JP4895348B2 - Plastic molded product, manufacturing apparatus and manufacturing method thereof - Google Patents

Description

  The present invention relates to a manufacturing method and a manufacturing apparatus for a plastic molded article including a plastic lens having a highly accurate mirror surface or fine pattern, a plastic mirror, or a plastic optical element such as a diffraction element.

An optical writing unit of a laser type digital copying machine, a printer, or a facsimile apparatus uses an optical element such as a rectangular lens or a mirror having a laser beam imaging and various correction functions.
In recent years, these optical elements have been changed from glass to plastic due to demand for cost reduction of products. In addition, in order to perform a plurality of functions with the minimum number of elements, the transfer surface has a complicated aspherical shape as well as a spherical shape. Furthermore, in the case of a lens, the shape of the lens is increasing in thickness in many cases, and the lens thickness is not uniform in the longitudinal direction.

The manufacturing method of these optical elements is an injection molding method suitable for mass production at a low manufacturing cost, or an insert for forming a transfer surface is movably arranged in a mold, and the resin filled in the mold is made. It is common to use a so-called injection compression molding method, which compensates for pressure by moving the movable nest in advance with respect to volume shrinkage due to cooling, and ensures shape accuracy.
However, when a lens having an uneven thickness is manufactured by the above-described injection molding method or injection compression molding method, the cooling rate of the filled resin differs depending on the lens thickness deviation. Stress is generated and birefringence is generated inside the lens. As a result, there is a problem that the spot diameter of the beam transmitted through the lens cannot be reduced to a desired size.
As a method of improving the drawbacks of such injection molding method or injection compression molding method, the internal distortion is small by heating the resin to a temperature above the glass transition temperature in the mold and then cooling to take out the molded product. Several methods have been proposed for obtaining molded products with good shape accuracy, as shown below.

In the invention described in Japanese Patent Application Laid-Open No. 4-163119 (Plastic Molded Product Manufacturing Method: Patent Document 1), a plastic base material prepared in advance is inserted into a mold, and heated and melted to a temperature equal to or higher than the glass transition temperature. After generating the above, by slowly cooling, a molded product with reduced distortion and good shape accuracy is produced.
In the invention described in JP-A-8-244085 (injection molding method: Patent Document 2), the glass transition is performed after injection and filling into a mold heated to a temperature higher than the glass transition temperature of the resin and holding for a certain period of time. By cooling to a temperature below the temperature and taking out the molded product, a molded product with reduced shape and good shape accuracy is produced.
Further, in the invention described in Japanese Patent Application Laid-Open No. 2000-25120 (Plastic Lens Manufacturing Method and Plastic Lens Manufacturing Apparatus: Patent Document 3), the glass transition temperature or higher is maintained with the resin held between the cavities. Heating and holding and cooling to near the glass transition temperature of the resin while adjusting the pressure from the outside so that the pressure applied to the resin does not change, thereby reducing the distortion and producing a molded product with good shape accuracy.

  In any of the production methods of Patent Documents 1 to 3, a process of heating to the glass transition temperature of the resin or higher and then cooling is required, so that the molding cycle becomes very long and the mold is molded every cycle. Since it is necessary to heat the whole to the glass transition temperature or higher, there arises a problem that a large amount of power is consumed.

In the invention described in Japanese Patent Application Laid-Open No. 2004-262145 (injection molding method: Patent Document 4), a resin heated to a glass transition temperature or higher is injected and filled, and a molded product is taken out at a temperature higher than the glass transition temperature. A lens with little residual stress is produced with a short molding cycle.
In this method, although the residual stress is small, the resin is not completely solidified at the time of mold release, so that deformation at the time of mold release is inevitable, and there is a problem that sufficient shape accuracy cannot be obtained.

In recent years, it has been attempted to form a fine pattern on the optical surface and add a new optical function to the optical element. For example, there is a diffractive lens that forms a diffraction pattern several times the wavelength on the optical surface and uses this diffraction to provide a lens effect. Further, by forming a diffractive lens on the optical mirror surface, it is possible to improve the aberration characteristics of the optical system and to provide wavelength selectivity.
The above-mentioned injection molding and injection compression molding, which are general processing methods for plastic optical elements, are generally performed by injecting molten resin into a mold held below the softening temperature of the resin used, in order to speed up the molding cycle, The molded product is produced by solidifying. When an optical element having a fine pattern on the optical mirror surface described above is processed by such a method, at the moment when the molten resin is filled in the mold, the surface layer portion comes into contact with the mold surface maintained at the softening temperature or lower. Due to the rapid cooling, there arises a problem that the fine pattern cannot be completely filled with resin.

In the invention described in Japanese Patent Application Laid-Open No. 2004-284110 (Optical Element Manufacturing Apparatus: Patent Document 5), the above-described method is performed by delaying rapid cooling of the resin by forming a surface film having a large thermal conductivity on the mold member. Although a diffractive lens is manufactured, if the surface film is too thin, the effect of cooling is reduced. Conversely, if the surface film is too thick, distortion due to the difference in thermal expansion occurs due to the difference between the surface film and the material of the base material. The problem that cannot be secured occurs.
On the other hand, even in such a case, as described above, the resin is heated and softened to the glass transition temperature or higher and then slowly cooled to the glass transition temperature or lower to completely fill the resin with the fine pattern formed on the optical surface. However, since a process of heating above the glass transition temperature of the resin and then cooling is necessary, the problem that the molding cycle becomes very long and consumes a large amount of power is avoided. It is not possible.

JP-A-4-163119 JP-A-8-244085 JP 2000-25120 A JP 2004-262145 A JP 2004-284110 A

As described above, in order to transfer the fine pattern formed on the optical mirror surface or its surface with high accuracy and reduce internal distortion, the temperature of the mold is set to the softening temperature or higher, and the resin is softened in the mold cavity. Although it is effective to cool slowly after it has been performed, the heating / cooling process is required, so the molding cycle is always long, and the entire mold needs to be heated, which causes a problem of consuming a large amount of power. there were.
Therefore, in order to solve such a conventional problem, the present invention provides a plastic molded product such as a plastic optical element that consumes less energy during molding in a short molding cycle, has excellent transferability, and has low internal distortion. The technical problem is to devise the manufacturing method and the manufacturing apparatus so that it can be molded.

As a result of earnest research to solve the above technical problem, the present invention swells a pressurized gas such as carbon dioxide or hydrocarbon or a supercritical fluid in a thermoplastic resin, which acts as a plasticizer for the resin and glass. Attention is paid to the fact that the volume of the resin at the time of swelling increases simultaneously with lowering the transition temperature.
Specifically, a plastic member is inserted into a cavity of a fixed volume mold, and then a pressurized gas or a supercritical fluid is swollen in the plastic member. At this time, since the glass transition temperature of the resin can be lowered, the resin can be softened by heating at a temperature lower than conventional. Moreover, volume expansion occurs when the pressurized gas swells inside the resin, thereby generating an internal pressure of the resin, so that the transfer surface can be transferred.
That is, according to the present invention, the viscosity of the resin can be lowered at a temperature lower than that of the conventional one, and the transfer surface can be transferred by generating the internal pressure of the resin. It is possible to obtain a plastic molded product such as an optical element with high power consumption and low internal distortion.

(1) Solution 1 (corresponding to claim 1) for solving the above-mentioned problem is that a plastic member is inserted into a cavity of a fixed volume in a mold having at least one transfer surface, and then the plastic A pressure gas or a supercritical fluid is swollen in the member to soften the plastic member at a temperature lower than the glass transition temperature inherent to the plastic member, and the pressure generated by the volume expansion of the plastic member causes the mold to Transferring the transfer surface to the plastic member.
By configuring in this way, the plastic member can be swollen with pressurized gas or supercritical fluid, thereby lowering the softening temperature of the plastic member and causing its volume expansion. It becomes possible to do.

(2) Solution 2 (corresponding to claim 2) for solving the above-mentioned problem is a first step of inserting a plastic member into a fixed volume cavity in a mold having at least one transfer surface. When,
A pressurized gas or supercritical fluid pressurized to a predetermined pressure is caused to flow into the cavity, and the plastic member is swollen to soften the plastic member at a temperature lower than the glass transition temperature inherent to the plastic member . A second step of transferring the transfer surface of the mold to the surface of the plastic member by pressure generated by volume expansion of the plastic member;
And a third step of solidifying the plastic member by depressurizing the inside of the cavity to degas pressurized gas or supercritical fluid from the plastic member.
With this configuration, the pressurized gas or supercritical fluid is swollen in the plastic member, and then the inside of the cavity is depressurized, whereby the swollen pressurized gas or supercritical fluid can be degassed from the plastic member. Therefore, the softening temperature of the plastic member can be lowered at the time of transfer, and the softening temperature can be raised at the time of mold release.

(3) The pressurized gas or supercritical fluid may be carbon dioxide. (Corresponding to claim 3)
With such a configuration, since the pressurized gas or the supercritical fluid is carbon dioxide, it can be used not only in terms of safety, price, and handleability, but also has solubility in a plastic member (resin). Can be bigger.

(4) Moreover, the decompression speed in the cavity can be adjusted. (Corresponding to claim 4)
With such a configuration, the decompression speed in the cavity can be adjusted, so that foaming does not occur inside the plastic molded product.

(5) Further, before the pressurized gas or the supercritical fluid is allowed to flow into the cavity, the inside of the cavity can be vacuumed. (Corresponding to claim 5)
With such a configuration, the air remaining in the gap is sucked by reducing the pressure in the cavity before the pressurized gas or the supercritical fluid flows into the cavity. The carbon dioxide concentration is uniform over the entire transfer surface, and carbon dioxide can be swollen at a uniform concentration in the plastic member.

(6) Moreover, it can have the process of heating / cooling a metal mold | die provided with the said transfer surface. (Corresponding to claim 6)
With such a configuration, since the mold is heated during processing, the expansion due to swelling and the thermal expansion due to heating can be used together, and the internal pressure necessary for transfer can be generated more reliably.

(7) Further, the temperature of the mold having the transfer surface is equal to or lower than the softening temperature under atmospheric pressure of the resin used as the plastic member, and softening when the pressurized gas or supercritical fluid is swollen. It can have the process of hold | maintaining to the fixed temperature which is more than temperature. (Corresponding to claim 7)
With such a configuration, by keeping the temperature of the mold below the softening temperature of the resin used and at a constant temperature above the softening temperature when the pressurized gas or supercritical fluid is swollen, No heating / cooling step is required during processing.

(8) Further, the plastic member may be processed in advance into a substantially final shape by injection molding. (Corresponding to claim 8)
With such a configuration, since the plastic member is processed into a substantially final shape by injection molding in advance, the plastic member can be easily manufactured at low cost.

(9) The plastic member may be a plastic sheet. (Corresponding to claim 9)
With such a configuration, since the plastic member is a plastic sheet, the plastic member can be manufactured in large quantities at low cost by extrusion molding or the like.

(10) Alternatively, the plastic sheets may be successively supplied between the molds and sequentially cut from the transferred one. (Corresponding to claim 10)
With such a configuration, the plastic sheets are successively supplied between the molds and sequentially cut from the transferred ones, so that the movement of the plastic sheets can be easily performed.

(11) The transfer surface of the mold may be an optical mirror surface processed with high accuracy. (Corresponding to claim 11)
With such a configuration, an optical component having an optical mirror surface such as a lens can be manufactured with high accuracy and at low cost.

(12) Further, a fine uneven pattern may be formed on the transfer surface of the mold. (Corresponding to claim 12)
With such a configuration, a plastic molded product such as an optical component having a fine concavo-convex pattern formed on a transfer surface such as a diffractive lens, a light guide plate, or an optical disc can be manufactured with high accuracy and at low cost.

(13) Further, a fine pattern may not be formed in advance on the plastic member or the plastic sheet. (Corresponding to claim 13)
With such a configuration, since a fine pattern is not formed on a plastic member or plastic sheet that has been processed into a substantially final shape in advance, accurate positioning is not necessary when the plastic member is inserted into the cavity. In addition, pattern processing on a mold for producing a plastic member becomes unnecessary.

(14) Solution 3 (corresponding to claim 14) for solving the above-mentioned problems includes a press apparatus in which a mold having at least one transfer surface is fixed, and pressurization in a cavity of the mold A pressurized gas generating means for introducing a gas or a supercritical fluid,
A pressurized gas or a supercritical fluid is caused to flow into the cavity, and the plastic member inserted into the cavity is swollen to soften the plastic member at a temperature lower than the glass transition temperature inherent to the plastic member , and The transfer surface of the mold is transferred to the surface of the plastic member by the pressure generated by the volume expansion of the plastic member.
By configuring in this way, the plastic member can be swollen with pressurized gas or supercritical fluid, thereby lowering the softening temperature of the plastic member and causing its volume expansion. It becomes possible to do.

(15) A vacuum generating means communicating with the cavity of the mold can be provided, and the inside of the cavity can be decompressed. (Corresponding to claim 15)
With such a configuration, the air remaining in the cavity is sucked by reducing the pressure in the cavity before the pressurized gas or supercritical fluid flows into the cavity. A uniform gas concentration is formed on the entire transfer surface, and the pressurized gas or supercritical fluid can be swollen in the plastic member at a uniform concentration.
In addition, the swollen pressurized gas or supercritical fluid can be degassed from the plastic member by reducing the pressure in the cavity after the pressurized gas or supercritical fluid is swollen in the plastic member. It is possible to raise the lowered softening temperature at the time of mold release.

(16) The pressurized gas or supercritical fluid may be carbon dioxide. (Corresponding to Claim 16)
With such a configuration, since the pressurized gas or the supercritical fluid is carbon dioxide, it can be used not only in terms of safety, price, and handleability, but also has solubility in a plastic member (resin). Can be bigger.

(17) Further, a decompression speed adjusting means for changing a decompression speed for decompressing the inside of the cavity can be provided. (Corresponding to Claim 17)
With such a configuration, the decompression speed in the cavity can be adjusted, so foaming does not occur inside the plastic molded product.

(18) Moreover, the said metal mold | die can have a heating means. (Corresponding to Claim 18)
With such a configuration, the mold can be heated at the time of processing. Therefore, expansion due to swelling and thermal expansion due to heating can be used in combination, and the internal pressure necessary for transfer can be more reliably generated.

(19) Further, it comprises a temperature control means for controlling the heating means of the mold, and the temperature of the mold is not higher than the softening temperature under the atmospheric pressure of the resin used as the plastic member, and is applied. It can be maintained at a constant temperature that is higher than the softening temperature when the pressurized gas or supercritical fluid is swollen. (Corresponding to Claim 19)
With such a configuration, the mold temperature is maintained at a constant temperature not higher than the softening temperature of the resin to be used and not lower than the softening temperature when the pressurized gas or supercritical fluid is swollen. There is no need to heat / cool.

(20) One of the molds is a stamper on which a predetermined fine uneven pattern is formed, the other is a mirror plate, and the cavity is a fine uneven pattern formed on the stamper. May be. (Corresponding to Claim 20)
With such a configuration, on the stamper side of the plastic sheet, the pressurized gas or supercritical fluid can be swollen to lower the softening temperature of the plastic sheet and cause its volume expansion. It is possible to transfer the concavo-convex pattern at a lower temperature.

(21) Further, the stamper and the specular plate can be provided with heating means. (Corresponding to Claim 21)
With such a configuration, the stamper and the specular plate can be heated at the time of processing, so expansion due to swelling and thermal expansion due to heating can be used together, and the internal pressure necessary for transfer can be generated more reliably. is there.

The effects of the present invention are summarized according to the claims as follows.
(1) Inventions according to claims 1 and 14 By swelling a pressurized gas or a supercritical fluid in a plastic member, the softening temperature of the plastic member can be lowered and its volume expansion can be caused. It is possible to perform transfer at a lower temperature, shorten the molding cycle during processing, and reduce energy consumption (power consumption).
(2) Inventions according to Claims 2 and 15 The compressed gas or supercritical fluid is swelled from the plastic member by swelling the pressurized gas or supercritical fluid in the plastic member and then reducing the pressure in the cavity. Since it can be degassed, the softening temperature of the plastic member can be lowered at the time of transfer, and the softening temperature can be raised at the time of releasing, shortening the molding cycle during processing, and reducing energy consumption. Can do.

(3) Inventions of Claims 3 and 16 Since the pressurized gas or supercritical fluid is carbon dioxide, it can be used not only in terms of safety, price, and handleability but also in a plastic member ( Since the solubility in (resin) can be increased, the effect of lowering the softening temperature of the plastic member can be increased.
(4) Inventions according to Claims 4 and 17 Since the pressure reduction speed in the cavity can be adjusted, it is possible to prevent foaming from occurring in the plastic molded product.

(5) Inventions according to claims 5 and 15 Before the pressurized gas or supercritical fluid flows into the cavity, the air remaining in the gap is sucked by reducing the pressure in the cavity. Therefore, the carbon dioxide concentration is uniform over the entire transfer surface through the gap, and carbon dioxide can be swollen in the plastic member at a uniform concentration, so that the softening temperature of the plastic member can be reduced uniformly, It is possible to perform highly accurate transfer.
(6) Inventions according to claims 6 and 18 By heating the mold during processing, expansion due to swelling and thermal expansion due to heating can be used in combination, and the internal pressure necessary for transfer can be more reliably generated. Therefore, it is possible to reliably perform highly accurate transfer.

(7) Inventions according to Claims 7 and 19 The temperature of the mold is equal to or lower than the softening temperature of the resin used and to a constant temperature equal to or higher than the softening temperature when the pressurized gas or supercritical fluid is swollen. By holding, there is no need to heat / cool at the time of processing, so the molding cycle at the time of processing can be shortened and the energy consumption at the time of processing can be reduced.
(8) Invention of Claim 8 Since the plastic member is processed into a substantially final shape by injection molding in advance, the plastic member can be easily produced at low cost.

(9) Invention according to claim 9 By using a plastic sheet as the plastic member, the plastic member can be produced in large quantities at low cost by extrusion molding or the like.
(10) The invention according to claim 10 Since the plastic sheets are successively supplied between the molds and sequentially cut from the transferred ones, the movement of the plastic sheets can be easily performed, and the efficiency is very high. It is possible to produce well.
(11) Invention of Claim 11 An optical component having an optical mirror surface such as a lens can be manufactured with high accuracy and at low cost.

(12) The invention according to claim 12 A plastic molded product such as an optical component having a fine concavo-convex pattern formed on a transfer surface such as a diffractive lens, a light guide plate, or an optical disc is manufactured with high accuracy and at low cost. Can do.
(13) The invention according to claim 13 Since a fine pattern is not formed on a plastic member or plastic sheet that has been processed into a substantially final shape in advance, accurate positioning is not necessary when the plastic member is inserted into the cavity. In addition, it is not necessary to perform pattern processing on a mold for producing a plastic member, and the manufacturing cost can be reduced.

(14) The invention according to claim 20 On the stamper side of the plastic sheet, the pressurized gas or supercritical fluid is swollen to lower the softening temperature of the plastic member and to cause its volume expansion. It is possible to transfer the concave / convex pattern of the stamper at the temperature, shorten the molding cycle during processing, and reduce the energy consumption (power consumption).
(15) The invention according to claim 21 By heating the stamper and the specular plate at the time of processing, the expansion due to swelling and the thermal expansion due to heating can be used together, so that the internal pressure necessary for transfer can be generated more reliably. It is possible to perform highly accurate transfer reliably.

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  Embodiments of the present invention will be described below by describing Examples 1 to 3 with reference to the drawings.

A first embodiment of the present invention will be described with reference to FIGS. 1 is a perspective view of an fθ lens, FIG. 2 is a schematic cross-sectional view of a plastic molding apparatus, FIG. 3 is an operation explanatory diagram of the plastic molding apparatus, and FIG. 4 is a graph of carbon dioxide gas pressure in a cavity of a mold for polycarbonate resin. It is a graph which shows the relationship between and the heating temperature required for transcription | transfer.
In Example 1, an fθ lens (1) for a laser beam printer as shown in FIG. 1 was produced using a plastic molding apparatus. The lens surface (2) of the fθ lens (1) has a highly accurate optical mirror surface. As the resin material, a polycarbonate resin having a glass transition temperature of 140 ° C. was used.

  As shown in FIG. 2, the plastic molding apparatus has a pressing device (5) composed of an upper die plate (3) and a lower die plate (4). 4) A predetermined pressure is applied in the meantime. Between the upper and lower die plates (3, 4), a pair of molds (9) having an upper mold (7) and a lower mold (8) having a transfer surface (6) mirror-finished with high accuracy is fixed. Has been. A cavity (11) is defined in the mold (9) by matching the opposing surfaces (10) of the upper mold (7) and the lower mold (8) of the mold (9). The upper die (7) and the lower die (8) are provided with a heater (12) for heating to an optimum temperature during processing. The heating means is not limited to a heater. For example, a temperature control medium can be circulated or a non-contact infrared heater can be used.

  In the cavity (11), communication holes (13A, 13B) communicating with the outside of the mold (9) are formed, and one communication hole (13A) is installed outside the press device (5). Connected to the pressurized gas generator (14), pressurized gas (pressurized gas) or supercritical fluid flows into the cavity (11). In this embodiment, carbon dioxide is used as the pressurized gas. The other communication hole (13B) is connected to a vacuum pump (15) so that the inside of the cavity (11) can be vacuumed and depressurized. In addition, electromagnetic valves (16A, 16B) are arranged at the connection portions between the communication holes (13A, 13B) and the pressurized gas generator (14) and the vacuum pump (15), respectively, so that they can be opened and closed. ing. In particular, the electromagnetic valve (16B) disposed between the vacuum pump (15) can change the suction speed as well as opening and closing.

Next, the operation of molding the fθ lens (1) by the plastic molding apparatus will be described with reference to FIG.
[Process I]
A plastic member (17) having a substantially final shape prepared in advance is inserted into the cavity (11) of the mold (9) (FIG. 3 (a)). Here, although the manufacturing method of the plastic member (17) is not limited, since the shape accuracy is not required, the plastic member (17) can be easily manufactured at low cost by using normal injection molding. can do.
[Process II]
By moving the upper die plate (3) of the pressing device (5) downward, the die (9) composed of the upper die (7) and the lower die (8) is closed (FIG. 3 (b)). Here, since the shapes of the plastic member (17) and the cavity (11) do not coincide completely, a gap (18) exists between them.

[Process III]
The electromagnetic valve (16A) on the pressurized gas generator (14) side is opened, carbon dioxide is allowed to flow into the cavity (11) at a predetermined gas pressure, and then the electromagnetic valve (16A) is closed. At this time, since the electromagnetic valve (16B) on the vacuum pump (15) side is closed, the carbon dioxide that has entered the cavity (11) fills the gap (18), and then is inserted into the cavity (11). The plastic member 17 is swollen (FIG. 3B).
In addition, before filling the cavity (11) with the pressurized carbon dioxide, the air remaining in the air gap (18) is maintained by reducing the pressure in the cavity (11) with the vacuum pump (15). Therefore, carbon dioxide having a uniform concentration can be swollen throughout the transfer surface of the plastic member (17) through the gap (18).

[Process IV]
The mold (9) is heated to a predetermined temperature by the heating heater (12), held for a predetermined time, and then cooled to the predetermined temperature (FIG. 3 (c)).
Note that the order of the heating and the step of swelling the carbon dioxide is not limited, and the carbon dioxide may be swollen after the heating. Heating and swelling may be performed at the same time, but if the swelling is performed while the temperature is varied, the amount of carbon dioxide dissolved in the plastic member (17) is not stabilized, so that the carbon dioxide is swollen either before or after heating. Is preferred.

[Process V]
The inside of the cavity (11) is depressurized by the vacuum pump (15) (FIG. 3 (c)). By reducing the pressure in the cavity (11) in this way, the carbon dioxide swollen in the resin is gasified and degassed outside the resin. The decompression in the cavity (11) may be performed before the mold temperature is lowered.
[Process VI]
By moving the upper die plate (3) of the press device (5) upward, the mold (9) composed of the upper die (7) and the lower die (8) is opened, and the fθ lens (1 ) Is taken out (FIG. 3D).

  In the present invention, since the glass transition temperature is lowered by swelling carbon dioxide in the plastic member (17), the plastic member (17) is softened by heating at a temperature lower than that of the conventional manufacturing method. It is possible to relieve the stress in the plastic member (17) and reduce the strain. Further, since the volume of the plastic member (17) increases due to the swelling of carbon dioxide, the pressure necessary for transferring the optical mirror surface can be sufficiently secured even when the heating temperature is low, and a highly accurate transfer surface is provided. A final molded product (fθ lens (1)) can be obtained. Further, at the end of cooling, the inside of the cavity is depressurized to degas the carbon dioxide swollen in the plastic member (17). As a result, since the glass transition temperature becomes high, it is not necessary to lower the temperature more than necessary, and the plastic member (17) can be solidified, which does not cause a delay in the molding cycle.

  FIG. 4 shows the relationship between the carbon dioxide gas pressure flowing into the cavity (11) and the heating temperature required for transferring the optical mirror surface in this embodiment. When carbon dioxide was not allowed to flow into the cavity (11), a heating temperature of 155 ° C. which was higher than the glass transition temperature (Tg: 140 ° C.) inherent to the polycarbonate resin was required. On the other hand, in the case of this example, it can be seen that the higher the gas pressure, the lower the heating temperature required for transfer. For example, when the gas inflow pressure is 15 MPa, the transfer can be performed at a heating temperature of 130 ° C. The higher the gas pressure, the greater the amount of carbon dioxide dissolved in the plastic member (17), the greater the plasticizing effect and the lower the glass transition temperature. However, if the gas pressure is increased too much, it becomes difficult to seal the gas, and the burden on the mold (9) increases. Therefore, it is preferable to set the pressure to about 30 MPa or less in practical use.

As described above, in the present invention, high-precision surface transfer is possible even at a low temperature compared to the conventional method, the molding cycle is very fast, and the heating temperature is lower than that of the conventional processing method. The necessary power consumption can be reduced. Further, in the present invention, it is only necessary to soften the surface layer portion that requires transferability, so it is not necessary to swell carbon dioxide gas into the plastic member (17), and swelling and degassing are very short. Can be done in time. Also, the internal strain existing in the plastic member (17) can be alleviated by remelting only the surface layer portion because it remains in the surface layer portion or thin portion that is rapidly cooled and solidified when the plastic member is molded.
Further, in the present embodiment, vacuum suction is performed at the time of deaeration, but this makes it possible to increase the deaeration speed and shorten the molding cycle. However, if the pressure is suddenly reduced during deaeration, foaming may occur inside the plastic member (17). The presence or absence of foaming varies depending on the resin used, the gas used, processing conditions, etc., but by providing an open / close solenoid valve (16B) that can adjust the degassing speed as in this embodiment, foaming occurs. The electromagnetic valve can be adjusted as appropriate so as not to be present.

The pressurized gas used in the examples of the present invention is not limited to carbon dioxide, but carbon dioxide can be used most favorably in terms of safety, price, handleability, etc., and is soluble in resin. Is large, and the effect of lowering the solidification temperature of the resin is great. Therefore, the pressurized gas used in the present invention is suitable.
In the present invention, simply by swelling the pressurized gas body into the plastic member (17), the glass transition temperature of the resin is lowered and the volume expansion occurs. Therefore, the temperature of the mold (9) is heated / heated as in this embodiment. Without cooling, a highly accurate transfer surface can be formed on the plastic member while maintaining a constant temperature (above the glass transition temperature when carbon dioxide is swollen). In order to keep the temperature of the mold (9) constant, a temperature control means for controlling the heater (12) according to the detected temperature of the mold (9) is provided. However, even if there is a volume difference between the plastic member (17) and the cavity (11) as in this embodiment, and the gap (18) becomes large by heating the plastic member (17), the expansion due to swelling is caused. By using thermal expansion by heating in combination, the internal pressure necessary for transfer can be generated more reliably.

A second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is an explanatory diagram of an optical pickup lens, and FIG. 6 is an operation explanatory diagram of a plastic molding apparatus.
In Example 2, an optical pickup lens (19) as shown in FIG. 5 was produced using a plastic molding apparatus. A diffraction pattern (20) having a fine structure is formed on the lens surface of the optical pickup lens (19). Also in the present embodiment, as in the first embodiment, polycarbonate resin is used as the plastic material, and carbon dioxide is used as the pressurized gas.

Next, the operation of molding the optical pickup lens (19) by the plastic molding apparatus of Example 2 will be described with reference to FIG. The basic configuration and operation are the same as those in the first embodiment, and detailed description thereof is omitted.
[Process I]
A substantially final shaped plastic member (17) prepared in advance is inserted into the cavity (11) of the mold (9) (FIG. 6 (a)). Here, a diffraction pattern is formed on the transfer surface (6) of the upper mold (7). On the other hand, the diffraction pattern (20) is not formed on the surface (21) of the plastic member (17) having a substantially final shape prepared in advance, and is processed into a substantially approximate shape of a convex curved surface.
[Process II]
The mold (9) composed of the upper mold (7) and the lower mold (8) is closed (FIG. 6 (b)). Here, the diffraction pattern (20) is not formed on the surface (21) of the plastic member (17), while the diffraction pattern is formed on the transfer surface (6) of the upper die (7). Since they are formed, a portion of the diffraction pattern (20) is formed as a gap (18) between them.

[Process III]
Carbon dioxide is caused to flow into the cavity (11) at a predetermined gas pressure from the pressurized gas generator (14). The carbon dioxide that has flowed into the cavity (11) is filled in the voids (18) made up of the diffraction pattern (20) and swells from the surface of the plastic member (17) (FIG. 6 (b)).
[Process IV]
The mold (9) is heated to a predetermined temperature by the heater (12), held for a predetermined time, and then cooled to the predetermined temperature (FIG. 6 (c)).
[Process V]
The inside of the cavity (11) is depressurized by the vacuum pump (15) (FIG. 6 (c)).
[Process VI]
By moving the upper die plate (3) of the press device (5) upward, the die (9) consisting of the upper die (7) and the lower die (8) is opened, and for the optical pickup as the final molded product The lens (19) is taken out (FIG. 6 (d)).

  By swelling the pressurized gas in the plastic member (17) inserted into the cavity (11), the glass transition temperature is lowered as described in Example 1, so that it is very low compared to the conventional manufacturing method. The plastic member (17) can be softened at the heating temperature. Further, the volume of the plastic member (17) increases due to the swelling of the pressurized gas, and an internal pressure is generated in the cavity (11). Accordingly, since the pressure is applied at a temperature higher than the softening temperature of the resin surface, the resin on the surface of the plastic member (17) is formed on the transfer surface (6) of the cavity (11) even if the heating temperature is low. 20), a final molded product (lens for optical pickup (19)) in which the fine portions are completely filled can be obtained.

  When a fine pattern of about several microns is transferred to the surface as in this embodiment, the transfer surface of the upper mold (7) (even if the fine pattern is not formed in advance on the plastic member (17)). The resin can be completely filled in the fine pattern of about several microns formed in 6). As a result, not only accurate positioning when the plastic member (17) is inserted into the cavity (11) becomes unnecessary, but also pattern processing on the mold for producing the plastic member (17) becomes unnecessary. Manufacturing cost can be reduced.

A third embodiment of the present invention will be described with reference to FIGS. 7 is an explanatory view of a light guide plate for a liquid crystal backlight, FIG. 8 is a schematic sectional view of the plastic molding apparatus, FIG. 9 is an operation explanatory view of the plastic molding apparatus, and FIG. 10 is an explanatory view of automation of the plastic molding apparatus.
In Example 3, a light guide plate (22) for a liquid crystal backlight as shown in FIG. 7 was produced using a plastic molding apparatus. A V-groove pattern (23) is formed on the transfer surface of the light guide plate (22). In this example, a polymethyl methacrylate resin having a glass transition temperature of 110 ° C. was used as the plastic material, and carbon dioxide was used as the pressurized gas in the same manner as in Examples 1 and 2.

As shown in FIG. 8, the plastic molding apparatus has a pressing device (5) composed of an upper die plate (3) and a lower die plate (4). 4) A predetermined pressure is applied in the meantime. A stamper (24) having a V-groove pattern (23) is fixed to the upper die plate (3) via a heating plate (27). On the other hand, a mirror plate (25) whose surface is processed into an optical mirror surface is fixed to the lower die plate (4) via a heating plate (27). A gas reservoir (26) is formed at both ends of the V-groove pattern (23) formed in the stamper (24), and communication holes (13A, 13A, 13B) are provided. One communication hole (13A) is connected to a pressurized gas generator (14) installed outside the press device (5), and the other communication hole (13B) is connected to a vacuum pump (15). The vacuum can be reduced by vacuum suction. Furthermore, electromagnetic valves (16A, 16B) are arranged at both of the connecting portions, and can be opened and closed. In particular, the solenoid valve (16B) disposed between the vacuum pump (15) can vary the suction speed as well as the opening and closing.
A heating plate (27) disposed between the stamper (24) and the mirror plate (25) and the upper die plate (3) and the lower die plate (4) is provided for heating. The heater (12) is held at an arbitrary constant temperature.

Next, the operation of molding the light guide plate (22) for the liquid crystal backlight by the plastic molding apparatus of Example 3 will be described with reference to FIG.
[Process I]
A flat plastic sheet (28) is placed on the mirror plate (25) fixed to the lower die plate (4) (FIG. 9 (a)).
[Process II]
The upper die plate (3) of the pressing device (5) is moved downward, and the stamper (24) fixed to the upper die plate (3) is moved at a position where it contacts the flat plastic sheet (28). Stop. At this time, the gas reservoirs (26) formed at both ends of the stamper (24) form a sealed space (29) with the plastic sheet (28) (FIG. 9B).

[Process III]
Carbon dioxide having a predetermined gas pressure is caused to flow into the V-groove pattern (23) through the sealed space (29) from the pressurized gas generator (14). At this time, carbon dioxide gas swells in the plastic sheet (28) (FIG. 9B).
[Process IV]
After opening the solenoid valve (16B) on the side of the communication hole (13B) connected to the vacuum pump (15) and reducing the gas pressure (FIG. 9 (b)), the upper die of the pressing device (5) When the plate (3) is moved upward, the stamper (24) and the plastic sheet (28) are peeled off, and the light guide plate (22) as the final molded product can be taken out (FIGS. 9 (c) and 9 (d)). ).
In this embodiment, the temperature of the stamper (24) and the mirror plate (25) is always kept at 80 ° C. by the heating plate (27) during the operation, and the heating / cooling operation is not performed.

According to this embodiment, since carbon dioxide flowing into the V-groove pattern (23) swells in the plastic sheet (28), the glass transition temperature is lowered. The surface of the plastic sheet (28) is softened at 80 ° C., which is a temperature below the transition temperature (Tg: 110 ° C.).
At the same time, volume expansion occurs due to the swelling of the pressurized gas and an internal pressure is generated. Therefore, the resin enters the V groove pattern (23) on the stamper (24) surface, and the V groove pattern ( 23) can be transferred. Further, since the glass transition temperature is increased without cooling by reducing the pressure of the pressurized gas, the V groove pattern (23) is maintained even when the temperature of the stamper (24) is kept constant (without cooling). ) Can be solidified.

In the case where the volume expansion at the time of swelling of the pressurized gas is very small like the portion of the V groove pattern (23) as in this embodiment, the heating / cooling process is not required, and the atmospheric pressure of the resin used Softening / transfer (internal pressure generation) / solidification can be performed at a constant temperature as long as it is below the softening temperature below and above the softening temperature when the pressurized gas or supercritical fluid is swollen. As a result, the molding cycle is very short, and processing with low energy consumption (power consumption) becomes possible. Further, since the temperature is constant during processing, the molded product can be stably produced with excellent temperature stability.
Further, when a fine pattern is formed on a flat plate as in this embodiment, it is possible to use a plastic sheet (28) prepared by extrusion or the like as a plastic member having a substantially final shape. It can be manufactured at low cost. As shown in FIG. 10, by sequentially feeding the plastic sheet (28) between the upper and lower die plates (3,4) of the press machine (5) and sequentially cutting from the transferred one, Automation of the movement of the plastic sheet (28) can be easily performed, and production can be performed very efficiently.

In the first to third embodiments, the processing of the fθ lens, the pickup lens, and the light guide plate for the liquid crystal backlight has been described. Needless to say, however, the recording medium such as an optical disk, The present invention can also be applied to plastic optical elements such as rear projection mirrors and reflection mirrors.
In the case of producing a molded product that does not require internal homogeneity such as a mirror, there is no problem even if foam is present inside the molded product. In this case, since it is not necessary to adjust the pressure reduction speed in the cavity to suppress foaming, it is not necessary to adjust the pressure reduction speed by the electromagnetic valve (16B), and it is only necessary to be able to open and close as its function. In addition to the lower cost, the molding cycle can be shortened.

These are the schematic diagrams of the f (theta) lens produced by Example 1 of this invention. These are the typical cross-sectional schematic diagrams of the plastic molding apparatus of Example 1 of this invention. These are the typical cross-sectional schematic explaining operation | movement of the plastic molding apparatus of Example 1 of this invention, (a)-(d) is explanatory drawing of the process I-the process VI. These are graphs showing the relationship between the carbon dioxide gas pressure introduced into the mold cavity and the heating temperature required for the transfer of the optical mirror surface in Example 1 of the present invention. These are the schematic diagrams of the lens for optical pick-ups produced by Example 2 of this invention. These are the typical cross-sectional schematic explaining operation | movement of the plastic molding apparatus of Example 2 of this invention, (a)-(d) is explanatory drawing of the process I-the process V. FIG. These are the schematic diagrams of the light-guide plate for liquid crystal backlights produced by Example 3 of this invention. These are the typical cross-sectional schematic diagrams of the plastic molding apparatus of Example 3 of this invention, (a) is front sectional drawing, (b) is side sectional drawing. These are the typical cross-sectional schematic explaining operation | movement of the plastic molding apparatus of Example 3 of this invention, (a)-(c) is front sectional drawing explaining the process I-process V, (d) is It is side surface sectional drawing of (c). These are the typical cross-sectional schematic diagrams explaining automation of the plastic molding apparatus of Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... f (theta) lens 2 ... Lens surface 3 ... Upper die plate 4 ... Lower die plate 5 ... Press apparatus 6 ... Transfer surface
7 ... Upper mold 8 ... Lower mold 9 ... Mold 10 ... Opposite surface 11 ... Cavity 12 ... Heating heater (heating means)
13A, 13B ... Communication hole 14 ... Pressurized gas generator (pressurized gas generating means)
15 ... Vacuum pump (vacuum generating means)
16A, 16B ... Solenoid valve 17 ... Plastic member 18 (substantially final shape) ... Air gap 19 ... Optical pickup lens 20 ... Diffraction pattern 21 ... Surface of plastic member 22 (substantially final shape) ... Light guide plate 23 ... V groove pattern 24 ... Stamper 25 ... Mirror plate 26 ... Gas reservoir 27 ... Heating plate 28 ... Plastic sheet 29 ... Sealed space

Claims (21)

  A plastic member is inserted into a fixed volume cavity in a mold having at least one transfer surface, and then the plastic member is swelled with a pressurized gas or a supercritical fluid so that the plastic member is inherent to the plastic member. A method for producing a plastic molded product, comprising: softening at a temperature lower than the glass transition temperature of the plastic member, and transferring the transfer surface of the mold onto the plastic member by pressure generated by volume expansion of the plastic member. A first step of inserting a plastic member into a fixed volume cavity in a mold having at least one transfer surface;
A pressurized gas or supercritical fluid pressurized to a predetermined pressure is caused to flow into the cavity, and the plastic member is swollen to soften the plastic member at a temperature lower than the glass transition temperature inherent to the plastic member. A second step of transferring the transfer surface of the mold to the surface of the plastic member by pressure generated by volume expansion of the plastic member;
A third step of solidifying the plastic member by depressurizing the inside of the cavity to degas pressurized gas or supercritical fluid from the plastic member;
A method for producing a plastic molded article having   The method for producing a plastic molded product according to claim 1 or 2, wherein the pressurized gas or supercritical fluid is carbon dioxide.   The method for producing a plastic molded product according to claim 2 or 3, wherein a pressure reduction speed in the cavity is adjusted.   The method for producing a plastic molded product according to any one of claims 2 to 4, wherein the cavity is sucked in vacuum before the pressurized gas or the supercritical fluid flows into the cavity. .   The method for producing a plastic molded product according to any one of claims 1 to 5, further comprising a step of heating / cooling a mold including the transfer surface.   The temperature of the mold having the transfer surface is not higher than the softening temperature under atmospheric pressure of the resin used as the plastic member, and is not lower than the softening temperature when the pressurized gas or supercritical fluid is swollen. The method for producing a plastic molded product according to any one of claims 1 to 5, further comprising a step of maintaining the temperature.   The method for producing a plastic molded product according to any one of claims 1 to 7, wherein the plastic member is processed in advance into a substantially final shape by injection molding.   The method for producing a plastic molded product according to any one of claims 1 to 7, wherein the plastic member is a plastic sheet.   10. The method for producing a plastic molded product according to claim 9, wherein the plastic sheet is successively supplied between molds and cut sequentially from the transferred one.   The method for producing a plastic molded product according to any one of claims 1 to 10, wherein the transfer surface of the mold is an optical mirror surface processed with high accuracy.   The method for producing a plastic molded product according to any one of claims 1 to 10, wherein a fine uneven pattern is formed on the transfer surface of the mold.   The method for producing a plastic molded product according to claim 12, wherein a fine pattern is not formed in advance on the plastic member or the plastic sheet. A pressing device to which a mold having at least one transfer surface is fixed;
A pressurized gas generating means for flowing a pressurized gas or a supercritical fluid into the cavity of the mold, and
A pressurized gas or a supercritical fluid is caused to flow into the cavity, and the plastic member inserted into the cavity is swollen to soften the plastic member at a temperature lower than the glass transition temperature inherent to the plastic member, and An apparatus for manufacturing a plastic molded product, wherein the transfer surface of the mold is transferred to the surface of the plastic member by pressure generated by volume expansion of the plastic member.   15. The apparatus for producing a plastic molded product according to claim 14, further comprising vacuum generating means communicating with the cavity of the mold, wherein the pressure in the cavity is reduced.   The apparatus for producing a plastic molded product according to claim 14 or 15, wherein the pressurized gas or supercritical fluid is carbon dioxide.   The apparatus for producing a plastic molded product according to claim 15 or 16, further comprising a decompression speed adjusting means for changing a decompression speed for decompressing the inside of the cavity.   The apparatus for producing a plastic molded product according to any one of claims 14 to 17, wherein the mold has a heating means.   It comprises a temperature control means for controlling the heating means of the mold, and the temperature of the mold is not higher than the softening temperature under the atmospheric pressure of the resin used as the plastic member, and is a pressurized gas or supercritical The apparatus for producing a plastic molded article according to claim 18, wherein the apparatus is maintained at a constant temperature that is equal to or higher than a softening temperature when the fluid is swollen.   One of the molds is a stamper on which a predetermined fine uneven pattern is formed, the other is a mirror plate, and the cavity is a fine uneven pattern formed on the stamper. The apparatus for producing a plastic molded product according to any one of claims 14 to 17.   21. The apparatus for producing a plastic molded product according to claim 20, wherein the stamper and the mirror plate are provided with heating means.

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