AT523204B1 - 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

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 obtain a foam molded article.

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 is injected into the resin at high pressure and high temperature, the physical foaming agent has a strong penetrating force and can be uniformly dispersed in the resin. Therefore, the obtained foam-molded article has an excellent property that uneven foaming is unlikely.

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 PTL1. 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 that is provided so that it can be driven in a rotating 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 vaporized and a foam-molded article is obtained.

In a case where an electroless plating method with respect to a resin molding

When a molten resin to which a surface modifying substance such as a metal complex is added is injected to obtain a molded article, the necessary pretreatment is omitted. 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, and the shallow groove portions 70 and 70 are formed in at least two locations in the axial direction . The throttling takes place in the shallow groove sections 70 and 70. When a resin flows from the high-pressure area 66 into the low-pressure area 67, its pressure is correspondingly reduced. An injection port 72 for injecting an inert gas or the like is provided in the heating cylinder 61 corresponding to the high pressure region 66, and a discharge port 73 for discharging the inert gas is provided on a downstream side of the lowering relaxation portion 68 of the low pressure region 67. The following is to be carried out to obtain a molded article by injecting a molten resin to which a surface modifying substance such as a metal complex is added. The screw 62 is rotated to melt a resin. The molten resin flows into the first seal structure 64 and is directed into the high pressure area 66. The screw 62 is reversely rotated to close the second seal structure 65. The high pressure region 66 then comes into a completely closed state through the first and second sealing structures 64 and 65. A surface modification substance such as a metal complex is injected from the injection port 72 together with a high pressure inert gas 74. The surface modification substance disperses in the resin melt in the high pressure area 66. When the screw 62 is rotated in the forward direction, the second seal structure 65 is opened, and the molten resin flows from the high pressure area 66 to the low pressure area 67. However, pressure thereof gently decreases due to the lowering relaxation portion 68 away. An inert gas is generated from the molten resin, and the inert gas is removed through the discharge port 73. When the molten resin to which the surface modification substance is added is injected into a mold, a desired molded article is obtained.

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. Specifically, only a high pressure inert gas is injected in the high pressure area 66 without injecting a surface modification substance. The inert gas is injected with e.g. 10 MPa or similar. The inert gas is sufficiently dispersed and penetrates a resin melt in the high pressure area 66 and is then passed into the low pressure area 67. A valve provided in the outlet port 73 in the low-pressure region 67 is controlled so that a pressure inside the heating cylinder 61 is about 5 MPa. An excess protective gas is then generated from the resin melt in the low-pressure region 67 and removed from the discharge opening 73. However, a molten resin containing the inert gas dissolved in a saturated state is obtained. When the melted

When resin is injected into a mold, the inert gas in the resin will bubble and a foam-molded article will be obtained.

SUMMARY OF THE INVENTION TECHNICAL PROBLEM

Although the injection molding machines 50 and 60 disclosed in PTLs 1 and 2 can mold a foam-molded article by appropriately injecting an inert gas into a melt, the respective injection molding machines have problems to be solved. First, the injection molding machine 50 disclosed in PTL 1 has a problem that an inert gas is reversed to inject from the hopper 59 or a molten resin is pushed back by the inert gas. When the screw 52 is rotated forward and a resin is sent forward, an inert gas injected into the decompression part 55 is unlikely to flow reversely. That is, when the screw 52 is rotated forward, a sufficient pressure difference arises between the first compression part 54 and the decompression part 55. The inert gas is passed forward when kneading with the molten resin without reversing flow, and 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, 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 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. Thus, the length of the injection molding machine 60 is increased by the length of the high pressure area 66. It is necessary to make the length of the injection molding machine 60 short in order to provide the injection molding machine in a limited mounting area.

Further injection molding machines for foam molding are known from JP 2002 192 583 A, JP 2001 001 379 A, US 2003/011090 A and JP 2002 210 793 A.

An object of the invention is to provide an injection molding machine for foam molding which has solved the problems described above, in particular, it is an object to provide an injection molding machine that injects a physical foaming agent formed from an inert gas into a resin melt to produce a to mold a foam-molded article, that is, an injection molding machine for foam molding which can perform stable molding without the possibility of occurrence of reverse flow of the inert gas in a heating cylinder, which is sufficiently small in length that it can be mounted even in a limited assembly area, and which can mold a foam-molded article which is excellent in quality because the inert gas permeates the melt sufficiently and uniformly.

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 is divided into a first stage at the rear and a second stage at the front according to the shape of a screw.

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 prevents backflow of the resin and the inert gas at a boundary between the first and second stages. Bridges in the second stage are configured as multiple start bridges (“multi-start flights”) such as double (“double-start flights”) or multi-start bridges (“more-start flights”), and a pitch angle of each of the bridges is configured in such a way that it is in a range of 10 to 45 degrees.

In order to achieve the above object, an illustrative aspect of the invention provides 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 supply 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, wherein ridges in the second stage are multiple start ridges of double or multiple start ridges s ind and a slope angle of each of the ridges is in a range of 10 to 45 degrees.

Conveniently, the screw in the second stage can be provided with a lowering relaxation section, which is adjacent to the sealing structure, and flat groove sections in which a screw groove between the webs is flat, can be at at least two or more points in the lowering relaxation section be formed in the axial direction.

The gas injection opening can advantageously be provided with an opening and closing mechanism.

The heating cylinder can advantageously be provided with the two or more gas injection openings at a predetermined distance in the axial direction.

Conveniently, the heating cylinder can be provided with a resin pressure sensor corresponding to the decompression section.

ADVANTAGEOUS EFFECTS OF THE INVENTION

In the above-described invention, which is associated with the injection molding machine for foam molding, the heating cylinder is divided according to the shape of the screw into the first stage at the rear and the second stage at the front, in the first stage is the first compression section in which a resin is compressed, formed in the second stage is 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 location in the heating cylinder that corresponds to the Corresponding to decompression section, a gas supply opening is provided in which an inert gas can be injected through. 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. Thus, the injection molding machine can be

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. However, backflow from the second stage to the first stage is completely prevented because the 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 multiple start webs such as double or multiple start webs, and the pitch angle of each of the webs is in a range from 10 to 45 degrees. The resin into which the inert gas is injected is kneaded in the second stage. Since the second stage has multiple start bars, the protective gas is kneaded efficiently and evenly. Accordingly, a high quality foam-molded article can be molded because the inert gas permeates the melt sufficiently and uniformly. The inert gas is injected in the decompression section, but it is necessary that the amount of the resin transported to the second stage is large in order to sufficiently reduce the pressure of the resin in the decompression section. According to the aspect of the invention, since the pitch angle of each of the second-stage lands is set to be in a range of 10 to 45 degrees, the transported amount of the resin is large and the pressure of the resin in the decompression area can be reliably reduced . Accordingly, the inert gas can be sufficiently injected. According to a further aspect of the invention, the screw is provided in the second stage with the lowering relaxation section adjoining the sealing structure, and flat groove sections are formed in at least two locations in the axial direction in the lowering relaxation section, in which the screw flights between the webs are flat . According to the aspect of the invention, by providing the descent relaxation portion, an effect of stable injection of the inert gas can be achieved. This is because the pressure of a high-pressure resin that is compressed in the first compression section decreases when the resin is sent to the decompression section via the descent relaxation section, since the throttling in two or more shallow groove sections provided in the descent relaxation section, he follows. Since the pressure of the high pressure resin gently decreases and the resin flows into the decompression section, an inert gas can be stably injected. According to yet another aspect of the invention, the gas injection port includes an opening and closing mechanism. The venting of the resin from the gas injection port can be prevented by opening and closing the gas injection port. According to yet another aspect of the invention, the heating cylinder is provided with two or more gas injection ports at a predetermined distance in the axial direction. As the resin continues to be measured, the screw moves rearward and the decompression section moves rearward accordingly. According to the aspect of the invention, however, a gas injection port through which an inert gas is to be supplied can be selected according to a position in which the screw has moved backward because the two or more gas injection ports are provided at a predetermined distance in the axial direction. Even if the decompression section is relatively short, an inert gas can be injected and the screw can be made even shorter. It is thus possible to make the length of the injection molding machine even shorter. According to still another aspect of the invention, the heating cylinder is provided with a resin pressure sensor corresponding to the decompression section. Although an inert gas is injected into the decompression section, a pressure detected by the resin pressure sensor is greater than the pressure of the inert gas when the gas supply port is blocked by a resin. With this invention, such an anomaly can be quickly 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 a portion of a second stage of the screw is enlarged and illustrated.

[0018] [FIG. 2] Figs. 2 (A) and 2 (B) are views illustrating a seal structure provided in the screw of the injection molding machine according to the embodiment of the invention, and Figs. 2 (A) and 2 (B) are cross-sectional views. obtained from sealing structures according to different embodiments 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 in a shape of a flight flight.

[FIG. 4] Fig. 4 is a side view illustrating a prior art injection molding machine.

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

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, the tape 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 corresponding to the shape of the screw 3, that is, there is a first stage 5 on the rear side and a second stage 6 on the front side. The first stage 5 is a portion where a resin melts, and the second stage 6 is a portion where an inert gas is injected and the inert gas penetrates into the resin. The first and second stages 5 and 6 are defined by a seal structure 7 according to the embodiment. That is, it can be said that the inside of the heating cylinder 2 is divided into the first and second stages 5 and 6 by the sealing structure 7. The fact that such a seal structure 7 is provided is a feature of the injection molding machine 1 according to the embodiment, and the seal structure 7 according to the embodiment will be described in detail later.

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 starts of webs is different. That is, while the first stage 5 is formed from a single launch bridge with a standard pitch and slope, the second stage 6 is formed from multiple launch 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 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 is configured with double start bars in the embodiment, the second stage can be configured with triple start bars or multiple start bars that have started more than three times in addition to the double start bars.

Although the first stage 5 is configured with the individual webs as described above, the screw grooves between the webs in the vicinity of a funnel are relatively deep (not shown). In the first stage, a first compression section is made near the front

8 formed with shallow helical grooves. As a result, the resin can be easily sent forward in the vicinity of the funnel when it is melted, and the resin is completely melted and compressed in the first compression section 8. The compressed resin is discharged to the second stage 6 via the sealing structure 7.

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 sagging 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.

The descent relaxation portion 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 double start webs as in the other section of the second stage 6. Deep groove portions 12 and 12 in which the worm grooves are deep and shallow groove portions 13 and 13 in which the worm grooves are shallow are formed in at least two locations in the axial direction. That is, the shallow groove portions 13 and 13 are formed at two or more locations at a predetermined interval in the axial direction. The throttling is performed by the shallow groove portions 13 and 13 so that a pressure can be lowered smoothly when a resin is sent through the descending relaxation portion 11. Thereby, a resin pressure in the decompression section 9 can be reliably reduced. The throttling of the shallow groove portions 13 and 13 also has the effect of preventing a backflow of a molten resin containing an inert gas when the rotation of the screw 3 is stopped.

A flow speed at which a resin is sent is high in the screw 3 according to the embodiment, since a pitch angle e of each of the lands in the second stage 6, particularly in the second compression section 10, is selected to be within a predetermined range. In particular, the slope 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.

[Equation 1] Voz W- Hr, + W HS} (2P) F 2 AP 270 \ oz) 7 v _mn-D-N-cos (e) bz - 60 where: p: the number of starts of webs, currently! the distance in the direction parallel to the web and distance along the web (m), Vez: the speed component in the direction parallel to the web by rotating the

Screw (m / s), W: the groove width of the land (m),

Q = P

H: the groove depth of the land (m), D: the diameter of the screw (m), N: the number of turns of the screw (rpm), öP / ö0z: the pressure gradient of the molten resin in the z-direction (Pa / m) , MW: the viscosity of the resin (Pa: s),: the slope angle of the ridge (rad), and Fa, Fo: the effect of the ridge edge on the flow.

The flow rate Q changes depending on the viscosity u of a resin. The flow rate Q of resins having different viscosities µ when the pitch angle or the like of each of the lands is changed is calculated according to the equation, and the calculation results are shown in a graph in FIG. 3. A horizontal axis represents a pitch PP in the diagram. The pitch PP is expressed as the screw diameter D x tı x cos @ / number p of web starts. As can be seen from the graph in FIG. 3, the flow rate Q changes depending on the viscosity u of the resin. Flow is relatively high when the slope is in a range from 0.5D to xD. That is, a flow rate is relatively high when the pitch angle @ is in a range from 10 to 45 degrees. If the pitch is in a range from 0.5D to 2.6D, i.e. if the pitch angle © is in a range from 10 to 40 degrees, the flow is relatively high regardless of the level of viscosity u. When the pitch is within a range of 1.1D to 2.2D, that is, when the pitch angle e @ is within a range of 20 to 35 degrees, the flow is more stable. Therefore, in the worm 3 according to the embodiment, the helix angle of each of the flights of the second stage 6 is selected to be within the range described above.

The seal structure 7 provided in the screw 3 according to the embodiment is formed of a seal 15 and a flow control mechanism 16 that regulates a pressure, as shown in Fig. 2 (A) in detail. 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 interior 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 which is formed within the screw 3 such that the first stage 5 can communicate with the second stage 6, and a valve mechanism 19 which 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 configured with the umbrella-shaped head part 23 and a shaft portion 24. A plurality of disc springs 26, 26, 26... Are provided in the shaft section 24. Such a cone valve 22, in which the plate springs 26, 26 are provided, is inserted into a holder 27 in which a bottom hole is formed. The holder 27 is screwed and fixed by a male screw in the outer peripheral surface thereof to a female screw formed in an inner peripheral surface of the communication path 18. Therefore, the cone valve 22 is 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 if the lowering relaxation section 11 has a higher pressure, a backflow of the resin melt is completely prevented, since the cone valve 22 sits on the seat surface 20 and the connection is shut 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 the opening-closing valves 32A and 32B are opened, the inert gas such as nitrogen and carbon dioxide is injected into the heating cylinder 2 from the first and second injection sections 29A and 29B. Since the two injection sections 29A and 29B according to the embodiment are provided in the axial direction as described above in the injection molding machine 1, each of the injection sections 29A and 29B can correspond to the decompression section 9, and the inert gas can be injected even when the screw 3 is turned towards Measurement of a resin moves backward and the position of the decompression section 9 moves in the axial direction. Therefore, the decompression section 9 is relatively short, and hence the length of the injection molding machine 1 is short in the embodiment. The first and second injection portions 29A and 29B are provided with the opening-closing valves made up 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 prevented from entering the first and second injection sections 29A and 29B.

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 which 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 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 melted by the heat of the heating cylinder 2 and the heat caused by the shear stress of the rotation of the screw 3, and passed through the first stage 5 to be compressed in the first compression section 8. Since the pressure of the melted resin in the first compression section 8 is large, the poppet valve 22 in the seal structure 7 is opened and the melted resin is supplied to the descent relaxation section 11 of the second stage 6. Then, the molten resin is fed into the decompression section 9 via the descending relaxation section 11. When the molten resin passes through the shallow groove portions 13 and 13 located at the two positions in the descending relaxation portion 11, the pressure thereof is gently decreased by the throttle. The resin pressure becomes small and stabilizes in the decompression section 9. An inert gas is injected into the heating cylinder 2 from each of the first and second injection sections 29A and 29B. The inert gas is injected e.g. with a pressure of 5 MPa or similar. Subsequently, the inert gas penetrates the molten resin in the decompression section 9. Next, when the screw 3 is rotated, the inert gas is fed forward while it penetrates the melt. Since the second stage 6 is made up of multi-stage webs, the inert gas penetrates the melt efficiently and evenly. Such a molten resin is compressed in the second stage 6 and measured at the front of the screw 3; as soon as a predetermined amount is measured, the rotation of the screw 3 is stopped. The screw 3 is driven in the axial direction to inject the molten resin into a mold. The inert gas in the resin melt

bubbles inside the mold and a foam molded article is obtained. When the screw 3 stops rotating and is driven in the axial direction, there arises a problem of backflow of the inert gas. However, the backflow is practically completely prevented since the injection molding machine 1 is provided with the sealing structure 7 in accordance with the embodiment. In addition, the flow of a reverse current is also weakened through the descent relaxation section 11 on the upstream side of the decompression section 9.

The injection molding machine 1 can be modified in various ways according to the embodiment. For example, the sealing structure 7 can also be modified. 2 (B) illustrates a sealing structure 7 'according to another embodiment. The seal structure 7 'according to the embodiment is configured with a reduced diameter portion 35 in which the diameter of the screw 3 decreases and a seal ring 36 mounted with a predetermined gap between the reduced diameter portion 35 and the seal ring. Since an outer peripheral surface of the seal ring 36 smoothly contacts the bore of the heating cylinder 2, molten resin does not flow from the outer peripheral surface. That is, the inside of the heating cylinder 2 is divided in a liquid-tight manner with the sealing ring 36 into the first stage 5 on the inflow side and the second step 6 on the outflow side. The reduced diameter portion 35 in which the seal ring 36 is mounted with a gap is enlarged in diameter on an upstream side thereof to form a tapered surface 37, and an upstream end portion of the seal ring 36 is also tapered Form formed. When the molten resin is sent forward by rotating the screw 3, the pressure of the molten resin in the first stage 5 is greater than the pressure of the molten resin in the second stage 6, and the seal ring 36 moves forward with respect to the screw 3 against to be pressed against abutment portion 38. At this time, the tapered end portion of the seal ring 36 is separated from the tapered surface 37, and the first stage 5 and the second stage 6 communicate with each other through a gap between the reduced diameter portion 35 and an inner peripheral surface of the seal ring 36 melted resin downstream. Predetermined notches are formed in one end surface of the seal ring 36 so that a flow path of the molten resin is secured even when the seal ring abuts against the abutment portion 38. When the rotation of the screw 3 stops or the screw 3 is driven in the axial direction, the pressure of the resin melt in the second stage 6 becomes greater than the pressure in the first stage 5. Then the sealing ring 36 sits on the conical surface 37, the connection is interrupted and the flow of the melt is hindered. That is, reverse current is prevented.

In the embodiment, the webs of the first stage 5 can be modified and are not limited 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 opening-closing 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 inert gas injection sections 29A and 29B are always located in the decompression section 9 even when the screw 3 moves back and forth. The inert gas injection sections 29A and 29B may be provided with check valves. Since the check valves automatically open and close in response to a resin pressure, a backflow of a resin from the injection portions 29A and 29B can be prevented when the injection portions 29A and 29B are removed from the decompression portion 9 or a resin pressure inside the heating cylinder 2 can be prevented

has risen. The resin pressure sensor 33 can also be modified. Two or more resin pressure sensors can be provided.

REFERENCE LIST

1: injection molding machine

2: heating cylinder

3: snail

5: First stage

6: Second stage

T: seal structure

8: first compression section 9: decompression section

10: Second compression section 11: Lowering relaxation section 12: Deep groove section

13: Flat groove section

15: Seal

16: flow control mechanism 18: communication path

19: Valve mechanism

20: seat

22: Cone valve

23: headboard

24: shaft section

26: Disc spring

27: Holder

28: Harz path

29: first and second injection sections 31: gas cylinder

32A, 32B: opening / closing valve

33: Resin pressure sensor

Claims (4)

Claims An injection molding machine (1) for foam molding, the injection molding machine (1) comprising: a heating cylinder (2); and a screw (3) provided in the heating cylinder (2) and configured to be driven in a rotating direction and an axial direction, the heating cylinder (2) in a first stage (5 ) is divided on a rear side and a second stage (6) on a front side, the first stage (5) including a first compression section (8) for compressing a resin and the second stage (6) a decompression section (9) for reducing a Pressure of the resin and a second compression section (10) for compressing the resin, wherein the heating cylinder (2) includes a gas injection port for supplying an inert gas at a position corresponding to the decompression section (9), and wherein the screw (3) with a predetermined sealing structure (7) is provided to prevent a backflow of each of the resin and the inert gas at a boundary between the first and second stages (5, 6), with ridges in the second stage are multiple start webs of double or multiple start webs and a pitch angle (@) of each of the webs is in a range of 10 to 45 degrees, and wherein the screw (3) in the second stage (6) with a lowering relaxation section ( 11) is provided which adjoins the sealing structure (7) and the decompression section (9), characterized in that flat groove sections (13), in which a screw groove between the webs is flat, at at least two or more points, and deep Groove sections (12) in which the screw groove is deep are formed at at least two points in the lowering relaxation section (11) in the axial direction. 2. Injection molding machine for foam molding according to claim 1, wherein the gas injection port is provided with an opening and closing mechanism. 3. Injection molding machine for foam molding according to claim 1 or 2, wherein the heating cylinder (2) is provided with the two or more gas injection ports at a predetermined distance in the axial direction. 4. Injection molding machine for foam molding according to any one of claims to 3, wherein the heating cylinder (2) corresponding to the decompression section (9) is provided with a resin pressure sensor (33). In addition 4 sheets of drawings