JPH06238704A - Injection molding method - Google Patents

Abstract

PURPOSE:To prevent a weld line from being expressed by controlling timing wherein resin is poured through a plurality of gates. CONSTITUTION:An injection mold is equipped with a plurality of gates incorporating both a first gate 11 positioned at the upstream side of a resin flow and a second gate 12 positioned at the downstream side from the first gate 11. A molded form having a unified shape is formed by using the injection mold. In the injection molding method, resin is poured from the first gate 11 in a state wherein the second gate 12 is closed. After injection of resin through the first gate 11 is detected and the prescribed time elapses from input of a detection signal thereof, the second gate 12 is opened to pour resin therefrom.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method, and more particularly, to an injection molding method in which a resin is injected from a plurality of gates into a cavity to form an integrally molded body.

[0002]

2. Description of the Related Art In recent years, in the automobile industry and the like, there is an increasing need for weight reduction in order to reduce fuel consumption and cost, and various parts have been replaced with resin parts. For example, the wheel cap was previously formed from sheet metal, but in recent years, it is manufactured from a resin material such as PP or nylon by a molding method such as injection molding.

By the way, the injection molding method is a method of injecting a molten resin from a gate of a molding die into a cavity and solidifying the molten resin by cooling the die to form a molded article. Therefore, for example, when forming a long article by injection molding,
A temperature distribution is generated in the molten resin flowing in the cavity, the temperature becomes lower toward the flow front, the flow velocity decreases, and the injection time becomes longer. In extreme cases, the flow of the tip may become difficult, resulting in defective molding.

Therefore, it is considered to inject the respective amounts from a plurality of gates into the cavity.

[0005]

However, when the resin is injected from a plurality of gates as described above, a portion where the resins injected from the respective gates merge with each other is inevitably formed, which causes a weld line appearance defect. As a result, a problem occurs that it appears in the molded product. The cause of the weld line is considered to be poor fusion due to the merging of the resins whose temperatures have dropped, and the inclusion of air in the merging portion.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to control the timing of injecting resin from a plurality of gates to prevent the weld lines from being exposed.

[0007]

[MEANS FOR SOLVING THE PROBLEMS] The injection molding method of the present invention for solving the above problems includes a plurality of first gates located upstream of the resin flow and second gates located downstream of the first gates. In an injection molding method for forming an integrally molded body using an injection molding die having a gate, the first gate is used to inject resin with the second gate closed.
An injection step, and a second injection step of detecting the injection of the resin from the first gate, opening the second gate and injecting the resin from the second gate after a predetermined time has elapsed from the input of the detection signal. Characterize.

[0008] In a further desirable mode of the above injection molding method, a valve having a heater portion built in at least one of the first gate and the second gate and arranged so as to be movable back and forth in a valve hole opened in a mold surface. It has a member and a nozzle member communicating with the valve hole, and the resin is injected from the nozzle member through the opening of the valve hole by retracting the valve member.

[0009]

In the first injection step of the injection molding method of the present invention, resin is injected from the first gate. The resin injected from the first gate comes into contact with the mold surface while being cooled in the cavity of the mold and is cooled, and the skin layer of the surface layer portion is cooled and solidified,
It is divided into a molten core layer. Then, the resin injected from the first gate flows in the cavity toward the second gate.

In the present invention, the first gate from the first gate is used.
The injection of the resin is detected, the second gate is opened after a predetermined time from the input of the detection signal, and the second resin is injected from the second gate. The injection timing of the second resin is determined by trial and error depending on the resin type, the cavity shape, etc.
It may be either the time when the first resin flow front reaches the vicinity of the second gate or the time when the first resin flow front passes through the second gate and the second gate is blocked by the first resin.

The reason why the weld line is prevented from occurring is unknown, but it is presumed as follows. For example, if the second resin is injected before the front end of the first resin flow reaches the second gate, the second resin flows not only in the front but also in the rear and joins with the first resin. Here, the first resin is a skin layer whose surface in contact with the mold surface is cooled to increase its viscosity, and the second resin merges into the core layer of the first resin having the highest temperature. Therefore, the welded portion does not appear on the surface of the molded product, and no weld line appears apparently.

Further, even after the merging, the first resin has a force to move forward, but since the second resin is an obstacle, the first resin flows so as to wrap around the edge of the second resin. . Therefore, the air entrained at the time of merging is prevented from being discharged from the parting surface of the mold existing at the edge and causing a weld line. When the second resin is injected after the first resin flow tip passes through the second gate and the second gate is blocked by the first resin, a skin layer in which the first resin is cooled and solidified on the surface of the second gate. Are formed. When the skin layer is sufficiently weak, the injection of the second resin is sufficient, and the second resin breaks the skin layer and joins at the core layer of the first resin. Since the core layer of the first resin has a sufficiently high temperature and fusion is performed well, no weld line occurs. Further, even if a weld line occurs, it does not appear on the surface of the molded body because it is in the core layer of the first resin.

If a mold including a valve member that has a heater portion built therein and is arranged to move forward and backward in a valve hole that opens in the mold surface and a nozzle member that communicates with the valve hole is used, The temperature of the injected resin can be controlled by the valve member. Therefore, it becomes possible to control the temperature at the start-up of the molding process. Moreover, since the resin in the nozzle member can be heated immediately before injection, temperature control is easy. Therefore, by using the above method, the second resin can be injected at a constant timing, and stable molding can be performed. And second
If the valve member is used for the gate, the skin layer of the first resin can be heated and softened, so that the degree of freedom in the timing of injecting the second resin is further increased.

[0014]

EXAMPLES Specific examples of the injection molding method of the present invention will be described below. The injection mold shown in FIG. 1 was prepared. This injection mold mainly comprises a fixed mold 1 and a movable mold 2, and a long-shaped (500 mm × 150 mm × 2 mm) cavity 10 filled with a molten resin is formed between the fixed mold 1 and the movable mold 2. Has been done.

The fixed mold 1 is formed with a first gate 11 opening to the end of the cavity 10 and a second gate 12 opening to the approximate center of the cavity 10. In addition, a first nozzle touch 13 to which the nozzle of the first injection device 3 is connected is formed on one side surface of the fixed mold 1, and the first hot runner block 14 includes the first nozzle touch 13 and the first gate 1.
1 is connected. A second nozzle touch 15 to which the nozzle of the second injection device 4 is connected is formed on the other side surface of the stationary die 1, and a second hot runner block 16 connects the second nozzle touch 15 and the second gate 12. ing.

The first gate 11 and the second gate 12 are each composed of a valve gate as shown in FIG. Hereinafter, the structure of the valve gate will be described by taking the second gate 12 as an example. This valve gate comprises a holding die 5 which constitutes a part of the die surface of the fixed die 1 and has a valve hole 50, a valve member 6 whose tip is held by the holding die 5 so as to be able to move forward and backward, and a tip of the holding die 5. The nozzle member 7 is fixed.

The holding mold 5 comprises a first member 51 made of beryllium-copper alloy and forming a mold surface, and a second member 5 made of SUS.
2 and the third member 53 made of beryllium-copper alloy are combined and configured. A valve hole 50 that is orthogonal to the mold surface is formed, and a nozzle hole 54 that communicates with the valve hole 50 and extends in a direction intersecting the valve hole 50 and penetrates therethrough is formed. In addition, the first member 51
A gap 55 is formed between the second member 52 and the second member 52.
Communicates with an air supply source (not shown) and allows compressed air to pass therethrough. As a result, overheating of the first member 51 is prevented.

The valve 6 is a heater portion 60 formed on the tip end side and having a thermocouple (not shown) made of beryllium-copper alloy.
And a shaft base portion 61 made of SUS as a heat insulating material and integrally formed with the heater portion 60 by welding. The valve member 6 is driven by a hydraulic cylinder device 62 connected to the shaft base 61, and can be inserted into and removed from the valve hole 50. Then, when the valve member 6 moves forward and the tip surface of the heater section 60 coincides with the mold surface of the fixed mold 1, the nozzle hole 5
No. 4 is closed by the heater portion 60, and injection of resin becomes impossible. When the valve member 6 is retracted, the valve hole 50 is opened in the surface of the fixed mold 1 as shown in FIG. 2, the nozzle hole 54 communicates with the valve hole 50, and the resin can be injected from the nozzle hole 54.

The nozzle member 7 has a cylindrical shape and is an extension of the second hot runner block 16 and has its tip fixed to the holding die 5. The runner 70 provided at the center communicates with the nozzle hole 54. On the mold surface of the movable mold 2, the first gate 11 is provided substantially in the middle of the first gate 11 and the second gate 12.
The melt front sensor 8 for detecting the pressure of the resin injected from the container is exposed. This melt front sensor 8
Consists of a limit switch 80 and a detection pin 81,
When the resin flow from the first gate 11 reaches the point of the detection pin 81, the pressure is applied to move the detection pin, and the limit switch 80 detects the movement of the detection pin 81. Then, this detection signal is input to a control device (not shown) and controls the second injection device 4 and the valve member 6 via a timer to control the injection from the second gate 12.

Molding was carried out as follows using the injection molding die constructed as described above. First, the first injection device 3 injects the first resin of yellow PP from the first gate 11. When the melt front sensor 8 detects that the injected first resin has traveled through the cavity 10 and reached the position of the melt front sensor 8, a timer (not shown) is activated. Then, when it is input from the timer that the predetermined time has elapsed, the second gate 12 injects the second resin of blue PP due to the retreat of the valve member 6.
The injection conditions from each gate are shown in Table 1.

[0021]

[Table 1] In this embodiment, when the second resin is injected 0.2 to 0.5 seconds after the detection signal of the melt front sensor 8 is input, the first resin and the second resin are the melt front sensor 8 and the second gate 12. It was a face-to-face fusion between. And no weld line was observed from the surface.

When the second resin is injected 0.6 to 1.2 seconds after the detection signal of the melt front sensor 8 is input, the second resin is the skin layer of the first resin on the mold surface side of the fixed mold 1. From the first resin into the core layer and flowed. However, the skin layer of the first resin on the mold surface side of the movable mold 2 was not disturbed, and no weld line was generated. If the second resin is injected 0.2 seconds before the detection signal of the melt front sensor 8 is input, the second resin will squeeze into the core layer of the first resin, and the first resin will be pressed against the second resin. Thus, the first resin and the second resin were face-to-face fused between the first gate 11 and the melt front sensor 8 while flowing on both edges of the cavity 10. When the second resin was injected after 1.6 seconds or more, only the periphery of the second gate 12 was flowing.

[0023]

As described above in detail, according to the injection molding method of the present invention, it is possible to control the timing when the resin is injected from the first gate and then the resin is injected from the second gate, thereby preventing the filling failure. It is possible to obtain a molded product that does not cause the weld line and does not expose the weld line. Therefore, it is possible to easily mold even a long-sized molded product molded by an injection molding mold having a plurality of gates, which has no weld line and is excellent in appearance quality without gloss unevenness. Become.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a schematic configuration of an injection mold used in an example of the present invention.

FIG. 2 is an enlarged sectional view of a main part of FIG.

[Explanation of symbols]

1: Fixed type 2: Movable type
3: First injection device 4: Second injection device 10: Cavity
11: First gate 12: Second gate 5: Holding type
6: Valve member 7: Nozzle member 50: Valve hole
60: heater part 70: runner 8: melt front sensor

Claims (2)

[Claims] 1. An integrally molded body is formed using an injection molding die having a plurality of gates including a first gate located upstream of the resin flow and a second gate located downstream of the first gate. In the injection molding method of forming, in the state that the second gate is closed, a first injection step of injecting a resin from the first gate, and an injection of the resin from the first gate are detected, and a detection signal thereof is input. A second injection step of opening the second gate and injecting resin from the second gate after a predetermined time has passed from the second injection step. 2. A valve member having a heater portion built in at least one of the first gate and the second gate, the valve member being arranged to move forward and backward in a valve hole opened in a mold surface, and a nozzle communicating with the valve hole. 2. The injection molding method according to claim 1, further comprising: a member, the valve member is retracted, and the resin is injected from the nozzle member through an opening of the valve hole.