Patent Application
20050285287
This application is based on Japanese Patent Application No. 2004-191837 filed on Jun. 29, 2004, the content of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to an injection mold and a method for molding an optical element, and more particularly to an injection mold for molding a small and light optical element, such as a lens, an optical waveguide, etc., and a method for molding an optical element.
2. Description of Related Art
In recent years, with improvement of resin materials and injection molding techniques, various kinds of small and light lenses, prism plates and optical waveguides have been developed, and a demand for use of these optical elements for optical pick-up devices and portable telephones has been stronger. In order to produce such optical elements, molds which permit accurate transfer of fine configurations for diffraction, fine configurations for prism surfaces, blaze surfaces, etc. and smooth surfaces are required.
In order to achieve high accuracy transfer, Japanese Patent Laid-Open Publication No. 2002-96335 suggests a mold 50 as shown by
Since the mold 50 has a heat insulating layer 53 in the rear of the fine configuration (blaze surface 54a), the heat retaining property of the blaze surface 54a is improved, and it is possible to transfer the fine configuration to a molded product at high accuracy. However, at an area 51a next to the blaze surface 54a, the mold base 51, which has a relatively high coefficient of thermal conductivity, is exposed. Therefore, in this area 51a, heat radiation from melted resin injected into the cavity 60 is large, and it has been found that this influences the transfer accuracy of the fine configuration.
An object of the present invention is to provide an injection mold and an optical element molding method which permit a further improvement in transfer accuracy of a fine configuration.
In order to achieve the object, a first aspect of the present invention provides an injection mold for molding an optical element out of resin comprising a heat insulating layer between a core base and a surface processed layer, wherein a mold base forming a cavity to be filled with resin comprises at least a part made of a heat insulating material, the part being adjacent to the surface processed layer.
The second aspect of the present invention provides a method for injection molding an optical element out of resin by use of an injection mold comprising at least a movable mold and a fixed mold, wherein the injection mold comprises a heat insulating layer between a core base and a surface processed layer, and a mold base forming a cavity to be filled with resin comprises at least a part made of a heat insulating material, the part being adjacent to the surface processed layer.
According to the first and second aspects of the present invention, the mold base may be wholly made of a heat insulating material, or alternatively, a heat insulator may be provided between the mold base and the surface processed layer. The heat insulating material and the heat insulator are, for example, stainless steel, titanium alloy, nickel alloy, ceramic or heat resistance resin.
According to the first and second aspects of the present invention, since a heat insulating layer is provided between the core base and the surface processed layer, the temperature of resin injected into the cavity can be kept well, and the transfer accuracy of especially a fine configuration formed on the surface processed layer is improved. Further, since the part of a mold base which is adjacent to the surface processed layer is made of a heat insulating material, heat radiation from resin around the fine configuration is inhibited, and the transfer accuracy of the fine configuration is further improved.
This and other objects and features of the present invention will be apparent from the following description with reference to the accompanying drawings, in which:
Preferred embodiments of an injection mold and an optical element molding method according to the present invention are hereinafter described with reference to the accompanying drawings. In the drawings showing the respective embodiments, the same parts/members are denoted by the same reference numbers, and repetitious descriptions are avoided.
The surface processed layer 14 is finished in accordance with the configuration of an optical surface of a product (optical element), such as a lens, a mirror, a prism plate, an optical waveguide, etc., and a fine configuration 14a, such as a diffraction grating, a prism surface, a blaze surface, etc., is formed. A cavity 30 is formed of the surface processed layer 14 and internal surfaces of the bases 21 and 11.
The bases 12 and 21 are made of a material usually used for mold bases, such as metal, for example, carbon steel, stainless steel or the like. The coefficient of thermal conductivity of carbon steel is 50 W/mK, and the coefficient of thermal conductivity of martensite stainless steel is 27 W/mK.
On the other hand, the base 11 is made of a heat insulating material. Here, for the base 11, various materials with lower coefficients of thermal conductivity than that of the material of the bases 12 and 21 are usable. For example, ferrite stainless steel (with a coefficient of thermal conductivity of 17 W/mK), austenitic stainless steel (with a coefficient of thermal conductivity of 13 W/mK), titanium alloy (Ti-6A1-4V with a coefficient of thermal conductivity of 7.5 W/mK), nickel alloy (inconel with a coefficient of thermal conductivity of 15 W/mK), etc. are usable.
The heat insulating layer 13 is, for example, of ceramic flame-coated on the core base 12, an organic material (heat resistant polymer) such as polyimide resin, sintered ceramic, which has a low coefficient of thermal conductivity, titanium alloy (Ti-6A1-4V, Ti-3A1-2.5V, Ti-6A1-7Nb, etc.), cermet (aluminum titanate, TiO2—Al2O3), stainless steel (ferrite, austenitic, etc.), nickel alloy (inconel, FeNi), etc. The ceramic may be zirconia, silicon nitride, titanium nitride, etc. The surface processed layer 14 is a non-ferrous metal plating, such as a nickel plating, on the heat insulating layer 13.
The heat insulating layer 13 is not necessarily made of one of the above materials, and can be made of any material as long as the material has a lower coefficient of thermal conductivity than that of the core base 12. For example, a material with a coefficient of thermal conductivity which is, for example, lower than 20 W/mK can be used.
According to the first embodiment, since the heat insulating layer 13 exists between the core base 12 and the surface processed layer 14, the temperature of resin injected into the cavity 30 is kept well. Thereby, the transfer accuracy of especially the fine configuration 14a formed on the surface processed layer 14 is improved.
The mold base 11, which is a wall of the cavity 30, has a part 11a adjacent to the surface processed layer 14. Since the mold base 11 is wholly made of a heat insulating material, heat radiation from the resin at the part 11a adjacent to the fine configuration 14a is small. Therefore, the transfer accuracy of the fine configuration 14a is further improved.
In the mold 1B, the base 11 is made of a usual mold base material. The heat insulator 15 can be made of various materials with low coefficients of thermal conductivity, such as stainless steel, titanium alloy, nickel alloy, etc. Alternatively, ceramic, such as silicon nitride (Si3N4 with a coefficient of thermal conductivity of 20 W/m·K), alminium titanium (Al2O3—TiO2 with a coefficient of thermal conductivity of 1.2 W/mK), etc., is usable for the heat insulator 15. Also, heat resistant polymer, such as polyimide resin (with a coefficient of thermal conductivity of 0.28 W/mK), etc. is usable. Further, other materials can be used, and ceramic of various formulas can be used. The other parts of the mold 1B are of the same structures and the same materials as those of the mold 1A according to the first embodiment.
According to the second embodiment, since the heat insulating layer 13 exists between the core base 12 and the surface processed layer 14, the temperature of resin injected into the cavity 30 can be kept well. Therefore, the transfer accuracy of especially the fine configuration 14a formed on the surface processed layer 14 is improved.
Further, since the heat insulator 15 exists between the surface processed layer 14 and the mold base 11 which is a wall of the cavity 30, heat radiation from the resin at the part adjacent to the fine configuration 14a is small, and the transfer accuracy of the fine configuration 14a is further improved.
The heat insulating layer 23 and the surface processed layer 24 are made of the materials used for the heat insulating layer 13 and the surface processed layer 14, which have been described in connection with the first embodiment. The bases 11 and 21 are made of a heat insulating material. The heat insulating material has been specifically described as the material of the base 11 in connection with the first embodiment. The core bases 12 and 22 are made of the material which has been described as the material of the base 12 in connection with the first embodiment.
According to the fourth embodiment, since the heat insulating layers 13 and 23 are provided respectively between the core base 12 and 14 and the surface processed layer 14 and between the core base 22 and the surface processed layer 24, the temperature of resin injected into the cavity 30 can be kept well. Therefore, the transfer accuracy of especially the fine configurations 14a and 24a formed on the surface processed layers 14 and 24 is improved.
The bases 11 and 21 form walls of the cavity 30 and have areas 11a and 21a, which are respectively adjacent to the surface processed layers 14 and 24. Since the bases 11 and 21 are wholly made of a heat insulating material, heat radiation from the resin at the areas 11a and 21a respectively adjacent to the fine configurations 14a and 24a is small, and the transfer accuracy of the fine configurations 14a and 24a is further improved. Additionally, the resin is heat-insulated both on the upper and lower surfaces, and there is no fear that the molded product may have a bend.
The bases 11 and 21 are made of a usual mold base material. The other parts of the mold 1E are of the same structures and of the same materials as those of the mold iD according to the fourth embodiment. The fifth embodiment has the same effect as the fourth embodiment.
An injection molding method by use of one of the molds 1A through 1F is briefly described.
First, melted resin at a specified temperature (for example, amorphous polyolefine resin) is injected into the cavity 30, and on completion of the injection, a pressure retention step starts immediately. The pressure retention step is a step of keeping a specified pressure applied to the resin so as to supply more resin to compensate shrinkage of the resin injected into the cavity 30 due to a fall in temperature. After the pressure retention step, a cooling (natural cooling) step starts. When at least the surface of the resin (molded product) cools down under a temperature to cause thermal deformation, the mold is opened, and the molded product is picked out of the mold by use of an eject pin or the like.
In the cavity 30, immediately after completion of the resin injection, the temperature of the resin starts falling. In the molds 1A through 1E, however, the heat insulating layers 13 and 23 exist in the rear of the fine configurations 14a and 24a, and the temperature of the resin injected into the cavity 30 can be kept. Also, the bases forming the cavity 30 are at least partly made of a heat insulating material, and heat radiation from the resin is inhibited. Therefore, the transfer accuracy of the fine configurations 14a and 24a is improved.
An injection mold and an optical element injection molding method according to the present invention are not limited to the above-described embodiment.
The details of the mold can be arbitrarily structured, and the materials named in the above embodiments are merely examples. In
Although the present invention has been described in connection with the preferred embodiments above, it is to be noted that various changes and modifications are possible to those who are skilled in the art. Such changes and modifications are to be understood as being within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-191837PAT | Jun 2004 | JP | national |
