JPH07314483A - Method and mold for gas-injection molding - Google Patents

Abstract

PURPOSE:To provide a method and mold for gas-injection molding without occurrence of sinks even at lower pressure. CONSTITUTION:The cavity 11 of a mold 10 includes a gas channel guide part 17 with a large thickness adequate to form a gas channel 21 in the inner part of molten resin 20 through injection of gas, a thin plate forming part 16 with a small thickness, and a boss forming part 40 disposed on a predetermined part of the cavity 11 and having a large thickness, and a gas injection port for injecting gas is made in the proximity of a boss forming part 40. Even where no gas channel 21 can be formed over the entire part of the molded item due to low gas pressure, in the part having no gas channel 21 of molten resin 20 formed therein, molten resin 20 is pressed by pressure of gas poured from the gas injection port between the surface of molten resin 20 and the inner surface of the cavity 11, so that the occurrence of sinks is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas injection injection molding method and a mold thereof, and can be used for molding interior and exterior products such as automobile bumpers and dashboards, or molded products such as casings of home electric appliances. .

[0002]

BACKGROUND ART Conventionally, in order to improve the production efficiency and productivity of molded products, the filling pressure applied to the molten resin when filling the molten resin into the mold has been lowered, and the molten resin in the mold has been reduced. It has been attempted to lower the mold clamping pressure applied to the mold when molding the same. By reducing the filling pressure and the mold clamping pressure, it is possible to reduce the size and weight of the injection device and mold and to increase the mold clamping speed, which reduces the scale of the injection molding equipment.
It is possible to improve the efficiency of injection molding.

[0003]

However, the "sink" which is one of the molding defects is caused by the volume shrinkage of the molten resin when it cools and solidifies during molding, and the injection pressure and the mold clamping pressure become low. As the amount of shrinkage of the molten resin increases accordingly, there is a problem that when the pressure is lowered, the amount of depression of the resin surface increases as compared with the case of molding at a high pressure, and "sinking" becomes noticeable. On the other hand, in order to prevent "sink", the following method can be considered. For example, it is conceivable to insert a separate member inside the thick part of the molded product and reduce the amount of molten resin to reduce the volumetric shrinkage of the molten resin and eliminate "sinker". Since the passage of the molten resin is narrowed by the separate member arranged in the mold, it becomes impossible to fill the entire mold with the molten resin at a low pressure, and therefore it cannot be used for low pressure injection molding.

Further, the gas injected into the molten resin filled in the mold forms a gas channel in the molten resin, and the pressure of the gas in the gas channel causes the molten resin to flow from the inside to the inside of the mold. It is conceivable to adopt a gas injection injection molding method that prevents the occurrence of “sink” by pressing. However, in this method, the gas channel needs to be spread over a necessary part of the molded product in order to prevent "sink", and the mold is designed so that the gas completely hollows a predetermined gas channel. It's difficult. Also, before the mold is completely closed, the molten resin is filled into the mold, and the molten resin is spread over the entire mold by clamping the mold, so that the occurrence of "sink" is suppressed. It is possible to adopt a pressure molding method, but in this method,
Since a large mold clamping pressure is required to prevent "sink", it is not a method to prevent "sink" in low pressure injection molding.

An object of the present invention is to provide a gas injection injection molding method and a mold for the same, in which "sink marks" are not generated even in low pressure injection molding.

[0006]

According to a first aspect of the present invention, after a molten resin is filled in a cavity of a mold, pressurized gas is injected into the cavity to pressurize the molten resin. A gas injection injection molding method of performing injection molding at low pressure while forming a gas channel that is a gas passage, after the molten resin reaches a predetermined portion of the cavity,
Gas is injected between the surface of the molten resin and the inner surface of the predetermined portion of the cavity. In the above, it is preferable to start the gas injection into the predetermined portion of the cavity after starting the gas injection into the filled molten resin. Further, a predetermined portion of the cavity into which the gas is injected is a thick-wall forming portion in which the thickness of the molten resin is increased and the filled molten resin becomes thick, and the thick-wall forming portion is completely filled with the molten resin. After that, start injecting gas toward the molten resin in the thick portion,
It is desirable that the molten resin filled in the thick portion is pressed against the inner surface of the cavity with this gas.

According to a second aspect of the present invention, after starting the filling of the molten resin with the molten resin, a pressurized gas is injected into the cavity to form a gas channel, which is a passage for the pressurized gas, inside the molten resin. While being a gas injection injection mold for performing injection molding, a gas channel guide having a large thickness dimension so that a gas channel is formed inside the molten resin by gas injection into the cavity. Part, a thin plate forming part having a reduced thickness so that a gas channel is not formed inside the molten resin even when gas is injected, and a thin plate forming part which is arranged in a predetermined portion of the cavity and is thicker than the thin plate forming part. A thick-wall forming portion is provided in which the molten resin having a large thickness and a large thickness is filled with the molten resin. In the vicinity of the thick-wall forming portion, the molten resin filled inside and the inside of the cavity are provided. Wherein the gas inlet for injecting a gas is provided between the.

[0008]

According to the present invention, after the molten resin is filled in the main cavity in the mold, gas is injected into the molten resin to form gas channels inside the molten resin. Then, after the molten resin reaches a predetermined portion of the cavity, gas is injected between the surface of the molten resin and the inner surface of the predetermined portion of the cavity to perform molding. Here, the molten resin was pressed against the inner surface of the cavity from the inside by the gas in the gas channel, and the gas was injected by the gas injected between the surface of the molten resin and the inner surface of the predetermined portion of the cavity. The inner surface of the cavity opposite the surface is pressed. Therefore, the molten resin inside the mold adheres to the inner surface of the cavity until it cools and solidifies,
By preventing the sink mark and lowering the pressure of the injected gas, even if the gas channel does not reach the entire molten resin in the mold, the portion where the molten resin does not reach is set as the predetermined portion in advance. If the gas is injected thereinto, not only the sink mark at the portion having the gas channel is prevented but also the sink mark at the portion having no gas channel is prevented, thereby achieving the above-mentioned object.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a mold 10 of this embodiment.
This mold 10 has a structure in which a cavity 11 is filled with a molten resin 20 and then a pressurized gas is injected into the cavity 11 to melt the molten resin 20.
It is for gas injection injection molding in which molding is carried out while forming a gas channel 21 which is a passage of a pressurized gas inside 20 and is divided into three mold parts 10A to 10C. The uppermost die part 10A in the figure is provided with a sprue 12 to which a nozzle of an injection device (not shown) is connected and which allows a molten resin 20 supplied from the injection device to flow. A mold part 10B below the mold part 10A in the figure is provided with a runner 13 branched from a sprue 12. In the mold part 10A, the flow path 14 of the molten resin 20 extending from the runner 13 to the cavity 11 is
Is provided. The lowermost die part 10C in the figure is provided with a cavity 11 for molding the molten resin 20.
The mold part 10C is provided with a gate 15 which communicates with the flow path 14 and which fills the cavity 11 with the molten resin 20.

The cavity 11 has a thin plate forming portion 16 having a small depth for molding the molten resin 20 into a thin flat plate shape.
And a gas channel guide portion 17 in which a concave portion obtained by denting a part of the bottom surface of the thin plate forming portion 16 is extended in a plane L-shape. The thin plate forming portion 16 is a space having a rectangular shape in a plane. In the vicinity of the right end of the thin plate forming portion 16 in the drawing, a boss forming portion 40 as a thick wall forming portion that is recessed in a substantially cylindrical shape is provided. The gas channel guide portion 17 is formed in an L shape over the entire length of two adjacent sides of the thin plate forming portion 16, and promotes the formation of the gas channel 21 inside the molten resin 20. By the gas channel guide portion 17, the gas channel 21 is formed inside the molten resin 20 over substantially the entire length of two adjacent sides of the thin plate forming portion 16. FIG. 2 shows a molded product 30 molded by the cavity 11. This molded product 30
The thin plate-shaped thin plate portion 31 formed in the thin plate forming portion 16 of the cavity 11, the L-shaped extending portion 32 formed in the gas channel guide portion 17, and the boss forming portion 40 are formed. And a boss 33. The gas channel 21 is formed inside the rib-shaped portion 32.

The boss forming portion 40, as shown in FIG.
A gas injection port 41 for injecting gas is provided on the bottom surface 42 between the molten resin 20 filled inside and the inner surface of the boss forming portion 40. The gas inlet 41 is an annular opening formed by arranging a throttle member 44 at the end opening of the flow path 43 that is bent in an L shape for supplying gas. Due to the arrangement of the throttle member 44, the cross-sectional area of the gas injection port 41 is made smaller than the cross-sectional area of the flow path 43, and the gas is diffused into the boss forming portion 40 in a ring shape and discharged. The throttle member 44 includes a head portion 44A having a large outer diameter and a rod portion 44B having a small outer diameter and having a thread groove on the side surface, and the entire flow passage 43.
The rod portion 44B is arranged along the extending portion 43A extending toward the cavity 11 side, and the rod portion 44B is screwed into the die portion 10C. In addition,
The outer diameter D1 of the gas inlet 41 is 5.0 mm, and the outer diameters D2 and D3 of the head portion 44A and the rod portion 44B of the throttle member 44.
Are 4.0mm and 3.95mm respectively.

The procedure of injection molding in this embodiment will be described below. First, after the molten resin 20 is started to be filled in the cavity 11, a gas having a predetermined pressure is started to be injected into the molten resin 20 filled in the cavity 11. Next, after the molten resin 20 reaches the boss forming portion 40 of the cavity 11, and after the boss forming portion 40 is filled with the molten resin 20, gas is sent into the gas injection port 41 of the boss forming portion 40, and the boss forming portion 40 Gas is injected between the surface of the molten resin 20 and the inner surface of the boss forming portion 40. At this time, the molten resin 20 inside the cavity 11 is the gas injected into the boss forming portion 40 for the portion with the gas channel 21 due to the pressure of the gas in the gas channel 21, and for the portion without the gas channel 21. The pressure of the cavity 11
It is pressed against the inner surface of the sheet and comes into close contact therewith, thereby preventing "sink". When the molten resin 20 is cooled and solidified, the gas inside the cavity 11 is released, and then the molded product 30 is taken out of the mold 10 to complete the injection molding.

According to this embodiment as described above, there are the following effects. That is, the gas channel 21 is formed inside the molten resin 20 in the cavity 11, the portion having the gas channel 21 inside is closely adhered to the inner surface of the cavity 11 by the pressure of the gas in the gas channel 21, and the boss is formed. Department
Due to the pressure of the gas injected into 40, the portion of the boss 33 without the gas channel 21 inside was brought into close contact with the inner surface of the cavity 11, so that even if the thick portion with the boss 33 formed on the back side has this thickness Since the sink mark does not occur on the surface of the meat portion, the sink mark can be prevented for the entire molded product 30.

Therefore, since it is not necessary to spread the gas channel 21 over the entire molded product 30, the design of the mold 10 can be facilitated, and the pressure of the gas injected into the molten resin 20 can be reduced. The gas that presses the molten resin 20 from its surface is such that after the boss forming portion 40 is filled with the molten resin 20, it is locally injected into the boss forming portion 40, so there is no need to extrude the molten resin 20. The injection pressure of the same gas can be lowered, which enables low-pressure injection molding that does not cause "sink". This low-pressure injection molding can improve production efficiency and productivity without degrading the quality of molded products. it can.

Further, the injection point of the gas injected into the surface of the molten resin 20 is a boss molding section 40 for molding the boss 33 which is the thick portion of the molded product 30, and the injected gas is applied to the end surface of the boss 33. Since it is received, even if the end surface of the boss 33 is slightly recessed by the pressure of the gas, the flat surface portion of the molded product 30 is not recessed, and the appearance of the molded product 30 is not deteriorated.

Further, by narrowing the gas inlet 41 with the throttle member 44, the cross-sectional area is smaller than that of the flow path 43, and the gas is diffused into the boss forming portion 40 in a ring shape and discharged. Even if the injected gas is received by the end surface of the boss 33, the momentum of the gas is weakened.Therefore, a gas channel is formed inside the boss 33 by breaking through the end surface of the boss 33, and at the end surface of the boss 33. It is possible to prevent the holes from opening.

Next, the effects of the present invention will be described based on concrete experimental examples. [Experimental Example] This experimental example is an experiment for performing gas injection molding based on the present invention. As the mold, the mold 10 for molding the substantially surface-shaped molded product 30 shown in FIG. 2 is adopted. The dimensions of such a molded product 30 are set as follows. Thickness t: 3 mm Length L: 420 mm Width W: 100 mm Rib width W1: 9 mm Rib height H1: 6 mm Boss diameter φ: 8 mm Boss height H2: 10 mm [Comparative example] This comparative example 2 is an experimental example of performing gas injection injection molding based on a conventional technique. Specifically, using the same mold 10 as in the experimental example, gas is injected into the molten resin 20 filled in the cavity 11, but the gas injection port of the boss forming portion 40 is used.
No gas is injected into 41, and gas injection molding is performed.

[Injection Conditions] In the above experimental examples and comparative examples, Toshiba Machine IS-200CN was used as the injection molding machine, polypropylene (Idemitsu Petrochemical Co., Ltd., Idemitsu Polypro J-750H), and , Polystyrene (Idemitsu Styrol HT-51 manufactured by Idemitsu Petrochemical Co., Ltd.)
Injection molding was performed under the same injection conditions as described below. Injection conditions Molding temperature: 220 ℃ Mold temperature: 40 ℃ Gas injection pressure: 8 MPa Resin filling time: 2.0 seconds Here, the injection of gas into the molten resin 20 is 2.0 seconds after the start of resin filling. Then, the gas is injected into the boss forming portion 40 3.5 seconds after the start of the resin filling.

[Experimental Results] In the case of molding with polypropylene, in the experimental example, the depth of the dent formed on the surface of the thick portion where the boss 33 is formed on the back side is 2 μm, and “a sink mark” is visually confirmed. I couldn't do that. On the other hand, in the comparative example, a "sink" could be easily confirmed by the naked eye on the surface of the thick portion where the boss 33 was formed on the back side, and the depth of the generated recess was 20 μm. Further, in the case of molding with polystyrene, in the experimental example, the depth of the recess formed on the surface of the thick portion where the boss 33 is formed on the back side is 0.1 μm,
It can be said that no "hike" occurred. On the other hand, in the comparative example, the depth of the recess formed on the surface of the thick portion where the boss 33 was formed on the back side was 6 μm, and the “sink” could be visually confirmed. From this, in the experimental example, there is no appearance problem in the molded product, whereas in the comparative example,
It can be seen that some problem occurs in the appearance of the molded product.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment, and various improvements and design changes can be made without departing from the gist of the present invention. It is possible. For example, the boss provided on the molded product is not limited to one location, and may be provided at a plurality of locations. As the installation location of the boss, as shown in FIG.
It may be provided not only in the thin plate portion 31 but also in the rib-like portion 32. In this case, the flow passage 43 for sending gas to the boss forming portion 40 is provided with the boss forming portion 40A.
If it is extended to, the gas can be injected also into the boss forming portion 40A formed in the gas channel guide portion 17. At this time, on at least one side of the boss forming portion 40 and the boss forming portion 40A, as shown in FIG.
In addition, the extension portion 43A is provided with a valve port 46 corresponding to the valve body 45 of the throttle member 44, and the throttle member 44 is rotated by using the hexagon wrench hole 47 or the like provided in the head portion 44A. The inflow amount of gas per unit time may be adjustable. In this way, the plurality of boss forming portions 40, 40A
The flow rate of each gas flowing into the can be balanced.

The gas injection port of the boss forming portion is a diaphragm member.
The flow rate is not limited to 44, and the gas inlet 41 may be closed by a porous member so as to be ventilated, or may be opened and closed by providing a valve mechanism. If a valve mechanism is adopted, the boss forming part
The flow rate of the gas injected into 40 can be continuously adjusted, and the flow of gas can be arbitrarily stopped. Further, regarding the position of the gas inlet, the boss forming portion 40
In addition to the bottom surface 42 of the boss forming portion 40,
Not only inside the boss forming portion 40, but when the surface on which the boss 33 is provided is the back surface of the molded product 30 hidden by other parts,
It may be the inner surface of the cavity 11 which is the outside of the boss forming portion 40 and the surface in the vicinity of the boss forming portion 40. Meanwhile, boss 33
When the surface provided with is a surface that is not hidden by the component, it may be the surface of the cavity 11 that is on the opposite side of the surface on which the boss forming portion 40 is formed and that is near the boss forming portion 40. Good. In short, the installation position of the gas injection port can be set according to the form and usage of the molded product as long as it is near the thick-walled forming portion such as the boss forming portion 40.

Further, the thick-wall forming portion is not limited to the one for molding the boss of the molded product, but may be one for molding a rib or fillet. Furthermore, in the above-described embodiment, the gas is injected into the molten resin 20 from the gate 15 for filling the molten resin 20, but the gas injection port for injecting the gas into the molten resin 20 is the molten resin. It may be provided separately from the gate 15 for filling 20.

As the molded product, a substantially flat plate-shaped molded product is used.
The shape of the molded product is not limited to 30 and may be a substantially box-like shape, and the shape of the molded product may be appropriately selected for implementation. At this time, if the number of thick-walled parts such as bosses and the number of places where they are installed are appropriately set according to the shape of the molded product, it is possible to effectively eliminate the sink marks in combination with the effect of forming gas channels. it can.

[0024]

As described above, according to the present invention, the production efficiency and the productivity can be improved by the low pressure injection molding, and the occurrence of "sink" can be prevented even in the low pressure injection molding.

[Brief description of drawings]

FIG. 1 is a sectional view showing a mold according to an embodiment of the present invention.

FIG. 2 is a four-sided view showing a molded product of the above example.

FIG. 3 is an enlarged cross-sectional view showing a boss forming portion which is a thick portion forming portion of the embodiment.

FIG. 4 is a diagram corresponding to FIG. 1 showing a modified example of the present invention.

FIG. 5 is a diagram corresponding to FIG. 3 showing a modified example of the present invention.

[Explanation of symbols]

 10 Mold 11 Cavity 17 Gas Channel Guide 16 Thin Plate Forming 20 Molten Resin 21 Gas Channel 40 Boss Forming as Thick Forming 41 Gas Injection Port

Claims (5)

[Claims] 1. A method for injecting a pressurized gas into the cavity after starting the filling of the molten resin into the cavity of the mold to form a gas channel, which is a passage for the pressurized gas, inside the molten resin and injects the gas. A gas injection injection molding method for molding, characterized in that after the molten resin reaches a predetermined portion of the cavity, gas is injected between the surface of the molten resin and the inner surface of the predetermined portion of the cavity. Gas injection molding method. 2. The gas injection injection molding method according to claim 1, wherein after injecting gas into the inside of the filled molten resin, injecting gas into a predetermined portion of the cavity is started. A gas injection injection molding method characterized by: 3. The gas injection molding method according to claim 2, wherein a predetermined portion of the cavity into which the gas is injected has a large thickness dimension so that the filled molten resin is thick. After the thick portion is completely filled with the molten resin, injection of gas toward the molten resin in the thick portion is started, and the thick portion is filled with the gas. A method of gas injection molding, characterized in that molten resin is pressed against the inner surface of the cavity. 4. After injection of the molten resin into the cavity is started, pressurized gas is injected into the cavity to perform injection molding while forming a gas channel, which is a passage for the pressurized gas, inside the molten resin. A gas injection guide mold for injecting gas into the cavity, the gas channel guide having a large thickness dimension so that a gas channel is formed inside the molten resin by injecting gas, and gas injection. Even if the thin plate forming portion has a reduced thickness dimension so that a gas channel is not formed inside the molten resin, and the thickness dimension is larger than that of the thin plate forming portion, the thin plate forming portion is arranged at a predetermined portion of the cavity. A thick-wall forming portion is provided in which the filled molten resin becomes thick, and a gas is injected between the molten resin filled inside and the inner surface of the cavity in the vicinity of the thick-wall forming portion. A gas injection injection mold, which is provided with a gas injection port for entering. 5. The gas injection injection mold according to claim 4, wherein the gas injection port of the thick-wall forming portion has a cross-sectional area smaller than that of a flow path for supplying gas to the gas injection port, and A gas injection injection molding die having a shape for diffusing gas into the thick portion forming portion and discharging the gas.