Injection foam molding metering control method and injection molding machine

Abstract

To provide a weighing control method capable of efficiently generating foaming gas and stabilizing foaming molten resin without being restricted by a combination of a resin material and a foaming agent in an injection foam molding using a foaming resin material in which a foaming agent that is decomposed by heating to generate a foaming gas is mixed with the resin material.SOLUTION: A weighing control method for injection foam molding is configured in that: a preheating temperature T11 is set in a transport zone FZ of an injection cylinder 11 at which foaming gas is not generated when a foaming resin material passes through the transport zone FZ; a plasticizing temperature T21 for generating foaming gas is set in a compression zone CZ when the foaming resin material passes through the compression zone CZ; from a melting zone MZ to a nozzle zone NZ, a holding temperature T31 is set at which a foaming molten resin is stabilized; and when a retraction speed of a screw 14 is decreased below a preset limit speed, a rotational speed of the screw 14 is corrected.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for controlling the amount of foam injection molding that involves supplying a foamable resin material containing a foaming agent that generates a foamable gas when heated from the rear of an injection cylinder, plasticizing the foamable resin material by rotating and retracting a screw, storing the foamable molten resin at the front of the injection cylinder, and injecting the foamable molten resin into a mold cavity to foam and expand it.

[0002] In injection foam molding, a foamable resin material, a mixture of a blowing agent and a resin material, is supplied into an injection cylinder. The foamable resin material is plasticized and melted by the rotation of a spiral-flighted screw and the heat of a heater or other device installed in the injection cylinder. The foamable resin material is then continuously transported toward the tip of the screw and stored in the injection cylinder as a foamable molten resin containing a foaming gas. As the amount of foamable molten resin stored increases, the screw retracts. This screw retraction is limited to adjust the quality of the stored foamable molten resin (a process known as backpressure control). The screw rotation is stopped at a predetermined retracted position, maintaining the screw position (this process is called the metering process). The screw is then advanced to the injection process, where the foamable molten resin is injected and filled into the mold cavity; the foaming process, where the foamable molten resin is foamed and expanded within the mold cavity; and the cooling process, where the resin is cooled to a temperature suitable for removal from the mold cavity. The injection foam-molded product is then removed from the mold cavity.

[0003] Here, blowing agents are classified into chemical blowing agents, which decompose when heated to produce a foaming gas, and physical blowing agents, which use pressure-adjusted nitrogen gas, carbon dioxide gas, or the like as the foaming gas. Injection foam molding using a chemical blowing agent is called chemical foam molding, while injection foam molding using a physical blowing agent is called physical foam molding. In either type of injection foam molding, a metering control method is required to homogeneously mix the foaming gas and molten resin and stably produce high-quality foamable molten resin.

[0004] For example, Patent Document 1 proposes increasing the back pressure relative to the pressure of the supplied foaming gas to perform plasticization and metering. This is believed to prevent separation of the molten resin and the foaming gas. Patent Document 2 also proposes maintaining a predetermined back pressure from immediately after the gaseous molten resin is injected into the mold cavity until the next injection. This is believed to prevent the problem of gas escaping from the gaseous molten resin due to a decrease in back pressure. Patent Document 3 also proposes maintaining the foaming resin in the cylinder below the decomposition temperature of the foaming agent, adjusting the temperature of the foaming resin by changing the injection speed, and foam-molding the foamed resin in the mold. This is believed to suppress foaming in the cylinder and produce a high-expansion foam-molded product with a beautiful appearance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-306296 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-178379 [Patent Document 3] Japanese Patent Application Publication No. 5-147091 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, physical foam molding requires a gas generating and supplying device that stores the foaming gas, adjusts the pressure and temperature of the foaming gas, and transports and adjusts the amount of foaming gas supplied to the injection cylinder. Furthermore, it requires an injection device with special specifications for plasticizing and melting the resin material, mixing the molten resin with the foaming gas, melting and kneading the foamable molten resin and storing it, and preventing foaming gas leakage. For this reason, the fields of use of physical foam molding are limited. In contrast, chemical foam molding is widely adopted in many fields because it can utilize the injection device and auxiliary equipment used in ordinary injection molding. Therefore, this invention focuses on chemical foam molding. Hereinafter, chemical foam molding will be referred to as injection foam molding, and the chemical foaming agent will be referred to as the foaming agent.

[0007] Resin pellets (called foaming agent MB) containing foaming components kneaded into a carrier resin are commercially available, making it convenient to use these. The foaming components decompose when heated to generate foaming gas. Examples of foaming gases include azo compounds (ADCA) that generate nitrogen gas and bicarbonates (NaHCO3) that generate carbon dioxide gas. The appropriate type is selected depending on the resin material and product application. Furthermore, a resin with a melting point lower than the decomposition temperature of the foaming components is selected as the carrier resin to prevent the foaming components from decomposing and generating foaming gas during the production of the foaming agent MB. For example, the decomposition temperature of bicarbonates used as the foaming agent is 150°C, so a polyethylene resin (HDPE) with a melting point of 120-140°C is used as the carrier resin. Furthermore, foaming agent MB is often blended with regulators, such as nucleating agents that adjust the number and size of foam cells and stabilizing agents that stabilize the decomposition temperature of the foaming components. Each of these regulators has a different decomposition temperature. To ensure consistent injection foam molding quality, it is necessary to properly control the decomposition temperatures of the foaming components and regulators.

[0008] Furthermore, in the metering process of injection foam molding, the following steps are performed consecutively: heating the foaming agent, initiating decomposition of the foaming agent, generating a foamable gas, plasticizing and melting the resin material, mixing the foamable gas with the molten resin, generating a foamable molten resin, and stably maintaining the foamable molten resin. These steps occur over the time period from when the foamable resin material is supplied to the injection cylinder to when it is injected from the injection cylinder into the mold cavity as a foamable molten resin. In other words, it is believed that each of these steps can be maintained in an appropriate state by appropriately managing the passage time of the resin material and the temperature rise of the resin material according to the location of the injection cylinder.

[0009] In contrast, Patent Documents 1 and 2 state that the stability of the foamable molten resin, one of the above-mentioned processes, can be achieved by appropriately controlling the back pressure. However, they do not take into consideration the passage time and temperature of the foamable resin material depending on the part of the injection cylinder. Therefore, it is unclear whether the processes other than the stability of the foamable molten resin are performed appropriately, making it difficult to achieve high-quality injection foam molding.

[0010] Patent Document 3 also describes temperature control of the injection cylinder, but states that the injection cylinder should be heated and maintained below the decomposition temperature of the blowing agent. However, depending on the combination of resin material and blowing agent, it is possible that the resin material may not be plasticized and melted in the injection cylinder and may not be injected into the mold. For example, when polypropylene resin (melting point 160-165°C), which is commonly used in automotive parts, is combined with a blowing agent containing bicarbonate as a foaming component (decomposition temperature 150°C), the heating temperature of the injection cylinder is below 150°C, at which temperature the polypropylene resin cannot be plasticized and melted and remains solid. Furthermore, even when a blowing agent containing an azo compound with a high decomposition temperature (decomposition temperature 200-210°C) is used, when nylon resin (melting point 220-225°C) is combined with the resin material, the heating temperature of the injection cylinder is below 200°C, at which temperature the nylon resin cannot be plasticized and melted and remains solid. This places significant restrictions on the combination of blowing agent and resin material. Furthermore, compared to the instantaneous temperature rise during the injection process, the time required for the foaming agent to be heated and for foaming gas to be generated is overwhelmingly longer, and it is therefore not possible to efficiently generate foaming gas during the injection process and mix it with the molten resin to produce a foamable molten resin. In other words, it is deemed that Patent Document 3 is difficult to put into practical use.

[0011] Therefore, the present invention aims to provide a metering control method that enables efficient generation of foamable gas and stabilization of foamable molten resin in injection foam molding using a foamable resin material obtained by mixing a resin material with a foaming agent that decomposes when heated to generate foamable gas, without being restricted by the combination of resin material and foaming agent. [Means for solving the problem]

[0012] The method for controlling the amount of injection foam molding of the present invention comprises: A method for controlling the amount of foam injection molding, comprising the steps of: supplying a foaming resin material containing a foaming agent that generates a foaming gas when heated from the rear of an injection cylinder; plasticizing the foaming resin material by rotating and retracting a screw; storing the foaming resin as a foamable molten resin in the front of the injection cylinder; and injecting the foamable molten resin into a mold cavity to foam and expand it; a screw retreat speed measuring means for measuring the retreat speed of the screw; The injection cylinder is divided into a transport zone, a compression zone, a melting zone, a storage zone, and a nozzle zone from the rear to the front, a preheating temperature at which the foamable gas is not generated is set in the transport zone, a plasticizing temperature at which the foamable gas is generated is set in the compression zone, and a holding temperature at which the foamable molten resin is stabilized is set from the melting zone to the nozzle zone, When the retreat speed of the screw retreating operation falls below a preset limit speed, the rotation speed of the rotation operation of the screw is corrected.

[0013] In the method for controlling the amount of injection foam molding of the present invention, The rotational speed correction is preferably performed by increasing the rotational speed of the screw while keeping the peripheral rotational speed value obtained by multiplying the diameter of the screw by the rotational speed within a predetermined range. [Effects of the Invention]

[0014] According to the present invention, in injection foam molding using a foamable resin material obtained by mixing a resin material with a foaming agent that decomposes when heated to generate a foamable gas, a metering control method can be provided that enables efficient generation of foamable gas and stabilization of foamable molten resin without being restricted by the combination of resin material and foaming agent. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a conceptual diagram of an injection molding machine used for injection foam molding according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing a procedure for setting the temperature of an injection cylinder according to an embodiment of the present invention. [Figure 3] FIG. 10 is a diagram showing a change in the effective length of the screw due to the backward movement of the screw. [Figure 4] FIG. 10 is a diagram illustrating rotation speed correction according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments for carrying out the present invention will be described below with reference to the drawings. Note that the following embodiments do not limit the inventions according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solutions of the inventions according to the claims. Furthermore, in the present embodiments, the scales and dimensions of each component may be exaggerated, and some components may be omitted.

[0017] (injection molding machine) First, an injection molding machine used for injection foam molding according to an embodiment of the present invention will be described with reference to Figure 1. In the following description, the injection molding machine according to an embodiment of the present invention will be based on a horizontal injection molding machine, but is not limited to this. The injection molding machine 100 shown in Figure 1 includes an injection unit 10, a temperature control unit 20, an injection drive unit 30, an injection control unit 40, and an injection mold 80.

[0018] The injection device 10 includes a cylindrical injection cylinder 11 and a screw 14 housed within the injection cylinder 11. A plurality of heating means 12, such as heaters, are arranged around the outer periphery of the injection cylinder 11, and a temperature control unit 20 controls the heating means 12 to heat the injection cylinder 11 to a predetermined temperature. During injection foam molding, the tip 11S of the injection cylinder 11 and an injection mold 80 are in contact with each other. The screw 14 is connected to an injection drive unit 30 via a connecting member 17 and a connecting rod 18. An injection control unit 40 controls the injection drive unit 30 to control the rotation and forward / backward movement of the screw 14 via the connecting rod 18 and the connecting member 17. Regarding the forward / backward movement of the screw 14, the direction toward the injection mold 80 is defined as forward F, the movement toward the forward F as forward movement, the direction away from the injection mold 80 as backward B, and the movement toward the backward B as backward movement.

[0019] The screw 14 also has a spiral flight 15 extending from the rear B toward the front F. The spiral direction and angle of the flight 15 are set relative to the rotation direction of the screw 14 so that the foamed resin material supplied from the material hopper 13 at the rear B can be rotated and transported to the front F. As shown in FIG. 1, the flight 15 is arranged in a single line at a fixed interval and a fixed angle, but this is not limited to this. For example, the interval and angle may be variable, or multiple lines may be arranged. Alternatively, multiple flights 15 may be arranged in only a portion of the screw 14. Here, with regard to the rotational movement of the screw, rotation in which the foamed resin material moves toward the front F is defined as forward rotation, and rotation in which the foamed resin material moves toward the rear B is defined as reverse rotation.

[0020] The screw 14 is conical, with its diameter gradually increasing from the rear B to the front F. In other words, the volume of the gap between the screw 14 and the injection cylinder 11 is gradually reduced from the rear B to the front F. As a result, the foamable resin material (solid) supplied from the material hopper 13 is rotationally transported toward the front F by the rotation of the screw 14 and flight 15. The reduction in volume causes compression and shear heat to act on the foamable resin material, and the synergistic effect of the heat provided by the heating means 12 causes it to gradually melt (called plasticization and melting). The range in which the foamable resin material is rotated and transported is called the transport zone, and the range in which it is plasticized and melted is called the compression zone. The foaming agent of the foamable resin material is heated in the transport zone and decomposes in the compression zone to generate foamable gas. This gas is mixed with the plasticized and melted molten resin to generate foamable molten resin. The foamable molten resin is further transported by rotation inside the screw 14 toward the front F (this range is called the melting zone), passes through the screw tip 16 equipped with a backflow prevention function, and is continuously stored at the tip of the injection cylinder 11. The injection control unit 40 controls the rotation of the screw 14 by operating the injection drive unit 30 based on a preset rotation speed of the screw 14.

[0021] As the amount of stored foamable molten resin increases, the screw 14 moves backward toward the rear B, stops rotating at a predetermined backward position, and remains at that position (called the metering completion position). The process up to this point is called the metering process, and the storage range of the foamable molten resin is called the metering zone. This backward movement of the screw 14 is limited to adjust the resin pressure and melt-kneadability of the stored foamable molten resin (called back pressure control). This resin pressure is called the back pressure value, and by maintaining the back pressure value at an appropriate value, it is possible to prevent foaming gas from being released from the foamable molten resin and stabilize the foamable molten resin. The injection control unit 40 operates the injection drive unit 30 to control the backward movement of the screw 14 based on a preset back pressure value.

[0022] The injection control unit 40 is also provided with a retraction speed measuring means for measuring the retraction speed of the retraction movement of the screw 14. For example, a position sensor is provided on the connecting rod 18, and the retraction speed of the screw 14 is calculated from the change in position of the connecting rod 18 per unit time. If the injection drive unit 30 is hydraulically driven, such as with a hydraulic cylinder, the retraction speed may be calculated by measuring the position of the hydraulic cylinder. If the injection drive unit 30 is electrically driven, combining a servomotor and a ball screw mechanism, the retraction speed may be calculated from the amount of movement of the ball screw mechanism or the amount of rotation of the servomotor.

[0023] The injection cylinder 11 is divided into a transport zone FZ, a compression zone CZ, a melting zone MZ, and a metering zone KZ, and heating means 12 are arranged corresponding to each zone of the screw 14. The cylinder tip 11S is also arranged as a nozzle zone NZ, and heating means 12 is arranged therein. The heating means 12 for each zone is connected to a temperature control unit 20, and temperature control is performed individually according to the characteristics of the foamed resin material. Details will be explained using FIG. 2.

[0024] The injection mold 80 includes a fixed mold 81 and a movable mold 82 supported by a mold clamping device (not shown). The fixed mold 81 and the movable mold 82 are clamped together to form a mold cavity 84. The mold cavity 84 and the cylinder tip 11S are connected by a resin flow path 83 equipped with an opening / closing mechanism. As the screw 14 advances, a foamable molten resin is injected into the mold cavity 84 via the resin flow path 83. The mold cavity 84 is then expanded to foam and expand the foamable molten resin (this is called mold expansion foaming). Alternatively, the foamable molten resin is injected and filled into the mold cavity 84 while foaming and expanding (this is called short-shot foaming). The opening / closing mechanism in the resin flow path 83 is provided to prevent foaming gas from being released from the foamable molten resin before injection and filling. The opening / closing mechanism may be provided not only in the resin flow path 83 but also in the cylinder tip 11S, or both in the resin flow path 83 and the cylinder tip 11S.

[0025] Here, for example, in the case of automotive interior parts, the resin material for the foamable resin material is typically a thermoplastic resin such as polypropylene (PP) resin or polyethylene (PE) resin, which is added with colorants such as black, red, or blue to adjust the color tone of the part. Various additives are also appropriately selected, such as plasticizers that impart flexibility to thermoplastic resins, nucleating agents or clarifying agents that control the crystallinity of crystalline resins, flame retardants that suppress combustion, antistatic agents that suppress static electricity buildup, lubricants that improve fluidity and mold release, weatherproofing agents and UV inhibitors that suppress degradation due to ultraviolet light, and reinforcing agents such as glass fiber or carbon fiber. Other suitable thermoplastic resins include general-purpose resins such as polypropylene (PP) resin or polyethylene (PE) resin, engineering resins such as polyamide (PA) resin or polycarbonate (PC) resin, and super-engineering resins such as polyphenylene sulfide (PPS) resin or polyether ether ketone (PEEK) resin. The thermoplastic resin and additives together are referred to as the resin material. Thermosetting resins such as phenolic (PF) resin or melamine (MF) resin may also be used instead of the thermoplastic resin.

[0026] In addition, resin pellets (foaming agent MB) in which foaming components are kneaded into a carrier resin are commercially available as foaming agents (chemical foaming agents) for foamed resin materials. These pellets can be handled in the same way as pellets of additives such as resin materials or colorants, making them convenient to use. The foaming components decompose when heated to generate a foaming gas. Examples of foaming gases include azo compounds (ADCA) that generate nitrogen gas and bicarbonates (NaHCO3) that generate carbon dioxide gas. The appropriate gas is selected depending on the resin material and product application. Furthermore, a resin with a melting point lower than the decomposition temperature of the foaming components is selected as the carrier resin, for example, to prevent the foaming components from decomposing and generating a foaming gas during the production of the foaming agent MB. For example, since the decomposition temperature of bicarbonates prepared as foaming agents is 150°C, a polyethylene resin (HDPE) with a melting point of 120-140°C is used as the carrier resin. The foaming agent MB also contains multiple regulators, such as a nucleating agent (adjusting the decomposition temperature to 200°C or higher) to adjust the number and size of foam cells and a stabilizing agent to stabilize the decomposition temperature of the foaming components. Each of these regulators has a different decomposition temperature. To ensure stable injection foam molding quality, it is necessary to properly control the decomposition temperatures of the foaming components and regulators. It has also been reported that encapsulated blowing agents, which contain volatile substances that vaporize when heated, are used in certain fields. As an exception, blowing agents are sometimes used in combination as nucleating agents in physical foam molding.

[0027] (Injection cylinder temperature setting procedure) Next, the temperature setting procedure for the injection cylinder 11 according to an embodiment of the present invention will be described with reference to FIG. 2. Here, the rotational speed of the screw 14 is expressed as a rotational peripheral speed value. The rotational peripheral speed value is the product of the screw diameter (unit: mm) and the screw rotation speed (rpm), and is treated as an index common to injection molding machines with different screw diameters. In addition, the rotational speed of the screw 14 is generally often used to set the conditions for the metering process, and it is easy to convert from the rotational speed to a rotational peripheral speed value, so it is preferable to express the rotational speed as a rotational peripheral speed value.

[0028] First, a back pressure value that prevents the release of foaming gas and stabilizes the foamable molten resin is set in the injection control unit 40. In other words, the back pressure value is set higher than the expansion pressure of the foaming gas generated by decomposition of the foaming agent. This back pressure value is used as a back pressure value that has been proven to produce good products based on past molding results. For example, in the injection foam molding of automotive interior parts, a foaming resin material consisting of a resin material (PP resin) and a foaming agent (bicarbonate) is used, and the expansion ratio is approximately 2 times in the product thickness direction. When the product weight is reduced by approximately 30 to 40% due to foam expansion, a back pressure value of 3 to 10 MPa (converted to resin pressure) is often used, so this back pressure value is used. The expansion pressure of the foaming gas generated by the foaming agent in this case is 0.3 to 0.5 MPa, and the back pressure value is set to approximately 10 to 20 times this value to ensure the stabilization of the foamable molten resin. If the back pressure value is set too high, the generated foamable gas may flow backward inside the injection cylinder 11 to the rear B side and escape from the material hopper 13 to the outside of the injection cylinder 11, resulting in a foamable molten resin with a small amount of foamable gas mixed in without being mixed with the molten resin. Even if the back pressure value is within the appropriate range, changing the back pressure value during the metering process will change the amount of foamable gas mixed in the foamable molten resin, so it is preferable to maintain the back pressure value at a constant value.

[0029] Next, the metering process is performed while maintaining the back pressure, and a correlation graph S1 of the rotational peripheral speed (horizontal axis) and the retreat speed (vertical axis) of the screw 14 is obtained, as shown in Figure 2(a). The rotational peripheral speed increases proportionally to the retreat speed. Note that this relationship between the rotational peripheral speed and the retreat speed is determined in advance, for example, from past molding results or trial molding. Here, for example, for a foaming resin material composed of a resin material (PP resin) and a foaming agent (bicarbonate), the lower limit rotational peripheral speed DN1 suitable for injection foam molding is set to 3,000, and the upper limit rotational peripheral speed DN2 is set to 15,000. From the perspective of temperature control of the foaming agent in the foaming resin material, these values ​​are slightly lower than those used in general injection molding. In other words, at rotational peripheral speeds below DN1, the rotational kinetic energy is low, resulting in insufficient plasticizing melting and rotational transport capabilities, making it difficult to produce a stable foamable molten resin. Conversely, at rotational peripheral speeds above DN2, the rotational kinetic energy becomes excessive, causing excessive decomposition of the foaming agent, resulting in unstable generation of foamable gas and making it difficult to produce a stable foamable molten resin. Therefore, a rotational peripheral speed value DN3 within the range of rotational peripheral speeds DN1 to DN2 is initially set in the injection control unit 40 as the rotational speed (or number of rotations) of the screw 14, and the rotation of the screw 14 is controlled by this. The retraction speed of the screw 14 at the rotational peripheral speed value DN3 is set to BV1.

[0030] Next, as shown in Figure 2(b), a correlation graph S2 is obtained between the transit time (horizontal axis) of the foaming resin material passing through the injection cylinder 11 from the material hopper 13 to the cylinder tip 11S and the resin temperature T (vertical axis) when the rotation of the screw 14 is controlled at a rotational peripheral speed value DN3 (recession speed BV1). The left end of the horizontal axis represents the transit time near the material hopper 13, and the right end of the horizontal axis represents the transit time near the cylinder tip 11S. The transit time and the resin temperature increase proportionally. Here, T1 is the decomposition temperature of the foaming component of the foaming agent, T2 is the melting point of the resin material (the glass transition temperature for amorphous resins), and T3 is the decomposition temperature of the nucleating agent, one of the additives contained in the foaming agent. The intersections with the correlation graph S2 are defined as the limit times (A1-A3).

[0031] When the transit time of the foamable resin material through the injection cylinder 11 exceeds the critical time A1, the foaming component of the foaming agent decomposes and foaming gas begins to be generated. When the transit time exceeds the critical time A2, the plasticization and melting of the resin material begins, and mixing of the foaming agent and molten resin begins. When the transit time exceeds the critical time A3, the nucleating agent in the foaming agent begins to decompose and gradually disappear. For example, if the foamable resin material exceeds the critical time A1 in the transport zone FZ near the material hopper 13, the generated foaming gas flows back toward the material hopper 13 and escapes from the material hopper 13 to the injection cylinder 11. As a result, the mixing of the molten resin and the foaming gas decreases, the amount of foaming gas in the foamable molten resin is insufficient, and proper foaming and expansion within the mold cavity 84 is not achieved. Furthermore, if the critical time A2 is not reached in the compression zone CZ, the plasticization and melting becomes unstable, resulting in fluctuations in the storage amount and metering time of the foamable molten resin. Furthermore, the mixing of the foaming gas and the molten resin becomes unstable, resulting in an unstable foamable molten resin. Furthermore, if the limit time A3 is exceeded in the range from the melting zone MZ to the nozzle zone NZ, the nucleating agent decomposes and disappears, significantly degrading the quality of the foamable molten resin and resulting in poor foaming, such as a decrease in the expansion ratio and a decrease in and coarsening of foam cells. Therefore, in high-quality injection foam molding, it is important to manage the passage time of the foamable resin material through the injection cylinder 11 and to manage the resin temperature of the foamable resin material appropriate for each zone of the injection cylinder 11.

[0032] Therefore, as shown in Figure 2(c), injection foam molding is characterized by controlling the heating of the injection cylinder 11 based on the thermal properties of the foaming agent. Specifically, a preheating temperature T11 is set in the transport zone FZ at which the foaming agent is heated to a temperature lower than the decomposition temperature T1 of the foaming agent and does not generate foaming gas as the foaming resin material passes through the transport zone FZ. In other words, by setting the preheating temperature T11 in the transport zone FZ lower than the decomposition temperature T1 of the foaming agent, the critical time A1 can be adjusted longer, thereby reliably suppressing the generation of foaming gas. The transit time is also related to the molding cycle. As the molding cycle becomes longer, the transit time, including the residence time, becomes longer, so the preheating temperature T11 is set lower. As the molding cycle becomes shorter, the transit time is also shorter, so the preheating temperature T11 can be set higher. Note that if the carrier resin of the foaming agent MB completely melts in the transport zone FZ, the rotational transport capacity of the foaming resin material decreases, which can cause the metering process to become unstable. Therefore, it is more preferable to adjust the transit time by adjusting the preliminary temperature T11 so that the carrier resin does not melt in the transport zone FZ.

[0033] Next, the plasticization temperature T21 is set in the compression zone CZ, where the foaming agent is heated to its decomposition temperature, efficiently generating the foamable gas, and simultaneously efficiently plasticizing and melting the resin material. In this compression zone CZ, the foamable molten resin is generated by mixing the plasticized melt with the foamable gas. To achieve this, the plasticization temperature T21 is set within the range of the critical time A1 and critical time A2, satisfying both conditions. As with the preliminary temperature T11, it is preferable to fine-tune the temperature according to the molding cycle. Furthermore, since the compression zone CZ is subject to shear heat generated by the rotation of the screw 14, it is more preferable to set the plasticization temperature T21 taking shear heat into consideration.

[0034] Finally, in the nozzle zone NZ from the melting zone MZ, a holding temperature T31 for stably holding the foaming molten resin is set. For example, the holding temperature T31 is set lower than the decomposition temperature T3 of the nucleating agent contained in the foaming agent. Here too, similar to the preliminary temperature T11 and the plasticizing temperature T21, it is preferable to finely adjust according to the molding cycle. Also, since the foaming gas such as carbon dioxide gas or nitrogen gas is an inert gas, an incidental effect of preventing oxidation of the resin material and preventing resin burning can be expected.

[0035] (Change in effective screw length) Next, the state in which the effective screw length changes due to the backward movement of the screw 14 during the metering process will be described using FIG. 3. The effective screw length indicates the distance from the material hopper 13 to the compression zone CZ, is related to the passing time of the foamed resin material in the transport zone FZ, and greatly affects the quality of preheating of the foamed resin material. Before the injection process ends and before the start of the metering process, as shown in FIG. 3(a), the screw 14 is at the forward position on the F side, and the effective screw length YL at this time shows the maximum value. When the metering process starts, as shown in FIG. 3(b), the storage amount of the foaming molten resin in the metering zone KZ gradually increases, and the screw 14 moves backward. For example, if the backward movement amount of the screw 14 is L1, the effective screw length YL1 becomes shorter by the amount of the backward movement L1 (YL1 = YL - L1, YL1 < YL). As the metering completion position increases, the backward movement amount of the screw 14 increases. As shown in FIG. 3(c), the effective screw length YL2 at the maximum metering completion position (backward movement amount L2) becomes the minimum (YL2 = YL - L2, YL2 < YL1 < YL).

[0036] The screw effective length YL is important for the process of preheating the foamable resin material supplied from the material hopper 13 to the appropriate temperature before transporting it to the compression zone CZ, where it is efficiently plasticized and melted, foamable gas is generated, and the foamable molten resin is produced by mixing the foamable gas with the molten resin. As the screw effective length YL shortens (YL ⇒ YL1 ⇒ YL2), the previously achieved appropriate preheating gradually becomes impossible, resulting in a decrease in the efficiency of each process from plasticization and melting in the compression zone CZ to the production of the foamable molten resin. As a result, even if the initial rotational speed of the screw 14 is maintained, the retreat speed of the screw 14 gradually decreases. This decreases the retreat speed of the screw 14, increasing the time it takes for the foamable resin material to pass through the injection cylinder 11 and significantly changing the timing at which the foaming agent decomposes and produces the foamable gas. Alternatively, the balance between plasticization and melting and the production of the foamable gas is disrupted, significantly reducing the efficiency of the production of the foamable molten resin. Furthermore, important additives such as nucleating agents will disappear, making the foamable molten resin unstable and significantly reducing the foaming quality of the injection foam molding. Therefore, the retreat speed of the screw 13 is measured, and when it falls below a preset limit speed, the rotational speed of the rotational movement of the screw 14 is corrected, so that the passage time of the foamable molten resin inside the injection cylinder 11 is returned to the initial state, and the timing of generation of the foamable gas is restored to normal. This will be explained in more detail using Figure 4.

[0037] (Rotational speed correction) Next, the rotational speed correction of the rotational movement of the screw 14 according to an embodiment of the present invention will be described with reference to FIG. 4. First, the retraction speed of the screw 14 during the metering process is measured by the injection control unit 40, and a correlation graph S3 of the retraction position (horizontal axis) and retraction speed (vertical axis) of the screw 14 is obtained, as shown in FIG. 4(a). The screw 14 retracts from the start of metering at the left end of the horizontal axis to the end of metering at the right end of the horizontal axis, and as shown in FIG. 3, the effective screw length YL gradually shortens (YL ⇒ YL1 ⇒ YL2). As the effective screw length YL decreases, the preheating effect of the foamable resin material in the transport zone FZ decreases. As a result, the efficiency of each process from plasticization and melting in the compression zone CZ to the generation of the foamable molten resin decreases, and the retraction speed of the screw 14 gradually decreases as the screw 14 retracts.

[0038] Due to this decrease in the screw retraction speed, the transit time of the foamed resin material in the injection cylinder 11 gradually increases, as shown in FIG. 4(b) (correlation graph S4). The retraction position B1 of the screw 14 where this increased transit time exceeds the limit time A1 is determined. Similarly, the retraction position B2 of the screw 14 where the limit time A2 is exceeded is determined. Here, by previously organizing the correlation between the retraction speed of the screw 14 and the transit time, the retraction positions (B1, B2) of the screw 14 can be determined from the measurement results of the retraction speed of the screw 14, as shown in FIG. 4(a). Then, the retraction speed of the screw 14 corresponding to the retraction positions (B1, B2) of the screw 14 is set in the injection control unit 40 as the limit speeds (C1, C2).

[0039] When the retreat speed of the screw 14 falls below the limit speed (C1, C2), the rotational speed of the screw 14 is corrected as shown in Figure 4(c). The range from the start of metering to the retreat position B1 is set to the initially set rotational speed N1 of the screw 14. As mentioned above, the rotational speed of the screw 14 may be determined using either the rotational speed or the rotational peripheral speed. In the range from the retreat position B1 to the retreat position B2, which falls below the limit speed C1, the rotational speed N2, which is faster than the rotational speed N1 (N2 > N1), is set. Increasing the rotational speed (N1 ⇒ N2) increases the rotational kinetic energy and the amount of shear heat generated. This restores the efficiency of each process, from plasticization and melting to molding of the foamable molten resin. Furthermore, the increased rotational transport capacity restores the increased storage of the foamable molten resin. As a result, the retreat speed of the screw 14 is restored, and the timing of foamable gas generation is stabilized. Here, the rotational peripheral speed N2 to be corrected is set to a predetermined range (lower limit rotational peripheral speed DN1=3000, upper limit rotational peripheral speed DN2=15000 suitable for injection foam molding).

[0040] Similarly, in the range from retraction position B2 to the end of metering, where the speed drops below the limit speed C2, a rotational speed N3 (N3 > N2) faster than the rotational speed N2 is set. This restores a stable balance between the plasticization of the resin material and the generation of foamable gas, restoring the efficient generation of the foamable molten resin. As a result, the stability of the foamable molten resin is restored. Note that in FIG. 4, the rotational speed correction for the rotational operation of the screw 14 is performed by calculating the retraction position (B1, B2) and the limit speed (C1, C2) from the limit time (A1, A2) and correcting the rotational speed (N2, N3). However, this is not limited to this. For example, the rotational speed correction may be performed by adding the limit time A3 to determine the retraction position B3 and the limit speed C3, and then adding the rotational speed N4. Alternatively, the rotational speed to be corrected may be increased, or conversely, decreased. The passage time of the foamable resin material through the injection cylinder 11 is appropriately adjusted to restore the initial setting. Here, the rotational speed N3 to be corrected is set to a predetermined range (lower limit rotational speed DN1=3000, upper limit rotational speed DN2=15000 suitable for injection foam molding).

[0041] Here, the retreat speed of the screw 14 can also be changed by changing the back pressure setting. However, the amount of foaming gas dissolved in the foamable molten resin varies depending on the resin pressure. Changing the back pressure value changes the resin pressure, which in turn changes the amount of foaming gas dissolved, causing the foamable molten resin to lose stability, so adjusting the retreat speed of the screw 14 by changing the back pressure value is not preferable.

[0042] [effect] Thus, in injection foam molding using a foamable resin material that generates foamable gas when heated, a preheating temperature T11 at which no foamable gas is generated is set in the transport zone FZ as the foamable resin material passes through, a plasticizing temperature T21 at which foamable gas is generated is set in the compression zone CZ as the foamable resin material passes through, a holding temperature T31 at which the foamable molten resin is stabilized is set from the melting zone MZ to the nozzle zone NZ, and the rotational speed of the screw 14 is corrected when the retreat speed of the screw 14 falls below a preset limit speed (C1 to C3). This makes it possible to efficiently generate foamable gas and stabilize the foamable molten resin without being restricted by the combination of resin material and foaming agent, and to steadily supply high-quality injection foam-molded products.

[0043] Although the preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the scope described in the above-described embodiments. Various modifications and improvements can be made to the above-described embodiments. [Explanation of symbols]

[0044] 100 injection molding machine 10 Injection device 11 Injection cylinder 11S Cylinder tip 12 Heating means 13 Material hopper 14 screws 15 flights 16 Screw tip 17 Connecting member 18 Connecting rod 20 Temperature control unit 30 Injection drive unit 40 Injection control unit 80 Injection mold 81 Fixed mold 82 Movable mold 83 Resin flow path 84 mold cavity F forward B Back FZ Transportation Zone CZ Compression Zone MZ Melting Zone KZ Weighing Zone NZ Nozzle Zone S1~S4 correlation graph DN1, DN2, DN3 Rotational peripheral speed values BV1 Retraction speed T Resin temperature T1 Decomposition temperature of foaming ingredients T2 Melting point of resin material T3 Decomposition temperature of nucleating agent A1~A3 Time Limit T11 Preheat temperature T21 Plasticizing temperature T31 holding temperature YL, YL1, YL2 screw effective length L1, L2 backward movement amount B1~B3 Backward operation position C1~C3 Limit speed N1~N4 rotation speed

Claims

1. A method for controlling the amount of foam injection molding, comprising the steps of: supplying a foaming resin material containing a foaming agent that generates a foaming gas when heated from the rear of an injection cylinder; plasticizing the foaming resin material by rotating and retracting a screw; storing the foaming resin as a foamable molten resin in the front of the injection cylinder; and injecting the foamable molten resin into a mold cavity to foam and expand it; a screw retreat speed measuring means for measuring the retreat speed of the screw; The injection cylinder is divided into a transport zone, a compression zone, a melting zone, a storage zone, and a nozzle zone from the rear to the front, a preheating temperature at which the foamable gas is not generated is set in the transport zone, a plasticizing temperature at which the foamable gas is generated is set in the compression zone, and a holding temperature at which the foamable molten resin is stabilized is set from the melting zone to the nozzle zone, A metering control method for injection foam molding, characterized in that when the retreat speed of the screw falls below a preset first limit speed, a first rotation speed correction is performed to increase the rotation speed of the rotation operation of the screw from the previous N1 to a preset N2 (N2 > N1).

2. 2. The method for controlling injection foam molding according to claim 1, wherein, if the retreat speed of the screw falls below a preset second limit speed after the first rotational speed correction, a second rotational speed correction is performed to increase the rotational speed of the screw rotation operation from N2 to a preset N3 (N3 > N2).

3. 3. The method for controlling injection foam molding according to claim 1, wherein the first rotational speed correction increases the rotational speed of the screw while the product of the diameter of the screw and the rotational speed of the screw is within a predetermined range.

4. A method for controlling the amount of foam injection molding, comprising the steps of: supplying a foaming resin material containing a foaming agent that generates a foaming gas when heated from the rear of an injection cylinder; plasticizing the foaming resin material by rotating and retracting a screw; storing the foaming resin as a foamable molten resin in the front of the injection cylinder; and injecting the foamable molten resin into a mold cavity to foam and expand it; a screw retreat speed measuring means for measuring the retreat speed of the screw; The injection cylinder is divided into a transport zone, a compression zone, a melting zone, a storage zone, and a nozzle zone from the rear to the front, a preheating temperature at which the foamable gas is not generated is set in the transport zone, a plasticizing temperature at which the foamable gas is generated is set in the compression zone, and a holding temperature at which the foamable molten resin is stabilized is set from the melting zone to the nozzle zone, When the retreat speed of the screw falls below a preset limit speed, a rotation speed correction is performed for the rotational operation of the screw; A metering control method for injection foam molding, characterized in that the rotational speed correction increases the rotational speed of the screw while the rotational peripheral speed value obtained by multiplying the diameter of the screw and the rotational speed is within a predetermined range.

5. An injection molding machine in which a foamable resin material containing a foaming agent that generates a foamable gas when heated is supplied from the rear of an injection cylinder, the foamable resin material is plasticized by the rotation and retreat of a screw, and stored as a foamable molten resin in the front of the injection cylinder, and the foamable molten resin is injected into a mold cavity to fill and foam and expand it, a temperature control unit that controls heating of the injection cylinder to a predetermined temperature by operating a heating means provided on the outer periphery of the injection cylinder; an injection control unit having a screw retreat speed measuring means for measuring the retreat speed of the screw and controlling the rotational movement and forward / backward movement of the screw, The injection cylinder can be divided into a transport zone, a compression zone, a melting zone, a storage zone, and a nozzle zone from rear to front. The temperature control unit In the transport zone, a preheating temperature at which the foaming gas is not generated is set, in the compression zone, a plasticization temperature at which the foaming gas is generated is set, and in the melting zone to the nozzle zone, a holding temperature at which the foamable molten resin is stabilized is set, The injection control unit an injection molding machine characterized in that, when the retreat speed of the screw falls below a preset first limit speed, a first rotational speed correction is performed to increase the rotational speed of the rotational operation of the screw from the previous N1 to a preset N2 (N2 > N1).

6. An injection molding machine in which a foamable resin material containing a foaming agent that generates a foamable gas when heated is supplied from the rear of an injection cylinder, the foamable resin material is plasticized by the rotation and retreat of a screw, and stored as a foamable molten resin in the front of the injection cylinder, and the foamable molten resin is injected into a mold cavity to fill and foam and expand it, a temperature control unit that controls heating of the injection cylinder to a predetermined temperature by operating a heating means provided on the outer periphery of the injection cylinder; an injection control unit having a screw retreat speed measuring means for measuring the retreat speed of the screw and controlling the rotational movement and forward / backward movement of the screw, The injection cylinder can be divided into a transport zone, a compression zone, a melting zone, a storage zone, and a nozzle zone from rear to front. The temperature control unit In the transport zone, a preheating temperature at which the foaming gas is not generated is set, in the compression zone, a plasticization temperature at which the foaming gas is generated is set, and in the melting zone to the nozzle zone, a holding temperature at which the foamable molten resin is stabilized is set, The injection control unit When the retreat speed of the screw falls below a preset limit speed, a rotation speed correction is performed for the rotational operation of the screw; The injection molding machine, characterized in that the rotational speed correction increases the rotational speed of the screw while the rotational peripheral speed value obtained by multiplying the diameter of the screw and the rotational speed of the screw is within a predetermined range.

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