JP2003089532A - Method for molding optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for molding an optical element by which a desired molded article can be obtained from a molding die having the same dimension as that of the article. SOLUTION: The difference between the thermal shrinkage of the molded article and the thermal shrinkage of a die material is controlled to substantially zero or within the allowance for design so that the dimension of the pressed faces of the molded article at room temperature is made consistent with the dimension of the pressing faces of the die with high accuracy. Further, relaxation in the inner strain of the article is suppressed by releasing the article from the die immediately after pressing or by increasing the cooling rate. The release temperature is controlled by fixing the upper and lower dies with a releasing member 6 attached to the inner circumference of a barrel 3 in the axial direction of pressing and by using the heat shrinking of a perform material during cooling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of molding an optical element such as a lens or a prism by pressurizing the optical element with a molding die while hot.

[0002]

2. Description of the Related Art In a molding method of an optical element in which a high-precision optical element such as a lens or a prism is hot pressed by a molding die, conventionally, a molded product is separated from the mold in general. This is done by utilizing the difference in heat shrinkage. Therefore, in many cases, a material having a large difference in heat shrinkage between the molding die and the molded product is selected to accelerate the mold release.

[0003]

However, in such a method of molding an optical element, the size of the mold at room temperature and the size of the molded product differ by at least a difference in heat shrinkage. Therefore, even if molding is performed with a mold having a desired size of the molded product, the size of the molded product having a large heat shrinkage is reduced by the difference in the heat shrinkage.

Therefore, the dimensions of the molding die are corrected in advance,
A technique for obtaining a molded product of a desired size is, for example, Japanese Patent Registration No.
No. 72482, Japanese Patent Application Laid-Open No. 06-048750, and Japanese Patent Application Laid-Open No. 10-236838. However, this technique is a technique for correcting the size of the mold to obtain a molded product of a desired size.
It is not a method of obtaining a molded product having the same size as the mold at room temperature.

As described above, even if a mold having the same size as a molded product having a desired size is manufactured, the size of the molded product does not reach the desired size due to the difference in heat shrinkage between the mold and the molded product. .

Therefore, an object of the present invention is to obtain a molding method of an optical element capable of obtaining a desired molded product with a molding die having the same size as that of the molded product.

[0007]

In order to solve the above-mentioned problems, the present invention provides the following molding method.

A method for molding an optical element according to claim 1 is
The difference between the heat shrinkage ratio of the molded product and the heat shrinkage ratio of the mold material is set to be substantially zero or within the design tolerance, and the dimension of the pressed surface of the molded product and the dimension of the pressed surface of the mold at room temperature are The feature is that they are almost the same.

A method of molding an optical element according to a second aspect is
The thermal shrinkage of the molded article is controlled by at least one of the coefficient of thermal expansion or the timing of relaxation of internal strain of the molded article or the timing of mold release, and the difference between the thermal shrinkage rate of the molded article and the thermal shrinkage rate of the mold material. Is substantially zero or within the range of design tolerance, and the dimension of the pressed surface of the molded product and the dimension of the pressed surface of the molding die at room temperature are substantially matched.

A method for molding an optical element according to a third aspect is
The heat shrinkage rate of the preform material and the heat shrinkage rate of the mold in the temperature range from pressing to immediately after the release are respectively Δlp (p
d) and Δld (pd), where Δlp is the heat shrinkage rate of the preform material and Δlp is the heat shrinkage rate of the mold material in the temperature range from room temperature to the mold release temperature, respectively,
It is characterized in that the molding is performed at a mold material and a cooling rate such that (pd) + Δlp−Δld (pd) −Δld is zero or within an error range of design allowable dimensions.

In the present molding method, the thermal contraction rate is divided into two parts such as the temperature range from the press temperature to the mold release temperature and the temperature range from the mold release temperature to the room temperature, with the mold release temperature as a delimiter. The reason for considering is as follows.

The coefficient of thermal shrinkage is determined by the coefficient of thermal expansion of the material and the amount of strain relaxation. Of these, the coefficient of thermal expansion is a value specific to the material and therefore has temperature dependence, but is not affected by time or mold release temperature in the temperature range where self-weight deformation or the like does not occur. On the other hand, the relaxation amount of strain changes under the influence of time, temperature, and the magnitude of strain. The higher the temperature and the longer the time, the greater the amount of strain relaxation.

However, of course, if no strain is generated, the temperature is high (however, the temperature is lower than the temperature at which self-weight deformation occurs).
Even if it is kept for a long time, the strain will not be relieved. Therefore, as long as the mold is released, the molded product and the mold are separated,
Internal strain of the molded product is removed, and strain relaxation is substantially eliminated.

That is, the coefficient of thermal contraction before releasing greatly changes depending on the coefficient of thermal expansion, time, temperature, and strain, but the coefficient of thermal contraction after releasing is almost the same as the coefficient of thermal expansion alone. It is determined. In this way, the factors that affect the thermal contraction rate change greatly with the release temperature as the delimiter.

In consideration of this, if the heat shrinkage rate is controlled with the mold release temperature as a boundary, the cooling rate (temperature and time) and the mold release temperature change, and the temperature from the press temperature to the mold release temperature is changed. Even if the amount of strain relaxation varies greatly, the dimensions of the molded product and the molding die can be made highly accurate. For the above reason, it is necessary to consider the heat shrinkage rate by dividing the temperature range into two with the mold release temperature as a delimiter.

A method of molding an optical element according to a fourth aspect is
The pressing temperature of the preform material is Tp, the strain point temperature is Ts,
When the mold release temperature is Td, Tp ≧ Tz ≧ Ts and T
With the strain relief temperature Tz satisfying the relation of z> Td at the same time, the internal strain of the molded product is made substantially zero at least once, and the heat shrinkage rate of the preform material and the mold material from room temperature to the strain relief temperature Tz It is characterized by molding with a mold material having a difference of zero or within an error range of design allowable dimensions.

Here, the lower limit of the strain removal temperature Tz is the strain point temperature T
The reason why s is set is that in a region lower than the strain point temperature Ts, it takes at least 4 hours until the internal strain becomes substantially zero, which is difficult to industrially adopt. In addition, the strain removal temperature Tz
The reason why the internal strain of the molded product is substantially zero is that the difference between the heat shrinkage ratio of the preform material and the mold material from room temperature to the strain removal temperature Tz is zero or within the error range of the design allowable dimension. This is to expand the choices of.

A general glass material has a glass transition temperature (Tg), and the volume thereof rapidly increases in a temperature range higher than that. That is, the thermal contraction rate at the glass transition temperature Tg or higher becomes relatively large during cooling. When looking for a mold material having a value equivalent to this heat shrinkage rate, the options are limited.

If the internal strain of the molded product is made substantially zero at the strain relief temperature Tz, a mold material having a heat shrinkage ratio from the strain relief temperature Tz to room temperature may be selected, so that the strain strain temperature Tz can be set to a higher value. By approaching the glass transition temperature Tg, the choice of materials that can be used as the mold material increases. Further, in the present molding method, the temperature history from the pressing temperature to the strain removal temperature Tz does not affect the dimensions of the molded product, the dimensions of the molded product are stable, and the dimensions with the mold are more accurate. Get closer.

Further, the closer the de-straining temperature Tz is to the strain point temperature Ts, the longer the time required for molding, but the de-straining temperature Tz.
Since the relaxation amount of the internal strain in the temperature range from to the strain point temperature Ts is small, the dimensions of the molded product and the molding die finally match with high accuracy at room temperature.

A method of molding an optical element according to claim 5 is
The pressing temperature of the preform material is Tp, the strain point temperature is Ts,
When the mold release temperature is Td, Tp ≧ Tz ≧ Ts and T
At the strain removal temperature Tz that simultaneously satisfies the relationship of z> Td, the internal strain of the molded product is made substantially zero at least once, and the rapid cooling is performed in the temperature range from the strain removal temperature Tz to the strain point temperature Ts. Alternatively, by releasing the mold at a temperature as close as possible to the strain removal temperature Tz, the relaxation amount of the internal strain of the molded product is made substantially zero, and further, the heat shrinkage of the preform material and the mold material from room temperature to the strain removal temperature Tz. It is characterized by molding with a mold material whose difference from the ratio is zero or within the error range of the design allowable dimension.

The reason why the quenching is performed in the temperature range from the strain removal temperature Tz to the strain point temperature Ts or the mold is released at a temperature as close to the strain removal temperature Tz as possible is the strain removal temperature Tz.
This is to minimize the amount of relaxation of internal strain of the molded product that occurs in the temperature range from the mold release temperature to the mold release temperature. If the relaxation amount of this strain does not decrease, even if the thermal contraction rate in the temperature range from room temperature to the strain removal temperature Tz is matched between the molded product and the mold, if the temperature conditions change unexpectedly, the room temperature There will be a slight difference between the two dimensions and the difference will occur.

Then, by rapidly cooling the molded product,
The internal strain was removed by eliminating the time and temperature required for relaxing the internal strain, or by releasing the mold so that the relaxation of the strain itself would not occur. Also,
In the temperature range from the strain removal temperature Tz to the strain point temperature Ts, when the time required for sufficient removal of the internal strain is long, even if the internal strain is made substantially zero at a higher temperature and a shorter time, According to the molding method, a molded product having a more stable shape can be obtained, and as a result, the dimensions of the molded product and the molding die at room temperature come close to high precision.

The molding method described in claim 6 is characterized in that, in the invention described in any one of claims 1 to 5, the mold release is performed by thermal contraction of the preform material in the axial direction of the press. According to the molding method of claims 1 to 5, there are cases where the mold and the molded product are difficult to release from each other, that is, the molded product and the molded mold have the same coefficient of thermal expansion. By utilizing the heat shrinkage of the preform material in the press axis direction, the mold can be easily released.

According to the above-mentioned molding method, the dimension of the surface to be pressed of the molded product at room temperature and the dimension of the pressing surface of the molding die can be matched with high accuracy.

[0026]

1 (a) and 1 (b) are graphs showing the relationship between the temperature and the coefficient of thermal expansion of a preform material and a mold material. In FIGS. 1A and 1B, the temperature Th
And the size of the mold is the same and the temperature T
If the thermal contraction rate of the molded product in the temperature range ΔT from h to room temperature Tr is equal, even if the coefficient of thermal expansion of the molding die and the molded product during that time is different, the temperature Tr ( At room temperature), the dimensions of the pressing surface of the mold and the non-pressing surface of the molded product are almost equal.

That is, the closer the area Sp of the shaded portion shown in FIG. 1A and the area Sd of the shaded portion of FIG. 1B are, the closer the dimension of the molded article at room temperature is to the dimension of the mold. You may However, the thermal contraction rate of the molded product is affected by the relaxation amount of the internal strain in addition to the thermal expansion coefficient. The relaxation amount of the internal strain has a correlation between the temperature, the time, and the magnitude of the internal strain. Therefore, the value changes depending on the timing (temperature) of the mold release, the cooling process, or the like.

The fact that the relaxation amount of the internal strain varies depending on the release timing (temperature) will be specifically described below. First, regarding internal strain, there are two materials (molds and molded products) with different coefficients of thermal expansion, and when given a change in temperature for a certain period of time, they adhere closely without slipping. It is caused by being present.

This internal strain is the temperature range in which the molding material behaves from a viscous body to a viscoelastic body (in viscosity, log η =
If it is in the range of 14.5 (dPa · s) or more), it will be gradually relaxed with the passage of time, but if there is no close contact due to mold release, the internal strain itself that is gradually relaxed will be close to zero. Even if the temperature or time changes, the internal strain will not relax. Therefore, when the release timing changes, the time during which internal strain relaxation can occur also changes, and as a result, the amount of internal strain relaxation changes. For the above reasons, the amount of relaxation of internal strain varies depending on the timing of mold release.

For the same reason, if the cooling process is different,
Since the time it takes for the molded product that is in close contact with the mold to reach a certain temperature changes, naturally the amount of relaxation of internal strain also differs. For example, the higher the cooling rate, the smaller the relaxation amount of the internal strain in the temperature range in which the molding material behaves as a viscous body to a viscoelastic body.

In the temperature range in which the molding material behaves from a viscous body to a viscoelastic body, it is necessary to note that the relaxation amount of the internal strain of the molded product changes depending on the release timing (temperature) and the cooling process. There is. However, if the heat shrinkage rates of the molded product and the molding die are matched in consideration of this, the dimensions of the pressed surface of the molding die and the non-pressed surface of the molded product can be matched more accurately at room temperature.

FIG. 2 is a schematic vertical sectional view showing the mold structure of the press molding apparatus adopted in this embodiment. In the figure, reference numeral 1 is an upper molding die, and reference numeral 2 is a lower molding die. In this embodiment, hard carbon films are formed on the pressing surfaces of the upper and lower molds 1 and 2 in order to improve the mold releasability between the mold and the molded product. The materials of these molds 1 and 2 are not particularly limited as long as they have excellent heat resistance and the heat shrinkage ratio in the temperature range from the press temperature to room temperature is equal to the heat shrinkage ratio of the preform material. .

Reference numeral 3 is a barrel die for guiding the upper and lower molding dies 1, 2, and reference numeral 4 is a preform material. The material of the preform material is glass, metal, amorphous or There is no particular limitation as long as it exhibits viscous flow at a high temperature, such as plastic, but in this embodiment, a phosphoric acid-based extremely low softening glass (Tg = 350 ° C.) was used. Reference numerals 5A and 5B are temperature measurement points for controlling the temperatures of the upper and lower molds, and reference numeral 6 is a ring-shaped member for controlling the mold release temperature.

FIG. 3 is a graph showing the relationship between the thermal expansion coefficient and the temperature of the phosphoric acid-based extremely low softening glass used as the preform material, and FIG. 4 is the thermal expansion coefficient and the temperature of the aluminum alloy used as the mold material. It is a graph which shows the relationship of.
As shown in FIGS. 3 and 4, the value obtained by integrating the coefficient of thermal expansion, which is a function of temperature, with temperature in the temperature range from the press temperature to room temperature, that is, the areas Sp and Sd of the shaded portions in FIG.
The corresponding values are 0.0078 for the preform material and 0.0079 for the mold material, which are almost the same.

On the other hand, the heat shrinkage ratio (= dimension at room temperature / dimension at press temperature) is 99.2261% for preform material and 99.216 for mold material in the range of room temperature to pressing temperature.
It is 2%. If molding is performed with a combination of these preform materials and mold materials, the difference in the shape of the molded product per mm due to heat shrinkage (= dimension of molded product-dimension of mold) is 70 if it matches the shape
nm.

In a WC-based cemented carbide, which is a general mold material, the difference between the shape of the molded product and the mold per 1 mm (= the size of the molded product-the size of the mold) is 6 μm. According to the molding method, the difference in shape between the molded product and the mold is about 1/86
Becomes

However, in practice, since the internal strain of the molded product is relaxed in the temperature range from the press temperature to the mold release temperature, the difference between the shape of the molded product and the mold per 1 mm is set to the maximum value of 70 nm. Requires any of the following measures for the above-mentioned molding method.

(1) Release the mold immediately after pressing or increase the cooling rate as much as possible to reduce the relaxation amount of the internal strain of the molded product as much as possible.

(2) Molding is performed by selecting a mold material or a preform material in which the heat shrinkage of the molded product considering the relaxation of the internal strain of the molded product and the heat shrinkage of the molding die are approximately the same. At this time, in the temperature range in which the preform material exhibits viscosity to viscoelasticity, the relaxation amount of the internal strain of the molded product changes depending on the mold release temperature and the cooling process, and the thermal contraction rate of the molded product varies due to the influence. Attention must be paid to which value the heat shrinkage ratio of the preform material and the mold material should be matched.

(3) At a strain-reducing temperature lower than the pressing temperature and higher than the mold-releasing temperature, the internal strain is made substantially zero, and the heat-shrinkage of the molded product and the mold from the strain-relieving temperature to the room temperature. Equal to the rate. At this time, the time required for the internal strain to become substantially zero becomes longer, but the closer the strain relief temperature is to the strain point temperature, the closer the strain is, so that the amount of relaxation of the internal strain of the molded product decreases, which is effective. .

(4) The internal strain is made substantially zero at a strain-removing temperature lower than the pressing temperature and higher than the strain-point temperature, and the relaxation amount of the internal strain of the molded product from the strain-relieving temperature to the strain-point temperature is Release as much as possible at the strain relief temperature, or by quenching as much as possible in the temperature range from the strain relief temperature to the strain point, reduce as much as possible, and between the molded product and the mold in the temperature range from the strain relief temperature to room temperature. Equivalent to heat shrinkage.

When the methods (1) to (4) are adopted, the mold release temperature is controlled by fixing the upper and lower molds in the axial direction of the press with the ring-shaped mold releasing member 6 shown in FIG. It is preferable to use the heat shrinkage of the preform material during cooling. Alternatively, immediately after pressing, a mechanical tensile force may be applied to the mold interface of the preform material to release the preform material. by this,
The mold release temperature of the molded product is stable, the shape variation of the molded product is reduced, and as a result, the dimensions of the mold of the molded product at room temperature match with high accuracy.

Since the molding methods described in the above (1) to (4) have different effects, it is preferable to use them properly according to the required dimensional error between the molded product and the molding die required.

[0044]

As described in detail above, according to the optical element molding method of the present invention, an optical element molding method capable of easily reducing the difference between the size of the molding die and the size of the molded product can be obtained. You can

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the temperature and the coefficient of thermal expansion of a preform material and a mold material for explaining the method for molding an optical element of the present invention, (a) shows the case of the preform material,
(B) shows the case of a mold material.

FIG. 2 is a schematic vertical sectional view showing the structure of a molding apparatus used in the method for molding an optical element of the present invention.

FIG. 3 is a graph showing the relationship between the coefficient of thermal expansion and the temperature of a phosphoric acid-based extremely low-softening glass employed in the method for molding an optical element of the present invention.

FIG. 4 is a graph showing the relationship between the thermal expansion coefficient and the temperature of the aluminum alloy used in the method for molding an optical element of the present invention.

[Explanation of symbols]

1 Upper mold 2 Lower mold 3 body type 4 Preform material 5A, 5B Temperature measurement point 6 Release material

Claims (6)

[Claims] 1. In a method of molding an optical element in which a preformed material such as softened glass or an amorphous alloy is pressure-molded by a pair of upper and lower molding dies, a difference between a heat shrinkage ratio of a molded product and a heat shrinkage ratio of a mold material is calculated. A method of molding an optical element, wherein the size of the surface to be pressed of the molded product and the size of the pressing surface of the molding die at room temperature are made substantially equal to each other within a range of zero or a design tolerance. 2. A method of molding an optical element in which a preform material such as softened glass or an amorphous alloy is pressure-molded by a pair of upper and lower molding dies, and the thermal shrinkage rate or the thermal expansion coefficient of the molded article or the internal strain of the molded article. Control by at least one of the relaxation amount or the timing (temperature) of mold release, and the difference between the heat shrinkage rate of the molded product and the heat shrinkage rate of the mold material is substantially zero or within the design tolerance range. The method for molding an optical element is characterized in that the dimensions of the surface to be pressed of the molded product at room temperature and the dimensions of the pressing surface of the molding die are substantially the same. 3. A method of molding an optical element in which a preformed material such as softened glass or amorphous alloy is pressure-molded by a pair of upper and lower molding dies, and the heat shrinkage of the preform material in a temperature range from pressing to immediately after release. Rate and the heat shrinkage rate of the mold are Δlp (pd) and Δld, respectively.
(Pd) and Δlp and Δld are the heat shrinkage rate of the preform material and the heat shrinkage rate of the mold material in the temperature range from room temperature to the mold release temperature, respectively, Δlp (pd) + Δ
A molding method of an optical element, characterized in that molding is performed with a mold material and a cooling rate in which lp-Δld (pd) -Δld is zero or within an error range of a design allowable dimension. 4. In a method of molding an optical element in which a preform material such as softened glass or an amorphous alloy is pressure-molded by a pair of upper and lower molding dies, the press temperature of the preform material is Tp, the strain point temperature is Ts, and the separation temperature is Ts. Mold temperature is Td
In such a case, the internal strain of the molded product is substantially zero at least once at the strain removal temperature Tz that satisfies the relations of Tp ≧ Tz ≧ Ts and Tz> Td at the same time, and the temperature from the room temperature to the strain removal temperature Tz is increased. A method for molding an optical element, which comprises molding with a mold material in which a difference in heat shrinkage between the reform material and the mold material is zero or within an error range of a design allowable dimension. 5. A method of molding an optical element in which a preform material such as softened glass or an amorphous alloy is pressure-molded by a pair of upper and lower molding dies, the pressing temperature of the preform material is Tp, the strain point temperature is Ts, and the separation temperature is Ts. Mold temperature is Td
, The internal strain of the molded product is substantially zero at least once at the strain removal temperature Tz that satisfies the relations of Tp ≧ Tz ≧ Ts and Tz> Td at the same time, and the strain removal temperature Tz
To the strain point temperature Ts, or the mold is released at a temperature as close to the strain removal temperature Tz as possible to make the relaxation amount of the internal strain of the molded product substantially zero, and
A molding method of an optical element, characterized in that molding is performed with a mold material in which a difference in heat shrinkage between the preform material and the mold material from room temperature to the strain removal temperature Tz is zero or within an error range of a design allowable dimension. 6. The method for molding an optical element according to claim 1, wherein the molded product is released from the mold by thermal contraction of the preform material in the axial direction of the press.