JPH10119077A - Gas combined injection molding method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To completely prevent appearance defects from occurring by a combined gas injection molding method. SOLUTION: In the injection molding of a molded article having an uneven thickness portion, after injection of a molten resin, a pressurized gas is press-fitted from a cavity surface 4b side corresponding to one surface of the molded article, and the other surface of the molded article is corresponding thereto. While being pressed against the cavity surface 4a, the pressurized pressurized gas is caused to enter the resin constituting the thick part of the molded product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method, and more particularly, to a combined gas injection molding method involving pressurized gas injection between a resin injected into a cavity and a cavity surface.

[0002]

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 sinking 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). Are known.

However, as described in Japanese Patent Application Laid-Open No. 50-75247, the prevention of sinking by the above-mentioned resin pressurization method requires complicated molding and work because the molding conditions vary depending on the thickness of the 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 Laid-Open Publication No. 50-75247, after injecting a molten resin into a cavity, one side of the molded product is pushed up with a valve body, and one side of the molded product and one side of the molded product 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 combined gas injection molding method, a pressurized gas is injected instead of applying a resin pressure in the resin pressurization method, thereby preventing sink marks from being generated by the pressurized gas injection. In this gas combined injection molding method, a pressurized gas is formed in a predetermined one side of a molded article, a pressurized gas is injected thereinto, and molding is performed by the pressure of the pressurized gas injected into one side of the molded article. Although it is intended to prevent sink marks by pressing the other surface of the product against the corresponding cavity surface, it is difficult to obtain a sufficient sink preventing effect only by pressing with the pressure of the pressurized gas.

As a method for preventing sink marks in a molded article having an uneven thickness portion, a hollow portion is formed by introducing a pressurized gas into a molten resin constituting the uneven thickness portion, which is generally called gas assist molding. Methods are known. According to this method, sinking of the uneven thickness portion can be prevented, but due to a difference in the pressing force of the uneven thickness portion and the thin portion against the cavity surface, and secondary transfer after the pressurized gas is introduced into the resin, Gloss and gloss unevenness often occur on the flat surface side corresponding to the portion where the uneven thickness portion protrudes.

Further, Japanese Patent Application Laid-Open No. 7-314483 discloses that after a pressurized gas is introduced into a molten resin, the pressurized gas is injected between a predetermined cavity surface and the resin. . Particularly, in this method, since the pressurized gas is first introduced into the molten resin, the same gloss and gloss unevenness as in the above-described gas assist molding is generated. Also, in this method, the pressurized gas is pressed into the cavity surface by pressurizing the pressurized gas between the independent uneven thickness portion and the cavity surface where it is difficult to introduce the pressurized gas into the inside. It is necessary to separately provide an injection port of the pressurized gas at a portion where the pressurized gas is injected between the resin and the cavity surface, and there is also a problem that the mold structure becomes complicated.

[0009]

However, in recent years,
Demand for large molded products such as housings of OA equipment and home electric appliances, and furthermore, automobile parts and the like is increasing, and demand for thinner molded products for cost reduction of products is also increasing. 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 the bosses have a higher reinforcing effect as the wall thickness is increased, and also have a flow assisting effect in which the resin can be easily filled in the mold.

However, when thick ribs or bosses are provided, appearance problems such as sinking of the surface (design surface) of the molded product corresponding to the ribs or the boss, glossiness, and uneven gloss 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, all of the techniques for preventing appearance defects are insufficient, and it is difficult to obtain satisfactory molded products.

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and has as its object to completely prevent appearance defects from occurring by the combined gas injection molding method.

[0012]

The present inventor has found that when a pressurized gas is injected between the resin in the cavity and the cavity surface, the injection pressure of the molten resin, the pressure of the pressurized gas and the thickness of the uneven portion are reduced. According to the shape and size, the pressurized gas injected does not stay between the resin and the cavity surface, but penetrates into the resin constituting the uneven thickness portion to form a hollow portion, and completed the present invention. That is what led to it.

That is, according to the present invention, in injection molding of a molded article having an uneven thickness portion, a molten resin is injected into a cavity,
At any time before or after, including when the injection is completed, pressurized gas is injected from the cavity surface side corresponding to one surface of the molded product, and the other surface of the molded product is pressed against the corresponding cavity surface, and the pressurized gas that has been injected is pressed. Injecting the resin into the resin constituting the thick part of the molded article.

According to the present invention, the other surface of the molded product is pressed against the corresponding cavity surface by the pressurized gas press-fitted between one surface of the molded product and the corresponding cavity surface, Since it is possible to prevent sinking by both introducing a pressurized gas into the part and forming a hollow part in the uneven thickness part, at the same time as in the case of conventional gas assist molding, it is possible to reliably prevent sinking. It can also prevent the occurrence of uneven gloss and gloss.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the injection of a molten resin may be a short shot or a full shot, and the injection of a pressurized fluid may be started at any time before or after, including when injection is completed. However, in order to easily prevent the pressurized gas from leaking from the mold, it is preferable to press-in the pressurized gas after injecting the molten resin in excess of the full shot or the volume of the cavity. 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 surface of the molded article is partially open to the atmosphere and an open area surface is opened to the atmosphere, and the cavity surface corresponding to the other surface of the molded article is the atmosphere. It is preferable to use a mold having a closed area surface in which communication with the mold is interrupted, and pressurize the pressurized gas from the cavity surface side corresponding to the other surface of the molded product which has become 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 path open to the atmosphere may use the gap left on the parting surface of the mold as it is.
It is preferable to provide grooves formed on the parting surface of the mold so that the air and / or gas can be released smoothly. In addition, an air release path is opened also on a cavity surface corresponding to the other surface of the molded product, and the cavity surface is also set as an open region surface so that the air and / or gas can be more reliably released. You can also. However, in this case, the open-to-atmosphere path that opens to at least the cavity surface corresponding to the other surface of the molded product is
It is preferable to be able to close when pressurized gas is injected from the cavity surface side.

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 described later, even if a dedicated passage is provided, the pressurizing gas is formed around the ejector pins. You may.

The uneven thickness portion according to the present invention includes a thick portion protruding like a rib or a boss, or a portion whose thickness is changed over a wide range over a certain portion.

The resin that can be used in the present invention is not particularly limited as long as it is generally called a thermoplastic resin. For example, rubber-reinforced styrene resins such as polystyrene, high impact polystyrene, and medium impact polystyrene, styrene-acrylonitrile copolymer (SAN resin), acrylonitrile-butyl acrylate rubber-styrene copolymer (AAS resin), acrylonitrile-ethylene Propyl rubber-styrene copolymer (AES), acrylonitrile-chlorinated polyethylene-styrene copolymer (ACS), ABS resin (for example,
Styrene resins such as acrylonitrile-butadiene-styrene copolymer, acrylonitrile-butadiene-styrene-alpha-methylstyrene copolymer, acrylonitrile-methyl methacrylate-butadiene-styrene copolymer), and acrylic resins such as polymethyl methacrylate (PMMA) Resin, low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (P
P) and the like; vinyl chloride resins such as polyvinyl chloride and polyvinylidene chloride; vinyl chloride copolymer resins such as ethylene vinyl chloride vinyl acetate copolymer and ethylene vinyl chloride copolymer; polyethylene terephthalate (PETP) , PET), polyester resins such as polybutylene terephthalate (PBTP, PBT), polycarbonate resins such as polycarbonate (PC) and modified polycarbonate, polyamide resins such as polyamide 66, polyamide 6, and polyamide 46, polyoxymethylene copolymers, Polyacetal (POM) resin such as polyoxymethylene homopolymer, other engineering resin, super-engineering resin such as polyether sulfone (PES), polyether imide (P
EI), thermoplastic polyimide (TPI), polyetherketone (PEK), polyetheretherketone (PE
EK), polyphenylene sulfide (PSU), etc., as well as cellulose acetate (CA), cellulose acetate butyrate (CAB), and ethyl cellulose (EC)
And liquid crystal polymers such as liquid crystal polymers and liquid crystal aromatic polyesters. In addition, thermoplastic polyurethane elastomer (TPU), thermoplastic styrene butadiene elastomer (TSBC),
Thermoplastic elastomers such as thermoplastic polyolefin elastomer (TPO), thermoplastic polyester elastomer (TPEE), thermoplastic vinyl chloride elastomer (TPVC), and thermoplastic polyamide elastomer (TPAE) can also be used. In the present invention, the above-mentioned thermoplastic resin may be synthesized in the molding process of the present invention, or a blend of one or more of the above-mentioned thermoplastic resins may be used, and a filler and / or an additive may be used. May be used.

Hereinafter, further description will be made with reference to the drawings.

FIG. 1 is a sectional view showing an example of a mold used in the present invention.

As shown in the figure, the mold 1 is composed of a fixed mold 2 and a movable mold 3, and a cavity 4 is formed between the two to be filled with a molten resin during molding.

A groove is formed on the fixed-side mold 2 side of the parting surface, and constitutes an air release path 5. The open-to-atmosphere path 5 is open to a cavity surface 4a corresponding to one surface of a molded product formed in the cavity 4, and the side of the cavity surface 4a is opened to the atmosphere to be an open area surface. At least the opening to the cavity 4 or the vicinity thereof is generated from the air or the molten resin in the cavity 4 without infiltrating the resin when the molten resin is injected and filled into the cavity 4. The gas has a thickness that allows the gas to be discharged to the outside of the mold 1. This thickness depends on the type of resin and the molding conditions, but is generally preferably from 1/200 mm to 1/10 mm, more preferably from 1/100 mm to 1/10 mm, even more preferably from 3/100 mm. It is 100 mm or more and 7/100 mm or less.

On the other hand, on the side of the cavity surface 4b corresponding to the other surface of the molded product, the area around the ejector pin 6 connected to the atmosphere is O
Sealed by a ring 7a and open to the atmosphere 5
And there is no opening, and it is a closed area surface in which communication with the atmosphere is cut off. A gas injection pin 8 is provided on the side of the cavity surface 4b which is the closed region surface.
The gas injection pin 8 is embedded in the movable mold 3 with its tip facing the cavity 4 from the cavity surface 4b, and is connected to a pressurized gas source (not shown) via a valve 9a. The pressurized gas sent from the connected gas introduction path 10 is supplied to the cavity 4 via a gap left between the moving-side mold 3. In addition, 7 in the figure
b is an O-ring for preventing the pressurized gas from escaping from the joint of the mold components.

The mold 1 shown in the figure 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 open-to-atmosphere path 5 is a cavity surface 4a corresponding to the outer surface of the box-shaped article, and is opened at a position corresponding to the bottom surface of the box-shaped article. The opening position of the air release path 5 is not limited to such a position, and may be the position shown in FIGS. 2 and 3 in accordance with the position of the parting surface.

In FIG. 2, the parting surface is located at the end of the side wall of the box-shaped article, and the open-to-atmosphere path 5 is provided.
Is a cavity surface 4a corresponding to the outer surface of the box-formed article, and is opened at a position corresponding to the tip of the side wall of the box-formed article. The gas injection pin 8 for pressurizing the pressurized gas is provided on the cavity surface 4 corresponding to the inner surface of the box-shaped product.
It is provided on the b side.

In FIG. 3, the parting surface is located in the middle of the side wall of the box-shaped product, and the open-to-atmosphere path 5 is formed.
Is a cavity surface 4a corresponding to the outer surface of the box-formed article, and is opened at a position corresponding to the intermediate portion of the side wall of the box-formed article. The gas injection pin 8 for pressurizing the pressurized gas is provided on the cavity surface 4 corresponding to the inner surface of the box-shaped product.
It is provided on the b side.

Further, the molding method of the present invention will be described with reference to FIG.

First, a molten resin is injected into the cavity 4 with the mold 1 closed. As described above, the injection amount is preferably an excessive amount of the molten resin compared to the volume of the cavity 4. At this time, the air in the cavity 4 and the gas generated from the molten resin are released from the open-to-atmosphere path 5 together with the filling of the molten resin.
Air bubbles are prevented from remaining between a and b. Further, in order to ensure this release, it is preferable to open the atmosphere opening path 5 at a position away from the gate 11.

Before, after or after the completion of the injection of the molten resin, the valve 9a is opened to supply a pressurized gas from a pressurized gas source (not shown) to the gas introduction passage 10 provided in the mold 1. 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.

The pressurized gas may be, for example, air or carbon dioxide gas, but is preferably an inert gas such as nitrogen. 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 article, the size of the molded article, and the like, but is usually 10 to 250 kgf / c.
m ² , preferably 40 to 200 kgf / cm ² .

The pressurized gas supplied to the gas introduction path 10 is
Through the gap between the gas injection pin 8 and the moving side mold 3, it is press-fitted into the cavity 4 from the cavity surface 4 b side, which is a closed area surface. The pressurized gas is pressed between the inner surface of the box-shaped article in the cavity 4 and the cavity surface 4b, thereby pressing the outer surface of the box-shaped article against the corresponding cavity surface 4a. By the pressing with the pressurized gas, the occurrence of sink marks on the surface of the molded product on the side of the cavity surface 4a is suppressed, and the transferability on the side of the cavity surface 4a is improved. Is also reduced. Further, the releasability of removing the molded product from the mold 1 is also improved.

On the other hand, the pressurized gas press-fitted between the inner surface of the box-shaped product in the cavity 4 and the cavity surface 4b is made to penetrate into the resin constituting the uneven thickness portion of the molded product, and is introduced into the uneven thickness portion. Form a hollow part. By doing so, both the pressing of the outer surface of the molded product against the cavity surface 4a and the formation of a hollow portion in the uneven thickness portion prevent shrinkage and prevent the occurrence of gloss and uneven gloss. Will be planned. The conditions for guiding the pressurized gas into the resin constituting the uneven thickness section are as follows:
It depends on the injection pressure of the molten resin, the pressure of the pressurized gas, the shape and size of the uneven thickness portion, and the pressure of the resin holding pressure, which will be described later. . For example, the lower the injection pressure or the resin holding pressure and the larger the uneven wall thickness, the more the pressure gas can be introduced into the resin even with a low pressure gas.

As shown in FIG. 4, the gap between the gas injection pin 8 and the moving mold 3 is a hole 1 provided in the moving mold 3.
It is preferable to form the gas injection pin 8 not in a circular shape but in a shape in which a part of the circular shape is cut away, in addition to making the gas injection pin 2 circular, since the desired width s can be easily obtained.
In particular, it is preferable that the width s of the gap around the tip of the gas injection pin 8 is set to a size that allows the pressurized gas to pass smoothly and prevents the molten resin from entering during injection filling. The width s of the gap depends on the shape of the mold, the position where the mold is provided, the material used, the molding conditions, and the like.
/ 5 mm or less, more preferably 1/100 mm or more
It is 10 mm or less, more preferably about 1/20 mm. In the region closer to the root than the tip of the gas injection pin 8, the cutting amount for forming the gap may be increased so that the pressurized gas can pass smoothly, and in some cases, it may be cut in a groove shape. preferable.

Here, in order for the pressurized gas introduced into the cavity 4 to effectively press one side of the molded product against the cavity surface 4a and to enter the uneven thickness portion of the molded product, It is effective to prevent the pressurized gas pressurized into the mold 4 from leaking out of the mold 1. For this reason, it is preferable that the cavity surface 4b be a closed region surface in which communication with the outside air is blocked.

FIG. 5 is a schematic view of the vicinity of the rib 13 and the side wall 14 when pressurized gas is injected into the cavity 4 after the mold 1 in FIG. The pressurized gas injected from the gap around the gas injection pin 8 reaches the base of the rib 13 while pressing the molded product against the cavity surface 4a. At this time, sinking is prevented on the opposite surface side corresponding to the position of the rib 13 where sink is likely to occur in normal molding by pressurized pressurized gas. Further, the pressurized gas enters the ribs 13 which are uneven thickness portions, and forms hollow portions 18 therein, thereby also preventing sink marks. The prevention of sink marks by the hollow portion 18 is the same as that of the conventional gas assist molding, but the pressurized gas also exists around the rib 13, and at the same time, the opposite surface corresponding to the position 13 ′ near the rib 13 has a cavity surface. Since it is pressed against 4a, it is possible to prevent the occurrence of gloss and uneven gloss on the opposite surface side corresponding to the position of the rib 13 as in conventional gas assist molding.

On the other hand, the pressurized gas also advances to the side wall portion 14 side, and presses the side wall portion 14 in the direction shown by the arrow. As a result, the side wall portion 14 of the molded product is pressed against the cavity surface 4a. In general, the higher the pressure of the pressurized gas, the easier the leakage occurs. However, as shown in FIG. 5, the higher the pressure of the pressurized gas, the stronger the side wall portion 14 is pressed against the cavity surface 4a, and the open air path 5 (see FIG. 5). 1) is prevented from flowing into the cavity surface 4a having the opening. Therefore, it is preferable to apply the present invention to the molding of a box-shaped product because gas sealing can be performed even when a high-pressure gas is used. This can be reliably obtained by filling the cavity 4 with the molten resin in an excessive amount. That is,
When the resin is sufficiently filled in the cavity 4 when the pressurized gas tries to flow toward the cavity surface 4a,
It is prevented that the pressurized gas pushes away the resin and goes around the cavity surface 4a to form a gas path, so that the gas seal by the side wall portion 14 can be reliably obtained.

Further, when the pressurized gas is injected, the molded article contracts due to cooling, and depending on the shape of the mold, the high-pressure gas may leak. In order to prevent this, it is preferable to use a resin dwelling pressure (hereinafter referred to as a resin dwelling pressure) that is used in ordinary injection molding to supplement a part of the shrinkage of the molded product. The resin holding pressure here is a pressure that is used in general injection molding, and is a pressure that does not cause burrs and warpage on molded products. By using this resin holding pressure together, it is possible to increase the thickness of a thick portion such as a rib or a boss, thereby further expanding the degree of freedom in product design. Further, there is an advantage that appearance defects due to excessive introduction of pressurized gas can be prevented.

The injection of the pressurized gas does not necessarily have to be performed from the moving mold 3 as shown in FIG. Whether the gas is introduced from the fixed mold 2 or the movable mold 3 generally depends on the shape of the mold 1. When the design surface of the molded product is on the fixed mold 2 side, the pressurized gas is introduced. Is easy to introduce from the moving mold 3 side as shown in FIG.
Conversely, when the design surface is on the movable mold 3 side, it is easier to introduce the pressurized gas from the fixed mold 2 side.

That is, in the present invention, the cavity surface 4a on the side opposite to the cavity surface 4b on the press-in side of the pressurized gas.
Since the molded product is pressed against the surface of the molded product on the pressurized gas injection side, the finished state of the surface of the molded product on the opposite side is better. Therefore, the pressurized gas is preferably injected from the back side (non-design side) of the molded product.

After the pressurized gas is injected as described above, the pressurized gas is discharged out of the mold 1 as necessary, and the molded product is taken out of the mold 1.

The present invention is effective for molding a molded product in which a thick portion partially projects on the back side (non-design surface side). That is,
This is effective for molding a molded product in which ribs, bosses, and the like protrude from the cavity surface 4b. On the design surface of the molded product, which is the surface of the molded product on the side of the cavity surface 4a, it is possible to prevent sink marks, glossiness, and unevenness that are likely to occur in response to ribs and bosses, and to eliminate appearance problems due to the presence of the ribs and bosses. can do.

In particular, as shown in FIG. 6, when the width of the thick portion is w and the thickness around the thick portion is t, w ≧
(3/5) It is effective for a molded product having a thick portion such as t. That is, it is difficult to prevent sinkage in a molded product having such a thick portion by ordinary injection molding, but according to the present invention, this can be surely solved.

FIG. 7 shows an example of the mold 1 which can be switched between the cavity face 4b, the open area face and the closed area face.

To explain further, the gas introduction path 10 is the same as that shown in FIG.
Similarly to the mold 1 described above, while connected to a pressurized gas source (not shown) via a valve 9a, it can communicate with the atmosphere via a valve 9b and a vacuum pump 15. That is, the valve 9a is closed and the valve 9b is closed.
Is opened and the vacuum pump 15 is operated, the cavity surface 4b becomes an open area surface communicating with the atmosphere, the operation of the vacuum pump 15 is stopped, and the valve 9b is closed (the valve 9a is closed. May also be open), the cavity surface 4b becomes a closed region surface in which communication with the atmosphere is blocked. Although the vacuum pump 15 may be omitted in the mold 1 shown in FIG.
Is provided, the pressure inside the cavity 4 is reduced by the vacuum pump 15 at the time of injection of the molten resin, so that the molten resin can easily spread to every corner of the cavity 4. in this case,
It is more effective if the cavity 4 can be made a closed system by providing an O-ring on the parting surface of the mold 1 without providing the open-to-atmosphere path 5.

FIG. 8 shows an example of a mold 1 in which a pressurized gas can be supplied to the cavity 4 by using the periphery of the ejector pin 6 without providing the gas injection pin 8.

More specifically, the rear part of the projecting ejector pin 6 and the projecting plate 16 are housed behind the movable mold 3 and connected to a pressurized gas source (not shown) via the valve 9a. A sealed chamber 17 is formed. In the mold 1, the pressurized gas is press-fitted into the cavity 4 by supplying the pressurized gas from the pressurized gas source to the sealed chamber 17 and through the gap between the movable mold 3 and the ejector pin 6. It has become something. When such a gas injection method is used, the gas seal around the individual ejector pins 6 and the gas seal at the joint thereof are not required even if there is a nest or the like leading to the ejector box (sealing chamber 17). Reference numerals 7c to 7e denote O-rings for forming the sealed chamber 17.

[0049]

【Example】

Example 1 As shown in FIG. 9, a molded product having a curved housing shape and a main portion thickness of 2.5 mm was formed. The injection of the pressurized gas and the gas seal were the same as those described with reference to FIG. 1, and the gas injection position G was between the ribs a to g. Further, the position of one parting surface is the position of H in FIG.
And the position of the other parting surface was the position shown in FIG. 3 at the position I in the drawing.

The thicknesses of the ribs indicated by a, b, c, d, e, f, and g are 2.5 mm, 2.5 mm, 1.
5mm, 3.75mm, 2.5mm, 1.25mm,
2.5 mm.

The molding material is high impact polystyrene (HIPS), ABS resin, modified PPE resin (m-PP
E) was used, and a molding was molded by immediately injecting a pressurized gas after injecting an excessive amount (103% by volume) of the molding material relative to the cavity volume. The respective molding conditions are shown below.

(A) Material used: HIPS Cylinder temperature: 200 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin holding pressure: 5 kg / cm ² (gauge pressure) Pressure of pressurized gas: 100 kg / cm ² (gauge (B) Material used: ABS Cylinder temperature: 230 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin pressure: 10 kg / cm ² (gauge pressure) Pressure of pressurized gas: 150 kg / cm ² (gauge pressure) (C) Material used: m-PPE Cylinder temperature: 260 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin holding pressure: 10 kg / cm ² (gauge pressure) Pressure of pressurized gas: 150 kg / cm ² (gauge Pressure) The appearance of the molded article was visually judged, and the sink of the design surface opposite to the rib was measured. Table 1 shows the measurement results. FIG. 10 shows the state of the hollow portion 18 formed in each rib portion.
(A).

As is clear from Table 1, the molded article according to the present invention had a good appearance and had almost no sink mark. Conventionally, thick ribs could not be provided due to sinking, but the present invention has made it possible. Also, gloss unevenness and gloss unevenness observed on the design surface located behind the thick rib, as seen in a gas assist molded article in which a pressurized gas is introduced into the interior of the molded article, were hardly recognized by the naked eye.

Comparative Example 1 The same injection molding was carried out using the same mold and the same resin as in Example 1. The respective molding conditions are shown below.

(A ′) Material used: HIPS Cylinder temperature: 200 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin holding pressure: 40 kg / cm ² (gauge pressure) (B ′) Material used: ABS cylinder temperature: 230 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin pressure: 40 kg / cm ² (gauge pressure) (C ′) Material used: m-PPE Cylinder temperature: 260 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin holding pressure: 40 kg / cm ² (gauge pressure) The appearance of the above molded product was judged with the naked eye, and the sink of the design surface opposite to the rib was measured. Table 1 shows the measurement results.

Comparative Example 2 The same mold and the same resin as in Example 1 were used except that the pressurized gas was press-fitted by providing a hollow pin protruding in the runner and then press-fitting it into the rib. Then, normal gas assist molding was performed. The respective molding conditions are shown below.

(A ′) Material used: HIPS Cylinder temperature: 200 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin holding pressure: 0 kg / cm ² (gauge pressure) Pressure of pressurized gas: 100 kg / cm ² ( Gauge pressure) (B ') Material used: ABS Cylinder temperature: 230 ° C Injection pressure: 100 kg / cm ² (gauge pressure) Resin pressure: 0 kg / cm ² (gauge pressure) Pressure of pressurized gas: 100 kg / cm ² ( Gauge pressure) (C ′) Material used: m-PPE Cylinder temperature: 260 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin pressure: 0 kg / cm ² (gauge pressure) Pressure of pressurized gas: 100 kg / cm ² (Gauge pressure) When the above molded product was judged with the naked eye, gloss or unevenness of gloss was observed on the opposite surface side corresponding to the rib position in any resin. Was. In each case, as shown in FIG. 10B, the hollow portion 18 formed in the rib portion was considerably larger than the hollow portion 18 in the first embodiment. The hollow portion 18 is the hollow portion 1 in the first embodiment.
When the molding was performed while reducing the pressure of the pressurized gas so as to have the same size as that of No. 8, the pressurized gas did not reach the entire rib, and sink occurred on the surface of the molded article on the opposite side of the rib. Table 1 shows the results of judgment of the appearance of the molded product with the naked eye and the results of measurement of sink in the design surface opposite to the rib.

[0058]

[Table 1]

Example 2 As shown in FIG. 11, a molded product having a box-shaped OA equipment housing shape and a main part thickness of 2.0 mm was formed. The injection of the pressurized gas and the gas seal were the same as those described in FIG. Further, the form of the parting surface was the form shown in FIG.

The thicknesses of the ribs h and i are 2 mm and 4 mm, respectively.

The molding material was ABS resin, and after injection of an excessive amount (104% by volume) of the molding material relative to the cavity volume, a molded product was formed by immediately injecting a pressurized gas. The molding conditions are shown below.

Material used: ABS resin Cylinder temperature: 230 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin pressure: 20 kg / cm ² (gauge pressure) Pressure of pressurized gas: 100 kg / cm ² (gauge pressure) 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. Table 2 shows the measurement results.

Comparative Example 3 A normal injection molding was performed using the same mold and the same resin as in Example 2. The molding conditions are shown below.

Materials used: ABS resin Cylinder temperature: 230 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin holding pressure: 40 kg / cm ² (gauge pressure) And the sink of the design surface on the opposite side were measured. Table 2 shows the measurement results.

Comparative Example 4 The same mold and the same resin as in Example 2 were used, except that the pressurized gas was press-fitted by providing a hollow pin protruding in the runner and then press-fitting it into the inside of the rib. To perform normal gas assist molding. The molding conditions are shown below.

Material used: ABS resin Cylinder temperature: 230 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin holding pressure: 0 kg / cm ² (gauge pressure) Pressure of pressurized gas: 100 kg / cm ² (gauge pressure) 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. Table 2 shows the measurement results.

[0067]

[Table 2]

Example 3 As shown in FIG. 12, a molded product having a box-shaped OA equipment housing shape and a main part thickness of 2.5 mm was formed. The injection of the pressurized gas and the gas seal were the same as those described in FIG. Further, the form of the parting surface was the form shown in FIG.

The thickness of each of the ribs h and i is 2.5 m.
m and 4 mm, and the boss j was a cylindrical shape having a diameter of 10 mm and a height of 10 mm.

The molding material was high impact polystyrene (HIPS), and the excess (10%)
(4% by volume), and immediately after injection of a pressurized gas, a molded article was molded. The molding conditions are shown below.

Materials used: HIPS Cylinder temperature: 200 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin holding pressure: 20 kg / cm ² (gauge pressure) Pressure of pressurized gas: 150 kg / cm ² (gauge pressure) Obtained The molded article obtained was a good one with no sink mark confirmed with the naked eye and without uneven gloss or luster. Further, a hollow portion was formed at the base of the boss j by injecting pressurized gas.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a mold used in the present invention.

FIG. 2 is a schematic cross-sectional view showing another example of the formation position of the open-to-atmosphere path.

FIG. 3 is a schematic cross-sectional view showing another example of the formation position of the open-to-atmosphere path.

FIG. 4 is an enlarged sectional view around a gas injection pin.

FIG. 5 is an explanatory view of a gas sealing action and a sink prevention action in the present invention.

FIG. 6 is an explanatory diagram of a thick portion suitable for applying the present invention.

FIG. 7 is a sectional view showing another example of a mold used in the present invention.

FIG. 8 is a cross-sectional view showing another example of a mold used in the present invention.

FIG. 9 is a schematic view of a molded article molded in Example 1, Comparative Examples 1 and 2.

FIG. 10 is a cross-sectional view showing a state of a hollow portion in a molded article molded in Example 1 and Comparative Example 2.

FIG. 11 is a schematic view of a molded article molded in Example 2, Comparative Examples 3 and 4.

FIG. 12 is a schematic view of a molded article molded in Example 3.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold 2 fixed mold 3 moving mold 4 cavity 4a, 4b cavity surface 5 atmosphere release path 6 ejector pin 7a-7e O-ring 8 gas injection pin 9a, 9b valve 10 gas introduction path 11 gate 12 hole 13 rib 13 'Near the rib 14 Side wall 15 Vacuum pump 16 Projection plate 17 Sealed chamber 18 Hollow

Claims (9)

[Claims] In the injection molding of a molded article having an uneven thickness portion, a molten resin is injected into a cavity, and before or after the injection is completed, the molten resin is injected from a cavity surface side corresponding to one surface of the molded article. Injection molding with gas, characterized by injecting pressurized gas and pressing the other surface of the molded product against the corresponding cavity surface, and injecting the pressurized gas into the resin constituting the thick part of the molded product Method. 2. A cavity surface corresponding to one surface of a molded product has an open-air path opened at a part thereof and an open region surface communicated with the atmosphere, and a cavity surface corresponding to the other surface of the molded product communicates with the atmosphere. Using a mold that has become a closed area surface where
After injecting an excessive amount of molten resin into the cavity compared to the volume of the cavity, pressurized gas is injected from the cavity surface side corresponding to the other surface of the molded product that has become the closed region surface. 1. A gas combined injection molding method. 3. A cavity surface corresponding to the other surface of the molded product also has an open area surface which is partially open to the atmosphere and communicates with the atmosphere. 3. The method for injection molding with gas according to claim 2, wherein the air release path on the cavity surface side corresponding to the other surface of the product is closed to make the cavity surface a closed region surface. 4. A molded product having a box shape, one surface of the molded product being an outer surface of the box-shaped molded product, and the other surface of the molded product being an inner surface of the box-shaped molded product. Injection molding method of any one of 1 to 3 above. 5. The injection molding method according to claim 1, wherein the molded article has a partially thick portion protruding to the other surface side. 6. The injection amount of the molten resin into the cavity is:
The injection molding method according to any one of claims 1 to 5, wherein the volume is 103% by volume or more of the volume of the cavity. 7. The injection molding method according to claim 1, wherein the open-to-atmosphere path is formed as a groove. 8. The method of claim 7, wherein the thickness of the groove at least near the opening to the cavity is 1/100 mm or more and 1/10 mm or less. 9. The method for injection molding with gas according to claim 1, wherein a resin holding pressure is applied after the injection of the molten resin.