JP2016112813A - Method for injection molding hollow molding, hollow molding and system for injection molding hollow molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a long hollow resin molding flexible in cross sectional shape, uniform in wall thickness and high in inner surface smoothness, and a method and system for injection molding the molding.SOLUTION: A method for injection molding a hollow molding comprises: charging a molten resin R into the cavity 2 of an injection molding die 10 in the state of closing a shut-off pin 3; injecting a compressible fluid G as a pressurized fluid while pressurizing the compressible fluid by an incompressible fluid W into the molten resin R in the cavity 2 in the state of opening the shut-off pin 3; discharging the excessive molten resin R into a waste cavity 4, pressurizing and holding the compressible fluid G into the molten resin R; and slowly cooling the inside of the molten resin R in the cavity 2.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a hollow molded article used for transportation vehicles, medical equipment, industrial equipment and handrails, an injection molding method thereof, and a hollow molded article injection molding system.

  In recent years, in hollow molded products, especially long hollow molded products with a long hollow part, there is an increasing need for molded products including irregular shapes from the viewpoints of weight reduction, space saving, design, ease of gripping, etc. There is a growing demand for products that have a high degree of freedom in cross-sectional shape, a uniform thickness, and high inner surface smoothness.

  An injection molding method is known as a method for forming a hollow molded product. In recent years, as a general injection molding method for hollow molded products, after filling a molten resin into a mold or in the middle of filling a molten resin, gas is injected to form a hollow in the molten resin. There is a molding method. However, in the gas-assisted injection molding method, when molding a long hollow molded product, a high-pressure is applied around the gas injection part, so that a thin cross section is obtained. Since the pressure dropped, the wall thickness increased, making it difficult to obtain a product with a uniform wall thickness, and the cross-sectional shape of the molded product including the irregular shape was poorly traceable.

  On the other hand, as an injection molding method capable of obtaining a product having a uniform thickness with a circular cross section, there is a long hollow molding method using a floating core in which a spherical or shell-shaped core is injected into a molten resin (see Patent Document 1). .

  In addition, as an injection molding method that can obtain a molded article having a high degree of freedom in cross-sectional shape and including an irregular shape, there is a water assist molding method that injects water instead of injecting gas into the above-described molten resin (patent) Reference 2).

  However, since the floating core molding method floats a sphere or a shell-shaped core in a resin to mold a hollow, it is limited to molding a pipe-shaped hollow molded product having a circular cross-sectional shape, and includes atypical molds that have been highly demanded. A hollow molded article cannot be molded. In addition, the water assist molding method has a high degree of freedom with respect to the cross-sectional shape of the molded product including the variant, but the inner surface of the molded product is rapidly cooled by water, so that the smoothness of the inner surface is lowered, and the water on the inner surface is reduced. There is a disadvantage that a drying step is required, and that when a resin having water absorption is reused, the resin cannot be recycled unless the resin discharged into the cavity is dried.

Japanese Patent Laid-Open No. 10-180812 JP 2006-213041 A

  As a long hollow molded product, it is required to apply a uniform internal pressure to the fluid injection portion and the end portion to obtain a molded product having a uniform thickness.

  In recent years, from the viewpoint of space saving, design, ease of gripping, and the like, a product having a high degree of freedom with respect to the cross-sectional shape of a molded product including an irregular shape and a high smoothness of the inner surface has been demanded.

  Therefore, the present invention provides a molded product having a high degree of freedom in the cross-sectional shape of a molded product including atypical shape, a uniform wall thickness, and a high inner surface smoothness in a long hollow molded product using a resin. It is the purpose. Another object of the present invention is to provide an injection molding method and an injection molding system for molding such a molded product.

  As described above, the water assist molding method has a high degree of freedom with respect to the cross-sectional shape of a molded product including an irregular shape, but the inner surface of the molded product is rapidly cooled by a fluid, so that the smoothness of the inner surface is lowered. is there. This is because the thermal conductivity of the fluid is higher than the thermal conductivity of the molded product. Even if the fluid is changed to oil or the like, the fluid is hardly changed as long as it is a liquid, and the smoothness of the inner surface cannot be improved.

  However, as a result of earnest research conducted day and night beyond the common knowledge of those skilled in the art, the present inventors changed the idea by 180 °, pressurized using a compressible fluid, and lowered the thermal conductivity to reduce the inside of the molded product. The present inventors have found a molding method in which molding is performed by slowly cooling and pressurizing with a non-compressible fluid so that the compressible fluid can be pressurized without losing the resin resistance in the molded product.

That is, according to the method for forming a hollow molded article of the present invention, the molten resin is injected into the cavity of the injection mold, and the pressurized fluid is allowed to flow into the molten resin, whereby the waste communicated with the cavity via the shut-off pin. A method of forming a hollow molded product by injection molding that forms a hollow portion in the molten resin in the cavity while discharging excess molten resin to the cavity,
After injecting and filling molten resin into the cavity with the shutoff pin closed,
With the shut-off pin open, compressible fluid such as nitrogen gas as pressurized fluid is injected into the molten resin in the cavity while being pressurized with incompressible fluid such as water, and the excess molten resin is discharged to the discarded cavity After
Only the compressive fluid is compressed and held in the molten resin, and the inside of the molten resin in the cavity is gradually cooled.

  When the compressive fluid is injected into the molten resin while being pressurized with an incompressible fluid, an amount smaller than the capacity of the fluid injection path is provided behind the compressive fluid supplied to the fluid injection path to the cavity. It is preferable to supply an incompressible fluid.

  The present invention is particularly effective when the hollow molded product is long. For example, the present invention is suitable for a long molded product having a total length / outer diameter ratio of 5 or more.

  The compressible fluid is mainly a gas, but is preferably an inert gas.

  The incompressible fluid is mainly a liquid, but is preferably water.

A hollow molded product injection molding system of the present invention includes a cavity, a waste cavity communicated with the cavity via a shut-off pin, an injection mold having a fluid injection valve for injecting fluid into the cavity,
Pressurized fluid that forms a hollow part in the molten resin in the cavity while discharging excess molten resin into the discarded cavity by injecting the pressurized fluid into the molten resin in the cavity via the fluid injection valve An injection device;
A fluid injection hose for introducing the pressurized fluid supplied from the pressurized fluid injection device into the fluid injection valve of the injection mold,
A fluid injection path including a fluid injection valve and a fluid injection hose has a capacity greater than the volume of excess molten resin discharged into the waste cavity;
This pressurized fluid injection device includes a compressible fluid containing portion that contains a compressible fluid, an incompressible fluid containing portion that contains an incompressible fluid, and compressive fluid and incompressible fluid from both of the containing portions. Fluid switching supply means for switching and supplying to the cavity is provided.

  Here, the “fluid injection hose” is not limited as long as it has a transport path for transporting fluid, and includes not only a flexible hose but also a non-flexible pipe (pipe) made of metal or resin. .

  In the hollow molded product injection molding system, it is preferable that the pressurized fluid injection device includes a measuring means for measuring the flow rate of the incompressible fluid supplied to the fluid injection path.

  In this hollow molded product injection molding system, it is preferable that the pressurized fluid injection device includes pressure control means for controlling the pressure applied to the compressive fluid by the incompressible fluid.

  The pressure control means preferably includes a mechanism for pressurizing the incompressible fluid supplied into the fluid injection path from the rear.

  According to the injection molding method and the hollow molding product injection molding system of the present invention, since the compressive fluid is injected into the molten resin while being pressurized with the incompressible fluid, pressurization is performed with sufficient pressure during molding. It is possible to obtain a hollow molded product having a high degree of freedom in shape, such as a cross-sectional shape including atypical shapes, and to obtain a molded product with a uniform thickness. In addition, since the compressive fluid is compressed and held and the inside of the molten resin is gradually cooled, a molded product with high smoothness on the inner surface can be obtained.

1 is a schematic diagram illustrating an overall configuration of an injection molding system according to an embodiment of the present invention. In the said embodiment, it is a schematic block diagram which shows the process of inject | pouring molten resin in a cavity. In the same embodiment, it is a schematic block diagram which shows the process of inject | pouring into the molten resin, pressurizing the inert gas which is a compressive fluid with the water which is an incompressible fluid. In the same embodiment, it is a schematic block diagram which shows the process cooled slowly in the state which injected and pressurized the inert gas in molten resin. In the same embodiment, it is a schematic block diagram which shows the process of collect | recovering the water which is an incompressible fluid after shaping | molding of a hollow molded product. It is the schematic which shows the whole structure of the injection molding system which concerns on other embodiment of this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a hollow molded product injection molding system and injection molding method according to the present invention will be described in detail with reference to the drawings. The same or equivalent parts are denoted by the same reference numerals.

  A configuration of a hollow molded product injection molding system according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing an overall schematic configuration of the present embodiment.

  A hollow molded product injection molding system 1 according to the present embodiment includes a cavity 2, a waste cavity 4 communicating with the cavity 2 via a shutoff pin 3, and an injection needle valve 5 for injecting fluid into the cavity 2. By injecting the pressurized fluid into the molding die 10 and the molten resin R in the cavity 2 through the fluid injection needle valve 5, the excess molten resin R is discharged into the waste cavity 4, while the cavity 2 is discharged. And a pressurized fluid injection device 20 for forming a hollow portion in the inner molten resin R.

  The pressurized fluid injection device 20 and the needle valve 5 of the injection mold 10 are connected by a fluid injection hose 19. That is, in this configuration, the fluid injection hose 19 and the needle valve 5 constitute a fluid injection path for pressurized fluid. At this time, the sum of the capacities of the needle valve 5 and the fluid injection hose 19 (hereinafter referred to as “injection path capacity”) connecting the pressurized fluid injection device 20 and the injection mold 10 is a desired molded product. Is set to be larger than the volume of the molten resin that is discarded by the pressurized fluid and discharged into the cavity. The injection path capacity is preferably 1.1 times or more, more preferably 1.2 times or more, and particularly 1.33 times or more of the volume of excess molten resin discharged into the disposal cavity. The capacity of the discarded cavity is set according to the amount of excess resin to be discharged, and is generally the same as the amount of resin excluded for forming a hollow.

The pressurized fluid injection device 20 includes a compressive fluid storage unit (inert gas tank here) 23 that stores a compressive fluid, and an incompressible fluid storage unit (here, a water tank) that stores incompressible fluid. 24, and a fluid switching supply means (here, a line switching valve) 21 that switches the compressive fluid and the incompressible fluid from both the housing portions 23 and 24 and supplies them to the cavity 2.
Each of the gas tank 23 and the water tank 24 includes a pump (pressure control means) capable of pressurization and depressurization, and can perform pressurization or depressurization as necessary. Moreover, in this embodiment, the drain 25 which collect | recovers and discharges an incompressible fluid and a compressive fluid after shaping | molding of a hollow molded article is provided.
The compressible fluid is mainly a gas, and specifically includes air, nitrogen gas, etc., but in order to prevent oxidative discoloration and burning due to compression in the hollow molded article, an easily available nitrogen gas is optimal. is there. The incompressible fluid is mainly a liquid, and specifically includes oil, water, and the like, but water is optimal in consideration of handleability and versatility.

  Each tank is preferably provided with a measuring means for measuring the flow rate of the fluid. By providing the incompressible fluid metering means, when the compressible fluid is pressurized by supplying the incompressible fluid from the rear of the compressible fluid for injecting the compressible fluid into the molten resin, the incompressible fluid is supplied. It is easy to adjust the supply amount of the incompressible fluid to be less than the injection path volume so that the fluid does not enter the cavity.

  The injection mold 10 includes a shutoff pin 6 for preventing a backflow of gas to a nozzle 31 described later and a resin flow path (sprue) 7 for injecting molten resin into the cavity 2. A molding machine nozzle 31 of a resin injection device (not shown) provided separately is connected to the sprue 7, and molten resin injected from the nozzle 31 is injected into the cavity 2 through the sprue 7.

  Next, with reference to FIGS. 1-5, the shaping | molding method of the elongate hollow molded product which concerns on this embodiment is demonstrated.

  FIG. 1 shows a process before injecting the resin R into the cavity 2 in the injection mold. Before filling the molten resin R, the valve 21 is adjusted so that the flow path from the inert gas tank 23 is opened, and the inert gas G is injected into the cavity 2 from the fluid injection hose 19, and the air Exhaust the air. That is, immediately before the resin injection, the fluid injection hose 19 and the cavity 2 are filled with an inert gas G of about atmospheric pressure. This purging step is performed in a state where the shut-off pin 3 on the disposal cavity 4 side is closed. The needle valve 5 is opened throughout the entire stroke, but the mold side opening of the needle valve 5 is adjusted to a clearance that prevents the molten resin R from entering the needle valve 5 when the molten resin R is filled into the cavity 2. Has been.

  FIG. 2 shows a process of injecting the molten resin R into the cavity 2 in the injection mold 10. The shut-off pin 6 of the resin flow path (sprue) 7 of the injection mold 10 is opened, and the melted resin R is completely filled into the cavity 2 from an injection molding machine nozzle 31 of a resin injection apparatus (not shown) that is provided separately. Is done. At this time, the waste cavity-side shutoff pin 3 leading from the cavity 2 to the waste cavity 4 is closed, so that the molten resin R is not discharged into the waste cavity 4 to form the surface appearance of the hollow molded product. By adopting the full shot method in which the molten resin is completely filled into the cavity, the outer surface of the molded product can be made into a smooth finish along the mold by filling.

FIG. 3 shows a process of injecting an inert gas G, which is a compressible fluid, into the molten resin in the cavity 2 after filling the cavity 2 with the resin.
After the cavity 2 is filled with the molten resin R, the waste cavity 4 side shut-off pin 3 leading to the waste cavity 4 is opened. Then, the switching valve 21 is adjusted so that the line on the water tank 24 side is opened, and water W that is an incompressible fluid is introduced into the injection hose 19 from behind the inert gas G in the injection hose 19. The inert gas G is injected into the cavity 2 from the injection needle valve 5 while pressurizing the inert gas G with water W. At this time, as the inert gas G is injected into the cavity 2, excess molten resin R is discarded and discharged into the cavity 4.

FIG. 4 shows a step of slowly cooling while injecting and pressurizing the inert gas G into the resin and maintaining the pressurized state.
Excess resin R is discharged to the disposal cavity 4, the inside of the resin R in the cavity is filled with the inert gas G, and the inert gas G is pressurized and compressed by the water W that is an incompressible fluid. Since pressurization is performed with water W, the compressive fluid injected into the molten resin can be pressurized more than the gas-assisted molding method using only a compressive fluid such as an inert gas G. The thickness non-uniformity which has been a problem with the assist molding method can be suppressed, and a molded product with a more uniform thickness can be obtained.

  Since the capacity of the injection hose 19 is larger than the capacity of the inert gas injected into the resin, the water W, which is an incompressible fluid, does not enter the cavity 2 and enters the injection needle valve 5 or the valve 5. Stay in the connected injection hose 19. In order to prevent the water W from entering the cavity 2, it is also necessary to make the amount of water W injected into the injection hose 19 equal to or less than the capacity of the injection hose 19.

  By holding the inert gas G in the resin in a pressurized state for a predetermined time and performing slow cooling for a predetermined time, the molten resin R is solidified and the hollow molded product 40 can be obtained. A compressible fluid such as inert gas G has a lower thermal conductivity than an incompressible fluid such as water W, so the resin can be cooled gradually without being rapidly cooled. Can be obtained.

FIG. 5 shows a step of recovering the water W in the injection hose 19 and the inert gas G in the cavity after the hollow molded product 40 is formed.
The injection switching valve 21 is adjusted so that the water line is opened, and the water line is depressurized by the pressure control means of the water tank 24 to draw water and the inert gas G toward the injection hose inner valve 21 side. Water W and gas G are discharged to the drain 25.

  The water W and the gas G may be collected in the respective tanks without being discharged to the drain. If recovered in a tank, water and gas can be reused. A configuration in which only one of water and gas is reused is also possible. In the case of the conventional water assist, since water is injected into the resin, the resin may be mixed in the water, and if the filter is not installed when water is reused, a reproducible molded product Could not get. If this structure is used, since water is not polluted, it can be recovered as it is and reused.

FIG. 6 is a schematic diagram showing the overall configuration of the injection molding system 11 of the design modification example of the above embodiment.
The point which provided the reservoir | reserver 29 in the middle of the injection | pouring hose 19 differs from embodiment shown in FIG. By providing the reservoir 29 and storing the inert gas G, the flow rate of the inert gas G compressed by the water from the rear and injected into the cavity is sufficient, so that water is not injected into the cavity. It can also be easily controlled. If the length of the injection hose 19 is sufficiently long, the reservoir may not be provided as in the previous embodiment shown in FIG.

The method for forming a hollow molded article according to the present embodiment is not limited to the production of a long hollow molded article, but is used for transportation vehicles, medical equipment, industrial equipment, handrails, etc. It is particularly suitable for the production of a long hollow molded product having a diameter ratio of 5 or more.
As the type of resin forming such a long hollow molded article, a thermoplastic resin used for extrusion, injection molding, hot pressing, vacuum forming, and the like can be used in consideration of productivity. Among thermoplastic resins, polyamide imide, PPS resin, LCP resin, polycarbonate, polyacetal, polyamide, PBT resin, PET resin, modified PPO resin, modified PPE resin, AS resin, ABS resin, polystyrene, polypropylene, polyethylene, etc. are used. In addition, alloy materials and copolymers containing these as one constituent component can also be used.

  Since it is necessary to make the wall thickness uniform and increase the rigidity of the long hollow molded article, it is preferable to add (contain) an inorganic filler to the resin forming the long hollow molded article. At this time, it is preferable to add 5 to 60% by weight of an inorganic filler to the long hollow molded article. As the resin containing the inorganic filler, a crystalline resin is preferable for applications requiring heat resistance and chemical resistance, and a polyamide resin is most preferable in consideration of a balance between both performances.

  The types of inorganic fillers added to the resin include glass fibers, PAN and pitch carbon fibers, stainless fibers, metal fibers such as aluminum fibers and brass fibers, organic fibers such as aromatic polyamide fibers, gypsum fibers, and ceramics. Fiber, asbestos fiber, zirconia fiber, alumina fiber, silica fiber, titanium oxide fiber, silicon carbide fiber, rock wool, potassium titanate whisker, silicon nitride whisker, wollastonite, etc., whisker-like filler, glass beads, glass Examples of the filler include balloons, talc, and barium sulfate. Among these, glass fiber is preferable in terms of rigidity, strength, and cost. A glass fiber having an average length of about 100 μm or more and 500 μm or less is preferably used. The glass fiber having an average diameter φ (diameter) of 3 μm or more and less than 50 μm can be used, and it is preferable to use a glass fiber having an average diameter of 5 μm or more and less than 30 μm from the viewpoint of cost and strength.

  Furthermore, the inorganic filler has its surface pretreated with an organic onium ion in the case of coupling agents such as silane coupling agents and titanate coupling agents, other surface treatment agents and swellable layered silicates. It is preferable because more excellent mechanical strength can be obtained.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments.

Hereinafter, the present invention will be described more specifically with reference to examples.
[Resin used]
In Examples 1 and 2 and Comparative Examples 1 to 4, one of the following two types of thermoplastic resins was used.
Resin 1: Leona 14G33 (trade name) manufactured by Asahi Kasei Chemicals Co., Ltd .; polyamide (PA) 66 resin, 33% by mass of glass fiber (GF) Density = 1390 kg / m ³
Resin 2: Leona 53G33 (trade name) manufactured by Asahi Kasei Chemicals Corporation; alloy product of PA66 resin and low water absorption PA, containing GF33% by mass Density = 1350 kg / m ³

[Injection mold]
In Examples 1 and 2 and Comparative Examples 1 to 4, one of the following two types of injection molds was used.
Mold 1: L-shaped mold having a circular cross section with an outer diameter of φ25 mm and a mold for a long molded product having a total length of about 400 mm Mold 2: An ellipse (long diameter 35 mm, short diameter 18 mm) only at the corner, The part is an L-shaped mold with a circular section with an outer diameter of φ25mm.

[Example 1]
A 180 ton horizontal injection molding machine, mold 1, was used. After purging the cavity of the mold 1 and the fluid injection hose with nitrogen gas (purity 99.99%), the resin 1 which is a thermoplastic resin is melted at a resin temperature setting of 290 ° C., and the mold temperature is set to 80 ° C. Fill the cavity of the mold 1 with a full shot, pressurize and inject nitrogen gas from the fluid injection needle valve with water, an incompressible fluid, and hold the compressed and compressed nitrogen gas in the resin in the cavity for a predetermined time. And slowly cooled to form an L-shaped long hollow molded product. At this time, the amount of water injected was 200 cc.
At this time, the total injection volume including water and nitrogen gas injected into the entire injection path including the injection hose, needle valve, and cavity was 550 cc.

[Example 2]
In Example 1, an L-shaped long hollow molded product was molded in the same manner as in Example 1 except that the amount of water injected was 250 cc.

[Example 3]
An L-shaped long hollow molded article including a variant was molded in the same manner as in Example 1 except that the mold 2 was used in place of the mold 1 and the amount of water injected was 220 cc.

[Example 4]
In Example 3, an L-shaped long hollow molded product including a variant was molded in the same manner as in Example 3 except that Resin 2 was used instead of Resin 1.

[Comparative Example 1]
In Example 2, a so-called gas-assisted molding method in which only nitrogen gas is supplied to the injection hose without pressurizing and injecting nitrogen gas with water, which is an incompressible fluid, and an L-shaped long hollow including an irregular shape. Molded product was molded.

[Comparative Example 2]
In Example 1, nitrogen gas (purity 99) was used as a compressible inert gas by using a bullet-shaped floating core set on the fluid injection needle valve side without pressurizing and injecting nitrogen gas with water as an incompressible fluid. The L-shaped long hollow molded product was molded by a so-called floating core molding method in which a hollow was formed in the molten resin while being pushed away at .99%).

[Comparative Example 3]
In Example 1, an L-shaped long hollow molded product is molded by a so-called water-assisted molding method in which a hollow is formed by injecting water into a molten resin instead of injecting only nitrogen gas into the molten resin. did. The amount of water injected was 400 cc.

[Comparative Example 4]
In Comparative Example 3, an L-shaped long hollow molded product was molded by a water assist molding method in which the resin 1 was replaced with the resin 2.

[Comparative Example 5]
In Example 2, instead of injecting only nitrogen gas into the molten resin, water is injected into the molten resin to form a hollow, so-called water-assist molding method, so that an L-shaped long hollow mold including atypical shapes is formed. The product was molded. The amount of water injected was 430 cc.

  The molded products obtained by the molding methods of Examples 1 and 2 and Comparative Examples 1 to 5 were evaluated as follows and are summarized in Table 1.

[Cross section shape]
It was evaluated that the cross-sectional shape along the shape of the mold was good (◯), and the cross-sectional shape along the shape of the mold was not obtained (×).

[Inner surface smoothness evaluation method]
Based on JIS B0601: 1982, a long hollow molded article was cut in the length direction as a scale for measuring the smoothness of the inner surface, and the maximum height Rmax of the inner surface was determined. A smaller Rmax means higher smoothness.

[Recyclability]
It was evaluated that it was possible to recycle the excess resin that was discarded in the hollow formation and discharged into the cavity as it was (◯), and that it was not recyclable, or that it was not possible to recycle (*).

[Necessity of drying process]
The molded product was evaluated as necessary when a drying step was necessary, and not necessary when a drying step was unnecessary.

  As shown in Table 1, Examples 1-4 of the present invention have higher inner surface smoothness than Comparative Examples 1 and 3-5, good recyclability, and do not require a drying step. In the floating core molding method of Comparative Example 2, the same effect as the present invention can be obtained with high inner surface smoothness, recyclability, and no drying process, but since the passage of the floating core is hollow, the hollow cross section covers the entire area. Only those having the same circular shape can be molded, and as described in the section of the prior art, a molded product having a shape including an irregular cross section cannot be molded. On the other hand, in the present invention, the cross-sectional shape traceability was high in the same way as in Example 1 for the mold 2 including an irregular cross-sectional shape as in Examples 3 and 4. In the gas assist molding of Comparative Example 1, the hollow shape was tapered on the end side opposite to the gas inlet, and the cross-sectional shape was hollow with respect to the mold including the atypical shape, and the cross-sectional shape traceability was low.

  In the case of water assist molding as in Comparative Example 3-5, although there is a cross-sectional trace property, the inner surface smoothness is low, the recyclability is poor, and further, a drying step of the molded product is required. Since the molding method of the present invention is slow cooling, it takes a cooling time as compared with the case of water assist, but a drying step is unnecessary and the cost required for the equipment can be suppressed.

  In Example 2, more incompressible fluid (water) is injected into the injection hose, and nitrogen gas, which is a compressive fluid, is held in a more compressed state in the cavity. A molded article having an inner surface with high smoothness could be obtained. In addition, although Example 3 and Example 4 differ only in the resin material, the difference arises in smoothness. This is a result showing that the smoothness also depends on the solidification speed of the resin material.

DESCRIPTION OF SYMBOLS 1,11 Injection molding system 2 Cavity 3 Waste cavity side shut-off pin 4 Waste cavity 5 Needle valve for fluid injection 6 Shut-off pin for injection-machine nozzle side backflow prevention 7 Resin passage (sprue)
DESCRIPTION OF SYMBOLS 10 Injection mold 19 Fluid injection hose 20 Pressurized fluid injection | pouring apparatus 21 Fluid switching supply means 23 Inert gas tank (compressible fluid storage part)
24 Water tank (incompressible fluid container)
25 Drain 29 Reservoir 31 Injection molding machine nozzle 40 Hollow molded product

Claims (11)

By injecting molten resin into the cavity of the injection mold and allowing a pressurized fluid to flow into the molten resin, the excess molten resin is discharged to a waste cavity communicated with the cavity via a shut-off pin. A method of forming a hollow molded article by injection molding to form a hollow portion in the molten resin in the cavity,
With the shutoff pin closed, after injection filling the molten resin into the cavity,
In a state where the shut-off pin is opened, a compressive fluid is injected as a pressurized fluid into the molten resin in the cavity while being pressurized with an incompressible fluid, and excess molten resin is discharged into the waste cavity. rear,
A method for injection molding a hollow molded article, wherein only the compressive fluid is compressed and held in the molten resin, and the inside of the molten resin in the cavity is gradually cooled.   An amount of the incompressible fluid less than the volume of the fluid injection path is supplied behind the compressive fluid supplied to the fluid injection path for injecting the compressive fluid into the cavity, and the compressive fluid is 2. The hollow molded article injection molding method according to claim 1, wherein the molten resin is injected while being pressurized with the incompressible fluid.   The hollow molded article injection molding method according to claim 1 or 2, wherein the hollow molded article has an overall length / outer diameter ratio of 5 or more.   The hollow molding product injection molding method according to any one of claims 1 to 3, wherein the compressive fluid is an inert gas.   The hollow molding product injection molding method according to any one of claims 1 to 4, wherein the incompressible fluid is water.   A hollow molded article molded by the hollow molded article injection molding method according to any one of claims 1 to 5.   The hollow molded article according to claim 6, wherein the ratio of the total length / outer diameter is 5 or more. An injection mold having a cavity, a discarded cavity communicated with the cavity via a shut-off pin, and a fluid injection valve for injecting fluid into the cavity;
By injecting the pressurized fluid into the molten resin in the cavity via the fluid injection valve, the hollow portion is formed in the molten resin in the cavity while discharging the excess molten resin into the waste cavity. A pressurized fluid injection device to form;
A fluid injection hose for introducing the pressurized fluid supplied from the pressurized fluid injection device into the fluid injection valve of the injection mold,
A fluid injection path including the fluid injection valve and the fluid injection hose has a capacity larger than the volume of the excess molten resin discharged to the waste cavity;
The pressurized fluid injecting device includes a compressible fluid containing portion that contains a compressible fluid, an incompressible fluid containing portion that contains an incompressible fluid, and the compressible fluid and the incompressible from both the containing portions. A hollow molded product injection molding system comprising fluid switching supply means for switching fluid to supply to the cavity.   9. The hollow molded product injection molding system according to claim 8, wherein the pressurized fluid injection device includes a metering unit that measures a flow rate of the incompressible fluid supplied to the fluid injection path.   10. The hollow molded product injection molding system according to claim 8 or 9, wherein the pressurized fluid injection device includes pressure control means for controlling the pressure applied to the compressive fluid by the incompressible fluid. .   11. The hollow molded product injection molding system according to claim 10, wherein the pressure control means includes a mechanism for pressurizing the incompressible fluid supplied into the fluid injection path from the rear.