JP4032996B2 - Injection molding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an injection molding method for producing a molded article with little birefringence.
[0002]
[Prior art]
Up to now, glass has been used as a material for optical components for applications where birefringence is a problem, but glass optical components are more expensive than resin molded products. Therefore, Patent Document 1 shown below proposes a method of molding an optical component such as a lens having a small birefringence by using a normal inexpensive transparent plastic resin material. This Patent Document 1 pays attention to the fact that the birefringence of an optical component due to plastic molding is caused by the residual stress generated during molding, and shows a molding method for reducing the residual stress.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 62-11619
[Problems to be solved by the invention]
However, according to this method, it is necessary to gradually cool the mold temperature from the glass transition temperature to the glass transition temperature. In the example of Patent Document 1, slow cooling of about 1 ° C./min to several ° C./min is shown, and the cycle time of molding must be much longer than that of normal molding. If the molding time is long, the production quantity decreases, so that the optical components are still expensive.
[0005]
The present invention has been made paying attention to such conventional problems, and the object of the present invention is to provide a plastic optical component with a low birefringence that can be used for applications utilizing polarization characteristics in a short time. It is to enable molding.
[0006]
[Means for Solving the Problems]
The injection molding method according to the present invention uses a pair of molds composed of a fixed side mold and a movable side mold, and the movable side mold has a hemispherical recess as a lens part of a molded product of an optical component on the cavity surface. A plurality of rod-shaped knockout pins for protruding and taking out the molded product contained in the cavity from both sides of the recess, and the temperature is equal to or lower than the temperature at the time of injection of the molding resin injected into the mold The plasticized molding resin is pressurized and injected through the gate into the mold cavity that is equal to or higher than the glass transition temperature at atmospheric pressure of the molding resin. After the molding resin is injected, the gate is sealed with the gate. The mass of the molding resin in the mold cavity after the gate is sealed is the mass of the molding resin having the same volume as the cavity volume under atmospheric pressure at room temperature. From After injecting the plasticized molding resin by pressurizing the gate so that the molding resin of the same volume as the cavity volume under the atmospheric pressure is within the mass range up to the mass at the time of opening the mold The injection pressure is cut off, the gate is then sealed by the gate sealing mechanism, and then the molding is performed within the mass range in a mold that is at or above the glass transition temperature and in the temperature range near the glass transition temperature. The temperature of the resin is lowered, and then the mold is opened while maintaining the temperature range above the glass transition temperature and in the vicinity of the glass transition temperature, and a plurality of rod-shaped knockout pins are ejected from below at the same time. This is an injection molding method of taking out from a mold.
[0007]
The glass transition temperature is a temperature at which a phase changes to a glassy hard state at a certain temperature when the polymer material in a rubbery state is cooled.
[0008]
The temperature range above the glass transition temperature and in the vicinity of the glass transition temperature refers to a range from the glass transition temperature to 20 degrees above the glass transition temperature, preferably at most 10 degrees.
[0009]
In the present invention, after the gate is sealed by the gate sealing mechanism, the molding resin in the mold cavity is cut off from the molding resin injection path and confined in the cavity.
[0010]
Since the mold temperature is always equal to or higher than the glass transition temperature immediately after the molding resin is injected and during cooling and further until the mold is opened, the entire molding resin in the mold is always in a rubbery state. Furthermore, since the molding resin in the cavity is disconnected from the molding resin outside the cavity at different temperatures and pressures, the temperature gradient and pressure of the molding resin, which are particularly prominent in the vicinity of the gate in the conventional molding method. The gradient is reduced, and the pressure distribution and temperature distribution of the molding resin in the cavity can be made uniform. Therefore, the molding resin is cooled while being kept at an equal pressure, and molding with little residual stress becomes possible.
[0011]
In addition, since the difference between the temperature when the mold is opened and the glass transition temperature is small, there is little change in shape until the molded product becomes glassy after the mold is opened, and the generation of internal stress due to cooling during the period is small. In cooling from below the glass transition temperature to room temperature, since the molded product is glassy, the volume change is small, and the internal stress generated at this time is also small.
[0012]
Therefore, according to the molding method of the present invention, it is possible to mold an optical component with little birefringence using a transparent resin used for a normal optical component. Transparent plastics used for ordinary optical parts include acrylic (PMMA), polycarbonate (PC), and other transparent plastics that could not be used due to birefringence due to residual stress. Is included.
[0013]
According to the present invention, unlike the above-described Patent Document 1, it is not necessary to gradually cool the mold temperature below the glass transition temperature, so that the molding time is short. Further, after the mold is opened, the time for raising the mold temperature from the glass transition temperature or lower to the glass transition temperature or higher for the next molding becomes unnecessary, and the preparation time for molding is shortened. That is, the time required for one molding cycle can be shortened.
[0014]
Oite to the present invention, the mass of the molding resin within the mold cavity after the gate has been sealed, a mass with molding resin of the same volume as the volume of the cavity is at normal temperature under atmospheric pressure, it is in the range of up to weight with a temperature at which the molding resin of the same volume as the volume of the cavity under atmospheric pressure to open the mold.
[0015]
Here, the normal temperature is an ambient temperature at which a molded product is usually placed, and is at most between 10 and 30 degrees Celsius. It also includes cases where it is set to 23 degrees Celsius or 25 degrees Celsius.
[0016]
As used herein, “the molding resin mass in the mold cavity after the gate is sealed is changed from the mass of the molding resin having the same volume as the cavity volume at room temperature to the temperature at which the mold is opened. The method of “within the range of the mass of the molding resin of the same volume as the volume of” is not only a method of directly measuring and controlling the mass of the molding resin injected into the cavity, but also indirectly having a constant relationship with the mass A method of measuring and managing parameters having That is, the mass may be controlled equivalently by controlling the temperature, pressure, volume, and parameters on the molding conditions having a certain relationship with those values. For example, by measuring the temperature and pressure of the molding resin in the cavity based on the volume of the known mold cavity and the density characteristics with respect to the temperature and pressure of the molding resin obtained as data in advance, The mass of the molding resin is obtained, and the pressure of the molding resin to be injected so as to obtain a desired mass can be controlled. The mass may be determined from the relationship between the temperature of the molding resin on the molding machine side and the volume injected into the cavity. The mass may be calculated by measuring these parameters in real time during molding, or may be measured in advance under conditions, and the mass may not be calculated during molding. For example, make moldings by changing molding conditions such as molding resin temperature and pressure in advance, measure the mass of the finished molding, determine the optimal molding conditions, and only mold resin temperature and pressure when molding You may control.
[0017]
According to the present invention , since the pressure of the molded product when opening the mold is equal to or slightly higher than the atmospheric pressure, even when the molded product is rubber-like, the shape change that occurs when the mold is opened is small. Therefore, deformation when taking out from the mold can be reduced. Further, until the mold is opened, the mold cavity is filled with the molding resin without any gap, the pressure in the molding resin becomes substantially uniform, and the internal stress is reduced. That is, it becomes possible to produce a molded product with little birefringence. It is also convenient from the viewpoint of making a molded product according to the mold dimensions.
[0018]
The mass of the molding resin in the mold cavity after the gate is sealed is the same as the volume of the cavity at the temperature when the mold is opened, from the mass of the molding resin having the same volume as the cavity volume at room temperature. It can also be realized by the following method to be within the range up to the mass of the volume molding resin. In other words, after the plasticized molding resin is pressurized and injected through the gate, the injection pressure is cut off, and then the gate is sealed by the gate sealing mechanism. In this method, first, a molding resin having a mass larger than the mass expected by pressure injection is injected into the cavity. Next, the molding resin in the filled cavity flows out of the gate until the gate is sealed by the gate sealing mechanism after the injection pressure is cut off, and the molding resin in the mold cavity is discharged. As the mass decreases, the pressure decreases. Thereafter, the gate is sealed to determine the mass of the molding resin in the cavity. If the time until the gate is sealed after the pressure in the cavity or the pressure to be injected is cut off is controlled, the mass of the molding resin in the cavity can be adjusted to a predetermined mass. The molding resin pressure in the cavity may be measured and the gate may be sealed when the pressure corresponding to the above-mentioned mass is reached. In the case of time-based control, the time may be determined in advance by determining the conditions. . When using these methods, it is desirable to consider the time lag until the gate completes sealing.
[0019]
According to this embodiment, it becomes possible to inject the molding resin into the cavity at a high speed. If injection is performed at a high speed, the temperature difference between the molding resin injected into the cavity at the start of injection and the molding resin injected at the completion of injection can be reduced, so that the molding resin in the mold cavity can be reduced. The temperature gradient is also reduced, and the temperature can be made uniform. Therefore, molding with even less birefringence is possible.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
The method of the embodiment of the present invention will be described below.
[0021]
FIG. 1 is a cross-sectional view of a mold and its peripheral portion in an example of a molding machine used for carrying out the molding method of the present invention. This figure shows a two-piece mold, and here shows a state in which a molding resin is filled. Reference numeral 1 is an injection cylinder, 2 is a long nozzle, 3a is a fixed member (fixed platen) fixed to an injection molding apparatus main body (not shown), 3b is a movable member (movable platen) fixed to the injection molding apparatus main body, 4a. Indicates a fixed side mold, and 4b indicates a movable side mold. Reference numeral 5a denotes a cavity surface of the fixed mold, and 5b denotes a cavity surface of the movable mold, and both form a molding cavity. 6 is a sprue, 7 is a runner, 8 is a molded product, and 9 is a gate part. The size of the opening of the gate portion is smaller than the size of the side surface of the molded product 8 on the gate portion side in the direction perpendicular to the paper surface. 10 is a guide pin, 11 is a return pin, 12 is a gate shut pin, 13 is a knockout pin, 14 is a knockout plate for gate shut for driving the gate shut pin 12, and 15 is for driving the knockout pin 13 This is a knockout plate for protruding a molded product. Reference numeral 16 denotes a protruding rod, 17 denotes a heat insulating plate, and 18 denotes a cooling water hole.
[0022]
Below, the shaping | molding method of embodiment of this invention is demonstrated, referring a figure for every step.
[0023]
In this molding method, as shown in FIG. 2, a light projection lens and a light reception lens for a retroreflective photoelectric switch are integrated, and a lens having a shape also used as a sensor cover is molded. Contact name, the shape of the molded article, isotropically resulting shaped expansion and contraction due to temperature changes, if the shape close to for example, a thin plate-like shape and a combination thereof, or a thin plate, less molding birefringence It becomes possible.
[0024]
First, as shown in FIG. 1, the fixed mold 4a and the movable mold 4b are closed and the mold is clamped, and the tip of the long nozzle 2 is attached to the sprue 6 of the fixed mold 4a. The molding resin that has been pressed and plasticized is injected. The molding resin is acrylic and plasticized, and the temperature is maintained at 270 ° C. to 280 ° C. The injected molding resin passes through the sprue 6, the runner 7, and the gate 9 and is injected into the cavity constituted by the cavity surfaces 5 a and 5 b. The injection pressure is about 1500 kgf / cm ² to 2000 kgf / cm ² , and at this time, the gate shut pin 12 is in a position where the gate 9 is not blocked. The mold temperature is maintained at a constant temperature by circulating cooling water with increased pressure through the cooling water hole 18. The glass transition temperature of acrylic resin of the molding resin in the molding method of this embodiment is 102 ° C., and the mold temperature is maintained at 106 ° C. at a temperature slightly higher than the glass transition temperature.
[0025]
Next, after the injection of the molding resin into the cavity is completed, the holding pressure of the injection pressure is cut off, and then the gate 9 is shut off by the gate shut pin 12 to seal the molding resin in the cavity. This state is shown in FIG. The volume inside the cavity when the gate 9 is blocked is about 406 mm ² , and the mass of the molding resin injected into the cavity is between 0.37 g and 0.42 g. By pushing out the protruding bar 16, the gate shut knockout plate 14 is pushed, and the gate shut pin 12 is pushed out to block the gate. Since the pressure in the cavity after the gate is cut off is set to 1000 kgf / cm ² to 1500 kgf / cm ² , the time from when the holding pressure of the injection pressure is turned off until the gate sealing is completed is 0.1 seconds to 1 second. Controlled to the extent possible. The mold temperature is maintained at 106 ° C. throughout the process, and after the gate is sealed, the mold is left for 35 seconds, then the mold is opened, and the molded product is protruded and taken out. During this 35 seconds, the molding resin is cooled to almost the mold temperature. FIG. 4 shows a state when the molded product is taken out. The movable side mold 4b is pulled away from the fixed side mold 4a, and the protruding bar 16 is further pushed out in this state, whereby the knockout plate 15 is pushed and the knockout pin 13 is pushed out. Thereby, the molded product stored in the cavity surface 5b of the movable mold 4b is taken out. Since the mold is opened above the glass transition temperature, the molded product when the mold is opened is rubbery and deforms when stress is concentrated locally. The entire molded product around the lens is projected.
[0026]
The time required for this series of molding is 2 seconds to close the mold, 2.5 seconds from the start of injection of the molding resin to resin filling and sealing the gate, cooling time 35 seconds, mold It takes 2 seconds to open and 2 seconds to protrude and take out the molded product, and it takes about 45 seconds in total. In the molding method as shown in Patent Document 1, it takes several minutes to several tens of minutes only for the cooling time, and it can be seen that one molding cycle is shorter than this. Therefore, mass production efficiency is high and the cost can be reduced.
[0027]
FIG. 5 shows a measurement result of retardation (phase difference due to birefringence) distribution of the lens corresponding to FIG. 2 molded by the molding method of the present embodiment. Moreover, the measurement result of the retardation distribution at the time of shape | molding by making the temperature of a metal mold | die into 80 degreeC which is a temperature considerably lower than a glass transition temperature like a normal shaping | molding method is shown in FIG. When both are compared, it can be seen that the birefringence is greatly reduced by the molding method of the present invention.
[0028]
【The invention's effect】
According to the present invention, it is possible to mold an optical component with little birefringence using the transparent resin used for a normal optical component. In addition, the molding time is short as compared with a molding method in which the temperature of the mold is cooled below the glass transition temperature.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a mold and its peripheral portion in an example of a molding machine used in an embodiment of a molding method of the present invention.
FIG. 2 is a diagram showing the shape of a molded product molded according to the embodiment of the present invention.
3 is a cross-sectional view showing the molding machine with the gate sealed in the molding machine of FIG.
4 is a cross-sectional view showing the molding machine in a state in which a molded product protrudes from the molding machine of FIG.
FIG. 5 is a diagram showing retardation distribution of a molded product molded according to the embodiment of the present invention.
FIG. 6 is a diagram showing retardation distribution of a molded product molded by a normal molding method in which a mold is set to a temperature sufficiently lower than a glass transition temperature.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Injection cylinder 2 Long nozzle 3a The fixed member (fixed platen) fixed to the injection molding apparatus main body
3b Movable member (movable platen) fixed to the injection molding machine body
4a Fixed mold 4b Movable mold 5a Fixed mold cavity surface 5b Movable mold cavity surface 6 Sprue 7 Runner 8 Molded product 9 Gate portion 10 Guide pin 11 Return pin 12 Gate shut pin 13 Knockout pin 14 Knockout plate for gate shut 15 Knockout plate 16 Protruding rod 17 Heat insulation plate 18 Cooling water hole

Claims (1)

A pair of molds consisting of a fixed mold and a movable mold are used, and the movable mold has a hemispherical concave portion on the cavity surface that serves as a lens part of a molded product of an optical component and fits in the cavity. A plurality of rod-shaped knockout pins for projecting and removing the molded product from below are arranged on both sides of the concave portion, and are below the temperature at the time of injection of the molding resin injected into the mold, The plasticized molding resin is pressurized and injected through the gate into the mold cavity that is above the glass transition temperature at atmospheric pressure. After the molding resin is injected, the gate is sealed by the gate sealing mechanism. To do,
The mass of the molding resin in the mold cavity after the gate is sealed is the same as the volume of the cavity of the molding resin under the atmospheric pressure. Originally, the plasticized molding resin was injected by pressurizing the gate so that the molding resin having the same volume as the volume of the cavity was within the mass range up to the mass at the temperature when the mold was opened. After that, cut off the pressure to inject, and then seal the gate by the gate sealing mechanism,
Next, in a mold that is equal to or higher than the glass transition temperature and in the temperature range near the glass transition temperature, the temperature of the molding resin in the mass range is decreased, and then the mold is equal to or higher than the glass transition temperature. An injection molding method, wherein the molded product is taken out from the mold by opening the plurality of rod-shaped knockout pins simultaneously from below while opening in a state where the temperature range near the glass transition temperature is maintained.

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