JPH0757697B2 - Glass lens molding method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass lens molding direction for forming a glass lens used in an optical device by a precision glass molding method.

2. Description of the Related Art In recent years, many attempts have been made to form an optical lens by one-shot molding without a polishing step. The most efficient method is to cast a glass material from a molten state into a mold and perform pressure molding, but it is difficult to control the shrinkage of the glass during cooling and is not suitable for precise lens molding. Therefore, it is a general method to pre-process a glass material into a certain shape, supply it between molds, heat it, and press-mold it. (For example,
JP-A-58-84134, JP-A-60-200833, etc.) And, in the conventional example of JP-A-58-84134, a glass material having a volume smaller than the cavity volume is used. A method of molding a lens is disclosed. Also, in the molding method using a glass material having a volume smaller than the cavity volume, in the outer peripheral portion of the lens,
It is disclosed that an unrestricted free surface is formed on the mold, and as a result, the effect that burrs do not occur in the obtained lens is obtained.

Hereinafter, the conventional molding method described above will be described with reference to the drawings.

FIG. 5 is a sectional view showing a state where a lens is formed by molding a disk-shaped glass material by one of the conventional methods. 14 is a molded lens, 11 and 12 are a pair of upper and lower molds, and 13 is a barrel mold. Reference numeral 15 is a heater, and 16 and 17 are parts of a molding apparatus having a pressure mechanism. Heat the glass material into the mold
The mold and glass material are heated to a temperature near the softening point by 15, and pressure-molded by the upper and lower molds 11 and 12. After the deformation, the mold and the molded lens are gradually cooled, and when the temperature reaches the temperature at which the lens can be taken out, the mold is opened and the lens is taken out.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the method as described above, the temperature at which the glass used for optics can be molded is as high as 500 to 700 ° C., so that the heating of the mold and the glass material, heat molding, and cooling are constant. It takes a long time, and it takes a long time from the introduction of the glass material to the molding of the lens. As a result, there is a problem that the efficiency of the molding apparatus does not increase and the cost required for molding is high.

As a method for shortening the molding time of the lens, it has already been disclosed in
There is 62-292636. As shown in FIG. 6, this molding method comprises placing a molding block K in which a pair of upper and lower molds, a barrel mold and a glass material are integrated on a preheating stage S ₁ and after heating up to near the softening point on a molding stage S ₂ . It is transferred and deformed under pressure.
After that, a desired lens is formed by sequentially cooling while applying pressure in the cooling stages S ₃ and S ₄ . By using such a molding method, the molding time depends on the time of the stage in which the molding die stays for the longest, but the molding process can be divided, and the molding time is greatly shortened. However, since pressurization is required at the time of cooling, the structure of the molding machine is complicated, and at the same time, the cost becomes high, and a simpler molding method and molding apparatus have been demanded.

Means for Solving the Problems To mold the glass lens of the present invention to solve the above problems, a pair of upper and lower molds, in a cavity composed of a barrel mold, a glass material of a volume equal to or less than the cavity volume As a molding block, the molding block is heated and then pressure-molded, and the molding block is heated at a preheating stage in a molding method of forming a desired glass lens by cooling to a glass transition point of the glass material. , After pressing and deforming the upper mold by pressurizing the upper mold until the pressing head of the molding machine contacts the main plane of the barrel mold at the molding stage, the molding is performed by the pressing head at the cooling stage. A state in which the upper and lower molds are slidable in the barrel mold so as to be able to come into contact with each other while following the heat contraction of the pressure-deformed glass lens without pressing the block. It is said that it cools with.

As shown in FIG. 7, the structure of the molding die in the case of molding while transferring the molding die according to the conventional method as shown in FIG. 6 has a thermal expansion coefficient smaller than that of the glass material 5 and that of the body material 3 and the glass material 5. A barrel holder 4 having a large expansion coefficient is provided, and a pair of upper and lower molds 1 and 2 are fitted in the barrel mold 3. Then, the barrel die 3 forms the glass lens barrel and regulates the deviation of the optical axes of the upper and lower optical surfaces, and the upper and lower flange portions 1a are brought into contact with the main plane 4a of the barrel die holder 4 so that the glass material 5 The thickness and the inclination of the upper and lower optical surfaces are regulated. Further, the body-shaped holder 4 has a coefficient of thermal expansion larger than that of the glass material so that the pressure of the pressure head 6 is sufficiently applied to the transfer surface of the glass material during cooling. However, as shown in FIG. 8, the optical material expands abnormally when the glass transition temperature (Tg) is exceeded, and the glass deformation temperature (A
In the vicinity of t), there is a region Z2 where the expansion coefficient of the glass material is larger than that of the barrel holder. Therefore, the body type holder 4
In this mold structure, in which the upper mold flange portion 1a abuts the main plane 4a of the upper mold, the transfer surfaces of the upper and lower molds cannot follow the contraction of the glass material 5 in the region, and the transferability is temporarily impaired. In the region Z1 where the thermal expansion of the mold holder 4 exceeds the thermal expansion of the glass material 5, sufficient pressure is applied to the optical surface of the glass material 5 again until the press is released, and good transferability is obtained. It was Therefore, pressurization at the time of cooling is indispensable, and a pressurizing mechanism is required even in the cooling stage of the molding apparatus. We used a mold that allows the entire upper and lower molds to be inserted into the barrel mold, and by pressurizing and deforming the pressure head of the molding machine into contact with the main plane of the barrel mold at the molding stage. It was found that good transferability can be obtained without applying pressure during cooling, and the molding method according to the present invention was made possible.

Advantageous Effects of Invention According to the invention of the present application, the thickness of the glass lens can be accurately controlled by "contacting the pressing head with the main plane of the body" by the above means, and "the upper and lower molds press at the cooling stage. It cools in a slidable state in the barrel mold so that it can contact and follow the heat contraction of the deformed glass lens. "
This allows the upper and lower molds to always follow the heat contraction of the glass lens even during heat contraction during cooling and adhere to the glass lens, resulting in extremely high precision of the shape and dimensional accuracy of the molding surface. It is possible to maintain the glass lens so that an excellent glass lens can be molded.

Examples Hereinafter, one example of the glass lens molding method of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the structure of a lens molding die in one embodiment of the present invention.

Reference numerals 1 and 2 are a pair of upper and lower molds, 3 is a body mold, and 4 is a glass material. The outer diameters of the upper and lower dies 1 and 2 are smaller than the inner diameter of the barrel die 3, and when the pressure deformation is completed, the pressing surface of the upper die 1 and the main plane of the barrel die 3 are flush with each other. At this time, the size of the body mold 3 is determined so that the center thickness of the glass material 4 has a predetermined size. The body mold 3 regulates the thickness of the glass material,
The upper and lower molds 1 and 2 serve to regulate the axial misalignment of the optical surfaces and form the ridges of the glass material, and by bringing the pressure head 6 into contact with the main plane 3a of the body mold 3, It works to regulate the tilt of the optical axis of the optical surface. With such a mold configuration, the upper mold 1 can freely move without being vertically displaced by the body mold 3, and can smoothly respond to the shrinkage of the glass material, so that the upper mold 1 can be heated during cooling. Good transferability can be maintained without pressure. In the present embodiment, both the upper and lower molds are slidable in the body mold 3, so that neither flange portion is formed.

The reason why not only the upper mold but also the lower mold can be slid in the barrel mold 3 is as shown in FIG. 5 and as will be described later, the barrel mold is the ridge (outer peripheral portion) of the molded lens. Has the function of forming In other words, the outer peripheral surface of the lens is usually formed in close contact with the inner wall surface of the barrel die.

When formed in this way, in the cooling process of the molded lens, the contact surface between the molded lens and the mold is the largest as shown in FIG.
First, heat is carried away in the thickness direction of the lens at the center of the lens.

As a result, the molded lens first undergoes thermal contraction in its thickness direction. At the stage when the heat contraction in the thickness direction starts, the heat contraction in the diametrical direction of the lens hardly occurs, so the molded lens remains in close contact with the barrel mold and is retained. Even if the weight of the upper die or the weight of the molded lens itself, the position does not move.

On the other hand, the contact surface of the molded lens with the lower mold moves a slight amount upward due to the heat shrinkage in the thickness direction.

In order to keep the lower mold in close contact with the molded lens by following this movement amount, the lower mold needs to be slidable in the body mold 3.

In the present invention, when the molded lens is heat-shrinked in the thickness direction, the lower mold is brought into close contact with the molded lens and moved upward by a small amount. It is presumed that it is obtained by the adhesive force between the mold and the molded lens glass.

Next, a molding method using the molding die will be described in detail.

FIG. 2 shows the flow of lens molding in one embodiment of the present invention, where K is a molding block in which a molding die and a glass material are integrally formed, as described above (FIG. 1).
The figure shows the temperature over time in the molding process. FIG. 3 (a) shows the temperature change of this embodiment, and FIG. 3 (b) shows the temperature change of the conventional example for comparison. T1 is the temperature at which the pressure changes. The solid line shows the temperature of the forming block, and the broken line shows the temperature of each stage.

The temperatures of the preheating stage S ₁ and the pressure forming stage S 2 in FIG. ₂ are maintained at the temperature T1 required for forming glass. The temperature of the cooling stage S ₃ is kept at the temperature T 2 at which the glass solidifies. It is desirable to keep T2 at or below the glass transition temperature Tg. The temperature of the cooling stage S ₄ is maintained at the cooling end temperature T 3. Next, the glass forming process will be described.

First, the forming block K is preheated as shown in FIG.
Place it on S ₁ . Temperature of the molding block K in FIG. 3 (a) as shown in the time t after ₁ becomes T1. Therefore, the molding block K
Is quickly sent to the molding stage S ₂ and pressure is applied for t ₂ hours to cause the glass to be molded and molding is performed. Immediately after the deformation is completed, the molding block K is sent to the cooling stage S ₃ to be cooled, and after t ₃ hours, when the temperature of the glass becomes the glass transition temperature T 2 or less, it is transferred to the cooling stage S ₄ and the mold after t ₄ hours The molding is finished when the temperature is cooled down to a handleable temperature T ₃ .

The above description is for one forming block, but when the first forming block moves to the forming stage S ₂ , the next forming block is placed on the preheating stage S ₁ and the forming blocks are sequentially and continuously fed. With this, continuous molding can be performed based on the longest time among t ₁ , t ₂ , t ₃ , and t ₄ .

On the other hand, for comparison, a conventional example not having a plurality of stages will be described with reference to FIG. The molding block temperature is set to T1 after t ₁₀ hours after the molding block is put on the molding stage in advance.
When the temperature reaches, pressure molding is performed, and after the deformation is completed at t ₁₁ hours, the heating of the molding stage is stopped and the material is gradually cooled. When the temperature reaches T3 ₁₂ hours after t, pressurization is terminated and the molded lens is taken out. With this method, only one lens can be molded in (t ₁₀ + t ₁₁ + t ₁₂ ) time.

In the molding apparatus as shown in FIG. 5, since the molding die is fixed to the molding apparatus, the cycle of preheating, molding and cooling follows the same process as in FIG. 3 (b).

The deformation time t ₂ in the present invention and the deformation time t in the conventional example
_{Since 11} is essentially the same, t ₂ <(t ₁₀ + t ₁₁ +
t ₁₂ ) is clear. Generally, preheating time t
_{It can be said that 10} and the cooling time t ₁₂ are much longer than the pressure molding time t ₁₁ , and the time required for molding depends on the preheating and cooling times. Therefore, in order to minimize the molding time according to the present invention, the preheating / cooling stage may be divided into a plurality of stages and the time spent in each stage may be adjusted to the deformation time t ₂ in the pressure molding stage. This makes it possible to mold the lens at each deformation time t ₂ .

The above is shown in the second embodiment in which the lens is actually molded. As shown in FIG. 4, in order to match the preheating and cooling times with the deformation time, each was divided into two stages. SF-6 was used as the glass material, and a convex lens having an outer diameter of 15 mm and a thickness of 3 mm was molded. Preheating stages S ₀ , S ₁ and forming stage S
The temperature T1 of ₂ is set to 500 ° C and the temperature T2 of the cooling stage S ₃ is set to 350 ° C.
° C., the temperature T3 of the cooling stage S ₄ was water cooled (not shown) so that it can cool in a short time to a temperature which can be taken out molding outside the mold. By setting the temperature and the stage configuration as described above, the time the mold stays in each stage can be matched with the glass deformation time in the molding stage S _2, and the lens can be molded every minute. The optical surface of the molded lens faithfully transferred the shape of the molding die.

In this embodiment, the preheating and cooling stages are divided into two. However, if the size of the lens is large, it takes a longer time for preheating and cooling, and to shorten the molding time, the number of preheating and cooling stages is increased. It goes without saying that it is necessary to increase it.

EFFECTS OF THE INVENTION According to the present invention, (1) the pressure head is brought into contact with the main plane of the barrel mold in the lens molding step, so that the height difference between the barrel mold and the upper and lower molds causes The desired lens center thickness can be realized stably and with high accuracy.

(2) The upper and lower molds can always be in close contact with the glass lens even when the lens is heat-shrinked during the cooling process of the molded lens, so that the accuracy of the transfer surface can be maintained with high accuracy and a high quality glass lens Can be molded.

(3) Since the pressurizing mechanism at the time of cooling is unnecessary, the device for carrying out the present invention can have a very simple structure.

Has the effect of saying.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a molding die used in one embodiment of the present invention, FIG. 2 is a schematic view showing the flow of a lens molding method in one embodiment of the present invention, and FIG. )
(B) is a graph showing the transition of temperature in the molding process, FIG. 4 is a schematic diagram showing the flow of the lens in the second embodiment of the present invention, and FIG. 5 is a cross section showing the molding state of the glass lens by the conventional method. FIG. 6 is a schematic diagram showing the flow of a conventional lens molding method, and FIG. 7 is a sectional view showing a conventional mold structure.
FIG. 8 is a graph showing the thermal expansion of the glass material and the body holder. 1,2,11,12 …… Molding die, 1a, 2a …… Flange part, 3,4,13…
… Body type, 3a, 4a …… Body type main plane, 4,5 …… Glass material, 6,
7 ... Pressure head, 14 ... Molded lens, 15 ... Heater, 16,17 ... Molding device, K ... Molding block, S ₀ , S ₁ , S
₂ , S ₃ , S ₄・ ・ ・ Each stage of the molding machine.

Claims (1)

[Claims] 1. A molding block in which a glass material having a volume equal to or smaller than the cavity volume is arranged in a cavity formed by a pair of upper and lower molds and a barrel mold, and the molding block is heated and pressure-molded, In the molding method for forming a desired glass lens by cooling to the glass transition point of the glass material, the temperature of the molding block is raised in the preheating stage,
In the molding stage, the upper die is pressed to deform the glass material until the pressure head of the molding machine comes into contact with the main plane of the barrel mold, and in the cooling stage, the molding head is pressed by the pressure head. The glass is characterized in that the upper and lower molds are cooled in a slidable state within the barrel mold so that the upper and lower molds can come into contact with each other while following the thermal contraction of the glass lens that has been deformed under pressure. Lens molding method.