JPH01188436A - Molding die made of glass for optical element - Google Patents

Abstract

PURPOSE:To reduce the production cost of an optical element by providing a lightening hole having specified diameter to the central part of a molding die and also regulating the surface roughness excepting a molding face to the prescribed value or below. CONSTITUTION:A molding die 5 made of glass is freely slidably fitted and provided in a cylindrical drum mold 2. In this case, the molding die 5 has the deverging temp. higher than the transition temp. of a glass stock 3 and a lightening hole 6 having diameter of 20-80% of the diameter of the die is formed in the central part thereof. Furthermore, the surface of the die 5 excepting the molding face is finished at surface roughness not larger than 0.1mum. The glass stock 3 is arranged between the molding dies 5 and press-molded at the temp. close to the softening temp. in the furnace of the nonoxidative atmosphere. Then an optical element is obtained by performing slow cooling and cooling therefor. Thereby a crack on the surface of a product during cooling is prevented and the time for cooling and molding is shortened. Thus, the production cost of the optical element is reduced by improvement of productivity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a lens made of glass or plastic;
The present invention relates to a glass mold for optical elements for press-molding optical elements such as prisms.

[Conventional technology]

Conventionally, to manufacture optical elements such as lenses and prisms,
A method has been adopted in which the optical element material is ground with a diamond grindstone or the like and then ground with cerium oxide or the like. However, in recent years, demand for aspherical lenses has increased,
With the conventional processing methods described above, it has become difficult to produce large quantities of aspherical lenses and the like at low cost. Therefore, the current manufacturing method for optical elements is to insert and place a heat-softened optical element material between a pair of molds with high surface precision, and pressurize it, without performing any grinding, polishing, etc. Press molding is carried out to obtain.

Some of the molds used for this pressure forming are made of metals such as stainless steel, but these metal molds cause crystal grains to grow due to the temperature cycles of glass molding and hot working. As a result, the mold surface becomes rough, deteriorating the surface shape and mold releasability, resulting in a very short mold life.

In order to solve this problem, for example, Japanese Patent Laid-Open No. 61-7263
As disclosed in Publication No. 4, it is known that a ceramic layer of 5i3Na or HfN is formed on the molding surface of a metal mold by PVD (physical vapor deposition) or CVD (chemical vapor deposition). ing.

However, even with a metal mold with a ceramic layer like this, the crystal grains of the mold base material itself grow due to the temperature cycles of glass molding and hot processing, and the crystal structure changes. This is unavoidable, and the surface of the thin ceramic layer becomes rough, and in some cases, the ceramic layer may peel off.

Therefore, it is desired to develop a mold for optical elements that has favorable glass molding properties and improved structural and thermal properties.

Therefore, the inventor previously proposed in Japanese Patent Application No. 62-134581 that the surface roughness of the press-molded product does not deteriorate even during temperature cycles during hot forming, has excellent mold releasability from glass, and is easy to process. We proposed an easy-to-use glass mold. This glass mold is made of glass having a devarging temperature higher than the molding holding temperature, and has a molding surface coated with a mold release film. Here, the deverging temperature refers to the temperature at the point where the thermal expansion curves of slowly strained glass and quenched glass intersect in a region below the glass transition temperature (Tg).

That is, as shown in FIG. 3, the glass mold 1
is slidably fitted into the cylindrical circular mold 2 with a predetermined clearance. This glass mold 1 uses a glass material having a devarging temperature higher than the transition point temperature of the glass material 3 which is the glass to be molded. For example, when the glass material 3 is made of SF7, Its glass transition temperature is about 530″C, so
La5 with debarging temperature higher than this temperature
Let FO8 be the glass material for the glass mold l.

Further, the molding surface of the glass mold 1 is formed to have desired shape accuracy and surface roughness, and the surface includes, for example, Aff.
A release film 4 made of i, 0, etc. is formed.

In order to manufacture, for example, a lens using the glass mold 1, first, a pair of glass molds 1 with a diameter of 20 mm and a length of 301 m1 are fitted into the circular mold 2. A glass material 3 is placed between them. and,
This assembly is heated in an electric furnace (not shown) in a non-oxidizing atmosphere. The heating temperature is 59, which is around the softening point of glass material 3.
Heating time is approximately 1 hour at 0°C. During this time, a weight W is placed on the upper glass mold 1 and a pressure of 50 g/cd is applied to the glass material 3. Note that the heating time can be increased or decreased depending on the difference in shape between the glass material 3 and the molded product.

After molding, the molded glass product (lens) was slowly cooled at a predetermined cooling rate, and when the temperature reached approximately 95°C, the glass molded product (lens) was taken out.

FIG. 4 is a graph showing the relationship between time and temperature in this molding process.

In the above molding, there is no fusion between the molded product and the mold release coating 4, and the high shape accuracy and surface roughness of the molding surface of the glass mold 1 are directly transferred, resulting in a press lens that does not require polishing. Obtained.

In addition, the material of the glass mold 1 has a devarging temperature of about 700°C, so as long as the molding is carried out below this temperature,
The shape of the molding surface does not change at all and is amorphous, so
Unlike metals, crystal grains do not grow and the surface roughness of the molded surface does not deteriorate.

[Problem to be solved by the invention]

However, when glass at a high temperature (but below its strain point) is taken out into the air at room temperature, the surface of the glass rapidly cools and contracts, while the interior lags behind.

As a result, tension is generated near the surface of the glass in a direction parallel to the surface. If this tension becomes greater than the tensile strength of the glass, cracks will occur in the glass and it will break.The stress that occurs increases as the size of the glass increases, the thickness increases, and the coefficient of thermal expansion increases.

Also, if the heat transfer coefficient of the glass surface is large, the stress on the surface will also be large (this kind of stress is called temporary strain because it only occurs temporarily when there is temperature non-uniformity in the glass.

Therefore, as in the conventional case, the diameter is 20 m and the length is 30 m.
When molding is performed using a relatively thick glass mold 1 such as rm, even if the mold temperature drops below the strain point, the temperature cannot be lowered rapidly. This is because if the glass mold l is suddenly taken out into the atmosphere at room temperature, it will crack and break.This is because the larger the diameter of the lens (optical element) to be molded, the more
It is necessary to slowly cool the glass mold 1 to near room temperature at a sufficiently slow rate so as not to cause formation of cans.

In other words, in the conventional glass mold 1, slow cooling must be carried out at a sufficiently slow rate to prevent formation of cans, which results in a significantly longer molding time for one molding process, which ultimately results in an increase in the price of the optical element. There was a problem in that it became high.

The present invention has been made in view of such conventional problems, and is an optical element that can slow down the cooling rate of the mold, shorten the molding time, and obtain the optical element at low cost. The purpose is to provide glass molds.

[Means to solve the problem]

In order to achieve the above object, the present invention is made of a glass having a debarring temperature higher than a forming holding temperature,
A blank hole with a diameter of 20 to 80% of the mold diameter is provided in the center of the mold, and the surface roughness of the surfaces other than the molding surface is reduced to 0.
The glass mold for the optical element is configured to have a thickness of 1 μm or less.

In the present invention, the diameter of the blank hole is 20 to 20% of the diameter of the mold.
The reason for setting it to 80% is that if it is less than 20%, the effect of uniformly thinning the mold wall thickness and preventing destruction due to temporary strain cannot be obtained, and if it exceeds 80%, the mold wall thickness will become too thin. ,
This is because the strength of the mold itself becomes weak.

[Effect]

In a glass mold for an optical element configured as above, the wall thickness of the mold becomes uniformly thin, and during the cooling process of the mold, the temperature difference between each part of the mold becomes small, causing damage due to -time strain. is prevented.

Further, even if the mold wall thickness is made uniformly thin as described above, some temperature difference occurs, and a slight tension is generated near the surface of the mold in a direction parallel to the surface. If a surface defect such as a scratch exists on the surface of the mold, there is a possibility that a hole may be generated from the location of the surface defect. Therefore, the glass mold according to the present invention has a surface roughness of 0.1 μm or less on surfaces other than the molding surface (including the surface of the white holes), which has not been considered in the past, so There are no defects, and destruction due to -time strain can be completely prevented.

〔Example〕

In FIG. 1, the glass mold 5 has an inner cylindrical mold 2.
It is slidably fitted inside with a predetermined clearance. This glass mold 5 uses a glass material having a devarging temperature higher than the transition point temperature of the glass material 3 which is the glass to be molded. In this embodiment, the glass material 3 is Nari, SF
Since the glass transition temperature of No. 7 is about 530°C, the glass material of the glass mold 5 is La5FO8 whose devarging temperature is about 700°C.

On the other hand, the optical effective diameter of the press lens, which is a molded product, is 19
Since it is a cabinet, the outer diameter of the glass mold 5 is set to 20 mm. Moreover, the length of the glass mold 5 is 30
It is formed in m. This is because if the glass mold 5 becomes eccentric due to the clearance with the mold 2, the molded product will also become eccentric, so in order to prevent this eccentricity, the clearance should be adjusted to a level that does not interfere with sliding. It is necessary to make it small and to make the fitting length long, in order to ensure eccentricity accuracy of the press lens.

In addition, the center part of the glass mold 5 has a diameter of 10++ u.
A white hole 6 is drilled. The blank hole 6 is formed by grinding the glass mold 5 from the side opposite to the molding surface using a diamond grindstone.

By providing the blank holes 6, the wall thickness of the glass mold 5 is 5 m over the entire surface, and the depth is approximately uniform.

Furthermore, the surface of the glass mold 5 processed as described above has many surface gaps such as minute scratches and cracks, so in order to remove these and make the surface smooth, Pickling was performed using acid or nitric acid. As a result, the surface roughness of the glass mold 5 other than the molding surface (including the surface of the white hole 6) is set to 0.1 #■ or less.

On the other hand, the molding surface of the glass mold 5 is processed into a desired pressed lens shape and mirror-polished with cerium oxide or the like. In this embodiment, the molding surface of one glass mold 5 is spherical. The molding surface of the other glass mold 5 is formed into an aspherical shape, and each has high shape accuracy and surface roughness. Furthermore, on the molding surface of the glass mold 5, a release film 7 made of Affi103 is formed with a thickness of 0.2 μm by vacuum deposition.

Next, a method of molding a lens using the glass mold 5 will be described.

First, a pair of glass molds 5 are fitted into the separate mold 2, and a Sr1 glass material 3 is placed between these glass molds 5. This assembly is then heated in an electric furnace (not shown) in a non-oxidizing atmosphere. The heating temperature is 590°C near the softening point of the glass material 3, and the heating time is about 1 hour. During this time, a weight W is placed on the upper glass mold 5.
is placed on the glass material 3 and a pressure of 50 g/cd is applied to the glass material 3.

After molding, it was slowly cooled at a rate of 3°C per minute to a temperature below the strain point of Sr8, for example 485°C, and then cooled while increasing the cooling rate appropriately within a range that does not cause destruction due to thermal shock stress. In the example, cooling was performed at a cooling rate of 20° C. per minute, and when the temperature reached approximately 95° C., the glass molded product (pressed lens) was taken out. FIG. 2 is a graph showing the relationship between time and temperature in this molding process.

Through the above molding, it was possible to obtain a press lens that did not require polishing and had high shape accuracy and surface roughness.

In addition, the glass mold 5 has a hollow hole 6 formed in its center so that the mold wall thickness is thin and almost uniform, so that the cooling rate during the cooling process can be adjusted to be slightly below the strain point of the glass material 3. Even if the glass mold 5 is cooled slowly and then cooled very quickly, the molding time that conventionally required 240 minutes (see Fig. 4) can be shortened to 130 minutes. was created (see Figure 2), and as a result,
Press lenses can be manufactured at low cost.

In the above example, the surface roughness of the surfaces other than the molding surface was set to 0. Although pickling was carried out to reduce the surface roughness to below III, the present invention is not limited to such examples. The mold 5 may be manufactured by molding.

In addition, the shape of the molding surface of the glass mold 5 is not limited to a combination of spherical and non-spherical shapes, but any combination of shapes including flat surfaces is possible, and it can be used as a glass mold for manufacturing prisms, etc. However, it does not necessarily have to be round.

Furthermore, in the present invention, the larger the lens diameter, the more
In other words, the larger the diameter and length of the glass mold, and the more accurate the eccentricity of the lens is required, the more effectively the effect will be exhibited.

〔Effect of the invention〕

As described above, according to the glass mold for an optical element of the present invention, the lightening hole is provided in the center of the mold to make the mold wall thickness almost uniform, and the surface roughness of the surfaces other than the molding surface is reduced to 0. Since the steel is made of 1μ or less, even if the cooling rate from the temperature below the strain point of the molded product is significantly increased, no breakage will occur due to thermal shock stress.

Therefore, molding time can be significantly shortened, and productivity is significantly improved. As a result, the number of molding machines for molding the same production quantity can be reduced, and the number of molds can also be reduced, so that optical elements can be obtained at low cost.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a main part of a molding machine equipped with a glass mold for an optical element according to an embodiment of the present invention, and FIG. A graph showing the relationship with temperature. Figure 3 is a longitudinal sectional view of the main parts of a molding machine equipped with a conventional glass mold for optical elements. Figure 4 is a graph showing the relationship between molding and temperature when molding is performed using the molding machine shown in Figure 3. It is a graph showing the relationship between time and temperature. 3...Glass material 5...Glass mold 6.
... Lightening hole 7 ... Mold release coating patent applicant
Olympus Optical Industry Co., Ltd. 1. Z. El. March 16, 1988 1. Indication of the case 1988 Patent Application No. 9243 2 Name of the invention Glass molding mold for optical elements 3 Person making the amendment Relationship to the case Patent applicant address 2-43-2 Hatagaya, Shibuya-ku, Tokyo Name
(037) Representative of Olympus Optical Industry Co., Ltd.
Satoshi Yama, Department 4, Agent 105 Address: 706 Hamamatsucho Dia Heights, 2-2-15 Hamamatsucho, Minato-ku, Tokyo 706 "Detailed Description of the Invention" Contents of Amendment (1) Specification "Late" written on page 7, line 12 of the book is "late".
"Fast," he corrected.

Claims (1)

[Claims] (1) Made of glass with a devarging temperature higher than the molding holding temperature, the center of the mold is
A glass mold for an optical element, characterized in that it has a hollow hole with a diameter of ~80% and has a surface roughness other than the molding surface of 0.1 μm or less.