JPH06304954A - Gas injection molded piece and molding method thereof - Google Patents

Abstract

PURPOSE:To provide a gas injection molded piece and its molding method wherein control in gas injection molding is easy and occurrence of defective parts such as sink marks and holes is prevented. CONSTITUTION:A mold 10 comprises a gas channel guide section 13 in which a thickness of a cavity 11 is made to be thicker than the periphery and a buffer forming section 15 made by tapering the end part of the gas channel guide section 13. After filling of the mold 10 with a melted resin is started, gas is injected into the melted resin in the mold 10. As the cross-sectional area of the buffer forming section 15 is reduced gradually in the direction of the head end, even when the filling quantity of the melted resin changes and the injecting quantity of the gas decreases, the melted resin filling the buffer forming section 15 will proceed in the inside due to 'wedge effect', so that a sink mark does not occur on a surface of a formed molded piece due to the proceeding gas.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, a gas injection molding method has been known as an injection molding method for obtaining a lightweight and highly rigid molded product. In this method, after injection of a molten resin into the main cavity in the mold, an inert gas such as pressurized nitrogen gas is injected into the cavity for injection molding. A gas flow path (hereinafter referred to as "gas channel") is formed in the filled molten resin by the gas pressure, and the molten resin pressed by the gas in the gas channel is pressed toward the inner surface of the mold. Therefore, it can be expected to form a thin hollow molded product having a uniform thickness.

[0003]

However, when the gas injection molding is continuously performed, "filling unevenness" occurs in which the filling amount of the resin varies for each injection molding. If the filling amount of the molten resin increases due to this "filling unevenness", when gas is injected under the same conditions, the gas cannot be injected even to the end portion of the gas channel, and the meat of the molten resin cannot be injected to the end portion. A thick part is formed in which the thickness is partially increased.
When the thick portion is solidified, a defective portion such as a sink mark is generated on the surface, which impairs the appearance of the molded product. On the other hand, when the filling amount of the molten resin decreases due to the "filling unevenness", the gas penetrates the molten resin and flows out to the outside in the vicinity of the end portion of the gas channel, and a hole is formed in the molded product, or the gas is formed on the general surface. Occurs, and the appearance of the molded product is impaired. Further, even if the filling amount of each injection molding is appropriate, if the gas pressure, the mold temperature, etc. are too high, the gas may break through the thin portion of the molten resin to open a hole, or the gas may leak to the general surface. Such a defective phenomenon occurs and the appearance of the molded product is impaired. Therefore, the filling amount of the molten resin is strictly controlled so that “uneven filling” does not occur, and the gas pressure and mold temperature are kept constant so that holes are not opened in the molten resin even if gas is injected. Therefore, it is very difficult to control the filling amount of the molten resin, the gas pressure, the mold temperature, etc., and there is a problem that the control device therefor becomes complicated and expensive.

An object of the present invention is to provide a gas injection-molded article which is easy to control for gas injection molding and does not cause defects such as sink marks and holes, and a molding method thereof.

[0005]

The first aspect of the present invention is a gas injection molded article, wherein the end portion of the hollow thick wall portion surrounding the gas channel formed by injecting gas is tapered. It is characterized by being

A second aspect of the present invention is a gas injection molding method, in which a gas channel guide portion in which the thickness of the cavity is made thicker than the surroundings and the end portion of the gas channel guide portion is formed by tapering. It is characterized in that after the molten resin is started to be filled in the mold provided with the buffer forming portion, gas is injected into the filled molten resin.

[0007]

In the present invention as described above, the tapered buffer portion is formed at the end portion of the gas channel by the buffer forming portion provided in the mold in advance. Here, even if the amount of gas that can be injected decreases due to an increase in the filling amount of the molten resin, since the buffer portion is tapered, sink marks do not occur on the surface of the molded product due to the pressure of the gas. On the other hand, if the volume of the buffer is set large enough, even if the amount of injected gas increases due to the decrease in the filling amount of the molten resin, a high gas pressure is required for the gas to break through the tapered portion of the buffer. Since the gas is required to penetrate through the buffer portion to form holes in the molten resin, it is possible to prevent the occurrence of defective phenomena such as formation of holes on the surface of the molded product. Therefore,
Even if the molten resin filling amount, gas pressure, mold temperature, etc. are not strictly controlled, fluctuations in the molten resin due to "filling unevenness" are absorbed in the buffer section, and defects such as sink marks and holes are not generated. It can be prevented in advance, thereby achieving the above-mentioned object.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the shape of a cavity 11 formed inside the mold 10 of this embodiment. This cavity
The reference numeral 11 has a planar portion 12 having a uniform thickness and a groove-shaped gas channel guide portion 13 having a thickness larger than that of the planar portion 12. The planar portion 12 is for flattening the molten resin filled inside, and is a flat portion 22 of the molded product 20.
Is the part to be molded. Gas channel guide 13
Is formed along the center line in the longitudinal direction of the cavity 11 and has a rod-like shape of the molten resin filled therein, which is a portion for molding the hollow thick portion 23 of the molded product 20. A molten resin is filled inside the gas channel guide portion 13, and a gas is injected into the filled molten resin to form a hollow thick portion 23, and a gas channel 24 inside the hollow thick portion 23. Are formed along the gas channel guide portion 13. A gas inlet 14 is connected to one end of the gas channel guide portion 13, and a buffer forming portion 15 having a tapered end portion is provided on the other end side of the gas channel guide portion 13.

Specifically, the buffer forming portion 15 is such that the height dimension H in the drawing is gradually reduced, and the cross-sectional area thereof becomes smaller toward the tip. The buffer forming part 15 forms a tapered buffer part 25 at the end of the hollow thick part 23. Here, the reduction rate of the cross-sectional area of the buffer forming portion 15, that is, the cross-sectional area of the buffer portion 25 is set to a small value so that a so-called “wedge effect” that promotes gas intrusion can be easily obtained. As a result, even if the filling amount of the molten resin increases and the gas injection amount decreases, the buffer section 25
A sufficient amount of gas can be injected into the interior of the buffer so that sink marks do not occur on the surface of the buffer section 25 due to the injection of this gas. In addition, the capacity of the buffer forming unit 15, that is, the buffer unit
The volume of 25 is set to be large enough so that the injected gas does not penetrate through the buffer portion 25 to form a hole in the molten resin. As a result, even if the filling amount of the molten resin is decreased and the injection amount of the gas is increased, the gas does not penetrate through the buffer section 25, and no hole is formed on the surface of the molded product 20. It should be noted that the buffer portion 25 is set to a size capable of absorbing the variation amount due to the variation even if the filling amount of the molten resin fluctuates by about ± 0.5% of the volume of the gas channel guide portion 13 due to “uneven filling”. Has been done.

In this embodiment, the mold 10 is set in the injection molding machine, the cavity 11 is filled with the molten resin, and the molten resin filled in the mold 10 is filled after the filling is started or after the filling is completed. Inject gas inside. Then, by injecting this gas, a gas channel 24 is formed along the gas channel guide portion 13, the surface of the molten resin is brought into close contact with the mold 10 by utilizing the gas pressure in the gas channel 24, and the molded product 20 Prevents the occurrence of defects such as sink marks from the surface. Here, since the buffer portion 25 formed by the buffer forming portion 15 provided in the gas channel guide portion 13 absorbs the variation of the molten resin due to "filling unevenness" or the like, the filling amount of the molten resin, the gas pressure, and Therefore, it becomes unnecessary to strictly control the mold temperature and the like.

According to this embodiment as described above, the following effects can be obtained. That is, the gas channel guide section 13
The buffer portion 25 is formed by the buffer forming portion 15 provided in
Since the buffer portion 25 is configured to absorb the fluctuation of the molten resin due to "filling unevenness" or the like, it is possible to obtain sink marks or the like without strictly controlling the filling amount of the molten resin, the gas pressure, the mold temperature, and the like. It is possible to prevent the occurrence of defective parts such as holes.

Further, since the good gas injection molding can be performed without strictly controlling the filling amount of the molten resin, the gas pressure, the mold temperature, etc., the control unit of the gas injection molding apparatus is relatively controlled. Can be simple.

Further, by only providing the tapered buffer forming portion 15 at the end portion of the gas channel guide portion 13, the buffer portion is formed.
Since 25 can be formed, the above effect can be obtained by a simple mold modification, and the buffer forming unit 15 can be applied to any mold as long as it has a gas channel. The moldability of the molded product can be improved.

Next, specific effects of the present invention will be described based on the following experimental examples. [Experimental Example] In this experimental example, gas injection molding is continuously performed 100 times based on the first embodiment of the present invention. As the mold, the mold 10 having the substantially flat plate-shaped cavity 11 shown in FIG. 1 is adopted. As an injection-molded product, as shown in FIG. 2, a test piece 30 which is a rectangular face material is molded. Comparative Example In this comparative example, gas injection molding is continuously performed 100 times based on the conventional technique. As the mold, the mold in which the buffer molding portion 15 is omitted from the mold 10 of the experimental example is adopted. As an injection-molded product, as shown in FIG. 3, a test piece 40 having the same shape as that of the above-described experimental example is molded except that the buffer portion 25 is not provided. [Dimension Setting of Test Piece] In these experimental examples and comparative examples, the dimension of the test piece was set as follows (see FIGS. 2 and 3). Total length L1: 420 mm Total width W1 W1: 100 mm Thickness of flat plate portion T: 3 mm Width of hollow thick portion W2: 6 mm Height of hollow thick portion H: 5 mm Length of buffer portion L2: 40 mm (only for experimental example) [ Injection Conditions] In addition, in the above experimental examples and comparative examples, injection molding was performed under the following injection conditions. Resin used: polypropylene (made by Idemitsu Petrochemical Co., Ltd.)
J-3054H) Resin temperature: 220 ° C Mold temperature: 30 ° C Gas pressure: 6 MPa Injection time: 2 seconds Injection molding machine: Toshiba Machine Co., Ltd. IS-200
CN

[Experimental Result] In the experimental example, all the obtained test pieces 30 were provided with a buffer section 25 as shown in FIG.
A gas channel 24 was formed to reach the inside of the. As a result of measuring the weight of each of the test pieces 30, the lightest one is 114.1 g and the heaviest one is 11.
It weighed 4.9 g, and its average weight was 114.6 g.
On the other hand, as a result of measuring the total length of the gas channel 24, the smallest one has a weight of 387 mm, and the largest one has a weight of 381 m.
m, and the average length was 383 mm. According to the above measured values, the filling amount of the molten resin in each injection molding is −
There is "filling unevenness" in the range of 0.5 to +0.3 g, and the length of the gas channel 24 is -2 to + due to this "filling unevenness".
It can be seen that it fluctuated within the range of 4 mm. Here, when all the test pieces 30 are visually inspected, there is no defective portion such as a sink mark on each surface. Therefore, the variation of the filling amount due to the "filling unevenness" is caused by the buffer portion 25 having a length of 40 mm. It can be seen that the absorption was sufficient.

In the comparative example, the weight and the total length of the gas channel 24 were measured for each of all the test pieces 40, and the lightest one was 113.
4 g, the heaviest one was 114.6 g, and the average weight was 114.3 g. On the other hand, the total length of the gas channel 24 was 377.8 mm for the minimum weight and 374.6 mm for the maximum weight, and the average length was 376.1 mm. According to the above measured values, the filling amount of the molten resin in each injection molding has "uneven filling" in the range of -0.9 to +0.3 g, and the length of the gas channel 24 is due to this "uneven filling". It can be seen that fluctuates within the range of -1.5 to +1.7 mm. Here, when all the test pieces 40 were visually inspected, defective parts such as sink marks were found on the surface of the heavy test piece. When an internal inspection was performed on the largest weight, the gas channel 24 was able to reach the inside of the end portion 31 of the hollow thick portion 23. The end portion 31 had a solid state in which resin was clogged. It was The end portion 31 had a length dimension L3 of 5.4 mm, and a sink mark 32 having a depth of 15 μm was formed on the surface thereof.

The present invention is not limited to the above-described embodiments, but includes the following modifications and the like. That is, the buffer forming portion and the buffer portion are not limited to those in which the height dimension H is gradually reduced, but those in which the width dimension W2 is gradually reduced as shown in FIG.
As shown in, both the height dimension H and the width dimension W2 may be gradually reduced.

Further, the shapes of the buffer forming portion and the buffer portion are not limited to those formed by only straight lines, and as shown in FIG. 8, the buffer forming portion 15A and the buffer portion 25A formed by curved lines, As shown in FIG. 9, the buffer forming portion 15B and the buffer portion 25B may have a stepwise decreasing cross-sectional area.

Further, the gas channel guide portion and the thick wall forming portion are not limited to those formed by a single straight line, but may be those formed in a plane H shape, etc. Just select it.

Further, the gas injection molded product is not limited to a flat plate-shaped product, but may be a box-shaped product. In short, according to the present invention, one or more flat surfaces or curved surfaces, or flat surfaces and curved surfaces are combined with each other. It can be applied to the molding of molded products composed of surfaces and the like.

[0021]

As described above, according to the present invention, it is possible to easily control the gas injection molding and prevent the occurrence of defective portions such as sink marks and holes.

[Brief description of drawings]

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

FIG. 2 is a three-view drawing showing a molded product in an experimental example of the present invention.

FIG. 3 is a trihedral view showing a molded product in a comparative example.

FIG. 4 is an enlarged cross-sectional view of an essential part showing a result of the experimental example.

FIG. 5 is an enlarged cross-sectional view of an essential part showing a result of the comparative example.

FIG. 6 is a perspective view showing a modified example of the present invention.

FIG. 7 is a perspective view showing another modification of the present invention.

FIG. 8 is a perspective view showing another modification of the present invention.

FIG. 9 is a perspective view showing still another modified example of the present invention.

[Explanation of symbols]

 10 Mold 11 Cavity 13 Gas channel guide part 15 Buffer forming part 20 Molded product 23 Hollow thick part 24 Gas channel 30 Test piece as molded product

Claims (2)

[Claims] 1. A gas injection molded article, characterized in that a hollow thick portion surrounding a gas channel formed by injecting gas inside has a tapered end portion. 2. A mold provided with a gas channel guide portion in which the thickness of the cavity is made thicker than the surroundings in advance, and a buffer forming portion formed by tapering the end portion of the gas channel guide portion. A gas injection molding method, comprising injecting a gas into the filled molten resin after starting the filling.