JP4972760B2 - Optical element manufacturing method - Google Patents

Description

The present invention relates to a method of manufacturing an optical element, in particular, it relates to a manufacturing method for manufacturing an optical element made of amorphous polyolefin resin.

  In recent years, various small and light resin lenses have been developed due to the development of resin materials and injection molding technology, and the demand for optical elements such as optical pickup devices and mobile phones is increasing. In particular, amorphous polyolefin resins have excellent transparency, high optical homogeneity (low birefringence), and favorable properties for transfer of fine shapes. It is a material suitable for molding optical elements such as lenses having performance (see Patent Document 1).

  However, since the material strength of amorphous polyolefin resin is low, cracks may occur due to residual stress generated in the molded product during the pressure-holding process or cooling process after filling the resin molding space during injection molding. However, the surface shape is distorted or the birefringence is increased.

On the other hand, in resin molding, shortening of the molding cycle (high cycle) is required, and it is important to meet this type of request. Even if the molding accuracy is improved by some means, it is not necessarily a preferable means as long as the high cycle is impaired.
Japanese Patent Laid-Open No. 2002-22907

Accordingly, an object of the present invention is to improve the transferability by reducing the residual stress generated in the molded product, and to effectively prevent the occurrence of cracks in the molded product, and without impairing the high cycle. An object of the present invention is to provide a method for manufacturing an optical element .

In order to achieve the above object, a method for manufacturing an optical element according to a first embodiment is a combination of a mold core for molding an optical surface and a mold cavity arranged so as to surround the mold core. The mold core is formed by injection molding an optical element made of an amorphous polyolefin resin using an injection mold in which a surface constituting a resin molding space is formed by a heat insulating material. In the manufacturing method, the heat insulating material is formed of a titanium alloy or stainless steel , and when the filling step for filling the molten amorphous polyolefin resin into the resin molding space in the mold is completed, It is characterized in that the surface temperature of the mold member constituting the resin molding space is maintained at or above the glass transition temperature of the amorphous polyolefin resin. The mold core may be composed of only a heat insulating material, or may be provided with a core mold that holds the heat insulating material.

In the method for manufacturing an optical element according to the first embodiment, a mold core for molding an optical surface has a surface forming a resin molding space formed of a heat insulating material, and a molten amorphous polyolefin resin is a resin. temperature and the for the surface temperature of the resin molding space is maintained above the glass transition temperature of the amorphous polyolefin resin, the surface portion (skin layer) and the central portion of the filled resin when filled in the molding space The difference is small, and the residual stress generated in the subsequent pressure holding process and cooling process is reduced. Accordingly, the transferability is improved, and problems such as cracks in the molded product, distortions in the surface shape of the molded product, and increased birefringence can be prevented. In particular, the transfer properties of special smooth surfaces and fine shapes are improved.

The method of manufacturing an optical element according to the second embodiment is configured by combining a mold core for molding an optical surface and a mold cavity arranged so as to surround the mold core, and the mold The core is provided with a heat insulating material, and an optical element made of an amorphous polyolefin resin is injection-molded by using an injection mold in which a surface constituting the resin molding space is formed of another material on the surface of the heat insulating material. A method of manufacturing an optical element, wherein the heat insulating material is formed of a titanium alloy or stainless steel, and includes a filling step for filling the molten amorphous polyolefin resin into the resin molding space in a mold. When completed, the surface temperature of the mold member constituting the resin molding space is maintained at a temperature equal to or higher than the glass transition temperature of the amorphous polyolefin resin. The mold core may be constituted only by a heat insulating material and a resin molding space constituting surface, or may be provided with a core mold for holding the heat insulating material.

In the method of manufacturing an optical element according to the second aspect, the mold core for molding the optical surface is provided with a heat insulating material, and the molten amorphous polyolefin resin is filled in the resin molding space. Since the surface temperature of the resin molding space is kept above the glass transition temperature of the amorphous polyolefin resin, the pressure holding step and the cooling step after the filling step are the same as in the manufacturing method of the optical element according to the first embodiment. Residual stress generated in the process is reduced, transferability is improved, and cracks in the molded product, distortion in the surface shape of the molded product, and increased birefringence can be prevented. In particular, the transfer properties of special smooth surfaces and fine shapes are improved.

In the optical element manufacturing method according to the first and second embodiments , at least the moving-side mold and the fixed-side mold are in close contact to form the resin molding space, and the moving-side mold and the fixed-side mold are respectively The mold core and the mold cavity can be combined.

Moreover, it is preferable that the heat conductivity of the said heat insulating material is 20 W / m * K or less.

In the optical element manufacturing method according to the first and second embodiments, the amorphous polyolefin resin may be a mixture of a plurality of components having different glass transition temperatures. In this case, it is preferable to keep the surface temperature of the mold member above the highest glass transition temperature among a plurality of components.

Embodiments of an optical element manufacturing method according to the present invention will be described below with reference to the accompanying drawings.

(Configuration of mold, see FIGS. 1-7)
First, the configuration of various injection molds used in the method for manufacturing an optical element according to the present invention will be described. 1 to 7, common members are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 shows a first example, and this mold 1 </ b> A includes a movable mold 10 and a fixed mold 20. The movable-side mold 10 includes a uniformly solid template 11, a uniformly solid core mold 12, a heat insulating material 14, and a surface processing layer 15. The fixed-side mold 20 includes a uniformly solid mold plate 21, a uniformly solid core mold 22, a heat insulating material 24, and a surface processed layer 25. The surface processed layers 15 and 25 are finished corresponding to a predetermined shape of a molded product such as a lens, and constitute a resin molding space 30. The core molds 12 and 22, the heat insulating materials 14 and 24, and the surface processed layer 25 are referred to as mold cores, and the mold plates 11 and 21 are referred to as mold cavities.

The mold plates 11 and 21 and the core molds 12 and 22 are made of a normal mold base material, for example, a metal material such as carbon steel or stainless steel. The heat insulating materials 14 and 24 are ceramics sprayed on the core molds 12 and 22, organic materials (heat-resistant polymer) such as polyimide resin, sintered ceramics that are low thermal conductive materials, titanium alloys (Ti-6Al-4V, Ti-3Al-2.5V, Ti-6Al-7Nb, etc.), cermet (aluminum titanate, TiO ₂ -Al ₂ O ₃ ), stainless steel (ferrite, austenite, etc.), nickel alloy (Inconel, FeNi), etc. It is formed by. As the ceramic, zirconia, silicon nitride, titanium nitride, or the like can be used. The surface processed layers 15 and 25 are formed on the heat insulating materials 14 and 24 by plating a non-ferrous metal material, for example, nickel.

  The heat insulating materials 14 and 24 are not limited to the above-described materials, and are materials having a lower thermal conductivity than the mold plates 11 and 21 and the core molds 12 and 22, for example, a thermal conductivity of 20 W / m · Any material may be used as long as it is K or less.

  FIG. 2 shows a second example. In the mold 1B, the surfaces of the heat insulating materials 14 and 24 are surface processed surfaces. For the heat insulating materials 14 and 24, for example, a heat resistant polymer such as polyimide resin is used. Other members and their materials are the same as those of the mold 1A as the first example.

  FIG. 3 shows a third example. In this mold 1C, the heat insulating materials 14 and 24 are formed of a relatively thick sintered ceramic. Other members and their materials are the same as those of the mold 1A as the first example.

  FIG. 4 shows a fourth example. In this mold 1D, the surface processed layer 25 has a fine shape for transferring the diffraction grating onto the surface of the molded product. Other members and their materials are the same as those of the mold 1A as the first example.

  FIG. 5 shows a fifth example. In this mold 1E, both of the surface processed layers 15 and 25 are formed with fine shapes for transferring the diffraction grating onto the surface of the molded product. Other members and their materials are the same as those of the mold 1A as the first example.

  FIG. 6 shows a sixth example. In this mold 1F, the mold core is composed of the heat insulating materials 14, 24 and the surface processed layers 15, 25. The materials of the heat insulating materials 14 and 24 and the surface processed layers 15 and 25 are the same as those of the mold 1A as the first example. The other members and their materials are the same as those of the mold 1A.

  FIG. 7 shows a seventh example. In the mold 1G, the mold core is composed of only the heat insulating materials 14 and 24, and the surfaces of the heat insulating materials 14 and 24 are the surface processed surfaces. For the heat insulating materials 14 and 24, for example, a heat resistant polymer such as polyimide resin is used. Other members and their materials are the same as those of the mold 1A as the first example.

(Refer to Example of manufacturing method, FIG. 8 and FIG. 9)
The manufacturing method according to the present invention will be described with reference to FIGS. FIG. 8 shows changes in the temperature and pressure of the resin in the mold along the time (horizontal axis). FIG. 9 shows the temperature distribution of the molded product at the completion of filling (see curve e) and the temperature distribution of the molded product at the time of mold release (see curve f) when the molded product is removed from the mold.

  First, the amorphous polyolefin resin melted at a predetermined temperature is filled into the resin molding space 30, and immediately after the filling is completed, the pressure holding process is started. The pressure holding step is a step of maintaining a predetermined pressure on the resin in order to compensate for the amount of shrinkage of the resin filled in the resin molding space 30 due to a decrease in temperature. After the pressure holding step, the cooling step (natural cooling) is entered. In FIG. 8, a curve a indicates a change in resin pressure in the resin molding space 30.

  The surface temperature of the resin filled in the resin molding space 30 changes as shown by a curve b, and the center temperature of the resin changes as shown by a curve c. The surface temperature of the resin molding space 30 when the amorphous polyolefin resin is filled in the resin molding space 30 (that is, the surface temperature of the filled resin, see point A in FIG. 8) is the glass of the amorphous polyolefin resin. Above the transition temperature.

  Thus, since the surface temperature of the resin molding space 30 when the amorphous polyolefin resin is filled in the resin molding space 30 is maintained at or above the glass transition temperature of the resin, the surface portion of the filled resin ( The temperature difference B between the skin layer) and the central portion is small, and the residual stress in the pressure holding process and the cooling process is reduced. Accordingly, it is possible to prevent problems such as cracks in the molded product, distortions in the surface shape, and increased birefringence. In addition, transferability of smooth surfaces and fine shapes is improved.

  The reason why the surface temperature of the resin molding space 30 when the resin is filled in the resin molding space 30 is equal to or higher than the glass transition temperature is that the heat insulating materials 14 and 24 are arranged around the resin molding space 30.

  Incidentally, specific examples of the glass transition temperature of the amorphous polyolefin resin are, for example, 139 ° C for ZEONEX and E48R manufactured by Nippon Zeon, and 123 ° C for ZEONEX and 330R. Further, APEL and APL5014 manufactured by Mitsui Petrochemical Industries, Ltd. are 135 ° C., and ARTON and FX4727 manufactured by JSR are 125 ° C.

  In some cases, the amorphous polyolefin resin is a mixture of a plurality of components having different glass transition temperatures. In this case, the surface temperature of the resin molding space 30 when the amorphous polyolefin resin is filled in the resin molding space 30 may be kept above the highest glass transition temperature.

  On the other hand, a curve d shown in FIG. 8 represents a change in the surface temperature of the amorphous polyolefin resin in the conventional example in which a heat insulating material is not provided in the mold. In this case, the surface temperature of the resin when the resin molding space 30 is filled is a point A ′ in FIG. 8, and the temperature difference B ′ between the surface portion and the central portion of the resin is relatively large. In the case of an amorphous polyolefin resin having a low material strength, the temperature difference B 'causes cracks in the molded product due to residual stress, distortion in the surface shape, and increased birefringence. In the present invention, such a problem can be prevented.

  In FIG. 9, a curve e indicates the temperature distribution of the molded product when filling is completed. The surface temperature of the molded product at the completion of filling is a point A on the curve e, and is kept at the glass transition temperature or higher.

  The molded product can be taken out from the mold at least when the surface of the molded product is lowered to a temperature equal to or lower than the heat deformation temperature, and this time is shown in FIGS. The curve f in FIG. 9 shows the temperature distribution of the molded product at the time of mold release, and the surface temperature of the molded product at the time of mold release is a point C on the curve f, which is below the mold release possible temperature.

  On the other hand, for comparison, FIG. 10 shows a temperature distribution of a molded product in a conventional example in which a heat insulating material is not provided in a mold. Curve e 'represents the temperature distribution of the molded product at the completion of filling, and curve f' represents the temperature distribution of the molded product at the time of mold release. As is apparent from the curves e 'and f', the surface temperature of the molded product at the completion of filling corresponds to the mold setting temperature and is equal to or lower than the glass transition temperature.

(Molding cycle)
In the production method according to the present invention described above, maintaining the surface temperature of the resin molding space when the amorphous polyolefin resin is filled in the resin molding space is equal to or higher than the glass transition temperature of the resin. This is achieved by placing thermal insulation around.

Keeping the surface temperature of the resin molding space above the glass transition temperature of the resin at the time of filling is not limited to the production method of the present invention, for example, a method of forcibly heating the mold to a higher temperature (heat cycle molding) It is conceivable to employ a method of covering a member constituting the resin molding space with a bulk material having a large heat capacity.

  However, keeping the surface of the resin molding space at the glass transition temperature at the time of filling by forcibly heating the mold requires a forced cooling step before taking out the molded product after the pressure-holding step, which takes time. However, the high cycle is impaired. Also, in the method using a bulk material, since it takes time to cool the bulk material, the high cycle is similarly impaired.

  On the other hand, the present invention enables preferable temperature control only by providing a heat insulating material in the mold, and it takes a short time until the molded article is lowered to a temperature at which the molded product can be taken out. Absent.

(Other examples)
In addition, the manufacturing method of the optical element which concerns on this invention is not limited to the said Example, It can change variously within the range of the summary.

  In particular, the details of the mold structure are arbitrary, and it is needless to say that the specific materials shown in the above-described embodiments are examples. 1 to 7, the mold 10 may be a fixed side, and the mold 20 may be a movable side. Alternatively, it may be a sleep rate type molding die provided with an intermediate die member.

It is sectional drawing which shows the 1st example of the metal mold | die used with the manufacturing method which concerns on this invention. It is sectional drawing which shows the 2nd example of the metal mold | die used with the manufacturing method which concerns on this invention. It is sectional drawing which shows the 3rd example of the metal mold | die used with the manufacturing method which concerns on this invention. It is sectional drawing which shows the 4th example of the metal mold | die used with the manufacturing method which concerns on this invention. It is sectional drawing which shows the 5th example of the metal mold | die used with the manufacturing method which concerns on this invention. It is sectional drawing which shows the 6th example of the metal mold | die used with the manufacturing method which concerns on this invention. It is sectional drawing which shows the 7th example of the metal mold | die used with the manufacturing method which concerns on this invention. It is a graph which shows the temperature of the resin in a metal mold | die, and the change of a pressure in the manufacturing method which concerns on this invention. It is a graph which shows the temperature distribution of the molded article in a metal mold | die in the manufacturing method which concerns on this invention. It is a graph which shows the temperature distribution of the molded article in a metal mold | die in the conventional shaping | molding method.

DESCRIPTION OF SYMBOLS 1A-1G ... Metal mold | die 11,21 ... Template 12,22 ... Core type | mold 14,24 ... Thermal insulation 15,25 ... Surface processed layer 30 ... Resin molding space

Claims (7)

A mold core for molding an optical surface and a mold cavity arranged so as to surround the mold core are combined, and the mold core has a surface that forms a resin molding space by a heat insulating material. An optical element manufacturing method for injection molding an optical element made of an amorphous polyolefin resin using a formed injection mold,
The heat insulating material is formed of titanium alloy or stainless steel,
At the completion of the filling process for filling the molten amorphous polyolefin resin into the resin molding space in the mold, the surface temperature of the mold member constituting the resin molding space is changed to a glass transition of the amorphous polyolefin resin. Keep above the point temperature,
A method for producing an optical element characterized by the above. A mold core for molding an optical surface and a mold cavity arranged so as to surround the mold core are combined, and the mold core includes a heat insulating material, and is provided on the surface of the heat insulating material. A method of manufacturing an optical element, wherein an optical element made of an amorphous polyolefin resin is injection-molded using an injection mold in which a surface constituting a resin molding space is formed of another material,
The heat insulating material is formed of titanium alloy or stainless steel,
At the completion of the filling process for filling the molten amorphous polyolefin resin into the resin molding space in the mold, the surface temperature of the mold member constituting the resin molding space is changed to a glass transition of the amorphous polyolefin resin. Keep above the point temperature,
A method for producing an optical element characterized by the above.   The method for producing an optical element according to claim 1 or 2, wherein the amorphous polyolefin resin is a mixture of a plurality of components each having a different glass transition temperature.   The method for manufacturing an optical element according to claim 3, wherein the surface temperature of the mold member is maintained at a temperature equal to or higher than the highest glass transition temperature among the plurality of components.   The method of manufacturing an optical element according to claim 1, wherein the mold core includes a core mold that holds the heat insulating material.   At least the moving mold and the fixed mold are in close contact to form the resin molding space, and the moving mold and the fixed mold are each configured by combining the mold core and the mold cavity. 6. The method of manufacturing an optical element according to claim 1, wherein   The method of manufacturing an optical element according to claim 1, wherein the heat conductivity of the heat insulating material is 20 W / m · K or less.

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