JP2008221514A - Injection molding method and optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an injection molding method capable of improving shape transfer property from a mold to a molded material and shortening a cycle time. <P>SOLUTION: In the injection molding method, an organic-inorganic material where inorganic particles are dispersed in a thermoplastic resin is injected and molded by using a mold 1 having a cavity 26 for receiving filling of the molded material. The injection molding method has a step for filling the organic-inorganic material into the cavity 26 in such a state that the mold temperature near the cavity 26 is made to be higher temperature than the glass transit temperature Tg of the thermoplastic resin by 20°C or more, a step for cooling the mold temperature near the cavity 26 to the lower temperature than the glass transit temperature Tg of the thermoplastic resin, and a step for taking out a molded article composed of the organic-inorganic composite material from the cavity in such a state that the mold temperature near the cavity 26 is made to be lower than the glass transit temperature Tg of the thermoplastic resin. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an injection molding method for manufacturing an optical element, and more particularly to an injection molding method for molding an organic-inorganic composite material in which inorganic fine particles are dispersed in a thermoplastic resin.

  In recent years, glass optical elements and plastic optical elements are known as optical elements used for various optical applications such as camera optical elements, optical pickup apparatus optical elements, and optical communication optical elements. In particular, plastic optical elements can be efficiently manufactured by using an injection molding method, and thus can be produced at a lower cost than glass optical elements and are widely used.

  In particular, development of plastic optical elements that can be produced at a lower cost than glass optical elements has been promoted as optical elements used in optical pickup devices for recording and / or reproducing CDs, DVDs, high-density DVDs, and the like. Yes. However, plastic optical elements have a problem that their optical performance varies significantly due to environmental changes such as ambient temperature changes and humidity changes compared to glass optical elements, so that they are unlike optical elements used in optical pickup devices. Improvements have been sought when used as an optical element that requires very precise optical performance. Therefore, an optical element using an organic-inorganic composite material in which optical performance is improved without impairing transparency as an optical element by dispersing minute inorganic fine particles in a thermoplastic resin has been proposed (for example, patents). Document 1 and Patent document 2). By using such an organic-inorganic composite material, an optical element that can be manufactured using an injection molding method that can be produced at low cost and that has improved optical performance has been studied.

  On the other hand, when molding a plastic optical element by an injection molding method, the glass temperature of the resin is usually reduced while keeping the resin temperature sufficiently higher than the glass transition temperature Tg of the resin. Molding is performed by injection into a mold kept at Tg or less. Furthermore, in order to enhance shape transferability, the mold temperature is kept at a temperature about 10 ° C. higher than the glass transition temperature Tg of the resin at the time of injection, the resin is cooled after filling, and the mold temperature is changed to the glass transition temperature Tg of the resin. In some cases, heat cycle molding in which the temperature is taken out after lowering the temperature is used.

  However, the organic-inorganic composite material in which the inorganic fine particles are dispersed in the thermoplastic resin as described above generally has a higher thermal conductivity and a higher viscosity than the resin itself that does not contain the inorganic fine particles. In the case of normal injection molding with the mold temperature lower than the glass transition temperature of the resin, there is a phenomenon called short shot in which the resin solidifies at the runner part that flows the resin into the mold cavity. It has been found that there is a problem that the resin is rapidly solidified in the cavity and a pattern called a linear or wrinkled weld line is generated on the molded product. In addition, the organic / inorganic composite material may solidify at the gate part that becomes the resin filling port into the mold cavity, and a phenomenon of gate seal that prevents sufficient pressure inside the mold cavity will also occur. There was found. Even if a short shot does not occur, it has been found that there is a problem that transfer of a sufficient shape is not performed. That is, it has been found that a problem occurs in the cavity and the vicinity thereof.

On the other hand, even if the shape transferability is improved by using heat cycle molding, the glass transition temperature Tg is increased from a temperature about 10 ° C. higher than the glass transition temperature Tg of the resin, as is done in normal resin molding. In heat cycle molding in which the temperature is cooled to a lower temperature, sufficient shape transferability from the mold to the resin could not be obtained. In particular, when it is necessary to transfer a fine surface shape such as a diffraction structure to the optical surface of the optical element, it is difficult to transfer the shape sufficiently.
JP 2002-207101 A Japanese Patent Laid-Open No. 2002-240901

  Accordingly, a main object of the present invention is an injection molding method of an organic-inorganic composite material in which inorganic fine particles are dispersed in a thermoplastic resin, and is intended to improve shape transferability from a mold to a molding material. Another object of the present invention is to provide an injection molding method that can be used, an optical element manufactured by the injection molding method, and an injection molding method that can shorten the cycle time while using a heat cycle molding method.

In order to solve the above problem, the injection molding method according to claim 1 is:
An injection molding method for injecting and molding an organic-inorganic composite material in which inorganic fine particles are dispersed in a thermoplastic resin using a mold having a cavity for receiving filling of a molding material,
Filling the cavity with the organic-inorganic composite material in a state where the mold temperature near the cavity is 20 ° C. or higher than the glass transition temperature Tg of the thermoplastic resin;
Cooling the mold temperature near the cavity to a temperature lower than the glass transition temperature Tg of the thermoplastic resin;
Taking out a molded article composed of the organic-inorganic composite material from the cavity in a state where the mold temperature near the cavity is lower than the glass transition temperature Tg of the thermoplastic resin;
It is characterized by having.

The invention described in claim 2
The injection molding method according to claim 1,
A heating means and a cooling means are provided in the vicinity of the cavity.

The invention described in claim 3
In the injection molding method according to claim 2,
The cooling means has a configuration in which a liquid is circulated in a flow path provided in the vicinity of the cavity.

The invention according to claim 4
In the injection molding method according to claim 2,
The cooling means has a configuration in which a gas is circulated in a flow path provided in the vicinity of the cavity.

The invention described in claim 5
In the injection molding method according to claim 2,
The cooling means has a configuration in which gas is injected in the vicinity of the cavity.

The invention described in claim 6
In the injection molding method according to any one of claims 1 to 5,
The mold has a peripheral portion farther from the vicinity than the vicinity when the vicinity of the cavity is a vicinity.
In the step of filling the organic-inorganic composite material, the temperature of at least a part of the peripheral portion is maintained at a temperature lower than the glass transition temperature Tg of the thermoplastic resin.

The invention described in claim 7
In the injection molding method according to any one of claims 1 to 6,
The mold has a peripheral portion farther from the vicinity than the vicinity when the vicinity of the cavity is a vicinity.
In the step of cooling the vicinity of the cavity, the temperature of at least a part of the peripheral portion is maintained at a temperature between the glass transition temperature Tg of the thermoplastic resin and the glass transition temperature Tg-30 ° C. of the thermoplastic resin. It is characterized by doing.

The invention according to claim 8 provides:
In the injection molding method according to claim 6 or 7,
The peripheral portion is provided with temperature adjusting means for adjusting the temperature of the peripheral portion.

The invention according to claim 9 is:
The injection molding method according to claim 8,
The temperature adjusting means has a configuration in which a liquid is circulated in a flow path provided in the peripheral portion.

The invention according to claim 10 is:
In the injection molding method according to claim 9,
The liquid is a liquid maintained at a temperature between the glass transition temperature Tg of the thermoplastic resin and the glass transition temperature Tg of the thermoplastic resin T-30C.

The invention according to claim 11
In the injection molding method according to any one of claims 1 to 10,
The molding surface of the cavity is provided with a fine structure.

The invention according to claim 12
It is an optical element manufactured by the injection molding method according to any one of claims 1 to 11.

  According to the injection molding method of claim 1, when filling the organic-inorganic composite material, the mold temperature in the vicinity of the cavity is set to 20 ° C. higher than the glass transition temperature Tg of the thermoplastic resin, and at the time of taking out the molded product, By setting the mold temperature in the vicinity of the cavity to a temperature lower than the glass transition temperature Tg of the thermoplastic resin, the shape transferability from the mold to the organic-inorganic composite material can be improved. In the present invention, the vicinity of the cavity means a portion including at least the molding surface (cavity) of the optical element of the mold, and at least when the organic-inorganic composite material is filled into the cavity and when the molded product is taken out. The shape transferability can be improved by adjusting the surface to the above temperature condition. Therefore, it is not always necessary to satisfy the above temperature condition for portions other than the vicinity of the cavity, but in order to prevent short shots in the runner portion and gate seal in the gate portion, the runner and the gate portion are also included in the vicinity of the cavity. Preferably, the sprue is also included in the vicinity of the cavity.

  According to the injection molding method of claim 2, since not only the heating means but also the cooling means is provided in the vicinity of the cavity, heat cycle molding can be performed in a short cycle time, so that the shape transfer can be performed at low cost. An injection molding method having properties can be provided.

  According to the injection molding methods of claims 3 to 5, the vicinity of the cavity can be efficiently cooled with a simple configuration, and heat cycle molding can be performed in a shorter cycle time.

  The mold temperature in the vicinity of the cavity at the time of resin filling is set to a temperature that is higher than the glass transition temperature Tg + 20 ° C. of the thermoplastic resin, and the temperature in the vicinity of the cavity at the time of taking out the molded product is lower than the glass transition temperature Tg of the thermoplastic resin. As a result, sufficient transferability can be obtained, but the temperature difference between filling and taking out increases, and the cycle time may increase. However, according to the injection molding method of claim 6, in the filling step of the organic-inorganic composite material, only the temperature in the vicinity of the mold that is in the vicinity of the cavity is higher than the glass transition temperature Tg + 20 ° C. of the thermoplastic resin. The temperature of at least a part of the periphery of the mold is lower than the glass transition temperature Tg of the thermoplastic resin, so that the entire mold needs to be cooled when the vicinity of the cavity is cooled after the filling process. Therefore, the vicinity of the cavity can be quickly cooled, and the cycle time can be shortened. Furthermore, when heating again, the cycle time can be shortened by setting only the mold temperature near the cavity to a glass transition temperature Tg + 20 ° C. higher than the thermoplastic resin.

  According to the injection molding method of claim 7, in the cooling step in the vicinity of the cavity, the temperature at the periphery of the mold is the glass transition temperature Tg of the thermoplastic resin and the glass transition temperature Tg-30 ° C. of the thermoplastic resin. By maintaining the temperature in between, the vicinity of the cavity can be prevented from being excessively cooled by the cooling means, and the mold temperature in the vicinity of the cavity is again 20 ° C. higher than the glass transition temperature Tg of the thermoplastic resin. The time for raising the temperature can be shortened.

  According to the injection molding method of claim 8, by providing the temperature adjusting means for adjusting the temperature of the peripheral part of the mold, the temperature of the peripheral part can be kept moderate, and heating and cooling are performed. In the process, the cycle time can be shortened because the temperature only needs to be adjusted in the vicinity.

  According to the injection molding method of the ninth aspect, the temperature can be adjusted without providing a complicated device in the periphery of the mold.

  According to the injection molding method of claim 10, the temperature of the peripheral portion is set to the glass transition temperature Tg of the thermoplastic resin and the glass transition temperature Tg of the thermoplastic resin without providing a complicated device in the peripheral portion of the mold. Since the temperature between −30 ° C. can be maintained, it is possible to prevent the vicinity of the cavity from being excessively cooled by the cooling means, and the mold temperature near the cavity is again set to the glass transition temperature of the thermoplastic resin. The time required for raising the temperature to 20 ° C. or more higher than Tg can be shortened.

  According to the injection molding method of the eleventh aspect, a fine structure can be imparted to the molded product corresponding to the optical element. Further, when a fine structure is provided on the molding surface, further excellent transferability is required, and therefore the injection molding method of the present invention is particularly effective.

  According to the injection molding method of claim 12, optical characteristics can be improved by using an organic-inorganic composite material in which inorganic fine particles are dispersed in a thermoplastic resin, and the shape of the mold is accurately transferred. The obtained optical element can be obtained.

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

  The present embodiment provides a method for producing an optical element by injecting and molding an organic-inorganic composite material in which inorganic fine particles are dispersed in a thermoplastic resin using a mold for injection molding. In the following, (1) the structure of the mold will be described first, then (2) the thermoplastic resin and (3) inorganic fine particles constituting the organic-inorganic composite material will be described, and finally (4) the mold will be described. A method (including an injection molding method) for producing an optical element using the above will be described.

(1) Configuration of mold A mold 1 according to this embodiment is an iron mold having a rectangular parallelepiped shape. Specifically, the mold 1 is composed of a male mold 10 and a female mold 20 as shown in the upper part of FIG. 1, and the male mold 10 and the female mold 20 are superposed on each other. The male mold 10 and the female mold 20 are separated from each other. When a molding material such as resin (organic-inorganic composite material in the present embodiment) is injected and molded (filled), the male mold 10 and the female mold 20 are in close contact with each other and closed. When the molding material (molded product) is taken out, it can be opened separately.

  As shown in the lower part of FIG. 1, the female mold 20 is provided with a sprue 22, a runner 23, a gate 24 and a cavity 26. The sprue 22 serves as an inlet for the material to be molded, and is disposed substantially at the center of the female mold 20. The runner 23 extends radially from the sprue 22 and communicates with the gate 24. The gate 24 is a portion that receives an inflow of the molding material from the runner 23 and injects the molding material into the cavity 26. The runner 23, the gate 24, and the like are arranged in the vicinity of the cavity 26.

  The cavity 26 is a part where a molded product is formed. The molded product is formed from the molding material by receiving injection (filling) of the molding material from the gate 26. The cavity 26 is formed with a microstructure 28 (for example, concentric steps) for imparting a microstructure to the molded product, and the microstructure is transferred to the molding material filled in the cavity 26. It is like that.

  A rod heater 30 is provided in the vicinity of the cavity 26, and a circular channel 32 is formed so as to surround the sprue 22, the runner 23, the gate 24, the cavity 26 and the rod heater 30. An inflow / outflow port (not shown) of fluid is connected to the flow path 32, and the fluid can be circulated through the flow path 32 by flowing in / out the fluid from the inflow / outflow path. Yes.

  A circular channel 42 larger than the diameter of the channel 32 is formed on the outer periphery of the channel 32. A fluid inflow / outflow port (not shown) is also connected to the flow path 42, and the fluid can be circulated through the flow path 32 by flowing the fluid in / out from the inflow / outflow port. Yes.

  On the other hand, the male mold 10 is formed with parts having a complementary relationship to the sprue 22, runner 23, gate 24, cavity 26, etc. of the female mold 20. The male mold 10 is substantially the same as the female mold 20. It has a configuration.

  In this embodiment, the vicinity of the cavity 26 is heated by operating the rod heater 30. On the other hand, a cooling medium is allowed to flow into and out of the flow path 32, and the vicinity of the cavity 26 is cooled by circulating the medium through the flow path 32. That is, both heating and cooling in the vicinity of the cavity 26 are performed by operating the rod heater 30 and circulating a cooling medium in the flow path 32.

  On the other hand, a constant temperature medium flows into and out of the flow path 42, and the medium is circulated in the flow path 42, thereby distant from the rod heater 30 and the flow path 32 with respect to the cavity 26. This part (peripheral part of the mold 1) is adjusted to a constant temperature according to the temperature of the medium. That is, by circulating a constant temperature medium in the flow path 42, the temperature of the peripheral portion of the mold 1 is kept constant.

(2) Thermoplastic resin From the viewpoint of processability as an optical element, the thermoplastic resin is preferably an acrylic resin, a cyclic olefin resin, a polycarbonate resin, a polyester resin, a polyether resin, a polyamide resin, or a polyimide resin. A cyclic olefin is particularly preferred. 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), 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, etc. Preferably used.

(3) Inorganic fine particles Examples of inorganic fine particles include oxide fine particles, metal salt fine particles, and semiconductor fine particles. Among these, those that do not generate absorption, light emission, fluorescence, etc. in the wavelength region used as an optical element are appropriately selected. Can be used.

As oxide fine particles, the metal constituting the metal oxide is Li, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Rb. 1 selected from the group consisting of Sr, Y, Nb, Zr, Mo, Ag, Cd, In, Sn, Sb, Cs, Ba, La, Ta, Hf, W, Ir, Tl, Pb, Bi and rare earth metals A metal oxide that is a seed or two or more metals can be used. Specifically, for example, silicon oxide, titanium oxide, zinc oxide, aluminum oxide, zirconium oxide, hafnium oxide, niobium oxide, tantalum oxide, oxide Magnesium, calcium oxide, strontium oxide, barium oxide, indium oxide, tin oxide, lead oxide, double oxides composed of these oxides, lithium niobate and potassium niobate , Lithium tantalate, the aluminum magnesium oxide (MgAl ₂ O _4), and the like.

  Rare earth oxides can also be used as other oxide fine particles, specifically scandium oxide, yttrium oxide, lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, oxide Examples also include dysprosium, holmium oxide, erbium oxide, thulium oxide, ytterbium oxide, and lutetium oxide. Examples of the metal salt fine particles include carbonates, phosphates, sulfates, and the like, specifically, calcium carbonate, aluminum phosphate, and the like.

The semiconductor fine particles mean fine particles having a semiconductor crystal composition. Specific examples of the semiconductor crystal composition include simple elements of Group 14 elements of the periodic table such as carbon, silicon, germanium, tin, and phosphorus (black phosphorus). A group consisting of a group 15 element such as selenium and tellurium, a compound composed of a group 14 element such as silicon carbide (SiC), tin oxide (IV) ( SnO ₂ ), tin sulfide (II, IV) (Sn (II) Sn (IV) S ₃ ), tin sulfide (IV) (SnS ₂ ), tin sulfide (II) (SnS), tin selenide (II) ( SnSe), tin telluride (II) (SnTe), lead (II) sulfide (PbS), lead selenide (II) (PbSe), lead telluride (II) (PbTe) group 14 elements Compounds with Group 16 elements of the periodic table, boron nitride (BN), boron phosphide (BP), boron arsenide BAs), aluminum nitride (AlN), aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminum antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), antimony Compound of periodic table group 13 element and periodic table group 15 element such as gallium (GaSb), indium nitride (InN), indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb) (or the like) III-V group compound semiconductor), aluminum sulfide (Al ₂ S ₃ ), aluminum selenide (Al ₂ Se ₃ ), gallium sulfide (Ga ₂ S ₃ ), gallium selenide (Ga ₂ Se ₃ ), gallium telluride ( Ga ₂ Te ₃ ), indium oxide (In ₂ O ₃ ), indium sulfide (In ₂ S ₃ ), indium selenide (In ₂ Se ₃ ), indium telluride (In ₂ Te ₃ ) and other compounds of group 13 elements of the periodic table and group 16 elements of the periodic table, thallium chloride (I) (TlCl) , Thallium bromide (I) (TlBr), thallium iodide (I) (TlI) compounds such as Group 13 elements and Periodic Table Group 17 elements, zinc oxide (ZnO), zinc sulfide (ZnS) , Zinc selenide (ZnSe), zinc telluride (ZnTe), cadmium oxide (CdO), cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), mercury sulfide (HgS), mercury selenide (HgSe), mercury telluride (HgTe) periodic table group 12 element and the periodic table compound of group 16 element such as (or II-VI compound semiconductor), arsenic sulfide (III) (as _{2 3),} selenium arsenic _{(III) (As 2 Se 3} ), telluride arsenic _{(III) (As 2 Te 3} ), antimony sulfide _{(III) (Sb 2 S 3} ), selenium antimony (III) (Sb ₂ Se ₃ ), antimony telluride (III) (Sb ₂ Te ₃ ), bismuth sulfide (III) (Bi ₂ S ₃ ), bismuth selenide (III) (Bi ₂ Se ₃ ), bismuth telluride (III) (Bi) ₂ Te ₃ ) periodic table group 15 element and periodic group 16 element compound, copper oxide (I) (Cu ₂ O), copper selenide (Cu ₂ Se) periodic table Compounds of Group 11 elements and Group 16 elements of the periodic table, copper chloride (I) (CuCl), copper bromide (I) (CuBr), copper iodide (I) (CuI), silver chloride (AgCl), odor Compounds of Group 11 elements of the periodic table and elements of Group 17 of the periodic table, such as silver halide (AgBr), nickel oxide (II) (N O) and other periodic table group 10 elements and periodic table group 16 elements, cobalt oxide (II) (CoO), cobalt sulfide (II) (CoS) and other periodic table group 9 elements and periodic table Compounds with Group 16 elements, compounds of Group 8 elements of the periodic table such as triiron tetroxide (Fe ₃ O ₄ ), iron sulfide (II) (FeS), and Group 16 elements of the periodic table, manganese (II) oxide A compound of a periodic table group 7 element such as (MnO) and a periodic table group 16 element, a periodic table group 6 element such as molybdenum sulfide (IV) (MoS ₂ ), tungsten oxide (IV) (WO ₂ ), etc. Periodic table Group 15 elements such as compounds with Group 16 elements of the periodic table, vanadium oxide (II) (VO), vanadium oxide (IV) (VO ₂ ), tantalum oxide (V) (Ta ₂ O ₅ ), etc. Table compound of group 16 element, titanium oxide _{(TiO 2, Ti 2 O 5} , Ti 2 O 3, Ti 5 O 9 , etc. A compound of a periodic table group 4 element such as a periodic table group 16 element, a compound of a periodic table group 2 element such as magnesium sulfide (MgS) and magnesium selenide (MgSe), and a periodic table group 16 element, Cadmium oxide (II) chromium (III) (CdCr ₂ O ₄ ), cadmium selenide (II) chromium (III) (CdCr ₂ Se ₄ ), copper sulfide (II) chromium (III) (CuCr ₂ S ₄ ), selenium Examples thereof include chalcogen spinels such as mercury (II) chromium (III) (HgCr ₂ Se ₄ ), barium titanate (BaTiO ₃ ), and the like. In addition, G. Schmid et al .; Adv. Mater. 4, 494 (1991) (BN) ₇₅ (BF ₂ ) ₁₅ F ₁₅ and D. Fenske et al .; Angew. Chem. Int. Ed. Engl. 29, page 1452 (1990), a semiconductor cluster having a fixed structure such as Cu ₁₄₆ Se ₇₃ (triethylphosphine) ₂₂ reported in the same manner is also exemplified.

  Among the above inorganic fine particles, a resin used as an optical material often has a refractive index of about 1.4 to 1.7, and therefore oxide fine particles having a refractive index close to this are preferably used. Specific examples include silica (silicon oxide), calcium carbonate, aluminum phosphate, aluminum oxide, magnesium oxide, and aluminum / magnesium oxide. From the viewpoint that the refractive index can be arbitrarily adjusted, composite oxide fine particles containing Si and a metal element other than Si are more preferably used.

  In the present embodiment, the inorganic fine particles dispersed in the thermoplastic resin may be one kind of inorganic fine particles or a combination of plural kinds of inorganic fine particles as long as the light transmittance is not deteriorated. . By using a plurality of types of fine particles having different properties, the required characteristics can be improved more efficiently.

  The average primary particle diameter of the inorganic fine particles is preferably 1 to 30 nm, more preferably 1 to 25 nm, and particularly preferably 1 to 10 nm. The average primary particle diameter of the inorganic fine particles indicates an average value of the diameters when the inorganic fine particles are converted into spheres having the same volume, and this value can be evaluated from a transmission electron micrograph.

  The shape of the inorganic fine particles is not particularly limited, but spherical fine particles are preferably used. Specifically, the minimum diameter of the particle (minimum value of the distance between the tangents when drawing two tangents in contact with the outer periphery of the fine particle) / maximum diameter (the value in drawing two tangents in contact with the outer periphery of the fine particle) The maximum value of the distance between tangents) is preferably 0.5 to 1.0, and more preferably 0.7 to 1.0.

  Moreover, in the state made into the organic-inorganic composite material (the state dispersed in the thermoplastic resin), the lower limit of the mixing ratio of the inorganic fine particles to the whole organic-inorganic composite material is 5% by volume or more, preferably 10 volumes. %, More preferably 20% by volume or more, and the upper limit is 50% by volume or less, preferably 40% by volume or less.

(4) Optical element manufacturing method (including injection molding method)
First, an organic-inorganic composite material in which inorganic fine particles are dispersed in a resin plastic resin is manufactured. Specifically, a method of forming a composite by polymerizing a thermoplastic resin in the presence of inorganic fine particles, a method of forming and combining inorganic fine particles in the presence of a thermoplastic resin, and the inorganic fine particles as a solvent for the thermoplastic resin A method of making a dispersion in a liquid and then compounding by removing the solvent, a method of preparing inorganic fine particles and a thermoplastic resin separately, and compounding by melt kneading, melt kneading in a state containing a solvent, etc. It can be produced by any method.

  Among these, the method of preparing the inorganic fine particles and the thermoplastic resin separately and combining them by melt-kneading is preferably used because it is simple and can suppress the manufacturing cost. As an apparatus which can be used for melt kneading, a closed kneading apparatus or a batch kneading apparatus such as a lab plast mill, a Brabender, a Banbury mixer, a kneader, a roll, and the like can be given. Moreover, it can also manufacture using a continuous melt-kneading apparatus like a single screw extruder, a twin screw extruder, etc.

  When melt kneading is used in the method for producing an organic-inorganic composite material, the thermoplastic resin and the inorganic fine particles may be added and kneaded all at once, or may be added in stages and kneaded. In this case, in a melt-kneading apparatus such as an extruder, it is possible to add the components to be added step by step from the middle of the cylinder. In addition, after kneading in advance, when components other than thermoplastic resin that have not been added in advance are added and further melt-kneaded, these may be added all at once and kneaded, or added in stages. And may be kneaded. The method of adding in a divided manner or the method of adding one component in several batches can be adopted, the method of adding one component at a time and the method of adding different components in stages can also be adopted, both of which are combined The method is fine.

  In the case of compounding by melt kneading, the inorganic fine particles can be added as a powder, or can be added in a dispersed state in the liquid, but the inorganic fine particles can be added in advance at a predetermined mixing ratio. A method is preferred in which a master batch in which fine particles and a resin are premixed is prepared, and then the master batch and the resin are combined by melt-kneading. In this case, as a method for producing a masterbatch, it is preferable to apply a wet mixing method from the viewpoint that the organic-inorganic composite material is less damaged and can be uniformly mixed. The wet mixing method is a method of preparing a masterbatch by dissolving a resin in an appropriately selected solvent and mixing the solvent in which the resin is dissolved and inorganic fine particles, and finally by volatilizing the solvent. A master batch can be obtained.

  Solvents applicable to the production of the masterbatch include, for example, aromatic hydrocarbons such as benzene, toluene, xylene, ketones such as acetone, methyl ethyl ketone, cyclohexanone, heptanone, ethyl acetate, acetic acid-t-butyl, acetic acid- Esters such as n-butyl and acetic acid-n-hexyl, halogenated hydrocarbons such as 1,2-dichloroethane, chloroform and chlorobenzene, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol diethyl ether, Ethers such as tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, Aprotic polar solvents such as Holland can be mentioned. These solvents can be used alone or in combination of two or more.

  When the production of the organic-inorganic composite material is finished, the organic-inorganic composite material is injected and molded using the mold 1 shown in FIG. 1 to produce an optical element. The injection molding process mainly includes (4.1) a step of filling the cavity 26 of the mold 1 with an organic-inorganic composite material, (4.2) a step of cooling the vicinity of the cavity 26, and (4.3) It consists of three steps including a step of taking out a molded product (optical element) from the cavity 26 of the mold 1. In the following, these three steps will be described in detail.

(4.1) Filling process The male mold 10 and the female mold 20 are closed, the rod heater 30 is operated, and the temperature near the cavity 26 is 20 ° C. or more higher than the glass transition temperature Tg of the thermoplastic resin in the organic-inorganic composite material. And In this state, the prepared organic / inorganic composite material is introduced from the sprue 22, and this organic / inorganic composite material is injected / filled into the cavity 26 from the runner 23 and the gate 24.

  At this time, a constant temperature medium having a temperature lower than the glass transition temperature Tg of the thermoplastic resin is circulated in the flow path 42, and the temperature of the periphery of the mold 1 is lower than the glass transition temperature Tg of the thermoplastic resin. Hold at temperature. As the “constant temperature medium”, any liquid having a temperature lower than the glass transition temperature Tg of the thermoplastic resin can be used. For example, a liquid such as oil can be used.

  In the above filling process, the temperature in the vicinity of the cavity 26 is set to the glass transition temperature Tg of the thermoplastic resin Tg + 20 ° C. or more with the periphery of the mold 1 kept at a temperature lower than the glass transition temperature Tg of the thermoplastic resin. The cavity 26 is filled with an inorganic composite material.

(4.2) Cooling Step After the cavity 26 is filled with the organic-inorganic composite material, the rod heater 30 is stopped to stop the heating in the vicinity of the cavity 26, and the glass transition of the thermoplastic resin to the flow path 32. A cooling medium having a temperature lower than the temperature Tg is circulated, and the vicinity of the cavity 26 is cooled to a temperature lower than the glass transition temperature Tg of the thermoplastic resin. As the “cooling medium”, any liquid or gas having a temperature lower than the glass transition temperature Tg of the thermoplastic resin can be used. For example, oil or steam can be used.

  At this time, the constant temperature medium is continuously circulated in the flow path 42, and the temperature of the peripheral portion of the mold 1 is maintained at a temperature lower than the glass transition temperature Tg of the thermoplastic resin.

  In the above cooling process, the temperature in the vicinity of the cavity 26 is set lower than the glass transition temperature Tg of the thermoplastic resin while the peripheral portion of the mold 1 is maintained at a temperature lower than the glass transition temperature Tg of the thermoplastic resin. The vicinity of the cavity 26 is cooled.

(4.3) Extraction Step If the temperature in the vicinity of the cavity 26 is set to a temperature lower than the glass transition temperature Tg of the thermoplastic resin, the cooling medium is continuously circulated through the flow path 32, In a state where the temperature is maintained at a temperature lower than the glass transition temperature Tg of the thermoplastic resin, the male mold 10 and the female mold 20 are separated, and a molded product composed of the organic-inorganic composite material is taken out from the cavity 26. As a result, the shape of the fine structure portion 28 of the cavity 26 is transferred, and an optical element having a fine structure can be manufactured.

  At this time, also in the flow path 42, the constant temperature medium is continuously circulated, and the temperature of the peripheral portion of the mold 1 is maintained at a temperature lower than the glass transition temperature Tg of the thermoplastic resin.

  In the above extraction process, the molded product is extracted from the cavity 26 in a state where the peripheral portion of the mold 1 and the vicinity of the cavity 26 are maintained at a temperature lower than the glass transition temperature Tg of the thermoplastic resin.

  Each process from the filling step to the cooling step through the removal step (from filling of the organic / inorganic composite material to the cavity 26 to the next filling) is defined as one cycle, and the cycle is repeated a plurality of times. A plurality of molded products (that is, optical elements) corresponding to the number can be mass-produced. In the present embodiment, since four cavities 26 are provided in the mold 1, four optical elements can be manufactured by one cycle molding.

  In the above embodiment, the temperature in the vicinity of the cavity 26 is fluctuated from the filling step to the removal step while the periphery of the mold is maintained at a temperature lower than the glass transition temperature Tg of the thermoplastic resin from the filling step to the removal step. (It is higher than the glass transition temperature Tg of the thermoplastic resin by 20 ° C. or more in the filling process, and lower than the glass transition temperature Tg of the thermoplastic resin in the cooling / removal process). A molded product of the material can be manufactured, and a large amount of optical elements can be manufactured with a short molding time and at a low cost.

  That is, an optical material composed of an organic-inorganic composite material exhibiting excellent shape transferability by setting the temperature in the vicinity of the cavity 26 at the time of filling with the organic-inorganic composite material to a temperature 20 ° C. or more higher than the glass transition temperature Tg of the thermoplastic resin. An element molding method can be provided, and furthermore, the occurrence of problems such as short shots, weld lines, and gate seals can be suppressed. Also, instead of heating and cooling the entire mold 1, only a specific part in the vicinity (near part) of the cavity 26 is heated and cooled while keeping the temperature around the mold 1 constant. Time can be shortened and an increase in cost can be avoided.

  In addition, this invention is not limited to said embodiment, You may perform a various improvement and change in the range which does not deviate from the main point of this invention.

  As one improvement / change matter, in the injection / molding of the organic-inorganic composite material, the mold 1 of FIG. 2 may be used instead of the mold 1 of FIG. The rod heater 30 is not provided in the mold 1 of FIG. 2, and this point is mainly different between the mold 1 of FIG. 1 and the mold 1 of FIG. When the mold 1 shown in FIG. 2 is used, the cooling medium and the heating medium may be alternately circulated through the flow path 32 to cool and heat the vicinity of the cavity 26. As the “heating medium”, any liquid or gas having a temperature 20 ° C. or more higher than the glass transition temperature Tg of the thermoplastic resin can be used. For example, oil or steam can be used.

  As another improvement / change, the heating means for heating the vicinity of the cavity 26 may be another heating means such as a plate heater or a wire heater in place of the rod heater 30, and the cooling for cooling the vicinity of the cavity 26 is possible. The means may be configured to inject gas in the vicinity of the cavity 26 in place of the configuration in which the refrigerant medium is circulated through the flow path 32.

  As another improvement / change, the temperature of the cooling medium circulated in the flow path 32 and the temperature of the constant temperature medium circulated in the flow path 42 may be the same in the cooling process and the extraction process. , May be different. If the temperature of the cooling medium and the temperature of the constant temperature medium are the same in the cooling process and the removal process, the same medium can be used in all processes from the filling process to the removal process. The supply sources can be combined into one to simplify the configuration.

  As another improvement / change matter, the medium for constant temperature to be circulated in the flow path 42 may be maintained at a temperature lower than the glass transition temperature Tg of the thermoplastic resin from the filling step to the removal step. It is good to hold | maintain to the temperature (including glass transition temperature Tg-30 degreeC) between the glass transition temperature Tg of a plastic resin, and glass transition temperature Tg-30 degreeC.

[Example 1]
An alicyclic cycloolefin resin (Z340R manufactured by Nippon Zeon Co., Ltd., glass transition temperature Tg = 125 ° C.), silica fine particles having an average primary particle size of 12 nm (RX200 manufactured by Nippon Aerosil Co., Ltd.), and the amount of fine particles being 20% by volume of the whole. The organic-inorganic composite material 1 was obtained by mixing and dispersing so that

  Thereafter, the organic-inorganic composite material 1 is injected into the mold 1 of FIG. 1 to form an objective lens for an optical pickup device having a diffractive structure on the optical surface, and the molded product is used as a sample of Example 1. did.

  Specifically, when the organic / inorganic composite material 1 is filled in the cavity 26, the rod heater 30 is operated to set the temperature of the cavity 26 and the vicinity thereof to 160 ° C. At the time of cooling and taking out the molded product, oil at 120 ° C. was circulated through the flow path 32 to set the mold temperature in the vicinity of the cavity 26 to 120 ° C. On the other hand, oil at 120 ° C. was continuously circulated through the flow path 42, and the temperature around the mold was kept constant at 120 ° C. from the time of filling the organic-inorganic composite material 1 to the time of cooling and taking out the molded product.

[Example 2]
When the organic / inorganic composite material 1 was filled in the cavity 26, the temperature in the vicinity of the cavity 26 was set to 150 ° C. Otherwise, the objective lens was molded by the same method as in Example 1, and the molded product was used as the sample of Example 2.

[Example 3]
The mold 1 shown in FIG. 2 was used as the mold 1 and an objective lens for an optical pickup device having a diffractive structure on the optical surface was molded. The molded product was used as a sample of Example 3.

  Specifically, when filling the cavity 26 with the organic-inorganic composite material 1, 160 ° C. oil was circulated through the flow path 32 to set the temperature in the vicinity of the cavity 26 to 160 ° C. At the time of cooling and taking out the molded product, oil at 120 ° C. was circulated through the flow path 32 to set the mold temperature in the vicinity of the cavity 26 to 120 ° C. On the other hand, oil at 120 ° C. was continuously circulated through the flow path 42, and the temperature around the mold was kept constant at 120 ° C. from the time of filling the organic-inorganic composite material 1 to the time of cooling and taking out the molded product.

[Comparative Example 1]
The mold 1 shown in FIG. 2 is used as the mold 1, and the oil at 120 ° C. is continuously circulated through the flow path 32 from the time of filling the organic-inorganic composite material 1 to the time of cooling and taking out the molded product. Was kept constant at 120 ° C. (the molded product was taken out without heating and cooling of the mold 1 itself). Otherwise, the objective lens was molded by the same method as in Example 3, and the molded product was used as a sample of Comparative Example 1.

[Comparative Example 2]
The mold 1 shown in FIG. 1 was used as the mold 1, and when the organic / inorganic composite material 1 was filled into the cavity 26, the rod heater 30 was operated to set the temperature near the cavity 26 to 140 ° C. Other than that, the objective lens was molded by the same method as in Example 1, and the molded product was used as a sample of Comparative Example 2.

[Evaluation of surface shape transferability]
In each sample of Examples 1 to 3 and Comparative Examples 1 and 2, the molded lens was cut along a cross section close to the optical axis, and the shape of the cut surface was observed with an electron microscope. The observation results are shown in Table 2 below. In Table 2, the criteria for “◯”, “×”, and “xxx” are as follows.

A: The surface shape was sufficiently transferred, and the performance showed no problem in practical use.
X: Although the lens could be molded, the shape of the optical surface was not sufficiently transferred, and a practically usable lens could not be obtained.
XX: Short shots, weld lines, etc. occurred, and the lens shape could not be obtained.

[Evaluation of cycle time]
In each sample of Examples 1 to 3 and Comparative Examples 1 and 2, the time from filling the mold 1 with the organic-inorganic composite material 1 and then filling the mold 1 with the organic-inorganic composite material 1 again is one cycle. The time per cycle (cycle time) was calculated. The calculation results are shown in Table 2 below.

However, in the sample of Comparative Example 1, since the temperature of the mold 1 was kept constant, the time required for taking out the molded product was evaluated as the cycle time.
If the cycle time exceeds 2 minutes, the cost reduction effect by injection molding is less than that of a glass optical element, but if it is within 7 minutes, it can be determined that the shortening has been achieved. .

[Summary]
As shown in Table 2 above, each sample of Examples 1 and 2 was able to perform injection molding in a short cycle time while exhibiting excellent surface shape transferability. On the other hand, in the sample of Example 3, the transferability was good by raising the temperature in the vicinity of the cavity 26 to 160 ° C., but the cycle time was slightly longer and the cost reduction effect by injection molding was small.

  On the other hand, in the sample of Comparative Example 1 in which the heat cycle was not performed, the shape was not transferred, but the runner 23 and the gate 24 were clogged, and the lens could not be molded. Even in the sample of Comparative Example 2, the temperature of the mold 1 at the time of filling was raised to 140 ° C., but the shape transferability was poor and a practical objective lens could not be obtained.

  From the above, when filling the cavity with the organic-inorganic composite material, the mold temperature in the vicinity of the cavity is set to 20 ° C. higher than the glass transition temperature Tg of the thermoplastic resin, and the temperature in the vicinity of the cavity is set at the time of cooling and taking out the molded product. It has been found that lowering the glass transition temperature Tg of the thermoplastic resin is useful in improving transferability from the mold to the molding material and preventing clogging in the runner and gate.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic of the metal mold | die which concerns on preferable embodiment of this invention, an upper stage is the front view of the said metal mold | die, and the lower stage is drawing (plan view of a female mold) which looked at the AA line in the upper stage from the upper direction. . It is the schematic which shows the modification of FIG.

Explanation of symbols

1 Mold 10 Male 20 Female 22 Sprue 24 Gate 26 Cavity 28 Fine structure 30 Rod heater 32, 42 Flow path

Claims (12)

An injection molding method for injecting and molding an organic-inorganic composite material in which inorganic fine particles are dispersed in a thermoplastic resin using a mold having a cavity for receiving filling of a molding material,
Filling the cavity with the organic-inorganic composite material in a state where the mold temperature in the vicinity of the cavity is 20 ° C. or higher than the glass transition temperature Tg of the thermoplastic resin;
Cooling the mold temperature in the vicinity of the cavity to a temperature lower than the glass transition temperature Tg of the thermoplastic resin;
Taking out a molded article composed of the organic-inorganic composite material from the cavity in a state where the mold temperature in the vicinity of the cavity is lower than the glass transition temperature Tg of the thermoplastic resin;
An injection molding method characterized by comprising: The injection molding method according to claim 1,
An injection molding method characterized in that heating means and cooling means are provided in the vicinity of the cavity. In the injection molding method according to claim 2,
An injection molding method, wherein the cooling means has a configuration for circulating a liquid in a flow path provided in the vicinity of the cavity. In the injection molding method according to claim 2,
An injection molding method, wherein the cooling means has a configuration for circulating a gas in a flow path provided in the vicinity of the cavity. In the injection molding method according to claim 2,
An injection molding method, wherein the cooling means has a configuration for injecting a gas in the vicinity of the cavity. In the injection molding method according to any one of claims 1 to 5,
The mold has a peripheral portion farther from the vicinity than the vicinity when the vicinity of the cavity is a vicinity.
In the step of filling the organic-inorganic composite material, the temperature of at least a part of the periphery of the mold is maintained at a temperature lower than the glass transition temperature Tg of the thermoplastic resin. In the injection molding method according to any one of claims 1 to 6,
The mold has a peripheral portion farther from the vicinity than the vicinity when the vicinity of the cavity is a vicinity.
In the step of cooling the vicinity of the cavity, the temperature of at least a part of the peripheral portion is maintained at a temperature between the glass transition temperature Tg of the thermoplastic resin and the glass transition temperature Tg-30 ° C. of the thermoplastic resin. An injection molding method characterized by: In the injection molding method according to claim 6 or 7,
An injection molding method according to claim 1, wherein temperature control means for adjusting the temperature of the peripheral portion is provided in the peripheral portion. The injection molding method according to claim 8,
An injection molding method characterized in that the temperature adjusting means has a configuration in which a liquid is circulated in a flow path provided in the peripheral portion. In the injection molding method according to claim 9,
The injection molding method, wherein the liquid is a liquid maintained at a temperature between a glass transition temperature Tg of the thermoplastic resin and a glass transition temperature Tg of the thermoplastic resin Tg-30 ° C. In the injection molding method according to any one of claims 1 to 10,
An injection molding method, wherein the molding surface of the cavity is provided with a fine structure.   The optical element manufactured by the injection molding method as described in any one of Claims 1-11.

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