JPH07132541A - Valve type hot runner structure and hot runner method - Google Patents

Abstract

PURPOSE:To provide a valve type hot runner structure in a mold which can cool rapidly a circumference of a gate and a hot runner method which is very generally used. CONSTITUTION:In a mold 1 for injection molding, a heating area and a cooling area including a circumference of a gate 6 are provided to a runner 2. A needle valve 3 is arranged to the runner 2 so that a tip head 4 can be reciprocated between a gate closed position and the heating area. A land opens an interval peripherally to the head 4, and an outer peripheral surface is provided in contact with an inner peripheral wall of the runner of the cooling area. Melt resin in the heating area is allowed to flow through the cooling area in a cavity 5 by reciprocative transfer of the needle valve 3. After molding, solidified resin in the cooling area is returned to the heating area. The head 4 of the needle valve 3 is arranged near a gate 6 of the cooling area in a process wherein the melt resin is allowed to flow in the cavity 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold hot runner structure for injecting and molding a molten resin and a hot runner method using the same.

[0002]

2. Description of the Related Art A mold having a hot runner structure is widely used for reducing material loss, shortening a molding cycle and reducing secondary work.

FIG. 4 shows a general hot runner structure in which a shut-off valve (needle valve) 3 is arranged on a runner 2 formed in a mold 1, and a head 4 at the tip is used to insert a cavity 5 into the mold 1. Open and close the connecting gate 6.
A heater 7 is arranged in the runner 2 until just before the cavity 5 so that the resin inside the runner 2 is maintained in a molten state. Reference numeral 8 is a heat insulating material, and reference numeral 9
Is an air layer for thermally separating the heated portion of the runner 2 from other portions. And the gate 6 of the mold 1
A portion 10 forming a water passage (not shown)
It is designed to be cooled by the cooling water flowing through.

That is, the hot runner structure has a mold 1
Arrangement of a mechanism that heats the vicinity of the runner 2 so that the molten resin does not solidify in the inner runner 2 and the heating region by these separates the cooling regions where rapid solidification is preferable in the molding cycle such as the gate 6 and the cavity 5. And the arrangement of a heat insulation mechanism for. In order to make these mutually contradictory functions compatible with each other, various heating control methods and shut-off valve driving methods using actuators or springs have been devised conventionally.

However, even with such a conventional device, P
There is a white product around the gate 6, such as a molded product of ET resin (so-called polyethylene terephthalate). This is because the resin crystallizes because the cooling rate around the gate is still insufficient for this resin. In the structure of FIG. 4, the portion 1 forming the gate 6
There is no room to provide a mechanism for performing sufficient cooling to 0, and if the needle valve 3 is simply lengthened, the resin that adheres to the valve and solidifies makes continuous injection impossible.

FIG. 5 and FIG. 6 show a structure proposed for solving such a situation. A runner 2 is formed on the die 1, and a part of the runner 2 near the gate 6 serves as a heating portion by the heater 7. Reference numeral 11 is a temperature sensor and is arranged to detect the temperature of the heating portion and adjust the temperature. A needle valve 3 is arranged in the heating portion of the runner 2, and is moved up and down (in the figure) in the axial direction of the heating portion by a pneumatic actuator 12 built in the mold 1. In this example, a pneumatic actuator is shown, but a hydraulic actuator may be used. On the other hand, the mold 1 is of a type in which the cavity 5 is formed on the movable side by using the core 13, and a hole is formed in the center of the molded product. A water passage 14 is usually formed in the core 13 so that sufficient cooling can be performed.

The head 4 of the needle valve 3 passes through the portion 10 of the mold 1 forming the gate 6 and passes through the core 1.
It extends to the portion 3 and is always in contact with the core 13 to be cooled by the core 13. Also,
The needle valve 3 has a stepped portion 15 formed by reducing the diameter above the head 4 having a predetermined length, and by moving this portion downward, the gate 6 is opened, and this portion is raised. The gate 6 is closed by being moved to. When the gate 6 is closed, the resin that has been cooled and solidified in the portion 10 forming the gate 6 is caught by the step portion 15 and sent upward, and is returned to the heating portion and remelted. The cooling in this portion is rapid because the tip of the needle valve 3 is constantly cooled by the core 13 via the head 4, and the PET resin solidifies without crystallization.

However, since this structure uses the core 13 of the movable mold for cooling, the needle valve 3 needs to pass through the gate 6, and therefore it can be applied only to a molded product having a hole. Further, in order to obtain a sufficient cooling effect, the head 4 is relatively long, and the head 4 is configured to reciprocate between two positions of the gate position and the heating region.
If the runner 2 in the cooling region is lengthened in order to improve the cooling effect, it tends to take time to open the gate 6.

[0009]

SUMMARY OF THE INVENTION The present invention provides a valve type hot runner structure and a hot runner method in a mold, which is capable of rapidly cooling around a gate even when a hole cannot be formed in the center of a molded product, that is, having high versatility. The challenge is to provide.

[0010]

[Means for Solving the Problems]

[Structure] A mold for injection molding. Both the heating region and the cooling region including the gate periphery are provided on the fixed side of the mold, and a runner that penetrates both regions and reaches the cavity is formed. A needle valve is arranged on the runner so that the head at the tip can reciprocate between the gate closed position and the heating region. Lands are provided on the head in such a manner that the lands are spaced apart in the circumferential direction with respect to the cross section of the needle valve, and the outer peripheral surface is in contact with the inner peripheral wall of the runner in the cooling region.

[Method] The present invention relates to a mold for injection molding. A heating area and a cooling area are provided in the runner reaching the gate. By the reciprocating movement of the needle valve arranged on the runner, the molten resin in the heating region penetrates the cooling region and flows into the cavity, and after molding, the solidified resin in the cooling region is returned to the heating region. In the step of flowing the molten resin into the cavity, the head of the needle valve is placed near the gate in the cooling area.

[0012]

[Operation] The heating area in the runner maintains the resin inside the runner in a molten state. The cooling area in the runner promotes solidification of the resin around the gate. The needle valve opens and closes the gate. The structure in which lands are provided on the head of the needle valve in a circumferentially spaced arrangement with respect to the cross section of the needle valve, and the outer peripheral surface is in contact with the inner peripheral wall of the runner in the cooling region, melts when the gate is opened. The resin is allowed to pass, and after molding, the solidified resin is pushed back to the heating area in the cooling area of the runner. Regarding the method, in the step of flowing the molten resin into the cavity, the means for arranging the head of the needle valve near the gate in the cooling area is to perform the gate closing quickly to improve the molding cycle, and before the gate is closed. Eliminates the risk of resin solidifying at the gate while the resin becomes too thick and the gate is incompletely closed.

[0013]

1 to 3 show a mold 1 having a hot runner structure according to the present invention. Further, the hot runner method of the present invention is carried out by this mold 1. Mold 1
Has a cavity 5 and a runner 2 connected to the cavity 5, and the connecting portion between the cavity 5 and the runner 2 is configured as a gate 6. The gate 6 is opened and closed by the head 4 of the needle valve 3 arranged inside the runner 2.

The runner 2 near the cavity 5 is provided with a heating region heated by the heater 7 and a cooling region cooled by the cooling block 16. Both areas belong to the fixed side of the mold. The cooling block 16 corresponds to the conventional gate forming portion 10 in which the gate 6 is formed. However, the cooling block 16
A water passage 14 is formed in the pipe so that it can receive sufficient cooling. In addition, the cooling block 16
The runner 2 (runner 2 in the cooling region) penetrating through is designed to have a predetermined length L (FIG. 1). The runner 2 in the heating area provided with the heater 7 is formed by another heating block 17 as shown in the figure, and is different from the cooling block 16.
They are connected via a heat insulating material 8. Reference numeral 9 is an air layer for preventing heat in the heating region from being directly transferred to the cooling region, and reference numeral 11 is a temperature sensor for detecting the temperature in the heating region and transmitting it to a control device provided in the injection molding machine. This is for properly adjusting the temperature of the region.

The needle valve 3 is arranged so as to pass through the runners 2 in the heating region and the cooling region so as to open and close the gate 5 with the head 4 at the tip, and is driven by the pneumatic actuator 12 built in the mold 1. It The head 4 is formed of a tapered portion at the tip and a tubular portion following the tapered portion. The cylindrical portion is a land 19 arranged with a space 18 in the circumferential direction, and a step portion 15 is formed in the axial direction of the needle valve 3 by this. The outer periphery of the land 19 is always in contact with the inner peripheral wall of the runner 2 in the cooling area.

The pneumatic actuator 12 has an upper port 20.
It is a reciprocating drive type that includes a and a lower port 20b and drives an internal piston 21 up and down, and has a spring 22 on the lower surface side (gate 6 side) of the piston 21. The needle valve 3 is fixed to the piston 21.

In this embodiment, the pneumatic actuator 12 includes the head 4 of the needle valve 3 as shown in FIG.
Place at B and C positions. The position A is the gate closed position, the position B is the return position set in the heating region, the position C is close to the gate 6, and the gate 6 is the standby position in the open state. The A position and the B position are achieved by the full stroke of the pneumatic actuator 12, and the C position is a position achieved during the resin injection operation. That is, the piston 21 is set in a free state during the injection operation of the resin, and the piston 21 is pushed down by the resin pressure acting on the land 19 and is balanced with the elastic force of the spring 22. .

The operation of the pneumatic actuator 12 is managed by a control device provided in the injection molding machine, and the hot runner method of the present invention is stored in the control device as a program.

In the injection process of the injection molding machine, initially, the piston 21 of the pneumatic actuator 12 is fully stroked upward by the pneumatic pressure from the lower port 20b, and the head 4 of the needle valve 3 moves to the position B in FIG. In position. Since the gate 6 is open in this state, when injection is performed, the molten resin is injected into the cavity 5 through the heating region and the cooling region of the runner 2.

When the injection is started, both the upper port 20a and the lower port 20b of the pneumatic actuator 12 are released to the drain, and the piston 21 is brought into a free state. On the other hand, since the needle valve 3 enters the land 19 of the head 4 under the pressure of the resin moving toward the cavity 5, the needle valve 3 is moved downward together with the piston 21 by this pressure. However, this movement eventually balances with the elastic force of the spring 22 on the lower surface side of the piston 20 and stops. In the stop position, the gate 6 is opened, and this position is, so to speak, a standby position waiting to close the gate 6. Further, during this time, the molten resin is cooled from the inner peripheral wall of the runner 2 in the cooling region and the needle valve 3 in which the land 19 is constantly in contact with the inner peripheral wall, but since the molten resin in this case is flowing, It is injected into the cavity 5 without solidifying.

When the injection is completed, the piston 21 is operated by a full stroke downward by the air pressure from the upper port 20a to compress the spring 22, the needle valve 3 is moved downward, and the gate 6 is closed by the conical portion of the head 4. . Since the head 4 of the needle valve 3 only moves a short distance from the C position (standby position) to the A position, the gate 6 is closed quickly.

In the pressure holding / cooling process of the injection molding machine, the gate 6 is used.
Is closed. During this period, the resin in the cooling region around the gate is cooled and solidified from the surroundings such as the inner peripheral wall of the runner 2 and the needle valve 3 in this region. Cooling is performed quickly because the cooling block 16 has sufficient water passages 14 formed therein. For this purpose, the runner 2 in the cooling region needs to have a predetermined length L, but in the structure of the embodiment, the needle valve 3 also passes through the land 19 in contact with the inner peripheral wall of the runner 2 in the cooling region. Since it is cooled, the length L may be small, and
The resin is solidified quickly.

In the metering process (mold opening / molded product removal process), pneumatic pressure is supplied from the lower port 20b, the piston 21 of the pneumatic actuator 12 is operated upward by a full stroke, and the needle valve 3 is pulled up. As a result, the head 4 comes to the B position (return position) indicated by the broken line in FIG. Along with this, the resin solidified inside the runner 2 in the cooling region at the end of the previous injection process is caught by the land 19 and rises together when the head 4 rises, is returned to the heating region, and is melted again. To be done. Then, the injection process is performed.

The above is an embodiment, and the present invention is not limited to the illustrated specific configurations and means. The position at which the needle valve 3 operates is not limited to the above-described three-position system, and there is no particular problem even if the needle valve 3 has two positions of only the A position and the B position. In this case, the piston 21 always operates in full stroke. Further, the spring 22 is unnecessary. However, in the three-position system, the time for closing the gate 6 is shorter as described above, and since the head 4 is near the gate 6, it is possible to quickly cool the vicinity of the gate. The pneumatic actuator 12 may be driven by another drive source such as hydraulic pressure or electromagnetic force.

[0025]

Since the vicinity of the gate can be rapidly cooled, the molding cycle can be shortened, and defective molding caused by delaying cooling such as whitening of the PET resin can be prevented. Since the needle valve does not penetrate the gate part, no holes can be made in the molded product, making it highly versatile. Regarding the head position control of the needle valve, by setting the waiting position C near the gate closing position in addition to the gate closing position A and the returning position B set in the heating area, the molding cycle is shortened further and the rapid cooling is performed. The effect can be improved.

[Brief description of drawings]

FIG. 1 is a front view of a cooling block shown in a section (a head is divided to show an upper and lower position).

FIG. 2 is a plan view (partial cross section) viewed from above the head portion of the needle valve.

FIG. 3 is a front view showing a cross section of a valve type hot runner structure in a mold.

FIG. 4 is a front view (conventional example) showing a gate portion in a mold in cross section.

FIG. 5 is a front view (conventional example) showing a cross section of a valve type hot runner structure in a mold.

FIG. 6 is an enlarged view of a circled portion in FIG. 5 (the head is divided to show the upper and lower positions).

[Explanation of symbols]

 1 Mold 2 Runner 3 Needle Valve 4 Head 5 Cavity 6 Gate 7 Heater 8 Insulating Material 9 Air Layer 10 Gate Forming Part 11 Temperature Sensor 12 Actuator 13 Core 14 Water Channel 15 Head 16 Cooling Block 17 Heating Block 18 Spacing 19 Land 20 Port 21 Piston 22 Spring

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kaname Kojima 3559 Kobaba, Oshinomura, Minamitsuru-gun, Yamanashi Prefecture 1559 Mold Lab Co., Ltd.

Claims (2)

[Claims] 1. A mold for injection molding is provided with both a heating region and a cooling region including a gate periphery on a fixed side, and a runner that penetrates both regions and reaches the gate is formed. The needle valve is arranged so that the head at the tip can be reciprocated between the gate closed position and the heating region, and the lands are arranged on the head in a circumferentially spaced manner with respect to the cross section of the needle valve and at the outer peripheral surface. A valve hot runner structure characterized by being installed in contact with the inner wall of the runner in the cooling area. 2. In an injection-molding die, a runner reaching a gate is provided with a heating region and a cooling region, and a needle valve arranged on the runner reciprocates to allow molten resin in the heating region to penetrate the cooling region into a cavity. It is a hot runner method of injecting and returning the solidified resin in the cooling area to the heating area after molding, and the head at the tip of the needle valve is placed near the gate in the cooling area in the step of flowing the molten resin into the cavity. A hot runner method characterized by that.