JPH0371252B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an injection molding apparatus for a foam molded article, the interior of which is a foam and the outer surface is a non-foamed synthetic resin.

<Prior Art> As a conventional injection molding apparatus for foam molded products, there is an apparatus as shown in FIG. 8, for example. This injection molding apparatus includes a main cylinder 2 and a hopper 1 for supplying non-foaming thermoplastic resin A into the main cylinder 2.
, a main screw 3 that is rotated by a transmission (not shown) connected to a screw rotation motor and moves forward or backward along the axial direction, and a cylinder 2.
A mixing nozzle 6 having a static mixer 5 is interposed between the head portion 4 of the head 4 and a mold 7 for resin molding, and non-foamable resin A is injected into the mold 7 by a screw 3. . In addition, the injection capacity of the cylinder head 4 is 5 of the injection capacity of the cylinder 2.
~10% of the secondary cylinder 8 is connected, and the secondary cylinder 8
Then, the foamable resin D, which is a mixture of a thermoplastic synthetic resin and a foaming agent supplied by a hopper (not shown) or the like, is injected into the cylinder head 4 by a screw provided in the sub-cylinder 8. Further, at the rear part of the mixing nozzle 6, that is, at the connection part of the sub-cylinder 8 including the cylinder head 4, the cylinder 2 is
The control mechanism 10 is provided to inject or stop the foamable resin D from the sub-cylinder 8 at a predetermined time during the process of injecting the thermoplastic resin A.

In this known injection molding apparatus, first, non-foamable resin A constituting the outer surface of the molded product is injected into a mold 7, then foamable resin D is fed, and resin A and resin D are mixed in a static mixer 5. and inject the foamable mixed resin into a mold 7 to form a foam that constitutes the core. Subsequently, the supply of the foamable resin D is stopped, and only the non-foamable resin A is fed to fill the sprues and runners of the mixing nozzle 6 and the mold 7 with the non-foamable resin A. Prepare for the molding cycle of molded products.

<Problems to be solved by the invention> However, in such conventional injection molding equipment, depending on the shape of the molded product and the way the gate is formed, the capacity of the sprue and runner is small, and the mixing nozzle The foamable resin in the molded article 6 may not be replaced sufficiently, and therefore, a small amount of air bubbles may be partially exposed on the surface and silver stripes may appear on the surface of the molded product at the beginning of the next cycle. In consideration of this situation, a resin reservoir with a capacity of about 50 to 80 c.c. is provided in the middle of the sprue or runner of the mold, and the resin that is likely to cause silver streaks at the initial stage of the injection process is introduced into this resin reservoir. A method is used to prevent silver streaks from forming on the surface of the molded product. In this case, the resin introduced into the resin reservoir is released from the mold together with the molded product, collected, and reused, so the loss of the resin itself is minimal, but additional man-hours are required for collection and crushing. This has the disadvantage that workability is reduced.

The present invention was made in view of these points, and its purpose is to provide injection molding of foam molded products that can obtain foam molded products with beautiful surfaces without silver streaks without creating resin pools by improving the mixing unit. The purpose is to provide equipment.

<Means for Solving the Problems> According to the present invention, in an apparatus for injection molding a synthetic resin molded product having a core formed of a foam and an outer surface layer of a non-foaming synthetic resin, the non-foaming a first feeding and injection device for kneading a synthetic resin and feeding and injecting a first flow of a non-foaming synthetic resin; and a synthetic resin containing a foaming agent and being compatible with the non-foaming resin. a second feeding/injection device for feeding and injecting a second stream of foamable synthetic resin; and a second feeding/injection device connected to the first and second feeding/injection devices for passing the first stream a passage unit including a first passage and a second passage for mixing the first flow and the second flow and passing the mixed flow; When feeding and injecting the flow, communication between the first passage and the second passage is cut off and the first flow is allowed to pass through the first passage, and when feeding and injecting the mixed flow, first valve means for communicating the first passage and the second passage to mix the first flow and the second flow; is in communication with a passageway for passing a first flow to a nozzle end that abuts the mold, and when said first valve means is open, for passing said mixed flow to the nozzle end and a first
a second valve means for closing the flow of the nozzle, and the second valve means is moved forward or backward along the feeding and injection direction to switch between the first flow and the mixing flow in the vicinity of the nozzle end. Provided is an injection molding apparatus for foam molded products.

<Example> Figures 1 to 4 show the structure of an injection molding apparatus according to an example of the present invention, and Figures 5 to 7 show the structure of injection molding using this injection molding apparatus. The molding process inside the mold is shown.

This injection molding apparatus includes a main cylinder 12, a screw 13 that rotates within the main cylinder 12 and advances or retreats along the axial direction, a mixing unit 16 connected to a cylinder head 14 of the main cylinder 12, and a connecting pipe. and a sub-cylinder 18 connected to the mixing unit 16 by 20. The main cylinder 12 is configured to inject the non-foaming thermoplastic resin A supplied into the main cylinder 12 from an opening 14a of a cylinder head 14 by means of a screw 13.

The mixing unit 16 includes a unit main body 15 having a cylindrical structure and having a nozzle 21 at the tip and a flange portion 22 at the rear end.
The control mechanism 23 controls the supply of resin material into the main cylinder 12 with the flange 22 in contact with the cylinder head 14.
is connected to. The unit main body 15 has a chamber 24 formed in the center of the flange portion 22, which communicates with the opening 14a of the cylinder head 14 and receives the non-foamable resin A sent from the main cylinder 12.
Also, a passage 25a that communicates with the chamber 24 and a central passage 25 extending along the central axis;
Side passages 26 and 27 which are spaced apart above and below (or left and right) and communicate with the chamber 24 are provided. The tips of the central passage 25 and side passages 26, 27 communicate with the nozzle 21. A cross-shaped mixing element 28 is loaded inside the central passage 25, and mixes the resins as will be described later.
Furthermore, an injection hole 29 connected to the connecting pipe 20 is provided at the rear end portion of the central passage 25 .

The control mechanism 23 has a first valve member 30 fitted in the rear end of the unit main body 15 of the mixing unit 16 in the vertical direction, and a distal end in the central passage 25, which slides into a forward or backward position along the longitudinal direction. The rear part of the operating cylinder 23a for operating the first and second valve members 30, 31 in conjunction with each other is pinned to a bracket 35 via a lever 33. A link device 34 is attached to the tip of the piston 37 to allow the second valve member 31 to slide.

In FIGS. 1 and 2, the cylinder 23a is marked with an arrow P.
This shows a case in which the lever 33 is actuated in the direction of arrow P' by applying fluid pressure in the direction shown in FIG. Ru. Further, since the piston 37 acts in the direction of the arrow P'', the second valve member 31 is advanced by the link device 34, and the central passage 25 and the nozzle hole 21a are closed, while the side passages 26 and 27 are closed. It communicates with the nozzle hole 21a via a Y-junction 36.

Next, when fluid pressure is applied in the direction of arrow Q and the lever 33 is actuated in the direction of arrow Q' as shown in FIGS. 3 and 4, the first valve member 30 is pressed by the tip 33a. It is released and slid upward by the injection pressure from the screw 13, and the passage 25a and the central passage 25 communicate with each other. Also, the piston 37 is indicated by an arrow
When actuated in the Q'' direction, the second valve member 31 is retracted by the link device 34, the central passage 25 and the nozzle hole 21a are communicated, and the side passages 26, 27 and the nozzle hole 21a are connected to the second valve member 31. It is closed by member 31.

The sub-cylinder 18 has a built-in sub-screw 19 in which a foamable resin D in which the thermoplastic resin B and the foaming agent C are mixed is produced, and the foamed resin D is passed through the connecting pipe 20 and the injection hole 29 to the central passage 2 of the mixing unit 16.
Send the foamable resin D to 5.

In the injection molding apparatus having such a configuration, when performing resin molding, the sub cylinder 18 has the following:
The same or different but compatible resin B supplied to the main cylinder 12 and the chemical blowing agent C2~
5 wt % is mixed and supplied, and kneaded by the sub-screw 19. Next, when injecting the resin material, the first and second valve members 30 and 31 are first set to the states shown in FIGS. 1 and 2, and the non-foaming molten resin A in the main cylinder 12 is injected into the main screw. 3, this non-foamable resin A is shot in a predetermined amount from the cylinder head 14 through the side passages 26, 27 of the mixing unit 16 and the Y-junction 36 through the nozzle hole 21a into the mold 7 ( Figure 5). At a predetermined time during this injection, the foamable resin D is injected from the sub-cylinder 18 through the connecting pipe 20 and the injection hole 29, and at the same time, the operating cylinder 23
Apply fluid pressure to a in the direction of arrow Q. As a result, the mixing unit 16 is brought into the state shown in FIGS. 3 and 4, and the non-foamable resin A injected from the main cylinder 12 is introduced into the central passage 25 and the cross-shaped mixing element 28 causes the non-foamable resin A to become foamable. While being kneaded with the resin D, the mixed resin E is supplied to the nozzle hole 21a through the through hole 37' and injected into the mold 7. The above-mentioned mixed resin E kneaded by this injection is processed according to the principle of molten resin flow.
It flows inside the previously shot thermoplastic resin A in the mold 7 and is shot, forming a fine closed-cell foam layer within the non-foaming thermoplastic resin A (FIG. 6). Such mixed resin E
Before completing injection of the predetermined amount of
At the same time, fluid pressure is applied to the operating cylinder 23a in the direction of arrow P to the first and second valve members 3.
0 and 31 are returned to the state shown in FIGS. 1 and 2, the non-foamable resin A injected from the main cylinder 12 passes through the side passages 26, 27 and the Y-junction 36 again, and passes through the nozzle hole 21a to the metal. Injected into mold 7. This allows the sprue and gate parts to be covered with non-foaming resin A.
(FIG. 7), and the injection process is completed.

The volume of the nozzle hole 21a is usually a small value of 0.04 to 0.14 cc, and while the resin at the final injection part fills the sprue and runner, the inside of the nozzle hole 21a completely changes from the mixed resin E containing the foaming agent to the resin A not containing the foaming agent. replaced by Therefore, there is no possibility that silver stripes will appear on the surface of the formed product at the beginning of the next shot.

Furthermore, since the second valve member 31 has a structure in which closing is completed only when its tip comes into contact with the nozzle hole 21a of the nozzle 21, when switching between the non-foaming resin A and the foamable mixed resin E, There is no interruption in injection, so there is no risk of switch marks appearing on the surface of the molded product.

Furthermore, the Y-junction 36 of the second valve member 31
is a passage for only non-foamable resin A, and is completely different from the passage for foamable mixed resin E and foamable resin D except for the nozzle hole 21a.
There is no risk that the resins will mix with each other.

<Effects of the Invention> As explained above, according to the present invention, a mixing unit connected to a plurality of cylinders for injecting different types of resin materials is provided with a flow path through which different resins pass through, thereby improving the efficiency of injection work. Since the communication to the nozzle is switched, the previously shot resin will not be mixed in when changing the cycle, and silver streaks will not appear on the surface of the molded product, making it possible to obtain a foamed molded product with a smooth and beautiful surface. I can do it.

[Brief explanation of drawings]

FIG. 1 is a partially sectional plan view showing an example of the injection molding apparatus of the present invention, FIG. 2 is a partially sectional side view of the apparatus shown in FIG. 1, and FIG. 3 shows a resin flow path different from that shown in FIG. 1. FIG. 4 is a partial cross-sectional side view of FIG. 3, FIGS. 5, 6, and 7 are cross-sectional views showing the molding process inside the mold, and FIG. 8 is a known FIG. 1 is a partially sectional side view showing an example of an injection molding apparatus. Main numbers in the diagram 12...Main cylinder, 16...
...Mixing unit, 18...Sub-cylinder, 2
DESCRIPTION OF SYMBOLS 1... Nozzle, 23... Control mechanism, 25... Central passage, 26, 27... Side passage, 30... First valve member, 31... Second valve member.

Claims (1)

[Scope of Claims] 1. In an apparatus for injection molding a synthetic resin molded product having a core formed of a foam and an outer surface layer of a non-foaming synthetic resin, the non-foaming synthetic resin is kneaded to form a non-foaming synthetic resin. a first feeding and injection device for feeding and injecting a first flow of synthetic resin; and a second flow of foamable synthetic resin for kneading a synthetic resin containing a foaming agent and being compatible with the non-foaming resin. a second feed and injection device for feeding and injecting the flow; connected to the first and second feed and injection devices;
a passage unit comprising a first passage for passing the first flow; and a second passage for mixing the first flow and the second flow and passing the mixed flow; In the passage unit, when feeding and injecting the first flow, communication between the first passage and the second passage is cut off, and the first flow is allowed to pass through the first passage;
a first valve means for communicating the first passage and the second passage to mix the first flow and the second flow when feeding and injecting the mixed flow;
valve means is in communication with the first passageway to pass a first flow to the nozzle end that abuts the mold when the first valve means is closed; second valve means for passing the mixed stream through the nozzle end and closing off the first stream; said second valve means being advanced or retracted along the feed injection direction to mix with the first stream; An injection molding apparatus for foam molded products, characterized in that the flow is switched close to the nozzle end.