JP2917208B2 - Manufacturing method of high hollow injection molded products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a high hollow injection molded article. More specifically, in one injection-molded product, it has a high hollow part and a general plate thickness part that is not hollow, and is lightweight but has excellent strength, and has excellent appearance without sink marks (dents). And a method for manufacturing a high hollow injection molded article.

[0002]

2. Description of the Related Art Conventionally, when a molded article is manufactured by injection molding, a molten resin is injected into a mold cavity in an amount smaller than the volume thereof, and simultaneously a pressurized fluid (mainly a gas body) is pressed into the mold cavity to melt the resin. A technique has been proposed and put to practical use in which a resin is cooled while being pressed against the inner surface of the cavity to form a molded article having a hollow portion inside. At this time, in order to improve the strength of the molded article, many molding methods for providing a reinforcing rib in a hollow portion inside the molded article have been proposed.

For example, in US Pat. No. 4,247,515, a projection is provided which protrudes from the surface of a mold cavity into a cavity space, and the viscosity, elastic density, and interfacial tension between the molten resin and a pressurized fluid are measured. An adjustment technique is described. The location where the protrusions are provided is narrower than the space between the opposing mold cavities, and in this part the molten resin is cooled faster than other parts, so the pressurized fluid is less likely to flow, and the molten resin Is solidified around the place where is provided, and remains as a reinforcing rib connecting both surfaces of the molded article.

Japanese Patent Publication No. Sho 61-53208 discloses that the flowability and injection amount of a molten resin injected into a mold cavity are made non-uniform, so that a molten resin portion having a high flowability,
A method is described in which a pressurized fluid is press-fitted into a molten resin portion having a small injection amount to form a hollow portion, and the other portion is left as a solid reinforcing rib having no hollow portion. This publication also discloses that a molten resin and a pressurized fluid are simultaneously injected into a mold cavity having a portion where the distance between opposing cavity surfaces is different, or that the molten resin is added to the cavity of such a mold. By simultaneously injecting the pressurized fluid and partially expanding the space between the mold cavity surfaces, the pressurized fluid is preferentially applied to the portion where the space between the cavity surfaces is large or the portion where the space between the mold cavity surfaces is expanded. It is described that solid ribs are formed without forming a hollow portion in a portion where the space between the cavity surfaces is small and a portion where the space between the mold cavity surfaces is not enlarged is formed into a hollow portion by introducing.

Further, Japanese Patent Publication No. Hei 7-12621 discloses a movable core which can move from a surface of a mold cavity to a projecting position into a cavity space and retreat from this position. Using an injection mold that can be reduced and enlarged, inject a sufficient amount of molten resin to fill the cavity with the reduced volume, and immediately thereafter, with the movable core protruding into the cavity space. A molding method is described in which a pressurized fluid is pressed into a molten resin, and then the movable core is retracted and the volume of the mold cavity is increased. According to the method described in this publication, the resin portion surrounding the movable core forms a reinforcing rib.

[0006]

In recent years, as the required performance of products has been diversified and advanced, there is no exception in the molded products by the above-mentioned molding technology. In some cases, the above-described molding technique is applied to the production of a molded product having the same. However, it is common practice to provide one injection port for pressurized fluid into the molten resin. According to this conventional method, the molten resin injected into the mold cavity has a higher cooling rate in the portion corresponding to the thin portion than in the portion corresponding to the thick portion, so that the molten portion is maintained in the thick portion where the molten state is maintained. The pressurized fluid flows into the corresponding portion, but the pressurized fluid hardly flows into the portion corresponding to the thin portion, and the rib / boss formed in the portion corresponding to the thin portion has a so-called sink mark (dent). ) Occurs, and a molded article with a beautiful appearance cannot be obtained.

Further, in order to obtain a molded article having a beautiful appearance, a portion in which the volume of the cavity can be reduced or expanded (hereinafter, referred to as a “cavity”).
Sometimes referred to as the “expandable part”. ) And a portion where the reduction / expansion of the cavity volume is not possible (hereinafter, sometimes referred to as an “impossible portion that cannot be expanded”) is provided locally so that the pressurized fluid can easily flow in. There is a way to lead to the “non-expandable part”, but to make it flow evenly into this part,
Since it is necessary to guide against the difference in cooling rate of the molten resin,
It is necessary to increase the injection pressure or to provide a flow path for a pressurized fluid necessary for the structure of the molded product, and the mold structure is inevitably complicated and expensive.

As described above, conventionally, the same molded article has a reinforcing rib in a hollow portion having an "expandable portion" and a "non-expandable portion", and is lightweight but excellent in strength, without sink marks and in appearance. There has been a keen need for a method of economically and advantageously producing a high hollow injection molded article. The present invention provides a method for manufacturing a molded article that has solved the problems existing in the above-described conventional techniques, that is,
An object of the present invention is to provide a method for industrially advantageously producing a high-hollow injection molded product having a reinforcing rib in a hollow portion, which is lightweight but has excellent strength, and has no sink mark and excellent appearance.

[0008]

In order to solve the above problems SUMMARY OF THE INVENTION In the present invention, a portion Scaling is made to be of the mold cavity volume by moving a portion of the mold cavity surface , Reduce / expand mold cavity volume
Using a mold with a part that is considered impossible ,
The molten resin is injected into the mold cavity, and while the molten resin is in the molten state, injection of the pressurized fluid is started to reduce the mold cavity volume while keeping the molten resin in close contact with the mold cavity surface. Enlarge the expandable part to complement the hollow
High hollow forming part with strong ribs and general thickness forming part
In manufacturing a high- hollow injection molded article having the above, the above-mentioned mold is provided with an injection port of the pressurized fluid into the molten resin, and a reinforcing rib is formed so that the volume of the mold cavity can be reduced or enlarged. High and middle
At least one location in the air forming portion, at least one location on Scaling is impossible part of the mold cavity volume, characterized by comprising respectively provided, to provide a method for producing a high hollow injection-molded article.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal sectional view of a main part showing an embodiment of the present invention. FIG. 1 shows a state before a molten resin is injected into an injection mold cavity and a cavity volume is enlarged.
FIG. 2 shows a state in which a pressurized fluid is injected into the molten resin so that the molten resin is in close contact with the mold cavity surface and the volume of the mold cavity is enlarged. FIG. 3 is a bottom view of an example of a high hollow injection molded article obtained by the method of the present invention, FIG. 4 is an end view of the section taken along the line AA in FIG. 3, and FIG. 5 is another embodiment. FIG.

1 to 5, reference numeral 1 denotes a fixed mold, 2 denotes a movable insert mounted on the movable platen, 3 denotes a movable mold, 4 denotes a stripper plate, 5 denotes a fixed mounting plate, 6
Is a movable mounting plate, 7 is a sprue, 8 is a runner, 9 is a resin gate, 10 is molten resin injected into a mold cavity having a minimum volume, 11 is a driving device, 12 is a ball screw, and 3 is a slide block. , 14 is a slide base, 1
5 , 16 are pressurized fluid injection nozzles, 17 is a non-expandable portion, 18 is an expandable portion, 19, 20, 21 are pressurized fluid injection ports, 22, 23 are hollow portions , and 24 is a void portion .

In practicing the present invention, an injection mold having a specific structure is used. That is, in this injection molding die, the volume of the cavity can be reduced or expanded by first moving a part of the cavity surface of the die.
The cavity surface of one mold is partially reduced in volume.
This means that the portion that can be expanded (“expandable portion”) and the portion where the volume cannot be reduced or expanded (“non-expandable portion”) are combined. Injection molding dies are further provided with an injection port for injecting pressurized fluid into the molten resin injected into the mold cavities.
At least one place and at least one in the “non-expandable part”
Location, respectively.

The procedure for producing a high hollow injection molded article by the method of the present invention will be described below. First, the mold is clamped by a mold clamping mechanism (not shown). At this time, the mold cavity of the injection molding machine is kept in a minimum volume. Then
A molten resin plasticized by a cylinder (not shown) is injected from a cylinder nozzle into a mold cavity via a sprue 7, a runner 8, and a resin gate 9 (1).
0 is the molten resin in the cavity). While the molten resin 10 is in a molten state and can flow without cooling, the pressurized fluid is simultaneously or slightly changed from the pressurized fluid inlets provided in the “expandable portion” and the “non-expandable portion”. The molten resin 10 is injected and pressed against the inner surface of the cavity.

The pressurized fluid injection nozzles 15 and 16 are fitted into nozzle insertion holes formed in a mold, respectively, and their respective ends are arranged in accordance with the pressurized fluid injection ports 19 and 20. In addition,
The pressurized fluid injection port can also serve as the same injection port as the resin gate, or can be separate. At the time of fluid injection, the tip of the nozzle is inserted into the molten resin 10, and after the fluid injection is completed, while preventing the resin from flowing back to the nozzle tip,
The tip inserted into the molten resin 10 is retracted. The injection of the pressurized fluid into the molten resin 10 is performed immediately before starting the expansion of the volume of the “expandable portion” of the mold cavity or simultaneously with the operation of expanding the volume. After expanding the mold cavity to a predetermined volume, the molten resin is brought into close contact with the mold cavity surface while maintaining the pressure of the pressurized fluid, and the molded product is cooled until it is not deformed even when it is removed from the mold cavity, The pressurized fluid remaining in the hollow part of the molded product is purged, and the molded product is taken out by opening the mold by a mold opening mechanism (not shown). After the molded product is released from the mold, the mold is clamped by a mold clamping mechanism (not shown), and the mold cavity volume is reduced to a minimum volume by a mold cavity volume reducing mechanism (not shown). After starting the cycle, continuous molding can be performed in the same procedure.

To increase the volume of the mold cavity “expandable portion”, an inclined surface is provided on the back surface of the movable insert 2, and the inclined surface is brought into contact with the inclined surface of the slide block 13.
This is possible by rotating the ball screw 12 which is made rotatable by and by separating the slide block 13. The volume of the mold cavity “expandable portion” can be reduced by moving the slide block 13 closer. The details of the technology for reducing / enlarging the cavity volume are described in JP-A-6-339950 filed by the applicant of the present invention.

The injection pressure of the molten resin into the mold cavity is preferably selected in the range of 50 to 150 kg / cm ² .
Even if the injection pressure is 50 kg / cm ² or less, the molten resin can be injected into the mold cavity, but it is not preferable because the molten resin does not sufficiently reach the thin-walled portion, resulting in a short shot. If the injection pressure exceeds 150 kg / cm ² , it is necessary to make the mold cavity volume enlarging mechanism withstand this pressure.

The speed at which the volume of the mold cavity "expandable portion" expands, that is, the speed at which the distance between the opposing mold cavity surfaces increases, depends on the size, shape, structure, thickness,
Depends on the type of resin used for molding, melt viscosity, resin additive, molding temperature, temperature of mold cavity surface, etc., but at the speed at which molten resin does not separate from mold cavity surface in the process of expanding mold cavity volume Anything is fine, 10-50mm
/ min range. Volume expansion rate is 10
If it is less than mm / min, the molten resin cools while expanding the mold cavity volume, and the resin does not follow the mold cavity surface, making it difficult to form a hollow portion, which is not preferable. On the other hand, if the speed exceeds 50 mm / min, the speed is too high, the molten resin separates from the mold cavity surface, and the pressurized fluid injected into the molten resin presses the softest part (mostly the hottest part) of the molten resin. In some cases, the molten resin is excessively locally stretched, so that a hole is formed and the pressurized fluid leaks, and a molded article having a target hollow portion is not obtained, which is not preferable.

The resin which can be used in carrying out the present invention is not particularly limited, and generally includes all thermoplastic resins to which injection molding can be applied. In the present invention, the pressurized fluid is a gas or a liquid at normal temperature and normal pressure, and does not chemically change when pressurized. Specifically, examples include a gas such as air, nitrogen gas, carbon dioxide gas, helium gas, and argon gas, and a liquid such as water, glycerin, and liquid paraffin. Among them, an inert gas such as a nitrogen gas and a helium gas is preferable.

According to the method of the present invention, an outer case such as a radio and a television, an electric product such as a television mounting table; a housing such as a personal computer and an office computer; and an OA such as a housing of a copying machine and a printer.
Equipment products; automobile parts such as automobile doorknobs and instrument panels; furniture parts such as doors, desks, cupboard bottom plates, top plates, partition boards, etc. Since there is no general plate thickness structure part at the same time, various constituent parts can be integrally arranged on the molded product, excellent in function, lightweight but excellent in strength, excellent in appearance without sink mark High hollow injection molded articles can be manufactured.

[0019]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to the following description unless it exceeds the gist.

Example 1 Impact-resistant polystyrene (manufactured by Mitsubishi Chemical Corporation, brand name: Dialex HT-60) was melted at a cylinder temperature of 220 ° C. using an injection molding machine (manufactured by Mitsubishi Heavy Industries, Ltd., model: 850MG). Was. In this molding machine, as shown in FIG. 1, "expandable portion" and "non-expandable portion"
And a mold having one pressurized fluid inlet in the “non-expandable portion” and one in the “non-expandable portion”. From this mold, FIG. 3 shows a bottom view, and FIG.
A molded product showing an end view when it is cut vertically at the -A portion is obtained. The mold cavity surface temperature is 50 ° C,
The molten resin was injected into the cavity with the minimum volume. Immediately after injection of the molten resin into the mold cavity, injection of 50 kg / cm ² of pressurized air into the molten resin is started. The section was enlarged at a speed of 30 mm / min. The molded product was cooled until it was not deformed even after being removed from the mold cavity, the pressurized fluid remaining in the hollow portion of the molded product was purged, the mold was opened, and the molded product was removed.

The molding cycle in this example requires 10 seconds for injection of the molten resin into the mold cavity, 30 seconds for expanding the cavity volume, 90 seconds for cooling, and 20 seconds for opening and releasing the mold.
The total cycle is 150 seconds. In the molded article obtained in this example, as shown in FIG. 4, the hollow portion 23 and the reinforcing rib are formed in the “expandable portion” portion, and the void is formed in the thick portion of the “non-expandable portion”. The portion 24 was formed, no sink marks were observed, and the surface of the molded product had a beautiful appearance throughout.

[Example 2] In the example described in Example 1, a mold for obtaining a molded article shown in FIG. 5 in which the number of pressurized fluid inlets to the “non-expandable portion” was increased by 21 was used. Manufactured a molded article having a hollow portion by an injection molding method in the same procedure as in the same example. The molded article obtained in this example was as excellent as the one obtained in Example 1 in both the reinforcing ribs and appearance.

[Comparative Example 1] In the example described in Example 1, except that the pressurized fluid inlet for the “non-expandable portion” was closed and no pressurized air was injected, A molded article having a hollow portion was produced by the injection molding method according to the above procedure. In the molded product obtained in this example, the reinforcing ribs were the same as in Example 1, but sink marks were observed on the surface of the “non-expandable portion”, and the appearance was not good.

[0024]

The method of the present invention has the following particularly advantageous effects, and its industrial utility value is extremely large. 1. According to the method of the present invention, in one injection-molded product, a high hollow portion and a general plate thickness portion which is not hollowed are combined, and various components are integrally disposed in the molded product and functionally. It is possible to produce a high hollow injection molded article which is excellent, lightweight, but excellent in strength and appearance. 2. According to the method of the present invention, since the pressurized fluid is injected into the high hollow portion and the non-hollowed general plate thickness portion, the surface of the molded product does not have sink marks, and a molded product having excellent appearance is produced. can do.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part showing a state before a molten resin is injected into an injection mold cavity and a cavity volume is enlarged.

2 is a sectional view of a main part showing a state where the by injecting pressurized air into the molten resin molten resin to expand a mold cavity volume while in close contact with the mold cavity surface.

FIG. 3 is a bottom view of an example of a high hollow injection molded product obtained by the manufacturing method according to the present invention .

FIG. 4 is an end view of the section taken along the line AA in FIG.

FIG. 5 is a diagram showing a high and middle part obtained by the manufacturing method according to the present invention .
It is a bottom view of another example of an empty injection molded product .

[Explanation of symbols]

1: fixed mold 2: movable insert 3: movable mold 4: stripper plate 5: fixed mounting plate 6: movable mounting plate 7: sprue 8: runner 9: resin gate 10: molten resin 11: drive device 12 : Ball screw 13: Slide block 14: Slide base 15 , 16 : Pressurized fluid injection nozzle 17: Non-expandable portion 18: Expandable portion 19, 20, 21: Pressurized fluid injection port 22, 23: Hollow portion 24: Void

Continuation of front page (56) References JP-A-8-267492 (JP, A) JP-A-7-223246 (JP, A) JP-A-7-164486 (JP, A) JP-A-4-212822 (JP, A) JP-A-6-339950 (JP, A) JP-A-6-34927 (JP, U) JP-B 7-12621 (JP, B2) JP-B-61-53208 (JP, B2) (58) Field surveyed (Int. Cl. ⁶ , DB name) B29C 45/00-45/84 B29C 33/00-33/76

Claims (1)

(57) [Claims] 1. A part in which a mold cavity volume can be reduced or enlarged by moving a part of a mold cavity surface, and an umbrella mold cavity volume cannot be reduced or enlarged.
A molten resin is injected into the mold cavity by using a mold having a part which is capable of functioning, and while the molten resin is in a molten state, injection of a pressurized fluid is started, and the molten resin is poured into the mold. completely by enlarging the reduced-expandable portions of the contact are allowed while the mold cavity volume to the mold cavity surface, the reinforcing rib in the hollow portion
It has a formed high hollow forming part and a general thickness forming part
In manufacturing a high hollow injection molded product, the above-mentioned mold is used as a high hollow forming part in which a reinforcing rib is formed by making it possible to reduce / enlarge the mold cavity volume and to provide an injection port of the pressurized fluid into the molten resin. A method for manufacturing a high hollow injection molded product, wherein at least one portion is provided at every one portion, and at least one portion is provided at a portion where the volume of the mold cavity cannot be reduced or expanded.