JP2642993B2 - Plastic molding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for molding a high-precision plastic molded product applied to an injection molding machine and a press molding machine.

(Prior art) After injecting an insufficient amount of molten resin into the mold cavity to fill the mold cavity, a gas body is continuously injected from the same inlet alone or while injecting the molten resin, and further, if necessary. Japanese Patent Publication No. Sho 57-14968 proposes a method for molding a hollow mold characterized by filling a mold cavity by injecting a molten resin.

Referring to FIG. 6, an apparatus for carrying out the above-mentioned conventional method will be described. A resin 39 plasticized by a screw 32 for plasticizing and injecting a resin is stored in an injection cylinder 31, and a molten resin
After injecting an insufficient amount of the resin 39 filling the mold cavity 43 into the mold cavity 43 formed by the molds 41 and 42, the gas body is subsequently press-fitted from the gas body injection port 34 formed in the nozzle portion. . The gas inlet 34 is fixed to the center of the nozzle portion by an apparatus component 33. The gas passes through the molten resin and is pressed into the mold cavity 43. In addition, the gas body is moved by the advance of the high pressure ram 36 of the gas press-in cylinder 35 separately provided.
The gas body 40 stored in the cylinder 35 is press-fitted. In addition, any one of the following four methods may be used for pressurizing the gas body. That is, after injecting an insufficient amount of molten resin to fill the mold cavity, (1) press-in the gas body, (2) press-in the gas body, then inject the molten resin further, and (3) inject the molten resin. (4) Pressurizing the gas while injecting the molten resin, and then injecting the molten resin.

However, in the above-mentioned conventional method, since the volume of the mold cavity 43 does not change and the plastic flows through the thin passage of the cavity, a high firing power and gas pressure are required, and a residual stress is generated in the shaped product.

(Problems to be Solved by the Invention) In order to increase the product accuracy (dimensions, surface accuracy) of a partially hollow molded article by the above-mentioned conventional method, a high-pressure gas is required. That is, there is a problem of being restricted by containers, instruments, handling rules, etc. of the High Pressure Gas Control Law, and when the mold is injected in a completely closed state, the plastic flows into the thin portion of the cavity and completely follows the shape of the cavity. A high injection pressure is required to maintain the shape, and if it is cooled and solidified as it is, a residual stress is generated in the molded product, and there is a disadvantage that the molded product is deformed after molding.

The present invention has been proposed to solve the above-mentioned conventional problems.

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for injecting an insufficient amount of molten plastic into a mold cavity while leaving the mold in a slightly open state that does not completely close the mold, and subsequently injecting the same mold inlet, or The plastic in the mold is inflated while injecting gas from the gas inlet provided at an arbitrary position in the plastic flow path.Then, the injection path for the molten plastic and the gas is closed, and then the mold clamping force is increased and complete. The mold cavity is filled with plastic having a hollow portion by closing the mold, and the gas in the plastic hollow portion is converted into a high-pressure gas, which is used as a means for solving the problem.

(Operation) After injecting molten plastic into the mold and subsequently injecting gas to inflate the plastic, the volume of the mold cavity is reduced and the gas is compressed to obtain a high pressure. The gas inside the plastic at high pressure holds and cools the plastic while remaining completely in line with the shape of the cavity.

(Embodiments) The present invention will be described below with reference to the embodiments in the drawings.
FIG. 2 and FIG. 2 show a first embodiment of the present invention, which is an example applied to a normal injection molding machine.

In the figure, reference numeral 1 denotes an injection cylinder, in which an injection screw 2 is mounted, and an injection cylinder tip 3 is mounted at the tip. Reference numeral 4 denotes a gas injection member to which a gas joint 8 is attached, and gas is injected, discharged and stopped by a three-way valve 7. Further, a two-way valve 5 is incorporated in the gas injection member 4. Reference numeral 6 denotes an injection nozzle provided at the tip of the gas injection member 4, through which the molten plastic 18 is injected into the mold.

Reference numeral 9 denotes a fixed mold plate on which a fixed mold 10 is attached.
Reference numeral 11 denotes a movable mold plate, on which a mold 12 is mounted. Reference numeral 13 denotes a mold-pressing hydraulic cylinder, in which a hydraulic piston 14 slides, and hydraulic pressure is transmitted to the mold plate 11 by a piston rod 15. Reference numeral 16 denotes a limit switch for detecting the position of the movable mold platen 11, which detects a position of the molds 10 and 12 slightly returned from the cut-off position, stops the piston 14 and holds the mold at a predetermined position, and also includes a support rod. The position can be adjusted by being supported by 17. Also molten plastic 18
In FIG. 1, the injection cylinder tip 3 and the injection cylinder 1
Fig. 3 shows a state in which a fixed amount is stored. Reference numeral 19 denotes a cavity formed by the molds 10 and 12, and FIG. 1 shows a state where the cavity is sensed by the limit switch 16 and is held at a position slightly returned from the cutoff of the molds 10 and 12 by the hydraulic piston 14. I have.

Next, the operation of the embodiment of FIG. 1 will be described in accordance with the working steps of FIG. 2 and in the order of (a) to (d).

(A). While holding the mold 12 slightly open, the molten plastic 18 is injected. The mold 12 has a weak force f so as not to open any more.
Or the flow passage is closed so that the hydraulic oil of the embossed hydraulic cylinder 13 does not escape.

(B). During or after the injection of molten plastic 18,
The gas is injected into the mold through the two-way valve 5 and the injection nozzle 6 by operating the three-way valve 7 for gas. At this time, the mold 10 and the mold 12 are slightly opened, the plastic flows at a low injection pressure because the cavity is thick, the core of the plastic thickness is still in a molten state, the viscosity is low, and the gas pressure is low. But gas goes into the plastic.

(C). With the two pieces 5 closed and the three-way valve 7 for gas closed, the mold is closed with a large mold clamping force F. At this time, the molten plastic 18 was filled into the cavity 19 formed by the molds 10 and 12 with a pressing force, and the gas in the hollow was also compressed to a high pressure, and the molten plastic 18 was strongly pressed along the cavity mold. Cool and solidify as it is.

(D). After cooling and solidifying the plastic material, gas three-way valve 7
Is operated to exhaust gas, the two-way valve 5 is opened to release the gas in the plastic hollow portion, the gas pressure in the plastic molded product is sufficiently reduced, and then the mold 12 is opened to take out the resin in the cavity 19 as a molded product. . The gas in the plastic hollow portion may be discharged from a gap formed by retracting the nozzle 6 from the fixed mold 10.

Next, the second embodiment of FIG. 3 will be described. In this embodiment, the mold is slightly opened at the time of injection of the molten plastic and at the time of gas injection of the first embodiment, and after closing the inlet of the molten plastic and gas, the mold is clamped. Instead of reducing the volume of the mold cavity by performing the above, the mold is fully closed and the plunger is pushed in from the side to reduce the volume of the mold cavity. FIG. 3 shows the same structure as that of the first embodiment, except that the mold is not opened slightly but a structure in which the plunger is pushed into the joint of the molds.

Now, in FIG. 3, reference numeral 25 denotes a fixed side mold, which is a hydraulic cylinder.
The hydraulic cylinder 21 has a built-in piston 22 and a plunger 23 also serving as a piston shaft. 26
Is a mold on the moving side, and when this mold is extruded and pressed against the mold 25 on the fixed side, a hollow cylinder is formed on the mating surface of the mold 25 and the mold 26. The center line of this cylinder is on the mating surface. Uranja 23 can enter and exit the cylinder formed by the molds 25 and 26, and the cylinder communicates with the mold cavity 24 formed by the molds 25 and 26.

Next, the operation of the second embodiment shown in FIG. 3 will be described. Here, a description will be given in comparison with the operation (work process) of the first embodiment.

(A). The mold 26 is pushed fully to the closed position and the molten plastic 18 is injected.

(B). During or after the injection of molten plastic 18,
The gas is injected into the molds 25 and 26 through the gas two-way valve 5 and the injection nozzle 6 by operating the gas three-way valve 7. Although the molten plastic 18 in the mold starts to solidify along the walls of the molds 25 and 26, the core is still in a molten state, and gas enters the molten plastic 18 even at a low gas pressure.

(C) With the two-way valve 5 closed and the three-way valve 7 for gas closed as well, the plunger 23 is pushed in by hydraulic pressure with sufficient mold clamping force applied to the mold 26. At this time, the molten plastic 18 is filled into the cavity 24 of the mold, and the gas in the plastic hollow is also compressed to a high pressure.
It cools and solidifies while being strongly pressed along the mold of the cavity 24 into 6.

(D). After cooling and solidifying the plastic material, gas three-way valve 7
, The two-way valve 5 is opened to release the gas pressure in the hollow portion of the plastic, the gas pressure in the molded product is sufficiently reduced, the mold 26 is opened, and the resin in the cavity 24 is taken out as a molded product. .

Next, a third embodiment of FIG. 4 will be described. Reference numeral 1 denotes an injection cylinder, in which an injection screw 2 is mounted, and an injection cylinder tip 3 is mounted at the tip. Reference numeral 31 denotes a check valve incorporating a spherical valve 32. A gas injection member 33 is connected to a gas supply source through a joint 8 and a three-way valve 7. Reference numeral 6 denotes an injection nozzle through which molten plastic and an injection gas are injected into the lower mold 10 '. 12 'is an upper die which is mounted on the mold plate 11. The mold plate 11 is a hydraulic cylinder of the press 35.
34 allows vertical movement and mold pressing. Reference numeral 16 denotes a limit switch for detecting the position of the mold board 11, and the position is adjusted on a bar 17. 35 is a press for press molding, and 36 is a jack for fixing the injection cylinder 1 and the nozzle.

Next, the operation of the third embodiment shown in FIG. 4 will be described in the order of FIGS.

(A). While the upper mold 12 'is kept separated, a certain amount of the molten plastic 18 is extruded from the nozzle 6 to the lower mold 10' by the injection cylinder 1 and the injection screw 2. At this time, the gas valve 7 is closed.

(B). After a certain amount of molten plastic 18 has been extruded, the upper mold 12 'is lowered and stopped shortly before the cutoff with the lower mold 10'. The detection of this position is performed by the limit switch 16, and a signal sent from the limit switch 16
The upper die 12 'is stopped and its position is maintained by hydraulic pressure. In this state, the molten plastic 18 is crushed, but is not filled up to the corners of the cavities 37. At this time, the gas three-way valve 7 is closed.

(C). When the gas is injected by switching the gas three-way valve 7,
The gas spreads the plastic from the nozzle 6 while forming a hollow in the soft plastic in the mold.

(D). When the gas three-way valve 7 is closed and the upper mold 12 'is pushed with a strong mold clamping force F, the gas in the plastic hollow becomes high pressure, the plastic is filled into the cavity 37, and the plastic is kept pressed strongly along the cavity 37. Cool and solidify.

After cooling and solidification, the gas three-way valve 7 is switched to the discharge side to release the gas inside the molded product in the cavity 37, or the lower mold 1
The gas is released from the gap formed by retracting the nozzle 6 from 0 ', and then the upper mold 12' is raised to take out the molded product.

(Effects of the Invention) As described in detail above, in the present invention, the gas pressure when injecting gas with the mold slightly opened is relatively low, but after gas injection, the gas passage is closed and the mold is strongly clamped. Since the mold is pressed by force, the gas pressure becomes high. Therefore, according to the present invention, using a relatively low supply of gas that is not applicable to the High Pressure Gas Control Law,
A high pressure gas is produced by using the mold clamping force, and the plastic material is pressed against the mold by a large internal pressure, so that a molded product with no sink marks, high accuracy, and a beautiful surface can be obtained. If the injection gas is injected while the mold is slightly opened, the injection pressure and gas pressure can be reduced, and after the injection, the mold is compressed, so that the molecular orientation is uniform, so that molding with small internal stress is performed. A molded article with a small deformation afterwards is obtained. If the internal gas pressure is increased by partially compressing the cavity and the plastic material is strongly pressed along the cavity of the mold with a large internal pressure, a beautiful molded product without sinking can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan sectional view of an apparatus for carrying out the method according to the first embodiment of the present invention, and FIGS. 2 (a), 2 (b), 2 (c) and 2 (d) show the order of operation in the apparatus of FIG. FIG. 3 is a plan sectional view of an apparatus for performing the method according to the second embodiment of the present invention;
FIG. 4 is a plan sectional view of an apparatus for performing the method of the third embodiment of the present invention, and FIGS. 5 (a), (b), (c) and (d) show the order of operation in the apparatus of FIG. FIG. 6 is a sectional view of an apparatus showing a conventional injection method. Description of main parts in the drawing 1 ... Injection cylinder 2 ... Injection screw 4 ... Gas injection member 5 ... 2 way valve 6 ... Injection nozzle 7 ... 3 way valve 9 ... Solid mold board 10 ... Fixed side Mold 11… Movable mold plate 12 …… Model 13 …… Hydraulic cylinder for stamping 14 …… Hydraulic piston 15 …… Piston rod 16 …… Limit switch for position detection 18 …… Molten plastic 19 …… Cavity

Claims (1)

(57) [Claims] 1. Injecting an insufficient amount of molten plastic into a mold cavity while leaving the mold in a slightly open state that does not completely close the mold, and subsequently injecting into the same mold, or any position in the plastic flow path. The plastic in the mold is inflated while injecting a gas body from the gas inlet provided, then the injection path of the molten plastic and the gas is closed, and then the mold clamping force is increased, and the mold is completely closed to form a hollow portion. A method of molding a plastic molded article, characterized in that a mold cavity is filled with a plastic and a gas in a plastic hollow portion is a high-pressure gas.