WO2011122174A1

WO2011122174A1 - Die

Info

Publication number: WO2011122174A1
Application number: PCT/JP2011/053805
Authority: WO
Inventors: 賢一石井
Original assignee: コニカミノルタオプト株式会社
Priority date: 2010-03-30
Filing date: 2011-02-22
Publication date: 2011-10-06
Also published as: JPWO2011122174A1; CN102821926A

Abstract

Disclosed is a die that has the following: a surface treatment layer (SM) having a concave, curved surface (SM1) for transfer molding an optical surface of an objective lens (OBJ), a base material (BD) having a supporting surface (BD1) that corresponds to the concave, curved surface (SM1) and which is for supporting the surface treatment layer (SM), and a heat insulating layer (HI) disposed between the surface treatment layer (SM) and the base material (BD). Therefore, it is possible to approach uniformity in the thickness of the heat-insulating layer (HI). Furthermore, because the thermal conductivity of the heat-insulating layer (HI) is lower than that of the surface treatment layer (SM), the cooling speed of the molding material in contact with the surface treatment layer (SM) can be made uniform. Hence, highly accurate transfer of the optical surface of the objective lens (OBJ) can be performed.

Description

Mold

The present invention relates to a mold for molding an optical element, and particularly to a mold suitable for molding an objective lens for a high-precision optical pickup device.

In recent years, in an optical pickup device, a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened. For example, a wavelength 390 such as a blue-violet semiconductor laser is used. A laser light source of ˜420 nm has been put into practical use. When these blue-violet laser light sources are used, 15 to 20 GB of information can be recorded on an optical disk having a diameter of 12 cm when an objective lens having the same numerical aperture (NA) as that of a DVD (Digital Versatile Disc) is used. When the NA of the objective optical element is increased to 0.85, 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm.

By the way, simply saying that information can be recorded / reproduced appropriately with respect to BD (Blu-ray Disc) cannot be said to have sufficient value as a product of an optical disc player / recorder (optical information recording / reproducing apparatus). . Considering the reality that DVDs and CDs (Compact Discs) on which a variety of information is recorded are currently being sold, it is not possible to record / reproduce information to / from a BD. For example, DVDs owned by users, Similarly, it is possible to appropriately record / reproduce information on a CD, which leads to an increase in the commercial value of an optical disc player / recorder for BD. From such a background, the optical pickup device mounted on the BD optical disc player / recorder can record / reproduce information appropriately while maintaining compatibility with any of BD, DVD, and CD. It is desirable to have

In such a BD / DVD / CD compatible optical pickup device, a compatible objective lens used in common for each optical disk has already been developed. However, such a compatible objective lens has a problem that it is difficult to mold because a fine diffractive structure is formed on the optical surface. In particular, the objective lens used in the BD / DVD / CD compatible optical pickup device has a deeper shape in order to cope with a high NA as compared with the objective lens used in the conventional DVD / CD compatible optical pickup device. In addition, since a more complicated diffractive structure is required, the problem of difficulty in molding is very large. More specifically, when an objective lens having a fine shape is injection-molded with a thermoplastic resin, the heat of the molten resin quickly moves to the mold as soon as it is injected into the mold, and the cavity mold or core mold The resin surface in contact with is rapidly cooled and solidified.

For this reason, in the pressure-holding step (step of maintaining the pressure for a predetermined time after the resin injection) that is a shape transfer step after the resin is injected, sufficient transferability cannot be obtained, that is, with a high accuracy of micron order or less. There is a problem that the shape of the mold cannot be transferred to the molded body.

On the other hand, Patent Document 1 discloses a technique for disposing a heat insulating layer between a surface processed layer and a base material. Resin filled in the mold in the injection process without the occurrence of mold temperature irregularity, resin flow irregularity, cooling solidification non-uniformity, etc. due to the presence of the heat insulating layer under the surface processed layer Can be kept at a high temperature until the pressure holding process, which is the subsequent shape transfer process, so that a highly accurate mold shape of micron order or less formed on the surface processed layer can be transferred to the molded product with high accuracy. be able to.

Japanese Patent No. 4135304

However, while the technique of Patent Document 1 is a technique for forming a diffractive structure on a relatively flat optical element, an objective lens for an optical pickup device has a convex optical surface. Even if the provided mold is used, the thickness of the heat insulating layer will be different between the center and the periphery of the optical surface, thereby making the heat conduction non-uniform, and the resin solidifies faster in the center of the optical surface, There is a possibility that the solidification of the resin will be delayed at the periphery, resulting in a variation in the solidification of the resin, leading to deterioration of the optical characteristics of the molded objective lens.

The present invention has been made in view of the problems of the prior art, and an object thereof is to provide a mold capable of molding an objective lens for a high-precision optical pickup device.

The mold according to claim 1 is a mold used for molding an objective lens for an optical pickup device, the surface processing layer having a concave curved surface for transferring and molding an optical surface of the objective lens, and the surface A base material having a support surface that is recessed corresponding to the concave curved surface to support the processed layer; and a heat insulating layer disposed between the surface processed layer and the support surface, and the heat insulating layer. The thermal conductivity of is lower than the thermal conductivity of the surface processed layer.

According to the present invention, a surface processing layer having a concave curved surface for transfer molding of the optical surface of the objective lens, and a base material having a support surface that is recessed corresponding to the concave curved surface to support the surface processing layer. And a heat insulating layer disposed between the surface processed layer and the support surface, the thickness of the heat insulating layer can be made uniform, and the thermal conductivity of the heat insulating layer is Since it is lower than the thermal conductivity of the processed layer, the cooling rate of the molding material in contact with the surface processed layer can be made uniform, and the optical surface of the objective lens can be transferred with high accuracy.

The mold according to claim 2 is characterized in that, in the invention according to claim 1, the thermal conductivity of the heat insulating layer is lower than the thermal conductivity of the base material. Thereby, the cooling rate of the molding material in contact with the surface processed layer can be made more uniform, and the optical surface of the objective lens can be transferred with high accuracy.

The mold according to claim 3 is characterized in that, in the invention according to claim 1, the thermal conductivity of the heat insulating layer is 10.0 W / m · K or less. As a result, the cooling rate of the molding material in contact with the surface processed layer can be reduced, and the optical surface of the objective lens can be transferred with high accuracy.

The mold according to claim 4 is the invention according to any one of claims 1 to 3, wherein the heat insulating layer has a difference between a thickness of a central thickness and a thickness of a peripheral thickness of 0.1 mm. It is characterized by the following. Thereby, the cooling rate of the molding material in contact with the surface processed layer can be made more uniform, and the optical surface of the objective lens can be transferred with high accuracy.

The mold according to claim 5 is characterized in that, in the invention according to any one of claims 1 to 4, the thickness of the heat insulating layer is 0.1 to 3 mm.

The mold according to claim 6 is characterized in that, in the invention according to any one of claims 1 to 5, the heat insulating layer is formed of ceramics.

The mold according to claim 7 is characterized in that, in the invention according to any one of claims 1 to 6, the surface processed layer is formed by electroless nickel plating.

The mold according to claim 8 is characterized in that, in the invention according to any one of claims 1 to 7, the objective lens is a BD / DVD / CD compatible objective lens.

The mold according to claim 9 is the invention according to any one of claims 1 to 8, wherein the objective lens has a central area, an intermediate area, and a peripheral area, and at least the center is formed by the mold. A fine shape is transferred and formed between the region and the intermediate region. According to the present invention, since the cooling rate of the molding material in contact with the surface processed layer can be made uniform, even when a fine groove corresponding to a fine shape is formed in the surface processed layer, the material is inserted to the back of the fine groove. The penetration transfer property is improved.

In this specification, the objective lens for BD / DVD / CD compatibility refers to an objective lens used in common for BD, DVD, and CD. A typical BD / DVD / CD compatible lens is a so-called deep lens that has a high NA of around NA 0.8, and therefore tends to have a small curvature radius and a thick on-axis, and is compatible with DVD / CD. Since it has a diffractive structure with a finer shape than a lens for use, a high-performance heat insulation is required to allow a resin or glass material to enter the fine shape, and the present invention is particularly effective. In particular, the central part of the objective lens is shared by BD / DVD / CD, and the central part is shared by BD / DVD, and flare light is formed on the information recording surface of the CD, so a very complicated diffraction structure is required. It can be said that the influence of heat insulation is great.

Here, the BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 415 nm and an objective lens having an NA of about 0.8 to 0.9, and the thickness of the protective substrate is about 0.05 to 0.125 mm. Is a generic name of a BD series optical disc, and includes a BD having only a single information recording layer, a BD having two information recording layers, and the like. Further, in this specification, DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.60 to 0.67 and the thickness of the protective substrate is about 0.6 mm. Including DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. In this specification, CD is a general term for CD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.45 to 0.51 and the thickness of the protective substrate is about 1.2 mm. Including CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and the like. As for the recording density, the recording density of BD is the highest, followed by the order of DVD and CD.

In this specification, the objective lens refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing a light beam emitted from the light source onto the information recording surface of the optical disk. The objective lens may be composed of two or more lenses and / or optical elements, or may be composed of a single lens, but is preferably an objective lens composed of a single convex lens. . The objective lens may be a glass lens, a plastic lens, or a light path difference providing structure (diffractive structure) with a photocurable resin, a UV curable resin, or a thermosetting resin on the glass lens. A hybrid lens provided with a When the objective lens has a plurality of lenses, a glass lens and a plastic lens may be mixed and used. When the objective lens includes a plurality of lenses, it may be a combination of a flat optical element having an optical path difference providing structure and an aspherical lens (which may or may not have an optical path difference providing structure). The objective lens preferably has a refractive surface that is aspheric. In the objective lens, the base surface on which the optical path difference providing structure is provided is preferably an aspherical surface.

Moreover, it is preferable that an objective lens satisfy | fills the following conditional expression (1).
1.0 ≦ dt / f ≦ 1.5 (1)
However, dt represents the thickness (mm) on the optical axis of the objective lens, and f represents the focal length of the objective lens in the first light flux.

The objective lens is described below. It is preferable that at least one optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region. The central region is preferably a region including the optical axis of the objective lens. However, a minute region including the optical axis may be an unused region or a special purpose region, and the periphery thereof may be a central region. The central region, the intermediate region, and the peripheral region are preferably provided on the same optical surface. As shown in FIG. 1, the central region CN, the intermediate region MD, and the peripheral region OT are preferably provided concentrically around the optical axis on the same optical surface. The central region, the intermediate region, and the peripheral region are preferably adjacent to each other, but there may be a slight gap between them.

In the case of a BD / DVD / CD compatible objective lens, it is preferable to provide a diffractive structure at least in the central region and the intermediate region. Thus, in the optical pickup device, the BD light flux that has passed through the central region CN is condensed on the BD information recording surface, the DVD light flux is condensed on the DVD information recording surface, and the CD light flux is on the CD. It is condensed on the information recording surface. Further, the BD light flux that has passed through the intermediate area MD is condensed on the BD information recording surface, and the DVD light flux is condensed on the DVD information recording surface, while the CD light flux is condensed on the CD information recording surface. The BD light flux that has not been condensed onto the BD and further passed through the peripheral area OT is condensed on the BD information recording surface, but the DVD light flux is not condensed on the DVD information recording surface, and the CD light flux is The light is not condensed on the information recording surface of the CD.

In addition, the diffractive structure referred to in this specification is a general term for structures that have a step and have a function of converging or diverging a light beam by diffraction. For example, a plurality of unit shapes are arranged around the optical axis, and a light beam is incident on each unit shape, and the wavefront of the transmitted light is shifted between adjacent annular zones, resulting in new It includes a structure that converges or diverges light by forming a simple wavefront. The diffractive structure preferably has a plurality of steps, and the steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis. The diffractive structures may be superimposed. For example, there may be a sawtooth (blazed) shape, a staircase shape, or a shape in which these are superimposed. In particular, when the width of the step shape of the diffractive structure is X and the height of the step shape is Y, 0.50 ≦ maximum value of (Y / X) ≦ 1.0 in the entire diffractive structure, that is, If the lens material has a deep step shape and the lens material is difficult to enter into the microstructure of the mold, problems such as solidification variation will be greater. Therefore, the effect becomes more remarkable. Here, Y / X is the value of the ratio between the width and height of the step shape. The maximum value of (Y / X) is a U-shaped step shape (such as when the step shape is a staircase shape, or a sawtooth structure superimposed in the opposite direction). In the case of having a U-shaped wall composed of a wall surface in the direction and a wall surface in the optical axis direction), it is obtained based on the ratio value of the width X and height Y of the U-shaped step shape. In addition, the height of the U-shaped step shape is the height of the wall surface with the higher height in the optical axis direction among the two wall surfaces in the optical axis direction forming the U-shaped step shape. And In the case where the step shape does not have a U-shaped step shape, for example, in the case of a saw-tooth type step shape, the step shape is obtained based on the value of the ratio between the width X and the height Y of the saw-tooth type step shape.

The mold according to the present invention includes a surface processing layer having a concave curved surface for transferring and molding the optical surface of an objective lens for an optical pickup device, and a recess corresponding to the concave curved surface to support the surface processing layer. It has at least a base material having a support surface, and a heat insulating layer disposed between the surface processed layer and the support surface. For example, a bond layer or an intermediate metal layer (see Japanese Patent Laid-Open No. 2008-24000) may be provided in addition to the heat insulating layer between the surface processed layer and the support surface of the base material.

The heat insulation layer is preferably a layer having a thermal conductivity of 10.0 W / m · K or less, and as the material of the heat insulation layer, for example, ceramic materials such as zirconia, alumina, titanium oxide, and chromium oxide may be used. I can do it.

The surface processed layer is a layer in which a fine shape is formed by cutting on the outermost surface. For example, an electroless nickel plating or a material containing Cu in electroless nickel plating (see Japanese Patent Application Laid-Open No. 2008-24000) can be used.

For example, stainless steel or the like can be used as the base material fixed to the molding apparatus.

According to the present invention, it is possible to provide a mold capable of forming a highly accurate objective lens for an optical pickup device.

It is the figure which looked at the objective lens to the optical axis direction. It is a figure which shows the manufacturing process of the metal mold | die for shape | molding the objective lens for optical pick-up apparatuses. It is sectional drawing which shows the state which shape | molds an objective lens using the manufactured metal mold | die.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a diagram showing a manufacturing process of a mold for forming an objective lens for an optical pickup device. FIG. 3 is a cross-sectional view showing a state in which an objective lens is molded using the manufactured mold. However, the diffraction structure and the like are exaggerated.

2A, first, a base material BD is processed from a cylindrical material such as stainless steel by cutting using a tool TL. At this time, a support surface BD1 that is recessed in a concave shape is formed on the end surface of the base material BD, and a groove BD2 that extends in the circumferential direction is formed on the peripheral surface of the base material BD.

Next, as shown in FIG. 2B, a NiCr bond layer AD is thinly formed on the support surface BD1 of the base material BD by plasma spraying. This has a function of increasing the adhesion between the heat insulating layer HI and the base material BD. Further, as indicated by a dashed line in FIG. 2C, a ceramic layer is deposited on the bond layer AD by plasma spraying. Plasma spraying is a technique in which a fine powder such as ceramics, a wire, or the like is introduced into a plasma heat source and sprayed onto a base material to be coated as fine particles in a molten or semi-molten state to form a coating. A plasma heat source is a high-temperature plasma gas in which a molecular gas is heated to a high temperature, dissociated into atoms, and energy is given to emit electrons. The plasma gas injection speed is high, and the sprayed material collides with the base material at a higher speed than conventional arc spraying or flame spraying, so that a high-density coating can be obtained with high adhesion strength. For details, a thermal spraying method for forming a heat shielding film on a high-temperature exposed member described in JP-A No. 2000-301655 can be referred to.

Then, the deposited ceramic layer is cut with a tool TL to adjust the shape and form a heat insulating layer HI. At this time, a concave curved surface HI1 is formed corresponding to the support surface BD1 (see the solid line in FIG. 2C). The thickness of the heat insulating layer HI is 0.1 mm to 3 mm, and the difference between the central thickness t1 and the peripheral thickness t2 is 0.1 mm or less.

Further, as shown in FIG. 2 (d), the surface processed layer SM is formed by plating so as to cover the entire heat insulating layer HI from the groove BD2 of the base material BD. In general, ceramics is relatively incompatible with plating, but by covering the entire surface with the surface processed layer SM in this way, it is possible to suppress the heat insulating layer HI from being peeled off from the base material BD. On the other hand, the surface processed layer SM covers only a part of the base material BD, which is to reduce the risk of plating defects.

Thereafter, as shown in FIG. 2E, the surface processing layer SM is cut with a tool TL to form a concave aspherical curved surface (transfer surface) SM1 corresponding to the support surface BD1, and a concave aspherical surface. The ring-shaped fine groove SV is formed at a position corresponding to at least the central region and the intermediate region of the objective lens formed by the curved surface SM1, and thus the mold M1 is completed. In the mold M1, the heat conductivity of the heat insulating layer HI is lower than the heat conductivity of the base material BD and the surface processed layer SM.

The mold M1 and the mold M2 manufactured in the same process (but not having a fine groove) are clamped so as to face each other as shown in FIG. 3, and resin or glass (molding material) is placed in the internal cavity. ) And then solidifying, the objective lens OBJ having an optical surface to which the shape of the concave aspherical curved surface SM1 of the surface processing layer SM is transferred can be formed. At this time, since the thermal conductivity of the heat insulating layer HI is lower than the thermal conductivity of the base material BD and the surface processed layer SM, the cooling rate of the temperature of the molding material in contact with the surface processed layer SM becomes uniform, Thereby, the fluidity of the molding material is increased, and the fine shape can be easily entered into the fine groove SV, and solidified in such a state, whereby the fine shape can be transferred with high accuracy. Thereafter, the molded objective lens OBJ can be taken out by releasing the molds M1 and M2.

The effect of the present invention is particularly effective in a mold having a transfer surface with a small curvature radius. Therefore, the mold having the heat insulating layer HI may be provided only in the mold M1 for transfer molding the light source side optical surface S1 of the objective lens OBJ. For example, the shape of the base material of the mold M2 on the heat insulating layer side may be a planar shape in the direction perpendicular to the optical axis without being a concave shape along the shape of the surface processed layer. Alternatively, the heat insulating layer may not be provided on the mold M2.

Table 1 summarizes the materials and thermal conductivity used in the present embodiment.

According to the present invention, it is possible to provide a mold capable of molding an objective lens for an optical pickup device with a simple configuration. However, the object of molding is not limited to a BD / DVD / CD compatible objective lens, and is compatible with two. It can also be applied to other objective lenses.

AD Bond layer BD Base material BD1 Support surface BD2 Groove HI Heat insulation layer HI1 Curved surface M1 Mold M2 Mold OBJ Objective lens SM Surface processed layer SM1 Curved surface SV Fine groove TL Tool

Claims

A mold used to mold an objective lens for an optical pickup device, the surface processing layer having a concave curved surface for transfer molding the optical surface of the objective lens, and the concave shape for supporting the surface processing layer A base material having a support surface that is recessed corresponding to the curved surface, and a heat insulating layer disposed between the surface processed layer and the support surface, and the thermal conductivity of the heat insulating layer is the surface processed A mold characterized by being lower than the thermal conductivity of the layer.
The mold according to claim 1, wherein the heat conductivity of the heat insulating layer is lower than the heat conductivity of the base material.
The mold according to claim 1 or 2, wherein the heat conductivity of the heat insulating layer is 10.0 W / m · K or less.
The mold according to any one of claims 1 to 3, wherein the heat insulating layer has a difference between a thickness of a central thickness and a thickness of a peripheral thickness of 0.1 mm or less.
The mold according to any one of claims 1 to 4, wherein the heat insulating layer has a thickness of 0.1 to 3 mm.
The mold according to any one of claims 1 to 5, wherein the heat insulating layer is made of ceramics.
The mold according to any one of claims 1 to 6, wherein the surface processed layer is formed from electroless nickel plating.
8. The mold according to claim 1, wherein the objective lens is a BD / DVD / CD compatible objective lens.
9. The objective lens according to claim 1, wherein the objective lens has a central area, an intermediate area, and a peripheral area, and a fine shape is transferred and formed at least in the central area and the intermediate area by the mold. A mold according to any one of the above.