JPH06198668A - Method for injection molding of high expantion molded material - Google Patents

Abstract

PURPOSE:To obtain a high expansion molded material which is excellent in surface appearance by a method wherein a cavity of a metal mold is filled with high pressure fluid, synthetic resin to which a foaming agent is added is injected therein to discharge the high pressure fluid, and the synthetic resin is foamed to be enlarged to a size larger than a molding product size, which is reduced to a final molding product size while a solid skin layer is soft. CONSTITUTION:A volume of a cavity 16 of an air-tight structured metal mold 10 capable of preliminarily heating is filled with high pressure fluid while it is being kept in a state reduced from a final molding product size. Then, while synthetic resin to which a foaming agent is preliminarily added is being casted into the cavity 16 of the metal mold 10, the high pressure fluid is discharged at a suitable point of time including before and after the casting. Thereafter, the volume of the cavity 16 is enlarged to a size larger than the final molding product size while the casted synthetic resin is foamed. The cavity volume of the metal mold 10 is reduced to a required final molding product size while a solid skin layer formed on a surface of the molded material keeps flexibility.

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 highly foamed synthetic resin and a molded article molded by the molding method.

[0002]

2. Description of the Related Art In order to produce a synthetic resin foam, a method is used in which a synthetic resin as a raw material is mixed with a foaming agent for molding, or a granular material prepared by previously mixing a synthetic resin raw material with a foaming agent, A bead molding method is known in which a foamed molded product is obtained from so-called expanded particles. It has been pointed out that these molding methods have the following drawbacks as compared with ordinary injection molding methods.

(1) Fusion lines between particles are likely to appear in the appearance, and the appearance is impaired. (2) Long molding cycle. (3) Energy loss is large due to repeated heating and cooling of the mold. (4) Poor mechanical strength and dimensional stability. (5) With the injection of the molten resin into the mold cavity, pressure release occurs, premature foaming occurs at the flow front, and a swirl pattern occurs.

The expanded particles that have been widely used in the past are mainly general-purpose resins such as styrene and polystyrene, and their applications are mainly cushioning materials and heat insulating materials. On the other hand, a technique for forming a foam using a functional resin, that is, an engineering plastic as a raw material has been attracting attention. As is well known, engineering plastics
Excellent heat resistance, wear resistance, toughness, etc.
It is a material that is being widely used as an alternative material for glass, ceramics, wood, and the like.

The foamed molded article made of such an engineering plastic is required to have heat resistance and mechanical strength in addition to its intended purpose of heat insulation, cushioning, insertion, etc. in conventional general-purpose plastics. It can be applied as a structural material for various office machines, automobiles and other equipment, a cushioning material, and a heat insulating material for buildings.

The foamed molded article made of such an engineering plastic has a high melting temperature of the resin material and is difficult to mold as compared with a general-purpose resin. In particular, in injection molding, the flow of resin becomes extremely poor, and the appearance of molded products tends to be poor. In order to eliminate such drawbacks, a so-called counter pressure method is known in which the inside of the mold cavity is pressurized with a high-pressure fluid before the injection of molten resin. It is difficult.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art and provides an injection-molding method of a high-foaming molded article, which is capable of obtaining a high-foaming molded article having an excellent surface appearance, and the molding. It is an object to provide a molded product molded by the method.

[0008]

The injection molding method according to the present invention is a process of filling a cavity volume of a mold which has an airtight structure and can be preheated with a high pressure fluid while keeping the cavity volume smaller than that of the final molded product. In the cavity of the mold,
A process of injecting a synthetic resin to which a foaming agent has been added, and discharging the high-pressure fluid at appropriate points before and after the injection.
A step of expanding the volume of the cavity beyond the size of the final molded product while the injected synthetic resin is foaming; the mold while the solid skin layer formed on the surface of the molded body maintains flexibility. Changing the cavity volume to a desired final molded product size; and a high-foam injection molding method, and a molded product molded by the high-foam injection molding method.

[0009]

The injection molding method according to the present invention uses a mold having an airtight structure. The cavity of this mold is held in a smaller volume than the molded product to be manufactured, preheated while being filled with high-pressure fluid, and molten resin is injected. In this case, as the raw material of the molten resin, synthetic resin raw material in which a foaming agent is appropriately mixed or synthetic resin foamed particles (beads) in which the foaming agent is mixed in a predetermined ratio is used.

According to the high-foam injection molding method of the present invention, the volume of the mold cavity is reduced when the molten resin is injected, and the mold cavity is filled with a high-pressure fluid such as nitrogen or other inert gas or liquid. Has been done. Therefore, premature foaming due to pressure release when the molten fluid under pressure is injected into the cavity is prevented, and a semi-molded product having a solid skin layer having a good surface appearance and smaller than the final molded product is formed. .

The high-pressure fluid is discharged out of the cavity at the same time as the injection of the molten resin is completed, or immediately before or after the injection is completed. Thereafter, while the mold is being cooled, the cavity is expanded to a volume corresponding to a desired molded product size or a slightly larger volume while the solid skin layer of the molded body still maintains flexibility. With the expansion of the cavity, the foaming gas inside the molded body expands until the solid skin layer contacts the inner wall of the cavity. During this time, the free space due to the foaming gas inside the molded body expands, and the internal elements in the direction of increasing the volume have a frame web structure, and the mechanical strength such as compressive strength and rigidity is improved.

Although a molded product having an excellent appearance can be obtained by the primary expansion of the cavity as described above, the cavity is once expanded slightly larger than the final size of the molded product and then slightly compressed. As a result, the mold cavity transferability and the dimensional accuracy stability can be further improved, and at the same time, the mechanical strength can be improved. Through these processes, the solid skin layer and the foam core layer of the material in the mold cavity are sufficiently cooled and solidified, and then taken out from the mold. The obtained molded product is capable of foaming at a high magnification of 1.5 to 20 times, and the mechanical properties can be significantly improved.

[0013]

The present invention will be disclosed below with reference to the accompanying drawings showing the embodiments. 1 to 3 show an embodiment of an apparatus suitable for carrying out the high foam injection molding method according to the present invention. In FIG. 1, the mold 10 comprises a fixed mold 12 and a movable mold 14. A cavity 16 is provided at the joint between the two molds and communicates with a gate 18 for injecting the molten resin. Since the cavity formed by both molds needs to be kept airtight, a seal 20 is provided between them.

Further, a fluid pipe 24 from a high pressure fluid generator 22 is connected to the cavity 16 via a solenoid valve 26 and a pressure switch 28. As the working fluid in this case, a liquid such as an inert gas such as nitrogen gas or argon gas can be used.

FIG. 4 is a flow chart showing a series of operations of the high foaming injection molding method according to the present invention. In this flow, in step S1, the mold 10 is preheated and a high pressure fluid is injected. During this time, the cavity volume is reduced below the desired compact size.

Then, after confirming that the mold temperature determined by various conditions including the type of raw material resin has been reached and the pressure inside the cavity has increased, the resin mixed with the foaming agent or the foaming agent in advance as in step S2. A melt of synthetic resin foamed particles containing is injected from a nozzle. The high-pressure fluid in the cavity is discharged before and after the completion of the resin injection or at the same time as the completion of the resin injection (step S2 ′). In response to such resin injection and discharge of the high-pressure fluid, the molten resin flows to the end of the cavity, forming a semi-molded body in contact with the entire cavity wall.

When the solid skin layer of the semi-molded resin in the cavity of the mold is not completely solidified,
The cavity volume is expanded as in step S3. This operation moves the movable mold 14 to the interval m in the X direction as shown by the arrow 30 in FIG.
Extend to. The volume expansion ratio in this case is determined by the cavity volume formed by the movement of the movable mold 14,
It is selected in a range that is slightly larger than the desired molded product size.

Further, after a lapse of a predetermined time, the volume of the mold cavity is compressed as in step S4. This behavior is
As indicated by an arrow 32 in FIG. 3, the movable mold 14 is moved in the −X direction as indicated by an arrow 32 to the interval n, and the cavity volume is reduced to the interval 1. The cavity volume at the final stage of this volume compression is controlled so as to have a desired size of the molded article to be obtained.

By such an operation, a high-magnification foamed molded article having excellent mechanical strength and dimensional stability, good cavity transferability, and excellent smoothness and appearance can be obtained. FIG. 5 is a model cross-sectional view of a molded product formed by the molding method according to the present invention. A solid skin layer SS having an appropriate thickness is formed on the surface, and a frame web structure FW is formed in the inner core layer along the X direction moved by the mold. The solid skin layer SS has a sufficient mechanical strength and has a good surface appearance. Therefore, in addition to a heat insulating material, a cushioning material, and the like peculiar to the foam, it can be used as an exterior material for various devices or devices. Further, the frame web structure FW of the inner core layer is appropriately foamed, and a reinforcing effect can be expected in terms of strength.

The mold and high-pressure fluid generator as described above were set in a molding machine equipped with a shut-off nozzle device with a mold clamping force of 150 T for manufacturing at Japan Steel Works, and molding was carried out. The mold size is 150 mm x 325 mm x 5 m
m.

The raw material for this molding is modified PPE.
Foamed bead material GESET F300 (trade name, manufactured by Huntsman Chemical Corporation) based on (polyphenylene ether) was used.

In each of the above constructions, the mold temperature is set to 80-9.
The temperature was maintained at 0 ° C., and nitrogen gas was further injected into the mold cavity having a thickness of 5 mm at a pressure of 13 kg / cm ₂ to 15 kg / cm ² . Then, the melt of the synthetic resin foamed particles was injected from a nozzle, and nitrogen gas was discharged at the same time when the injection of a predetermined amount was completed. Then, while the solid skin layer of the semi-molded body in the mold maintained flexibility, the mold clamping unit of the molding machine was controlled to retreat to 10 mm, 15 mm, 20 mm to expand the cavity volume.

Further, after a predetermined time, the mold clamping device of the molding machine was operated for several mm to compress the cavity volume and thus the compact. The total molding cycle time for the above construction and raw materials was 60 to 120 seconds.

In the expanded beads used in this example, a highly expanded molded product having an expansion ratio of 2 to 5 and excellent smoothness and good appearance was obtained. Further, it was confirmed that the specific compressive strength was also improved by 20 to 30% as compared with the conventional foamed molded product. According to the findings obtained in this example, it was expected that a better foaming molded article with higher magnification could be obtained by improving the molding conditions and selecting the resin raw material to be used.

[0025]

According to the method for injection-molding a high-foam product according to the present invention, it is possible to obtain a high-foaming product having excellent smoothness and good appearance. Therefore, it can be applied to a new application which has been difficult to apply with a conventional foamed molded article. In this case, the molding cycle is shortened to about 1/2 to 1/3 as compared with the conventionally performed foam molding method, and the energy consumption associated with the mold temperature control is significantly reduced.

According to the injection molding method of the present invention, by adopting the above-mentioned mold and high-pressure fluid generating device, it is possible to use a normal injection molding machine or a pre-plastic molding machine. .

The molded product molded by the method shown here has excellent surface appearance and smoothness, and can be applied to exterior parts. This is because the dimensional accuracy is improved, and the inner foam core layer formed when the mold cavity is expanded functions as a frame web and maintains sufficient mechanical strength. Therefore, it can be expected to have a wide range of applications in which effects such as a cushioning material and a heat insulating material are added to the applications as various structural members.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a configuration of a mold and a high-pressure fluid system for carrying out a method for molding a high foam according to the present invention.

FIG. 2 is an explanatory view showing an expanded state of a cavity of a mold for carrying out the method for molding a high foam according to the present invention.

FIG. 3 is an explanatory view showing a compressed state of a cavity of a mold for carrying out the method for molding a high foam according to the present invention.

FIG. 4 is a flow diagram showing an operating state for carrying out the method for molding a high foam according to the present invention.

FIG. 5 is a cross-sectional view showing a structural example of a molded product formed by the method for molding a high foam according to the present invention.

[Explanation of symbols]

 10 Mold 12 Fixed Mold 14 Movable Mold 16 Cavity 18 Nozzle 20 Seal 22 High Pressure Fluid Generator 24 Fluid Passage 26 Solenoid Valve 28 Pressure Switch SS Solid Skin Layer FW Frame Web Structure

Claims (2)

[Claims] 1. A method for injection-molding a high-foam synthetic resin, comprising: a high-pressure fluid while maintaining a cavity of a mold having an airtight structure and capable of being preheated in a state where its volume is smaller than that of a final molded product. Filling step (S1) with the step (S1); step (S2, S2 ′) of injecting the synthetic resin to which the foaming agent has been added into the cavity of the mold, and discharging the high-pressure fluid at an appropriate time point before and after the step. A step of expanding the volume of the cavity beyond the size of the final molded product while the injected synthetic resin foams (S3); while the solid skin layer formed on the surface of the molded body maintains flexibility. An injection molding method for a high-foam body, comprising the steps of reducing the cavity volume of the mold to a size corresponding to a desired final molded product (S4); 2. A solid skin layer (SS) is formed on the surface, and a frame web structure (FW) is formed inside.
A molded article molded by the injection molding method for a high foam according to claim 1.