JP5067664B2 - Mold for optical element and optical element - Google Patents

Description

  The present invention relates to a resin molding technique, and more particularly to a molding die suitable for molding an optical element and an optical element molded thereby.

  In recent years, research and development of high-density optical disc systems that can record and / or reproduce information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm. Development is progressing rapidly. As an example, in an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4.7 GB) It is possible to record information of 23 to 27 GB per layer on an optical disc having a diameter of 12 cm which is the same size as the above. This optical disc is referred to as a high density optical disc in this specification.

By the way, such an optical element for an optical disk is formed by injection molding of resin and generally uses a mold having a movable mold and a fixed mold, and when these molds are clamped, these molds are interposed between the molds. The obtained space (cavity) is filled with resin and molded by injection molding in which heating and pressing are performed. Here, when injection molding or the like is performed by feeding the molten resin in this way, air in the cavity remains, and when the resin is solidified as it is, the shape of the molded product may be damaged. On the other hand, as shown in Patent Document 1, there is known a molding method in which an air escape passage (air vent) communicating with a cavity is provided in addition to a gate for supplying a melted resin so that unnecessary air is allowed to escape during injection molding. It has been.
JP 2004-264538 A

  However, in the molding method in which such an air vent is provided, the following problems may occur conversely. That is, there is a problem that an unexpected burr (air vent burr) is generated when the resin enters the air vent and is solidified. In particular, when a thermosetting resin or an ultraviolet curable resin having a viscosity before molding lower than that of a thermoplastic resin is used as a material as a resin material, the resin is likely to enter a narrow gap, which further increases the occurrence of air vent burrs.

  However, for such burrs, it is not practical to employ a cutting process similar to that normally performed at a gate, for example, a cutting process using a tool such as a cutter.

  Because it is common sense that burrs do not occur in the first place, the burrs that are formed are non-uniform in frequency and amount of generation depending on the molding conditions, and the gates that are expected to be formed in advance. Compared with it, it is very thin and brittle. For this reason, even if the cutting method is the same as that for the gate, fine cutting powder is generated and pinched at the mounting position with the lens, and the mounting position is adversely affected. As a result, excessive stress is applied and distortion occurs, resulting in problems such as the characteristics of the optical element becoming unstable in mass-produced products.

  In the method of Patent Document 1, such a problem is dealt with by adjusting the burr length and position within a predetermined range. However, as described above, since such burrs are not expected to occur from the beginning, such adjustment leads to adjustment of molding conditions such as adjustment of resin pressure from the gate, and balance with optical element characteristics. The adjustment while taking is more difficult.

  The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a molding die and an optical element that can be used to mold a high-quality optical element without taking time and effort.

  A first embodiment of the present invention is a molding die for an optical element for molding a resin optical element, and a movable side mold having a transfer surface for transferring one of the two optical surfaces; A fixed side mold having a transfer surface for transferring the other optical surface of the two optical surfaces, and the movable side and the fixed side mold are brought into contact with the movable side and the fixed side mold. Each of the opposing surfaces of the movable side and fixed side molds form a cavity between the molds clamped, and the cavity Forming a gate for supplying a resin material from the inside to the inside and an air vent for discharging air from the inside of the cavity, and at least of the opposing surfaces of the movable side and fixed side molds forming the air vent One side is fed into the air vent It is molding die for optical element characterized that projections to reduce a portion of the cross-sectional area of the air vent resin portion resin is formed by solidifying partially are formed.

  According to a second aspect of the present invention, there is provided the optical element molding die according to the first aspect, wherein the protrusion has a shape in which a tip is narrow along a protruding direction.

  According to a third aspect of the present invention, the air vent has a cross-sectional area of 50 to 70% of a portion where the protrusion is provided with respect to a portion where the protrusion is not provided. An optical element molding die according to any one of the first and second embodiments.

  According to a fourth aspect of the present invention, the gate and the air vent are formed at positions symmetrical to each other with respect to an optical axis of an optical element molded by the molding apparatus. It is a molding die for optical elements concerning any one of the 3rd forms.

  According to a fifth aspect of the present invention, there is provided the optical element molding die according to any one of the first to fourth aspects, wherein the optical element is an objective lens having an NA of 0.8 or more. .

  According to a sixth aspect of the present invention, in the optical element in which an optical surface and a flange portion formed in a circle on the outer periphery thereof are formed by resin molding, a part of the flange portion is linear in the flange portion. A notch surface formed so as to be cut out, and the notch surface has an air vent resin cut portion formed by cutting away a portion of the air vent resin portion connected to the flange portion. The end portion of the air vent resin excision portion is located inside the outer radius from the optical axis center to the outer periphery of the flange portion, and is smaller than the cross-sectional area other than the end portion of the air vent resin excision portion. This is an optical element.

  According to a seventh aspect of the present invention, the flange portion includes a gate cut portion formed by cutting a gate portion connected to the flange portion at a position different from the cutout portion. It is an optical element which concerns on the said 6th form.

  According to an eighth aspect of the present invention, in the seventh aspect, the gate cut portion and the air vent resin cut portion are formed at positions symmetrical to each other with respect to the optical axis of the optical element. It is an optical element concerning.

  In the ninth aspect of the present invention, the cross-sectional area of the end portion of the air vent resin excision part is formed to have a cross-sectional area of 50 to 70% with respect to the cross-sectional area other than the end part of the air vent resin excision part. An optical element according to any one of the sixth to eighth aspects.

  According to a tenth aspect of the present invention, any one of the sixth to ninth aspects is characterized in that the end portion of the air vent resin excision portion has a larger surface roughness than the other surface portion of the optical element. One of the optical elements.

An eleventh aspect of the present invention is the optical element according to any one of the sixth to tenth aspects, wherein the optical element is an objective lens for an optical pickup device having an NA of 0.8 or more. is there.

  Note that the term “projection” as used herein refers to a portion that protrudes locally from the formation surface, as well as the end of the air vent where the structure is formed so that the cross-sectional area decreases from the other end. Alternatively, it may be connected to one end as it is.

  According to the present invention, based on the conventional concept of molding, that is, the concept of suppressing the generation of burrs as much as possible, the resin is positively applied at a pressure high enough to allow the resin to enter the air vent. Is a solidified resin in the air vent that is formed in the opposite direction, that is, the air vent resin part is different from the gate cutting and can be cut easily and without affecting the optical element and its positioning A type is provided. The resulting optical element is of stable quality with good optical properties. This is particularly true even for an objective lens having a large curvature, such as a high NA objective lens of NA 0.8 or higher that focuses laser light for recording / reproducing information on the information recording surface of a high-density optical disc. Since the resin can be supplied at a high pressure without worrying about the resin intrusion into the air vent, the resin is transferred to every corner, and as a result, it is possible to provide a stable objective lens having high optical characteristics. .

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a process of molding a resin using the molding apparatus according to the present embodiment. FIG. 2 is an enlarged cross-sectional view of the molding apparatus according to the present embodiment with the mold clamped. FIG. 3 is a view of a part of the fixed mold 20 as viewed from the movable mold 10 side.

  In FIG. 1, a movable mold (first mold) 10 has a plurality of first optical transfer surfaces (first transfer surfaces) 11a and a first flange transfer surface 11b. The fixed mold (second mold) 20 includes a plurality of second optical transfer surfaces (second transfer surfaces) 21a, a second flange transfer surface 21b, a spool 22 formed therebetween, and a second flange transfer surface 21b. And a runner 23 connecting the spool 22. A gate (inlet channel) GT is formed between the runner 12 and the second flange transfer surface 21b. The spool 22 is connected to a nozzle N which is a resin supply unit.

  2 and 3, a shallow groove 24 that connects the second flange transfer surface 21 b and the outside is formed on the surface of the fixed mold 20. As a result, when the mold is clamped, an air vent (air vent) AB having a thin cross section is formed between the lower surface of the opposed movable mold 10 and the cavity CB formed by the first transfer surface 11 and the second transfer surface 21. And the outside of the mold are in fluid communication with each other. In the present embodiment, the triangular wall-shaped protrusion 13 is substantially grooved when viewed in a cross section in a direction parallel to the direction of the air vent, which is formed thinly along the direction protruding from the lower surface of the movable mold 10. It is formed so as to protrude into the air vent AB with a width. The protrusion amount Δ of the protrusion 13 is set so as to have a cross-sectional area of 50 to 70% with respect to the cross-sectional area of the section of the air vent AB where the protrusion is not formed in a direction orthogonal to the direction of the air vent. Preferably it is done.

  In FIG. 3, the position where the shallow groove 24 is connected projects inward on the inner periphery forming the second flange transfer surface 21 b of the fixed mold 20. That is, the inner circumference forming the second flange transfer surface 21b is a plane formed by connecting the circumferential surface 21c of radius R from the center O of the optical transfer surface 21a and both circumferential ends P of the circumferential surface 21c in a string shape. 21d. Here, the tip of the protrusion 13 of the movable mold 10 is located at a distance L (L <R) from the center O, as indicated by a one-dot chain line.

  When the projection 13 is viewed from the molded optical element, when the air vent resin portion formed on the optical element is formed beyond the position to the outside, a cutting operation as described later is performed. It corresponds to the position of the end of the air vent resin excision part connected to the remaining part after the air vent resin part excision obtained in this way, that is, the flange part.

  Next, a method for molding an optical element will be described. First, as shown in FIG. 1A, the movable mold 10 is set above the fixed mold 20. Thereafter, as shown in FIG. 1B, the movable mold 10 is brought into close contact with the fixed mold 20, and the mold is clamped at a predetermined holding pressure.

  Further, by heating the movable mold 10 and the fixed mold 20 with the heater 50, the optical transfer surfaces 11a and 21a at the time of mold clamping are heated to a predetermined temperature, and then the nozzle N is pressurized to an arbitrary pressure. Resin is supplied (see FIG. 1C). At this time, since air remaining in the cavity CB is released from the air vent AB, the formation of an air reservoir in the cavity CB is suppressed, and the resin can be closely adhered to the transfer surface with high accuracy.

  Then, after the molten resin is solidified in a state where the shapes of the transfer surfaces 11a, 11b, 21a, and 21b are transferred, the mold temperature is lowered to cool and solidify the resin. In addition, when the raw material supplied in a type | mold is a thermosetting resin, it can be solidified by heating to hardening temperature.

  Thereafter, when the movable mold 10 is moved upward to open the mold, the molded product M rises in a state where it is adhered to the movable mold 10. At this time, when the resin enters the air vent AB and solidifies, an air vent resin portion associated with the molded product is formed. In such a case, for example, if the resistance at the time of mold opening is relatively increased by making the outer draft angle shallower than the draft angle of the shallow groove 24 on the inner side from the narrowed portion, the protrusions 13 are formed by the stress at the time of mold opening. As a starting point, the air vent resin part breaks and remains on the fixed mold 20 side. Thereby, mold opening and removal of an air vent resin part can be performed simultaneously, and reduction of a manufacturing man-hour can be aimed at.

  On the other hand, as another method, a method in which the air vent resin portion is left attached to the molded product M and a breakage operation is performed in a later process can be taken.

  FIG. 4 is a diagram illustrating a state in which the air vent resin portion is removed from the molded product M in a subsequent process. FIG. 5 is a view of the molded product M after removing the air vent resin portion as seen from the optical axis direction of the optical element OE. FIG. 6 is a view of the air vent resin portion BR remaining after the breakage shown in FIG. 5, that is, the air vent resin cut portion as viewed in the direction of arrow VI. FIG. 7 is a view of the air vent resin portion BR shown in FIG. It is the figure seen in the direction.

  In FIG. 4, when the operator grips the spool SP side with the hand H, sandwiches the tip side of the air vent resin portion with tweezers PS, and applies a downward (or upward) force, the cross-sectional area is locally increased. Stress concentration occurs in the notch NT having a triangular groove shape formed corresponding to the protrusion 13 that is smaller than the other portions, so that the air vent resin portion can be easily and reliably positioned at a predetermined position. Can break. In addition, it is possible to cut the gate first while supporting the flange portion, thereby suppressing the influence on the distortion of the optical surface.

  By adopting a configuration in which such a protrusion is provided, it is possible to cut a cutting operation that has been performed with a conventional tool even by a manual operation with a small stress, and the cutting position is determined at the predetermined position, so that the cutting is performed reliably. I can do things.

  As shown in FIGS. 6 and 7, the front end surface of the air vent resin cut portion BR remaining in the flange portion after being broken has a smooth tapered surface BR1 to which the shape of the protrusion 13 is transferred, and the broken surface has a large roughness. It consists of a fracture surface BR2. Here, assuming that the height A of the air vent resin excision BR is uniform, B / A = 0.5 to 0.7 when the height of the fracture surface BR2 is B.

  As shown in FIG. 5, the optical element OE includes an optical surface OE1 transferred from the optical transfer surfaces 11a and 21a, and a flange portion OE2 transferred from the flange transfer surfaces 11b and 21b. Further, the outer peripheral surface of the flange portion OE2 has a notch that is notched by connecting the cylindrical surface OE2a having a radius R that is a predetermined angle range and both ends in the circumferential direction of the cylindrical surface OE2a in a string shape, so-called D-cut. Surface OE2b. The air vent resin excision part BR is formed at the center of the notch surface OE2b, and the tip thereof, that is, the end part of the air vent excision part is located at a distance L (L <R) from the optical axis X of the optical surface OE1. If the distance L is made closer to the radius R, the influence on the distortion of the optical surface can be reduced. Of course, it goes without saying that the closer the amount of protrusion from the cut-out surface OE2b of the air vent resin excision BR is closer to zero, the better the optical element OE can be handled.

  Therefore, the optical element after molding as described above has an advantage that the burr BR does not get in the way when the gate is cut at the position shown in the figure and then installed on a lens frame having an inner periphery with a radius R. The gate excision GT after cutting the gate is used for determining the phase in the rotational direction about the optical axis X of the optical surface OE1, but in this case, the air vent resin excision BR is molded except for breakage. Since the surface roughness is larger than the cut trace of the cut gate cut portion GT as well as the surface of the optical element, the operator who determines the phase may mistake the air vent resin cut portion BR and the gate cut portion GT. There are few.

  In the present embodiment, the gate excision part that has been excised while leaving a part of the gate in the flange part is described as an example, but the present invention is not particularly limited to this, and the gate part is cleaned along the circumferential shape of the flange part. The removed optical element may be used.

  According to the present embodiment, since the protrusion 13 is formed on the movable mold 10, the air vent resin portion formed by solidifying the resin material in the air vent AB has a notch NT corresponding to the protrusion 13. Therefore, the air vent resin part can be easily separated from the optical element OE by breaking it from the starting point, and the processing of the cutting powder does not take time as in the case of cutting. Further, since the air vent resin part is always broken at the same position (distance L from the optical axis), the distortion applied to the optical surface OE1 is minimized, the quality of the optical element OE is stabilized, and the post-process is performed. Processing can be reduced.

  FIG. 8 is a diagram illustrating a protrusion according to a modified example. The cross section may not be triangular like the protrusion 13 shown in FIG. 8A, but the cross section may be semicircular like the protrusion 13 ′ shown in FIG. 8B. The cross section may be rectangular as in the case of a protrusion 13 ″ shown in FIG. 8C. However, in order to form a notch where stress concentration tends to occur, the protrusion shown in FIG. The protrusion may be formed not on the surface of the movable mold side but on the surface of the fixed mold side, or may be formed on both the movable mold side and the fixed mold side. The phase relationship between the gate and the air vent resin portion is preferably symmetric with respect to the optical axis, that is, if each is at a position of 180 degrees, the resin in the cavity tends to circulate at the time of molding and the remaining of air can be suppressed. However, the position is not necessarily limited to this, 90 degrees or other It can be arranged arbitrarily in correlation.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate.

It is a figure which shows the molding process of resin concerning this Embodiment. It is sectional drawing expanded in the state which clamped the shaping | molding apparatus concerning this Embodiment. It is the figure which looked at a part of fixed mold | type 20 from the movable mold | type 10 side. It is a figure which shows the state which removes an air vent resin part from the molded article M at a post process. It is the figure which looked at the molded article M after removing the air vent resin part from the optical axis direction of the optical element OE. It is the figure which looked at the air vent resin part BR shown in FIG. 5 in the arrow VI direction. It is the figure which looked at the air vent resin part BR shown in FIG. 5 in the arrow VII direction. It is a figure which shows the protrusion concerning a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Movable type 11 Transfer surface 11a Optical transfer surface 11b Flange transfer surface 12 Runner 13 Protrusion 20 Fixed mold 21a Optical transfer surface 21b Flange transfer surface 21c Circumferential surface 21d Plane 22 Spool 23 Runner 24 Groove 50 Heater AB Air vent BR Air vent resin part BR1 Tapered surface BR2 Fracture surface CB Cavity GT Gate H Hand M Molded product N Nozzle NT Notch O Center OE Optical element OE1 Optical surface OE2 Flange OE2a Cylindrical surface OE2b Notch surface PS Tweezers SP Spool X Optical axis

Claims (11)

An optical element molding die for molding a resin optical element,
A movable mold having a transfer surface for transferring one of the two optical surfaces;
A fixed mold having a transfer surface for transferring the other optical surface of the two optical surfaces;
The movable side and fixed side molds each have opposing surfaces that face each other when the movable side and fixed side molds are brought into contact with each other and clamped,
A part of each facing surface of the movable side and fixed side molds forms a cavity between the clamped molds, a gate for supplying a resin material from the outside into the cavity, and the cavity Forming an air vent for exhausting air from inside,
At least one of the opposing surfaces of the movable side and fixed side molds forming the air vent has a partial cross-sectional area of an air vent resin portion formed by solidifying the resin supplied into the air vent. A molding die for an optical element, characterized in that a projecting portion for reducing the size is formed.   2. The molding die for an optical element according to claim 1, wherein the protrusion has a shape in which a tip is narrow along a protruding direction.   3. The air vent according to claim 1, wherein a cross-sectional area of a portion where the protrusion is provided is 50 to 70% with respect to a portion where the protrusion is not provided. Mold for optical elements.   The said gate and the said air vent are formed in the mutually symmetrical position with respect to the optical axis of the optical element shape | molded by the said shaping | molding apparatus, The Claim 1 characterized by the above-mentioned. Mold for optical elements.   The optical element molding die according to any one of claims 1 to 4, wherein the optical element is an objective lens having an NA of 0.8 or more. In an optical element formed by resin molding an optical surface and a flange portion formed in a circle on the outer periphery thereof,
The flange portion includes a notch surface formed so as to cut out a part of the flange portion in a straight line, and a part of the air vent resin portion connected to the flange portion is cut out on the notch surface. An air vent resin excision formed by the remaining part of the air vent resin, and an end of the air vent resin excision is located on the inner side of the outer radius from the center of the optical axis to the outer periphery of the flange, and An optical element having a smaller cross-sectional area than the end of the part.   The optical element according to claim 6, wherein a gate cut portion formed by cutting a gate portion connected to the flange portion is disposed in the flange portion at a position different from the cutout portion.   The optical element according to claim 7, wherein the gate excision part and the air vent resin excision part are formed at positions symmetrical to each other with respect to the optical axis of the optical element.   The cross-sectional area of the end portion of the air vent resin excision part is formed with a cross-sectional area of 50 to 70% with respect to the cross-sectional area other than the end part of the air vent resin excision part. An optical element according to any one of the above.   The optical element according to any one of claims 6 to 9, wherein an end portion of the air vent resin excision portion has a surface roughness larger than that of the other surface portion of the optical element. The optical element according to any one of claims 6 to 10 , wherein the optical element is an objective lens for an optical pickup device having an NA of 0.8 or more.

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