JP3181749B2 - Gas injection molding method and its mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas injection molding method and a mold thereof, and can be used for molding interior and exterior parts such as bumpers and dashboards of automobiles, and resin products such as casings of home electric appliances.

[0002]

2. Description of the Related Art Conventionally, a gas injection molding method has been known as an injection molding method capable of obtaining a lightweight and highly rigid molded product. In this method, after filling a molten resin into a cavity of a mold, injection molding is performed while injecting an inert gas such as pressurized nitrogen gas into the cavity. According to such a gas injection molding method, the molten resin in the cavity is inflated like a balloon and pressed toward the inner surface of the cavity by the inflation force of the pressurized gas. Injection molding can be performed in a good condition without sink even with a material having such a thickness.

[0003] As a method for injection molding a partially thick molded product, a direct injection type gas injection molding method,
A gas channel type gas injection molding method is known. The direct injection method is a method in which a gas injection port is provided in a thickened portion of a mold cavity, and the gas is injected after the molten resin filled in the mold reaches the gas injection port. . Thus, the gas is directly injected into the thickened portion of the cavity, so that a partially thick product can be injection molded.

[0004] In the gas channel type, a gas channel guide portion in which the inner surface of a cavity of a mold is recessed is provided from a gas injection port toward the flow end of the molten resin, and the gas injected into the cavity after the filling of the molten resin is started. Inflating the molten resin toward the inside of the gas channel guide by the expansion force,
This is a gas injection molding method in which a gas passage (hereinafter, referred to as “gas channel”) is formed. In such a gas channel type, the gas channel is guided by the gas channel guide, and the extension direction of the gas channel that is to be obtained when the gas channel guide is not provided is determined by the gas channel guide. For this reason, if a gas channel can be formed long enough to reach the flow end from the gas inlet, gas will be injected into the flow end through the gas channel, and even if the flow end is partially thick, there will be no sink mark due to gas pressure. Can be obtained.

[0005]

However, in the direct injection method, if the gas injection is too early, the gas is injected outside the molten resin, while if the gas injection is too slow, the molten resin reaches the flow end. There is no room for gas to enter and gas cannot be injected. Therefore, there is a problem that it is difficult to control the timing of gas injection. In addition, the injection-molded product must be provided with a gas injection port at a position where the molten resin flows, so that the gas injection port is inevitably impaired in appearance of the product.

In the gas channel type, the gas channel guide portion has a lower flow resistance of the molten resin than the other portion of the cavity. Therefore, when the molten resin is filled, the molten resin flows into the gas channel guide portion first. . In this state, when gas is injected into the cavity, the injected gas must form a gas channel while pushing the molten resin flowing into the gas channel guide out of the gas channel guide. For this reason, when the formed gas channel guide is long because the shape of the cavity is elongated or the size of the cavity is large, all of the molten resin that has flowed into the gas channel guide is completely extruded. Because it becomes difficult, depending on the shape and dimensions of the product,
The desired gas channel cannot be completely formed,
There is a problem that defective parts such as sink marks occur in the molded product. Here, in order to completely expel the molten resin, it is conceivable to increase the gas pressure to be injected. However, if the gas pressure is increased, the gas enters other parts other than the gas channel guide part, and the other parts are not. The gas that has penetrated into the pipe causes defective spots such as sink marks and welds, so that raising the gas pressure does not solve the problem.

[0007] An object of the present invention is to provide a gas injection molding method and a mold thereof that can be molded without impairing the appearance of the product regardless of the shape or size of the product.

[0008]

According to the gas injection molding method of the present invention, after the filling of the molten resin into the cavity of the mold is started, a pressurized gas is further injected into the cavity to form the inside of the molten resin. A gas injection molding method for performing injection molding while forming a gas channel serving as a passage of a pressurized gas,
A gas channel guide is provided in the mold, wherein the inner surface of the cavity is continuously recessed from the gas inlet toward the flow end of the molten resin, and when the cavity is filled with the molten resin, The gas channel guide may be closed in advance, and the gas channel guide may be opened when pressurized gas is injected into the cavity.

In the injection molding die of the present invention, after the inside of the cavity is filled with the molten resin, a pressurized gas is further injected into the cavity to form a passage for the pressurized gas inside the molten resin. A gas injection mold for performing injection molding while forming a gas channel, wherein the inner surface of the cavity is continuously recessed from the gas inlet toward the flow end of the molten resin. And a closing means capable of closing the gas channel guide portion.

[0010]

According to the present invention, since the molten resin is filled while the gas channel guide is closed by the closing means, the molten resin enters the gas channel guide by the closing means until gas injection is started. Thus, the gas channel guide section has room for accommodating an increase in volume caused by expansion of the molten resin during gas injection.
Here, if the closing means is opened, the molten resin easily expands into the gas channel guide portion, so that the gas injected into the cavity advances along the gas channel guide portion while expanding the molten resin, This ensures that the gas channel is formed up to the end of the gas channel guide. For this reason, if the gas channel guide is set in the cavity of the mold, the gas channel following the gas channel guide is reliably formed, so that the desired gas channel can be obtained regardless of the shape and dimensions of the product to be subjected to gas injection molding. Can be formed in the molten resin. Therefore, even in a product having a portion where the thickness dimension is increased at the flow end of the molten resin, a gas channel reaching the portion is reliably formed, and a defect such as sink mark is reliably prevented by the gas pressure in the gas channel. For,
The product can be formed with a good appearance regardless of the shape and dimensions, thereby achieving the above-mentioned object.

[0011]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a main part of an injection molding machine 1 of the present embodiment. The injection molding machine 1 has an injection device 10 for injecting a synthetic resin and a molding die 20. The injection device 10 includes a synthetic resin in a molten state inside a cylindrical barrel 11.
A screw 12 for kneading 30 is provided. barrel
A nozzle 13 is provided at the tip of 11. By connecting the nozzle 13 to the bush 21 of the mold 20 and injecting the molten resin 30, the interior of the mold 20 is filled with the molten resin 30. Inside the nozzle 13, a blowing pipe 14 that receives a supply of an inert gas such as nitrogen gas from a supply source (not shown) and injects a pressurized gas into the molded article 31 is inserted.

The mold 20 is divided into an upper core part 20A and a lower cavity part 20B in the figure. In one of the divided cavities 20B, a cavity 22, which is a mold for molding a large planar molded product or the like, is carved. At the left end of the cavity 22 in the figure, the nozzle of the injection device 10
A bush 21 to which 13 is connected is provided. bush
A sprue 23 serving as an injection port for injecting a pressurized gas for gas injection molding is provided at a central portion of 21. As shown in FIGS. 2 and 3, the cavity 22 has a substantially rectangular flat plate shape as a whole. Cavity 22
A thin plate portion 24 having a small thickness is formed on both sides. In the center of the cavity 22, a gas channel guide portion 25 is formed in which the inner surface of the cavity 22 is continuously recessed from the sprue 23 toward the flow end side (the right side in the figure) of the molten resin 30. At the flow end of the cavity 22, a thick plate portion 26 having a large thickness dimension is formed. Inside the gas channel guide portion 25, a position A at which a blocking portion 27 as a closing means closes the gas channel guide portion 25 and a position B at which the gas channel guide portion 25 is opened.
Are movably provided between the two positions.

The closing portion 27 is a square rod-shaped member having a length corresponding to the entire length of the gas channel guiding portion 25. Closed part 27
The four corners 27A are engaged with a guide mechanism (not shown) provided on the gas channel guide section 25, and the guide mechanism restricts the movement direction of the closing section 27 in one direction and smoothly moves the closing section 27. Slidable. The cross-sectional shape of the closing portion 27 corresponds to the cross-sectional shape of the gas channel guide 25. Thereby, when the closing portion 27 moves to the position A,
The contact surface 27 </ b> B of the closed portion 27 that contacts the molten resin 30 is continuous with the inner surface of the cavity 22. A hydraulic cylinder device 28 for moving the closing portion 27 between two positions A and B is provided on a surface 27C of the closing portion 27 opposite to the contact surface 27B.
Is provided. The hydraulic cylinder device 28 includes the injection device 10
Is controlled by a control device (not shown), and operates in conjunction with the injection device 10.

Here, as shown in FIG. 4, the cavity 22 is filled with the molten resin 30 in a state where the closing portion 27 is moved to the position A and the gas channel guide portion 25 is closed. ing. As a result, the molten resin 30 is prevented from entering the gas channel guide portion 25, and the gas channel guide portion 25 has room for accommodating a volume increase caused by expansion of the molten resin at the time of gas injection. It has become. When the gas channel guide portion 25 is opened by moving the closing portion 27 to the position B as shown in FIG.
The volume increase of 30 can be stored in the gas channel guide 25. By opening the gas channel guide 25, the molten resin 30 can easily expand in the direction toward the gas channel guide 25, and if the gas channel guide 25 is opened when injecting gas into the cavity, the gas will melt. It is possible to easily advance along the gas channel guide portion 25 while expanding the resin 30, and reach the thick plate portion 26 (see FIG. 1) in the molten resin 30 following the gas channel guide portion 25. A gas channel 31 is formed. The gas sent to the thick plate portion 26 through the gas channel 31 forms a hollow portion inside the thick plate portion 26, and due to the pressure of the gas in the hollow portion, the thick plate portion 26 does not cause defects such as sink marks on the surface. It has become.

In this embodiment, the hydraulic cylinder device 28 is driven to move the closing portion 27 to the position A, and then the injection device 10 is driven to melt the molten resin 30 into the thick plate portion of the cavity 22.
After filling up to 26, the pressurized gas is injected into the mold 20, and at the same time, the hydraulic cylinder 28 is driven to move the closing portion 27 to the position B. Thereby, while the gas channel 31 is formed in the molten resin 30 to the end of the gas channel guide portion 25,
The gas is sent into the thick plate portion 26 through the gas channel 31 to form a hollow portion in the thick plate portion 26. And molten resin
The entire surface of the mold 30 is pressed by the gas pressure and closely adheres to the inner surface of the mold 20. After cooling in this state, the mold 30 is taken out of the mold 20 to be a product.

According to the above-described embodiment, the following effects can be obtained. That is, a closing portion 27 for closing the gas channel guide portion 25 is provided, and when the molten resin 30 is filled, the closing portion 27 is closed.
Is closed to prevent the molten resin 30 from entering the gas channel guide portion 25, so that room for accommodating an increase in volume due to expansion of the molten resin 30 during gas injection is secured in the gas channel guide portion 25. be able to.

Therefore, by opening the closing portion 27, the filled molten resin 30 easily expands toward the inside of the gas channel guide portion 25, and the gas channel 31 is formed by the injected gas. The guide portion 25 can be reliably formed up to the end. Thereby, even for a product having the thick plate portion 26 at the flow end of the molten resin 30, it is possible to reliably prevent a defect such as sink mark due to the pressure of the gas passing through the gas channel 31.

Accordingly, since the gas channel 31 following the gas channel guide portion 25 set in the mold 20 can be reliably formed, the gas channel 31 can be formed according to the shape of the product to be gas-injection-molded. The gas channel 31 can be formed, and injection molding can be performed without impairing the appearance regardless of the shape and dimensions of the product to be molded.

When the closing portion 27 is closed, the closing portion 27 is closed.
Since the contact surface 27B of 27 is continuous with the inner surface of the cavity 22, the flow mark generated due to uneven flow is not formed on the filled molten resin 30, and the injection is performed without impairing the appearance of the product from this point. Can be molded.

Next, the effects of the present invention will be described based on specific experimental examples. [Experimental Example] This experimental example is an experiment in which gas injection molding is performed using a mold according to the present invention, and the same basic structure as the mold 20 shown in the above embodiment is used as the mold. This is to perform gas injection molding. Comparative Example This comparative example is an experimental example performed for comparison with the experimental example. That is, a mold having a cavity having the same shape as the mold of the experimental example and omitting the closing portion, and having the same shape as that of the experimental example is to be subjected to gas injection molding.

[Cavity Dimension Setting] In these experimental examples and comparative examples, the dimensions of the mold cavity (see FIG. 3) were set as follows. Total length L1 = 420mm Total width W1 = 100mm Total height (height of thick plate) H1 = 15mm Length of thick plate L2 = 20mm Height of thin plate H2 = 3mm Width of gas channel guide W2 = 6mm Gas Height of the channel guide portion H3 = 9 mm [Injection conditions] In the above experimental examples and comparative examples, injection molding was performed under the same injection conditions as described below. Resin used Polypropylene (Idemitsu Petrochemical Co., Ltd.)
J-750) Resin temperature: 240 ° C Mold temperature: 40 ° C Gas pressure: 10 MPa Gas injection delay time: 3.0 seconds Resin filling time: 2.0 seconds

[Experimental Results] In the experimental example, as shown in FIG. 6, a gas channel 31 was formed following the gas channel guide portion 25 set in the mold. A hollow portion 26A is formed inside the thick plate portion 26 at the flow end. Gas channel 31 and hollow
Due to the gas pressure in 26A, a good product 2 having no defective portions such as sink marks on the entire surface could be obtained. On the other hand, in the comparative example, when the cavity 22 is filled with the molten resin, as shown in FIG.
The molten resin flows into the gas channel guide 25 first, and the gas channel guide portion 25 is completely filled with the molten resin. On the other hand, a portion of the thin plate portion 24 where the molten resin is not filled is formed. When gas is injected in this state, the gas forms a gas channel 31 reaching the thick plate portion 26 and enters the thin plate portion 24 side. The gas that has entered the thin plate portion 24 causes the molten resin to flow backward to generate a weld mark 3 as shown in FIG. 8 to form a defective portion. In addition, since the volume of the hollow portion 26C included in the thick plate portion 26 is reduced by the amount of the gas entering the thin plate portion 24 side, a solid portion 26D that is not hollow is generated in the thick plate portion 26, and the solid portion 26D is When cooled, sink marks 4 are generated on the surface.

The present invention is not limited to the above-described embodiment, but includes the following modifications. That is, the closing means is not limited to the gas channel guide having a single closed portion 27 extending over the entire length of the gas channel guide, but may be a plurality of pin-shaped ones protruding and retracting toward the gas channel guide, as shown in FIG. For example, a plurality of block-shaped closing portions 40 may be arranged along the gas channel guide portion 25. When adopting such closing means, a driving means 41 for independently driving each closing portion 40 is provided,
A controller that performs control based on the pressure applied to the mold, etc.
The operation of each drive means 41 may be controlled by 42.

Further, the closing means is not limited to the one having the same length as the gas channel guide part. As shown in FIG. 11, a closed part 43 of about half the length of the gas channel guide part 25 may be used. Further, the present invention is not limited to the one that moves while maintaining a state parallel to the gas channel guide portion 25. As shown in FIG. 12, one end 44 is rotatably attached to the mold side, and the other end 45 Is closed by a hydraulic cylinder device or the like.
May be.

The closing means is not limited to a means for moving with respect to the gas channel guide, but a block 48 provided with a gas channel guide 47 as shown in FIG.
May be moved with respect to the cavity 49.

Further, the closing part and the gas channel guiding part are not limited to linear ones, but may be circular closing part 50A and gas channel guiding part 50 as shown in FIG.
B or a cross-shaped closed portion 51A and a gas channel guide portion 51B may be used, and a specific shape may be appropriately selected for implementation.

In the above embodiment, the height H3 of the gas channel guide portion 25 is set to be three times the height H2 of the thin plate portion 24.
The height of the gas channel guide portion 25 may be larger or smaller than the thin plate portion 24. However, when the height of the gas channel guide portion 25 is made larger, the formation of the gas channel becomes easier.

Further, the installation position of the driving means such as a hydraulic cylinder device for driving the closing portion is not limited to the core portion 20A of the mold 20 but may be the cavity portion 20B of the mold 20. In this case, FIG. The gas channel guide 52 is also provided on the cavity 20B side, as shown in FIG.
May be driven by a hydraulic cylinder device 54 on the side of the cavity 20B, or a gas channel guide 55 is provided on the side of the core 20A, as shown in FIG.
The gas channel guide section 55 may be closed by a closing section 56 driven by the hydraulic cylinder device 54 of the cavity section 20B.

The driving means for driving the closing portion is not limited to the hydraulic cylinder device, but may be an urging device such as a spring or the like.
It may be an electric type. Further, the pressurized gas is not limited to nitrogen gas, but may be another inert gas such as argon gas. Further, the timing of gas injection is not limited to the time after completion of filling, but may be during filling, and an appropriate timing can be set after the start of filling.

[0030]

As described above, according to the present invention, it is possible to mold a product without impairing its appearance regardless of the shape and size of the product.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the overall configuration of an embodiment of the present invention.

FIG. 2 is a plan view showing a cavity of the present embodiment.

FIG. 3 is a perspective view showing a cavity of the present embodiment.

FIG. 4 is a cross-sectional view illustrating a closed state of a closing unit according to the present embodiment.

FIG. 5 is a sectional view showing an open state of the closing means of the embodiment.

FIG. 6 is a plan view showing experimental results of an experimental example of the present invention.

FIG. 7 is a plan view showing a filling state of a molten resin in a comparative example of the present invention.

FIG. 8 is a plan view showing an experimental result of a comparative example of the present invention.

FIG. 9 is a schematic configuration diagram showing a modification of the present invention.

FIG. 10 is a side view showing a closing means according to a modified example of the present invention.

FIG. 11 is a side view showing a closing means according to a different modification of the present invention.

FIG. 12 is a view corresponding to FIG. 4 showing a closing means according to still another modification of the present invention.

FIG. 13 is a plan view showing a closing means and a channel guide portion according to a modification of the present invention.

FIG. 14 is a view corresponding to FIG. 4 showing a modification of the present invention.

FIG. 15 is a view corresponding to FIG. 4 showing another modified example of the present invention.

[Explanation of symbols]

 20 Mold 22 Cavity 30 Molten resin 31 Gas channel 23 Gas injection sprue 25,47,50B, 51B, 52,55 Gas channel guide 27,40,43,46,50A, 51A, 53,56 Blockage Blockage as a means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-121820 (JP, A) JP-A-4-125116 (JP, A) JP-A-3-293618 (JP, A) JP-A-6-129 246765 (JP, A) Japanese Utility Model 4-52020 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) B29C 45/00-45/84

Claims (2)

(57) [Claims] After the filling of the molten resin into the cavity of the mold is started, a pressurized gas is further injected into the cavity to form a gas channel serving as a passage for the pressurized gas inside the molten resin. A gas injection molding method for performing injection molding while providing a gas channel guide portion in which the inner surface of the cavity is continuously recessed from the gas inlet toward the flow end side of the molten resin in the mold, When filling the cavity with the molten resin, the gas channel guide is closed in advance, and the gas channel guide is opened when a pressurized gas is injected into the cavity. Gas injection molding method. 2. After the filling of the molten resin into the internal cavity is started, a pressurized gas is further injected into the cavity to form a gas channel serving as a passage for the pressurized gas inside the molten resin. A gas injection molding mold for injection molding, wherein a gas channel guide portion in which an inner surface of the cavity is continuously recessed from a gas injection port toward a flow terminal side of a molten resin, and a gas channel guide portion. And a closing means for closing the gas injection mold.