JP2002079586A - Optical element and manufacturing method thereof, and resin material for optical element, optical head and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element having an excellent optical performance and uniform performances and a manufacturing method thereof, and a resin material for the optical element, an optical head and an optical disk device. SOLUTION: The manufacturing method has a first process wherein a substantially spherical resin lump constituted of a resin is molded by injection molding, a second process wherein a spherical resin material 31 is formed by grinding the resin lump and a third process wherein the resin material 31 is formed with heat and pressure by using a forming mold 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element and a method of manufacturing the same, as well as an optical head and an optical disk device.

[0002]

2. Description of the Related Art Optical elements are used in optical heads and the like of optical disk devices. Conventional methods for molding an optical element using a plastic material include, for example, an injection molding method and a compression molding method. The injection molding method is a method in which a pellet is heated and melted, and injected and filled into a cavity formed by an insert. The compression molding method
This is a method in which a plastic material preprocessed to a substantially final shape by injection molding is supplied into a mold maintained at a constant temperature and then pressed (see JP-A-5-177725). Hereinafter, conventional molding methods, molding dies, and optical elements will be briefly described with reference to the drawings.

FIG. 5 is a schematic sectional view showing a molding state when a conventional molding die is used. Referring to FIG. 5, a conventional molding die includes a trunk die 1 composed of trunk dies 1a and 1b, and an upper die 2 and a lower die 3 which are inserted from above and below the die 1.

In a conventional manufacturing method, first, an optical element material (polycarbonate) 4a pre-processed into a substantially final shape (shape of an optical element) by injection molding is applied to a body mold 1 and an upper mold 2.
And the inside of the cavity formed by the lower mold 3. The mold is a press head 5 having a heating and pressing mechanism.
And the press stage 6 having a heating mechanism, the temperature is previously raised to a temperature equal to or higher than the deflection temperature under load and lower than the glass transition point. When the temperature of the optical element material 4a substantially coincides with the temperatures of the body mold 1, the upper mold 2 and the lower mold 3, and reaches a certain temperature which is equal to or higher than the deflection temperature under load and lower than the glass transition point, the press head 5 is lowered. The optical element material 4a is deformed by applying a pressure of about 9.8 × 10 ⁶ Pa (about 100 kgf / cm ² ) by the mold 2, and the state is maintained for a certain time. Then, release the pressing force and cool to the deflection temperature under load.
The upper mold 2 is removed, and the molded optical element 4 is taken out.
FIG. 5 is a cross-sectional view of the optical element 4 thus formed.

[0005]

However, an optical element material (polycarbonate) pre-processed to a substantially final shape.
4a has a surface defect based on being formed by injection molding. For this reason, in the above-mentioned conventional manufacturing method, there is a problem that a defect remains on the surface of the optical element and the optical performance is likely to be affected. Further, when a plurality of optical element materials are simultaneously molded by injection molding, the weight may vary slightly, and burrs 4b as shown in FIG. 5 may be generated. In addition, there is a problem that the performance of the optical element varies due to, for example, residual strain being generated in the gate portion.

When an optical head, an optical disk, or the like is manufactured using an optical element having a surface defect or an optical element having a variation in optical performance, there is a problem that these performances also vary.

In order to solve the above problems, the present invention provides an optical element having good optical performance and uniform performance, a method for manufacturing the same,
It is another object of the present invention to provide an optical head and an optical disk device using the same.

[0008]

In order to achieve the above object, an optical element according to the present invention forms a substantially spherical resin mass made of resin by injection molding, and grinds the resin mass to form a spherical resin mass. It is an optical element obtained by forming a material and further heating and pressing the resin material using a molding die. In the above optical element, a spherical resin material having high transparency and small internal distortion obtained by polishing is used. Therefore, according to the above optical element, an optical element having good optical performance and uniform performance can be obtained.

In the method of manufacturing an optical element according to the present invention, a first step of forming a substantially spherical resin block made of resin by injection molding, and a step of forming a spherical resin material by polishing the resin block. A second step; and a third step of heating and pressing the resin material using a molding die. In the method for manufacturing an optical element, a spherical resin material having high transparency and small internal distortion is formed by polishing, and then the optical element is manufactured using the resin. Therefore, according to the above manufacturing method, an optical element having good optical performance and uniform performance can be manufactured.

In the above manufacturing method, the third step includes a preheating step of heating the resin material, a molding step of molding the heated resin material, and a cooling step of cooling the molded resin material. Preferably, in the forming step and the cooling step, the resin material is pressurized with a higher pressing force than in the preheating step. According to the above configuration, the transferability of the optical surface of the mold of the resin material in the molding step and the cooling step is improved, and an optical element surface having a stable shape is obtained.

In the above-mentioned manufacturing method, it is preferable that in the second step, the resin block is removed by polishing to a depth of 0.5 mm or more from the surface. According to the above configuration, an optical element having particularly excellent optical performance can be manufactured.

The resin material for an optical element of the present invention is a resin material for an optical element for producing an optical element by heating and pressing using a molding die, and is spherical and formed by injection molding. Characterized by being formed into a spherical shape by polishing a substantially spherical resin block made of resin.
According to the above configuration, an optical element having good optical performance and uniform performance can be manufactured.

It is preferable that the resin material for an optical element is removed by polishing to a depth of 0.5 mm or more from the surface of the resin mass during the polishing.

Further, an optical head according to the present invention is an optical head including a light source and an optical element arranged on the optical axis of the light source, wherein the optical element is the optical element according to the present invention. Features.

An optical disk device according to the present invention is an optical disk device for recording or reproducing information on or from an optical disk, comprising a light source, and an optical element disposed between the light source and the optical disk. The optical element is the optical element of the present invention.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 In Embodiment 1, a resin material for an optical element of the present invention will be described. The resin material for an optical element according to the first embodiment is a resin material for an optical element for manufacturing an optical element by heating and pressing using a molding die.
It has a spherical shape (preferably a true spherical shape), and is characterized by being formed into a spherical shape by polishing a substantially spherical resin block made of resin formed by injection molding. That is,
The optical element resin material of the first embodiment is processed into a final shape by polishing.

As the resin as the material, for example, polyolefin resin, polycarbonate resin, acrylic resin, polyester resin and the like can be used. Among them, a polyolefin resin or an acrylic resin having high transparency after polishing is preferable.

The above polishing can be performed, for example, by a ball polishing method. In the ball polishing method, the resin blocks are arranged on a concentric circular table having a radius substantially equal to that of a substantially spherical resin block, or a disk-shaped rotatable table having a spiral groove, and a disk-shaped table is formed. Polishing is performed by a polishing apparatus comprising a flat disk-shaped holding plate having the same outer diameter as that of the above. The resin mass is arranged in a groove of the table. The holding plate is made of alumina abrasive or
A silicon carbide-based abrasive is stuck. The table is rotated at a predetermined rotation speed, and the pressing plate is pressed with a predetermined pressing force. The holding plate moves toward the table as the resin mass is processed. While confirming this dimensional change, the resin mass is finished to the final size of the resin material. Thus, a spherical optical element resin material is formed.

It is preferable that the resin material for an optical element is removed by polishing to a depth of 0.5 mm or more from the surface of the resin mass during polishing.

The spherical resin material is preferably processed to an outer diameter accuracy of about ± 5 μm in order to stabilize optical performance.

Embodiment 2 In Embodiment 2, an optical element of the present invention will be described. The optical element of the second embodiment includes:
A substantially spherical resin mass made of resin is formed by injection molding, and a spherical (preferably true spherical) resin material is formed by polishing the resin mass, and then the resin material is heated and pressed using a molding die. This is an optical element obtained by performing That is, the optical element of the second embodiment is obtained by heating and pressing the optical element resin material of the first embodiment. Therefore, the resin described in Embodiment 1 can be used as the material resin.

(Embodiment 3) In Embodiment 3, a method for manufacturing an optical element of the present invention will be described. This manufacturing method is a manufacturing method for manufacturing the optical element described in the second embodiment.

In the manufacturing method according to the third embodiment, first, a substantially spherical resin block made of resin is formed by injection molding (first step).

After that, a spherical (preferably true spherical) resin material is formed by polishing the resin mass (second step). The resin material is the same as the resin material for an optical element described in the first embodiment. Therefore, the resin described in Embodiment 1 can be used as the material resin.

Thereafter, an optical element is formed by heating and pressing the resin material using a mold (third step). Thus, an optical element can be manufactured.

According to the manufacturing method of the third embodiment, an optical element having good characteristics and uniform performance can be manufactured. In particular, in the manufacturing method according to the third embodiment, since the heat and pressure molding is performed using a spherical resin material having a shape close to a true sphere, the resin reaches the entire circumference of the inner surface of the body mold at the same time during molding. The time is also longer compared to conventional materials. Therefore, according to the manufacturing method of the third embodiment, generation of burrs can be suppressed.

(Embodiment 4) In Embodiment 4, an example of the optical head of the present invention will be described.

The configuration of the optical head of the fourth embodiment is schematically shown in FIG. 1 (hatching is omitted). Referring to FIG. 1, an optical head 10 includes a light source (laser light source) 11,
A half mirror 12, a collimating lens 13, an optical element (objective lens) 14, and a light receiving element 15 are provided. The optical element 14 is the optical element described in the first embodiment (the optical element manufactured by the manufacturing method of the second embodiment). The optical element 14 is arranged on the optical axis of the light source 11.

In the optical head 10, the light emitted from the light source 11 is reflected by the half mirror 12 and is made substantially collimated by the collimating lens 13. Next, the substantially parallel light is condensed on the information medium 16 by the optical element 14 and reflected. Here, the information medium 16 is, for example, an optical disk. The reflected light from the information medium 16 passes through the optical element 14, the collimating lens 13, and the half mirror 12, and reaches the light receiving element 15. Light receiving element 15
Converts the incident light into an electric signal and outputs the electric signal. Thus, the information signal recorded on the information medium 16 is reproduced.

In the optical head of the fourth embodiment, since the optical element of the present invention is used, an optical head having excellent optical performance can be obtained.

The configuration of the optical head shown in FIG. 1 is an example, and if the optical head uses the optical element of the present invention,
Other configurations may be any.

An optical disk device according to the present invention is an optical disk device for recording or reproducing information on or from an optical disk, comprising a light source, and an optical element disposed between the light source and the optical disk. 6 is an optical element described in the first embodiment (an optical element manufactured by the manufacturing method of the second embodiment). That is, the optical disc device of the present invention
An optical disk device including the optical head 10. According to the above optical disk device, an optical disk device having excellent optical performance can be obtained.

[0034]

The present invention will be described in more detail with reference to the following examples.

Example 1 In Example 1, an example of manufacturing the optical element resin material described in Embodiment 3 will be described with reference to FIG.

First, as shown in FIG. 2 (a), a resin 22 was injected from a gate 21 of an injection molding apparatus to have a substantially spherical shape. As the resin 22, a polyolefin resin (glass transition point Tg = 140 ° C., deflection temperature under load Tt = 123 ° C.) was used.

Thereafter, as shown in FIG. 2B, the substantially spherical resin block 23 (about 5 mm in diameter) was cut off from the gate 21. At this time, the surface of the gate cut portion 23a, which is a portion separated from the gate 21, was uneven.
Finally, as shown in FIG. 2C, the resin mass 23 is polished to form a spherical optical element resin material 24 (having a diameter of 3 m).
m). The polishing at this time was performed by the ball polishing method described in the first embodiment, and a silicon carbide abrasive was used.

A resin material for an optical element was produced by the above method using a polycarbonate resin, an acrylic resin, and a polyester resin instead of the polyolefin resin. As a result, the optical element resin material using a polyolefin resin or an acrylic resin had higher transparency after polishing than the optical element resin material using a polycarbonate resin or a polyester resin.

Example 2 In Example 2, an example in which the optical element described in Embodiment 2 was manufactured by the manufacturing method in Embodiment 3 will be described with reference to FIGS.
In this embodiment, the radius of curvature R of the first optically effective surface is
1 = 7 mm, radius of curvature R2 = 2.0 of the second optically effective surface
mm, the center thickness t = 1.6 mm, and the outer diameter = 4.5 mm.

First, in the same manner as in Example 1, a polyolefin resin (glass transition point Tg = 140 ° C., deflection temperature under load T
(t = 123 ° C.) to form a substantially spherical resin block (about 5 mm in diameter). Thereafter, the resin mass is polished to form a spherical resin material 31 (3 m in diameter).
m) was formed. Thereafter, as shown in FIG. 3A, the resin material 31 was placed in the molding die 32.

The molding die 32 includes a substantially cylindrical trunk die 33, and a first die 34 and a second die 35 which are inserted into the trunk die 33. The body mold 33 is made of stainless steel. First mold 3
The fourth and second molds 35 are made of a super hard material. Second mold 3
Reference numeral 5 denotes a mold for forming a second optically effective surface having a small radius of curvature. The first mold 34 is fitted into the body mold 33 from below, and the second mold 35 is fitted into the body mold 33 from above.

Thereafter, as shown in FIG. 3 (b), the second mold 35 is moved from above, so that the resin material 31 is moved.
Was heated and pressed. Thus, the optical element 30 shown in FIG. 3C was manufactured. The heat and pressure molding was performed using a molding apparatus 40 shown in FIG.

The molding device 40 includes stages 40a to 40d
And a loading stage 41 and a take-out stage 42. Each of the stages 40a to 40d includes a press stage 43 in contact with the first mold 34, and a press head 44 for pressing the second mold 35. The press stage 43 and the press head 44 each have a built-in heater so that the temperature can be freely set. Each stage is heated to a desired temperature in advance, and the mold 32 is sequentially conveyed to the next stage at predetermined time intervals. The molding die 32 is transported by a transport arm (not shown). In this example, molding was performed with the tact time set to 50 seconds. Table 1 shows the set temperature of each stage.

[0044]

[Table 1]

Hereinafter, the method of the heat and pressure molding will be described. First, the molding die 32 on which the resin material 31 is arranged is inserted into the molding device
Was transported by a robot (not shown) to the charging stage 41, the charging door was opened, and the substrate was charged into the preheating stage 40a.
The loading door is closed until the next mold is loaded.

Next, the press head 44 of the preheating stage 40a was brought into contact with the second mold 35. Preheating stage 40a
Then, the resin material 31 is heated by a heater incorporated in the press stage 43 and the press head 44 (preheating step). However, in the preheating stage 40a, the temperature of the resin material 31 does not reach a deformable temperature within a predetermined time. Therefore, the bottom dead center of the press head 44 is set so that the pressing force is hardly applied to the resin material 31.

After the elapse of the tact time, the molding die 32 was transported by the transport arm to the next stage, the molding stage 40b. Then, the press head 44 of the molding stage 40b was brought into contact with the second mold 35. Also in the molding stage 40b, the resin material 31 was heated similarly to the preheating stage 40a. In the molding stage 40b, the resin material 31
After reaching the deformable temperature (load deflection temperature),
Heat and pressure molding was performed by moving only the second mold 35 by the press head 44 (molding step). Press pressure is
Approximately 29.4 N (3 kgf) or less. At this time, since the resin material 31 has a viscosity that allows molding, the resin material 31 is deformed even with a low pressing force.

Next, the mold 32 is moved to the first cooling stage 40.
c. Then, the press head 44 of the first cooling stage 40c was lowered to come into contact with the second mold 35, and pressurized with a pressure of about 490 N (about 50 kgf). The first cooling stage 40c was set to a set temperature at which the molded optical element became equal to or lower than the deflection temperature under load at the end of the tact.

Next, the mold 32 is moved to the second cooling stage 40.
d. Then, similarly to the first cooling stage 40c, cooling was performed by bringing the press head 44 into contact with the second mold 35. At this time, pressurization was performed with a pressing force equivalent to that of the first cooling stage 40c. Thus, in the first cooling stage 40c and the second cooling stage 40d, the molded resin material was cooled (cooling step). Then, in the molding step and the cooling step, the resin material was pressed with a higher pressing force than in the preheating step.

Next, after the optical element 30 was cooled to a temperature at which it could be taken out by a robot in the second cooling stage 40 d, the molding die 32 was transported to the take-out stage 52. Thereafter, the mold 32 was transferred to a disassembly / assembly stage (not shown) by a robot. In the disassembly and assembly stage, the mold 32 was disassembled and the optical element 30 was taken out. Thus, the optical element 30 was manufactured.

The clearance between the barrel mold 33 and the second mold 35 has a gap into which the softened resin material 31 enters during molding. However, in the method of Example 1, the resin material 31 hardly entered the clearance portion. This is because the bottom dead center is determined so that the pressing force is not applied to the second mold 35 in the preheating stage 40a, and the pressing and deforming is performed with a low pressing force in the forming stage 40b.

Optical element 3 obtained by the manufacturing method of Example 1
0 had no burrs and was excellent in optical performance. Also, the variation in characteristics among the plurality of optical elements was very small.

On the other hand, as a comparative example, an optical element was manufactured in the same manner as described above, using an optical element material manufactured without using a polishing step. This conventional optical element and the second embodiment
Table 2 shows the measurement results of the transmittance and the transmitted wavefront aberration for the optical element obtained in the above. The values in Table 2 are values obtained by averaging 20 optical elements.

[0054]

[Table 2]

As is clear from Table 2, the optical element of Example 2 was superior to the conventional optical element in both transmittance and transmitted wavefront aberration. This is because the resin material processed into a spherical shape by polishing (the resin material for an optical element of the present invention) has smaller surface roughness, better shape accuracy, and smaller internal strain. In addition, this is because, in the conventional optical element material formed only by injection molding, sink occurs due to shrinkage, the desired shape accuracy is hardly obtained, and the shape is unstable. Further, the conventional optical element material is easily affected by large distortion remaining in the gate portion, and tends to cause performance variation.

Next, there is a margin for polishing when forming the spherical resin material 31 (same as the optical element resin material 24) (the depth from the surface of the substantially spherical resin block to the portion to be removed by polishing). Was changed to form a resin material. Then, an optical element was manufactured using the resin material by the method described above, and the transmitted wavefront aberration was measured for each optical element. Table 3 shows the results. The values in Table 3 are values obtained by averaging ten optical elements.

[0057]

[Table 3]

As is apparent from Table 3, the processing margin is set at 0.
5 mm or more, that is, 0.1 mm from the surface of the resin mass.
It is preferable to remove by polishing to a depth of 5 mm or more. By making the processing margin 0.5 mm or more,
Transmitted wavefront aberration can be reduced. This is because the distortion remaining in the gate cut portion (see the gate cut portion 23a in FIG. 2) is removed by polishing to a certain depth. Also, as is clear from Table 3,
By setting the processing margin to 1.0 mm or more, the transmitted wavefront aberration can be particularly reduced.

Next, an optical head and an optical disk device were manufactured using the optical element 30 of the first embodiment. Optical element 30
The optical head or optical disk device equipped with the optical element 30 has good initial characteristics because the optical head has a smaller amount of internal strain and a higher transmittance than the conventional optical element.

Further, since no burrs were generated on the optical element 30, the inclination of the lens effective surface with respect to the optical axis caused by the burrs hardly occurred particularly when assembling the optical head, thereby reducing the number of assembling steps. Furthermore, when assembling an optical head using a conventional optical element, in the step of bonding the bobbin and the optical element, there is a problem that the adhesive layer varies due to the influence of burrs and the optical performance after bonding deteriorates. This problem did not occur in the optical element 30.

As described above, the optical disk device equipped with the optical head using the optical element of the present invention has better optical performance than the conventional optical disk device.

Although the embodiments of the present invention have been described with reference to the examples, the present invention is not limited to the above-described embodiments, and can be applied to other embodiments based on the technical idea of the present invention. it can.

For example, the molding temperature, the heating time, the holding time, and the cooling time from the molding temperature to the deflection temperature under load are not limited to those in the above embodiment.

The optical element material may be molded using a molding apparatus that performs preheating, pressure molding and cooling in one stage. In this case, the pressing force at the time of pressure molding may be set to about 9.8 N (about 1 kgf) or less.

[0065]

As described above, according to the optical element and the method for manufacturing the optical element of the present invention, an optical element having good characteristics and uniform performance can be obtained. In particular, since the resin material formed into a spherical shape by polishing has a higher specularity on the surface than a resin material formed only by injection molding, an optical element having a high transmittance can be obtained. Further, according to the present invention, an optical element without burrs can be obtained. For this reason, in the manufacturing method of the present invention, it is not necessary to remove burrs after molding, and the burrs removing step that may cause scratches on the optical element becomes unnecessary. Therefore, according to the manufacturing method of the present invention, an optical element can be manufactured with good yield and low cost. Further, according to the manufacturing method of the present invention, since the adhesion of the optical element material to the mold due to burrs can be suppressed, the number of times of maintenance of the mold can be reduced.

Further, in the optical head or optical disk device of the present invention, since the optical element of the present invention is used, an optical head or optical disk device having excellent optical performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of the configuration of an optical head according to the present invention.

FIG. 2 is a process chart showing an example of a method for producing a resin material for an optical element of the present invention.

FIG. 3 is a process chart showing one example of a method for manufacturing an optical element of the present invention.

FIG. 4 is a schematic view showing an example of a manufacturing apparatus used in the method for manufacturing an optical element of the present invention.

FIG. 5 is a cross-sectional view illustrating an example of a conventional method for manufacturing an optical element.

FIG. 6 is a cross-sectional view showing an example of an optical element manufactured by a conventional manufacturing method.

[Explanation of symbols]

 Reference Signs List 10 optical head 11 light source 14 optical element 11 resin material 23 resin mass 24 resin material for optical element 31 resin material 32 molding die 33 trunk die 34 first die 35 second die 40 molding device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) G11B 7/135 G11B 7/135 A 7/22 7/22 // B29L 11:00 B29L 11:00 (72 ) Inventor: Shoji Nakamura 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. AA38 BA01 JA02 JA43 NA05

Claims (8)

[Claims] 1. A substantially spherical resin mass made of resin is formed by injection molding, a spherical resin material is formed by polishing the resin mass, and the resin material is heated and pressed using a molding die. An optical element obtained by molding. 2. A first step of forming a substantially spherical resin mass made of resin by injection molding, a second step of forming a spherical resin material by polishing the resin mass, and using a molding die. And a third step of heating and pressing the resin material. 3. The third step includes a preheating step of heating the resin material, a molding step of molding the heated resin material, and a cooling step of cooling the molded resin material, The method of manufacturing an optical element according to claim 2, wherein in the forming step and the cooling step, the resin material is pressed with a higher pressing force than in the preheating step. 4. The method for manufacturing an optical element according to claim 2, wherein, in the second step, the resin mass is removed by polishing to a depth of 0.5 mm or more from the surface of the resin mass. 5. A resin material for an optical element for manufacturing an optical element by heat-press molding using a molding die, wherein the resin material is a spherical, substantially spherical resin block made of a resin formed by injection molding. A resin material for an optical element, which is formed into a spherical shape by polishing. 6. The resin material for an optical element according to claim 5, wherein said resin material is removed by polishing to a depth of 0.5 mm or more from the surface of said resin mass during said polishing. 7. An optical head comprising a light source and an optical element arranged on the optical axis of the light source, wherein the optical element is the optical element according to claim 1. . 8. An optical disk device for recording or reproducing information on or from an optical disk, comprising: a light source; and an optical element disposed between the light source and the optical disk, wherein the optical element is An optical disc device, which is the optical element according to claim 1.