JPS595417B2 - Injection molding method using hot runner mold - Google Patents

Description

[Detailed Description of the Invention] Conventionally, in injection molding using a hot runner mold, synthetic resins with poor thermal stability such as vinyl chloride resin and acetal resin tend to decompose or solidify in the hot runner. As a result, cloudiness and froni marks are likely to occur on the surface of the resulting molded product, and it often carbonizes in the runner, making it impossible to mold, so it is rarely practiced at present.

In this invention, before injecting the molten resin into the cavity, defective resin and gas due to decomposition and solidification that remain in the real runner are discharged out of the mold through a valve body provided at the end of the real runner. Molding is performed by injecting only the desired resin into the cavity.

This will be explained below with reference to the attached drawings. FIG. 1 shows an example of a hot runner mold for carrying out the present invention. In the figure, 1 is a hot runner block, and 2 is a hot runner that serves as a molten resin passage formed inside the block. , 3 is an exit gate provided at the end of the runner, and 04 is the exit gate of the hot runner 2 immediately before the exit gate 3.
It is a valve body provided at the end portion of the valve body, and has an escape port 5 for the residual resin inside.

The details are shown in FIG.

The tip of the valve body 4 engages with the outlet gate 3,
The rear part is connected to the piston 1 of the cylinder 6 by a screw 8, and is adapted to fit into the hot runner block 1 and slide in the axial direction.

9 is an escape hole drilled in the hot runner block 1 to guide the retained resin to the outside; io and 1i are fluid supply holes for operating the piston 1; 12 is a fixed type; 13 is a movable type;
14 is a cavity.

Next, an embodiment of the present invention will be described. Before the resin is injected into the cavity 14, that is, at the time of plasticization when the screw of the injection molding machine is rotating, or for a short period of time after injection is started from the injection molding machine, , as shown in Figure 1,
Fluid is forced into the fluid supply hole 10 to move the piston 1 and the valve body 4 forward in the direction of the outlet gate 3, close the outlet gate 3 at the tip of the valve body 4, and connect the relief port 5 of the valve body 4 to the hot runner 2. The mold is maintained in a communicating state, and the defective resin that is injected from the hot runner 2 toward the exit gate 3 and accumulated in the nostle of the injection molding machine and the runner is released through the relief port 5 of the valve body 4. It is discharged from the hole 9 to the outside.

After discharging the defective resin in this way, that is, at the same time as or immediately after the injection of new resin, the fluid supply to the cylinder 6 is switched, and as shown in FIG.
The piston 7 and the valve body 4 are moved back toward the cylinder by pressurizing fluid from the inside, and the mold is kept in a state where the outlet gate 3 is kept open while the relief port 5 of the valve body 4 is isolated from the hot runner 2. It is injected from the runner 2 into the cavity 14 via the exit gate 3.

After filling the cavity 14 with resin, the fluid supply is switched in conjunction with the operation of the injection molding machine, and the mold is returned to the state shown in FIG. 1.

In this way, the screw of the injection molding machine rotates at the same time as the exit gate 3 is closed, and plasticization of the resin begins. However, if appropriate back pressure is applied to the screw at this time, the accumulated resin will be discharged in a cascading state. be done.

Furthermore, if the retained resin is to be discharged at the same time as or immediately after the start of injection, the opening timing of the valve body is adjusted by changing the fluid supply rate using an accurate timer or the like.

In addition, as a means of discharging defective resin from the escape hole,
Any method may be used, such as natural falling, concentrated treatment using a pipe, or vacuum suction, but vacuum suction is the most preferable in terms of the discharge effect.

According to the present invention, the defective resin accumulated in the nostle of the molding machine and the hot runner of the mold is discharged to the outside every time injection molding is performed.
Only good resins that do not tend to decompose or solidify can be filled into the cavity, and therefore molded products of excellent quality can be stably obtained.

In addition, there is no need to clean the gate when opening the mold as in the past, which is a great advantage in terms of labor savings.

[Brief explanation of the drawing]

FIGS. 1 and 2 are sectional views showing the operating state of a mold used in the present invention, and FIG. 3 is a partially enlarged perspective view of the mold. 2...Hot runner, 3...Ejector gate, 4...90, valve body, 5...Escape port,
6...Cylinder, 1...91, Piston, 9
...Escape hole, 10, 11...Fluid supply hole.

Claims (1)

[Claims] 1. In a synthetic resin injection molding method using a hot runner mold, a valve body having a resin passage is provided near the exit gate of the hot runner, and a relief hole is provided in the mold to communicate the hot runner with the outside of the mold, The valve body is moved away from the exit gate to open the gate, the communication between the hot runner and the outside of the mold is cut off, and molding is performed by a conventional method, and then the valve body is moved toward the exit gate. The hot runner is characterized in that the hot runner is opened to close the cage, and the hot runner and the escape hole are communicated through the resin passage to discharge defective resin and gas remaining in the hot runner to the outside of the mold. Injection molding force method using a mold.