JPH03133618A - Molding method for plastic molded product - Google Patents

Abstract

PURPOSE:To obtain a molded product which is free from a sink, accurate and has a beautiful surface, by a method wherein molten plastic is cast into a mold, gas is injected in succession and after expansion of the plastic, the gas is compressed by contracting volume of a mold cavity. CONSTITUTION:A mold 12 is held under a state where it is broken a little, into which molten plastic 18 is cast. Then in the middle of casting or after the casting of the molten plastic 18, gas is injected into the mold through a two-way valve 5 and injection nozzle 6 by operating a three-way valve 7 for the gas. In this instance, the gas is entering away into the plastic. Then the mold is clamped down with greet mold clamping force by making the two-way valve 5 and also the three-way valve 7 close. In this instance, the molten plastic 18 is filled into a cavity 19 formed of the molds 10, 12 with pushing force, the gas also in a hollow part is compressed, becomes high pressure, the molten plastic 18 is cooled and solidified as it is pressed strongly along the mold of the cavity. Then the three-way valve for the gas is operated for discharge, the gas in the hollow part of the plastic is released, the mold 12 is broken and a molded product is taken out.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for molding a high-precision plastic molded product that is applied to an injection molding machine and a breath mold Y 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 then press-fitted from the same inlet either alone or while injecting the molten resin, and further as necessary. Japanese Patent Publication No. 57-14968 has proposed a method for molding a hollow molded article, which is characterized by injecting molten resin to fill the mold cavity.

An apparatus for carrying out the conventional method will be described with reference to FIG. 6. In an injection cylinder 31, resin 39 plasticized by a screw 32 for plasticizing and injecting the resin is stored, and the molten resin 39 is transferred to molds 41 and 42. Mold cavity 43 made of
Insufficient amount of resin 3 to fill the same type cavity 43
After injecting the gas 9, the gas is subsequently pressurized through the gas injection port 34 formed in the nozzle portion. The gas inlet 34 is
It is fixed at the center of the nozzle part by a device part 33, and the gas is forced into the mold cavity 43 through the molten resin. Note that the gas body is a gas press-in cylinder 35 provided separately.
As the high-pressure ram 36 advances, the gas body 40 stored in the cylinder 35 is forced into the cylinder 35. Further, any of the following four methods may be used for press-fitting the gas body. That is, after injecting an insufficient amount of molten resin to fill the mold cavity,
(1) Inject the gas under pressure, (2) Inject the molten resin after pressurizing the gas, (3) Inject the gas while injecting the molten resin, (4) Inject the gas while injecting the molten resin. Any of the following four methods may be used: after press-fitting, molten resin is further injected.

However, in the conventional method described above, the volume of the mold cavity 43 is not changed, and the plastic is flowed through a thin passage in the cavity, so a high injection force and gas pressure are required, and residual stress is generated in the molded product.

(Problems to be Solved by the Invention) In order to improve the product precision (dimensions, surface precision) of a partially hollow molded article using the conventional method described above, high pressure gas is required. In other words, there are problems with restrictions such as containers, equipment, handling regulations, etc. under the High Pressure Gas Control Act, and if the mold is injected when the mold is completely closed, the plastic will flow into the thin part of the cavity and completely follow the shape of the cavity. High injection pressure is required to maintain this shape, and if it is cooled and solidified,
There was a drawback that residual stress was generated in the molded product, causing deformation after molding.

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

(Means for Solving the Problems) For this reason, the present invention injects an insufficient amount of molten plastic into the mold cavity while the mold is not completely closed, and subsequently injects the molten plastic into the injection port into the same mold, or The plastic in the mold is inflated by injecting gas from the gas inlet set at an arbitrary position in the plastic flow path, and then, after closing the molten plastic and gas injection path, the mold clamping force is increased and the mold is fully inflated. The mold is closed, the mold cavity is filled with plastic having a hollow part, and the gas inside the hollow part of the plastic is turned into high-pressure gas.This is a means to solve the problem.

(Operation) After injecting molten plastic into the mold and subsequently injecting gas to inflate the plastic, high pressure is obtained by contracting the volume of the mold cavity and compressing the gas. The high-pressure gas inside the plastic holds the plastic perfectly conforming to the shape of the cavity and cools it.

(Example) The present invention will be described below with reference to the embodiments shown in the drawings. Figs. 1 and 2 show a first embodiment of the present invention, which is an example applicable to a normal injection molding machine.

In the figure, 1 is an injection cylinder, and there is an injection screw 2 inside.
, the injection cylinder tip 3 is attached to the tip. Reference numeral 4 denotes a gas injection member, to which a gas fitting 8 is attached, and gas is injected, discharged, and stopped by a three-way valve 7.

Further, a two-way valve 5 is incorporated into the gas injection member 4. 6
is an injection nozzle provided at the tip of the gas injection member 4, and the molten plastic 18 is injected into the mold through this nozzle 6.

9 is a fixed type board, and the fixed side type IO is attached.

Further, 11 is a movable mold board, on which a mold 12 is attached. 1
3 is a hydraulic cylinder for embossing, 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 glue switch for detecting the position of the movable mold board 11, which detects the position of the mold 10.12 that is slightly back from the cut-off position, stops the piston 14, holds the mold at a predetermined position, and supports it. Bar 17
Its position can be adjusted by supporting it. Further, the molten plastic 18 is shown in a state in which a fixed amount is stored in the injection cylinder tip 3 and the injection cylinder 1 in FIG. Reference numeral 19 denotes a cavity formed by the molds 10 and 12, and FIG. 1 shows a state in which it is sensed by a limit switch and held in position by a hydraulic piston 11I at a position slightly back from the cutoff of the molds 10 and 12. There is.

Next, the operation of the embodiment shown in FIG. 1 will be explained in accordance with the work steps shown in FIG. 2 in the order of (a) to (d).

(a) The mold 12 is held slightly open and molten plastic 18 is injected. The mold 12 is held down with a weak force f so that it does not open any further, or the flow path is closed so that the hydraulic oil in the mold pressing hydraulic cylinder 13 does not escape.

(b) During or after the injection of the molten plastic 18, the three-way gas valve 7 is operated to inject the gas into the mold through the two-way valve 5 and the injection nozzle 6. This poet 10 and type 1
2 is slightly open, and the cavity is thick, so the plastic flows at a low injection pressure, and the core part of the plastic thickness is still in a molten state, and even though the viscosity is low and the gas pressure is low, the gas flows through the plastic. Go inside.

(c) The mold is closed with a large mold clamping force F with the two-way valve 5 closed and the three-way gas valve 7 also closed.

At this time, the molten plastic 18 is filled into the cavity 19 formed by the mold 1012 by the pushing force, and the gas inside the hollow is also compressed to a high pressure, so that the molten plastic 18
is strongly pressed along the mold of the cavity as it cools and solidifies.

(d) After cooling and solidifying the plastic material, the gas three-way valve 7
is operated to exhaust, the two-way valve 5 is opened to release the gas inside the plastic hollow part, and after the gas pressure inside the plastic molded product is sufficiently reduced, the mold 12 is opened and the resin in the cavity 19 is taken out as a molded product. . Note that the gas in the plastic hollow part may be released from a gap created by retracting the nozzle 6 from the mold 10 on the stationary side.

Next, the second embodiment shown in Fig. 3 will be explained. In this embodiment, a small amount of the mold is used during the injection of molten plastic and gas in the first embodiment, and the mold is clamped after the inlets of the molten plastic and gas are closed. Instead of reducing the mold cavity volume by doing this, the mold is kept fully closed and a plunger is pushed in from the side to try to reduce the mold cavity volume. Note that FIG. 3 has the same structure as the first embodiment, except that the method of making the mold a little larger is not adopted, and a structure is adopted in which a plunger is pushed into the joint of the molds.

In FIG. 3, reference numeral 25 denotes a stationary type, to which a hydraulic cylinder 21 is attached, and the hydraulic cylinder 21 houses a piston 22 and a plunger 23 which also serves as the piston shaft. Reference numeral 26 denotes a mold on the movable side, and when this mold is extruded and pressed against the mold 25 on the stationary side, a hollow cylinder is formed on the mating surface of the molds 25 and 26. Note that the center line of this cylinder is on the mating surface. The plunger 23 can also move in and out of the cylinder formed by the molds 25 and 26, which 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 explained. Note that the explanation will be made here in comparison with the operation (work process) of the first embodiment.

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

(b) During or after the injection of the molten plastic 18, the three-way gas valve 7 is operated to inject it into the mold 25, 26 through the two-way gas valve 5 and the injection nozzle 6. The molten plastic 18 in the mold begins to solidify along the walls of the mold 25, 26, but the core is still in a molten state, allowing gas to enter the molten plastic 18 even at low gas pressures.

(C) The two-way valve 5 is closed, the three-way gas valve 7 is also closed, and the plunger 23 is pushed in by hydraulic pressure while applying sufficient mold clamping force to the mold 26.

At this time, the molten plastic 18 is filled into the cavity 24 of the mold, and the gas inside the plastic hollow is also compressed to a high pressure, and the plastic is cooled and solidified while being strongly pressed against the mold 25, 26 along the mold of the cavity 24. do.

(d) After cooling and solidifying the plastic material, the gas three-way valve 7
is operated to exhaust, the two-way valve 5 is opened to release the gas pressure inside the plastic hollow part, and after the gas pressure inside the molded product is sufficiently reduced, the mold 26 is opened and the resin inside the cavity 24 is taken out as a molded product. .

Next, the third embodiment shown in FIG. 4 will be described. Reference numeral 1 denotes an injection cylinder, and an injection screw 2 is attached inside the injection cylinder, and an injection cylinder tip 3 is attached to the tip. 31 is a check valve incorporating a spherical valve 32. 33 is a gas injection member, joint 8.3
It is connected to a gas supply source through a direction valve 7. 6 is an injection nozzle through which the molten plastic and the injection gas are injected into the lower mold lO'. 12' is an upper die which is attached to the die plate 11, and the same die plate 11 is attached to the press 35.
A hydraulic cylinder 34 is used to move the mold up and down and apply mold pressing force. 16 is a limit switch for detecting the position of the mold board 11, and the position is adjusted on the bar 17. 35 is a press for press molding, and 36 is an injection cylinder l and a nozzle fixing jack.

Next, the operation of the third embodiment shown in FIG. 4 will be explained in the order of (a) to (d) according to the work steps shown in FIG. 5.

(a) A fixed amount of molten plastic 18 is extruded from the nozzle 6 into the lower mold 10' using the injection cylinder 1 and the injection screw 2 while keeping the upper mold 12' separated. At this time, 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 just before the cut-off with the lower mold 10'. This position is detected by a limit switch 16, and in response to a signal sent from the limit switch 16, the upper die 12' is stopped and held in position by hydraulic pressure. In this state, the molten plastic 18 is crushed, but not all the corners of the cavity 37 are filled.

At this time, the three-way gas valve 7 is closed.

(C) When gas is injected by switching the three-way gas valve 7,
The gas from the nozzle 6 forms a hollow part in the soft plastic inside the mold and expands the plastic.

(d), when the three-way gas valve 7 is closed and the upper mold 12' is pushed with a strong mold clamping force F, the gas inside the plastic hollow part becomes high pressure, the plastic is filled into the cavity 37, and the plastic is strongly pushed along the cavity 37. Cools and solidifies while being pressed.

After cooling and solidifying, either switch the gas three-way valve 7 to the discharge side to vent the gas inside the molded product in the cavity 37, or
After the nozzle 6 is moved back from 0' and the gas is released from the gap created, the upper mold 12' is raised and the molded product is taken out.

(Effects of the Invention) As explained in detail above, in the present invention, the gas pressure is relatively low when gas is injected with the mold slightly open, but after the gas is injected, the gas passage is closed and the mold is clamped strongly. Since the mold is pressed with force, the gas pressure becomes high. Therefore, according to the present invention, a relatively low gas supply source that is not subject to the High Pressure Gas Control Law is used, and the mold clamping force is used to generate high pressure gas, thereby pressing the plastic material against the mold with a large internal pressure. As a result, a molded product with no whiskers, high precision, and a beautiful surface can be obtained. Note that if the injection gas is injected with the mold slightly open, the injection pressure and gas pressure can be lowered, and since the mold is compressed after injection, the molecular orientation will be uniform, resulting in molding with low internal stress. A molded product with little subsequent deformation can be obtained. Moreover, if the cavity is partially compressed to increase the internal gas pressure and the plastic 10A is strongly pressed along the cavity of the mold with a large internal pressure, a beautiful molded product without sink marks can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a plan sectional view of an apparatus for implementing the method of the first embodiment of the present invention, and FIGS. 2(a), (b), (c), and (d) sequentially show the order of operation in the apparatus of FIG. 1. Explanatory drawings, FIG. 3 is a plan sectional view of an apparatus for implementing the method of the second embodiment of the present invention, FIG. 4 is a plan sectional view of the apparatus for implementing the method of the third embodiment of the invention, and FIG. (a) (b) (C) (d) are explanatory diagrams sequentially showing the order of operation in the device of Fig. 4;
The figure is a sectional view of an apparatus showing a conventional injection method. Explanation of the main parts of the figure - Injection cylinder 2 - Injection screw 4 - Gas injection member 5 - Two-way valve 6 - Injection nozzle 7 - Three-way valve 9 - Fixed mold platen 10 - Fixed side mold 11 - Movement Mold board 12 - Mold 13 - Hydraulic cylinder for stamping 14 - Hydraulic piston 15 - Piston rod 16 - Limit switch for position detection 18 - ? Fusing plastic 19- Cavity patent application person Mitsubishi Heavy Industries, Ltd. fi3 Figure 5 for Figure 6 Figure 7

Claims (1)

[Claims] Injecting an insufficient amount of molten plastic into the mold cavity while leaving the mold partially open without completely closing it, and then continuing to inject into the same mold, or by providing a gas inlet at any position in the plastic flow path. The plastic inside the mold is inflated by injecting gas from the inside of the mold, and then after closing the injection path for the molten plastic and gas, the mold clamping force is increased, and the mold is completely closed to fill the mold cavity with the hollow plastic. 1. A method for molding a plastic molded product, which is characterized in that the gas inside the plastic hollow part is filled with high-pressure gas.