JP6560470B1 - Foam molded body manufacturing apparatus, foam molded body manufacturing method, and foam molded body manufacturing apparatus screw - Google Patents

Abstract

An object of the present invention is to realize good foam molding in which fine cells are formed inside a molded body even when the apparatus for foam molding by constantly pressurizing molten resin with a physical foaming agent at a constant pressure in the starvation zone is enlarged. An apparatus for producing a foamed molded product in which the foaming performance of the molded product does not deteriorate is provided. An apparatus 1 for producing a foam molded article has a plasticizing zone 40 in which a thermoplastic resin is plasticized and melted to become a molten resin, and a starvation zone 16 in which the molten resin is starved. A cylinder 10 provided with a physical foaming agent introduction port 2, a screw 20 disposed in the cylinder 10 so as to be rotatable about an axis and movable back and forth in the axial direction, and a physical foaming agent at a constant pressure. The pressure adjusting container 5 is introduced into the starvation zone 16 through the inlet 2 and keeps the starvation zone 16 at a constant pressure. The screw 20 has a multi-flight structure in the starvation zone 16. [Selection] Figure 1

Description

  The present invention relates to an apparatus for manufacturing a foam molded body, a method for manufacturing a foam molded body, and a screw for a foam molded body manufacturing apparatus.

  As a foam injection molding method using nitrogen or carbon dioxide as a physical foaming agent, there is a method in which a high-pressure fluid serving as a supercritical fluid is sheared and kneaded with a molten resin. On the other hand, Patent Document 1 discloses a method of forming a foamed molded article using nitrogen, carbon dioxide or the like having a relatively low pressure without requiring a supercritical fluid. According to this method, it is possible to form fine foam cells in a molded body by a simple process using a low-pressure physical foaming agent without using a special high-pressure apparatus.

  FIG. 10 is a reference schematic configuration diagram illustrating an example of a molding machine that performs foam molding using a relatively low-pressure physical foaming agent. In the molding machine 100, the resin pellets supplied from the hopper 130 are given preheat in the feed zone 112, and are melted and compressed through the compression zone 113 and the metering zone 114. Then, the supply amount of the molten resin downstream is limited in the seal zone 115, and the density of the molten resin is reduced in the starvation zone 116. In the starvation zone 116, the relatively low-pressure physical foaming agent introduced through the introduction port 102 stays in contact with the low-density molten resin and penetrates (dissolves) into the molten resin. . The molten resin infiltrated with the physical foaming agent is re-kneaded through the recompression zone 117 and the re-metering zone 118 so that the dissolved amount of the physical foaming agent is stabilized. The recompressed molten resin moves to the front of the screw 120 via the check ring 119. At this time, the internal pressure of the molten resin is controlled as a screw back pressure.

Japanese Patent No. 6139038

  Incidentally, in the molding machine 100 shown in FIG. 10, the screw 120 is a single flight in the starvation zone 116. When the molding machine 100 is made larger in order to mold a relatively large part such as an automobile part, that is, when the outer diameter (screw diameter) of the screw 120 is made larger, the depth of the screw flight 121 is increased. As the depth increases, the absolute amount of molten resin deposited between the screw flights 121 in the screw 120 increases. In this case, since the increase rate of the surface area of the molten resin is small with respect to the increase rate of the volume of the molten resin, the contact area between the physical foaming agent and the molten resin per unit volume with respect to the molten resin decreases. As a result, the time required for the physical foaming agent to penetrate the molten resin is insufficient, and there is a possibility that the physical foaming agent may not sufficiently permeate. Such a problem becomes a factor which reduces the foaming performance of a molded object. Note that when the amount of the molten resin supplied to the starvation zone 116 is decreased and the amount of the molten resin staying between the screw flights 121 is reduced to avoid the above problem, the cylinder 110 in the starvation zone 116 is used. Due to the decrease in the frictional resistance between the molten resin and the molten resin, there arises a problem that the moving speed of the molten resin in the starvation zone 116 decreases and the plasticization time becomes long. This is not preferable because it causes problems such as a long molding cycle time and difficulty in resin replacement.

  Here, the maximum amount of the molten resin that moves as the screw 120 rotates once will be described with reference to FIG. In the measurement zone 114, the maximum amount of resin that moves downstream as the screw 120 rotates once is the volume A per one circumference around the axis between adjacent screw flights 121. In the starvation zone 116, the maximum amount of resin that moves downstream as the screw 120 rotates once is the volume B per one circumference around the axis between adjacent screw flights 121. At this time, when the difference between the volume A and the volume B is increased, that is, when the volume B is increased with respect to the volume A, the starvation zone 116 is likely to be starved. The “starvation state” refers to a state in which the molten resin is not filled in the starvation zone 116 and is not filled, or a state in which the density of the molten resin is reduced. However, if the difference between the volume A and the volume B becomes too large, the amount of the molten resin staying there is significantly reduced with respect to the volume of the starvation zone 116, and the amount of physical foaming agent staying in the starvation zone 116 is increased. End up. In this case, a large amount of undissolved physical foaming agent (surplus gas) is entrained in the recompression zone 117 (see FIG. 10), thereby generating bubble breakage (large-diameter voids) in the molded body. There was a possibility that the foaming performance of the would be reduced.

  The present invention has been made in view of the above circumstances, and even when the apparatus for performing foam molding by constantly pressing a molten resin with a physical foaming agent at a constant pressure in the starvation zone is enlarged, that is, a screw. Even when the diameter is larger, it is possible to realize good foam molding in which fine cells are formed inside the molded body, and a foam molded body manufacturing apparatus that does not deteriorate the foaming performance of the molded body, and the foam molded body It aims at providing the manufacturing method of. Moreover, it aims at providing the screw for this foaming molding manufacturing apparatus.

  In order to solve the above-mentioned problems, an apparatus for producing a foamed molded article of the present invention has a plasticization zone in which a thermoplastic resin is plasticized and melted to become a molten resin, and a starvation zone in which the molten resin is in a starved state. A cylinder provided with an introduction port of a physical foaming agent to the starvation zone, a screw disposed inside the cylinder so as to be rotatable about an axis and movable back and forth in the axial direction, and the physical at a constant pressure. A foaming agent is introduced into the starvation zone through the inlet, and a pressure regulating container that constantly maintains the starvation zone at the constant pressure, and the screw has a multi-flight structure in the starvation zone. It is characterized by being.

  Further, the method for producing a foamed molded article of the present invention includes a plasticizing zone and a starvation zone, a cylinder provided with an introduction port of a physical foaming agent to the starvation zone, and an inside of the cylinder around the axis. And a pressure regulating container that introduces the screw having a multi-flight flight structure in the starvation zone and the physical foaming agent into the starvation zone through the introduction port. In the plasticizing zone, the production method comprises a step of plasticizing and melting a thermoplastic resin to obtain a molten resin, and introducing the physical foaming agent at a constant pressure into the starvation zone, At the constant pressure, and in the starvation zone, the molten resin transfer path is divided by the multi-strip flight structure to make each of the starved state, Contacting a serial molten resin and the physical foaming agent of the constant pressure, characterized by a step of molding the molten resin in contact with a physical blowing agent of the constant pressure in the foam molded article.

  Further, the screw for producing a foamed molded article of the present invention includes a cylinder having a plasticizing zone in which a thermoplastic resin is plasticized and melted to become a molten resin, and a starvation zone in which the molten resin is in a starved state, and is physically foamed. An agent is introduced into the starvation zone, and the screw disposed in the cylinder is used in a foamed molded product manufacturing apparatus in which the starvation zone is constantly maintained at a constant pressure. It is characterized by becoming.

According to such a configuration, even when the molten resin is constantly pressurized with a physical foaming agent at a constant pressure in the starvation zone and the apparatus for performing foam molding is made larger, that is, even when the screw diameter is made larger. Since the flight structure in the starvation zone is a multi-flight flight structure, the same amount of molten resin as in the case of single flight is divided and transferred. At this time, since the volume between adjacent screw flights does not become excessively large, the amount of molten resin deposited there can be reduced. For this reason, while the fall of the contact area of a physical foaming agent and molten resin is suppressed, the osmosis | permeation time to the molten resin of a physical foaming agent is ensured. Thereby, favorable foam molding in which fine cells are formed inside the foam molded article can be realized, and deterioration of the foaming performance of the foam molded article can be suppressed.
In other words, in a manufacturing apparatus (manufacturing method) that pressurizes the starvation zone with a relatively low-pressure physical foaming agent, even if the apparatus is larger, that is, when the screw diameter is larger, the flight structure in the starvation zone is Due to the multi-strip flight structure, the same amount of molten resin as in the case of single flight is divided and transferred. At this time, since the volume between adjacent screw flights does not become excessively large, the amount of molten resin deposited there can be reduced. For this reason, while the fall of the contact area of a physical foaming agent and molten resin is suppressed, the osmosis | permeation time to the molten resin of a physical foaming agent is ensured. Thereby, it is possible to realize good foam molding without lowering the foaming performance of the molded body, and it is possible to stably form fine foam cells inside the molded body.

Also, in the configuration of the present invention, the multi-strip flight structure of the screw, the volume per one revolution about the axis of the adjacent screw flights, characterized in that has a 5 cm ³ or more 100 cm ³ or less.

According to this structure, since the volume of the axis per one rotation between adjacent screw flights it has a 5 cm ³ 100 cm ³ of the hunger zone, in hunger zones, while maintaining the starved, the molten resin While the ability to supply downstream is maintained, the fall of the penetration efficiency of the physical foaming agent by the excessive amount of resin depositing between adjacent screw flights is suppressed. Thereby, the enlargement of the foam cell size in a molded object, generation | occurrence | production of a bubble breakage, etc. can be suppressed more reliably, and a molded object with a favorable foaming state can be obtained.

  Further, in the above-described configuration of the present invention, the plasticizing zone is located upstream of the starvation zone in the flow direction of the molten resin and is compressed by a mechanism that increases the flow resistance of the molten resin. The volume per axis around the adjacent screw flights in the measuring zone is defined as volume A, and the volume per axis around the adjacent screw flights in the starvation zone is When a volume obtained by multiplying the number of screw flights in the starvation zone is defined as a volume B, a value obtained by dividing the volume A by the volume B is 0.1 or more and 1.0 or less.

  According to such a configuration, since the ratio A / B of the volume A and the volume B is 0.1 to 1.0, the physical foaming agent is suppressed from being excessive in the starvation zone, and It is possible to suppress the occurrence of vent-up, that is, the phenomenon that the molten resin swells from the inlet of the starvation zone. Thereby, generation | occurrence | production of the bubble breakage in a molded object can be suppressed more reliably, while a molded object with a favorable foaming state can be obtained, and the productivity of a molded object can be improved more.

  According to the present invention, even when the apparatus for performing foam molding by pressurizing the molten resin with a constant pressure physical foaming agent in the starvation zone is made larger, that is, even when the screw diameter is larger, foam molding is performed. Good foam molding in which fine cells are formed inside the body can be realized, and deterioration of foaming performance of the foam molded body can be suppressed.

It is a schematic block diagram which shows the manufacturing apparatus of the foaming molding which concerns on embodiment of this invention. It is a flowchart which shows the manufacturing method of a foaming molding similarly. It is the schematic which shows the whole screw same as the above. FIG. 2 is a schematic view showing a part of the screw and for explaining the dimensions of the screw. FIG. 3 is a schematic diagram showing a part of a screw and explaining a volume per one rotation around an axis between adjacent screw flights. It is the schematic which shows a part of 2 double flight structure part of the screw used for the manufacturing apparatus of the foaming molding which concerns on embodiment of this invention. It is a schematic block diagram which shows the modification of the manufacturing apparatus of the foaming molding which concerns on embodiment of this invention. It is the schematic which shows a part of 3 thread flight structure part of a screw same as the above. It is a figure which shows the conditions and result of evaluation performed using the manufacturing apparatus of the foaming molding which concerns on embodiment of this invention. It is a reference schematic block diagram for showing a molding machine and explaining a subject. It is the schematic which shows a part of screw similarly.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the present embodiment, a foamed molded product is manufactured using the manufacturing apparatus 1 shown in FIG. The manufacturing apparatus 1 mainly includes a plasticizing cylinder (cylinder) 10, a plasticizing screw (screw) 20 disposed inside the cylinder 10 so as to be rotatable about an axis and movable back and forth in the axial direction, and a physical foaming agent A cylinder (physical foaming agent supply mechanism) 50 for supplying the cylinder 10 to the cylinder 10, a mold clamping unit (not shown) provided with a mold, and a control device (not shown) for controlling the operation of the cylinder 10 and the mold clamping unit. )).
In the cylinder 10, the plasticized and melted molten resin flows from the right hand to the left hand in FIG. Hereinafter, in the cylinder 10, the right hand in FIG. 1 is referred to as “upstream” or “rear”, and the left hand in FIG. 1 is referred to as “downstream” or “front”. In the present embodiment, the manufacturing apparatus 1 is an injection molding apparatus (foaming injection molding machine), but the manufacturing apparatus 1 may be, for example, an extrusion molding apparatus.

  In the manufacturing apparatus 1, the resin pellets are plasticized and melted by the rotation of the screw 20 in the cylinder 10, and the molten resin is sent to the front side in the cylinder 10. In addition, the molten resin is sent to the front side in the cylinder 10, and the screw 20 moves rearward to measure the molten resin. Further, the screw 20 moves forward at the time of injection.

  The cylinder 10 has a plasticizing zone 40 provided on the upstream side and a starvation zone 16 provided on the downstream side. The plasticizing zone 40 is a zone in which a thermoplastic resin is plasticized and melted to become a molten resin. The starvation zone 16 is a zone where the molten resin is starved. The “starvation state” refers to a state in which the molten resin does not fill the starvation zone 16 and is not full, or a state in which the density of the molten resin is reduced. Accordingly, a space other than the portion occupied by the molten resin may exist in the starvation zone 16.

The cylinder 10 includes a feed zone 12, a compression zone 13, a metering zone 14, a seal zone 15, a starvation zone 16, a recompression zone 17, and a remetering zone 18 in order from the upstream side to the downstream side. have. The feed zone 12, the compression zone 13 and the metering zone 14 constitute a plasticizing zone 40. The feed zone 12 is a zone where residual heat is applied to the pellets of the thermoplastic resin. The compression zone 13 is a zone in which the thermoplastic resin is shear kneaded and plasticized and melted, and the molten resin is compressed. The metering zone 14 is a zone where the density of the compressed molten resin is kept constant. The seal zone 15 is a zone where the supply amount of the molten resin downstream is limited. The recompression zone 17 is a zone where the molten resin is recompressed. The re-metering zone 18 is a zone where the molten resin is metered.
In addition, although illustration is abbreviate | omitted, between the seal zone 15 and the starvation zone 16, you may provide further the zone which adjusts the moving speed of molten resin, and the zone where the flight structure which kneads molten resin was provided. .

  The cylinder 10 is provided with an inlet 2 as an opening for introducing a physical foaming agent into the starvation zone 16. The inlet 2 is connected to a pressure regulating container 5 described later. A cylinder 50 is connected to the pressure regulating container 5 by a pipe 54 via a pressure reducing valve 51 and a pressure gauge 52. The cylinder 50 supplies a physical foaming agent into the cylinder 10 via the pressure regulating container 5.

With reference to the flowchart shown in FIG. 2, the manufacturing method of the foaming molding of this Embodiment is demonstrated.
(1) Plasticizing and melting a thermoplastic resin.
First, in the plasticizing zone 40 of the cylinder 10, the thermoplastic resin is plasticized and melted to obtain a molten resin (step S1 in FIG. 2). As the thermoplastic resin, various resins can be used depending on the intended heat resistance and use of the molded body. Specifically, for example, polypropylene, polymethyl methacrylate, polyamide, polyethylene, polycarbonate, polybutylene terephthalate, amorphous polyolefin, polyetherimide, polyethylene terephthalate, polyether ether ketone, ABS resin (acrylonitrile / butadiene / styrene copolymer resin) , Thermoplastic resins such as polyphenylene sulfide, polyamideimide, polylactic acid, polycaprolactone, and composite materials thereof can be used. In particular, a crystalline resin is desirable because it easily forms fine cells. These thermoplastic resins may be used alone or in combination of two or more. Moreover, what knead | mixed various inorganic fillers, such as glass fiber, a talc, a carbon fiber, and ceramics, and organic fillers, such as a cellulose nanofiber, a cellulose, and a wood powder, can also be used for these thermoplastic resins. The thermoplastic resin is preferably mixed with an inorganic filler that functions as a foam nucleating agent, an organic filler, and an additive that increases the melt tension. By mixing these, the foamed cell can be miniaturized. Moreover, the thermoplastic resin may contain other general-purpose various additives as required.

  In the cylinder 10 in which the screw 20 is provided, the thermoplastic resin is plasticized and melted. A band heater (not shown) is disposed on the outer wall surface of the cylinder 10, so that the cylinder 10 is heated, and shear heat generated by the rotation of the screw 20 is further applied, so that the thermoplastic resin is plasticized and melted. It has become.

(2) Maintain the pressure of the starvation zone.
Next, a physical foaming agent having a constant pressure is supplied to the pressure regulating container 5, and a pressurized fluid having a constant pressure is introduced from the pressure regulating container 5 to the starvation zone 16 to keep the starvation zone 16 at the constant pressure (FIG. 2 step S2).

  A pressurized fluid is used as the physical foaming agent. In the present embodiment, “fluid” means any of liquid, gas, and supercritical fluid. The physical foaming agent is preferably carbon dioxide, nitrogen or the like from the viewpoint of cost and environmental load. Since the pressure of the physical foaming agent of the present embodiment is relatively low, for example, the pressure is reduced to a constant pressure from the cylinder 50 storing a fluid such as a nitrogen cylinder, a carbon dioxide cylinder, and an air cylinder by the pressure reducing valve 51. The removed fluid can be used. In this case, since the booster is not necessary, the cost of the entire manufacturing apparatus can be reduced. If necessary, a fluid whose pressure has been increased to a predetermined pressure may be used as the physical foaming agent. For example, when nitrogen is used as the physical foaming agent, the physical foaming agent can be generated by the following method. First, nitrogen is purified through a nitrogen separation membrane while compressing atmospheric air with a compressor. Next, the purified nitrogen is pressurized to a predetermined pressure using a booster pump, a syringe pump or the like to generate a physical foaming agent.

The pressure of the physical foaming agent introduced into the starvation zone 16 is constant, and the pressure of the starvation zone 16 is maintained at the same constant pressure as the physical foaming agent introduced. The pressure of the physical foaming agent is preferably 0.5 MPa to 12 MPa, more preferably 1 MPa to 10 MPa, and even more preferably 1 MPa to 8 MPa. Although the optimum pressure differs depending on the type of the molten resin, by setting the pressure of the physical foaming agent to 1 MPa or more, an amount of the physical foaming agent necessary for foaming can be infiltrated into the molten resin, and the pressure is 12 MPa or less. By doing, the heat resistance of a foaming molding can be improved. If the pressure is higher than 12 MPa (high pressure), the foam cell itself is in a high pressure state, and if the foam molding is heated to a high temperature, the phenomenon of post-swelling occurs, which reduces the heat resistance of the foam molding. To do. On the other hand, when foaming is performed at a pressure of 12 MPa or less (low pressure), the occurrence of such a phenomenon is suppressed, and the heat resistance of the foamed molded product is improved.
The pressure of the physical foaming agent that pressurizes the molten resin is “constant” means that the fluctuation range of the pressure with respect to the predetermined pressure is preferably within ± 20%, more preferably within ± 10%. . The pressure in the starvation zone 16 is measured by, for example, a pressure sensor (not shown) provided at a position facing the inlet 2 of the cylinder 10.

  A physical foaming agent is supplied from the cylinder 50 to the starvation zone 16 through the pressure regulating container 5 and the inlet 2. The physical foaming agent is reduced to a predetermined pressure using the pressure reducing valve 51 and then introduced into the starvation zone 16 from the inlet 2 without passing through a pressure increasing device or the like. In the present embodiment, the introduction amount and introduction time of the physical foaming agent introduced into the cylinder 10 are not controlled. Therefore, a mechanism for controlling them, for example, a drive valve using a check valve, a solenoid valve or the like is unnecessary, and the introduction port 2 does not have a drive valve and is always open. In the present embodiment, the physical foaming agent supplied from the cylinder 50 is maintained at a constant physical foaming agent pressure from the pressure reducing valve 51 through the pressure regulating container 5 to the starvation zone 16 in the cylinder 10.

  Further, the physical foaming agent introduction port 2 has a larger inner diameter than the physical foaming agent introduction port of the conventional manufacturing apparatus. For this reason, even a relatively low-pressure physical foaming agent is efficiently introduced into the cylinder 10. Further, even when a part of the molten resin comes into contact with the inlet 2 and solidifies, it functions as an inlet without being completely blocked because the inner diameter is large. For example, when the inner diameter of the cylinder 10 is large, that is, when the outer diameter of the cylinder 10 is large, the inner diameter of the introduction port 2 can be easily increased. On the other hand, if the inner diameter of the introduction port 2 is too large, the molten resin may stay and cause molding defects, and the pressure control container 5 connected to the introduction port 2 may be enlarged to increase the cost of the entire apparatus. End up. Specifically, the inner diameter of the introduction port 2 is preferably 20% to 100% of the inner diameter of the cylinder 10, and more preferably 30% to 80%. Alternatively, the inner diameter of the introduction port 2 does not depend on the inner diameter of the cylinder 10 and is preferably 3 mm to 150 mm, more preferably 5 mm to 100 mm. In addition, these internal diameters point out the diameter of a short diameter side, when the inlet 2 is a long hole or an elliptical hole.

  Next, the pressure adjustment container 5 (introduction speed adjustment container) connected to the introduction port 2 will be described. The pressure adjusting container 5 has a function of keeping the pressure of the physical foaming agent and the pressure of the starvation zone 16 in the cylinder 10 at the same constant pressure and maintaining the starvation zone 16 at the constant pressure. For example, when a large amount of the physical foaming agent is consumed in the starvation zone 16, the supply of the physical foaming agent may not be in time, and the pressure in the starvation zone 16 may drop rapidly. Therefore, the pressure fluctuation in the starvation zone 16 can be suppressed. Further, the pressure regulating container 5 is formed so as to have a certain volume or more, and the flow rate of the physical foaming agent introduced into the cylinder 10 is made slow so that a time for the physical foaming agent to stay in the pressure regulating container 5 is secured. ing. The pressure regulating container 5 is directly connected to the cylinder 10 heated by a band heater (not shown) disposed around the pressure regulating container 5, and the heat of the cylinder 10 is also conducted to the pressure regulating container 5. Thereby, the physical foaming agent inside the pressure regulating container 5 is heated, the temperature difference between the physical foaming agent and the molten resin is reduced, and it is suppressed that the temperature of the molten resin with which the physical foaming agent contacts is extremely lowered. The dissolved amount (penetration amount) of the physical foaming agent in the molten resin is stabilized. That is, the pressure adjusting container 5 functions as a buffer container having a function of heating the physical foaming agent. On the other hand, if the volume of the pressure regulating container 5 is too large, the cost of the entire apparatus increases. Although the volume of the pressure regulation container 5 is dependent also on the quantity of the molten resin which exists in the starvation zone 16, 5 mL-20L are preferable, 10 mL-2L are more preferable, 10 mL-1L are still more preferable. By setting the volume of the pressure regulating container 5 within this range, it is possible to secure the time for the physical foaming agent to stay while considering the cost. The pressure regulating container 5 is connected to the introduction port 2 and is provided adjacent to the cylindrical first straight portion 5a having a constant inner diameter and the first straight portion 5a, and is separated from the introduction port 2. Accordingly, there are a tapered portion 5b whose inner diameter is increased and a cylindrical second straight portion 5c which is provided adjacent to the tapered portion 5b and has a constant inner diameter. In the pressure regulating container 5, the first straight portion 5a having a small inner diameter and the second straight portion 5c having a large inner diameter are provided so that the central axes thereof are on the same straight line, and the first straight portion 5a and the second straight portion 5c. The straight portion 5c is coupled to the tapered portion 5b. The maximum inner diameter of the pressure regulating container 5 (that is, the inner diameter of the second straight portion 5 c) is larger than the inner diameter of the introduction port 2. For this reason, even when the molten resin enters the inside of the pressure regulating container 5, the flow path of the physical foaming agent is easily secured. That is, it is possible to suppress the physical foaming agent introduction path from being blocked by the solidified molten resin. In addition, a larger amount of physical foaming agent tends to stay in the lower part of the pressure regulating container 5. Since heat from the cylinder 10 is transmitted to the lower part of the pressure regulating container 5, a larger amount of the physical foaming agent is efficiently heated. Thereby, the dissolution amount (penetration amount) of the physical foaming agent into the molten resin is further stabilized.

  Further, the physical foaming agent is consumed in the cylinder 10 by penetrating into the molten resin. In order to keep the pressure in the starvation zone 16 constant, the consumed physical foaming agent is introduced from the pressure regulating container 5 to the starvation zone 16. When the volume of the pressure regulating container 5 is too small, the replacement frequency of the physical foaming agent becomes high, so that the temperature of the physical foaming agent becomes unstable, and as a result, the supply of the physical foaming agent may become unstable. For this reason, it is preferable that the pressure regulating container 5 has a volume capable of retaining the physical foaming agent in an amount consumed in the plasticizing cylinder in 1 to 10 minutes. In addition, for example, the volume of the pressure regulating container 5 is preferably 0.1 to 5 times, more preferably 0.5 to 2 times the volume of the starvation zone 16 to which the pressure regulating container 5 is connected. In the present embodiment, the volume of the starvation zone 16 refers to a portion where the shaft diameter of the screw 20 and the depth of the screw flight are constant in an empty cylinder 10 that does not contain molten resin (a deep groove portion 20D described later). ) Refers to the volume of the region in which it is located. The pressure adjustment container 5 may be a container separate from the cylinder 10 or may be formed integrally with the cylinder 10 and constitute a part of the cylinder 10.

(3) The molten resin is starved.
Next, the molten resin is caused to flow into the starvation zone 16, and the molten resin is starved in the starvation zone 16 (step S3 in FIG. 2). In the present embodiment, the molten resin is in a starved state in the starvation zone 16 by providing the compression zone 13 in which the molten resin is compressed and pressure is increased upstream of the starvation zone 16. The starvation state is determined by the balance between the amount of molten resin fed from the upstream of the starvation zone 16 to the starvation zone 16 and the amount of molten resin fed from the starvation zone 16 to the downstream thereof. The hunger zone 16 is starved when the former is less.

  The screw 20 is a screw used in the manufacturing apparatus 1 that constantly pressurizes a low-density resin in a plasticized molten state with a physical foaming agent having a constant pressure in the starvation zone 16. As shown in FIG. 3, the screw 20 includes a first transition part (first groove depth transition part) 20A located on the upstream side, a first shallow groove part 20B adjacent to the downstream side of the first transition part 20A, The seal part 20C adjacent to the downstream side of the first shallow groove part 20B, the deep groove part 20D adjacent to the downstream side of the seal part 20C, and the second transition part (second groove depth transition) adjacent to the downstream side of the deep groove part 20D Part) 20E and a second shallow groove part 20F adjacent to the downstream side of the second transition part 20E. The first transition part 20 </ b> A is located in the compression zone 13. The first shallow groove portion 20B is located in the measurement zone 14. The seal portion 20 </ b> C is located in the seal zone 15. The deep groove portion 20 </ b> D is located in the starvation zone 16. The second transition unit 20E is located in the recompression zone 17. The second shallow groove portion 20F is located in the reweighing zone 18.

  Here, as shown in FIG. 4, in the screw 20, the screw diameter is D, the screw shaft diameter is d (groove diameter d in the screw 20), the screw flight depth (flight depth) is h, and the screw pitch. (Interval between adjacent screw flights) P. The flight depth h is represented by h = (D−d) / 2. D can also be referred to as a screw outer diameter, and d can also be referred to as a screw inner diameter.

Returning to FIG. The portions corresponding to the plasticizing zone 40, the recompression zone 17 and the reweighing zone 18 in the screw 20 have a single flight structure, that is, a structure in which one screw flight 7 is formed on the outer peripheral surface of the screw 20.
The first transition portion 20A is formed such that the diameter d of the screw shaft gradually increases and the flight depth h decreases stepwise from the upstream side toward the downstream side. In the first transition portion 20A, the diameter d of the screw shaft is larger and the flight depth h is smaller than the portion located in the upstream feed zone 12. It can also be said that the first transition portion 20A is formed such that the groove between the adjacent screw flights 7 becomes shallower in steps from the upstream side to the downstream side. In addition, since the 2nd transfer part 20E is substantially the same as the 1st transfer part 20A, the overlapping description is abbreviate | omitted.

  The first shallow groove portion 20B has a large diameter portion in the first transition portion 20A (a most downstream portion in the first transition portion 20A), a screw shaft diameter d and a flight depth h that are substantially the same. It can also be said that the first shallow groove portion 20B is formed so that the groove between the adjacent screw flights 7 becomes shallow. In addition, since the 2nd shallow groove part 20F is substantially the same as the 1st shallow groove part 20B, the overlapping description is abbreviate | omitted.

  A screw flight is not formed at a portion corresponding to the seal zone 15 in the screw 20. The seal portion 20C has a screw shaft diameter d substantially the same as the first shallow groove portion 20B, and a plurality of shallow grooves are formed on the screw shaft instead of the screw flight. In the first shallow groove portion 20B and the seal portion 20C, the diameter of the screw shaft is large, and the clearance between the inner wall of the cylinder 10 and the screw 20 is reduced, so that the amount of resin supplied downstream is reduced. This increases the flow resistance of the molten resin. In the present embodiment, the first shallow groove portion 20B and the seal portion 20C are mechanisms that increase the flow resistance of the molten resin. The seal portion 20C also has an effect of suppressing the backflow of the physical foaming agent, that is, the movement of the physical foaming agent from the downstream side to the upstream side of the seal portion 20C. Note that the seal portion 20C may have a structure in which a ring (provided with a plurality of grooves) separate from the screw 20 is provided instead of the screw flight.

  When the shaft diameter d of the screw 20 is increased, or when a ring that is a separate member from the screw 20 is provided, the clearance between the inner peripheral surface of the cylinder 10 and the screw 20 is reduced, and the supply amount of resin sent downstream Is reduced. This increases the flow resistance of the molten resin. In the present embodiment, at least the first transition portion 20A has a mechanism for increasing the flow resistance of the molten resin. Due to the presence of the first transition portion 20A, the first shallow groove portion 20B, and the seal portion 20C, the flow rate of the resin supplied to the starvation zone 16 from the upstream side decreases, the molten resin is compressed on the upstream side, the pressure increases, and the downstream side In the starvation zone 16, the molten resin is not filled (that is, starved).

  Note that the mechanism for increasing the flow resistance of the molten resin is not particularly limited as long as it is a mechanism that temporarily reduces the flow area through which the molten resin passes in order to limit the flow rate of the resin supplied from the upstream side to the starvation zone 16. Not. In addition, as a mechanism which raises flow resistance, the structure where the screw flight was provided in the opposite direction to the other part, the labyrinth structure provided on the screw, etc. are mentioned.

  The mechanism for increasing the flow resistance of the molten resin may be provided in the screw as a ring or the like that is a separate member from the screw, or may be provided integrally with the screw as part of the screw structure. If the mechanism that increases the flow resistance of the molten resin is provided as a ring that is a separate member from the screw, the size of the clearance, which is the flow path of the molten resin, can be changed by changing the ring. There is an advantage that the magnitude of the resistance can be changed.

  The deep groove portion 20D (the portion corresponding to the starvation zone 16) in the screw 20 has a screw shaft diameter d larger than that of the portion located in the upstream plasticization zone 40 in order to promote the starvation state of the molten resin. It is smaller and the flight depth h is larger. The deep groove portion 20D has a two-flight flight structure, which will be described later, and it can also be said that the groove between the adjacent screw flights 21, 22 is formed deep.

  Compared with the first transition portion 20A and the first shallow groove portion 20B, the deep groove portion 20D has a small diameter d of the screw shaft at the portion located in the starvation zone 16 over the entire starvation zone 16, and a flight depth h. It is preferable to have a large structure. Further, in the deep groove portion 20D, it is preferable that the shaft diameter d and the flight depth h of the screw 20 are substantially constant over the entire starvation zone 16. Thereby, the pressure in the starvation zone 16 can be kept substantially constant, and the starvation state of the molten resin can be stabilized. In the present embodiment, the deep groove 20D corresponding to the starvation zone 16 has a constant shaft diameter d and a flight depth h of the screw 20.

Here, the maximum amount of the molten resin that moves as the screw rotates once will be described with reference to FIG. FIG. 5 is a view showing a part of the screw 20 corresponding to the measuring zone 14, a part corresponding to the seal zone 15, and a part corresponding to the starvation zone 16. In FIG. 5, for the sake of explanation, the part corresponding to the hunger zone 16 is not a multi-flight flight but a single flight.
In the measuring zone 14, the maximum amount of molten resin that moves (sends out) downstream with one rotation of the screw is the volume per one circumference around the axis between adjacent screw flights 7. (This is referred to as volume A.) In the starvation zone 16, the maximum amount of molten resin that moves (sent out) downstream with one rotation of the screw is 1 around the axis between adjacent screw flights 21. It is the volume per circumference. (This is referred to as volume B.)

(Multiple flight structure)
Returning to FIG. In the present embodiment, the deep groove portion 20D (portion corresponding to the starvation zone 16) has a multi-strip flight structure. In FIG. 3, a two-flight flight structure (double flight structure) is used as an example of a multi-flight flight structure. The deep groove portion 20 </ b> D includes a first screw flight 21 and a second screw flight 22 formed on the outer peripheral surface thereof. According to the multi-strip flight structure, the molten resin can be distributed and transferred to a plurality of flights. Moreover, by setting it as a multiple flight structure, the same amount of molten resin as the case of single flight can be divided | segmented into several and transferred. Thereby, even when the manufacturing apparatus 1 is made larger and the screw diameter D is made larger, the molten resin can be sent downstream without excessively increasing the volume between adjacent screw flights. Moreover, according to the multi-strip flight structure, even when the screw diameter D is made larger, it is possible to suppress an increase in the volume between adjacent flights. For this reason, the quantity of the molten resin deposited between adjacent flights can be reduced, and the starvation state can be stabilized. As a result, a decrease in the contact area between the physical foaming agent and the molten resin is suppressed (the contact area between the physical foaming agent and the molten resin can be increased), and the penetration time of the physical foaming agent into the molten resin is ensured. Therefore, the permeability of the physical foaming agent in the starvation zone 16 can be increased.

  FIG. 6 is an enlarged view of a part of the double flight. The route through which the molten resin is transferred includes two routes: a route transferred by the first screw flight 21 and a route transferred by the second screw flight 22. Here, “volume per one axis circumference between adjacent screw flights” is defined as volume C. The volume C is a volume per one circumference around the axis between the first screw flight 21 and the second screw flight 22. In FIG. 6, the volume C at one location is a hatched portion. At this time, in the starvation zone 16, the maximum amount of the molten resin that moves downstream as the screw makes one rotation, that is, the volume B shown in FIG. 5, is obtained by multiplying the volume C by the number of screw flights “2”. It will be.

  Here, as another example of the multi-strip flight structure, a case where the deep groove 20D (part corresponding to the starvation zone 16) is a 3-strip flight will be described. FIG. 7 is an overall view of the manufacturing apparatus 1 including the screw 20 in which the deep groove portion 20D is a triple flight, and FIG. 8 is an enlarged view of a part of the triple flight. The deep groove portion 20 </ b> D is provided with a first screw flight 21, a second screw flight 22, and a third screw flight 23. In this case, there are three routes for the molten resin to be transferred: a route transferred by the first screw flight 21, a route transferred by the second screw flight 22, and a route transferred by the third screw flight 23. There is a route. In this case, the volume C per circumference around the axis between adjacent screw flights is equal to the volume per circumference around the axis between the first screw flight 21 and the second screw flight 22, and the second screw flight 22 and the second. There is a volume per axis around the axis between the 3 screw flights 23 and a volume per axis around the axis between the third screw flights and the first screw flights. In FIG. 8, the volume C at one location is a hatched portion. At this time, in the starvation zone 16, the maximum amount of molten resin that moves downstream as the screw makes one rotation, that is, the volume B shown in FIG. 5, is obtained by multiplying the volume C by the number of screw flights “3”. It will be. When generalized, the volume B is a volume C × n in the case of n-flight flights (n is an integer of 2 or more).

In the present embodiment, the volume C per one circumference around the axis between adjacent screw flights in the multi-flight structure is 5 cm ³ or more and 100 cm ³ or less. Although the optimum value of the volume C varies depending on the screw diameter D, it is preferably at least 5 cm ³ or more. When the volume C is less than 5 cm ³ , it is difficult to achieve both of maintaining the starvation state in the starvation zone 16 and maintaining the supply capability of sending the molten resin downstream in the starvation zone 16. It is. Further, the volume C is preferably 100 cm ³ or less. When the volume C is larger than 100 cm ³ , the amount of resin deposited between adjacent screw flights becomes excessive, and the penetration efficiency of the physical foaming agent in the starvation zone 16 decreases. Furthermore, the volume C is more preferably 10 cm ³ or more and 50 cm ³ or less.

  In the present embodiment, the value (A / B) obtained by dividing the volume A by the volume B is 0.1 or more and 1.0 or less. This is because a decrease in foaming performance of the foamed molded product can be suppressed and occurrence of vent-up (a phenomenon in which the molten resin swells from the inlet 2 of the starvation zone 16) can be suppressed. Furthermore, A / B is more preferably 0.4 or more and 0.9 or less. When A / B is less than 0.4, the amount of molten resin in the starvation zone 16 is reduced and the starvation rate is increased, but the surplus gas is increased, so that the foaming efficiency is lowered and the foamed foam is broken. Tends to occur. On the other hand, when A / B is larger than 0.9, the starvation rate and the solubility of the physical foaming agent are lowered, and vent-up tends to occur.

  Moreover, the internal diameter (screw diameter D of the screw 20) of the cylinder 10 in which the screw 20 is installed is 40 mm-300 mm. In the present invention, for example, it is defined as follows. When the manufacturing apparatus 1 is a medium size, the inner diameter of the cylinder 10 is about 40 mm to about 60 mm. When the manufacturing apparatus 1 is made large, the inner diameter of the cylinder 10 is about 60 mm to about 300 mm. Even when the manufacturing apparatus 1 is a medium size, the effect of the present invention is sufficiently exerted. However, when the manufacturing apparatus 1 is large, the reduction in the contact area between the physical foaming agent and the molten resin becomes more significant. The effect of the invention will be exhibited more. When the inner diameter of the cylinder 10 is less than about 40 mm, for example, even if the portion corresponding to the starvation zone 16 in the screw 20 is not a multi-flight flight but a single flight, the volume between adjacent flights in the starvation zone 16 is small, Since the amount of resin deposited there is small, there is a tendency that the foaming performance of the molded body is not lowered. The reason why the upper limit of the inner diameter of the cylinder 10 is set to 300 mm is that, in the foam injection molding machine, the inner diameter of the cylinder 10 is practically a maximum of 300 mm.

  Further, the value (P / D) obtained by dividing the screw pitch P (see FIG. 4) in the multi-flight flight portion by the screw diameter D of the screw 20 may be larger than 1.0. P / D is generally around 1.0, but when distributing flights to multiple, it is necessary to make P / D larger than 1.0 and ensure the minimum volume required between adjacent flights. Because there is. Further, the P / D in the starvation zone 16 may be larger than the P / D in the measurement zone 14. In that case, the feed rate of the molten resin in the hunger zone 16 is increased, and the hunger rate in the hunger zone 16 can be increased.

  In addition, in the screw 20, the multi-strip flight structure of the deep groove 20D (the part corresponding to the starvation zone 16) may be three or more flights. Moreover, it is good also considering the other location other than the starvation zone 16 as a multi-strip flight structure. The said other location is a part corresponding to the recompression zone 17 in the screw 20, the reweighing zone 18, etc., for example. Further, in the multi-flight flight structure, the thickness of the subflight may be formed thinner than that of the main flight. The thickness refers to the width of the screw 20 with respect to the axial direction. For example, in the case of double flight (see FIG. 6), the thickness of the second screw flight 22 may be made thinner than the thickness of the first screw flight 21.

  Further, in order to stabilize the starvation state of the molten resin in the starvation zone 16, the amount of thermoplastic resin supplied from the hopper 30 to the cylinder 10 may be controlled. It is because it will become difficult to maintain a starvation state when there is too much supply amount of a thermoplastic resin. In the present embodiment, a general-purpose feeder screw (not shown) is used to control the supply amount of the thermoplastic resin. By limiting the supply amount of the thermoplastic resin, the measurement rate of the molten resin in the re-measurement zone 18 becomes larger than the plasticization rate in the compression zone 13. As a result, the density of the molten resin in the starvation zone 16 is stably reduced, and the penetration of the physical foaming agent into the molten resin is promoted. In addition, since the plasticization time will become long if the supply amount of the thermoplastic resin supplied from the hopper 30 to the cylinder 10 is excessively reduced, it is not preferable.

  In the present embodiment, the length of the starvation zone 16 in the flow direction of the molten resin is preferably longer in order to secure the contact area and contact time between the molten resin and the physical foaming agent. And the adverse effect of increasing the screw length. For this reason, the length of the starvation zone 16 is preferably 2 to 12 times the inner diameter of the cylinder 10, and more preferably 4 to 10 times. Moreover, it is preferable that the length of the starvation zone 16 covers the whole range of the metering stroke in injection molding. That is, the length of the starvation zone 16 in the flow direction of the molten resin is preferably equal to or longer than the length of the metering stroke in the injection molding.

  In addition, the screw 20 moves forward and backward along with plasticizing and injection of the molten resin, but by making the length of the starvation zone 16 longer than the length of the measurement stroke, it is always possible during the production of the foam molded body. The inlet 2 can be located in the starvation zone 16. In other words, even if the screw 20 moves forward and backward during the production of the foamed molded product, no zone other than the starvation zone 16 comes to the position of the inlet 2. Thereby, the physical foaming agent introduced from the inlet 2 is always introduced into the starvation zone 16 during the production of the foamed molded product. By providing the starvation zone 16 having a sufficient and appropriate size (length) and introducing a physical foaming agent having a constant pressure therein, the starvation zone 16 can be easily held at a constant pressure. In the present embodiment, the length of the starvation zone 16 is substantially the same as the length of the screw 20 in which the diameter of the shaft of the screw 20 and the depth of the screw flight are constant, that is, the length of the deep groove portion 20D. It has become.

  In the present embodiment, the manufacturing apparatus 1 has one starvation zone 16, but the number of starvation zones 16 is not limited to this. For example, in order to promote the penetration of the physical foaming agent into the molten resin, a plurality of starvation zones 16 and introduction ports 2 may be provided, and the physical foaming agent may be introduced into the cylinder 10 through the plurality of introduction ports 2. .

(4) The molten resin is brought into contact with the physical foaming agent.
Next, in a state in which the starvation zone 16 is maintained at a constant pressure, the starved molten resin is brought into contact with the physical foaming agent at a constant pressure in the starvation zone 16 (step S4 in FIG. 2). That is, in the starvation zone 16, the molten resin is pressurized with a physical foaming agent at a constant pressure. Since the starvation zone 16 has a space in which the molten resin is not filled (starved state) and the physical foaming agent can exist, the physical foaming agent and the molten resin can be efficiently contacted. The physical foaming agent in contact with the molten resin penetrates into the molten resin and is consumed. When the physical foaming agent is consumed, the physical foaming agent staying in the pressure regulating container 5 is smoothly supplied to the starvation zone 16. Thereby, the pressure of the starvation zone 16 is maintained at a constant pressure, and the molten resin continues to contact the physical foaming agent at a constant pressure.

  In foam molding using a conventional physical foaming agent, a predetermined amount of a high-pressure physical foaming agent is forcibly introduced into a plasticizing cylinder within a predetermined time. For this reason, it is necessary to increase the pressure of the physical foaming agent to a high pressure and accurately control the introduction amount and introduction time into the molten resin, and the physical foaming agent contacts the molten resin only for a short introduction time. It was. On the other hand, in the present embodiment, the physical foaming agent is not continuously introduced into the cylinder 10 but the physical foaming agent at a constant pressure is continuously applied to the cylinder 10 so that the pressure in the starvation zone 16 is constant. And the physical foaming agent is continuously brought into contact with the molten resin. Thereby, the dissolution amount (penetration amount) of the physical foaming agent in the molten resin determined by the temperature and pressure can be stabilized. In the present embodiment, since the physical foaming agent is always in contact with the molten resin, a necessary and sufficient amount of the physical foaming agent penetrates into the molten resin. As a result, the foamed molded body manufactured by the manufacturing apparatus 1 according to the present embodiment is foamed in spite of using a low-pressure physical foaming agent as compared with a conventional molding method using a physical foaming agent. The cell is fine.

  In addition, according to the manufacturing method according to the present embodiment, since it is not necessary to control the introduction amount, introduction time, etc. of the physical foaming agent, a drive valve such as a check valve or a solenoid valve, and a control mechanism for controlling them. Is unnecessary, and the cost of the apparatus can be reduced. Further, the physical foaming agent used in the present embodiment has an advantage that the apparatus load is small because it has a lower pressure than the conventional physical foaming agent.

Moreover, in this Embodiment, the starvation zone 16 is always hold | maintained at a fixed pressure during manufacture of a foaming molding. That is, in order to supplement the physical foaming agent consumed in the cylinder 10, all the steps of the method for producing the foamed molded product are performed while continuously supplying the physical foaming agent at the constant pressure. In this embodiment, for example, when performing injection molding of a plurality of shots continuously, molten resin for the next shot is also performed during the injection process, the cooling process of the molded body, and the process of taking out the molded body. Is prepared in the cylinder 10, and the molten resin for the next shot is pressurized with a physical foaming agent at a constant pressure. That is, in the multiple shot injection molding performed continuously, the molten resin and the physical foaming agent at a constant pressure are always present and in contact in the cylinder 10, that is, the molten resin is in the cylinder 10 due to the physical foaming agent. One cycle of injection molding is performed, including a plasticizing and metering step, an injection step, a molded body cooling step, a removal step, and the like, under constant pressure at a constant pressure. Similarly, when continuous molding such as extrusion molding is performed, a state in which the molten resin and a physical foaming agent at a constant pressure are always present and in contact in the cylinder 10, that is, the molten resin is physically in the cylinder 10. Molding is performed in a state of being constantly pressurized with a foaming agent at a constant pressure.
Even when the manufacturing apparatus 1 is made large in size, by providing the pressure regulating container 5 of an appropriate size, the molding is performed in a state where the molten resin is always pressurized at a constant pressure with a physical foaming agent in the cylinder 10. Thus, the effect of the molding method using a low-pressure physical foaming agent that can realize good foam molding in which fine cells are formed inside the molded body can be enjoyed. For example, when a large amount of the physical foaming agent is consumed in the starvation zone 16, the supply of the physical foaming agent may not be in time, and the pressure in the starvation zone 16 may rapidly decrease. By supplying the agent, the pressure fluctuation in the starvation zone 16 is suppressed, and the molding can be performed in the cylinder 10 in a state where the molten resin is always pressurized at a constant pressure by the physical foaming agent.

(5) Molding the molten resin into foam molding.
Next, the molten resin in contact with the physical foaming agent is molded into a foam molded body (step S5 in FIG. 2). The cylinder 10 is provided with a recompression zone 17 adjacent to the downstream of the starvation zone 16. Due to the rotation of the screw 20, the molten resin in the starvation zone 16 flows into the recompression zone 17. In the recompression zone 17, the molten resin is recompressed to increase the pressure. The molten resin containing the physical foaming agent is pressure-adjusted in the recompression zone 17 and is pushed out and measured in front of the screw 20. The cylinder 10 is provided with a reweighing zone 18 adjacent to the downstream side of the recompression zone 17 as a zone for performing the measurement.

  At this time, the internal pressure of the molten resin extruded to the front of the screw 20 is controlled as a screw back pressure by a hydraulic motor, a hydraulic cylinder, or an electric motor (not shown) connected to the rear of the screw 20. In the present embodiment, the internal pressure of the molten resin extruded to the front of the screw 20, that is, the screw back pressure, is constant so that the physical foaming agent is uniformly mixed without being separated from the molten resin and the resin density is stabilized. It is preferable to control the pressure so as to be about 1 to 6 MPa higher than the pressure of the starvation zone 16 held in the tank. In the present embodiment, a check ring 19 is provided at the tip of the screw 20 so that the compressed resin in front of the screw 20 does not flow backward upstream. Thereby, at the time of measurement, the pressure in the starvation zone 16 is not affected by the resin pressure in front of the screw 20.

  In addition, the molding method of a foaming molding is not specifically limited, For example, a molding can be shape | molded by injection foam molding, extrusion foam molding, foam blow molding, etc. In the present embodiment, molten resin measured in the re-metering zone 18 is injected and filled from a cylinder 10 into a cavity (not shown) in a mold, and injection foam molding is performed. For injection foam molding, a short shot method is used in which the mold cavity is filled with molten resin having a filling capacity of 75% to 95% of the mold cavity volume, and the mold cavity is filled while bubbles expand. May be. Alternatively, a core back method may be used in which after filling a molten resin having a filling amount of 90% to 100% of the mold cavity volume, the cavity volume is expanded and foamed. The resulting foamed molded article has foamed cells inside, and the shrinkage of the thermoplastic resin during cooling is suppressed and the cooling strain is alleviated, so that sink marks and warpage are reduced, and a foam molded article with a low specific gravity is reduced. Can be obtained.

  In the manufacturing method according to the present embodiment, since it is not necessary to control the amount of introduction of the physical foaming agent into the molten resin, the introduction time, etc., a complicated control device can be omitted or simplified, and the device cost can be reduced. it can. Further, in a state where the starvation zone 16 is maintained at a constant pressure, in the starvation zone 16, the starved molten resin is brought into contact with the physical foaming agent at the constant pressure. Thereby, the dissolution amount (penetration amount) of the physical foaming agent with respect to the molten resin can be stabilized by a simple mechanism.

(Evaluation of foam molding)
An evaluation method of the (injection) foamed molded product (molded product) manufactured by the manufacturing apparatus 1 will be described. Polypropylene mixed with 20% talc (made by Idemitsu Lion Composite, 4700G) was used as the thermoplastic resin. The thickness of the molded product (2.5 mm) was constant, and the size of the molded product was changed according to the diameter of the screw cylinder (150 mm square to 800 mm square). The state of the foam cell of the molded product in the gate part, the central part and the flow end part was evaluated by a cross-sectional SEM. Foamed cells in a 1 mm square field of view were observed, and an average cell of 50 μm or less was accepted. In addition, the uniformity of the foamed cells was visually confirmed through the molded product to evaluate whether or not bubble breakage could be confirmed.

  Hereinafter, the present invention will be further described using examples and comparative examples. However, the present invention is not limited to the examples and comparative examples described below. FIG. 9 shows a summary of examples and comparative examples.

[Example 1]
In Example 1, foam injection molding was performed using a screw having an inner diameter of 56 mm. The screw in the hunger zone 16 has a double flight structure. Regarding the maximum capacity of the molten resin that moves with one screw rotation, the volume A in the measurement zone 14 was 30 cm ^3, and the volume B (volume C × 2 paths) in the starvation zone 16 was 38 cm ³ . Moreover, A / B (0.1-1.0 is desirable) was set to 0.78. Further, the volume per one rotation axis between the screw flight adjacent the multiple lead flight starvation zone 16 ^C a (preferably 5 cm 3 100 cm ^3), was 19cm ^3.
Using a 150 mm square plate for the mold, the pressure of the physical foaming agent by nitrogen by adjusting the pressure reducing valve 51 is 8 MPa, the screw back pressure is 10 MPa, the resin temperature is 180 to 210 ° C., and the mold temperature is 40 ° C., After plasticization weighing, injection filling was performed at an injection speed of 50 mm / s. After applying for 2 seconds at a pressure of 20 MPa, the mold was opened 5 mm, and core back foaming was performed 3 times.

  When the cell diameter of the molded product of Example 1 was evaluated by a cross-sectional SEM, the average cell diameter was as small as 22 μm and was favorable. Moreover, no bubble breakage was observed. Further, although 100 shots were continuously formed, no vent-up occurred.

[Example 2]
In Example 2, a screw having an inner diameter of 80 mm was used. The screw in the hunger zone 16 has a double flight structure. The volume A in the measurement zone 14 was 43 cm ^3, and the volume B (volume C × 2 paths) in the starvation zone 16 was 52 cm ³ . A / B was set to 0.82. The volume C was 26 cm ³ . Other than that was the same as in Example 1, and core-back foaming was performed.

  When the cell diameter of the molded product of Example 2 was evaluated by a cross-sectional SEM, the average cell diameter was as small as 28 μm and was favorable. Moreover, no bubble breakage was observed. Further, although 100 shots were continuously formed, no vent-up occurred.

[Example 3]
In Example 3, a screw having an inner diameter of 100 mm was used. The screw in the hunger zone 16 has a double flight structure. Further, the volume A in the measurement zone 14 was 55 cm ^3, and the volume B (volume C × 2 paths) in the starvation zone 16 was 86 cm ³ . A / B was set to 0.63. The volume C was 43 cm ³ . The mold used was a 250 × 400 mm square plate. Other than that was the same as in Example 1, and core-back foaming was performed.

  When the cell diameter of the molded product of Example 3 was evaluated by a cross-sectional SEM, the average cell diameter was as small as 35 μm and was favorable. Moreover, no bubble breakage was observed. Further, although 100 shots were continuously formed, no vent-up occurred.

[Example 4]
In Example 4, a screw having a screw cylinder inner diameter of φ200 mm was used. The screw in the hunger zone 16 has a triple flight structure. Further, the volume A in the measurement zone 14 was 110 cm ^3, and the volume B (volume C × 3 path) in the starvation zone 16 was 171 cm ³ . A / B was set to 0.64. Further, the volume C was 57 cm ³ . Moreover, the metal mold | die used the flat plate of 800 mm square. Other than that was the same as in Example 1, and core-back foaming was performed.

  When the cell diameter of the molded product of Example 4 was evaluated by a cross-sectional SEM, the average cell diameter was as small as 38 μm and was favorable. Moreover, no bubble breakage was observed. Further, although 100 shots were continuously formed, no vent-up occurred.

[Comparative Example 1]
In Comparative Example 1, a screw with a screw cylinder inner diameter of φ100 mm was used. The screw in the hunger zone 16 has a single flight structure. The volume A in the measurement zone 14 was 55 cm ^3, and the volume B in the starvation zone 16 was 86 cm ³ . A / B was set to 0.63. Other than that was the same as in Example 3, and core-back foaming was performed.

  When the cell diameter of the molded product of Comparative Example 1 was evaluated by a cross-sectional SEM, the average cell diameter was 47 μm, which was slightly enlarged. Moreover, bubble breakage was observed at the flow end. This is a single flight, because the difference between the volume A and the volume B is large, in the starvation zone 16, the amount of resin deposited between adjacent flights decreases, and the amount of physical foaming agent staying increases, It is presumed that excess gas that could not be dissolved was entrained during recompression.

[Comparative Example 2]
In Comparative Example 2, a screw with a screw cylinder inner diameter of φ200 mm was used. The screw in the hunger zone 16 has a double flight structure. Further, the volume C was set to 105 cm ³ . Other than that was the same as in Example 4, and core-back foaming was performed.

  When the cell diameter of the molded product of Comparative Example 2 was evaluated with a cross-sectional SEM, the cell diameter was large, and bubbles were scattered. This is presumably because in the starvation zone 16, the amount of resin staying between adjacent screw flights increased and the contact area with the physical foaming agent decreased, resulting in an insufficient amount of dissolution of the physical foaming agent. The Moreover, it is estimated that the quantity of the physical foaming agent which stays increases too much, and the surplus gas was involved at the time of recompression.

[Comparative Example 3]
In Comparative Example 3, a screw having an inner diameter of 56 mm was used. The screw in the hunger zone 16 has a double flight structure. Further, the volume B in the starvation zone 16 was set to 28 cm ³ . A / B was set to 1.07 (that is, the hunger rate was lowered). The others were the same as in Example 1, and core back foaming was performed.

  In Comparative Example 3, vent-up occurred frequently, and it was difficult to continuously mold unless a considerable amount of resin was squeezed.

As described above, in the manufacturing apparatus and the manufacturing method according to the present embodiment, the apparatus for performing foam molding by constantly pressing the molten resin with the physical foaming agent at a constant pressure in the starvation zone 16 is further enlarged. In other words, even if the screw diameter is larger, the flight structure in the starvation zone 16 is a multi-strip flight structure, so that the same amount of molten resin as in single flight is divided into a plurality of parts. Then transferred. At this time, since the volume between adjacent screw flights does not become excessively large, the amount of molten resin deposited there can be reduced. For this reason, while the fall of the contact area of a physical foaming agent and molten resin is suppressed, the osmosis | permeation time to the molten resin of a physical foaming agent is ensured. For this reason, favorable foam molding in which fine cells are formed inside the foam molded article (molded product) can be realized, and deterioration of the foaming performance of the foam molded article can be suppressed.
In other words, in a manufacturing apparatus (manufacturing method) that pressurizes the starvation zone 16 with a relatively low pressure physical foaming agent, even when the apparatus is made larger, that is, when the inner diameter (screw diameter) of the screw cylinder is made larger. Since the flight structure in the starvation zone 16 is a multi-strip flight structure, the same amount of molten resin as in the case of single flight is divided and transferred. At this time, since the volume between adjacent screw flights does not become excessively large, the amount of molten resin deposited there can be reduced. For this reason, while the fall of the contact area of a physical foaming agent and molten resin is suppressed, the osmosis | permeation time to the molten resin of a physical foaming agent is ensured. Thereby, it is possible to realize good foam molding without lowering the foaming performance of the molded body, and it is possible to stably form fine foam cells inside the molded body.

Further, since the volume per one revolution about the axis of the adjacent screw flights of the starvation zone 16 (volume C) is in the range of ^{5 cm} 3 100 cm ^3, the starvation zone 16, while maintaining the starved, melting The ability to feed the resin downstream is maintained, and a decrease in the penetration efficiency of the physical foaming agent due to an excessive amount of resin deposited between adjacent screw flights is suppressed. Thereby, the enlargement of the foam cell size in a molded object, generation | occurrence | production of a bubble breakage, etc. can be suppressed more reliably, and a molded object with a favorable foaming state can be obtained.

  Further, a volume B obtained by multiplying the volume A per circumference around the axis between adjacent screw flights in the measurement zone 14 and the volume per axis around the axis between adjacent screw flights in the starvation zone 16 by the number of screw flights. Since the ratio A / B is in the range of 0.1 to 1.0, the excess of the physical foaming agent in the starvation zone 16 is suppressed, and the occurrence of vent-up is suppressed. Thereby, generation | occurrence | production of the bubble breakage in a molded object can be suppressed more reliably, while a molded object with a favorable foaming state can be obtained, and productivity of a molded object can be improved.

DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus 2 Inlet 5 Pressure regulating container 7 Screw flight (of a measurement zone) 10 Plasticizing cylinder (cylinder)
14 Weighing zone 16 Hunger zone 20 Screws 21, 22, 23 Screw flight 40 (of starvation zone) Plasticizing zone

Claims (6)

An apparatus for producing a foam molded article,
A cylinder having a plasticizing zone in which a thermoplastic resin is plasticized and melted to become a molten resin, and a starvation zone in which the molten resin is in a starvation state, and an introduction port of a physical foaming agent to the starvation zone is provided; ,
A screw disposed in the cylinder so as to be rotatable about an axis and movable in an axial direction; and
A pressure regulating container that introduces the physical foaming agent at a constant pressure into the starvation zone through the inlet, and constantly maintains the starvation zone at the constant pressure;
The screw has a multi-flight structure in the hunger zone ,
The multi-strip flight structure is an apparatus for producing a foamed molded article, wherein the volume per circumference of an axis between adjacent screw flights is 5 cm ³ or more and 100 cm ³ or less . The plasticizing zone is located upstream of the starvation zone in the flow direction of the molten resin, and has a measuring zone that holds the molten resin in a state compressed by a mechanism that increases the flow resistance of the molten resin,
The volume per axis circumference between adjacent screw flights in the measurement zone is defined as volume A,
When a volume obtained by multiplying the volume per axis around the adjacent screw flights in the starvation zone by the number of screw flights in the starvation zone is defined as volume B,
The value obtained by dividing the volume A in volume B is foam molded article of manufacture according to claim 1, characterized in that has a 0.1 to 1.0. A method for producing a foam molded article,
A cylinder having a plasticizing zone and a starvation zone, provided with an introduction port of a physical foaming agent to the starvation zone, and disposed inside the cylinder so as to be rotatable about an axis and movable in an axial direction. In the hunger zone, a multi-strip flight structure is formed, and the multi-strip flight structure includes a screw having a volume per axis around an adjacent screw flight of 5 cm ³ or more and 100 cm ³ or less , Using a pressure regulating container that introduces a physical foaming agent into the starvation zone through the inlet,
The manufacturing method includes:
In the plasticizing zone, plasticizing and melting the thermoplastic resin to form a molten resin;
Introducing the physical blowing agent at a constant pressure into the starvation zone to maintain the starvation zone at the constant pressure at all times;
In the starvation zone, dividing the molten resin transfer path by the multi-strip flight structure, and making each starved state,
Contacting the starved molten resin with the constant pressure physical blowing agent;
And a step of molding the molten resin in contact with the physical foaming agent at a constant pressure into a foamed molded product. The plasticizing zone is located upstream of the starvation zone in the flow direction of the molten resin, and has a measuring zone that holds the molten resin in a state compressed by a mechanism that increases the flow resistance of the molten resin,
The volume per axis circumference between adjacent screw flights in the measurement zone is defined as volume A,
When a volume obtained by multiplying the volume per axis around the adjacent screw flights in the starvation zone by the number of screw flights in the starvation zone is defined as volume B,
Divided by the in volume B volume A, method for producing a foamed molded article according to claim 3, characterized in that has a 0.1 to 1.0. A cylinder having a plasticization zone in which a thermoplastic resin is plasticized and melted to become a molten resin and a starvation zone in which the molten resin is in a starvation state, a physical foaming agent is introduced into the starvation zone, A screw used in a foam molded product manufacturing apparatus that is constantly maintained at a constant pressure,
The screw disposed inside the cylinder has a multi-strip flight structure in the starvation zone, and the multi-strip flight structure has a volume per axis around an axis between adjacent screw flights of 5 cm ³ or more. A screw for a foam-molded article manufacturing apparatus, characterized by being 100 cm ³ or less . The plasticizing zone is located upstream of the starvation zone in the flow direction of the molten resin, and has a measuring zone that holds the molten resin in a state compressed by a mechanism that increases the flow resistance of the molten resin,
The volume per axis circumference between adjacent screw flights in the measurement zone is defined as volume A,
When a volume obtained by multiplying the volume per axis around the adjacent screw flights in the starvation zone by the number of screw flights in the starvation zone is defined as volume B,
6. The foam molded body manufacturing apparatus screw according to claim 5 , wherein a value obtained by dividing the volume A by the volume B is 0.1 or more and 1.0 or less.

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