JP3108871B2 - Gas pressure injection molding method - Google Patents

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 gas pressure 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 Generally, in injection molding, when molding a molded product having a thick portion protruding on the back surface (non-design surface) side, the resin shrinks due to cooling, so that it is possible to cope with the thick portion on the back surface side. It is widely known that a recess called a sink is formed on the surface (design surface) side of a molded product to be formed.

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.

[0004] However, as described in Japanese Patent Application Laid-Open No. 50-75247, the prevention of sinking by the resin pressurization method is complicated because the molding conditions vary depending on the thickness of the molded product and the like. Unless resin pressure is applied, sufficient shrinkage prevention cannot be achieved, causing burrs on the parting surface, and there is a problem that the work load for removing the burrs increases. In addition, 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 by a valve body, and one side of the molded product and one side of the molded product are molded. A pressurized gas injection molding method is proposed in which a cavity is formed between the core and a pressurized gas, and a pressurized gas is press-fitted into the cavity and the other surface of the molded product is pressed against the corresponding cavity surface. .

In this gas pressure injection molding method, a pressurized gas is injected instead of applying the resin pressure in the resin pressurization method, and the occurrence of sink marks is prevented by the pressurized gas injection. In particular, in order to be able to press-fit the pressurized gas to a predetermined one side of the molded article, the need to form a cavity I previously elevational <br/> the injection of pressurized gas, a molding method exits the gas pressurization pressure injection The amount of injection of the molten resin into the cavity in the above is an amount that at most just fills the cavity. When the injection conditions in the resin pressurization method are used, as a result, an amount of molten resin exceeding the capacity of the cavity is injected, but such an excessive amount of molten resin is not injected. In addition, in this gas pressurized injection molding method, the pressurized pressurized gas leaks from the parting surface of the mold, making it difficult to perform sufficient pressing, and insufficiently preventing sinking.

Japanese Patent Application Laid-Open No. 4-501090 discloses that a molten resin having a volume smaller than the volume of a cavity, specifically, a molten resin having a volume of 90 to 95% by volume of a cavity is injected and then left in the cavity. A pressurized gas injection molding method for pressurizing a pressurized gas into an empty space is described.

This gas pressure injection molding method is basically the same as the above gas pressure injection molding method, and does not inject an excessive amount of molten resin into the cavity.
The pressurized pressurized gas easily escapes from the parting surface, and is only inferior in the effect of preventing sink marks.

[0009] Further, in the specification of WO93 / 14918, in a gas pressure injection molding method, in order to increase the pressure efficiency of a pressurized gas, a sealed structure for preventing gas leakage from a parting surface of a mold is provided. A method is disclosed which uses a mold in which a weir having a tapered shape such as a triangle is provided in a cavity, in addition to a mold.

However, the injection amount of the molten resin in this gas combined injection molding method is, as in the case of the injection performed in the general gas pressure injection molding method described above, only about an amount that substantially fills the cavity. It has been revealed that there is no. In addition, although the effect of preventing sink marks has not been sufficiently improved, the load on the device is large due to the mold having a sealed structure, and furthermore, the air in the cavity is trapped between the resin and the cavity surface at the time of injection. There is also a problem that it is lost.

Further, in the specification of WO96-02379, a mold having a sealing structure in which a sealing material is applied to a parting surface or the like of a mold is used. 30 to 90% of the difference between the volume of the molten resin and the volume of the resin that shrinks when cooled to room temperature
After filling an excess resin), a pressurized gas is injected between the molten resin mass and the mold, and the molten resin mass is pressed against the inner surface of the mold cavity to form the mold. ing.

However, in this method, it is necessary to provide a sealed chamber capable of gas sealing, for example, around the protruding pin, which causes a problem that the load on the apparatus is large, and the air or gas in the mold is removed from the inside of the mold cavity. However, there is a problem that it is necessary to fill a relatively large amount of excess resin or to fill the resin at a high pressure in order to drive the resin.

That is, in the conventional gas pressure injection molding method, a small amount of resin is injected into a mold cavity volume in order to smoothly fill the pressurized gas, and leakage of the pressurized gas is prevented. For this reason, the mold is made to have a sealed structure as much as possible.

[0014]

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 and large molded product, a reinforcing portion generally called a rib or a boss is usually provided on the back surface in order to maintain strength. The thicker the ribs and bosses are, the higher the reinforcing effect is, and a flow assisting effect that allows the resin to be easily filled in the mold is obtained.

However, when thick ribs and bosses are provided, the surface of the molded product corresponding to the ribs and bosses tends to sink, and problems in appearance tend 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 satisfactory molded products due to insufficient sink protection technology.

The present invention has been made in view of such conventional problems, and has as its object to completely prevent sinking by a gas pressure injection molding method.

[0017]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention is directed to an injection molding of a molded article having a thick part protruding on the back side, which is open to the atmosphere open to a part of the cavity surface. While evacuating the gas in the cavity from the path, the cavity is injected and filled with an excessive amount of molten resin compared to the cavity volume, and then the cavity between the cavity on the back surface of the molded product serving as the gas injection region and the corresponding cavity surface is formed. The present invention provides a gas pressure injection molding method characterized in that a pressurized gas is press-fitted therebetween, and a molded product surface corresponding to a gas press-in area is pressed against a corresponding cavity surface.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The object to be molded according to the present invention is a molded article having a thick portion protruding toward the rear surface, which is liable to cause sink marks on the surface. The thick portion includes, for example, a locally protruding thick portion such as a rib or a boss, as well as a region in which the thickness is varied over a wide range over a fixed portion.

In the present invention, the recess on the back side of the molded product adjacent to the thick portion or including the thick portion is referred to as a gas injection region. The concave portion serving as the gas injection region is provided to form a thick portion such as a rib for reinforcement, a side wall portion of the molded product, a curved portion of the molded product, and a concave portion serving as the gas injection region. This is a region surrounded by auxiliary ribs and the like.

The mold used in the present invention has an atmosphere opening path opened in a part of the cavity other than the gas injection region. The open-to-atmosphere path connects the cavity to the atmosphere. When the cavity is filled with the molten resin, the air and the like (gas generated from the air and / or the molten resin) in the cavity are released to the outside of the mold. It plays a role.

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 a groove formed on the parting surface of the mold so that the gas in the cavity can be released smoothly. Particularly, by opening the groove near the flow end of the molten resin, a higher effect is obtained. can get. In addition, when the molten resin is filled in the mold cavity, the atmosphere opening path is opened at a position where the side opposite to the opening side is a gas injection region, specifically, a cavity surface on the front side of the molded product. Is desirable.

According to the present invention, a structure in which a parting surface or the like is purposely sealed by injecting and filling an excessive amount of molten resin in comparison with the volume of the cavity by using the above-described mold having good outgassing. Thus, a gas sealing property of a pressurized gas that can obtain a sufficient sink preventing effect without taking the above-described method can be obtained.

That is, according to the present invention, when the molten resin is injected and filled, the cavity can be filled with the molten resin while the air or the like in the cavity is smoothly discharged out of the mold. Can be prevented from being confined. In addition, by being able to smoothly discharge air and the like in the cavity, and by injecting and filling an excessive amount of molten resin compared to the volume of the cavity, the molten resin can be filled into every corner of the cavity and the resin in the cavity and the surface of the cavity can be filled. And the adhesion to the film is improved. Therefore, the gas injection region can be a closed region where leakage of the pressurized gas injected between the resin and the cavity surface of the region is less likely to occur, and gas leakage during pressurized gas injection into the gas injection region described later can be reduced. Can be prevented. In other words, the present invention can prevent gas leakage necessary for preventing sink marks by using an unsealed mold and by injecting and filling an excessive amount of molten resin relative to the cavity volume. It provides a method that could not have been considered.

In the present invention, an excessive amount of the molten resin relative to the cavity volume refers to an amount of the molten resin in which the volume of the molten resin becomes larger than the cavity volume. When the weight is 100% by weight, the amount is 101 to 110% by weight, more preferably 103 to 107% by weight. If the amount of molten resin to be injected and filled is too small, it is difficult to make the gas injection area a closed area.On the other hand, if the amount of molten resin to be injected and filled is too large, burrs will occur on the parting surface and dimensional accuracy will decrease due to warpage. It is easy to occur.

The pressurized gas is injected by means of a pin that forms a gap that is opened in a slit shape that does not allow the molten resin to enter at the time of injection but allows the pressurized gas to pass through, a sintered body, and a valve body that has a poppet mechanism. Etc. are available. In particular, in the present invention,
Since the resin pressure is increased by filling an excessive amount of the molten resin into the mold as compared with a case where a small amount of the molten resin is injected into the mold compared to the cavity volume, the gap opening in the slit shape is used. Is most suitable. Further, around the ejector pin which does not move when pressurized gas is press-fitted can be used as the fixing pin.

In the method according to the present invention, after filling the molten resin into the mold cavity by injecting the molten resin, if the resin pressure is kept within a range that does not cause burrs on the parting surface, the mold of the pressurized gas is discharged. The effect of preventing leakage to the outside can be enhanced.

In the conventional gas-assisted injection of injecting a pressurized gas into a molten resin, almost no resin holding pressure is used in order to smoothly inject the pressurized gas. Also, in the conventional gas pressure injection molding method in which a pressurized gas is injected between the molten resin and the cavity, the resin holding pressure is not used in order to smoothly fill the pressurized gas into the mold, It was also considered difficult.

However, when the resin holding pressure is used in combination with the method of the present invention, it is possible to prevent the resin from flowing back to the runner and the nozzle portion when pressurized gas is injected, thereby preventing unnecessary shrinkage near the resin gate portion. It has been found that this can more effectively prevent the pressurized gas from leaking out of the mold. It has also been found that the amount of narrowing of the base of the thick portion (hereinafter referred to as "squeeze") by pressurized gas injection can be controlled by the resin holding pressure. Furthermore, if resin holding pressure is used in combination with gas pressurization, the entire molded product can be pressed uniformly to the mold, so that unnecessary residual stress is less likely to remain on the molded product, causing warpage and other problems in ordinary injection molding. It has been found that the occurrence of the occurrence can also be prevented.

The above resin holding pressure is effective whether a normal cold runner mold or a hot runner mold is used. In the case of a hot runner, when a hot runner gate having a valve element having an opening / closing function is used, which is generally called a valve gate, it is possible to prevent gas from entering the hot runner, and at the same time, prevent backflow of resin. It is effective.

When the pressurized gas is injected between the back surface of the molded article in the gas injection region and the corresponding cavity surface, the inventor of the present invention obtains the injection pressure of the molten resin, the pressure of the pressurized gas,
Depending on the shape and size of the thick part, a part of the pressurized pressurized gas does not stay between the resin and the cavity surface, and is injected into the resin constituting the thick part to form a hollow part. I found that there are things. The formation of the hollow portion does not involve injecting a part of the pressurized gas pressed between the back surface of the molded product in the gas injection region and the corresponding cavity surface into the resin, but the back surface of the molded product in the gas injection region. A pressurized gas is press-fitted between the cavity and the corresponding cavity surface, and the molded product surface corresponding to the gas press-in area is pressed against the corresponding cavity surface, and the pressurized gas inlet is provided separately. It can also be performed by injecting a pressurized gas into the resin in the cavity.

That is, in the present invention, a pressurized gas is press-fitted between the back surface of the molded product in the gas injection region and the cavity surface corresponding thereto, and the surface of the molded product corresponding to the gas injection region corresponds to this. In the state of being pressed against the cavity surface, the pressurized gas pressurized into the gas press-in area or the pressurized gas separately provided inside the molten resin filled in the cavity tee (particularly, inside the resin constituting the thick portion). A hollow portion can be formed by injecting a pressurized gas from a gas inlet.

When the hollow portion is formed as described above,
The advantages of the gas pressure injection molding method and the advantages of the gas assisted injection can be obtained synergistically. Specifically, the pressurized gas is injected into the molded product, particularly into the thick portion, while the surface of the molded product is pressed against the cavity surface corresponding to the molded product by the pressurized gas. And secondary transfer due to the introduction of pressurized gas into the resin is unlikely to occur.
Therefore, it is possible to eliminate unevenness in gloss and gloss between the surface corresponding to the thick portion and the other surface, which is a problem in the conventional gas assisted injection. In addition, the pressurized gas injected into the thick portion is less likely to protrude into the thin portion, and the appearance defect due to the pressurized gas protruding can be prevented. In particular, when a molded article of a crystalline resin is molded by ordinary gas assisted injection in which a pressurized gas is injected into the molten resin, the gas easily protrudes from the thick part to the thin part, which has caused a problem in appearance. According to the method involving the formation of the hollow portion, the appearance can be remarkably improved. Further, sinking can be prevented by both the pressurized gas press-fitted between the back surface of the molded article and the cavity surface corresponding to the molded article and the pressurized gas injected into the molded article.

The mold temperature in the present invention can be the usual mold temperature for the resin to be used, but in order to mold a molded article having a higher appearance and no sink marks, the mold temperature used in ordinary injection molding is used. It is preferable that the temperature be set higher than the mold temperature. For example, while maintaining the temperature T ₁ (° C.) of the cavity surface corresponding to at least the back surface of the molded product to satisfy the following formula (I) with respect to the Vicat softening point V (° C.) of the resin used, Preferably, it is injected into the cavity.

V−30 <T ₁ <V−15 (I)

The Vicat softening point V (° C.) of the resin used
Is a value measured based on the test method ASTM D1525.

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, and polyamide resins such as polyamide 66, polyamide 6, and polyamide 46. Polyacetal (POM) resins such as polyoxymethylene copolymers and polyoxymethylene homopolymers, other engineering resins, super-engineering resins such as polyethersulfone (PES), polyetherimide (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, one or more blends of the above-described thermoplastic resins may be used, or a filler and / or an additive may be contained.

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

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

As shown, the mold 1 is composed of a fixed mold 2 and a movable mold 3, and a cavity 4 is formed between the mold 2 and the molten resin at the time of molding.

FIGS. 2A and 2B show a molded product 20 using the mold 1, wherein FIG. 2A is a perspective view and FIG. 2B is a plan view.
The molded product 20 is a box-shaped product having two thick portions (reinforcing ribs) 13 across the base 24 on the bottom surface and having side walls 14a to 14d around the periphery. The back surface (non-design surface) and the outside surface are the front surface (design surface). Also, the side wall portion 1
Recess surrounded by 4a to 14d (entire inside of molded product 20)
Is a gas injection region 25, and the thick portion 13 is included in the gas injection region 25. In addition, 26
Indicates a gas injection port formed by a gas injection pin 8 described later.

A groove is formed on the fixed side mold 2 side of the parting surface, and forms a path 5 for opening to the atmosphere. The open-to-atmosphere path 5 is provided for the molded product 20 formed in the cavity 4.
The cavity surface 4a corresponding to the surface is opened, and the cavity surface 4a side is open to the atmosphere. At least the opening to the cavity 4 or its vicinity is formed by the molten resin
When injecting and filling the inside, without invading the resin,
It has a thickness capable of discharging air and the like in the cavity 4 to the outside of the mold 1. Although this thickness depends on the type of resin and molding conditions, it is generally 1/200 mm or more and 1/1.
0 mm or less, more preferably 1 /
100 mm or more and 1/10 mm or less, more preferably 3
/ 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 back surface of the molded product 20, the periphery of the ejector pin 6 connected to the atmosphere is sealed with an O-ring 7a, and there is no opening of the atmosphere opening path 5 and there is no communication with the atmosphere. Is shut off. A gas injection pin 8 is provided on the cavity surface 4b side. The gas injection pin 8 has a front end facing the cavity 4 from the cavity surface 4b, and
And a gas introduction passage 10 connected to a pressurized gas source (not shown) via a valve 9a.
The pressurized gas sent from a is supplied to the cavity 4 through a gap left between the movable mold 3 and the moving mold 3. In the drawing, reference numeral 7b denotes an O-ring for preventing pressurized gas from escaping from the joint of the mold components.

The parting surface of the mold 1 shown in FIG.
The open-to-atmosphere path 5 is located along the outer surface of the base portion 24 of the box-shaped molded product 20, and is the cavity surface 4 a corresponding to the surface of the molded product 20, and
It is open at the position corresponding to. The opening position of the air release path 5 is not limited to such a position, and may be the position shown in FIGS. 3 and 4 according to the position of the parting surface.

In FIG. 3, the side wall portion 14 of the molded product 20 is shown.
The parting surface is located at the tip of each of the molded products 20, and the open-to-atmosphere path 5 is the cavity surface 4 a corresponding to the surface of the molded product 20, and the side walls 14 a to 14 d of the molded product 20
It is open at a position corresponding to the tip of the. The gas injection pins 8 for pressurizing the pressurized gas are provided on the side of the cavity surface 4b corresponding to the back surface of the molded product 20.

In FIG. 4, the side wall portion 14 of the molded product 20 is shown.
The parting surface is located in the middle part of a to 14d,
The open-to-atmosphere path 5 is a cavity surface 4 a corresponding to the surface of the molded product 20, and the side walls 14 a to 14 of the molded product 20.
It is open at a position corresponding to the middle part of d. The gas injection pins 8 for pressurizing the pressurized gas are provided on the side of the cavity surface 4b corresponding to the back surface of the molded product 20.

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

First, with the mold 1 closed, an excessive amount of molten resin is injected into the cavity 4 in comparison with the volume of the cavity 4. At this time, the air or the like in the cavity 4 is filled with the molten resin. Is released from the open air channel 5
Air bubbles are prevented from remaining between the resin and the cavity surfaces 4a and 4b. Further, in order to ensure this release, it is preferable to open the open-to-atmosphere path 5 near the flow end, which is a position away from the gate 11.

Immediately after the injection and filling 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 10a provided in the mold 1.

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 10a passes through a gap between the gas injection pin 8 and the movable mold 3, and
It is pressed into the cavity 4 from the cavity surface 4b side.
This pressurized gas is applied to the molded product 20 in the gas injection region 25.
Is pressed between the back surface of the molded product 20 and the corresponding cavity surface 4b, whereby the surface of the molded product 20 is pressed against the corresponding cavity surface 4a. The pressing by the pressurized gas suppresses the occurrence of sink marks on the surface of the molded product 20 on the cavity surface 4a side, improves the transferability on the cavity surface 4a side, and reduces the appearance defect due to sink marks, uneven gloss, and the like. Problems are also reduced. Further, the releasability of removing the molded product 20 from the mold 1 is also improved.

As shown in FIG. 5, the gap between the gas injection pin 8 and the movable mold 3 is a hole 1 provided in the movable 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 cavity 4, the position where the cavity 4 is provided, the material used, the molding conditions, and the like, but is preferably 1/200.
mm or more and 1/5 mm or less, more preferably 1/100 m
m or more and 1/10 mm or less, more preferably 1/20 m
m. 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.

In order for the pressure of the pressurized gas introduced into the cavity 4 to effectively press the surface of the molded article 20 against the cavity surface 4a, the cavity 4
It is necessary to prevent the pressurized gas injected into the mold from leaking out of the mold 1.

FIG. 6 is a schematic view showing the state near the thick portion 13 and the side wall 14b when pressurized gas is injected into the cavity 4 after the mold 1 in FIG. is there.

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 20 against the cavity surface 4a. At this time, on the surface side corresponding to the position of the rib 13 where sink is likely to occur in normal molding, sink is prevented by pressing with the pressurized pressurized gas.

On the other hand, the pressurized gas also advances to the side wall portion 14b, and presses the side wall portion 14b in the direction shown by the arrow. As a result, the side wall portion 14b of the molded product 20 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. 6, the higher the pressure of the pressurized gas, the stronger the side wall portion 14b is pressed against the cavity surface 4a, thereby closing the gas press-in region 25. As a region, the pressurized gas is prevented from flowing around the cavity surface 4a where the open-to-atmosphere path 5 (see FIG. 1) is open.

The leakage of the pressurized gas can only be achieved by sufficiently filling the cavity 4 with an excessive amount of molten resin. In other words, if the resin is not sufficiently filled in the cavity 4 when the pressurized gas tries to flow around the cavity surface 4a, the pressurized gas pushes the resin away and wraps around the cavity surface 4a to form a gas passage. Therefore, it is difficult to perform gas sealing using the side wall portion 14b (the same applies to the side wall portions 14a, 14c, and 14d). Leakage of pressurized gas outside the mold 1
Although the parting surface easily occurs when the parting surface is in the form shown in FIG. 3, the excess resin is removed by the method according to the present invention, that is, by using the excellent degassing mold 1 in which the molten resin is easily filled to every corner in the mold 1. By filling, the leakage of the pressurized gas outside the mold 1 can be sufficiently prevented.

When the pressurized gas is injected, a runner,
The resin flows backward to the nozzle portion, causing unnecessary shrinkage in the vicinity of the resin gate portion, and depending on the shape of the cavity 4, the high-pressure gas may leak. To prevent this, a combination of the extent of tree Aburaho圧used in ordinary injection molding, it is preferable to supplement a portion of the molded article of the shrinkage of the resin. The resin holding pressure here is a pressure that is used in general injection molding, and is a pressure that does not cause burrs on the molded product 20. By using the resin holding pressure together, it is possible to make the thickness of the thick portion 13 such as a rib and a boss larger than when not using the resin holding pressure, and it is easy to improve the strength of the molded product 20. Thus, the degree of freedom in product design can be further expanded.

The press-fitting 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 either the fixed mold 2 or the movable mold 3 generally depends on the shape of the mold 1.
0 is on the fixed mold 2 side, the pressurized gas is
It is convenient to introduce the pressurized gas from the fixed mold 2 side when the surface is on the movable mold 3 side as shown in FIG. is there.

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

According to the present invention, as shown in FIG. 7, when the width of the thick portion 13 is defined as w and the thickness around the thick portion 13 is defined as t, w ≧ (3/5) t. This is effective for a molded product 20 having the thick portion 13. That is, the molded product 20 having such a thick portion 13 is difficult to prevent sink in normal injection molding, but according to the present invention, this can be surely solved.

FIG. 8 shows an example of the 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, a rear portion of the ejector pin 6 and a protruding plate 15 are accommodated behind the movable mold 3 and connected to a pressurized gas source (not shown) via a valve 9a. A sealed chamber 16 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 16 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, even if there is a gas seal around each ejector pin 6 or a nest or the like leading to the ejector box (sealing chamber 16), there is no need for a gas seal at the joint. Reference numerals 7c to 7e denote O-rings for forming the sealed chamber 16.

FIG. 9 shows the molded product 20 of FIG.
After molding, when the molten resin is filled, pressurized gas is injected between the back surface of the molded article 20 in the gas injection area 25 and the corresponding cavity surface 4b, and the pressurized gas is injected into the thick portion 13
FIG. 4 is a schematic view of a state in the vicinity of a thick portion 13 and a side wall portion 14b when penetrating into a resin constituting the same.

The pressurized gas press-fitted from the gap around the gas injection pin 8 reaches the base of the thick portion 13 while pressing the molded product 20 against the cavity surface 4a. At this time, the surface of the molded product 20 corresponding to the position of the thick portion 13 where sinks are likely to occur in normal molding is prevented from sinking by being pressed by the pressurized pressurized gas. Further, the pressurized gas enters the thick portion 13 and forms a hollow portion 17 therein, thereby preventing sink marks. The prevention of sink marks by the hollow portion 17 is the same as that of the conventional gas assisted injection, but the pressurized gas also exists around the thick portion 13 and at the same time, the surface of the molded product 20 corresponding to the position 21 near the thick portion. Is pressed against the cavity surface 4a, thereby preventing the occurrence of gloss or uneven gloss on the surface of the molded article 20 corresponding to the position of the thick portion 13 as in the conventional gas assist injection.

FIGS. 10A and 10B are schematic diagrams of the hollow portions 17 and 19 formed by the pressurized gas injected into the thick portion 13, wherein FIG. 10A is an example of the hollow portion 17 according to the present invention, and FIG. 1 shows an example of the hollow portion 19 by the gas assisted injection.

In the conventional gas assisted injection, the pressure of the pressurized gas and the design of the thick portion 13 also
Although it is possible to prevent the gas from protruding as shown in the hollow portion 19 of (b), it is easy to prevent the gas from protruding particularly when a crystalline resin is used or when a high-pressure gas is used. is not. However, according to the present invention, the protrusion of the gas can be easily prevented.

FIG. 11 shows that the pressurized gas is injected between the back surface of the molded product 20 and the corresponding cavity surface 4b in the gas injection region 25 shown in FIG. This is an example of a mold 1 for injecting a pressurized gas into the resin inside the cavity 4 from another path.

The gas injection needle 18 shown in the figure is provided on the fixed mold 2 and has a tip facing the inside of the runner, and is connected to a pressurized gas source (not shown) via the valve 9b. This is for supplying the pressurized gas sent from the gas introduction passage 10b into the molded product 20 (see FIG. 2) from inside the runner.

FIG. 12 shows that after filling the mold 1 of FIG. 11 with molten resin, pressurized gas (back gas) is injected between the resin in the gas injection area 25 (see FIG. 2) and the cavity surface 4b. FIG. 4 is a schematic view of a state near a thick portion 13 and a side wall portion 14b when a pressurized gas (internal gas) is separately injected into a molten resin.

The back gas press-fitted from the gap around the gas pressure pin 8 reaches the base of the thick portion 13 while pressing the molded product 20 against the cavity surface 4a. At this time, the surface side corresponding to the position of the thick portion 13 where sink is likely to occur in normal molding is prevented from being sink by pressing with the press-fitted back gas. Further, the internal gas injected into the molten resin is injected into a thick portion 13 which is a thick portion, and a hollow portion 1 is formed therein.
7, whereby the sink is completely prevented. The prevention of sink marks by the hollow portion 17 is the same as that of the conventional gas assisted injection, but the back gas introduced from another route reaches between the cavity surface 4b and the molten resin, and also exists around the thick portion 13. , At the same time near the thick part
1 is also pressed against the cavity surface 4a, so that the occurrence of gloss and gloss unevenness on the surface side corresponding to the position of the thick portion 13 is prevented as in the conventional gas assist injection. Will be done.
In addition, the situation of the hollow portion 17 when this method is used and the hollow portion 19 by the conventional gas injection are shown in FIG.
Similarly to the description of 0, the gas is prevented from protruding into a thin portion such as the hollow portion 19.

FIG. 13 shows another example of the shape of the molded product 20 according to the present invention. FIGS. 14 (a) to (c) show the thick portion 13 and the thick portion 13 of the molded product 20 shown in FIG. Auxiliary rib 23
It is the top view, front sectional view, and side sectional view of the vicinity.

As described with reference to FIG. 1 and FIG. 2, when the cavity 4 is filled with the molten resin, a box-shaped molded article 20 having side walls 14 a to 14 d formed around the cavity 4 is formed. the entire side may be pressed pressurized <br/> pressure gas as the gas injection region 25. However, among the molds 1 used industrially, one mold 1 is often configured as an aggregate of divided molds (referred to as insert pieces) divided at various portions. For this reason, it is not always advisable to make the entire surface of the mold 1 into the gas injection region 25.

In the case described above, the auxiliary ribs 23 are provided as in the molded article 20 of the present embodiment, the gas injection region 25 is set in a part of the mold 1, and the gas opening into the gas injection region 25 is performed. Pressurized gas can be injected from the inlet 26 to prevent the desired thick portion 13 from sinking. In the molded article 20 of the present example, the side walls 14a to 14d are connected around the base 24, and the thick part 13 is connected to the side wall 14b. In this molded product 20, an auxiliary rib 23 is further connected to the side wall portion 14a, and the auxiliary rib 23 and the thick portion 1 are formed.
3 are side wall portions 14a, 14b and side wall portions 14a,
It is connected in a T-shape with 14b as the top. In the present invention, as shown in FIG.
4a and the auxiliary rib 23, the side wall 14a
Is called a top part, and a part of the auxiliary rib 23 is called a leg part.

As shown by oblique lines in FIG. 14A, a recess surrounded by the side walls 14a, 14b, the thick portion 13, and the auxiliary ribs 23 forms a gas injection region 25. That is, in FIG. 1 and FIG.
FIG. 13 and FIG.
In the example shown in FIG. 5, the gas injection region 25 is adjacent to the thick portion 13.

When the gas injection region 25 is made to be adjacent to the thick portion 13, the thick portion 13 may be used as a concave component surrounding the gas injection region 25 formed as a concave. In the case where the thick portion 13 is included in the gas injection region 25, the thick portion 13 may be accommodated in a recess component surrounding the gas injection region 25 formed as a recess.

In the present invention, in a portion where a part of the concave component extends outside the gas injection region 25 and is connected in a substantially T-shape, the inside of the gas injection region 25 of the concave component is gas-injected. It is preferable that the height is set to be equal to or higher than the outside of the region 25. That is, in the molded product 20 shown in FIGS. 13 and 14, since the side wall portions 14 a and 14 b extend outside the gas injection region 25, the gas injection region 2
The rising ribs 22a and 22b are formed at the respective T-shaped joints of the auxiliary rib 23 and the thick part 13 surrounding the rib 5, and the height thereof is equal to or higher than the side walls 14a and 14b. In the present invention, “equal or more” preferably means 90% or more. Specifically, the molded product 20 shown in FIGS.
H ₁ the height of the side wall portions 14a~14d of the height d ₂ of the thick portion 13 and the auxiliary ribs 23, raising the ribs 22a, 22
When b in the height and h _1, a _{h 1 + d 2 ≧ 0.9 ×} H 1. The molded product 20 shown in FIGS. 13 and 14 in which h ₁ + d ₂ = H is a preferable embodiment.

As described above, when the concave components surrounding the gas injection region 25 are connected to each other in a substantially T-shape (in FIGS. 13 and 14, the side wall portion 14 b and the thick portion 13, By designing the side wall portion 14a and the auxiliary rib 23) to compensate for the height of the concave component member at this connection portion, it is easy to prevent the pressurized gas from leaking out of the gas press-fitting region 25, and the cavity surface is sufficiently formed. 4a (see FIG. 1), molded article 2
By pressing 0, the occurrence of sink marks can be prevented.

In the present invention, the substantially T-shaped connection in the concave component member includes a case where the other member is connected to the linear member at a non-perpendicular angle, and as shown in FIG. In addition to the case where there is a difference in height between the part side member and the top part side member, a member having the same height is formed into a substantially L-shape like a connecting portion between the side wall parts 14b and 14c and the auxiliary rib 29 shown in FIG. This includes the case where members of different heights are joined to the joined portions to form a substantially T-shape.

In the substantially T-shaped joint according to the present invention,
As shown in FIG.
In addition to forming the a and 22b, the height may be adjusted by cutting out the higher member in accordance with the lower member. In addition, the upper end of each component in the substantially T-shaped coupling portion does not need to be particularly formed horizontally, and may be non-horizontal or curved.

In the present invention, the rising ribs 22a, 22
The width d ₁ of the _second rib 2b and the height d ₂ of the auxiliary rib 23 correspond to the side wall 1
Thickness T ₁ of the 4A～14c, relative to the thickness t ₁ of the base portion _{24, d 1> 2T 1,} d 2> 2t 1, and most preferably d ₁
> 3T ₁ , d ₂ > 3t ₁ .

Here, the thickness of the auxiliary rib 23 for forming the gas injection region 25 is not particularly limited as long as it is less than the thickness of the thick portion 13. If it is not necessary to increase the thickness, it is preferable that the thickness is set to a thickness designed by ordinary injection molding, that is, _１ ／ or less of the thickness t ₁ of the base portion 24. Further, as shown in FIG. 16, the thick portion 13 may be designed to be included in the gas injection region 25. Further, as shown in FIG.
Also in the molded product 20 in which 3 is connected to the side wall portion 14a, it is possible to form the gas injection region 25 by providing the auxiliary ribs 23.

Similarly, as shown in FIG.
In the molded product in which the base 3 is connected to the side wall 14a, the auxiliary rib 23 connected along the side wall 14a is provided.
The gas press-fitting region 25 may be formed so as to include the thick portion 13 with the auxiliary ribs 23 connected along 4.

[0083]

【Example】

Example 1 In a curved housing shape as shown in FIG.
A molded product having 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 with reference to FIG. 1, and the gas injection position G was between the ribs a to g. In addition, the position of one parting surface is the position of H in FIG.
And the position of the other parting surface is the position shown in FIG. 4 at the position I in the figure.

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 materials are 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 weight) of the molding material relative to the cavity volume. The respective molding conditions are shown below. In addition, the ratio of the filled molten resin, in each mold, resin used, molding conditions,
The molded product was molded by the usual molding so as to just fill the cavity, and the weight of the molded product was calculated by measuring the weight of the molded product filled with an excessive amount of the molten resin, with the weight of the molded product being 100% by weight.

(A) 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: 100 kg / cm ² (gauge pressure)

(B) Material used: ABS ・ Cylinder temperature: 230 ° C. ・ Injection pressure: 100 kg / cm ² (gauge pressure) ・ Resin holding pressure: 20 kg / cm ² (gauge pressure) ・ Pressurized gas pressure: 100 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: 20 kg / cm ² (gauge pressure) Pressure of pressurized gas: 100 kg / cm ² (gauge pressure)

The appearance of the molded article was visually judged, and the sink of the design surface on the side opposite to the rib was measured. Table 1 shows the measurement results.

Comparative Example 1 A normal 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 holding 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 molded article was visually judged, and the sink of the design surface on the side opposite to the rib was measured. Table 1 shows the measurement results.

[0095]

[Table 1]

From the results shown in Table 1, the molded article according to the present invention was
The molded article had good appearance and 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.

Example 2 A molded product having a box-shaped OA equipment housing shape as shown in FIG. 20 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 m, respectively.
m.

The molding materials are high impact polystyrene (HIPS), ABS resin, modified PPE resin (m-PP
E), a molding was molded by injecting an excessive amount (104% by weight) of the molding material with respect to the cavity volume and immediately injecting a pressurized gas into each of them. 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: 20 kg / cm ² (gauge pressure) Pressure of pressurized gas: 100 kg / cm ² (gauge pressure)

(B) Materials used: ABS ・ Cylinder temperature: 230 ° C. ・ Injection pressure: 100 kg / cm ² (gauge pressure) ・ Resin pressure: 20 kg / cm ² (gauge pressure) ・ Pressurized gas pressure: 100 kg / cm ² (gauge pressure)

(C) Material: m-PPE Cylinder temperature: 260 ° C. Injection pressure: 100 kg / cm ² (gauge pressure) Resin holding 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 2 The same injection molding was carried out using the same mold and the same resin as in Example 2. 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 holding 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 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.

[0108]

[Table 2]

Example 3 A molded product having a box-shaped housing shape as shown in FIG. 21 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 for k, l, m, n, and o are 1 mm, 1.5 mm, 2 mm, 3 mm, and 4 mm, respectively.

The molding material was molded by injecting an excessive amount of molding material with respect to the cavity volume using an ABS resin, and then immediately injecting a pressurized gas. Excess amounts of 100.5 wt%, 101 wt%, 102 wt%, 1
The holding of the pressurized gas was measured at 03% by weight and 104% by weight. Other molding conditions are shown below.

[0112] Cylinder temperature: 240 ° C., mold temperature: 60 ° C · Injection pressure: 140 kgf / cm ² gauge pressure) Resin dwell pressure: 0 kgf / cm ² gauge pressure) • pressurized gas pressure: 150 kgf / cm ^2. Pressurized gas injection time: 3 seconds ・ Pressurized gas retention time: 20 seconds

Comparative Example 3 Injection molding with gas was carried out under the same conditions as in Example 3 except for the amount of resin to be filled by using the same mold and the same resin as in Example 3. Molded articles were formed with a small amount (99%) of resin filling and a small amount (100%) just filling the cavity as compared to the cavity volume.

Table 3 shows the results of the gas sealing properties and the measurement results of the sink marks in Example 3 and Comparative Example 3. The gas sealability was evaluated by the residual pressure at the end of the pressurized gas holding time. The higher the residual pressure, the better the gas sealing properties.

[0115]

[Table 3]

From the results in Table 3, it can be seen that the method of the present invention
That is, it was proved that the leakage of the pressurized gas can be prevented and the sink of the thick portion can be prevented by filling the mold with an excessive amount of resin by using a mold having good gas release.

Example 4 A molded product having a box-shaped OA equipment housing shape as shown in FIG. 22 and a main part thickness of 2.0 mm was formed. As the form of the side wall, the one shown in FIG. 1 was used. As the mold, a non-sealed mold without an O-ring was used on the parting surface (PL surface). By using the method, excess gas in the mold at the time of filling the molten resin was discharged out of the mold. The thickness of the rib p is 3 mm.

The molding material was molded by injecting an excess amount of molding material with respect to the cavity volume using an ABS resin, and then immediately injecting a pressurized gas. The amount of resin injected and filled into the mold cavity is 1 when the amount of resin just filling the mold cavity is 100%.
00.5% by weight, 101% by weight, 102% by weight, 103
% By weight, 104% by weight, 106% by weight and 107% by weight. Although this method is different from the present method in that an excessive amount of resin is filled, for comparison, 99.5% by weight and 100% by weight are also molded. Other molding conditions are shown below.

・ Cylinder temperature: 240 ° C. ・ Mold temperature: 60 ° C. ・ Injection pressure: 140 kgf / cm ² (gauge pressure) ・ Resin pressure: 0 kgf / cm ² (gauge pressure) ・ Pressurized gas pressure: 150 kgf / Cm ²・ Pressure injection time of pressurized gas: 3 seconds ・ Holding time of pressurized gas: 20 seconds

Table 4 shows the result of measurement of the sink amount on the design surface side with respect to the thick rib p of the molded product.

Comparative Example 4 As in Example 4, a box-shaped OA as shown in FIG.
A molded product having an apparatus housing shape and a main part thickness of 2.0 mm was formed. For the injection of the pressurized gas and the gas seal, those having the form shown in FIG. 1 were used. The difference from Example 3 was that a sealing mold having an O-ring also provided on the parting surface was used.

Other molding conditions such as cylinder temperature, mold temperature, injection conditions, and pressurized gas conditions are the same as those in the fourth embodiment. The amount of resin injected and filled into the mold cavity is 99.5% by weight, 100.5% by weight, 10% by weight when the amount of resin just filling the mold cavity is 100%.
They were 1% by weight, 103% by weight, 104% by weight, 105% by weight, 106% by weight and 107% by weight.

Table 4 shows the result of measuring the sink amount on the design surface side with respect to the thick rib p of the molded product.

[0124]

[Table 4] The values in parentheses are values that are not according to the present invention, although a non-sealed mold is used.

[0125] From the results of Table 4, preferable to use a mold unsealed system definitive to the onset Ming, than when using a mold of the sealing system, the shrinkage in the loading of a smaller amount of excess resin It can be seen that the effect can be obtained. In addition, in the range of the above-mentioned excessive amount of resin filling, no large burrs were generated, and a molded product having good appearance was obtained.

[0126]

As described above, according to the present invention, an injection-molded article excellent in appearance without sink marks and burrs can be obtained with a mold having a small facility load.

[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 view showing a molded product obtained by the mold of FIG. 1;

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

FIG. 4 is a schematic cross-sectional view showing another example of the formation position of the open air path.

FIG. 5 is an enlarged sectional view around a gas injection pin.

FIG. 6 is an explanatory view of a gas sealing action and a sink prevention action in the present invention.

FIG. 7 is an explanatory diagram of a thick portion suitable for applying the present invention.

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

FIG. 9 is an explanatory view of the vicinity of the thick part when the pressurized gas is also allowed to enter the thick part in the present invention.

FIG. 10 is an explanatory diagram of a hollow portion formed.

FIG. 11 is a cross-sectional view showing another example of a mold used in the present invention.

FIG. 12 is an explanatory view of the vicinity of a thick part when a pressurized gas is caused to enter the thick part from another path in the present invention.

FIG. 13 is a perspective view showing another example of a molded product formed by the present invention.

FIG. 14 is a view showing the vicinity of a gas injection area in FIG. 13;

FIG. 15 is a perspective view showing another example of a molded product formed by the present invention.

FIG. 16 is a perspective view showing another example of a molded product formed by the present invention.

FIG. 17 is a perspective view showing another example of a molded product formed by the present invention.

FIG. 18 is a perspective view showing another example of a molded product formed by the present invention.

FIG. 19 is a schematic view of a molded article molded in Example 1 and Comparative Example 1.

FIG. 20 is a schematic view of a molded article molded in Example 2 and Comparative Example 2.

FIG. 21 is a schematic view of a molded article molded in Example 3 and Comparative Example 3.

FIG. 22 is a schematic view of a molded article molded in Example 4 and Comparative Example 4.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold 2 fixed mold 3 moving mold 4 cavity 4a, 4b cavity surface 5 air release path 6 ejector pin 7a to 7e O-ring 8 gas injection pin 9a, 9b valve 10a, 10b gas introduction path 11 gate 12 hole DESCRIPTION OF SYMBOLS 13 Thick part 14a-14d Side wall part 15 Projection plate 16 Sealing chamber 17 Hollow part (according to the present invention) 18 Gas injection needle 19 Hollow part (according to conventional technology) 20 Molded product 21 Near thick part 22a, 22b Rise rib 23 Auxiliary rib 24 Base 25 Gas injection area 26 Gas inlet

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-315947 (JP, A) JP-T10-503719 (JP, A) JP-T4-501090 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) B29C 45/00-45/84

Claims (7)

(57) [Claims] In an injection molding of a molded product having a thick portion protruding on a back surface side, a gas in a cavity is extracted from a cavity opening path through a path open to a part of a cavity surface, while the gas in the cavity is compared with the cavity volume. excess molten resin injected and filled Te, then concave moldings backside serving as a gas injection region
Pressurizing gas between a place and a cavity surface corresponding thereto, and pressing a molded product surface corresponding to the gas injection region against the corresponding cavity surface. . 2. The gas pressure injection molding method according to claim 1, wherein the open-to-atmosphere path is formed as a groove. 3. The gas pressure injection molding method according to claim 2, wherein the thickness of at least the groove near the opening to the cavity is 1/100 mm or more and 1/10 mm or less. 4. The injection amount of the molten resin into the cavity is:
4. The gas pressure injection molding method according to claim 1, wherein the amount is 101 to 110% by weight when the weight of the molten resin for the cavity volume is 100% by weight. 5. The gas pressure injection molding method according to claim 1, wherein a resin holding pressure is applied after the injection of the molten resin. 6. The gas pressure injection molding method according to claim 5, wherein the resin holding pressure is applied also when pressurized gas is injected. 7. A pressurized gas is press-fitted between a concave portion on the back surface of a molded product serving as a gas injection region and a cavity surface corresponding thereto, and the surface of the molded product corresponding to the gas injection region is moved to a cavity corresponding thereto. while pressing on the surface, according to claim 6 or a gas pressurized pressure injection molding method, and forming a hollow portion by injecting inside pressurized gas filling molten resin into the cavitation I .