JPH06246765A - Gas injection molding method and mold thereof - Google Patents

Abstract

PURPOSE:To obtain excellent moldability even when a partially thick molded form has a large size and plane state. CONSTITUTION:A mold 11 has a gas channel guide 23 in which a thickness size of a main cavity 13 is continuously increased larger than a periphery up to a passage end position of a gas channel 22 to become a passage of a pressurized gas 22A from at least a sprue 14, a subcavity 24 provided in an outer cavity of the cavity 13 of the passage end position, and an operating pin 32 provided openably in a communicating part 25 for communicating the subcavity 24 with the main cavity 13. After melted resin is started to be charged in the cavity 13 in a state that the pin 32 is closed, gas 22A is charged in the cavity 13 in a state that the pin 32 is opened, and resin is discharged into the cavity 24 by a strong pressing pressure of the gas arriving at the passage end position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas injection molding method for a partially thick-walled molded product and its mold, and for molding interior and exterior products such as automobile bumpers and dashboards, or casings of home electric appliances. Available.

[0002]

2. Description of the Related Art Conventionally, a gas injection molding method has been known as an injection molding method capable of obtaining a lightweight and highly rigid molded product (JP-A-3-138126). In this method, after injection of a molten resin into the main cavity in the mold, an inert gas such as pressurized nitrogen gas is injected into the cavity for injection molding. A gas flow path (hereinafter referred to as “gas channel”) is formed by the gas pressure in the filled molten resin, and a small space in which the molten resin pressed by the gas in the gas channel communicates with the outside of the mold ( Hereafter, it is discharged to the "sub-cavity"), so that a uniform thin hollow molded product can be obtained. By this gas injection molding, it is attempted to mold a large-sized molded product used for the interior and exterior of automobile bumpers and dashboards.

[0003]

In such gas injection molding, if the shape of the molded product is a plane, the wall thickness of the molded product becomes thin and the filled resin has a viscosity due to solidification by cooling. To increase. Due to this increase in viscosity, a high gas pressure is required in order to form the gas channel up to the gas flow path end position and completely fill the cavity with resin. However, when the gas is injected at a high gas pressure,
There is a problem that gas invades other than the gas channel guide portion and impairs the appearance and function of the molded product. Further, when molding a large-sized molded product, in order for the communicating portion that communicates the main cavity and the sub-cavity to function as planned, it is necessary to perform a finishing operation for finely adjusting the inner diameter of the communicating portion to an appropriate size. Since this finishing work is delicate, many trials and errors are required to complete the mold, and there is a problem that it becomes a heavy burden in manufacturing the mold. That is, if the inner diameter of the communication part is too large, the resin filled in the main cavity will enter the sub-cavity through the communication part before the gas is injected, and the sub-cavity will not be able to exhibit its original function during gas injection. . On the other hand, if the inner diameter of the communication part is too small, the molten resin will not be sufficiently discharged to the sub-cavity with normal gas pressure, and if the gas pressure is increased to compensate the amount of molten resin discharged, a stable gas channel is formed. Will be difficult. Therefore, in order to finish the die, it is necessary to repeat trial and error such as finely adjusting the communicating portion while actually performing molding of the resin, and this finishing work is a heavy burden in manufacturing the die. .

An object of the present invention is to provide a gas injection molding method and a mold for the same which can obtain good moldability even if the partially thick molded product is large and planar.

[0005]

According to the gas injection molding method of the present invention, after the molten resin is filled into the main cavity of the mold, a pressurized gas is injected into the main cavity so that the inside of the molten resin is filled. A method for gas injection molding of a partially thick-walled molded article, wherein injection molding is performed while forming a gas channel that is a passage for a pressurized gas in a mold, wherein a passage of the gas channel is formed at least from a position where the pressurized gas is injected into the mold. One or more gas channel guides (partially thick walled parts) whose thickness dimension of the main cavity is larger than the circumference are provided continuously to the end position, and at the end of the passage, outside the product of the main cavity and outside A sub-cavity is provided in the cavity and / or the core part, and a communication part for connecting the sub-cavity and the main cavity is provided so as to be openable and closable, and the main key is closed with the communication part closed. After the start of the filling of the molten resin Activity, when injecting a pressurized gas into said main cavity, characterized in that opening and closing the communicating portion with time control.

In the injection molding die of the present invention, after the molten resin is filled in the internal main cavity, a pressurized gas is further injected into the main cavity to form a passage for the pressurized gas inside the molten resin. A mold for gas injection molding of a partially thick-walled molded product for performing injection molding while forming a gas channel, wherein at least the gas channel guide portion in which the thickness dimension of the main cavity is larger than the surroundings is provided. It is provided continuously from the injection position of the pressurized gas to the passage end position of the gas channel, and an auxiliary cavity is provided in the outer cavity and / or the core portion of the main cavity at the passage end position. It is characterized in that a means for opening and closing by time control is provided in the communication part connecting the.

[0007]

In the present invention as described above, since the molten resin is filled in the closed state of the communication portion, there is no inconvenience that the molten resin enters the sub-cavity even if the filling pressure of the molten resin becomes high. As a result, the molten resin can be pushed into the main cavity under high pressure and filled up to the flow end position of the resin. After the start of filling, inject a pressurized gas into the molten resin,
By injecting the pressurized gas, a gas channel serving as a passage for the pressurized gas is formed inside the molten resin along the gas channel guide portion. At this time, since the valve of the communication section is opened for a predetermined time at a proper time after the start of filling by the time control, the pressurized gas proceeds toward the passage terminal position while pushing the molten resin into the sub-cavity. Is reliably formed up to the passage end position set in the main cavity. This eliminates the need for delicate finishing work, such as the conventional fine adjustment of the communicating parts of the mold, and significantly reduces the burden on the mold manufacturing work, while at the same time obtaining a stable molded product. Therefore, the above-mentioned object is achieved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a main part of an injection molding machine 10 of this embodiment. The injection molding machine 10 has a molding die 11 and an injection device 12 for injecting a synthetic resin. Mold
Reference numeral 11 has a large-sized main cavity 13 for integrally molding a large-sized sheet-like molded product or the like. The main cavity 13 communicates with the outside through a sprue 14 at the central portion of the bush 15. The injection device 12 is for kneading a molten synthetic resin 20 with a screw 17 in a cylindrical barrel 16.
A nozzle 18 is provided at the tip of the barrel 16. nozzle
By connecting 18 to the bush 15 of the mold 11 and injecting the resin 20 and filling the resin 20 into the main cavity 13, a molded product 21 is molded by the injection molding machine 10.

A blow-in pipe 19 for injecting a pressurized gas is inserted inside the nozzle 18. The blow-in pipe 19 is supplied with an inert gas such as nitrogen gas from a supply source (not shown) to form a gas channel 22 inside the molded product 21. The mold 11 of the present embodiment is configured so that the gas channel 22 is reliably formed up to the passage end position set inside the main cavity 13 by such gas injection.
A gas channel guide portion 23 continuously formed in a skeletal shape by making the thickness dimension of the main cavity 13 larger than the surroundings, and a sub-cavity installed outside the main cavity 13.
24 and a communication portion 25 that connects the sub-cavity 24 to the main cavity 13.

As shown in FIGS. 2 and 3, the main cavity 13 is formed by forming a gas channel guide portion 23 on one surface side of a substantially rectangular thin plate portion 26. The gas channel guide portion 23 continuously extends in an “A” shape from the opening position 31 of the sprue 14 which is a gas injection position to the corner portions 27 to 30 of the main cavity 13 which is a passage end position of the gas channel 22. It is an extension. Resin 20 of gas channel guide 23
The gas dimension of the gas channel guide portion 23 facilitates gas flow. As a result, the gas channel 22 is surely formed inside the gas channel guide portion 23 by injecting the gas.

A sub-cavity 24 is connected to the corners 29 and 30 of the corners 27 to 30 of the main cavity 13 which are the farthest end positions from the opening position 31 of the gas channel 22. The sub-cavity 24 has a volume corresponding to the gas channel 22 formed by gas injection, and communicates with the main cavity 13 at the passage terminal position of the gas channel guide portion 23.

The communicating portion 25 is provided with a passage 31 for communicating the sub cavity 24 and the main cavity 13 therein. An operating pin 32 as a valve is provided in the communicating portion 25 so as to be capable of projecting and retracting with respect to the passage 31, and the operating pin 32 allows the passage 31 to be opened and closed. The actuating pin 32, as shown in FIG.
The upper side in the drawing is a columnar shape that is fitted in the inside of a hydraulic cylinder 33 as an opening / closing drive mechanism, and is driven to project and retract by the hydraulic pressure applied to the hydraulic cylinder 33.
A cylindrical heating band 34 made of an electric heating member or the like is wound around an intermediate portion of the operating pin 32. The heating band 34 heats the vicinity of the operating pin 32 and the communicating portion 25, and the resin 20 filled in the corners 29, 30 of the main cavity 13 is kept at a predetermined temperature until the gas injection is completed. This allows the resin
The fluidity of 20 is ensured, and the resin 20 is smoothly pushed into the sub-cavity 24 by the pressure of the gas.

The procedure of injection molding in this embodiment will be described below. First, as shown in FIG. 5, the injection device 12 is operated with the operation pin 32 closing the passage 31, and the resin 20 is pushed into the main cavity 13 to fill the resin 20 to the flow end position of the resin. Here, since the passage 31 is closed, there is no possibility that the resin 20 will be pushed into the sub-cavity 24. Therefore, the filling pressure of the resin 20 should be sufficient to surely fill the resin 20 to the resin flow end position. Can be set high to fill.

Next, as shown in FIGS. 6 and 7, a gas 22A is injected into the main cavity 13 to form a gas channel 22 inside the resin 20 along the gas channel guide portion 23. At this time, since the passage 31 is open, the resin 20
Is filled up to the flow end position of the resin, gas 22A
Since the resin 20 pushes the resin 20 into the sub-cavity 24 and advances, the gas channel 22 is reliably formed up to the passage end position set in the main cavity 13. Further, the gas 22A reaching the passage end position has a sufficiently strong pressing force, so
Is pressed to its flow end position by the gas 22A, spreads over the entire main cavity 13, and is molded with the entire surface in close contact with the mold 11.

Then, the mold 11 is left for an appropriate length of time.
After cooling, the molded product 21 is taken out of the mold 11 and the injection molding is completed.

According to this embodiment as described above, there are the following effects. That is, the main cavity 13 and the sub-cavity
The operating pin 32 is provided in the passage 31 communicating with 24, and the operating pin 32
Since the resin 20 is filled in the closed state, it is possible to surely fill the resin 20 up to the flow end position of the resin by high pressure filling, and also to ensure that the resin 20 does not enter the sub-cavity 24. It can be lost.

Further, the operating pin 32 is provided in the passage 31, and the gas channel guide portion 23 continuing from the sprue 14 to the sub-cavity 24 is provided in the main cavity 13 and after filling the main cavity 13 with the resin 20, Since the high pressure gas 22A is injected into the resin 20 when the operating pin 32 is opened, the gas channel 22 extends along the gas channel guide portion 23, and the gas 22A pushes the resin 20 into the sub-cavity 24 and the passage end. Gas channel to move towards position
22 can be reliably formed in the main cavity 13 up to the end position of the passage.

Further, the resin filled in the main cavity 13
Since the gas channel 22 extending to the passage end position set in the main cavity 13 is surely formed in the inside of 20, the resin 20 is protected by the sufficiently strong pressing force of the gas 22A reaching the passage end position. Since it is pressed to the flow end position and spreads over the entire main cavity 13 and the entire surface is molded in a state of being in close contact with the mold 11, "sink marks" and the like do not occur at the flow end position, and the molded product is Even a large planar member can be a good product.

Further, since the cylindrical heating band 34 is wound around the intermediate portion of the operating pin 32 and the vicinity of the communicating portion 25 is heated by this heating band 34, the corner portion 29 of the main cavity 13 is
The resin 20 filled in 30 is maintained at a predetermined temperature and its fluidity is secured even if it takes time to inject the gas 22A. Therefore, until the injection of gas 22A is completed, the resin
Since 20 is smoothly moved to the sub-cavity 24 and the progress of the gas 22A is promoted, from this point as well, the gas channel 22
Can be reliably formed to the passage end position.

Further, the moldability is not affected by the size and shape of the mold, and the product does not depend strongly on the finishing accuracy of the mold, and stable and good products can be obtained. The degree of flexibility can be greatly increased, and the burden on the mold manufacturing work can be significantly reduced.

Next, the effects of the present invention will be described based on concrete experimental examples. [Experimental Example] This experimental example is an experiment in which injection molding is performed using a mold according to the present invention. As shown in FIG. 8, the mold of this experimental example has a gas channel guide portion 41 having an “A” shape, and the main cavity communicating with the sub-cavity 44 at the passage end positions 42 and 43 on the left and right sides in the figure. 45 are provided. A dashboard, which is an interior part of an automobile, was molded with this mold. [Comparative Example] In order to compare with the present experimental example, comparative examples 1 and 2 in which a dashboard having the same shape as the experimental example is injection-molded by using a mold in which a part of the mold is omitted are performed. In Comparative Example 1, as shown in FIG. 9, injection molding is performed using a mold of the present experimental example, in which a sub-cavity and a communicating portion are omitted. In Comparative Example 2, injection molding is performed using a mold (not shown) in which only the operation pin is omitted from the mold of this experimental example. [Injection conditions] In these experimental examples, comparative examples 1, and comparative example 2, injection molding was performed under the same injection conditions as described below, using an injection molding machine of 1800 tons. Injection conditions Materials used: Polypropylene (MI = 10) Molding temperature: 240 ° C Mold temperature: 30 ° C Filling time: 5. 0 seconds Gas injection pressure: 10 MPa (4.0 seconds)

[Experimental Results] In the experimental example, it was possible to obtain a non-defective product having no defective portion such as a sink mark on the surface of the molded product. In Comparative Example 1, as shown in FIG. 9, the resin 52 (hatched portion in the figure) filled in the main cavity 51 of the mold is formed in the defroster portion 55 formed at the flow end position 54 on the right side in the figure.
The area where the resin is not reachable and the resin 52 does not spread
There has occurred. In Comparative Example 2, when the resin was filled up to the flow end position of the resin, the resin was also filled inside the sub-cavity, so that there was no room for gas to enter the inside of the mold and gas could not be injected well. Gas injection molding was not successful.

It should be noted that the present invention is not limited to the above-mentioned embodiment, but includes the following modifications and the like. That is, the gas channel guide portion formed in the main cavity is not limited to the one extending in the “A” shape,
It may be a "king" shape or an "X" shape, in short, as long as it has a skeletal shape extending at least from the gas injection position to the end position of the gas channel set in the main cavity. The shape and the like of the portion can be appropriately selected in practice.

Further, the opening / closing means for opening / closing the communicating portion is not limited to the actuating pin 32 shown in the above-mentioned embodiment, but may be a sluice valve type provided so as to be able to project into and retract from the passage 31, or the passage 31 may be closed. It may be of a butterfly valve type or a ball valve type having a rotary valve body having a size capable of controlling. The drive source for driving these opening / closing means is not limited to hydraulic pressure,
It may be driven by gas such as air, or may be driven by electromagnetic force.

Further, the timing of gas injection may be any time after the start of filling, and may be before or after the completion of filling. Further, the sub-cavity is not limited to one provided in the outer cavity of the main cavity, but is provided inside the main cavity, that is, in the core part of the mold when the gas channel passage end position is on the inner surface of the main cavity. Alternatively, the installation position of the sub-cavity may be appropriately set according to the shape of the molded product and the like. Further, the heating unit is not limited to the electric heating type heater, but may be a combustion type heater or a heater utilizing high frequency, in short, the molten resin is not solidified in the vicinity of the portion where the molten resin and the opening / closing means come into contact with each other,
It is sufficient if the fluidity of the molten resin can be maintained.

The pressurized gas is not limited to nitrogen gas, but may be an inert gas such as argon, that is, any gas that can avoid the danger of explosion even at high pressure. The present invention is not limited to the molding of sheet-shaped molded articles such as automobile dashboards, but can also be applied to, for example, box-shaped casings of large television receivers and three-dimensional parts of home appliances such as wall-mounted air conditioners. Applicable.

[0027]

As described above, according to the present invention, since the shape of the molded product is composed of the planar portion, even if the molded product has a small thickness, the gas channel is extended to the gas flow path terminal position. Since the resin can be formed and the main cavity can be completely filled with the resin, sink, warp, and deformation of the molded product near the end of the gas flow path can be eliminated. In addition, since the molding can be performed at a low gas pressure, it is possible to prevent the appearance and function of the molded product from being impaired due to a defective phenomenon that occurs when molding at a high gas pressure, that is, gas invades other than the gas channel guide. It can be prevented. Further, since the valve of the communicating portion eliminates the inconvenience of the molten resin entering the sub-cavity, a delicate finishing work for the mold is unnecessary, and the load on the mold manufacturing work can be significantly reduced.

[Brief description of drawings]

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

FIG. 2 is a sectional view taken along line S2-S2 of FIG.

FIG. 3 is a plan view showing a main cavity of this embodiment.

FIG. 4 is an enlarged cross-sectional view showing an operation pin of this embodiment.

FIG. 5 is a cross-sectional view showing a resin filled state of the present embodiment.

FIG. 6 is a cross-sectional view showing a gas injection state of the present embodiment.

7 is a cross-sectional view taken along the line S7-S7 of FIG.

FIG. 8 is a diagram for explaining the shapes of the plane and the front surface of the cavity in one experimental example of the present invention.

9A and 9B are views for explaining the shapes of a plane and a front surface of a cavity of a comparative example.

[Explanation of symbols]

 11 Mold 13 Main cavity 14 Sprue which is the injection position of pressurized gas 20 Resin 21 Molded product 22 Gas channel 22A Pressurized gas 23 Gas channel guide 24, 44 Sub cavity 25 Communication part 29, 30 Corner at the end of passage Part 32 Actuating pin as opening / closing means 33 Hydraulic cylinder as opening / closing drive mechanism 34 Heating band as heating part

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location // B29L 31:30 4F (72) Inventor Hideki Tajima 10-1 Amanuma, Hiratsuka, Kanagawa Nissan Shatai Stock company (72) Inventor Tsutomu Hiranuma 10-1 Amanuma, Hiratsuka, Kanagawa Nissan Shatai Co., Ltd.

Claims (3)

[Claims] 1. A method for injecting a pressurized gas into the main cavity after starting the filling of the molten resin into the main cavity of the mold to form a gas channel as a passage for the pressurized gas inside the molten resin. While the method is a gas injection molding method for a partially thick-walled molded product to perform injection molding, the thickness dimension of the main cavity is continuous from at least the injection position of the pressurized gas to the passage terminal position of the gas channel in the mold. One or more gas channel guides that are larger than the surroundings are provided, and a sub-cavity is provided outside the main cavity at the end of the passage and outside the product and / or in the core portion. A communication part that connects the and is provided so as to be openable and closable, and after starting the filling of the molten resin into the main cavity with the communication part closed, When injecting the pressurized gas, the gas injection molding method characterized by opening and closing the communicating portion with time control. 2. A main cavity inside is filled with a molten resin, and then a pressurized gas is further injected into the main cavity to form a gas channel, which is a passage for the pressurized gas, inside the molten resin for injection. A mold for gas injection molding of a partially thick-walled molded product for molding, wherein a gas channel guide portion in which the thickness dimension of the main cavity is larger than the surroundings is provided at least from the injection position of the pressurized gas. The gas channel is continuously provided up to the passage end position, and an external cavity and / or a core portion of the main cavity at the passage end position is provided with a sub-cavity, and a communication portion connecting the sub-cavity and the main cavity is provided with a time. A gas injection mold, which is provided with means for opening and closing under control. 3. The gas injection molding die according to claim 2, wherein the valve is provided with a drive mechanism for driving the valve to open and close, and a heating unit for heating the valve. Gas injection mold.