JPH07164486A - Mold for molding - Google Patents

Abstract

PURPOSE:To prevent the generation of sink marks at the end, etc., of a thick- walled part remote from a pressurized fluid injection port by installing a movable core in or near a thick-walled part in the cavity of a mold which has continuously thick-walled parts for forming a hollow structure and in which the pressurized fluid injection port is communicated with the central part of the thick-walled part. CONSTITUTION:In a mold cavity 8, a movable core 4 arranged in or near a thick-walled part for forming a hollow part in a molded article is to change the volume of the cavity 8 at its position. A molten resin is injected into the cavity 8 with the movable core 4 advanced. A pressurized fluid is then injected from a pressurized fluid injection port 7 through a gas injection nozzle. In this operation, the movable core 4 is made to retreat by a hydraulic cylinder 5 for the movable core. In this way, a hollow part can be formed to the end of the thick-walled part. The movable core 4 is preferably placed at the end of the thick-walled part or close to the part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding die used for molding a beautiful molded product which has a beautiful appearance without sink marks or warpage. More specifically, the present invention relates to a molding die used for producing a molded article having a hollow structure by pressurizing a pressurized fluid into the molten resin injected into the die from the inside of the die.

[0002]

2. Description of the Related Art When a molten thermoplastic resin is molded by injection molding, in order to obtain a beautiful molded product without a sink mark or warp, JP-A-63-268611 and Japanese Patent Application Laid-Open No. 03-
Japanese Patent No. 47171 discloses that a molten thermoplastic resin is injected and injected into a mold cavity, and then a pressurized fluid such as a pressurized gas is injected to produce a synthetic resin molded product having a hollow structure. And, the thick portion thereof is filled with a molten thermoplastic resin into a mold cavity designed to form a molded article communicating with the pressurized gas discharge portion, and then the resin is filled into the mold cavity, and then, Disclosed is a method for producing a synthetic resin molded product having an unevenly distributed reinforcing structure, which comprises injecting a pressurized gas and cooling and solidifying the synthetic resin molded product in a mold under gas pressure.

However, in the prior art, the cavity of the mold is filled with the molten thermoplastic resin, and then the pressurized fluid under pressure is injected, and the pressurized fluid cools the molten resin in the uneven thickness portion. Flow through only the volume reduction of the molded product corresponding to the volume contraction due to the pressure shrinkage, the pressurizing fluid flow end of the uneven thickness portion and the pressurized fluid of the uneven thickness portion installed at a long distance from the pressurized fluid inlet. In the case of a molded product having an uneven thickness shaped portion such as a boss or rib at the flow end, the pressurized fluid does not reach the desired part, and the uneven thickness part installed at a long distance from the pressurized fluid inlet is added. In some cases, sink marks are generated in the pressure fluid flow end or the uneven thickness portion of the pressurized fluid flow end of the uneven thickness portion.

When sink marks occur, increasing the pressure of the pressurized fluid is one of the countermeasures, but the effect is low, and conversely, the pressurized fluid may squeeze out into the thin portion or the surface appearance may be deteriorated. is there. When manufacturing an injection-molded article having a hollow structure, JP-A-5-96560 discloses the use of a sub-cavity, and the use of the sub-cavity at the flow end of the uneven thickness portion can also be expected to be effective, This complicates the process of cutting off the sub-cavity after molding and impairs the appearance of the treated part of the molded product after the sub-cavity is processed, and significantly impairs its productivity.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art as described above, to smoothly press the pressurized fluid into the molten resin, and to pressurize the fluid to a desired portion. Beautiful molding that does not cause sink marks on the end of the pressurized fluid flow at the uneven thickness portion installed at a distance from the pressurized fluid injection port or the uneven thickness shape portion at the end of the pressurized fluid flow at the uneven thickness portion. It is to provide a molding die capable of manufacturing a product.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies on a molding die for solving the above problems, and as a result,
In a molding method in which a pressurized fluid is pressed into the molten resin injected into a mold to obtain a molded product having a hollow structure, an uneven thickness portion is continuously provided in the molded product, and In a mold designed so that a pressurized fluid communicates with the central portion of the uneven thickness portion, a pressurized fluid flows through a mold core movable to the uneven thickness portion in a mold cavity that can form the molded product. By arranging at the end, the flow distance of the pressurized fluid is extended, the pressurized fluid is smoothly pressed into the inside of the molten resin, the pressurized fluid is allowed to flow to a desired portion, and it is installed at a long distance from the gate. Finding a molding die capable of producing a beautiful molded product which does not cause sink marks in the pressurized fluid flow end of the uneven thickness portion or the pressurized fluid flow end of the uneven thickness portion, The present invention has been reached.

That is, the present invention is for molding for molding a molded article having a hollow structure by injecting a molten resin into a mold using an injection molding machine and then pressurizing a pressurized fluid into the molten resin. A mold, which is a mold in which a thick uneven thickness portion for forming a hollow structure is continuously provided in the molded product, and
A thick mold eccentric part or a movable mold core is disposed in the vicinity of the eccentric part in the mold cavity of the mold having a structure in which the injection part of the pressurized fluid communicates with the center part of the eccentric part. The present invention relates to a characteristic molding die.

The number of movable cores used in the present invention is not particularly limited, and it is also possible to install a plurality of movable cores in the uneven thickness portion unevenly distributed in one mold cavity. For example,
In a molding die having a plurality of uneven thickness portions, an uneven thickness portion such as a boss or a rib at an uneven thickness portion installed at a distance from a pressurized fluid injection port and a pressurized fluid flow end of the uneven thickness portion. If there are parts, it is sufficient to install the required number. It is also possible to connect a plurality of uneven thickness portions to one movable core.

The movable core of the present invention expands and contracts the cavity volume of the movable core portion, and the forward and backward movement of the movable core is performed by a hydraulic cylinder.
Other power sources, such as air pressure, electric power, etc., may be used. It is also effective to control the expansion speed according to the hollowing speed.

The forward / backward control of the movable core of the present invention is performed by a molding machine,
This can be implemented by a control signal transmitted from a pressurized fluid supply device, and the control of the retracted position and speed of the movable core is determined by the effect of preventing sink of the desired pressurized fluid, and the retracted position is extremely simple. It is reliable to use mechanical position control, for example, a backstop sleeve, a backstop knock pin, a backstop block or the like.

The wall thickness of the movable core portion or the uneven thickness portion in the vicinity according to the present invention is preferably 1.0 to 5.0 times the average wall thickness of the molded product when injecting the molten resin, and molded when injecting a pressurized fluid. It is desirable to have a structure that expands to more than 2.0 times the average wall thickness of the product. If the expansion ratio is small, the effect of the above problem is small, and the upper limit of the expansion ratio is that the pressurized fluid breaks through the molded product. Instead, it is possible to increase the thickness until the desired molded product functions.

The movable core of the present invention is basically retracted after the movable core is filled with the molten resin, but the movable core may be retracted during the filling if desired. The expanded molded product part obtained by the present invention can be used as a functional part of the molded product and is extremely practical.

Further, an extremely excellent feature of the present invention is that the pressurized fluid flows through the uneven thickness portion and allows the pressurized fluid to flow to a desired portion, and the uneven thickness is installed at a long distance from the pressurized fluid inlet. If a pressurized fluid flow path that does not cause sink marks is formed in the pressurized fluid flow end of the part or the uneven thickness shape part of the pressurized fluid flow end of the part, the molten resin is in a semi-molten state. At some point, the retracted mold core is moved forward again and the enlarged part can be made smaller until there is a flow path volume through which the pressurized fluid penetrates the enlarged part of the molded product. Is possible.

The present invention will be described with reference to FIGS. still,
The symbols used in the figure are as follows. 1 Fixed type 2 Movable type 3 Resin gate 4 Movable core 5 Hydraulic cylinder for movable core 6 Boss 7 Pressurized fluid injection port 8 Cavity 9 Gas injection nozzle 10 Hydraulic cylinder for gas injection nozzle

FIG. 1 is a schematic view of a die cross section showing an installation place of the movable core of the present invention. Molten resin is injected from the resin gate 3 into the cavity 8 with the movable core 4 advanced. The pressurized fluid is then passed through the gas injection nozzle 9 ,
It is injected from the pressurized fluid injection port 7. At this time, by retracting the movable core 4 by the movable core hydraulic cylinder 5, it becomes possible to form the hollow portion up to the end of the thick-walled uneven thickness portion. Although there is only one pressurized fluid inlet in FIG. 1,
As shown in FIG. 2, it may be provided at two locations, or may be provided at a plurality of locations of three or more locations if necessary.

[0016]

In the mold cavity of the present invention, by using the mold in which the mold core movable in the uneven thickness portion and the vicinity thereof is arranged at the end of the flow of the pressurized fluid, the flow distance of the pressurized fluid is extended and the pressure is increased. The fluid is smoothly pressed into the molten resin to allow the pressurized fluid to flow through to the desired part, and the pressurized fluid flow end and the uneven thickness of the uneven thickness portion installed at a distance from the pressurized fluid inlet It is possible to manufacture a beautiful molded product that does not cause sink marks in the uneven thickness shaped portion at the end of the pressurized fluid flow portion.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described based on the preferred embodiments with reference to the drawings. Example 1 The mold shown in FIG. 1 has a gas injection nozzle, the average thickness of the molded product obtained from the mold is 2.5 mm, and the moving distance of the movable core is 5 mm. A hollow molded product was molded using a mold. In FIG. 1, a cavity 8 of a movable mold 2 of a mold is provided with an uneven thickness portion communicating with a pressurized fluid inlet 7 , and a movable core hydraulic cylinder 5 is driven at both ends of a pressurized fluid flow end of the uneven thickness portion. The movable core 4 which can be moved is provided. In addition, a boss 6 is provided on one end of the pressurized fluid flow end.
Was set up.

Polycarbonate resin (manufactured by Mitsubishi Gas Chemical Co., Inc., trade name: Iupilon S3000 natural color) is melted to a resin temperature of 280 ° C. in an injection molding machine cylinder,
Plasticized. After the mold is clamped, the movable core 4 provided in the movable mold 2 is moved forward by the movable core hydraulic cylinder 5 , and the resin gate 3 is placed in the cavity 8 at an injection pressure of 1130 kg / cm ² .
The more molten polycarbonate resin was injected. After the cavity 8 was filled with the molten resin, the movable core 4 was retracted while the compressed nitrogen gas of 80 kg / cm ² was pressed from the pressurized fluid inlet 7 . Then compensate for volume shrinkage due to thermal contraction of the molten resin in the compressed nitrogen gas, after the molded product was cooled for 60 seconds in close contact with the cavity surface, the atmosphere in the compressed nitrogen gas in the molded product from the gas pressurized fluid inlet 7 , The mold was opened, and the molded product was taken out. The obtained molded product had a hollow structure that penetrated to the end of the uneven thickness portion, and a beautiful molded product without sink marks was obtained. A sectional view of the obtained molded product is shown in FIG.

Comparative Example 1 A comparative experiment was conducted using the mold shown in FIG. The same polycarbonate resin as used in Example 1 was melted and plasticized at a resin temperature of 280 ° C. in an injection molding machine cylinder. After clamping the mold, move it with the movable core hydraulic cylinder 5
In the mode in which the movable core 4 provided in FIG.
The molten polycarbonate resin was injected and injected from the resin gate 3 into the cavity 8 at 30 kg / cm ² . cavity
A molten resin was filled in the container 8 , and the movable core 4 was retracted, and 80 kg / cm ² of compressed nitrogen gas was injected from the pressurized fluid inlet 7 .

The volumetric shrinkage due to the thermal shrinkage of the molten resin is compensated by the compressed nitrogen gas, the molded product is brought into close contact with the cavity surface and cooled for 60 seconds, and then the compressed nitrogen gas in the molded product is discharged from the pressurized fluid injection port 7 into the atmosphere. , The mold was opened, and the molded product was taken out. Although the obtained molded product had a compressed nitrogen gas flow path that flowed through the uneven thickness portion, it was far from the example, and a boss provided at the end of the molded product and a pressurized fluid for the uneven thickness portion. There was a sink mark at the flow end. A cross-sectional view of the obtained molded product is shown in FIG.
Shown in.

[0021]

EFFECTS OF THE INVENTION By using a mold in which a mold core movable in the uneven thickness portion in the mold cavity of the present invention is arranged at the end of the pressurized fluid flow end, the flow distance of the pressurized fluid is extended and the pressure is increased. The fluid is smoothly pressed into the molten resin to allow the pressurized fluid to flow through to the desired part, and the pressurized fluid flow end and the uneven thickness of the uneven thickness portion installed at a distance from the pressurized fluid inlet It is possible to mold a beautiful molded product having a desired hollow structure in a stable continuous cycle without causing sink marks in the uneven thickness shape of the pressurized fluid flow end of the portion.

[Brief description of drawings]

FIG. 1 is a schematic view of a cross section of a mold showing an installation place of a movable core of the present invention.

FIG. 2 is a schematic view of a mold cross section in which the movable core of the present invention is installed at two locations.

FIG. 3 is a cross-sectional view of a molded product obtained in Example 1.

FIG. 4 is a cross-sectional view of a molded product obtained in Comparative Example 1.

[Explanation of symbols]

1 Fixed type 2 Movable type 3 Resin gate 4 Movable core 5 Hydraulic cylinder for movable core 6 Boss 7 Pressurized fluid injection port 8 Cavity 9 Gas injection nozzle 10 Hydraulic cylinder for gas injection nozzle

Claims (2)

[Claims] 1. A molding die for molding a molded product having a hollow structure by injecting a molten resin into a mold using an injection molding machine and then pressurizing a pressurized fluid into the molten resin. Is a mold in which a thick-walled uneven thickness portion for forming a hollow structure is continuously provided in the molded product, and the pressurized fluid injection portion communicates with the central portion of the uneven thickness portion. A molding die, wherein a movable mold core is arranged in a thick-walled uneven thickness portion or in the vicinity of the uneven thickness portion in a mold cavity of a certain mold. 2. The molding die according to claim 1, wherein the movable die core is arranged at or near the end of the thick-walled uneven thickness portion.