JP2019104140A - Plastic optical element, mold for manufacturing plastic optical element, and method for manufacturing the mold - Google Patents

Abstract

To provide a plastic optical element of high quality which has high form accuracy and can effectively suppress internal reflection inside, a mold for manufacturing the optical element, and a method of manufacturing the mold.SOLUTION: In order to achieve this object, a plastic optical element is provided with an optical surface and an edge surface located on an outer periphery of the optical surface, and the edge surface is an optical element-side rough surface provided with irregular asperity shape, and the optical surface is made of a plastic optical element or the like characterized in that a surface roughness Ra measured by a noncontact three-dimensional surface texture measuring apparatus is 20 nm or less. Further, in a production of a mold for plastic optical element production, an optical element molding surface of a fixed core and a movable core constituting a mold for plastic optical element production are roughened by sandblasting, and after the roughening, optical surface forming regions of the fixed core and the movable core are subjected to a lathe turning processing using a polycrystalline diamond bite or the like.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a plastic optical element used for an optical device, a mold for manufacturing the plastic optical element, and a method for manufacturing the mold.

  A lens incorporated in an imaging apparatus such as a camera or an optical apparatus such as an in-vehicle imaging apparatus is required to refract light incident from the object side as the optical design and emit it toward the image plane side. However, contrary to the original optical design, there may be a case where a ray of light is emitted after performing one or more internal reflections on the edge of the lens or the like. A light beam internally reflected in the lens as described above is an unnecessary light beam because it causes ghosts, flares, and the like, impairs the function of the original optical device, and degrades the imaging quality. Therefore, it has been required for the optical element to prevent light rays internally reflected in the lens as much as possible.

  In an effort to solve such a problem, conventionally, "painting" was performed by manually applying an anti-reflection paint (for example, a black matting paint) using a brush or the like to a part that reflects harmful light . In this redaction operation, the redaction range varies, and it is difficult to finish the boundary position between the lens surface and the redaction range with high accuracy. In addition, since the inking process is performed after lens production, the number of man-hours increases, and there is a problem that the manufacturing cost is increased.

  Therefore, in order to solve the problem of blackening, when manufacturing a plastic optical element by a resin molding method, rough surface is used to reduce light reflection on the mold surface of the part that reflects harmful light in advance. A method is used in which processing is performed to simultaneously transfer the optical surface and the rough surface to the surface of the molded lens. The sand blasting method is one of the roughening methods using this lens molding die. In this case, in order to ensure the accuracy of the boundary position between the optical surface forming region of the mold and the rough surface, roughening processing is performed on the entire surface of the die diameter of the mold by the sand blast method. Then, only the range to be the optical surface forming region of the mold is turned by using an ultra-precision processing machine to make a smooth surface, and a gold for obtaining an optical element having both the optical surface forming region and the rough surface. Mold processing methods are known. Certainly, using this mold, it is possible to omit the painting process.

  However, in the method of roughening the entire die diameter of the mold by sandblasting, the sandblasting is used to turn only the area that will be the optical surface forming area of the mold using an ultra-precision processing machine. There is a high probability that chipping of the cutting edge of the diamond cutting tool occurs due to the turning of the formed rough surface. When the optical surface forming region is processed with this broken diamond bit, local surface roughness may occur in the optical surface forming region of the lens molding die. In general, the local surface roughness portion of the optical surface forming region formed by the diamond bite breakage is not preferable because the surface roughness Ra becomes about 50 nm and it becomes impossible to obtain an optical element of good quality.

  Therefore, for example, a lens molding die shown in Patent Document 1 and a surface roughening system shown in Patent Document 2 are examples of devices that do not require turning of the optical forming surface of the die to be performed later. Patent Document 1 discloses a lens molding die having a mirror surface piece provided with a mirror surface transferred to the optical surface of the lens, and a flange forming surface formed around the mirror surface piece and forming a flange portion of the lens. ing. Grinding marks are intermittently formed on the flange formation surface in order to roughen the flange surface of the lens.

  Further, according to Patent Document 2, when manufacturing a plastic optical element, NC data for processing the main shape of the mold for manufacturing a plastic optical element only has a predetermined cycle in a region that prevents generation of harmful light. The pulse data (data for rough surface processing) alternately emitting the processing signal (ON) and the raw signal (OFF) is incorporated, and the processing machine is feedback-controlled to roughen the lens forming mold, and this processing is performed. A method is disclosed for transferring a surface to an optical element to obtain an optical element comprising both an optical surface and a rough surface.

JP, 2008-194995, A JP 2012-121122 A

  However, in the lens molding die disclosed in Patent Document 1, since the flange forming surface forming the flange portion of the lens is constituted by a member different from the mirror surface piece to be transferred to the optical surface of the lens, There is not a small gap between the peripheral portion and the flange forming surface. Therefore, when the optical surface and the rough surface are simultaneously transferred to the surface of the molded lens using this mirror surface piece and the flange forming surface, the boundary between the optical surface of the lens and the rough surface has a boundary area with a predetermined width. Become. As the boundary area becomes wider, the effect of suppressing the internally reflected light in the lens becomes insufficient, and it becomes difficult to obtain the designed optical device function and imaging quality.

  On the other hand, when the method disclosed in Patent Document 2 is used, NC data is used to process the surface of the plastic optical element manufacturing mold, so that the rough surface created by turning has a periodic uneven shape and Become. In this case, since the boundary between the optical surface of the molded lens and the rough surface has a concavo-convex shape meandering with periodicity, it becomes a boundary region having a predetermined width as in the case of Patent Document 1. Although it differs depending on the NC program, by performing roughening with regularity, the width of the boundary region tends to be wider as the turning depth is deeper. If the periodic boundary region becomes wide, diffracted components are likely to remain in the lens, making it difficult to achieve complete scattering. Therefore, even in the case of the roughening method using NC data, the effect of suppressing the light ray reflected internally in the lens becomes insufficient, and it is difficult to obtain the optical device function as designed and the imaging quality. there were.

  As can be understood from the above, the object of the present invention is to provide a plastic optical element of good quality which has high shape accuracy and can effectively suppress internal reflection inside, a mold for manufacturing the optical element, and its gold It is in providing the manufacturing method of a type | mold.

  Then, as a result of earnest research of the present inventors et al., It was conceived to solve the problem with the following invention contents.

The plastic optical element according to the present invention: The plastic optical element according to the present invention is a plastic optical element provided with an optical surface and an edge surface located on the outer periphery of the optical surface, and the edge surface has irregular irregularities. It is an optical element side rough surface provided with a shape, and the optical surface concerned is characterized in that surface roughness Ra measured with a noncontact three-dimensional surface texture measuring device is 20 nm or less.

The mold for manufacturing a plastic optical element according to the present invention: The mold for manufacturing a plastic optical element according to the present invention is an optical element provided on an optical surface forming region for forming an optical surface of the optical element and an edge surface of the optical element. A mold for manufacturing a plastic optical element comprising a mold-side rough surface area for forming a side rough surface, wherein the mold-side rough surface area has an irregular asperity shape, The optical surface forming region disposed adjacent to the rough surface region on the mold side is characterized in that the surface roughness Ra obtained using the noncontact three-dimensional surface texture measuring apparatus is 20 nm or less.

The method for producing a mold for producing a plastic optical element according to the present invention: The method for producing a mold for producing a plastic optical element according to the present invention is a method for producing a mold for producing a plastic optical element according to the present invention The mold for manufacturing the element is such that the fixed side mold block constituted by the fixed core and the fixed core side cavitation type is brought into opposed contact with the movable side mold block constituted by the movable core and the movable core side cavitation type An optical element forming surface of the fixed core and the movable core is roughened by sandblasting, and after the roughening, the fixed core and the movable core are The optical surface forming region is turned using a polycrystalline diamond bite.

  The optical element according to the present invention can effectively suppress unnecessary light entering the edge surface from being mixed into the optical surface by providing the edge surface with a predetermined rough surface. As a result, it is possible to provide an imaging device or the like having good optical performance. Further, the optical element according to the present invention can be obtained for the first time by using a predetermined diamond bite in its manufacturing method. This manufacturing method allows the use of conventional manufacturing equipment without causing any equipment loss.

It is a sectional view showing typically the structure of the plastic optical element concerning the present invention. It is a partial expanded sectional view of FIG. It is sectional drawing which shows typically the structure of the metal mold | die for plastic optical element manufacture. It is sectional drawing which shows the state which combined the metal mold | die for plastic optical element manufacture of FIG. 3, and the other metal mold | die. It is explanatory drawing of the lathe turning process of the metal mold | die for plastic optical element manufacture of this invention. It is a partial expanded sectional view of a diamond cutting tool. It is a microscope observation photograph of the mold side rough surface area | region of an Example. It is a microscope picture of the mold side rough surface field of a comparative example. It is a microscope picture of a boundary part of a mold side rough surface field and an optical surface formation field of an example. It is a microscope picture of a boundary part of a mold side rough surface field and an optical surface formation field of a comparative example.

  Hereinafter, embodiments of a plastic optical element, a mold for manufacturing a plastic optical element, and a method for manufacturing a mold for manufacturing a plastic optical element according to the present invention will be described with reference to the drawings.

1. Plastic Optical Element First, a plastic optical element (hereinafter simply referred to as "optical element") 10 according to the present invention will be described. The present invention relates to various optical systems such as imaging optical systems such as lenses, prisms (color separation prisms, color synthesis prisms, etc.), polarization beam splitters (PBS), cut filters (for infrared, ultraviolet etc.), projection optical systems, etc. Can be applied to the various optical elements 10 that make up the In the optical element 10 according to the present invention, a plastic material is supplied to a plastic optical element manufacturing mold (hereinafter simply referred to as “optical element manufacturing mold”) as described later, and the shape of the mold surface is determined. There is no particular limitation on the type of lens, the shape of the lens, etc. as long as it is a plastic optical element manufactured by transferring to a plastic material. For example, as the optical element 10, various elements such as a biconvex lens, a biconcave lens, a planoconvex lens, a planoconcave lens, a concave meniscus lens, a convex meniscus lens, an aspheric lens, a free curved lens, and a prism can be used.

  A concave meniscus lens is shown in FIG. 1 and FIG. 2 as an example of the optical element 10 of the present invention. FIG. 1 is a cross-sectional view schematically showing the structure of an optical element 10 according to the present invention. FIG. 2 is a partial enlarged cross-sectional view of FIG. 1 and 2 omit the hatching of the cross section in consideration of the viewability of the drawing, and show the optical surfaces 12 and 13 and the edge surface 14 described below in an area representation. The shapes, ranges, and the like of the optical surfaces 12 and 13 and the edge surface 14 shown in FIGS. 1 and 2 are merely examples, and the optical surface and the optical surface may be selected depending on the optical characteristics of the optical element 10 and the specific shape thereof. The shape, range, etc. of the edge surface can be changed as appropriate.

  The optical element 10 according to the present invention has "the edge surface 14 is the optical element side rough surface 15 having irregular asperity shape" and "the optical surface 12 adjacent to the optical element side rough surface 15". , And 13 have a surface roughness Ra of 20 nm or less. The optical element-side rough surface 15 and the optical surfaces 12 and 13 will be described in detail below.

(1) Optical Surface The optical surfaces 12 and 13 provided in the optical element 10 according to the present invention will be described. The optical surfaces 12 and 13 are located adjacent to the optical element-side rough surface 15 described later, and are optical effective areas for transmitting an effective light beam contributing to image formation, and have a feature that the surface roughness Ra is 20 nm or less . Conventionally, mass production is impossible for the optical element 10 that satisfies the condition of “surface roughness Ra of 20 nm or less” of the optical surfaces 12 and 13, and mass production is possible for the first time by the manufacturing method described later. . The “surface roughness Ra of 20 nm or less” of the optical surfaces 12 and 13 means that there is no part where the surface roughness Ra locally exceeds 20 nm, and the surface is a smooth surface unlike in the prior art. Further, in the present invention, the surface roughness Ra of the optical surfaces 12 and 13 of the optical element 10 is preferably 10 nm or less, more preferably 5 nm or less, and still more preferably 2 nm or less. Here, although the lower limit value of the “surface roughness Ra” is not determined, the smaller the surface roughness Ra, the closer to an ideal smooth surface, so it is considered as an index that does not need to particularly define the lower limit value. (Empirically, about 0.5 nm is considered to be the lower limit.) The optical element 10 provided with such optical surfaces 12 and 13 can exhibit the designed optical function as long as unnecessary light is not mixed in the edge surface, and high imaging quality can be realized. It becomes. In addition, about the measuring method of surface roughness Ra of the optical surface said to this invention, it measures with the non-contact three-dimensional surface texture measuring apparatus which used the white_light | sunlight interferometer, and mentions it later.

(2) Optical element-side rough surface The optical element-side rough surface 15 is a rough surface formed on the edge surface 14 located adjacent to the outside in the radial direction of the optical surfaces 12 and 13 and has irregular asperity shapes. doing. That is, the optical element-side rough surface 15 is a surface having a fine concavo-convex shape formed irregularly without specific directionality and specific periodicity. The optical element-side rough surface 15 having such a concavo-convex shape is a rough surface having regular irregularities obtained by using a mold provided with a die-side rough surface formed by machining using conventional NC data and Will be totally different. In the case of the optical element rough surface 15 as referred to in the present invention, light incident on the optical element rough surface 15 can be almost completely scattered, and scattering on the optical surface 12 or 13 of the optical element 10 by the peripheral surface 14 -It becomes difficult to mix the diffracted light. Therefore, the edge surface 14 provided with the rough surface 15 in the present invention can effectively suppress the occurrence of flare and ghost caused by the fact that unnecessary light finally enters the image forming surface.

  The optical element side rough surface 15 in the present invention preferably has a surface roughness Rz of 5 μm or more and 20 μm or less. If the surface roughness Rz of the optical element-side rough surface 15 is less than 5 μm, there is a possibility that the light scattering and absorption efficiency may be improved, but it is difficult to uniformly form a transfer surface less than 5 μm on the mold by sandblasting. It is not preferable because the productivity is lowered. On the other hand, when the surface roughness Rz of the rough surface 15 exceeds 20 μm, the light scattering and absorption efficiency decreases, and the reflection reduction effect of the light on the optical element side rough surface 15 can not be sufficiently exhibited. It is difficult to effectively suppress the occurrence of flare and flare, which is not preferable. From the viewpoint of the light reflection reduction effect on the optical element-side rough surface 15, the surface roughness Rz of the rough surface 15 is preferably 15 μm or less, and more preferably 10 μm or less.

  In addition to the above, the optical element-side rough surface 15 in the present invention preferably has a width of 10 μm or less at the boundary region with the adjacent optical surfaces 12 and 13. Here, the boundary region refers to the “micro-relief portion of the optical element-side rough surface 15 when the portion where the optical element-side rough surface 15 of the optical element 10 is adjacent to the optical surfaces 12 and 13 is microscopically observed. And the “smooth portion of the optical surfaces 12 and 13” are regions having a certain width observed in a mixed state. As the width of the boundary area is increased, the dimensional accuracy of the optical surfaces 12 and 13 is reduced and the design quality can not be maintained. In addition, if the boundary area where the light reflection reducing effect is low is wider than the optical element side rough surface 15, flare and ghost are easily generated, which is not preferable. Therefore, by adopting a manufacturing method described later, the width of the boundary area can be minimized to 10 μm or less, and the dimensional accuracy of the optical surfaces 12 and 13 of the optical element 10 can be maintained as designed. Internal reflection of incident light on the optical element-side rough surface 15 can be efficiently suppressed. Although the lower limit of the boundary region is not particularly limited, in the case of the processing technology at the current stage, the lower limit is about 5 μm.

  Moreover, as for the fine concavo-convex shape of the optical element side rough surface 15 mentioned above, it is also preferable that the average value of the convex part vertex spacing of the concavo-convex shape (average vertex spacing) is within a predetermined range. Also here, any convex apex that can be observed in one field of view obtained by a noncontact three-dimensional surface texture measuring apparatus using a white light interferometer described later is defined as a reference apex, and a plurality of adjacent convex apexes The distance of is measured, and the average of the distances (hereinafter referred to as "average vertex spacing") is adopted as an index. The average vertex spacing is preferably 15 μm or more and 20 μm or less. If the average vertex spacing is less than 15 μm, this means that the presence density of the convex parts constituting the fine uneven shape is high, but the convex parts become excessively fine and are vulnerable to damage by an impact due to an external factor. Unfavorably because it weakens. On the other hand, when the average vertex spacing exceeds 20 μm, the existing density of the convex portions constituting the fine concavo-convex shape decreases, which makes it difficult to efficiently perform the reflection prevention / diffraction prevention of unnecessary light, which is not preferable.

  In the present invention, the values of the surface roughness Rz and the vertex spacing of the convex portions described above were measured by a noncontact three-dimensional surface texture measuring apparatus (for example, NewView 7300 manufactured by Zygo Corporation) using a white light interferometer. It is a thing. The measurement conditions here were an objective lens of 10 ×, an image zoom of 1 ×, and a measurement field of view of 0.69 mm × 0.52 mm.

2. Mold for Manufacturing Plastic Optical Element A mold 50 for manufacturing an optical element according to the present invention will be described with reference to FIGS. 3 and 4. As can be understood from FIG. 4, the optical element manufacturing mold 50 according to the present invention comprises “a fixed side mold block 24 composed of a fixed core 20 and a fixed core side cavitation mold 21 disposed on the outer periphery thereof” A molded body forming space 35 is constituted by a core 30 and a movable side mold block 33 comprising the movable core side cavitation mold 31 disposed on the outer periphery thereof and is formed by the fixed side mold block 24 and the movable side mold block 33. The optical element 10 is manufactured by injection molding of a resin material. There is no particular limitation on the constituent materials of the fixed core 20, the fixed core side cavitation type 21, the movable core 30, and the movable core side cavitation type 31 at this time, considering hardness, corrosion resistance, ease of cutting, etc. It can be arbitrarily selected and used out of the plastic mold material used from the above. Hereinafter, each component will be described in detail.

2-1. The stationary mold block The stationary mold block 24 is composed of a stationary core 20 and a stationary core side cavitation die 21 disposed on the outer periphery thereof. Hereinafter, "fixed core 20" and "fixed core side cavitation type 21" will be described.

(1) Fixed Core FIG. 3 shows the fixed core 20 (in FIG. 3, the hatching of the cross section is omitted in consideration of the legibility of the drawing). The fixed core 20 includes an optical surface forming area 22 for forming the optical surface 12 on one surface side of the optical element 10, and a mold-side rough surface area 23 adjacent to the outer side. Hereinafter, the mold side rough surface area 23 and the optical surface forming area 22 will be described.

Optical Surface Forming Region: The optical surface forming region 22 of the fixed core 20 should be a replica thereof and have the same surface state as one of the optical surfaces 12 of the optical element 10. That is, the optical surface forming region 22 of the fixed core 20 used in the present invention must have a surface roughness Ra of 20 nm or less, preferably 10 nm or less, 5 nm or less, and 2 nm or less. More preferable. When the surface roughness Ra of the optical surface forming region 22 of the fixed core 20 exceeds 20 nm, the surface roughness Ra of the optical surface 12 of the optical element 10 which is the replica thereof can not be 20 nm or less.

Mold side rough surface area: In the fixed core 20, the mold side rough surface area 23 is disposed on the outer periphery of the optical surface forming area 22 in the radial direction. The mold-side rough surface area 23 transfers the surface roughness shape to the edge surface 14 of the optical element 10 to form the optical element-side rough surface 15 as a replica surface. The mold-side rough surface region 23 of the fixed core 20 in the present invention is formed by sandblasting. The mold-side rough surface area 23 formed by the sandblasting method is completely different from the mold-side rough surface provided with a regular uneven shape formed by the conventional NC processing. The mold-side rough surface region 23 of the fixed core 20 must be a replica thereof and have the same surface state as the one optical element-side rough surface 15 of the optical element 10. That is, the surface roughness Rz of the rough surface region 23 on the mold side needs to be 5 μm or more and 20 μm or less, and the upper limit thereof is preferably 15 μm or less, and more preferably 10 μm or less. The width of the boundary area between the mold-side rough surface area 23 and the adjacent optical surface forming area 22 is more preferably 10 μm or less as in the case of the optical element 10 which is a replica. Further, as in the case of the optical element 10 which is a replica, the mold-side rough surface region 23 more preferably has an average vertex distance of 15 μm to 20 μm in the distance between the apexes of the convex portions in the fine concavo-convex shape. This is because the optical element 10 having the above-mentioned quality can not be obtained unless the mold-side rough surface area 23 has such a surface quality.

  And although this optical surface formation area 22 and the metal mold side rough surface area 23 are described by the manufacturing method of the following metal molds, it is preferable to equip the surface with an electroless nickel plating layer. It is because it is excellent in the workability by the sand blasting method adopted by the manufacturing method concerned. The thickness of the electroless nickel plating layer is preferably 100 μm or more before processing by the sand blast method. If the thickness of the electroless nickel plating layer before processing is 100 μm or more, the thickness of the electroless nickel plating layer of the optical surface forming region 22 formed by roughing by sand blasting and subsequent turning is 50 μm. It can be more than. If the thickness of the electroless nickel plating layer in the optical surface forming area 22 after the turning process is 50 μm or more, even if the dimensional error of the mold material 25 is affected, the mold material 25 can be obtained from the electroless nickel plating layer. The inconvenience of being exposed can be avoided. In addition, in the manufacturing method, the electroless nickel plating layer of the optical surface forming area 22 which is subjected to turning in addition to the processing by the sand blast method and the electroless nickel plating of the rough surface area 23 on the mold side which is not subjected to the subsequent turning. The difference of the layer thickness is preferably in the range of 35 μm to 65 μm, and more preferably 30 μm to 60 μm. The difference between the thickness of the electroless nickel plating layer of the ideal optical surface forming area 22 and the thickness of the electroless nickel plating layer of the mold-side rough surface area 23 is 50 μm.

(2) Fixed Core Side Cavitation Type As can be understood from FIG. 4, the fixed core side cavitation type 21 is disposed on the outer periphery of the above-mentioned fixed core 20. The fixed core mold block 24 shown in FIG. 4 is a state in which the fixed core 20 is housed and fitted inside the fixed core side cavitation mold 21.

2-2. Movable side mold block The movable side mold block 33 is composed of a movable core 30 and a movable core side cavitation mold 31 disposed on the outer periphery thereof. As described above, the movable-side mold block 33 is combined with the fixed-side mold block 24 to form the molded body forming space 35, and the resin material is injection-molded there to manufacture the optical element 10. . Hereinafter, the "movable core 30" and the "movable core side cavitation type 31" will be described.

(1) Movable core This movable core 30 fixes the optical surface forming area 22 for forming the optical surface 13 on the other surface side of the optical element 10 and the mold-side rough surface area 23 adjacent to the outer side thereof. Similar to the core 20. The same concept as that of the fixed core 20 can be applied to the mold-side rough surface area 23 and the optical surface forming area 22 of the movable core 30, and therefore, the duplicated description here is omitted.

(2) Movable core side cavitation type As can be understood from FIG. 4, the movable core side cavitation type 31 is disposed on the outer periphery of the movable core 30 described above. Then, the movable core mold block 24 shown in FIG. 4 is a state in which the movable core 30 is accommodated and fitted inside the movable core side cavitation mold 31.

  It should be mentioned just in advance that the surface roughness Rz of the mold-side rough surface area 23 of the fixed core 20 and the movable core 30 described above, the average vertex distance, and the surface roughness of the optical surface forming area 22 As Ra, a value similarly measured by a noncontact three-dimensional surface texture measuring apparatus using the above-mentioned white light interferometer is adopted.

3. A method of manufacturing a mold for manufacturing a plastic optical element The mold 50 for manufacturing an optical element according to the present invention is "a fixed side mold block 24 comprising a fixed core 20 and a fixed core side cavitation mold 21 arranged on the outer periphery thereof" It is comprised from "the movable side metal mold block 33 which consists of the movable core 30 and the movable core side cavitation type | mold 31 distribute | arranged to the outer periphery." In the method of manufacturing the optical element manufacturing mold 50, the method of forming the optical surface forming region 22 of the fixed core 20 and the movable core 30 has the most significant feature. Hereinafter, “the mold side rough surface region processing step” and the “optical surface forming region processing step” will be described in order.

(1) Mold side rough surface area processing form In processing of the mold side rough surface area in the present invention, the whole surface of the optical element formation surface of fixed core 20 and movable core 30 is roughened by sand blast method. As an example, FIG. 5 shows a mold material 25 for producing the fixed core 20. The entire optical element forming surface 26 including the rough surface area 23 on the mold side and the optical surface forming area 22 of the mold material 25 for obtaining the fixed core 20 and the movable core 30 is roughened using a sand blast method.

  At this time, the mold material 25 preferably has an electroless nickel plating layer on the optical element molding surface 26 of the mold material 25. By the presence of the electroless nickel plating layer, it becomes easy to obtain the optical element molding surface 26 of the mold material 25 having properties suitable for forming the optical element-side rough surface 15 of the optical element 10. is there. It is preferable that the electroless nickel plating layer before the process by the sandblasting method is 100 micrometers or more by the reason mentioned above. Here, the upper limit of the thickness of the electroless nickel plating layer before processing is not particularly limited. If the thickness of the electroless nickel plating layer is 100 μm or more, roughening can be appropriately performed by the sand blast method, and the optical surface forming region 22 can be formed without exposing the mold material 25 by the subsequent turning process. It is because it can form. In this manner, only the optical surface forming area 22 of the optical element forming surface 26 provided with the electroless nickel plating layer on the entire surface is subjected to turning processing, whereby the thickness of the electroless nickel plating layer of the optical surface forming area 22 is obtained. Is thinner than the thickness of the electroless nickel plating layer of the die-side rough surface area 23 which has not been subjected to the turning process.

  As the sand blasting method used here, it is possible to adopt a method conventionally used as a surface roughening method of a mold. By roughening the optical element molding surface 26 of the mold material 25 by sand blasting, it is possible to obtain a rough surface having irregular asperity shape without specific directionality and specific periodicity. There are no particular limitations on the conditions for roughening by the sand blast method.

(2) Optical Surface Forming Region Processing Form The optical surface forming region processing will be described with reference to FIG. The optical surface forming area processing in the present invention is a so-called turning process. This is a step of turning only the optical surface forming area 22 on the optical element forming surface 26 where the roughening of the mold material 25 is performed in the mold side rough surface area processing step described above. For turning of the optical surface forming area 22, it is preferable to use an ultra-precision processing machine 40 capable of fine cutting with high accuracy and a diamond cutting tool 42. As shown in FIG. 5, the mold material 25 is fixed to the rotation shaft 41 of the ultra-precision processing machine 40, and the diamond cutting tool 42 is disposed opposite to the optical element molding surface 26 of the mold material 25. The ultra precision processing machine 40 and the diamond cutting tool 42 move the diamond cutting tool 42 in the horizontal axis (z axis) parallel to the parallel horizontal axis (z axis) with respect to the rotation axis 41 of the ultra precision processing machine 40 It is possible. According to the configuration, a certain amount of cut is added to the mold material 25 so that the contact point (cutting point 46) of the diamond cutting tool 42 with the mold material 25 follows a target shape trajectory. The optical element molding surface 26 is turned while moving in the x-axis direction and the z-axis direction to form a target optical surface forming area 22.

  A major feature of the diamond cutting tool 42 used in optical surface forming area processing (turning) in the present invention is. This will be described below with reference to FIG. FIG. 6 is a partial enlarged cross-sectional view of the diamond cutting tool 42. As shown in FIG. The diamond cutting tool 42 shown in FIG. 6 has an arc-shaped cutting edge. The diamond cutting tool 42 is preferably manufactured using nano-polycrystalline diamond having a grain size of 100 μm or less. When a rough surface (concave and convex shape) on the optical element forming surface 26 is turned using a cutting tool using single crystal diamond, chipping of the cutting edge of the single crystal diamond cutting tool is likely to occur. On the other hand, when the nano-polycrystalline diamond cutting tool is used to carry out the turning process, chipping of the cutting edge is unlikely to occur, and the surface roughness of the optical surface forming area 22 obtained after turning is uniform and does not vary And is preferable.

  And, as shown in FIG. 6, the diamond cutting tool 42 used in the present invention has the "rake surface 44" on the ridge of the arc-shaped cutting edge 43, and the "rake surface 44" and the "front flank 45". Preferably, there is a "cutting point 46" between them. At this time, the "rake angle 47" formed by the "rake surface 44" and the "scanning direction of the diamond cutting tool 42" is the diamond relative to the axial direction A of the diamond cutting tool 42 disposed opposite to the object to be cut. When the scanning direction of the cutting tool 42 is positive, a negative rake angle is preferable. As can be understood from FIG. 6, it is preferable that the “rake angle 47” is inclined in the negative direction in the range of 25 ° or more and 30 ° or less with reference to “the axial direction A of the diamond bite 42”. If this "rake angle 47" is less than 25 °, damage from the cutting point 46 of the diamond cutting tool 42 is likely to occur, and discharge of turning chips becomes difficult, which is not preferable. On the other hand, if the “rake angle 47” exceeds 35 °, the cutting performance of the diamond cutting tool 42 is unfavorably reduced.

  In the diamond cutting tool 42 used in the present invention, the width 48 of the rake surface 44 on the ridge line of the cutting edge 43 is preferably 1 μm or more and 3 μm or less. If the width of the rake face 44 of the diamond cutting tool 42 is less than 1 μm, it is not preferable because the cutting tool life is reduced. On the other hand, when the width of the rake face 44 exceeds 3 μm, discharge of turning chips becomes difficult, which is not preferable.

  Since the diamond cutting tool 42 satisfying the above-described conditions is unlikely to be chipped when turning the optical surface forming area 22 of the mold (the fixed core 20 and the movable core 30), the diamond cutting tool 42 locally This makes it difficult to form a rough surface, and a surface quality such that the surface roughness Ra is 20 nm or less can be obtained. In addition, the entire surface of the optical element forming surface 26 of the mold material 25 for obtaining the fixed core 20 and the movable core 30 is roughened, and thereafter only the optical surface forming area 22 is formed by using the diamond cutting tool 42. Thus, the width of the boundary region between the optical surface forming region 22 and the die-side rough surface region 23 on the outer periphery thereof can be reduced to 10 μm or less. In the optical element forming surface 26 whose entire surface is roughened, only the optical surface forming region 22 is subjected to turning processing, so that the outer periphery of the optical surface forming region 22 not subjected to the turning processing is the rough surface on the mold side It will be 23.

(3) Cavitation type form In the cavitation type according to the present invention, as shown in FIG. 4, “fixed core side cavitation type 21 arranged on the outer periphery of fixed core 20” and “movable on the outer periphery of movable core 30” There is a core side cavitation type 31 ". There is no particular limitation on these cavitation types, and a mold design according to product specifications may be adopted.

(4) Form of mold for manufacturing optical element The fixed side is obtained by applying the manufacturing method described above and accommodating the "fixed core 20" and fitting with the "fixed core side cavitation mold 21". A mold block 24 "is obtained. On the other hand, the "movable side mold block 33" is obtained by accommodating the "movable core 30" and fitting with the "movable core side cavitation type 31". The "fixed side mold block 24" and the "movable side mold block 33" are brought into opposed contact as shown in FIG. 4 to form a molded body between the "fixed core 20" and the "movable core 30". The optical element manufacturing mold 50 including the space 35 is obtained.

4. Manufacturing Method of Plastic Optical Element A method of manufacturing the optical element 10 using the above-described optical element manufacturing mold 50 will be described. A resin material to be a material of the optical element 10 is injected and filled in the molded body forming space 35 of the optical element manufacturing mold 50 shown in FIG. 4 to form an optical element. Thereafter, the “movable mold block 33” constituting the optical element manufacturing mold 50 shown in FIG. 4 is separated from the “fixed mold block 24”, and the “fixed core 20 of the fixed mold block 24” is separated. The optical element 10 described in the above is released and collected. Therefore, the surface shapes of the optical surface forming area 22 and the mold side rough surface area 23 in the optical element manufacturing mold 20 are the optical surfaces 12 and 13 of the obtained optical element 10 and the optical element side rough surface 15. It will be in the state of being transferred.

  Hereinafter, the present invention will be specifically described by showing Examples and Comparative Examples. It should be noted that the present invention should not be construed as being limited to the following examples.

(1) Mold side rough surface area processing step In the mold for manufacturing an optical element of the embodiment, in order to obtain the fixed core 20 and the movable core 30, a mold steel (STAVAX (made by Uddeholm KK)) is used as a mold material An optical element molding surface 26 was formed with an electroless nickel plating layer having a thickness of 200 μm.

  Then, alumina particles having a medium particle size of 74 μm or less are sprayed from the surface of the electroless nickel plating layer by sand blasting to make the entire surface of the optical element molding surface 26 of the mold material 25 rough. The surface roughness Rz at this time was 10 μm.

(2) Optical surface forming area processing step The mold material 25 obtained by roughening the optical element molding surface 26 is attached to the rotating shaft 41 of the super precision processing machine (manufactured by Fujikoshi Co., Ltd.) 40, and polycrystalline diamond is provided at the opposite position. A diamond cutting tool 42 was used to turn only the optical surface forming area 22 of the optical element forming surface 26. The diamond cutting tool 42 used at this time was composed of polycrystalline diamond having a grain size of 100 nm or less, the rake angle was 28 ° negative angle, and the width 48 of the rake face 44 was 2 μm. Thus, the fixed core 20 and the movable core 30 provided with the optical surface forming area 22 and the mold-side rough surface area 23 on the outer periphery thereof were obtained.

(3) Mold for manufacturing optical element The above-described “fixed core 20” and “fixed core side cavitation type 21” were fitted to obtain “fixed side mold block 24”. On the other hand, the movable core 30 and the movable core cavitation mold 31 were fitted to obtain the movable mold block 33. Then, the “fixed side mold block 24” and the “movable side mold block 33” are brought into opposed contact as shown in FIG. 4 to form between the “fixed core 20” and the “movable core 30”. The optical element manufacturing mold 50 is provided with the body forming space 35.

(4) Production of Plastic Optical Element In the production of the optical element 10 using the above-described optical element production mold 50, an injection molding machine (S-2000i 50B (S-2000i 50B (in the mold forming space 35) of the optical element production mold 50). A thermoplastic resin (ZEONEX E-48R (manufactured by Nippon Zeon Co., Ltd.)) was injected and filled with the resin using FANUC Co., Ltd.). After that, the "movable mold block 33" constituting the optical element manufacturing mold 50 is separated from the "fixed mold block 24", and the optical in the "fixed core 20" of the "fixed mold block 24" The element 10 was released and collected. The optical element 10 obtained in this manner is the optical element 10 in which the surface shape of the optical surface forming area 22 and the mold side rough surface area 23 in the optical element manufacturing mold 50 used for manufacturing is obtained. The optical surface 12, 13 and the rough surface 15 on the optical element side are in a transferred state.

Comparative example

  In the comparative example, instead of the sandblasting method which is a roughening method of the embodiment, NC processing is adopted to adopt a regular uneven shape and only the optical surface forming region 22 of the optical element molding surface 26 The only difference is that a diamond cutting tool 42 using single crystal diamond is used in turning. Therefore, duplicate explanations are omitted here.

[Evaluation results]
Hereinafter, evaluation results of each example and comparative example will be described.

Surface roughness of the optical surface of the optical element: The surface roughness Ra of the optical surface of the optical element obtained in each of the examples and the comparative examples is NewView 7300 (a noncontact three-dimensional surface texture measuring apparatus using a white light interferometer) It measured on the same measurement conditions as the above-mentioned by Zygo company make). The surface roughness Ra of the optical surface of the optical element of the example was 2 nm or less over the entire area, and no local surface roughness was observed. On the other hand, in the case of the comparative example using a single crystal diamond bite for die processing, damage to the diamond bite occurred, so that local surface roughness was generated on the die side, and a place was obtained also in the obtained optical element The surface roughness Ra was about 50 nm, and the condition that the surface roughness Ra was 20 nm or less was not satisfied in the entire region.

Surface Properties of Optical Element Manufacturing Mold: The surface of the rough surface of the optical element manufacturing mold of Examples and Comparative Examples is observed at a magnification of 1000 using a differential interference microscope (STM6 (manufactured by Olympus Corporation)) did. As a result, the microscopic observation photograph of the rough surface part of an Example and a comparative example is shown in FIG.7 and FIG.8. Moreover, the microscope observation photograph of the boundary part of the rough surface and optical surface formation area of an Example and a comparative example is shown in FIG.9 and FIG.10. Furthermore, the surface property of the rough surface of the mold for manufacturing an optical element of the example and the comparative example was measured by a noncontact three-dimensional surface property measuring apparatus (NewView 7300 manufactured by Zygo) using a white light interferometer. The measurement conditions at this time were the same as the measurement conditions of the surface roughness Ra of the optical surface of the optical element described above. Table 1 shows the surface roughness Rz of the rough surface on the mold side of the example and the comparative example, and the average vertex distance of the concavo-convex shape.

  In the example roughened by sandblasting, the surface roughness Rz was 10 μm, and the average vertex spacing was 16 μm (standard deviation 2 μm). It can be confirmed from FIG. 7 that the surface texture of the example is an irregular fine uneven shape without specific directionality and specific periodicity. On the other hand, in the comparative example formed by the machine tool using the NC processing method, the surface roughness Rz is 5 μm, “the average vertex distance in the radial direction is 34 μm (standard deviation 1.5 μm)”, “the circumferential direction The average vertex spacing was 140 μm (standard deviation 6 μm). The surface texture of the comparative example can be confirmed also from FIG. 8 as a fine uneven shape having a constant pattern. In the comparative example, the data in the radial direction and the circumferential direction are considered separately because the concavo-convex shape has regularity, and this regularity differs depending on the direction.

  Further, the difference in the surface shape caused by the difference between the manufacturing method of this embodiment and the comparative example appears notably at the boundary between the rough surface on the mold side and the optical surface forming region. That is, the width of the boundary area between the rough surface on the mold side and the optical surface forming area in the embodiment shown in FIG. 9 is as narrow as about 5 μm as compared with the scale bar of 10 μm in the figure. It can be seen that is not greatly disturbed. On the other hand, the width of the boundary area between the mold-side rough surface and the optical surface forming area in the comparative example shown in FIG. 10 is as wide as about 15 μm as compared to the scale bar of 10 μm in the figure. It can be recognized that the contour line clearly shows the pattern shape of the unevenness forming the rough surface on the mold side.

  The plastic optical element according to the present invention can effectively suppress the mixing of unnecessary light entering the edge surface of the optical element into the optical surface of the optical element. Therefore, an optical apparatus such as an imaging device adopting this plastic optical element can refract a light beam incident from the object side as the optical design and emit it toward the image plane side.

DESCRIPTION OF SYMBOLS 10 plastic optical element 12, 13 optical surface 14 edge surface 15 rough surface 20 fixed core 21 fixed core side cavity type 22 optical surface formation area 23 mold side rough surface area 24 fixed side mold block 25 mold material 26 optical element formation Face 30 Movable core 31 Movable core side cavity type 33 Movable side mold block 35 Mold forming space 40 Ultra precision processing machine 41 Rotary shaft 42 Diamond cutting tool 43 Cutting edge 44 Rake surface 45 Front flank surface 46 Machining point 47 Rake angle 48 Width of face

Claims (13)

A plastic optical element comprising an optical surface and an edge surface located on the outer periphery of the optical surface,
The edge surface is an optical element-side rough surface having irregular asperity shape,
A plastic optical element characterized in that the optical surface has a surface roughness Ra of 20 nm or less measured by a noncontact three-dimensional surface texture measuring apparatus. The plastic optical element according to claim 1, wherein a width of a boundary area between the rough surface on the optical element side and the optical surface is 10 μm or less. The plastic optical element according to claim 1 or 2, wherein the rough surface on the optical element side has a surface roughness Rz of 5 μm to 20 μm as measured by a noncontact three-dimensional surface texture measuring device. The uneven shape of the rough surface on the optical element side is an average vertex distance of 15 μm or more and 20 μm or less of convex portions of the uneven shape measured using a noncontact three-dimensional surface texture measuring device. The plastic optical element according to one item. To manufacture a plastic optical element having an optical surface forming area for forming an optical surface of an optical element and a mold-side rough surface area for forming an optical element-side rough surface provided on an edge surface of the optical element Is a mold of
The mold side rough surface area has an irregular asperity shape,
The optical surface forming region disposed adjacent to the rough surface region on the side of the mold has a surface roughness Ra of 20 nm or less obtained by using a noncontact three-dimensional surface texture measuring apparatus. Mold. The mold for manufacturing a plastic optical element according to claim 5, wherein a width of a boundary area between the rough surface area on the mold side and the optical surface forming area is 10 μm or less. The mold according to claim 5 or 6, wherein the rough surface region on the side of the mold has a surface roughness Rz of 5 μm to 20 μm as measured using a noncontact three-dimensional surface texture measuring device. . The uneven shape of the rough surface on the side of the mold has an average vertex distance between adjacent protrusions obtained by using a noncontact three-dimensional surface texture measuring apparatus of 15 μm to 20 μm. A mold for producing a plastic optical element according to any one of the preceding claims. The mold for manufacturing a plastic optical element according to any one of claims 5 to 8, wherein the rough surface region on the mold side and the optical surface forming region are provided with an electroless nickel plating layer on the surface thereof. A method of manufacturing a plastic optical element manufacturing mold according to any one of claims 5 to 9, wherein
The plastic optical element manufacturing mold comprises a fixed side mold block constituted by a fixed core and a fixed core side cavitation type, and a movable side mold block constituted by a movable core and a movable core side cavitation type It is a counter contact and is provided with a molded body forming space between the fixed core and the movable core,
The optical element forming surface of the fixed core and the movable core is roughened by sandblasting, and after roughening, the optical surface forming region of the fixed core and the movable core is turned using a polycrystalline diamond bite. A method of manufacturing a mold for manufacturing a plastic optical element. The method for producing a mold for producing a plastic optical element according to claim 10, wherein the polycrystalline diamond bite is obtained by using nano-polycrystalline particles having a particle diameter of 100 μm or less. The angle between the polycrystalline diamond bite scan direction and the rake face of the polycrystalline diamond bite, where the polycrystalline diamond bite is relative to the axial direction and when the polycrystalline diamond bite scanning direction is positive. The method of manufacturing a mold for manufacturing a plastic optical element according to claim 10 or 11, wherein the light emitting element is inclined in the negative direction in the range of 25 ° to 30 °. The method for manufacturing a mold for manufacturing a plastic optical element according to any one of claims 10 to 12, wherein a rake surface on the cutting edge ridge line of the polycrystalline diamond bite has a width of 1 μm to 3 μm.