JP2014140970A - Method of producing mold for molding of optical element and mold for molding optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a mold for molding an optical element which has excellent durability and a shape of a high-precision transfer surface while securing machinability of a substrate and a mold for molding an optical element.SOLUTION: Execution of a vacuum heat treatment before finishing processing tends to increase the hardness of a plating layer 12, resulting in severe wear of a cutting tool used in the finishing processing. In the vacuum heating treatment step, the increase of the hardness of the plating layer 12 can be substantially suppressed by carrying out the heat treatment at temperatures equal to or higher than 200°C and lower than 260°C for 3.5 h in a vacuum environment, leading to maximal suppression of wear of the cutting tool used in the finishing process.

Description

  The present invention relates to a method for manufacturing an optical element molding die used for forming an optical element and an optical element molding die.

  In general, optical elements used in optical pickup devices, imaging devices, etc. require high precision, but in recent years, competition with overseas manufacturers has intensified, and in order to increase the competitiveness of products, costs can be further reduced. It is requested to do. Here, in order to mass-produce high-precision optical elements at low cost, it can be said that injection molding using a mold is preferable, but the mold becomes a bottleneck when the cost is further suppressed in the injection molding. More specifically, if the mold processing cost is high, the cost of the optical element as a molded product will be raised, and if the mold durability is low, it will be necessary to replace it frequently. Will be raised. In particular, high-performance optical elements have a diffractive structure on the optical surface, so when cutting fine irregularities corresponding to the diffractive structure etc. on the surface of the mold for transferring the diffractive structure, an expensive narrow bite In addition, since the amount of wear in one cutting tends to be large, frequent replacement is necessary, which is a factor that greatly increases the cost.

  A general optical element molding die is first subjected to preliminary processing of a base material, a plating layer is applied, rough processing similar to a desired transfer surface shape is performed, heat treatment is performed, and further finishing processing is performed. Is going. However, if heat treatment is performed after rough processing, foreign matters such as dust may adhere to the processed surface and be seized, resulting in surface defects such as pinholes and spots. When such a surface defect occurs, reworking becomes necessary and time-consuming, and in some cases, the base material must be discarded, and materials and processing are wasted.

  On the other hand, if heat treatment is not performed, surface defects such as pinholes and spots will not occur in the processing process, but the hardness of the mold cannot be ensured, so that the mold may be damaged due to sliding during molding, There is a risk of surface defects such as pinholes and spots caused by heat during molding. If such a problem occurs during molding, the mold must be replaced at a timing earlier than the normal mold replacement timing, which may increase the maintenance cost.

  On the other hand, Patent Document 1 discloses a method for manufacturing a mold for molding a glass lens, in which a rough heat treatment is performed on a plated base material after a preliminary heat treatment, and a second heat treatment is performed. It is disclosed to finish after doing.

JP 2010-215425 A

  According to the technique of Patent Document 1, since the roughing process is performed to process the shape close to the desired final shape before the plating layer is cured by the high-temperature heat treatment, the plating during the finishing process performed after curing is performed. The machining allowance of the layer can be reduced, and wear of the cutting tool used for roughing can be suppressed. In addition, after finishing the crystallization of the plating layer by a high-temperature heat treatment, the finishing process is carried out to the desired final shape, so that the shape once finished can be prevented from collapsing in the subsequent steps, and increased by crystallization. Surface roughness can be reduced by finishing.

  However, according to the technique of Patent Document 1, since the heat treatment is performed before the roughing process, the hardness of the surface of the base material is increased, and the wear of the cutting tool during the cutting is severe, which may increase the cost. . In particular, since the cutting tool for processing a fine concavo-convex structure corresponding to the diffractive structure in the finishing process is generally narrow, it is easily worn and damaged in combination with the high temperature of the heat treatment performed before the finishing process. This makes the cutting process more difficult.

  The object of the present invention has been made in view of the above-described problems, and is capable of manufacturing an optical element molding die having excellent durability and a highly accurate transfer surface shape while ensuring the machinability of the substrate. A method and an optical element molding die are provided.

The molding die according to claim 1 is:
A method of manufacturing an optical element molding die for molding an optical element,
Forming a plating layer made of Ni-P plating on the surface of the substrate;
A roughing step of processing the plating layer into a shape approximating a desired final shape;
After the roughing step, a vacuum heat treatment step for curing the plating layer by heat treatment,
A finishing process for processing the plated layer cured by the vacuum heat treatment process into the desired final shape;
The heat treatment is not performed before the roughing process.

  According to the present invention, since the heat treatment is not performed before the rough machining step, the plating layer is not hardened, so that the wear of the tool during the rough machining for cutting the plated layer can be suppressed as much as possible. On the other hand, since vacuum heat treatment is performed before the finishing process, even when pinholes or spots are generated, the transfer surface shape can be efficiently removed by the finishing process, and the yield is improved. Moreover, since the oxidation of the base material during the treatment can be suppressed by performing the vacuum heat treatment, the generation of fine crystal grain boundaries in the plating layer can be prevented, and the smoothness of the processed surface by the finishing process can be ensured. it can. Since the mold formed in this manner secures hardness by vacuum heat treatment, it is possible to suppress scratches by sliding during molding, and it can be used for molding stably over a long period of time.

  According to a second aspect of the present invention, there is provided the method for manufacturing an optical element molding die according to the first aspect of the invention, wherein the vacuum heat treatment step is a heat treatment in a vacuum environment at a temperature of 200 ° C. or more and less than 260 ° C. for 3.5 hours. It is characterized by performing.

  When a vacuum heat treatment is performed before the finishing process, the hardness of the plating layer increases, and the wear of the cutting tool used for the finishing process tends to progress. Therefore, in the vacuum heat treatment step, by performing heat treatment at 200 ° C. or higher and less than 260 ° C. for 3.5 hours in a vacuum environment, an increase in the hardness of the plating layer is suppressed, and wear of the cutting tool used for the finishing process is lost. Is to be suppressed as much as possible. In addition, since the hardness of the said plating layer can be ensured by performing heat processing at 200 degreeC or more, the damage at the time of shaping | molding can be suppressed. In addition, by performing the heat treatment at less than 260 ° C., the hardness of the plating layer can be prevented from becoming too high, so that in the finishing process of the next process, the machinability of the plating layer is ensured and the wear of the tool is suppressed. Can do. However, more preferably, the heat treatment is performed at 210 ° C. or higher and 250 ° C. or lower.

  According to a third aspect of the present invention, there is provided a method for manufacturing an optical element molding die according to the first or second aspect, wherein the diffractive structure is transferred to the optical surface of the optical element as the desired final shape in the finishing step. Forming a transfer surface.

  A tool for processing a fine concavo-convex structure for transferring a diffractive structure or the like is generally thin and easy to be worn and damaged, but according to the present invention, an increase in the hardness of the plating layer can be suppressed. Therefore, the wear of the cutting tool used for the finishing process can be suppressed as much as possible.

  The method for manufacturing an optical element molding die according to claim 4 is the invention according to any one of claims 1 to 3, wherein the optical element molding die is formed of plastic as a raw material. It is characterized by.

  Since plastic has a lower glass transition temperature than glass, it is easy to handle and suitable for mass production.

  According to a fifth aspect of the present invention, there is provided a method for manufacturing an optical element molding die according to any one of the first to fourth aspects, wherein after the vacuum heat treatment step, the substrate is kept in a vacuum environment until the temperature becomes 130 ° C. or lower. It is characterized by holding.

  Thereby, the said base material is stabilized and handling becomes easy.

  An optical element molding die according to a sixth aspect is manufactured by the manufacturing method according to any one of the first to fifth aspects.

  According to the present invention, it is possible to provide a method for manufacturing an optical element molding die and an optical element molding die that have excellent durability and have a highly accurate transfer surface shape while ensuring the machinability of a substrate. Can do.

It is a flowchart which shows the manufacturing method of the optical element shaping die in this embodiment. It is sectional drawing which shows each process typically. It is a graph which shows the relationship between the heat processing temperature of a plating layer, and Vickers hardness (Hv).

  Embodiments according to the present invention will be described below with reference to the drawings. However, although various technically preferable limitations for carrying out the present invention are given to the embodiments described below, the scope of the invention is not limited to the following embodiments and illustrated examples.

  FIG. 1 is a flowchart showing a method of manufacturing an optical element molding die in this embodiment, FIG. 2 is a cross-sectional view schematically showing each step, and FIG. 3 is a graph showing the heat treatment temperature and Vickers hardness (Hv) of the plating layer. It is a graph which shows a relationship. Hereinafter, each process will be described in order according to the flowchart of FIG.

  First, in step S101 in FIG. 1, the base material is preliminarily processed. More specifically, the molding surface 15 of the cylindrical base material 11 is processed into a predetermined shape corresponding to the optical surface of the optical element to be molded using the tool T1 (FIG. 2A). There is no restriction | limiting in particular in the material of the base material 11. FIG. Examples of materials that can be preferably used include various heat-resistant alloys (such as stainless steel), super hard materials mainly composed of tungsten carbide, various ceramics (such as silicon carbide and silicon nitride), and composite materials including carbon. However, here, a pre-hardened steel material is used.

  Further, the shape of the molding surface 15 is not particularly limited, and may be any one of a flat surface, a convex surface, and a concave surface. From the viewpoint of reducing the thickness of the plated layer 12 formed in the next step and suppressing the peeling of the plated layer 12, it is preferable to have a shape close to the final shape corresponding to the surface shape of the plastic molded body to be manufactured. Since the processing cost increases, it is not necessary to make the shape closer to the final shape than necessary. The difference between the final shape and the shape of the molding surface of the base material 11 in this step is preferably 1 μm to 50 μm, more preferably 2 μm to 20 μm, at the largest position.

  Next, in step S102 of FIG. 1, an electroless plating layer is formed. More specifically, the plating layer 12 made of Ni—P plating is formed on the surface (molding surface 15) of the base material 11 (FIG. 2B). Here, the Ni-P plating is electroless nickel plating containing P, and can be formed by a known method. As the plating solution, for example, a plating solution using hypophosphorous acid as a reducing agent may be used. The thickness of the plating layer 12 need only be as much as the allowance for obtaining the final shape by processing, but also consider the allowance for repeated chasing to obtain the required shape accuracy. It is preferable to keep it. However, if it is thicker than necessary, defects such as film peeling may easily occur. Therefore, the thickness of the plating layer 12 is preferably 1 μm to 50 μm thicker than the maximum value of the difference between the shape of the molding surface 15 of the substrate 11 and the final shape. Therefore, the film thickness of the plating layer 12 is preferably 2 μm to 100 μm, and more preferably 3 μm to 70 μm.

  Next, a roughing process is performed in step S103 of FIG. More specifically, the plated layer 12 is processed into a shape approximating a desired final shape using a bit T2 such as a diamond bit (FIG. 2C).

  The roughing process may be performed by a known processing apparatus and processing method. The shape of the plating layer 12 after the roughing process is a shape that approximates the final shape, and the difference from the final shape is smaller than that before the roughing process. Therefore, the machining allowance in the finishing process (step S105) performed after the plating layer 12 is cured can be reduced, and wear of the cutting tool can be suppressed. From the viewpoint of effectively suppressing the wear of the cutting tool in the finishing process, it is preferable that the maximum value of the machining allowance of the plating layer 12 in the roughing process is larger than the maximum value of the machining allowance in the finishing process. It is preferable to process to the shape as close as possible to the final shape by the roughing process, but considering that it will be deformed in the next vacuum heat treatment step, bringing the final shape closer than necessary only increases the processing cost. It is not preferable. Therefore, the difference between the shape after the rough machining step and the final shape is preferably 0.5 to 5 μm, and more preferably 1 to 4 μm.

  Next, in step S104 of FIG. 1, a vacuum heat treatment step is performed. More specifically, in FIG. 2C, the base material 11 is placed in a sealed vacuum furnace VF, and the negative pressure pump P is used to set the inside to a negative pressure of 0.09 Pa as a target. Then, the internal temperature is raised to 200 ° C. or higher and lower than 260 ° C. by the heater HT, and held for 3.5 hours. Thereafter, the substrate 11 is left in the vacuum furnace VF to be gradually cooled until the internal temperature falls below 130 ° C., and is taken out and sent to the next step.

  As shown in FIG. 3, when heat treatment at 200 ° C. or higher and lower than 260 ° C. is performed, the Vickers hardness of the plating layer 12 is about 560 Hv to 620 Hv, and the increase in Vickers hardness is slight. Thereby, the hardness of the plating layer 12 required at the time of shaping | molding can be ensured, improving the workability of the finishing process at the next process and suppressing the wear of the cutting tool.

  Next, in step S106 in FIG. 1, a finishing process is performed. More specifically, the plating layer 12 that has been heat-treated in the vacuum heat treatment step is processed into a final transfer surface shape to which the diffractive structure is transferred, using a sword tip tool T3 such as a diamond tool (FIG. 2D). Since the plating layer 12 is hardened by the vacuum heat treatment process and processed to the shape approximate to the final shape by the roughing process (step S103) described above, wear of the sword tip bit T3 is minimized. Therefore, even if the sword tip T3 has a narrow width suitable for forming the fine annular zone shape 13, a relatively long cutting distance can be maintained.

  Further, by performing the finishing process, it is possible to reduce the surface roughness of the plating layer 12 increased by crystallization in the vacuum heat treatment process, and to eliminate pinholes and spots generated during the heat treatment. What is necessary is just to implement a process with a well-known processing apparatus and a processing method. The maximum value of the machining allowance in the finishing process is usually preferably 0.5 to 5 μm and more preferably 1 to 4 μm.

  When the finishing process is completed, the optical element molding die is completed. However, from the viewpoint of obtaining the effects of suppressing the deterioration of the plating layer 12 and suppressing the occurrence of air accumulation in the plastic molded body, a step of forming a protective film may be provided following the finishing process.

Hereinafter, the results of studies conducted by the present inventors will be described. In the process shown in FIG. 1, the inventors manufactured an optical element molding die with or without changing the temperature during vacuum heat treatment, and evaluated hardness, machinability, and product quality stability. . The rotation speed of the lathe to which the substrate was attached was 1000 min ⁻¹ (rpm). The evaluation results are shown in Table 1.

  As shown in Table 1, when heat treatment was not performed, the machinability was excellent, but the hardness of the mold was insufficient, and problems such as galling occurred during molding. On the other hand, when heat treatment is performed at 260 ° C., the hardness of the mold is sufficient and the product quality stability is excellent without galling, but the number of substrates that can be cut with the same tool is 4 or more and 9 or less, It was found that there was some difficulty in cutting. In particular, when heat treatment was performed at 265 ° C., the number of base materials that could be cut with the same tool deteriorated to 3 or less. In contrast, when heat treatment is performed at 210 ° C. to 250 ° C., the hardness of the mold is sufficient, the product quality is stable, and the number of base materials that can be cut with the same tool is 10 or more. It turned out to be excellent.

  The present invention is not limited to the embodiments described in the specification, and other embodiments and modifications are apparent to those skilled in the art from the embodiments and ideas described in the present specification. It is. For example, optical elements that can be molded with a mold manufactured according to the present invention include an objective lens for an optical pickup device and a lens for an imaging device.

11 Substrate 12 Plating layer 13 Ring-shaped VF Vacuum furnace HT Heater P Negative pressure pump

Claims (6)

A method of manufacturing an optical element molding die for molding an optical element,
Forming a plating layer made of Ni-P plating on the surface of the substrate;
A roughing step of processing the plating layer into a shape approximating a desired final shape;
After the roughing step, a vacuum heat treatment step for curing the plating layer by heat treatment,
A finishing process for processing the plated layer cured by the vacuum heat treatment process into the desired final shape;
A method for producing an optical element molding die, wherein heat treatment is not performed before the roughing step.   2. The method of manufacturing an optical element molding die according to claim 1, wherein the vacuum heat treatment step is performed in a vacuum environment at a temperature of 200 ° C. or higher and lower than 260 ° C. for 3.5 hours.   3. The method of manufacturing an optical element molding die according to claim 1, wherein a transfer surface for transferring the diffractive structure to the optical surface of the optical element is formed as the desired final shape in the finishing step. .   The method for manufacturing an optical element molding die according to any one of claims 1 to 3, wherein the optical element molding die is an optical element molded from plastic.   5. The method for manufacturing an optical element molding die according to claim 1, wherein after the vacuum heat treatment step, the base material is held in a vacuum environment until the temperature becomes 130 ° C. or lower.   An optical element molding die manufactured by the manufacturing method according to claim 1.

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