JP2001353761A - Method for injection molding and mold used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of introducing a decrease in an accuracy of an obtained injection molding due to occurrence of an unevenness of a temperature at a core opposed to a molding cavity in the case of heating the core. SOLUTION: The mold for injection molding to manufacture the injection molding of a shape corresponding to a molding cavity by injecting a plastic in the cavity 15 comprises cores 12 and 14 connected to a power source opposed at least partly to the cavity 15 in such a manner that the cores 12 and 14 are each constituted of ceramics having volume resistivity of a range of 1×10-2 to 1×103 Ωcm and electrically insulating layers 25 and 26 are respectively formed on contact surfaces of the cores 12 and 14 with another mold constituting members 11 and 13 to heat the cores 12 and 14 themselves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injection-molding a thermoplastic, particularly an optical component made from the thermoplastic, with high accuracy, and a mold for performing the method.

[0002]

2. Description of the Related Art Japanese Patent Publication No. 3-5460 proposes a method of injection-molding optical parts such as lenses, prisms or reflectors, which require high shape accuracy, using thermoplastics. According to this method, after injecting a thermoplastic into a mold cavity of a mold heated to a temperature higher than its glass transition temperature, the temperature of the mold is slowly cooled to the glass transition temperature over at least 10 seconds or more. By doing so, non-uniform shrinkage due to variation in temperature distribution occurring in the injection molded product in the molding cavity is prevented, and a highly accurate injection molded product that can withstand use as an optical component is obtained.

Further, Japanese Utility Model Publication No. 5-40984 discloses a mold for molding a plastic lens with high precision. According to this, an electric heating member such as a heater is annularly dispersed in a mold so as to surround a molding cavity, and an annular cooling passage is provided in the mold concentrically with the electric heating member. In addition, the temperature balance of the entire mold is kept good and uniform so that a high-precision plastic lens can be easily molded.

[0004]

In the conventional method disclosed in Japanese Patent Publication No. 3-5460, as a specific means for heating the mold temperature to a temperature higher than the glass point transfer temperature of plastic, a movable side and a fixed side are used. Although it is described that a heater is arranged in each of the side core portions, a temperature difference is inevitably generated between the vicinity of the heater and a portion distant from the heater. Therefore, a temperature difference is generated in the vicinity of the molding surface of the core portion facing the molding cavity. There is a problem that the shape accuracy of the obtained injection-molded product is impaired due to the uneven temperature distribution.

In the conventional mold disclosed in Japanese Utility Model Publication No. 5-40984, an electric heating member and a cooling passage are provided concentrically with the optical axis of the lens. However, since the electric heating members are dispersed and arranged in a ring shape, the temperature distribution in the circumferential direction along the arrangement direction of these electric heating members is similar to that disclosed in Japanese Patent Publication No. 3-5460. Inevitably, there is a problem that the accuracy of the shape of the obtained injection-molded article is impaired.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method by which a thermoplastic, particularly an optical component made from the thermoplastic, can be injection-molded with high precision, and an injection mold for performing the method. It is in.

[0007]

According to a first aspect of the present invention, there is provided:
An injection molding method for injecting plastic into a molding cavity to produce an injection molded product having a shape corresponding to the molding cavity, wherein a current is supplied to a core portion facing at least a part of the molding cavity, and the core portion itself is energized. The temperature of the plastic injected into the molding cavity is adjusted by generating heat.

According to a second aspect of the present invention, there is provided an injection mold for injecting plastic into a molding cavity to produce an injection molded article having a shape corresponding to the molding cavity, wherein at least one of the molding cavities is provided. And a core part connected to the power supply facing the part, and this core part is 1 × 10 ^-2
It is composed of ceramics having a volume resistivity in the range of 1 × 10 ³ Ωcm. An electric insulating layer is formed on a contact surface of the core portion with another mold component, and the core portion itself generates heat. It is characterized in that it is made to be.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the injection molding method according to the first embodiment of the present invention, the core portion is 1 × 10 ^-2 to 1 × 10 ³ Ωcm.
Is preferably formed of ceramics having a volume resistivity in the range described above.

In the injection molding apparatus according to the second aspect of the present invention, the ceramic may be silicon carbide. Preferably, a metal layer is formed on a surface of the core portion facing the molding cavity, and an electrical insulating layer is formed inside the metal layer. In this case, the metal layer may be formed by nickel plating, and the surface of the metal layer may be mirror-finished.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to the production of a plastic optical component will be described in detail with reference to FIGS. 1 to 4. However, the present invention is not limited to such an embodiment. It can be combined or applied to other techniques that are to be encompassed by the inventive concept described in the claims herein.

FIG. 1 shows an external view of a pentaprism as an example of an optical component to which the present invention is applied, and shows a schematic structure of an embodiment of an injection mold according to the present invention having a molding cavity corresponding thereto. It is shown in FIG. That is, a mounting portion 3 for fixing the pentaprism 1 to a camera body (not shown) in a positioned state is integrally formed on a pair of left and right side end surfaces 2 of the pentaprism 1 to which the present invention is applied. . The injection mold according to the present embodiment includes a fixed mold plate 11 connected to an injection cylinder (not shown), a fixed core 12 held by the fixed mold plate 11, and a mold clamping device (not shown). Molding cavity 15 corresponding to the contour shape of pentaprism 1 having movable side mold plate 13 connected to the side and movable side core portion 14 held by movable side mold plate 13 therebetween. The gate 16 and the runner 17 are formed in this order, and the fixed side mold plate 11 is formed.
The molten plastic is injected from the injection cylinder into the molding cavity 15 through a sprue 18 provided in the mold.

The movable mold plate 13 is connected to a movable end plate 19, and a pin driving device 20 for taking out the injection-molded pentaprism 1 is incorporated between them. The pin driving device 20 includes a pair of knock pins 21 for pushing up the mounting portion 3 of the injection-molded pentaprism 1 from the molding surface of the movable side core portion 14, and a knock pin 22 for removing the solidified gate 17 and runner 17.
And are slidably held on the movable mold plate 13 respectively.

The fixed side mold plate 11 and the movable side mold plate 13 have cooling passages 23, 24 through which a cooling medium such as water flows.
Are formed, and these cooling passages 23 and 24 are formed.
The fixed core 12 and the movable core 14 are cooled by flowing a cooling medium such as water through the core. Electrical insulating layers 25 and 26 are formed on the outer peripheral surface of the fixed-side core portion 12 that contacts the fixed-side template 11 and the outer peripheral surface of the movable-side core portion 14 that contacts the movable-side template 13, respectively. . As the electric insulating layers 25 and 26, alumina (Al ₂ O ₃ ) by sputtering or polyimide resin by baking coating can be used. Also,
A pair of electrodes 27 and 28 facing each other at a distance from each other are attached to the fixed-side core portion 12 and the movable-side core portion 14 in a state surrounded by electric insulating layers 25 and 26, respectively. Is connected to a power supply via a heater temperature controller (not shown). The fixed core 12 and the movable core 14 have a fixed core 12.
And temperature sensors 29 and 30 insulated from the movable-side core portion 14, respectively. The fixed-side core portion 12 and the movable-side core portion 14 are based on the temperatures detected by the temperature sensors 29 and 30. The heater temperature controller supplies electricity to the fixed-side core portion 12 and the movable-side core portion 14 so that the temperature becomes equal to or higher than a predetermined temperature, for example, the glass transition point temperature of the plastic filled in the molding cavity 15. The side core portions 14 are each caused to generate heat. In this case, a timer may be built in the heater temperature controller, and the fixed-side core unit 12 and the movable-side core unit 14 may be energized for a predetermined time to generate heat for a predetermined time.

Fixed core 12 and movable core 14
For example, silicon carbide (SiC) can be used. However, when the volume resistivity is less than 0.01 Ωcm, even if the voltage between the pair of electrodes 27 and 28 is several volts, a current of several hundred amperes or more will flow. Out of control. On the other hand, when the volume resistivity exceeds 1 × 10 ³ Ωcm, even if the voltage between the pair of electrodes 27 and 28 is applied so as to be 200 to 300 volts, only a few hundred milliamps of current flows, Heat generation is poor, and the fixed core 12 and the movable core 14 cannot be heated to a predetermined temperature.

In the mold of this embodiment, since the fixed core 12 and the movable core 14 themselves generate heat, they can be heated to a predetermined temperature in a short time, and the dispersion of the temperature distribution is small. The prism 1 can be injection molded. Although the dimensional tolerance of the conventional mold cannot be kept within 0.5 μm, the pentaprism 1 formed by using the injection mold of the present embodiment can be kept within the dimensional tolerance of 0.5 μm or less. Was. Further, since there is no heat generating member such as a heater other than the fixed-side core portion 12 and the movable-side core portion 14, the cooling passages 23, which have a relatively small cooling capacity,
Even if these are cooled using the cooling medium 24, the fixed-side core portion 12 and the movable-side core portion 14 can be efficiently cooled in a minimum necessary time.

On the other hand, a plastic biconvex lens 5 having a flange portion 4 integrally formed on the outer peripheral edge as shown in FIG.
FIG. 4 shows a schematic structure of another embodiment of the injection molding die according to the present invention, which is also suitable as an optical component to which the present invention is applied, and has a molding cavity 15 corresponding to such a biconvex lens 5. The members having the same functions as those of the previous embodiment are denoted by the same reference numerals, and the duplicate description will be omitted. That is, similarly to the previous embodiment, the fixed side template 1
Electrical insulating layers 25 and 26 are formed on the outer peripheral edge of the fixed-side core portion 12 contacting the movable side mold plate 13 and the outer peripheral edge of the movable-side core portion 14 contacting the movable-side mold plate 13. In the embodiment, electric insulating layers 25 and 26 are also formed on the molding surfaces of the fixed-side core portion 12 and the movable-side core portion 14 that form the optical surface 6 of the biconvex lens 5, respectively. Further, the fixed-side core portion 12 that forms the optical surface 6 of the biconvex lens 5
The metal layers 31 such as KN plating are formed on the surfaces of the electric insulating layers 25 and 26 constituting the molding surface of the movable side core portion 14.
32 are provided, and are cut to a predetermined optical surface accuracy using a diamond tool or the like.

It is preferable that the metal layers 31 and 32 have excellent workability and durability. For example, in the case of an optical component having a fine shape such as a diffraction grating, the workability is emphasized and copper is used. It is also possible to employ plating or the like.

In this embodiment, since the molding surfaces of the fixed core 12 and the movable core 14 facing the molding cavity 15 corresponding to the optical surface 6 of the biconvex lens 5 are formed of the metal layers 31 and 32, It is also possible to injection mold an aspherical optical surface or a diffraction grating such as a Fresnel lens, which is difficult to process with ceramics.

As in the previous embodiment, also in this embodiment, since the fixed core 12 and the movable core 14 themselves generate heat, the fixed core 12 and the movable core 12 reach a predetermined temperature in a short time. Since the temperature of the biconvex lens 14 can be heated, and the variation in the temperature distribution is small, the biconvex lens 5 can be injection-molded with high precision. Although the dimensional tolerance of the optical surface 6 cannot be kept within 0.5 μm in the conventional injection molding die, the dimensional tolerance of the optical surface 6 of the biconvex lens 5 is set to 0.5 μm or less in the injection molding die according to the present embodiment. Could fit.

[0021]

According to the present invention, the temperature of the plastic injected into the molding cavity is adjusted by energizing the core facing at least a part of the molding cavity and generating heat in the core itself. Therefore, the entire core portion can be heated to a predetermined temperature in a short time and the temperature of the core portion can be kept uniform. As a result, a particularly high-precision optical component can be obtained by injection molding.

When the core is made of ceramics having a volume resistivity in the range of 1 × 10 ^-2 to 1 × 10 ³ Ωcm, the core can be more uniformly heated.

When silicon carbide is used as the ceramic, a core having excellent heat resistance and compressive strength can be obtained.

When a metal layer is formed on the surface of the core portion facing the molding cavity, and an electric insulating layer is formed inside the metal layer, electricity is prevented from flowing through the metal layer, and the heat generation distribution of the core portion is prevented. Can be kept uniform.

When the metal layer is formed by nickel plating, it is possible to process the surface of the metal layer, and it is possible to form a fine optical surface such as a Fresnel lens and a diffraction grating or an aspheric optical surface. Can be easily formed by injection molding.

When the surface of the metal layer is mirror-finished, an optical part having the optical surface as an optical surface can be easily injection-formed.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating an appearance of a plastic pentaprism which is an object of the present invention.

FIG. 2 is a sectional view showing a schematic structure of an embodiment of an injection molding die according to the present invention for injection molding the pentaprism shown in FIG.

FIG. 3 is a perspective view illustrating an appearance of a plastic biconvex lens that is an object of the present invention.

FIG. 4 is a sectional view showing a schematic structure of another embodiment of an injection mold according to the present invention for injection-molding the biconvex lens shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pentaprism 2 Side end surface 3 Mounting part 4 Flange part 5 Biconvex lens 6 Optical surface 11 Fixed side mold plate 12 Fixed side core part 13 Movable side mold plate 14 Movable core part 15 Molding cavity 16 Gate 17 Runner 18 Sprue 19 Movable side End plate 20 Pin drive device 21,22 Dowel pin 23,24 Cooling passage 25,26 Electrical insulation layer 27,28 Electrode 29,30 Temperature sensor 31,32 Metal layer

Claims (7)

[Claims] 1. An injection molding method for injecting plastic into a molding cavity to produce an injection molded product having a shape corresponding to the molding cavity, wherein a current is applied to a core portion facing at least a part of the molding cavity. An injection molding method wherein the temperature of the plastic injected into the molding cavity is adjusted by causing the core itself to generate heat. 2. The method according to claim 1, wherein the core portion is 1 × 10 ⁻² to 1 × 10 ³ Ωc.
The injection molding method according to claim 1, wherein the injection molding method is formed of a ceramic having a volume resistivity in a range of m. 3. An injection molding die for injecting plastic into a molding cavity to produce an injection molded product having a shape corresponding to the molding cavity, wherein the injection molding die is connected to a power source while facing at least a part of the molding cavity. The core portion is made of ceramics having a volume resistivity in the range of 1 × 10 ^-2 to 1 × 10 ³ Ωcm, and the core portion is made of a ceramic having a volume resistivity of 1 × 10 ⁻² to 1 × 10 ³ Ωcm. An injection molding die, wherein an electrical insulating layer is formed on the contact surface so that the core itself generates heat. 4. The injection mold according to claim 3, wherein the ceramic is silicon carbide. 5. The injection according to claim 3, wherein a metal layer is formed on a surface of the core portion facing the molding cavity, and an electric insulating layer is formed inside the metal layer. Molding mold. 6. The injection mold according to claim 5, wherein the metal layer is formed by nickel plating. 7. The injection molding die according to claim 5, wherein a surface of the metal layer is mirror-finished.