JP3215751B2 - Gas injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas injection molding method, and relates to the appearance of a bumper, a dashboard, a wheel cap, a door panel and the like of an automobile, a casing of a home appliance, and a back cover of a television receiver. It can be used for manufacturing resin products that require quality.

[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. 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 surface does not sink due to the expansion force of the high-pressure gas. A molded article can be obtained.

In such a gas injection molding method, in order to obtain a thin molded product having strength and rigidity, a gas channel, which is a high-pressure gas passage, is provided in a rib shape inside the injection molded product and injection molding is performed. There is a rib type gas channel type gas injection molding method. According to this method, a rib-shaped thick portion having a partially thickened surface is formed into a thin-walled molded product by providing a gas channel guide portion by depressing the surface of a mold cavity. Is to form a gas channel inside. The thin molded article formed by this method can obtain sufficient strength and rigidity by the thick part formed in a rib shape, and can be reduced in weight by the gas channel which is a cavity formed inside the thick part. The generation of sink marks on the surface can be prevented by the high-pressure gas in the gas channel.

[0004] Further, by filling the molten resin into a mold that is imperfectly closed so that the molten resin does not leak to the outside, and spreading the filled molten resin by clamping the mold, every corner of the mold is removed. There is a spread-type gas injection molding method in which a molten resin is spread all the way. According to this method, even if the molded product is thin, the molten resin can be filled up to every corner of the mold due to the extension at the time of mold clamping, so that a failure due to a short shot can be reliably prevented.

[0005]

However, in the gas channel type gas injection molding method, the distance between the gas channel guides provided in the mold is wider than the surroundings, and the flow resistance of the molten resin is smaller than that of the cavity of the mold. Therefore, the molten resin flowing in the gas channel guide moves at a higher speed than the molten resin flowing in the thin-walled portion where the space between the mold cavities is narrow. Therefore, when the molten resin in the gas channel guide reaches the edge of the mold earlier than the molten resin in the thin-walled portion, it flows backward and collides with the molten resin in the thin-walled portion. As a result, a flow mark (hereinafter, referred to as a "weld mark") is generated on the surface of the molded product.

In addition, since the flow resistance of the molten resin in the thin-walled portion is large, a sufficient pressing force cannot be obtained in the vicinity of the edge of the mold even during filling, so that the flow front of the molten resin temporarily stops. Cheap. For this reason, the flow front of the molten resin is temporarily stopped when the filling is completed, and when the flow of the molten resin is restarted by mold clamping or gas injection, another flow mark (hereinafter, referred to as a hesitation mark) is formed on the surface of the molded product. "). Therefore, in the conventional gas injection molding method, there is a problem that the appearance of the molded product may be impaired due to the occurrence of weld marks and hesitation marks when molding a thin molded product.

An object of the present invention is to provide a gas injection molding method which does not generate weld marks and hesitation marks on a molded product.

[0008]

According to the present invention, there is provided a first step of filling a mold with a predetermined size open from a completely closed state with a molten resin, and clamping the incompletely closed mold. a second step of spreading the molten resin filled in the pressurizing manner, and a third step of injecting the gas into the molten resin filled in the mold, the second and 3
Starting each step of the first step before the end of the first step ,
After the start of the second step and before the completion of the second step
The third step is started at a point in time . 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 Figure 1, the first step begins by initiating the filling of the molten resin at the time 0 seconds, filling time T _S seconds to the molten resin is completed by completing. The second step begins by the time T _P seconds to resume clamping of the mold is terminated by clamping the time T _E seconds to complete. The third step begins by starting the gas injection time T _I s, is terminated by completing the gas injection time T _C seconds. The present invention is, start time _{T P} seconds a second step, and, the start time _{T I} s of the third step,
Time earlier der than the end time T _S seconds of the first step is, first
Start time T _I s of 3 steps is, the start time T of the second step
_{After P} seconds and before the completion time _TE seconds of the second step
Is the time of

[0009] Here, the timing of starting the second step and the third step, simultaneously, i.e., it is desirable that the time T _P seconds and time T _I s is the same time. Also,
It is preferable that the mold in the first step is closed in an open state while leaving a closing margin of 1 to 3 mm from a completely closed state. Further, it is desirable that the second and third steps are started when the filling amount of the molten resin in the first step reaches a range of 80 to 99% of the total amount to be filled in the mold. Further, to terminate the third step after finishing the second step, i.e., the end time T _E s of the second step is a time earlier than the end time T _C seconds in the third step Is preferred.

[0010]

According to the present invention, since the mold filled with the molten resin is opened to a predetermined dimension from the completely closed state, the interval between the thin-walled portions of the mold is enlarged, and the flow resistance of the thin-walled portion is increased. Is not much different from the flow resistance of the gas channel guide. For this reason, the molten resin in the thin-wall forming portion reaches the edge of the mold almost at the same time as the molten resin in the gas channel guide portion, so that the molten resins do not collide with each other, thereby preventing the occurrence of weld marks. Will be done.

Further, after the second and third steps are overlapped with the first step, second step and
Since the third step overlaps with each other, the leading end of the flow of the molten resin moves from the movement due to the filling pressure in the first step to the movement due to the spreading in the second step, and
The movement by spreading in the second step is seamlessly shifted to the movement by gas injection in the third step. For this reason, the tip portion of the molten resin does not stop once, and the occurrence of hesitation marks is prevented beforehand,
Thereby, the above object is achieved.

[0012]

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 the present 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 synthetic resin in a molten state inside a cylindrical 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 interior of the mold 20 is filled with the molten resin 30. Inside the nozzle 13, a blowing pipe 14 for injecting a pressurized gas into the molded article 31 is inserted, and the blowing pipe 14 receives supply of an inert gas such as nitrogen gas from a supply source (not shown). .

The mold 20 is divided into a lower core 20A and an upper cavity 20B in the figure. As shown in FIG. 3, the cavity portion 20B has a cavity 22 which is a concave portion for forming a rectangular thin 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 is formed in the center of the molding surface 23 so as to penetrate the core 20A. The nozzle 13 of the injection device 10 abutting on the bush 21 via the sprue 24
It is connected to 22. Molding surface of core 20A
In the groove 23, a groove-shaped gas channel guide 25 is formed along the periphery of the forming surface 23 and along a diagonal line. The portion other than the gas channel guide portion 25 is a thin-walled portion 26 where the space between the cavities 22 is narrow. Here, by filling the molten resin 30 between the cavity 22 and the molding surface 23, a thick portion 32 having a large thickness is formed inside the gas channel guide portion 25, and a thin portion 26 is formed in the thin portion forming portion 26. A thin portion 33 having a small thickness is formed (see FIG. 2). The gas channel, which is a gas passage, is formed by injecting a gas into the molten resin 30 inside the thick portion 32.
34 are formed. The mold 20 is pressed by a pressing means such as a hydraulic cylinder device (not shown) by a core 20A.
By pressing one of the cavities 20B toward the other, the mold is closed and closed. The mold 20 is also capable of opening the core portion 20A and the cavity portion 20B by a predetermined dimension R from the completely closed state (see FIG. 3).

In this embodiment, as shown in FIG. 4A, the core 20A is moved from the completely closed state of the mold 20.
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 dimension R is set in a range of 1 to 3 mm. Next, as shown in FIG. 4B, the filling amount of the molten resin 30 is set to 80 to 80% of the total amount to be filled in the mold 20 so that the leading end 35 of the flow of the molten resin 30 does not stop. When reaching the range of 99%, 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, whereby the molten resin 30 is spread and filled with the molten resin 30. Is completed, the tip 35 of the molten resin 30 continues to move. Here, if the timing of the mold clamping is too early, the flow resistance of the thin-wall forming portion 26 will increase 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. With the start of the third step,
Inject gas into the molten resin 30 filled in the mold 20,
Ahead end 35 by the injection of gas so as to continue to move. Subsequently, after the completion of the mold clamping of the mold 20, which is the end of the second step, gas injection is continued within a 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 25, and after the gas channel 34 has spread over the entire molten resin 30, the gas injection is completed and the third step is completed.
Thereafter, the mold 20 is opened and the molded product 31 is taken out.

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

Further, the second and third step starts before the first step is completed, spreading from movement by charging pressure of the first step of the second step, and, in a third step Since the movement of the front end 35 of the flow of the molten resin 30 is made continuous throughout by making a continuous transition to the movement by gas injection, the front end 35 of the molten resin 30 does not stop once, and the hesitation mark The occurrence can be prevented beforehand.

Furthermore, the second step and the third step are started simultaneously, and the movement of the tip 35 of the molten resin 30 is continued by both the spreading of the molten resin 30 and the gas injection. In addition, the driving force for moving the distal end portion 35 of the molten resin 30 is strengthened, and the temporary stop of the distal end portion 35 of the molten resin 30 is more unlikely to occur, and the occurrence of hesitation marks can be more reliably prevented.

Also, when the mold 20 is completely closed,
A and the cavity portion 20B are opened by a predetermined dimension R, the dimension R is set in a range of 1 to 3 mm, and the filling amount of the molten resin 30 in the second and third steps is set in the first step. Is started when it reaches the range of 80 to 99% of the total amount to be filled in the mold 20, so that the above-mentioned effect can be surely obtained, so that even if injection molding is repeated many times, uniform quality can be obtained. Can be obtained.

Further, by completing the third step after the completion of the second step, the gas injection is continued even after the mold 20 is completely clamped. The formed gas channel 34 is not crushed by the mold clamping, and the initially set gas channel 34 is reliably formed, so that the obtained molded product 31 does not have defects such as sink marks.

Next, the effects of the present invention will be described based on specific experimental examples. [Experimental Example] This experimental example is an experiment in which gas injection molding is performed using a mold according to the present invention. In this experimental example, a mold having the same basic configuration as the mold 20 shown in the above embodiment is used, and under injection conditions set within a range where the present invention described in the above embodiment can be achieved. Experimental Examples 1 to 3 are performed. Table 1 shows the injection conditions of Experimental Examples 1 to 3.
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 that of the experimental example is used. Also,
Table 1 also shows the injection conditions of this comparative example.

Here, a specific description of these comparative examples 1 to 7 will be simplified. Comparative Example 1 is an experimental example of ordinary 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 was 1 mm.
This is an experimental example performed as follows. 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, contrary to Comparative Example 2. Comparative Example 4 is an experimental example in which the mold clamping is restarted earlier, 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. Comparative Example 5 is an experimental example in which the mold reopening time is later than the comparative example 4, 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 the gas injection is started at the end of filling of the molten resin 30. Comparative Example 7 is an experimental example of gas injection molding in which the gas injection time is short and the gas injection is completed before the end of the mold clamping.

[Common Injection Conditions] In the above experimental examples and comparative examples, 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. The thickness t of the thin-walled portion 26 of the mold 20 (see FIG. 2)
Set to 1.5mm. [Experimental results] Each experimental result is as follows. In the rightmost column of Table 1, the summary of the result is described in one word. That is, in Experimental Examples 1 to 3, as shown in FIG. 5, a molded product 31 having a good appearance without any sink marks, weld marks, hesitation marks, etc. on the surface could be obtained.

On the other hand, Comparative Example 1, Comparative Example 4, and
In Comparative Example 5, as shown in FIG. 6, both the weld mark 41 and the hesitation mark 42 are formed on the peripheral portion 50A of the molded product 50, and the central portion near the sprue 51 has a general surface. There were traces 43 of gas leaks. As a result, the appearance of the molded product 50 was impaired. In Comparative Example 2, as shown in FIG. 7, a remarkable weld mark 41 was formed on the surface of the peripheral 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. The molded product 52
Appearance was impaired. In Comparative Example 3, as shown in FIG. 8, traces of gas leak were found near the center of the long side 53A of the molded product 53.
44 remained, which impaired the appearance of the molded article 53. In Comparative Example 6, as shown in FIG. 9, a significant hesitation mark 42 is formed on the surface of the peripheral portion 54A, and
A weld mark 41 was also formed. As a result, the appearance of the molded product 54 was impaired. 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 due to insufficient gas injection. There was a sink mark 45. These deteriorated the appearance of the molded article 55.

The present invention is not limited to the above-described embodiment, but includes the following modifications. That is, the molded product is not limited to a substantially planar shape,
It may be box-shaped or container-shaped, and in short, may be thin. Further, the thick portion formed on the molded product is not limited to the strut shape, but may be a checkerboard 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 may be other resins such as polypropylene. The driving means for driving the closing portion is not limited to the hydraulic cylinder device, but may be an air cylinder device, an electric type or an electromagnetic type. Further, the pressurized gas is not limited to the nitrogen gas, but may be another inert gas such as an argon gas.

[0030]

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

[Brief description of the 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 one embodiment of the present invention.

FIG. 3 is a perspective view showing a disassembled state of a mold according to the present embodiment.

FIG. 4 is an explanatory diagram showing a procedure of the present 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 Core, which is the male mold 20B Cavity, which is the female mold 30 Mold 31 Molded product

Continuation of the front page (56) References JP-A-3-133618 (JP, A) JP-A-63-27219 (JP, A) JP-A-4-353408 (JP, A) JP-A-4-255314 (JP) JP-A-4-284213 (JP, A) JP-A-1-157823 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 45/00-45/84

Claims (5)

(57) [Claims] 1. A first step of filling a molten resin into a mold opened to a predetermined dimension from a completely closed state, and the molten resin filled inside by closing the incompletely closed mold. And a third step of injecting a gas into the molten resin filled in the mold, wherein the second and third steps are performed by the first step. Starting before the end of the step, and starting after the start of the second step.
The gas injection molding method , wherein the third step is started before the completion of the second step . 2. The gas injection molding method according to claim 1, wherein the second step and the third step are started simultaneously. 3. The gas injection molding method according to claim 1, wherein the mold in the first step is closed in a state where the mold is opened with a margin of 1 to 3 mm from a completely closed state. A gas injection molding method characterized by being performed. 4. The gas injection molding method according to claim 1, wherein the second and third steps are such that the filling amount of the molten resin in the first step is equal to the filling amount of the mold. Gas injection molding method, which is started when the range of 80 to 99% of the total amount to be obtained 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.