JP2794261B2 - Mold for molding synthetic resin products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding die for a synthetic resin molded product, which is obtained by injecting a molten resin into a mold cavity and solidifying it by cooling to obtain a synthetic resin molded product.

[0002]

2. Description of the Related Art A large number of synthetic resin molded articles are used without mentioning home electric appliances, automobiles, household goods, etc., and these synthetic resin molded articles are injection molded, compression molded, extruded, and vacuum molded. It is molded by a molding method or the like. Incidentally, the injection molding method is widely used because it has an advantage that a molded article having a complicated shape can be relatively easily molded. As is well known, an injection molding machine used to carry out this injection molding method includes a screw for plasticizing a thermoplastic molding material such as polystyrene and ABS resin, a mold for injection-filling a plasticized molten resin, and the like. It is composed of Therefore, the screw is rotated in a cylinder to plasticize the resin, and the fluidized thermoplastic molding material is injected and filled into the cavity of the closed mold by driving the screw in the axial direction to obtain a desired shape. Is molded.

[0003]

In this way, a synthetic resin molded article is molded, but a defective article may occur in the molded article. The most frequently occurring of the molding defects is sink marks. The sink is a phenomenon in which a concave portion is formed on the surface of a synthetic resin molded product, and particularly occurs on the surface of a thick portion of the synthetic resin molded product. The mechanism of occurrence will be described in more detail. FIG. 4 is a cross-sectional view of a synthetic resin molded article 01 molded by a conventional molding method. As shown in FIG. The rib portion 03 is formed of a plate portion 02 and a rib portion 03. A root portion of the rib portion 03 with respect to the plate portion 02 is a thick portion 04. Since the thick portion 04 has poor heat conduction, the heat shrinkage due to cooling becomes slow. For this reason, the synthetic resin is drawn to the thin portion in the vicinity where heat shrinks quickly, and a concave portion, that is, sink mark 05 is generated on the surface of the thick portion 04. When sink 05 occurs in this way,
The appearance of the molded article 01 is impaired, and the commercial value is reduced.

A sink 05 that impairs the appearance of the molded article 01
Can be suppressed to some extent by increasing the injection pressure or by taking a sufficient holding pressure so as to compensate for the heat shrinkage of the thermoplastic molding material. However, if the injection pressure or the holding pressure is increased, other molding defects such as burrs, cracks, and mold release defects occur. Thus the injection pressure,
If the holding pressure or the like is lowered, sink marks 05 occur in the thick-walled portion 04, whereas if the holding pressure is increased, other molding defects such as burrs are caused, and the injection pressure and the holding pressure are reduced so that there are no defective synthetic resin molded products. It is generally difficult to control to an appropriate pressure. Also, the appropriate pressure varies depending on the shape, size, etc. of the molded product, and it is difficult to adjust the pressure. The present invention has been made in view of such a problem, and even if the injection pressure and the holding pressure are not strictly controlled, the problem of the concave portion, ie, sink mark, which impairs the appearance of the synthetic resin molded article, and the flash It is an object of the present invention to provide a molding die for a synthetic resin molded product, which does not cause other problems of molding failure such as cracking, mold release failure, and the like.

[0005]

In order to achieve the above object, the present invention provides a fixed mold and a movable mold, and a cavity for molding a synthetic resin molded product between these molds. In at least one of the fixed mold 1 and the movable mold, a needle passage and a gas suction passage are provided, and the needle passage has the cavity at the time of injection. A retractable needle is provided to reach the thick hollow portion of the airbag, and when the needle is retracted from the cavity, the gas suction path is configured to be in communication with the cavity.

[0006]

[Operation] The movable mold is clamped to the fixed mold. Advance the needle to the thick cavity of the cavity before injecting the molten resin. Then, the molten resin is injected and filled into the cavity by a conventionally known means. The needle is retracted before the resin in the filled cavity cools and solidifies.
Then, the gas suction path communicates with the inside of the resin filled in the thick hollow portion. When cooling, the thick portion of the molten resin is drawn in the direction of the rapid thermal contraction of the peripheral thin portion, but since the inside of the thick portion of the resin is in communication with the gas suction path, it is connected through the gas suction path. Thus, a gas such as air is introduced from the outside into the thick portion of the molten resin. As a result, a cavity is generated inside the thick portion. Since cavities are generated inside the thick part, sink marks do not occur on the outer surface of the synthetic resin molded product.

[0007]

FIG. 1 is a sectional view showing an embodiment of a mold, and FIGS. 2 and 3 are explanatory views for explaining the steps of one embodiment of the synthetic resin molding method of the present invention. An embodiment of a molding die will be described with reference to FIG. The molding die includes a fixed die 1 and a movable die 10 as shown in FIG. The movable mold 1 is clamped or opened with respect to the fixed mold 10 by a conventionally known toggle mechanism or the like. A sprue bush 2 is exchangeably fitted to a substantially central portion of the fixed mold 1. A sprue 3 is provided at the center of the sprue bush 2. Therefore, when the nozzle 5 of the injection machine is pressed against the sprue bush 2 and molten resin is injected from the injection machine, the cavity described later is filled with the molten resin via the sprue 3.

[0008] Along the parting line of the movable mold 10, a cavity 11 cooperating with the parting line of the fixed mold 1 is provided. The cavity 11 includes a first cavity 12 for molding a plate-like portion of a molded product, and a second cavity 1 extending at right angles from the first cavity 12 and molding a rib portion.
And 3. And the first cavity 12 and the second
The thick hollow portion 1 where the portion where the hollow portion 13 intersects is relatively thick
It is 5.

In the movable mold 10, a needle passage 20 is opened obliquely upward from the thick cavity portion 15. A needle 21 is slidably provided in the needle passage 20. The needle 21 is driven to a first position where the tip is located in the thick cavity portion 15 of the cavity 11 and a second position where the needle 21 is retracted by a predetermined distance from the cavity 11 during injection filling. An air cylinder 23 is provided. Air cylinder 23
A piston 24 is slidably provided therein, and the end of the needle 21 is attached to the piston 24. The needle 21 in the air cylinder 23
A return spring 25 is provided to pull back the tip of the air cylinder 23 from the thick portion 22.
1 is provided with a compressed air supply port 26 for supplying compressed air that pushes the compressed air 1 toward the thick cavity 15. This compressed air supply port 26 is connected to a compressed air source (not shown). Therefore, the air cylinder 2
When air is supplied or exhausted into the needle 3, the needle 21 reciprocates in the needle passage 20 between the first position and the second position. The movable mold 10 is provided with an air suction passage 27, one of which is open to the atmosphere. And air suction path 2
The other lower end of 7 communicates with the needle passage 20. In addition, other reference numerals 28 and 29 in FIG. 1 indicate large and small ejector pins of an ejector device for projecting a molded product from the dies 1 and 10.

Next, a description will be given of a molding method for molding a synthetic resin molded product by using the molding die. The fixed mold 1 and the movable mold 10 are abutted against each other to perform mold clamping by a conventionally known method. Then, the fixed mold 1 and the movable mold 10
A cavity 11 is formed as a hermetically sealed cavity. Compressed air is introduced into the air cylinder 23 through a compressed air supply port 26. Then, the piston 24 is driven against the return spring 25, and the tip of the needle 21 is located at the first position substantially at the center of the thick cavity 15 in the cavity 11. This state is shown in FIG. The nozzle 5 of the injection machine is crimped to the sprue bush 2 of the fixed mold 1. From the nozzle 5 of the injection machine, the plasticized molten resin is injected. The molten resin fills the cavity 11 through the sprue 3 and the like. This completes the injection process. During this injection filling, the tip of the needle 21 is
5, the molten resin does not flow into the needle passage 20 because it has closed the needle passage 20.

Next, the temperature of the molds 1 and 10 is maintained at a constant temperature of, for example, about 20 ° C.
To cool. 50-80% of injection pressure from nozzle 5
Some pressure is applied to the cavity 11.
This is the pressure-holding step. During this pressure-holding step, the compressed air in the air cylinder 23 is discharged through the compressed air supply port 26. The needle 21 is moved by the return force of the return spring 25.
Is retracted from the molten resin J in the thick cavity portion 15 and located at the second position. Then, the air suction passage 27 communicates with the inside of the molten resin J in the thick cavity portion 15 via the needle passage 20. In the molten resin J filled in the cavity 11, the thin portions filled in the first cavity 12, the second cavity 13, and the like are cooled first and thermally shrink. At this time, the molten resin J is attracted to the thin portion that cools quickly, and the tree finger pressure in the thick cavity portion 15 becomes a negative pressure. As a result, when molded by the conventional mold as described above, sinks occur on the surface of the thick portion, but according to the present embodiment, the inside of the molten resin J filled in the thick cavity portion 15 communicates with the atmosphere. Since it is cooled in the state, the air is supplied from the air suction path 27 into the molten resin J. As a result, as shown in FIG.
A cavity K is formed inside the resin J, and becomes a so-called internal sink K. Therefore, the synthetic resin molded product S is composed of the plate-shaped portion S1 and the rib-shaped portion S2, and the base portion of the rib-shaped portion S2 is the thick portion S3, but the outer surface of the plate-shaped portion S1 has sink marks. Does not occur.

When the molten resin molded product S has been cooled and solidified, a mold opening process is started. When the mold is opened, ejector pin 2
8 and 29 project, and the synthetic resin molded product S is moved to the movable mold 10.
Taken out of The state of being removed is shown in FIG. Hereinafter, the above operation is repeated to obtain a synthetic resin molded product S.

According to this embodiment, various effects can be obtained,
Further, the present embodiment can be variously modified. For example, the air suction passage 27 is connected to the thick hollow portion 1 through the needle passage 20.
5, when the molten resin is injected, the needle 21 closes the air suction path 27, so that the molten resin does not enter the air suction path 27 and is not clogged. However, the air suction passage 27 can be directly communicated with the thick cavity portion 15 without passing through the needle passage. Also,
In the above embodiment, since the needle 21 is driven by the compressed air and the return spring 25, the needle 21 can be driven only by supplying and discharging the compressed air to and from the air cylinder 23. In place of the return spring 25, the return may be performed by compressed air. Obviously, the driving can be performed by other means instead of the air cylinder 23, for example, a rotary motor. Further, in the present embodiment, the needle passage 20, the needle 21, the air suction passage 2
7 and the like are provided on the movable mold 10 side, but may be provided on the fixed mold 1. Further, according to the present embodiment, the air is naturally introduced into the resin J filled in the thick hollow portion 15, but the air can be forcibly supplied from the air suction passage 27. Furthermore, in the present embodiment, the joint between the plate-shaped portion S1 and the rib-shaped portion S2, that is, the base portion of the rib-shaped portion S2 is a position where the appearance of the outer surface is not impaired. Thus, the sink may be positively generated in this portion.

[0014]

As described above, at least one of the fixed mold and the movable mold is provided with the needle passage and the gas suction passage, and the needle passage is provided with the cavity at the time of injection. A retractable needle that reaches the thick cavity of the tee is provided, and when the needle is retracted from the cavity, the gas suction path is connected to the cavity, so the molten resin is injected and filled into the mold cavity, and cooled and solidified When a synthetic resin molded article is obtained, a thick portion of the filled molten resin can be cooled and solidified by introducing gas from the outside to a portion that does not impair the appearance, and as a result, a portion that does not impair the appearance, for example, a thickness An effect peculiar to the present invention is obtained, in which sink marks are actively generated inside the meat portion, and a high-quality molded product having no sink marks on the surface can be obtained. As described above, since molding can be performed so that sinks are positively generated in a portion that does not impair the appearance, the injection pressure and the holding pressure can also be reduced. Therefore, according to the present invention, the problems of other molding defects such as burrs, cracks, and mold release defects can be solved to some extent.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a molding die according to the present invention, partially cut away.

FIG. 2 is a cross-sectional view of a synthetic resin molded product being molded using the molding die shown in FIG.

FIG. 3 is a cross-sectional view showing a state in which the synthetic resin molded product is being removed using the mold shown in FIG.

FIG. 4 is a cross-sectional view of a synthetic resin molded product molded by a conventional method.

[Explanation of symbols]

 Reference Signs List 1 fixed mold 10 movable mold 11 cavity 15 thick cavity section 20 needle passage 21 needle 27 air suction path S synthetic resin molded product S3 thick section

Claims (1)

(57) [Claims] 1. A fixed mold (1) and a movable mold (10), and a cavity (11) for molding a synthetic resin molded product (S) between these molds (1, 10). ), Wherein at least one of the fixed mold (1) and the movable mold (10) has a needle passage (20).
And a gas suction passage (27) are provided, and the needle passage (20) has a retractable needle (21) which reaches the thick cavity portion (15) of the cavity (11) at the time of injection.
Is provided, and when the needle (21) is retracted from the cavity (11), the gas suction path (27) is in communication with the cavity (11). Type.