JPH09262880A - High pressure injection molding method and high pressure injection mold apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the reliability of a mechanism for opening and closing a gate by making it possible to perform accurate weighing or compression in the so-called high pressure injection molding. SOLUTION: In high pressure injection molding, a movable mold 2 is opened by resin pressure when a mold is filled with a resin R and, thereafter, mold clamping force is increased to close a gate 23 while closing the movable mold 2. By this constitution, pressure control and weighing are performed and the pressure and amt. of the resin in a cavity 3 become constant. The resin R in the material passage 22 up to the gate 23 is always held to a molten state. In order to hold this state, the valve pin 26 closing the gate 23 is provided on the side of a fixed mold separately from the gate closing part 33 of the movable mold 2. An escape passage 28 is provided to the valve pin 26 so that the resin R is not left between the valve pin 26 and the gate closing part 33 when the valve pin 26 is fitted in the gate 23. At a time of mold opening, the side surface opening 28b of the escape passage 28 is closed by the side surface of the gate 23.

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 called high pressure injection molding (in-mold metering compression molding) and a mold apparatus used for the method, and more particularly to a method and a mechanism for opening and closing a gate.

[0002]

2. Description of the Related Art In the so-called high-pressure injection molding which has recently been adopted, as a cavity is filled with resin, the movable die is retracted in the opening direction by the resin pressure, and then the mold clamping force is increased. When the mold is finally closed, the mold structure is such that the gate closes midway.Until the gate is closed, the excess resin in the cavity is returned to the molding material supply device such as the heating cylinder and the gate is closed. After closing, the resin in the cavity is compressed. In this way, the amount and pressure of the resin in the cavity at the time when the gate is closed are made constant by the process of opening the movable mold by the resin pressure and the process of returning the resin in the cavity to the molding material supply device side (measurement and To regulate).

[0003]

Therefore, for accurate measurement, the resin in the cavity must be smoothly returned to the molding material supplying device side. However, in the conventional high-pressure injection molding, the resin in the material passage is solidified by the time the mold is opened. However, the resin cannot be smoothly returned to the molding material supply device side, accurate measurement cannot be performed, and the mold clamping force is insufficient, so that the product may not be compressed to a predetermined size.
In order to prevent this, there is a means for thickening the material passage, but this takes time for the resin in the material passage to cool, which causes an increase in the molding cycle.

Therefore, it is conceivable to heat the resin in the material passage and always keep it in a molten state, as is conventionally done in a hot runner type mold apparatus. In this case, a mechanism for opening and closing the gate from the material passage to the cavity is necessary so that the resin does not leak when the mold is opened. This gate opening / closing mechanism includes, for example, a valve gate system in which a gate is mechanically opened / closed by a valve pin driven by a hydraulic drive device.

By the way, in the high-pressure injection molding, various configurations are conceivable for closing the gate in conjunction with the final closing of the mold. The convex gate closing portion provided on the movable mold is fitted to the fixed direct gate. It is also possible to combine. However, in this case, if the valve gate system was adopted for the fixed mold to close the gate when the mold was opened, both the movable gate closing part and the valve pin on the fixed mold side would fit into the gate. The resin may be left behind between the valve pin and the tip end surface of the gate closing portion in the gate. The resin left behind in this way leaks out when the gate closing part comes out of the gate when the mold is opened, and this hinders molding.

The present invention is intended to solve such a problem, and enables high-precision injection molding to perform accurate weighing and compression, and to increase the reliability of the mechanism for opening and closing the gate. The purpose is to do.

[0007]

In order to achieve the above object, the invention of claim 1 fills a cavity formed between molds whose molding material supply device is closed with a thermoplastic molding material. Along with this, the molds move in the direction of opening each other, and after the completion of filling, the mold clamping force is strengthened to finally close the molds, while the gate from the molding material supply device to the cavity is closed. In the molding method, the molding material in the material passage that is formed inside one mold body and that leads from the molding material supply device to the gate is constantly kept in a molten state by heating, and the mold clamping force after the molding material is filled into the cavity is maintained. When strengthened, the gate is closed by fitting the gate closing part provided in the other mold body to the gate of the mold body having the material passage, and then the gate provided in the mold body having the material passage. Open The member is fitted to the gate and abuts against the gate closing portion, and at this time, the molding material between the tip surfaces of the gate opening / closing member and the gate closing portion is passed through an escape passage leading from the tip surface of the gate opening / closing member to the side surface. When returning to the inside of the material passage and opening the mold, the opening of the escape passage to the side surface of the gate opening / closing member is closed by the side surface of the gate.

In high-pressure injection molding, the pressure of the molding material in the cavity becomes constant when the molding material is filled and the mold body is opened according to the pressure (pressure adjusting step). Then, when the mold is finally closed, the molding material in the cavity returns to the molding material supply device side, and when the gate is closed, a certain amount of molding material remains in the cavity (measurement step). Then, the molding material in the cavity is compressed (compression step). Since the molding material in the material passage is always kept in a molten state, the molding material smoothly returns from the inside of the cavity to the molding material supply device side during the measuring step.

From the measuring step to the compressing step, the gate closing portion of the other mold body is fitted into the gate of the mold body having the material passage, but when the mold is opened, the molding material should not leak from the material passage. The gate must be closed by the gate opening and closing member in the mold with the material passage. Therefore, the gate opening / closing member must be fitted to the gate while the gate closing portion is fitted to the gate. At this time, the molding material between the front end surfaces of the gate opening / closing member and the gate closing portion returns into the resin passage through the escape passage of the gate opening / closing member, and no molding material remains between the front end surfaces of the gate opening / closing member and the gate closing portion. Further, when the mold is opened, the opening of the escape passage to the side surface of the gate opening / closing member is closed by the side surface of the gate so that the molding material in the material passage does not leak out.

According to a second aspect of the present invention, there is provided a die device used in the high pressure injection molding method according to the first aspect, wherein the first die body and the first die body which are opened and closed to form a cavity therebetween when the die is closed. Two mold bodies, wherein the first mold body has a material passage located inside the first mold body, a gate for opening the material passage to the cavity, and a thermoplastic material in the material passage. A heating means for always keeping the molding material in a molten state and a movable gate opening / closing member which slidably fits into the gate to open / close the gate are provided, and the gate opening / closing member is provided with a side surface from a tip end surface thereof. The opening of the escape passage to the side surface of the gate opening / closing member is provided at a position opened / closed by the side surface of the gate, while the second mold body is slidable on the gate. Fit and butt against the gate opening / closing member It is provided with a upcoming gate occlusion.

Throughout the whole process including the mold opening, the molding material in the material passage is always kept in a molten state by the heating means. Then, after the mold material is filled in the cavity and the mold clamping force is strengthened to finally close the first mold body and the second mold body, first, the gate closing portion of the second mold body becomes the first mold body. Close the gate by fitting it to the gate of the mold. Next, the gate opening / closing member of the first mold is fitted to the gate. At this time, the molding material between the gate opening / closing member and the tip end face of the gate closing portion is introduced into the resin passage through the escape passage of the gate opening / closing member. Returning, the tip end surface of the gate opening / closing member can abut the tip end surface of the gate closing portion, and no molding material remains in the gate. When the mold is opened thereafter, the gate opening / closing member is moved to some extent in the first mold, and the tip of the gate opening / closing member and the gate closing portion is closed until the opening of the escape passage to the side surface of the gate opening / closing member is closed by the side surface of the gate. Holds the state where the faces abut.

According to a third aspect of the present invention, in the high-pressure injection molding die device according to the second aspect of the invention, the tip end surface of the gate opening / closing member is an inverse taper surface which becomes narrower toward the opening of the escape passage, and the gate is formed. The front end surface of the closing portion is a tapered surface that fits into the reverse tapered surface of the gate opening / closing member.

When the gate opening / closing member is fitted in the gate, the molding material between the gate opening / closing member and the tip surface of the gate closing portion is guided by the reverse taper surface and the taper surface, and the tip surface of the gate opening / closing member is smoothly moved. To the opening of the escape passage at which the material passage is returned.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below.
This will be described with reference to the drawings. First, the structure of the high-pressure injection molding die device will be described. The mold apparatus of this embodiment is for molding a thin disc-shaped product having an opening hole in the center such as a recording disk. However, the molded product is not limited to the recording disk. Reference numeral 1 is a fixed mold which is a first mold body, 2 is a movable mold which is a second mold body, and these fixed mold 1 and movable mold 2 move in the vertical direction in the figure (hereinafter referred to as mold opening / closing direction). The mold-shaped cavities 3 are formed between them when the molds are closed.

The fixed mold 1 has a fixed side receiving plate 8 via a spacer block 7 under a fixed side mounting plate 6 attached to a fixed side platen of a mold clamping device of an injection molding machine (not shown). It is fixed, and the fixed-side template 9 is fixed to the lower side of the fixed-side receiving plate 8. A concave portion 10 that forms the cavity 3 is formed on the lower surface of the stationary mold plate 9. A locating ring 11 is fixed to the fixed side mounting plate 6, and a sprue bush 14 to which a nozzle 13 of a heating cylinder device 12 which is a molding material supply device of an injection molding machine is connected is fixed in a penetrating state. ing. This sprue bush 14 forms a sprue 15 which is a resin passage inside, and is provided with a heater 16 which is a heating means for keeping the thermoplastic resin R which is a molding material in the sprue 15 always in a molten state. There is. Further, the fixed side mounting plate 6 is provided inside the spacer block 7.
A manifold 17 is provided between the fixed side receiving plate 8 and the fixed side receiving plate 8. A runner 18 which is a material passage leading to the sprue 15 is formed inside the manifold 17, and a heater 19 which is a heating means for keeping the resin R in the runner 18 always in a molten state is provided. ing.

A valve casing 21 fixed to the manifold 17 penetrates the fixed side mounting plate 6 and the fixed side mold plate 9. The inside of the valve casing 21 is a sprue portion which is a material passage leading to the runner 18.
It is 22. A gate 23, which is a direct gate for opening the sprue portion 22 into the cavity 3, is formed at the tip of the valve casing 21. The side surface of the hole-shaped gate 23 is parallel to the mold opening / closing direction.
Further, the sprue portion 22 is provided on the peripheral wall portion of the valve casing 21.
The heater 24 is provided as a heating means for keeping the resin R of FIG.

A valve pin 26, which is a gate opening / closing member for opening / closing the gate 23, is incorporated in the fixed mold 1 so as to be movable in the mold opening / closing direction. The valve pin 26 is driven by a fluid pressure drive device 27 such as a hydraulic drive device provided on the fixed side mounting plate 6, penetrates the inside of the manifold 17 and the valve casing 21, and is slidable on the gate 23. It fits. Further, at the tip of the valve pin 26 whose side surface is parallel to the mold opening / closing direction for fitting into the gate 23, there is formed an escape passage 28 communicating from the tip surface to the side surface. The tip end surface of the valve pin 26 is a conical surface or a reverse taper surface 29 such as a spherical surface that tapers toward the tip opening 28a of the escape passage 28 at the center thereof. In addition, the relief path opened on the side of the valve pin 26
The side surface opening 28b of 28 is located at a position closed by the side surface of the gate 23 when the valve pin 26 reaches the lower limit position in the fixed mold 1.

Although not shown, the movable mold 2 has a movable side mold plate 31 fixed to the upper side of a movable side mounting plate attached to a movable side platen of a mold clamping device via a spacer block and a movable side receiving plate. Has been done. On the upper surface of the movable side mold plate 31, there is formed a convex portion 32 which fits into the concave portion 10 of the fixed side mold plate 9 to form the cavity 3. The side surfaces of the concave portion 10 and the convex portion 32 are parallel to the mold opening / closing direction, and the volume of the cavity 3 can be changed by the mutual sliding of the concave portion 10 and the convex portion 32. Note that, contrary to the present embodiment, the fixed die may be provided with the convex portion and the movable die may be provided with the concave portion. In addition, the movable die 2 has a gate closing portion at the upper end.
Pin 34, now 33, is fixed. The gate block
33 has a side surface parallel to the mold opening / closing direction and is slidably fitted to the gate 23. In addition, the tip end surface of the gate closing portion 33 has a reverse tapered surface 29 of the valve pin 26.
The taper surface 35 has the same shape as that of the taper surface 35 and is fitted to the reverse taper surface 29 and abuts against it. Further, a protruding sleeve 36 for protruding the molded product P is incorporated in the movable mold 2 so as to be movable in the mold opening / closing direction. The protruding sleeve 36 is fitted on the outer peripheral side of the pin 34.

Further, on the upper side of the movable die 2, that is, on the side of the fixed die 1, a pressure plate 41 abutting against the fixed side die plate 9 and the movable side die plate 31 is assembled so as to be movable in a predetermined range in the die opening / closing direction. . The pressing plate 41 is applied with a force in the opening direction with respect to the movable mold plate 31 by a spring 42 as a biasing means. In addition, the convex portion 32 of the movable side template 31
Penetrates the pressure plate 41 slidably. In addition, 43
Is a guide pin for guiding the pressure plate 41 with respect to the fixed mold 1. The pressure plate may be provided on the fixed mold 1 side instead of the movable mold 2 side.

Next, a high-pressure injection molding method using the mold device will be described. 1 to 4, the flow of the resin R and the movements of the movable die 2 and the valve pin 26 are indicated by arrows. Through opening and closing of the mold, the thermoplastic resin R, which is the molding material in the sprue 15, the runner 18, and the sprue portion 22 of the valve casing 21, which are the material passages in the mold device, is heated by the heaters 16, 19, 24. It is always kept in a molten state by heating.

Then, the fixed mold 1 and the movable mold 2 are first closed by the mold clamping device with a weak mold clamping force. As a result, FIG.
As shown in FIG.
The convex portion 32 is fitted to form the cavity 3 between the fixed mold 1 and the movable mold 2. At the same time, the pressure plate 41 abuts on the stationary mold plate 9, but the pressure plate 41 does not abut the movable mold plate 31 due to the balance between the spring 42 and the mold clamping force. When the mold is closed in this way, the valve pin 26 that has closed the gate 23 until then is closed by the fluid pressure drive device 27 as shown in FIG.
Is driven to raise the fixed mold 1, and the gate 23 is opened. In this state, the nozzle 13 of the heating cylinder device 12
The resin R melted by heating is injected from the sprue 15 into the sprue 15. The resin R passes through the sprue 15, the runner 18, and the sprue portion 22 of the valve casing 21 and is filled into the cavity 3 from the gate 23 (filling step).

In the case of the in-line screw type, for example, the resin R is supplied from the heating cylinder device 12 until the screw reaches a predetermined position such as the forward limit. Along with this, the resin pressure in the cavity 3 pushes down the movable mold 2 against the mold clamping force, as shown by the solid line and the chain line in FIG. 1, and the fixed mold 1 and the movable mold 2 open. This opening amount is determined by the balance between the resin pressure in the cavity 3 and the force of the spring 42 and the mold clamping force, and becomes larger as more resin R is filled in the cavity 3. In other words, even if there is an error in the amount of resin R supplied from the heating cylinder device 12, the error is absorbed by the change in the opening amount, and the pressure of the resin in the cavity 3 is adjusted and becomes constant (adjustment). Pressure process).

After that, the mold clamping force applied to the fixed mold 1 and the movable mold 2 by the mold clamping device is strengthened. This allows the movable mold 2
Rises and the movable mold 2 closes with respect to the fixed mold 1. Thus, when the fixed mold 1 and the movable mold 2 are finally closed, the excess resin R in the cavity 3 is discharged from the gate 23 which is still open due to the final mold closing.
Returning to 11, the resin R in the material passage 11 returns to the heating cylinder device 12. Then, as shown in FIG. 2, when the gate closing portion 33 of the movable mold 2 starts to be fitted into the gate 23, the gate 23 is closed, and at this point, a certain amount of the resin R remains in the cavity 3. (Measuring process) After that, the pressure plate 41 and the movable side mold plate 31 are closed until they abut each other, and accordingly, as shown in FIG. 3, the resin R in the cavity 3 is closed.
Is pressed and compressed (compression step). The gate closing portion 33 forms an opening hole of the product P.

After that, the valve pin 26 is lowered in the fixed mold 1 by the drive of the fluid pressure drive device 27, and is fitted into the gate 23. At that time, the resin R between the tip surfaces of the valve pin 26 and the gate closing portion 33 returns to the sprue portion 22 in the valve casing 21 through the relief passage 28 by pressurization. Then, finally, the reverse taper surface 29 at the tip of the valve pin 26 is fitted into the taper surface 35 at the tip of the gate closing portion 33 and abuts,
The resin R does not remain between the tip surfaces of the valve pin 26 and the gate closing portion 33. At this time, the tip end surface of the valve pin 26 becomes narrower toward the tip end opening 28a of the escape passage 28, and the reverse taper surface 29
Since the gate closing portion 33 has a corresponding tapered surface 35, the resin R between the valve pin 26 and the gate closing portion 33 has a reverse tapered surface 29.
And, guided by the tapered surface 35, guided to the tip opening 28a of the escape passage 28, and smoothly returned to the inside of the sprue portion 22.

After the resin R in the cavity 3 is sufficiently cooled and solidified, the mold is opened as shown in FIG. For a short time after this mold opening is started, the fluid pressure drive device 27
The valve pin 26 descends together with the movable die 2 by the drive of the. When the valve pin 26 of the fixed mold 1 reaches the lower limit, the side opening 28b of the relief passage 28 of the valve pin 26 is opened.
Is closed by the side surface of the gate 23. Until then, the state in which the reverse taper surface 29 of the valve pin 26 and the taper surface 35 of the gate blocking portion 33 are in contact with each other is maintained. In this way, when the fixed mold 1 and the movable mold 2 are open,
Since the side opening 28b of the escape passage 28 is closed and the escape passage 28 is cut off from the sprue portion 22 in the valve casing 21, the resin R in the molten state in the sprue portion 22 is closed.
Does not leak out from the tip opening 28a of the escape passage 28. The resin R remains in the escape passage 28, and this resin R is also kept in a substantially molten state. However, the volume of the escape passage 28 is very small, and the escape is blocked from the sprue portion 22. Since no large pressure is applied to the passage 28, the resin R in the escape passage 28 does not leak from the tip opening 28a. Even if it leaks out, it is a small amount and does not cause malfunction of the mold device or molding failure.

When the mold is opened, the resin R in the cavity 3, that is, the product P, first separates from the fixed mold 1. Then, in the movable die 2, the ejection sleeve 36 rises to eject the product P, and the product P is released from the movable die 2.
At the same time, a take-out device (not shown) takes out the product P from the mold device. After that, the mold is closed again,
The above steps are repeated.

According to the high-pressure injection molding as described above, the product P of stable quality and high precision can be obtained by the pressure adjusting process and the measuring process. Further, since the density is increased by the compression step, a product P excellent in mechanical properties and optical properties can be obtained.

Further, since the heaters 16, 19, and 24 are heated, the resin R in the sprue 15, the runner 18, and the sprue portion 22 of the valve casing 21 which are material passages in the mold apparatus is always kept in a molten state. During the measuring step, the resin R in the cavity 3 can smoothly return to the material passage, and the resin R in the material passage can smoothly return to the heating cylinder device 12. At the same time, the resin R in the cavity 3 is smoothly compressed after the measuring step, and the mold clamping force of the mold clamping device may be relatively low. Therefore, the metering and compression can be accurately performed without impairing the pressure regulation result in the pressure regulation process, and the features of the high pressure injection molding can be maximized. This is particularly advantageous in forming a thin product P such as a recording disk. Further, since the resistance is small, the time required for the measuring step and the compression step is shortened, which is also advantageous in increasing the speed of the molding cycle.

Further, as described above, the gate closing portion 33 is fitted to the gate 23 from the measuring step to the compressing step, while the gate 23 is closed by the valve pin 26 when the mold is opened. When the valve pin 26 is fitted to the gate 23, the relief path 28 formed in the valve pin 26 returns the resin R between the tip end surfaces of the valve pin 26 and the gate closing portion 33 into the sprue portion 22. It is possible to prevent the gap from remaining between the tip surfaces of the gate 26 and the gate closing portion 33 and leaking when the mold is opened. Moreover, since the side surface opening 28b of the escape passage 28 is closed by the side surface of the gate 23 when the mold is opened, the gate 23 can be reliably closed. In this way, the reliability of the mechanism for opening and closing the gate 23 can be maintained.

It should be noted that the present invention is not limited to the above embodiment, and various modifications can be made. For example,
In the above embodiment, the tip surfaces of the valve pin 26 and the gate closing portion 33 are the reverse tapered surface 29 and the tapered surface 35, respectively, but the tip surfaces of the valve pin and the gate closing portion may be flat. Further, in the above-mentioned embodiment, the description has been made by taking the case of forming the recording disk as an example, but the present invention can be applied to appropriate products other than the recording disk. Also,
INDUSTRIAL APPLICABILITY The present invention can be applied not only to injection molding of thermoplastic resins but also to injection molding of thermoplastic molding materials in general, such as injection molding of ceramics using a thermoplastic resin as a binder and injection molding powder metallurgy. Furthermore, the mold clamping device and the material supply device of the injection molding machine can also have various configurations.

[0031]

According to the invention of claim 1, in the high-pressure injection molding, the molding material in the material passage formed inside one mold is always kept in a molten state, so that the cavity is filled with the molding material. When the mold clamping force is increased later, the molding material in the cavity smoothly returns to the molding material supply device side,
The molding material in the cavity is also smoothly compressed, and accurate metering and compression can be achieved. In addition, in the steps of measuring and compressing, the gate closing part provided in another mold is fitted to the gate, while the mold is opened, the gate is closed by the gate opening / closing member provided in the mold having the material passage. However, when the gate opening / closing member is fitted to the gate,
The escape passage provided in the gate opening / closing member returns the molding material between the gate opening / closing member and the tip end surface of the gate closing portion into the material passage, so that the molding material remains between the gate opening / closing member and the tip end surface of the gate closing portion. It is possible to prevent leakage when opening. Moreover, since the opening of the escape passage to the side surface of the gate opening / closing member is closed by the side surface of the gate when the mold is opened,
The gate can be reliably closed, and the reliability of the mechanism for opening and closing the gate can be maintained.

According to the second aspect of the present invention, by providing the heating means for keeping the molding material in the material passage of the first mold body always in a molten state, it is possible to accurately measure and compress at the time of high pressure injection molding. . Further, the first mold body is provided with a movable gate opening / closing member, and the second mold body is provided with a gate closing portion that fits into the gate during the weighing process and the compression process. , Since the escape path leading from the tip end surface to the side surface is provided and the opening of the escape path to the side surface of the gate opening / closing member is provided at a position opened / closed by the side surface of the gate, when the gate opening / closing member is fitted to the gate. It is possible to prevent the molding material from remaining between the front end surfaces of the gate opening / closing member and the gate closing part, and at the time of mold opening,
The gate can be closed securely.

According to the invention of claim 3, in addition to the effect of the invention of claim 2, the tip end surface of the gate opening / closing member is formed into an inverse taper surface which becomes narrower toward the opening of the escape passage, and the tip end surface of the gate closing portion. By forming the corresponding taper surface, it is possible to smoothly return the molding material between the gate opening / closing member and the tip end surface of the gate closing portion to the resin passage.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view near a gate of a mold device showing an embodiment of the present invention, showing a filling process and a pressure adjusting process.

FIG. 2 is a vertical cross-sectional view of the vicinity of the gate, showing the completion of the weighing process.

FIG. 3 is a vertical cross-sectional view of the vicinity of the gate, showing the time when the compression step is completed.

FIG. 4 is a vertical cross-sectional view of the vicinity of the gate, showing immediately after the start of mold opening.

FIG. 5 is a transverse sectional view of the valve pin of the above.

FIG. 6 is a vertical cross-sectional view showing a wider range of the same mold apparatus.

[Explanation of symbols]

1 Fixed type (one type body, first type body) 2 Movable type (other type body, second type body) 3 Cavity 12 Heating cylinder device (molding material supply device) 15 Sprue (material passage) 16 Heater (Heating means) 18 Runner (material passage) 19 Heater (heating means) 22 Sprue part (material passage) 23 Gate 24 Heater (heating means) 26 Valve pin (gate opening / closing member) 28 Relief passage 28a Tip opening (tip of gate opening / closing member) 28b Side opening (opening of escape path to side of gate opening / closing member) 29 Reverse taper surface 33 Gate blocking part 35 Taper surface R Thermoplastic resin (molding material)

Claims (3)

[Claims] 1. A mold material supply device fills a cavity formed between closed mold bodies with a thermoplastic molding material, and the mold bodies move in a direction in which the mold bodies open to each other. In the high-pressure injection molding method, in which the clamping force is strengthened and finally the mold bodies are closed to each other, and the gate from the molding material supply device to the cavity is closed therebetween, the molding material is formed inside one mold body from the molding material supply device. The molding material in the material passage leading to the gate is always kept in a molten state by heating,
When the mold clamping force is increased after the cavity is filled with the molding material, the gate is closed by fitting the gate closing portion provided in another mold body to the gate of the mold body having the material passage, and then closing the gate. The gate opening / closing member provided on the mold having the material passage is fitted to the gate and abutted against the gate closing portion, and at this time, a molding material between the gate opening / closing member and the tip end surface of the gate closing portion is The gate opening / closing member is configured to return to the inside of the material passage through an escape passage leading to a side surface and to close the opening of the escape passage to the side surface of the gate opening / closing member by the side surface of the gate when the mold is opened. A high-pressure injection molding method characterized by: 2. A mold apparatus used in the high-pressure injection molding method according to claim 1, wherein the first mold body and the second mold body are opened and closed to form a cavity between them when the mold is closed. The first mold body is provided with a material passage located inside the first mold body, a gate for opening the material passage to the cavity, and a thermoplastic molding material in the material passage is always melted. A heating means for keeping the state and a movable gate opening / closing member which slidably fits to the gate to open / close the gate are provided, and the gate opening / closing member is provided with a relief passage leading from the tip end surface to the side surface. The opening of the escape passage to the side surface of the gate opening / closing member is provided at a position opened / closed by the side surface of the gate, slidably fitted to the second mold body and abutted on the gate opening / closing member. The gate is closed A mold device for high-pressure injection molding characterized by: 3. A front end surface of the gate opening / closing member is a reverse taper surface that narrows toward the opening of the escape passage, and a front end surface of the gate closing portion is a taper surface that is fitted to the reverse taper surface of the gate opening / closing member. The mold device for high-pressure injection molding according to claim 2, wherein