JPH06328488A - Gas injection molding method - Google Patents

Abstract

PURPOSE:To provide a gas injection molding method in which weld marks and hesitation marks do not cause in molded products. CONSTITUTION:The mold 20 is allowed to remain opened in its state (A) by a specific dimension R from a completely closed state to an opened state, wherein it incudes a first process for filling molten resin 30 in the mold 20, a second process (B) for pressurizing and rolling the inside-filled molten resin by effecting the mold clamping of the incompletely closed mold 20, and a third process (C) for injecting gas into the inside of the molten resin filled in the mold, and each process of the second or third process is initiated to be overlapped prior to the completion of the first process, whereby the tip end of flow of the molten resin 30 is not stopped once. Thus, the occurrence of hesitation marks or the like can be prevented beforehand.

Description

Detailed Description of the Invention

The present invention relates to a gas injection molding method, and relates to a bumper, a dashboard, a wheel cap of an automobile, a door panel or the like, or a casing of a home electric appliance,
It can also be used for manufacturing resin products such as back covers of television receivers, which require appearance quality.

[0002]

2. Description of the Related Art Conventionally, a gas injection molding method has been known as an injection molding method for obtaining a lightweight and highly rigid molded product. According to this method, injection molding is performed while injecting an inert high-pressure gas such as nitrogen gas into the molten resin filled in the cavity of the mold, so that the expansion force of the high-pressure gas does not cause sink marks on the surface. A molded product can be obtained.

In such a gas injection molding method, in order to obtain a thin-walled molded product having strength and rigidity, a gas channel, which is a passage for high-pressure gas, is provided inside the injection-molded product in a rib-like shape, and injection molding is performed. There is a rib type gas channel type gas injection molding method. In this method, the surface of the cavity of the mold is recessed and the gas channel guide is provided to form a rib-shaped thick-walled part whose surface is partially thickened into a thin-walled molded product. A gas channel is formed inside the. The thin-walled molded product formed by this method has sufficient strength and rigidity due to the rib-shaped thick-walled part, and is lightweight due to the hollow gas channel formed inside the thick-walled part. The high-pressure gas in the gas channel can prevent sink marks on the surface.

Further, by filling the molten resin in a mold that is incompletely closed to such an extent that the molten resin does not leak to the outside, and spreading the filled molten resin by clamping the mold, the mold is kept in a closed position. There is a spread-type gas injection molding method in which the molten resin is evenly distributed. According to this method, even if the molded product has a thin wall, the molten resin can be filled up to every corner of the mold due to the spreading at the time of mold clamping, so that a defect due to a short shot can be reliably prevented.

[0005]

However, in the gas channel type gas injection molding method, the gap between the gas channel guide portions provided in the mold is wider than the surroundings, and the flow resistance of the molten resin is different from that of the mold cavity. The molten resin flowing in the gas channel guide portion moves at a higher speed than the molten resin flowing in the thin-wall forming portion in which the space between the mold cavities is narrow. Therefore, if the molten resin in the gas channel guide portion reaches the edge of the mold before the molten resin in the thin-wall forming portion, it flows backward toward the upstream side and collides with the molten resin in the thin-wall forming portion. As a result, a flow mark (hereinafter referred to as "weld mark") is generated on the surface of the molded product.

Further, since the molten resin has a high flow resistance in the thin-walled forming portion, sufficient pressing force cannot be obtained near the edge of the mold even during filling, and the flow front of the molten resin temporarily stops. Cheap. For this reason, when the end of the molten resin flow is stopped near the end of filling, and when the molten resin flow resumes due to mold clamping and gas injection, another flow trace (hereinafter referred to as “hesitation mark”) on the surface of the molded product. ")) Will occur. Therefore, the conventional gas injection molding method has a problem that when a thin molded product is to be molded, the appearance of the molded product may be impaired due to the generation of weld marks and hesitation marks.

It is an object of the present invention to provide a gas injection molding method in which a weld mark and a hesitation mark are not generated in a molded product.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a first step of filling a mold in a state where a mold is opened from a completely closed state to a predetermined size with a molten resin and a mold which is incompletely closed are clamped. And a third step of injecting a gas into the molten resin filled in the die, the second step of pressurizing and spreading the molten resin filled in Three
Each step is started before the end of the first step. The present invention will be described with reference to the drawings.
FIG. 1 is a time chart of gas injection molding performed according to the present invention. In FIG. 1, the first step starts by starting the filling of the molten resin at time 0 seconds and ends by the completion of the filling of the molten resin at time T _S seconds. The second step starts by restarting the mold clamping of the mold at time T _P seconds and ends by the completion of mold clamping at time T _E seconds. The third step begins by initiating gas injection at time T _I seconds and ends by completing gas injection at time T _C seconds. The present invention is characterized in that the start time T _P seconds of the second process and the start time T _I seconds of the third process are earlier than the end time T _S seconds of the first process. Is.

Here, it is desirable that the second step and the third step are started at the same time, that is, the time T _P seconds and the time T _I seconds are the same. Also,
It is preferable that the mold in the first step is closed in a state in which the mold is completely opened, leaving a closing margin of 1 to 3 mm. Further, the second and third steps are preferably started when the amount of the molten resin filled in the first step reaches a range of 80 to 99% of the total amount to be filled in the mold. Further, the third step is ended after the second step is ended, that is, the end time T _E seconds of the second step is earlier than the end time T _C seconds of the third step. It is preferable.

[0010]

In the present invention as described above, since the mold filled with the molten resin is opened to a predetermined size from the completely closed state, the thin-wall forming portion of the mold has an increased space and the flow resistance of the thin-wall forming portion. Is in a state not much different from the flow resistance of the gas channel guide. For this reason, the molten resin in the thin-walled forming portion reaches the edge of the mold almost at the same time as the molten resin in the gas channel guide portion, the molten resins do not collide with each other, and weld marks are prevented from occurring. Will be done.

Further, since the second and third steps overlap with the first step, the front end portion of the flow of the molten resin moves from the movement due to the filling pressure in the first step to the second step. There is no interruption in the movement due to the spreading of the step (3) and the movement due to the gas injection of the third step. Therefore, the front end portion of the molten resin does not stop once, and the generation of hesitation marks is prevented in advance, thereby achieving the above object.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows a main part of the injection molding machine 1 of this embodiment. The injection molding machine 1 has an injection device 10 for injecting a synthetic resin and a molding die 20. The injection device 10 includes a molten barrel-shaped synthetic resin inside a barrel 11.
A screw 12 for kneading 30 is provided. barrel
A nozzle 13 is provided at the tip of 11. By connecting the nozzle 13 to the bush 21 of the mold 20 and injecting the molten resin 30, the inside of the mold 20 is filled with the molten resin 30. A blow-in pipe 14 for injecting a pressurized gas into the molded product 31 is inserted inside the nozzle 13, and the blow-in pipe 14 is supplied with an inert gas such as nitrogen gas from a supply source (not shown). .

The mold 20 is divided into a lower core portion 20A and an upper cavity portion 20B in the figure. As shown in FIG. 3, the cavity portion 20B has a cavity 22 which is a concave portion for molding a rectangular thin-walled molded product.

The core portion 20A has a molding surface 23 formed on the upper side corresponding to the cavity 22 of the cavity portion 20B. A sprue 24 penetrating the core portion 20A is opened at the center of the molding surface 23. The nozzle 13 of the injection device 10 that is in contact with the bush 21 through the sprue 24 is
It is designed to communicate with 22. Molding surface of core 20A
In the groove 23, a groove-shaped gas channel guide portion 25 is formed along the peripheral edge of the molding surface 23 and the diagonal line. The portion other than the gas channel guide portion 25 is a thin wall forming portion 26 that is a portion having a narrow space between the cavities 22. Here, by filling the molten resin 30 between the cavity 22 and the molding surface 23, a thick wall portion 32 having a large thickness is formed inside the gas channel guide portion 25, and a thin wall portion 26 is formed. A thin portion 33 having a small thickness is formed (see FIG. 2). A gas channel, which is a gas passage, is formed inside the thick portion 32 by injecting gas into the molten resin 30.
34 is to be formed. Further, the mold 20 is a pressing means such as a hydraulic cylinder device (not shown),
By pressing one of the cavities 20B toward the other, the mold is closed. Further, the mold 20 can be set to a state in which the core portion 20A and the cavity portion 20B are opened from the completely closed state by a predetermined dimension R (see FIG. 3).

In this embodiment, as shown in FIG. 4A, the mold 20 is completely closed and the core portion 20A is removed.
The cavity 20B is opened by a predetermined dimension R, and the mold 20 in this state is filled with the molten resin 30 to start the first step. The size R is set in the range of 1 to 3 mm. Next, as shown in FIG. 4B, the filling amount of the molten resin 30 is 80 to 80% of the total amount to be filled in the mold 20 so that the front end portion 35 of the flow of the molten resin 30 does not stop. When the range of 99% is reached, the second step and the third step are started simultaneously.

At the start of the second step, the core portion 20A and the cavity portion 20B are clamped, and the molten resin 30 filled therein is pressed to spread the molten resin 30 and fill the molten resin 30. Even if is completed, the tip portion 35 of the molten resin 30 is allowed to continue moving. Here, if the mold clamping timing is too early, the flow resistance of the thin-walled forming portion 26 becomes large at an early stage, so that the effect of opening the mold 20 by the predetermined dimension R cannot be obtained, and the air pocket ( Holes) or weld marks occur. With the start of the third step,
Inject gas into the molten resin 30 filled in the mold 20,
The injection of this gas causes the tip 35 to continue to move. Then, after the completion of the mold clamping of the mold 20, which is the end of the second step, the gas injection is continued within the range of 0.1 to 1 second, and as shown in FIG. A gas channel 34 is formed inside the molten resin 30 along the gas channel guide portion 25, and after the gas channel 34 is spread over the entire molten resin 30, gas injection is completed and the third step is ended. Then, the mold 20 is opened and the molded product 31 is taken out.

According to this embodiment as described above, the following effects can be obtained. That is, in a state where the mold 20 is opened from the completely closed state to the predetermined dimension, the molten resin 30 is filled, and the flow resistances of the thin-wall forming portion 26 and the gas channel guide portion 25 are set to be substantially the same as each other. The molten resin 30 of the portion 26 reaches the end edge of the mold 20 almost at the same time as the molten resin 30 of the gas channel guide portion 25, the molten resins 30 do not collide with each other, and weld marks are generated in advance. It can be prevented.

Further, the second and third steps are started before the first step is completed, and the second step is expanded and the third step is gas-injected from the movement by the filling pressure in the first step. The molten resin 30
Since the movement of the front end portion 35 of the flow is continuous throughout, the front end portion 35 of the molten resin 30 does not stop once, and the generation of hesitation marks can be prevented.

Further, since the second step and the third step are started at the same time, the movement of the tip portion 35 of the molten resin 30 is continued by both spreading the molten resin 30 and injecting the gas. Further, the propulsive force for moving the front end portion 35 of the molten resin 30 is strengthened, the temporary stop of the front end portion 35 of the molten resin 30 is less likely to occur, and the generation of the hesitation mark can be prevented more reliably.

Further, when the mold 20 is completely closed, the core 20
A and the cavity portion 20B are opened by a predetermined dimension R, the dimension R is set within a range of 1 to 3 mm, and the second and third steps are filled with the molten resin 30 in the first step. The above effect can be surely obtained by starting when the amount reaches 80 to 99% of the total amount to be filled in the mold 20, so that even if the injection molding is repeated many times, a uniform quality can be obtained. It is possible to obtain the molded article 31 of.

Further, since the gas injection is continued even after the mold clamping of the mold 20 is completed by completing the third process after the completion of the second process, the inside of the molten resin 30 can be maintained. The formed gas channel 34 will not be crushed by mold clamping, and the initially set gas channel 34 will be formed reliably, and defects such as sink marks will not occur in the obtained molded product 31.

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 gas injection molding is performed using the mold according to the present invention. In this experimental example, a mold having the same basic structure as the mold 20 shown in the above-mentioned embodiment is used, and under the injection condition set within the range in which the present invention described in the above-mentioned embodiment can be achieved. Experimental Examples 1 to 3 are performed. The injection conditions of Experimental Examples 1 to 3 are shown in Table 1.
It is shown in.

[0023]

[Table 1]

Comparative Example This comparative example is an experimental example in which gas injection molding is performed under injection conditions outside the range in which the present invention can be achieved, in order to compare with the experimental example. In this comparative example, a mold 20 having the same shape as the experimental example is used. Also,
The injection conditions of this comparative example are also shown in Table 1.

Here, a concrete description of these Comparative Examples 1 to 7 will be briefly made. Comparative Example 1 is an experimental example of normal gas injection molding in which the mold 20 is completely closed. In Comparative Example 2, the dimension R for opening the mold 20 in the first step is 1 mm.
This is an example of an experiment performed below. Contrary to Comparative Example 2, Comparative Example 3 is an experimental example in which the dimension R for opening the mold 20 is set to 3 mm or more in the first step. Comparative Example 4 is an experimental example in which the mold clamping is restarted quickly and the mold clamping is started before the filling amount of the molten resin 30 reaches the range of 80 to 99% of the total amount to be filled in the mold 20. Contrary to Comparative Example 4, Comparative Example 5 is an experimental example in which the mold clamping restart time is late and the mold clamping is started after the filling of the molten resin 30 is completed. Comparative Example 6 is an experimental example in which the gas injection start time is late and gas injection is started at the end of the filling of the molten resin 30. Comparative Example 7 is an experimental example of gas injection molding in which gas injection time is short and gas injection is completed before the end of mold clamping.

[Common Injection Conditions] In the above experimental example and comparative example, the common injection conditions which are the premise of gas injection molding are set as follows. Resin used: Noryl Molding temperature: 270 ° C. Mold temperature: 60 ° C. Note that the thickness t (see FIG. 2) of the thin wall forming portion 26 of the mold 20 is
Set to 1.5 mm. [Experimental Results] The results of each experiment are as follows. In addition, in the rightmost column of Table 1, an outline of the result is described in one word. That is, in Experimental Examples 1 to 3, as shown in FIG. 5, it was possible to obtain a molded article 31 having a good appearance with no sink marks, weld marks, hesitation marks or the like on the surface.

On the other hand, Comparative Example 1, Comparative Example 4, and
In Comparative Example 5, as shown in FIG. 6, both a weld mark 41 and a hesitation mark 42 are formed on the surface of the peripheral edge portion 50A of the molded product 50, and a general surface is formed in the central portion near the sprue 51. There was a trace 43 of gas leaking in. As a result, the appearance of the molded product 50 was impaired. In Comparative Example 2, as shown in FIG. 7, a marked weld mark 41 was formed on the surface of the peripheral edge portion 52A, and a hesitation mark 42 was also formed. Only the weld mark 41 was formed on the surface of the thin portion 52B. With these, molded products 52
The appearance of was damaged. In Comparative Example 3, as shown in FIG. 8, traces of gas leak near the center of the long side 53A of the molded product 53.
44 remains, which impairs the appearance of the molded product 53. In Comparative Example 6, as shown in FIG. 9, a significant hesitation mark 42 is generated on the surface of the peripheral edge portion 54A, and
Weld mark 41 was also occurring. This impaired the external appearance of the molded product 54. In Comparative Example 7, as shown in FIG. 10, a weld mark 41 is formed on the surface near the center of both the long side 55A and the short side 55B, and the surface near the center of the short side 55B is formed due to insufficient gas injection. There was a sink mark 45. As a result, the appearance of the molded product 55 was impaired.

The present invention is not limited to the above-mentioned embodiment, but includes the following modifications. That is, the molded product is not limited to a substantially planar product,
It may be box-shaped or container-shaped, in short, as long as it is thin. Further, the thick portion formed in the molded product is not limited to the brace shape, but may be a lattice stripe shape, and may be set so as to obtain a required strength in a required direction.

Further, the molten resin is not limited to Noryl, but other resin such as polypropylene may be used. Further, the driving means for driving the closing portion is not limited to the hydraulic cylinder device, and may be an air cylinder device, an electric type or an electromagnetic type. Further, the pressurized gas is not limited to nitrogen gas, and other inert gas such as argon gas may be adopted.

[0030]

As described above, according to the present invention, it is possible to prevent the formation of weld marks and hesitation marks on a molded product and to improve the appearance of the molded product.

[Brief description of drawings]

FIG. 1 is a time chart illustrating the present invention.

FIG. 2 is a sectional view showing a gas injection molding machine according to an embodiment of the present invention.

FIG. 3 is a perspective view showing a disassembled state of the mold of this embodiment.

FIG. 4 is an explanatory diagram showing a procedure of this embodiment.

FIG. 5 is a plan view showing experimental results of Experimental Examples 1 to 3 of the present invention.

FIG. 6 is a plan view showing experimental results of Comparative Examples 1, 4, and 5 of the present invention.

FIG. 7 is a plan view showing an experimental result of Comparative Example 2 of the present invention.

FIG. 8 is a plan view showing an experimental result of Comparative Example 3 of the present invention.

FIG. 9 is a plan view showing an experimental result of Comparative Example 6 of the present invention.

FIG. 10 is a plan view showing an experimental result of Comparative Example 7 of the present invention.

[Explanation of symbols]

 20 Mold 20A Mold core, which is the male mold 20B Mold cavity, which is the female mold 30 Molten resin 31 Molded product

Claims (5)

[Claims] 1. A first step of filling a molten resin from a completely closed state to a state in which a predetermined dimension is opened, and a molten resin filled inside by closing the incompletely closed die. And a third step of injecting a gas into the molten resin filled in the mold, the second to third steps being the first step. The method for gas injection molding, which is started before the step of (1) is finished. 2. The gas injection molding method according to claim 1, wherein the second step and the third step are simultaneously started. 3. The gas injection molding method according to any one of claims 1 and 2, wherein the mold in the first step is closed from a completely closed state with an opening margin of 1 to 3 mm. A gas injection molding method characterized in that 4. The gas injection molding method according to claim 1, wherein in the second and third steps, the amount of molten resin filled in the mold is the first step. Gas injection molding method, characterized in that it is started when the range of 80-99% of the total amount to be reached is reached. 5. The gas injection molding method according to claim 1, wherein the third step is completed after the second step is completed. Method.