JPH11277575A - Production of foamed resin molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the pressure of a cavity to a level which causes a molten resin to foam and thereby, generate a foam in the molten resin by first forming a skin layer, then moving a movable half of a mold backward and expanding the volume of the cavity. SOLUTION: The volume of a cavity 2a is diminished by advancing a movable half 2 of a mold with the cavity 2a to a fixed half 1, and the interior or the cavity 2a is pressurized to a foaming suppression pressure level. After that, a molten resin containing a foaming agent is injected into the cavity 2a, then the resin coming into contact with the inner face of the cavity 2a, is cured by cooling, and a skin layer is molded. After these steps, the volume of the cavity 2a is expanded by moving the movable half 2 backward and thus the interior pressure of the cavity 2a is lowered to a level which causes the foaming of the resin, so that the molten resin inside the skin layer develops a foam. Consequently, it is possible to mold a core consisting of a foam layer and dispense with a pressurizing means to be installed inside the mold. After all, the structure of the mold can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a foamed resin article having a skin layer on the surface.

[0002]

2. Description of the Related Art Conventionally, a method and an apparatus for molding a molded article whose interior is formed of a foam and whose surface is covered with a skin layer are disclosed in, for example, JP-A-63-281810 and JP-A-9-199927. Japanese Patent Application Laid-Open Publication No. H10-209, etc. are publicly known.

[0003] "Forming method of foam molding material" in the former publication
Injects molten foamable resin while applying gas pressure to the mold cavity at a pressure that can suppress foaming of the foamable resin, and then lowers the gas pressure to atmospheric pressure to foam the molten resin inside. At the same time, a predetermined portion of the mold cavity is pressurized at a predetermined timing, and the resin before complete solidification is pressed against a predetermined portion in the cavity.

The "compression device" disclosed in the latter publication forms an operating chamber communicating with the cavity outside a cavity for molding a molded product, and an operating element provided in the operating chamber when the movable mold portion is closed. To pressurize the gas medium in the working chamber, and pressurize the inside of the cavity by supplying the pressurized gas medium to the cavity via or without the intermediate storage unit, and pressurize the resin. It is characterized by suppressing foaming.

[0005]

The molding method and apparatus disclosed in the above publications employ a counter pressure method in which the inside of a cavity is pressurized to a high pressure with air or a gas medium to suppress foaming of a foaming agent-containing resin. I have.

However, in this counter pressure method, since the inside of the cavity is pressurized with high-pressure air or a gas medium, a means for generating high pressure is required in the mold, and the structure of the mold is complicated and expensive. is there.

[0007] Further, since it takes time until the inside of the cavity is set to a predetermined pressure, there is also a problem that the molding cycle becomes long and the productivity is poor.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem, and has as its object to provide a foam molding method of a molded article which does not require a complicated mold and has high productivity. is there.

[0009]

According to the first aspect of the present invention, a movable mold having a cavity is advanced with respect to a fixed mold to reduce the volume of the cavity. The inside of the cavity is pressurized to the foam suppression pressure, then the molten resin containing the foaming agent is injected into the cavity, and the resin that comes into contact with the inside of the cavity is cooled and hardened to form the skin layer first, and then the movable mold By retracting to increase the volume of the cavity,
By reducing the pressure inside the cavity to a foamable pressure and foaming the molten resin inside the skin layer, a core layer composed of a foamed layer is formed.

According to the above method, the inside of the cavity can be pressurized to the foaming suppression pressure without providing a pressurizing means in the mold in advance, so that the structure of the mold is simplified and
It is also possible to reduce the size of the mold.

Further, since the pressure in the cavity can be increased to the foaming suppression pressure in a short time, the molding cycle can be shortened.

In order to achieve the above object, according to the second aspect of the present invention, the movable mold having the cavity is advanced with respect to the fixed mold to reduce the volume of the cavity, thereby enclosing the cavity in the cavity in advance. By applying a gas above the normal pressure and below the foam suppression pressure to the foam suppression pressure, then injecting a molten resin containing a foaming agent into the cavity, and cooling and curing the resin that contacts the inside surface of the cavity. By molding the skin layer and then retracting the movable mold to expand the volume of the cavity, the molten resin inside the skin layer is foamed to form a core layer made of a foamed layer. .

According to the above method, the inside of the cavity can be pressurized to the foaming suppression pressure without providing a pressurizing means in the mold in advance, so that the structure of the mold is simplified and
It is also possible to reduce the size of the mold.

[0014] Also, at least normal pressure sealed in the cavity,
Since the gas below the foaming suppression pressure is pressurized to the foaming suppression pressure by the movable mold, the pressurizing time can be greatly reduced.

In order to achieve the above object, the invention according to claim 3 is characterized in that a movable mold having a cavity is advanced with respect to a fixed mold while reducing the volume of the cavity.
By injecting a molten resin containing a foaming agent into the cavity and cooling and curing the resin that comes into contact with the inner surface of the cavity, the skin layer is first formed, and then the movable mold is retracted to expand the volume of the cavity. In addition, a core layer made of a foamed layer is formed by foaming the molten resin inside the skin layer.

According to the above method, the inside of the cavity can be pressurized to the foaming suppressing pressure without providing a pressurizing means in the mold in advance, so that the structure of the mold is simplified and
It is also possible to reduce the size of the mold.

Further, since the molten resin is injected into the cavity while the movable mold is advanced and the inside of the cavity is pressurized, the pressurizing time can be shortened and the productivity is improved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described in detail with reference to the drawings shown in FIGS. 1 to 5 show a molding process of a molded product. In these figures, 1 denotes a fixed mold, 2 denotes a movable mold, and 3 denotes an injection nozzle.

The fixed mold 1 has a substantially convex cross section, and is fixed to an injection molding machine (not shown) so that a flange 1a protruding from one end face is vertical. One end of a sprue 1c is opened in a concave portion 1b formed substantially at the center, and the injection nozzle 3 is connected to the opening of the sprue 1c.

The other end of the sprue 1c has a diameter gradually increasing. The other end of the sprue 1c is open to the other end surface of the fixed mold 1, and the movable mold 2 is provided on the outer periphery of the fixed mold 1. Are slidably fitted in the horizontal direction.

The movable mold 2 is formed to have a substantially convex cross section having a cavity 2a therein, and the other end of the fixed mold 1 is fitted into an opening of the cavity 2a opened at one end. By moving the movable mold 2 with respect to the fixed mold 1 in the horizontal direction, the volume of the cavity 2a can be changed.

In order to maintain the airtightness in the cavity 2a, a sealing means 4 such as an O-ring is interposed between the stationary mold 1 and the sliding surfaces 1d and 2b of the movable mold 2, and the movable mold 2 is movable. On the other end side of the mold 2, a flange portion 2c is provided so as to be attached to a mold closing means (not shown) of the injection molding machine.

Next, a method for molding a molded article using the above-configured foaming mold will be described.

In molding a molded product, the movable mold 2 is first retracted to the position shown in FIG.

In this position, the cavity 2a of the movable mold 2 is
Has the largest volume.

Next, in this state, an inert gas, for example, air or nitrogen gas, having a pressure not lower than the normal pressure and not higher than the foaming suppressing pressure is injected into the cavity 2a. The injection nozzle 3 is connected to the section.

When air at normal pressure is used as the inert gas, the step of injecting the inert gas becomes unnecessary.

Next, the movable mold 2 is advanced to the position shown in FIG. 2 by the mold closing means to pressurize the inert gas in the cavity 2a and to maintain the inside of the cavity 2 at the foaming suppressing pressure.

In this state, as shown in FIG. 3, a molten resin containing a foaming agent is injected from the injection nozzle 3 into the cavity 2a through the sprue 1c at a pressure sufficiently higher than the pressure in the cavity 2a, for example, 300 to 300. When injected at 400 kg / cm ² , the molten resin injected into the cavity 2a is prevented from foaming by the foaming suppression pressure in the cavity 2a, and as shown in FIG. After being cooled and cured, the skin layer 5a of the molded article 5 is first molded.

Thereafter, as shown in FIG. 5, when the retreat of the movable mold 2 is started, the pressure in the cavity 2a is reduced to a pressure at which foaming is possible due to the expansion of the volume of the cavity 2a. Starts foaming.

Then, the movable mold 2 is retracted to the molded product shape position and stopped at that position, and the position is maintained until foaming is completed.
The movable mold 2 is retracted to a position where the mold 2 is released, and the cavity 2a is opened.
a, the movable mold 2 is moved to pressurize the cavity 2a to a high pressure.
It is not necessary to separately provide a pressurizing means for pressurizing the inside of the mold a. This simplifies the structure of the mold and pressurizes the inside of the cavity 2a to a high pressure in a short time. It can also be shortened.

In the first embodiment, the movable mold 2 is moved forward to pressurize the inside of the cavity 2a to a pressure at which foaming can be suppressed, and then the molten resin is injected into the cavity 2a. As in the second embodiment shown in FIG. 10, the movable mold 2 is advanced to inject the molten resin containing the foaming agent into the cavity 2a while pressurizing the inside of the cavity 2a to the foam suppression pressure. You may do so.

Next, the method will be described.

The mold to be used is the same as that of the first embodiment, and a description thereof will be omitted.

When the inert gas is injected into the cavity 2a with the movable mold 2 retracted to the position shown in FIG.
The injection nozzle 3 is connected to the small diameter side opening of the sprue 1c,
Next, as shown in FIG. 7, the movable mold 2 is advanced to pressurize the inert gas in the cavity 2a.

When the pressure of the inert gas reaches a pressure close to the foaming suppression pressure of the molten resin, the sprue 1
7C, the molten resin containing the foaming agent is injected into the cavity 2a as shown in FIG.
Is advanced to the position shown in FIG. 8 to pressurize the inside of the cavity 2a to the foam suppression pressure.

The molten resin injected into the cavity 2a is first cooled and hardened in the portion in contact with the inner surface of the cavity 2a while suppressing foaming, thereby forming the skin layer 5a.

After that, as shown in FIG. 9, when the movable mold 2 is retracted, the pressure in the cavity 2a is reduced to a pressure at which foaming is possible, so that the molten resin inside the skin layer 5a starts foaming and is movable. The mold 2 is retracted to the molded product shape position and held at that position. When the foaming of the molten resin is completed and the core layer 5b formed of the foamed layer is formed in the skin layer 5a, the movable mold 2 is opened and the cavity 2a is opened.
The molded product 5 is taken out from the inside.

In the above embodiment, no means for adjusting the pressure in the cavity 2a has been described. However, as shown in FIG.
The pressure in the cavity 2a can be adjusted by piercing the passage 2d communicating with the hole a and providing the pressure adjusting means 7 in the opening on the atmosphere side of the passage 2c.

That is, by setting the upper limit of the foaming suppression pressure in the cavity 2a in advance by the pressure adjusting means 7, when the foaming suppression pressure in the cavity 2a exceeds the upper limit, the pressure adjusting means 7 controls the inside of the cavity 2a. Is released, it is possible to prevent the pressure in the cavity 2a from exceeding the upper limit of the foaming suppression pressure.

When the pressure in the cavity 2a escapes from the connection surface of the injection nozzle 3 by using the opening on the small diameter side of the sprue 1c, it can be opened and closed by an actuator 8 such as an air cylinder in the middle of the sprue 1c as shown in FIG. The opening / closing means 9 may be provided so that the opening / closing means 9 is opened only when the molten resin is injected.

[0042]

As described in detail above, the present invention moves the movable mold relative to the fixed mold to reduce the volume of the cavity, thereby pressurizing the inside of the cavity to the foaming suppression pressure. Inject the molten resin containing the foaming agent into the cavity, first form the skin layer, then retract the movable mold, and expand the cavity volume to reduce the pressure to the pressure at which the cavity can be foamed. Since the molten resin is foamed in this manner, the inside of the cavity can be pressurized to the foaming suppression pressure without providing a pressurizing means in the mold as in the related art.

This simplifies the structure of the mold, and
Since the mold can be downsized, the cost of the mold can be significantly reduced.In addition, the cavity can be quickly pressurized just by moving the movable mold forward. Can improve productivity.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method for molding a foamed resin molded product according to a first embodiment of the present invention.

FIG. 2 is a process chart showing a method for molding a foamed resin molded product according to the first embodiment of the present invention.

FIG. 3 is a process chart showing a method for molding a foamed resin molded product according to the first embodiment of the present invention.

FIG. 4 is a process chart showing a method for molding a foamed resin molded product according to the first embodiment of the present invention.

FIG. 5 is a process chart showing a method for molding a foamed resin molded product according to the first embodiment of the present invention.

FIG. 6 is a process chart showing a molding method of a foamed resin molded product according to a second embodiment of the present invention.

FIG. 7 is a process chart showing a method for molding a foamed resin molded product according to a second embodiment of the present invention.

FIG. 8 is a process chart showing a method for molding a foamed resin molded product according to a second embodiment of the present invention.

FIG. 9 is a process chart showing a method for molding a foamed resin molded product according to a second embodiment of the present invention.

FIG. 10 is a process chart showing a molding method of a foamed resin molded product according to a second embodiment of the present invention.

FIG. 11 is an explanatory diagram showing an embodiment in which a movable mold is provided with pressure adjusting means.

FIG. 12 is an explanatory diagram showing an embodiment in which a sprue of a movable mold is provided with opening / closing means.

[Explanation of symbols]

 Reference Signs List 1 fixed mold 1a flange 1b recess 1c sprue 1d sliding surface 2 movable mold 2a cavity 2b sliding surface 2c flange 2d passage 3 injection nozzle 4 sealing means 5 molded product 5a skin layer 5b core layer 7 pressure adjusting means 8 Actuator 9 Opening / closing means

Claims (3)

[Claims] 1. A movable mold having a cavity is advanced with respect to a fixed mold to reduce the volume of the cavity to pressurize the inside of the cavity to a foaming suppressing pressure, and then include a foaming agent in the cavity. First, the skin layer is formed by injecting the molten resin and cooling and hardening the resin that comes into contact with the inner surface of the cavity, and then the movable mold is retracted to expand the volume of the cavity, thereby forming the molten resin inside the skin layer. A method for molding a foamed resin molded article, characterized in that a core layer composed of a foamed layer is molded by foaming. 2. A movable mold having a cavity is advanced with respect to a fixed mold to reduce the volume of the cavity, so that a gas previously filled in the cavity and having a pressure equal to or higher than normal pressure and equal to or lower than the foaming suppression pressure is reduced. Pressurize to the foam suppression pressure, then inject the molten resin containing the foaming agent into the cavity, cool and cure the resin that contacts the inside surface of the cavity, first form the skin layer, and then retract the movable mold A method for forming a foamed resin molded product, comprising: forming a core layer composed of a foamed layer by expanding a volume of a cavity to foam a molten resin inside a skin layer. 3. A movable mold having a cavity is advanced with respect to a fixed mold, and a molten resin containing a foaming agent is injected into the cavity while reducing the volume of the cavity, thereby making contact with the inner surface of the cavity. First, the skin layer is formed by cooling and curing the resin to be formed, and then the movable mold is retracted to expand the volume of the cavity, thereby foaming the molten resin inside the skin layer, thereby forming a core layer composed of a foamed layer. A method for molding a foamed resin molded article, characterized by molding.