JPH0615702A - Mold for injection molding of hollow moldings, and molding method therefor - Google Patents

Abstract

PURPOSE:To facilitate filling of melted resin into a surrounding base part of a needle pin, and to obtain moldings having larger distribution of hollows by a method wherein a rib is formed round the base part of the needle pin with a specified distance kept from the base part so that aeration can be made therethrough. CONSTITUTION:A needle pin 24, provided with a plurality of ejection ports 25 on its upper end, is installed to a gas hole 23a of a core 20 for a cavity 21. A rib 27 is formed to the installation base of the needle pin 24. The rib 27 is made up in the shape of a ring, opening toward the upside and surrounding the pin with a space (t) kept at a specified distance from the base part of the needle pin 24, and a slit 28 is provided to one side of the rib 27. As melted resin flowing into the cavity 21 is flowed into the space (t) through the slit 28 and the opening looking toward the upside, no vacant space is produced between the needle pin 24 and the rib 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to molding a hollow molded product by injection molding, and more specifically, an injection mold for molding a hollow molded product by a gas injection method from a cavity, which is one of gas injection methods. And a molding method thereof.

[0002]

2. Description of the Related Art Conventionally, the purpose of molding a hollow molded product by a method of injecting gas into a cavity of this type is to reduce the weight of the molded product. As shown in a) and (b), the upper mold 1 and the lower mold 2 are formed into a mating mold, and a cavity 3 is formed between the mating surfaces,
Gate 4 for injecting the molten resin W into one side of the cavity 3
Are formed. Further, a mounting hole 5 that fits into the cavity 3 is formed at a predetermined position of the lower mold 2, for example, a position near the gate 4, and a needle pin 6 having a gas ejection hole at its tip projects from the mounting hole 5. It is provided in a shape.

In the molding die thus provided,
As shown in FIG. 4 (a), when the molten resin W is filled in the cavity 3 from the gate 4 to some extent, the needle pin 6
More gas is ejected to fill the cavity 3 and the hollow portion 7
However, the molten resin W is often not completely filled around the needle pin 6 immediately before the gas is injected, and even if the molten resin W is completely filled, the molten resin W is completely cooled. Since it is not cured, there is a problem that when the gas is injected, the gas leaks from around the needle pin 6 and the hollow portion 7 cannot be molded. Therefore, as shown in FIGS. 6A and 6B, a configuration in which the rib 8 having a predetermined height is formed around the needle pin 6 is considered.

Forming the rib 8 having a predetermined height around the needle pin 6 is to accelerate the hardening of the molten resin W around the needle pin 6 by the rib 8, but in this case, the base of the needle pin 6 is formed. If the molten resin W is sufficiently filled between the ribs 8 and the ribs 8 and the gas is not injected, the effect of molding the hollow portion 7 is not natural. However, in order to accelerate the cooling and hardening of the ribs 8, the smaller the gap, the better (for example, 1 mm or less), so that the hollow portion 7 was formed.

[0005]

However, the smaller the gap, the more difficult it becomes to fill the molten resin W. For example, in FIGS. 7 (a) and 7 (b), the same cavity 3 is filled with the molten resin W. In the state of FIG. 7 (a), the base portion of the needle pin 6 is not sufficiently filled with the resin W, and there is a space portion 9. Therefore, when gas injection is started by the needle pin 6 in this state, a space is generated. Gas leaks to the part 9 side. Therefore, in order to completely fill the space portion 9, more molten resin W must be filled in the cavity 3. Then, the flow front of the molten resin W is located at the position a in FIG. 7 (a). As shown in Fig. 7 (b), gate 4
It has advanced to a farther position b. Therefore, in the gas injection method, the lighter the amount of molten resin filled before gas injection is, the more gas is injected to form a lightweight molded product. The molded product injected with was a heavy molded product, and there was a problem against the purpose of weight reduction.

The present invention has been made to solve the above-mentioned conventional problems. A first object is to fill a cavity with a small amount of molten resin and to provide a needle pin for gas injection around a base portion. It is to provide an injection molding die capable of accelerating the filling of the molten resin, and a second object thereof is to provide a molding method of a molded product having a good hollow ratio.

[0007]

In order to solve the above technical problems, the present invention is capable of ejecting gas to a gate side in a cavity formed in a mold matching surface of a fixed side mold plate and a movable side mold plate. In an injection molding die for injection-molding a hollow molded article by projecting a needle pin having a hole, it is configured to form ribs having ventilation means in a surrounding shape at a predetermined interval on the base side of the needle pin, Further, an injection molding die for injection molding a hollow molded product by projecting a needle pin having an ejection hole capable of ejecting gas to a gate side inside a cavity formed on a mold matching surface of a fixed side mold plate and a movable side mold plate. In, while forming a rib having a ventilation means in a surrounding shape at a predetermined interval on the base side of the needle pin, through the ventilation means, melting into the cavity before the gas injection by the needle pin Filling amount of fat with less is that complete configured to be able to fill the gap between the needle pin base and the ribs.

[0008]

According to the present invention, with the above configuration, the filling of the needle pin into the base portion is promoted, and the filling of the gap is completed in a state where the amount of the molten resin before gas injection is small.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a cross section of an injection molding die 11. This molding die 11 includes a fixed side mold plate 12 and a movable side mold. Board 1
7, the fixed-side template 12 is a fixed-side mounting plate 13
And a sprue bush 14 having a runner hole 15 is attached to a substantially central portion thereof. In addition, a plurality of molding recesses 16 that form the cavity 21 are provided on the lower surface of the stationary mold plate 12. Further, the movable-side template 17 is attached to the movable-side mounting plate 18, and the fixed-side template 1 via the guide pin 19 and the moving means.
2 and the movable side mold plate 17 is provided with a core 20 forming a cavity 21 corresponding to the molding recess 16 formed in the fixed side mold plate 12 in a protruding manner. . As described above, the cavity 21 is formed by aligning the movable side mold plate 17 to which the core 20 is attached with the fixed side mold plate 12, and the cavity 21 is formed by the gate 22.
Through the runner hole 15 of the sprue bush 14.

The core 2 attached to the movable side template 17
0 is provided with a substantially L-shaped gas hole 23 that rises horizontally and vertically from the side thereof, and the vertically rising hole 23a is opened at a position close to the gate 22. A needle pin 24 having a plurality of injection holes 25 at the upper end is attached to the hole 23a so as to project into the cavity 21 by a predetermined length, and the gas hole 23 is provided so as to penetrate to the side of the movable side mold plate 17 so as to penetrate the gas. Gas supply hole 26 connected to the supply source
It is formed in communication with. Further, a rib 27 is formed on the mounting base portion of the needle pin 24 of the core 20 as shown in FIGS. The rib 27 is formed in a ring shape having a predetermined interval t with respect to the base of the needle pin 24 and opening upward in a surrounding shape, and a slit 28 (also referred to as ventilation means) is formed in one direction of the rib 27. The slit 28 is formed with a cutout, and the molten resin W is formed in the slit 28 by the needle pin 24.
The slit 28 is formed so that it can be easily filled into the space t in the direction toward the gate 22, that is, toward the gate 22. The width h is preferably about 1 to 5 mm.

Since the slit 28 is formed in the mounting base of the needle pin 24 projecting into the cavity 21 toward the gate 22 as described above, when the molten resin W is injected from the sprue bush 14, the runner is runner. Hole 1
5, and flows into the cavity 21 through the gate 22. Since the molten resin W flows into the cavity 21 and flows into the rib 27 within the space t from the slit 28 and the upper opening, the space 9 is formed between the needle pin 24 and the rib 27 as in the conventional case. Since the filling is performed promptly without occurrence of, the filling of the gap t is completed in a state where the filling amount of the molten resin before gas injection is small. Therefore, it becomes possible to mold a molded product having a larger hollow distribution, and by injecting a gas when a predetermined molten resin W is injected, a target molded product having a hollow distribution can be molded. Table 1 compares the hollow ratio of the hollow molded product molded by the conventional rib 8 and the slit 28 of the present embodiment, and is calculated assuming that the weight of the non-hollow molded product is 81 g.

[Table 1]

In the above embodiment, the slit 28 is formed as a ventilation means in order to remove the gas (air) from the space 9 in the related art, but as shown in FIG. 3, the core 20 has a small diameter hole 31 and a large diameter hole. The small diameter hole 31 is formed concentrically, and the small diameter hole 31 is made of, for example, a porous metal member having air permeability, a ceramic material, etc., a rib 34 is formed on the upper end side, and the needle pin 24 is fitted in the center. The rib member 33 penetrating the insertion hole 35 to be attached is fitted, the rib 34 is projected into the cavity 21, the needle pin 24 is inserted into the insertion hole 35, and the tip thereof is in the cavity 21 of a predetermined length. The rib member 33 and the needle pin 2 are projected while being projected.
1 is fixed by a lock pin 36 having a gas hole 37. With this arrangement, the molten resin W flows in from the upper opening side of the rib 34 as in the conventional case. Due to this inflow, the gas (air) in the rib 34 is permeated by the porosity of the rib member 33 and the cavity 21 is expelled to the outside, so that the filling of the needle pin 24 into the base portion is promoted, and thus the filling of the gap t is completed in a state where the amount of the molten resin before gas injection is small. Therefore, as in the above-described embodiment, it is possible to mold a molded product having a larger hollow distribution, and by injecting a gas when a predetermined molten resin W is injected, a target molded product having a hollow distribution is molded. be able to.

[0013]

As described above, since the rib is provided with the ventilation means, the filling of the needle pin into the base portion is promoted, and the gap between the needle pin and the molten resin before gas injection is small. Since the filling is completed, it becomes possible to mold a molded product having a larger hollow distribution, and the predetermined molten resin W
By injecting gas at the time of injecting, it is possible to mold a target molded product having a hollow distribution.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an injection molding die.

FIG. 2A is a perspective view showing a relationship between a rib and a needle pin. (b) is a plan view showing the relationship between the rib and the needle pin.

FIG. 3 is a cross-sectional view of a movable-side template showing another ventilation means of ribs.

4 (a) and (b) are explanatory views of a conventional hollow molding process.

FIG. 5 is an explanatory diagram of a problem of FIG.

FIG. 6A is a partial cross-sectional view in which a rib is formed on a base portion of a conventional cordol pin. 6 (b) is a perspective view of FIG. 6 (a).

7 (a) and (b) are explanatory views of a molding process in the case of FIG.

[Explanation of symbols]

 11 Injection Mold 12 Fixed Side Mold Plate 17 Movable Side Mold Plate 21 Cavity 22 Gate 24 Needle Pin 27 Rib 28 Slit 33 Rib Member 34 Rib

Claims (4)

[Claims] 1. An injection molding method for injection molding a hollow molded product by projecting a needle pin having a jet hole capable of jetting gas toward a gate side in a cavity formed on a mating surface of a fixed side mold plate and a movable side mold plate. In the molding die, an injection molding die for a hollow molded article, which is configured to form ribs having ventilation means in a surrounding shape at a predetermined interval on the base side of the needle pin. 2. The injection molding die for a hollow molded article according to claim 1, wherein the ventilation means of the rib is a slit directed toward the gate side. 3. The injection molding die for a hollow molded article according to claim 1, wherein the rib is formed of a porous member. 4. An injection for injection-molding a hollow molded product by projecting a needle pin having a jet hole capable of jetting gas toward a gate side in a cavity formed on a mold matching surface of a fixed side mold plate and a movable side mold plate. In the molding die, while forming a rib having a ventilation means in a surrounding shape at a predetermined interval on the base side of the needle pin, through the ventilation means of the molten resin into the cavity before gas injection by the needle pin A method for molding a hollow molded article, which is configured to be able to complete filling of a gap between a needle pin base and a rib with a small filling amount.