AT523204A1 - Molding machine for foam molding - Google Patents

Abstract

[Problem] There is provided an injection molding machine screw in which the backflow of an inert gas is prevented, thus enabling high quality foam molded articles to be stably produced even when the length of the machine is short. Solution The present invention provides a molding machine for foam molding in which a heating cylinder (2) is divided into a first stage (5) and a second stage (6) according to the shape of a screw (3). In the first stage (5), a first compression section (8) for compressing a resin is formed, and in the second stage (6) a starvation section (9) for reducing the resin and a second compression section (10) for compressing the resin are formed. A protective gas is injected into this starvation section (9). The screw (3) is provided with a specific sealing structure (7) at the boundary between the first and second stages (5, 6), which prevents the resin and the protective gas from flowing back. The screw (3) is configured to have several (two or more) second stage (6) flights, the pitch angle of the flights being in the range of 10 to 45 degrees.

Description

TECHNICAL AREA

The present invention relates to an injection molding machine used in a molding method for a foam molded article in which a protective gas is injected into a molten resin and the molten resin is injected into a mold to form a foam molded article

Obtain item.

TECHNICAL BACKGROUND

A molded article in which a large number of fine bubbles are formed, that is, a foam molded article is not only light but also excellent in strength. Thus, the foam-molded article can be used for a variety of areas. It is necessary to mix a foaming agent into a resin in order to obtain a foam-molded article by injection molding. As the foaming agent, a so-called chemical foaming agent which is thermally decomposed to generate a gas is used. A physical foaming agent formed from an inert gas is also used as a foaming agent. Nitrogen and carbon dioxide are used relatively frequently as physical foaming agents. Such an inert gas is injected into a resin melted in a heating cylinder at a predetermined pressure, and the resin is kneaded so that the inert gas is dissolved in the resin. When this is injected into a mold, pressure is released in the resin and the protective gas bubbles. When the resin is solidified by cooling, a foam-molded article is obtained. Since the physical foaming agent formed from the inert gas at high pressure and high temperature in the

Resin is injected, the physical foaming agent has 1; N

a strong penetration force and can be evenly distributed in the resin. Therefore, the obtained foam-molded article has an excellent property that uneven foaming "

is unlikely. fi

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CITATION LIST OF PATENT LITERATURE

PTL 1: JP-A-2002-7954545 PTL 2: JP-A-2015-168079

An injection molding machine for obtaining a foam molded article by a physical foaming agent formed from an inert gas is disclosed in PTL 1. An injection molding machine 50 will be described with reference to FIG. 4. The injection molding machine 50 includes a heating cylinder 51 and a screw 52 which is provided so

that it can be driven in a rotational direction and an axial direction within the heating cylinder 51. Compression parts in which the worm grooves are shallow, that is, first and second compression parts 54 and 56 are formed in two places in the worm 52, and a decompression part 55 in which the worm grooves are deep is formed between the first and second compression parts 54 and 56 . An inert gas injection portion 57 is provided in the heating cylinder 51 to correspond to the decompression part 55 so that an inert gas 58 is injected therethrough. Resin pellets are introduced into the injection molding machine 50 from a hopper 59 and the screw 52 is rotated. Then the resin pellets melt and are fed to the front of the screw 52. As the molten resin is fed forward, the molten resin is compressed in the first compression part 54, and a pressure thereof in the decompression part 55 is decreased. The inert gas

58 is injected into the decompression part 55. Then, the inert gas 58 is mixed with the molten resin and becomes saturated. Such a molten resin is recompressed in the second compression part 56 and measured at the front of the screw 52. When the molten resin is injected into a mold, the inert gas in the molten resin is evaporated and a

obtained foam-molded article.

3

In a case where an electroless plating process is performed on a resin molded article, the required pretreatment is omitted when a molten resin to which a surface modification substance such as a metal complex is added is injected to obtain a molded article. An injection molding machine 60 which can inject and knead a surface-modifying substance such as a metal complex into a resin melt and inject this mixture is disclosed in PTL 2, the injection molding machine 60, as shown in FIG. 5, having a heating cylinder 61 and a Screw 62 is configured. The screw 62 is provided with first and second seal structures 64 and 65 at predetermined positions. A high pressure area 66 and a low pressure area 67 are formed in the screw 62 by the first and second seal structures 64 and 65. The first seal structure 64 includes a predetermined valve arrangement, and backflow from the high pressure area 66 is prevented although resin directed forward from the rear of the screw 62 is directed into the high pressure area 66. The second sealing structure 65 contains a valve arrangement which is opened and closed in the direction of rotation of the screw 62. When the valve structure of the second seal structure 65 is closed, the high pressure area 66 and the low pressure area 67 are closed so that a resin cannot flow. However, when the valve structure is opened, the resin can flow freely. The low pressure area 67 of the scroll 62 is provided with a descent relaxation portion 68 on a downstream side of the second seal structure 65. Deep groove portions 69 in which worm grooves are deep between the lands and # shallow groove portions 70 in which the worm grooves are shallow, © are alternately formed in the descending relaxation portion 68, 1 and the shallow groove portions 70 and 70 are in at least two "locations is formed in the axial direction. The throttling takes place f in the shallow groove portions 70 and 70. When a resin from the ©

High pressure area 66 flows into the low pressure area 67, becomes |

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desired shaped article. m

The injection molding machine 60 having the screw 62 disclosed in PTL 2 can also be used in a method of molding a foam molded article using a physical foaming agent, i.e., an inert gas

only a high-pressure inert gas without 1

5

Injection of a surface modification substance.

The inert gas is injected with e.g. 10 MPa or similar. The

Inert gas is sufficiently dispersed and penetrates the

High pressure area 66 in a resin melt and then is in

the low pressure area 67 passed. One in the outlet port 73

The valve provided in the low pressure area 67 is controlled so that a pressure inside the heating cylinder 61 is about 5 MPa. Subsequently, an excess protective gas is generated from the resin melt in the low-pressure region 67 and

removed from the discharge port 73. However, a molten resin is obtained, which is in a saturated

State contains dissolved inert gas. When the melted resin

Injected into a mold, the inert gas in the resin becomes too

Obtain bubbles and a foam molded article.

SUMMARY OF THE INVENTION

TECHNICAL PROBLEM

Although the injection molding machines disclosed in PTLs 1 and 2

50 and 60 a foam molded article by the same

Injection of an inert gas into a melt,

the respective injection molding machines have to solve problems.

First, the injection molding machine 50 disclosed in PTL 1 has this

Problem that an inert gas is reversed to get out of the funnel

59 or a molten resin is pushed back by the inert gas. When the auger 52 rotated forward

and a resin is sent forward, it is

unlikely that an in the decompression part 55

injected inert gas flows in reverse. That is, if the

Screw 52 is rotated forward, a sufficient pressure difference is created between the first compression part 54 and the decompression part 55. The inert gas is fed forward while kneading with the molten resin without reversing its flow, and becomes after passing through the second compression part 56 measured. However, when the rotation of the screw 52 is stopped, the pressure difference inside the heating cylinder 51 becomes small. %

Since a high pressure inert gas has a strong penetrating force, 4

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6th

there is a possibility that the inert gas reversely flows beyond the first compression part 54, the molten resin is pushed back by the reversely flowing inert gas, and a resin level in the hopper 59 rises. Since the rotation of the screw 52 is stopped at least at the time of injection, it is difficult to completely prevent the inert gas from flowing back. So there is a problem that a molding cycle cannot be stably performed. In addition, the injection molding machine 50 disclosed in PTL 1 also has the problem that the inert gas does not sufficiently penetrate into the melt or is not mixed with it. The inert gas is injected only in the decompression part 55, and the inert gas penetrates the melt only in the vicinity of the second compression part 56. This means that the inert gas must penetrate from a relatively short distance. As a result, the inert gas does not penetrate sufficiently and uniformly into the resin melt in some cases. Next, the injection molding machine 60 disclosed in PTL 2 is considered. Since the injection molding machine 60 is provided with the first sealing structure 64, no inert gas flows in reverse even when the screw 62 is at a standstill, and a pressure difference inside the heating cylinder 61 becomes smaller. In addition, it can also be ensured that the inert gas penetrates sufficiently and uniformly, since the inert gas is injected and kneaded into the high-pressure region 66 defined by the first and second sealing structures 64 and 65. Therefore, a foam-molded article can be stably molded. The injection molding machine 60 disclosed in PTL 2, however, requires the high pressure area 66 of the screw 62, which is defined by the first and second sealing structures 64 and 65. The length of the injection molding machine 60 is thus lengthened by the length of the high pressure region 66. It is necessary to make the length of the "injection molding machine 60" short to accommodate the injection molding machine

to be provided in a limited assembly area.

An object of the invention is to provide an injection molding machine for

to provide foam molding that meets the above

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penetrates sufficiently and evenly into the melt.

THE SOLUTION OF THE PROBLEM

In order to achieve the object, the invention is associated with an injection molding machine for foam molding, in which a heating cylinder corresponding to the shape of a screw is divided into a first stage at the rear and a second stage at the front

is divided.

In the first stage, a first compression portion in which a resin is compressed is formed. A decompression section in which the pressure of the resin is reduced and a second compression section in which the resin is compressed are formed in the second stage. An inert gas is injected into the decompression section. A screw is provided with a predetermined seal structure that allows the resin and the inert gas to flow back to a

Border between the first and second stage prevented. Bridges

in the second stage are configured as multi-start webs such as double or 1 multi-start webs, and a pitch angle of each of the webs is configured so that it is in a range from 10 to "

45 degrees. 1

To achieve the above goal, there is an illustrative one

Aspect of the invention an injection molding machine for foam molding 4

each of the ridges is in a range of 10 to 45 degrees.

The screw in the second stage can advantageously be provided with a lowering relaxation section which adjoins the sealing structure, and flat groove sections in which a screw groove between the webs is flat can be at least two or more points in the lowering

Relaxation section be formed in the axial direction.

Conveniently, the gas injection port with an opening

and locking mechanism.

4. 1 Conveniently, the heating cylinder with the two or more 5 1%

Gas injection ports at a predetermined distance in axial direction |

Direction to be provided. ©

The heating cylinder can advantageously be provided with a resin pressure sensor in accordance with the fi M decompression section. 1

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In the above-described invention, which is associated with the injection molding machine for foam molding, the heating cylinder is divided into the first stage at the rear and the second stage at the front according to the shape of the screw, in the first stage is the first compression section in which a resin is compressed, is formed, in the second stage, the decompression section, in which the pressure of the resin is reduced, and in the second stage, the second compression section, in which the resin is compressed, is formed, and at a position in the heating cylinder corresponding to the decompression section, a gas supply opening is provided through which an inert gas can be injected. That is, in the injection molding machine to which the invention is associated, a resin is melted and compressed in the first stage, which is discharged to the second stage, and an inert gas is injected in the decompression section of the second stage. Since the inside of the heating cylinder is only divided into the first and second stages, the injection molding machine has a short length regardless of whether it is an injection molding machine for foam molding. The injection molding machine can thus be installed in a limited installation space. According to one aspect of the invention, the screw is provided with the predetermined seal structure that prevents backflow of the resin and the inert gas at the boundary between the first and second stages. When the rotation of the screw is stopped, there is a possibility that a backflow of the resin into which an inert gas is injected will occur. A backflow from the second stage to (

however, the first stage is completely prevented because the Be

Sealing structure is in place. Although backflow is to be expected especially when the screw is at a standstill, e.g. when injecting, the sealing structure can reliably prevent backflow. According to the aspect of the invention, the webs in the second stage are multi-start webs

Double or multiple start bridges, and the pitch angle of each of the 1

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the gas injection port can be opened and closed by opening and closing the

be recognized.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] Figs. 1 (A) and 1 (B) are views showing an injection molding machine according to an embodiment of the invention, Fig. 1 (A) is a front view of the injection molding machine, and Fig. 1 (B) is a front view of a screw, in which part of a second stage of the screw 5

is enlarged and illustrated.

[FIG. 2] Figs. 2 (A) and 2 (B) are views illustrating a seal structure incorporated in the screw of the injection molding machine according to the embodiment of the invention

is provided, and Figs. 2 (A) and 2 (B) are ‘1

12/33 l

are cut parallel to an axis of the screw.

[FIG. 3] Fig. 3 is a diagram showing a flow rate of the screw that changes according to a difference of a shape

of a screw flight changes.

[FIG. 4] Fig. 4 is a side view showing a

Prior art injection molding machine illustrated.

[FIG. 5] Fig. 5 is a side sectional view showing an injection molding machine of another prior art

illustrated.

DESCRIPTION OF THE EMBODIMENTS

An embodiment of the invention is described below. An injection molding machine 1 according to an embodiment of the invention is configured with a heating cylinder 2 and a screw 3 that is provided so that it can be driven in a rotating direction and an axial direction within the heating cylinder 2, as in FIGS. 1 (A) and 1 (B) shown. Although a plurality of tape heaters are wound around an outer peripheral surface of the heating cylinder 2, are

the band heaters are not shown in Figs. 1 (A) and 1 (B).

An inside of the heating cylinder 2 of the injection molding machine 1 of the embodiment is substantially divided into two sections according to the shape of the screw 3, i.e., there are

fi a first level 5 on the back and a second level 6 on% *

the front. The first stage 5 is a section in which a “resin is melted, and the second stage 6 is a section in which an inert gas is injected and the inert gas is injected into the resin

penetrates. The first and second stages 5 and 6 are defined by a} seal structure 7 according to the embodiment. The

means, you can say that the inside of the heating cylinder is 2 4

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described in detail.

The webs of the screw 3 in the embodiment differ between the first stage 5 and the second stage 6. In particular, the number of webs starts is different. That is, while the first stage 5 is formed from a single-start bridge with a standard pitch and slope, the second stage 6 is formed from multi-start bridges. The fact that the second stage 6 is configured with multiple webs is also a characteristic of the injection molding machine 1 according to the embodiment. Since the number of web tangs is larger in the second stage 6, a resin to be sent is easily forwarded without disturbing a current or vice versa, even if the resin has a low viscosity. The second stage 6 is a stage in which an inert gas is injected, and since the resin is gently conveyed while it is kneaded appropriately by the multi-stage webs, the inert gas penetrates the resin uniformly and sufficiently. Although not limited, it is preferable that the multiple start lands in the second stage 6 do not have a notch. When the notch is provided, the kneading performance improves. However, the transmission power of a resin decreases slightly because a backflow takes place in the notch area. Although the second stage 6 in the embodiment is configured with double start bars, the second stage can, in addition to the double start bars, with triple start bars or multiple start bars, ©

that have been started more than three times.

Although the first stage 5 is configured with the individual webs as described above fd, the worm grooves are between

the ridges near a funnel relatively deep (not 7

Sealing structure 7 delivered to the second stage 6.

The depths of the worm grooves also change in the second stage 6 as in the first stage 5, and a plurality of sections are correspondingly formed in the axial direction. First of all, a sagging relaxation section 11 is formed adjacent to the sealing structure 7. The lowering relaxation portion 11 is also a characteristic of the injection molding machine 1 according to the embodiment which will be described below. On a downstream side of the descent relaxation section 11, a decompression section 9 having deep scroll grooves is formed. Since the decompression section 9 has the deep scroll grooves and a large volume inside the heating cylinder 2, the pressure of a resin decreases. Therefore, as described later, a physical foaming agent made of an inert gas is injected into this section 9. In the second stage 6, in front of the decompression section 9, i.e. on the downstream side of the decompression section, a second compression section 10 with shallow screw grooves is formed in which a resin is compressed. Since the resin is compressed in the second compression portion 10, the inert gas permeates the resin sufficiently and uniformly. "A (8

=

The descent relaxation section 11, which is a characteristic structure of the embodiment, will be described. In addition, | the webs of the lowering relaxation section 11 are configured with it double start webs as in the other section of the second stage 6 6. Deep groove sections 12 and 12 in which the 8 worm grooves are deep, and shallow groove sections 13 and 13, inf

1

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Screw 3 is stopped.

A flow speed at which a resin is sent becomes high in the screw 3 according to the embodiment because a pitch angle of each of the lands in the second stage 6, particularly in the second compression portion 10, is set to be within a predetermined range. In particular, the pitch angle is selected in a range from 10 to 45 degrees, preferably 10 to 40 degrees, preferably 20 to 35 degrees. Accordingly, in the second compression section 10, a flow rate can be increased sufficiently. Thus, the pressure of a resin in the decompression area 9 can be reliably reduced. A reason why the pitch angle is selected to be in such a range will be described. A flow rate Q of a resin sent from the screw 3 in the axial direction can be derived from the following equation.

1} di

[Equation 1] a

—_ VW-H W-H) 'ÖP m grandpa az Fe |

x: D-N-cos (g @) 0 Vu "SO!

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z: the distance in the direction parallel to the web and distance along the web (m), Vobz: the speed component in the direction

parallel to the web by turning the worm (m / s), W: the groove width of the web (m),

H: the groove depth of the land (m), D: the diameter of the worm (m), N: the number of rotations of the worm (rpm),

ÖP / Öz: the pressure gradient of the molten resin in the z-direction (Pa / m), 4: the viscosity of the resin (Pa - s), O: the pitch angle of the web (rad), and Fa, Fe: the effect of the web edge the flow is.

The flow rate Q changes depending on the viscosity 4% of a resin.

The flow rate Q of resins with different viscosities

4, when the lead angle or the like of each of the ridges is changed, it is calculated according to the equation, and the calculation results are shown in a graph in FIG. A horizontal axis represents a pitch PP in the diagram. The pitch PP is expressed as the screw diameter D x xt x cos @ / number p of web starts. As can be seen from the graph in FIG. 3, the flow rate Q changes as a function of

Viscosity u of the resin. A flow rate is relatively high, though

the slope is in a range from 0.5D to zD. This means that a flow rate is relatively high if the pitch angle @ in

ranges from 10 to 45 degrees. When the pitch in one

Is in the range from 0.5D to 2.6D, i.e. when the pitch angle ©

is in a range of 10 to 40 degrees, the flow is

relatively high regardless of the viscosity level. When the pitch is within a range of 1.1D to 2.2D, i.e. when the pitch angle @ is within a range of 20 to 35 degrees, the flow is more stable. Therefore, in the

Screw 3 according to the embodiment of the helix angle ©

is within the range described above.

The seal structure 7 provided in the screw 3 according to the embodiment is formed from a seal 15 and a flow control mechanism 16 which regulates a pressure, as shown in detail in FIG. 2 (A). The seal 15 is slidably fitted in a predetermined groove formed in an outer peripheral surface of the worm 3. Although Fig. 2 (A) does not illustrate the heating cylinder 2, an outer peripheral surface of the gasket 15 slides smoothly in a state of contact with a bore of the heating cylinder 2. The gasket 15 prevents a resin melt from flowing. The inside of the heating cylinder 2 is liquid-tightly divided into the first stage 5 on the upstream side and the second stage 6 on the downstream side. One or more flow control mechanisms 16 are provided in the sealing structure 7. The flow control mechanism 16 is configured with a communication path 18 that is formed within the screw 3 such that the first stage 5 can communicate with the second stage 6, and a valve mechanism 19 that opens and closes the communication path 18. A portion in the middle of the communication path 18 has a conical shape, the diameter of which is reduced, and a seat surface 20 is formed, which has a corresponding conical shape. When a head part 23 of a cone valve 22, which configures the valve mechanism 19, is seated on the seat surface 20, the communication path 18 is closed. The cone valve 22 is with

the umbrella-shaped head part 23 and a shaft section 24

configured. A large number of disc springs 26, 26, 26 ... are available in the P®

ad 8 pe

Shank portion 24 is provided. Such a cone valve 22, in

which the disc springs 26, 26 are provided is in a holder |

27 is used, in which a bottom hole is formed. The holder V

Outer peripheral surface attached to a female screw that fi

in an inner circumference of the communication path 18 1

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nd 27 is screwed and by a male screw in its

18th

is trained. The cone valve 22 is therefore pressed by the plate springs 26, 26, 26 .. in order to press the head part 23 against the seat surface 20 and the communication path 18 is closed. When a molten resin in the first stage 5 reaches a predetermined pressure, the poppet valve 22 moves against the compressive force of the plate springs 26, 26, 26, backwards and the first stage 5 and the second stage 6 communicate with each other. Thus, the molten resin flows into the second stage 6, that is, the descending relaxation portion 11. A resin path 28 is formed in the holder 27, and when the first stage 5 and the second stage 6 communicate with each other, the molten resin flows from the resin path 28 to Lowering relaxation section 11. When the first compression section 8 of the first stage 5 and the lowering relaxation section 11 of the second stage 6 have the same pressure, or when the lowering relaxation section 11 has a higher pressure, backflow of the resin melt is completely prevented because the poppet valve 22 sits on the seat 20 and the connection is turned off.

As shown in Figs. 1 (A) and 1 (B), the injection molding machine 1 according to the embodiment is provided with two injection sections for injecting an inert gas, i.e., first and second injection sections 29A and 29B, at positions in the heating cylinder 2 corresponding to the decompression section 9. The first and second injection portions 29A and 29B are provided at a predetermined interval in the axial direction and are connected to a tube of a gas cylinder 31 containing an inert gas through opening / closing valves 32A, 32B, respectively. When opening * the opening-closing valves 32A and 32B, the inert gas such as nitrogen and carbon dioxide is injected into the heating cylinder 2 from the first and second HM injection sections 29A and 29B. Since the two injection portions 29A and 29B I according to the embodiment in the axial direction, as n

described are provided in the injection molding machine 1, i

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19th

each of the injection sections 29A and 29B dem

Decompression section 9 correspond and the inert gas can also

then be injected when the screw 3 is ready for measurement

of a resin moves rearward and the position of the decompression portion 9 moves in the axial direction. thats why

the decompression section 9 is relatively short, and thus the

Length of the injection molding machine 1 in the embodiment is short. The first and second injection portions 29A and 29B are provided with the opening-closing valves formed of needle valves at positions near the bore of the heating cylinder 2. When the screw 3 moves in the axial direction and the first and second injection sections 29A and 29B are removed from the decompression section 9 at the time of measurement, the needle valves are closed and the resin is penetrated into the

the first and second injection portions 29A and 29B are prevented.

According to the embodiment, the injection molding machine 1 is provided with a resin pressure sensor 33 at a position in the heating cylinder 2 that corresponds to the decompression section 9. The pressure of a resin in the decompression section 9 is practically atmospheric pressure. Thus, when an inert gas is injected, a pressure detected by the resin pressure sensor 33 is the pressure of the inert gas. The pressure detected by the resin pressure sensor 33 is monitored, and when the pressure is higher than the pressure of an inert gas supplied from the gas cylinder 31, it is determined that the openings of the first and second injection portions 29A and 29B are closed by the resin and that the occurrence of

Anomaly can be determined.

Effects of the injection molding machine 1 according to the embodiment of the invention will be described. The heating cylinder 2 is heated, l. to rotate the screw 3 in the forward direction, and a resin material is fed from the hopper (not

shown). The supplied resin material is affected by the heat x of the heating cylinder 2 and the heat generated by the 1st

Shear stress is caused by the rotation of the screw 3, 4

of the decompression section 9 weakened.

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reduced diameter and an inner peripheral surface of the

Seal ring 36. Thus, the molten resin flows downstream. ı

In one end face of the seal ring 36 are predetermined ones

Notches are formed so that a flow path of the molten resin

means that a reverse current is prevented.

In the embodiment, the webs of the first stage 5 can also be modified and are not restricted to the individual webs. The number of ridge beginnings or a ridge shape can be changed accordingly depending on the type of resin to be used or the size of a device. The inert gas injection sections 29A and 29B can also be modified. First, the number of injection sections can be changed. Only one injection section or three or more injection sections can be provided. The open and closed states of the injection sections 29A and 29B for the inert gas can also be modified. Each of the injection sections can always be in an open state, or the injection sections can be limited to be opened only for a predetermined step of a molding cycle, e.g., during plasticizing. The inert gas injection sections 29A and 29B do not necessarily require the port-and-close valves 32A and 32B. That is, the injection sections can always be open. In this case, however, it is preferable to design the screw 3 so that the ff injection sections 29A and 29B for the inert gas are always in the 1st position

Decompression section 9 are located, even if the screw ©

3 moves forward and backward. The injection sections 29A and |

+ 29B for the inert gas can be fitted with non-return valves'

u ae

be. Since the check valves are automatically closed after a 1

Resin pressure opening and closing, a backflow of a resin 5 fh from the injection portions 29A and 29B can be prevented when]

1 g ‘

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23, the injection sections 29A and 29B are removed from the decompression section 9 or a resin pressure inside the heating cylinder 2 has risen. The resin pressure sensor 33 can also be modified. Two or more

Resin pressure sensors can be provided.

REFERENCE SIGNS LIST 1: Injection Molding Machine 2: Heating Cylinder 3: Screw 5: First Stage 6: Second Stage 7: Seal Structure 8: First Compression Section 9: Decompression Section 10: Second Compression Section 11: Lowering Relaxation Section 12: Deep Groove Section 13: Shallow Groove Section 15: Gasket 16: Flow control mechanism 18: communication path 19: valve mechanism 20: seat 22: cone valve 23: head part 24: stem section 26: plate spring 27: holder I} 28: resin path 8 31: gas cylinder 4 32A, 32B: first and second injection section N

33: Resin pressure sensor

Claims (3)

24 claims: Claims 1. An injection molding machine for foam molding, the injection molding machine comprising: a heating cylinder; and a screw provided in the heating cylinder and configured to be driven in a rotating direction and an axial direction, the heating cylinder being divided into a first stage on a rear side and a second stage on a front side according to a shape of the screw the first stage includes a first compression section for compressing a resin and the second stage includes a decompression section for reducing a pressure of the resin and a second compression section for compressing the resin, the heating cylinder including a gas injection port for supplying an inert gas at a position corresponding to the decompression section, and wherein the screw is provided with a predetermined seal structure to prevent a backflow of each of the resin and the inert gas at a boundary between the first and second stages, the flights in the second stage being multiple flights of double or multiple flights d and a pitch angle of each the web is in a range of 10 to 45 degrees. 2. Injection molding machine for foam molding according to claim 1, wherein the screw in the second stage is provided with a lowering relaxation section adjoining the sealing structure, and wherein flat groove sections in which a helical groove is flat between the webs at at least two or more locations in the Lowering 8, Relaxation section are formed in the axial direction. 5 3. Injection molding machine for foam molding according to claim 1 or 2, * wherein the gas injection port with an opening and Locking mechanism is provided. 25/33 7 25 injection molding machine for foam molding according to any one of claims 1 to 3, wherein the heating cylinder with the two or more gas injection ports at a predetermined distance in is provided in the axial direction. An injection molding machine for foam molding according to any one of claims 1 to 4, wherein the heating cylinder corresponding to the decompression portion is provided with a resin pressure sensor is.