JPH1015990A - Molding of injection-molded product using sandwich molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of a flow mark on an injection molded product, by allowing the screw of an injection unit to advance to a core material passage, under such a state that a core material resin passage is closed by a needle valve during the injection of a skin material resin to prellminarily apply pressure. SOLUTION: When pressure oil is introduced into a hydraulic cylinder 15 in such a state that a mold cavity is filled with a skin material resin in an uncompleted filled state to allow a shaft 19 to retreat to open a first opening part 22, the core material molten resin on the side of a first injection unit 1A held to the pressure state of the same degree as the skin material resin during preliminary injection flows through a sprue part 10 from a resin passage 38, the first opening part 22 and a second opening part 24 by the advance of a screw 5A to be injected into a mold cavity 2 under high pressure to fill the cavity 2. At this time, the pressure difference between the skin material resin and the core material resin is eliminated and the skin material resin does not flow back from an outside passage 16 to an inside passage 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding machine in which a core material resin is filled into a skin material resin using a sandwich molding machine, and the core material resin is pre-pressed during the injection filling of the skin material resin. The present invention relates to a method for molding a molded article.

[0002]

2. Description of the Related Art Conventionally, a sandwich molding machine having an injection unit in which an inner nozzle is arranged coaxially at the center of an outer nozzle is known. An inner nozzle is provided at the center of the outer nozzle,
It is well known that a method of molding a molded product having a multilayered cross-sectional structure by simultaneously or continuously injecting a resin serving as a core of the molded product from the inner nozzle and a skin resin serving as a surface layer of the molded product from the outer nozzle simultaneously or continuously. Has become.

[0003]

However, injection molding using a conventional sandwich molding machine has the following problems. That is, during the sandwich molding, the skin material resin serving as the skin is injected, the resin flow path of the core material resin is opened during the injection of the skin material resin, and the core material resin is subsequently injected after the skin material resin. When the core material resin flow path is opened to inject the core material resin during injection filling of the skin material resin into the cavity, the unpressurized core material resin staying in the core material resin flow path and the high pressure A pressure difference is generated between the skin material resin and the high-pressure skin material resin temporarily flows into the core material resin flow path through the open hole, and the flow of the resin from the injection unit to the mold cavity is temporarily stopped. Decelerates or stops. When such a phenomenon occurs, there is a problem that a flow mark is generated in the molded product, and the injection molded product becomes defective in molding.

[0004] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method of molding an injection molded article using a sandwich molding machine in which a flow mark is not generated in the injection molded article. Is to do.

[0005]

In order to achieve the above object, according to the present invention, there is provided a second method of injecting a skin material resin using a sandwich molding machine having an injection unit for co-injecting two or more kinds of resins. The cavity material formed between the movable mold and the fixed mold is injected and filled with the skin material resin from the injection unit via the skin material resin flow path, the spool, and the runner part, and the core material resin flow path is formed from the first injection unit. A method for molding an injection-molded product, wherein the core material resin is completely filled into the skin material resin in the cavity portion via the spool and the runner portion to obtain an injection-molded product. The screw of the first injection unit is advanced to the core material flow path in advance in a state where the core material flow path is closed by a needle valve for opening and closing the core material resin flow path.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a specific embodiment of a method for molding an injection-molded article using a sandwich molding machine according to the present invention will be described in detail with reference to FIGS.

FIG. 1 is a sectional view of an injection unit used in the present invention, FIG. 2 is a front view showing a part of the injection molding machine cut away, and FIG. 3 is a state in which a cavity is injected and filled by using the injection unit. FIG.

In FIG. 2, reference numeral 30 denotes the injection unit 1
Is a fixed plate provided in front of. The fixed board 30 has an opening 32 of a predetermined size. The injection unit 1
The injection units 1A and 1B are constituted by two injection units 1A and 1B, and the injection units 1A and 1B are mounted on the moving tables 34A and 34B, respectively, and the tips of the injection nozzles 6A and 6B are formed by appropriate means such as hydraulic cylinders 36A and 36B. The portion is slidable back and forth between a position where it is in contact with the contact portion 10a of the spool portion 10 of the fixed mold 13 and a position where it is separated.

The injection unit 1 includes a first injection unit 1A for melting a core material resin and injecting and filling a mold cavity 2;
And a second injection unit 1B that injects and fills the second injection unit. The first injection unit 1A includes a hopper 3A for supplying core resin, a barrel 4A, a screw 5A, and an injection nozzle 6A.

The second injection unit 1B also includes a hopper 3B for supplying a skin material resin, a barrel 4B, a screw 5B, and an injection nozzle 6B, similarly to the first injection unit 1A. An injection nozzle 6B is disposed coaxially around the injection nozzle 6A at the distal end of the two injection nozzles where the injection nozzles 6A and 6B are united. An annular nozzle portion 8 having a ring-shaped structure with a space portion 7 between the foremost portions.

Reference numeral 38 denotes a resin passage connected from the first injection unit 1A to the inner passage 14 of the annular nozzle portion 8, and reference numeral 40 denotes a resin passage connected from the second injection unit 1B to the outer passage 16 of the annular nozzle portion 8. It is a resin passage formed. The annular nozzle portion 8 includes an inner ejection nozzle 6A located inside and an outer ejection nozzle 6B located concentrically and outside the inner ejection nozzle 6A.

The mold 11 used in this embodiment includes a movable mold 12 and a fixed mold 13. The fixed mold 13 is mounted on the fixed platen 30, and the movable mold 1
Reference numeral 2 denotes a movable platen (not shown),
Is movable forward and backward with respect to the fixed mold 13. As shown in FIG. 3, when the movable mold 12 comes into contact with the fixed mold 13, the mold cavity 2 is formed between the movable mold 12 and the fixed mold 13.

The tip of the injection nozzle 6B is a fixed mold 1
3 and is in contact with a spool portion 10 extending straight from the injection nozzle 6B to a substantially central portion of the mold cavity 2. Further, a shaft 19 which is reciprocated by reciprocating drive means including a hydraulic cylinder 15 attached to the rear end face or the like and a piston 17 provided therein is inserted into the axis of the injection nozzle 6A. That is, the inner passage 20 is formed between the inner peripheral surface of the injection nozzle 6A and the outer peripheral surface of the shaft 19. And the injection nozzle 6A
A first opening 22 is formed at the end of the first opening so that the molten resin injected from the first injection unit 1A is injected into the space 7. The first opening 22 is opened and closed by the forward and backward movement of the shaft 19.
Reference numerals 42 and 44 denote rotating motors of the screws 5A and 5B,
Reference numerals 6 and 48 denote forward and backward cylinders of the screws 5A and 5B, respectively.

The operation will be described using the sandwich molding machine configured as described above. First, pressurized oil is introduced into the hydraulic cylinder 15 to advance the shaft 19 so that the first opening 22
Is closed. Under these conditions, the core material resin is supplied to the hopper 3A of the first injection unit 1A. Next, when the screw 5A is retracted while rotating, the hopper 3A
The core resin supplied into the barrel 4A from the outside is heated by external heat from a heater (not shown) wound around the outer periphery of the barrel 4A, and the resin and the inner wall surface of the barrel 4A when the core resin is supplied by the screw 5A. The core material resin is melted by the shearing heat generated therebetween, and the space of the resin passage 38 and the inner passage 14 is filled with the molten resin.

As with the first injection unit 1A, the hopper 3B of the second injection unit 1B is supplied with a skin material resin pulverized to an appropriate diameter. Next, when the screw 5B is retracted while rotating, the skin material resin supplied into the barrel 4B from the hopper 3B is heated by a heater (not shown) wound around the outer periphery of the barrel 4B.
The new resin is melted and stored at the tip of the screw 5B by the external heat from the screw and the shear heat generated between the resin and the inner wall surface of the barrel 4B when the skin material resin is fed by the screw 5B.

On the other hand, the movable mold 12 and the fixed mold 13 constituting the mold 11 are closed, and the screw 5B is advanced from the second injection unit 1B first and the skin stored in front of the screw 5B. The molten material flows through the spool 10 from the resin passage 40 and the second opening 24 and is injected and filled into the mold cavity 2. The core material resin is preliminarily pressurized at the same time as the start of the skin material resin injection, and the degree of the pressurization is desirably the same as the pressure at the time of the skin material resin injection. To do this, the injection pressure of the skin material resin is directly
The detection is performed from the inside passage 14 or the hydraulic circuit, and the first injection unit 1A performs feedback control. When the mold cavity 2 is injected and filled, the skin material resin is not completely filled in the mold cavity 2 but is incompletely filled.

In such an incompletely filled state, when pressure oil is introduced into the hydraulic cylinder 15 to retreat the shaft 19 and open the first opening 22, the pressure under the same pressure as the skin material resin being injected beforehand is obtained. The core material molten resin on the side of the first injection unit 1A, which has been held in the state, flows through the resin passage 38, the first opening 22, and the second opening 24 through the spool 10 by moving the screw 5A forward. The mold cavity 2 is injection-filled at a high pressure. In this case, even if the first opening 22 is continuously opened after the filling of the skin material resin, since the core material molten resin on the first injection unit 1A side is in a pressurized state in advance, the skin material resin pressure and the core The material resin pressure difference disappears, and the skin material resin does not flow backward from the outside passage 19 side to the inside passage 16 side through the first opening 22.
For this reason, the flow mark of the molded product caused by the temporary rapid deceleration or stoppage of the skin material to be originally injected into the mold cavity 2 is prevented. For this reason, effects such as an increase in the yield of the molded product are obtained.

After injecting and filling a predetermined amount of the core resin, the shaft 19 is advanced again to close the first opening 22.
Subsequently, the screw 5B of the second injection unit 1B is advanced to inject and fill the skin material resin into the mold cavity 2. After the injection and filling of the skin material resin, the movable mold 12 and the fixed mold 13 are cooled for a predetermined time, and then the movable mold 12 and the fixed mold 13 are separated from each other and opened, and the movable mold 12 and the fixed mold 13 are opened. An injection-molded product is taken out from the mold cavity 2 between them.

[0019]

As is apparent from the above description, according to the present invention, the injection molded article has no flow mark at all, the product yield is greatly improved, and high quality can be maintained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an injection unit used in the present invention.

FIG. 2 is a partially cutaway front view of the injection molding machine.

FIG. 3 is an explanatory view showing a state in which a cavity is injected and filled by using an injection unit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 injection unit 1A first injection unit 1B second injection unit 2 mold cavity 3A, 3B hopper 4A, 4B barrel 5A, 5B screw 6A, 6B injection nozzle 7 space 8 annular nozzle 10 spool 11 mold 12 movable mold Mold 13 Fixed mold 14 Inner passage 15 Hydraulic cylinder 16 Outer passage 17 Piston 19 Shaft 20 Inner passage 22 First opening 24 Second opening 30 Fixing plate 32 Opening 34A, 34B Moving table 36A, 36B Hydraulic pressure Cylinders 38, 40 Resin passages 42, 44 Rotating motors 46, 48 for screws 5A, 5B Cylinder for forward / backward movement of screws 5A, 5B

Claims (1)

[Claims] 1. Using a sandwich molding machine having an injection unit for co-injecting two or more types of resins, a second injection unit for injecting a skin material resin through a skin material resin flow path, a spool, and a runner section. The cavity portion formed between the movable mold and the fixed mold is injection-filled with the skin material resin, and the first injection unit passes through the core material resin flow path, the spool, and the runner portion into the skin material resin in the cavity portion. A method of molding an injection-molded article, wherein an injection-molded article is obtained by completely filling the core material resin, wherein a needle valve for opening and closing the core material resin flow path during injection of the skin material resin. A method for molding an injection-molded article using a sandwich molding machine, wherein a screw of a first injection unit is advanced in advance in a core material flow path in a state where a path is closed, and is pressurized in advance.