JPH0985771A - Gas pressure-supported blow injection molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a cooling effect in a gas pressure-supported blow injection molding method wherein a hollow part is formed in a synthetic resin material in a cavity by a method wherein after injecting a fluid synthetic resin material into a cavity of a mold, gas is force injected therein. SOLUTION: After injecting a fluid thermoplastic synthetic resin material 10 from a material injection opening 23 of a cored mold 24 interconnected to a central part 22a into a cavity 22 having a plurality of arm parts 22b extending radially by being continuously connected to a center part 22a by a planar view on a mating surface of top and bottom tools 20, 21, gas of a suitable pressure such as compressed air or the like is force injected into the thermoplastic resin material 10 from a pipe 26 on a base part side of each arm part 22b near the material injection opening 23 to form a hollow part 28 in each arm part 22b. Then, by force injected the gas of a suitable pressure such as compressed air or the like from a pipe 27 on a tip side of each arm part 22b into each hollow part 28 and force injecting a new gas of a lower temperature therein, cooling of the thermoplastic synthetic resin material 10 in the arm part 22 is accelerated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of injection molding by filling a fluid synthetic resin material in a closed cavity of a mold, and more specifically, to a fluid synthetic resin material in the closed cavity. The present invention relates to a gas pressure assisted hollow injection molding method in which a hollow molded article can be obtained by injecting a gas of appropriate pressure such as compressed air into the interior of a synthetic resin material.

[0002]

2. Description of the Related Art Conventionally, when a thermoplastic synthetic resin material is blow-molded, a pipe-shaped synthetic resin material (varison) is sandwiched between a pair of molds and placed in a cavity between mating surfaces of the molds. It is known to inject compressed air from a nozzle into the ballison to obtain a hollow molded article having a predetermined shape.

Further, in Japanese Patent Publication No. 4-71692, for example, a blowing pipe having one mold penetrating it is made to face the inside of the blow-molded hollow molded article, and a foaming resin is injected into the hollow portion. Is disclosed. by the way,
Recently, in order to reduce the amount of synthetic resin material used, to reduce the weight, and to eliminate locations where the variation in wall thickness is large due to reinforcing ribs, etc., to change to an injection molded product having a hollow portion, After filling a fluid synthetic resin material into the closed cavity of the mold, a gas having an appropriate pressure such as compressed air is pressed into the synthetic resin material from one ejection port to form a hollow molded product. An obtainable gas pressure assisted hollow injection molding method has been developed [Practical Plastics Encyclopedia (see pages 768 to 769): Published January 5, 1994 (second printing), Publisher: Sangyo Co., Ltd. Research Encyclopedia Publishing Center].

[0004]

However, in the case of a thermoplastic synthetic resin material having a high fluidity such as nylon resin or ABS resin, the cooling property of the resin is poor, so that compressed air is pressed into the synthetic resin material in the cavity. However, it is difficult to cool the inside of the hollow part of the molded product, and therefore, after the molded product is taken out of the mold, the product contracts, resulting in dimensional defects and surface sink marks.

In particular, when the size of the molded product is large, or in the legs of a chair, a plurality of (4 to 5) horizontal legs are radially formed from the base of a vertical support pillar that supports the seat. And in the molded article continuously connected in a substantially horizontal direction, after injecting a fluid thermoplastic synthetic resin material from the column base portion, after reaching the portion of each horizontal foot portion close to the column base, In each horizontal foot, gas must be injected into the material to spread the synthetic resin material to form each horizontal foot in a hollow shape. Since each horizontal foot is elongated, the injection pressure is high. As a result, it is difficult to cool the inside of the hollow part of the molded product, the cooling time is long and the mass productivity is poor, and if the cooling rate is greatly different in the longitudinal direction of the horizontal foot part, the problem that the product shrinks and deforms easily occurs is solved. I couldn't.

The present invention has been made to solve these conventional technical problems, and an object of the present invention is to provide a gas pressure assisted hollow injection molding method having excellent cooling efficiency.

[0007]

In order to achieve the above-mentioned object, the gas pressure assisted hollow injection molding method of the present invention according to claim 1 forms a closed cavity by combining a plurality of molds,
After injecting a fluid synthetic resin material into the closed cavity from one material injection port, a gas having an appropriate pressure such as compressed air is injected from the first injection port near the material injection port into the synthetic resin material inside the cavity. It is characterized in that a hollow part is formed by press-fitting into the hollow part, and then a gas having an appropriate pressure such as compressed air is press-fitted into the hollow part from a second injection port located far from the material injection port.

Further, in the gas pressure assisted hollow injection molding method according to the second aspect of the present invention, a closed cavity is formed by combining a plurality of molds, and a single material injection port is used to synthesize a fluid in the closed cavity. After injecting the resin material, a gas having an appropriate pressure such as compressed air is press-fitted into the synthetic resin material in the cavity from the first injection port close to the material injection port to form a hollow portion, while the material injection port is formed. An exhaust pipe is injected into the hollow portion from an exhaust port located at a position far from the exhaust port, and the gas is exhausted from the inside of the hollow portion through the exhaust pipe.

In the gas pressure assisted hollow injection molding method according to the third aspect of the present invention, at least a pair of molds are combined, and inside thereof, a central portion and a central portion which are connected to the central portion in a plan view are radially arranged. After forming a closed cavity composed of a plurality of extending arm portions and injecting a fluid synthetic resin material from one material injection port communicating with the central portion of the closed cavity, each arm is close to the material injection port and A gas having an appropriate pressure such as compressed air is press-fitted into the synthetic resin material in the cavity from the first injection port communicating with the base side of the section to form a hollow section in each arm section, and then the hollow section is formed in each hollow section. A gas having an appropriate pressure such as compressed air is press-injected from the second injection port on the tip end side of each arm portion.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment embodying the present invention will be described. 1 is a perspective view of a chair 1, and FIG. 2 is a partial cross-sectional view of a synthetic resin leg 2 in the chair 1, the leg 2 being a gas spring 4 extending downward from a lower end of a seat 3 of the chair 1. Of the guide cylinder 4a, the base 5 (center) is in the form of a cylindrical column, and five horizontal legs 6 extend radially from the base 5 in a plan view. As shown in FIG. 2 and FIG. 6, the inner shaft is hollow, and the mounting shaft 7 of the caster 7 is attached to the lower surface on the tip side of each horizontal foot 6.
A mounting hole 8 into which a is fitted is formed as a recess. Reference numeral 9 covers the outer circumferences of the gas spring 4 and the guide cylinder 4a,
It is an expandable and contractible bellows-shaped cover body that is connected to the upper end of the base portion 5 of the leg body 2 and the lower end of the support frame 3a of the seat body 3.

Next, the gas pressure assisted hollow injection molding method of the present invention will be described with reference to FIGS. The product manufactured by the gas pressure assisted hollow injection molding method of the present invention is the leg body 2, and the synthetic resin material used is an ABS resin having a large mechanical strength (rigidity, hardness, impact resistance, etc.),
The thermoplastic synthetic resin material 10 is a polyamide resin (nylon 66 resin or the like) or a polyimide resin. These synthetic resins have high fluidity at the time of injection for injection molding.

In FIG. 3, a cavity 22 corresponding to the outer shape of the leg 2 is formed as a recess between the mating surfaces of the upper mold 20 and the lower mold 21. And leg 2
The central portion 22 of the cavity 22 corresponding to the location of the base portion 5 of
A core mold 24 having an opening 23 at the lower end of the thermoplastic synthetic resin material 10 having a high fluidity to be injected is inserted into a from the upper surface of the upper mold 20. A pin 25 for forming the attachment hole 8 is projected into the arm portion 22b toward the lower end tip side of the elongated arm 22b corresponding to each horizontal foot portion 6 of the leg body 2.

Further, two passages are bored from the lower surface of the lower die 21 into the respective arm portions 22b of the cavity 22, and a pipe through which a gas such as compressed air or nitrogen gas passes is provided in each passage. 26 and 27 are movably fitted and inserted, and each pipe 26 and 27 is provided with a valve (not shown) that can be opened and closed. The installation positions of the pipes 26 and 27 are appropriately separated by a dimension H1 between the pipe 26 on the side closer to the central portion 22a (injection port 23) of the cavity 22 and the pipe 27 on the far side. The pipe 26 on the side closer to the central portion 22a (injection port 23) is referred to as a first injection port, and the pipe 27 farther from the central portion 22a (injection port 23) with the pipe 26 sandwiched therebetween is used as the second injection port. It is also used as an exhaust port.

First, in the first stage of manufacturing, as shown in FIG. 3, the upper die 20 and the lower die 21 are aligned with each other, and the core die 24 is inserted from above the upper die 20 to be hermetically sealed. A predetermined amount of the thermoplastic synthetic resin material 10 which is heated and has fluidity is injected through the injection port 23 so that the cavity 22 is formed. When the injection (filling) of the thermoplastic synthetic resin material 10 is completed, then the thermoplastic synthetic resin material 10 that has entered the respective arm portions 22b of the cavity 22.
When the opening portion of the pipe 26 as the first injection port is closed, the pipe 26 is placed in each arm portion 22b such that the tip end thereof is located at the upper and lower intermediate position in the thermoplastic synthetic resin material 10. After pushing forward, appropriate pressure (5-20
Inject gas such as compressed air (kg / cm ² ). Then, as shown in FIG. 4, a hollow portion 28 is formed in the inner diameter portion of the thermoplastic synthetic resin material 10 in each arm portion 22b of the cavity 22, and the volume of the hollow portion 28 increases as the amount of gas press-fitted increases. . Next, when the thermoplastic synthetic resin material 10 in each arm portion 22b closes the location of the pipe 27, each of the pipes 27 is placed so that its tip is located at an intermediate position in the vertical direction in the thermoplastic synthetic resin material 10. After pushing it into the arm portion 22b, a gas such as compressed air having an appropriate pressure (5 to 20 kg / cm ² ) is injected again.

After the gas is injected from the pipe 26 which is the first injection port, the gas is injected from the pipe 27 which is the second injection port, and then the gas is injected from the pipe 26 while the gas is injected from the pipe 26. May employ a step of exhausting gas. Further, even if the gas is pressed into the arm portion 22b without the pipes 26 and 27 entering the arm portion 22b, the hollow portion 28 is formed in the inner diameter portion of the thermoplastic synthetic resin material 10 in each arm portion 22b of the cavity 22. Can be formed.

After these steps, both pipes 26 and 27 may be extracted from the arm portion 22b of the cavity 22, and then the upper and lower molds 20 and 21 may be opened to take out the leg 2 which is an injection molded product. With this manufacturing method, as shown in FIG. 5, in each arm portion 22 b of the cavity 22, the cavity 2 sealed by the internal pressure of the grown hollow portion 28 is used.
The thermoplastic synthetic resin material 10 is pressed against the wall surface of 2 with an appropriate thickness, the internal pressure applied to the inside of the cavity 22 is made uniform at each portion, and the residual strain of the injection molded product is also reduced.

When a certain amount of gas is injected from the pipe 26 which is the first injection port, the temperature of the gas inside the hollow portion 28 rises due to the contact with the thermoplastic synthetic resin material 10 as the hollow portion 28 grows. Then, after the cooling effect declines, a gas with a lower temperature is newly injected again from the pipe 27 that is the second injection port. Therefore, as compared with the conventional technology in which the gas is injected from one place, the arm It is possible to improve the cooling effect on the tip side of the portion 22b, reduce the surface sink in the portion where the wall thickness varies, and shorten the injection molding cycle time, thus improving mass productivity. Further, the hollow portion 2
The weight of each horizontal foot portion 6 of the leg body 2 which is a molded product is reduced by 8 and the amount of synthetic resin used can be reduced to reduce the cost.

FIG. 6 is a bottom view of a leg 2 which is an injection-molded product obtained by opening and taking out the upper and lower molds 20 and 21. Traces 26a and 27a that penetrate the two pipes 26 and 27 can be seen. 7 and 8 show another embodiment, which is the first embodiment described above.
When the injection (filling) of the predetermined amount of the thermoplastic synthetic resin material 10 having the fluidity of the stage from the injection port 23 is completed, the thermoplastic synthetic resin material 10 that has entered each arm portion 22b of the cavity 22 is Pipe 2 as the first injection port
When the opening portion of 6 was closed, a gas having a predetermined pressure was injected from the pipe 26 (see FIG. 7), and then the thermoplastic synthetic resin material 10 in each arm portion 22b closed the portion of the pipe 27. At this point, the pipe 27 is pushed into each arm portion 22b so that the tip of the pipe 27 is located at the upper and lower intermediate positions in the thermoplastic synthetic resin material 10, and the hollow portion 28 grows to cause the surface of the thermoplastic synthetic resin material 10 to grow. When the valve of the pipe 27 is opened while the inner surfaces of the arms 22b are evenly pressed and the appearance of the injection-molded product is adjusted, the gas supplied from the pipe 26, which is the first injection port, passes through the hollow portion 28. It can be exhausted outside the mold (see FIG. 8). Therefore, the cooling effect can be further improved by the circulation of the low-temperature gas into which the temperature inside the hollow portion 28 is newly injected.

In the above embodiment, the leg 2 of the chair 1 is used.
Was molded by the gas pressure assisted hollow injection molding method, but it goes without saying that it can be applied to relatively large parts, for example, long parts such as automobile bumpers. In this case, the injection port 23 of the thermoplastic synthetic resin material 10 is at the longitudinal center of the bumper, the first injection port is located close to the injection port 23 in the longitudinal direction, and the second injection port and the exhaust port are far from each other. It should be placed on the side.

[0020]

As described above, according to the first aspect of the present invention, a plurality of molds are combined to form a closed cavity, and a synthetic resin material that is fluid from one material injection port into the closed cavity. After injecting the
A gas having an appropriate pressure such as compressed air is press-fitted from the injection port into the synthetic resin material in the cavity to form a hollow portion, and then the hollow portion is formed from a second injection port far from the material injection port. It is characterized in that a gas having an appropriate pressure such as compressed air is injected.

Therefore, even if the temperature of the gas injected from the first injection port rises as the hollow portion of the inner diameter of the fluid synthetic resin material grows and the cooling effect decreases, a new gas is introduced from the second injection port. Since the synthetic resin material can be cooled again by pressurizing the gas, even if the cycle time of injection molding is shortened, the occurrence of surface sink marks and the shrinkage rate of the synthetic resin material after taking out from the mold are reduced, Although it can be mass-produced, it is possible to prevent the occurrence of defects and improve the production efficiency.

Further, in the gas pressure assisted hollow injection molding method of the present invention as defined in claim 2, a closed cavity is formed by combining a plurality of molds, and one material injection port is used to synthesize a fluid in the closed cavity. After injecting the resin material, a gas having an appropriate pressure such as compressed air is press-fitted into the synthetic resin material in the cavity from the first injection port close to the material injection port to form a hollow portion, while the material injection port is formed. An exhaust pipe is injected into the hollow portion from an exhaust port located at a position far from the exhaust port, and the gas is exhausted from the inside of the hollow portion through the exhaust pipe.

Therefore, the gas having a high temperature passing through the hollow portion is discharged to the outside of the mold from one of the exhaust ports, and the new gas having a low temperature is introduced from the first jet port, so that the gas is discharged from the two ports. The gas flow is smoothly circulated in the hollow portion as compared with the case where the gas is injected, and the effect that the customer effect can be further improved. And the gas pressure assisted hollow injection molding method of the invention according to claim 3 is such that at least a pair of molds are combined, and inside thereof, a plurality of radially extending parts are continuously provided in the central portion and the central portion in plan view. After forming a closed cavity consisting of an arm part and injecting a fluid synthetic resin material from one material injection port communicating with the central part of the closed cavity, it is close to the material injection port and the base part of each arm part A gas having an appropriate pressure such as compressed air is press-fitted into the synthetic resin material in the cavity from the first injection port communicating with the side to form a hollow portion in each arm portion, and then the hollow portion is formed in each hollow portion. It is characterized in that a gas having an appropriate pressure such as compressed air is injected from the second injection port on the tip side of the arm portion.

As described above, when the injection-molded article is composed of the central portion and a plurality of arm portions connected to the central portion and extending radially, the side closer to the injection port, which is the central portion, for each arm portion. By providing the second injection port on the far side from the first injection port,
An independent hollow part is formed for each arm part,
Cooling of the part where the wall thickness changes between the center part and the arm part and the variation of the cooling rate to the tip of the elongated arm part can be reduced, the cooling effect can be increased, and the cycle time of injection molding can be shortened while defective products are generated. The effect is that a small number of hollow injection-molded products can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of a chair.

FIG. 2 is a partially cutaway cross-sectional view of a synthetic resin leg of a chair.

FIG. 3 is an explanatory diagram showing a state of fluid synthetic resin material injection in a first step of the gas-assisted hollow injection molding method.

FIG. 4 is an explanatory diagram showing a state in which gas is pressed in from a first injection port.

FIG. 5 is an explanatory diagram showing a state in which gas is press-fitted from a second injection port.

FIG. 6 is a bottom view of a leg that is an injection molded product.

FIG. 7 is an explanatory diagram showing a state in which gas is press-fitted from the first injection port.

FIG. 8 is an explanatory diagram showing a state in which gas is exhausted from the exhaust port while being press-fitted from the first injection port.

[Explanation of symbols]

 2 Leg 5 Base 6 Horizontal foot 10 Thermoplastic synthetic resin material 20 Upper mold 21 Lower mold 22 Cavity 22a Center part 22b Arm part 23 Injection port 24 Core mold 26, 27 Pipe

Claims (3)

[Claims] 1. A closed cavity is formed by combining a plurality of molds, and a fluid synthetic resin material is injected into the closed cavity from one material injection port, and then a first injection port close to the material injection port. A compressed gas such as compressed air into the synthetic resin material in the cavity to form a hollow portion, and then the second portion at a position distant from the material injection port is formed in the hollow portion.
A gas pressure assisted hollow injection molding method, characterized in that a gas having an appropriate pressure such as compressed air is injected from an injection port. 2. A closed cavity is formed by combining a plurality of molds, and a fluid synthetic resin material is injected into the closed cavity from one material injection port, and then a first injection port close to the material injection port. While forming a hollow portion by press-fitting a gas of appropriate pressure such as compressed air into the synthetic resin material in the cavity, while injecting an exhaust pipe into the hollow portion from an exhaust port located far from the material injection port, A gas pressure assisted hollow injection molding method, characterized in that the gas is exhausted from inside the hollow portion via the exhaust pipe. 3. A hermetically sealed cavity comprising at least a pair of molds, a hermetically sealed cavity having a central portion and a plurality of radially extending arm portions connected to the central portion in a plan view. After injecting a fluid synthetic resin material from one material injection port that communicates with the central part of the, the first injection port that is close to the material injection port and that communicates with the base side of each arm section appropriately supplies compressed air or the like. Pressure gas is pressed into the synthetic resin material in the cavity to form a hollow portion in each arm portion, and then compressed air or the like is supplied to each hollow portion from the second injection port on the tip side of each arm portion. A gas pressure assisted hollow injection molding method, characterized in that a gas having an appropriate pressure is injected.