without deteriorating the quality of the lens.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a molding die of an optical material and a glass lump showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a mold and an optical material (an approximate glass material).

FIG. 3 is a side view showing an optical material (approximate glass material: preform) formed by the present invention.

FIG. 4 is a sectional view of a final mold and a molded optical element showing an embodiment of the present invention.

FIG. 5 is an enlarged cross-sectional view showing a main part before molding, similarly.

FIG. 6 is an enlarged cross-sectional view showing a main part after molding.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Female type (carbon type) 2 Male type 3 Glass block 4 Optical material (glass material) of approximate shape 4 'Ridge part of optical material (with R) 5 Upper die 6 Lower die 6' Ridge part (acute angle) 7 Side type (Body type) 8 Optical element (molded product) 8 'Ridge of optical element (molded product) (with R)

Claims (6)

[Claims] 1. A method for molding an optical element, wherein a heat-softened optical material is press-molded with a pair of molding dies. was charged within, the above glass gobs, the viscosity thereof is heated to a temperature corresponding to 10 ⁵ ~10 ^8.5 dpa · s, by holding that state, by softening and fluidization of the glass mass in the cavity A method for forming an optical element, comprising: filling an ingot of glass, forming an optical material having a shape approximating a finished product of the optical element, and using the optical material to perform press molding with the molding die. 2. The method according to claim 1, wherein the male mold is slidably fitted to the female mold so that the glass block in the cavity has a pressure of 30 KPa.
The method for manufacturing an optical element according to claim 1, wherein the following pressing force is applied to transfer the inner surface of the cavity to the surface of the glass lump. 3. The method according to claim 1, wherein the female mold is made of a carbon material. 4. The optical material has a non-axially symmetric shape, and R = 0.5 to
1.5mm (radius of curvature) or C = 0.5-1.5m
The method for molding an optical element according to claim 1, wherein the optical element is in contact with an inner surface of the cavity so that m (chamfer) is formed. 5. The optical material having a surface roughness Ra = 5.
The optical material is molded with the above-mentioned mold so as to have a thickness of 0.1 to 1 μm, and the optical material is heated and softened, and the surface roughness of the optical material is Ra = 10 nm or less under vacuum using the above-mentioned mold. The pressure molding is performed as follows.
5. The method for molding an optical element according to any one of 4. 6. The optical material having a glass viscosity of 10
⁹ to 10 ¹¹ dpa · s, press pressure 0.5MPa to 2
The molding method of an optical element according to claim 1, wherein the molding is performed by pressing with the molding die in MPa.