JP2008257261A - Optical device, optical device molding die, and method for molding optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that an optical device having excellent optical characteristics based on a highly accurate transferability can not be stably obtained at high yield even by controlling molding conditions such as a gate shape formed in a molding die for filling a molding material, injection, pressure holding, and cooling, in an optical device requiring many apertures, a small size and a thin shape, and a multi-function property. <P>SOLUTION: Since the optical performance of an optical device is made different by making the outer diameter of the optical device and the shape of edge thickness different from each other, relation between the outer diameter size and the edge thickness of the optical device can be greatly affected to the transferability. When it is defined that the outer diameter of the optical device is ϕG and the thinnest edge thickness of the optical device is K, the optical device is set to satisfy relation ϕG/K≤12.5. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to high-precision optical elements such as lenses, prisms, and mirrors used in optical equipment such as digital video disk players and compact disk players, and a molding die used for molding the optical elements, and a molding method therefor About.

  Conventionally, molding of an optical element such as a lens used in a digital video disk player or the like, for example, as disclosed in Patent Document 1, a molding material (resin pellet) is heated and kneaded and melted, and this is used as a molding die. An injection molding method in which a cavity is injection-filled and molded is generally used.

  FIG. 3 is a schematic cross-sectional view of an injection molding machine that is molding a plurality of optical elements at a time by an injection molding method, wherein 7 is a hopper, 8 is a molding material, 9 is an injection cylinder, 10 is a heating cylinder, and 11 is a screw. , 12 is a nozzle, 13 is a fixed die plate, 14 is a moving die plate, 15 is a clamping cylinder, 5 is an optical element molding die on the fixed side, 5a is integrally formed by embedding in the optical element molding die 5 on the fixed side, etc. Fixed side insert 6, 6 is a movable side optical element molding die, 6 a is a movable side insert integrally formed by embedding in the movable side optical element molding die 6, 4 is a sprue, 3 is a runner, 2 is a gate Reference numeral 1 denotes an optical element.

  The optical element 1 is transfer-molded by the shape of the cavity 16 formed on the abutting surface of the fixed-side insert 5a and the movable-side insert 6a.

The molding material 8 put into the hopper 7 moves in the direction of the nozzle 12 as the screw 11 in the heating cylinder 10 rotates. At this time, the molding material 8 is heated and kneaded and melted by the screw 11 and the heating cylinder 10, and passes from the nozzle 12 through the portion where the sprue 4, the runner 3 and the gate 2 are formed, and then the fixed side insert 5a and the movable side insert 6a. Are injected and filled into the cavity 16 of the butt portion. The optical element molding dies 5 and 6 are set to a predetermined temperature, for example, a glass transition temperature or higher. After the molding material 8 is filled, the optical element molding dies 5 and 6 are cooled to change the molding material in the cavity 16. Cool and solidify. As a result, the optical element 1 can be taken out, and the movable side insert element 6a is moved backward by opening the cavity 16 by moving the movable side optical element forming die 6 back by the clamping cylinder 15. And the optical element 1 is separated from the sprue 4, runner 3, and gate 2.
JP-A-61-233520

  In recent years and in the future, optical devices required for multi-function optical devices such as multi-type optical devices capable of reproducing and recording both digital video discs and compact discs have an unprecedented high optical element. There is a tendency to reduce the numerical aperture, reduce the thickness, and increase the number of functions (optical elements that can handle multiple wavelengths). For this reason, the edge part formed outside the effective surface of the optical element of the optical element becomes thinner, In addition, it is desired to form a diffraction grating having a fine step shape on the lens effective diameter surface with high accuracy, and high accuracy and high transferability that are not conventionally required are required.

  Optical elements that have been required to have a high numerical aperture, small thickness, and multi-function as described above have the gate shape formed in the mold for filling the molding material, and molding conditions such as injection, holding pressure, and cooling. Regardless of how it is controlled, it is difficult to achieve high-precision transferability, and it is therefore difficult to stably obtain an optical element having excellent optical characteristics at a high yield.

  In addition, these optical elements have a small diameter and a fine surface, which requires more care than conventional optical elements. In the post-molding process, for example, a holder for holding an optical element is used. In addition to the need to pay close attention to conveyance during bonding, etc., problems such as adverse effects on optical characteristics due to slight external forces have arisen.

  In order to solve the above-mentioned problems, the present inventor has conducted various experiments and identifications, and as a result, the transferability of the optical element other than the shape of the gate of the optical element mold and the injection, filling, holding pressure, and cooling conditions has been improved. As a factor which influences, it discovered that the optical performance of the optical element obtained changes by changing the shape of the outer diameter and edge thickness of an optical element.

  This means that in a highly accurate optical element, particularly an optical element in which a diffractive surface is formed on the effective diameter of the lens, the relationship between the outer diameter dimension and the edge thickness greatly affects the transferability.

  As a result of various verifications, when the outer diameter of the optical element is φG (mm, the following is the same), and the thinnest edge thickness of the optical element is K (mm, the following is the same), φG / K ≦ 12. It has been found that it is desirable to configure the relationship of five.

  Further, in the present invention, the lens has an effective lens diameter φLY (mm, hereinafter the same unit) through which light passes through the optical element 1, and a lens processing diameter φLK (mm, hereinafter the same unit) slightly larger than that. The lens processing diameter φLK and the thinnest edge thickness portion are adjacent to each other.

  Further, a diffractive surface is formed on the lens effective diameter φLY on either the light incident surface side or the light exit surface side.

  Further, when the center thickness of the optical element is T (mm, the following unit is the same) and the thinnest edge thickness is K, the relationship is T / K ≦ 8.75.

  Further, the material for forming the optical element is any one of acrylic, polycarbonate, norbornene, and amorphous polyolefin.

  Furthermore, a part of the gate portion formed on the outer diameter portion of the optical element is left by injection-filling a molding material into the cavity.

  The optical element, the optical element molding die, and the optical element molding method of the present invention are reduced in diameter, thinned, increased in numerical aperture, and enhanced in function by managing the outer diameter of the optical element and the thinnest edge thickness of the optical element. Can be obtained with good transferability (optical characteristics), and the cost of the optical element can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings and tables.

  FIG. 1 is a schematic diagram of the shape of an optical element in the embodiment, FIG. 1 (a) is a schematic top view, FIG. 1 (b) is a schematic cross-sectional view, and FIG. 1 (c) is a 1d portion of FIG. FIG. FIG. 2 is a schematic diagram of the shape of an optical element molded product in the process of molding a plurality of optical elements shown in FIG. 1 at a time, FIG. 2 (a) is a schematic top view, and FIG. 2 (b) is a schematic cross-sectional view. . In addition, FIG. 3 is used about the injection molding machine in embodiment described here.

  1 is an optical element, 1a is a lens portion including the effective lens diameter φLY of the optical element 1, 1b is an edge portion integrally formed adjacent to the outer edge of the lens portion 1a, and 1c is formed on a lower end surface of the outer edge of the edge portion 1b. , 2 is a gate, 3 is a runner, and 4 is a sprue.

  The effective diameter φLY of the lens portion 1a is an optical action surface that is minimally required to produce the optical characteristics required for the optical element 1, and serves as a light path.

  The shrinkage rate of the molding material is expected to be at least about 0.1 to 0.9% of the effective diameter of the lens on the butting surface of the inserts 5a and 6a of the optical element molds 5 and 6 to be transferred corresponding to the lens effective diameter φLY. A cavity 16 is formed with an effective diameter. The lens processing diameter φLK is slightly larger than the lens effective diameter φLY, specifically, it is formed to be at least about 0.1 to 0.9% shrinkage of the molding material. As a result, it is possible to cope with subtle shrinkage of the molding material and generation of warpage accompanying changes in molding conditions.

  Further, the thinnest edge thickness K referred to in this example is the thickness of the thinnest part of the edge part 1b formed adjacent to the lens processing diameter φLK.

  The inventor manufactured a plurality of inserts so as to variously change the outer diameter φG and the thinnest edge thickness K of the optical element shown in FIG. These optical characteristics were evaluated and confirmed by molding optical elements having different sizes. During this work, depending on the shape of each optical element, the molding conditions and the gate shape of the mold are examined each time, the optimum conditions are extracted, and the transferability (optical characteristics) of each optical element shape is determined. Verified.

  Here, the optical element shaping | molding method is demonstrated concretely.

  As the molding material, a trade name “APEL” manufactured by Mitsui Chemicals, Inc., which is an amorphous polyolefin resin, a glass transition point Tg = 135 ° C., and a thermal deformation temperature Tt = 125 ° C. were used.

  The injection molding machine is of the type shown in FIG. 3, and the optical element molding dies 5 and 6 are made of prehardened steel, stainless steel (S55C, HPM, NAK) or the like, and the effective lens diameter of the optical element 1 The inserts 5a and 6a formed with a transfer surface corresponding to φLY were made of cemented carbide material. There are no problems with the optical element molds 5 and 6 as long as they can be used for injection molding other than the materials described above. In addition, as a material of the inserts 5a and 6a, if the surface property as the optical element 1 is obtained, a material having stainless steel (STAVAX) or the like as a base material and electroless nickel plating on the surface thereof is processed. There is no problem even if used. However, when the strength is considered, it is preferable to use a cemented carbide as the base material. Further, a protective film or the like may be applied to the surface in order to improve releasability and prevent mold oxidation and corrosion.

  Next, a molding process using the above-described optical element mold will be described with reference to FIG.

  The molding material 8 put into the hopper 7 moves in the direction of the nozzle 12 as the screw 11 in the heating cylinder 10 rotates. At this time, the molding material 8 is heated, kneaded and melted by the screw 11 and the heating cylinder 10 set at a set temperature of 260 ° C., and the sprue 4, the runner 3, and the gate 2 are formed from the nozzle 12 heated to 260 ° C. After passing through the section, the cavity 16 formed by the fixed-side insert 5a and the movable-side insert 6a that are integrally formed by being embedded in the optical element molds 5 and 6 is injected and filled, and the pressure is maintained.

The optical element molds 5 and 6 are set and held at a predetermined constant temperature, here, 135 ° C. which is the same as the glass transition temperature Tg of 135 ° C., and at the same time the molding material 8 begins to fill the cavity 16, It will be cooled. Unless appropriate injection conditions, filling conditions, pressure holding conditions, and temperature conditions of the optical element molds 5 and 6 are selected, desired optical characteristics of the optical element 1 cannot be obtained. In particular, the set temperature of the optical element molds 5 and 6 is an important factor. From various verifications, the set temperature of the optical element molds 5 and 6 is maintained at a temperature within a range of ± 10 ° C. with respect to the glass transition point. For example, it has been found that good transferability can be obtained without changing the set temperature of the optical element molds 5 and 6 between filling of the molding material 8 and cooling.

  When the set temperature of the optical element molds 5 and 6 is higher than the above-described range, the optical element 1 cannot be sufficiently cooled, and the transfer shape may be deformed after removal, or the optical element mold 5 , 6 is set to a temperature lower than the above-mentioned range, the surface layer generated by the premature cooling when the molten molding material comes into contact with the inner surface of the cavity 16 is improved even after the subsequent cooling time. It was never done.

  As described above, after the cooling process is completed in the cavity 16 for 10 to 180 seconds depending on the shape of the optical element 1 in a state where the temperature of the optical element molds 5 and 6 is maintained at a predetermined temperature of 135 ° C. The movable optical element molding die 6 is moved backward by the clamping cylinder 15 to open the cavity 16, and the molded product is taken out with the sprue 4, the runner 3, the gate 2 and the optical element 1 being integrated.

  In the effective lens portion of the optical element, a fine diffractive surface is formed on either the light incident surface side or the light exit surface side based on the diffractive shape forming surface formed on the transfer surface of the cavity 16. This diffractive surface shape is to obtain the optical performance of the optical element required for multi-type optical equipment, etc., and since the shape is an extremely fine sawtooth shape, the molding conditions and the shape as the optical element are transferable. It was found that it greatly affects

  In particular, the transfer accuracy of the sawtooth shape, which is a diffractive shape, such as the pitch interval of the sawtooth shape, the height of the sawtooth shape, the sharpness of the sawtooth shape, the shape of the valley bottom, and the like, the outer diameter φG of the optical element and its optical element It has been proved by verification that the thickness changes greatly depending on the thinnest edge thickness K of the edge portion formed at the outer edge portion and the center thickness T of the optical element.

  Here, as shown in FIG. 1C, a plurality of sawtooth shapes centering on the optical axis of the optical element 1 are concentrically formed on the lens surface of the optical element 1 having a lens effective diameter φLY on the light incident side. Diffractive shapes are formed. The plurality of sawtooth shapes forming the diffractive shape have different pitch intervals, height dimensions, and the like. The narrowest pitch interval is 5 μm, the highest height dimension is 1.2 μm, and the radius R of the arc shape of the acute angle portion is 0. 1 μm. This diffractive shape is designed into a desired shape depending on the application of the optical element 1.

  When the optical element 1 having a diffractive shape is molded, good optical characteristics cannot be obtained unless the molding material is filled and transferred to the serrated acute angle portion which is a very fine portion as described above. That is, when an optical element having a diffractive shape is molded under molding conditions (control of only temperature and pressure) of an optical element having no diffractive shape, it is difficult to transfer to a sufficiently fine shape. Although the R shape at the acute angle portion should be transferred at 0.1 μm, for example, the R shape becomes 0.8 μm with insufficient transfer, and the initial lens performance cannot be obtained.

  Next, evaluation of the optical element will be described.

  First, in addition to the molding conditions, the gate shapes of the optical element molds 5 and 6 were also examined, and the best transferability was obtained with each optical element shape.

For evaluation of transferability, optical characteristics were confirmed by measuring transmitted wavefront aberration using an interferometer. If the optical characteristics are good, it can be determined that the transferability is good. Here, each sample optical element was measured and evaluated so that it was satisfactory if the measurement result of the transmitted wavefront aberration was 40 mλ or less (λ≈655 nm) in terms of RMS aberration, and whether the RMS aberration was greater than 40 mλ.

  Table 1 shows the evaluation confirmation results of optical characteristics (transferability) of optical element samples having different shapes. In the table, ◯ indicates that desired optical characteristics are obtained and transferability is good, and x indicates that transferability is insufficient.

As can be seen from Table 1, it was found that good transferability could be obtained if the relationship of outer diameter φG / thinnest edge thickness K ≦ 12.5 was satisfied. In Table 1, the units such as the outer diameter φG and the thinnest edge thickness K are mm.

  Furthermore, the inventor in order to verify whether or not the above relationship is reliable and applicable, a plurality of molding materials, specifically, a trade name “Acrypet” manufactured by Mitsubishi Rayon Co., Ltd., which is an acrylic material. The product name “Panlite” manufactured by Teijin Chemicals Co., Ltd., which is a polycarbonate material (polycarbonate ester type), and the product name “ARTON” manufactured by Nippon Synthetic Rubber Co., Ltd., which is a norbornene material, are used as shown in Table 2. A plurality of optical elements 1 having dimensions and shapes were molded, and these were examined under the same evaluation conditions as described above to confirm transferability. The center thickness T in the table indicates the thickness of the optical element 1 on the optical axis as shown in FIG.

  From Table 2, it can be confirmed that the same results are obtained for any of the molding materials described above.

  In any of the above molding materials, the set holding temperature of the optical element molds 5 and 6 is good if it is in the range of the glass transition point Tg ± 10 ° C., similar to the amorphous polyolefin-based material described above. Transferability was obtained.

From the result of the present embodiment, if the relationship of the outer diameter φG / thinnest edge thickness K ≦ 12.5 is satisfied, the uneven thickness ratio represented by the ratio of the center thickness T and the thinnest edge thickness K = Even when the center thickness T / the thinnest edge thickness K was as large as 8.75 as in sample No. 14 or 30, good transferability could be obtained.

  In addition, optical elements required for optical equipment for realizing both reproduction and recording of a plurality of optical media such as digital video discs and compact discs are reduced in diameter, thinned, increased in numerical aperture, and improved in functionality. At the same time, cost reduction is desired, and in order to realize these, the optical element not only obtains good transferability, that is, optical characteristics as described above, but also in post-molding processes. Ingenuity is necessary.

  The process after the molding will be specifically described. In a relatively small and thin element having an outer diameter φG of the optical element 1 of 5 mm or less and a thinnest edge thickness K of 0.5 mm or less, holding when holding the optical element 1 in the optical element 1 at the time of gate cutting after molding. Force, stress, heat, and the like are generated at the time of cutting, and the transferability of the lens effective diameter portion thus obtained is impaired and the yield is greatly reduced. In addition, holding force and stress are applied to the optical element when it is transported to a holder for holding the optical element 1, and careful handling is required. In particular, in the small optical element 1 having an outer diameter of 3 mm or less and the thinnest edge thickness K of 0.4 mm or less, the productivity is greatly hindered.

  In order to solve these problems, in the present invention, the gate is cut so that the gate portion formed in the outer diameter portion of the optical element 1 remains. Thereby, stress, heat, etc. at the time of gate cutting do not affect the lens effective diameter portion of the optical element, and good transferability can be maintained. In addition, the high accuracy of the cut dimensions at the time of gate cut is no longer required, and the gate cut itself becomes easy and the cost of the gate cut equipment can be reduced. In addition, it is possible to transport the optical element 1 using the remaining gate portion, or to use the gate portion as a guide for positioning on the holder, thereby improving the production efficiency.

  The present invention has been found based on the verification by the above-described embodiment, that good transferability can be obtained by the optical element shape, the optical element molding die, and the optical element molding method that satisfy the above-mentioned requirements. As a result, the optical element can be made smaller in diameter, thinner, higher numerical aperture, higher functionality, and lower cost.

  In the above embodiment, a fine diffractive surface is formed on the lens effective diameter surface of one of the optical elements, that is, on the incident surface side or the exit surface side of the light beam, but the present invention forms a diffractive surface. Of course, the present invention can be applied to optical elements that do not. Further, the convex portion 1c is provided on the edge portion of the optical element. However, the shape of the convex portion is, for example, a shape that matches the shape of the holder that holds the optical element, or to increase the rigidity of the optical element. Convex portions may be provided on both sides as well as on one side. Furthermore, an optical element having a shape in which no convex portion is provided may be used.

  The present invention relates to high-precision optical elements such as lenses, prisms, and mirrors, and molding thereof, and is suitable for optical elements used in optical equipment such as digital video disk players and compact disk players.

BRIEF DESCRIPTION OF THE DRAWINGS It is a shape schematic of the optical element in embodiment of this invention, (a) is a schematic top view, (b) is a schematic sectional drawing, (c) is an expanded schematic sectional drawing of the 1d part of (b) figure. FIG. 2 is a schematic diagram of a shape of an optical element molded article including the optical element shown in FIG. 1 according to an embodiment of the present invention, where (a) is a schematic top view and (b) is a schematic cross-sectional view. Schematic cross-sectional view of an injection molding machine during molding of an optical element in an embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical element 1a Lens part 1b Edge part 1c Convex part 2 Gate 3 Runner 4 Sprue 5 Fixed side optical element molding die 5a Fixed side insert 6 Movable side optical element molding die 6a Movable side insert 7 Hopper 8 Molding material 9 Injection cylinder DESCRIPTION OF SYMBOLS 10 Heating cylinder 11 Screw 12 Nozzle 13 Fixed die plate 14 Moving die plate 15 Clamping cylinder 16 Cavity

Claims (10)

An optical element that is molded by injection-filling a molding material that has been heat-kneaded and melted into a cavity formed in an optical element mold,
When the outer diameter of the optical element is φG (mm) and the thinnest edge thickness of the edge portion formed at the outer edge of the optical element is K (mm), the relationship was φG / K ≦ 12.5 An optical element characterized by the above. The optical element has a lens effective diameter φLY (mm) through which light passes and a lens processing diameter φLK (mm) slightly larger than that, and an edge portion is formed on the outer edge of the lens processing diameter φLK (mm). The thinnest edge of the edge is adjacent to the lens processing diameter φLK (mm), and the diffractive surface has a lens effective diameter φLY (mm) on either the incident surface side or the exit surface side of the light beam. The optical element according to claim 1, wherein the optical element is formed. 2. The optical element according to claim 1, wherein T / K ≦ 8.75 is satisfied, where T (mm) is the center thickness of the optical element and K (mm) is the thinnest edge thickness of the edge portion. 2. The optical element according to 2. The optical element according to any one of claims 1 to 3, wherein a material forming the optical element is any one of an acrylic, a polycarbonate, a norbornene, and an amorphous polyolefin. The optical element according to any one of claims 1 to 4, wherein a gate formed in an outer diameter portion of the optical element molded by injection filling of the molding material remains. An optical element mold for molding an optical element by heating and kneading and melting a molding material, and injection-filling this into a cavity,
When the outer diameter of the optical element is φG (mm) and the thinnest edge thickness of the edge portion formed on the outer edge of the optical element is K (mm), the cavity has a relationship of φG / K ≦ 12.5. An optical element molding die formed. On the cavity forming surface of the movable side insert and the fixed side insert of the optical element forming die constituting the cavity, an effective lens diameter φLY (mm) through which light passes through the optical element and a lens processing diameter φLK (mm slightly larger than that) 7. An optical element according to claim 6, wherein a diffraction surface is formed on the transfer surface having a lens effective diameter φLY (mm) on either the light incident surface side or the light exit surface side. Mold. When the center thickness of the optical element molded by injection filling of the molding material into the cavity is T (mm) and the thinnest edge thickness is K (mm), T / K ≦ 8.75. 8. The optical element mold according to claim 6, wherein the optical element mold is used. An optical element molding method in which a molding material heated and kneaded and melted is molded by injection filling into a cavity formed in an optical element molding die,
Using an optical element mold in which a cavity having a relationship of φG / K ≦ 12.5 is formed, where the outer diameter of the optical element is φG (mm) and the thinnest edge thickness of the optical element is K (mm) The optical element molding is characterized in that the temperature of the optical element molding die is set in the vicinity of the glass transition point, the molding material heated and kneaded and melted is filled in the cavity and then held in pressure, and cooled near the glass transition temperature. Method. 10. The optical element molding method according to claim 9, wherein the set temperature of the optical element mold is a temperature in the range of −10 ° C. to + 10 ° C. based on the glass transition temperature.