JPH0724890A - Injection mold and injection molding method - Google Patents

Abstract

PURPOSE:To provide an injection mold and a method for injection molding in which a molded form having extremely high accuracy and transferability is molded in a short cycle time. CONSTITUTION:The injection mold comprises an insert 1 for forming a cavity, a gas communicating hole 2 for communicating with an interior of the insert 1, a permeable member 3 provided near a surface of the cavity, and a gas heater 4 arranged in the hole 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold and a molding method used for injection molding of plastic products and the like, and more particularly, to a molded product such as an optical component which is required to have a highly accurate transfer property very quickly. The present invention relates to an injection molding die and an injection molding method which can be obtained.

[0002]

2. Description of the Related Art Conventionally, regarding molding of this type of molded article,
For example, as described in Japanese Patent Application Laid-Open No. 61-279515, a heating member and a cooling member are provided in a mold, and heating / cooling (heat cycle) is performed after injection filling to improve the precision of a molded product. Further, as described in JP-A-63-286312, after opening the mold and taking out the molded product, prior to the next molding, hot air is blown directly onto the cavity surface to heat the cavity surface. , Improving the fluidity of molding materials and improving the precision of molded products.

[0003]

However, among the above-mentioned conventional techniques, in the invention described in Japanese Patent Laid-Open No. 61-279515, since the distance from the cavity surface to the heating member is large, the cavity surface is There is a problem in that it takes a long time to heat up to a predetermined temperature. further,
In order to solve this problem, if the heating member and the cavity surface are brought too close to each other, the temperature distribution on the cavity surface becomes uneven, and the surface shape is distorted so that the surface accuracy is significantly deteriorated.

Further, in the invention described in Japanese Patent Laid-Open No. 63-28612, it is necessary to perform a heating process after taking out a molded product by the previous molding shot and before the next shot. However, there is a problem that the molding cycle time becomes long. Further, even if the surface of the cavity is heated, the temperature of the entire mold is low, so the heat is absorbed more and more, and there is a problem that substantial heating takes a long time. Further, even if heating is performed for such a long time, there is a problem that the cavity surface temperature is lowered within a few seconds until the mold is closed and the mold is injected, and a sufficient effect cannot be obtained. The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an injection molding die and an injection molding method capable of molding a molded article having extremely high precision transferability in a short cycle time.

[0005]

The injection molding die of the present invention having the above-described structure will be described with reference to the reference numerals shown in FIG. 1. The injection molding has a fixed side, a movable side and a cavity portion therebetween. In a molding die, an insert 1 forming a cavity, a gas communication hole 2 communicating with the inside of the insert 1, and a gas permeable member provided in the middle of the gas communication hole 2 and near the cavity surface. 3 and the heater 4 for heating the gas arranged in the gas communication hole 2.

[0006]

In the present invention having the above structure, as shown in FIG. 2, the heater 4 is turned on a few seconds before the molded product obtained by the previous shot is taken out. Then, after taking out the molded product, gas is passed through the gas communication hole 2. Gas is heater 4
After being heated at, it passes through the breathable member 3. here,
Since the gas permeable member 3 has a porous structure and has a large area in contact with the gas, when the heated gas passes through the gas permeable member 3, the heat quantity of the gas is efficiently stored in the gas permeable member 3. Therefore, the breathable member 3 is heated very quickly,
The amount of heat is transferred to the cavity surface 5 and kept at a high temperature. After the mold is clamped, the molten resin is injected and filled while the cavity surface 5 is kept at a high temperature (above the glass transition point of the resin to be molded). After that, after the temperature of the thick portion of the molded product becomes uniform, the power source of the heater 4 is turned off. By turning off the heater 4, the gas passing through the breathable member 3 becomes cooler,
The molded product can be cooled. After the molded article has cooled, the inflow of gas is stopped. After that, the mold is opened to take out the molded product. At this time, at the same time, the gas heating heater 4 is turned on to preheat it for the next shot.
By preheating, a high temperature gas can be obtained immediately when the gas is made to flow next time. Also, even if it is preheated,
Since no gas is flowing and there is a distance from the heater 4 to the cavity surface 5, it does not affect the molding protrusion.

Embodiments of an injection molding die and an injection molding method according to the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

[0008]

First Embodiment First, a first embodiment of the present invention will be described. Figure 3
Is a cross-sectional view showing an injection molding die, and FIG. 4 is a cross-sectional view showing an insert used in this die. In the figure, 6 is a movable side mounting plate, and 7 is a fixed side mounting plate, which are fixed to a platen of a molding machine (not shown). 8 is a movable plate, 9 is a fixed plate, 10 is a movable side insert, 11 is a fixed side insert, and resin is injected into a region sandwiched between the movable side insert 10 and the fixed side insert 11. The cavity portion 12 is formed. Further, the movable insert 10 is fixed to the projecting plate 13, and can slide in the movable plate 8 in the direction perpendicular to the parting surface when the mold is opened. Further, the fixed side insert 11 is fixed in the fixed plate 9.

As shown in FIG. 4, the movable insert 10 has a gas inflow hole 14 formed in the bottom surface thereof, and the hole 14 and the gas pressure feeding device 25 are connected by a hose 16. The gas communication hole 15 communicating with the gas inflow hole 14 is provided as a cylindrical hole from the center of the bottom surface portion of the movable side insert 10 toward the cavity surface, and further communicates with this to form a movable side insertion hole. A plurality of cylindrical holes are also formed in the outer peripheral portion inside the child 10, and these holes communicate with the gas outflow holes 17. A coil heater 18 having a built-in thermocouple is embedded in the gas communication hole 15 at the center of the movable-side insert 10 and connected to a temperature controller 19 installed outside. In the vicinity of the cavity surface in the movable side insert 10, a breathable member 20 having a thickness of several millimeters (for example, porcerax II type PM30 (Shinto Kogyo Co., Ltd.)) 20 is fixed to the core material 21, and 0.1 is provided outside thereof. A nickel plating 22 having a thickness of 1.0 mm is applied. The breathable member 20 communicates with the gas communication hole 15. That is, the gas flowing in from the gas inflow hole 14 passes through the gas permeable member 20 and flows out from the gas outflow hole 17.

The fixed-side insert 11 has the same structure as the movable-side insert 10. The gas inflow hole 23 is connected to the gas pressure feeding device 25 through a hole 24 opened inside the fixing plate 9,
The gas outflow hole 26 is open to the outside through a hole 27 opened inside the fixed plate 9. Other parts are composed of the coil heater 28, the air permeable member 29, the gas communication hole 30, and the nickel plating 31, as in the movable side.

When using the injection molding die of the embodiment thus constructed, the coil heaters 18, 28 are turned on when the mold is opened a few seconds before the molded product is taken out. The set temperature at this time is set to a temperature about 20 ° C. higher than the heat transition point of the resin (for example, in the case of PC resin, about 165 ° C.,
(Around 130 ° C for PMMA resin). Then, after taking out the molded product, the gas pressure feeding device 25 is operated to pass air through the gas communication holes 15 and 30. (Note that an inert gas such as nitrogen may be used instead of air.) The air is heated by the heaters 18 and 28 and then passes through the breathable members 20 and 29. When the heated air passes, the heat is transferred to the breathable members 20, 29, and further heats the nickel platings 22, 31 on the surfaces of the cavities. After clamping the mold, inject and fill the molten resin with the cavity surface heated, and after a few seconds,
The power sources of the heaters 18 and 28 are turned off. After that, the inflow amount of air is reduced, and after the molded product is cooled, the inflow of gas is stopped and the molded product is taken out.

If injection molding is performed according to the above procedure, the nickel plating 22 and 31 on the cavity surface can be heated in a few seconds by passing heated air through the breathable members 20 and 29. Moreover, since the nickel plating layer is thin, the response of heating / cooling is excellent. Therefore, there is an effect that heat cycle molding, which conventionally takes time to heat, can be realized in a short time. Also, the cooling curve can be delicately controlled by controlling the amount of inflowing air. Also,
Since the gas uniformly passes through the inside of the breathable members 20 and 29, there is little local temperature unevenness on the cavity surface. Also,
Cooling is started after the entire molded product (both thick and thin parts) is in a state of higher temperature than the heat transition point, so that a molded product with highly accurate transferability can be obtained as in normal heat cycle molding. be able to.

[0013]

Second Embodiment Next, a second embodiment of the present invention will be described. Figure 5
FIG. 6 is an overall cross-sectional view showing an injection mold, FIG. 6 is a view for explaining a heater used in this embodiment, and FIG. 7 is a view for explaining changes in cavity surface temperature. Example 1
In the above, the cavity portion had a different planar shape, but in this embodiment, it has a concave lens shape. Therefore, the cavity surface of the movable insert 32 has a spherical shape. The shape of the breathable member 33 fixed in the movable side insert 32 on the cavity surface side is also spherical. Further, a cylindrical hole 34 is opened in the center of the air permeable member 33 on the side opposite to the cavity surface, and communicates with the gas communication hole 35. Further, as the heater 36, a film heater as shown in FIG. 6 which is wound in a roll shape is used.

When the breathable member 33 has a convex shape as described above, the wall thickness becomes thicker at the central portion, so that the heated gas may not reach the thick wall portion. . Therefore, in this embodiment, the heat of the high temperature gas is evenly transferred to the cavity surface by forming the cylindrical hole 34 in the thick portion of the breathable member 33. In addition, in the case of the present embodiment, since the air is heated by passing through the gap of the roll-shaped film heater 36 which is wound by rotation, the heat of the heater can be efficiently transmitted to the air.

The lens of this embodiment has a center wall thickness of 1 mm,
The outer peripheral portion has a maximum thickness of 2.5 mm and an outer diameter of 20 mm. In such a lens, it takes about 5 to 6 seconds for a portion having a thickness of 1 mm to be solidified from a high temperature state at the time of filling, whereas a portion having a thickness of 2.5 mm requires about 30 seconds. . Therefore, when normal molding is performed, the shrinkage rate of the thin-walled part that solidifies in the high internal pressure state at the beginning of cooling is small, and the shrinkage rate of the thick-walled part that solidifies at the low internal pressure state at the end of cooling is large, resulting in waviness (Internal pressure decreases with time as the resin shrinks). Therefore, in this embodiment, the cavity surface temperature is set to the glass transition point of the resin or higher by passing heated air through the breathable member 33 before injection. Inject in that state, and continue to send heated air until the temperature of the thick portion becomes the same as the temperature of the thin portion. Specifically, the cavity surface temperature is maintained above the glass transition point of the resin for about 30 seconds after injection filling. After that, the power of the heater is turned off, and the flow rate of air is reduced to gradually cool the cavity. (If the cooling rate is still high, the inflow of air may be completely stopped.) FIG. 7 is a temperature change diagram of the cavity surface when molding is performed using PC resin. After injection, the entire cavity has a uniform temperature of 160 ° C. Since the temperature is above the glass transition temperature, pressure can be transmitted and the pressure is uniform. Since cooling is performed from this state to the take-out temperature, the thin portion and the thick portion can be cooled under almost the same internal pressure state. Therefore, there is almost no difference in the shrinkage ratio, and a highly accurate plastic lens can be obtained. In the case of this embodiment, the cycle time is 75 seconds,
Molding was possible with almost the same productivity as conventional standard molding.

[0016]

Third Embodiment Next, a third embodiment of the present invention will be described. Figure 8
FIG. 9 is a cross-sectional view showing the insert of the injection molding die, and FIG.
It is a figure explaining the change of cavity surface temperature. As illustrated, in this embodiment, the cavity surface has a Fresnel shape 37.
It was decided to use the nest 38 of the above.

Since the purpose of the heat cycle molding of this embodiment is the high filling property of the Fresnel shape 37, the heater 39 is turned off immediately after heating and filling. Then, in order to cool as quickly as possible, air continues to flow in the same state until just before opening the mold.

In this way, if cooling air continues to flow immediately after filling, it is possible to form a highly filled Fresnel with an extremely high cycle. Specifically, in this embodiment, PM
When MA resin was used, molding could be performed in a cycle of about 17 seconds.

[0019]

As described above, according to the injection molding die and the injection molding method of the present invention, the cavity surface can be heated or cooled at an extremely high speed by passing a high temperature gas through the gas permeable member. The cycle molding time can be significantly reduced. Moreover, since the gas uniformly passes through the inside of the breathable member, there is little local temperature unevenness.
Furthermore, cooling is started after the entire molded product (both thick and thin parts) is brought into a uniform state where the temperature is higher than the thermal transition point.
It is possible to obtain a molded product having extremely high precision transferability.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a basic configuration of an injection molding die according to the present invention.

FIG. 2 is a diagram illustrating a change in cavity surface temperature by the injection molding method according to the present invention.

FIG. 3 is a cross-sectional view showing an injection molding die of Example 1 of the present invention.

FIG. 4 is a cross-sectional view showing an insert used in the mold of Example 1 of the present invention.

FIG. 5 is an overall cross-sectional view showing an injection molding die of Example 2 of the present invention.

FIG. 6 is a diagram illustrating a heater used in a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a change in cavity surface temperature according to the second embodiment of the present invention.

FIG. 8 is a cross-sectional view showing an insert used in a mold of Example 3 of the present invention.

FIG. 9 is a diagram illustrating a change in cavity surface temperature according to the third embodiment of the present invention.

[Explanation of symbols]

 1 Nest 2 Gas communication hole 3 Communication member 4 Gas heating heater 5 Cavity surface

Claims (2)

[Claims] 1. An injection molding die having a fixed side, a movable side, and a cavity portion therebetween, and a nest forming the cavity portion and a gas communication hole communicating the inside of the nest.
An injection mold comprising: a gas permeable member provided in the vicinity of the cavity surface in the middle of the gas communication hole, and a gas heating heater arranged in the gas communication hole. 2. When the injection molding die according to claim 1 is used for injection molding, a heater for heating gas provided inside the insert is energized to allow the gas to flow through the gas communication hole and the cavity surface. A gas heating heater is used after heating an air-permeable member provided in the vicinity above the glass transition temperature of the resin, and then filling the resin in the cavity to make the resin temperature in the thick portion inside the cavity uniform. The injection molding method is characterized in that the power of is turned off and the molded product is cooled.