Foam molding

Abstract

A method for producing a foamed molded article having high heat resistance is provided. [Solution] A method for producing a foamed molded article using a plasticizing cylinder having a plasticizing zone and a starvation zone, comprising the steps of plasticizing and melting a thermoplastic resin in the plasticizing zone to form a molten resin, introducing a pressurized fluid containing a physical foaming agent at a constant pressure into the starvation zone and maintaining the starvation zone at the constant pressure, starving the molten resin in the starvation zone, bringing the molten resin in the starved state into contact with a pressurized fluid containing a physical foaming agent at the constant pressure in the starvation zone while maintaining the starvation zone at the constant pressure, and molding the molten resin that has been contacted with the pressurized fluid containing the physical foaming agent into a foamed molded article, wherein the thermoplastic resin is a super engineering plastic, and the constant pressure is 0.5 MPa to 12 MPa.

Description

[Technical field]

[0001] The present invention relates to a method for producing a foamed molded article and the foamed molded article. [Background technology]

[0002] In recent years, with the trend toward lighter and more electric automobiles, there has been a demand for lightweight, insulating metal parts for automobiles. Therefore, the manufacturing method of foamed molded products (foamed molded products) Research and practical application of foam molding has been active. General-purpose engineering plastics such as polypropylene (PP) and acrylonitrile-butadiene ABS (acrylic styrene copolymer) has been used. Glass fiber reinforced resins such as polyamide 6 and polyamide 66 are also used in foam molding. The blowing agents used in foam molding can be roughly divided into two types: physical blowing agents and chemical blowing agents. It is difficult to apply chemical foaming agents to high melting point materials. For foam molding of fiber-reinforced resins, foam injection molding is used, which uses high-pressure supercritical fluid as a physical foaming agent. The method is adopted (for example, Patent Documents 1 to 3).

[0003] The heat resistance temperature of the general-purpose engineering plastics mentioned above is usually around 100℃, but they can be used in higher temperature environments. For applications where this is expected, polyphenylene sulfide (PS) with a normal heat resistance of 150°C or higher is used. Super engineering plastics such as polypropylene (PPS) and liquid crystal polymer (LCP) PPS is a cost-effective material and is widely used in automotive parts. It is a super engineering plastic that is seeing the greatest growth in adoption. LCP is used for small parts such as high-precision connectors. Patent documents 4 and 5 disclose methods for producing foamed PPS products. It has been done. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 2625576 [Patent Document 2] Patent No. 3788750 [Patent Document 3] Patent No. 4144916 [Patent Document 4] JP 2013-60508 A [Patent Document 5] JP 2012-251022 A Summary of the Invention [Problem to be solved by the invention]

[0005] The methods for producing a foamed molded PPS article disclosed in Patent Documents 4 and 5 include the steps of: a step of permeating the inert gas by holding the material in a pressurized inert gas atmosphere; and a step of heating the PPS under normal pressure to foam it. For this reason, there is a problem that productivity is inferior to continuous molding such as injection molding and extrusion molding. is doing.

[0006] The foam molding methods using physical foaming agents disclosed in Patent Documents 1 to 3 are continuous foaming methods with high productivity. It is a foam molding technology that is relatively resin-independent. The methods disclosed in References 1 to 3 are believed to enable foam molding of super engineering plastics such as PPS. However, in recent years, foam molded products have been used as substitutes for metal parts, and According to the study by the inventors of the present application, the Such foamed products using conventional high-pressure physical foaming agents are made by adding super engineering plastics to the resin material. However, it was found that even if such a material was used, sufficient heat resistance could not be obtained.

[0007] The present invention solves the above problems, and is a highly productive continuous molding method that has high heat resistance The present invention provides a method for producing a foamed molded article of a super engineering plastic having excellent mechanical properties. [Means for solving the problem]

[0008] According to a first aspect of the present invention, a plasticizing method is provided in which a thermoplastic resin is plasticized and melted to become a molten resin. A starvation zone in which the molten resin is starved, and a physical generation A foamed molded article is produced using a plasticizing cylinder having an inlet for introducing a foaming agent. The method further comprises the steps of: in the plasticization zone, plasticizing and melting the thermoplastic resin to form the melt; A pressurized fluid containing the physical foaming agent is introduced into the starvation zone at a constant pressure. maintaining said starvation zone at said constant pressure; starving the molten resin; and maintaining the starvation zone at the constant pressure. In a starvation zone, a pressurized flow containing the starved molten resin and the physical blowing agent at a constant pressure is and a pressurized fluid containing the physical foaming agent is brought into contact with the molten resin to form a foam. and forming the thermoplastic resin into a foam body, the thermoplastic resin being a super engineering plastic. and the constant pressure is 0.5 MPa to 12 MPa. A method for manufacturing a feature is provided.

[0009] In this embodiment, the super engineering plastic is polyphenylene sulfide. The super engineering plus may contain a polymer such as a fluoride or a liquid crystal polymer. The thermoplastic resin contains polyphenylene sulfide, and the constant pressure is 2 MPa to 12 MPa. It may be 2 MPa to 10 MPa, or it may be 2 MPa to 8 MPa. In addition, the super engineering plastic contains a liquid crystal polymer, and the constant pressure The pressure may be 1 MPa to 6 MPa. The physical foaming agent may be nitrogen.

[0010] In the starvation zone, the molten resin is pressurized with a pressurized fluid containing the physical foaming agent. Alternatively, the starvation zone may be maintained at the constant pressure throughout the production of the foamed article. stomach.

[0011] In this embodiment, the plasticizing cylinder has an introduction speed adjusting container connected to the introduction port. The manufacturing method may further include introducing a pressurized fluid containing the physical foaming agent into the introduction rate adjusting vessel. and supplying the constant pressure of the mixture from the introduction rate regulating vessel to the starvation zone. A pressurized fluid containing a physical foaming agent may be introduced. The inlet is always open. During the production of the foamed molded article, the introduction rate adjusting vessel and the starvation zone are kept at the constant pressure. may be held at

[0012] According to a second aspect of the present invention, a foam molding comprising a super engineering plastic is provided. The foamed molded body is heated to a surface temperature of 240° C. to 260° C. When maintained at ℃ for 5 minutes, the change in thickness of the foamed molded product due to heating is -2% to 2%. The foamed molded article is characterized by the above.

[0013] In this embodiment, the foamed molded article may be heated in a reflow furnace. The super engineering plastic is polyphenylene sulfide or liquid crystal poly It may also include mers. Effect of the Invention

[0014] The method for producing a foamed molded article of the present invention is a highly productive continuous molding method, and can produce a foamed molded article of a super engineering plastic having high heat resistance. [Brief description of the drawings]

[0015] [Figure 1] 1 is a flowchart showing a method for producing a foamed molded article according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing a production apparatus for a foamed molded article used in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The method for producing a foamed molded article according to this embodiment will be described with reference to the flow chart shown in FIG.

[0017] [Foam molding manufacturing equipment] First, a manufacturing apparatus for manufacturing a foam molded article used in this embodiment will be described. In this embodiment, a manufacturing apparatus (injection molding apparatus) 1000 shown in FIG. The manufacturing apparatus 1000 mainly includes a plasticizing cylinder 210 having a screw 20 installed therein, a cylinder 100 which is a physical foaming agent supplying mechanism for supplying a physical foaming agent to the plasticizing cylinder 210, a mold clamping unit (not shown) having a mold, and a control device (not shown) for controlling the operation of the plasticizing cylinder 210 and the mold clamping unit. The molten resin plasticized and melted in the plasticizing cylinder 210 flows from the right hand to the left hand in FIG. 2. Therefore, inside the plasticizing cylinder 210 of this embodiment, the right hand in FIG. 2 is defined as "upstream" or "rear", and the left hand is defined as "downstream" or "front".

[0018] The plasticizing cylinder has a plasticizing zone 21 where the thermoplastic resin is plasticized and melted to become a molten resin, and a starvation zone 23 downstream of the plasticizing zone 21 where the molten resin is in a starved state. The "starved state" refers to a state in which the molten resin does not fill the starvation zone 23, but is not filled therewith. Therefore, there is space in the starvation zone 23 other than the portion occupied by the molten resin. Also, an inlet 202 for introducing a physical foaming agent into the starvation zone 23 is formed, and an introduction speed adjusting container 300 is connected to the inlet 202. The cylinder 100 supplies the physical foaming agent to the plasticizing cylinder 210 via the introduction speed adjusting container 300.

[0019] Although the manufacturing apparatus 1000 has only one starvation zone 23, the manufacturing apparatus used in this embodiment is not limited to this. For example, in order to promote the penetration of the physical foaming agent into the molten resin, the manufacturing apparatus may have a structure in which a plurality of starvation zones 23 and inlets 202 formed therein are provided, and the physical foaming agent is introduced into the plasticizing cylinder 210 from the plurality of inlets 202. In addition, although the manufacturing apparatus 1000 is an injection molding apparatus, the manufacturing apparatus used in this embodiment is not limited to this and may be, for example, an extrusion molding apparatus.

[0020] [Method of manufacturing foam molded products] (1) Plasticization and melting of thermoplastic resin First, in the plasticizing zone 21 of the plasticizing cylinder 210, the thermoplastic resin is plasticized and melted to form a molten resin (step S1 in FIG. 1). In this embodiment, super engineering plastics (hereinafter, appropriately referred to as "super engineering plastics") are used as the thermoplastic resin. Generally, plastics with a continuous use temperature of 150° C. or higher are classified as super engineering plastics, and the definition of super engineering plastics in this specification follows this definition. Many super engineering plastics contain benzene rings in their molecular chains, so the molecular chains are thick and strong. Even when the environmental temperature becomes high, the molecules are less likely to move, so they have excellent heat resistance. Note that some fluororesins have excellent heat resistance even without a benzene ring structure and are classified as super engineering plastics. This is because fluororesins are very stable when bonded to carbon.

[0021] Super engineering plastics are broadly classified into amorphous (transparent) resins and crystalline resins. Examples of amorphous (transparent) resins include polyphenylsulfone (PPSU), polysulfone (PSU), polyarylate (PAR), and polyetherimide (PEI), and examples of crystalline resins include polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polyethersulfone (PES), polyamideimide (PAI), liquid crystal polymer (LCP), and polyvinylidene fluoride (PVDF). The super engineering plastics of this embodiment may be used alone or in combination of two or more types, or may be a polymer alloy containing these engineering plastics. As the super engineering plastics used in this embodiment, crystalline resins that are easy to form fine cells are preferred, and among them, polyphenylene sulfide (PPS) and liquid crystal polymer (LCP) are more preferred.

[0022] Polyphenylene sulfide (PPS) has advantages such as being relatively inexpensive, being chemically stable, being easy to achieve dimensional accuracy, and having high strength, and therefore the demand for it is expanding, mainly for automotive parts. On the other hand, PPS has problems such as being prone to burrs during molding, being prone to warping when long glass fibers or the like are mixed, and having a large specific gravity. In this embodiment, by foaming PPS, burrs and warping can be suppressed and the specific gravity can be further reduced. Liquid crystal polymers (LCPs) have the advantages that burrs are unlikely to occur during molding because the shear rate dependency of molten resin is high, and high dimensional accuracy can be obtained even in thin-walled molded parts. In automotive parts, LCPs are used in connectors that require high heat resistance. On the other hand, LCPs have problems such as being expensive and having a large specific gravity. In this embodiment, by foaming LCP, the specific gravity can be reduced, and the amount used can be reduced compared to solid molded bodies (non-foamed molded bodies) of the same size, so that costs can be reduced.

[0023] The thermoplastic resin of the present embodiment may be kneaded with various inorganic fillers such as glass fiber, talc, and carbon fiber. By mixing the thermoplastic resin with an inorganic filler that functions as a foaming nucleating agent or an additive that increases melt tension, the foam cells can be made fine. The thermoplastic resin of the present embodiment may contain various other general-purpose additives as necessary.

[0024] In this embodiment, only super engineering plastics are used as the thermoplastic resin, but depending on the application of the foam molded body, general-purpose thermoplastic resins other than super engineering plastics may be mixed and used to the extent that the heat resistance of the foam molded body is not affected. In this embodiment, the main component of the thermoplastic resin constituting the foam molded body is super engineering plastics, and for example, the ratio of super engineering plastics in the thermoplastic resin constituting the foam molded body is preferably 60% by weight to 100% by weight, more preferably 95% by weight to 100% by weight. In this embodiment, physical foaming is used as the foaming agent, and no chemical foaming agent is used in combination. Therefore, the super engineering plastics, which are the thermoplastic resin of this embodiment, do not contain a chemical foaming agent. Since the melting temperature of super engineering plastics is high, it is difficult to use a chemical foaming agent in combination.

[0025] In this embodiment, the thermoplastic resin is plasticized and melted in a plasticizing cylinder 210 in which the screw 20 shown in Fig. 2 is installed. A band heater (not shown) is provided on the outer wall surface of the plasticizing cylinder 210, which heats the plasticizing cylinder 210. Furthermore, shear heat generated by the rotation of the screw 20 is also added, and the thermoplastic resin is plasticized and melted.

[0026] (2) Maintaining pressure in the starvation zone Next, a physical foaming agent is introduced into the starvation zone 23 at a constant pressure, and the starvation zone 23 is maintained at said constant pressure (step S2 in FIG. 1).

[0027] A pressurized fluid is used as the physical foaming agent. In this embodiment, the term "fluid" means any one of a liquid, a gas, and a supercritical fluid. In addition, from the viewpoint of cost and environmental load, carbon dioxide, nitrogen, and the like are preferable as the physical foaming agent. Since the pressure of the physical foaming agent in this embodiment is relatively low, for example, a fluid that is decompressed to a constant pressure by a pressure reducing valve and taken out from a cylinder in which a fluid is stored, such as a nitrogen cylinder, a carbon dioxide cylinder, or an air cylinder, can be used. In this case, a pressure boosting device is not required, so the cost of the entire manufacturing apparatus can be reduced. In addition, if necessary, a fluid that has been pressurized 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, the air in the atmosphere is compressed by a compressor and passed through a nitrogen separation membrane to purify the nitrogen. Next, the purified nitrogen is pressurized to a predetermined pressure using a booster pump, a syringe pump, or the like to generate the physical foaming agent. In addition, compressed air may be used as the physical foaming agent. In this embodiment, forced shear mixing of the physical foaming agent and the molten resin is not performed. For this reason, even if compressed air is used as a physical foaming agent, oxygen, which has low solubility in molten resin, is less likely to dissolve in the molten resin, and oxidation deterioration of the molten resin can be suppressed.

[0028] The pressure of the physical foaming agent introduced into the starvation zone 23 is constant, and the pressure of the starvation zone 23 is maintained at the same constant pressure as the physical foaming agent introduced. The pressure of this physical foaming agent is 0.5 MPa to 12 MPa, preferably 2 MPa to 12 MPa, more preferably 2 MPa to 10 MPa, and even more preferably 2 MPa to 8 MPa. The pressure of the physical foaming agent is preferably 1 MPa to 6 MPa. Although the optimal pressure varies depending on the type of molten resin, by setting the pressure of the physical foaming agent to 0.5 MPa or more, the amount of physical foaming agent required for foaming can penetrate into the molten resin, and the foamability of the foamed molded body is improved. By setting the pressure of the physical foaming agent to 12 MPa or less, the heat resistance of the foamed molded body is improved, the occurrence of swirl marks is suppressed, and the load on the device can be further reduced. The pressure of the physical foaming agent pressurizing the molten resin is "constant" means that the fluctuation range of the pressure relative to the predetermined pressure is preferably within ±20%, more preferably within ±10%. The pressure in the starvation zone is measured, for example, by a pressure sensor 27 provided in the starvation zone 23 of the plasticizing cylinder 210. Although the starvation zone 23 moves forward and backward within the plasticizing cylinder 210 as the screw 20 advances and retreats, the pressure sensor 27 shown in FIG. 2 is provided at a position that is always within the starvation zone 23 at the most advanced position and the most retreated position of the starvation zone 23. In addition, the position facing the introduction port 202 is also always within the starvation zone 23. Therefore, although the pressure sensor 27 is not provided at a position facing the introduction port 202, the pressure indicated by the pressure sensor 27 and the pressure at the position facing the introduction port 202 are almost the same. In this embodiment, only the physical foaming agent is introduced into the starvation zone 23, but pressurized fluids other than the physical foaming agent may be simultaneously introduced into the starvation zone 23 to the extent that the effect of the present invention is not affected. In this case, the pressurized fluid containing the physical foaming agent introduced into the starvation zone 23 has the above-mentioned constant pressure.

[0029] In this embodiment, as shown in FIG. 2, the physical foaming agent is supplied from the cylinder 100 through the introduction speed adjusting container 300 and from the introduction port 202 to the starvation zone 23. The physical foaming agent is reduced to a predetermined pressure using the pressure reducing valve 151, and then introduced into the starvation zone 23 from the introduction port 202 without passing through a booster or the like. In this embodiment, the amount and introduction time of the physical foaming agent introduced into the plasticizing cylinder 210 are not controlled. Therefore, a mechanism for controlling them, for example, a drive valve using a check valve or an electromagnetic valve, is not required, and the introduction port 202 does not have a drive valve and is always open. In this embodiment, the pressure of the physical foaming agent is maintained constant from the pressure reducing valve 151 through the introduction speed adjusting container 300 to the starvation zone 23 in the plasticizing cylinder 210 by the physical foaming agent supplied from the cylinder 100.

[0030] The inlet 202 for the physical foaming agent has a larger inner diameter than the inlet for the physical foaming agent of the conventional manufacturing apparatus. The reason why the inner diameter of the inlet 202 can be made larger is because the amount of molten resin in the starvation zone 23 facing the inlet 202 during molding is smaller than that of the conventional manufacturing apparatus. Therefore, even a relatively low-pressure physical foaming agent can be efficiently introduced into the plasticizing cylinder 210. Even if a part of the molten resin comes into contact with the inlet 202 and solidifies, the large inner diameter allows it to function as an inlet without being completely blocked. For example, when the inner diameter of the plasticizing cylinder 210 is large, that is, when the outer diameter of the plasticizing cylinder is large, it is easy to make the inner diameter of the inlet 202 large. On the other hand, if the inner diameter of the inlet 202 is extremely large, the molten resin will stagnate, causing molding defects, and the introduction speed adjustment container 300 connected to the inlet 202 will become larger, increasing the cost of the entire apparatus. Specifically, the inner diameter of the introduction port 202 is preferably 20% to 100% of the inner diameter of the plasticizing cylinder 210, and more preferably 30% to 80%. Alternatively, regardless of the inner diameter of the plasticizing cylinder 210, the inner diameter of the introduction port 202 is preferably 3 mm to 150 mm, and more preferably 5 mm to 100 mm. Here, the inner diameter of the introduction port 202 means the inner diameter of the opening on the inner wall 210a of the plasticizing cylinder 210. In addition, the shape of the introduction port 202, i.e., the opening on the inner wall 210a of the plasticizing cylinder 210, The shape of the opening is not limited to a perfect circle, and may be an ellipse or a polygon. When the shape of the inlet 202 is an ellipse or a polygon, the diameter of a perfect circle having the same area as the area of ​​the inlet 202 is defined as the "inner diameter of the inlet 202."

[0031] Next, the introduction speed adjusting container 300 connected to the introduction port 202 will be described. The introduction speed adjusting container 300 connected to the introduction port 202 has a certain volume or more, so that the flow rate of the physical foaming agent introduced into the plasticizing cylinder 210 can be slowed down, and the time for the physical foaming agent to stay in the introduction speed adjusting container 300 can be secured. The introduction speed adjusting container 300 is directly connected to the plasticizing cylinder 210 heated by a band heater (not shown) arranged around it, so that the heat of the plasticizing cylinder 210 is conducted to the introduction speed adjusting container 300. As a result, the physical foaming agent inside the introduction speed adjusting container 300 is heated, the temperature difference between the physical foaming agent and the molten resin is reduced, and the temperature of the molten resin in contact with the physical foaming agent is prevented from being extremely lowered, and the amount of the physical foaming agent dissolved (permeated) into the molten resin can be stabilized. That is, the introduction speed adjusting container 300 functions as a buffer container having a function of heating the physical foaming agent. On the other hand, if the volume of the introduction speed adjusting vessel 300 is too large, the cost of the entire apparatus increases. The volume of the introduction speed adjusting vessel 300 depends on the amount of molten resin present in the starvation zone 23, but is preferably 5 mL to 20 L, more preferably 10 mL to 2 L, and even more preferably 10 mL to 1 L. By setting the volume of the introduction speed adjusting vessel 300 within this range, the residence time of the physical foaming agent can be secured while taking costs into consideration.

[0032] As described later, the physical foaming agent is consumed in the plasticizing cylinder 210 by contacting and penetrating the molten resin. In order to keep the pressure in the starvation zone 23 constant, the consumed amount of physical foaming agent is introduced from the introduction speed adjusting container 300 to the starvation zone 23. If the volume of the introduction speed adjusting container 300 is too small, the frequency of replacement of the physical foaming agent increases, so the temperature of the physical foaming agent becomes unstable, and as a result, there is a risk that the supply of the physical foaming agent becomes unstable. Therefore, it is preferable that the introduction speed adjusting container 300 has a volume that can retain the amount of physical foaming agent consumed in the plasticizing cylinder for 1 to 10 minutes. Also, for example, the volume of the introduction speed adjusting container 300 is preferably 0.1 to 5 times, more preferably 0.5 to 2 times, the volume of the starvation zone 23 to which the introduction speed adjusting container 300 is connected. In this embodiment, the volume of the starvation zone 23 means the volume of the region (23) where the diameter of the axis of the screw 20 and the depth of the screw flight are constant in the empty plasticizing cylinder 210 that does not contain molten resin. Since the inlet 202 is always open, the introduction speed adjusting vessel 300 and the starvation zone 23 are always maintained at a constant pressure of the physical foaming agent during the production of the foamed molded product.

[0033] (3) Starving the molten resin Next, the molten resin is caused to flow into starvation zone 23, where the molten resin is put into a starvation state (step S3 in FIG. 1). The starvation state is determined by the balance between the amount of molten resin sent from the upstream of starvation zone 23 to starvation zone 23 and the amount of molten resin sent from starvation zone 23 to its downstream; if the former is smaller, the starvation state occurs.

[0034] In this embodiment, the compression zone 22, where the molten resin is compressed and the pressure increases, is provided upstream of the starvation zone 23, so that the molten resin is starved in the starvation zone 23. In the compression zone 22, the diameter of the screw 20 is made larger (thicker) than that of the plasticization zone 21 located upstream, and a large diameter portion 20A is provided in which the screw flight is gradually shallower, and further, a seal portion 26 is provided adjacent to the downstream side of the large diameter portion 20A. The seal portion 26 has a large (thicker) diameter of the screw 20 shaft like the large diameter portion 20A, and further, no screw flight is provided, and instead of the screw flight, a plurality of shallow grooves are formed on the shaft of the screw 20. The large diameter portion 20A and the seal portion 26 reduce the clearance between the inner wall of the plasticization cylinder 210 and the screw 20 by increasing the diameter of the shaft of the screw 20, and the amount of resin supplied downstream can be reduced, so that the flow resistance of the molten resin can be increased. Therefore, in this embodiment, the large diameter portion 20A and the seal portion 26 are a mechanism for increasing the flow resistance of the molten resin. The seal portion 26 also has the 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 26.

[0035] Due to the presence of the large diameter portion 20A and the seal portion 26, the resin flow rate supplied from the compression zone 22 to the starvation zone 23 decreases, the molten resin is compressed in the upstream compression zone 22 and the pressure increases, and the molten resin is not filled (starved) in the downstream starvation zone 23. In order to promote the starvation state of the molten resin, the screw 20 has a structure in which the diameter of the shaft of the portion located in the starvation zone 23 is smaller (thinner) and the screw flight is deeper than the portion located in the compression zone 22. Furthermore, it is preferable that the screw 20 has a structure in which the diameter of the shaft of the portion located in the starvation zone 23 is smaller (thinner) and the screw flight is deeper than the portion located in the compression zone 22. Furthermore, it is preferable that the diameter of the shaft of the screw 20 and the depth of the screw flight are approximately constant throughout the starvation zone 23. This allows the pressure in the starvation zone 23 to be kept approximately constant, stabilizing the starvation state of the molten resin. In this embodiment, the starvation zone 23 is formed in a portion of the screw 20 where the diameter of the axis of the screw 20 and the depth of the screw flight are constant, as shown in FIG.

[0036] The mechanism for increasing the flow resistance of the molten resin provided in the compression zone 22 is not particularly limited as long as it is a mechanism for temporarily reducing the flow path area through which the molten resin passes in order to limit the resin flow rate supplied from the compression zone 22 to the starvation zone 23. In this embodiment, both the large diameter portion 20A of the screw and the seal portion 26 are used, but only one of them may be used. Mechanisms for increasing the flow resistance other than the large diameter portion 20A of the screw and the seal portion 26 include a structure in which a screw flight is provided in the opposite direction to other portions, a labyrinth structure provided on the screw, and the like.

[0037] The mechanism for increasing the flow resistance of the molten resin may be provided on the screw as a ring or the like that is separate from the screw, or may be provided integrally with the screw as part of the screw structure. If the mechanism for increasing the flow resistance of the molten resin is provided as a ring or the like that is separate from the screw, the size of the clearance portion, which is the flow path for the molten resin, can be changed by changing the ring, which has the advantage that the magnitude of the flow resistance of the molten resin can be easily changed.

[0038] In addition to the mechanism for increasing the flow resistance of the molten resin, a backflow prevention mechanism (sealing mechanism) that prevents the molten resin from flowing back from the starvation zone 23 to the upstream compression zone 22 can also be provided between the compression zone 22 and the starvation zone 23 to put the molten resin in a starvation state in the starvation zone 23. For example, a sealing mechanism such as a ring or steel ball that can move upstream due to the pressure of the physical foaming agent can be used. However, since the backflow prevention mechanism requires a drive unit, there is a risk of resin stagnation. For this reason, a mechanism for increasing flow resistance that does not have a drive unit is preferable.

[0039] In this embodiment, the amount of thermoplastic resin supplied to the plasticizing cylinder 210 may be controlled in order to stabilize the starvation state of the molten resin in the starvation zone 23. If the amount of thermoplastic resin supplied is too large, it becomes difficult to maintain the starvation state. In this embodiment, a general-purpose feeder screw 212 is used to control the amount of thermoplastic resin supplied. By limiting the amount of thermoplastic resin supplied, the metering speed of the molten resin in the starvation zone 23 becomes higher than the plasticization speed in the compression zone 22. As a result, the density of the molten resin in the starvation zone 23 is stably reduced, and the penetration of the physical foaming agent into the molten resin is promoted.

[0040] In this embodiment, the length of the starvation zone 23 in the flow direction of the molten resin is preferably long in order to secure the contact area and contact time between the molten resin and the physical foaming agent, but if it is too long, the molding cycle and the screw length will be longer. For this reason, the length of the starvation zone 23 is preferably 2 to 12 times, more preferably 4 to 10 times, the inner diameter of the plasticizing cylinder 210. In addition, the length of the starvation zone 23 preferably covers the entire range of the metering stroke in injection molding. That is, the length of the starvation zone 23 in the flow direction of the molten resin is preferably equal to or longer than the length of the metering stroke in injection molding. The screw 20 moves forward and backward with the plasticization, metering, and injection of the molten resin, but by making the length of the starvation zone 23 equal to or longer than the length of the metering stroke, the inlet 202 can always be arranged (formed) within the starvation zone 23 during the production of the foamed molded body. In other words, even if the screw 20 moves forward and backward during the production of the foamed molded body, no zone other than the starvation zone 23 comes to the position of the inlet 202. As a result, the physical foaming agent introduced from the inlet 202 is always introduced into the starvation zone 23 during the production of the foamed molded body. By providing a starvation zone having a sufficient and appropriate size (length) in this way and introducing a physical foaming agent therein at a constant pressure, it becomes easy to maintain the starvation zone 23 at a constant pressure. In this embodiment, the length of the starvation zone 23 is approximately the same as the length of the part of the screw 20 where the diameter of the axis of the screw 20 and the depth of the screw flight are constant, as shown in FIG. 2.

[0041] Furthermore, a flow rate adjusting zone 25 may be provided between the compression zone 22 and the starvation zone 23. When comparing the flow rate of the molten resin in the compression zone 22 upstream of the flow rate adjusting zone 25 with the flow rate of the molten resin in the starvation zone 23 downstream, the flow rate of the molten resin in the starvation zone 23 is faster. The inventors of the present application have found that the foamability of the produced foamed molded product is improved by providing the flow rate adjusting zone 25 as a buffer zone between the compression zone 22 and the starvation zone 23 and suppressing this sudden change (increase) in the flow rate of the molten resin. Although the details of the reason why the foamability of the foamed molded product is improved by providing the flow rate adjusting zone 25 as a buffer zone between the compression zone 22 and the starvation zone 23 are unclear, it is speculated that one of the reasons is that the physical foaming agent flowing in from the starvation zone 23 and the molten resin are forcibly kneaded with each other by the molten resin being retained in the flow rate adjusting zone 25, and the time for kneading is extended. In this embodiment, the molten resin and the physical foaming agent are decompressed and recompressed by changing the flow path area by providing a decompression section and a compression section in the portion located in the flow rate adjustment zone 25 of the plasticizing screw 20 shown in Fig. 2. Furthermore, the flow rate of the molten resin is adjusted by providing a notch in the screw flight. The decompression section and the compression section can be formed, for example, by changing the depth of the screw flight, in other words, by changing the size (thickness) of the screw diameter.

[0042] (4) Contact between molten resin and physical foaming agent Next, while the starvation zone 23 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 23 (step S4 in FIG. 1). That is, in the starvation zone 23, the molten resin is pressurized at a constant pressure by the physical foaming agent. Since the starvation zone 23 is not filled with molten resin (starved state) and has a space in which the physical foaming agent can exist, the physical foaming agent and the molten resin can be efficiently brought into contact with each other. The physical foaming agent that comes into contact with the molten resin penetrates into the molten resin and is consumed. When the physical foaming agent is consumed, the physical foaming agent that remains in the introduction speed adjustment container 300 is supplied to the starvation zone 23. As a result, the pressure in the starvation zone 23 is maintained at a constant pressure, and the molten resin continues to come into contact with the physical foaming agent at a constant pressure.

[0043] In the conventional foam molding using a physical foaming agent, a predetermined amount of high-pressure physical foaming agent was forcibly introduced into the plasticizing cylinder within a predetermined time. Therefore, it is necessary to pressurize the physical foaming agent to a high pressure and accurately control the amount and time of introduction into the molten resin, and the physical foaming agent contacts the molten resin only for a short introduction time. In contrast, in this embodiment, the physical foaming agent is not forcibly introduced into the plasticizing cylinder 210, but a constant pressure physical foaming agent is continuously supplied into the plasticizing cylinder so that the pressure in the starvation zone 23 is constant, and the physical foaming agent is continuously brought into contact with the molten resin. This stabilizes the amount of dissolution (permeation amount) of the physical foaming agent into the molten resin, which is determined by the temperature and pressure. In addition, since the physical foaming agent of this embodiment is always in contact with the molten resin, a necessary and sufficient amount of the physical foaming agent can permeate into the molten resin. As a result, the foam molded product produced in this embodiment has fine foam cells, even though a low-pressure physical foaming agent is used compared to the conventional molding method using a physical foaming agent.

[0044] In addition, since the manufacturing method of the present embodiment does not require control of the amount and time of introduction of the physical foaming agent, it does not require a check valve, a solenoid valve, or other driving valve, or a control mechanism for controlling them, and therefore the cost of the device can be reduced. In addition, the physical foaming agent used in the present embodiment has a lower pressure than conventional physical foaming agents, so the load on the device is also small.

[0045] In this embodiment, the starvation zone 23 is always kept at a constant pressure during the continuous production of foamed molded bodies in the injection molding cycle. That is, in order to make up for the physical foaming agent consumed in the plasticizing cylinder, all steps of the method for producing a foamed molded body are carried out while continuously supplying the physical foaming agent at the constant pressure. In addition, in this embodiment, for example, when performing multiple shots of injection molding continuously, the molten resin for the next shot is prepared in the plasticizing cylinder even during the injection process, the cooling process of the molded body, and the removal process of the molded body, and the molten resin for the next shot is pressurized at a constant pressure by the physical foaming agent. That is, in the case of multiple shots of injection molding performed continuously, one cycle of injection molding including the plasticization metering process, the injection process, the cooling process of the molded body, the removal process, etc. is performed in a state in which the molten resin and the physical foaming agent at a constant pressure are always present and in contact with each other in the plasticizing cylinder, that is, in a state in which the molten resin is always pressurized at a constant pressure by the physical foaming agent in the plasticizing cylinder. Similarly, when performing continuous molding such as extrusion molding, molding is performed in a state where the molten resin and the physical foaming agent at a constant pressure are always present and in contact with each other inside the plasticizing cylinder, that is, the molten resin is always pressurized at a constant pressure by the physical foaming agent inside the plasticizing cylinder.

[0046] (5) Foam molding Next, the molten resin contacted with the physical foaming agent is molded into a foamed molded body (step S5 in FIG. 1). The plasticizing cylinder 210 used in this embodiment is disposed downstream of the starvation zone 23 and adjacent to the starvation zone 23, and has a recompression zone 24 where the molten resin is compressed and the pressure increases. First, the molten resin in the starvation zone 23 is caused to flow into the recompression zone 24 by the rotation of the plasticizing screw 20. The molten resin containing the physical foaming agent is pressure-adjusted in the recompression zone 24, and is extruded forward of the plasticizing screw 20 and metered. At this time, the internal pressure of the molten resin extruded forward of the plasticizing screw 20 is controlled as a screw back pressure by a hydraulic motor or an electric motor (not shown) connected to the rear of the plasticizing screw 20. In this embodiment, in order to homogeneously dissolve the physical foaming agent in the molten resin without separating it and to stabilize the resin density, it is preferable to control the internal pressure of the molten resin extruded forward of the plasticizing screw 20, i.e., the screw back pressure, to be about 1 to 6 MPa higher than the pressure in the starvation zone 23, which is kept constant. In this embodiment, a check ring 50 is provided at the tip of the screw 20 so that the compressed resin in front of the screw 20 does not flow back upstream. As a result, the pressure in the starvation zone 23 is not affected by the resin pressure in front of the screw 20 during metering.

[0047] The molding method of the foam molded body is not particularly limited, and the molded body can be molded by, for example, injection foam molding, extrusion foam molding, foam blow molding, etc. In this embodiment, a measured amount of molten resin is injected and filled into a cavity (not shown) in a mold from a plasticizing cylinder 210 shown in FIG. 2 to perform injection foam molding. For injection foam molding, a short shot method may be used in which a molten resin is filled into the mold cavity at a filling volume of 75% to 95% of the mold cavity volume, and the mold cavity is filled while the bubbles expand, or a core back method may be used in which a molten resin is filled in an amount to fill 100% of the mold cavity volume, and then the cavity volume is expanded and foamed. Since the obtained foam molded body has foam cells inside, contraction of the thermoplastic resin during cooling is suppressed, sink marks and warpage are reduced, and a molded body with a low specific gravity is obtained. The shape of the foam molded body is not particularly limited. It may be a sheet or cylinder by extrusion molding, or a complex shape by injection molding.

[0048] In the manufacturing method of this embodiment described above, since there is no need to control the amount of physical foaming agent introduced into the molten resin, the introduction time, etc., a complex control device can be omitted or simplified, and the equipment cost can be reduced. Also, in the manufacturing method of the foamed molded article of this embodiment, the molten resin in a starved state is brought into contact with the physical foaming agent at the constant pressure in the starvation zone 23 while the starvation zone 23 is kept at a constant pressure. This makes it possible to stabilize the amount of physical foaming agent dissolved (penetrated) into the molten resin by a simple mechanism.

[0049] (6) Foam molded products The inventors of the present application have found that the manufacturing method of this embodiment can produce a foamed molded article having high heat resistance. The super engineering plastic used in the manufacturing method of this embodiment has a high normal heat resistance temperature of 150°C or more. However, foamed molded articles generally have lower heat resistance than solid molded articles (non-foamed molded articles), and foamed molded articles manufactured using conventional high-pressure physical foaming agents cannot obtain sufficient heat resistance even if super engineering plastics are used as thermoplastic resins. When a foamed molded article made of conventional super engineering plastics is passed through a reflow furnace, for example, the foam cells expand, causing problems such as an increase in the thickness of the molded article. In contrast, the foamed molded article obtained in this embodiment has a thickness change rate of -2% to 2%, preferably -1% to 1%, due to heating, when the foamed molded article is heated and the surface temperature of the foamed molded article is maintained at 240°C to 260°C for 5 minutes. Furthermore, the foam molded article obtained in this embodiment has a thickness change rate of -2% to 2%, and preferably -1% to 1%, due to heating when the surface temperature of the foam molded article is maintained at 200° C. to 260° C. for 3 to 10 minutes. Such a foam molded article with high heat resistance undergoes little change in shape and is less likely to blister even when passed through a reflow furnace for lead-free solder.

[0050] Here, the "rate of change in thickness of a foamed molded article due to heating" is defined by the following formula. (Da-Db) / Db x 100(%) Db: Thickness of foamed molded body before heating Da: Thickness of foamed molded body after heating

[0051] It is presumed that the high heat resistance of the foam molded body of this embodiment is achieved by using super engineering plastic as the thermoplastic resin and setting the constant pressure of the physical foaming agent to be in contact with the starved molten resin within a specific range of 0.5 MPa to 12 MPa. In conventional foam molding using supercritical fluids, etc., a high-pressure physical foaming agent of 15 to 20 MPa is used on average. The manufacturing method of this embodiment differs from conventional foam molding in that a relatively low and constant pressure physical foaming agent is brought into contact with the molten resin. The inventors of the present application have found that the heat resistance of the foam molded body is improved by setting the constant pressure of the physical foaming agent to 12 MPa or less, preferably 10 MPa or less, more preferably 8 MPa or less, and even more preferably 6 MPa or less. Furthermore, by lowering the constant pressure of the physical foaming agent, poor appearance (swirl marks) can also be improved. The lower limit of the constant pressure of the physical foaming agent is 0.5 MPa or more, preferably 1 MPa or more, and more preferably 2 MPa or more, from the viewpoint of penetrating the amount of physical foaming agent required for foaming into the molten resin.

[0052] The mechanism by which the foam molded body of this embodiment has high heat resistance is unclear, but it is possible that some structural change, for example, a very microscopic structural change, different from that of conventional foam molded bodies has occurred in the foam molded body of this embodiment due to the combination of a specific type of thermoplastic resin (super engineering plastic) and a specific range of constant pressure (0.5 MPa to 12 MPa) of the physical foaming agent. It is also speculated that the residual foaming agent in the foam molded body expands when heated and adversely affects the heat resistance of the foam molded body. For this reason, it is also thought that the reason why the foam molded body of this embodiment has high heat resistance is simply because there is a small amount of residual foaming agent in the foam molded body. However, according to the inventors' studies, it has been found that even if the residual foaming agent is degassed to a certain extent from a conventional foam molded body by annealing treatment or the like, the same heat resistance as that of the foam molded body of this embodiment cannot be obtained, and swelling or the like occurs when heated. Therefore, it is speculated that the amount of residual foaming agent is not the main factor of the high heat resistance of the foam molded body of this embodiment. Note that the above consideration is the inventors' speculation based on their current knowledge and does not limit the scope of the present invention in any way.

[0053] In this embodiment, the constant pressure of the physical foaming agent is 0.5 MPa to 12 MPa, but there are more preferable ranges depending on the type of super engineering plastic. For example, when the super engineering plastic is polyphenylene sulfide (PPS), the constant pressure of the physical foaming agent is preferably 2 MPa to 12 MPa, more preferably 2 MPa to 10 MPa, and even more preferably 2 MPa to 8 MPa. When the super engineering plastic is liquid crystal polymer (LCP), the constant pressure of the physical foaming agent is preferably 1 MPa to 6 MPa. When the type of super engineering plastic and the range of the constant pressure of the physical foaming agent are combined as above, a foamed molded product with better foaming properties and higher heat resistance can be obtained, and further, the occurrence of swirl marks can be suppressed.

[0054] The foamed molded article produced in this embodiment has an average cell diameter of 100 μm or less, and more preferably 50 μm or less. When the average cell diameter of the foamed cells is within the above range, the side walls of the cells become small, making them less likely to expand when heated, and as a result, the heat resistance of the foamed molded article is further improved. The average cell diameter of the foamed cells can be determined, for example, by image analysis of a cross-sectional SEM photograph of the foamed molded article.

[0055] In the foam molded product produced in this embodiment, the thickness of the foam part in which the foam cells are formed inside is preferably 0.5 mm or more, more preferably 1 mm or more, and even more preferably 2 mm or more. When the thickness is in the above range, a skin layer of sufficient thickness can be formed on the molded product. The skin layer can suppress the expansion of the foam cells when the foam molded product is heated, so that the heat resistance of the foam molded product is further improved. In particular, when LCP is used as the super engineering plastic, the encapsulated gas containing the physical foaming agent is less likely to escape from the foam molded product of LCP. By increasing the thickness of the foam part, the expansion of the foam cells due to the expansion of the encapsulated gas is suppressed, and the heat resistance of the foam molded product using LCP is further improved. In addition, in the foam molded product produced in this embodiment, the thickness of the foam part in which the foam cells are formed inside may be 3 mm or less, 2 mm or less, or 1 mm or less. The thinner the foamed portion, the greater the rate of change in thickness of the foamed molded body due to heating tends to be; however, because the foamed molded body produced by the production method of this embodiment has high heat resistance, even for foamed portions with thicknesses within the above range, the rate of change in thickness of the foamed molded body due to heating can be suppressed to -2% to 2%, preferably -1% to 1%.

[0056] In this embodiment, the produced foamed molded article may be further annealed. By heating the foamed molded article in the annealing treatment, the encapsulated gas containing the physical foaming agent can be degassed from the foamed molded article. This suppresses the expansion of the foam cells due to the expansion of the encapsulated gas, and further improves the heat resistance of the foamed molded article. EXAMPLES

[0057] The present invention will be further described below using examples and comparative examples. However, the present invention is not limited to the examples and comparative examples described below.

[0058] [Preparation of Sample 1-1] Sample 1-1 (foamed molded product) was manufactured using polyphenylene sulfide (PPS) (polyplastic, Gelafide 1130T6) as the thermoplastic resin and nitrogen as the physical foaming agent. The pressure of the physical foaming agent introduced into the starvation zone of the plasticizing cylinder was 1 MPa.

[0059] (1) Manufacturing equipment In this example, the manufacturing apparatus 1000 shown in Fig. 2 used in the above-mentioned embodiment is used. The manufacturing apparatus 1000 will be described in detail. As described above, the manufacturing apparatus 1000 is an injection molding apparatus, and includes the plasticizing cylinder 210, the cylinder 100 which is a physical foaming agent supply mechanism that supplies a physical foaming agent to the plasticizing cylinder 210, a mold clamping unit (not shown) in which a mold is provided, and a control device (not shown) for controlling the operation of the plasticizing cylinder 210 and the mold clamping unit.

[0060] A nozzle tip 29 of the plasticizing cylinder 210 is provided with a shutoff valve 28 that opens and closes by driving an air cylinder, and the inside of the plasticizing cylinder 210 can be kept at high pressure. A mold (not shown) is in close contact with the nozzle tip 29, and molten resin is injected from the nozzle tip 29 into a cavity formed by the mold. On the upper side surface of the plasticizing cylinder 210, a resin supply port 201 for supplying a thermoplastic resin to the plasticizing cylinder 210 and an introduction port 202 for introducing a physical foaming agent into the plasticizing cylinder 210 are formed in this order from the upstream side. A resin supply hopper 211, a feeder screw 212, and an introduction speed adjustment container 300 are disposed in the resin supply port 201 and the introduction port 202, respectively. The introduction speed adjustment container 300 is connected to the cylinder 100 by a piping 154 via a pressure reducing valve 151, a pressure gauge 152, and an open valve 153. Also provided within the starvation zone 23 of the plasticizing cylinder 210 is a sensor 27 for monitoring the pressure in the starvation zone 23 .

[0061] The screw 20 is disposed in the plasticizing cylinder 210 so as to be freely rotatable and movable forward and backward in order to promote the plasticization and melting of the thermoplastic resin and to measure and inject the molten resin. As described above, the screw 20 is provided with the seal portion 26 and the large diameter portion 20A of the screw 20 as a mechanism for increasing the flow resistance of the molten resin.

[0062] In the plasticizing cylinder 210, thermoplastic resin is supplied into the plasticizing cylinder 210 from the resin supply port 201, and the thermoplastic resin is plasticized by a band heater (not shown) to become molten resin, which is sent downstream by the forward rotation of the screw 20. Due to the presence of the seal portion 26 and the large diameter portion 20A provided on the screw 20, the molten resin is compressed and the pressure increases upstream of the seal portion 26, and the starvation zone 23 downstream of the seal portion 26 is not filled with molten resin (starved state). The molten resin sent further downstream is recompressed and measured near the tip of the plasticizing cylinder 210 before injection.

[0063] As a result, within the plasticizing cylinder 210, from the upstream side, there are formed a plasticization zone 21 where the thermoplastic resin is plasticized and melted, a compression zone 22 where the molten resin is compressed and the pressure increases, a flow speed adjustment zone 25 where the flow speed of the molten resin is adjusted, a starvation zone 23 where the molten resin is not yet filled, and a re-compression zone 24 where the molten resin whose pressure has been reduced in the starvation zone is compressed again.

[0064] In the manufacturing apparatus 1000, the inner diameter of the plasticizing cylinder 210 was 22 mm, and the inner diameter of the inlet 202 was 6 mm. Therefore, the inner diameter of the inlet 202 was about 27% of the inner diameter of the plasticizing cylinder 210. Moreover, the volume of the introduction speed adjusting container 300 was about 80 mL, and the volume of the starvation zone 23 was 110 mL. Therefore, the volume of the introduction speed adjusting container 300 was about 0.7 times the volume of the starvation zone 23. Moreover, in this embodiment, a mold with a cavity size of 5 cm x 5 cm x 2 mm was used.

[0065] (2) Manufacturing of foamed molded products In this embodiment, a nitrogen cylinder with a volume of 47 L filled with nitrogen at 14.5 MPa was used as the cylinder 100. First, the pressure reducing valve 151 was set to 1 MPa, the cylinder 100 was opened, and nitrogen at 1 MPa was supplied to the starvation zone 23 from the inlet 202 of the plasticizing cylinder 210 via the pressure reducing valve 151, the pressure gauge 152, and the introduction rate adjusting container 300. During the production of the molded body, the cylinder 100 was always in an open state.

[0066] In the plasticizing cylinder 210, the plasticizing zone 21 was adjusted to 320-300°C, the compression zone 22 to 320°C, the flow speed adjustment zone 25 and the starvation zone 23 to 300°C, and the recompression zone 24 to 320°C by a band heater (not shown). Then, while rotating the feeder screw 212 at a rotation speed of 30 rpm, resin pellets of thermoplastic resin (PPS) were supplied from the resin supply hopper 211 to the plasticizing cylinder 210, and the screw 20 was rotated forward. As a result, the thermoplastic resin was heated and kneaded in the plasticizing zone 21 to become a molten resin.

[0067] The rotation speed of the feeder screw 212 was determined as the rotation speed at which the resin pellets were starved for supply by setting (setting) the molding conditions of this embodiment in advance by molding a solid molded body (non-foamed molded body). Here, the starved supply of the resin pellets means a state in which the plasticizing cylinder is not filled with the resin pellets or their molten resin during the supply of the resin pellets in the plasticizing zone 21, and the flight of the screw 20 is exposed from the supplied resin pellets or their molten resin. The starved supply of the resin pellets can be confirmed, for example, by a method of confirming the presence or absence of the resin pellets or the molten resin on the screw 20 using an infrared sensor or a visualization camera. In this embodiment, a transparent window was provided in the feeder screw 212 used, and the state of the plasticizing zone 21 directly below the resin supply port 201 was visually confirmed through the transparent window.

[0068] The back pressure of the screw 20 was set to 3 MPa (pressure of the physical foaming agent: 1 MPa + 2 MPa = 3 MPa) and the screw was rotated forward at a rotation speed of 100 rpm, causing the molten resin to flow from the plasticization zone 21 to the compression zone 22, and then to the flow rate adjustment zone 25 and the starvation zone 23.

[0069] The molten resin flows from the gap between the large diameter screw portion 20A and the seal portion 26 and the inner wall of the plasticizing cylinder 210 into the flow speed adjustment zone 25 and the starvation zone 23, so the amount of molten resin supplied to the starvation zone 23 is restricted. As a result, the molten resin is compressed in the compression zone 22, increasing the pressure, and the downstream starvation zone 23 becomes underfilled with molten resin (starved state). Since the starvation zone 23 is underfilled with molten resin (starved state), the physical foaming agent (nitrogen) introduced from the inlet 202 is present in the space where no molten resin is present, and the molten resin is pressurized by the physical foaming agent.

[0070] The molten resin was then sent to the recompression zone 24 and recompressed, and as the screw 20 retreated, one shot of molten resin was metered at the tip of the plasticizing cylinder 210. The shut-off valve 28 was then opened, and the molten resin was injected and filled into the cavity to fill 90% of the cavity volume, forming a flat-plate shaped foamed molded body (short shot method). The mold temperature was 150°C. After molding, the foamed molded body was allowed to cool, and then removed from the mold. The cooling time was 10 seconds.

[0071] The injection molding of the molded body described above was performed continuously for 20 shots to obtain 20 foam molded bodies. During the production of the 20 foam molded bodies, the pressure in the starvation zone 23 in the plasticizing cylinder 210 was constantly measured by the pressure sensor 27. As a result, the pressure in the starvation zone 23 was always constant at 1 MPa. In addition, the value of the pressure gauge 152 indicating the pressure of the nitrogen supplied to the starvation zone 23 was also always 1 MPa during the production of the foam molded body. From the above, it was confirmed that the molten resin was constantly pressurized by nitrogen at 1 MPa in the starvation zone 23 throughout one cycle of injection molding including the plasticization metering step, the injection step, the cooling step of the molded body, the removal step, etc., and that the molten resin was constantly pressurized by nitrogen in the starvation zone 23 during the continuous molding of the 20 molded bodies.

[0072] [Preparation of Samples 1-2 to 1-10] Samples 1-2 to 1-10 (foamed molded bodies) were produced in the same manner as sample 1-1, except that the pressures of the physical foaming agent introduced into the starvation zone of the plasticizing cylinder were 2 MPa, 4 MPa, 6 MPa, 8 MPa, 10 MPa, 12 MPa, 14 MPa, 18 MPa, and 0.4 MPa, respectively.

[0073] During the production of each sample (foam molded body), the pressure in the starvation zone 23 in the plasticizing cylinder 210 was constantly measured by the pressure sensor 27. As a result, the pressure in the starvation zone 23 was a constant pressure equal to that of the introduced physical foaming agent. In addition, the value of the pressure gauge 152 indicating the pressure of the nitrogen supplied to the starvation zone 23 was also a constant pressure set for each sample during the production of the foam molded body. From the above, it was confirmed that the molten resin was constantly pressurized by nitrogen at a constant pressure set for each sample in the starvation zone 23 throughout one cycle of injection molding including the plasticization metering process, the injection process, the cooling process of the molded body, the removal process, etc., and that the molten resin was constantly pressurized by nitrogen in the starvation zone 23 during the continuous molding of 20 molded bodies.

[0074] [Evaluation of Samples 1-1 to 1-10] Samples 1-1 to 1-10 (foamed molded articles) were evaluated by the methods described below. The evaluation results of each sample are shown in Tables 1 and 2 together with the pressure of the physical foaming agent used in the production of each sample. Samples 1-1 to 1-7, in which the pressure of the physical foaming agent used in the production was 1 to 12 MPa, correspond to Examples, and Samples 1-8 to 1-10, in which the pressure was 14 MPa, 18 MPa, and 0.4 MPa, correspond to Comparative Examples.

[0075] (1) Foamability of foamed molded products The shape and cross section of the foamed molded article were observed, and the foamability of the foamed molded article was evaluated according to the following evaluation criteria. The foamed molded article rated A according to the following evaluation criteria had a specific gravity reduced by about 10% compared to the solid molded article.

[0076] <Evaluation criteria for foaming> A: It is sufficiently foamed. The foamed molded product completely fills the cavity of the mold, and the foam cells formed inside the foamed molded product are fine (cell diameter is about 30 to 50 μm). B: It is foaming. Although the foamed molded product does not completely fill the cavity of the mold, there are no unfilled areas at the ends of the cavity. In other words, the flow end of the molten resin reaches the ends of the cavity. Enlarged cells (cell diameter of about 100 to 200 μm) are occasionally found among the foamed cells formed inside the foamed molded product. C: Only a part of the molded article is foamed. There is an unfilled portion at the end of the mold cavity. In other words, the flow end of the molten resin has not reached the end of the cavity. The foam cells formed near the end of the foamed molded product (near the flow end of the molten resin) are enlarged (cell diameter is about 100 to 200 μm).

[0077] (2) Change in thickness of foamed molded body due to heating test Five pieces of each foam molded body were randomly selected from the 20 pieces of each of the samples 1-1 to 1-10 prepared above. First, the length of the part corresponding to the thickness of the flat plate (the part corresponding to the width of the cavity of the mold, 2 mm) was measured at four points for each foam molded body (thickness Db). Then, the heating test described below was performed. First, the foam molded body was placed in an electric furnace heated to a set temperature of 250°C, assuming a reflow furnace for lead-free solder. A thermocouple was contacted with the surface of the foam molded body to measure the surface temperature, and it was confirmed that the maximum temperature reached was 240°C to 260°C. Five minutes after the surface temperature reached the maximum temperature, the foam molded body was removed from the electric furnace. The time for which the foam molded body was placed in the electric furnace was about 8 to 9 minutes. After cooling the foam molded body to room temperature, the thickness of the part where the thickness was measured before heating was measured again (thickness Da), and the change rate of the thickness of the foam molded body due to the heating test was calculated by the following formula. (Da-Db) / Db x 100(%) Db: Thickness of foamed molded body before heating Da: Thickness of foamed molded body after heating

[0078] The thickness change rate was determined at four points for each foam molded body, and the thickness change rate was determined in the same manner for five foam molded bodies for each sample (4 points x 5 = 20 points in total). The average value of the thickness change rates at these 20 points was taken as the thickness change rate of the foam molded body of each sample due to the heating test.

[0079] (3) Surface swelling after heating test The surface of the foamed molded article after the above-mentioned heating test was observed, and the presence or absence of surface blistering was evaluated according to the following evaluation criteria.

[0080] <Evaluation criteria for surface swelling after heating test> A: There is no blister on the surface of the foamed molded article. B: There is a small bulge (less than 1 mm in diameter) on part of the surface of the foamed molded article. C: There is a large blister on the surface of the foamed molded article (diameter 1mm to 3mm). D: There is a large blister on the surface of the foamed molded article (diameter 3 mm or more).

[0081] (4) Swirl marks on the surface of foamed molded products The surface of the foamed molded article before the heating test was observed, and the presence or absence of swirl marks on the surface was evaluated according to the following evaluation criteria.

[0082] <Swirl mark evaluation criteria> A: No swirl marks or very few swirl marks. B: Swirl marks have occurred on some parts of the foamed molded article surface. C: Swirl marks are observed all over the surface of the foamed molded article, and the surface of the foamed molded article is cloudy and white.

[0083] [Table 1] [Table 2]

[0084] Samples 1-1 to 1-7, which were produced using a physical foaming agent at a pressure of 1 to 12 MPa, had good foaming properties, and the rate of change in thickness of the foamed molded body due to the heating test was small, and the surface swelling was also small, so it was confirmed that they had high heat resistance. Furthermore, the occurrence of swirl marks was also suppressed. Samples 1-2 to 1-6, which were produced using a physical foaming agent at a pressure of 2 to 10 MPa, had better foaming properties, higher heat resistance, and less occurrence of swirl marks.

[0085] On the other hand, in the samples 1-8 and 1-9, which were produced using a physical foaming agent with a pressure of more than 12 MPa, the thickness change rate of the foamed molded body was large during the heating test, and the surface bulging was also large, indicating that the heat resistance was low. In addition, the occurrence of swirl marks was significant in the samples 1-8 and 1-9. In the sample 1-10, which was produced using a physical foaming agent with a pressure of less than 0.5 MPa, the foamability of the foamed molded body was insufficient.

[0086] [Preparation of Samples 2-1 to 2-8] Samples 2-1 to 2-8 (foam molded articles) were produced in the same manner as Sample 1-1, except that a liquid crystal polymer (LCP) (LAPEROS S135, made by Hori Plastic) was used as the thermoplastic resin and the pressures of the physical foaming agent (nitrogen) introduced into the starvation zone of the plasticizing cylinder were 0.5 MPa, 1 MPa, 2 MPa, 4 MPa, 6 MPa, 8 MPa, 10 MPa, and 0.4 MPa, respectively.

[0087] During the production of each sample (foam molded body), the pressure in the starvation zone 23 in the plasticizing cylinder 210 was constantly measured by the pressure sensor 27. As a result, the pressure in the starvation zone 23 was a constant pressure equal to that of the introduced physical foaming agent. In addition, the value of the pressure gauge 152 indicating the pressure of the nitrogen supplied to the starvation zone 23 was also a constant pressure set for each sample during the production of the foam molded body. From the above, it was confirmed that the molten resin was constantly pressurized by nitrogen at a constant pressure set for each sample in the starvation zone 23 throughout one cycle of injection molding including the plasticization metering process, the injection process, the cooling process of the molded body, the removal process, etc., and that the molten resin was constantly pressurized by nitrogen in the starvation zone 23 during the continuous molding of 20 molded bodies.

[0088] [Evaluation of Samples 2-1 to 2-8] The above-prepared samples 2-1 to 2-8 (foam molded articles) were evaluated in the following items (1) to (4) by the same methods as those for the above-mentioned samples 1-1 to 1-10. (1) Foamability of foamed molded products (2) Change in thickness of foamed molded body due to heating test (3) Surface swelling after heating test (4) Swirl marks on the surface of foamed molded products

[0089] The evaluation results of each sample are shown in Table 3 together with the pressure of the physical foaming agent used in the production of each sample. Samples 2-1 to 2-7, in which the pressure of the physical foaming agent used in the production was 0.5 to 10 MPa, correspond to Examples, and Sample 2-8, in which the pressure was 0.4 MPa, corresponds to Comparative Example.

[0090] [Table 3]

[0091] Samples 2-1 to 2-7, which were produced using a physical foaming agent with a pressure of 0.5 to 10 MPa, had good foaming properties and showed a small change in thickness of the foamed molded body due to the heating test, which confirmed that they had high heat resistance. Furthermore, the occurrence of swirl marks was also suppressed. Samples 2-2 to 2-5, which were produced using a physical foaming agent with a pressure of 1 to 6 MPa, had better foaming properties, higher heat resistance, and less occurrence of swirl marks.

[0092] On the other hand, in the case of Sample 2-8, in which the pressure of the physical foaming agent used during production was 0.4 MPa, the foaming properties of the foamed molded article were insufficient. [Industrial Applicability]

[0093] The manufacturing method of the present invention can simplify the device mechanism related to the physical foaming agent. It can also efficiently manufacture foamed molded articles with excellent foaming properties at low cost. Furthermore, it can manufacture foamed molded articles of super engineering plastics with high heat resistance. [Explanation of symbols]

[0094] 20 Screw 21 Plasticization Zone 22 Compression Zone 23 Starvation Zone 24 Recompression Zone 25 Flow rate control zone 26 Seal part 27 Pressure Sensor 100 Cylinders 210 Plasticizing Cylinder 300 Introduction speed adjustment container 1000 manufacturing equipment

Claims

1. A foamed molded article formed by contacting a starved depopulated molten thermoplastic resin with a pressurized fluid containing a physical foaming agent at a constant pressure of 0.5 MPa to 6 MPa, The thermoplastic resin contains 60% by weight or more of super engineering plastics, When the foamed molded article containing a thermoplastic resin is heated and the surface temperature of the foamed molded article is maintained at 240° C. to 260° C. for 5 minutes, the rate of change in thickness of the foamed molded article due to heating is −2% to 2%; The foam molded body is formed by injection foam molding in which the molten resin is filled into a mold cavity, The resin density of the foamed molded body (here, resin density refers to the ratio of the resin volume to the mold cavity volume) is 75% to 95%, The foamed molded article has an average cell diameter of 100 μm or less.

2. The foam molded article according to claim 1, characterized in that when the foam molded article is heated and the surface temperature of the foam molded article is maintained at 240°C to 260°C for 5 minutes, the rate of change in thickness of the foam molded article due to heating is -0.4% to 0.7%.

3. 3. The foam molded article according to claim 1, wherein the super engineering plastic contains polyphenylene sulfide or a liquid crystal polymer.

4. 3. The foam molded article according to claim 1, wherein the foam molded article is heated in a reflow furnace.

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