JP2820601B2 - Injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injection molding a resin molded product.

[0002]

2. Description of the Related Art A molten resin is press-fitted into a cavity (cavity, gap) formed by fitting a pair of molds of a predetermined shape through a tapered nozzle, and the resin inside the cavity is hardened. An injection molding method in which a pair of molds is separated and a molded product is subsequently removed has been generally used.

[0003]

However, in the conventional injection molding method, the resin in the gate adheres to a portion corresponding to the gate at the tip of the resin press-fitting nozzle of the molded product, and irregular unnecessary protrusions remain. There was a problem that would. For example, when the resin molded product is the core material of a crash pad of an instrument panel of an automobile, which is formed by integrally laminating a pad made of a skin material and a semi-rigid urethane foam and a core material, Since the projections hinder lamination, it is necessary to cut off the unnecessary projections from the resin molded product, and there has been a problem that the number of working steps is required.

[0004] The present invention has been made in view of such a point, and an object thereof is to generate unnecessary projections formed on a resin molded product corresponding to a gate at the tip of a nozzle for press-fitting a resin. It is an object of the present invention to provide an injection molding method which can prevent the unnecessary projection and reduce the number of work steps for cutting off the unnecessary projection.

[0005]

In order to achieve this object, injection molding is carried out in which a molten resin is press-fitted through a gate into a cavity formed when a pair of separable molds are fitted. As a method, the following method is provided.

That is, the portion of the cavity corresponding to the gate is a thick portion which is thicker than the general portion which is the other portion of the cavity, and after the molten resin is pressed through the gate, Before the resin in the general portion of the cavity is cured and before the resin in the thick portion of the cavity is cured, the pair of molds is separated and the molded product is released.

[0007]

According to the method of the present invention, since a part of the cavity is formed as a thick part, a difference occurs in the curing time of the molten resin as compared with other general parts, and the resin in the general part of the cavity hardens. In addition, it is possible to obtain a semi-cured state of the resin in the thick part of the cavity (generally, the resin is cured with time from the outside in contact with the mold, but the inside is not yet cured). .

In this state, when the mold is opened, a part of the resin on the side of the molded article in a semi-cured state adheres to the gate side of the mold and is torn, and the part of the molded article corresponding to the gate becomes concave. In addition, it is possible to prevent the generation of irregular projections of the molded product caused by the resin inside the gate.
This eliminates the need for the conventional man-hours for cutting off unnecessary projections.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 are views showing an embodiment of the present invention. FIG. 1 is a cross-sectional view showing an entire injection mold mounted on an injection molding machine. FIG. 2 is a cross-sectional view showing an enlarged part of FIG. FIG. 3 is an enlarged cross-sectional view of the portion a in FIG.

In FIG. 1, reference numeral 1 denotes a fixed type constituting one of the injection types, and reference numeral 2 denotes a movable type constituting the other of the injection types. The fixed die 1 is attached to the fixed mounting plate 4 with a bolt (not shown) via a spacer block 3, and the movable die 2 is mounted on the movable mounting plate 6 with a bolt (not shown) via a spacer block 5.
It is fixed to. The fixed mold 1 and the movable mold 2 are formed such that a cavity 7 having a predetermined shape (a shape corresponding to a product shape) is formed when the fixed mold 1 and the movable mold 2 are fitted.

On the other hand, a plurality of ejector pins 9 each having one end fixed to an ejector plate 8 are provided on the movable mold 2 side for removing the molded product. Further, one end of an ejector rod 10 is fixed to the ejector plate 8, and in a state where the fixed mold 1 and the movable mold 2 are fitted, the other end of the ejector rod 10 abuts on the fixed mold 1 and the ejector rod 10 is erroneously operated. The pin 9 is prevented from entering the cavity 7.

A locating ring 11 for guiding the fitting with a nozzle (a molten resin delivery port) of an injection molding machine (not shown) is attached to the fixed mold side mounting plate 4. A nozzle bush 14 that connects one end of a hot runner 13 pierced in a hot runner block 12 and a nozzle of the injection molding machine is attached to a central portion of the locate ring 11 of the fixed type mounting plate 4.

The other end of the hot runner 13 pierced in the hot runner block 12 is branched and communicates with a plurality of nozzles 15 provided on the fixed mold 1.

FIG. 2 shows the structure of the nozzle 15 and its vicinity.
The nozzle 15 is formed in a substantially cylindrical shape, and is fitted into a hole 16 formed in the fixed mold 1. A torpedo 18 having a heater 17 for keeping the molten resin in a molten state is provided inside the nozzle 15, and a passage 19 for the molten resin is formed by the outer wall of the torpedo 18 and the inner wall of the cylindrical portion of the nozzle 15. Heater 1
7 is supplied with electric power by a heater wiring 20.

In the cavity 7 formed by the fixed mold 1 and the movable mold 2, the portion corresponding to the gate 21 at the tip of the nozzle 15 and the vicinity thereof have a wide gap and become a thick portion 22. I have. The thick portion 22 is formed to be thicker on the movable mold 2 side than the thickness of the general portion 23 corresponding to the thickness of the product to be molded.

When the movable mold side mounting plate 6 is moved to fit the movable mold 2 to the fixed mold 1 and the injection of the molten resin from the injection molding machine is started, the molten resin is supplied to the nozzle bush 14 and the hot runner block. The nozzle 15 is fed through the hot runner 13 and the molten resin passage 19 in the nozzle 15, and is pressed into the cavity 7 from the tapered gate 21 at the tip of the nozzle 15. After the cavity 7 is filled with the molten resin, the feeding of the molten resin is stopped.

The molten resin in the cavity 7 is
And it is cooled by the movable mold 2 and starts to harden. Then, a predetermined time until the resin of the general portion 23 of the cavity 7 is cured to a state in which the resin can be removed (for example, in the case of a pad core of an automobile instrument panel formed of ABS resin, 30 to This state is maintained until about 40 seconds have elapsed.

In this state, as shown in FIG. 3A, the resin of the general portion 23 of the cavity 7 is hardened, but the resin of the thick portion 22 has a large heat capacity of the molten resin. Although a part of the side is hardened, the interior 24 is not yet hardened.

In this state, as shown in FIG. 3B, when the movable mold side mounting plate 6 is moved to separate the movable mold 2 from the fixed plate 1 and the mold is opened, the molded article 25 is moved. 2 and is released from the fixed mold 1. At this time, a part 26 of the resin on the surface of the thick part 22 which is hardened integrally with the resin in the gate 21 becomes the inside 24 of the thick part 22.
Is not yet cured, so the molded article 2
5 and adheres to the vicinity of the gate 21 of the fixed mold 1 and comes off. As a result, a concave portion 27 is formed in a portion corresponding to the gate 21 of the molded product 25, and an unnecessary protrusion is not formed.

Next, the molded product 2 adhered to the movable mold 2
5 is released from the movable mold 2 by the protrusion of the ejector pin 9 accompanying the movement of the ejector plate 8. The portion 26 of the resin adhered to the vicinity of the gate 21 of the fixed mold 1 is melted at the time of the next molding because the portion corresponding to the gate 21 of the cavity 7 is the thick portion 22. The resin can be released into the thick portion 22 by the injection of the resin, and does not hinder the next molding.

FIG. 4 is a view showing a pad core formed by the above-described injection molding method. The pad core 28 is used as a core material of a crash pad of an instrument panel of an automobile, and after injection molding into a predetermined shape as shown in FIG.
A pad made of a skin material and a semi-rigid urethane foam is accommodated in a foaming mold having a predetermined shape together with a pad made of a semi-rigid urethane foam on the surface side, and the semi-rigid urethane foam is foamed, so that the crash pads are integrally laminated. It is formed.

When the pad core 28 is injection-molded, the resin press-fitting gate has a pair of louver portions 29, a meter hood portion 30, and an airbag, some of which are removed (cut off) as openings after lamination of the pad core. It is provided on the mounting part 31. The reason why these are removed after lamination is to prevent the urethane from leaking to the back surface of the pad core and forming burrs by closing the opening with the pad core when urethane is foamed.

Therefore, these portions become urethane sealing portions in which the skin material and the pad core are in close contact with each other. If these portions have irregular unnecessary projections due to gates, they interfere with the skin material and the foaming mold, Poor molding of the crash pad occurs due to displacement of the pad core 28.

However, by forming the pad core 28 by the injection molding method of the present invention, the recesses 27 are formed in the respective portions of the pad core 28 corresponding to the respective gates for resin press-fitting, as described above. Since no projection is formed, such a problem is prevented from occurring.

[0025]

By using the injection molding method of the present invention to produce a resin molded product, unnecessary projections formed on the resin molded product corresponding to the gate at the tip of the resin press-fitting nozzle can be prevented. This prevents the unnecessary protrusions from being cut off, thereby reducing the number of man-hours for cutting the unnecessary projections.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of the present invention, and is a cross-sectional view showing an entire injection mold mounted on an injection molding machine.

FIG. 2 is an enlarged sectional view of a part of FIG.

FIG. 3 is an enlarged cross-sectional view of a part “a” in FIG. 2, and FIG.
Indicates a state in which the mold is closed, and (B) indicates a state in which the mold is opened.

FIG. 4 is a view showing a pad core constituting an instrument panel of an automatic operator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixed type 2 Movable type 7 Cavity 15 Nozzle 21 Gate 22 Thick part 23 General part 25 Molded article 27 Depression

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-19126 (JP, A) JP-A-58-222829 (JP, A) JP-A-2-263616 (JP, A) JP-A 62-1986 68716 (JP, A) Fully open 1979-166626 (JP, U) Fully open, 57-144526 (JP, U) Fully open, 51-161466 (JP, U) Fully open, 57-156317 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) B29C 45/00-45/44

Claims (1)

(57) [Claims] 1. An injection molding method wherein a molten resin is press-fitted into a cavity formed when a pair of separable molds are fitted through a gate, the injection molding method corresponding to the gate of the cavity. The portion to be formed is a thick portion which is thicker than the general portion which is the other portion of the cavity, and after the molten resin is pressed through the gate, the resin in the general portion of the cavity is cured, and An injection molding method, wherein the pair of dies is separated and the molded product is released before the resin in the thick portion of the cavity is cured.