JPS59220335A - Method and apparatus for injection molding of expanded molded article - Google Patents

Abstract

PURPOSE:To obtain an expanded molded article free from a swirl mark or expansion irregularity, by a method wherein a synthetic resin containing a blowing agent is injected into a mold while held to the decomposition temp. or less of the blowing agent to form an outer surface layer and, thereafter, a heated resin is injected to perform expansion. CONSTITUTION:After a mixture consisting of a blowing agent and a synthetic resin is stored in the leading end 15 of a heating cylinder 13 by a screw 13, a screw 15 is allowed to advance to permit the mixture to pass through a flow passage 25, a valve 31 and a nozzle orifice 17 isolated from the heater 23 of an expanding and preheating apparatus 20 through a joint pipe 16 and injected into a mold to form an outer surface layer. In the next step, a fluid pressure cylinder 36 is operated to change over the valve 31 and the mixture is introduced into a stay heating passage 24 to be heated to the decomposition temp. of the blowing agent as well as stayed so as to bring a decomposed gas amount to a max. value while the heated mixture is injected into the mold through communication passages 26, 26', valves 32, 32' and the nozzle orifice 17 to form a uniform expanded layer in the outer surface layer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an injection molding method and apparatus for a foam molded product, and more particularly, to injection molding of a foam molded product in which the inside of the molded product is a foam and the outer surface layer is made of a non-foamed synthetic resin. This article relates to a molding method and its device.

Various proposals have been made regarding injection molding methods for foam molded products. For example, Japanese Patent Publication No. 46-13151 discloses a method in which a mixture containing a foaming agent and a synthetic resin is injected into a mold through a narrow passage. A method is disclosed in which the foaming agent is heated to a temperature higher than its decomposition temperature by frictional heat when passing through the passage, and foamed in a mold.

This method uses frictional heat to instantly raise the resin temperature below the decomposition temperature of the blowing agent, but in general, gas is gradually generated after the blowing agent reaches its decomposition temperature, and the amount of gas generated reaches its maximum value. Since a certain amount of time is required for this to occur, it usually depends on the conditions, but if the temperature is not maintained at the decomposition temperature of the blowing agent for more than one minute, the foaming of the blowing agent may be insufficient or non-uniform. Therefore, uniform and sufficient gas generation cannot be achieved by short-time friction such as passing through a passage during injection as in this method.

As a method for injection molding a foamed molded article made of a synthetic resin whose outer surface layer is not foamed or foamed inside the molded article, the method described in JP-A-58-1.4725 is known. In this method, a mixture containing a blowing agent and a synthetic resin is passed through an alternating current through two types of channels with different cross-sectional areas, and the blowing agent is The decomposition and foaming temperature is controlled, and the above-mentioned foamed molded article is produced by passing the mixture through the mixture at a temperature below the decomposition and foaming temperature in the tenth channel and at a temperature above the decomposition and foaming temperature in the second channel.

However, in this method as well as in the above-mentioned method, the foaming agent does not foam instantaneously, so foaming may be insufficient or uneven9, making it difficult to obtain an excellent foamed molded product.

The present invention has no swirl marks and the blowing agent foams evenly.
Another object of the present invention is to provide a method and an apparatus for injection molding a foam molded product, which can be carried out satisfactorily and, as a result, can produce an excellent foam molded product without uneven foaming.

According to the present invention, when injection molding a foam molded product made of a foamed interior and an unfoamed synthetic resin outer surface layer, a mixture containing a foaming agent and a synthetic resin is placed at a location away from a heat source. The blowing agent is passed through a flow path that is substantially unaffected by a heating source while being maintained at a temperature lower than the decomposition and foaming temperature of the blowing agent, and then injected into a mold through a nozzle to form the outer surface layer. , a retention heating path that is located close to the heat source and is heated by the heat source (the mixture is heated in advance to a temperature higher than the decomposition temperature of the blowing agent, so that the amount of cracked gas generated is The mixture is injected into the mold through the nozzle at a predetermined time so as to reach the maximum value, and then the mixture is injected into the mold through the flow path and the nozzle again. Provided is a method for injection molding a foam molded product, which comprises injecting into a mold, completing an injection cycle, then cooling and removing the molded product to complete one cycle, and repeating the cycle as necessary. be done.

Further, according to the present invention, in an apparatus for injection molding a foam molded product having a foamed interior and an unfoamed synthetic resin outer surface layer, a mixture containing a foaming agent and a synthetic resin is continuously fed into a mold. A foaming preheating device comprising: a feeding injection device for feeding and injecting the mixture; a flow passage through which the mixture sent from the feeding injection device passes; a retention heating passage for heating the mixture for a predetermined time; and a heater. the flow path is located at a location remote from the heater, and the mixture is maintained at a temperature that is seconds lower than the decomposition and foaming temperature of the blowing agent so as not to be substantially affected by the heater. passing through, and the retention heating path is provided at a position close to the heater,
The mixture is heated to a temperature higher than the decomposition and foaming temperature of the blowing agent, and the volume size is such that the mixture is sufficiently heated for a predetermined time and the amount of decomposed gas reaches a maximum value when injected into a mold,
a switching valve for alternately sending the mixture that has passed through the flow path and the mixture that has passed through the retention heating path to a nozzle; and a nozzle for injecting the mixture that is sent through the switching valve into a mold. The feeding and injection device injects the mixture that has passed through the flow path and the switching valve into the mold through a nozzle to form the outer surface layer, and then, by switching the switching valve, the mixture is heated by the stagnation. In the process, the mixture, which has been retained and heated for a predetermined period of time, is injected into the mold through the nozzle so that the amount of decomposed gas of the foaming agent reaches a maximum value, thereby forming a foam layer. A molding device is provided.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a schematic cross-sectional view of an injection device 10 of the present invention. In FIG. 1, a heating cylinder 11 houses a screw 13 that receives a mixture of synthetic resin and a foaming agent from a hopper (not shown) and feeds and injects the mixture to a nozzle 12. can move forward or backward. A band heater 14 is attached to the heating cylinder 11, which heats and melts the mixture to a temperature below the decomposition and foaming temperature of the blowing agent, and maintains this state.

The mixture is kneaded in the heating cylinder 11 by the rotation of the screw 13, and the amount of mixture required for normal injection is stored in the tip 15 of the heating cylinder 11.

The configurations of the above-mentioned devices are all components of a general-purpose injection molding device, and therefore will not be described in detail.

The present invention is characterized in that a foaming preheating device 20 and a switching valve device 30 are newly provided between the heating cylinder 11 and the nozzle 12.

The foaming preheating device 20 includes an outer cylinder 21, an inner cylinder 22, and a heater 2.
3, and an annular retention heating path 24 is formed between the outer cylinder 21 and the inner cylinder 22 to heat the aforementioned mixture. Further, a flow path 25 is formed in the center of the inner cylinder 22 to allow the mixture to flow therethrough.

The foaming preheating device 20 connects the heating cylinder 11 with the joint pipe 16.
connected to.

In the switching valve device 30, a cylindrical valve 31 is rotatably inserted into an outer cylinder 21 as shown, and the valve 31 has two valve holes 32 and 32' bored in the same direction. One valve hole 33 is drilled at right angles to these valve holes.

A link member 34 is fixed to the valve 31, and rods 35 are rotatably connected to each other by a pin 36 near an end portion 34a of the link member 34. The rod 35 is connected to a hydraulic cylinder 36, and the rod 35 can be moved back and forth by actuation of the hydraulic cylinder 36. Although the illustrated example shows a hydraulic cylinder, the valve 31
Of course, other devices can also be used as long as they have a mechanism that can rotate the In FIG. 1, rod 35 is shown in a retracted position. In this position, the valve hole 33 of the valve 31
communicates with the flow path 25, but the valve hole 32, 32' does not communicate with the communicating hole 26, 26' of the retention heating path 24 and is closed. As the rod 35 advances, the valve 31 rotates, and when rotated 90'', the valve hole 33 is aligned with the flow path 25, as shown in FIG.
The valve holes 32, 32' are closed without communicating with the connecting holes 26, 26', respectively. Tip 25 of flow path 25
a communicates with the nozzle hole 17.

In operation, a mixture of a thermoplastic synthetic resin and a blowing agent, which is in a molten state but at a temperature below the decomposition and foaming temperature of the blowing agent, is prepared and stored at the tip 15 of the heating cylinder 11 by rotational kneading of the screw 13.

Examples of thermoplastic synthetic resins include polyethylene, polypropylene, polystyrene, ABs resin, modified polyphenylene oxide (trade name Noryl, manufactured by GE), krafted polyphenylene ether (trade name Zylon, manufactured by Asahi Kasei Corporation), polyamide (nylon 6, nylon 66, etc.). ) or polycarbonate, etc. can be used. In addition, as blowing agents, azodecarbonamide, azobisisobutyronitrile, P,P'-oxybisbenzenesulfonyl hydrazide, N,N'-dinitrosopentamethylenetetramine, P-toluenesulfonyl semicarbazide, etc. Can be used. The foaming degree of the commonly used blowing agent is 8[ordinarily 150a to 150a, although it varies depending on the particle size, etc.]
260'e, a blowing agent suitable for the melting temperature of the resin is selected and used, and the temperature of the molten mixture is maintained below the decomposition temperature of the blowing agent used.

By advancing the screw 13, the molten mixture in the tip 15 is sent to the foam preheating device 20 through the joint pipe 16. The flow passage 251 and valve 31 of the foaming preheating device 20 are positioned as shown in FIG. 1, with the valve hole 33 and the tip 25a1
The mixture is injected into the mold 40 through the nozzle hole 17 . Since the inner cylinder 22 is separated from the heater 23 and is made of a material with low thermal conductivity, such as nickel, titanium, or an alloy thereof, the molten mixture C cannot be foamed at a temperature below the decomposition foaming temperature. It is injected into the mold 40 through the preheating device 20 and forms an outer surface layer without foaming, as shown in Figure 3a.

The hydraulic cylinder 36 is then energized in conjunction with the screw 13, and the valve 31 is rotated and switched to the state shown in FIG. At this position, the molten mixture is injected into the mold 40 through the retention heating path 24, communication hole 26.26', valve hole 32.32', and nozzle hole 17 at the tip 25a1 (Fig. 3b).
. The retention heating path 24 is close to the heating mold 23 and forms an annular chamber.

Therefore, the molten mixture remains for a predetermined period of time, for example, 3 minutes or more, and is heated to a temperature of 260° to 270°C, which is higher than the decomposition temperature of the blowing agent. Since the foaming agent does not foam immediately even when heated below the decomposition temperature, by allowing the foaming agent to stagnate in the stagnation heating path for the specified period of time, the amount of decomposed gas reaches its maximum value and is injected into the mold 40. A uniform foam layer is then formed.

Immediately before injection is completed, the hydraulic cylinder 36 is energized again in conjunction with the screw, the valve 31 is switched to the state shown in FIG.
As the gate sealing is performed, the mixture in the nozzle hole 17 also becomes below the foaming decomposition temperature in preparation for the next cycle of injection (FIG. 3c).

Next, the screw 13 is automatically retracted by an automatic control device, such as a combination of a cam mechanism and a limit switch, and the same cycle is repeated.

According to the present invention, even if the blowing agent is heated above the decomposition and foaming temperature, it does not foam immediately, but usually begins to foam rapidly after about 1 to 5 minutes, increasing the gas pressure. The amount of foaming gas is maximized, uniform foaming is performed in the mold, a foamed layer is formed, and an excellent foamed molded product with no so-called swirl marks on the outer surface layer is obtained. Further, the device of the present invention allows the foaming preheating device and the valve device to be attached to a general-purpose device, and there is no need to newly manufacture the entire device.

Hereinafter, the present invention will be explained with reference to examples. In addition, parts are dead weight parts.

Example 1 A foam molded product having a foamed interior and an unfoamed outer surface layer was injection molded using the apparatus shown in FIG.

100 parts of polystyrene (product name: "Diaflex HT-59" Mitsubishi Monsanto Chemicals ■) and a decomposition temperature of 205 ml as a foaming agent were placed at the tip 15 of a heating cylinder 11 with an injection chamber volume of 340 cc.
1Zodicarbonamide (trade name: "Celmic C-1")
91J Sankyo Kasei ■) A mixture consisting of 0.3 parts was heated to a temperature of 1
After maintaining the temperature at 90 DEG C. and injecting 60 g in the state shown in FIG. 1, the valve 31 was switched to the state shown in FIG. 2, and the heated mixture was injected at a temperature of 225 DEG C. for a residence time of 130 seconds. Then, just before the injection was completed, the valve 31 was switched again to the state shown in FIG.

Molded product wall thickness 45, outer surface layer wall thickness 07~1.2++
A foam molded product (weight: 143 g) of +m was obtained. There were no swirl marks on the surface, and the inside was uniformly foamed.

Example 2 Polyphenylene oxide (trade name: "Noryl FN215J, manufactured by General Electric Company)" as a raw material 10
Using 0 parts and 07 parts of azodicarbonamide (trade name "Cellmic 142" Sanbe Kasei ■) with a decomposition temperature of 245 to 250°C as a foaming agent, store it at the tip 15 at a temperature of 235°C,
In the same manner as in Example 1, the first rI! Inject in state i, 7
After injecting 0g, the molded product was molded in the same manner as in Example 1, except that injection was carried out at a temperature of 265°C for 150 seconds in the state shown in Figure 2, with a wall thickness of 6 m and an outer surface layer of 0.8 m. ~185m
A foam molded article (weight 195 g) was produced.

There were no swirl marks on the surface of the molded product, and the inside was uniformly foamed.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an outline of the injection molding apparatus of the present invention;
FIG. 2 is a partial sectional view showing a state in which the valve device of the apparatus shown in FIG. In the figure, 10 is an injection molding device, 11 is a heating cylinder, 13 is a screw, 20 is a foaming preheating device, 24 is a retention heating path,
25 is a flow path, 30 is a valve device, 32, 32', 33 are valve holes, and 40 is a mold. Patent Applicant Orion Kasei Co., Ltd. Commissioner of the Patent Office Mr. Kazuo Wakasugi1 Indication of the Case Patent Application No. 93980 of 1982 Name of the Invention Method and Apparatus for Injection Molding of Foam Molded Products 3 Relationship with the Amendment Person Case Patent Application Orion Kasei Co., Ltd. 4. Agent 5. Item 6 of “Detailed Description of the Invention” of the specification subject to amendment Contents of the amendment “Diaflex” was changed from page 14, line 14 of the specification of the present application to “Diaflex”.
Dialex,” he corrected.

Claims (2)

[Claims] (1) When injection molding a foam molded product made of a synthetic resin with a foamed interior and an unfoamed outer surface layer, a mixture containing a foaming agent and a synthetic resin is placed at a location away from the heating source. The blowing agent is passed through a flow path that is substantially unaffected by the blowing agent while being maintained at a temperature lower than the decomposition and foaming temperature of the blowing agent, and then injected into a mold through a nozzle to form the outer surface layer, and then the heating source The mixture is passed in advance through a retention heating path located close to the heating source and heated by the heating source, and heated to a temperature higher than the decomposition temperature of the blowing agent, so that the amount of decomposed gas generated reaches its maximum value. The mixture, which has been retained and heated for a predetermined period of time, is injected into the mold through the nozzle to form a foam layer, and then the mixture is again injected into the mold through the flow path and the nozzle. . A method for injection molding a foam molded product, characterized in that the injection cycle is completed, followed by cooling and removal of the molded product to complete one cycle, and the cycle is repeated as necessary. (2) In an apparatus for injection molding a foam molded product made of a synthetic resin with a foamed interior and an unfoamed outer surface layer, a mixture containing a foaming agent and a synthetic resin is continuously fed and injected into a mold. a foaming preheating device including a flow path through which the mixture sent from the feed injection device passes, a retention heating path and a heater that heats the mixture for a predetermined time, The flow path ζ is located at a position away from the heater and is maintained at a temperature lower than the decomposition and foaming temperature of the blowing agent so as to be substantially unaffected by the heater, and the mixture is allowed to pass therethrough. The reservoir heating path is provided at a position close to the heater, and heats the mixture to a temperature higher than the decomposition and foaming temperature of the blowing agent, and heats the mixture sufficiently for a predetermined time so that the amount of decomposed gas reaches the maximum when injected into the mold. a switching valve for alternately sending the mixture that has passed through the flow path and the mixture that has passed through the retention heating path to the nozzle, and the mixture that is sent through the switching valve. a nozzle for injecting into the mold, the feeding injection device injects the mixture that has passed through the flow path and the switching valve into the mold through the nozzle to form the outer surface layer; By switching the valve, the mixture heated in the retention reservoir is injected into the mold through the nozzle and foamed at a predetermined time so that the amount of decomposed gas of the foaming agent reaches the maximum value in advance in the retention heating path. An injection molding device characterized by forming a layer.