JP2010042517A - Manufacturing method for optical element, optical element, and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for an optical element capable of enhancing surely a light fastness, and the optical element. <P>SOLUTION: A thermoplastic resin pellet is fluorination-treated by exposing the pellet in a fluorine gas atmosphere. Fluorine is thereby introduced gradually into a molecular inside from a surface of the pellet toward the inside (C-H bond is substitution-converted into C-F bond), to increase a fluorine content in a material. A manufacturing method for an objective lens 37 is provided with a fluorination-treating process, and a molding process for fusion-kneading and molding the fluorination-treated pellet. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical element manufacturing method, an optical element, and an optical pickup device.

  Conventionally, as a material of an optical element, a resin material is often used from the viewpoints of moldability and cost, and in such an optical element, there is a strong demand for increasing light resistance.

  Here, in general, the cause of light resistance deterioration is a radical reaction starting from dissociation of C—H bonds, and radicals are not generated unless C—H bonds are broken. For this reason, the present inventors have conducted intensive research. As a result, the C—F bond has higher binding energy than the C—H bond, and if this C—F bond is increased in the optical element, the generation of radicals can be suppressed. It was found that the light resistance can be improved.

By the way, in the technical field of an antireflection film, instead of providing an antireflection film made of an inorganic material, a resin base material (molded product) is exposed to fluorine gas to fluorinate the surface to obtain C—H. A technique for replacing the bond with a C—F bond and controlling the refractive index has been developed (for example, see Patent Document 1).
JP 2005-274748 A

  However, since the range in which the fluorine gas has an effect is limited only to the vicinity of the surface of the molded product, if the molded product is subjected to a fluorination treatment, the inside is not replaced with fluorine and remains a C—H bond. In particular, an optical element that transmits light having a short wavelength of 405 nm or the like cannot still improve light resistance.

  The subject of this invention is providing the manufacturing method and optical element of an optical element which can improve light resistance reliably.

According to one aspect of the present invention, there is provided a method for producing an optical element having a resin molded part,
A fluorination step of fluorinating a pellet containing a thermoplastic resin;
And a molding step of molding the molded part by melt-kneading the fluorinated pellets.

In the method for producing an optical element of the present invention,
The thermoplastic resin is preferably an alicyclic polyolefin.

In the method for producing an optical element of the present invention,
It is preferable to manufacture an objective lens used in a blue optical pickup device as the optical element.

According to another aspect of the invention, an optical element comprising:
It is manufactured by the method for manufacturing an optical element of the present invention.

According to another aspect of the present invention, there is provided an optical pickup device,
A light source that emits blue light;
Comprising the optical element of the present invention,
The optical element is used as an objective lens.

  According to the present invention, the pellet containing the thermoplastic resin is fluorinated, and the fluorinated pellet is melt-kneaded and molded, so the surface and the inside of the optical element are uniformly fluorinated. It will be in the state. Therefore, the light resistance can be reliably improved as compared with the case where the surface of the optical element is fluorinated.

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

  As shown in FIG. 1, the optical pickup device 30 includes a semiconductor laser oscillator 32 as a light source. The semiconductor laser oscillator 32 emits a blue laser (blue-violet laser) having a specific wavelength (for example, 405 nm) having a wavelength of 380 to 420 nm for BD (Blu-ray Disc). On the optical axis of the blue-violet light emitted from the semiconductor laser oscillator 32, a collimator 33, a beam splitter 34, a ¼ wavelength plate 35, an aperture 36, and an objective lens 37 are arranged in a direction away from the semiconductor laser oscillator 32. Are sequentially arranged.

  A sensor lens group 38 and a sensor 39 each including two sets of lenses are sequentially arranged at a position close to the beam splitter 34 and in a direction orthogonal to the optical axis of the blue-violet light described above.

  The objective lens 37 is disposed at a position facing the high-density optical disc D (BD optical disc), and collects blue-violet light emitted from the semiconductor laser oscillator 32 on one surface of the optical disc D. Yes. The objective lens 37 has an image-side numerical aperture NA of 0.7 or more. The objective lens 37 is provided with a two-dimensional actuator 40, and the objective lens 37 is movable on the optical axis by the operation of the two-dimensional actuator 40.

  As shown in the enlarged view of FIG. 1, the objective lens 37 is mainly composed of a molding part 50, and an antireflection film 60 is formed on the surface 37a thereof.

  Among these, the shaping | molding part 50 is shape | molded by the lens shape, and exhibits essential optical functions, such as a condensing function. The molding part 50 is made of a resin material containing a thermoplastic resin. Examples of such a thermoplastic resin include acrylic resin, cyclic olefin resin, polycarbonate resin, polyester resin, polyether resin, polyamide resin, or polyimide resin. And is particularly preferably a cyclic olefin. Specific examples include compounds described in JP-A-2003-73559, and preferred compounds are shown in Table 1 below.

  The above-mentioned thermoplastic resin desirably has a moisture absorption rate of 0.2% or less from the viewpoint of dimensional stability as an optical material. Therefore, polyolefin resin (polyethylene, polypropylene), fluororesin (polytetrafluoroethylene) , Teflon (registered trademark) AF: manufactured by DuPont), alicyclic polyolefin resin (cyclic olefin resin) (manufactured by Nippon Zeon: ZEONEX, manufactured by Mitsui Chemicals: APEL, manufactured by JSR: Arton, manufactured by Chicona: TOPAS), indene / styrene Resin, polycarbonate resin and the like are preferably used.

  The molded part 50 is a polymer composed of carbon and hydrogen as a constituent element of a thermoplastic resin. In addition to the above examples, the molded part 50 is particularly limited. is not.

  In addition, the constituent elements of additives such as antioxidants, ultraviolet absorbers, and plasticizers that are added to the molded part 50 and whose addition amount is 5% or less of the total weight may be other than carbon and hydrogen. .

  Further, even when a polymerization auxiliary material such as a catalyst or a reaction terminator used in manufacturing the molded part 50 remains, if the residual amount is less than 1% with respect to the total weight, its constituent elements Is not limited to carbon and hydrogen.

  In the present embodiment, the molded part 50 is not particularly limited as long as the above conditions are satisfied. However, when high transparency, high heat resistance, low water absorption, high purity, and low birefringence are added, the cyclic olefin weight is considered. More preferably, it is a coalescence.

  The antireflection film 60 basically has a two-layer structure. A first layer 61 is formed directly on the surface 37a of the molded part 50, and a second layer 62 is formed thereon.

The first layer 61 is a layer made of a high refractive index material having a refractive index of 1.7 or more, preferably Ta ₂ O ₅ , a mixture of Ta ₂ O ₅ and TiO ₂ , ZrO ₂ , ZrO ₂ and TiO _2. And is composed of any mixture. The first layer 61 may be composed of TiO ₂ , Nb ₂ O ₃ , and HfO ₂ . The second layer 62 is a layer made of a low refractive index material having a refractive index of less than 1.7, and is preferably made of SiO ₂ and MgF ₂ .

  In the objective lens 37, the first layer 61 and the second layer 62 may be alternately stacked on the first layer 61 and the second layer 62, and the antireflection film 60 may have a 2 to 7 layer structure as a whole. In this case, the layer that is in direct contact with the surface 37a of the molded part 50 may be a high refractive index material layer (first layer 61) or a low refractive index material layer (first layer 61) depending on the type of the molded part 50. It may be the second layer 62). In this embodiment, the layer that is in direct contact with the surface 37a of the molded part 50 is a layer of a high refractive index material.

  In the objective lens 37, the antireflection film 60 is formed on the back surface 37b in the same manner as the antireflection film 60 is formed on the front surface 37a, and the both surfaces of the front surface 37a and the back surface 37b are formed. An antireflection film 60 is formed. However, the objective lens 37 may not have the antireflection film 60.

Then, the shaping | molding apparatus of the shaping | molding part 50 is demonstrated.
FIG. 2 is a conceptual diagram showing a schematic configuration of the molding apparatus 1 for injection molding the molding part 50 of the objective lens 37.

  As shown in this figure, the molding apparatus 1 includes a hopper 11, a cylinder 12, a nozzle 13, an injection mold 10 and the like from the upstream side to the downstream side in the transport direction of the resin material.

  The hopper 11 is a portion to which a thermoplastic resin pellet as a main component of the molding unit 50 and a resin material made of other additive materials are supplied, and is connected to the cylinder 12. The cylinder 12 includes a screw 120 inside, and is connected to the nozzle 13 at the tip, and pushes the resin material supplied from the hopper 11 to the nozzle 13 side while kneading with the screw 120. A heater 121 for melting the resin material inside the cylinder 12 is provided on the side surface of the cylinder 12.

  The nozzle 13 is a portion that injects the resin material extruded from the cylinder 12 into the injection mold 10 and communicates with a sprue 103 of the injection mold 10 described later.

  The injection mold 10 includes a fixed mold 101 fixed to the nozzle 13 and a movable mold 102 provided so as to be able to contact with and separate from the fixed mold 101 in the X direction. When the movable mold 102 abuts, the sprue 103, the runner 104, and the gate 105 as a flow path of the resin material, and the cavity 106 for molding the resin material into the shape of the molding portion 50 are formed. .

Here, the fixed mold 101 molds one surface of the molding unit 50, and the movable mold 102 molds the other surface.
Among these, the movable mold 102 has an annular mold body 102A that molds the outer peripheral side portion of the molding portion 50, and a protruding mold 102B that is fitted to the mold body 102A and molds the center side portion. The protruding mold 102B is slidable in the X direction while being fitted to the mold main body 102A, and is pressed by the protruding member 102C to protrude toward the fixed mold 101, thereby forming the molded portion 50 after molding. The mold is released from the injection mold 10.

  Then, the manufacturing method of the objective lens 37 is demonstrated.

  First, the pellet of the thermoplastic resin is exposed to a fluorine gas atmosphere to subject the pellet to fluorination treatment (fluorination treatment step). As a result, fluorine is gradually introduced into the molecule from the surface to the inside of the pellet (substitution from C—H bond to C—F bond), and the fluorine content of the material increases. Improves.

  Here, the fluorine gas atmosphere means being covered with a gas containing fluorine gas, and includes being covered with a mixed gas of fluorine gas and an inert gas such as nitrogen or argon.

  Moreover, a pellet is a granular material obtained by solidifying a resin, and has a size of about 5 mm square, for example. If the pellet size is large, the fluorinated portion is reduced, but there is no particular problem as long as the size is general. This pellet may be mixed with an additive other than the thermoplastic resin.

  In this fluorination treatment process, the penetration depth of fluorine from the material surface and the fluorine content in the material after fluorination depend on the concentration of fluorine gas in the fluorine gas atmosphere, the fluorination treatment temperature, and the fluorination treatment time. Specifically, when the fluorine concentration is high, when the treatment time is long, when the treatment temperature is high, the penetration depth of fluorine becomes deep, and the polymer material after the fluorination treatment Increases fluorine content. Therefore, the fluorinated layer thickness and fluorination rate of the pellet can be arbitrarily controlled by appropriately selecting these conditions. And since the light resistance of a pellet improves with the increase in fluorine content, it is possible to form a pellet having a desired light resistance by appropriately selecting the fluorine concentration, processing temperature, and processing time. However, if the fluorination treatment is carried out by extremely increasing the fluorine concentration or at an extremely high temperature for a long time, the molecule deteriorates. Therefore, as a normal fluorination treatment condition, the fluorine concentration is 1 ppm to 25%, the treatment temperature. Is preferably 0 to 100 ° C. and a treatment time of 0.1 second to 120 minutes.

  Next, the molding part 50 is shape | molded using the pellet which carried out the fluorination process for the shaping | molding apparatus 1 (molding process).

  Specifically, the pellets are put into the hopper 11, kneaded by the screw 120 while being melted by the heater 121, and conveyed in the direction of the nozzle 13. As a result, the resin portion that has been fluorinated on the pellet surface side and the resin portion that has not been fluorinated on the inside of the pellet are uniformly mixed. At this time, various materials may be put into the hopper 11 as necessary.

  Next, the melted resin material is injected from the nozzle 13 into the sprue 103, the runner 104, the gate 105, and the cavity 106 of the injection mold 10, and pressure-molded in the cavity 106. Thereby, the resin material is solidified to form the molded part 50.

  Next, after moving the movable mold 102 away from the fixed mold 101 and leaving the molding part 50 on the movable mold 102 side, the projecting mold 102B is projected from the mold body 102A by the projecting member 102C, and the molding part 50 is ejected from the mold body 102A. Extrude

Next, the antireflection film 60 is formed on the molding part 50. Specifically, the first layer 61 is formed using a vapor deposition source that constitutes the first layer 61. For example, when a (Ta ₂ O ₅ + 5% TiO ₂ ) film is formed as the first layer 61, OA600 manufactured by Optran Co., Ltd. may be used as the evaporation source, and the evaporation source may be evaporated by electron gun heating. During vapor deposition, it is preferable to form a film while introducing an O ₂ gas up to a pressure of 1.0 × 10 ⁻² Pa inside the vacuum vapor deposition apparatus and controlling the vapor deposition rate at 5 Å / sec. Then, the film forming temperature (temperature in the vapor deposition apparatus) is maintained within an appropriate temperature range.

  Next, in order to form the first layer 61 on the opposite surface of the molding portion 50, the molding portion 50 is reversed by the reversing mechanism inside the vapor deposition apparatus, and the first layer 61 is also formed on the opposite surface in the same manner as described above. (The same applies to the film formation on the back surface of the second layer 62.)

Then, following the first layer 61, the second layer 62 is formed using a vapor deposition source constituting the second layer 62. For example, when a SiO ₂ film is formed as the second layer 62, O ₂ gas is introduced until the pressure inside the vacuum vapor deposition apparatus is 1.0 × 10 ⁻² Pa, and the vapor deposition rate is controlled to 5 liters / sec. It is better to form the film while doing so. Then, the film forming temperature (temperature in the vapor deposition apparatus) is maintained within an appropriate temperature range.

  Through the above steps, the objective lens 37 is manufactured.

  Next, the operation of the optical pickup device 30 will be described.

Blue-violet light is emitted from the semiconductor laser oscillator 32 during an operation of recording information on the optical disc D or an operation of reproducing information recorded on the optical disc D. The emitted blue-violet light is transmitted through the collimator 33 and collimated into infinite parallel light, then transmitted through the beam splitter 34 and transmitted through the quarter wavelength plate 35. Furthermore, after passing through the blue-violet light aperture 36 and the objective lens 37, forms a converged spot on an information recording surface D ₂ through the protective substrate D ₁ of the optical disc D.

Violet light that formed the concentrated light spot is modulated by the information recording surface D ₂ of the optical disk D by the information bits, is reflected by the information recording surface D _2. Then, the reflected light is sequentially transmitted through the objective lens 37 and the diaphragm 36, the polarization direction is changed by the quarter wavelength plate 35, and the reflected light is reflected by the beam splitter 34. Thereafter, the reflected light passes through the sensor lens group 38 to be given astigmatism, is received by the sensor 39, and finally is photoelectrically converted by the sensor 39 to become an electrical signal.

  Thereafter, such an operation is repeatedly performed, and the operation of recording information on the optical disc D and the operation of reproducing information recorded on the optical disc D are completed.

  According to the above embodiment, the pellet containing the thermoplastic resin is subjected to fluorination treatment, and the fluorinated pellet is melt-kneaded and molded, so that the molding portion 50 (objective lens 37) is molded. The surface and the inside are uniformly fluorinated. Therefore, compared with the case where the surface of the molding part 50 is fluorinated, the light resistance can be reliably improved.

In the above embodiment, the optical element according to the present invention has been described as the objective lens 37. However, other types and applications of optical elements may be used.
Moreover, although it demonstrated as forming the anti-reflective film 60 in the surface 37a of the shaping | molding part 50 shape | molded with the pellet which carried out the fluorination process, after further fluorinating the surface of the shaping | molding part 50, the anti-reflective film 60 is formed. It may be formed. In this case, the light resistance can be further improved.

  Hereinafter, the optical element according to the present invention will be described more specifically by giving examples and comparative examples. However, the present invention is not limited to the examples. In the following examples and comparative examples, the above-described antireflection film 60 is not provided on the objective lens.

(1) Production of Samples As examples and comparative examples of the present invention, samples as shown in Table 2 below were produced. Hereinafter, each sample will be specifically described.

(1.1) Example 1
The inside of the stainless steel reactor equipped with a stirrer was sufficiently dried and purged with nitrogen. Thereafter, 300 parts by mass of dehydrated cyclohexane, 60 parts by mass of styrene and 0.38 parts by mass of dibutyl ether were charged into the reactor, and the n-butyllithium solution (15% hexane solution) 0 was added while stirring these at 60 ° C. .36 parts by mass was added to initiate the polymerization reaction.

  A polymerization reaction is performed for 1 hour, and then the reaction solution is mixed with 8 parts by mass of styrene, 12 parts by mass of isoprene, and 0.8 parts by mass of 1,2,2,6,6-pentamethyl-4-piperidylmethacrylate. A monomer was added and the polymerization reaction was further performed for 1 hour, and then 0.2 parts by mass of isopropyl alcohol was added to the reaction solution to stop the reaction.

  Next, 300 parts by mass of the polymerization reaction solution was transferred to a pressure-resistant reactor equipped with a stirrer, and as a hydrogenation catalyst, a silica-alumina supported nickel catalyst (manufactured by JGC Kagaku Kogyo: E22U, nickel supported type 60 %) 10 parts by mass were added and mixed. The inside of the reactor was replaced with hydrogen gas, hydrogen was further supplied while stirring the solution, the temperature was set to 160 ° C., and then a hydrogenation reaction was performed at a pressure of 4.5 MPa for 8 hours.

  After completion of the reaction, the reaction solution was filtered to remove the hydrogenation catalyst, 800 parts by mass of cyclohexane was added for dilution, and then the reaction solution was poured into 3500 parts by mass of isopropanol to precipitate a copolymer. Thereafter, this copolymer was filtered out and dried under reduced pressure at 80 ° C. for 48 hours to obtain “resin material 1”.

This “resin material 1” was pelletized to about 3 mm square, and fluorinated for 30 minutes under conditions of 1.1 atm, normal temperature, and F ₂ gas concentration of 5%. The obtained pellets were injection-molded to form an objective lens with NA of 0.85, and used as a sample of “Example 1”.

(1.2) Example 2
The objective lens of Example 1 was further subjected to fluorination treatment for 10 minutes under the conditions of 1.1 atm, normal temperature, and F ₂ gas concentration of 5%. The obtained objective lens was a sample of “Example 2”. It was.

(1.3) Example 3
100 parts by mass of a random copolymer of ethylene and bicyclo [2,2,1] hept-2-ene, 0.5 parts by mass of pentaerythritol distearate as a surfactant, and pentaerythritol tetrakis [ 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] 0.3 part by mass and bis (2,2,6,6-tetramethyl) as a HALS agent (hindered amine light resistance stabilizer) -4-Piperidyl) 1 part by mass of sebacate was kneaded with a biaxial kneader to obtain “resin material 2”.

This “resin material 2” was pelletized to about 3 mm square, and fluorinated for 30 minutes under the conditions of 1.1 atm, normal temperature, and F ₂ gas concentration of 5%. The obtained pellets were injection-molded to form an objective lens with NA of 0.85, and used as a sample of “Example 3”.

(1.4) Example 4
To 100 parts by mass of methyl methacrylate and 1 part by mass of methyl acrylate, 0.006 parts by mass of azobisisobutyronitrile and 0.008 parts by mass of n-octyl mercaptan were added and stirred to obtain a uniform solution. Next, this homogeneous solution was put into a 50 L jacketed polymerization tank containing a solution obtained by adding 0.003 parts by mass of poly (sodium methacrylate) to 300 parts by mass of water and stirred. Then, warm water was passed through the jacket and a polymerization reaction was carried out at 80 ° C. for 3 hours. The obtained polymer was washed with water and dried to obtain “resin material 3” containing methyl methacrylate as a main component.

This “resin material 3” was pelletized to about 3 mm square, and fluorinated for 30 minutes under the conditions of 1.1 atm, normal temperature, and F ₂ gas concentration of 5%. The obtained pellet was injection-molded to form an objective lens with NA of 0.85, and a sample of “Example 4” was obtained.

(1.5) Comparative Example 1
“Resin material 1” of Example 1 was injection molded to form an objective lens with NA of 0.85, and then fluorinated for 30 minutes under the conditions of 1.1 atm, normal temperature, and F ₂ gas concentration 5%. The objective lens thus obtained was used as a sample of “Comparative Example 1”.

(1.6) Comparative Example 2
“Resin material 2” of Example 3 was injection molded to form an objective lens with NA of 0.85, and then fluorinated for 30 minutes under the conditions of 1.1 atm, normal temperature and F ₂ gas concentration of 5%. The obtained objective lens was used as a sample of “Comparative Example 2”.

(1.7) Comparative Example 3
The “resin material 3” of Example 4 was injection molded to form an objective lens with NA of 0.85, and then fluorinated for 30 minutes under conditions of 1.1 atm, normal temperature, and F ₂ gas concentration of 5%. The obtained objective lens was used as a sample of “Comparative Example 3”.

(2) Evaluation of Samples Each sample prepared was irradiated with a 20 mW laser at 75 ° C. for 3000 h, and the light resistance was evaluated according to the following criteria. The results were as shown in Table 2 above.

A: There is no change before and after laser irradiation.
○: Slight white turbidity occurred after laser irradiation, but there is no problem in performance.
Δ: Slight change in performance occurred after laser irradiation, but no problem in practical use.
X: Irradiation cloudiness or shape change occurred by laser irradiation.

(3) Summary From the results in Table 2, in the samples of Examples 1 to 4, there is no significant change in shape and optical performance after laser irradiation, and the light resistance is particularly high when using short-wavelength light. It turns out that it is useful to improve.

It is drawing which shows schematic structure of the optical pick-up apparatus used by preferable embodiment of this invention. It is a conceptual diagram which shows schematic structure of the shaping | molding apparatus for injection-molding an objective lens.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molding apparatus 30 Optical pick-up apparatus 32 Semiconductor laser oscillator 33 Collimator 34 Beam splitter 35 1/4 wavelength plate 36 Diaphragm 37 Objective lens 37a Front surface 37b Back surface 38 Sensor lens group 39 Sensor 40 Two-dimensional actuator 50 Molding part 60 Antireflection film 61 1st 1 layer 62 2nd layer D optical disk D ₁ protective substrate D ₂ information recording surface

Claims (5)

A method for producing an optical element having a resin molded part,
A fluorination step of fluorinating a pellet containing a thermoplastic resin;
And a molding step of molding the molded part by melt-kneading the fluorinated pellets. In the manufacturing method of the optical element of Claim 1,
The method for producing an optical element, wherein the thermoplastic resin is an alicyclic polyolefin. In the manufacturing method of the optical element of Claim 1 or 2,
An optical element manufacturing method comprising manufacturing an objective lens used in a blue optical pickup device as the optical element.   An optical element manufactured by the method for manufacturing an optical element according to claim 1. A light source that emits blue light;
An optical element according to claim 4,
An optical pickup device, wherein the optical element is used as an objective lens.

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