Method for producing foamed-particle molded body

Abstract

To provide a method for producing a foamed-particle molded body that can improve energy loss during in-mold molding.SOLUTION: There is provided a method for producing a foamed-particle molded body in which foamed thermoplastic resin particles are filled into a cavity of a split mold consisting of a first mold and a second mold, and the foamed particles are heated with steam to form the particles in the mold. The first mold (30A) and / or the second mold (30B) have the cavity (10) and an exhaust chamber (20) that are ventilated with the cavity. The method includes: a pre-pressurization step of supplying a pressurized gas other than steam into the cavity (10) to adjust a pressure in the cavity (10) filled with foamed particles (50) to a pressure (P1) exceeding atmospheric pressure; and a heating step in which steam at a pressure (P2) higher than the pressure (P1) is supplied into the cavity (10) adjusted to the pressure (P1) in the pre-pressurization step, and the steam is exhausted into the exhaust chamber (20) to heat the foamed particles (50). In the heating step, while supplying steam at the pressure (P2) into the cavity (10), a pressure in the exhaust chamber (20) is adjusted to a pressure (P3) that exceeds atmospheric pressure and is lower than the pressure (P2).SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[0003] More specifically, for example, Patent Document 1 discloses a method for producing an expanded bead molded article by compressing pre-expanded propylene-based resin beads with gas pressure, compressing and filling a pair of molds together with the compressed gas, and then evacuating the gas from the molds to reduce the internal pressure. After that, steam is supplied to the molds to heat-seal the expanded beads in the molds. This production method is sometimes referred to as Prior Art 1 below. Patent Document 2 discloses a method for producing an in-mold expanded polypropylene-based resin article by a compression-filling method using multistage expanded polypropylene-based resin beads. Patent Document 2 (Figure 1) shows a mold 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 is to use a mold having a cavity and a chamber similar to the mold disclosed in Patent Document 1, fill the cavity with foamed thermoplastic resin beads without using pressurized gas, and then perform steam heating. This production method is sometimes referred to as Prior Art 2 below. In the steam heating, the air in the chamber and cavity is first replaced with steam under atmospheric pressure. Next, after sealing the mold, steam is supplied to the chamber, introducing the steam into the first space as well, and increasing the pressure and temperature in the second space and the first space to heat-seal the foamed beads, thereby 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. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 8-300387 [Patent Document 2] Patent Publication No. 2010-138226 Summary of the Invention [Problem to be solved by the invention]

[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 in the mold. [Means for solving the problem]

[0008] The method for producing an expanded bead molded body of the present invention is a method for producing an expanded bead molded body, in which thermoplastic resin expanded beads are filled into the cavity of a split molding die consisting of a first die and a second die, 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 arranged to be 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 the exhaust chamber to heat the expanded beads, characterized in that 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). [Effects of the Invention]

[0009] The method for producing an expanded bead molding of the present invention involves preliminarily adjusting the pressure inside 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 inside the cavity (P1) into the cavity, thereby making it possible to significantly reduce the amount of steam supplied compared to conventional in-mold molding. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a vertical cross-sectional view of a molding die used in the first embodiment of the present invention. [Figure 2] FIG. 2 is a partially enlarged cross-sectional view of the molding die shown in FIG. [Figure 3] FIG. 4 is a vertical cross-sectional view of a molding die used in a second embodiment of the present invention. [Figure 4] FIG. 10 is a vertical cross-sectional view of a molding die used in a third embodiment of the present invention. [Figure 5] 1 is a graph showing pressure and temperature in a model of the manufacturing method of the present invention. [Figure 6] 1 is a graph showing pressure and temperature in a model of a conventional manufacturing method. DETAILED DESCRIPTION OF THE INVENTION

[0011] The method for producing an expanded bead molding 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. Furthermore, in the present invention, the gauge pressure is 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 the gauge pressure is expressed as MPa (G). In the present invention, the pressure (P1) refers to the pressure inside the cavity adjusted by the pre-pressure step, the pressure (P2) refers to the steam pressure used in the heating step, and the pressure (P3) refers to the pressure inside the exhaust chamber in the heating step, and they have the relationship atmospheric pressure < pressure (P3) < pressure (P2). Note that the pressure (P3) is the molding pressure during the production of the molded body.

[0012] The manufacturing method of the present invention produces an expanded bead molded article by 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 mold the expanded beads within the die. The first die and / or the second die have a cavity and an exhaust chamber that is provided to allow ventilation to the cavity. The manufacturing method of the present invention includes a pre-pressure step and a heating step. The pre-pressurization step is a step of supplying a pressurized gas other than steam into the cavity filled with the expanded beads to adjust the pressure in the cavity filled with the expanded beads to a pressure (P1) exceeding atmospheric pressure. Note that a filling step may be performed before or overlapping with the pre-pressurization step. The filling step is a step of filling the cavity with expanded thermoplastic resin beads. The heating step is performed following the pre-pressure step or overlapping with the pre-pressure 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. In 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) higher than atmospheric pressure but lower than the pressure (P2). In the manufacturing method of the present invention, the expanded thermoplastic resin beads are molded by carrying out the above steps.

[0013] According to the investigations of the present inventors, in conventional in-mold molding, most of the steam supplied to the mold before the expanded beads are heated and reach a state where they can be fused is used to increase the internal pressure of the entire mold, resulting in a significant loss of energy. This is because the steam is supplied into the mold, which is at atmospheric pressure, and the pressure and temperature of the steam drop immediately after supply because the steam is consumed to heat the mold. 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 fuse the expanded beads filled in the cavity. In consideration of the above problems, the manufacturing method of the present invention described above is essential in that in the pre-pressurization step, the pressure in the cavity formed in the mold is adjusted to a pressure (P1) above atmospheric pressure using a pressurized gas other than steam, and in the subsequent heating step, steam at a pressure (P2) higher than the pressure in 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) above atmospheric pressure but lower than the pressure (P2). This makes it easier for steam to flow from the cavity to the exhaust chamber during the heating step. In the present invention, steam refers to water vapor. The pressure inside the cavity in the pre-pressurization 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 inside the cavity becomes the predetermined pressure. These adjustments can also be appropriately determined 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 in in-mold molding. In other words, the manufacturing method of the present invention performs the heating step after the pre-pressure step, so that the supplied steam can be efficiently used to heat-fuse the expanded beads, and it is possible to appropriately shorten the heating time compared to conventional methods. The present invention will be described in further detail below.

[0015] [First embodiment] (divided 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 vertical 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 not shown. 1, the split molding die 100 used in this embodiment includes a first die 34 and a second die 36. The split molding die 100 is provided with a cavity 10 and an exhaust chamber 20. The first die 34 includes a first inner die 30A and a first frame 40A, and the second die 36 includes a second inner die 30B and a second frame 40B. The first inner mold 30A and the second inner mold 30B are paired 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 may be provided 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. The 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 toward 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, an opening / closing mechanism refers to a mechanism that switches a through hole between an open state and a closed state, and examples thereof include, but are 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 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 expanded thermoplastic resin beads 50 for producing an expanded bead molding are filled, and one end region of a filling feeder 52 provided to penetrate the frame 40 is inserted into 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. The expanded thermoplastic resin beads 50 may be abbreviated as expanded beads 50 where appropriate. Each pair of molds 30 is provided with 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 / closing mechanism 65 is provided that can open and close the opening in order 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. The steam supply unit 60 in this embodiment 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 channel 60A for introducing steam from the outside of the split mold 100 to the interior and multiple sub-channels 60B branching from the main channel 60A. The supply holes 68 are formed in the downstream end regions of the sub-channels 60B. In this embodiment, the supply holes 68 are located on the same plane as the cavity surface, allowing steam to be directly introduced into the cavity 10. Here, the cavity surface refers to the same plane as the molding wall 32 of the pair of dies 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 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 holes 68 are open to the interior of the cavity 10, and steam can be supplied to the cavity 10 through these openings. 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, and 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 alternate 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 cavity 10 in the pre-pressurization step from cavity 10 to at least one of exhaust chambers 20 in the heating step and facilitating the distribution of steam supplied in the heating step throughout 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 cavity 10 are located on the same plane as the cavity surface, and the first mold 34 and / or second mold 36 have vent holes 64 arranged on the cavity surface to allow ventilation between cavity 10 and exhaust chamber 20. In such a split mold 100, the ratio of the total open area of ​​vent holes 64 to the total open area of ​​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. Furthermore, 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 relative to the total area of ​​the inner peripheral surface (hereinafter also referred to as the cavity surface) of the molding wall 32 separating the cavity 10 from the exhaust chamber 20, the following configuration is preferred. That is, in the split molding die 100, the ratio of the total open area of ​​the vent holes 64 relative to the total area of ​​the cavity surface is preferably greater 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%. Note that, whether the exhaust chamber 20 is provided in only one of the first mold 34 and the second mold 36, or in both, the ratio of the total open area of ​​the vent holes 64 relative to the total area of ​​the cavity surface preferably satisfies the above-mentioned numerical range. As described above, the pair of dies 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 to 5 times, 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 from the exhaust chamber 20 is greater than 0% and less than 2%. 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, because this makes it easier for steam to be distributed throughout the entire cavity 10. In particular, in a split molding die 100 in which any one or combination of the first to third embodiments of the arrangement position of the supply holes 68 described below is implemented, the magnification and ratio of the opening area of ​​the air vent holes 64 described above may be implemented. In this embodiment, the following steps are carried out using the split mold 100 described above.

[0019] The above-described split mold 100 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 such as resin with a lower thermal conductivity than metal. The surface of the split mold 100 made of a metal material may also be coated with a material such as resin with a lower thermal conductivity than metal. In particular, the molding wall 32 forming the cavity 10 may be made of a material such as resin with a lower thermal conductivity, or the inner and / or outer surfaces of the molding wall 32 may be coated with a material such as resin with a lower thermal conductivity. The coating method described above is not limited, and examples include coating the entire split mold 100 made of a metal material or a partial region such as the molding wall 32 with a resin paint to form a coating layer, or applying a resin tape. Examples of materials with low thermal conductivity include polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), and polyetherimide (PEI).

[0020] (filling process) The filling step in this embodiment will be described. The filling step is a step 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, pressurizing the expanded beads 50 with pressurized gas, thereby enhancing the secondary expansion property. Since the manufacturing method of the present invention includes a pre-pressurizing 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 the foaming temperature, and expanded by releasing the expanded beads under a pressure lower than the pressure inside the pressure vessel. This produces expanded beads.

[0024] Examples of the thermoplastic resin constituting the expanded beads 50 include polyolefin resins such as polypropylene resins and polyethylene resins, as well as polystyrene resins, polyamide resins, polyester resins, polycarbonate resins, modified polyphenylene ether resins, polyvinyl chloride resins, polymethacrylic resins, and acrylonitrile resins. Among these, it is preferable to use one or more resins selected from polypropylene resins, polyethylene resins, and polystyrene resins as the base resin of the expanded beads 50, and it is more preferable to use one or more resins selected from polyolefin resins. That is, it is more preferable that the expanded beads 50 be polyolefin resin expanded beads. Furthermore, polypropylene resin expanded beads generally require high molding pressure during in-mold molding, and therefore have traditionally required a particularly large amount of steam. Therefore, from the perspective of more fully enjoying the effects of the present invention, it is preferable to use polypropylene 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 resin foam molded articles.

[0025] Polypropylene resin: The polypropylene resin refers to a propylene homopolymer and / or a propylene 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 the propylene homopolymer may be used alone or in combination of two or more. The propylene copolymer preferably has a content of structural units derived from propylene in the polypropylene resin of 80% by mass or more, more preferably 90% by mass or more. The content of structural units derived from propylene in the propylene copolymer is preferably 99% by mass or less, more preferably 98% by mass or less. Examples of such propylene copolymers include copolymers of propylene and ethylene and / or an α-olefin having 4 to 20 carbon atoms. Examples of the α-olefins include 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-butene. Other examples of propylene copolymers include ethylene-propylene random copolymers, propylene-butene random copolymers, and ethylene-propylene-butene random copolymers. These propylene copolymers may be, for example, random copolymers or block copolymers, but are preferably random copolymers. Examples of the propylene copolymer include impact-resistant polypropylene (block polypropylene) which is 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 in the continuous phase. These resins exemplified as the propylene copolymer may be used alone or in combination of two or more. The polypropylene resin may be a linear polypropylene resin, a branched polypropylene resin, or a combination thereof.

[0026] Polyethylene resin: The polyethylene resin refers to an ethylene homopolymer or an ethylene copolymer containing 50% by mass or more of structural units derived from ethylene. Specific examples include polyethylenes such as 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; and ethylene copolymers such as ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, and ethylene-α-olefin copolymer. The ethylene copolymer preferably has a content of structural units derived from ethylene in the polyethylene resin of 80% by mass or more, more preferably 90% by mass or more, and preferably has a content of structural units derived from ethylene in the polyethylene copolymer of 99% by mass or less, more preferably 98% by mass or less.

[0027] Polystyrene resin: The polystyrene resin is a styrene resin in which the styrene component unit accounts for 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, pt-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 of achieving the intended object of the present invention. Examples of monomers copolymerizable with styrene include acrylic monomers such as 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 such 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 a 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 in accordance with JIS K7171:2008.

[0032] Optional additives: The expanded beads 50 may contain any additives as appropriate within the scope of not impairing the objects and effects of the present invention. For example, the optional additives may 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 foamed particles 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 saturation is 15 kg / m or more. 3More 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 The following is the result. That is, the bulk density of the expanded beads of the present invention is preferably 10 kg / m 3 More than 200kg / m 3 More preferably, it is 20 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 as a core layer and a covering layer covering the foam layer. The covering 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] (Preload process) In this embodiment, after the filling step is completed, a pre-pressurization step is carried out. In the pre-pressurization step 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 increasing the pressure in the cavity 10 to a pressure (P1) exceeding atmospheric pressure. The pressurized gas other than steam may be, for example, an inorganic gas, an organic gas, or a mixture thereof. From the viewpoints of safety and economy, the pressurized gas is preferably one or a combination of two or more inorganic gases such as air, nitrogen, and carbon dioxide, with air being 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 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. Alternatively, a flow path switching mechanism (not shown) can be provided in the steam supply unit 60 to supply a pressurized gas other than steam 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) inside the cavity 10 after the pre-pressure step has been carried out 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) inside the cavity 10 in 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) inside the cavity 10 adjusted by the pre-pressure step is equal to or less than the above pressure, the expanded beads 50 shrink, increasing the gap inside the cavity 10, thereby preventing shrinkage and deterioration of internal fusion in the resulting expanded bead molding. Furthermore, from the viewpoint that pre-pressurization enables the amount of steam used in the heating process described below to be sufficiently reduced, it is preferable that the pressure (P1) inside the cavity 10 is adjusted to 0.02 MPa (G) or more, and more preferably 0.05 MPa (G) or more. From the above viewpoint, the pressure (P1) inside the cavity 10 adjusted by the pre-pressure step 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 may be adjusted taking into consideration the heating temperature of the resin constituting the expanded beads 50 used. For example, when the base resin of the expanded beads 50 is a polypropylene-based resin, the pressure (P1) inside the cavity 10 adjusted by carrying out the pre-pressure process 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. Furthermore, 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, more preferably 0.05 MPa (G) or more, and even more preferably 0.07 MPa (G) or more, and is 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. 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 process is preferably 0.02 MPa (G) or more, more preferably 0.03 MPa (G) or more, and even more preferably 0.04 MPa (G) or more, and is 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.

[0039] In addition, 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 also adjust the pressure by exhausting excess pressurized gas to the outside of the split molding die 100 through the exhaust hole 66.

[0040] (Heating process) By carrying out the pre-pressure step, the pressure (P1) inside the cavity 10 is already adjusted to a pressure exceeding atmospheric pressure when the heating step is started. 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. 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 exhaust hole 66 may be closed and the pressure (P3) may be adjusted by adjusting the relationship between the pressure (P1) and the pressure (P2), or the pressure (P3) may be adjusted by exhausting air to the outside of the split mold 100 through the exhaust hole 66. From the viewpoint of quickly discharging pressurized gas other than steam from the cavity in the pre-pressurization step, it is preferable to adjust the discharge of the gas from exhaust holes 66 to the outside of split molding die 100 . In conventional in-mold molding, steam is supplied to a mold at atmospheric pressure, requiring a large amount of steam to raise the pressure and temperature within the mold to the desired levels. However, in the heating step of the manufacturing method of the present invention, the pressure within the 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 the cavity 10 to be raised quickly. 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 Figures 5 and 6, respectively. Specifically, Figures 5 and 6 show the surface pressure (MPa (G)) of an expanded bead molding formed in an exhaust chamber, the pressure within the cavity (MPa (G)), the temperature of the first inner mold (°C), and the internal temperature (°C) of the expanded bead molding over the course of molding. Note that the surface pressure and internal temperature of the expanded bead molding refer to the surface pressure and internal temperature of the expanded bead molding within the cavity before the expanded beads fuse 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 expanded beads 50, a pre-pressure 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). This was followed by a heating step 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 inside each exhaust chamber 20 for 7 seconds. The amount of steam used in this 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-pressure 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 FIG. 6 is described. The model shown in FIG. 6 uses a conventional mold configured similarly to the split mold 100 shown in FIG. 1 , except that it does not have a steam supply unit 60 and the air inlet 69 functions 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 primary heating, the cavity was heated by supplying steam through the air inlet 69 provided in the first frame. The steam was then supplied into the exhaust chamber and discharged from the second frame. In the secondary heating, the steam supply and discharge were reversed from the primary heating. As a result, it took about 10 seconds for the pressure in the cavity and the internal temperature of the molded product to rise sufficiently through the primary and secondary heating processes. The amount of steam used in the heating process was 4.08 kg. Next, the pressure in the mold was released, and a cooling process was carried out to obtain a foamed bead molded product. Furthermore, as shown in Figure 6, in the conventional in-mold molding model, the temperature of the first mold increased significantly during the heating process, confirming that the heat of the steam was absorbed by the mold.

[0043] As mentioned 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] Differential pressure (P2-P1): From the viewpoint of more fully enjoying the effects of the present invention, the differential pressure (P2-P1) obtained by subtracting the pressure (P1) in the cavity 10 to which the pressurized gas is supplied by carrying out the pre-pressurization step from the pressure (P2) of the steam supplied into the cavity 10 from the steam supply section 60 during the heating step is preferably 0.10 MPa or more and 0.40 MPa or less, and 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 in the heating step can be shortened. That is, the steam output time is shortened. As a result, the expanded beads 50 begin to expand midway through 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 holes 68 and the end of the cavity 10. Therefore, when the pressure difference (P2-P1) is equal to or greater than the preferred pressure described above, it becomes easier to obtain a good expanded bead molded article that is free from shrinkage in the area corresponding to the periphery of the supply holes 68, shrinkage of the entire molded article, and heating unevenness. On the other hand, when the pressure difference (P2-P1) is equal to or less than the upper limit of the above-mentioned preferred pressure range, excessive compression of the expanded beads due to the pressure difference (P2-P1) can be suppressed. As a result, a high filling rate of the expanded beads 50 in the cavity 10 is maintained, which facilitates the production of a uniformly expanded expanded bead molding with good fusion properties and no uneven heating. 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) inside the cavity 10 to which pressurized gas is supplied by performing the pre-pressure step refers to the pressure inside the cavity after the pre-pressure step has been performed.

[0045] Differential pressure (P1-P3): From the viewpoint of enjoying the effects of the present invention more fully, 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 even more preferably 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, in the heating step, steam at a pressure (P2) higher than the pressure (P1) in the cavity 10 is supplied from the steam supply unit 60 into the cavity 10. This adjusts the pressure in the cavity 10 to a pressure suitable for thermal fusion of the expanded beads 10. To more fully implement this adjustment, steam exhaust adjustment may be performed as described below while supplying steam into the cavity 10 in the heating step. Furthermore, adjusting the steam exhaust also makes it easier to adjust the differential pressure (P2-P1) described above. The steam exhaust adjustment is performed by exhausting a portion of the steam inside the cavity 10 from the cavity 10 to each exhaust chamber 20 through vent holes 64 provided in the molding walls 32 that constitute the pair of dies 30. The vent holes 64 are provided in the molding walls 32 that separate the inside of the cavity 10 from the inside of the exhaust chamber 20, and ensure ventilation between the exhaust chamber 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 in the vent holes 64. Alternatively, the steam exhaust adjustment may be performed by exhausting steam from the cavity 10 to the exhaust chamber 20 through a 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 an exhaust hole 66 that connects 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 an opening / closing mechanism 65 provided in the vent hole 64 and / or an opening / closing mechanism 67 provided in the exhaust hole 66. In the steam exhaust adjustment, it is preferable to adjust the exhaust using the opening / closing mechanism 65 provided in the vent hole 64, since this facilitates adjustment of the pressure difference (P2-P1). By adjusting the steam exhaust as 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 beads 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 process) The cooling step is a step of cooling the foamed bead molding produced in the cavity 10. The cooling means is not particularly limited, and for example, the following means, such as pressure release means, vacuum means, air cooling means, cooling by radiation means, and water cooling means, can be used alone or in combination. The pressure release means is a means for releasing the pressure in the split molding die 100 and lowering the temperature by lowering the internal pressure. The vacuum means is a means for lowering the temperature by vacuuming the inside of split molding die 100 to liquefy steam and utilize the heat of vaporization of water that adheres to split molding die 100 . The air-cooling means is a means for lowering the temperature by blowing a gas such as air into the split molding die 100. The air-cooling means can also be used to blow away and remove water droplets that have formed inside the split molding die 100. The cooling means is a means for lowering the temperature by leaving the exhaust hole and the vent hole in the split molding die 100 open at the ambient temperature. The water cooling means is a means for supplying cooling water into the split molding die 100 to lower the temperature.

[0050] Feed hole location: 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 any one of or a combination of the following first to third aspects.

[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 that 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 arranged to terminate 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 half the thickness of the molding wall 32 or less. 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. Furthermore, 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. This 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 arranged on the same surface as the cavity 10 surface. 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 40 mm or more, more preferably 45 mm or more, and even more preferably 50 mm or more. Satisfying this average distance facilitates the formation of a direction in which steam supplied from the supply holes 68 into the cavity 10 flows 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. Furthermore, steam can be more easily supplied uniformly to each expanded bead, making it easier to obtain a molded article 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 ventilation holes 64 is preferably 100 mm or less, more preferably 90 mm or less, and even more preferably 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 unit 60 extends inside 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 inside the cavity 10 can be supplied from the supply hole 68 to the cavity 10, which has already been adjusted to a pressure exceeding atmospheric pressure, from a position inside the expanded bead molding. Therefore, in the second embodiment, the supplied steam can be used solely for heat-sealing the expanded beads 50, resulting in little 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 unit 60 extending into the cavity 10 will be left on the surface of the molding, which is detrimental to the design and impact resistance of the molding. 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 of the steam supply section 60 that protrudes into the inside of the molding wall 32 is preferably half or less of the thickness of the cavity 10. 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.

[0054] In the third embodiment, the supply holes 68 are provided outside the cavity 10, i.e., in 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, it is preferable that the volume of the exhaust chamber 20 be small in order to reduce the energy loss of steam. 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] (Foamed bead molding) A preferred embodiment of the expanded bead molded article produced by the production method of the present invention will now 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, it is 15 kg / m or more. 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 The following is the result. That is, 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. 3More than 50kg / m 3 The following is the result. The 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 methods, 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 methods, making it less likely that excessive heat capacity will be applied to the expanded beads 50, which is presumably why the shrinkage rate of the expanded bead moldings is improved. For a method for confirming the shrinkage rate, see the description in the Examples section below.

[0058] Shrinkage (denting): 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 is significantly longer. In such cases, 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 cases, the steam pressure increases around the supply holes 68, and the heating temperature becomes concentrated, which may cause the expanded bead molding around the overheated supply holes 68 to shrink and become dented. In contrast, in the production method of the present invention, in which the pre-pressure step is performed followed by the heating step, the above-mentioned dents formed 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 of the first embodiment described above in that it uses a split molding mold 100 that forms a cavity 10 by clamping a pair of molds 30 having a first inner mold 30A and a corresponding 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 compared to when the first inner mold 30A and the second inner mold 30B are fully clamped. The expanded cavity 10 is filled with expanded beads 50. Next, the pair of molds 30 are fully clamped to reduce the volume of the cavity 10, thereby compressing the expanded beads 50 in the cavity 10, thereby performing the filling process. The filling process in the second embodiment may be 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 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 to a specific value or less, it is possible to prevent the expanded beads 50 from becoming too densely packed together, which would impair the passage of steam between the expanded beads 50. As a result, it is possible to prevent the expansion bead molding to be produced from shrinking around the steam supply holes 68 or from having uneven heating in the corner regions of the supply holes 68 and the cavity 10. From this viewpoint, the cracking rate is preferably 35% or less, and more preferably 25% or less. Furthermore, by setting the cracking rate to 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 otherwise reduce the fusion properties of the resulting expanded bead molding. From this perspective, the cracking rate is preferably 5% or more, and more preferably 8% or more. The cracking rate can be determined 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 previously pressurized 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 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 expanded thermoplastic resin beads 50 that have been compressed in advance with a pressurized gas other than steam. The filling step in the third embodiment may be referred to as a compression filling step. In this embodiment, when the filling step is carried out, the pressurized gas is supplied to the cavity 10 together with the expanded thermoplastic resin beads 50. That is, the compression filling step includes a filling step of filling the cavity 10 with the expanded beads and part or all of a pre-pressurization step of increasing the pressure inside the cavity. More specifically, as shown in Fig. 4, the split molding die 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 expanded 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 expanded beads filled in the pressurized filling tank 200 can be pressurized to a desired pressure. The pressurized expanded beads are supplied in a compressed state from the filling feeder 52 to the cavity 10 together with pressurized gas.

[0066] As described above, the pre-pressure process in this embodiment is carried out in overlap with the filling process, but if the internal pressure in the cavity 10 does not reach the desired pressure, the pre-pressure process may be carried out separately. On the other hand, if the internal pressure in the cavity 10 exceeds a desired pressure due to the compression filling process, pressure gas exhaust adjustment may be performed. Such pressure 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 exhausting a portion of the pressurized gas in the cavity 10 from the cavity 10 to at least one of the exhaust chambers 20 through an air vent 64 provided in the molding wall 32 that constitutes the pair of molds 30, and adjusting the pressure in the cavity 10 by opening and closing an opening / closing mechanism 65 provided in the air vent 64. The pressurized gas exhaust adjustment may also be performed by exhausting a portion of the pressurized gas in the cavity 10 from the cavity 10 to at least one of the exhaust chambers 20 through an air vent 64 provided in the molding wall 32, and exhausting a portion of the pressurized gas in the exhaust chamber 20 from the exhaust chamber 20 to the outside of the split molding die 100 through an exhaust hole 66 that connects the exhaust chamber 20 to the outside of the split molding die 100, and adjusting the pressure in the cavity 10 by opening and closing an opening / closing mechanism 65 provided in the air vent 64 and / or an opening / closing mechanism 67 provided in the exhaust hole 66.

[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 0.1 MPa (G) or more, more preferably 0.15 MPa (G) or more, and even more preferably 0.18 MPa (G) or more. When the base resin of the expanded beads 50 is a polyethylene-based resin, the pressure for performing 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. When the base resin of the expanded beads 50 is a polystyrene-based resin, the pressure for performing 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.

[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 previously pressurized with pressurized gas to increase the internal pressure and enhance secondary foaming properties, as described in the first embodiment. [Example]

[0069] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. In these examples, molds having the same configuration as the molds 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 used in each Example and Comparative Example, as well as the bulk density of the polystyrene-based resin expanded beads, are shown in the Example Table. <Polypropylene resin expanded particles 1 (referred to as EPP1 in the table)> The foamed particles used were made from an ethylene-propylene random copolymer with a melting point of 141.5°C, an ethylene content of 3.1 mass%, and an MFR (load 2.16 kg, 230°C, JIS K7210-1:2014) of 7 g / 10 min. <Polypropylene resin expanded particles 2 (referred to as EPP2 in the table)> The foamed particles used were made from an ethylene-propylene random copolymer with 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 resin foam particles (referred to as EPE in the table)> Melting point: 121°C, density: 0.928g / cm 3 The foamed particles used were made of ethylene-α-olefin copolymer with an MFR (load 2.16 kg, 190°C, JIS K7210-1:2014) of 1.0 g / 10 min. <Polystyrene resin expanded particles (referred to as EPS in the table)> Styrodia FA200 manufactured by JSP Co., Ltd. was used as the expandable styrene 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 the tank was left standing for 24 hours, until the internal pressure of the expanded polypropylene resin beads reached 0.14 MPa (G). A split mold having a configuration similar to that shown in Figure 1 was used to produce the expanded bead molded article. Specifically, a split mold was used, which had a cavity capable of molding a flat-shaped molded 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 to the total open area of ​​the supply holes was 3.4 times, and the ratio of the total open area of ​​the vent holes to the total area of ​​the inner circumferential surface of the mold wall forming the cavity was 0.6%. Furthermore, the average distance between the supply holes and the vent holes in the pair of dies was 52 mm. The split mold was adjusted so that the cracking distance was 6 mm (cracking rate 10%), and in this state, the filling step was carried out by filling the mold with expanded polypropylene resin particles to which internal pressure had been applied in advance (see FIG. 3). Next, pressurized air was supplied from the air intake holes provided in the frame of the split molding mold to pressurize each exhaust chamber, and pressurized air was also supplied to the cavity through the air vents, performing a pre-pressure process so that the pressure inside the cavity was 0.25 MPa (G). Next, steam at an output pressure of 0.45 MPa (G) was supplied directly to the cavity for 6 seconds from a steam supply unit with a supply hole located inside the cavity, and the heating process was carried out. The differential pressure (P2 - P1), obtained by subtracting the pressure inside the cavity (P1) adjusted in the pre-pressure process from the output pressure (P2) of the steam used in this heating process, was 0.20 MPa. The pressure inside the split mold was 0.25 MPa (G). The amount of steam consumed in each heating process 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 was measured using a thermocouple inserted into the cavity in advance (at a position halfway along the length and width of the compact, and 20 mm from the cavity surface of the first inner mold toward the interior of the compact). This temperature represents the highest temperature during the heating process. 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, followed by air cooling for 5 seconds, and then natural cooling for 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, the split mold was opened, and the expanded bead molding was removed. 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. The time from immediately before the foamed beads were filled after ensuring a predetermined cracking distance to the time when the mold was opened after cooling was completed was measured, and this is 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 being filled into cavities. The method for measuring the bulk density is shown below, and the measurement results are shown in Table 1.

[0072] (Bulk density of expanded particles) Expanded particles with internal pressure were prepared. A mass of W (g) of expanded particles 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 packed height of the expanded particles in the measuring cylinder. The bulk volume V (L) of the expanded particles indicated on the measuring cylinder was read, and the mass W of the expanded particles was divided by the bulk volume V of the expanded particles (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 foamed bead molding) The volume was calculated by dividing the mass of the expanded bead molding 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 mold used for in-mold molding was measured as follows. First, after in-mold molding, the expanded bead molding was removed from the split mold 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 of the cavity (LA) and the long side dimension (LB) of the expanded bead molding relative to the long side dimension of the cavity was calculated to obtain the shrinkage rate of the expanded bead molding relative to the dimensions of the split mold.

[0075] (internal fusion) The expanded bead molding was bent and broken, and the number of expanded beads present on the fracture surface (C1) and the number of broken expanded beads (C2) were counted. The ratio of the number of broken expanded beads to the number of expanded beads present on the fracture surface [(C2 / C1) × 100] was calculated as the material failure rate. The above measurement was carried out five times using different test pieces, and the material failure rate for each test piece was determined and the arithmetic mean value was calculated. The arithmetic mean value was used to evaluate the material failure rate according to the following evaluation criteria. ◎: Material destruction rate is 91% or more 〇: Material destruction rate is 71% or more but less than 91% △: Material destruction rate is over 0% and less than 71% ×: Material destruction rate is 0%

[0076] (shrinkage (dent)) First, the outer surface of the expanded bead molding removed from the split mold was visually observed. Then, the expanded bead molding was left to stand for 24 hours in an environment of 23°C and 50% relative humidity for aging. The expanded bead molding was visually observed and evaluated as follows. ◎: Small shrinkage before curing, and no shrinkage observed after curing. ◯: Significant shrinkage was observed before curing, but the shrinkage recovered after curing. △: Large shrinkage was observed before and after curing. ×: Significant shrinkage was observed before and after curing, and some melted portions were observed.

[0077] (Uneven heating) The outer surface of the expanded bead molded article removed from the split mold was visually observed, and heating unevenness was evaluated as follows. ⊚: It was confirmed that the entire material was foamed uniformly and no uneven heating occurred. ◯: There were voids between the foam particles on some parts of the surface, but it was confirmed that the foam was generally uniform and there was almost no uneven heating. △: Expanded particles were detached from part of the surface, and insufficient expansion due to uneven heating was confirmed. ×: Many foam particles were detached from the surface, and overall insufficient foaming due to uneven heating was confirmed.

[0078] <Examples 2 to 7, 9, and 10, and Comparative Example 1> An expanded bead molding was 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 produced expanded bead molding were measured and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0079] Example 8 An expanded bead molding was produced in the same manner as in Example 1, except that the contents were changed as shown in Table 2 and the filling step and pre-pressure step were carried out as follows. The expanded beads used and the produced expanded bead molding were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1. In Example 8, a mold having the same configuration as in Figure 4 was used. First, foamed polypropylene resin beads before pressurization were filled into a pressure filling tank. Pressurized air was then supplied into the tank and the tank was left to stand for 24 hours, increasing the internal pressure of the foamed polypropylene resin to 0.10 MPa (G). The foamed beads with increased internal pressure and the pressurized air 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 process and pre-pressurization process were carried out simultaneously.

[0080] <Examples 11 to 13, Comparative Example 2> Examples 11 to 13 and Comparative Example 2 were carried out using expanded polyethylene resin beads. 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 expanded bead moldings produced were measured and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0081] <Examples 14 to 17, Comparative Example 3> Examples 14 to 17 and Comparative Example 3 were carried out using expanded polystyrene resin beads. 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.

[0082] <Comparative Example 4> A conventional split mold was prepared, similar to the split mold shown in Figure 1 except that it did not have a steam supply section. Expanded beads similar to the expanded polypropylene resin 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 (cracking rate of 10%), and then the mold was clamped. 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 opening / closing mechanism of the split mold open, replacing the air in the split mold with steam. Next, one-sided heating was performed by supplying steam at an output pressure of 0.60 MPa (G) from the first frame side into the exhaust chamber for 5 seconds, raising the pressure to 0.26 MPa (G) and heating the foamed beads. Furthermore, reverse one-sided heating was performed by supplying steam at an output pressure of 0.60 MPa (G) from the second frame side into the exhaust chamber for 3 seconds, raising the pressure to 0.36 MPa (G) and heating the foamed beads. Next, double-sided heating was performed by opening and closing the supply holes on both sides of the split mold (the first frame side and the second frame side) to maintain a pressure of 0.38 MPa (G) inside the split mold, completing the heating process. During heating, the exhaust holes in the frame of the split mold were closed except for the part used to supply steam, and the vent holes in the pair of molds were left open. This allowed the steam supplied to the split mold to enter the chamber. The pressure inside the split mold means the pressure inside the chamber. The total amount of steam consumed in the heating step was 4.08 kg. After the above-mentioned heating step was carried out, cooling was carried out by the same cooling method as in Example 1, except that the cooling time shown in Table 5 was used. Then, after it was confirmed that the ejection pressure had reached the value shown in Table 5, the expanded bead molding was removed from the mold. Using the expanded beads used in Comparative Example 4 and the expanded bead molding obtained by Comparative Example 4, measurements and evaluations similar to those in Example 1 were carried out. The results are shown in Table 5.

[0083] <Comparative Examples 5 and 6> Except for the changes shown in Table 5, foamed bead moldings were produced in the same manner as in Comparative Example 4. Double-sided heating was not performed in Comparative Examples 5 and 6. The foamed beads used and the foamed bead moldings produced were subjected to the same measurements and evaluations as in Example 1. The results are shown in Table 5.

[0084] As shown in Tables 1 to 5, it was confirmed that the steam output time and consumption amount in the heating step of each Example were significantly reduced compared to Comparative Examples 4 to 6 in which conventional in-mold molding was performed. In addition, in Examples 1 to 10, the steam output time was short and the steam consumption was small, and good foamed bead moldings were produced in all cases. In contrast, in Comparative Example 1, in which the pre-pressurization step was not performed, the steam output time was long and the steam consumption was large. In addition, the foamed bead molding obtained in Comparative Example 1 had poor fusion between the foamed beads, and some of the foamed bead molding remained as expanded beads, and the shape of the foamed bead molding could not be maintained, so the molding could not be evaluated. In Examples 11 to 13, the steam output time was short and the steam consumption was small, and good foamed bead moldings were produced in all cases. In contrast, in Comparative Example 2, in which the pre-pressurization step was not performed, the steam output time was long and the steam consumption was large. Furthermore, in Comparative Example 2, the fusion between the foamed beads was poor, making it impossible to measure the density and shrinkage rate. In Examples 14 to 17, the steam output time and consumption were short, and good foamed bead moldings were produced in all cases. In contrast, in Comparative Example 3, in which the pre-pressurization step was not performed, the steam output time was long and the steam consumption was high.

[0085] [Table 1]

[0086] [Table 2]

[0087] [Table 3]

[0088] [Table 4]

[0089] [Table 5]

[0090] The present invention described above encompasses the following technical ideas. (1) A method for producing a foamed bead molded article, comprising filling foamed thermoplastic resin beads into a cavity of a split mold consisting of a first mold and a second mold, and then heating the foamed beads with steam to form an in-mold mold, the first mold and / or the second mold have a cavity and an exhaust chamber that is ventilated; 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 foamed beads to a pressure (P1) exceeding atmospheric pressure; 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-pressure step, and discharging the steam supplied into the cavity into an exhaust chamber to heat the foamed beads; A method for producing an expanded bead molding, characterized in that 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) In the heating step, steam having a pressure (P2) higher than the pressure (P1) in the cavity is supplied from the steam supply unit into the cavity, and the steam in the cavity is exhausted to the outside of the cavity through a vent hole provided in a molding wall separating the cavity from the exhaust chamber, the vent hole ensuring ventilation between the exhaust chamber and the cavity; The method for producing the expanded bead molded article described in (1) above is characterized in that the pressure inside the exhaust chamber is adjusted through an exhaust hole with an opening / closing mechanism provided in at least one of the first mold and the second mold, which ensures ventilation between the exhaust chamber and the outside of the molding mold, and the thermoplastic resin expanded beads are fused to each other. (3) The method for producing a foamed bead molding according to (1) or (2), wherein the pressure in the cavity is adjusted to 0.05 MPa (G) or more and 0.4 MPa (G) or less in the pre-pressurizing step. (4) The method for producing an expanded bead molding according to any one of (1) to (3), wherein 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. (5) The method for producing an expanded bead molding according to any one of (1) to (4), 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. (6) The method for producing a foamed bead molding according to any one of (1) to (5), wherein the foamed thermoplastic resin beads are foamed polypropylene-based resin beads. (7) The method for producing a foamed bead molding according to any one of (1) to (6), characterized in that a supply hole for supplying the steam is arranged on the same plane as the cavity surface, and in the heating step, steam having a pressure higher than the pressure inside the cavity is directly supplied from the supply hole into the cavity. (8) A supply hole for supplying steam into the cavity is arranged on the same surface as the cavity surface, and the first mold and / or the second mold have an air hole on the cavity surface that allows ventilation between the cavity and the exhaust chamber, The method for producing an expanded bead molding according to any one of (1) to (7), wherein the average distance between the supply holes and the vent holes is 40 mm or more. (9) A supply hole for supplying steam into the cavity is arranged on the same surface as the cavity surface, and the first mold and / or the second mold have an air hole on the cavity surface that allows ventilation between the cavity and the exhaust chamber, the total opening area of ​​the vent holes is 1.2 times or more and 5 times or less than the total opening area of ​​the supply holes, The method for producing an expanded bead molding according to any one of (1) to (8), characterized in that the ratio of the total open area of ​​the air holes to the total area of ​​the cavity surface is greater than 0% and not more than 2%. (10) The cavity is formed by a first inner mold provided in the first mold and a second inner mold provided in the second mold, The method for producing a foamed bead molding according to any one of (1) to (9), characterized in that 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) A filling step is performed before the pre-pressurizing step or overlaps with the pre-pressurizing step, the filling step uses the pair of molds to provide a cracking distance between the first inner mold and the second inner mold in a mold clamping direction to expand the volume of the cavity; Filling the expanded cavity with thermoplastic resin foam particles; The method for producing the expanded bead molding described in any one of (1) to (10) above, characterized in that the pair of molds are then completely clamped together to reduce the volume of the cavity, thereby compressing the expanded thermoplastic resin beads in the cavity. (12) A filling step is performed before the pre-pressurizing step or overlaps with the pre-pressurizing step, the filling step is a step of filling the cavity with foamed thermoplastic resin particles that have been compressed in advance by a pressurized gas other than steam, The method for producing an expanded bead molding according to any one of (1) to (11), characterized in that when the filling step is carried out, the pressurized gas is supplied to the cavity together with the thermoplastic resin expanded beads, so that part or all of the pre-pressurization step is carried out at the same time as the filling step. [Explanation of symbols]

[0091] 10. Cavity 20. Exhaust chamber 30....A pair of molds 30A···First inner type 30B...Second inner type 32...molded wall 34. First Type 36...Second Type 40 frames 40A···First frame 40B... Second frame 50...Thermoplastic resin foam particles 52 Filling feeder 60 Steam supply unit 60A...Main flow path 60B Sub-channel 64 Ventilation hole 65... Opening and closing mechanism 66 Exhaust vent 67 Opening and closing mechanism 68...supply hole 69 Air intake hole 100...Divided mold 200...Pressurized filling tank 202 Pressurized pressure adjustment unit 204 Exhaust pressure adjustment unit C···Mold clamping direction d1: distance x Cracking distance

Claims

1. A method for producing an expanded bead molded article, comprising filling a cavity of a split molding die comprising a first die and a second die with expanded thermoplastic resin beads, and heating the expanded beads with steam to form an in-mold molding product, the first mold and / or the second mold have an exhaust chamber that is provided to be able to communicate with the cavity; 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 foamed beads to a pressure (P1) exceeding 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-pressure step, and discharging the steam supplied into the cavity into an exhaust chamber to heat the foamed beads; a step of supplying steam at the pressure (P2) into the cavity while adjusting the pressure in the exhaust chamber to a pressure (P3) that exceeds atmospheric pressure but is lower than the pressure (P2).

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

3. 3. The method for producing an expanded bead molded article according to claim 1, 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.

4. 3. The method for producing an expanded bead molding according to claim 1, wherein a differential pressure (P1-P3) obtained by subtracting the pressure (P3) in the heating step from the pressure (P1) in the pre-pressurizing step is −0.1 MPa or more and +0.1 MPa or less.

5. 3. The method for producing a foamed bead molding according to claim 1, wherein the foamed thermoplastic resin beads are foamed polypropylene-based resin beads.

6. 3. The method for producing a foamed bead molding according to claim 1, wherein 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. 3. The method for producing an expanded bead molding according to claim 1, wherein 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 air vents on the cavity surface that allow ventilation between the cavity and the exhaust chamber, the total open area of ​​the air vents being 1.2 to 5 times the total open area of ​​the supply holes, and the ratio of the total open area of ​​the air vents to the total area of ​​the cavity surface is more than 0% and 2% or less.

8. 3. The method for producing a foamed bead molding according to claim 1, wherein the cavity is formed by a first inner mold of the first mold and a second inner mold of 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.

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