JP2003191272A - Method for manufacturing thermoplastic resin foam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing thermoplastic resin foam which of supplies a sufficient amount of gas to a molten resin under relatively low pressure, dissolves the gas in the molten resin in such a state that the gas is uniformly dispersed in the molten resin, and stably obtains the uniform foam. <P>SOLUTION: The method for manufacturing the thermoplastic resin foam includes: a gas injection process of lowering the pressure of a resin in the vicinity of the gas supply port 6 in a cylinder 3 and injecting non-reactive gas in cylinder 3 from a gas supply port 6; and a gas dispersing and dissolving process of raising the pressure of the resin in a molten resin storage part while infiltrating the injected non-reactive gas in the resin by the shearing and kneading of the molten resin, and feeding the gas infiltrated molten resin to the molten resin storage part provided to the leading end of the cylinder. In the gas injection process, the non-reactive gas is introduced from the gas introducing port 11 provided to the rear end of a screw 4, and injected in the cylinder from the gas supply port communicating with the leading end of the gas supply passage 7, which communicates with the introducing port and is provided in a state piercing through the screw in the lengthwise direction thereof, and opened to the molten resin non-filling part of the screw through the gas supply passage 7. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to measure a gas-impregnated molten resin by supplying non-reactive gas as a foaming agent and impregnating the resin in a molten state by a screw rotating in a cylinder of an injection molding machine. The present invention relates to a method for producing a thermoplastic resin foam, in which a metering resin is injected into a mold cavity and foamed to obtain a foamed molded product, and a production apparatus used for the method.

Throughout the present specification, with respect to the context, the injection direction, that is, the left direction in FIG. 1, is the front or the front, and the opposite direction is the rear, with the direction in which the screw injects the molten resin into the mold cavity as a reference. Or to the rear.

[0003]

2. Description of the Related Art Conventionally, in foaming injection molding by physical foaming using an inert gas or the like, in order to supply and dissolve the gas into a molten resin, as disclosed in Japanese Patent Laid-Open No. 2001-138371, During the measurement, the gas was melted while being supplied so as to be pushed into the molten resin at a supercritical gas pressure, for example, carbon dioxide gas of 7.4 MPa.

However, in order to supply and dissolve the gas at such a high pressure, the equipment becomes large and a large amount of equipment cost is required. Practically, it is desirable to supply gas at a relatively low pressure of about 6 MPa or less in cylinder pressure. However,
If the gas supply pressure is too low, the amount of dissolved gas will be insufficient,
Gas may not be supplied at all. Further, in the case of supplying gas at a low pressure, the gas tends to be non-uniformly dispersed in the molten resin as compared with high pressure, and a foamed product having a non-uniform cell distribution tends to be obtained.

Conventionally, as a means for promoting gas dissolution in a molten resin, there is one in which a mixing screw is provided at the tip of a main screw as described in JP-A-8-258096. However, in this structure, since the diameter of the mixing screw is small, the resin is not sufficiently sheared or kneaded, and the dissolution promoting effect is small. Japanese Patent Laid-Open No. 11-341
Japanese Patent No. 30 discloses a method of continuing the rotation of the screw even after the screw is retracted for measuring, and lengthening the time during which the screw is rotating. However, in this method, the molten resin accumulated in the molten resin storage portion at the tip of the cylinder has no effect of promoting dissolution.

[0006]

In view of the above situation, an object of the present invention is to supply a sufficient amount of gas to a molten resin at a relatively low pressure and to dissolve the gas in a state where the gas is uniformly dispersed in the molten resin. Another object of the present invention is to provide a method for producing a thermoplastic resin foam capable of stably obtaining a uniform foam.

[0007]

The invention according to claim 1 is
Non-reactive gas is supplied and impregnated into the molten resin by the screw rotating in the cylinder of the injection molding machine, the gas-impregnated molten resin is measured, and the measured resin is injected into the mold cavity and foamed. In the method of obtaining a molded article,
Reduce the resin pressure near the gas supply port in the cylinder,
Gas injection step of injecting non-reactive gas into the cylinder from the gas supply port, and gas impregnated molten resin is stored at the tip of the cylinder while impregnating the injected non-reactive gas into the same resin by shearing and kneading the molten resin. And a gas dispersion / melting step of increasing the resin pressure in the storage part while sending the resin to the storage part.

According to a second aspect of the invention, in the gas injection step, the non-reactive gas is introduced from a gas introduction port provided at the rear end of the screw, communicates with the introduction port, and has a length inside the screw. 2. The gas is introduced into the cylinder from a gas supply port that is communicated with the tip of the gas supply passage through a gas supply passage that is provided so as to penetrate in the direction and that is opened in the molten resin unfilled portion of the screw. It is a method for producing the thermoplastic resin foam described.

According to the third aspect of the invention, in the gas injecting step, the back pressure is lowered to lower the resin pressure in the vicinity of the gas supply port in the cylinder, and in the gas dispersion and melting step, the back pressure is increased to inject. The resin pressure in the reservoir is increased while the gas-impregnated molten resin is sent to the molten resin reservoir at the tip of the cylinder while the molten resin is impregnated with the non-reactive gas by shearing and kneading. 1
Alternatively, it is the method for producing a thermoplastic resin foam described in 2.

According to a fourth aspect of the invention, in the gas injection step, the resin pressure near the gas supply port in the cylinder is lowered by suck back, and in the gas dispersion and dissolution step,
Increase the back pressure and increase the resin pressure in the gas-impregnated molten resin while sending the gas-impregnated molten resin to the molten resin reservoir at the tip of the cylinder while impregnating the injected non-reactive gas into the molten resin by shearing and kneading. It is a manufacturing method of the thermoplastic resin foam according to claim 1 or 2 characterized by things.

According to a fifth aspect of the invention, in the gas injecting step, the resin pressure in the vicinity of the gas supply port in the cylinder is reduced by reducing the amount of resin supplied into the cylinder, and in the gas dispersing and dissolving step, the cylinder is The amount of resin supplied to the inside is increased, and while the injected non-reactive gas is impregnated into the molten resin by shearing and kneading the molten resin, the gas-impregnated molten resin is sent to the molten resin storage portion at the tip of the cylinder 3. The method for producing a thermoplastic resin foam according to claim 1, wherein the pressure is increased.

According to a sixth aspect of the invention, a gas supply passage (7) communicating with a gas introduction port (11) provided at the rear end of the screw (4) is provided inside the screw so as to penetrate in the longitudinal direction. The gas supply port communicating with the tip of the supply path opens in the molten resin unfilled portion of the screw, and the unfilled portion is reduced by decreasing the screw shaft diameter or increasing the flight pitch of the screw. The thermoplastic resin foam manufacturing apparatus used for carrying out the method according to claim 2, wherein the apparatus is a portion that increases a space surrounded by the flight, the cylinder, and the screw.

According to a seventh aspect of the present invention, the supply is provided at the lower end of the raw material hopper (21) provided upright at the rear end of the cylinder (3) for adjusting the amount of the raw material resin fed into the cylinder (3). An apparatus for producing a thermoplastic resin foam used for carrying out the method according to claim 5, characterized in that a quantity adjusting valve (22) is provided.

The thermoplastic resin to which the method of the present invention is applied is not particularly limited, but examples thereof include polyolefins such as polypropylene and polyethylene, or PET, ABS and P.
C, PS, PBT, etc. Resins that are difficult to melt-mold because of high melt viscosity, resins that are easily decomposed by heat, and low-boiling additives or difficult-molding resins that contain additives that are easily decomposed by heat can be used.

Examples of the resin which is difficult to be melt-molded due to its high melt viscosity include resins for engineering plastics such as ultrahigh molecular weight polyethylene, ultrahigh polymerization degree polyvinyl chloride, polytetrafluoroethylene, and polyimide.

Examples of the resin that is easily decomposed by heat include biodegradable resins such as polylactic acid and polyhydroxybutyrate, polyvinyl chloride, polyvinyl chloride having a high degree of chlorination, and polyacrylonitrile.

The non-reactive gas used in the present invention is not particularly limited as long as it does not react with the resin and does not adversely affect the resin such as degrading the resin. For example, carbon dioxide, nitrogen and argon. , Neon, helium,
Examples thereof include inorganic gases such as oxygen, and fluorocarbons and organic gases such as low molecular weight hydrocarbons.

Of these, inorganic gases are preferred because they have a low adverse effect on the environment and do not require gas recovery, have a high solubility in difficult-to-mold resins, have a great effect of melting resins, and release them directly into the atmosphere. However, carbon dioxide is more preferable from the viewpoint of causing almost no harm. The non-reactive gas may be used alone or 2
You may use together more than one kind of gas.

In order to obtain a non-reactive gas-impregnated molten resin, it is necessary to satisfy the following two requirements.

1) A desired amount of non-reactive gas is supplied to the molten resin.

2) The pressure of the molten resin is increased in order to dissolve the non-reactive gas in the resin while kneading the molten resin.

In order to achieve the requirement 1), it is necessary to make the resin pressure near the gas supply port as low as possible than the gas supply pressure. However, in foam injection molding, it is inevitable to lower the resin pressure in the vicinity of the gas supply port so that the resin is melted inside the cylinder where many zones are in series and impregnated with non-reactive gas. Therefore, the resin pressure in the entire cylinder is lowered. This results in a failure to meet requirement 2). Thus, requirements 1) and 2) are in a trade-off relationship. The method according to the present invention is designed to satisfy both of these two requirements by temporally separating the gas injection step and the gas dispersion and dissolution step.

[0023]

By the method for producing a thermoplastic resin foam according to the first or second aspect, stable molding can be realized.

The reason is as follows. In injection molding, the resin moves forward relative to the cylinder during plasticization of the resin. When the gas supply port is provided on the cylinder side, as shown in FIG. 7, even if the gas injection process and the gas dispersion / melting process are separated in the time direction, the resin near the non-reactive gas supply port moves when the screw moves. The pressure rises and hinders the stable supply of non-reactive gas.

On the other hand, when the gas supply port is on the screw side as described in claim 2, the gas supply port is fixed to the moving screw as shown in FIG. Is constant, the resin pressure in the vicinity of the gas supply port does not rise and the non-reactive gas can be stably supplied.

Moreover, since the gas supply port is opened in the molten resin unfilled portion of the screw, the resin pressure in the vicinity of the gas supply port in the cylinder is reduced, and non-reactive gas is introduced from the gas supply port into the cylinder. Can be easily injected.

Furthermore, in the method for producing a thermoplastic resin foam according to claims 3, 4 and 5, the condition setting function of an existing molding machine can be used, and in the gas dispersion and dissolution step, a non-reactive gas is used. It is also possible to increase the screw rotation speed in order to promote dispersion.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to the drawings.

Embodiment 1 This embodiment corresponds to the inventions of claims 2 and 3.

The injection molding apparatus (A) is, as shown in FIG.
Injection molding machine (1) and gas injection device (2) that sends gas to it
Consists of. The injection molding machine (1) consists of a cylinder (3), a screw (4) arranged inside the cylinder (3), a mold (10) connected to the front end of the cylinder (3), and a rear of the cylinder (3). It is mainly composed of a raw material hopper (21) erected on the upper end.

As shown in FIG. 1 (b), the screw (4) is composed of a resin melting portion, a molten resin unfilled portion and a gas impregnated portion from the rear end to the tip.

The unfilled portion of the molten resin is to increase the space surrounded by the flight, the cylinder and the screw by decreasing the shaft diameter of the screw or increasing the flight pitch of the screw (this embodiment will be described later). As described above, the shaft diameter of the screw is made small), and as a result, the resin pressure is reduced here, so that the molten resin is not filled when the gas is supplied.

In the gas-impregnated portion, the screw shaft diameter is again increased or the flight pitch of the screw is reduced, and the space surrounded by the flight, the cylinder and the screw is reduced from the molten resin unfilled portion by the molten resin. It is full and as a result the resin pressure rises in the downstream direction.

The resin melting portion comprises, from the rear end to the front end, a powder transportation zone, a compression melting zone and a molten resin transportation zone.

In this embodiment, the molten resin unfilled portion is provided slightly toward the tip from the center of the length of the screw, and in this portion, the screw (4) has a screw groove deeper than the other portions, that is, the screw. The shaft diameter is reduced, and as a result, the distance between the inner surface of the cylinder (3) and the outer surface of the screw shaft is increased.

The rear end of the screw (4) is connected to a screw driving device (13) equipped with a weighing device,
A gas supply passage (7) is provided in the inside of (4) so as to extend through it in the longitudinal direction. Gas supply port at the tip of the gas supply path (7)
The portion (6) is opened in the peripheral surface of the screw (4) in the portion where the molten resin is not filled, at the cone portion which increases in diameter from the minimum shaft diameter portion toward the tip. The opening position of the gas supply port (6) may be anywhere as long as it is a portion not filled with the molten resin. As described above, the screw (4) has the molten resin unfilled portion, so that the molten resin unfilled state is formed here, and the molten resin is gasified by providing the gas supply port from the screw side in the state. Can be stably supplied.

A gas introduction port (11) for introducing carbon dioxide from the gas injection device (2) to the gas supply passage (7) is provided at the rear end of the screw (4). The gas injection device (2) is a carbon dioxide gas cylinder (19) equipped with a temperature controller (18) and a gas introduction pipe (9) having a pressure regulating valve (14), a flow meter (15) and a solenoid valve (16). And a control device (17) for controlling the flow meter (15) and the solenoid valve (16). The downstream end of the gas introduction pipe (9) is connected to a seal box (12) that covers the gas introduction port (11), and the sealed space inside the seal box (12) communicates with the gas introduction port (11). Gas coming from the gas inlet pipe (9) is sealed box (1
2) Gas supply path from the enclosed space through the gas inlet (11)
It enters into (7) and is then injected into the cylinder (3) from the gas supply port (6).

Check rings (5) and (20) each having a diameter larger than the screw shaft diameter are provided at the front end of the gas-impregnated portion and the front end of the resin melting portion to prevent the molten resin from flowing backward. There is.

Near the front end of the gas supply passage (7), a check valve (8) for preventing backflow that prevents molten resin from entering from the gas supply port (6)
Is provided.

The inner diameter of the cylinder (3) is 50 mm, and the die (1
The cavity shape of 0) is a disk shape with an inner diameter of 200 mm. Polypropylene pellets (grade: Novatec PP MA2) manufactured by Nippon Polychem Co., Ltd. were used as the thermoplastic resin, and this was supplied from the hopper (21) into the cylinder (3). The temperature and pressure of carbon dioxide gas were adjusted by the cylinder temperature controller (18) and the pressure control valve (14), and the carbon dioxide gas pressure at the gas supply port (6) was controlled to 6 MPa.

The molding conditions were set to the values shown below.

Measurement value: 100 mm Screw rotation speed: 60 rpm Back pressure condition Number of steps: 2 steps Back pressure switching weighing position: 60 mm First stage back pressure: 7 MPa Second stage back pressure: 10 MPa Suck back amount: 0mm

The amount of carbon dioxide gas supplied, the resin pressure at the time of completion of measurement, measured by a pressure sensor provided at the tip of the molding machine, and the thermoplastic resin foam obtained, filling the foam resin in the mold cavity. The state was examined and the foaming state was observed. The results are shown in Table 1.

The filling state of the foamed resin was investigated by converting the area of the surface of the disk-shaped foam seen in the injection direction into a circle having a corresponding area and determining the diameter of the foam. When the resin is completely filled in the mold cavity by foaming, the diameter of the foam becomes 200 mm, and a foam having a foaming ratio of 2 is obtained.

FIG. 2 schematically shows the change over time in the resin pressure distribution of Example 1.

Embodiment 2 This embodiment corresponds to the inventions of claims 2 and 4.

Except that the molding conditions were changed to the values shown below,
The same operation as in Example 1 was performed.

Measurement value: 100 mm Screw rotation speed: 60 rpm Back pressure condition Number of steps: 1 step Back pressure switching weighing position: − First stage back pressure: 10 MPa Second stage back pressure:- Suck back amount: 30mm

The amount of carbon dioxide gas supplied in Example 2, the resin pressure at the time of completion of measurement, which was measured by the pressure sensor provided at the tip of the molding machine, and the thermoplastic resin foam thus obtained, Check the filling state of the foam resin,
The foaming state was observed. The results are shown in Table 1.

FIG. 3 schematically shows the change over time in the resin pressure distribution of Example 2.

Embodiment 3 This embodiment corresponds to the invention of claims 2 and 5.

As shown in FIG. 4, a feed amount adjusting valve (22) is provided at a lower end vertical portion of a raw material hopper (21) standing upright at the rear end of the cylinder (3), whereby the cylinder (3) is provided.
The amount of the raw material resin supplied to the inside was adjusted, and the molding conditions were set to the values shown below. Otherwise, the same operation as in Example 1 was performed.

Measured value: 100 mm Screw rotation speed: 60 rpm Back pressure condition step number: 1 step back pressure switching measurement position:-1st step back pressure: 10 MPa 2nd step back pressure:-suck back amount: 0 mm Feeder rotation speed switching step number : 2 stage feeder rotation number switching Weighing position: 60 mm 1st stage feeder rotation number: 20 rpm 2nd stage feeder rotation number: 40 rpm Measured with the supply amount of carbon dioxide gas in Example 3 and the pressure sensor provided at the tip of the molding machine The filling state of the foamed resin in the mold cavity was examined from the resin pressure upon completion of the measurement and the obtained thermoplastic resin foam, and the foamed state was observed. The results are shown in Table 1.

FIG. 5 schematically shows the change over time in the resin pressure distribution of Example 3.

Comparative Example 1 In FIG. 6, the gas supply path (2) coming from the gas injection device (2)
The gas supply port (24) at the tip of (3) passes through the cylinder (3) at the cone part where the diameter increases from the smallest shaft diameter part toward the tip in the molten resin unfilled part of the screw (4). It has an opening on its inner surface. Gas supply port (24) to cylinder
(3) Carbon dioxide gas is supplied into the mixture to mix and impregnate the molten resin.

By providing the screw (4) with a portion not filled with molten resin, an unfilled state of molten resin is formed,
By providing a carbon dioxide gas supply port at a position in that state, gas can be supplied in the initial stage of measurement.

The molding conditions were set to the values shown below.

Measurement value: 100 mm Screw rotation speed: 60 rpm Back pressure condition Number of steps: 1 step Back pressure switching weighing position: − First stage back pressure: 7 MPa Second stage back pressure:- Suck back amount: 0mm

Under the above conditions, the amount of injected resin is 1/2 of the mold cavity space.

The amount of carbon dioxide gas supplied in Comparative Example 1, the resin pressure at the time of completion of measurement measured by a pressure sensor provided at the tip of the molding machine, and the thermoplastic resin foam obtained were used to measure Check the filling state of the foam resin,
The foaming state was observed. The results are shown in Table 1.

FIG. 7 schematically shows the change over time in the resin pressure distribution of Comparative Example 1.

[0062]

[Table 1]

In each of Examples 1, 2 and 3, the supply amount of carbon dioxide gas was large and the resin pressure in the resin reservoir was high as compared with Comparative Example 1, so that gas impregnation was sufficient. Can be done. Therefore, the above-mentioned two requirements, that is, 1) supply a desired amount of non-reactive gas to the resin in a molten state.

2) Increase the pressure of the molten resin in order to dissolve the non-reactive gas in the resin while kneading the molten resin.

It is possible to satisfy both.

As a result, in each of the examples, it was possible to fill the resin into the mold cavity by foaming, and to obtain a foam having a foaming ratio of 2 times. From this, it can be said that good non-reactive gas-impregnated molten resin could be obtained in Examples.

[0067]

According to the present invention, a sufficient amount of gas can be supplied to a molten resin at a relatively low pressure, and the gas can be dissolved in the molten resin in a uniformly dispersed state, so that a uniform foam can be stably obtained. Obtainable.

[Brief description of drawings]

FIG. 1 is a cutaway side view showing an injection molding apparatus used in a first embodiment.

FIG. 2 is a diagram schematically showing a temporal change of a resin pressure distribution of Example 1.

FIG. 3 is a diagram schematically showing a temporal change in a resin pressure distribution of Example 2.

FIG. 4 is a cutaway side view showing an injection molding device used in a third embodiment.

FIG. 5 is a diagram schematically showing a temporal change of a resin pressure distribution of Example 3.

6 is a cutaway side view showing the injection molding apparatus used in Comparative Example 1. FIG.

FIG. 7 is a diagram schematically showing a temporal change in resin pressure distribution of Comparative Example 1.

[Explanation of symbols]

(A): Injection molding machine (1): Injection molding machine (2): Gas injection device (3): Cylinder (4): Screw (6): Gas supply port (7): Gas supply path (10): Mold (11): Gas inlet (21): Hopper (22): Supply amount adjustment valve

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // B29K 105: 04 B29K 105: 04 C08L 101: 00 ZBP C08L 101: 00 ZBP F term (reference) 4F074 AA08A AA08B AA16 AA17 AA24 AA32 AA32A AA32B AA49A AA49B AA66 AA70 BA31 BA32 BA33 BA35 BA53 CA22 CA26 4F206 AA11 AB02 AG20 AL16 AR02 JA04 JD03 JF04 JF11 JF13 JF47 JM01 JM04 JN06 JQ17 JQ11 JQ02 JQ11 JQ11

Claims (7)

[Claims] 1. A non-reactive gas is supplied and impregnated into a resin in a molten state by a screw rotating in a cylinder of an injection molding machine, the gas-impregnated molten resin is weighed, and the weighing resin is placed in a mold cavity. In the method of obtaining a foam-molded article by injecting into, the resin pressure near the gas supply port in the cylinder is lowered,
Gas injection step of injecting non-reactive gas into the cylinder from the gas supply port, and gas impregnated molten resin is stored at the tip of the cylinder while impregnating the injected non-reactive gas into the same resin by shearing and kneading the molten resin. And a gas dispersion / melting step of increasing the resin pressure in the storage section while sending the resin to the storage section. 2. In the gas injection step, a non-reactive gas is introduced through a gas introduction port provided at the rear end of the screw, communicated with the introduction port, and provided in the screw in a longitudinally penetrating manner. 2. The thermoplastic resin foaming according to claim 1, wherein the thermoplastic resin foam is injected into the cylinder through a gas supply passage, which is communicated with the tip of the supply passage and is opened in the molten resin unfilled portion of the screw. Body manufacturing method. 3. In the gas injection step, the back pressure is lowered to reduce the resin pressure in the vicinity of the gas supply port in the cylinder, and in the gas dispersion and dissolution step, the back pressure is increased.
The resin pressure in the reservoir is increased while sending the gas-impregnated molten resin to the molten resin reservoir at the tip of the cylinder while impregnating the injected non-reactive gas into the molten resin by shearing and kneading the molten resin. Item 3. A method for producing a thermoplastic resin foam according to Item 1 or 2. 4. The gas injection step reduces the resin pressure in the vicinity of the gas supply port in the cylinder by suck back, and the back pressure is increased in the gas dispersion / melting step to shear the injected non-reactive gas of the molten resin. 3. The thermoplastic resin foam according to claim 1 or 2, wherein the resin pressure in the reservoir is increased while the gas-impregnated molten resin is sent to the molten resin reservoir at the tip of the cylinder while impregnating the same resin by kneading. Manufacturing method. 5. The amount of resin supplied to the cylinder is reduced in the gas injection step to reduce the resin pressure in the vicinity of the gas supply port in the cylinder, and the amount of resin supplied to the cylinder in the gas dispersion and dissolution step. To increase the resin pressure in the gas-impregnated molten resin while sending the gas-impregnated molten resin to the molten resin reservoir at the tip of the cylinder while impregnating the injected non-reactive gas into the molten resin by shearing and kneading. The method for producing a thermoplastic resin foam according to claim 1 or 2, which is characterized in that. 6. A gas supply passage (7) communicating with a gas introduction port (11) provided at the rear end of the screw (4) is provided inside the screw in a lengthwise penetrating manner, and the tip of the supply passage is provided. A gas supply port that communicates with the screw opens into the molten resin unfilled portion of the screw, and the unfilled portion of the screw can be reduced by reducing the screw shaft diameter or increasing the flight pitch of the screw, and the flight, cylinder, and screw. An apparatus for producing a thermoplastic resin foam used for carrying out the method according to claim 2, which is a portion for increasing a space surrounded by. 7. A feed amount adjusting valve (22) for adjusting a feed amount of a raw material resin into the cylinder (3) at a lower end portion of a raw material hopper (21) provided upright at a rear end portion of the cylinder (3). 6. The apparatus for producing a thermoplastic resin foam used for carrying out the method according to claim 5, wherein: