JPH0691686A - Gas injection molded product and gas injection molding method and apparatus - Google Patents

Abstract

PURPOSE:To shorten an injection molding cycle time by forming a cavity in a resin by gas and injecting low temp. gas into the cavity from a gas injection device to cool the resin from the interior of the cavity. CONSTITUTION:A gas injection device 30 is incorporated in a movable mold 10. A resin is injected into a cavity 20 from a cylinder nozzle and, subsequently, high pressure gas is blown in the resin from a nozzle to form a hollow part 21 in the resin received in the cavity 20. Next, gas whose temp. is lower than that of the high pressure gas from the nozzle is injected into the hollow part 21 from the gas injection device and a changeover valve 26b is changed over to discharge the gas in the hollow part 21 and the hollow part 21 is filled with the low temp. gas from the gas injection device 30. Therefore, the resin in the cavity 20 is cooled from the hollow part 21 and the cooling time of the resin becomes short. Since gas injection can be performed from the cylinder nozzle and the gas injection device 30, an injection molding cycle time can be shortened.

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 forming a cavity inside a resin.

[0002]

2. Description of the Related Art Recently, a resin molding method has been widely used in which a molten resin is injected into a mold and a gas is injected into the resin while the molten resin is not yet solidified.
(For example, Japanese Patent Application No. 57-14968). Hereinafter, this molding method will be referred to as a gas assist molding method. gas·
The assist molding method is particularly effective for molding a box body 21 having a hollow portion 21c as shown in FIG. 9 and a thick product such as a handle 60 shown in FIG.

First, a box body 21 formed by the gas assist molding method.
The conventional molding method will be described with reference to FIGS. 12 (a) and 12 (b). In FIG. 12A, 8 is a fixed type and 10 is a movable type. The movable die 10 is the movable core 12
The movable core 12 can reciprocate in the directions of arrows C and D by the gas piston 14 of the hydraulic cylinder 16. The hydraulic cylinder 16 is attached to the movable die 10. The movable die 10 is moved in the direction of the arrow X and pressed against the fixed die 8. This operation is called closing the mold. A molding cavity 20 is formed between the fixed mold 8 and the movable core 12 by the closing operation of the mold. At this time, the movable core 12 is pushed in the direction of arrow C by the hydraulic cylinder 16 and occupies the forward position. Then, the cylinder nozzle 2a at the tip of the plasticizing cylinder 2 is pressed against the locate ring 9 of the fixed die 8, and the molten resin 18 inside the plasticizing cylinder 2 is injected into the molding cavity 20 by the screw 4.

On the other hand, a gas nozzle 6 is attached to the nozzle portion 2a at the tip of the plasticizing cylinder 2, and the gas nozzle 6
Can be reciprocated in the directions of arrows A and B by a drive source (not shown). Further, the high pressure gas source 22 is connected to the gas nozzle 6 via the pressure reducing valve 24 and the sluice valve 26a. Then, at the same time when the injection of the resin into the molding cavity 20 is completed, the gas nozzle 6 is advanced in the direction of arrow A to move the cylinder nozzle 2a.
The tip of the gas nozzle 6 is brought into contact with the inner wall of the
And a high pressure gas is blown from the high pressure gas source 26. Simultaneously with the injection of high-pressure gas, the hydraulic cylinder 16 is operated to move the movable core 12 backward in the direction of arrow D. As a result, the high-pressure gas is transferred to the sprue hole 21e as shown in FIG.
While passing through the sprue 21f, it is blown into the molding cavity 20 and the resin already injected into the molding cavity 20 is pressed against the wall surface of the mold to form the hollow portion 21c as shown in FIG. 12 (b). When the hollow portion 21c is formed, a resin having high viscosity may be pulled to form the rib 21g. The ribs 21g are useful for improving the compressive strength of the box body 21, and therefore, if the mold is made uneven at the place where the ribs are to be formed, the ribs can be formed at those places. After that, if the predetermined cooling time elapses,
Move the movable mold 10 in the direction of the arrow Y to open the mold, and
Take 1 out.

Next, a case where a thick product such as the handle 60 shown in FIG. 11A is molded by a normal injection molding method will be described. Here, ordinary injection molding is a method in which a molten resin is injected into a predetermined cavity of a mold, and after a predetermined cooling time has elapsed, it is taken out of the mold. Figure 11
FIG. 11B is a sectional view taken along the line L-L in FIG. 11A. When a thick product is manufactured by the normal injection molding method as described above, as shown in the sectional view of FIG. A concave portion 60a is formed around the thick portion, and the appearance is not good. The concave portion 60a is usually called a "sink", but when the molten resin injected into the mold cools, solidification starts from the outer peripheral portion in contact with the mold, and the solidification of the resin inside the thick portion is delayed. Therefore, when the resin inside is solidified, the resin in the outer peripheral portion that has already solidified is pulled inward. FIG. 13 illustrates a method of molding the handle 60 by the gas assist molding method. After the resin is injected from the sprue 62 of the handle, high pressure gas is blown from the sprue 62 to the inside of the runner 64 and the handle 60. A hollow portion 60b as shown in the sectional view of (b) is formed. The molten resin begins to solidify from the outside in contact with the mold, but high-pressure gas is present in the hollow portion 60b and constantly exerts pressure from the inside to the outside. It does not cause "sink".

As described above, the gas assist molding method is extremely effective for molding a box having a hollow portion and a product such as a handle having a thick portion.

[0007]

In the resin injection molding method, it is generally necessary to inject the molten resin into the mold cavity and then cool the molten resin until it solidifies.
For this reason, a cooling water pipe is arranged in the mold so that the mold is cooled by water and the amount of heat until the molten resin is solidified is taken out to shorten the cooling time. Even in the gas-assisted molding method, the cooling water pipe is arranged in the mold to cool the molten resin, so the resin on the outer peripheral portion in contact with the mold is effectively cooled by the mold. The heat of the resin in the vicinity of the hollow portion is first transferred to the resin in the outer peripheral portion and then to the mold to reach the cooling water pipe. However,
Resin is generally a poor conductor of heat, and its thermal conductivity is about 1/500 that of iron. Therefore, the heat quantity of the resin near the hollow part cannot be removed unless it passes through the resin on the outer peripheral part, which has poor thermal conductivity, and therefore the cooling time until the resin near the hollow part solidifies is the time during which the resin on the outer peripheral part solidifies. It will be extremely long compared to.

In particular, as shown in FIG. 12 (b), the rib 21
When g is formed, the heat of the central portion of the rib 21g cannot be transferred to the gas because the periphery is surrounded by the gas having a high temperature. Therefore, as shown in the enlarged view of FIG. 12B, the heat at the center of the rib must be transferred in the directions T1 and T2. This corresponds to an increase in the thickness of the heat-defective conductor of resin, so the cooling time of the rib portion becomes longer and longer.

If the cooling time is long in the injection molding of resin, the injection molding machine occupies a long time per product, and the cost of the product increases.

As described above, the conventional gas-assisted molding method has a feature that a hollow box shape or a thick product can be molded without a sink mark, but the cooling time becomes long and the cost increases. Had a problem. The present invention solves the above-mentioned problems by using a gas that can reduce the cooling time.
It is intended to provide an assist molding method.

[0011]

In order to achieve the above object, the present invention provides a resin molding method in which an injection step of injecting a molten resin from a tip nozzle of a plasticizing cylinder into a cavity of a mold and a tip nozzle A first gas injection step of forming a cavity by a gas pressure inside the resin injected into the mold cavity while forming a gas passage from the tip nozzle to the mold cavity by ejecting gas; A gas is injected into the cavity from a gas injection device having an opening in the cavity, and the gas is caused to flow through the gas passage formed in the first gas injection step in a direction opposite to the gas flow of the first gas injection step. A gas injection molding method comprising a second gas injection step of discharging gas from the.

Further, the present invention has a first gas injection hole which has a cavity therein and in which the first gas injection is performed, and a second gas injection in which the gas injection is performed in a direction opposite to the first gas injection. A gas injection molded product having holes.

Further, according to the present invention, since gas is injected into the resin injected into the mold, a gas cylinder,
A sleeve having a long hole fixed to the gas cylinder, a gas piston reciprocating inside the gas cylinder, and a gas piston rod fixed to the gas piston and guided by the long hole of the sleeve. A gas injection device that injects gas into the cavity of the mold from the opening of the sleeve by reciprocating the gas piston rod in the sleeve by attaching the tip to the cavity of the mold. Is.

[0014]

Since the present invention has the above-described structure, after the cavity is formed by the gas in the resin in the first gas injecting step, in the second gas injecting step, the temperature lower than that of the gas in the cavity is set by the gas injecting device. Since the gas is injected, the resin can be cooled from the inside of the cavity by the low temperature gas. In addition to performing the first gas injection step from the cylinder nozzle, the first gas injection step can be performed from the gas injection device.
As a result, the injection molding cycle time can be shortened and the range of selection of injection cooling conditions can be expanded.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining the operation of a mold when a hollow box is molded using a mold incorporating the gas injection device according to the present invention, and FIG. 2 is a detailed view of the gas injection device according to the present invention. FIG. The method of forming the hollow box body by the conventional method has been described with reference to FIG. 12, but FIG. 1 is almost the same as FIG. 12, and the same parts are denoted by the same reference numerals. The difference is that the gas injection device 30 is incorporated in the movable mold 10 in FIG. 1. As shown in FIG. 1A, the fixed die 8 and the movable die 10 are closed, resin is injected into the cavity 20 from the cylinder nozzle 2a, and then the hydraulic cylinder 16,
The movable core 12 is retracted by the gas piston 14. At the same time, high-pressure gas is blown from the nozzle 2a to form the hollow portion 21c, but the basic steps up to this point are the same as in the conventional method. However, for convenience of the following description, the step of blowing the high-pressure gas from the nozzle 2a to form the hollow portion 21c will be referred to as a first gas injection step.

After the hollow portion 21c was formed by the first gas injection step, the conventional method waited for the cooling time until the resin inside the hollow portion solidified, but in the present invention, the gas is injected from the gas injection device 30. Is blown, and at the same time, the flow path of the switching valve 26b is switched to discharge the gas from the hollow portion 21. As a result, the resin in contact with the hollow portion 21c is cooled by the gas injected from the gas injection device 30, so that the cooling time can be significantly shortened as compared with the conventional method. The step of blowing gas from the gas injection device 30 and simultaneously switching the flow path of the switching valve 26b to discharge the gas from the hollow portion 21c is referred to as a second gas injection step.

2A and 2B show the detailed structure of the gas injection device 30 described above. A gas cylinder 32 is attached to the movable core 12. A sleeve 31 is attached to one end of the gas cylinder 32, and the sleeve 31 is positioned with respect to the mold by being fitted into a predetermined hole of the movable core 12. Gas piston 3 having an O-ring 36 inside the gas cylinder 32
4, when the gas is injected from the gas pipe A48, the reciprocating motion can be performed in the arrow E direction, and when the gas is injected from the gas pipe B50, the reciprocating motion can be performed in the arrow F direction. An elongated gas piston rod 38 is attached to the gas piston 34,
The outer circumference of the gas piston rod 38 is a long hole 31a of the sleeve 31.
However, a long hole 40 and a horizontal hole 42 are provided inside.

When gas is supplied from the gas pipe B50, the gas piston 34 moves in the direction of arrow F and occupies the retracted position. This state is the standby position. Horizontal hole 4 in standby position
Since No. 2 is located in the long hole 31a of the sleeve 31, gas will not be ejected through the lateral hole.

When it is necessary to eject gas, the gas pipe A48
Since more gas is supplied and the gas pipe B50 is connected to the atmosphere, the gas piston 34 moves in the direction of arrow E by the gas pressure. Therefore, the gas piston rod 38 also moves in the direction of the arrow E, and breaks the resin layer in contact with the mold by the acute-angled head 44. The gas cylinder 32 is provided with an introduction pin 46, and the introduction pin 46 is fitted into the long hole 40 of the gas piston rod 38 described above. Therefore, the gas pressure is applied to the gas piston 34 until the gas piston 34 moves in the direction of the arrow E and the elongated hole 40 is completely removed from the tip of the introduction pin 46. When the gas piston 34 moves more than the dimension l shown in FIG. 2B, the tip of the introduction pin 46 comes out of the elongated hole 40, so that the gas passes through the elongated hole 40 and the lateral hole 42, and the resin layer is pressurized with gas. It breaks and squirts into the hollow portion 21C. The blown out gas is hollow 21c
While drawing heat from the resin in contact with the air, it is discharged from the switching valve 26b to the atmosphere through the sprue hole 21e and the gas nozzle 6 shown in FIG.

In the structure of the gas injection device 30 described above,
When the introduction pin 46 comes out of the long hole 40, the gas flows
Since it is ejected into the hollow portion through the gas piston 34, the gas pressure applied to the gas piston 34 is reduced and the force for moving the gas piston 34 is lost, and the gas piston stops at that position. That is, the position at which the gas is ejected from the injection nozzle can be changed by changing the length of the introduction pin 46.

In the operation of the gas injection device described above, when the gas piston rod 38 moves in the direction of the arrow E, the gas is normally enclosed in the hollow portion inside the resin by the first gas injection step. Therefore, the gas pressure in the hollow portion acts on the tip of the gas piston rod 38 in a direction in which the movement of the gas piston rod 38 is hindered. For this reason, in order for the gas piston rod 38 to break the resin layer of the box body 21 and to project the tip into the hollow portion, in addition to the force of breaking through the resin layer, a force that opposes the gas pressure in the hollow portion is required. . First of the present invention
In the embodiment, the gas operating area of the gas piston 34 added from the gas pipe A48 to move the gas piston rod 38 is made larger than the gas operating area of the hollow portion added to the gas piston rod 38 due to the gas. Therefore, it is possible to give the gas piston rod 38 a sufficient force against the gas pressure in the hollow portion and to break the resin layer.

FIG. 10 shows a cross section of the molded box body 21, and FIG. 9 shows a perspective view thereof. Figure 10,
As can be seen from FIG. 9, the present invention is used in the box body 21, in addition to the sprue holes 21e formed in the first gas injection step, a plurality of gas holes 21d formed in the second gas injection step. This is a characteristic of the molded product. Sprue hole 21e when the first gas injection step is performed from the sprue side for injecting the resin
The diameter of is usually larger than the gas holes 21d formed by the second gas injection step.

By mounting the gas injection device 30 described above in a mold and cooling the hollow portion 21c of the box body 21, the cooling time can be shortened as compared with the conventional method.
Although the cooling effect of the gas injection device varies depending on the size of the box, according to the experiments by the inventors, the cooling time of the conventional method is 12
When the gas injection device is used at 0 seconds, the cooling time is 100
I was able to reduce it to seconds.

Next, FIG. 3 shows an embodiment in which a gas injection device is used when molding a thick handle-like product. FIG.
Similarly to the conventional gas assist molding method described above, in the embodiment of the present invention, after the resin is injected from the sprue 62 of the handle, high pressure gas is blown from the sprue 62 to remove the runner 64 and the handle 60. A hollow portion 60b as shown in the sectional view of FIG. 13B is formed inside. Again, from the sprue 62 to the handle 60
The step of blowing gas into the inside of the chamber is called the first gas injection step.

In the embodiment of the present invention, as shown in FIG. 3, from the end portion 60c of the thick handle to the resin reservoir A66 through the connecting portion 70, and further through the connecting portion 72, the resin reservoir 68 is formed.
A resin passage is provided to the resin reservoir 66, and the resin reservoir 66 is attached so that the acute-angled head 44 at the tip of the gas injection device 30 projects. The structure of the gas injection device 30 is the same as that described in FIG. As described above, the sprue 6 is formed by the resin injection step and the first gas injection step.
A molded product having a hollow portion 60b extending from 2 to the resin reservoir 68 through the thick handle 60 is molded. Then, the gas injection device 30 is operated to blow the gas into the hollow portion 60b,
The gas is discharged through the sprue 62. As a result, the gas pressure is exerted on the hollow portion 60b of the thick-walled handle to cause "sinking".
Since the resin contacting the hollow portion 60b can be cooled while preventing this, the cooling time can be shortened.

In the experimental example, the cooling time of 150 seconds was required when the gas injection device 30 was not operated, but the cooling time was 120 by operating the gas injection device 30.
I was able to reduce it to seconds. Again, the gas injection device 3
A step of operating 0 to blow gas into the hollow portion 60b and discharging the gas through the sprue 62 is called a second gas injection step.

FIG. 4 shows a second embodiment of the gas injection method. As can be easily understood by comparing with FIG. 3, a resin reservoir 66b is provided in a part of the runner 64 from the sprue 62 which is a resin injection hole to the handle portion 60, and a gas injection device 30b is additionally installed. In this case, the resin is injected into the handle portion 60 through the sprue 62, but in the first gas injecting step, the gas injecting device 30b near the sprue 62 is operated to inject the gas into the handle portion and the cavity 6
0b is formed. In the second gas injecting step, gas is ejected from the gas injecting device 30 as in FIG.
The gas is discharged from b.

Also in the embodiment of FIG. 1, there is also a method of injecting the gas from the gas injecting device provided on the cavity side in the first gas injecting step, instead of injecting the gas from the tip nozzle of the plasticizing cylinder. In this case, a plurality of gas injecting devices are divided into two groups, a first group and a second group, and gas is injected from all the gas injecting devices in the first gas injecting step and the first gas injecting step is performed in the second gas injecting step. Gas is injected from the first group of gas injectors and exhausted from the second group of gas injectors.

When the gas injection device 30 is operated to blow the gas into the hollow portion 60b, the gas is ejected from the tip of the gas piston rod 38 or the tip of the sleeve. Gas may escape along the interface. FIG. 5 shows a device made on the tip of the sleeve in order to prevent this. FIG. 5A is a cross-sectional view of the sleeve tip portion, and FIG. 5B shows a view N-N in the figure. As shown in FIG. 5, an annular groove 31b is provided at the tip of the sleeve 31. At the time of resin molding, as shown in FIG. 6, an annular resin 21g is formed in the annular groove 31b. 21 g of resin that protrudes in an annular shape
Therefore, the gas leakage passage is bent as shown by arrows m and n, so that gas leakage can be prevented.

FIG. 7 shows a second embodiment of the gas leakage prevention means. As can be easily seen by comparing with FIG.
An annular projection 31c is provided instead of the annular groove 31b in FIG. In this case, an annular groove is formed in the injected resin.

FIG. 8 shows a second embodiment of the gas injection device. Similar to the first embodiment shown in FIG. 2, the gas piston 34 reciprocates due to gas pressure, but the gas piston 34 is provided with an elongated gas piston rod 39. In FIG. 2, gas pressure is applied to the gas pipe B50 during standby, and the gas piston 34 is retracted. However, in the second embodiment of FIG. 8, gas pressure is applied to the gas pipe A48 during standby and the gas piston 34 moves. Occupies the forward position. In this state, the hole 31a at the tip of the sleeve 31 is closed by the fitting portion 44a at the tip of the gas piston rod 39. When the gas pressure is applied to the gas pipe B50 and the gas piston 34 occupies the retracted position, the piston rod 39 also occupies the retracted position, so that the hole 31a at the tip of the sleeve 31 is opened and the gas is ejected through the hole 31a.

[0032]

As described above, according to the present invention, after the cavity is formed by the gas in the resin in the first gas injecting step, the temperature of the gas in the cavity is lower than that of the gas in the cavity in the second gas injecting step. Since the gas is injected, cooling from the inside of the cavity is promoted by the low-temperature gas, the injection molding cycle time can be shortened, and the range of selection of injection conditions can be widened.

[Brief description of drawings]

1A and 1B are explanatory views of a box body molding operation by a gas injection molding method of the present invention.

2 (a) and 2 (b) are explanatory views of the operation of the first embodiment of the gas injection apparatus used in the gas injection molding method of the present invention.

FIG. 3 is an explanatory view of the molding operation of the first embodiment of the thick resin product by the gas injection molding method of the present invention.

FIG. 4 is an explanatory view of the molding operation of the second embodiment of the thick resin product by the gas injection molding method of the present invention.

FIG. 5 (a) is a sectional view of the first embodiment of the sleeve tip portion of the gas injection device used in the gas injection molding method of the present invention. (B) The top view in the arrow N-N.

FIG. 6 is a cross-sectional view including the injection resin at the tip of the sleeve of the gas injection device of the present invention.

FIG. 7 (a) is a sectional view of a second embodiment of the sleeve tip portion of the gas injection device used in the gas injection molding method of the present invention. (B) The top view in arrow P-P.

8 (a) and 8 (b) are explanatory views of the operation of the second embodiment of the gas injection apparatus used in the gas injection molding method of the present invention.

FIG. 9 is a perspective view of a box formed by the gas injection molding method of the present invention.

FIG. 10 is a sectional view of a box formed by the gas injection molding method of the present invention.

FIG. 11A is a perspective view of a handle which is an example of a thick product. (B) Sectional drawing in the arrow LL.

12 (a) and 12 (b) are views for explaining the forming operation of the box body by the conventional gas injection molding method.

FIG. 13A is an explanatory view of a molding operation of a thick resin product by a conventional gas injection molding method. (B) Sectional drawing in the arrow MM.

[Explanation of supplements]

 2 plasticizing cylinder 2a cylinder nozzle 20 molding cavity 30 gas injection device 31 sleeve 31b annular groove 31c annular protrusion 32 gas cylinder 34 gas piston 38 piston rod 40 gas injection hole 46 introduction pin

Claims (10)

[Claims] 1. An injection step of injecting a molten resin from a tip nozzle of a plasticizing cylinder into a cavity of a mold, and forming a gas passage from the tip nozzle to eject gas from the tip nozzle to the mold cavity. Meanwhile, a first gas injection step of forming a cavity by the gas pressure inside the resin injected into the mold cavity, and a gas is injected into the cavity from a gas injection device having an opening in the mold cavity. A gas injection molding method comprising: a second gas injection step of flowing gas through the gas passage formed in the first gas injection step in a direction opposite to the gas flow of the first gas injection step to discharge the gas from the tip nozzle. 2. A plurality of gas injection devices having openings in a mold cavity are divided into a first group of gas injection devices and a second group of gas injection devices, and the first gas injection process is performed from all the gas injection devices. The gas injection molding method according to claim 1, wherein the gas injection is performed by injecting a gas, and the second gas injection step is performed by injecting a gas from a gas injection device of the second group and discharging the gas from the gas injection device of the first group. 3. A gas injection molding having a gas injection hole in the first gas injection step and a gas injection hole in the second gas injection step, and having a cavity inside. 4. A gas cylinder, a sleeve fixed to the gas cylinder and having an elongated hole, a gas piston reciprocating inside the gas cylinder, and a gas fixed to the gas piston and guided by the elongated hole of the sleeve. It is composed of a piston rod, the tip of the sleeve is opened in the cavity of the mold and attached to the mold, and the gas piston rod is reciprocated in the sleeve to allow the cavity of the mold from the opening of the sleeve. Gas injection device that injects gas into the area. 5. A gas injection hole penetrating the gas piston rod is provided, and a hollow portion is formed in the resin in the first gas injection step, and then the gas piston rod is moved toward the hollow portion of the resin to form the gas piston. The gas injection device according to claim 4, wherein the tip of the rod is projected into the resin hollow portion to inject gas. 6. After forming a hollow portion in the resin in the first gas injecting step, the gas piston rod is moved in a direction opposite to the direction of the hollow portion of the resin so as to move the gas piston rod from the gap between the tip of the gas piston rod and the sleeve. The gas injection device according to claim 4, wherein gas is injected into the hollow resin portion. 7. The gas injection device according to claim 4, wherein an annular groove is provided at the tip of the sleeve. 8. The gas injection device according to claim 4, wherein an annular protrusion is provided at the tip of the sleeve opened in the mold. 9. The gas injection device according to claim 4, wherein the cross-sectional area of the gas cylinder is made larger than the cross-sectional area of the tip hole of the sleeve opened to the cavity. 10. A gas cylinder is provided with an introduction pin, the introduction pin is fitted into a gas injection hole provided in a gas piston rod, and the gas piston is fitted to the gas piston while the introduction pin is fitted in the gas injection hole. The gas pressure is applied to move the gas piston and the gas piston rod, and after the introduction pin comes out of the gas injection hole, the gas pressure applied to the gas piston decreases due to the gas ejected from the gas injection hole. The gas injection device according to claim 4, wherein the movement of the gas piston and the gas piston rod is stopped by means of the gas injection device.