JPH08118392A - Injection molding method - Google Patents

Abstract

PURPOSE: To provide an injection molding method through which a molded product superior in a quality is obtained by a method wherein at the time of molding of a hollow and deep-bottomed molded product, the molded product in released from a mold smoothly by floating the molded product from a movable retainer plate by discharging pressurized gas, which is injected into the molded product, to a boundary between the molded product and a cavity surface of the movable retainer plate by a movement of a gas nozzle to be used for hollow molding. CONSTITUTION: In an injection molding method molding a molded product having a hollow part 3b by injecting molten resin and pressurizing gas into a cavity 3 formed of a movable retainer plate 2 and stationary retainer plate, the molten resin is injected into a cavity and pressurized gas in injected in the cavity 3 in succession through a gas nozzle 5 provided in the cavity by projecting from the movable retainer plate 2 and the hollow part 3b is formed. Then the gas nozzle 5 is moved backward, the pressurized gas injected into the molded product through a gas injection hole is discharged to a boundary between the molded product and a cavity surface of the movable retainer plate 2 and the molded product is floated from the movable retainer plate 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method, and more particularly to an injection molding method for releasing a molded article having a hollow portion having a deep bottom from a mold.

[0002]

2. Description of the Related Art Conventionally, when releasing an injection-molded product from a mold after molding, a so-called projecting pin provided on a movable mold plate or the like is operated to press a part of the molded product after cooling. The method of sticking out is adopted. In addition, an air vent that penetrates the movable side mold plate and communicates with the cavity is provided, and pressurized air is blown from the tip of this air vent to the boundary between the molded product and the cavity surface of the movable side mold plate to move the molded product to the movable side mold. A method is also adopted in which the surface is levitated from the plate and released.

On the other hand, regarding a gas injection molding method which has been widely spread in recent years, a molding method in which a pressurized gas is injected from a tip of a gas nozzle into a molten resin filled in a cavity of a mold to form a hollow portion in a molded product. Is. For example, Tokuhei 3-
In Japanese Patent No. 47171, the weight of a molded product is reduced,
In order to modify the surface, a gate part of the molten resin in the mold or a gas channel communicating with the cavity is provided in the mold, and injection of filling the molten resin in the cavity with a pressurized gas from this gas channel A molding method and apparatus is described.

[0004]

However, in the former method for releasing a molded product by the above-mentioned protruding pin, especially when the molded product has a deep bottom shape, the boundary surface between the molded product and the movable side mold plate is Due to the vacuum action due to the close contact, if it is forcedly ejected and released from the mold, there arises a problem that the molded product is deformed or damaged.

Further, although the method of providing the above-mentioned air vent on the movable side mold plate and releasing the molded product from the mold is effective, the structure of the mold becomes complicated and a separate device for supplying pressurized air is required. In addition to increasing the cost of molds and equipment, there is a problem that air vent marks are left on the surface (design surface) of the molded product in some cases, impairing the appearance and affecting product quality.

The present invention has been made in view of the above problems, and an object thereof is to solve these problems and to provide a deep-bottomed molded product having a hollow portion. In an injection molding method for molding, a gas nozzle provided so as to project into a cavity from a template of a device for injecting a pressurized gas provided to form a hollow portion is used, and the gas nozzle is retracted to form a molded product. The pressurized gas injected into the mold is discharged to the boundary between the cavity surface of the mold plate and the molded product, and the molded product is floated above the mold plate and released from the mold, so that there is no adverse effect of protrusion by the protrusion pin, and
There is no need to install a new air vent and its equipment,
It is intended to provide an injection molding method capable of smoothly releasing a mold and obtaining a molded product of excellent quality.

[0007]

In the injection molding method of the present invention, a molded product having a hollow portion by injecting a molten resin and injecting a pressurized gas into a cavity formed by a movable mold plate and a fixed mold plate. In the injection molding method of molding, a molten resin is injected into the cavity, and then a pressurized gas is injected into the molten resin in the cavity from a gas nozzle provided by protruding from the template into the cavity to form a hollow portion. ,
Then, by retracting the gas nozzle, the pressurized gas injected into the molded product is discharged from the gas injection hole formed in the molded product by injecting the pressurized gas into the boundary between the molded product and the cavity surface of the template. To form a thin gas layer,
It is characterized in that the molded product is released from the template by releasing the mold.

[0008]

In the injection molding method of the present invention, the molten resin is first injected into the cavity, and then the pressurized gas is injected into the molten resin in the cavity from the gas nozzle provided in the mold plate to form the hollow portion. After the formation, the gas nozzle is retracted, the pressurized gas is discharged at the boundary between the molded product and the cavity surface of the mold plate to form a thin gas layer, and the molded product floats above the mold plate and is smoothly separated. Since the molded product is molded, it is possible to obtain a molded product having excellent quality without affecting the shape and appearance quality of the molded product.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an injection molding die showing an example of the injection molding method of the present invention, and FIG. 2 is an enlarged detailed view of a portion A of FIG. In FIG. 1, 1 is a fixed-side template, 2
Is a movable side template. Fixed-side template 1 and movable-side template 2
A cavity 3 for molding a deep-bottomed molded product having a hollow portion is provided between and, and a molten resin is injected into the cavity 3 from a sprue 4 provided on the stationary mold plate 1. .

A gas nozzle 5 connected to a gas injection device (not shown) is provided in the movable side mold plate 2 so that a nozzle tip 5a projects into the cavity 3 to generate a pressurized gas. It is supposed to be injected.

The injection molding method of the present invention will be described below. As shown in FIG. 1, in the mold closed, the sprue 4 of the stationary mold plate 1 injects a sufficient amount of molten resin into the cavity 3 to fill the cavity 3 and fills the cavity 3. . Next, a pressurized gas is injected from a nozzle tip 5a that has been preliminarily projected to a predetermined position in the cavity 3, and a hollow portion 3b is formed in the molded portion 3a molded into the shape of the cavity 3 by the resin pressure and the gas pressure. Hold pressure.

After the shape of the molding portion 3a and the hollow portion 3b are formed as described above, the gas nozzle 5 in the movable side mold plate 2 is retracted immediately before the start of mold release after the cooling step, and the nozzle tip 5a is retracted to near the cavity 3 surface.

Nozzle tip 5a of the retracted gas nozzle 5
Is the cavity surface 2 of the movable mold plate 2 as shown in FIG.
It is moved to a position retracted to a. In this state, when the pressurized gas is discharged from the gas injection hole 3c, the pressurized gas is applied to the cavity surface 2a of the movable side mold plate 2 and the molding portion 3a.
A thin air layer 6 is formed by penetrating into the boundary between and. Therefore, the molded product floats above the movable-side mold plate 2 when the mold opening is started, and can be taken out when the mold opening is completed.

The retracted position of the nozzle tip 5a of the gas nozzle 5 is preferably within the range of the distance D shown in the drawing from the cavity surface 2a of the movable mold plate 2. If the position of the nozzle tip 5a is further retracted from this distance D and is further retracted from the tip 2c of the insertion hole 2b of the movable side mold plate 2, gas leakage to the rear occurs, which is not preferable. On the other hand, if it protrudes from the cavity surface 2a, it becomes difficult for the pressurized gas to enter the boundary between the cavity surface 2a and the molding portion 3a, making it difficult to form the air layer 6.

For comparison with the present embodiment, the same injection molding die was used and injection molding was carried out without performing a releasing operation by discharging gas from a gas nozzle. The molded product was in close contact with the movable side mold plate. In such a state, it was difficult to release the mold, and it was pulled by force to cause deformation, and the effect of the injection molding method of the present invention was confirmed.

The injection molding method of the present invention is particularly suitable for a deep-bottomed molded product, but other shapes having a small draft or a shape having an undercut portion can be used. It is also suitable for injection molding of molded products that are difficult to release from the stationary mold plate.

Further, in the injection molding method of the present invention, the gas nozzle provided in the injection mold is provided on the movable mold plate side in the embodiment, but the invention is not limited to this, and it is fixed. It may be provided on the side template.

[0018]

In the injection molding method of the present invention, the molten resin is first injected into the cavity, and then the pressurized gas is injected into the molten resin inside the cavity from the gas nozzle provided in the template. After the part is formed, the gas nozzle is retracted, the pressurized gas is discharged at the boundary between the molded product and the cavity surface of the mold plate to form a thin gas layer, and the molded product floats above the mold plate and is smooth. Since it is released from the mold, it is possible to obtain a molded product of excellent quality without affecting the shape and appearance quality of the molded product. Therefore, it is preferably used as an injection molding method for a molded product having a hollow portion.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an injection molding die showing an example of an injection molding method of the present invention.

FIG. 2 is an enlarged detailed view of a portion A of FIG.

[Explanation of symbols]

 1 Fixed-side template 2 Movable-side template 2a Cavity surface 2b Insertion hole 2c Tip 3 Cavity 3a Molded part 3b Hollow part 3c Gas injection hole 6 Gas layer D Distance

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B29C 49/78 7619-4F B29L 22:00

Claims (1)

[Claims] 1. An injection molding method for molding a molded product having a hollow portion by injecting a molten resin and injecting a pressurized gas into a cavity formed by a movable side mold plate and a fixed side mold plate. Then, a pressurized gas is injected into the molten resin in the cavity from a gas nozzle provided by protruding from the template to the cavity to form a hollow portion, and then the gas nozzle is retracted to form the molding. The thin gas layer is formed by discharging the pressurized gas injected into the molded product from the gas injection hole formed in the molded product by injecting the pressurized gas at the boundary between the product and the cavity surface of the mold plate. An injection molding method, characterized in that the product is released from the template by releasing it.