JPH0976297A - Injection molding method of foamed plastic molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively manufacture a foamed plastic molding, satisfying required durability and having excellent appearance. SOLUTION: A molten resin is injected into a cavity from a nozzle 305 of an injection molding machine and, immediately thereafter, compressed air is supplied from a pipeline 306 into an injection molding die 300. The pressure of the compressed air is exerted as a foaming restraining force with respect to the molten resin in the cavity. In this case, a proper foaming restraining force is exerted quickly in areas 303a, 304a, having a large porocity, whereby the foaming of the molten resin can be restrained effectively and the foamed body of a high density, which is provided with fine bubbles, can be formed. At the same time, a proper foaming restraining force is exerted gradually on areas 304b, 304b, having a small porocity, whereby foaming of the molten resin is advanced smoothly and the foamed body of a low density, which is provided with fine bubbles, can be molded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method suitable for molding a foamed plastic molded article having regions having different densities.

[0002]

2. Description of the Related Art As a method for producing a synthetic resin foam molded article, a foam injection molding method described in JP-A-59-10134 is known. This method is an application of the counter pressure method developed in the United States in 1963. According to this method, a foam injection-molded article having a uniform foam structure with a good surface condition without a sink mark is obtained. Can be created. Specifically, the molten synthetic resin is injected into the mold filled with gas (air, etc.) to about 1.5 MPa in advance, and the contact portion of the synthetic resin with the inner surface of the mold, that is, the surface of the foam injection molded product is cured. In this state, the inside of the mold is depressurized to the atmospheric pressure to foam and cure the uncured portion of the synthetic resin.

By the way, since the foam-molded article manufactured by this method has a uniform foam structure, the region having the threaded portion is made thicker in order to secure the strength than other regions. Tend to be designed. For example, if this is a product in which the design of the shape is important, the value of the product will be impaired, and if it is an essential component for a device or the like that is desired to be downsized. This is one of the causes of inconvenience in device design.

Alternatively, if a high-strength metal fitting or the like is inserted into such a portion, the required strength can be obtained, but since a new step is added for that purpose, there is a problem that the manufacturing cost increases accordingly. Occurs.

As a technique for solving such a problem, there is known a method of manufacturing a heat insulating unit case for a car cooler by reaction injection molding described in JP-A-61-59207. This method manufactures a foam-molded article of synthetic resin having regions having different foam structures, that is, different density regions, by controlling the temperature of the mold. According to this method, for example, a low-density portion having a heat insulating property (heat insulating portion), such as an automobile air conditioner housing,
A foamed product that requires a high-density portion (mounting bracket) that requires strength can be integrally molded in one shot.

In addition to this, a manufacturing process of microcellular plastic (hereinafter referred to as MCP) developed by Massachusetts Institute of Technology (hereinafter referred to as MIT) in the United States is known. In this, the synthetic resin is hardened with almost no foaming in the surface area, while the inner area is hardened while forming fine foamed cells by the inert gas previously dissolved. According to this process, it is possible to manufacture a small foam-molded article having excellent mechanical properties. Also, there is no need to use a chemical blowing agent. In addition, regarding this process, US Pat.
No. 0,674, but no mention is made of a practical device configuration for implementing this process.

[0007]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No. Sho 61
In the method described in Japanese Patent No. 59207, the cooling rate of the molten resin is remarkably different partially, so that the internal state of the foamed molded product, that is, the degree of crystallinity and the size of crystal grains become non-uniform. Therefore, this method has a drawback in that the glossiness of the surface of the foamed molded product is often partially lost. Further, in order to finish the surface of the foam-molded product smoothly, it is desirable to include fine bubble cells inside, but since this method does not control the foaming state when the molten resin is cured, There is a defect that the surface of the molded product, particularly the surface of the fine low density portion, is rough.

By the way, since the difference in the cooling rate of the molten resin causes the difference in the molding shrinkage, there is a high possibility that residual stress is generated inside the foamed molded product. Therefore, there is a drawback that cracks and the like are likely to occur inside the foamed molded product molded by this method. Further, since the high-density portion of the foam-molded product is hardened and molded before the crystallization is sufficiently progressed by rapid cooling, the strength of the finally obtained high-density portion is limited. For example, the impact strength of the high density part of this foam molded product is about 20 kgf · m / cm ²
It is. Therefore, the durability suitable for the purpose of use may not be secured in some cases.

Further, in the present method, in order to form a low temperature portion for molding a high density portion in the cavity, it is necessary to perform a preparatory work such as mounting an insert piece that has been appropriately cooled in advance in the cavity. Therefore, there is a drawback that it takes a long time from the start of work to the molding of the foam-molded article. That is, the production line of the foam-molded product adopting this method has poor production efficiency.

Therefore, it is an object of the present invention to provide an injection molding method capable of efficiently producing a foamed plastic molded product which satisfies the required durability and looks good.

[0011]

In order to achieve the above object, the present invention is an injection molding method in which a foamable melted resin is filled in a cavity inside a mold and cured to form a foamable plastic molded article. In the method, a cavity formed of a porous material having a porosity distribution according to a desired density distribution of the foamed plastic molded product is prepared as the cavity inside the mold, and the foam is formed inside the cavity. The step of injecting gas into the gap between the mold and the cavity while injecting a soluble resin, and the pressure inside the die caused by the gas being injected into the gap between the mold and the cavity. While holding, cooling and curing the foamable melted resin filled in the cavity by injecting the foamable melted resin into the cavity. To provide an injection molding method characterized by comprising

[0012]

According to the method of injection molding a foamed plastic molded article according to the present invention, the foamable melted resin filled in the cavity by the injection of the foamable melted resin into the cavity is Cooling and curing are performed in a state where the pressure inside the mold, which is generated by the pressure injection of gas into the gap between the mold and the cavity, is maintained. That is, the molten resin filled in the cavity formed of the porous material having the porosity distribution according to the intended density distribution of the expandable plastic molded product is The distributed pressure acts as a foam suppression force. Therefore, a foamed plastic molded product having a foamed state that achieves a desired density distribution can be efficiently molded in one shot. Also,
At this time, since the injection molding method according to the present invention does not require special preparations and the like, it is possible to finish the molding of the foamed plastic molded product in a molding time which is not much different from that of normal injection molding. That is, according to the present injection molding method, it is possible to efficiently mold a foamed plastic molded product having a desired density distribution.

Further, since the cooling rate at the time of hardening the molten resin is substantially constant as a whole, the difference in molding shrinkage inside the foamed plastic molded article is reduced, and the internal crystallinity and the size of the crystal grains are reduced. Can be in a substantially uniform state.
Further, since an appropriate foaming suppressing force acts on the molten resin filled in the cavity, the bubble cells contained in the foamed plastic molded product are in a finer state. That is, according to this injection molding method, durability, particularly excellent impact resistance,
In addition, it is possible to efficiently mold a foamed plastic molded product having a surface in a good state.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First, a nozzle 100 of a household cleaner, which is an example of a foamed plastic molded product manufactured by the injection molding method according to this embodiment, will be described with reference to FIGS. 1 and 2. In this example, ABS resin in which carbon dioxide gas was dissolved was used as a molding material.

Now, in the nozzle 100 of the household cleaner, both end portions 100a of the nozzle, which is a joint portion with other parts, have appropriate strength, and the user does not feel uncomfortable during use. It needs to be lightweight. In order to achieve this, the nozzle 100 of the household vacuum cleaner shown in FIG. 2 is molded so that the inside thereof has an appropriate density distribution, that is, an appropriate foam structure, which satisfies the required strength and the degree of weight reduction. ing. That is, the nozzle 100 of the household cleaner of FIG. 1 is molded so that both end portions 100a of the nozzle have a density (about 700 to 850 kg / m ³ ) that can secure the strength required as a joint portion with other parts. In addition, the nozzle middle portion 100b is formed to have the minimum density (about 550 to 650 kg / m ³ ) that can secure the strength enough to endure general use at home. However, in order to determine the density distribution inside the foamed plastic molded product in this way, it is necessary to mold the foam with the molding material used and evaluate the relationship between the density and strength of the foam in advance. (See FIG. 2).

Although the ABS resin in which carbon dioxide gas is dissolved is used as the molding material in this embodiment, a thermoplastic resin in which other inert gas is dissolved may be used. For example, PP resin or PS in which nitrogen gas is dissolved
You may use resin etc.

Next, the nozzle 10 of such a household vacuum cleaner
The basic structure of the injection molding die for manufacturing 0 will be described with reference to FIG. The injection molding die shown here can be attached to a generally used injection molding machine. It should be noted that here, a device for ejecting a molded product, a cooling device for adjusting the temperature inside the cavity, a mounting portion for mounting the fixed-side mold plate 301 of the mold base on a fixed plate of the injection molding machine, and a movable mold base. A general structure to be provided as an injection molding die, such as a mounting portion for mounting the side mold plate 302 on a movable plate of an injection molding machine, is not shown.

The feature of the injection molding die 300 is that a cavity composed of a cavity block 303 and a core block 304 made of a porous metal having an appropriate porosity determined by the density of a desired foamed plastic molded product is formed. Be prepared. As a substitute for the porous metal used here, other porous materials such as ceramics formed to have pores inside may be used.
Now, in this embodiment, since the inside of the nozzle 100 of the household vacuum cleaner, which is a target molded product, needs to have the density distribution as described above, this cavity is formed in the household vacuum cleaner which is a molded product. Regions 303a, 303b, 304a formed of porous metal having different porosities so as to have a porosity distribution according to the density distribution inside the nozzle 100,
304b continuously. The structure of such a cavity will be described in more detail with reference to FIG.
Region 3 for molding high-density nozzle end portions 100a
03a and 304a have a low density nozzle intermediate portion 100b.
A porous metal having a porosity larger than those of the regions 303b and 304b for molding is used. The specific porosity value takes into consideration a predetermined density distribution of the molded product, a cooling rate determined according to the material of the molten resin, and a pressure generated by the supply of compressed air from a pipe 306 described later. Needs to be decided.

The inside of the cavity is filled with the molten resin injected from the nozzle 305 of the injection molding machine joined to the sprue by being guided by the runner 306. Further, inside the injection molding die 300, a direction (arrow B in the figure) opposite to the direction of injection of molten resin from the pipe 306 into the cavity (the direction indicated by arrow A in the figure).
Compressed air is supplied from the direction indicated by. Although compressed air is supplied from the pipe 306 in the present embodiment, other inert gas such as nitrogen gas may be injected under pressure.

Above, the description of the basic structure of the injection molding die is completed, and then the injection molding processing method using such an injection molding die will be described. In addition,
It is assumed that the ABS resin, which is a molding material, is previously heated and fluidized in the cylinder of the injection molding machine.

Molten resin is injected into the cavity from the nozzle 305 of the injection molding machine, and immediately thereafter, compressed air is supplied from the pipe 306 into the injection molding die 300. When compressed air is supplied to the inside of the injection molding die 300 in this way, the pressure exerted by the compressed air is filled in the cavity because the cavity is made of porous metal as described above. It acts as a foam suppression force for the molten resin. Therefore, inside the regions 303a and 304a formed of a porous metal having a large porosity, an appropriate foaming suppressing force quickly acts on the filled molten resin, so that the foaming of the molten resin during curing is effective. Will be suppressed. On the other hand, inside the regions 6b and 7b formed of a porous metal having a small porosity, an appropriate foaming suppressing force gradually acts on the filled molten resin, so that the foaming of the molten resin at the time of curing is smooth. Proceed to. As a result, in the present embodiment, inside the regions 303a and 304a formed of the porous metal having a large porosity, a high-density foamed plastic having a small amount of foaming containing fine foam cells is formed, and at the same time, Inside the regions 304b and 304b formed of a porous metal having a small porosity, a low-density foamed plastic having a large amount of foaming and containing fine foamed cells is formed.

As described above, according to the injection molding method of this embodiment, a foamed plastic molded product having a desired density distribution can be efficiently molded in one shot.
Further, at this time, since no special preparations and the like that require labor are required, the molding of the foamed plastic molded product can be completed within a molding time which is not much different from that of normal injection molding.

Now, comparing the foamed plastic molded product molded by the injection molding method according to this embodiment with the foamed plastic molded product molded by the method described in the section of the prior art, the former is as follows. The surface condition is better than that of the latter, and the durability, particularly impact resistance (impact strength is about 2 to 3 times), is excellent. This is because, firstly, in the injection molding method, the cooling rate at the time of curing is almost constant as a whole, so that the difference in molding shrinkage inside the foamed plastic molded product is reduced, and This is because the crystallinity and the size of crystal grains can be made substantially uniform. Secondly, in this injection molding method, since a suitable foaming suppressing force is applied to the molten resin filled in the cavity, the foamed cells contained in the foamed plastic molded product can be made into a fine state. Is.

Although the nozzle 100 of the household vacuum cleaner has been described as the foamed plastic molded product, the foamed plastic molded product that can be molded by the injection molding method according to this embodiment is not limited to this. For example, if an injection molding die having a cavity as shown in FIG. 4 is used, it is possible to mold an automobile air conditioner housing 500 as shown in FIG. 5 according to the same procedure as described above. However, even in this case, the cavity forms the nozzle of the household cleaner so that the density distribution inside the air conditioner housing 500 for automobiles, which is a desired molded product, corresponds to a desired strength. Similar to the cavities for the above, it has a plurality of regions 400a and 400b formed of porous metals having different porosities. That is, a high density portion (mounting portion 500a or fitting portion 500b) of which strength is required in the air conditioner housing 500 for automobiles.
Etc.) in the region 400a for molding other than the region 400b for molding the other low density portion 500c,
A porous metal having a high porosity is used (see FIG. 6).

By the way, in the present embodiment, by supplying compressed air to the inside of the injection molding die, an appropriate foaming suppressing force is exerted on the molten resin filled in the cavity formed of the porous metal. The foamed state of the molten resin at the time of curing is adjusted by the action of the above, but in order to generate such a foaming suppressing force, it is not always necessary to supply compressed air into the injection molding die. For example, when an injection molding die having an air pocket 701 for exhausting air inside the cavity is used around the cavity as shown in FIGS. 7 and 8, when the molten resin is injected into the cavity, It is possible to appropriately release the pressure acting on the molten resin filled in the cavity formed of the porous metal, that is, the foam suppression force. However, in this case, the structure of the cavity according to the density distribution of the target molded product is opposite to the above-described case in which compressed air is supplied during injection of the molten resin. Specifically, the regions 700a and 800a for molding the high-density portion of the molded product are formed of a porous metal having a small porosity, and the regions 700b and 800b for molding the other low-density portions are pores. It is formed of a porous metal having a high rate (see FIG. 9). With such a structure of the cavity, the pressure acting as a foaming suppressing force on the molten resin is rapidly released inside the regions 700a and 800a formed of the porous metal having a large porosity, and the molten resin is cured. Bubbling proceeds smoothly. On the other hand, inside the regions 700b and 800b formed of a porous metal having a small porosity, the pressure acting as a foaming suppression force on the molten resin is gradually released, and the foaming during curing of the molten resin is effectively performed. Suppressed. As a result, as in the case where the compressed air was supplied at the time of injecting the molten resin, the high density portion (the fitting portion 1000a, the nozzle connecting portion 1000b, the axle bearing portion 1000c, the handle attaching portion 1000d) was low. For a household vacuum cleaner housing 1000 having a density portion 400e (see FIG. 10), or for a ceiling mounting having a high density portion (ceiling mounting portion 1100a or exhaust pipe mounting portion 1100b) and a low density portion 1100c. Air conditioner housing 1100 (Fig. 1
1) can be molded in one shot.

Above, the description of the embodiment according to the present invention is finished, but finally, the porous metal used in this embodiment will be described. The porous metal having a large porosity and the porous metal having a small porosity used in this example are, respectively, a pore diameter of about 0.007 mm and a pore diameter of about 0.00.
It is a ready-made porcerax having 3 mm holes.

[0028]

EFFECTS OF THE INVENTION According to the method for injection-molding a foamed plastic molded product according to the present invention, a foamed plastic molded product that satisfies the required durability and looks good can be efficiently molded.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a nozzle of a household cleaner, which is an example of a foamed plastic molded product molded by an injection molding method according to the present invention.

FIG. 2 is a graph showing the relationship between the density and impact strength of foams used in the examples according to the present invention.

FIG. 3 is a cross-sectional view of an injection molding die for molding the nozzle of the household vacuum cleaner of FIG.

FIG. 4 is a cross-sectional view of an injection molding die for molding an automobile air conditioner housing.

5 is a cross-sectional view of an automobile air conditioner housing molded using the injection molding die of FIG.

FIG. 6 is a diagram showing the relationship between the porosity of the porous metal used in the cavities of FIGS. 3 and 4 and the density of the foamed plastic molded product to be molded.

FIG. 7 is a cross-sectional view of an injection mold for molding a housing of a household cleaner.

FIG. 8 is a cross-sectional view of an injection molding die for molding a housing for a ceiling-mounted package air conditioner.

9 is a diagram showing the relationship between the porosity of the porous metal used in the cavities of FIGS. 7 and 8 and the density of the foamed plastic molded product to be molded.

10 is a cross-sectional view of a housing of a household cleaner that is molded using the injection molding die of FIG.

11 is a cross-sectional view of a housing for a ceiling-mounted package air conditioner molded using the injection molding die of FIG.

[Explanation of symbols]

100 ... Nozzle of household vacuum cleaner, 100a ... Both ends of nozzle, 100b ... Nozzle middle part, 300 ... Mold for injection molding, 301 ... Fixed side template, 302 ... Movable side template, 303
… Cavity block, 304… Core block, 305
... Nozzle of injection molding machine, 306 ... Runner, 500 ... Air conditioner housing for automobile, 701 ... Air pool for exhausting air inside cavity, 1000 ... Housing for home vacuum cleaner, 1100 ... Air conditioner housing for ceiling mounting

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location B29K 105: 04 (72) Inventor Makoto Iida 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Hitachi Ltd. (72) Inventor Ikuo Kawaguchi, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Ltd.

Claims (6)

[Claims] 1. An injection molding method for molding a foamable plastic molded product by filling a foamable melted resin into a cavity inside the mold and curing the resin, wherein the foamed plastic is used as the cavity inside the mold. Prepare a cavity formed of a porous material having a porosity distribution according to the desired density distribution of the molded product, while injecting the foamable molten resin inside the cavity, the mold and the cavity The step of pressurizing a gas into the gap, while maintaining the pressure inside the mold caused by the pressurization of the gas into the gap between the mold and the cavity, the foamable dissolved resin into the cavity And a step of cooling and hardening the foamable dissolved resin filled in the cavity by injection. 2. An injection molding method for molding a foamable plastic molded product by filling a foamable melted resin into a cavity inside the mold and curing the resin, wherein the foamable resin is used as the cavity inside the mold. A cavity formed of a porous material having a predetermined porosity distribution so as to cause air leakage to the gap between the mold when filling the melted resin, and the foamable melted resin inside the cavity. And a step of filling the inside of the cavity while releasing the pressure inside the cavity by air leakage to the gap between the cavity and the mold that occurs with the filling of the foamable dissolved resin into the inside of the cavity. And a step of cooling and curing the foamable dissolved resin filled in the injection molding method. 3. An injection molding die used in an injection molding machine for molding a plastic molded product by curing an injected foamable molten resin while cooling, the inside of said injection molding die. A cavity formed of a porous material having a fixed porosity distribution according to the intended density distribution of the plastic molded article, for filling the injected foamable molten resin; An injection molding die, comprising: a press-fitting means for press-fitting a gas into a gap between the injection molding die and the cavity when filling the melted resin into the cavity. 4. A mold for injection molding used in an injection molding machine for molding a plastic molded product by curing an injected foamable molten resin while cooling, wherein the mold is used in the injection molding mold. Predetermined pores so as to cause air leakage to a gap between the injection molding mold and the inner surface of the injection molding die, which is fixed when the injection molding foam resin is filled. An injection molding die comprising a cavity formed of a porous material having a rate distribution. 5. The injection-molding die according to claim 3, wherein the porous material forming the cavity has a region for molding a portion of the plastic molded article having a higher density, An injection-molding die having a porosity distribution with a larger porosity. 6. The injection-molding die according to claim 4, wherein the porous material forming the cavity has a region for molding a portion of the plastic molded article having a higher intended density, An injection molding die having a porosity distribution with a smaller porosity.