JP2018058267A - Screw of injection molding machine and injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw of an injection molding machine capable of preventing reverse flow of inert gas and stably molding a foam molded product even if a machine length is short.SOLUTION: Provided is a screw (3) of an injection molding machine (1)composed of, in a heating cylinder (2) from rear to front, a first compression section (6) in which a resin is compressed, a starvation section (9) in which a resin pressure is stepped down and an inert gas is injected, and a second compression section (10) in which the resin is compressed. The screw (3) has a predetermined seal structure (7) for preventing reverse flow of the resin, and a step-down relaxing section (5) having a predetermined flight shape at a downstream side of the seal structure (7) between the first compression section (6) and the starvation section (9). The step-down relaxing section (5) forms shallow grooves (13) having shallow screw grooves between flights at least in two parts in the axial direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an injection molding machine screw and an injection molding machine used in a molding method of a foam molded product, in which an inert gas is injected into a molten resin and injected into a mold to obtain a foam molded product.

  A molded product in which many fine bubbles are formed, that is, a foam molded product, is not only lightweight but also excellent in strength, and has a wide range of application fields. In order to obtain a foam molded product by injection molding, it is necessary to mix a foaming agent into the resin, and the foaming agent includes a chemical foaming agent and a physical foaming agent. The former is known as a chemical foaming agent that decomposes by heat to generate gas, such as azodicarboxylic acid amide. The chemical foaming agent is mixed into the resin pellets of the material, put into a heating cylinder, and mixed with the molten resin. When the molten resin is injected into the mold, the chemical foaming agent foams to obtain a foam molded product. On the other hand, a physical foaming agent consists of inert gas, such as nitrogen and a carbon dioxide. An inert gas is injected at a predetermined pressure into the resin melted in the heating cylinder so that the inert gas is saturated in the resin. When this is injected into the mold, the pressure is released in the resin and the inert gas is bubbled. When the resin is cooled and solidified, a foam molded product is obtained. A physical foaming agent made of an inert gas is injected into the resin at a high pressure and a high temperature, so that it has a strong penetrating power and is more easily dispersed uniformly in the resin than a chemical foaming agent. Therefore, the obtained foamed molded article has an excellent feature that foaming unevenness hardly occurs.

JP 2002-79545 A Japanese Patent Laying-Open No. 2015-168079

  Patent Document 1 describes a molding method for obtaining a foam molded article using a physical foaming agent made of an inert gas. An injection molding machine 50 used in the molding method of the foam molded product will be described with reference to FIG. The injection molding machine 50 includes a heating cylinder 51 and a screw 52 provided in the heating cylinder 51 so as to be driven in the rotational direction and the axial direction. The screw 52 is formed with two compression portions where the screw grooves are shallow, that is, first and second compression portions 54 and 56, and the screw groove is deeply starved between the first and second compression portions 54 and 56. A portion 55 is formed. The heating cylinder 51 is provided with an inert gas injection part 57 so as to correspond to the starvation part 55, and an inert gas 58 is injected therein. In the injection molding machine 50, resin pellets are introduced from the hopper 59 and the screw 52 is rotated. Then, the resin pellet is melted and sent to the front of the screw 52. When the molten resin is sent forward, the molten resin is compressed by the first compression unit 54 and is made low by the starvation unit 55. An inert gas 58 is injected through the starvation part 55. Then, the inert gas 58 is mixed in the molten resin and becomes saturated. Such a molten resin is compressed again by the second compression unit 56 and is measured at the tip of the screw 52. When injected into the mold, the inert gas is vaporized in the resin to obtain a foam molded product.

  When the electroless plating method is performed on a molded product made of resin, the required pre-treatment is not required if a molded product is obtained by injecting a molten resin to which a surface modifying material such as a metal complex is added. Become. Patent Document 2 describes an injection molding machine 60 that can inject a surface modifying substance such as a metal complex into a molten resin, knead and inject it. As shown in FIG. 4, the injection molding machine 60 includes a heating cylinder 61 and a screw 62. 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 has a predetermined valve structure so that the resin sent forward from the rear of the screw 62 is sent to the high-pressure area 66, but backflow from the high-pressure area 66 to the rear is prevented. Has been. The second seal structure 65 includes a valve structure that is opened and closed according to the rotation direction 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 blocked and the resin cannot flow, but when the valve structure is open, the resin can flow freely. The screw 62 is provided with a pressure reduction mitigation section 68 on the downstream side of the second seal structure 65 in the low pressure area 67. In the step-down relaxation section 68, deep groove portions 69 and shallow shallow groove portions 70 having deep screw grooves between flights are alternately formed, and at least two shallow groove portions 70 and 70 are formed in the axial direction. In the shallow groove portions 70, 70, a squeezing action is performed, and when the resin flows from the high pressure area 66 to the low pressure area 67, the pressure is appropriately lowered. The heating cylinder 61 is provided with an inlet 72 for injecting an inert gas or the like corresponding to the high pressure area 66, and a discharge port 73 for discharging the inert gas downstream of the pressure reduction mitigation section 68 of the low pressure area 67. Is provided. In order to obtain a molded product by injecting a molten resin to which a surface modifying substance such as a metal complex is added, the following is performed. The screw 62 is rotated to melt the resin. The molten resin flows through the first seal structure 64 and is sent to the high pressure area 66. The screw 62 is reversely rotated to close the second seal structure 65. Then, the high pressure area 66 is completely closed by the first and second seal structures 64 and 65. A surface modifying substance such as a metal complex is injected from the injection port 72 together with the high-pressure inert gas 74. In the high pressure area 66, the surface modifying material is dispersed in the molten resin. 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, but the pressure is gradually reduced by the pressure reduction relaxation section 68. An inert gas is generated from the molten resin, and the inert gas is degassed from the discharge port 73. When the molten resin to which the surface modifying substance is added is injected into a mold, a desired molded product is obtained.

  The injection molding machine 60 provided with the screw 62 described in Patent Document 2 can also be used for a molding method of a foam molded product using a physical foaming agent, that is, an inert gas. Specifically, in the high pressure area 66, only the high pressure inert gas is injected without injecting the surface modifying substance. The inert gas is injected at 10 MPa, for example. The inert gas is sufficiently dispersed and permeated into the molten resin in the high pressure area 66 and then sent to the low pressure area 67. In the low pressure area 67, the valve provided in the discharge port 73 is controlled so that the pressure in the heating cylinder 61 becomes about 5 MPa. Then, excess inert gas is generated from the molten resin in the low pressure area 67 and is degassed from the discharge port 73, but a molten resin in which the inert gas is dissolved in a saturated state is obtained. When this is injected into the mold, the inert gas becomes bubbles in the resin, and a foam molded product is obtained.

  Although the injection molding machines 50 and 60 described in Patent Documents 1 and 2 can appropriately inject an inert gas into a molten resin to form a foam molded product, there are problems to be solved for each. First, the injection molding machine 50 described in Patent Document 1 has a problem that the inert gas flows backward and is ejected from the hopper 59 or the molten resin is pushed back by the inert gas. At first, when the resin is fed forward by rotating the screw 52 forward, there is no fear that the inert gas injected in the starvation part 55 flows backward. That is, when the screw 52 is rotating forward, there is a sufficient pressure difference between the first compression portion 54 and the starvation portion 55, and the inert gas is fed forward while being kneaded with the molten resin without flowing back. Then, it is measured through the second compression unit 56. However, when the rotation of the screw 52 is stopped, the pressure difference in the heating cylinder 51 becomes small. Since the high-pressure inert gas has a strong osmotic force, the inert gas flows backward past the first compression portion 54 at this time. There is a possibility that the molten resin is pushed back by the backflowed inert gas and rises in the hopper 59. Since the screw 52 stops rotating at least at the time of injection, it is difficult to completely prevent the backflow of the inert gas, and there is a problem that the molding cycle cannot be stably performed. Next, considering the injection molding machine 60 described in Patent Document 2, since the first sealing structure 64 is provided in the injection molding machine 60, the rotation of the screw 62 is stopped and the pressure in the heating cylinder 61 is reduced. Even if the difference is reduced, the inert gas does not flow backward. Therefore, the foam molded product can be stably molded. However, in the injection molding machine 60 described in Patent Document 2, a high pressure area 66 divided by first and second seal structures 64 and 65 in the screw 62 is essential. If it does so, the machine length of the injection molding machine 60 will become long by the part of the high voltage | pressure area 66. FIG. In order to provide the injection molding machine 60 in a limited installation area, there is a demand for shortening the machine length.

  An object of the present invention is to provide an injection molding machine screw and an injection molding machine that have solved the above-described problems, and specifically, a physical foaming agent made of an inert gas is injected into a molten resin. In an injection molding machine designed to mold foamed molded products, there is no risk of the inert gas flowing back in the heating cylinder, so it can be molded stably and installed in a limited installation area. An object of the present invention is to provide an injection molding machine screw having a sufficiently short machine length and an injection molding machine.

  In order to achieve the above object, the present invention achieves the first compression section in which the resin is compressed in the heating cylinder from the rear to the front, and the starvation in which the pressure of the resin is reduced. A section and a second compression section in which the resin is compressed are formed, and an injection molding machine screw in which an inert gas is injected into the starvation section is targeted. The screw is provided with a predetermined seal structure for preventing the backflow of the resin between the first compression section and the starvation section, and a pressure reducing relief section having a predetermined flight shape on the downstream side of the seal structure. In the step-down relaxation section, at least two shallow groove portions with shallow screw grooves between flights are formed in the axial direction.

Thus, in order to achieve the above object, the invention according to claim 1 includes a first compression section in which resin is compressed in the heating cylinder from the rear to the front depending on the shape of the screw; A starvation zone in which the pressure of the resin is reduced and a second compression zone in which the resin is compressed are formed, and an inert gas is injected into the starvation zone. A screw for an injection molding machine, wherein the screw has a predetermined sealing structure for preventing a back flow of resin between the first compression section and the starvation section, and a predetermined downstream side of the sealing structure. A step-down relaxation section having a flight shape is provided, and in the step-down relaxation section, at least two shallow groove portions with shallow screw grooves between flights are formed in the axial direction. Configured as a Ryu.
According to a second aspect of the present invention, the screw according to the first aspect is configured as a screw of an injection molding machine, wherein the step-down relaxation section is composed of two or more multi-flight flights.
According to a third aspect of the present invention, in the screw according to the first or second aspect, the seal structure includes a seal that liquid-tightly partitions the first compression section and the step-down relaxation section, and the first A communication path communicating the compression section and the pressure reduction relaxation section; and a valve mechanism that closes the communication path and causes the molten resin to flow into the pressure reduction relaxation section when the molten resin in the first compression section exceeds a predetermined pressure; It is comprised as a screw of the injection molding machine characterized by providing.
According to a fourth aspect of the present invention, in the screw according to the first or second aspect, the seal structure is fitted into the reduced diameter portion with a reduced diameter portion where the screw diameter is reduced and a predetermined gap. And a seal ring that is liquid-tightly slid with respect to the bore of the heating cylinder, and when the seal ring is seated on the reduced diameter portion, the first compression section and the step-down relaxation section A screw surface of the injection molding machine is formed, which has a tapered surface that blocks communication with the screw.
The invention according to claim 5 includes the screw according to any one of claims 1 to 4, and the heating cylinder is provided with an inlet for injecting an inert gas at a predetermined position corresponding to the starvation section. It is configured as an injection molding machine characterized by

  According to the above, according to the present invention, depending on the shape of the screw, the first compression section in which the resin is compressed in the heating cylinder from the rear to the front, and the pressure of the resin are reduced. A starvation section and a second compression section in which the resin is compressed are formed, and configured as a screw of an injection molding machine in which an inert gas is injected into the starvation section. The screw is provided with a predetermined seal structure for preventing the backflow of the resin between the first compression section and the starvation section, and a pressure reduction relaxation section having a predetermined flight shape on the downstream side of the seal structure. In the step-down relaxation section, at least two shallow groove portions with shallow screw grooves between flights are formed in the axial direction. This screw is a screw provided in an injection molding machine for molding a foam molded product. Thus, the screw only needs to have the first and second compression sections, the starvation section, the seal structure, and the pressure reduction relaxation section. For molding, the screw length is much shorter. Therefore, the machine length of the injection molding machine can be shortened and installed in a limited installation space. And since the pressure | voltage fall relaxation area is provided in this invention, the effect that an inert gas can be inject | poured stably is acquired. The reason is that when the high-pressure resin compressed in the first compression section is sent to the starvation section through the pressure reduction relaxation section, the pressure drops due to the squeezing action at two or more shallow grooves provided in the pressure reduction relaxation section. Because it does. Since the high-pressure resin gradually decreases in pressure and flows into the starvation section, the inert gas can be stably injected. By the way, when the screw stops rotating at the time of injection or the like, the pressure difference of the resin in the heating cylinder becomes small, and the high-pressure inert gas having strong osmotic force tends to flow backward. However, since the screw structure of the present invention is provided with the seal structure and the pressure reduction mitigation section upstream from the starvation section into which the inert gas is injected, the backflow can be reliably prevented. In the pressure reduction mitigation section, there are two or more shallow grooves with an squeezing function in the axial direction, so that even if the molten resin tries to flow back together with the inert gas, this is hindered, and the backflow is substantially completely prevented in the seal structure. This is because it is prevented. Accordingly, the inert gas does not enter the first compression section, and the inert gas is not ejected from the hopper, and the molten resin pushed back by the inert gas does not flow backward from the hopper. The injection molding machine provided with the screw according to the present invention can stably form a foam molded product.

It is side surface sectional drawing of the injection molding machine which concerns on this Embodiment provided with the screw which concerns on embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the seal structure provided in the screw which concerns on embodiment of this invention, (a), (b) shows the seal structure which concerns on each different embodiment cut | disconnected in parallel with the axis | shaft of a screw. It is sectional drawing. It is side surface sectional drawing which shows the conventional injection molding machine. It is side surface sectional drawing which shows the conventional injection molding machine.

  Embodiments of the present invention will be described below. The injection molding machine according to the embodiment of the present invention is also shown in FIG. 1 and can be driven in the heating direction and the axial direction in the heating cylinder 2 as in the conventional injection molding machine. It is comprised from the screw 3 provided in this. A plurality of band heaters are wound around the outer peripheral surface of the heating cylinder 2, but these are not shown in the figure.

  In the injection molding machine 1 according to the present embodiment, a plurality of sections are formed in the heating cylinder 2 depending on the shape of the screw 3. In this embodiment, the flight of the screw 3 includes a single flight of a general pitch and lead except for the step-down relaxation section 5 described below. The screw 3 has a relatively deep screw groove between flights in the vicinity of a hopper not shown in the figure, and is designed to feed the resin forward while melting the resin. A seal structure 7 to be described later from a predetermined position. A screw groove is formed shallowly, thereby forming a first compression section 6 in which the resin is compressed. A pressure reduction mitigation section 5 is formed adjacent to the seal structure 7 in the front, that is, downstream of the seal structure 7, and a starvation section 9 having a deep screw groove is formed downstream thereof. Since the screw groove is deep and the volume in the heating cylinder 2 is large, the pressure of the resin sent forward in the starvation section 9 decreases. Therefore, a physical foaming agent made of an inert gas is injected in this section 9 as will be described later. The screw 3 has a second compression section 10 in which the screw groove is shallow and the resin is compressed in front of the starvation section 9, that is, downstream. In the present embodiment, of the screw shape, the depth of the screw groove is changed to form the first and second compression sections 6 and 10 and the starvation section 9. However, the same sections 6, 9, and 10 can be formed even if other flight shapes such as the flight pitch and flight width are changed among the screw shapes.

  The step-down relaxation section 5 which is a characteristic structure in the screw 3 according to the present embodiment will be described. In the present embodiment, the flight in the step-down relaxation section 5 is composed of two-flight flights. As described above, since the two-flight flight is used, the molten resin sent out in the step-down relaxation section 5 is smoothly sent downstream without turbulent flow or reverse flow even if the viscosity is small. In such a step-down relaxation section 5, at least two deep groove portions 12, 12 with deep screw grooves and shallow shallow groove portions 13, 13 are formed in the axial direction. That is, two or more shallow groove portions 13 are formed. The shallow groove portions 13 and 13 have a squeezing action. Therefore, the pressure-lowering relaxation section 5 can gradually reduce the pressure when the molten resin is sent forward, and inhibits the molten resin containing the inert gas from flowing backward when the screw 3 stops rotating. become.

  As shown in detail in FIG. 2A, the seal structure 7 provided in the screw 3 according to the present embodiment includes a seal 15 and a flow control mechanism 16 having a pressure adjusting action. . The seal 15 is slidably fitted in a predetermined groove formed on the outer peripheral surface of the screw 3. The heating cylinder 2 is not shown in FIG. 2A, but the outer peripheral surface of the seal 15 slides smoothly in contact with the bore of the heating cylinder 2. The seal 15 prevents the molten resin from flowing, and the inside of the heating cylinder 2 is liquid-tightly divided into the first compression section 10 on the upstream side and the step-down relaxation section 5 on the downstream side. The seal structure 7 is provided with one or a plurality of flow control mechanisms 16. The flow control mechanism 16 includes a communication path 18 opened in the screw 3 so as to communicate the first compression section 6 and the pressure reduction relaxation section 5, and a valve mechanism 19 that opens and closes the communication path 18. ing. A midway portion of the communication path 18 is tapered so that a tapered seating surface 20 is formed. When the head 23 of the poppet valve 22 constituting the valve mechanism 19 is seated on the seating surface 20, the communication path 18 is closed. The poppet valve 22 includes an umbrella-shaped head portion 23 and a shaft portion 24, and the shaft portion 24 is provided with a plurality of disc springs 26, 26,. In this way, the poppet valve 22 provided with the disc springs 26, 26,... Is placed in a retainer 27 having a hole with a bottom. The retainer 27 is screwed and fixed to a female screw formed on the inner peripheral surface of the communication path 18 by a male screw formed on the outer peripheral surface thereof. Therefore, the poppet valve 22 is urged by the disc springs 26, 26,..., The head 23 is pressed against the seating surface 20, and the communication path 18 is closed. When the molten resin in the first compression section 6 reaches a predetermined pressure, the poppet valve 22 moves backward against the bias of the disc springs 26, 26,... And the molten resin flows into the pressure-lowering relaxation section 5. The resin passage 28 is opened in the retainer 27, and when the first compression section 6 and the pressure reduction relaxation section 5 communicate with each other, the molten resin flows from the resin passage 28 to the pressure reduction relaxation section 5. . When the pressure in the first compression zone 6 and the pressure reduction relaxation zone 5 is equal, or when the pressure in the pressure reduction relaxation zone 5 is higher, the poppet valve 22 is seated on the seating surface 20 and the communication is cut off. The backflow of the molten resin from the section 5 to the first compression section 6 is completely prevented.

  In the injection molding machine 1 according to the present embodiment, as shown in FIG. 1, an inert gas inlet 29 is provided at a position corresponding to the step-down relaxation zone 5 in the heating cylinder 2. A pipe from a gas cylinder 31 containing an inert gas is connected to the injection port 29 via an on-off valve 32. When the on-off valve 32 is opened, an inert gas such as nitrogen or carbon dioxide is injected into the heating cylinder 2 from the injection port 29.

  The operation of the injection molding machine 1 according to the embodiment of the present invention will be described. The heating cylinder 2 is heated to rotate the screw 3 in the forward direction, and the resin material is supplied from a hopper not shown in the drawing. The supplied resin material is melted by the heat of the heating cylinder 2 and the heat generated by the shearing force of the screw 3, sent forward, and compressed in the first compression section 6. Since the pressure of the molten resin in the first compression section 6 is large, the poppet valve 22 is opened in the seal structure 7, and the molten resin is sent to the pressure reduction relaxation section 5. If it does so, molten resin will be sent to the starvation area 9 through the pressure reduction relaxation area 5. FIG. Since the screw groove is deep in the starvation section 9 as described above, the pressure of the molten resin is small, and the pressure difference from the pressure in the first compression section 6 is large. However, when the molten resin passes through the two shallow grooves 13 and 13 of the pressure-lowering relaxation section 5, the pressure is reduced by the squeezing action. Accordingly, the resin pressure is stabilized in the starvation section 9. The on-off valve 32 is opened to inject inert gas into the heating cylinder 2. The inert gas is injected at a pressure of 5 MPa, for example. Then, in the starvation section 9, the inert gas permeates into the molten resin and becomes saturated. When the screw 3 is continuously rotated, the molten resin in which the inert gas has permeated in the starvation zone 9 in a saturated state is compressed in the second compression zone 10 and measured at the head of the screw 3. When the predetermined amount is measured, the rotation of the screw 3 is stopped. The screw 3 is driven in the axial direction to inject molten resin into the mold. In the mold, the inert gas is bubbled in the molten resin to obtain a foam molded product. By the way, when the rotation of the screw 3 is stopped and driven in the axial direction, the backflow of the inert gas becomes a problem. In the injection molding machine 1 according to the present embodiment, the pressure reduction mitigation section 5 having a throttling effect is provided at two locations upstream of the starvation section 9, so that even if the inert gas tries to backflow, The flow is weakened. And since the seal structure 7 is provided in the upstream of the pressure | voltage fall mitigation area 5, a backflow is prevented substantially completely. Accordingly, the inert gas does not flow back through the heating cylinder 2.

In the injection molding machine 1 provided with the screw 3 according to the present embodiment, an experiment was conducted to confirm that a foam molded product can be stably molded.
"Experiment 1"
A predetermined mold is used by using an injection molding machine 1 according to the present embodiment shown in FIG. 1 and using polypropylene containing 20% talc as a resin material and injecting an inert gas from an injection port 29. The product was injected into a foamed molded product. In the injection molding, a metering standby time for stopping the rotation of the screw 3 for 1 second when the metering of the resin is completed is provided, and then the screw 3 is driven in the axial direction for injection. The molding cycle was repeated 30 times to obtain 30 foam molded products. The average weight of these foam-molded articles was 6.1 g, and the value obtained by dividing the standard deviation by the average weight was 0.3%. In this experiment, it was confirmed that the inert gas did not flow backward across the seal structure 7.
"Experiment 2"
The injection molding was performed using the same injection molding machine 1 as in Experiment 1 without injecting the inert gas. That is, a molded product without foaming was molded. The molding cycle was repeated 30 times to obtain 30 molded products. The average weight of these molded articles was 6.8 g, and the value obtained by dividing the standard deviation by the average weight was 0.2%.
“Experiment 3”
The injection molding machine 1 used in Experiment 1 was deformed to prepare an injection molding machine with the seal structure 7 removed. A foam-molded article was molded under the same conditions as in Experiment 1 using an injection molding machine without the seal structure 7. When injection molding was repeated several times, a phenomenon was observed in which the inert gas flowed backward in the heating cylinder 2.
“Experiment 4”
Using a conventional injection molding machine 60 shown in FIG. The inert gas was injected from the inlet 72, and excess inert gas was discharged from the outlet 73. The same resin and mold as those used in Experiment 1 were used. The molding cycle was repeated 30 times to obtain 30 foam molded products. The average weight of these foam-molded articles was 6.1 g, and the value obtained by dividing the standard deviation by the average weight was 0.3%. In this experiment, it was confirmed that the inert gas did not flow backward.
"Discussion"
In Experiment 1, the variation in the weight of the foamed molded product is 0.3%. This is because the variation in the weight of the molded product without foaming is 0.2% from Experiment 2, and thus the variation is not large. . That is, in Experiment 1, it can be said that the foam molded product was stably molded. This is also true from comparison with Experiment 4. That is, in the injection molding machine 60 shown in FIG. 4, the backflow of the inert gas is completely prevented, but the variation in the weight of the foam molded product molded by the injection molding machine 60 is also zero. .3%, which is equivalent to the variation in the weight of the foamed molded product of Experiment 1. That is, it can be said that the injection molding machine 1 according to the present embodiment used in Experiment 1 was able to stably form a homogeneous foam molded product. And since the backflow of the inert gas was not seen in Experiment 1, it can be said that the injection molding machine 1 provided with the screw 3 which concerns on this Embodiment is suitable for shaping | molding of a foaming molded product. Next, from the results of Experiment 3, it was confirmed that the seal structure 7 was essential. This is because a phenomenon in which the inert gas flows backward in the heating cylinder 2 was observed when the foamed molded product was molded by an injection molding machine without the seal structure 7.

  The injection molding machine 1 according to the present embodiment can be variously modified. For example, the seal structure 7 can be modified. FIG. 2A shows a seal structure 7 'according to another embodiment. The seal structure 7 ′ according to this embodiment includes a reduced diameter portion 35 obtained by reducing the diameter of the screw 3 and a seal ring 36 provided in the reduced diameter portion 35 with a predetermined gap. The outer peripheral surface of the seal ring 36 is in smooth contact with the bore of the heating cylinder 2 so that the molten resin does not flow from the outer peripheral surface. In other words, the inside of the heating cylinder 2 is liquid-tightly divided into the first compression section 6 on the upstream side and the pressure reduction / relief section 5 on the downstream side by the seal ring 36. The diameter-reduced portion 35 into which the seal ring 36 is fitted with a gap is expanded on the upstream side to form a tapered surface 37, and the upstream end portion of the seal ring 36 is also tapered. ing. In the screw 3, an abutting portion 38 with which the seal ring 36 abuts is formed in front of the reduced diameter portion 35. When the molten resin is fed forward by rotating the screw 3, the pressure of the molten resin in the first compression section 6 is larger than the pressure in the pressure reduction relaxation section 5, and the seal ring 36 moves forward with respect to the screw 3. Then, it is pressed against the contact portion 38. At this time, the tapered end portion of the seal ring 36 is separated from the tapered surface 37, and the first compression section 6 and the pressure reduction relaxation section 5 are interposed via a gap between the reduced diameter portion 35 and the inner peripheral surface of the seal ring 36. Communicate with each other and the molten resin flows downstream. The seal ring 36 is formed with a predetermined notch on the end face so that a flow path of the molten resin is ensured even if the seal ring 36 abuts against the abutment portion 38. On the other hand, when the rotation of the screw 3 is stopped or the screw 3 is driven in the axial direction, the pressure of the molten resin in the step-down relaxation zone 5 becomes larger than the pressure in the first compression zone 6. Then, the seal ring 36 is seated on the tapered surface 37, the communication is cut off, and the flow of the molten resin is inhibited. That is, backflow is prevented.

DESCRIPTION OF SYMBOLS 1 Injection molding machine 2 Heating cylinder 3 Screw 5 Decrease pressure reduction zone 6 1st compression zone 7 Seal structure 9 Starvation zone 10 2nd compression zone 12 Deep groove part 13 Shallow groove part 15 Seal 16 Flow control mechanism 18 Communication path 19 Valve mechanism 20 Seating surface 22 Poppet valve 23 Head 24 Shaft 26 Belleville spring 27 Retina 28 Resin passage 29 Inlet 31 Gas cylinder 32 On-off valve

In order to achieve the above object, the present invention achieves the first compression section in which the resin is compressed in the heating cylinder from the rear to the front, and the starvation in which the pressure of the resin is reduced. A section and a second compression section in which the resin is compressed are formed, and an injection molding machine screw in which an inert gas is injected into the starvation section is targeted. The screw has a predetermined seal structure for preventing a back flow of the resin between the first compression section and the starvation section, and a predetermined flight shape adjacent to the seal structure on the downstream side of the seal structure. Establish a step-down relief section. In the step-down relaxation section, at least two shallow groove portions with shallow screw grooves between flights are formed in the axial direction.

Thus, in order to achieve the above object, the invention according to claim 1 includes a first compression section in which resin is compressed in the heating cylinder from the rear to the front depending on the shape of the screw; A starvation zone in which the pressure of the resin is reduced and a second compression zone in which the resin is compressed are formed, and an inert gas is injected into the starvation zone. a screw of the injection molding machine are, in the screw, the between the first compression section and the starvation period, a predetermined sealing structure to prevent backflow of the resin, the downstream side of the seal structure adjacent to the seal structure is provided with a step-down relaxation interval of a predetermined flight shape, the step-down relaxation section, especially that screw groove is shallow shallow groove between the flight is formed over two locations in at least the axial direction Configured as screw of an injection molding machine according to.
According to a second aspect of the present invention, the screw according to the first aspect is configured as a screw of an injection molding machine, wherein the step-down relaxation section is composed of two or more multi-flight flights.
According to a third aspect of the present invention, in the screw according to the first or second aspect, the seal structure includes a seal that liquid-tightly partitions the first compression section and the step-down relaxation section, and the first A communication path communicating the compression section and the pressure reduction relaxation section; and a valve mechanism that closes the communication path and causes the molten resin to flow into the pressure reduction relaxation section when the molten resin in the first compression section exceeds a predetermined pressure; It is comprised as a screw of the injection molding machine characterized by providing.
According to a fourth aspect of the present invention, in the screw according to the first or second aspect, the seal structure is fitted into the reduced diameter portion with a reduced diameter portion where the screw diameter is reduced and a predetermined gap. And a seal ring that is liquid-tightly slid with respect to the bore of the heating cylinder, and when the seal ring is seated on the reduced diameter portion, the first compression section and the step-down relaxation section A screw surface of the injection molding machine is formed, which has a tapered surface that blocks communication with the screw.
The invention according to claim 5 includes the screw according to any one of claims 1 to 4, and the heating cylinder is provided with an inlet for injecting an inert gas at a predetermined position corresponding to the starvation section. It is configured as an injection molding machine characterized by

According to the above, according to the present invention, depending on the shape of the screw, the first compression section in which the resin is compressed in the heating cylinder from the rear to the front, and the pressure of the resin are reduced. A starvation section and a second compression section in which the resin is compressed are formed, and configured as a screw of an injection molding machine in which an inert gas is injected into the starvation section. The screw has a predetermined seal structure for preventing a back flow of the resin between the first compression section and the starvation section, and a predetermined flight shape adjacent to the seal structure on the downstream side of the seal structure. A step-down relaxation section is provided, and in the step-down relaxation section, at least two shallow groove portions with shallow screw grooves between flights are formed in the axial direction. This screw is a screw provided in an injection molding machine for molding a foam molded product. Thus, the screw only needs to have the first and second compression sections, the starvation section, the seal structure, and the pressure reduction relaxation section. For molding, the screw length is much shorter. Therefore, the machine length of the injection molding machine can be shortened and installed in a limited installation space. And since the pressure | voltage fall relaxation area is provided in this invention, the effect that an inert gas can be inject | poured stably is acquired. The reason is that when the high-pressure resin compressed in the first compression section is sent to the starvation section through the pressure reduction relaxation section, the pressure drops due to the squeezing action at two or more shallow grooves provided in the pressure reduction relaxation section. Because it does. Since the high-pressure resin gradually decreases in pressure and flows into the starvation section, the inert gas can be stably injected. By the way, when the screw stops rotating at the time of injection or the like, the pressure difference of the resin in the heating cylinder becomes small, and the high-pressure inert gas having strong osmotic force easily flows backward. However, since the screw structure of the present invention is provided with the seal structure and the pressure reduction mitigation section upstream from the starvation section into which the inert gas is injected, the backflow can be reliably prevented. In the pressure reduction mitigation section, there are two or more shallow grooves with an squeezing function in the axial direction, so that even if the molten resin tries to flow back together with the inert gas, this is hindered, and the backflow is substantially completely prevented in the seal structure. This is because it is prevented. Accordingly, the inert gas does not enter the first compression section, and the inert gas is not ejected from the hopper, and the molten resin pushed back by the inert gas does not flow backward from the hopper. The injection molding machine provided with the screw according to the present invention can stably form a foam molded product.

Claims (5)

Depending on the shape of the screw, the first compression section in which the resin is compressed in the heating cylinder from the rear to the front, the starvation section in which the pressure of the resin is reduced, and the resin is compressed A screw of an injection molding machine, wherein a second compression section is formed and an inert gas is injected into the starvation section,
The screw has a predetermined seal structure for preventing a back flow of the resin between the first compression section and the starvation section, and a pressure reduction relaxation section having a predetermined flight shape downstream of the seal structure. Provided,
The screw of the injection molding machine, wherein the step-down relaxation section has at least two shallow groove portions in the axial direction where the screw grooves between the flights are shallow.   The screw according to claim 1, wherein the step-down relaxation section is composed of two or more multi-strip flights.   3. The screw according to claim 1, wherein the seal structure includes a seal that liquid-tightly partitions the first compression section and the step-down relaxation section, and the first compression section and the step-down relaxation section. The communication path includes: a communication path; and a valve mechanism that closes the communication path and causes the molten resin to flow into the step-down relaxation section when the molten resin in the first compression section exceeds a predetermined pressure. Screw for injection molding machine.   3. The screw according to claim 1, wherein the seal structure includes a reduced diameter portion in which the screw has a reduced diameter, and a fit in the reduced diameter portion with a predetermined gap therebetween. A seal ring that is slid in a liquid-tight manner with respect to the bore, and a tapered surface that blocks communication between the first compression section and the step-down relaxation section when the seal ring is seated on the reduced diameter portion. An injection molding machine screw characterized by being formed. A screw according to any one of claims 1 to 4,
The heating cylinder is provided with an injection port for injecting an inert gas at a predetermined position corresponding to the starvation section.

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