WO2009096606A1

WO2009096606A1 - Preform for press working and manufacturing method thereof

Info

Publication number: WO2009096606A1
Application number: PCT/JP2009/052011
Authority: WO
Inventors: Noriko Eiha; Seiichi Watanabe
Original assignee: Fujifilm Corporation
Priority date: 2008-01-30
Filing date: 2009-01-30
Publication date: 2009-08-06
Also published as: TW200940300A; JP2009202561A

Abstract

A preform for press working which is an aggregate with fluidity and a manufacturing method thereof are provided, the preform being obtained by a method comprising: aggregating a thermoplastic resin containing inorganic fine particles supplied as a powder-particle material while at least partially maintaining a state of the powder-particle material.

Description

DESCRIPTION

PREFORM FOR PRESS WORKING AND MANUFACTURING METHOD

THEREOF

Technical Field

The present invention relates to a preform for press working which allows, e.g., a high-quality optical component having a high refractivity and a low linear expansion coefficient, such as a lens, to be manufactured by heat press molding with a high yield, and a manufacturing method thereof.

Background Art

In recent years, as optical information recording equipment such as a mobile camera, a DVD, a CD, and a MO drive has become higher in performance, smaller in size, and lower in cost, it has been strongly demanded to develop an excellent material and an excellent process even for an optical component used in the recording equipment, such as an optical lens or a filter.

A plastic lens is lighter in weight and more resistant to cracking than an inorganic material such as glass, can be worked into various shapes, and is advantageous over a glass lens in terms of cost so that the plastic lens has rapidly become prevalent not only as an eye-glass lens, but also as the optical component mentioned above.

With the prevalence, increasing the refractivity of a raw material to reduce the size and thickness of the lens, reducing the linear expansion coefficient thereof to prevent the optical refractivity from varying due to the influence of thermal expansion and temperature fluctuation, or the like has been an important challenge.

In order to increase the refractivity of the lens and reduce the linear expansion coefficient as mentioned above, it has been studied to use, as a resin material for the plastic resin, a thermoplastic resin (called also as a nano-composite resin) containing inorganic fine particles in which inorganic fine particles such as metal oxide fine particles are uniformly dispersed.

A conventional mainstream method for mass-producing a lens from a resin material for a plastic lens has been a method using injection molding, or a method using heat press molding.

In the manufacturing method using injection molding, as long as a sufficient heat fluidity can be imparted to the resin material, a high-quality lens having a uniform size, a uniform weight, and a uniform optical property can be obtained relatively easily by causing the resin material to completely fill the inner space of a mold die .

However, since the nano-composite resin is typically inferior in fluidity when heated, and cannot completely fill the inner space of the mold die, it is not suited to injection molding of a component which requires high- precision transfer, such as a lens (see, e.g., Japanese Unexamined Patent Publication No. 2006-343387) .

In view of this, there have been proposed a method which molds a powdery nano-composite resin into a predetermined lens shape by heat press molding (see, e.g., Japanese Unexamined Patent Publication No. HEI07- 133119), and a method which temporarily brings a powdery nano-composite resin into a molten state, forms the resin into a preform for press working having a predetermined size by extrusion molding using an extruder, and then molds the preform for press working into a final lens shape by heat press molding (see, e.g., Japanese Unexamined Patent Publication No. 2003-147090 and Japanese Unexamined Patent Publication No. 2005-146116).

Disclosure of the Invention

However, in the method of molding the powdery nano- composite resin into the predetermined lens shape by heat press molding, it is difficult to control an amount of the resin material loaded in the mold die to a uniform value. In a lens of a small-size camera, variations in the amount of load are particularly large relative to the size of the lens to cause variations in optical property or the like, which leads to the problem of a significant reduction in product yield.

In the method of forming the preform for press working from the nano-composite resin temporarily brought into the molten state, and further molding the preform for press working into the final lens shape by heat press molding, the nano-composite resin in the molten state has a low fluidity. As a result, due to an excessively large shear stress exerted during extrusion and under the influence of long-period residence in the extruder, a failure such as unrecoverable birefringence or coloring is likely to occur in the manufactured lens body, which also leads to the problem of a significant reduction in product yield.

The present invention has been achieved in view of such conventional problems, and an object of the present invention is to provide a preform for press working which allows, when applied to the manufacturing of an optical component such as a lens, a high-quality optical component having a high refractivity and a low linear expansion coefficient to be manufactured by heat press molding with a high yield, and a manufacturing method thereof.

The object of the present invention mentioned above is attained by the following preform for press working and manufacturing method thereof.

(1) A preform for press working, which is an aggregate with fluidity obtained by a method comprising: aggregating a thermoplastic resin containing inorganic fine particles supplied as a powder-particle material while at least partially maintaining a state of the powder-particle material.

In the preform for press working mentioned above, by aggregating the thermoplastic resin containing the inorganic fine particles supplied as the powder-particle material with the state of the powder-particle material (also referred to as the powder-particle state) maintained therein, a minute gap is left between the individual powder-particle materials constituting the aggregate. With the minute gap, it is possible to obtain a high fluidity compared with a fluidity obtained with a lump of a nano-composite resin which has been brought into a molten state. As a result, when the preform for press working is formed into a product shape by heat press molding, even in transformation to a desired shape, the high fluidity prevents the occurrence of unneeded birefringence or coloring, and allows an excellent product to be provided with a high yield.

Because the preform for press working mentioned above is a lump of the aggregate, it is easy to handle and, compared with the case where a powdery nano- composite resin is loaded in a mold die, an amount of a resin material loaded into the mold die can be easily controlled to a uniform value during heat press molding for product formation. In addition, because there is no scattering to the ambient environment, the occurrence of environmental contamination can also be suppressed, and contamination on the aggregate itself is suppressed.

That is, since the .amount of the resin material loaded in the mold die can be easily controlled to a uniform value, and the resin material loaded in the mold die is allowed to completely fill the inner space of the mold die, it becomes possible to produce a high-precision resin molded product by heat press molding with stability, and manufacture the resin molded product utilizing the characteristic property of the thermoplastic resin containing the inorganic fine particles with a high yield.

(2) The preform for press working as described in (1) above, wherein the thermoplastic resin containing the inorganic fine particles is a powder-particle material for an optical component, and the preform is used as a preform for an optical component .

In accordance with the preform for press working mentioned above, a component of the thermoplastic resin containing the inorganic fine particles has been prepared as the powder-particle material for an optical component and, even by heat press molding, it becomes possible to suppress unneeded variations in optical properties, and produce a high-precision optical component with stability. For example, it is possible to implement a higher-precision optical component such as an extremely- small lens used in a digital camera or a mobile phone with a camera, and simultaneously improve a product yield.

Additionally, in the case of manufacturing a lens from the preform for press working, since the fluidity is ensured for the preform for press working, a local stress which is likely to occur in a material during heat press molding or the like is absorbed. As a result, a defect such as birefringence or coloring does not occur in a lens being manufactured, and it becomes possible to manufacture a high-quality lens having a high refractivity and a low linear expansion coefficient with a high yield by utilizing the characteristic property of the thermoplastic resin containing the inorganic fine particles .

(3) A manufacturing method of the preform for press working as described in (1) or (2) above, the method comprising: extruding the thermoplastic resin containing the inorganic fine particles supplied as a powder-particle material under heating as an aggregate in which a state of the powder-particle material is at least partially maintained; and cutting the aggregate when a given extruded amount is reached so as to obtain a lump of the preform for press working with a given volume.

In accordance with the constitution of the manufacturing method of the preform for press working mentioned above, given heat and pressure are applied in an extruder to retain an aggregated state with the state of the powder-particle material maintained, and extrusion is performed, while leaving a minute gap between the individual powder-particle materials constituting the aggregate. In this manner, it is possible to obtain a high fluidity compared with a fluidity obtained with a lump of a nano-composite resin which has been brought into a molten state, perform extrusion of a fixed amount using the extruder, and mass-produce a lump of the preform for press working with a uniform volume.

(4) The manufacturing method as described in (3) above, wherein the preform for press working is obtained by continuously extruding the aggregate and cutting the aggregate when a given length is reached.

In accordance with the constitution of the manufacturing method of the preform for press working mentioned above, the preform for press working can be continuously obtained, and productivity can be increased.

(5) The manufacturing method as described in (3) above, wherein the preform for press working is obtained by- extruding the aggregate till a given length is reached to form the aggregate into a rod-like shape with a given cross section, and then cutting the aggregate in the rod- like shape to a given length.

In accordance with the constitution of the manufacturing method of the preform for press working mentioned above, the aggregate for press working is obtained by forming the aggregate into a rod-like shape, and then cutting the aggregate in the rod-like shape to a given length. This eliminates the need to cut the rod- like material immediately after the formation thereof, and allows choices for cutting measures to be increased. As a result, high-accuracy cutting becomes possible, and measuring accuracy is increased. In addition, by stocking the aggregate as the rod-like material, the preform for press working with an optional thickness can be easily prepared, and convenience can be enhanced.

(6) The manufacturing method as described in (3) above, wherein the powder-particle material of the thermoplastic resin containing the inorganic fine particles and a liquid mixable with the powder-particle material are supplied and brought into a kneaded state, and at a time of the extrusion of the thermoplastic resin containing the inorganic fine particles under heating as the aggregate in which the state of the powder-particle material is at least partially maintained, the powder-particle material and the liquid in the kneaded state are extruded.

By providing a structure in which the powder- particle material and the liquid in the kneaded state are heat-extruded as the aggregate in which the state of the powder-particle material is maintained, it is possible to controllably impart a fluidity higher than in the case where only the powder-particle material is used as described above in (3) above, perform extrusion of a fixed amount using the extruder, and facilitate mass- production of a lump of the preform for press working with a uniform volume.

(7) A manufacturing method of the preform for press working as described in (1) or (2) above, the method comprising : loading the thermoplastic resin containing the inorganic fine particles supplied as a powder-particle material in a die till a given amount is reached; and changing the thermoplastic resin containing the inorganic fine particles into an aggregate in which a state of the powder-particle material is at least partially maintained by heat pressing so as to obtain a lump of the preform for press working with a given volume .

In accordance with the manufacturing method of the preform for press working mentioned above, the thermoplastic resin containing the inorganic fine particles as the powder-particle material is loaded in a die for a preform, measured to be a given amount by scraping a redundant portion thereof off, and molded into the aggregate in which the state of the powder-particle material is maintained by heat pressing. In this manner, the shape as the preform for press working can be set to a shape close to that of a finished product, and the preform for press working which further facilitates heat press molding for product formation can be obtained.

Brief Description of the Drawing

FIG. 1 is a schematic structural view of a first exemplary embodiment of a manufacturing method of a preform for press working according to an aspect of the present invention;

FIG. 2 is a view obtained when viewed in the direction indicated by the arrow A of FIG. 1; and

FIGS. 3A, 3B, 3C and 3D are cross-sectional views schematically showing manufacturing processes of a second exemplary embodiment of the manufacturing method of a preform for press working 21 according to another aspect of the present invention.

Best Mode For Carrying Out the Invention

Hereinbelow, preferred embodiments of a preform for press working and a manufacturing method thereof according to the present invention will be described in detail with reference to the drawings. In the present specification, a range of numerical values represented by using "to" indicates a range including numerical values previous and subsequent to "to" as a lower limit value and an upper limit value.

FIG. 1 is a schematic structural view of a first exemplary embodiment of an apparatus for manufacturing the preform for press working according to an aspect of the present invention. FIG. 2 is a view obtained when viewed in the direction indicated by the arrow A of FIG. 1.

A preform for press working 21 according to the present embodiment is a lump of an aggregate having a predetermined fluidity and a predetermined size which is obtained by loading, in an extruder 1, a nano-composite resin powder-particle material 7 (a powder-particle material of a thermoplastic resin containing inorganic fine particles) supplied as a powder-particle material having a predetermined particle diameter, aggregating the nano-composite resin powder-particle material 7 with a state of the powder-particle material maintained therein through heating in the extruder 1, extruding an aggregate 23 from the extruder 1, and cutting, when the aggregate 23 is extruded from the extruder 1, the aggregate 23 when a predetermined extruded amount is reached.

The nano-composite resin powder-particle material 7 is defined herein as a material in which inorganic fine particles each having a predetermined particle diameter are uniformly dispersed in a thermoplastic resin, and the dispersed inorganic fine particles have different particle diameters depending on applications.

For example, when the nano-composite resin powder- particle material 7 is used as a powder-particle material for an optical component such as a lens, the average particle diameter of the dispersed inorganic fine particles is set to a range of 1 to 15 nm. When the nano-composite resin powder-particle material 7 is used for applications other than that, the average particle diameter of the dispersed inorganic fine particles is set to a range of about 1 to 300 nm.

As the nano-composite resin powder-particle material 7, there may be used a powder obtained by completely- mixing the inorganic fine particles and a polymer, and then powdering the mixture, a mixture obtained by physically mixing the inorganic fine particles with a powder-particle material of a polymer, or a mixture obtained by mixing a polymer powder (master batch) containing the inorganic fine particles at a high concentration with a polymer powder which does not contain the inorganic fine particles by stirring. A more detailed description will be given later.

As described above, when the nano-composite resin powder-particle material 7 is aggregated with the state of the powder-particle material maintained therein, the preform for press working 21 and the aggregate 23 are in an opaque state.

The extruder 1 shown in FIG. 1 includes a heating cylinder 3 having a nozzle 2 on the tip thereof. In the heating cylinder 3, an extrusion screw 4 for sending out a material fed in the heating cylinder 3 toward the nozzle 2 is disposed. A heater 5 is attached to the outer periphery of the heating cylinder 3. To the proximal end side of the heating cylinder 3, a hopper 6 for feeding the nano-composite resin powder-particle material 7 as the material into the heating cylinder 3 is attached.

Over the hopper 6, there is disposed a powder supplier 30 capable of feeding a fixed amount of the nano-composite resin powder-particle material 7 into the hopper 6. In the hopper 6, a vibrating unit βa is disposed at a side-surface position in order to prevent the nano-composite resin powder-particle material 7 from remaining due to the occurrence of a bridge or the like. Besides the vibrating unit 6a, any measures may be provided as long as it can suppress the remaining of the nano-composite resin powder-particle material 7 in the hopper 6. Because the portion of the hopper 6 in contact with the heating cylinder 3 naturally becomes hot, and the nano-composite resin powder-particle material 7 may be fusion-bonded thereto, a cooling unit 6b is disposed at the portion to allow reliable feeding of the nano- composite resin powder-particle material 7 into the heating cylinder 3.

At the rear end of the extrusion screw 4, there are provided a motor/speed reducer set 9 which causes the screw 4 to rotate to perform a extruding rotation operation, and a load cell 8 for receiving a signal from a resin pressure sensor 2a disposed inside the tip portion of the nozzle 2 to detect an extrusion pressure, and further detecting a motor rotation load of the motor/speed reducer set 9.

In addition, on the tip of the nozzle 2, a cutter 10 for cutting the aggregate 23 extruded from the nozzle 2 to a predetermined length is provided.

The extruder 1 includes a double-shaft-type extruder that is equipped with two extrusion screws 4 arranged in parallel with each other in the heating cylinder 3, and a single-shaft-type extruder that is equipped with one extrusion screw 4. From the viewpoint that a thermal load to the nano-composite resin powder-particle material 7 can be suppressed and a uniform extrusion force can be obtained with stability, it is preferable to use the double-shaft-type extruder.

Further, when the resin material fed into the heating cylinder 3 is excessively compressed by the extrusion screw 4, the bonding among the powder-particle materials is promoted so that the fluidity as the aggregate 23 is lowered. Therefore, it is preferable to use the double-shaft-type extruder having two extrusion screws 4 rotating in the same direction which can suppress a compression force of the extrusion screws 4 and control the compression force to a constant pressure. Furthermore, by supplying a fixed amount of the nano- composite resin powder-particle material 7 from the powder supplier 30 in accordance with the extrusion of the aggregate 23, a uniform extrusion force to the aggregate 23 can be stabilized more reliably and constantly.

Further, because the extrusion screw 4 reduces the compression force applied to the material during the rotation, the extrusion screw 4 preferably has a simple spiral groove structure in which the pitch of the spiral is constant or small in change, and a structure having a large rotating vane (disk) or a twisted vane is preferably avoided.

As the powder supplier 30, a vibration-type powder supplier can most stably supply the nano-composite resin powder-particle material 7. However, any type of the powder supplier such as a table-type powder supplier, a screw-type powder supplier, and the like can be adopted as long as the powder supplier can supply a fixed amount of the nano-composite resin powder-particle material 7 in accordance with the extrusion of the aggregate 23.

For the stable supplying of the nano-composite resin powder-particle material 7 by the powder supplier 30, the nano-composite resin powder-particle material 7 is preferably in a state with high fluidity as a powder, and is preferably provided as, e.g., a product obtained by evaporation and dryness.

The extrusion of the aggregate 23 in a nitrogen atmosphere may be executed by substituting the atmosphere in the place where the extruder 1 is disposed with nitrogen.

In order to remove a residual solvent, a low- molecular volatile component, or a dispersing medium volatilized from the nano-composite resin powder-particle material 7 during heat extrusion, a ventilation hole may be provided in the heating cylinder 3, and further, by reducing the pressure by using the ventilation hole, the volatile component can also be removed more aggressively.

The cross-sectional configuration (die configuration) of an opening portion of the nozzle 2 from which the nano-composite resin powder-particle material 7 is extruded includes a circle, a polygon, a star-like configuration, and the like, and is not limited as long as the extrusion can be performed therethrough. When the die configuration is circular, the diameter may be set to a range of 0.5 to 4 mm.

When the opening portion of the nozzle 2 has a circular cross section, with the diameter of less than 0.5 mm, excessive pressure is applied to the aggregate 23 being extruded due to an excessively small size of the opening so that the aggregate 23 disadvantageously becomes a transparent lump that is inferior in fluidity. With the diameter of more than 4 mm, it becomes difficult to perform minute measurement adjustment and improve the accuracy of the measurement.

The pressure applied to the nano-composite resin powder-particle material 7 in the heating cylinder 3 is set to a range of about 0.5 to 7.0 MPa. The rpm of the extrusion screw 4 is preferably in a range of about 50 to 400 rpm. When the rpm is less than 50 rpm, the speed of a rotary blade is reduced so that the sharpness thereof is degraded. When the rpm is more than 400 rpm, the extrusion of the aggregate 23 is not stabilized.

With regard to the nano-composite resin powder- particle material 7 fed into the hopper 6, a method in which only the nano-composite resin powder-particle material 7 is simply fed is preferred. However, for the purpose of improving the fluidity of the powder-particle material, it is also possible to feed the nano-composite resin powder-particle material 7 as a mixture in a paste state obtained by preliminarily mixing the nano-composite resin powder-particle material 7 with a liquid.

In addition, the nano-composite resin powder- particle material 7 and the liquid may be separately fed into the heating cylinder 3, and either one of them may be fed first.

Preparing a dispersion liquid from the liquid in advance and mixing the dispersion liquid with the nano- composite resin powder-particle material 7 prevent the powder from scattering around the ambient environment during a feeding operation, and facilitate the supply of a fixed amount of the nano-composite resin powder- particle material 7 into the, heating cylinder 3.

The liquid to be mixed is not limited as long as it mixes with the powder-particle material, and a liquid mixture of water and alcohol is preferable in terms of dispersibility, operability (explosion protection is not necessary) , and volatility. A liquid for dissolving the powder may be used. However, in this case, since it takes time to dry the added liquid, the liquid for dissolving the powder is not preferable.

In the liquid to be mixed, the concentration of the liquid is preferably not more than 50 wt% in the vicinity of the nozzle, more preferably not more than 40 wt%. (In this specification, weight ratio is equal to mass ratio.) When the concentration is excessively high, the paste state is brought into nearly liquid state so that it becomes difficult for a blade to cut.

Examples of alcohol that can be used include methanol, ethanol, isopropanol, t-butyl alcohol, and the like. As a dispersion liquid mixture other than those shown above, there can be used DMF (dimethylformamide) as an amide-based compound or NMP (N-methylpyrrolidone) . Besides, acetonitrile, acetone, DMSO (dimethylsulfoxide) , or the like can be used.

The temperature of the aggregate 23 extruded from the nozzle 2 is preferably in a range of the glass transition temperature Tg to Tg + 100⁰C.

When the temperature of the aggregate 23 to be extruded is lower than the glass transition temperature Tg, the powder-particle materials are not brought into an aggregated state where the powder-particle materials are bonded to each other due to excessive low temperature. When the temperature is higher than Tg + 100⁰C, the grain boundary between the individual powder-particle materials disappears and the fluidity is lost.

The glass transition temperature in the nano- composite resin powder-particle material 7 used in the present embodiment is Tg = 85⁰C. Accordingly, the temperature of the aggregate 23 extruded from the nozzle 2 is preferably set to a range of 85 to 185°C. As a preset temperature of the extrusion, the same temperature may be set from a powder inlet to an outlet, or the temperature only at the outlet may be increased by about 10⁰C to increase the fluidity of the material.

When the liquid is used, a "drying" process may be added after a cutting process. Temperatures for the drying process are preferably in a range of a boiling point of the liquid to the boiling point + 50⁰C. A drying method includes an air-blast drying, vacuum drying, or the like, and is not particularly limited. The liquid concentration after the drying process is preferably set to not more than 3 wt%. When the liquid concentration is high, there is a case where the problem of a mold release failure occurs in a subsequent compression process or a case where the configuration is changed after molding, and therefore high liquid concentration is not preferable.

Next, as shown in FIG. 2, a cutter 10 is obtained by providing a single cutting blade 12 on the outer periphery of a disk 11 that rotates at a constant speed. When the aggregate 23 is extruded from the opening portion of the nozzle 2 at a constant speed, the cutting blade 12 passes over the opening portion of the nozzle 2 at a given time interval so that the aggregate 23 is cut into the preform for press working 21 with a given length.

As the cutter 10, there may be used a cutter having a structure in which a plurality of cutting blades 12 are radially provided on the outer periphery of the disk 11 at regular intervals. A cutter of a fan-cutter type may also be used. Further, a cutter of rotation about a parallel axis with a cutting plane line may be used.

The temperature of the cutting blade 12 is preferably maintained within a range of the glass transition temperature Tg to Tg + 50⁰C.

When the temperature of a cutting edge is excessively low, the temperature of the material is lowered and the material is broken so that high-accuracy cutting can not be performed. When the temperature of the cutting edge is excessively high, the material adheres to the cutting edge so that accuracy is degraded or productivity is reduced.

In the present embodiment, when a portion of a predetermined length of the aggregate 23 is extruded from the nozzle 2, the cutting blade 12 passes over the opening of the nozzle 2 to cut the aggregate 23, and the cutting process of the aggregate 23 is performed when the aggregate 23 is in a sol state. However, the cutting process may also be performed when a portion of a longer length of the aggregate 23 is extruded and the portion thereof is in a cooled and hardened state. It is preferable to cut the aggregate 23 in a hot sol state because the powder does not tend to be generated during the cutting process.

The present embodiment describes a method in which the preform for press working 21 with a given length is obtained by setting the extrusion speed of the aggregate 23 in the extruder 1 so as to be constant, and causing the cutting blade 12 to pass immediately over the nozzle 2 at a given time interval by the rotation of the disk 11 at a constant speed. In other words, the aggregate 23 is continuously extruded from the nozzle 2, and cut by the cutting blade 12 when a given length is reached by the aggregate 23 so that the preform for press working 21 is obtained. According to this method, control is facilitated and productivity is improved.

A method may be adopted in which a length of the extruded portion of the aggregate 23 from the nozzle 2 is monitored, and the cutter 10 is intermittently operated such that the cutting blade 12 passes immediately over the nozzle 2 when the length of the extruded portion reaches a predetermined length. That is, after the aggregate 23 is extruded from the nozzle 2 by a predetermined length and formed into a rod-like shape with a given cross-section, the aggregate in the rod-like shape is cut to a predetermined length to obtain the preform for press working 21. According to this method, it is not necessary to cut the rod-like material immediately after the formation thereof, and choices of cutting measures can be increased. For example, by making a section to be a high-precision flat surface using a precision cutter such as a diamond cutter or the like, measuring accuracy can be enhanced. By stocking a plurality of the aggregates 23 as the rod-like material, the preform with an optional thickness can be easily prepared by cutting the stocked aggregates 23 as the rod- like material to a desired thickness, and thereby convenience can be enhanced.

Additionally, it is possible to measure the breadth of the aggregate 23 being extruded using laser detection or the like so that the timing of cutting can be set with improved precision.

In front of the cutter 10, a preform reception container 25 for receiving the preform for press working 21 that has been cut, and a conveyor-belt-type transfer unit 26 that transfers the preform reception container 25 in the direction indicated by the arrow B of FIG. 2 are equipped.

In the present embodiment, the preform reception container 25 and the transfer unit 26 are provided. However, the conveyor belt may simply catch the preform for press working 21 that has been cut thereon, or a structure may also be adopted in which a container capable of holding a plurality of the preforms for press working 21 catches the preforms for press working 21.

In the preform for press working 21 according to the present embodiment, by performing the extrusion under the conditions described above, a minute gap is left between the individual powder-particle materials constituting the aggregate 23 while the nano-composite resin powder- particle material 7 is aggregated with the state of the powder-particle material maintained therein. With the minute gap, it is possible to obtain a high fluidity- compared with a fluidity obtained with a lump of a nano- composite resin that has been brought into a molten state and, when the preform for press working 21 is formed into a product shape by heat press molding afterwards, the inner space of the mold die can be completely filled with the preform for press working 21 due to its fluidity without uneven distribution of a stress.

In addition, since the preform for press working mentioned above is a lump of the aggregate 23, it is excellent in operability (handleability) and measurability, an amount of a resin material loaded in the mold die can be easily controlled to a uniform value during heat press molding for product formation.

That is, during the heat press molding for the product formation, since the amount of the resin material loaded in the mold die can be easily controlled to a uniform value, and the resin material loaded in the mold die is allowed to completely fill the inner space of the mold die, it becomes possible to produce a high-precision resin molded product by heat press molding with stability, and manufacture the resin molded product utilizing the characteristic property of the thermoplastic resin containing inorganic fine particles with a high yield.

Further, in the preform for press working 21 according to the embodiment mentioned above, when a component of the thermoplastic resin containing inorganic fine particles has been prepared as the powder-particle material for an optical component, it becomes possible to stably produce a high-precision optical component having excellent optical properties by heat press molding. For example, it is possible to implement a higher -precision optical component such as an extremely small lens used in a digital camera or a mobile phone with a camera, and simultaneously improve a product yield.

Additionally, in the case of manufacturing a lens from the preform for press working 21, since the fluidity- is ensured for the preform for press working 21, a local stress or the like is not exerted on the material during heat press molding. As a result, a defect such as birefringence or coloring does not occur in a lens being manufactured, and it becomes possible to manufacture a high-quality lens having a high refractivity and a low linear expansion coefficient with a high yield by- utilizing the characteristic property of the thermoplastic resin containing inorganic fine particles.

Each of FIGS. 3A, 3B, 3C and 3D is a cross-sectional view schematically showing manufacturing processes in a second exemplary embodiment of the manufacturing method of the preform for press working 21 according to another aspect of the present invention.

In the manufacturing method in the second exemplary embodiment, as shown in FIG. 3A, with regard to a heat press molding machine 16 including a lower die 17, an upper die 18, and a cylindrical die 19, the nano- composite resin powder-particle material 7 supplied as a powder-particle material is loaded into a cavity formed of the lower die 17 and the cylindrical die 19 by a feeder 15 such that the loaded amount of the nano- composite resin powder-particle material 7 exceeds the amount required for the preform for press working 21. Subsequently, as shown in FIG. 3B, a redundant portion of the nano-composite resin powder-particle material 7 is scraped off by a scraper which is not shown such that the amount of the nano-composite resin powder-particle material 7 is equal to a predetermined amount which is the capacity of the cavity formed of the lower die 17 and the cylindrical die 19. Then, as shown in FIG. 3C, the cavity is closed by the upper die 18 of the heat press molding machine 16 and heat-pressing is performed to form the preform for press working 21 as the aggregate with the state of- the powder-particle material maintained therein. Thereafter, as shown in FIG. 3D, the cavity is opened by moving the upper and lower dies 18 and 17 of the heat press molding machine 16 to take out the preform for press working 21 formed to have predetermined size and shape.

The nano-composite resin powder-particle material 7 used herein is preferably a powder having a fluidity enhanced by evaporation to dryness in order to increase the precision of the loaded amount of the powder.

The heat press molding machine 16 according to the present embodiment has a structure in which the upper and lower dies 18 and 17, which mold the preform for press working 21, have curved surfaces similar to those of the product shape. However, a flat die with which the cavity is formed of planes may be used. By having such a configuration of the die, a die for molding the preform 21 can be produced at low cost.

Although the upper and lower dies 18 and 17 of the heat press molding machine 16 mentioned above mold the preform for press working 21 one by one, a structure may also be adopted in which a plurality of cavities are provided so as to simultaneously mold a plurality of the preforms for press working 21.

In the heat press molding machine 16 mentioned above, the amount of the nano-composite resin powder- particle material 7 loaded in the lower die 17 is measured to be a predetermined amount by scraping the redundant portion off, as shown in FIG. 3B. At that time, it is preferable to make a filling density of the powder-particle material uniform by lightly apply pressure or vibration.

In the heat press molding machine 16, when the heat pressing of FIG. 3C is performed, either one of pressurization and heating may be performed first. The heating temperature of the heat press molding machine 16 is preferably kept in a range of the glass transition temperature Tg to Tg + 70⁰C. In accordance with the heating temperature, the pressure to be applied may appropriately be adjusted.

The heat pressing process by the heat press molding machine 16 mentioned above is preferably performed under a vacuum atmosphere, a nitrogen atmosphere, or a carbon dioxide atmosphere.

Further, when the nano-composite resin powder- particle material 7 contains a dispersing medium, with regard to the removal of a volatile component in the dispersing medium, after the volatile component is removed by heating the nano-composite resin powder- particle material 7 or setting the nano-composite resin powder-particle material 7 under a vacuum atmosphere, the heat pressing may be started, or the volatile component may be removed by setting the heating time during the heat pressing to be longer than usual.

According to the manufacturing method in the second exemplary embodiment, since the nano-composite resin powder-particle material 7 is molded into the preform for pressing work 21 as the aggregate with the state of the powder-particle material maintained therein by the heat pressing, when compared with the case where the nano- composite resin powder-particle material 7 is molded into the preform for press working 21 with the state of the powder-particle material maintained therein by the extrusion molding as in the first exemplary embodiment, the shape as the preform for press working 21 can be set to be similar to the shape of a finished product so that the preform for press working 21 which further facilitates the heat press molding for product formation can be obtained.

The present invention is not limited to the embodiments described above, and various changes and modifications can be appropriately made. Examples of the optical component to which the present invention is applicable include not only various lenses but also a light guide plate such as a liquid crystal display or the like, and an optical film such as a polarizing film, a phase difference film, or the like. (Nano-composite Resin Powder-particle Material)

Next, a detailed description will be given hereinbelow to the nano-composite resin powder-particle material (nano-composite material in which inorganic fine particles are bonded to a thermoplastic resin) as a powder-particle material for an optical material molded to be molded into a preform for an optical component in the present invention. (Inorganic Fine Particles)

In an organic-inorganic composite material used in the present invention, inorganic fine particles having a number average particle size of 1 to 15 nm are used. When the number average particle size of the inorganic fine particles is excessively low, characteristics inherent to a substance constituting each of the fine particles may be changed. Conversely, when the number average particle size is excessively high, the influence of Rayleigh scattering becomes outstanding so that the transparency of the organic-inorganic composite material may be extremely lowered. Therefore, the number average particle size of the inorganic fine particles in the present invention needs to be 1 to 15 nm, preferably 2 to 13 nm, and more preferably 3 to 10 nm.

Examples of the inorganic fine particles used in the present invention include oxide fine particles, sulfide fine particles, selenide fine particles, telluride fine particles, and the like. More specifically, there can be listed titania fine particles, zinc oxide fine particles, zirconia fine particles, tin oxide fine particles, and zinc sulfide fine particles. The titania fine particles, zirconia fine particles, and zinc sulfide fine particles are preferable, and the titania fine particles and the zirconia fine particles are more preferable. However, the inorganic fine particles used in the present invention is not limited thereto. In the present invention, one type of the inorganic fine particles may be used, or a plurality of types of the inorganic fine particles may be used in combination.

The refractivity of the inorganic fine particles used in the present invention at a wavelength of 589 nm is preferably 1.90 to 3.00, more preferably 1.90 to 2.70, and even more preferably 2.00 to 2.70. The use of the inorganic fine particles having the refractivity of not less than 1.90 tends to facilitate the formation of the organic-inorganic composite material having the refractivity of more than 1.65, while the use of the inorganic fine particles having the refractivity of not more than 3.00 tends to facilitate the formation of the organic-inorganic composite material having the transmittance of not less than 80%. The refractivity in the present invention is a value obtained by measuring light at the wavelength of 589 nm at 25°C by an Abbe's refractometer (ATAGO CO., LTD. DR-M4). (Thermoplastic Resin)

The structure of the thermoplastic resin used in the present invention is not particularly limited. For example, a resin having a known structure can be listed, such as poly (meth) acrylic acid ester, polystyrene, polyamide, polyvinyl ether, polyvinyl ester, polyvinyl carbazole, polyolefin, polyester, polycarbonate, polyurethane, polythiourethane, polyimide, polyether, polythioether, polyetherketone, polysulfone, or polyethersulfone. In the present invention,- it is particularly preferred to use a thermoplastic resin having a functional group capable of forming an arbitrary chemical bond with inorganic fine particles at least at an end of a polymer chain, or at a side chain. Preferred examples of such a thermoplastic resin include:

(1) A thermoplastic resin having a functional group selected from those shown below at an end of a polymer chain or at a side chain: Formula (A) Formula (B)

OR¹¹ OR¹³

— P-OR¹² — 0 — P-OR¹⁴ il if

0 0

[wherein R¹¹, R¹², R¹³ and R¹⁴ each independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, or a substituted or unsubstituted aryl group] , -SO₃H, -OSO₃H, - CO₂H and -Si (OR¹⁵) _miR¹⁵ ₃-_mi [wherein R¹⁵ and R¹⁶ each independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group or a substituted or unsubstituted aryl group, and ml represents an integer of 1 to 3] ; and

(2) A block copolymer including a hydrophobic segment and a hydrophilic segment.

Hereinbelow, the thermoplastic resin (1) will be described in detail. Thermoplastic Resin (1)

The thermoplastic resin (1) used in the present invention has a functional group capable of forming a chemical bond with inorganic fine particles at an end of a polymer chain, or at a side chain. Examples of the "chemical bond" that can be listed include a covalent bond, an ionic bond, a coordinate bond, and a hydrogen bond. When there are a plurality of functional groups, they may be capable of forming individually different chemical bonds with inorganic fine particles. Whether or not the functional group is capable of forming a chemical bond is determined depending on whether or not the functional group in the thermoplastic resin is capable of forming a chemical bond with the inorganic fine particles when the thermoplastic resin and the inorganic fine particles are mixed in an organic solvent. All of the functional groups in the thermoplastic resin may form chemical bonds with the inorganic fine particles, or a part of them may form chemical bonds with the inorganic fine particles.

It is particularly preferred that the thermoplastic resin used in the present invention is a copolymer having a repeating unit represented by the following formula (1). Such a copolymer can be obtained by copolymerizing a vinyl monomer represented by the following formula (2). Formula (1)

Formula (2)

In formulae (1) and (2), R represents a hydrogen atom, a halogen atom or a methyl group, X represents a divalent linking group selected from the group consisting of -CO₂-, -OCO-, -CONH-, -OCONH-, -OCOO-, -0-, -S-, -NH- and a substituted or unsubstituted arylene group, and is preferably -CO₂- or a p-phenylene group.

Y represents a divalent linking group having 1 to 30 carbon atoms. The number of carbon atoms is preferably 1 to 20, more preferably 2 to 10, and even more preferably 2 to 5. Specifically, examples that can be listed include an alkylene group, an alkyleneoxy group, an alkyleneoxycarbonyl group, an arylene group, an aryleneoxy group, an aryleneoxycarbonyl group, and a group as a combination thereof. Preferably, Y is an alkylene group. q represents an integer of 0 to 18, preferably 0 to 10, more preferably 0 to 5, and particularly preferably 0 to 1.

Z is a functional group selected from the group consisting of a group represented by formula (A) or (B) , -SO₃H, -OSO₃H, -CO₂H and -Si (OR¹⁵)_miR¹⁶ ₃-mi as defined above.

The following are specific examples of the monomer represented by formula (2). However, the monomer that can be used in the present invention is not limited thereto.

A-1

Mixture of q=5 and 6

Mixture of q=4 and 5

A-4

A-5

As other monomers that can be copolymerized with the monomers represented by formula (2) in the present invention, monomers described in Polymer Handbook 2nd ed., J. Brandrup, Wiley Interscience (1975) Chapter 2 Page 1 to 483 can be used.

Specifically, there can be listed, for example, a compound having one addition-polymerizable unsaturated bond selected from a styrene derivative, 1- vinylnaphthalene, 2-vinylnaphthalene, vinylcarbazole, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, acrylamides, methacrylamides, an allyl compound, vinyl ethers, vinyl esters, itaconic acid dialkyls, fumaric acid dialkyl esters or monoalkyl esters, and the like.

The weight average molecular weight of the thermoplastic resin (1) used in the present invention is preferably in a range of 1,000 to 500,000, more preferably 3,000 to 300,000, and particularly preferably 10,000 to 100,000. By setting the weight average molecular weight of the thermoplastic resin (1) mentioned above to not more than 500,000, the moldability tends to be increased, and by setting the weight average molecular weight to not less than 1,000, the mechanical strength tends to be increased.

In the thermoplastic resin (1) used in the present invention, the average number of functional groups mentioned above bonded to inorganic fine particles is preferably 0.1 to 20 for each polymer chain, more preferably 0.5 to 10, and particularly preferably 1 to 5. When the average number of contained functional groups mentioned above is not more than 20 for each polymer chain, the thermoplastic resin (1) tends to be coordinately bonded to a plurality of inorganic fine particles, and prevent viscosity increase and gelling in a solution state. When the average number of contained functional groups is not less than 0.1 for each polymer chain, inorganic fine particles tend to be stably dispersed .

The glass transition temperature of the thermoplastic resin (1) used in the present invention is preferably in a range of 80⁰C to 400⁰C, and more preferably 130⁰C to 380⁰C. The use of the resin having the glass transition temperature of not less than 80⁰C tends to facilitate the obtainment of an optical component having a sufficient heat-resisting property, while the use of the resin having the glass transition temperature of not more than 400⁰C tends to facilitate the performance of molding work.

As has been described above, the nano-composite resin material as a material for an optical component according to the present invention can improve the mold releasability from a mold die without impairing high refraction properties and high transparency of the organic-inorganic composite material in which inorganic fine particles are dispersed by providing a unit structure having a specific structure in the resin.

With the use of the material mentioned above, there can be provided an organic-inorganic composite material having excellent mold releasability, high refraction properties, and high transparency, and an optical component having high precision, high transparency, and high refraction properties constituted by including the organic-inorganic composite material.

Industrial Applicability

In accordance with the present invention, it is possible to provide a preform for press working which allows a thermoplastic resin containing inorganic fine particles, which is used for an optical component such as a high-quality lens having a high refractivity and a low linear expansion coefficient or the like, to be manufactured by heat press molding as a desired product with a high yield, and a manufacturing method thereof.

The entire disclosure of each and every foreign patent application from which the benefit of foreign priority has been claimed in the present application is incorporated herein by reference, as if fully set forth.

Claims

1. A preform for press working, which is an aggregate with fluidity obtained by a method comprising: aggregating a thermoplastic resin containing inorganic fine particles supplied as a powder-particle material while at least partially maintaining a state of the powder-particle material.

2. The preform for press working according to claim

1, wherein the thermoplastic resin containing the inorganic fine particles is a powder-particle material for an optical component, and the preform is used as a preform for an optical component .

3. A manufacturing method of the preform for press working according to claim 1 or 2, the method comprising: extruding the thermoplastic resin containing the inorganic fine particles supplied as a powder-particle material under heating as an aggregate in which a state of the powder-particle material is at least partially maintained; and cutting the aggregate when a given extruded amount is reached so as to obtain a lump of the preform for press working with a given volume.

4. The manufacturing method according to claim 3, wherein the preform for press working is obtained by continuously extruding the aggregate and cutting the aggregate when a given length is reached.

5. The manufacturing method according to claim 3, wherein the preform for press working is obtained by extruding the aggregate till a given length is reached to form the aggregate into a rod-like shape with a given cross section, and then cutting the aggregate in the rod- like shape to a given length.

6. The manufacturing method according to claim 3, wherein the powder-particle material of the thermoplastic resin containing the inorganic fine particles and a liquid mixable with the powder-particle material are supplied and brought into a kneaded state, and at a time of the extrusion of the thermoplastic resin containing the inorganic fine particles under heating as the aggregate in which the state of the powder-particle material is at least partially maintained, the powder-particle material and the liquid in the kneaded state are extruded.

7. A manufacturing method of the preform for press working according to claim 1 or 2, the method comprising: loading the thermoplastic resin containing the inorganic fine particles supplied as a powder-particle material in a die till a given amount is reached; and changing the thermoplastic resin containing the inorganic fine particles into an aggregate in which a state of the powder-particle material is at least partially maintained by heat pressing so as to obtain a lump of the preform for press working with a given volume .