JPS6153931B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method and apparatus for injection molding a foam molded article, and more particularly to a method and apparatus for injection molding a foam molded article, in which the inside of the molded article is made of foam and the outer surface is made of an unfoamed synthetic resin. In general, products made by low-foaming injection molding (hereinafter referred to as SF molding) of synthetic resins have characteristics such as excellent rigidity, sound insulation, and heat insulation, and a wide variety of product designs. The spiral pattern formed on the surface impairs the external appearance, and some products have the disadvantage that the surface must be painted after molding. In order to eliminate these drawbacks, various devices and methods have been developed for the SF molding method, one of which is equipped with two sets of injection molding units of the same capacity, and from these two sets of injection molding units are used to mold two types of synthetic resin into valves. There have been methods of alternately or simultaneously injecting resin by switching, but the basis of this method is the characteristics of the resin flow within the mold. In other words, when observing the flow of resin injected into the cavity, the injected resin first touches the cavity wall, its temperature decreases, the viscosity decreases, and the resin continues to be injected while remaining on the cavity wall near the gate. The resin passes through the inside and stagnates on the wall beyond, and the same state is repeated one after another until the filling is completed. Therefore, of the resin injected at one time, the resin injected earlier will fill the wall of the cavity (on the surface of the product), and the resin injected later will fill the center of the wall thickness. It is well known that this is the case. However, in order for this to be carried out according to theory, it is necessary that the viscosity of the resin injected at one time be as uniform as possible, and that the flow rate be constant without interruption. However, in the conventional method, two sets of injection units inject resins in different states, so it is difficult to keep the viscosity of both resins constant, and it is difficult to continuously inject resins without interruption. is difficult. Therefore, switching of the valve for alternate injection may cause hesitation marks, or in the case of a molded product with a somewhat complicated shape, the foam layer may be exposed to the surface or the foam layer may not reach the ends. It was hot. The present invention maintains the viscosity of the resin injected by a cylinder from beginning to end and performs continuous injection without interruption, thereby creating a foam layer inside even complex-shaped molded products, and forming a foam layer on the surface (skin layer). The aim was to create a molded product that could be molded from a resin that did not contain any foaming agents and did not require painting.The aim was to add a small amount of auxiliary equipment to a conventional injection molding machine, and thereby It is an object of the present invention to provide a method for continuously obtaining foamed molded products with good appearance. That is, the present inventor used a conventional injection molding machine consisting of a cylinder with a screw inside, connected a sub-cylinder to this, and used a mixing nozzle in contact with the mold to mold thermoplastic resin from the cylinder. The mixture of thermoplastic resin and foaming agent from the sub-cylinder can be injected from the cylinder at any time during the injection process, mixed with a mixing nozzle, and shot into the mold. We aim to provide an injection molding method and apparatus for foam molded products. Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a partial cross-sectional view showing one embodiment of the device of the present invention, in which a hopper 1 is for supplying thermoplastic resin A into a cylinder 2, and the cylinder 2 is equipped with an electric motor and a speed changer connected thereto. It has a built-in screw 3 that moves forward and backward while rotating depending on the machine. Cylinder head 4 and mold 7 for resin molding
A mixing nozzle 6 incorporating various static mixers 5 consisting of left-handed and right-handed elements is interposed between the mixing nozzles 6 and the screw 3 to inject the thermoplastic resin A into the mold 7. There is. Therefore, the injection capacity of the cylinder head 4 is 3 of the injection capacity of the cylinder 2.
%~20%, preferably 5~10% secondary cylinder 8
are connected by a connecting pipe 9, and a mixture D of thermoplastic synthetic resin B and foaming agent C, which is supplied to the sub-cylinder 8 by a hopper (not shown), etc., is transferred to the cylinder by a sub-screw 14 installed in the sub-cylinder. The liquid is ejected into the head 4. Note that the cylinder head 4 here includes the tip of the screw 2 where the screw 3 is located. In addition, at the rear of the mixing nozzle 6, that is, at the connection part of the sub-cylinder 8 including the cylinder head 4,
A control mechanism is provided for injecting or stopping the mixture D from the sub-cylinder 8 at any time during the process of injecting the thermoplastic resin A from the cylinder 2. This control mechanism consists of a cam 10 and limit switches LS-1, LS-2, which are interlocked at the rear of the screw 3, as shown in FIGS. 1 and 2.
A hydraulic cylinder 11 and a needle valve 12 which are electrically actuated are provided in the cylinder head 4 on the opposite side of the connecting pipe 9, and the injection or stopping of the mixture D from the auxiliary cylinder 8 is performed by the needle valve. It is set up so that it can be controlled. Next, to explain the injection molding method for foam molded products, which is the method of the present invention, thermoplastic resin A is supplied from the hopper 1 into the main cylinder 2, and thermoplastic resin B is supplied into the separately provided small-capacity sub-cylinder 8. Supply mixture D of blowing agent C. Thermoplastic resin A
and B are, for example, polyethylene, polypropylene,
Polystyrene, ABS resin, modified polyphenylene oxide (manufactured by GE, product name Noryl), grafted polyphenylene ether (product name Zylon, manufactured by Asahi Dow), polyamide (nylon 6, nylon 66)
etc.) or polycarbonate. Furthermore, the thermoplastic resins A and B may be different types as long as they are compatible with each other.
Examples of compatible materials include polypropylene and polyethylene, ABS resin and polystyrene, modified polyphenylene oxide and polystyrene, grafted polyphenylene ether and polystyrene,
Nylon 66 and nylon 6 or polycarbonate
Examples include ABS resin. The blowing agent C mixed with the thermoplastic resin B includes azodicarbonamide (ADCA), azobisisobutyronitrile (AZDN), P.P'-oxybisbenzenesulfonylhydrazide (OBSH), N.N. Possible examples include '-dinitrosopentamethylenetetramine (DPT) and P-toluenesulfonyl semicarbazide (TSSC). As the screw 3 moves forward, the thermoplastic resin A supplied into the cylinder 2 is shot in a required amount from the cylinder head 4 through the mixing nozzle 6 and into the mold 7 from the sprue 15 (FIG. 3). At this time, the cam 10 at the rear of the screw 3 starts from the limit switch LS-3, and the cam 10 moves forward together with the screw 3, but until the cam 10 reaches the limit switch LS-1, the needle valve of the hydraulic cylinder 11 closes the mixing nozzle 6. Secondary cylinder 8 located at the rear
The connection between the cylinder 2 and the auxiliary cylinder 8 is closed at the outlet 13 of the connecting pipe 9 into the cylinder head 4. Furthermore, the screw 3 moves forward and the cam 10 switches the limit switch.
When LS-1 is pressed, the hydraulic cylinder 11 is released and the needle valve 12 opens at the outlet 13, and at the same time the secondary screw 14 starts moving forward and the mixture D of the thermoplastic resin B and the blowing agent C flows into the cylinder head 4. Eject inward. In this way, mixture D
is mixed with the thermoplastic resin A in the mixing nozzle 6 and shot into the mold 7 through the sprue 15. In this case, the weight ratio of the blowing agent to the weight of the thermoplastic resins A and B is 0.2 to 0.8.
% is desirable to obtain suitable foaming conditions. In this case, the kneaded product E of the thermoplastic resin A and the mixture D has a small ratio of the mixture to the resin A, as will be described later, and is sufficiently kneaded in the mixing nozzle, so that there is a difference between the original resin A and the kneaded product. There is almost no difference in viscosity from E, and according to the principle of ideal molten resin flow, it flows inside the previously shot thermoplastic resin A and is shot into the mold 7, forming fine independent particles within the resin 1. A foam layer is formed in the form of bubbles (Fig. 4). Next, when the screw 3 moves further forward and the cam 10 pushes the limit switch LS-2, the sub-screw 14 stops and stops feeding the mixture D to the cylinder head 4. At the same time, the needle valve 12 is closed by the hydraulic cylinder and the metal Only the thermoplastic resin A is shot into the mold 7 again. In this way, the inside of the mixing nozzle 6 and the inside of the sprue 15 are filled with the synthetic resin A, and the cam 10 pushes the limit switch LS-4 to complete the injection. Next, screw 3 rotates and the limit switch
It is possible to move back to LS-3 and stop, and then perform the next process continuously. The above process description is one embodiment of the present invention, and for example, the process starts by injecting the mixture from the sub cylinder 8 from a state in which the sprue 15 and the mixing nozzle 6 are filled with thermoplastic resin. Therefore, the present invention can also be used for cylinder 2.
The purpose can be achieved by any method that injects the mixture in the secondary cylinder at any time during injection from the secondary cylinder. The foam molded product obtained in this way has a synthetic resin foam inside (core layer resin) and an outer surface made of synthetic resin skin (skin layer resin), so it not only has a beautiful appearance but also has good rigidity and elasticity. Excellent acoustic and thermal insulation properties are obtained by the very simple improved device and easy operation of the present invention. Example 1 Cylinder 2 with injection capacity 3600g and injection capacity 200
A secondary cylinder 8 of g was used. Polystyrene was supplied to cylinder 2, and a mixture premixed at the following ratio was supplied to sub-cylinder 8.

[Table] Foam molded products were manufactured using these raw materials according to the method described above.

[Table] The SF molded product thus produced according to the present invention exhibited an appearance without any spiral pattern or silver stripes, and did not require painting. Example 2 Using the same equipment and mold as in Example 1, modified polyphenylene oxide (trade name Noryl FN-215) was supplied to the main cylinder, and a mixture premixed in the following ratio was supplied to the sub cylinder. supplied.

[Table] Similar to Example 1, the molded product thus produced had an appearance without any spiral pattern or silver stripes, and did not require painting.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the main parts of an injection device according to the present invention, FIG. 2 is a layout diagram of a limit switch, and FIGS. 3, 4, and 5 are sectional views showing resin flow within a mold. 1...Hopper, 2...Main cylinder, 3...
Main screw, 4... Cylinder head, 6...
Mixing nozzle, 7... Mold, 8... Sub cylinder, 9... Connecting pipe, 10... Cam, 11... Hydraulic cylinder, 12... Needle valve, 14... Sub screw, LS-1... Sub Cylinder injection start limit switch, LS-2...Sub-cylinder injection stop limit switch, LS-3...
Limit switch for main cylinder metering completion;
LS-4... Limit switch for main cylinder injection completion, A, B... Synthetic resin, C... Foaming agent,
D...Mixture of B and C, E...Foam kneaded product of A, B and C.

Claims (1)

[Scope of Claims] 1. An injection molding machine in which thermoplastic resin is shot from a cylinder head to a mold by a screw installed in a cylinder, with a mixing nozzle interposed between the cylinder head and the mold,
A foam molded product characterized in that a sub-cylinder is connected to the rear of the mixing nozzle and is equipped with a control mechanism for injecting or stopping the mixture of thermoplastic resin and foaming agent at any time during the injection process of the cylinder. injection molding equipment. 2. The injection molding apparatus for foam molded products according to claim 1, wherein a sub-cylinder connected to the rear of the mixing nozzle is connected to the cylinder head via a connecting pipe. . 3. The control mechanism for feeding or stopping the mixture in the sub-cylinder to the rear of the mixing nozzle at any time during the injection process of the cylinder is a valve that operates in electrical conjunction with the screw. An injection molding apparatus for a foam molded product according to claim 1 or 2. 4. Any one of claims 1 to 3, characterized in that the sub-cylinder is provided with a sub-screw for injecting the mixture, and the injection capacity is 5 to 10% of the injection capacity of the cylinder. An injection molding device for a foam molded product according to claim 1. 5 In an injection molding method in which a thermoplastic resin is shot from a cylinder head into a mold using a cylinder screw, a mixture of a thermoplastic resin of the same type as the thermoplastic resin and a blowing agent is supplied into a sub-cylinder prepared in advance, and the The mixture of thermoplastic resin and foaming agent in the secondary cylinder is injected at any time during the injection process of the cylinder, and the mixture is mixed with the thermoplastic resin from the cylinder by a mixing nozzle interposed between the cylinder head and the mold. A method for injection molding foam molded products, which is characterized by continuously shooting into a mold while kneading. 6. Claim 5, wherein the arbitrary timing during the injection process of the cylinder is selected from the beginning, middle, or end of the injection of the thermoplastic resin from the cylinder.
Injection molding method for foam molded products described in Section. 7. In an injection molding method in which a thermoplastic resin is shot from a cylinder head into a mold using a cylinder screw, a different type of thermoplastic resin and a blowing agent that are compatible with the thermoplastic resin are supplied into a sub-cylinder prepared in advance, The mixture of thermoplastic resin and foaming agent in the sub-cylinder is injected at any time during injection of the cylinder, and the mixture is mixed with the thermoplastic resin from the cylinder by a mixing nozzle interposed between the cylinder head and the mold. An injection molding method for foam molded products characterized by continuously shooting into a mold while kneading. 8. Claim 7, wherein the arbitrary time during the injection process of the cylinder is selected from the beginning, middle, or end of the injection of the thermoplastic resin from the cylinder.
Injection molding method for foam molded products described in Section.