JP2816280B2 - Gas injection molding method and gas injection device - 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 for forming a cavity in a resin.

[0002]

Recently, the molten resin into the mold while the injected molten resin does not yet solidified, the resin molding method of injecting a gas into the resin has come to be extensively used. ( See, for example, Japanese Patent Publication No. 57-14968 ). This molding method is hereinafter referred to as a gas assist molding method. gas·
The assist molding method involves molding a box 21 having a hollow portion 21c as shown in FIG. 9 or a handle 60 as shown in FIG.
It is particularly effective for molding thick products such as

First, a box 21 formed by a gas assist molding method
12 (a) and 12 (b) will be described with reference to FIG. In FIG. 12A, reference numeral 8 denotes a fixed type, and reference numeral 10 denotes a movable type. The movable mold 10 has a movable core 12
The have, piston movable core 12 is a hydraulic cylinder 16
The ton 14 can reciprocate in the directions of arrows C and D. The hydraulic cylinder 16 is attached to the movable mold 10. The movable die 10 is moved in the arrow X direction and pressed against the fixed die 8.
This operation is called closing the mold. By closing the mold,
A molding cavity 20 is formed between the fixed die 8 and the movable core 12. At this time, the movable core 12 is
And is pushed in the direction of arrow C to occupy the forward position. Next, the cylinder nozzle 2a at the tip of the plasticizing cylinder 2 is pressed against the locating ring 9 of the fixed die 8 to
To inject the molten resin 18 inside the plasticizing cylinder 2 into the molding cavity 20.

On the other hand, a gas nozzle 6 is mounted on the nozzle portion 2a at the tip of the plasticizing cylinder 2, and the gas nozzle 6
Is reciprocable in the directions of arrows A and B by a drive source (not shown). A high-pressure gas source 22 is connected to the gas nozzle 6 via a pressure reducing valve 24 and a gate valve 26a. At the same time as 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 release the cylinder nozzle 2a.
The tip of the gas nozzle 6 is brought into contact with the inner wall of the
Is opened and high-pressure gas is blown from the high-pressure gas source 26. The hydraulic cylinder 16 is operated at the same time as the high-pressure gas is blown to move the movable core 12 backward in the direction of arrow D. As a result, the high pressure gas is supplied to the sprue hole 21e as shown in FIG.
Is formed and blown into the molding cavity 20 through the sprue 21f, 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, the resin having high viscosity may be pulled to form the rib 21g. Since the rib 21g is useful for improving the compressive strength of the box 21, the rib can be formed at the place where the rib is formed at the place where the rib is to be formed. After that, if a predetermined cooling time has passed,
The movable mold 10 is moved in the arrow Y direction to open the mold, and the box 2 is opened.
Take 1 out.

Next, a case where a thick product such as the handle 60 shown in FIG. 11A is formed by a usual injection molding method will be described. Here, the normal injection molding is a method in which a molten resin is injected into a predetermined cavity of a mold, and is taken out from the mold after a predetermined cooling time has elapsed. FIG.
FIG. 11B is a cross-sectional view taken along the line LL in FIG. 11A. When a thick product is manufactured by the normal injection molding method as described above, as shown in the cross-sectional view of FIG. The concave portion 60a is formed around the thick portion and the appearance is not good. The concave portion 60a is usually called "sink", but when the molten resin injected into the mold cools, solidification starts from the outer peripheral portion in contact with the mold, and solidification of the resin inside the thick portion is delayed. Therefore, when the internal resin is solidified, the solidified outer peripheral resin is pulled inward to generate. FIG. 13 illustrates a method of forming 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 so that the inside of the runner 64 and the handle 60 is removed. A hollow portion 60b is formed as shown in the sectional view of FIG. The molten resin starts to solidify from the outside in contact with the mold, but the 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 marks.

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 general, in a resin injection molding method, it is necessary to cool the molten resin until the molten resin is solidified after the molten resin is injected into a mold cavity.
For this reason, a cooling water pipe is arranged in the mold, the mold is cooled with water, and the amount of heat until the molten resin is solidified is taken out to shorten the cooling time. Also in the gas assist molding method, a cooling water pipe is arranged in the mold to cool the molten resin, so that the resin at 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 transmitted to the resin in the outer peripheral portion, and then transmitted to the mold and reaches the cooling water pipe. However,
Resins are generally poor conductors of heat and have a thermal conductivity that is about 500 times lower than that of iron. Therefore, the amount of heat of the resin in the vicinity of the hollow portion cannot be removed unless it passes through the resin in the outer peripheral portion having poor thermal conductivity. It will be extremely long compared to.

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

If the cooling time is long in the injection molding of the resin, the occupation time of the injection molding machine per product becomes long, and therefore the cost of the product increases.

As described above, the conventional gas-assist molding method has a feature that a hollow box-shaped product or a thick product can be molded without sink marks, but the cooling time becomes longer and the cost increases. Had a problem. The present invention solves the above-mentioned problem, and it is possible to reduce the cooling time of the gas.
The purpose is to provide an assist molding method.

[0011]

According to the present invention, there is provided a resin molding method, comprising: an injection step of injecting a molten resin from a tip nozzle of a plasticizing cylinder into a cavity of a mold; A first gas injection step of injecting a gas to form a cavity by a gas pressure in a resin injected into the mold cavity while forming a gas passage from the tip nozzle to the mold cavity; A gas is injected from the gas injection device having an opening in the cavity into the cavity, and the gas flows in the gas passage formed in the first gas injection step in a direction opposite to the gas flow in the first gas injection step, thereby forming the tip nozzle. This is a gas injection molding method including a second gas injection step of discharging a gas from the substrate.

[0012] Further , a cavity is provided inside, and
A first gas injection hole for performing a first gas injection, and the first gas
Second gas injection hole for performing gas injection in the opposite direction to the injection
Thus, a gas injection molded product having the following is obtained.

The present invention further provides a gas cylinder for injecting gas into the resin injected into the mold,
A sleeve fixed to the gas cylinder and having a long hole, 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 for injecting gas from the opening of the sleeve into the cavity of the mold by attaching the tip to the mold by opening the tip into the cavity of the mold and reciprocating the gas piston rod in the sleeve. It is.

[0014]

According to the present invention having the above-described structure, after a cavity is formed by gas in the resin in the first gas injecting step, in the second gas injecting step, the temperature of the gas in the cavity is lower than that of the gas in the cavity. 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 a cylinder nozzle, the first gas injection step can be performed from a gas injection device.
As a result, the injection molding cycle time can be shortened, and the range of injection cooling conditions can be broadened.

[0015]

FIG. 1 is a diagram illustrating the operation of a mold when a hollow box is formed using a mold incorporating a 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. It is sectional drawing. The method of forming a hollow box by a 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. As shown in FIG. 1A, the fixed mold 8 and the movable mold 10 are closed, resin is injected from the cylinder nozzle 2a into the cavity 20, and then the hydraulic cylinder 16,
The movable core 12 is moved backward 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 high-pressure gas from the nozzle 2a to form the hollow portion 21c is referred to as a first gas injection step.

After the hollow portion 21c is formed by the first gas injection step, the conventional method waits for a cooling time until the resin inside the hollow portion is solidified, but in the present invention, the gas injection device 30 And at the same time, the flow path of the switching valve 26b is switched to discharge the gas from the hollow portion 21c . 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 reduced as compared with the conventional method. The step of injecting gas from the gas injection device 30 and simultaneously switching the flow path of the switching valve 26b to discharge gas from the hollow portion 21c is referred to as a second gas injection step.

FIGS. 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 fitting into a predetermined hole of the movable core 12. Gas piston 3 having O-ring 36 inside gas cylinder 32
4, when the gas is injected from the gas pipe A48, it can reciprocate in the direction of arrow E, and when the gas is injected from the gas pipe B50, it can reciprocate in the direction of arrow F. An elongated gas piston rod 38 is attached to the gas piston 34,
The outer periphery of the gas piston rod 38 is the long hole 31a of the sleeve 31
However, a long hole 40 and a lateral 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. Side hole 4 at standby position
Since 2 is located in the long hole 31a of the sleeve 31, gas does not blow out through the horizontal hole.

When gas injection is required, the gas pipe A48
Since the gas is supplied more 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 arrow E, and breaks the resin layer in contact with the mold with the acute angle head 44. An introduction pin 46 is provided in the gas cylinder 32, and the introduction pin 46 is fitted in the long hole 40 of the gas piston rod 38 described above. Therefore, gas pressure is applied to the gas piston 34 until the gas piston 34 moves in the direction of arrow E and the long hole 40 is completely removed from the tip of the introduction pin 46. When the gas piston 34 moves by a dimension l or more as shown in FIG. It breaks and squirts into the hollow part 21C. The ejected gas is hollow part 21c.
The heat is removed from the resin that comes in contact with the resin, and is released 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 is pulled out of the long hole 40, gas is released from the long hole 40.
Therefore, the gas pressure applied to the gas piston 34 decreases, and the gas piston 34 stops moving at that position. That is, by changing the length of the introduction pin 46, the position at which gas is ejected from the injection nozzle can be changed.

In the operation of the gas injection device described above, when the gas piston rod 38 moves in the direction of arrow E, the gas is usually sealed in the hollow portion inside the resin by the first gas injection step. Therefore, the gas pressure in the above-mentioned hollow portion acts on the tip of the gas piston rod 38 in a direction that hinders the movement of the gas piston rod 38. For this reason, in order for the gas piston rod 38 to break the resin layer of the box body 21 and project the tip into the hollow portion, a force against the gas pressure in the hollow portion is required in addition to the force for breaking through the resin layer. . First of the present invention
In this embodiment, the gas operating area of the gas piston 34 applied from the gas pipe A48 to move the gas piston rod 38 is made larger than the gas operating area of the gas in the hollow portion applied to the gas piston rod 38. Therefore, the gas piston rod 38 can be given a sufficient force against the gas pressure in the hollow portion and necessary to break the resin layer.

FIG. 10 shows a cross section of the molded box 21 and FIG. 9 shows a perspective view. FIG.
As can be seen from FIG. 9, the present invention uses the present invention in which the box 21 has a plurality of gas holes 21d from the second gas injection step, in addition to the sprue holes 21e formed in the first gas injection step. This is a characteristic of molded products. The sprue hole 21e when the first gas injection step is performed from the sprue side for injecting the resin.
Is generally larger than the diameter of the gas hole 21d in the second gas injection step.

By mounting the gas injection device 30 described above on a mold and cooling the hollow portion 21c of the box 21, the cooling time can be reduced as compared with the conventional method.
Although the cooling effect of the gas injection device differs depending on the size of the box, according to experiments performed by the inventors, the cooling time of the conventional method is 12 hours.
At 0 seconds, the cooling time can be reduced to 100
Could be reduced to seconds.

Next, FIG. 3 shows an embodiment in which a gas injection device is used for molding a thick handle-shaped product. FIG.
In the embodiment of the present invention, the resin is injected from the sprue 62 of the handle, and then the high-pressure gas is blown from the sprue 62 to form the runner 64 and the handle 60 in the same manner as described in the conventional gas assist molding method. A hollow portion 60b as shown in the sectional view of FIG. Again, from the sprue 62 to the handle 60
Is referred to as a first gas injection step.

In the embodiment of the present invention, as shown in FIG. 3, the thick end portion 60c of the thick handle passes through the connecting portion 70 to the resin reservoir A66, and further passes through the connecting portion 72 to the resin reservoir 68.
Is provided to the resin reservoir 66 so that the acute angle head 44 at the tip of the gas injection device 30 protrudes. 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 from 2 through the thick handle 60 to the resin reservoir 68 is formed. Thereafter, the gas injection device 30 is operated to blow gas into the hollow portion 60b,
The gas is discharged through the sprue 62. As a result, gas pressure is exerted on the hollow portion 60b of the thick-walled handle, and "hike"
While cooling, the resin in contact with the hollow portion 60b can be cooled, so that the cooling time can be reduced.

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 reduced to 120 by operating the gas injection device 30.
Could be reduced to seconds. Again, the gas injection device 3
The step of operating 0 to blow gas into the hollow portion 60b and discharging the gas through the sprue 62 is referred to as a second gas injection step.

FIG. 4 shows a second embodiment of the gas injection method. As can be easily understood from comparison 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 the gas injection device 30b is additionally provided. In this case, the resin is injected into the handle portion 60 through the sprue 62. In the first gas injection step, the gas is injected into the handle portion by operating the gas injection device 30b close to the sprue 62 and the cavity 6 is formed.
0b is formed. In the second gas injection step, gas is ejected from the gas injection device 30 as in FIG.
Gas is discharged from b.

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

When the gas is injected into the hollow portion 60b by operating the gas injection device 30, the gas is ejected from the tip of the gas piston rod 38 or the tip of the sleeve. Gas may leak out along the interface. FIG. 5 shows a device applied to the tip of the sleeve to prevent this. FIG. 5A is a cross-sectional view of the distal end portion of the sleeve, and FIG. 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. 21g of this annularly projecting resin
Therefore, the gas leakage path 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 preventing means. As can be easily understood from comparison 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. As in the first embodiment shown in FIG. 2, the gas piston 34 reciprocates by gas pressure, and the gas piston 34 is provided with an elongated gas piston rod 39. In FIG. 2, during standby, gas pressure is applied to the gas pipe B50 and the gas piston 34 is retracted. However, in the second embodiment of FIG. 8, during standby, the gas pressure is applied to the gas pipe A48 and the gas piston 34 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 retreat position, the piston rod 39 also occupies the retreat 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 a gas cavity is formed in a resin in a first gas injection step, in a second gas injection step, a temperature lower than that of the gas in the cavity is supplied from a gas injection device. Since the gas is injected, the cooling from the inside of the cavity is promoted by the low-temperature gas, so that the injection molding cycle time can be shortened, and the range of selection of the injection conditions can be widened.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are explanatory views of a molding operation of a box by a gas injection molding method of the present invention.

FIGS. 2A and 2B are explanatory views of the operation of a first embodiment of a gas injection device used in the gas injection molding method of the present invention.

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

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

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

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

FIGS. 8A and 8B are explanatory views of the operation of a second embodiment of the gas injection device 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.

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

FIGS. 12A and 12B are explanatory diagrams of a box forming operation by a conventional gas injection molding method.

FIG. 13 (a) is a diagram illustrating a molding operation of a thick resin product by a conventional gas injection molding method. (B) Sectional drawing in the direction of arrows MM.

[Description of numbering]

 Reference Signs List 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

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-261748 (JP, A) JP-A-1-154718 (JP, A) JP-A-3-9820 (JP, A) 133618 (JP, A) JP-A-3-268913 (JP, A) JP-A-3-274120 (JP, A) JP-A-4-37511 (JP, A) JP-A-4-45909 (JP, A) JP-A-6-55563 (JP, A) JP-A-5-293854 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B29C 45/00-45/84

Claims (9)

(57) [Claims] 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 the mold cavity by ejecting gas from the tip nozzle. A first gas injecting step of forming a cavity by gas pressure in the resin injected into the mold cavity while injecting gas into the cavity from a gas injecting device having an opening in the mold cavity; A gas injection molding method comprising: a second gas injection step of flowing gas in a gas passage formed in one gas injection step in a direction opposite to a gas flow of the first gas injection step and discharging gas from the tip nozzle. 2. A plurality of gas injection devices having an opening in a mold cavity are divided into a first group of gas injection devices and a second group of 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 second group of gas injection devices and discharging the gas from the first group of gas injection devices. 3. A gas cylinder, a sleeve fixed to the gas cylinder and having a long hole, a gas piston reciprocating inside the gas cylinder, and a gas fixed to the gas piston and guided by the long hole of the sleeve. A piston rod is formed, the tip of the sleeve is opened to the cavity of the mold and attached to the mold, and the gas piston rod is reciprocated in the sleeve so that the cavity of the mold is opened from the opening of the sleeve. Gas injection device that injects gas into the section. 4. A gas injection hole penetrating a gas piston rod, a hollow portion is formed in the resin in a 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 3, wherein the gas is injected by projecting a tip of the rod into the resin hollow portion. (5) Hollow part is formed in resin in the first gas injection process
After that, the gas piston rod is
Move the tip of the gas piston rod and the three
4. A gas is injected into the hollow portion of the resin through a gap between the grooves.
A gas injection device as described. 6. The gas injection device according to claim 3, wherein an annular groove is provided at a tip of the sleeve. 7. A mold gas injection device according to claim 3, wherein providing the annular protrusion at the tip of the opened above sleeve 8. The gas injection device according to claim 3, wherein a cross-sectional area of the gas cylinder is larger than a cross-sectional area of a tip end hole of the sleeve opened in the cavity. 9. An introduction pin is provided in a gas cylinder, the introduction pin is fitted to 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 to the gas injection hole. After 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 is injected from the gas injection hole, so that the gas pressure applied to the gas piston decreases. And stopping the movement of the gas piston and the gas piston rod.
A gas injection device as described.