JP3168447B2 - Injection molding method - Google Patents

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 for injecting a molten resin into a mold cavity through a sprue using an injection molding nozzle having a valve member provided in a resin passage. Things.

[0002]

2. Description of the Related Art The injection mechanism of an injection molding machine is of a screw type, a pre-plastic type or the like. In any case, a screw and a screw cylinder are provided. An injection molding nozzle for injecting the molten resin into the cavity of the mold is provided in front of the screw cylinder.
As injection molding nozzles, needle nozzles, slide nozzles, open nozzles and the like are known.

As is well known, a needle nozzle is composed of a nozzle head provided with a passage through which a molten resin passes in a main body, and a needle for opening and closing the passage. The nozzle head is attached to the tip of the screw cylinder, and the needle is spring-biased in a direction to close the passage by a spring. Therefore, when the screw is driven, the resin material supplied from the hopper is melted by heat applied from the outside and heat generated by a shearing action, a frictional action, and the like due to the rotation of the screw in a process of being fed by the rotating action of the screw. When the screw is driven in the axial direction, the needle retreats due to the resin pressure. Therefore, the molten resin is injected into the mold cavity through the resin passage. When the injection is completed, the resin pressure is released and the needle returns to the original position by the spring and closes the passage. Since the passage is closed by the needle, it is possible to prevent the molten resin from unintentionally flowing out of the nozzle after the injection. The slide nozzle also has a slide valve that moves in the axial direction, and since this slide valve is also urged by a spring in a direction to close the resin passage with a spring, injection is completed and the nozzle is moved from the mold as in the case of the needle nozzle described above. When released, the slide valve returns to its original position with a spring,
The resin passage is closed.

[0004]

As described above, apart from the open nozzle, the injection molding nozzle is generally provided with a needle or a slide valve for opening and closing the resin passage. Does not flow out of the nozzle tip. However , in the conventional injection molding nozzle, a spring is provided, for example, on the outer peripheral portion of the nozzle, so that when the tip of the nozzle is touched or separated from the mold during injection molding, the spring becomes an obstacle, and Operation may be complicated.
Further , since the spring is provided, the structure of the injection molding nozzle is complicated, and there is a disadvantage that the cost is increased.
Accordingly, an object of the present invention is to provide an injection molding method in which the molten resin does not flow out of the tip of the nozzle unnecessarily and the injection operation of the molten resin can be simplified.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention uses an injection molding nozzle in which a traction rod is provided on a valve body that opens and closes a resin passage, and melts the resin in a molten state. when injection molding via the sprue into the mold of the cavity, when the injection is the valve body by the resin pressure, the
The tow bar is retracted so as to remain in the sprue, the resin passage is opened and injected.After the injection is completed, when the mold is opened, the tow bar is filled with the resin filled in the sprue.
The valve body is pulled toward the resin passage through the resin passage, thereby closing the resin passage and preventing the resin from flowing out.

[0006]

For example , the movable mold is clamped to the fixed mold. Then , the injection molding nozzle is touched to the mold.
Next , the molten resin is injected through a sprue toward the cavity of the mold as is well known in the art. The valve body opens resin passage retracts by the resin pressure by the injection start, key
It is injected into the Yabitei. At this time, the tow bar is in the sprue
Remains. The molten resin fills the cavities as well as the sprue. After cooling and solidifying, open the movable mold. Then, the tow bar is pulled by the resin filled in the sprue and solidified . Since the tow bar is pulled, the valve body contacts the resin passage, and the resin passage is closed. Thereby, outflow of the resin is prevented. Further , as the molded article moves, the sprue resin separates from the drawbar. The molded article is taken out and the molding is completed. Hereinafter, a molded article is obtained in the same manner.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention can be implemented in various forms. For example,
A valve body is provided in the resin passage through which the molten resin is fed under pressure, and a towbar is provided in the valve body. The shape of the towbar can be implemented in various forms. That is, the tow bar extends at least to the sprue of the mold when injected, and its tip is buried in the resin that is injected and filled into the sprue. When the mold is opened, the resin filled in the sprue comes out of the sprue.However, the valve body is pulled toward the resin passage by the resistance force when it comes off, and the resin passage is closed. It can be adjusted by changing the shape. For example, if the taper is tapered toward the tip, the resistance at the time of pulling out is reduced, and the force for closing the resin passage is also reduced. On the other hand, the taper angle can be reduced to increase the pull-out resistance. In addition, the length of the tow bar can be appropriately selected, and the resistance at the time of pulling can be adjusted by the contact area with the resin. When the length is shortened, the length immersed in the resin to be injected and filled is shortened. In this case, the surface of the tow bar is made uneven so that the pull-out resistance can be increased. Obviously, the pull-out resistance can also be adjusted by the diameter of the towbar. As described above, the towbar can be implemented in various forms. However, the drawing shows only an example in which the towbar is implemented simply by parallel bars, and does not show an example in which towbars having different shapes are selectively used.

Although the drawing shows an example in which the tow bar is formed integrally with the valve body, the tow bar is formed separately from the valve body, and the tow bar is attached to the valve body by, for example, a screw. It can also be implemented as follows. When implemented in this manner, various drawbars can be prepared, and the advantage can be obtained that can cope with injection molding conditions, resin types, and the like.

The valve body provided with the tow bar is provided movably in the axial direction at the tip of the screw cylinder or inside the nozzle head. At this time, the valve housing supporting the valve body is attached to the nozzle head. It can also be guided at the inner periphery. However, the figure shows an example in which the valve housing is fixed to the inner peripheral portion of the screw cylinder, and the axial movement is guided by the valve housing.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a state where the tip of the injection molding nozzle N touches the mold. The injection molding nozzle N according to the present embodiment includes a nozzle head 5 attached to the tip of the screw cylinder 1 with a screw, a valve housing 10 fixed to the inside tip of the screw cylinder 1, and a valve housing 10. And a valve 20 movably provided in the axial direction.

The screw cylinder 1 has a conventionally well-known shape, and the inner peripheral portion at the distal end thereof is expanded to a predetermined depth to form a stepped portion 2. The valve housing 10 is mounted on the stepped portion 2. The outer peripheral portion of the tip of the screw cylinder 1 is also cut off so as to reduce the diameter by a predetermined length, and a male screw 3 is formed on the cut outer peripheral portion.

The nozzle head 5 also has a generally well-known shape. That is, the rear end portion has an outer diameter that is substantially the same as the outer diameter of the screw cylinder 1 and is narrowed toward the tip end in a curved shape. The inner peripheral portion at the rear end of the nozzle head 5 is expanded over a predetermined length to form a stepped portion 6. A female screw 7 to be screwed to the male screw 3 of the screw cylinder 1 is formed on the inner peripheral wall whose diameter has been increased. The inner diameter of the nozzle head 5 is also gradually reduced toward the tip,
A valve seat 8 having a tapered diameter is formed near the distal end. In the center of the tip of the nozzle head 5,
A resin passage 9 having a relatively large diameter is formed, and this resin passage 9 is connected to the valve seat 8.

The valve housing 10 supports a valve 20, which will be described later, and has a generally columnar shape. The outer peripheral portion of the valve housing 10 is mounted on the inner peripheral wall of the screw cylinder 1 at the distal end where the diameter is increased. ing. The backward movement is restricted by the step 2 of the screw cylinder 1. A cylindrical hole 11 having a predetermined depth is formed in the axial direction at the end of the valve housing 10 or on the downstream side of the flow of the resin, and a valve 20 is movably provided in the hole 11.
A conical resin guide protrusion 12 is provided on the upstream side of the valve housing 10. The valve housing 10
Are provided with a plurality of resin passages in the axial direction, but are not shown in the figure.

The valve 20 includes a tubular portion 21 and the tubular portion 21.
The seat portion 22 has a diameter reduced in a tapered shape, and a thin rod-shaped tow bar 23 extending in a pair from the leading end of the seat portion 22. The cylindrical portion 21 of the valve 20 is formed to have a predetermined length, and is loosely fitted in a hole 11 of the valve housing 10 and is guided in the axial direction by the hole 11. The outer diameter of the cylindrical portion 21 is sufficiently smaller than the inner diameter of the nozzle head 5, so that a space through which the resin flows can be ensured even when the valve 20 is mounted on the tip of the screw cylinder 1 as described later. When the valve 20 moves to the left in the figure, the seat 22 is seated on the valve seat 8 of the nozzle head 5 and closes the resin passage 9. The tow bar 23 extends sufficiently in the axial direction from the leading end of the sheet 22, and as shown in FIG. 1, when the nozzle head 5 touches the mold 30,
Has reached enough. Its outer diameter is smaller than the resin passage 9,
Even when the tow bar 23 is inserted into the resin passage 9, a resin flow path is secured between the inner peripheral surface of the resin passage 9 and the outer peripheral surface of the tow bar 23.

The mold has a conventionally well-known structure.
At 0, a sprue 31 having a tapered diameter is provided, and a runner 33 is formed between the fixed mold 30 and the movable mold 32. The figures do not show the cavities for molding the molded article.

Next, an example of injection molding using the above-described injection molding nozzle N and the molds 30 and 32 will be described. The valve housing 10 is mounted on the inner peripheral wall of the screw cylinder 1 whose diameter is enlarged at the tip end, and the cylindrical portion 21 of the valve 20 is inserted into the hole 11. Then, the female screw 7 of the nozzle head 5 is screwed into the male screw 3 of the screw cylinder 1. Thus, the injection molding nozzle N is assembled as shown in FIG. The injection molding nozzle N is touched to the fixed mold 30. When touched, the tip of the tow bar 23 of the valve 20 comes to be located in the sprue 31. At this time, the seat portion 22 of the valve 20 may be seated on the valve seat 8 of the nozzle head 5 or may be separated.

Next, when the screw is driven in a conventionally well-known manner, the resin material is fed by the heat applied from the outside and the heat generated by the shearing action, frictional action and the like due to the rotation of the screw in the process of being fed by the rotating action of the screw. Melts. The screw is driven in the axial direction to inject the molten resin. Then, the molten resin is fed to the tip portion through the resin passage of the valve housing 10, and the resin pressure causes the valve 20 to retreat to the right in the drawing. Therefore,
The seat portion 22 of the valve 20 is connected to the valve seat 8 of the nozzle head 5.
And the resin passage 9 is opened. The molten resin is injected into the cavity from the resin passage 9 through the sprue 31, the runner 33, the gate and the like. At this time, the sprue 31 is also filled, and the periphery of the tow bar 23 is also filled.

After cooling and solidification, the movable mold 32 is opened. Then, as shown in FIG. 2, the resin J filled and solidified in the runner 33 and the sprue 31 also moves leftward in the figure. Then, resin J and tow bar 23
, There is frictional resistance between them, so that the tow bar 23 is pulled to the left in the figure. Then, the seat portion 2 of the valve 20
2 comes into contact with the valve seat 8 of the nozzle head 5. That is, the resin passage 9 is closed to prevent the resin from flowing out. When the resin J further moves to the left, the frictional resistance between the resin J and the tow bar 23 has a limit, so that only the resin J moves,
Move away from the towbar 23. This completes one cycle of molding. Hereinafter, the same operation is repeated to mold.

[0019]

As described above, according to the present invention, a molten resin is sprued into a mold cavity by using an injection molding nozzle provided with a traction rod on a valve body for opening and closing a resin passage. When performing injection molding through the valve, the valve body is retracted by the resin pressure so that the traction rod remains in the sprue, and the resin passage is opened and injected. Since the resin is pulled by the drawn resin toward the resin passage via the drawbar, the resin passage is closed, so that the resin can be prevented from flowing out after the injection. In particular, according to the present invention, the resin passage is automatically closed when the mold is opened without using a means such as a spring as in the related art, so that the effect of closing the resin passage easily and inexpensively can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of an injection molding nozzle of the present invention in a state where a mold is touched.

FIG. 2 is a cross-sectional view showing the injection molding nozzle and the resin with the mold partially opened after the injection molding with the injection molding nozzle shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Screw cylinder 5 Nozzle head 8 Valve seat 9 Resin passage 20 Valve (valve element) 22 Seat part 23 Tow bar 30 Fixed mold 31 Sprue 32 Movable mold J Resin

Claims (1)

(57) [Claims] 1. A valve element (20) for opening and closing a resin passage (9).
The molten resin is poured into a mold (30, 3) using an injection molding nozzle (N) provided with a tow rod (23 ).
When injection molding the cavity of 2) through the sprue (31), when injecting, the valve body (20) is pressed by resin pressure .
The towbar (23) will remain in the sprue (31)
Injection open the resin passage (9) with sea urchin retracted after the injection finished, when opening the mold (32), the drawbar by the sprue (31) in the filled resin (J) (2
3) pulling the valve body (20) toward the resin passage (9) through the resin passage (9) to prevent the resin from flowing out;
An injection molding method characterized by the above-mentioned.