JP3325532B2 - Injection molding method for thermoplastic resin molded article and injection molding apparatus used for this 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 for a thermoplastic resin molded article, especially a thermoplastic resin foam molded article or a thermoplastic resin molded article having a high melt viscosity and which is difficult to melt-mold, and an injection molding method used for this molding method. The present invention relates to a molding device.

[0002]

2. Description of the Related Art As a method of obtaining a thermoplastic resin foam by injection molding, a gaseous inert gas such as carbon dioxide or nitrogen gas serving as a foaming agent is impregnated in a molten resin to be injected at normal temperature and normal pressure. There is a way. As a method for impregnating the molten resin with the inert gas as described above, 1) a method of impregnating a raw material resin in a solid state before being charged into a cylinder under high pressure in advance, and 2) US Pat. No. 5,158,986 There is a method of impregnating a resin in a molten state in a cylinder as described in the gazette.

However, the method 1) of impregnating the raw material resin in the solid state with a gas can obtain a thermoplastic resin foam, but a gas in a gaseous state at normal temperature and normal pressure, particularly an inert gas, is used. Because of its low affinity with the resin, it takes several tens of hours to completely impregnate the gas with the resin, and it is difficult to carry out the method industrially. That is, it is necessary to stop supplying the resin to the molding machine until the saturated impregnation state is reached, and to impregnate the gas in the pressure chamber.
Incidentally, thermoplastic resin pellets (high density polyethylene,
FIG. 9 shows an impregnation amount curve when carbon dioxide gas is impregnated into a size of φ4 × 2.3 mm) at room temperature (20 ° C.) and a pressure of 10.0 MPa. Therefore, it takes 1960 minutes to reach the saturated impregnation state.

On the other hand, in a method of impregnating a resin in a molten state in a cylinder as disclosed in US Pat. No. 5,158,986, resin pellets supplied from a raw material supply port are used.
While rotating the screw inside the cylinder, it melts, and at the same time, retracts the screw to supply carbon dioxide gas from the gas supply port provided in one place of the cylinder while plasticizing and metering to the measuring section at the tip of the cylinder. However, since the resin in the cylinder being measured is in a high pressure state, it is very difficult to inject the gas unless the pressure of the supplied gas is higher than the pressure of the molten resin. However, if a high-pressure gas is used, the apparatus itself must have a pressure-resistant structure that can withstand the high-pressure gas, and there is a problem that the manufacturing cost is high.

[0005]

SUMMARY OF THE INVENTION In view of such circumstances, the present invention provides a stable and continuous supply of a gas in a gaseous state at normal temperature and normal pressure, particularly an inert gas, to a thermoplastic resin at a relatively low pressure. Injection of thermoplastic resin moldings that can be impregnated
An object of the present invention is to provide a molding method and an injection molding apparatus used for the molding method.

[0006]

In order to achieve the above object, an injection molding method for a thermoplastic resin molded article according to claim 1 of the present invention (hereinafter referred to as "a molding method of claim 1"). ) Is to supply a gas in a gaseous state at normal temperature and normal pressure from a gas supply port provided in the cylinder to the molten resin in a molten state in the cylinder of the injection machine, and to supply the molten resin pressure from the gas supply port.
Low pressure forming a low pressure section that is lower than the pressure of the supplied gas
Thermoplastic resin comprising a gas impregnating step of supplying and impregnating the formed gas impregnating section, and an injection molding step of plasticizing and measuring the obtained gas impregnated resin and then injecting it into a mold to obtain a mold-shaped molded product. In the injection molding method for molded articles, the gas supply ports are arranged in the front-rear direction of the cylinder, and the plurality of gas supply ports are arranged at pitches.
(P) ≦ (length of low pressure part) / 2 and number of gas supply ports
(N) ≧ (the moving distance of the screw that moves during plasticization measurement
Separation) / Pitch (P), and the pressure of the molten resin at a portion facing at least one of the gas supply ports is always lower than the pressure of the gas supplied from the gas supply port. The gas was impregnated while maintaining the state.

[0007] The injection molding apparatus for a thermoplastic resin molded product according to the second aspect of the present invention (hereinafter referred to as "the molding apparatus of the second aspect") is capable of forming a molten resin melt-kneaded by rotation of a screw in a cylinder. In an injection molding apparatus adapted to supply a gas in a gaseous state at normal temperature and normal pressure from a gas supply port provided in a cylinder and impregnate the gas, an inner wall surface of the cylinder and an outer wall surface of the screw are formed. A gap is large, a low-pressure part forming part that forms a low-pressure part where the pressure of the molten resin is lower than the pressure of the gas supplied from the gas supply port is provided in a part of the screw, and the low-pressure part is used for measuring the screw. always to face any of the gas supply ports in the moving area, the plurality of gas supply ports, pip
H (P) ≦ (length of low pressure part) / 2 and number of gas supply ports
(N) ≧ (the moving distance of the screw that moves during plasticization measurement
(Separation) / pitch (P) is provided at a plurality of positions in the axial direction of the cylinder so as to satisfy .

According to a third aspect of the present invention, there is provided a thermoplastic resin molded article injection molding apparatus (hereinafter referred to as a "third molding apparatus"). A check valve for preventing the molten resin from entering the cylinder into the passage is provided at the gas supply port.

According to a fourth aspect of the present invention, there is provided an injection molding apparatus for a thermoplastic resin molded article (hereinafter referred to as a "molding apparatus of the fourth aspect"). Either the ball type or the ball check type was used.

In the present invention, the number (n) of gas supply ports and the pitch (P) are determined by the molding method of claim 1 and claim 2.
A low-pressure section is provided as in the molding apparatus of
It is provided to satisfy (2).

[0011]

(Equation 1) Number of gas supply ports (n) and pitch (P) and low pressure part forming part
By providing the relationship with
The low-pressure part is located at multiple locations within the range of plasticizer
It will face any of the gas supply ports.
And stable to molten resin in the cylinder of the injection molding machine.
Can supply gas in gaseous state at normal temperature and normal pressure at relatively low pressure
It works.

In the molding apparatus according to the third aspect, the check valve is not particularly limited as long as it opens the gas supply port when the gas pressure becomes higher than the molten resin pressure. It is preferable to use a spring-type or ball-check-type device that reliably operates as in the molding device of (1). Alternatively, the pressure of the molten resin may be detected, and the electromagnetic valve may be opened when the pressure of the molten resin becomes lower than a preset gas pressure. The material of the check valve has heat resistance of 2
It is not specified as long as it has a temperature of 00 ° C. or higher, but from the viewpoint of strength, heat resistance, slidability, and workability, metal, particularly stainless steel is preferable.

The thermoplastic resin used in the present invention is not particularly limited. For example, a resin having a high melt viscosity, which is difficult to melt-mold such as melt extrusion, a resin which is easily decomposed by heat, a low-boiling additive or Examples include hard-to-mold resins containing additives that are easily decomposed by heat.

Examples of resins which are difficult to melt-mold such as melt-extrusion due to high melt viscosity include resins for engineering plastics such as ultra-high molecular weight polyethylene, ultra-high polymerization degree polyvinyl chloride, polytetrafluoroethylene and polyimide. No. Examples of resins that are easily thermally decomposed include biodegradable resins such as polylactic acid and polyhydroxybutyrate, polyvinyl chloride having a high degree of chlorination, and polyacrylonitrile.

The gas that is in a gaseous state at normal temperature and normal pressure is not particularly limited as long as it does not react with the resin and does not adversely affect the resin such as deteriorating the resin. Examples include inorganic gases such as nitrogen, argon, neon, helium, and oxygen, and organic gases such as chlorofluorocarbon and low molecular weight hydrocarbons. Of these gases, inorganic gases are preferred because they have a low adverse effect on the environment and do not require gas recovery, have high solubility in difficult-to-mold resins, have a large plasticizing effect on resins, and are released directly into the atmosphere. Carbon dioxide is preferred from the viewpoint that it hardly causes any harm. Note that such a non-reactive gas may be used alone, or two or more non-reactive gases may be used in combination.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described in detail with reference to the drawings. 1 to 5 show one embodiment of an injection molding apparatus according to the present invention.

As shown in FIG. 1, this injection molding apparatus A
Has an injection machine 1 and a gas supply device 5. The injection machine 1 includes a cylinder 2 and a screw 3.

As shown in FIGS. 2 and 3, the screw 3 has a low-pressure portion forming portion 31 at an intermediate portion thereof. The low-pressure part forming part 31 makes the gap between the cylinder 2 and the cylinder 2 larger than the other part by making the depth of the screw groove deeper than the other parts. Is formed at a normal temperature and a normal pressure supplied into the cylinder 2 to form a low pressure portion 29 which is lower than the gas pressure in a gaseous state.

The cylinder 2 has four gas supply ports 21 to 24 and a material supply port 25 as shown in FIGS. The raw material supply port 25 is provided with a pressure-resistant hopper 26 so that the raw material resin in the pressure-resistant hopper 26 can be supplied into the cylinder 2.

The four gas supply ports 21 to 24 are provided in the melt portion of the cylinder 2 in the axial direction so as to satisfy the following equations (1) and (2).

(Equation 2) That is, within the moving range of the screw 3 during the plasticization measurement, the low-pressure portion 29 is connected to one of the gas supply ports 21 (22, 2).
3, 24).

Each of the gas supply ports 21 (22, 23, 2)
4), a spring-type check valve 4 is provided between the gas supply device 5 and the gas supply path 51, as shown in FIGS. The check valve 4 includes a casing 41, a valve body (shut-off valve) 42, and a coil spring 43, as shown in FIGS.

The casing 41 has a gas supply port 21 (2
2, 23, 24) and a gas supply path 51, a gas flow path 44 is provided inside, and a valve body 42
Are accommodated so as to be able to advance and retreat in the direction of the gas supply ports 21 (22, 23, 24). The gas flow path 44 includes a large-diameter portion 44a in which a spring holding member 45 of the valve body 42 described later is housed from the gas supply path 51 side to the gas supply port 21 (22, 23, 24) side, and a coil spring. An intermediate diameter portion 44b for accommodating 43, a small diameter portion 44c having substantially the same diameter as or slightly larger than the valve shaft 47 described later, and a diameter increasing portion 44d which expands in a trumpet shape from the small diameter portion 44c are sequentially provided. I have.

The valve body 42 includes a valve body 46, a valve shaft 47,
And a spring holding member 45. The valve body 46 has a conical seal portion 48 having the same taper angle as the enlarged diameter portion 44d whose outer peripheral surface is a seal surface 48a closely contacting the inner peripheral surface of the enlarged diameter portion 44d, and an inverted conical outer peripheral surface. Has a spindle shape composed of a pressure receiving portion 49 serving as a pressure receiving surface 49a.

One end of the valve shaft 47 has a sealing portion 4 of the valve body 46.
A screw portion 47b is provided at the other end, and is screwed with a nut 47a. The coil spring holding member 45 includes a coil spring 43 externally fitted to the valve shaft 47.
Is locked at one end.

The valve body 42 has a gas groove 48 extending from the end on the valve body 46 side to a part of the sealing surface 48a of the valve body 46.
b is recessed. The coil spring 43 is accommodated in the middle diameter portion 44b in a state of being fitted to the valve shaft 47, one end of the coil spring 43 is locked by the spring holding member 45, and the other end is formed of the middle diameter portion 44b and the small diameter portion 44c of the gas flow path 44. 44f formed at the boundary with
Has been received.

That is, when the pressure of the molten resin in the cylinder 2 is higher than the supplied gas pressure, the check valve 4 is activated by the pressure of the molten resin as shown in FIG.
6 is pressed, and the sealing surface 4 of the valve body 46 is pressed.
8a closely adheres to the inner wall surface of the enlarged diameter portion 44d, and the inflow of resin from the cylinder 2 side can be prevented. On the other hand, when the gas pressure supplied is higher than the molten resin pressure, as shown in FIG. 5, the gas is fed between the sealing surface 48a of the valve body 46 and the enlarged diameter portion 44d via the gas groove 48b. The valve body 42 moves toward the cylinder 2 against the urging force of the coil spring 43 due to the gas pressure. Then, the gas flows into the gas groove 48 b and the sealing surface 48 a of the valve
The air is supplied into the cylinder 2 through a gap with the cylinder d.

Since the injection molding apparatus A is configured as described above, when the raw material resin is supplied from the raw material supply port 25, the raw material resin is melted and kneaded by the rotation of the screw 3, and the leading end of the cylinder 2 is rotated. Sent to Then, as the screw 3 plasticizes and the molten resin is sent to the tip of the cylinder 2 one after another, as shown in FIG. The resin is measured at the tip of the cylinder 2.

Further, four gas supply ports 21 are provided in the melt portion.
(22, 23, 24) is provided, and the gas sent from the gas supply device 5 via the gas supply path 51 is supplied from one of the gas supply ports 21 (22, 23, 24) into the cylinder 2. Supplied to molten resin.

Then, the gas supply port is made one and the low pressure
When the screw 9 is only provided, the screw 3 retreats as the plasticization measurement proceeds, so that the gas supply port may not reach the low-pressure portion 29, and it becomes difficult to supply a stable gas.
The screw 3 is provided with a low-pressure portion forming portion 31, and the low-pressure portion 2 formed by the low-pressure portion forming portion 31 is provided.
At 9, the pressure of the resin is changed to the gas supply port 21 (22, 23, 24).
Is designed to be always lower than the gas pressure supplied from the low pressure section 29, and at least one of the gas supply ports 21 (22, 23, 24) faces the low pressure section 29. Gas supply port 21 facing 29
Gas is always supplied to the molten resin from (22, 23, 24). Therefore, the gas can be uniformly impregnated in a short time.

The gas-impregnated molten resin having undergone plasticization measurement in this manner is injected into an injection mold (not shown) from an injection port 28 at the tip of the cylinder 2 to obtain a molded product. .

As described above, according to the method for producing a thermoplastic resin molded article using the injection molding apparatus A, the molten resin can be uniformly impregnated with the gas in a short time. Therefore, a molded article having new functions (insulation, cushioning, heat resistance, low friction) such as a uniform and fine foam molded article and a difficult-to-mold material can be obtained at low cost by injection molding. In addition, the gas pressure of the supplied gas can be reduced, and the manufacturing cost of the apparatus can be reduced.

FIGS. 6 and 7 show another embodiment of the injection molding apparatus according to the present invention. As shown in FIG. 6 and FIG. 7, this injection molding apparatus B has a ball check type between a gas supply port 21 (22, 23, 24) and a gas supply path 51 instead of a spring-type check valve 4. It is the same as the injection molding apparatus A except that the check valve 7 is provided.

That is, the check valve 7 is connected to the casing 7
1, a small-diameter first ball valve 72, a large-diameter second ball valve 73, and a ball support 75. The casing 71 is provided therein with a gas flow path 74 that connects the gas supply ports 21 (22, 23, 24) and the gas supply path 51.

The gas flow path 74 extends from the gas supply path 51 toward the gas supply port 21 (22, 23, 24) toward the small-diameter portion 7.
4a, a middle diameter part 74b, and a large diameter part 74c. The middle diameter portion 74b has a larger diameter than the small diameter portion 74a, and has a slightly larger diameter than the outer diameter of the first ball valve 72, so that the first ball valve 72 can move freely in the middle diameter portion 74b. Has become.

The large diameter portion 74c is connected to the gas supply port 21 (22,
23, 24), the diameter is larger than the middle diameter part 74b, and the diameter is slightly larger than the outer diameter of the second ball valve 73, and the second ball valve 73 moves in the large diameter part 74c. It is free. The ball support 75 has a plate shape having a large number of gas permeable holes 75a formed therein.
The end of 4c is closed to prevent the first ball valve 72 and the second ball valve 73 from coming off to the gas supply port 21 (22, 23, 24) side.

That is, when the pressure of the molten resin is higher than the gas pressure, the check valve 7 pushes the second ball valve 73 toward the middle diameter portion 44b by the pressure of the molten resin as shown in FIG. The inlet portion of the middle diameter portion 44b is closed to prevent the molten resin from flowing into the gas supply path 51. When the first ball valve 72 is not sufficiently closed by the second ball valve 73, the first ball valve 72 is pressed toward the small diameter portion 74a by the molten resin that has entered the middle diameter portion 74b, and the small diameter portion 7 is pressed.
The entrance portion 4a is closed.

On the other hand, when the pressure of the molten resin is smaller than the gas pressure, the pressure is lowered until the gas supplied to the gas flow path 74 via the gas supply path 51 is received by the ball support 75. Then, the gas flows into the gas passage 7
The gas supplied into the cylinder 4 is supplied to the molten resin in the cylinder 2 through a gap formed between the first ball valve 72, the second ball valve 73, and the inner wall surface of the large diameter portion 74c and the gas permeable hole 75a. Will be supplied to Therefore, according to the check valve 7, when the molten resin pressure at the portion facing the gas supply port 21 (22, 23, 24) is higher than the gas pressure, similarly to the spring-type check valve 4, The backflow of the molten resin can be prevented, and the gas supply ports 21 (22, 23,
When the pressure of the molten resin in the portion facing 24) is lower than the gas pressure, the gas can be smoothly supplied into the cylinder to impregnate the molten resin.

The present invention is not limited to the above embodiment. For example, in the above-described injection molding apparatus B, two ball valves, a first ball valve 72 and a second ball valve 73, are provided. However, the first ball valve 72 is used to prevent a backflow of high-pressure gas. Since it is provided only as an auxiliary, it need not be provided. In the above embodiment,
Although the low-pressure section 29 is provided at one location, it may be provided at two or more locations. Further, the number of gas supply ports may be five or more.

[0039]

EXAMPLES Examples of the present invention will be described in detail below in comparison with comparative examples.

Example 1 An injection molding apparatus B as shown in FIGS. 6 and 7 designed so that the pressure of the molten resin in the low-pressure section 29 is 3 MPa or less.
Is prepared and, as a resin raw material, a difficult-to-form ultra-high molecular weight polyethylene (“HostalenGUR” manufactured by Hoechst)
4120 ”is supplied from the raw material supply port 25 into the cylinder 2 set at 180 ° C., and carbon dioxide gas is supplied at a pressure of 5 MPa to each of the gas supply ports 21 (22, 23) facing the low pressure part 29. , 24) into the cylinder 2 to plasticize and measure the gas-impregnated molten resin, and then inject it into a mold having a disk-shaped cavity of 225 mm in diameter and 3 mm in thickness and having a mold temperature of 40 ° C., and cooling. Thereafter, the molded product was taken out of the mold to obtain a disk-shaped molded product having a diameter of 225 mm and a thickness of 3 mm.

Comparative Example 1 Out of the four gas supply ports 21 to 24, the gas supply ports 21 and
A molded product was obtained in the same manner as in Example 1 except that the gas supply port 22 was used to supply the gas only by closing the ports 23 and 24.

As shown in FIG. 8, the molded product 9 obtained in Example 1 and Comparative Example 1 was folded in two and the folds were observed.
Although no peeling phenomenon was observed, the molded article of Comparative Example 1
A peeling phenomenon occurred at the interface between the surface layer and the inner layer. This is considered to be caused by insufficient gas impregnation into the resin.

Example 2 An ABS resin (Acrylonitrile butadiene styrene resin CL-301Q manufactured by Denki Kagaku Kogyo Co., Ltd.) was used as a resin raw material, the temperature of the cylinder 2 was set to 200 ° C., and the gas-impregnated molten resin was plasticized and measured. A disk-shaped foam molded product having a diameter of 225 mm and a thickness of 6 mm was obtained in the same manner as in Example 1 except that a gas-impregnated molten resin having 66% of the mold cavity capacity was injected into the mold in consideration of foaming. . The obtained foamed molded product was smooth, and an average foaming ratio was 1.5 times, and a foamed molded product having an almost uniform foaming ratio error of 5% or less in each part of the product could be obtained.

Comparative Example 2 Out of the four gas supply ports 21 to 24, the gas supply ports 21 and
A molded product was obtained in the same manner as in Example 2 except that the gas was supplied only from the gas supply port 22 by closing 23 and 24. The obtained molded product was not transferred to the mold, the dimensions of the molded product were smaller than the mold cavity, and the surface of the molded product was uneven. In the foaming state, a part where foaming was completely not observed was partially observed.

[0045]

The injection molding method and the injection molding apparatus for a thermoplastic resin molded article according to the present invention are constructed as described above, so that the molten resin in the cylinder of the injection molding apparatus can be stably and continuously supplied. A gas in a gaseous state can be supplied at normal temperature and normal pressure. By this effect, a molded article having new functions (insulation, cushioning, heat resistance, low friction) such as a uniform and fine foam molded article and a difficult-to-mold material can be obtained at low cost by injection molding.

In addition, the pressure of the supplied gas can be reduced, and the manufacturing cost of the apparatus itself can be reduced. Also,
According to the third aspect, it is possible to prevent the thermoplastic resin from flowing back into the gas supply path for supplying gaseous gas at normal temperature and normal pressure, thereby preventing clogging of the gas supply path.

According to the fourth aspect, the structure of the check valve is simple, the manufacturing cost of the apparatus can be reduced , and the maintenance is easy.

[Brief description of the drawings]

FIG. 1 is a schematic view schematically showing one embodiment of an injection molding apparatus according to the present invention.

FIG. 2 is a sectional view of a main part showing a state immediately after the start of plasticization measurement of an injection machine of the injection molding apparatus of FIG. 1;

FIG. 3 is a sectional view of a main part showing a state immediately before the end of plasticization measurement of an injection machine of the injection molding apparatus of FIG. 1;

FIG. 4 is a cross-sectional view of the check valve portion of the injection molding apparatus of FIG. 1 in a state where a molten resin pressure is higher than a gas pressure.

FIG. 5 is a cross-sectional view of a check valve portion of the injection molding apparatus of FIG. 1 in a state where a molten resin pressure is lower than a gas pressure.

FIG. 6 is a cross-sectional view of a check valve according to another embodiment of the injection molding apparatus of the present invention, in which a molten resin pressure is higher than a gas pressure.

7 is a cross-sectional view of a check valve portion of the injection molding apparatus of FIG. 6 in a state where a molten resin pressure is lower than a gas pressure.

FIG. 8 is an explanatory diagram illustrating a peel test method.

FIG. 9 shows thermoplastic resin pellets (high-density polyethylene,
The graph shows an impregnation amount curve when carbon dioxide gas is impregnated with a carbon dioxide gas at room temperature (20 ° C.) and a pressure of 10.0 MPa into a size φ4 × 2.3 mm).

[Explanation of symbols]

 A, B Injection molding apparatus 1 Injection machine 2 Cylinder 21 to 24 Gas supply port 29 Low pressure part 3 Screw 31 Low pressure part formation part 4, 7 Check valve 5 Gas supply device 51 Gas supply path 9 Molded product

Claims (4)

(57) [Claims] To 1. A molten resin becomes molten state in the injection machine cylinder, the gas in a gaseous state at normal temperature and normal pressure from the gas supply port formed in a cylinder, from the pressure gas supply port of the molten resin
Low forming a low pressure section that is lower than the pressure of the supplied gas
A thermoplastic process comprising a gas impregnation step of supplying and impregnating the pressure-forming section to the pressure-forming section, and an injection molding step of plasticizing and measuring the obtained gas-impregnated resin and then injecting it into a mold to obtain a mold-shaped molded product. In the injection molding method of a resin molded product , a plurality of gas supply ports are arranged in a pitch direction in a front-rear direction of a cylinder.
(P) ≦ (length of low pressure part) / 2 and number of gas supply ports
(N) ≧ (the moving distance of the screw that moves during plasticization measurement
Separation) / Pitch (P), and the pressure of the molten resin at a portion facing at least one of the gas supply ports is always lower than the pressure of the gas supplied from the gas supply port. An injection molding method for a thermoplastic resin molded product, wherein a gas is impregnated while maintaining the state. 2. A gas in a gaseous state is supplied to a molten resin melt-kneaded by rotation of a screw in a cylinder at a normal temperature and a normal pressure from a gas supply port provided in the cylinder to impregnate the gas. In the injection molding apparatus, the gap between the inner wall surface of the cylinder and the outer wall surface of the screw is large, and a low-pressure portion forming portion that forms a low-pressure portion in which the pressure of the molten resin is lower than the pressure of the gas supplied from the gas supply port There together are provided on a part of the screw, the so as to face the low-pressure part is always one of the gas supply ports in the metering movement area of the screw, a plurality of gas supply ports, pip
H (P) ≦ (length of low pressure part) / 2 and number of gas supply ports
(N) ≧ (the moving distance of the screw that moves during plasticization measurement
An injection molding apparatus, which is provided at a plurality of positions in the axial direction of a cylinder so as to satisfy (release) / pitch (P) . 3. The injection molding apparatus according to claim 2, wherein a check valve for preventing molten resin from entering the cylinder from the gas supply port into the gas supply path is provided at the gas supply port. 4. The injection molding apparatus according to claim 3, wherein the check valve is of a spring type or a ball check type.