JP3199825B2 - 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 optical elements such as lenses and prisms by press molding.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing an optical element, an effective molding surface according to the design of an optical element is formed in a mold made of various materials, and the material of the optical element is heated and softened. 2. Description of the Related Art A press forming method is known in which pressing is performed between a pair of forming dies including a die and a lower die and a body die to form a predetermined shape corresponding to an effective forming surface. As the optical element material used in this method, a ball-shaped one is usually used because the surface is a polished surface and the amount can be easily adjusted.

However, the ball-shaped optical element material is difficult to set at the center of the mold by shaking, and cannot be used particularly when the lower mold has a convex surface. On the other hand, if the diameter of the optical element is too small as compared with the inner diameter of the body mold, it is difficult to install the optical element at the center, and there is a great risk that eccentricity and uneven thickness will occur due to uneven molding. The required eccentricity accuracy is a few microns, and the very slight thickness deviation causes the meat to enter between the mold and the body mold, resulting in poor mold release, making it difficult to remove the molded product, The product will be chipped.
In addition, the contact with the body mold is too strong, so that the body mold adheres.

[0004] Furthermore, the difference between the thermal expansion coefficient of the barrel die and the thermal expansion coefficient of the optical element material causes a remarkable dimensional change in the barrel die and the optical element material, causing defective products and lowering the molding efficiency. I do. For this reason, considerably high precision is required for the diameter of the optical element material (hereinafter, also referred to as a preform) and the inner diameter of the barrel, and the precision of the preform is required to be about 10 μm, and the inner diameter of the barrel is 1 μm. ~
An accuracy of 2 μm is required. However, it has hitherto not been possible to precisely calculate these dimensions in relation to the coefficients of thermal expansion of the shell and the optical element material.

[0005]

SUMMARY OF THE INVENTION According to the present invention, an optical element material can be placed in a molding die and a barrel mold without bias, can be molded with excellent releasability, and can efficiently produce an optical element having desired dimensions without eccentricity. It is an object to provide a molding method.

[0006]

According to the present invention, a diameter of an optical element material is made equal to a desired diameter of an optical element, and a body mold and an optical element material whose thermal expansion coefficients are in an appropriate relationship with each other are used. The above object has been achieved by determining the inner diameter of the mold and the diameter of the optical element material to be equal.

That is, a method for molding an optical element according to the present invention is a method for molding an optical element, which comprises heating and softening an optical element material and pressing and molding between a pair of molding dies and a body mold.
The diameter of the optical element material before molding is made substantially the same as the design diameter of the optical element after molding, the design diameter of this optical element is indicated by x, the coefficient of thermal expansion of the optical element material is α ₁ , When the thermal expansion coefficient is α ₂ and the difference between the molding temperature and the room temperature is T, a material satisfying α ₁ > α ₂ is used, and the inner diameter y of the body mold is expressed by the following equation (I): y = x (1 + α ₁₎ T) / (1 + α ₂ T) (I)

As the material of the molding die and the body die used in the method of the present invention, any known materials can be used. For example, various compounds mainly composed of carbide compounds such as tungsten carbide, stainless steel and nickel can be used. Heat-resistant alloys and various ceramics are used. As a molding die, in consideration of oxidation resistance and wettability, a molding surface of a base material is coated with a thin film of various ceramics or a noble metal such as gold, platinum, and platinum group metals. -23
For example, those having the structure described in Japanese Patent No. 7024 can be used.

In the present invention, when selecting the body member and the optical element material, the thermal expansion coefficient of the optical element material is α ₁ and the thermal expansion coefficient of the body member is α ₂ in consideration of the respective thermal expansion coefficients. Then, a material that satisfies α ₁ > α ₂ is selected. α
₁ <If it is alpha _2, not the diameter of the inner diameter and the optical element material body mold at the molding temperature is equal, the optical element material is present unevenly in the body mold, eccentric molded article is produced Probability is high. If α ₁ = α ₂ , y = x, and difficulties arise when the optical element material is set on the lower mold (room temperature). Also, in the case of α ₁ = α _{2 and in} the case of α ₁ <α ₂ , the diameter of the optical element after being gradually cooled after molding becomes the same as the inner diameter of the barrel mold, making it difficult to take out the molded product. .

Further, in the present invention, it is necessary that the optical element material be a preform having a diameter substantially the same as the designed diameter of the optical element after molding. If the diameter of the optical element material is larger than the designed diameter x after molding, if the inner diameter of the barrel is selected based on the value y calculated from the formula (I), the optical element will be stronger against the barrel during molding. Because of this, the releasability deteriorates. If the diameter of the optical element material is smaller than x, the inner diameter of the body mold does not match the diameter of the optical element material at the time of molding. There is.

Further, in the present invention, the inner diameter dimension y of the body mold is set to a dimension calculated from the above formula (I). If this condition is not satisfied, the inner diameter of the barrel and the diameter of the optical element material will not be equal at the molding temperature, and the optical element material will be unevenly distributed in the barrel, resulting in an eccentric molded product. I do.

Next, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a schematic explanatory view showing a state of a molding portion before press molding using an optical element molding die. In FIG. 1, a thin film 3 is applied to the effective forming surfaces of the base materials of the upper mold 1 and the lower mold 2. Reference numeral 4 denotes a body mold, and reference numeral 5 denotes a member for adjusting the thickness of a molded product. The effective forming surface of the base material of the upper mold 1 and the lower mold 2 is cut into an aspherical shape using a machine tool such as an ultra-precision lathe, and then the surface roughness _Rmax is set to 0. The thin film 3 is polished until the thickness becomes equal to or less than 02 μm, and then the thin film 3 having substantially the same surface shape as the effective molding surface of the molding die by an arbitrary method such as a sputtering method, an ion plating method, and a chemical vapor deposition (CVD) method. Can be deposited.

The optical element material 6 used as the material of the body mold 4 is
The coefficient of thermal expansion is selected so as to satisfy α ₁ > α _2, and y is determined by equation (I). The shape of the optical element material 6 is not limited, except that the diameter is substantially the same as the diameter x of the optical element after molding.

The materials and dimensions are determined as described above,
After assembling the lower mold 2 and the body mold 4, the optical element material 6 is placed on the lower mold 2, the upper mold 1 is set, and the process proceeds to a heating step of the optical element material. 5 is a thickness adjusting member.

Next, the state of the forming part during the press forming will be described with reference to FIG. The optical element material 6 placed between the upper mold 1 and the lower mold 2 and the body mold 3 as shown in FIG. 1 is heated and softened by the heater 7 as shown in FIG. The heating temperature is measured by the thermocouple 10. At a high temperature, an inert gas, for example, a nitrogen gas can be supplied from the atmosphere gas supply port 9 in order to prevent deterioration of the mold member due to oxidation. When the optical element material 6 is softened, the cylinder 8 is lowered and pressed with a desired pressure to be molded. Thereafter, the molded product is gradually cooled, and when the temperature of the molded portion becomes lower than the transition point of the optical element material, the pressure is removed, and the molded product can be taken out with good releasability. Thus, a good optical element molded product without eccentricity can be obtained.

[0016]

Next, the present invention will be described more specifically based on examples, but the present invention is not limited thereto.

Example 1 After the tungsten carbide WC was cut into a desired aspherical shape with an ultra-precision lathe, the base material was polished with a diamond paste abrasive so that the surface roughness of the effective forming surface was 0.02 μm or less. A platinum film was formed to a thickness of 1 μm on the molding surface by sputtering for the purpose of oxidation resistance and wetting resistance to obtain a molding die.

The barrel mold is made of the same WC as the mold base material.
The optical element material used was LF5 glass (manufactured by Ohara Optical Glass Co., Ltd.), and the average coefficient of thermal expansion (α ₁ ) up to the molding temperature was 130 × 10 ⁻⁷ / deg. The average thermal expansion coefficient (α ₂ ) of the body material WC is 50 × 10 ⁻⁷ / deg.
It is. The design diameter of the optical element after molding is 15.0 in diameter.
Since the molding temperature is 500 mm and the room temperature is 20 ° C., the difference between them is 480 ° C. Therefore, the cylinder inner diameter dimension (y) at the time of molding is calculated from the above formula (I) as y = 15.0 (1 + 130 × 10 ⁻⁷ × 480) / (1 + 5).
0 × 10 ⁻⁷ × 480) = 15.057, which is 15.057
mm.

The shape of the effective molding surface of the lower mold is a radius of curvature of 18
mm, and the shape of the effective molding surface of the upper mold is a concave surface with a radius of curvature of 50 mm. Further, as an optical element material, L
It is made of F5 glass (manufactured by Kohara Optical Glass Co., Ltd.), the surface in contact with the lower mold is a convex surface with a radius of curvature of 16 mm, the surface in contact with the upper mold is a convex surface with a radius of curvature of 38 mm, center thickness 4 mm, diameter 15,000 mm
Was used.

First, after combining the body mold and the lower mold, the preform was placed on the lower mold, and the upper mold was placed thereon and set. At this time, the trunk mold diameter> the preform diameter,
We were able to set without problem. After that, 500
Heated to ° C. Temperature was measured with a thermocouple. In order to prevent the mold member from deteriorating due to oxidation at a high temperature, nitrogen gas was introduced from the atmosphere gas supply port.

[0021] was pressed molded at a pressure of about 100 kg / cm ² a preform lowers the cylinder when it reaches 500 ° C.. At the time of 500 ° C., the inner diameter of the barrel is equal to the diameter of the optical element material, and the preform is placed in the barrel without eccentricity before the pressure is applied.

Thereafter, the molded product was gradually cooled, and when the temperature of the molded portion reached 400 ° C., which was lower than the transition point of the preform, the pressure was removed and the molded product was taken out. The obtained molded product has good mold releasability because it does not receive any biased pressure with the body mold, there is no eccentricity, and the outer diameter of the molded product is the same as the desired value. There was no need to obtain a good lens.

[0023]

According to the method of the present invention, the inner diameter of the barrel mold and the diameter of the optical element material become equal at the molding temperature.
The optical element material fits evenly in the barrel mold, and an optical element having desired dimensions without uneven thickness and eccentricity can be obtained. Since an optical element having no eccentricity can be obtained, the centering step can be omitted in the subsequent steps, and the cost can be significantly reduced. In addition, uniform pressure is applied to the edge portion of the optical element material and the inner diameter of the body mold during molding, and there is no biased strong pressure, so no fusion occurs between the two, and the mold releasability is excellent. Molding is possible.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing a state of a molding portion before press molding of an optical element material.

FIG. 2 is a schematic explanatory view showing a state of a molding portion during press molding of an optical element material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper mold 2 Lower mold 3 Thin film 4 Body mold 5 Thickness adjusting member 6 Optical element material 7 Heater 8 Cylinder 9 Atmospheric gas supply port 10 Thermocouple

Claims (1)

(57) [Claims] 1. A method for molding an optical element, in which a material of an optical element is heated and softened and pressed between a pair of a molding die and a body die, the diameter of the optical element material before molding is set to the design of the optical element after molding. the same diameter, shows a design diameter of the optical elements in x, ₁ thermal expansion coefficient of the optical element material alpha, ₂ thermal expansion coefficient of the barrel-type material alpha, when a difference between the molding temperature and room temperature is T , Α ₁ > α _2, and the inner diameter dimension y of the body mold is a dimension calculated from the following equation: y = x (1 + α ₁ T) / (1 + α ₂ T). Molding method.