JPH10180809A - Die for gas jointly using injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a mold used for a gas jointly using injection molding method which is excellent in prevention of generation of unfavorable external appearance by a method wherein a width of at least a partial longitudinal section on a side facing a mold cavity surface of an ejector pin is made larger than a width of a longitudinal section of a barrel part. SOLUTION: An ejector pin 1 is of a T-form wherein a width 1a in a longitudinal sectional form of an upper end part 5C of an ejctor pin facing a mold cavity surface is larger than a width 1b in a sectional form of an ejector pin barrel part. When a longitudinal sectional form of an ejector pin upper end part (1α) has the T-form, that wherein an area of the ejector pin upper end facing the mold cavity surface is larger than an area of a sectional form of cutting an ejector pin barrel part (1β) with a surface parallel to the mold cavity, is contained. When pressure is applied from the mold cavity surface, pressure is loaded on a touch surface 10 to the mold, and injected pressure gas is prevented from leaking from a clearance between the ejctor pin and the mold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

2. Description of the Related Art In injection molding, when molding a relatively thick molded product or a molded product having a partially thick portion, the surface of the molded product is called sink mark due to shrinkage of the resin due to cooling. It is widely known to produce depressions. Conventionally, the most common method for preventing sink marks is to increase the injection pressure, extend the injection time, and cool the resin in the cavity to some extent while applying the supply pressure of the molten resin (resin pressurization method). I have.

However, as described in Japanese Patent Application Laid-Open No. 50-75247, the prevention of sink by the above-mentioned resin pressurizing method requires complicated molding and operation because molding conditions are different depending on the thickness of a molded product. Unless a high resin pressure is applied, sufficient shrinkage cannot be prevented, so that burrs are generated on the parting surface, and there is a problem that the work load for removing the burrs increases. Further, when an excessive resin pressure is applied, there is a problem in dimensional accuracy such that warpage occurs in a molded product. Furthermore, in the resin pressurization method, pressure is easily transmitted to a thick portion near the gate, but pressure is not sufficiently applied to a thick portion away from the gate portion, and depending on the position of the thick portion, the pressure is not completely increased. For example, the sink cannot be eliminated.

In Japanese Patent Application Laid-Open No. 50-75247, after injecting a molten resin into a cavity, one side of a molded product is pushed up with a valve body, and the one surface of the molded product and this one surface are molded. A gas injection molding method is proposed in which a cavity is formed between the core and a pressurized gas is press-fitted into the cavity, and the other surface of the molded product is pressed into contact with the corresponding cavity surface.

In this gas combined injection molding method, pressurized gas is injected instead of applying resin pressure in the resin pressurization method, and the occurrence of sink marks is prevented by the pressurized gas injection. However, in this method, the parting surface of the pressurized gas injected into the mold and the problem of the pressurized gas leaking from between the ejection pin and the mold are solved.
No solution is disclosed. Therefore, the uneven thickness part,
In particular, this method was insufficient to completely solve sink marks of a molded product having a partially thick portion.

On the other hand, the specification of WO93 / 14918 discloses that in a combined gas injection molding method, a mold having a sealed structure is used to prevent leakage of pressurized pressurized gas and increase pressure efficiency. Have been. according to this,
Regarding the prevention of gas leakage from the ejector pin, the disclosure of providing an O-ring around the ordinary ejector pin is disclosed. However, in this method, it takes time and effort to assemble the mold, and the O-ring is liable to be deteriorated by sliding with the mold portion, and it is necessary to remodel the mold to install the O-ring on the sliding portion. Is a problem.

[0006] In recent years, the demand for large-sized molded products such as housings of OA equipment and household electric appliances, and furthermore, automobile parts and the like has been increased, and the demand for thinned molded products for cost reduction of products has also increased. ing. In the case of a thin, large-sized molded product, a reinforcing portion generally called a rib or a boss is usually provided to maintain strength. The ribs and bosses have a greater reinforcing effect as the wall thickness is increased, and the ribs also have a flow assisting effect that allows the resin to be easily filled in the mold.

However, when thick ribs or bosses are provided, appearance problems such as sink marks on the surface (design surface) of a molded product corresponding to the ribs or bosses are likely to occur. In other words, thin and large molded products, which have been growing in demand in recent years, are provided with thick ribs and bosses in order to maintain necessary strength, but when such thick ribs and bosses are provided. At present, it is difficult to obtain a satisfactory molded product due to insufficient methods and molds for preventing appearance defects.

Further, Japanese Patent Application Laid-Open No. 50-75247,
After injecting a molten resin into a cavity described in WO93 / 14918, pressurized gas is injected between one side of a molded article and a core for molding the one side to prevent sink marks. However, it has been insufficient to prevent the leakage of the pressurized gas from the gap between the protrusion pin and the mold.

[0009] In order to fix the normal protruding pin to the protruding plate due to its function and ease of installation, the lower end has a T-shaped vertical cross-section, and the upper end (1α) facing the mold cavity has an upper end (1α). It is designed so as to be straight with respect to the protruding direction or to be tapered more than the body portion (1β), and it was not conceivable to make this a valve-like structure. That is, except for the lower end portion (1γ), the protruding pin was in contact with the mold portion accommodating the protruding pin only on a plane parallel to the protruding direction.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and provides a mold used for a gas combined injection molding method to completely prevent appearance defects from occurring. The purpose is to do.

[0011]

According to the present invention, the width of the vertical section of at least a part of the side of the protrusion pin facing the mold cavity surface in the gas injection molding mold is made larger than the vertical section width of the body. By preventing the pressurized gas injected between the mold and the molten resin from leaking from the gap between the protruding pin and the mold, the design surface of the molded product can be pressed efficiently against the mold. And completed the present invention.

That is, the present invention is as follows. (1) In the injection molding die, in a state in which the width of the vertical section of a part other than the lower end of the protrusion pin is larger than the width of the vertical section of the protrusion pin body, and the mold is closed,
A mold for injection molding with gas, characterized in that the mold has a portion where a portion larger than the width of the longitudinal section of the protrusion pin body contacts a surface that is not parallel to the protrusion direction. (2) In the injection molding die, the vertical cross-sectional shape of the upper end of the protruding pin facing the mold cavity surface is T-shaped, and the T-shaped portion of the upper end of the protruding pin in a state where the die is closed is: A mold for combined use with gas, characterized in that the mold has a portion in contact with a surface that is not parallel to the protruding direction. (3) The mold for combined use with gas according to the above (1) or (2), wherein the protrusion pins can be separated.

According to the present invention, in the injection molding of a molded article having an uneven thickness portion, a molten resin is injected into a cavity, and the cavity surface corresponding to one surface of the molded article before or after the injection is completed. Injection mold for combined use with gas that prevents pressurized gas from leaking out of the gap between the protruding pin and the mold in order to pressurize the pressurized gas from above and effectively press the other surface of the molded product against the corresponding cavity surface Is provided.

Further, the mold for gas injection molding according to the present invention can be used for counter pressure injection molding in which a resin is filled after injecting a pressurized gas into the mold, or a fluid exceeding 1 atm in the mold for any purpose. It can also be used to prevent leakage of the fluid from between the protrusion pin and the mold in injection molding for injecting the fluid. In the molding method using the combined gas injection molding mold of the present invention, the injection of the molten resin may be a short shot or a full shot, and the injection of the pressurized gas is started at any time before or after the injection including the completion of the injection. May be. However, in order to prevent the pressurized gas from leaking from the parting line (PL) portion of the mold or the like, pressurization of the pressurized gas is performed after injecting an excessive amount of molten resin compared to the full shot or the volume of the cavity. Is preferred. Here, the excess amount of the molten resin compared to the cavity volume means that the volume of the molten resin at the temperature of the resin immediately after injection filling into the mold and the average mold pressure is smaller than the cavity volume. It means that it is large, and it is preferably an amount which becomes 103% by volume or more.

In the present invention, the cavity surface corresponding to one side of the molded article has an open area path which is partially open to the atmosphere and communicates with the atmosphere, and the cavity surface corresponding to the other side of the molded article. It is preferable that a mold having a closed area surface that is cut off from communication with the atmosphere is used, and pressurized gas is injected from the cavity surface side corresponding to the other surface of the molded product, which is the closed area surface. The air release path plays a role of releasing air and / or gas generated from the molten resin to the outside of the cavity when the cavity is filled with the molten resin. The reason why the pressurized gas is press-fitted from the cavity surface side that is the closed area surface is to make it easier to prevent the pressurized gas from escaping from the mold.

The press-fitting of the pressurized gas is not particularly limited as long as the press-fitting can be performed from a predetermined cavity surface side. As will be described later, even if a dedicated passage is provided, a part of the projecting pin having a normal shape is used. You may go around. The uneven thickness portion according to the present invention includes a thick portion protruding like a rib or a boss, or a portion where the thickness is changed in a wide range over a certain portion.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal cross-sectional view of a protruding pin having an T-shaped vertical cross section at the upper end (1α) of the protruding pin 1 which is an example of the protruding pin used in the present invention. Since the normal protruding pin is installed in the mold from the rear part of the mold, a straight shape or a tip whose end portion is cut in accordance with the shape of the molded product is used. That is, hitherto, those in which the upper end (5c) of the protruding pin facing the mold cavity surface has a larger shape than the protruding pin body (1β) connected thereto have not been generally used. On the other hand, as shown in the drawing, the protrusion pin 1 of FIG. 1 which is an example of the present invention has a protrusion pin having a width (1a) in the vertical cross-sectional shape of the upper end portion (5c) of the protrusion pin facing the mold cavity surface. It has a T-shape larger than the width (1b) in the cross-sectional shape of the body.

In the present invention, the upper end (1
α) has a T-shape when the area of the upper end of the protruding pin facing the mold cavity surface is cut by a plane parallel to the mold cavity of the protruding pin body (1β). Includes all that are larger than the area of That is, when pressure is applied from the mold cavity surface, pressure is applied to the contact surface with the mold, and the pressurized gas injected between the mold and the molten resin is prevented from leaking from the gap between the ejection pin and the mold. It works as a valve.

FIG. 2 is a sectional view of the mold 2 corresponding to the protruding pin of FIG. As shown, the mold of the present invention has a surface 11 that is not parallel to the ejection direction of the ejection pin, and this surface 11 contacts the ejection pin surface 10 of FIG. 1 with the mold closed. It is designed like. Next, a combined gas injection molding method using the combined gas injection molding mold of the present invention will be described with reference to FIG.

The mold 2 is composed of a fixed mold 3 and a movable mold 4, and a cavity 5 is formed between the mold 3 and the molten resin during molding. Gas injection pins 6 are provided on the cavity surface (5b) corresponding to the non-design surface of the molded product. The gas injection pin 6 is embedded in the movable mold 4 with its tip facing the cavity 5 from the cavity surface (5b). The gas injection pin 6 is provided with a pressurized gas source (not shown) through a valve 7. ) Is supplied to the cavity 5 through a gap left between the moving side mold 4 and the pressurized gas sent from the gas introduction path 8 connected to the cavity 5. 9a is an O-ring for preventing the pressurized gas from escaping from the joint of the mold components.

The mold 2 shown in FIG. 3 is for molding a substantially box-shaped molded product having a rib on the inside, and the parting surface is located along the outer surface of the bottom of the box-formed product. ,
The cavity surface 5a corresponding to the outer surface of the box-formed article is open at a position corresponding to the bottom surface of the box-formed article. As the protrusion pin in the present invention, there is a protrusion pin in which the width of the vertical cross section of a part other than the lower end portion (1γ) is larger than the width of the vertical cross section of the protrusion pin body (1β). The width of the upper end portion (5c) facing the mold cavity surface (5b) as shown in FIG. It is preferable in consideration of the properties. 1 and 2
In the case where no sealing material is provided, it is preferable that the contact surface 10 of the ejector pin and the contact surface 11 of the mold not parallel to the projecting direction be smooth so that no gap is formed at the time of contact. More preferably, the mold portion, which is the contact surface between the protruding pin 1 and the mold 2, is shown in FIG.
An O-ring (9b) as shown in FIG. 5 may be provided, or an O-ring may be provided on the protruding pin side as shown in FIG. Further, a gas seal material may be provided at a position as shown in FIGS. Here, the gas seal material is not particularly limited in material, but is desirably smooth and / or resilient so that there is no gap between the protrusion pin and the die contact surface. For example, silicon rubber or butadiene rubber may be used. As the existence form, 12a in FIG.
May be connected to the protruding pin as shown in FIG.
As shown in b, it may be connected to the mold, or a sealing material with a hole according to the shape of the protruding pin may be simply passed through the protruding pin to be present without being connected to the protruding pin or the mold. Is also good.

Further, a molding method using the combined gas injection molding mold of the present invention will be described with reference to FIG. First, a molten resin is injected into the cavity 5 with the mold 2 closed. As described above, the injection amount is preferably an excessive amount of the molten resin in comparison with the volume of the cavity 5.

Before, at or after the completion of the injection of the molten resin, the valve 7 is opened to supply a pressurized gas from a pressurized gas source (not shown) to a gas introduction passage 8 provided in the mold 4. I do. As described above, the injection of the pressurized gas may be started before, after, or after the completion of the injection, but is preferably immediately after the injection is completed. As the pressurized gas, for example, air, carbon dioxide, nitrogen or the like is used. The type of gas used is preferably selected depending on the pressure of the pressurized gas, molding material, molding conditions, and the like. The pressure of the pressurized gas varies depending on the type of resin used, the shape of the molded product, the size of the molded product, and the like, but is usually 10 to 250 kgf / cm.
² , preferably 20 to 200 kgf / cm ² .

The pressurized gas supplied to the gas introduction passage 8 passes through a gap between the gas injection pin 6 and the movable mold 4, and enters the cavity 5 from the cavity surface (5 b), which is a closed area surface. Press-fit. This pressurized gas is pressed into the cavity 5 between the inner surface of the box-shaped part and the cavity surface (5b), whereby the outer surface of the box-shaped part is moved to the corresponding cavity surface (5a). Press. And
By the pressing with the pressurized gas, the occurrence of sink marks on the surface of the molded product on the cavity surface (5a) side is suppressed, and the transferability on the cavity surface (5a) side is improved.
The problem of poor appearance due to sink marks and uneven gloss is also reduced. Further, the releasability when removing the molded product from the mold 3 is also improved.

Here, in order for the pressurized gas introduced into the cavity 5 to effectively press one surface of the molded article against the cavity surface (5a), the pressurized gas injected into the cavity 5 must be used. It is important to prevent the outside of the mold 2 from leaking. For this reason, it is preferable that the cavity surface (5b) is a closed region surface in which communication with outside air is blocked. Therefore, by using the protruding pin having the shape of the present invention, leakage of the pressurized gas from the gap between the protruding pin and the mold can be reliably and easily prevented.

The protruding pin of the present invention has a portion other than the lower end portion having a width wider than the width of the body portion. In order to install the protruding pin in a mold, it can be separated as shown in FIGS. It is more practical to design it. The separation of the protruding pin is performed by the upper end (1α) shown in FIGS.
The separation may be performed not only at the lower end (1γ) but also at the body. The protrusion pins may be separated into two parts as shown in FIGS. 8 and 9, but may be further divided into three parts or four parts for convenience. In this case, if it can be removed from the mold cavity surface as shown in FIG.
Workability at the time of replacement of the O-ring etc. is improved.

Further, the principle of the protrusion pin of the present invention will be described with reference to FIG. FIG. 10 is a schematic diagram when the pressurized gas is injected between the mold cavity (5b) and the resin 13 injected and filled. Here, the pressurized gas 14 is injected into the mold through a gap between the gas injection pin 6 and the mold 4.
The pressurized gas injected into the cavity is closed at the side wall by the side wall. The pressurized gas presses the resin 13 against the mold design surface, and at the same time, presses the resin cavity surface (5).
b) is also pressurized. At this time, pressure is applied to a portion of the protruding pin facing the mold cavity as shown in a. When the pressurized gas enters between the ejection pin and the mold and presses the pin in the direction in which the pin is ejected at b, as a result, the ejection pin becomes
It is pressed by the force of (ab) in the direction opposite to the protrusion as indicated by α in the figure. That is, this force acts to bring the surface of the protruding pin at the position where the O-ring (9b) is installed into close contact with the metal surface, whereby the pressurized gas cannot leak from the gap between the protruding pin and the mold.

Further, the protruding pin of the present invention can be formed by forcibly pulling the pin in the direction in which the pin returns with the return pin when the mold is closed, or by pressing the pin in the direction in which the pin returns by attaching a spring to the root of the pin. It is effective. The shape of the tip of the protruding pin is not particularly limited to the shape shown in FIG. 1 but may be, for example, the shape shown in FIG. 11 as long as the shape spreads toward the mold cavity surface side where the principle of the present invention can be used.

The protruding pin of the present invention has a shape in which the width 20 of the vertical section of a part other than the lower end portion (1γ) of the protruding pin is larger than the width 21 of the vertical section of the protruding pin body (1β). The portion 22 larger than the width of the longitudinal section of the body portion is not particularly limited to the tip portion, but may have a structure as shown in FIG. 13 in which the principle of the present invention can be used. Considering the convenience of the mold structure, it is preferable that the upper end portion facing the mold cavity surface is wider than the body portion as shown in FIGS. 1 and 11, but the reason is that the protruding portion should be as small as possible. In some cases, the configuration of FIG. 13 is also effective. At this time, in order to install the protruding pin of FIG. 13 in the mold, as shown in FIG.
May be provided so that the mold can be divided. Further, it is preferable that the protruding pins be separable at a position indicated by 23, for example, in terms of installation on a mold.

[0030]

Embodiment 1 Using the mold shown in FIG.
mm was formed into a box-shaped molded product. This box-shaped molded product has a thick rib 15 having a thickness of 3 mm. An ABS resin was used as a molding material, and after an excessive amount (103% by volume) of the molding material was injected with respect to the cavity volume, a pressurized gas was immediately injected for 3 seconds to mold a molded article. After the pressurized gas was injected, the valve 7 was closed, the pressurized gas was held in the cavity for 20 seconds, and then the valve 7 was opened to collect the pressurized gas. The respective molding conditions are shown below. Cylinder temperature: 230 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin pressure: 10 kg / cm ² (gauge pressure) Pressure of pressurized gas: 100 kg / cm ² (gauge pressure) And the sink of the design surface opposite to the rib was measured. Table 1 shows the gas pressure (pressure after holding for 20 seconds) immediately before opening the valve 7 measured by the pressure gauge 16. As is clear from Table 1, the molded article according to the present invention had a good appearance, and had a good appearance with almost no sink marks and uneven gloss.

[0031]

COMPARATIVE EXAMPLE 1 Molding was performed under the same conditions as in Example 1 except for using a normal mold having a protruding pin shown in FIG. The appearance of the molded article was judged with the naked eye, and the sink of the design surface opposite to the rib was measured. Pressure gauge 1
Table 1 shows the gas pressure (pressure after holding for 20 seconds) immediately before opening the valve 7 measured in 6.

[0032]

[Table 1]

[0033]

From the above results, it can be seen that the mold of the present invention is capable of injecting a pressurized gas between the resin and the mold, pressing the uneven thickness portion against the design surface, and obtaining a molded article having a good appearance. It turned out to be very effective. Prevention of leakage of pressurized gas from the protrusion pins, which is indispensable in many injection molding dies, can be achieved very easily and reliably.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an upper portion of a protrusion pin used in the present invention.

FIG. 2 is a partial sectional view showing an example of a mold section used in the present invention.

FIG. 3 is a cross-sectional view illustrating an example of a mold according to the present invention.

FIG. 4 is a partial sectional view showing an example of a mold section provided with an O-ring used in the present invention.

FIG. 5 is an upper longitudinal sectional view showing an example of a protruding pin provided with an O-ring used in the present invention.

FIG. 6 is an upper longitudinal sectional view showing an example of a protruding pin provided with a gas sealing material used in the present invention.

FIG. 7 is a partial sectional view showing an example of a mold section provided with a gas seal material used in the present invention.

FIG. 8 is a longitudinal sectional view showing an example of a protruding pin which can be divided into an upper part, a body part, and a lower part, which is used in the present invention.

FIG. 9 is a longitudinal sectional view showing an example of a protruding pin that can be divided into two parts, an upper part, a body part, and a lower part, used in the present invention.

FIG. 10 is an explanatory view of the principle of gas sealing when using the mold of the present invention.

FIG. 11 is an upper longitudinal sectional view showing an example of an upper portion of a protrusion pin of the present invention.

FIG. 12 is a cross-sectional view of a mold using a normal-shaped protrusion pin used in Comparative Example 1.

FIG. 13 is a partial sectional view showing an example of a protrusion pin and a mold according to the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 ejection pin 2 mold 3 fixed mold 4 moving mold 5 mold cavity 5 a cavity surface 5 b cavity surface 5 c upper end of ejection pin 6 gas injection pin 7 valve 8 gas introduction path 9 a O-ring 9 b O-ring 9 c O Ring 10 Contact surface of the ejection pin with the mold 11 Contact surface of the mold with the ejection pin 12a Seal material 12b Seal material 13 Resin 14 Pressurized gas 15 Thick rib 16 Pressure gauge 17 Normal shape ejection pin 18 Mold dividing position Reference Signs List 19 O-ring 20 Width of vertical section of body section larger than width of longitudinal section 21 Width of longitudinal section of body section 22 Width of section of body section larger than vertical section 23 Projection pin separation section

Claims (3)

[Claims] In the injection molding die, the width of the vertical cross section of a part other than the lower end of the protrusion pin is larger than the width of the vertical cross section of the protrusion pin body, and the mold is closed. Wherein the mold has a portion in which a portion larger than the width of the longitudinal section of the protrusion pin body contacts a surface that is not parallel to the protrusion direction. 2. An injection molding die, wherein a vertical cross-sectional shape of an upper end portion of a protruding pin facing a mold cavity surface is T-shaped, and a T-shaped portion of the upper end portion of the protruding pin when the die is closed. Wherein the mold has a portion in contact with a surface that is not parallel to the protruding direction. 3. The mold for injection molding with gas according to claim 1, wherein the protrusion pins can be separated.