JP2004330676A - Mold assembly and molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively prevent an inverted blister from occurring in injection molding. <P>SOLUTION: In this method, a specified quantity of thermoplastic resin 8 is injected from a gate into a cavity formed between a movable half 2 and a cavity side half 1, of a mold by clamping the mold and the injection of the resin 8 is suspended. Next, a dwell pressure is applied and a nitrogen gas is supplied from a gas feed means through a gas ventilation hole 9. The nitrogen gas is injected into the cavity passing through a fine communication hole of a piece 6 made of a porous metal and presses the thermoplastic resin 8 to the inner wall surface 1a of the cavity by pressurizing the resin 8. That is, a dent(sink) is prevented from occurring by offsetting a depressing force F<SB>A</SB>due to contraction by a pressure F<SB>B</SB>applied by the nitrogen gas. When the cooling and hardening of the thermoplastic resin 8 are completed, the dwell pressure application and the nitrogen gas supply are suspended and the mold is opened to unload a molded article from the cavity. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a mold apparatus and a molding method using the same.
[0002]
[Prior art]
Conventionally, synthetic resin molded products manufactured by injection molding and the like have a great advantage that they can be freely formed into various shapes, so they are used in a wide range of fields, and the product shapes are extremely diverse. is there. Generally, a plurality of synthetic resin molded products are often used in combination by fitting, screwing, etc., so that a convex portion such as a boss or a rib is used for fitting or as the shape of the product itself. Very often they are integrally formed.
[0003]
When molding a product having a convex portion such as a boss or a rib, a concave portion 13 is formed in a cavity 12 into which a resin 11 is injected, as shown in FIG. By solidifying the resin 11 that has penetrated into the substrate, a convex portion is formed. In the case where a synthetic resin molded article integrally having convex portions such as bosses and ribs is formed as described above, defects are likely to occur in these convex portions. Specifically, defects such as sinks 14a and 14b in which a concave portion is partially formed due to shrinkage of the resin during cooling occur in a convex portion formed by filling the concave portion 13 of the cavity 12 with the resin 11. Easy to do. In particular, when these defects occur on the external appearance (the appearance) of the product, there is a high possibility that the product cannot be used.
[0004]
The sink is most commonly generated on the surface opposite to the convex portion (such as a boss or a rib) of the molded product (see 14a in FIG. 5). Explaining the principle, the molten resin 11 shrinks when solidified and the volume decreases. When the resin 11 is cooled and solidified in the course of the injection molding, a smooth surface can be obtained if the resin 11 is cooled uniformly. However, if the cooling is not uniform, sink occurs on the product surface of the portion where the solidification is delayed. . Convex parts such as bosses and ribs are filled with more resin than other parts, so they store more heat than other parts, so they solidify when the resin cools during the injection molding process Is behind other parts. For this reason, sinking is an inevitable defect phenomenon in a product having a convex portion such as a boss or a rib. Generally, even when the resin 11 is cooled and solidified around the recess 13, the resin 11 in the recess 13 for forming the convex portion is still at a high temperature and does not shrink much. Thereafter, when the resin 11 in the concave portion 13 is cooled and solidifies and contracts, the resin 11 is already solidified around the concave portion 13 and cannot flow. A depression (a sink 14a) often occurs on the top surface. That is, such a sink 14a often occurs on a surface (for example, a top surface) opposite to a convex portion in a molded product, and usually occurs on the appearance surface which is a product appearance, and the sink 14a is generated. Molded products become defective products. The sink 14b may also be formed on the side surface of the convex portion, but the sink 14b is not present on the appearance surface, and thus is relatively easily accepted.
[0005]
Various injection molding methods have been conventionally proposed in order to minimize the above-described disadvantage of the sink 14a. For example, a method of maintaining the resin pressure during cooling after the cavity 12 is filled with the resin 11, that is, applying a so-called holding pressure, and a method of filling the cavity 12 with the resin 11 in a large amount are considered. Although not shown, it is considered that the mold has a structure in which sink marks are hardly generated. For example, a convex shape (so-called fleshyness) is provided in the vicinity of the concave portion of the cavity so as to form a thin portion with a small amount of resin at a position other than the appearance surface near the convex portion so as to form a dent when the resin shrinks. A structure has been conceived that does not occur on the appearance surface such as the top surface portion, but occurs on a thin portion other than the appearance surface, so that even if sink marks occur, the appearance of the product is not affected. Further, a structure has been considered in which the position of the gate and the like are devised so that pressure is applied to the top surface as uniformly as possible.
[0006]
[Patent Document 1]
JP-A-6-320583 [Patent Document 2]
JP-A-8-66948 [Patent Document 3]
JP-A-7-266388 [Patent Document 4]
JP-A-5-261785 [Patent Document 5]
JP-A-9-85784 [Patent Document 6]
JP-A-2002-347059 [Patent Document 7]
JP 2001-105446 A [Patent Document 8]
JP 2000-289074 A
[Problems to be solved by the invention]
Among the above-mentioned conventional methods, the method of applying a dwell pressure is widely used as a basic measure against sinking, but it has not been sufficiently effective to completely prevent sinking. Therefore, in addition to the method of applying the holding pressure, prevention of sinking has been attempted by taking other measures. However, when the method of filling the cavity with a large amount of resin as described above is employed, there is a disadvantage that burrs are easily generated.
[0008]
Also, in addition to the method of applying a holding pressure, devising the structure of the mold, such as providing a thickened wall as described above, the temperature of the resin, the injection pressure, the magnitude of the holding pressure, the filling time of the resin, the holding time, and the like. It is also conceivable to suppress sink marks by adjusting various molding conditions. However, these methods rely on the experience and intuition of the operator to determine the mold structure and determine the molding conditions by trial and error, which is extremely troublesome and time-consuming, and also reduces the ability of the individual worker. Due to large dependence, reproducibility and certainty are poor. Further, even if such a large amount of labor is used to apply the holding pressure and the molding conditions are optimized, the solution is not fundamentally solved, and the occurrence of sink marks cannot be completely prevented. These methods are very complicated because they are not universal measures for preventing sink marks and must be set individually for each injection molding apparatus and each molded product.
[0009]
Furthermore, in recent years, a method of using a gas pressure to prevent sink marks has been considered. As one example, there is a method in which molding is performed using a foaming resin, and the resin is brought into close contact with the inner wall surface of the cavity by foaming pressure to prevent sink marks. However, since the molding material is limited, there is a possibility that a molded product having desired characteristics may not be obtained, and the original purpose of injection molding for molding a product according to a use may not be achieved. In addition, a method of sending gas into the resin filled in the cavity and causing the resin to adhere to the cavity inner wall surface from the inside to prevent sink marks, or by injecting gas to at least one entire surface of the cavity inner wall surface There is also a method of uniformly applying pressure to the resin. However, in these methods, the mold apparatus has a special configuration compared to the conventional one, such as a configuration for injecting gas into the resin and a configuration capable of injecting gas over a wide range such as the entire surface of the cavity inner wall surface. Because it is necessary to use, there may be a case where the cost is high, and since the configuration is such that the pressure of the gas is evenly applied to a portion other than a convex portion such as a boss or a rib, which is usually hard to generate sink marks, Injecting gas more than necessary is very inefficient.
[0010]
Therefore, an object of the present invention is to apply a gas pressure only to a portion where a convex portion where a sink mark is likely to be formed can be used as it is, using substantially the same mold apparatus as a conventional one except for a piece. An object of the present invention is to provide a mold apparatus and a molding method capable of efficiently taking measures to prevent sink marks.
[0011]
[Means for Solving the Problems]
The present invention provides, in a mold apparatus for injection molding, a concave portion provided on at least one inner wall surface of a cavity formed when the mold is closed, and the bottom surface of the concave portion is formed of a breathable metal. It is characterized by having gas sending means capable of sending gas into the cavity through the bottom surface of the recess. The portion of the inner wall surface of the cavity other than the bottom surface of the concave portion is formed of a non-permeable gas. The bottom surface of the concave portion is one surface of a piece made of a breathable metal inserted into the concave portion.
[0012]
The molding method of the present invention is a molding method for molding a product having a convex portion by using the mold device having the above-described configuration.After injecting the resin into the cavity in a mold closed state, the gas delivery means Gas is injected through the bottom surface of the concave portion made of a gas permeable metal to pressurize the resin in the concave portion. Pressurization of the resin in the concave portion by gas injection is performed at least until the resin is cooled and solidified.
[0013]
According to such a configuration and method, it is possible to prevent the occurrence of sink marks by injecting a gas into a portion where a convex portion that is likely to cause sink marks at the time of molding is formed and pressurizing the resin. And it is a configuration in which gas is injected only to a portion where sink marks are likely to occur, and the configuration is substantially the same as a normal mold apparatus except that the bottom surface of the concave portion is made of a breathable metal, so that the cost is reduced. Can be suppressed.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0015]
First, the configuration of an injection molding die apparatus according to an embodiment of the present invention will be described. As shown in FIG. 1, this mold apparatus has a fixed mold 1 and a movable mold 2 that can move so as to come into contact with or move away from the fixed mold 1. In the present embodiment, the movable mold 2 has two movable mold plates 2a and 2b. As shown in FIG. 1A, a cavity 3 is formed between the dies 1 and 2 in a state where the fixing die 1 and the movable die 2 are joined (when the dies are closed). Although only the gate 4 is shown in a simplified manner in the drawing, the fixed mold 1 is provided with an injection mechanism for injecting a molding resin (for example, a thermoplastic resin 8) into the cavity 3. .
[0016]
The cavity 3 is formed in a shape corresponding to a desired product shape. Of the cavity inner wall surfaces 1a and 2c constituting the cavity 3, portions corresponding to convex portions such as bosses and ribs of a desired product ( In the example shown, two concave portions 5 are provided. The concave portion 5 is provided so as to penetrate the movable-side mold plate 2a, and communicates with the gas circulation hole 9 provided in the movable-side mold plate 2b. The gas flow holes 9 are connected to gas delivery means 10 which is schematically shown. A piece 6 having a substantially same planar shape as the cross-sectional shape of the concave portion 5 is inserted into the concave portion 5. The piece 6 has the flange 6a fitted into the locking recess provided in the movable mold plate 2a and abuts against the wall of the gas flow hole 9 having a smaller diameter than the piece 6, so that the recess 5 is at least in the closed state. Is held immovable within. An O-ring 7 is arranged between the movable mold plates 2a and 2b so as to be located outside the outer periphery of the concave portion 5, and when the mold is closed, gas flowing through the gas flow holes 9 allows the movable mold plate to move. It is configured such that it does not leak outside through the gap between 2a and 2b.
[0017]
Both the fixed mold 1 and the movable mold 2 (movable mold plates 2a, 2b) are made of a general mold steel material and are non-permeable. On the other hand, the piece 6 is made of a breathable metal (for example, Porcelax II (trade name) manufactured by Shinto Kogyo Co., Ltd.). The gas-permeable metal is a metal having fine communication holes through which a gas such as air or nitrogen gas can easily pass. The average pore size of the fine communication holes of the air-permeable metal is not particularly limited, but after the molten resin flows into the communication holes when the concave portion 5 is filled, the molten resin flows out of the molded product and is released. In order to prevent clogging of the communication hole, the diameter must be small enough not to allow molten resin to enter, and small enough so that the surface of the convex portion of the molded product is maintained to some extent. Considering these conditions, it is preferable that the average pore size of the communication hole of the gas-permeable metal is 100 μm or less.
[0018]
As described above, in the present embodiment, of the cavity inner wall surfaces 1a and 2c, only the piece 6 serving as the bottom surface of the concave portion 5 is made of a gas-permeable metal, and all other portions are made of a gas-impermeable metal.
[0019]
The method of fixing the piece 6 is not limited to the above-described example, and the piece 6 may be fixed in the recess 5 by screwing or the like. Further, as long as the piece 6 is fixed, a configuration may be adopted in which only the movable mold plate 2a is present without the movable mold plate 2b. In that case, the gas delivery means 10 is connected to the recess 5 directly without passing through the gas flow hole 9 or through a communication pipe other than the gas flow hole 9.
[0020]
A method for performing injection molding using this mold apparatus will be described with reference to FIGS. First, the mold is closed and the movable mold 2 is brought into close contact with the fixed mold 1 to form a cavity 3 between the molds 1 and 2. As shown in FIG. 2A, the thermoplastic resin 8 is injected into the cavity 3 from the gate 4 of the injection mechanism.
[0021]
Then, when the injection of the thermoplastic resin 8 is stopped by injecting a predetermined amount of the thermoplastic resin 8 into the cavity 3 including the concave portion 5, the pressure is maintained as in the conventional case, and as shown in FIGS. As schematically shown, a gas such as nitrogen gas is supplied from the gas delivery means 10 through the gas flow holes 9. This gas is injected into the cavity 3 through minute communication holes (not shown) of the piece 6 having air permeability, and pressurizes the thermoplastic resin 8. Cooling is performed in such a state, and the thermoplastic resin 8 solidifies. At this time, the thermoplastic resin 8 in the concave portion 5 shrinks slowly because the thickness is large and the amount of resin is large, and often shrinks after other portions are solidified. However, according to the present embodiment, when the thermoplastic resin 8 in the concave portion 5 is cooled and contracts, a gas is injected into the thermoplastic resin 8 via the piece 6 made of a breathable metal, and the thermoplastic resin 8 is cooled. Pressurized. Therefore, as shown in FIG. 3, the force F _A to recess longer the contraction, the pressure F _B exerted by the gas is offset, occurrence of depression (sink) is prevented. In particular, the direction in which the top surface on the opposite side of the convex portion tends to be depressed, in which the sink is likely to occur and the occurrence of defects such as sink marks is not allowed because of the appearance of the surface (see FIGS. 2 and 3). And the direction in which the gas is injected to pressurize the thermoplastic resin 8 (to the left in FIGS. 2 and 3) is exactly opposite, so that the pressure by the gas effectively reduces the force of the thermoplastic resin 8 on the top surface portion to depress. By pushing back, the thermoplastic resin 8 can be pressed against the cavity inner wall surface 1a, and the occurrence of sink marks can be suppressed.
[0022]
When the cooling and solidification of the thermoplastic resin 8 are completed in this way, the holding pressure and the supply of gas from the gas delivery means 10 through the gas flow holes 9 are stopped. Then, the mold is opened and the molded product is taken out from the cavity 3.
[0023]
Note that the injection pressure and the holding pressure may be the same as those in the related art. The pressure of the gas supplied from the gas delivery means 10 through the gas flow holes 9 is preferably 20 kg / cm ² or more, and if it is less than 20 kg / cm ² , a sufficient effect may not be obtained. The pressure of the gas needs to be sufficient to press the resin against the inner wall surface 1a of the cavity at the top surface, and has never been subjected to a high pressure, but is realistically about 300 kg / cm ² or less. The timing of supplying the gas can be arbitrarily set, but generally, the supply of the gas is started when the injection of the thermoplastic resin 8 into the cavity 3 is completed, and the thermoplastic resin 8 is cooled. It is preferable to stop the supply of gas after solidification. The type of gas is not particularly limited, and may be a gas that is easily available and easy to use, and includes nitrogen, carbon dioxide, and an inert gas. However, easily combustible gases such as hydrogen and oxygen are not preferred because they may cause accidents or cause seizure on molded products and molds.
[0024]
The example shown in FIGS. 1 to 3 is a configuration for molding a product having a boss-shaped protrusion, but as shown in FIG. 4, over the entire periphery along the outer edge, such as a case-shaped member. The present invention is also effective for products having ribs. That is, conventionally, there has been a problem that sink is easily generated in a rib portion. However, by adopting the present invention, the gas delivery means 10 can be provided through the gas flow hole 9 and the piece 6 made of permeable metal. Then, by injecting gas into the cavity 3 and pressurizing the thermoplastic resin 8 to press it against the cavity inner wall surface 1a, the occurrence of sink marks can be prevented.
[0025]
In the present embodiment, the outer surface of the molded product (formation surface) is formed by the cavity inner wall surface 1a of the fixed mold 1 and the back surface (non-format surface) of the molded product is formed by the cavity inner wall surface 2c of the movable mold 2. The concave portion 5 is provided on the inner wall surface 2 c of the cavity of the movable mold 2 in order to provide a convex portion on the rear side surface which is not visible. However, the present invention is not limited to such a configuration. The concave portion 5 may be provided on the cavity inner wall surface 1a of the fixed mold 1, or the concave portion 5 may be provided on both the cavity inner wall surfaces 1a and 2c. May be any number. It is preferable that the pieces 6 made of non-breathable metal are inserted into the recesses 5 respectively, and it is preferable that the gas delivery means 10 and the gas flow holes 9 are connected to all the recesses 5.
[0026]
Also, the outer surface (the appearance surface) of the molded product may be formed not by the inner wall surface 1a of the fixed mold 1 but by the inner wall surface 2c of the movable mold 2 or by both inner wall surfaces. Both surfaces formed by 1a and 2c may be appearance surfaces. In any configuration, the recess 5 and the bridge 6 of the present invention may be arbitrarily arranged so that sink marks do not occur on the appearance of the molded product. Further, the position of the gate 4 may be appropriately changed as necessary, but it is preferable to dispose the gate 4 in consideration of leaving no gate mark on the appearance surface.
[0027]
In the present invention, it is not necessary to distinguish between the cavity surface and the core surface. Therefore, in the present specification, the fixed mold or the movable mold is the inner wall of the cavity 3. In each case, it is expressed as the cavity inner wall surface.
[0028]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of a sink part can be prevented by injecting gas to the part which shape | molds the convex part which is easy to generate | occur | produce at the time of injection molding, pressurizing resin, and pressing resin against a cavity inner wall surface. .
[0029]
In particular, when only the bottom surface of the concave portion for forming the convex portion which is likely to cause sink marks on the inner wall surface of the cavity is formed of a permeable metal and the other portions are formed of a non-permeable metal, gas Pressure can be accurately applied only to locations that are effective in preventing sink marks, and there is no need to supply more gas than necessary. Since there is no possibility of leakage, the pressure of the gas can be applied very efficiently to prevent sink marks. Further, since the mold apparatus substantially the same as the conventional mold apparatus can be used as it is, the cost can be reduced.
[Brief description of the drawings]
1A is a schematic cross-sectional view of a main part of a mold apparatus according to an embodiment of the present invention when the mold is closed, and FIG. 1B is a schematic cross-sectional view of the main part when the mold is opened.
2A is a schematic cross-sectional view of a main part during a resin injection step of a molding method using the mold apparatus shown in FIG. 1, and FIG. 2B is a schematic cross-sectional view of a main part during a gas supply step following FIG. FIG.
3 is an enlarged view of a main part of FIG. 2 (b). FIG. 4 is an enlarged cross-sectional view of a main part of a modified example of the mold apparatus shown in FIG.
FIG. 5 is an enlarged schematic cross-sectional view of a main part of a mold apparatus for explaining the occurrence of sink marks in a conventional mold apparatus.
[Explanation of symbols]
1 Fixed side mold 1a Cavity inner wall surface (Appearance surface)
2 Movable molds 2a, 2b Movable mold plate 2c Cavity inner wall surface (non-formatted surface)
3 Cavity 4 Gate 5 Depression 6 Piece 6a Flange 7 O-ring 8 Resin (thermoplastic resin)
9 the gas flow hole 10 the gas delivery means 11 resin 12 cavity 13 recess 14a, the force exerted by the force _{F B} gas to be 14b shrinkage _{F A} shrinkage

Claims (5)

In a mold device for injection molding,
A concave portion is provided on at least one inner wall surface of the cavity formed when the mold is closed, and the bottom surface of the concave portion is formed of a breathable metal, and gas is supplied from outside the cavity to the inside of the cavity through the bottom surface of the concave portion. A mold sending device having gas sending means capable of sending the mold. The mold device according to claim 1, wherein a portion of the inner wall surface of the cavity other than the bottom surface of the concave portion is formed of a non-permeable metal. The mold device according to claim 1, wherein a bottom surface of the concave portion is one surface of a piece made of a gas-permeable metal inserted into the concave portion. A molding method for molding a product having a convex portion, using the mold device according to any one of claims 1 to 3,
After the resin is injected into the cavity with the mold closed, a gas is injected through the bottom surface of the concave portion made of a gas permeable metal to pressurize the resin in the concave portion by the gas sending means. . The molding method according to claim 4, wherein the pressurization of the resin in the concave portion by the injection of the gas is performed at least until the resin is cooled and solidified.

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