JPH10138274A - Method for molding hollow molded product fitted with opening and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an opening having a relatively large caliber to the surface of a hollow molded product with high accuracy and good reproducibility so as to communicate with the hollow part of the hollow molded product without applying secondary processing. SOLUTION: A molten resin 5 is injected into a mold cavity having a main cavity 3 and the auxiliary cavity 4 branched from the main cavity 3 and, thereafter, a pressure fluid is introduced under pressure from the pressure fluid introducing part 8 arranged at a place separated from an auxiliary cavity branch part by three times or more the diameter D of the auxiliary cavity branch part to form a hollow part 6. The molded object in the auxiliary cavity 4 is separated from the hollow molded product in the main cavity 3 after cooling and solidification.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a hollow molded article having a relatively large-diameter opening communicating with an internal hollow portion on the surface thereof, and a hollow body forming apparatus used in the method.

[0002]

2. Description of the Related Art Heretofore, as a method for forming a hollow portion inside a molded article, a gas injection molding method for injecting a gas into a molten resin in a cavity to make it hollow is widely known.

In order to obtain a molded article having an excellent appearance in such a gas injection molding method, it is necessary to inject a high-pressure gas into the molten resin with good controllability. Since it is necessary to minimize the hole remaining on the surface of the molded product due to the injection, a needle 41a or 41b having an extremely small injection port 42 is used, for example, as shown in the cross-sectional views of FIGS. It is common to inject a gas into the molten resin.

Using the above needles 41a and 41b,
As shown in FIGS. 5 (a) and 5 (b), when a gas is injected into the molten resin 52 in the mold cavity to form a hollow molded product, as shown in FIGS. 6 (a) and 6 (b), respectively. Then, a small hole 62 remains on the surface of the hollow molded product 61. Such a hole 62
Is sealed with silicone, resin, emblem, or the like in external parts.

[0005]

As described above, in the conventional general gas injection molding method, a method of minimizing a hole remaining on the surface of a molded product by gas injection is adopted. It was not intended to actively give the hollow part a special function.

[0006] However, in recent years, in particular, in hollow molded articles used as interior parts, it has been required to provide the hollow portion with various functions. Specifically, for example, in a molded product covering a heating element such as a headlamp cover of an automobile, a function of facilitating the flow of air in a hollow portion to suppress a rise in temperature is used, or used as a floor heating panel. In the case of a molded product, the hollow portion has a function as an internal pipe in order to reduce the cost so that the housing and the internal pipe are formed as one component.

In order for the hollow portion of the hollow molded product to function as a fluid path as described above, it is necessary to form a relatively large-diameter opening communicating with the hollow portion on the surface. Only a small opening can be formed by the molding method.

To increase the size of such an opening, it is conceivable to increase the size of the gas injection port. However, since the molten resin flows back from the injection port into the gas passage, the size of the gas injection port is limited. There is a limit. In addition, if the gas inlet is enlarged, it becomes difficult to inject the high-pressure gas into the molten resin with good controllability, and the appearance is reduced,
There is a problem that a desired opening shape cannot be obtained.

Under these circumstances, conventionally, when a relatively large-diameter opening communicating with a hollow portion is formed on the surface of a hollow molded product, it is necessary to perform secondary processing on the hollow molded product to provide the opening. In some cases, the number of manufacturing steps increases, leading to an increase in cost.

[0010] The present invention solves the above-mentioned conventional problems, and provides a relatively large-diameter opening communicating with the hollow portion on the surface of the hollow molded product without performing secondary processing, and further, achieves high precision and reproducibility. An object of the present invention is to provide a molding method that can be formed well, and a hollow body molding apparatus used in the molding method.

[0011]

The structure of the present invention to achieve the above object is as follows.

That is, the present invention relates to a method for molding a hollow molded article having an opening communicating with a hollow portion inside the molded article, the method comprising: melting a mold in a mold cavity having a main cavity and a sub-cavity branched from the main cavity. After injecting the resin, pressurized fluid is injected from the pressurized fluid pressure inlet arranged near the end of the sub-cavity to form a hollow portion in the resin in the sub-cavity and the main cavity, and after cooling and solidifying, the main cavity is formed. A method for molding a hollow molded article with an opening, comprising separating a molded article in a subcavity from a hollow molded article in the inside.

Preferably, the molding method of the present invention further includes, as a further feature, "a distance from the sub-cavity branch to the pressurized fluid pressure inlet is at least three times the diameter of the sub-cavity branch.""The sub-cavity has a cone shape having a central axis in the mold opening and closing direction, and the sub-cavity branches off from the main cavity at the top of the cone, and a hollow molded product in the main cavity when the mold is opened after cooling and solidification. Separating the molded body in the sub-cavity from the above.

The present invention also relates to a hollow body molding apparatus used for molding a hollow molded article having an opening communicating with a hollow portion inside the molded article, the apparatus comprising a main cavity and a sub cavity branched from the main cavity. A hollow body forming apparatus, wherein a cross-sectional shape of the sub-cavity branch portion is substantially the same as an opening shape formed in the hollow molded product, and a pressurized fluid pressure inlet is provided near an end of the sub-cavity. .

Preferably, the molding apparatus of the present invention further includes, as a further feature, "L = the distance from the sub-cavity branch to the pressurized fluid pressure inlet, and D = the diameter of the sub-cavity branch. Satisfying the relationship of D ≦ L ”,“ the sub-cavity forms a cone having a central axis in the mold opening and closing direction,
The sub-cavity branches off from the main cavity at the top of the cone. "

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an example of a sectional view showing a state in the middle of molding a hollow molded article for explaining the features of the present invention. In FIG. 1, 1 and 2 are molds, 3 is a main cavity, 4 is a sub-cavity branched from the main cavity 3, 5 is a molten resin, 6 is a hollow portion, 7 is a needle as shown in FIG. This is a pressurized fluid pressure inlet at the tip of the needle.

According to the molding method of the present invention, a molded product molded in the main cavity 3 is obtained as a hollow molded product. The hollow portion 6 of the hollow molded product is provided at a portion where the sub cavity 4 of the main cavity 3 branches. A relatively large opening that communicates is formed. Hereinafter, a specific description will be given.

In the molten resin 5 in the main cavity 3 and the sub-cavity 4, a pressure inlet 8 located near the end of the sub-cavity, which is located to some extent from the position of the opening (sub-cavity branch) to be formed in the hollow molded product. Pressurized fluid is injected.

By providing the approach distance of the pressurized fluid between the pressure inlet 8 and the main cavity 3 as described above, the pressurized fluid can be diffused before reaching the sub-cavity branch. Since the pressurized fluid tends to diffuse into the molten resin in the main cavity 3 through the shortest distance, FIG.
As shown in (2), at the branch portion of the sub cavity 4, the thickness of the molten resin becomes thin, and a large hollow portion similar to the cross section of the branch portion is formed.

The distance L from the branching portion of the sub-cavity to the pressure inlet 8, that is, the approach distance of the pressurized fluid, varies depending on the pressure of the molten resin, the pressure of the pressurized fluid, and the like, but the molding conditions set by the usual gas injection molding method. (Resin pressure: 100-
150 kg / cm ² or so, gas pressure: 150～200Kg
/ Cm ² ), when the diameter of the sub-cavity branch portion is D, L is preferably set to 3D or more, more preferably 5D or more. Note that the diameter D of the sub-cavity branch portion having a shape other than the circular shape can be considered in terms of equivalent diameter D ′ = 2 × (area / π) ^1/2 .

By setting L to 3D or more, the pressurized fluid can be diffused sufficiently and stably until it reaches the sub-cavity branch, and the sub-cavity branch has substantially the same size as the cross-section of the branch. The hollow portion of the hole can be formed. That is, the resin thickness of the sub-cavity branch can be made very small, and the hollow molded product in the main cavity 1 obtained by separating the molded product formed in the sub-cavity 4 has a cross section of the sub-cavity branch. An opening having substantially the same shape and size as that of FIG.

The shape of the sub-cavity 4 is not particularly limited, but is preferably a simple shape in consideration of the diffusibility of the pressurized fluid. For example, as shown in FIG. It can be a cylinder or a prism depending on the shape of the opening formed in the molded article. In particular, as shown in FIG. 1 (b), the shape of the cone has a central axis in the mold opening and closing direction (the shape can be a truncated cone or a truncated pyramid depending on the opening shape). When the cavity 4 is configured to branch off from the main cavity 3, the hollow molded article in the main cavity 3 and the molded body in the sub cavity 4 can be separated at the same time as the mold opening after cooling and solidification.

As the resin according to the present invention, thermoplastic resins used in general injection molding and extrusion molding can be used. Further, a thermosetting resin can be used if necessary. Further, in these resins, for example, fillers such as fillers and reinforcing fibers and various additives (eg, plasticizers, lubricants, ultraviolet absorbers, dyes, pigments, antifogging agents, antistatic agents, flame retardants, etc.) Can be added.

As the pressurized fluid, for example, a gas such as carbon dioxide gas, nitrogen gas, or air, or a liquid such as oligomer or liquid paraffin can be used. Nitrogen gas is preferred.

In the present invention, when a subcavity having a relatively small volume and a small volume is used in the molded article, there is not much problem, but a relatively large hollow section is formed in the molded article. When using a large-volume sub-cavity or the like, it is necessary to inject an amount of resin in consideration of the volume of the hollow portion, and it becomes difficult to control the amount of injected resin. In such a case, it is preferable to provide a disposal cavity communicating with the main cavity. As a result, surplus resin generated by press-fitting of the pressurized fluid can be discarded and received in the cavity, and the amount of injected resin can be easily controlled.

The above-mentioned waste cavity is preferably provided at the periphery of the main cavity far away from the pressure inlet of the pressurized fluid, so that the pressurized fluid pressurizes the hollow portion to the end portion of the molded article. Can be formed.

The molded body in the disposal cavity may be cut from the hollow molded product in the main cavity 3 by a cutting tool such as a nipper. However, in order to reduce the number of manufacturing steps, the disposal cavity is replaced with the auxiliary cavity 4 described above. It is preferable to form a cone having a central axis in the mold opening / closing direction in the same manner as described above, and to communicate with the main cavity at the top of the cone. As a result, the molded body in the discarded cavity can be separated from the hollow molded article in the main cavity 3 simultaneously with opening of the mold after cooling and solidification.

[0028]

Next, an embodiment of the present invention will be described in detail.

FIG. 2 is a partially cutaway sectional view of the headlamp cover of the automobile formed in the present embodiment. A relatively large opening 9 communicating with the hollow portion 6 is formed on the surface of the hollow molded product.
have. FIG. 3 is a cross-sectional view showing a molding step of the hollow molded article.

First, the molding apparatus used in this embodiment will be described. As shown in FIG. 3, the movable mold 1 and the fixed mold 2
A main cavity 3 is formed therebetween. In the drawings, the mold is the movable mold 1 and the core is the fixed mold 2. However, the mold may be the fixed mold 2 and the core may be the movable mold 1.

On the side of the fixed mold 2, a sub cavity 4 is formed so as to branch off from the main cavity 3. This sub-cavity 4 has a conical shape having a central axis in the mold opening and closing direction as in FIG. 1B, and the cross-sectional shape of the branch portion is an opening 9 formed in a hollow molded product (see FIG. 2). ) Is substantially the same as the shape of FIG.

In this embodiment, since the sub-cavity 4 is formed in a cone shape and the sub-cavity 4 is branched from the main cavity 3 at the top of the cone, the hollow in the main cavity 3 is opened at the same time when the mold is opened after cooling and solidification. The molded product and the molded body in the sub cavity 4 are separated. In this embodiment, the fixed mold 2 is divided into two molds 2 at a portion defining the bottom surface of the sub cavity 4 so that the molded body in the separated sub cavity 4 can be extracted.
a and 2b.

Further, the end of the sub cavity 4 is
A needle 7 having a cross section as shown in FIG. In this embodiment, the distance L from the pressurized fluid pressure inlet 8 at the tip of the needle 7 to the sub-cavity branch is set to be three times as large as the equivalent diameter D of the sub-cavity branch.
The molding was set in stages, and molding was performed 10 times under each set condition.
In FIG. 3, reference numeral 10 denotes an injection nozzle, and reference numeral 11 denotes a sealing material.

Next, the molding procedure will be specifically described with reference to FIG.

First, the molten resin 5 was injected from the injection nozzle 10 into the mold cavity in the mold opening state shown in FIG. In this example, polypropylene was used as the resin.

Next, as shown in FIG. 3B, after closing the mold, a pressure of 100 kg / c is applied through the pressurized fluid pressure inlet 8.
m ² of nitrogen gas was injected for 5 seconds.

After the pressure is maintained for a certain period of time and the resin is cooled and solidified, the mold 1 is retracted and the mold is opened as shown in FIG. The molded body in 4 was separated.

The hollow molded article in the main cavity 3 and the molded article in the sub cavity 4 were taken out and their shapes and the like were observed.

As a result, when molded with L = 2D, a relatively large opening was formed in each of the hollow molded products, but this opening was 80 ± 5% of the cross section of the branch portion of the sub cavity 4. Area. When molding was performed with L = 3D, the opening formed in the hollow molded product had an area of 95 ± 2% of the cross section of the branch portion of the sub cavity 4. L = 5
When molded as D, each of the openings formed in the hollow molded product is about 98% of the cross section of the branch portion of the sub-cavity 4.
Area.

As described above, the pressurized gas is supplied to the sub cavity 4
By press-fitting from the pressure inlet 7 away from the branch portion of
A large opening could be formed in the hollow molded product. Further, by setting L to 3D or more, particularly 5D or more, it was possible to stably form an opening having substantially the same shape and size as the cross section of the sub-cavity branch portion with good reproducibility.

In the embodiment described above, only one opening is formed in the hollow molded product. However, when the hollow portion functions as a fluid path as in a floor heating panel, a plurality of openings may be provided. In addition, the timing of injection of the resin, closing of the mold, and press-in of the pressurized gas during molding can be set as appropriate.

[0042]

The present invention is as described above, and an opening having a relatively large diameter communicating with the hollow portion can be formed on the surface of the hollow molded article without performing secondary processing. In particular, by setting the distance L from the sub-cavity branch to the pressurized fluid pressure inlet at least three times the diameter D of the sub-cavity branch, an opening having substantially the same shape and size as the cross section of the sub-cavity branch is formed. Can be formed into hollow molded products with good reproducibility,
The present invention can be sufficiently applied to the formation of an opening that requires a certain high dimensional accuracy.

[Brief description of the drawings]

FIG. 1 is an example of a cross-sectional view showing a state in the middle of molding a hollow molded article to explain an operation according to the present invention.

FIG. 2 is a partially cutaway cross section of a hollow molded product (an automobile headlamp cover) according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view for explaining a molding apparatus and a molding procedure according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view of a needle used for gas injection.

FIG. 5 is a cross-sectional view for explaining a conventional gas injection molding method.

FIG. 6 is a diagram showing holes formed on the surface of a hollow molded product obtained by a conventional gas injection molding method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Movable type (cavity type) 2 Fixed type (core type) 3 Main cavity 4 Subcavity 5 Molten resin 6 Hollow part 7 Needle 8 Pressurized fluid pressure inlet 9 Opening 10 Injector 11 Seal material 41a, 41b Needle 42 Injection 51a , 51b Mold 52 Molten resin 53 Hollow part 61 Hollow molded product 62 hole

Claims (6)

[Claims] 1. A method for molding a hollow molded article having an opening on its surface communicating with a hollow portion inside the molded article, wherein molten resin is injected into a mold cavity having a main cavity and a sub-cavity branched from the main cavity. Then, pressurized fluid is press-fitted from a pressurized fluid pressure inlet arranged near the end of the sub-cavity to form a hollow portion in the resin in the sub-cavity and the main cavity, and after cooling and solidification, hollow molding in the main cavity A method for molding a hollow molded article having an opening, comprising separating a molded article in a subcavity from an article. 2. The molding of a hollow molded article with an opening according to claim 1, wherein the distance from the sub-cavity branch to the pressurized fluid pressure inlet is at least three times the diameter of the sub-cavity branch. Method. 3. The sub-cavity has a cone shape having a central axis in the mold opening / closing direction, and the sub-cavity branches off from the main cavity at the top of the cone. The method for molding a hollow molded article with an opening according to claim 1 or 2, wherein the molded article in the sub cavity is separated from the hollow molded article. 4. A hollow body molding apparatus used for molding a hollow molded article having an opening on its surface communicating with a hollow portion inside the molded article, comprising a main cavity and a sub cavity branched from the main cavity. A hollow body forming apparatus, wherein a cross-sectional shape of a cavity branch portion is substantially the same as an opening shape formed in a hollow molded product, and a pressurized fluid pressure inlet is provided near an end of a subcavity. 5. The relationship of 3.times.D.ltoreq.L, where L is the distance from the sub-cavity branch to the pressurized fluid pressure inlet, and D is the diameter of the sub-cavity branch. Item 5. A hollow body molding apparatus according to Item 4. 6. The method according to claim 4, wherein the sub-cavity has a cone shape having a central axis in the mold opening / closing direction, and the sub-cavity branches off from the main cavity at the top of the cone. The hollow body forming apparatus as described in the above.