JPH09131768A - Injection molding nozzle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out an injection molding nozzle, both the closing and opening of the gate of the injection molding nozzle can be performed by utilizing the injection pressure of molding material requiring neither motive power nor elastic power for its closing and opening at either one of the closing and opening of the gate of the injection molding nozzle. SOLUTION: In an injection molding nozzle used together with a runnerless mold, a valve pin 2, which slides due to the pressure difference between in a cavity 6 and in a runner 3, is fillted to the tip of a nozzle body 1 so as to close and open a gate 4 by means of the sliding of the valve pin 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding nozzle used for injection molding a molding material such as plastic using a runnerless mold. More specifically, the invention relates to an injection molding nozzle that opens and closes a gate by the injection pressure of a molding material.

[0002]

2. Description of the Related Art Molds of injection molding machines generally used for injection molding of plastics include a two-plate mold, a sleep rate mold and a runnerless mold. Above all, the runnerless mold is also called a hot runner mold, which keeps the plastic in a fluid state at all times so as to heat the sprue and runner parts and not solidify the melted material in it.
It is designed so that only the product is taken out after each injection operation, and when compared to two-plate molds and sleep rate molds, molding materials that solidify at the sprue and runner parts and are discarded ( (Plastic) can be saved, which is preferable.

When such a runnerless die is used, a nozzle formed at the tip of the runner and injecting the molding material into the cavity of the die in contact with the die is inside the cavity when the injection is completed. It is necessary to prevent the molten molding material from leaking to the outside (such as inside the cavity).

Therefore, generally, as a nozzle corresponding to a runnerless mold, the temperature at the tip of the gate is raised and lowered,
A heat gate type nozzle that cures the gate with a resin (molding material) and a valve gate type nozzle that opens and closes the gate by operating a needle valve or the like by a power mechanism such as an external hydraulic device have been adopted. However, in the case of the heat gate type nozzle, delicate temperature control for curing the resin is required, which makes the control complicated, and in the valve gate type nozzle, the power mechanism for operating the needle valve etc. is required. There is a problem in that the device becomes large in scale because it is required.

Also disclosed is a differential pressure type nozzle in which a spring coil or the like is attached to a valve pin, and a gate is opened and closed by balancing the repulsive force of the spring and the injection pressure. An example of such a differential pressure type nozzle is described in Japanese Examined Patent Publication No. 59-42618, and in this publication, the difference in which the outer diameter of the front portion is slightly larger than the outer diameter of the rear portion is formed in the hollow portion of the cylinder. There is disclosed a differential pressure type nozzle in which a pressure piston is swept and the differential pressure piston is slid by utilizing a pressure difference between the front surface and the rear surface of the differential pressure piston of the injection pressure of the resin to open and close a gate.

However, although the differential pressure type nozzle allows the opening operation by the injection pressure of the resin, the closing operation is to always push the differential pressure piston by the elastic force of the spring to close the gate. Therefore, when closing the gate, it becomes difficult to perform the initial closing operation when the characteristics of the spring change due to corrosion or wear due to long-term use. In addition, regarding the opening operation of the gate, there is a problem in use that the injection pressure above a certain level, which can withstand the elastic force of the spring coil or the like for closing the gate, is required for the opening operation. Had.

[0007]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have decided to use a novel gate opening / closing means for opening and closing the gate. Also, there is provided an injection molding nozzle capable of opening or closing the gate by utilizing the injection pressure of the molding material without requiring any power such as hydraulic pressure or pneumatic pressure or elastic force such as a spring for that purpose. It has come to do.

That is, according to the present invention, in an injection molding nozzle used with a runnerless mold, a valve pin which slides only due to a pressure difference between the inside of the cavity and the inside of the runner is fitted into the tip of the nozzle body, and the valve pin slides. It is an injection molding nozzle that opens and closes the gate by movement.

As described above, the injection molding nozzle of the present invention ejects the molding material sequentially extruded by the various injection devices such as the plunger injection device, the pre-plastic injection device and the screw injection device into the cavity from the nozzle. The injection molding nozzle is characterized in that the opening and closing of the gate is performed by sliding the valve pin by utilizing the pressure difference between the inside of the cavity and the inside of the runner. The valve pin, which is freely slidable in the nozzle axis direction, is inserted into the tip of the runner. The pressure in the rear end direction (runner side) of the valve pin is changed by the injection pressure when the molding material is injected. Side) pressure, resulting in the valve pin being pushed distally to open the gate. Further, when the gate is closed, the injection pressure decreases when the injection of the molding material is finished and the loading of the molding material is stopped. The pressure on the (runner side) becomes lower than the pressure in the tip direction (cavity side), and as a result, the valve pin is pushed into the runner,
It has a structure that closes the gate.

In the present invention, it is necessary that the valve pin is fitted into the valve pin fitting inlet while controlling the valve pin so that the molding material does not leak due to a gap therebetween and the valve pin can slide smoothly.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The structure for opening and closing the gate by sliding the valve pin by the injection pressure according to the present invention can be realized, for example, by the following gate structure. (1) A nozzle body having a torpedo at the position of the inner shaft is adopted, and a gate is formed between the outer peripheral surface of the torpedo tip and the inner peripheral surface of the tip of the valve pin slidably fitted, and the gate is opened. Also, due to the sliding of the valve pin, the torpedo tip and the inner circumferential surface of the valve pin tip are separated.
It is realized by abutting.

(2) The valve pin structure employs a hollow valve pin that opens from the rear end to one or more locations laterally of the tip end, and is slidably fitted into the valve pin fitting inlet,
The gap between the opening on the side of the valve pin and the nozzle body is used as a gate, and the opening and closing of the gate is realized by exposing the opening from the lower end of the nozzle body into the cavity by sliding the valve pin. It This is useful for nozzle bodies that do not have torpedo.

(3) The structure of the valve pin is such that a flow path of the molding material is provided on the side surface thereof and a flange having a shape for closing the valve pin fitting inlet is provided at the tip, and the valve pin is slidable on the valve pin fitting inlet. The opening and closing of the gate formed by the gap between the side of the valve pin and the nozzle body is realized by exposing and accommodating the flange from the lower end of the nozzle body into the cavity by sliding the valve pin. This is also useful for nozzle bodies that do not have a torpedo.

In the case of the gate having the structure shown in (1) above, the outer periphery of the torpedo tip of the nozzle body is chamfered and the inner surface of the tip of the valve pin is surrounded by the outer periphery of the torpedo tip as shown in the following embodiments. In addition to forming an inclination so as to match with, the valve pin tip direction is formed in an inward flange shape, and the gate is closed by abutting the inner surface of the inward flange portion and the torpedo tip surface. be able to.

Further, in the case of the gate having the structure as shown in (2), the shape of the gate is such that the hollow portion formed from the approximate center of the rear end of the valve pin is branched into a "Y" shape and the side thereof is formed. In addition to the shape that opens to the side, the hollow part formed from the approximate center of the rear end of the valve pin is branched into a “Y” shape and opened to the side, and from that opening to slightly behind the valve pin tip. At least when the valve pin is projected into the cavity due to injection pressure, such as a shape that forms a groove along the communicating axial direction or a shape that curves from the rear end to the side and forms a small hole. , The opening on the side of the valve pin is also projected into the cavity to open the gate,
When the valve pin is housed in the runner, the opening also needs to be housed in the runner and formed so as to close the gate.

Further, the valve pin of (3) is a valve pin having a flow path of a molding material formed on the side surface of the valve pin and a flange formed at the tip so as to close the valve pin fitting inlet, and the flange at the tip of the valve pin is inside the cavity. By protruding to the side, the runner, the flow path on the side surface of the valve pin, and the cavity communicate with each other. The flow path of the molding material formed on the side surface of the valve pin is formed by, for example, forming a groove on the side surface near the rear end of the valve pin, and further narrowing the outer diameter between the groove forming portion and the flange at the front end of the nozzle. It can be realized by forming a space between the body and the valve pin.

In implementing the injection molding nozzle of the present invention, a heating source for heating the runner may be internally or externally installed so that the molding material passing through the runner is not hardened, if desired. Yes, for example in Figure 1
It is also possible to incorporate a heater for heating in the torpedo as shown in FIG. At that time, some heat insulating means is provided between the heating source and the cavity so that the heat emitted from the heating source does not conduct to the cavity and hinder the curing of the molding material in the cavity. Will be needed. As such means, a method of forming a heat insulating groove on the outer side of the injection molding nozzle as in the embodiment shown in FIG. 1 or attaching a heat insulating material to the outer circumference of the nozzle is adopted.

[0018]

EXAMPLES The basic structure of the present invention will be described below based on examples, but the present invention is not limited to these examples.

[Embodiment 1] FIG. 1 is a schematic sectional view showing an embodiment of the present invention, and FIG. 2 is an enlarged sectional schematic view of an essential part showing an embodiment of the present invention. The injection molding nozzle shown in FIG. 1 has a torpedo 1b at an inner shaft center position, a nozzle body 1 having a valve pin fitting port 1c at its tip, a runner 3 in the nozzle body 1, and a tip of the nozzle body 1. The valve pin 2 is fitted in the valve pin fitting port 1c.

The nozzle body 1 is formed in a tapered shape gradually toward the tip, has a molding material inlet 1a at the rear end, and a valve pin fitting inlet 1c at the tip, which are connected by a runner 3. The valve pin fitting port 1c at the tip of the nozzle body 1 is formed in a stepped shape having a narrower inner diameter in the front end direction than the rear end, and the valve pin 2 having an outer shape corresponding to the stepped shape is slid on the valve pin fitting port 1c. It is inserted freely. Therefore, the outer shape of the valve pin 2 fitted in the valve pin fitting port 1c needs to be formed as a stepped shape in which the inner diameter in the front end direction is narrower than the rear end, like the inner diameter of the valve pin fitting port 1c. The inner side of the valve pin 2 is formed so as to gradually open toward the rear end and gradually close to the front end with the stepped portion as a boundary, and the inner surface of the front end thereof can be aligned with the front end of the torpedo 1b described later. Restricted to form the inner diameter gradually smaller, Torpedo 1b
Between the tip of the gate and the inner peripheral surface of the tip of the valve pin 2.
Has made.

On the other hand, the nozzle body 1 has a torpedo 1b which is separated by a runner 3 at the position of the inner shaft center thereof, and the tip end direction of the torpedo 1b is also the nozzle body 1.
It is formed in a tapered shape similarly to the tip direction, and its tip is regulated so as to be aligned with the tip of the nozzle body 1. The outer periphery of the tip portion of the torpedo 1b is chamfered and abuts the inner surface of the tip of the valve pin 2, thereby closing the gate 4.

Next, the sliding of the valve pin 2 and the opening or closing of the gate 4 due to the injection pressure in the present invention will be described in detail.

The molding material is carried into the nozzle through the molding material inlet 1a, passes through the runner 3 and reaches the gate 4. At that time, the molding material in the runner 3 is heated by the heater 5 for heating arranged in the torpedo 1b to prevent the hardening.

When the molding material reaches the gate 4, the valve pin 2 slidably fitted by its injection pressure is brought into contact with the valve pin fitting inlet 1c and the stepped notch of the valve pin 3 (the tip of the valve pin 2 is the cavity. The molding material is extruded to the tee 6 (protruding position), and the molding material is injected into the cavity 6 from the gate 4 formed in the gap between the tip of the torpedo 1b and the inner peripheral surface of the tip of the valve pin 3 (FIG. B)).

When the carry-in of the molding material is stopped at the time when the injection material is filled in the cavity 6, the injection pressure of the molding material is lowered and the valve pin 2 is directed toward the rear end (that is,
The pressure in the runner 3) becomes lower than the pressure in the cavity 6, and as a result, the pressure in the cavity 6, which in turn causes the valve pin 2 protruding into the cavity 6, In the direction (runner 3 direction), that is, the tip of the torpedo 1b and the inner peripheral surface of the tip of the valve pin 2 come into contact with each other, and the gate 4 is pushed out (FIG. 2 (a)).

Therefore, by constantly supporting the valve pin 2 with the pressure in the cavity 6, the tip of the torpedo 1b and the inner peripheral surface of the tip of the valve pin 2 come into contact with each other to close the gate 4 and the space of the runner 3 of the nozzle. It is possible to prevent the molding material remaining in the runner 3 from leaking into the cavity 6 by blocking the space between the cavity 6 of the mold.

In connection with this embodiment, as shown in FIG. 6, the rear end of the valve pin 2 is slidably fitted in the torpedo 1b, and the runner portion 2a is gradually widened toward the front end. Adopted valve pin 2 exposed in 3,
It can also be used as an injection molding nozzle. When the molding material is supplied, the gate 2 of the injection molding nozzle is opened and closed. When the molding material is supplied, the wide hakama-shaped portion 2a of the valve pin 2 is pushed by the injection pressure of the molding material, and the valve pin 2 projects into the cavity 6. Open the gate (Fig. 6
(B)) When the supply of the molding material is stopped, the valve pin 2 is pushed out toward the rear end by the pressure inside the cavity 6, and the tip pin outer periphery of the valve pin 2 and the nozzle body 1
By aligning with the valve pin fitting port 1c at the tip,
The gate 4 is closed to prevent leakage of the molding material in the cavity 6. When the gate 4 is closed, the tip of the valve pin 2 is flush with the tip of the nozzle body 1 (FIG. 6A).

[Embodiment 2] FIG. 3 is another embodiment embodying the injection molding nozzle of the present invention, and is an enlarged sectional schematic view of an essential part showing another embodiment of the present invention. This embodiment is an injection molding nozzle which is characterized by the shape of the valve pin 2.

That is, a molding material carry-in port (not shown) at the rear end
A nozzle body 1 having a hollow structure having a valve pin fitting port 1c in the distal direction and a valve pin 2 slidably fitted in the valve pin fitting port 1c. The valve pin fitting port 1c is a nozzle. A concave portion 7 having a predetermined width is formed in the circumferential direction on the inner surface slightly rearward of the tip of the body 1. The outer shape of the valve pin 2 is the concave portion 7 of the valve pin fitting inlet 1c and the axial center of the nozzle body 1. It has a stepped shape that allows free sliding in the direction and the rear end is inserted, and the inner shape is a hollow structure that opens from the rear end to one or more locations on the side of the tip and on the side of the valve pin 2. The gap between the nozzle and the nozzle body 1 is a gate 4, and the opening of the gate 4 causes the valve pin 2 to project into the cavity 6 due to the injection pressure of the molding material so that the gate 4 is at the lower end of the nozzle body 1. Performed by exposing (Figure 3
(B)) The closing is performed by the valve pin 1 moving in the rear end direction due to the pressure in the cavity 6 and the opening on the side of the valve pin 2 being housed in the nozzle body 1. And when the gate 4 is closed,
The nozzle for injection molding is characterized in that the tip of the nozzle body 1 and the tip of the valve pin 2 are flush with each other (FIG. 3A).

In this embodiment, the gate 4 for injecting the molding material into the cavity 6 comprises the nozzle body 1 and
It is formed between the opening on the side of the valve pin 2 and the valve pin 2 is pushed in the rear end direction by the pressure in the cavity 6 and is housed in the valve pin fitting inlet 1c.
The valve pin 2 is closed, and the opening of the valve pin 2 is closed by the inner peripheral surface of the runner 3 (that is, the inner peripheral surface of the valve pin fitting port 1c) to prevent leakage of the molding material remaining in the runner 3. Therefore, in the injection molding nozzle according to the present embodiment, unlike the nozzle body 1 of the first embodiment, the nozzle body 1 having no torpedo 1b can sufficiently achieve the intended purpose.

The shape of the valve pin 2 in this embodiment is not particularly limited as long as it is a shape that opens at least to the side thereof and forms a gate in the gap between the valve pin 2 and the nozzle body 1. As such a shape, for example, as shown in FIG. 3, the hollow portion 8 formed from the approximate center of the rear end of the valve pin 2 may be branched into a “Y” shape and opened laterally. .

The sliding of the valve pin 3 is such that the rear end of which the outer diameter is larger than that of the front due to the stepped notch shape is fitted into the recess 7 formed horizontally in a predetermined vertical range slightly rearward of the tip of the runner 3. It is regulated by

Therefore, in the drawing (FIG. 3), since the recess 7 formed in the valve pin fitting port 1c is for restricting the sliding width of the valve pin 2, the recess 7 as shown in FIG. Besides, to support the rear end of the valve pin 2,
Even if the protrusions are formed on the entire inner surface of the runner 3 in the circumferential direction or at appropriate intervals, substantially the same effect as that of the injection molding nozzle according to the present embodiment can be obtained.

Particularly, in the injection molding nozzle of this embodiment, since the nozzle body 1 does not have the torpedo 1b as described above, the heat source for preventing the hardening of the molding material in the runner 3 is the nozzle body 1 Will be installed in place.

Furthermore, as shown in FIG. 4, the valve pin 2 having a hollow structure as shown in this embodiment is divided into a "Y" -shaped branch of a hollow portion 8 formed from the approximate center of the rear end of the valve pin 2. And open it to the side,
A groove 9 is formed along the axial direction that communicates from the opening to a position slightly rearward of the tip of the valve pin 2.
It is also possible to use the valve pin 2 in which a flange 10 having a shape closing the valve pin fitting port 1c is formed at the tip.
In this valve pin 2, the gate 4 is formed by the nozzle body 1, the groove 9 and a part of the valve pin 2 when the flange 10 projects into the cavity 6. When the gate 4 is opened and closed, the flange 10 at the front end is opened by the injection pressure of the molding material so as to project into the cavity 6, and the gate 4 is closed by pushing the valve pin 2 toward the rear end. By being accommodated in the valve pin 1c, the flange 10 at the tip of the valve pin 2 is inserted into the valve pin fitting port 1c.
It is realized by blocking.

[Embodiment 3] FIG. 5 shows another embodiment embodying the injection molding nozzle of the present invention, and is an enlarged sectional schematic view of an essential portion showing another embodiment of the present invention (FIG. 5 (a), FIG. 6B is a perspective view of the valve pin (FIG. 5C). Similar to the second embodiment, this embodiment is useful for the nozzle body 1 having no torpedo 1b and is an injection molding nozzle characterized by the shape of the valve pin 2.

As shown in the perspective view of the valve pin in FIG. 5C, the valve pin 2 is provided on the side surface near the rear end (that is, the rear end direction from the stepped portion) in the axial direction of the flow path of the molding material. A groove 11 is formed along the groove 11, the outer diameter in the front end direction is narrower than that of the portion where the groove 11 is formed, and a flange 10 for closing the valve pin fitting inlet 1c is formed at the tip of the valve pin 2.

In the valve pin 2 in this embodiment, the flange 10 at the tip of the valve pin 2 projects into the cavity 6 by the injection pressure of the molding material, so that the runner 3,
The groove 11, a portion of which the outer diameter in the front end direction is narrower than the groove 11 and the cavity 6 are in communication with each other, and the molding material is injected from the gate 4 between the side surface of the valve pin 2 and the nozzle body 1 into the cavity 6. To be done.

The gate 4 is closed by pushing the valve pin 2 toward the rear end and storing it in the valve pin fitting port 1c so that the flange 10 at the tip of the valve pin 2 closes the valve pin fitting port 1c.

[0040]

According to the nozzle for injection molding of the present invention, the opening and closing operation of the gate can be performed without requiring a mechanism such as a hydraulic / pneumatic cylinder or a spring coil for opening and / or closing the gate. Any of the above can be performed by utilizing the injection pressure of the molding material. This means that since no member that reduces the initial characteristics such as spring characteristics is used, the initial characteristics of the nozzle can be maintained even after long-term use, and it has excellent durability for injection molding. Become a nozzle.

In the injection molding nozzle of the present invention, the opening / closing operation of the nozzle can be performed without detecting the drive start / end point signals, as in the case of restricting the opening / closing operation of the gate by the hydraulic / pneumatic cylinder. It can be carried out. Furthermore, since a device for driving the valve pin on the extension shaft of the valve pin is not required, the injection molding nozzle can be installed on the axis of the injection cylinder of the injection molding machine, and as a result, injection molding with a simpler structure is possible. It can be a device.

Further, according to the injection molding nozzle of the present invention, unlike the conventional nozzle in which the gate is opened / closed by hydraulic pressure / air pressure, the runner space of the nozzle is opened to the outside in addition to the molding material inlet or the gate. Since there are no openings, there is no risk of the molding material leaking outside the cavity from the inside of the nozzle at high temperature (usually 150 to 400 ° C.) and high pressure (usually 500 to 2000 kg / cm ² ).

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of an essential part showing an embodiment of the present invention. In the figure, (A) is an enlarged cross-sectional view of a main part showing a state where the gate is closed, and (B) is an enlarged cross-sectional view of the main part showing a state where the gate is opened.

FIG. 3 is an enlarged cross-sectional view of essential parts showing another embodiment of the present invention. In the figure, (A) is an enlarged cross-sectional view of a main part showing a state where the gate is closed, and (B) is an enlarged cross-sectional view of the main part showing a state where the gate is opened.

FIG. 4 is an enlarged cross-sectional view of an essential part showing another embodiment of the present invention. In the figure, (a) is an enlarged cross-sectional view of a main part showing a state in which the gate is closed, (b) is an enlarged cross-sectional view of a main part in a state in which the gate is opened, and (c) is a valve pin of this embodiment. It is a perspective view.

FIG. 5 is an enlarged sectional view of an essential part showing another embodiment of the present invention. In the figure, (a) is an enlarged cross-sectional view of a main part showing a state in which the gate is closed, (b) is an enlarged cross-sectional view of a main part in a state in which the gate is opened, and (c) is a valve pin of this embodiment. It is a perspective view.

FIG. 6 is an enlarged cross-sectional view of an essential part showing another embodiment of the present invention. In the figure, (A) is an enlarged cross-sectional view of a main part showing a state where the gate is closed, and (B) is an enlarged cross-sectional view of the main part showing a state where the gate is opened.

[Explanation of symbols]

 1 Nozzle Body 1a Molding Material Inlet 1b Torpedo 1c Valve Pin Fitting Inlet 2 Valve Pin 2a Wide Hakama Part 3 Runner 4 Gate 5 Heating Heater 6 Cavity 7 Recess 8 Hollow 9 Groove 10 Flange 11 Groove

Claims (8)

[Claims] 1. An injection molding nozzle used with a runnerless mold, wherein a valve pin that slides only due to a pressure difference between a cavity of the mold and a runner of the nozzle is fitted at the tip of the nozzle body, and the valve pin is fitted. Injection molding nozzle that opens and closes the gate by sliding. 2. The injection molding nozzle according to claim 1, wherein the gate is formed between the nozzle body and the valve pin. 3. A hollow nozzle body having a molding material inlet at its rear end and a valve pin fitting inlet at its tip,
The valve pin is slidably aligned and fitted into the valve pin fitting port, and the valve pin moves in the direction of the cavity by the injection pressure of the molding material to open the gate, and the pressure in the cavity causes the rear of the nozzle. The injection molding according to claim 1 or 2, wherein the nozzle body tip and the valve pin tip are flush with each other when the gate is closed by moving in the end direction while closing the gate. Nozzle. 4. The injection molding according to any one of claims 1 to 3, wherein the nozzle body has a torpedo in a direction of an inner axis thereof, and a gate is provided between the torpedo tip and the valve pin tip. nozzle. 5. The valve pin according to claim 1, wherein the valve pin has a hollow structure that opens from the rear end to one or more positions laterally of the tip, and a gate is provided between the opening and the nozzle body. The injection molding nozzle according to claim 1. 6. The valve body comprises a molding material inlet at the rear end, a torpedo arranged on the inner shaft core, and a valve pin fitting inlet formed by narrowing the inner diameter in the front end direction into a stepped shape. Is a hollow shape whose outer shape is the same as the stepped shape of the inner surface of the tip of the nozzle body, the gate is formed between the inner surface of the valve pin and the torpedo tip of the nozzle body, and the valve pin is the injection pressure of the molding material. By moving in the cavity direction, the inner peripheral surface of the hollow part of the valve pin and the tip of the torpedo of the nozzle body are separated to open the gate, and the valve pin moves toward the rear end of the nozzle body due to the pressure difference between the cavity and the runner. By moving, the inner peripheral surface of the hollow part of the valve pin comes into contact with the torpedo tip of the nozzle body to close the gate. Claim 1 characterized by the following.
The injection molding nozzle according to any one of 3 above. 7. A valve pin fitting inlet is formed by forming a recess of a predetermined width in the inner circumferential direction slightly rearward of the tip of the nozzle body, and the outer shape of the valve pin is in the recess of the valve pin fitting inlet in the axial direction of the nozzle body. It has a stepped shape in which the rear end can be freely slid into, and the inner shape is a hollow structure that opens from the rear end to one or more places on the side of the tip, and the opening on the side of the valve pin. The gap with the nozzle body is used as a gate, and the gate is opened by the injection pressure of the molding material causing the valve pin to project into the cavity and exposing the gate from the tip of the nozzle body. The valve pin is moved toward the rear end by the internal pressure, and the opening on the side of the valve pin is housed in the nozzle body. The injection molding nozzle according to any one of items 1 to 3. 8. The injection molding nozzle according to claim 1, further comprising heating means for suppressing hardening of the molding material in the runner.