Method for producing foamed particle molded body

Abstract

Provided is a method for producing a foamed particle molded body enabling a reduction in the amount of steam supplied into a mold and an improvement in energy loss during in-mold molding.　The method involves filling a cavity (10) of a split mold (100) composed of a first mold (30A) and a second mold (30B) with thermoplastic resin foam particles (50) and performing heating using steam to carry out in-mold molding. The first mold (30A) and / or the second mold (30B) have an exhaust chamber (20) provided so as to allow ventilation from the cavity (10). The method includes: a pressurizing step of supplying a pressurizing gas other than steam into the cavity (10) to adjust the pressure in the cavity (10) filled with the foam particles (50) to a pressure (P1) higher than atmospheric pressure; and a heating step of heating the foam particles (50) by supplying steam at a pressure (P2) higher than the pressure (P1) into the cavity (10) adjusted to the pressure (P1) in the pressurizing step, and exhausting the steam supplied into the cavity (10) to the exhaust chamber (20). In the heating step, the steam at the pressure (P2) is supplied into the cavity (10) while adjusting the pressure in the exhaust chamber (20) to a pressure (P3) higher than atmospheric pressure and lower than the pressure (P2).

Description

Method for producing expanded bead molded body

[0001] The present invention relates to a method for producing an expanded bead molding using expanded thermoplastic resin beads.

[0002] Expanded bead molded articles obtained by in-mold molding using expanded thermoplastic resin beads are widely used in various technical fields, such as vehicle components, cushioning materials, building materials, and heat insulating materials. Such expanded bead molded articles are generally produced by supplying expanded thermoplastic resin beads into a space formed by a pair of molds, supplying steam to the space, and heating and fusing the expanded thermoplastic resin beads. Hereinafter, the space may be referred to as a cavity.

[0003] More specifically, for example, Patent Document 1 discloses the following method: First, propylene-based resin pre-expanded beads are compressed under gas pressure and then compressed and packed into a pair of molds together with the compressed gas. Next, the compressed gas is released from the molds to reduce the internal pressure, and steam is then supplied to the molds to heat-fuse the expanded beads in the molds, thereby producing an expanded bead molded article. This production method may be referred to as Prior Art 1 below. Furthermore, Patent Document 2 discloses a method for producing an in-mold expanded polypropylene-based resin article by a compression-filling method using multi-stage expanded polypropylene-based resin beads. According to Figure 1 of Patent Document 2, the mold is shown to have a cavity into which the expanded beads are filled and a steam chamber, and it can be seen that steam supplied to the steam chamber is introduced into the cavity.

[0004] Another known method for producing a foamed bead molding involves using a mold having a cavity and a chamber similar to the mold disclosed in Patent Document 1, filling the cavity with foamed thermoplastic resin beads without using pressurized gas, and then steam heating the cavity. This method is hereinafter sometimes referred to as Prior Art 2. In the steam heating, the air in the chamber and the cavity is first replaced with steam under atmospheric pressure. Next, after sealing the mold, steam is supplied to the chamber, which then introduces the steam into the first and second spaces in the chamber. The pressure and temperature in the first and second spaces and the cavity are increased, thereby heat-fusing the foamed beads and producing a foamed bead molding.

[0005] As described above, in conventional in-mold molding, after foamed beads are supplied to a cavity, high-pressure steam is supplied to a mold whose internal pressure is atmospheric pressure, thereby smoothly supplying steam to the cavity provided in the mold and heat-fusing the foamed beads.

[0006] JP 8-300387 JP 2010-138226

[0007] An object of the present invention is to provide a method for producing an expanded bead molding that can reduce the amount of steam supplied into a mold and improve energy loss during molding within the mold.

[0008] The method for producing an expanded bead molded body of the present invention involves filling the cavity of a split molding die consisting of a first die and a second die with expanded thermoplastic resin beads, and heating the expanded beads with steam to form them in the die. The first die and / or the second die has an exhaust chamber that is airtight with the cavity. The method includes a pre-pressurization step in which a pressurized gas other than steam is supplied into the cavity to adjust the pressure in the cavity filled with the expanded beads to a pressure (P1) that exceeds atmospheric pressure, and a heating step in which steam at a pressure (P2) higher than the pressure (P1) is supplied into the cavity adjusted to the pressure (P1) in the pre-pressurization step, and the steam supplied into the cavity is exhausted into the exhaust chamber to heat the expanded beads. The heating step is characterized in that, while supplying steam at the pressure (P2) into the cavity, the pressure in the exhaust chamber is adjusted to a pressure (P3) that exceeds atmospheric pressure but is lower than the pressure (P2).

[0009] The method for producing an expanded bead molding of the present invention involves preliminarily adjusting the pressure in the cavity to a pressure (P1) above atmospheric pressure using a pressurized gas other than steam, and then supplying steam at a pressure (P2) higher than the pressure in the cavity (P1) into the cavity, thereby making it possible to significantly reduce the amount of steam supplied compared to conventional in-mold molding.

[0010] Fig. 1 is a longitudinal sectional view of a molding die used in a first embodiment of the present invention. Fig. 2 is a partially enlarged sectional view of the molding die shown in Fig. 1. Fig. 3 is a longitudinal sectional view of a molding die used in a second embodiment of the present invention. Fig. 4 is a longitudinal sectional view of a molding die used in a third embodiment of the present invention. Fig. 5 is a graph showing pressure and temperature in a model of a manufacturing method of the present invention. Fig. 6 is a graph showing pressure and temperature in a model of a manufacturing method of a conventional example.

[0011] The method for producing an expanded bead molded article of the present invention (hereinafter, sometimes simply referred to as the production method of the present invention) will be described below. In the following description, preferred numerical ranges of the present invention may be indicated as appropriate. In the present invention, the term "gauge pressure" refers to a pressure determined based on atmospheric pressure, and is a pressure obtained by subtracting atmospheric pressure from absolute pressure. In this specification, the unit for gauge pressure is MPa (G). In the present invention, the term "pressure (P1)" refers to the pressure inside the cavity adjusted by the pre-pressure step. The term "pressure (P2)" refers to the pressure of the steam used in the heating step. The term "pressure (P3)" refers to the pressure inside the exhaust chamber during the heating step. These have the relationship atmospheric pressure < pressure (P1) < pressure (P2), and also atmospheric pressure < pressure (P3) < pressure (P2). The term "pressure (P3)" refers to the molding pressure during production of the molded article.

[0012] The manufacturing method of the present invention produces a foamed bead molded article by filling a cavity of a split mold consisting of a first mold and a second mold with expanded thermoplastic resin beads and heating the expanded beads with steam to mold the expanded beads in-mold. The first mold and / or the second mold have a cavity and an exhaust chamber provided to allow ventilation to the cavity. The manufacturing method of the present invention includes a pre-pressurizing step and a heating step. The pre-pressurizing step is a step of supplying a pressurized gas other than steam into the cavity filled with expanded beads to adjust the pressure in the cavity filled with the expanded beads to a pressure (P1) exceeding atmospheric pressure. The filling step may be performed before or overlapping with the pre-pressurizing step. The filling step is a step of filling the cavity with expanded thermoplastic resin beads. The heating step is performed subsequent to or overlapping with the pre-pressurizing step. The heating step is a step of supplying steam at a pressure (P2) higher than the pressure (P1) into the cavity adjusted to the pressure (P1) in the pre-pressure step, and exhausting the steam supplied into the cavity to an exhaust chamber, thereby heating the expanded beads. Furthermore, in the heating step, while supplying steam at the pressure (P2) into the cavity, the pressure in the exhaust chamber is adjusted to a pressure (P3) higher than atmospheric pressure but lower than the pressure (P2). The manufacturing method of the present invention performs the above steps to mold expanded thermoplastic resin beads and produce an expanded bead molding.

[0013] The inventors' investigations revealed that in conventional in-mold molding, most of the steam supplied to the mold before the expanded beads are heated and fused is used to increase the internal pressure of the entire mold, resulting in significant energy loss. This is because the steam is supplied into a mold at atmospheric pressure, and the steam is consumed to heat the mold, causing the pressure and temperature of the steam to drop immediately after supply. In other words, it is estimated that in conventional in-mold molding, an amount of steam supplied is several to several dozen times the amount actually required to heat and fused the expanded beads filled in the cavity. In consideration of this problem, the manufacturing method of the present invention described above requires that in the pre-pressurization step, the pressure inside the mold cavity is adjusted to a pressure (P1) above atmospheric pressure using a pressurized gas other than steam, and that in the subsequent heating step, steam at a pressure (P2) higher than the pressure inside the cavity is supplied to the cavity. Additionally, in the manufacturing method of the present invention, in the heating step, while supplying steam at the pressure (P2) into the cavity, the pressure in the exhaust chamber is adjusted to a pressure (P3) that exceeds atmospheric pressure and is lower than the pressure (P2). This allows steam to easily flow from the cavity to the exhaust chamber in the heating step. Note that in the present invention, steam refers to water vapor. The pressure in the cavity in the pre-pressure step may be adjusted to a predetermined pressure as appropriate. Furthermore, the heating step can be performed by adjusting the supply of steam under conditions that the pressure in the cavity becomes the predetermined pressure. These adjustments can also be determined as appropriate taking into account the constituent resin of the expanded beads used, etc. Details will be described further below.

[0014] According to the present invention described above, it is possible to significantly reduce the amount of steam used compared to conventional in-mold molding, thereby improving energy loss during in-mold molding. In other words, the manufacturing method of the present invention performs the heating step after the pre-pressure step, thereby allowing the supplied steam to be efficiently used for heat-fusing the expanded beads, and making it possible to appropriately shorten the heating time compared to conventional methods. The present invention will be described in further detail below. Furthermore, in the manufacturing method of the present invention, the pre-pressure step and the heating step may completely or partially overlap, which also achieves the same effects as described above.

[0015] First Embodiment (Split Mold) First, a split mold 100 used in the manufacturing method of this embodiment will be described with reference to Figures 1 and 2. Figure 1 is a longitudinal cross-sectional view of the split mold 100 used in this embodiment. Figure 2 is a partially enlarged cross-sectional view of the split mold 100 shown in Figure 1, with the expanded thermoplastic resin particles 50 in the cavity 10 omitted. As shown in Figure 1, the split mold 100 used in this embodiment includes a first mold 34 and a second mold 36. The split mold 100 is provided with the cavity 10 and an exhaust chamber 20. The first mold 34 includes a first inner mold 30A and a first frame 40A, and the second mold 36 includes a second inner mold 30B and a second frame 40B. The first inner mold 30A and the second inner mold 30B are paired together to form a pair of molds 30. The internal space of this pair of molds 30 is the cavity 10. An exhaust chamber 20 is provided on the back side of the first inner mold 30A and / or the back side of the second inner mold 30B. In this embodiment, the exhaust chamber 20 is the space between the first inner mold 30A and the first frame 40A covering it, and the space between the second inner mold 30B and the second frame 40B covering it. However, the exhaust chamber 20 in the present invention is not limited to this. For example, the exhaust chamber 20 may be provided in only one of the first mold 34 or the second mold 36, or in both the first mold 34 and the second mold 36. The first frame 40A and the second frame 40B form a frame 40 that constitutes the exterior of the split molding die 100. A pair of molds 30 are provided inside the frame 40. The frame 40 is provided with exhaust holes 66 that can exhaust gas from the exhaust chamber 20 to the outside of the split molding die 100. The provision of the exhaust holes 66 allows ventilation between the exhaust chamber 20 and the outside of the split molding die 100. In this embodiment, exhaust holes 66 are provided in the wall surface of the first frame 40A and the wall surface of the second frame 40B, and each exhaust hole 66 is provided with an opening / closing mechanism 67 that can open and close the opening. In the context of the present invention, the opening / closing mechanism refers to a mechanism that switches the through hole between an open state and a closed state, and includes, but is not limited to, a drain valve.In this embodiment, the first inner mold 30A is a concave mold, and the second inner mold 30B is a convex mold. However, the pair of molds 30 used in the present invention is not limited to this, and for example, both the first inner mold 30A and the second inner mold 30B may be concave molds. In addition, with regard to each of the above terms, the first inner mold 30A is also referred to as the mold cavity side inner mold, and the second inner mold 30B is also referred to as the mold core side inner mold.

[0016] The cavity 10 is a space into which the expanded thermoplastic resin beads 50 are filled to produce an expanded bead molding. One end region of a filling feeder 52, which penetrates the frame 40, is inserted into the cavity 10. Here, "one end region of the filling feeder 52 being inserted into the cavity 10" refers to a state in which the expanded thermoplastic resin beads 10 can be supplied into the cavity 10 from the end region. This includes both a state in which the end region is inserted into the cavity 10 and a state in which the end region faces the inner surface of the cavity 10. The other end region of the filling feeder 52 is located outside the split mold 100, and the expanded thermoplastic resin beads 50 are filled from that end region. The expanded thermoplastic resin beads 50 may also be referred to as "expanded beads 50" as appropriate. Each of the pair of molds 30 has a vent hole 64 to ensure ventilation between the cavity 10 and at least one of the exhaust chambers 20. Pressurized gas other than steam or steam can ventilate between the cavity 10 and the exhaust chamber 20 through the vent hole 64. In this embodiment, the vent hole 64 is provided in the molding wall 32, which is the wall surface of the first inner mold 30A, thereby allowing ventilation between the cavity 10 and the exhaust chamber 20 provided on the back side of the first inner mold 30A. The molding wall 32 is a wall surface that separates the cavity 10 and the exhaust chamber 20 of the split molding mold 100. However, the present invention also includes an embodiment in which the vent hole 64 is provided in the second inner mold 30B and an embodiment in which the vent hole 64 is provided in both the first inner mold 30A and the second inner mold 30B. The vent hole 64 may be always open, but in this embodiment, an opening and closing mechanism 65 is provided that can open and close the opening to properly adjust the internal pressure of the cavity 10.

[0017] The split mold 100 is provided with a steam supply unit 60 for supplying steam to the interior. In this embodiment, the steam supply unit 60 is a tubular body for supplying steam from the outside of the split mold 100 to the interior. When the steam inlet side is defined as the upstream side and the steam outlet side is defined as the downstream side, one or more supply holes 68 for discharging steam are provided in the downstream end region. More specifically, in this embodiment, the steam supply unit 60 is provided with a main flow path 60A for introducing steam from the outside of the split mold 100 to the interior and multiple sub-flow paths 60B branching from the main flow path 60A. The supply holes 68 are formed in the downstream end regions of the sub-flow paths 60B. In this embodiment, the supply holes 68 are located flush with the cavity surface, allowing steam to be directly introduced into the cavity 10. Here, the cavity surface refers to the same surface as the molding wall 32 of the pair of molds 30 whose internal space defines the cavity 10. However, the supply holes 68 in the present invention are not limited thereto. Although not shown, the present invention also encompasses an embodiment in which, for example, the downstream region of the sub-channel 60B penetrates the molding wall 32 and projects into the cavity 10, thereby providing a supply hole 68 inside the cavity 10. The supply hole 68 is open to the interior of the cavity 10, and steam can be supplied to the cavity 10 through the opening. In this embodiment, a steam supply unit 60 is provided in the molding wall 32 of each of the first inner mold 30A and the second inner mold 30B, so that steam is supplied to the cavity 10 from both opposing sides. The multiple supply holes 68 are arranged alternately across the cavity 10, and the staggered arrangement of the multiple supply holes 68 makes it easier for steam to reach the entire cavity 10.

[0018] From the viewpoint of smoothly discharging the pressurized gas supplied into the cavity 10 in the pre-pressurization step from the cavity 10 to at least one of the exhaust chambers 20 in the heating step and facilitating the distribution of the steam supplied in the heating step throughout the cavity 10, the following configuration is preferred. That is, in this embodiment, a split mold 100 is used in which supply holes 68 for supplying steam into the cavity 10 are arranged on the same plane as the cavity surface, and the first mold 34 and / or the second mold 36 have vent holes 64 arranged on the cavity surface that allow ventilation between the cavity 10 and the exhaust chambers 20. In such a split mold 100, the ratio of the total open area of ​​the vent holes 64 to the total open area of ​​the supply holes 68 for supplying steam is preferably more than 1 and not more than 10, more preferably 1.1 to 7, and even more preferably 1.2 to 5. The numerical range of the ratio of the total open area of ​​the vent holes 64 to the total open area of ​​the supply holes 68 can be, for example, a range with a lower limit of more than 1, 1.1, or 1.2, and an upper limit of 10, 7, or 5. The following configuration is preferable from the viewpoint of facilitating the distribution of steam supplied in the heating step throughout the cavity 10 by reducing the total open area of ​​the vent holes 64 to the total area of ​​the inner circumferential surface of the molding wall 32 separating the cavity 10 from the exhaust chamber 20. The inner circumferential surface of the molding wall 32 will also be referred to as the cavity surface hereinafter. That is, in the split molding die 100, the ratio of the total open area of ​​the vent holes 64 to the total area of ​​the cavity surface is preferably more than 0% and not more than 2%, more preferably 0.05% to 1.5%, even more preferably 0.07% to 1.2%, and even more preferably 0.1% to 1%. The numerical range of the ratio of the total open area of ​​the ventilation holes 64 to the total area of ​​the cavity surface can be, for example, a range with a lower limit of more than 0%, 0.05%, 0.07%, or 0.1%, and an upper limit of 2%, 1.5%, 1.2%, or 1%.Whether the exhaust chamber 20 is provided in only one of the first mold 34 and the second mold 36, or in both, it is preferable that the ratio of the total open area of ​​the vent holes 64 to the total area of ​​the cavity surface satisfy the above-mentioned numerical range. As described above, the pair of molds 30 in the split mold 100 are provided with vent holes 64, and the steam supply unit 60 is provided with supply holes 68. It is preferable that the ratio of the total open area of ​​the vent holes 64 to the total open area of ​​the supply holes 68 is 1.2 times or more and 5 times or less, and that the ratio of the total open area of ​​the vent holes 64 to the total area of ​​the inner circumferential surface of the molding wall 32 separating the cavity 10 and the exhaust chamber 20 is more than 0% and 2% or less. It is particularly preferable that both the ratio of the total open area of ​​the vent holes 64 to the total open area of ​​the supply holes 68 and the ratio of the total open area of ​​the vent holes 64 to the total area of ​​the inner circumferential surface of the molding wall 32 satisfy the above ranges, since this makes it easier to distribute steam throughout the entire cavity 10. In particular, the above-described ratio and magnification of the open area of ​​the vent holes 64 are preferably implemented in a split molding die 100 in which any one or a combination of the first to third aspects of the arrangement of the supply holes 68 described below is implemented. In this embodiment, the following steps are carried out using the split molding die 100 described above.

[0019] The split mold 100 described above is generally made of metal, but the heat of the steam supplied into the mold during the heating process described below may be absorbed by the metal. From this perspective, the split mold 100 may be made of a material with a lower thermal conductivity than metal. Furthermore, the surface of the split mold 100 made of a metal material may be coated with a material with a lower thermal conductivity than metal. In particular, the molding wall 32 forming the cavity 10 may be made of a material with a lower thermal conductivity, or the inner and / or outer surfaces of the molding wall 32 may be coated with a material with a lower thermal conductivity. The coating method described above is not limited, and examples include applying a coating layer to the entire split mold 100 made of a metal material or to a partial region, such as the molding wall 32, by applying a paint containing a material with a lower thermal conductivity than metal, or by attaching a tape made of a material with a lower thermal conductivity than metal. Here, examples of "materials with lower thermal conductivity than metal" include resin materials, and more specifically, examples include polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), and polyetherimide (PEI).

[0020] (Filling Process) The filling process in this embodiment will be described. The filling process is a process of filling the cavity 10 with the expanded beads 50. In this embodiment, the expanded beads 50 are filled into the cavity 10 from a filling feeder 52 provided in the split molding die 100. The method of filling the expanded beads 50 can be carried out by appropriately imitating the filling method used in conventional in-mold molding. In this embodiment, the expanded beads 10 are filled under atmospheric pressure into the cavity 10 provided inside a pair of clamped molds 30.

[0021] The expanded beads 50 may be filled into the cavity 10 in a state where the internal pressure has been increased by, for example, a pressurized gas, thereby enhancing the secondary expansion property. Since the manufacturing method of the present invention includes a pre-pressurization step described below, the expanded beads 50 are preferably pressurized as described above, since the expanded beads 50 are less likely to be compressed by the pre-pressure. The internal pressure of the expanded beads 50 is not particularly limited, but when the base resin of the expanded beads 50 is a polypropylene-based resin, the internal pressure of the expanded beads 50 is preferably 0.1 MPa (G) or more and 0.2 MPa (G) or less. When the base resin of the expanded beads 50 is a polyethylene-based resin, the internal pressure of the expanded beads 50 is preferably 0.03 MPa (G) or more and 0.13 MPa (G) or less. When the base resin of the expanded beads 50 is a polystyrene-based resin, the internal pressure of the expanded beads 50 is preferably 0.01 MPa (G) or more and 0.1 MPa (G) or less. The internal pressure of the expanded beads (pressure inside the cells) can be measured by the method described in JP-A-2003-201361.

[0022] In this specification, the base resin refers to a resin that accounts for 50% by mass or more in 100% by mass of the resin member that constitutes the expanded thermoplastic resin beads.

[0023] The expanded beads 50 are made using a thermoplastic resin. The expanded beads 50 can be produced by appropriately following conventional methods for producing expanded thermoplastic resin beads. For example, first, necessary materials are charged into an extruder and melt-kneaded to prepare a resin melt, which is then extruded from the extruder in the form of a strand and cut to an appropriate length to produce pellet-shaped resin beads. The resin beads are then charged into a pressure vessel together with a dispersion medium such as water, impregnated with a blowing agent, heated to a foaming temperature, and released under a pressure lower than the pressure inside the pressure vessel to expand the expanded beads, thereby producing the expanded beads.

[0024] Examples of thermoplastic resins constituting the expanded beads 50 include polypropylene-based resins, polyolefin-based resins such as polyethylene-based resins, polystyrene-based resins, polyamide-based resins, polyester-based resins, polycarbonate-based resins, modified polyphenylene ether-based resins, polyvinyl chloride-based resins, polymethacrylic resins, and acrylonitrile-based resins. Among these, it is preferable to use one or more resins selected from the group consisting of polypropylene-based resins, polyethylene-based resins, and polystyrene-based resins as the base resin of the expanded beads 50, and it is more preferable to use one or more resins selected from polyolefin-based resins. That is, it is more preferable that the expanded beads 50 are polyolefin-based resin expanded beads. Furthermore, polypropylene-based resin expanded beads generally require high molding pressure during in-mold molding, and therefore, in the past, a particularly large amount of steam was used. Therefore, from the viewpoint of more fully enjoying the effects of the present invention, it is preferable to use polypropylene-based resin expanded beads as the thermoplastic resin expanded beads. In other words, the manufacturing method of the present invention is preferably applied to the manufacture of polypropylene-based resin foam molded articles.

[0025] Polypropylene-based resin: The polypropylene-based resin refers to a propylene homopolymer and / or a propylene-based copolymer containing 50% by mass or more of structural units derived from propylene. Examples of the propylene homopolymer include propylene-based resins such as isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. These resins exemplified as propylene homopolymers may be used alone or in combination of two or more. The content of propylene-derived structural units in the propylene-based copolymer is preferably 80% by mass or more, more preferably 90% by mass or more. The content of propylene-derived structural units in the propylene-based copolymer is preferably 99% by mass or less, more preferably 98% by mass or less. Examples of such propylene-based copolymers include copolymers of propylene and ethylene and / or an α-olefin having 4 to 20 carbon atoms. Examples of the α-olefin include 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-butene. Other examples of propylene-based copolymers include ethylene-propylene random copolymers, propylene-butene random copolymers, and ethylene-propylene-butene random copolymers. These propylene-based copolymers may be, for example, random copolymers or block copolymers, with random copolymers being preferred. Examples of the propylene-based copolymers include impact-resistant polypropylenes (block polypropylenes) composed of two or more phases, including a continuous phase of propylene polymer and a rubber phase such as an ethylene-α-olefin copolymer present as a dispersed phase within the continuous phase. These resins exemplified as propylene-based copolymers may be used alone or in combination of two or more. The polypropylene-based resin may be a linear polypropylene-based resin, a branched polypropylene-based resin, or a combination thereof.

[0026] Polyethylene-based resin: The polyethylene-based resin refers to an ethylene homopolymer or an ethylene-based copolymer containing 50% by mass or more of structural units derived from ethylene. Specific examples of polyethylene-based resins include polyethylenes exemplified by high-density polyethylene (PE-HD), medium-density polyethylene (PE-MD), low-density polyethylene (PE-LD), linear low-density polyethylene (PE-LLD), and linear very low-density polyethylene. Further specific examples of polyethylene-based resins include ethylene-based copolymers exemplified by ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, and ethylene-α-olefin copolymer. The content of structural units derived from ethylene in the ethylene-based copolymer is preferably 80% by mass or more, more preferably 90% by mass or more. The content of structural units derived from ethylene in the polyethylene-based copolymer is preferably 99% by mass or less, more preferably 98% by mass or less.

[0027] Polystyrene-based resin: The polystyrene-based resin is a styrene-based resin in which the styrene component unit is 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more.

[0028] Examples of styrene-based monomers constituting the styrene-based resin include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-methoxystyrene, p-n-butylstyrene, p-t-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4,6-tribromostyrene, styrenesulfonic acid, and sodium styrenesulfonate. Furthermore, monomers copolymerizable with styrene may be used within the scope that allows the intended object of the present invention to be achieved. Examples of monomers copolymerizable with styrene include acrylic monomers exemplified by methyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate.

[0029] Other Polymers: The expanded beads 50 may contain other polymers besides the thermoplastic resins as long as the objects and effects of the present invention are not impaired. Examples of the other polymers include thermoplastic elastomers such as olefin-based thermoplastic elastomers (TPO) and urethane-based thermoplastic elastomers (TPU). The other polymers may be one type or a combination of two or more types.

[0030] The content of the other polymer in the expanded beads 50 is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and particularly preferably 0% by mass. In other words, it is particularly preferable that the expanded beads contain substantially only a thermoplastic resin as the polymer.

[0031] Those skilled in the art can distinguish between thermoplastic resins and thermoplastic elastomers. Thermoplastic resins typically exhibit a flexural modulus of 100 MPa or more. From the viewpoint of moldability of expanded beads, the flexural modulus of thermoplastic resins is preferably 3000 MPa or less, more preferably 2000 MPa or less, even more preferably 1500 MPa or less, and particularly preferably 1200 MPa or less. On the other hand, thermoplastic elastomers exhibit rubber elasticity at room temperature and typically exhibit a flexural modulus of less than 100 MPa. The flexural modulus of thermoplastic polymers is determined based on JIS K7171:2008.

[0032] Optional Additives: The expanded beads 50 may contain any optional additives as appropriate within the scope of not impairing the objects and effects of the present invention. For example, optional additives include various conventionally known additives such as conductive materials, antioxidants, flame retardants, flame retardant assistants, radiation suppressants, cell regulators, lubricants, crystal nucleating agents, light stabilizers such as ultraviolet inhibitors, antistatic agents, and colorants.

[0033] Bulk Density of Expanded Beads The bulk density of the expanded beads 50 used in the present invention is not particularly limited, but is preferably 10 kg / m ３ It is preferable that the viscosity is 15 kg / m or more. ３ More preferably, it is 20 kg / m or more. ３ More preferably, it is 200 kg / m or more.３ More preferably, it is 100 kg / m or less. ３ More preferably, it is 50 kg / m or less. ３ In other words, the bulk density of the expanded beads of the present invention is preferably 10 kg / m or less. ３ More than 200kg / m ３ More preferably, it is 15 kg / m or less. ３ More than 100kg / m ３ More preferably, it is 20 kg / m or less. ３ More than 50kg / m ３ The bulk density of the expanded beads 50 is preferably within the above range, since it is possible to obtain an expanded bead molding that is lightweight and has excellent fusibility. The bulk density of the expanded beads 50 can be measured by the method used in the examples described below.

[0034] The expanded beads 50 may be single-layer expanded beads having only a particulate foam layer, or may be multi-layer expanded beads having a particulate foam layer serving as a core layer and a coating layer covering the foam layer. The coating layer may cover the entire surface of the foam layer, or may cover only a portion of the surface of the foam layer. Furthermore, the single-layer expanded beads or the particulate foam layer may have through holes.

[0035] (Pre-pressurization Process) In this embodiment, a pre-pressurization process is carried out after the filling process is completed. In the pre-pressurization process in this embodiment, a pressurized gas other than steam is supplied into each exhaust chamber 20 and the cavity 10, and the pressure in the cavity 10 is adjusted to a pressure exceeding atmospheric pressure. The pressurized gas is a gas for pressurizing the pressure in the cavity 10 to a pressure (P1) exceeding atmospheric pressure. As the pressurized gas other than steam, for example, an inorganic gas, an organic gas, or a mixture thereof can be used. From the viewpoints of safety and economy, the pressurized gas is preferably one or a combination of two or more inorganic gases exemplified by air, nitrogen, and carbon dioxide, and air is particularly preferred.

[0036] The means for supplying pressurized gas during the pre-pressurization step is not particularly limited. For example, as shown in FIG. 1 , an air supply hole 69 capable of supplying gas can be provided inside the split mold 100, and the pressurized gas can be supplied through the air supply hole 69. Alternatively, the formation of the air supply hole 69 can be omitted, and one or more of the exhaust holes 66 can be used as the pressurized gas supply hole. Furthermore, a flow path switching mechanism (not shown) may be provided in the steam supply unit 60. Using the flow path switching mechanism, a pressurized gas other than steam can be supplied from the steam supply unit 60 into the split mold 100 during the pre-pressurization step, and then the flow path can be switched to supply steam into the split mold 100 during the heating step described below. During the pre-pressurization step, the exhaust holes 66 not used to supply pressurized gas can be closed, and the vent holes 64 provided in the pair of molds 30 can be left open. This allows the internal pressure of the exhaust chamber 20 and the cavity 10 to be adjusted to a pressure (P1) exceeding atmospheric pressure.

[0037] The pressure (P1) in the cavity 10 after the pre-pressure step has been performed need only exceed atmospheric pressure and is not limited to a predetermined value. From the viewpoint of preventing the filled expanded beads 50 from being compressed by the pressure of a pressurized gas other than steam, the pressure (P1) in the cavity 10 during the pre-pressure step is preferably adjusted to 0.5 MPa (G) or less, more preferably 0.4 MPa (G) or less. When the pressure (P1) in the cavity 10 adjusted during the pre-pressure step is within the above pressure range, the expanded beads 50 shrink, increasing the gap within the cavity 10 and preventing shrinkage or deterioration of internal fusion in the resulting expanded bead molding. Furthermore, from the viewpoint of enabling sufficient reduction in the amount of steam used in the heating step described below by pre-pressure, the pressure (P1) in the cavity 10 is preferably adjusted to 0.02 MPa (G) or more, more preferably 0.05 MPa (G) or more. From the above viewpoint, the pressure (P1) in the cavity 10 adjusted by the pre-pressure process is preferably 0.02 MPa (G) or more and 0.5 MPa (G) or less, and more preferably 0.05 MPa (G) or more and 0.4 MPa (G) or less.

[0038] The pressure (P1) inside the cavity 10 in the pre-pressure step should be adjusted taking into consideration the heating temperature of the resin constituting the expanded beads 50. For example, when the base resin of the expanded beads 50 is a polypropylene resin, the pressure (P1) inside the cavity 10 adjusted by carrying out the pre-pressure step is preferably 0.15 MPa (G) or more, more preferably 0.18 MPa (G) or more, and even more preferably 0.2 MPa (G) or more, and is preferably 0.5 MPa (G) or less, more preferably 0.45 MPa (G) or less, and even more preferably 0.4 MPa (G) or less. In other words, when the base resin of the expanded beads 50 is a polypropylene-based resin, the pressure (P1) in the cavity 10 adjusted by carrying out the pre-pressure step is preferably 0.15 MPa (G) or more and 0.5 MPa (G) or less, more preferably 0.18 MPa (G) or more and 0.45 MPa (G) or less, and even more preferably 0.2 MPa (G) or more and 0.4 MPa (G) or less. When the base resin of the expanded beads 50 is a polyethylene-based resin, the pressure (P1) in the cavity 10 adjusted by carrying out the pre-pressure step is preferably 0.03 MPa (G) or more, more preferably 0.05 MPa (G) or more, even more preferably 0.07 MPa (G) or more, and preferably 0.5 MPa (G) or less, more preferably 0.4 MPa (G) or less, and even more preferably 0.3 MPa (G) or less. In other words, when the base resin of the expanded beads 50 is a polyethylene-based resin, the pressure (P1) within the cavity 10 adjusted by carrying out the pre-pressure process is preferably 0.03 MPa (G) or more and 0.5 MPa (G) or less, more preferably 0.05 MPa (G) or more and 0.4 MPa (G) or less, and even more preferably 0.07 MPa (G) or more and 0.3 MPa (G) or less.Furthermore, when the base resin of the expanded beads 50 is a polystyrene-based resin, the pressure (P1) within the cavity 10 adjusted by carrying out the pre-pressure step is preferably 0.02 MPa (G) or more, more preferably 0.03 MPa (G) or more, even more preferably 0.04 MPa (G) or more, and preferably 0.4 MPa (G) or less, more preferably 0.3 MPa (G) or less, and even more preferably 0.2 MPa (G) or less. In other words, when the base resin of the expanded beads 50 is a polystyrene-based resin, the pressure (P1) within the cavity 10 adjusted by carrying out the pre-pressure step is preferably 0.02 MPa (G) or more and 0.4 MPa (G) or less, more preferably 0.03 MPa (G) or more and 0.3 MPa (G) or less, and even more preferably 0.04 MPa (G) or more and 0.2 MPa (G) or less.

[0039] Furthermore, from the viewpoint of making it easier to adjust the pressure (P1) inside the cavity 10 to the desired pressure in the pre-pressure process, it is preferable to supply pressurized gas as described above and adjust the pressure by exhausting excess pressurized gas to the outside of the split molding die 100 through the exhaust hole 66.

[0040] (Heating Step) By carrying out the pre-pressure step, the pressure (P1) inside the cavity 10 is already adjusted to a pressure exceeding atmospheric pressure at the start of the heating step. In this state, steam at a pressure (P2) higher than the pressure (P1) inside the cavity 10 is supplied from the steam supply unit 60 provided in the split mold 100 into the cavity 10 to heat the expanded beads 50. Furthermore, in the heating step, steam at the pressure (P2) is supplied into the cavity while adjusting the pressure inside the exhaust chamber to a pressure (P3) exceeding atmospheric pressure but lower than the pressure (P2). During the heating step, the pressure (P3) may be adjusted by closing the exhaust hole 66 and adjusting the relationship between the pressure (P1) and the pressure (P2), or by opening the exhaust hole 66 and venting air to the outside of the split mold 100 through the exhaust hole 66. From the viewpoint of quickly venting pressurized gases other than steam from cavity 10 during the pre-pressurization step, it is preferable to open exhaust hole 66 and adjust the exhaust to the outside of split mold 100 through exhaust hole 66. In conventional in-mold molding, steam is supplied to a mold under atmospheric pressure, and a large amount of steam is required to raise the pressure and temperature within the mold to desired values. However, in the heating step of the manufacturing method of the present invention, the pressure within cavity 10 is already adjusted to a high pressure exceeding atmospheric pressure, and steam with an even higher pressure is supplied, allowing the temperature within cavity 10 to be quickly raised. To more specifically explain the effects of the present invention, graphs of a model of the manufacturing method of the present invention and a model of conventional in-mold molding are shown in FIGS. 5 and 6, respectively. Specifically, FIGS. 5 and 6 each show the surface pressure (MPa (G)), the pressure within the cavity (MPa (G)), the temperature of the first inner mold (°C), and the internal temperature (°C) of the foamed bead molding formed in the exhaust chamber over the course of molding time. The surface pressure and internal temperature of the expanded bead molding herein refer to the surface pressure and internal temperature of the expanded bead molding in the cavity before the expanded beads are fused together.The surface pressure is measured by a surface pressure gauge provided on the molding walls of a pair of molds, and is the pressure with which the foamed bead molding presses against the inner surface of the molding walls during molding in the mold.

[0041] First, a model of the manufacturing method of the present invention will be described using FIG. 5 . In the model shown in FIG. 5 , after filling the cavity 10 with the expanded beads 50, a pre-pressurization step was performed in which compressed air was supplied through the air inlet 69 until the pressure inside the cavity 10 exceeded atmospheric pressure and reached 0.25 MPa (G). Subsequently, a heating step was performed in which steam at 0.45 MPa (G) was supplied to the cavity 10 through the supply holes 68 provided in the steam supply units 60 located in each exhaust chamber 20 for 7 seconds. The amount of steam used in the heating step was 0.29 kg. During this short steam supply, the pressure inside the cavity 10 was maintained at the same level as at the end of the pre-pressurization step, and the internal temperature of the molded product quickly rose to approximately 130°C. Next, the pressure in the split mold 100 was released, and a cooling step was performed to obtain an expanded bead molded product. Furthermore, as shown in FIG. 5, in the model of the present invention, the temperature of the first mold 30A remained almost constant even during the heating step, and it was confirmed that the heat of the steam was not absorbed by the mold.

[0042] Next, a conventional in-mold molding model shown in Figure 6 will be described. The model shown in Figure 6 used a conventional mold with a similar configuration to the split mold 100 shown in Figure 1, except that it did not have a steam supply unit 60 and air inlet 69 functioned as a steam supply unit. The same amount of foamed beads were used as in the model of the present invention described above. First, the cavity of the conventional mold was filled with foamed beads, and then the air in the mold was replaced with steam over a period of 5 seconds. Next, primary heating was performed by supplying steam at 0.60 MPa (G) through the air inlet provided in the first frame. Secondary heating was then performed by supplying steam at 0.60 MPa (G) through the air inlet provided in the second frame. Double-sided heating was then performed by supplying steam at 0.60 MPa (G) through the air inlet provided in both frames. During the primary heating, the cavity was heated by supplying steam through the air inlet 69 in the first frame, and then the steam was supplied into the exhaust chamber and discharged through the second frame. During the secondary heating, the steam supply and discharge were reversed from the primary heating. As a result, it took approximately 10 seconds for the pressure in the cavity and the internal temperature of the molded product to rise sufficiently after the primary and secondary heating processes. The amount of steam used during the heating process was 4.08 kg. The mold pressure was then released, and a cooling process was carried out to obtain a foamed bead molded product. As shown in Figure 6, in the conventional in-mold molding model, the temperature of the first mold rose significantly during the heating process, confirming that the heat of the steam was absorbed by the mold.

[0043] As described above, the amount of steam used in the model of the present invention shown in Figure 5 was approximately 7% of the amount of steam used in the conventional in-mold molding shown in Figure 6, and the steam output time was also short. From these results, it can be seen that the manufacturing method of the present invention reduces the amount of steam used and eliminates energy loss.

[0044] Pressure difference (P2-P1): From the viewpoint of more fully enjoying the effects of the present invention, the pressure difference (P2-P1) obtained by subtracting the pressure (P1) in the cavity 10 to which pressurized gas is supplied during the pre-pressurization step from the pressure (P2) of the steam supplied from the steam supply unit 60 during the heating step is preferably 0.05 MPa or more and 0.45 MPa or less, more preferably 0.10 MPa or more and 0.40 MPa or less, and even more preferably 0.15 MPa or more and 0.35 MPa or less. When the pressure difference (P2-P1) is equal to or greater than the lower limit of the preferred pressure range described above, the heating time during the heating step can be shortened. In other words, the steam output time is shortened. As a result, the expanded beads 50 begin to expand during the heating step, making it difficult for steam to pass between the expanded beads 50, thereby suppressing the generation of a temperature difference between the periphery of the supply hole 68 and the end of the cavity 10. Therefore, by ensuring that the pressure difference (P2-P1) is equal to or greater than the lower limit of the preferred pressure range described above, a good expanded bead molding is readily obtained, free of any one or more of the following: shrinkage of the area around the supply hole 68, shrinkage of the entire molding, and heating unevenness. On the other hand, by ensuring that the pressure difference (P2-P1) is equal to or less than the upper limit of the preferred pressure range described above, excessive compression of the expanded beads due to the pressure difference (P2-P1) can be suppressed. This facilitates maintaining a high filling rate of the expanded beads 50 in the cavity 10, providing good fusion properties and a uniformly expanded expanded bead molding free of heating unevenness. Note that the pressure (P2) of the steam supplied from the steam supply unit 60 into the cavity 10 during the heating step refers to the average pressure of the steam supplied from the steam supply unit 60 into the cavity 10. Furthermore, the pressure (P1) within the cavity 10 into which pressurized gas is supplied during the pre-pressurization step refers to the pressure within the cavity after the pre-pressurization step.

[0045] Differential pressure (P1-P3): From the viewpoint of more fully enjoying the effects of the present invention, the differential pressure (P1-P3) obtained by subtracting the pressure (P3) in the heating step from the pressure (P1) in the pre-pressure step is preferably -0.1 MPa or more and +0.1 MPa or less, more preferably -0.05 MPa or more and +0.05 MPa or less, and it is even more preferable that the pressure (P1) and the pressure (P3) are the same. When the differential pressure (P1-P3) satisfies the above range, compressed air other than steam in the cavity can be efficiently replaced with steam in the heating step, and molding can be performed with a short steam output time.

[0046] Steam Exhaust Adjustment: As described above, during the heating step, steam at a pressure (P2) higher than the pressure (P1) within the cavity 10 is supplied from the steam supply unit 60 into the cavity 10. This adjusts the pressure within the cavity 10 to a pressure suitable for thermal fusion of the expanded beads 10. To ensure this adjustment, steam exhaust adjustment may be performed as described below while supplying steam into the cavity 10 during the heating step. Adjusting the steam exhaust also facilitates adjustment of the pressure difference (P2-P1) described above. The steam exhaust adjustment involves exhausting a portion of the steam within the cavity 10 to each exhaust chamber 20 from the cavity 10 through vent holes 64 provided in the molding walls 32 that constitute the pair of molds 30. The vent holes 64 are provided in the molding walls 32 that separate the cavity 10 from the exhaust chambers 20, ensuring ventilation between the exhaust chambers 20 and the cavity 10. In addition to this exhaust, the pressure inside the cavity 10 can be adjusted by opening and closing the opening / closing mechanism 65 provided on the vent hole 64. Alternatively, the steam exhaust adjustment may be performed by exhausting steam from the cavity 10 to the exhaust chamber 20 through the vent hole 64 provided in the molding wall 32, and then exhausting the steam from the exhaust chamber 20 to the outside of the split mold 100 through the exhaust hole 66 connecting the exhaust chamber 20 to the outside of the split mold 100. In addition to this exhaust, the pressure inside the cavity 10 can also be adjusted by opening and closing the opening / closing mechanism 65 provided on the vent hole 64 and / or the opening / closing mechanism 67 provided on the exhaust hole 66. In the steam exhaust adjustment, the exhaust is preferably adjusted using the opening / closing mechanism 65 provided on the vent hole 64, since this facilitates adjustment of the pressure difference (P2-P1). By performing the steam exhaust adjustment described above, it is possible to adjust the heating temperature of the expanded beads 50 filled in the cavity 10. This allows the expanded thermoplastic resin particles 50 to be more effectively fused to each other.

[0047] In addition to carrying out the steam exhaust adjustment described above, it is advisable to check the change in temperature inside the cavity 10 by monitoring a thermometer installed inside the cavity 10. Here, the temperature inside the cavity 10 refers to one or more of the ambient temperature inside the cavity 10, the temperature of the expanded beads 50 filled in the cavity 10, and the temperature of the expanded bead molding molded inside the cavity 10.

[0048] An expanded bead molded article is produced by carrying out the filling step, pre-pressure step, and heating step described above. In the production method of the present invention, one cycle is defined as the period from clamping the split molding die 100 to opening the die. Mold opening is generally carried out after confirming that the surface pressure of the expanded bead molded article molded in the cavity 10 has reached a surface pressure suitable for removal. In the present invention, one or a combination of the following cooling steps may be carried out before mold opening.

[0049] (Cooling Step) The cooling step is a step of cooling the foamed bead molded article produced in the cavity 10. The cooling means is not particularly limited, but examples include the pressure release means, vacuum means, air-cooling means, cooling radiation means, and water-cooling means described below. The cooling step can be carried out by combining one or more of these means. The pressure release means is a means of releasing the pressure in the split mold 100 to lower the internal pressure and thereby lowering the temperature. The vacuum means is a means of lowering the temperature by vacuuming the inside of the split mold 100, liquefying steam, and utilizing the heat of vaporization of water that adheres to the split mold 100. The air-cooling means is a means of lowering the temperature by blowing a gas such as air into the split mold 100. Water droplets that form inside the split mold 100 can also be blown away and removed by the air-cooling means. The cooling radiation means is a means of lowering the temperature by leaving the split mold 100 at ambient temperature with the exhaust and vent holes in the split mold 100 open. The water cooling means is a means for supplying cooling water into the split mold 100 to lower the temperature.

[0050] Position of supply holes: In order to carry out the heating step more effectively, it is preferable that the position of the supply holes 68 provided in the steam supply section 60 in the split mold 100 be one of or a combination of the following first to third embodiments.

[0051] In a first mode of the arrangement of the supply holes 68, the supply holes 68 are arranged on the same plane as the molding walls 32 of the pair of dies 30. That is, in the first mode, the supply holes 68 for supplying steam are arranged on the same plane as the cavity surface. Therefore, during the heating process, steam at a pressure higher than the pressure inside the cavity 10 can be supplied directly from the supply holes 68 into the cavity 10 without passing through an exhaust chamber. The sub-channel 60B shown in FIG. 2 can be terminated at the molding wall 32 of the second inner die 30B, and the supply holes 68 can be arranged to open in the molding wall 32 of the second inner die 30B. In this embodiment, a supply hole 68 is also provided in the molding wall 32 of the first inner die 30A. Note that "the cavity surface and the supply holes 68 are arranged on the same plane" does not necessarily mean that they are arranged exactly the same; it is sufficient that the difference between the cavity surface and the opening surface of the supply holes 68 is approximately equal to or less than half the thickness of the molding wall 32. For example, when the thickness of the molding wall 32 is 10 mm, the difference between the cavity surface and the opening surface of the supply hole 68 may be 5 mm or less, and the difference between the outer surface of the molding wall 32 and the opening surface of the supply hole 68 may be 5 mm or less. Here, the difference between the cavity surface and the opening surface refers to the distance between the cavity surface and the opening surface facing it. In the first embodiment, the supply hole 68, which serves as the steam outlet, is adjacent to the pair of molds 30. This allows a portion or the entire pair of molds 30 to be sufficiently heated, thereby appropriately leveling the surface of the expanded bead molding and improving its aesthetic appearance. The first embodiment is also preferable when it is desired to transfer a design, such as a grain, onto the surface of the expanded bead molding. In other words, the first embodiment can provide an expanded bead molding with excellent design while enjoying the excellent effects of the present invention.

[0052] In the first embodiment, the exhaust chamber 20 is preferably provided on the back side of the first inner mold 30A and / or the back side of the second inner mold 30B, and the supply holes 68 for supplying steam into the cavity 10 are preferably located on the same surface as the cavity 10. The first mold 34 and / or the second mold 36 may also be provided with vent holes 64 on the cavity 10 surface, allowing ventilation between the cavity 10 and the exhaust chamber 20. The average distance between the supply holes 68 and the vent holes 64 is preferably 30 mm or more, more preferably 40 mm or more, even more preferably 45 mm or more, and even more preferably 50 mm or more. Satisfying this average distance facilitates the formation of a directional flow of steam supplied from the supply holes 68 into the cavity 10 to the vent holes 64. As a result, pressurized gas other than steam present in the cavity is quickly replaced with steam, reducing steam consumption and facilitating the uniform supply of steam to each expanded bead, making it easier to obtain a molded product with excellent fusion properties. On the other hand, from the viewpoint of uniformly supplying steam, the average distance between the supply holes 68 and the vent holes 64 is preferably 100 mm or less, more preferably 90 mm or less, and even more preferably 80 mm or less. In other words, from the viewpoint of easily forming a direction in which steam supplied from the supply holes 68 into the cavity 10 flows to the vent holes 64 and also from the viewpoint of uniformly supplying steam, the average distance between the supply holes 68 and the vent holes 64 is preferably 40 mm or more and 100 mm or less, more preferably 45 mm or more and 90 mm or less, and even more preferably 50 mm or more and 80 mm or less. The average distance is obtained by measuring all distances d1 (see FIG. 2) from the center of each supply hole 68 to the center of the nearest vent hole 64 and arithmetically averaging the measured values.

[0053] In the second embodiment, the downstream region of the steam supply section 60 extends into the molding wall 32 of the pair of molds 30, and the supply hole 68 is disposed within the cavity 10 (not shown). According to this embodiment, during the heating process, steam at a pressure higher than the pressure within the cavity 10 can be supplied from the supply hole 68 to a position inside the expanded bead molding, even though the cavity 10 has already been adjusted to a pressure exceeding atmospheric pressure. Therefore, in the second embodiment, the supplied steam can be used solely for heat-sealing the expanded beads 50, resulting in minimal energy loss. In the second embodiment, the inner diameter (hole diameter) of the supply hole 68 disposed within the cavity 10 is preferably 2 mm to 8 mm, more preferably 2 mm to 6 mm, because this facilitates adjustment of the steam supply amount and steam flow rate. Furthermore, if the outer diameter of the supply hole 68 is too large, a large trace of the steam supply section 60 extending into the cavity 10 will be left on the surface of the molding, which is detrimental to design and impact resistance. Therefore, the outer diameter of the supply hole 68 is preferably 15 mm or less, and more preferably 10 mm or less. From the viewpoint of more efficient steam supply, the length by which the steam supply section 60 protrudes into the inside of the molding wall 32 is preferably half the thickness of the cavity 10 or less. Note that, in the present invention, the thickness of the cavity 10 refers to the inner dimension of the cavity 10 in the direction C (see FIG. 3 ) in which the first die 34 and the second die 36 face each other. In other words, the thickness of the cavity 10 refers to the distance from one inner surface of the molding wall 32 to the other inner surface of the molding wall 32 facing it.

[0054] In the third embodiment, the supply holes 68 are provided outside the cavity 10, i.e., within the exhaust chamber 20 (not shown). The third embodiment is the first embodiment described above, but does not include the embodiment in which the difference between the surface of the molding wall 32 and the opening surface of the supply holes 68 is approximately half the thickness of the molding wall 32 or less. In the third embodiment, not all of the steam discharged from the supply holes 68 is introduced into the cavity 10, resulting in greater energy loss than in the first and second embodiments in which steam is supplied directly into the cavity 10 without passing through the exhaust chamber 20. However, because the manufacturing method of the present invention applies prepressure, even in the third embodiment, the amount of steam used can be reduced compared to conventional in-mold molding. In the third embodiment, a small volume of the exhaust chamber 20 is preferred to reduce steam energy loss. Specifically, it is preferable that the volume of each exhaust chamber 20 possessed by the first mold 34 and the second mold 36 is smaller than the volume of the cavity 10, and it is even more preferable that the sum of the volumes of the exhaust chambers 20 is smaller than the volume of the cavity 10.

[0055] (Expanded Bead Molded Article) A preferred embodiment of the expanded bead molded article produced by the production method of the present invention will be described.

[0056] Density: The density of the expanded bead molding produced according to the present invention is preferably 10 kg / m ３ More preferably, 15 kg / m ３ More preferably, it is 20 kg / m or more. ３ The density is preferably 200 kg / m or more. ３ More preferably, it is 100 kg / m or less. ３ More preferably, it is 50 kg / m or less. ３ In other words, the density is preferably 10 kg / m ３ More than 200kg / m ３ More preferably, it is 15 kg / m or less. ３ More than 100kg / m ３ More preferably, it is 20 kg / m or less. ３ More than 50kg / m ３The density of the expanded bead molding is calculated by dividing the mass of the expanded bead molding by the volume calculated based on its dimensions.

[0057] Shrinkage rate: The expanded bead moldings produced by the production method of the present invention tend to have a smaller shrinkage rate than conventional moldings, which is preferable. The improvement in shrinkage rate is presumably due to the fact that the heating step is performed after the pre-pressing step in the present invention, thereby appropriately shortening the heating time. In other words, the production method of the present invention shortens the heating time in the heating step compared to conventional moldings, making it less likely to impart excessive heat capacity to the expanded beads 50, and is therefore presumably responsible for the improved shrinkage rate of the expanded bead moldings. For a method for confirming the shrinkage rate, see the description in the Examples section below.

[0058] Shrinkage (depression): When an expanded bead molding is produced in the same manner as the production method of the present invention, except that the pre-pressure step is not performed, the heating time in the heating step becomes significantly longer. In such a case, the expanded beads 50 may become closely attached to each other as the expansion progresses during the heating step, making it difficult for the supplied steam to pass between the expanded beads. In such a case, the steam pressure increases around the supply holes 68, and the heating temperature becomes concentrated and high, which may cause the expanded bead molding around the excessively heated supply holes 68 to shrink and become depressed. In contrast, in the production method of the present invention, in which the heating step is performed after the pre-pressure step, the aforementioned depressions caused by shrinkage due to excessive heating are less likely to occur in the expanded bead molding.

[0059] [Second Embodiment] A second embodiment of the present invention will be described with reference to Fig. 3. The second embodiment is carried out in the same manner as the first embodiment described above, except that the filling step is carried out as follows. Fig. 3 is a vertical cross-sectional view of a molding die used in the second embodiment of the present invention, showing a state in which a cracking distance X is provided.

[0060] That is, the filling process in this embodiment is similar to that in the first embodiment described above in that a split mold 100 is used to form the cavity 10 by clamping a pair of molds 30 having a first inner mold 30A and a mating second inner mold 30B. In the second embodiment, as shown in FIG. 3 , the volume of the cavity 10 is expanded by providing a cracking distance X between the first inner mold 30A and the second inner mold 30B in the mold clamping direction C. This results in a larger volume of the cavity 10 than when the first inner mold 30A and the second inner mold 30B are fully clamped. The expanded cavity 10 is then filled with expanded beads 50. The pair of molds 30 are then fully clamped to reduce the volume of the cavity 10, thereby compressing the expanded beads 50 in the cavity 10, thereby completing the filling process. The filling process in the second embodiment is sometimes referred to as a cracking filling process. Since the first inner mold 30A and the second inner mold 30B are fixed to the first frame 40A and the second frame 40B, respectively, the cracking distance X between them is referred to in the drawings as the distance between the first frame 40A and the second frame 40B for convenience.

[0061] By carrying out the cracking and filling step, the expanded beads 50 can be filled into the cavity 10 in a moderately dense state, and the gaps between the expanded beads can be made moderately small. As a result, an expanded bead molding having better fusion properties between the expanded beads 50 can be produced. Furthermore, by carrying out the cracking and filling step, the gaps between the expanded beads 50 are made moderately small, so that the passage of steam between the expanded beads 50 is appropriately suppressed. As a result, excessive heating is effectively avoided, and an expanded bead molding having a small shrinkage rate can be produced.

[0062] By setting the cracking rate at a specific value or less, it is possible to prevent the expanded beads 50 from becoming too densely packed, which would result in poor steam passage between the expanded beads 50. As a result, it is possible to prevent shrinkage around the steam supply holes 68 or uneven heating at the corner regions of the supply holes 68 and the cavity 10 in the produced expanded bead molding. From this perspective, the cracking rate is preferably 35% or less, and more preferably 25% or less. Furthermore, by setting the cracking rate at a specific value or more, it is possible to prevent gaps from forming between the expanded beads 50 filled in the cavity 10, which would result in a decrease in the fusion property of the resulting expanded bead molding. From this perspective, it is preferable that the cracking rate be 5% or more, and more preferably 8% or more. The cracking rate can be calculated from the ratio of the cracking distance (mm) to the thickness (mm) of the cavity 10.

[0063] Furthermore, from the viewpoint of preventing the expanded beads 50 from being excessively compressed, when carrying out the cracking filling process, it is more preferable to use expanded beads 50 that have been pressurized in advance with a pressurized gas to increase the internal pressure and enhance the secondary expandability, as described in the first embodiment.

[0064] [Third Embodiment] A third embodiment of the present invention will be described with reference to Fig. 4. Fig. 4 is a vertical cross-sectional view of a molding die used in the third embodiment of the present invention. The third embodiment is carried out in the same manner as the first embodiment described above, except that the filling step and the pre-pressure step are carried out as follows.

[0065] That is, the filling step in this embodiment is a step of filling the cavity 10 with the expanded thermoplastic resin beads 50, which have been compressed in advance with a pressurized gas other than steam, together with the pressurized gas. The filling step in the third embodiment may be referred to as a compression filling step. In this embodiment, when the compression filling step is performed, the pressurized gas is supplied to the cavity 10 along with the expanded thermoplastic resin beads 50. That is, the compression filling step includes part or all of a filling step of filling the cavity 10 with the expanded beads and a pre-pressurization step of increasing the pressure inside the cavity. More specifically, as shown in FIG. 4 , the split mold 100 used in the third embodiment is connected to a filling feeder 52 for filling the expanded beads 50 and a pressurized filling tank 200 capable of pressurizing the filled foamed beads. The pressurized filling tank 200 is connected to a pressurized pressure adjustment unit 202 and an exhaust pressure adjustment unit 204, and by adjusting these, the foamed beads filled in the pressurized filling tank 200 can be pressurized to a desired pressure. The pressurized foam particles are supplied in a compressed state to the cavity 10 from the filling feeder 52 together with the pressurized gas.

[0066] As described above, the pre-pressurization step in this embodiment is performed in conjunction with the filling step. However, if the internal pressure in the cavity 10 does not reach the desired pressure, the pre-pressurization step may be performed separately. On the other hand, if the internal pressure in the cavity 10 exceeds the desired pressure as a result of the compression filling step, pressurized gas exhaust adjustment may be performed. Such pressurized gas exhaust adjustment can be performed in the same manner as the steam exhaust adjustment described in the first embodiment. The pressurized gas exhaust adjustment is performed by venting a portion of the pressurized gas in the cavity 10 to at least one of the exhaust chambers 20 through the vent holes 64 provided in the molding walls 32 of the pair of molds 30, and adjusting the pressure in the cavity 10 by opening and closing the opening / closing mechanism 65 provided in the vent holes 64. In another embodiment, the pressurized gas exhaust adjustment is performed by exhausting a portion of the pressurized gas in cavity 10 from cavity 10 to at least one of exhaust chambers 20 via vent holes 64 provided in molding wall 32, and exhausting a portion of the pressurized gas in exhaust chamber 20 from exhaust chamber 20 to the outside of split molding die 100 via exhaust holes 66 that connect exhaust chamber 20 to the outside of split molding die 100. The pressurized gas exhaust adjustment may be performed by adjusting the pressure in cavity 10 by opening and closing opening / closing mechanisms 65 provided in vent holes 64 and / or opening / closing mechanisms 67 provided in exhaust holes 66, along with the exhaust of gas to the outside of split molding die 100.

[0067] When performing compression filling, the preferred range of pressure for compressing the expanded beads 50 varies depending on the resin constituting the expanded beads 50. For example, when the base resin of the expanded beads 50 is a polypropylene-based resin, the pressure for performing compression filling is preferably 0.10 MPa (G) or more, more preferably 0.15 MPa (G) or more, and even more preferably 0.18 MPa (G) or more. On the other hand, when the base resin of the expanded beads 50 is a polypropylene-based resin, the pressure for performing compression filling is preferably 0.30 MPa (G) or less, more preferably 0.25 MPa (G) or less, and even more preferably 0.23 MPa (G) or less. In other words, when the base resin of the expanded beads 50 is a polypropylene-based resin, the pressure during compression filling is preferably 0.10 MPa (G) or more and 0.30 MPa (G) or less, more preferably 0.15 MPa (G) or more and 0.25 MPa (G) or less, and even more preferably 0.18 MPa (G) or more and 0.23 MPa (G) or less. When the base resin of the expanded beads 50 is a polyethylene-based resin, the pressure during compression filling is preferably 0.05 MPa (G) or more, more preferably 0.08 MPa (G) or more, and even more preferably 0.10 MPa (G) or more. On the other hand, when the base resin of the expanded beads 50 is a polyethylene-based resin, the pressure during compression filling is preferably 0.20 MPa (G) or less, more preferably 0.17 MPa (G) or less, and even more preferably 0.15 MPa (G) or less. In other words, when the base resin of the expanded beads 50 is a polyethylene-based resin, the pressure during compression filling is preferably 0.05 MPa (G) or more and 0.20 MPa (G) or less, more preferably 0.08 MPa (G) or more and 0.17 MPa (G) or less, and even more preferably 0.10 MPa (G) or more and 0.15 MPa (G) or less. When the base resin of the expanded beads 50 is a polystyrene-based resin, the pressure during compression filling is preferably 0.03 MPa (G) or more, more preferably 0.04 MPa (G) or more, and even more preferably 0.05 MPa (G) or more.On the other hand, when the base resin of the expanded beads 50 is a polystyrene-based resin, the pressure during compression filling is preferably 0.15 MPa (G) or less, more preferably 0.10 MPa (G) or less, and even more preferably 0.08 MPa (G) or less. In other words, when the base resin of the expanded beads 50 is a polystyrene-based resin, the pressure during compression filling is preferably 0.03 MPa (G) or more and 0.15 MPa (G) or less, more preferably 0.04 MPa (G) or more and 0.10 MPa (G) or less, and even more preferably 0.05 MPa (G) or more and 0.08 MPa (G) or less.

[0068] Furthermore, from the viewpoint of preventing the expanded beads 50 from being excessively compressed, when performing compression filling, it is more preferable to use expanded beads 50 that have been pressurized in advance with pressurized gas to increase the internal pressure and enhance secondary foaming properties, as described in the first embodiment.

[0069] The present invention will be described in detail below with reference to examples, but is not limited thereto. In these examples, molds having the same configuration as those shown in Figures 1 to 4 were used as appropriate. The thermoplastic resin expanded beads used in the examples and comparative examples are as follows. The bulk density and internal pressure of the polypropylene-based resin expanded beads and polyethylene-based resin expanded beads, as well as the bulk density of the polystyrene-based resin expanded beads used in each example and comparative example, are shown in the example tables. The "MFR" below stands for melt flow rate. <Polypropylene-based Resin Expanded Beads 1 (referred to as EPP1 in the tables)> Expanded beads were prepared using an ethylene-propylene random copolymer having a melting point of 141.5°C, an ethylene content of 3.1% by mass, and an MFR (load 2.16 kg, 230°C, JIS K7210-1:2014) of 7 g / 10 min. <Polypropylene-based resin expanded beads 2 (referred to as EPP2 in the table)> Expanded beads were used, which were made using an ethylene-propylene random copolymer having a melting point of 153°C, an ethylene content of 1.4 mass%, and an MFR (load 2.16 kg, 230°C, JIS K7210-1:2014) of 7 g / 10 min. <Polyethylene-based resin expanded beads (referred to as EPE in the table)> Melting point 121°C, density 0.928 g / cm3 The expanded particles used were made of an ethylene-α-olefin copolymer having an MFR (load 2.16 kg, 190°C, JIS K7210-1:2014) of 1.0 g / 10 min. <Polystyrene-based resin expanded particles (referred to as EPS in the table)> Styrodia FA200 manufactured by JSP Co., Ltd. was used as the expandable styrene-based resin particles.

[0070] Example 1 First, unpressurized expanded polypropylene resin beads were filled into a pressure-filling tank. Pressurized air was then supplied into the tank and allowed to stand for 24 hours, bringing the internal pressure of the expanded polypropylene resin beads to 0.14 MPa (G). A split mold having a configuration similar to that shown in FIG. 1 was used to produce an expanded bead molded article. Specifically, a split mold was used, having a cavity capable of molding a flat-plate-shaped article measuring 306 mm long, 255 mm wide, and 61.2 mm high when clamped. In the pair of dies in the split mold, the ratio of the total open area of ​​the vent holes provided in the molding walls to the total open area of ​​the steam supply holes was 3.4 times, and the ratio of the total open area of ​​the vent holes provided in the molding walls to the total area of ​​the inner circumferential surface of the molding walls forming the cavity was 0.6%. Furthermore, the average distance between the supply holes and the vent holes provided in the molding walls in the pair of dies was 52 mm. The split mold was adjusted to a cracking distance of 6 mm, and in this state, a filling process was carried out by filling the mold with polypropylene-based resin foam beads to which internal pressure had been applied (see Figure 3). The cracking rate was 10%. Next, pressurized air was supplied through the air inlet provided in the frame of the split mold to pressurize each exhaust chamber, and pressurized air was also supplied to the cavity through the air vent, thereby carrying out a pre-pressurization process until the pressure inside the cavity reached 0.25 MPa (G). Next, steam at an output pressure of 0.45 MPa (G) was directly supplied to the cavity for 6 seconds from a steam supply unit with a supply hole located inside the cavity, thereby carrying out a heating process. The differential pressure (P2 - P1), obtained by subtracting the pressure inside the cavity (P1) adjusted in the pre-pressurization process from the steam output pressure (P2) used in the heating process, was 0.20 MPa. The pressure inside the split mold was 0.25 MPa (G). The amount of steam consumed in one heating step was 0.24 kg. The pressure inside the split mold refers to the pressure (P3) inside the exhaust chamber. The maximum temperature of the first inner mold refers to the highest temperature during the heating step, measured in advance using a thermocouple placed inside the cavity. The inside of the molded body here refers to a position halfway along the vertical and horizontal directions of the molded body, and 20 mm from the cavity surface of the first inner mold toward the inside of the molded body.After the heating step, a cooling step was carried out. In the cooling step, the pressure inside the split mold was first released over 5 seconds, followed by vacuum cooling for 261 seconds, air cooling for 5 seconds, and then natural cooling for another 5 seconds. After confirming that the surface pressure of the expanded bead molding in the cavity had dropped to 0.05 MPa (G), the cooling step was terminated, and the split mold was opened to remove the expanded bead molding. The surface pressure at the time of removal is shown in Table 1 as the removal surface pressure. The surface pressure of the expanded bead molding in the cavity after the heating step is shown in Table 1 as the maximum surface pressure after heating. The time from immediately before the foamed beads were filled after ensuring a predetermined cracking distance to the time when cooling was completed and the mold was opened was measured, and this was shown in Table 1 as the cycle time, which is the time required for one molding cycle.

[0071] The expanded bead moldings obtained as described above were measured and evaluated as follows. The expanded beads used in the examples were measured for bulk density before filling them into cavities. The method for measuring bulk density is shown below, and the measurement results are shown in Table 1. Regarding the evaluation criteria described below, ◎ means very good, ○ means good, △ means poor, and × means poor.

[0072] (Bulk Density of Expanded Beads) Expanded beads to which internal pressure was applied were prepared. A mass W (g) of expanded beads was filled into a measuring cylinder so that they would naturally accumulate, and the bottom of the measuring cylinder was lightly tapped against a horizontal surface several times to stabilize the filling height of the expanded beads in the measuring cylinder. The bulk volume V (L) of the expanded beads indicated on the measuring cylinder was read, and the mass W of the expanded beads was divided by the bulk volume V of the expanded beads (W / V), and the unit was expressed as [kg / m ３ The bulk density of the expanded beads was calculated by converting the value into the value of the particle diameter.

[0073] (Density of Expanded Bead Molded Article) The density was calculated by dividing the mass of the expanded bead molded article by the volume calculated based on the dimensions.

[0074] (Shrinkage Rate) The dimensional change rate (shrinkage rate) of the expanded bead molding relative to the dimensions of the split molding die used for in-mold molding was measured as follows. First, after in-mold molding, the expanded bead molding was removed from the split molding die and allowed to stand for 24 hours at a temperature of 23°C and a relative humidity of 50% for aging. The long side dimension (LB) of the expanded bead molding was then measured. The ratio (([LA - LB] / LA) x 100) of the difference between the long side dimension (LA) of the cavity and the long side dimension (LB) of the expanded bead molding relative to the long side dimension (LA) of the cavity was calculated to obtain the shrinkage rate of the expanded bead molding relative to the dimensions of the split molding die.

[0075] (Internal fusion) The foamed bead molding was bent and broken, and the number of foamed beads present on the fracture surface (C1) and the number of broken foamed beads (C2) were counted. The ratio of the number of broken foamed beads to the number of foamed beads present on the fracture surface [(C2 / C1) x 100] was calculated as the material failure rate. The measurement was carried out five times using different test pieces, and the material failure rates were determined for each test piece, and the arithmetic mean value was calculated. The arithmetic mean value was used to evaluate the material failure rate according to the following criteria: ◎: Material failure rate is 91% or more; ◯: Material failure rate is 71% or more but less than 91%; Δ: Material failure rate is more than 0% but less than 71%; ×: Material failure rate is 0%

[0076] (Shrinkage (Dent)) First, the outer surface of the expanded bead molding removed from the split mold was visually observed. Next, the expanded bead molding was left to stand for 24 hours in an environment at a temperature of 23°C and a relative humidity of 50% for curing. After curing, the expanded bead molding was visually observed again and evaluated as follows: ⊚: Small shrinkage was observed before curing, and no shrinkage was observed after curing. ◯: Large shrinkage was observed before curing, but the shrinkage recovered after curing. Δ: Large shrinkage was observed both before and after curing. ×: Large shrinkage was observed both before and after curing, and the presence of partial melted areas was also observed.

[0077] (Uneven heating) The outer surface of the expanded bead molded article removed from the split mold was visually observed, and uneven heating was evaluated as follows: ◎: It was confirmed that the entire article was uniformly expanded and no uneven heating occurred. ◯: Although voids between the expanded beads were present in part of the surface, it was confirmed that the article was generally uniformly expanded and there was almost no uneven heating. △: Expanded beads had detached from part of the surface, and insufficient expansion due to uneven heating was confirmed. ×: A large number of expanded beads had detached from the surface, and overall insufficient expansion due to uneven heating was confirmed.

[0078] (Water Leakage Test) A test specimen measuring 50 mm thick and 150 mm long and wide was cut from the center of the foamed bead molding to be tested. A cylindrical acrylic tube with an inner diameter of 80 mm, a thickness of 6 mm, and a height of 120 mm was also prepared. A silicone sealant was applied to one open end of the tube, and the test specimen and the tube were adhesively fixed together, with the center of the tube opening approximately aligned with the center of the length and width of the test specimen. After the silicone sealant dried, the test specimen was placed face down and water was poured into the tube through the other opening. The water depth was 5 cm. The tube was left undisturbed for 24 hours, and the occurrence of water leakage through the test specimen was confirmed and evaluated according to the following criteria. None of the examples or comparative examples were rated as poor (△). ◯: The underside of the test specimen was dry, and the water depth was 5 cm, and no water leakage was observed. △: Wetness was observed on the underside of the test specimen, and the water depth was 2.5 cm to less than 5 cm, and water leakage was observed. ×: The underside of the test piece was wet, the water depth was less than 2.5 cm, and water leakage was confirmed.

[0079] (Leak Test) A leak test was conducted as follows, with reference to the pressure change pressurization method described in Appendix A of JIS Z2332:2012, to measure the gas leakage rate of the expanded bead molding. First, a metal test specimen mounting stand was prepared for the leak test, which was disk-shaped, 30 mm thick and 180 mm in diameter, and had an opening communicating in the thickness direction. The opening of the test specimen mounting stand had a first opening with a diameter of 80 mm and a depth of 25 mm extending from one opening to the other, and a second opening with a diameter of 70 mm and a depth of 5 mm connected to the first opening. Four bolt insertion holes were also provided at equal intervals around the opening of the test specimen mounting stand. A pressurized gas introduction device was also prepared, which had a pressurized gas flow path and a first flange welded to the downstream end of the pressurized gas flow path. A flow control valve, a regulator, and a discharge valve were provided upstream of the pressurized gas supply device. The first flange was disk-shaped, 14 mm thick and 180 mm in diameter, with a flange opening 80 mm in diameter penetrating the thickness direction and four bolt insertion holes equally spaced about the flange opening. A second flange was also prepared, having the same shape as the first flange. Sealing packing was provided on one side of each of the first and second flanges.

[0080] A cylindrical test specimen measuring 80 mm in diameter and 25 mm in height was cut from the center of the foamed bead molded article to be tested. The test specimen was then placed in the first opening of the test specimen mounting stand. During installation, the test specimen and the test specimen mounting stand were bonded together with a silicone sealant to prevent any air-permeable gaps from forming between them, thereby obtaining a leak test specimen. The first flange was placed on the first opening side of the leak test specimen, and the second flange was placed on the second opening side. Bolts were inserted through the bolt insertion holes provided on each flange to secure the leak test specimen to the pressurized gas supply device. A pressure sensor, pressure indicator, and recorder were also connected to the pressurized gas supply device. The first and second flanges were tightly attached to the test specimen mounting stand sandwiched between them by packings provided on the first and second flanges, thereby sealing the interior of the leak test specimen. Next, the power to the pressurized gas supply device was turned on, and with the exhaust valve open, the pressure indicator was reset to zero, and then the exhaust valve was closed. Then, with the flow control valve closed, the introduction of air began, and the flow control valve was gradually opened and adjusted with the regulator until the gauge pressure reached 3 kPa, which was the gauge pressure at the start of detection. After confirming that the gauge pressure had reached 3 kPa, the flow control valve was quickly closed to stop the supply of pressurized gas, and detection began. The pressurized gas passed through the test piece, and the detection was terminated after confirming that the pressure inside the leak test specimen had decayed to atmospheric pressure. The time from the start of detection to the end of detection was measured. The gas leak rate was then calculated using the following equation (1): [Formula 1] Q = V (P2 - P1) / Δt (1) Q: Leak rate (Pa·L / s) P1: Gauge pressure of the leak test device at the start of detection (Pa) P2: Gauge pressure of the leak test device at the end of detection (Pa) Δt: Time from the start of detection to the end of detection (s) V: Volume of the test piece (L)

[0081] Examples 2 to 7, 9, and 10, Comparative Example 1 Expanded bead moldings were produced in the same manner as in Example 1, except for the changes shown in Tables 1 and 2. The expanded beads used and the expanded bead moldings produced were measured and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0082] Example 8 An expanded bead molded article was produced in the same manner as in Example 1, except for the changes shown in Table 2 and the filling and pre-pressurization steps as follows. The expanded beads used and the produced expanded bead molded article were measured and evaluated in the same manner as in Example 1. The results are shown in Table 2. In Example 8, a mold having a configuration similar to that shown in FIG. 4 was used. First, unpressurized polypropylene-based resin expanded beads were filled into a pressure filling tank. Pressurized air was then supplied into the tank and allowed to stand for 24 hours, increasing the internal pressure of the polypropylene-based resin foam to 0.10 MPa (G). The expanded beads and pressurized air with increased internal pressure were then compressed and filled into the cavity. The cavity pressure was adjusted to 0.25 MPa (G) by this compression filling. In other words, in Example 8, the filling and pre-pressurization steps were carried out simultaneously.

[0083] Examples 11 to 13 and Comparative Example 2 were carried out using expanded polyethylene resin beads. Specifically, expanded bead moldings were produced in the same manner as in Example 1, except for the changes shown in Table 3. The expanded beads used and the produced expanded bead moldings were measured and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0084] Examples 14 to 17 and Comparative Example 3 were carried out using expanded polystyrene resin beads. Specifically, expanded bead moldings were produced in the same manner as in Example 1, except for the changes shown in Table 4. The expanded beads used and the produced expanded bead moldings were measured and evaluated in the same manner as in Example 1. The results are shown in Table 4.

[0085] Comparative Example 4 A conventional split mold was prepared, similar to the split mold shown in FIG. 1 except that it lacked a steam supply unit. Expanded beads similar to the polypropylene-based resin expanded beads used in Example 1 were also prepared. The expanded beads, with an internal pressure adjusted to 0.14 MPa, were filled into an exhaust chamber with a cracking distance of 6 mm, followed by mold clamping. The cracking rate was 10%. Thereafter, without performing a pre-pressurization step, steam at an output pressure of 0.60 MPa (G) was supplied to the split mold for 5 seconds with the split mold opening / closing mechanism open, replacing the air in the split mold with steam. Subsequently, as one-sided heating, steam at an output pressure of 0.60 MPa (G) was supplied into the exhaust chamber from the first frame side for 5 seconds, raising the pressure to 0.26 MPa (G), and heating the expanded beads. Further, as a reverse one-way heating, steam at an output pressure of 0.60 MPa (G) was supplied from the second frame side into the exhaust chamber for 3 seconds to raise the pressure to 0.36 MPa (G) and heat the foamed beads. Subsequently, as a double-sided heating, steam at an output pressure of 0.60 MPa (G) was supplied for 7 seconds by opening and closing the supply holes on both sides (the first frame side and the second frame side) of the split mold to maintain the pressure inside the split mold at 0.38 MPa (G), and the heating process was completed. During heating, the exhaust holes in the frame of the split mold were closed except for the portion used for supplying steam, and the vent holes on the pair of molds were left open. This allowed the steam supplied to the split mold to be introduced into the chamber. The pressure inside the split mold refers to the pressure inside the chamber. The total amount of steam consumed in the heating process was 4.08 kg. After the above heating process, cooling was performed using the same cooling method as in Example 1, except for the cooling time shown in Table 5. The expanded bead molding was then removed from the mold after confirming that the ejection pressure had reached the values ​​shown in Table 5. The expanded beads used in Comparative Example 4 and the expanded bead molding obtained by Comparative Example 4 were subjected to the same measurements and evaluations as in Example 1. The results are shown in Table 5.

[0086] Comparative Examples 5 and 6 Expanded bead moldings were produced in the same manner as in Comparative Example 4, except that the contents were changed as shown in Table 5 and that double-sided heating was not performed. The expanded beads used and the expanded bead moldings produced were subjected to the same measurements and evaluations as in Example 1. The results are shown in Table 5.

[0087] Example 18: An expanded bead molding was produced in the same manner as in Example 1, except that a split mold having a cavity capable of molding a flat-plate-shaped molded article measuring 1004 mm long, 308 mm wide, and 153 mm high when clamped was used, and the details were changed as shown in Table 6. The expanded beads used and the expanded bead molding produced were measured and evaluated in the same manner as in Example 1. Furthermore, a water leakage test and a leak test were conducted for Example 18. The results are shown in Table 6. Comparative Example 7: An expanded bead molding was produced in the same manner as in Comparative Example 4, except that a split mold having a cavity capable of molding a flat-plate-shaped molded article measuring 1004 mm long, 308 mm wide, and 153 mm high when clamped was used, and the details were changed as shown in Table 7, and double-sided heating was not performed. The expanded beads used and the expanded bead molding produced were measured and evaluated in the same manner as in Example 1. Furthermore, a water leakage test and a leak test were conducted for Comparative Example 7, and the results are shown in Table 7.

[0088] As shown in Tables 1 to 7, the steam output time and steam consumption during the heating step in each Example were significantly reduced compared to Comparative Examples 4 to 7, which employed conventional in-mold molding. Furthermore, in Examples 1 to 10 and 18, the steam output time was short and the steam consumption was low, and all of these produced good expanded bead moldings. In contrast, in Comparative Example 1, in which the pre-pressure step was not performed, the steam output time was long and the steam consumption was high. Furthermore, the expanded bead molding obtained in Comparative Example 1 had poor fusion between the expanded beads, and some of the expanded bead molding remained as expanded beads, preventing the molding from maintaining its shape, making it impossible to evaluate the molding. In Examples 11 to 13, the steam output time was short and the steam consumption was low, and all of these produced good expanded bead moldings. In contrast, in Comparative Example 2, in which the pre-pressure step was not performed, the steam output time was long and the steam consumption was high. Furthermore, in Comparative Example 2, the fusion between the expanded beads was poor, making it impossible to measure the density and shrinkage rate. In Examples 14 to 17, the steam output time and steam consumption were short, and all of these produced good expanded bead moldings. In contrast, in Comparative Example 3, in which the pre-pressurization step was not performed, the steam output time was long and the amount of steam consumed was large. Comparing Example 18 and Comparative Example 7, in which the water leakage test and the leak test were performed, it was confirmed that the expanded bead molding produced by the production method of the present invention is an expanded bead molding that is difficult for liquids and gases to pass through and has high airtightness.

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096] The present invention described above encompasses the following technical ideas. (1) A method for producing an expanded bead molded body, which comprises filling a cavity of a split molding die consisting of a first die and a second die with expanded thermoplastic resin beads, and heating the expanded beads with steam to form them in the die, wherein the first die and / or the second die has an exhaust chamber that is airtight with the cavity, and the method comprises a pre-pressurization step of supplying a pressurized gas other than steam into the cavity to adjust the pressure in the cavity filled with the expanded beads to a pressure (P1) that exceeds atmospheric pressure, and a heating step of supplying steam at a pressure (P2) higher than the pressure (P1) into the cavity adjusted to the pressure (P1) in the pre-pressurization step, and exhausting the steam supplied into the cavity to an exhaust chamber to heat the expanded beads, wherein in the heating step, while supplying steam at the pressure (P2) into the cavity, the pressure in the exhaust chamber is adjusted to a pressure (P3) that exceeds atmospheric pressure but is lower than the pressure (P2). (2) The method for producing an expanded bead molded article according to (1), wherein in the heating step, steam at a pressure (P2) higher than the pressure (P1) inside the cavity is supplied from the steam supply unit into the cavity, and the steam inside the cavity is exhausted to the outside of the cavity through an air vent provided in a molding wall separating the inside of the cavity from the inside of the exhaust chamber to ensure ventilation between the exhaust chamber and the cavity, and the pressure inside the exhaust chamber is adjusted to fuse the expanded thermoplastic resin beads to each other through an exhaust hole with an opening / closing mechanism provided in at least one of the first mold and the second mold to ensure ventilation between the exhaust chamber and the outside of the molding die. (3) The method for producing an expanded bead molded article according to (1) or (2), wherein in the pre-pressurizing step, the pressure inside the cavity is adjusted to be 0.05 MPa(G) or more and 0.4 MPa(G) or less. (4) The method for producing an expanded bead molding according to any one of (1) to (3), wherein in the heating step, a differential pressure (P2-P1) obtained by subtracting the pressure (P1) from the pressure (P2) is 0.15 MPa or more and 0.35 MPa or less.(5) The method for producing an expanded bead molded article according to any one of (1) to (4), wherein a differential pressure (P1-P3) obtained by subtracting the pressure (P3) in the heating step from the pressure (P1) in the pre-pressurization step is -0.1 MPa or more and +0.1 MPa or less. (6) The method for producing an expanded bead molded article according to any one of (1) to (5), wherein the expanded thermoplastic resin beads are expanded polypropylene resin beads. (7) The method for producing an expanded bead molded article according to any one of (1) to (6), wherein a supply hole for supplying the steam is disposed on the same plane as the cavity surface, and wherein steam having a pressure higher than the pressure in the cavity is supplied from the supply hole directly into the cavity in the heating step. (8) The method for producing an expanded bead molding according to any one of (1) to (7), wherein a supply hole for supplying steam into the cavity is located on the same plane as the cavity surface, and the first mold and / or the second mold have vent holes in the cavity surface that allow ventilation between the cavity and the exhaust chamber, and the average distance between the supply hole and the vent hole is 40 mm or more. (9) The method for producing an expanded bead molding according to any one of (1) to (8), wherein a supply hole for supplying steam into the cavity is located on the same plane as the cavity surface, and the first mold and / or the second mold have vent holes in the cavity surface that allow ventilation between the cavity and the exhaust chamber, and the total open area of ​​the vent holes is 1.2 to 5 times the total open area of ​​the supply holes, and the ratio of the total open area of ​​the vent holes to the total area of ​​the cavity surface is more than 0% and 2% or less. (10) The method for producing a foamed bead molding according to any one of (1) to (9), characterized in that the cavity is formed by a first inner mold provided in the first mold and a second inner mold provided in the second mold, and the exhaust chamber is provided on the back side of the first inner mold and / or the back side of the second inner mold.(11) The method for producing an expanded bead molded article according to any one of (1) to (10), further comprising a filling step which is carried out before the pre-pressure step or overlaps with the pre-pressure step, wherein the filling step is a step of using the pair of molds to provide a cracking distance between the first inner mold and the second inner mold in the mold clamping direction to expand the volume of the cavity, filling the expanded cavity with thermoplastic resin expanded beads, and then completely clamping the pair of molds to reduce the volume of the cavity, thereby compressing the thermoplastic resin expanded beads in the cavity. (12) The method for producing an expanded bead molding according to any one of (1) to (11), further comprising a filling step which is carried out before the pre-pressurizing step or overlaps with the pre-pressurizing step, wherein the filling step is a step of filling the cavity with expanded thermoplastic resin beads which have been compressed in advance with a pressurized gas other than steam, and wherein when the filling step is carried out, the pressurized gas is supplied to the cavity together with the expanded thermoplastic resin beads, thereby carrying out part or all of the pre-pressurizing step at the same time as the filling step.

[0097] DESCRIPTION OF SYMBOLS 10: Cavity 20: Exhaust chamber 30: Pair of molds 30A: First inner mold 30B: Second inner mold 32: Molding wall 34: First mold 36: Second mold 40: Frame 40A: First frame 40B: Second frame 50: Thermoplastic resin foam particles 52: Filling feeder 60: Steam supply section 60A: Main flow path 60B: Sub-flow path 64: Vent hole 65: Opening / closing mechanism 66: Exhaust hole 67: Opening / closing mechanism 68: Supply hole 69: Air supply hole 100: Split mold 200: Pressurized filling tank 202: Pressurized pressure adjustment section 204: Exhaust pressure adjustment section C: Mold clamping direction d1: Distance X: Cracking distance

Claims

1. A method for producing expanded bead molded articles, in which the cavity of a split molding die consisting of a first die and a second die is filled with expanded thermoplastic resin beads, and the expanded beads are heated with steam to form an in-mold mold, wherein the first die and / or the second die has an exhaust chamber that is airtight with the cavity, and the method includes a pre-pressurization step in which a pressurized gas other than steam is supplied into the cavity to adjust the pressure in the cavity filled with the expanded beads to a pressure (P1) that exceeds atmospheric pressure, and a heating step in which steam at a pressure (P2) higher than the pressure (P1) is supplied into the cavity adjusted to the pressure (P1) in the pre-pressurization step, and the steam supplied into the cavity is exhausted into an exhaust chamber to heat the expanded beads, wherein during the heating step, while supplying steam at the pressure (P2) into the cavity, the pressure in the exhaust chamber is adjusted to a pressure (P3) that exceeds atmospheric pressure but is lower than the pressure (P2).

2. The method for producing a foamed bead molding according to claim 1, characterized in that in the pre-pressurizing step, the pressure (P1) is adjusted to 0.05 MPa (G) or more and 0.4 MPa (G) or less.

3. The method for producing a foamed bead molding according to claim 1 or 2, characterized in that in the heating step, the differential pressure (P2-P1) obtained by subtracting the pressure (P1) from the pressure (P2) is 0.15 MPa or more and 0.35 MPa or less.

4. A method for producing a foamed bead molding according to any one of claims 1 to 3, characterized in that the differential pressure (P1-P3) obtained by subtracting the pressure (P3) in the heating step from the pressure (P1) in the pre-pressurization step is -0.1 MPa or more and +0.1 MPa or less.

5. The method for producing a foamed bead molding according to any one of claims 1 to 4, characterized in that the foamed thermoplastic resin beads are foamed polypropylene resin beads.

6. A method for producing a foamed bead molding according to any one of claims 1 to 5, characterized in that a supply hole for supplying steam into the cavity is arranged on the same plane as the cavity surface, and the first mold and / or the second mold have an air vent on the cavity surface that allows ventilation between the cavity and the exhaust chamber, and the average distance between the supply hole and the air vent is 40 mm or more.

7. A method for producing an expanded bead molding according to any one of claims 1 to 6, characterized in that supply holes for supplying steam into the cavity are arranged on the same plane as the cavity surface, and the first mold and / or the second mold have ventilation holes on the cavity surface that allow ventilation between the cavity and the exhaust chamber, the total opening area of ​​the ventilation holes is 1.2 to 5 times the total opening area of ​​the supply holes, and the ratio of the total opening area of ​​the ventilation holes to the total area of ​​the cavity surface is more than 0% and 2% or less.

8. A method for producing a foamed bead molding described in any one of claims 1 to 7, characterized in that the cavity is formed by a first inner mold possessed by a first mold and a second inner mold possessed by a second mold, and the exhaust chamber is provided on the back side of the first inner mold and / or the back side of the second inner mold.

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