WO2022270425A1 - ポリプロピレン系樹脂発泡粒子成形体及びその製造方法 - Google Patents

ポリプロピレン系樹脂発泡粒子成形体及びその製造方法 Download PDF

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Publication number
WO2022270425A1
WO2022270425A1 PCT/JP2022/024273 JP2022024273W WO2022270425A1 WO 2022270425 A1 WO2022270425 A1 WO 2022270425A1 JP 2022024273 W JP2022024273 W JP 2022024273W WO 2022270425 A1 WO2022270425 A1 WO 2022270425A1
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expanded
polypropylene
molded article
particles
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PCT/JP2022/024273
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English (en)
French (fr)
Japanese (ja)
Inventor
拓映 坂村
肇 太田
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JSP Corp
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JSP Corp
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Priority to EP22828342.0A priority Critical patent/EP4342936A4/en
Priority to KR1020247002569A priority patent/KR20240027023A/ko
Priority to CN202280037618.8A priority patent/CN117396546A/zh
Priority to JP2022568977A priority patent/JP7299555B2/ja
Priority to MX2023015339A priority patent/MX2023015339A/es
Publication of WO2022270425A1 publication Critical patent/WO2022270425A1/ja
Priority to US18/392,071 priority patent/US20240124674A1/en
Anticipated expiration legal-status Critical
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/22—After-treatment of expandable particles; Forming foamed products
    • C08J9/228—Forming foamed products
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/22—After-treatment of expandable particles; Forming foamed products
    • C08J9/228—Forming foamed products
    • C08J9/232—Forming foamed products by sintering expandable particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/3415—Heating or cooling
    • B29C44/3426—Heating by introducing steam in the mould
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/36—Feeding the material to be shaped
    • B29C44/38—Feeding the material to be shaped into a closed space, i.e. to make articles of definite length
    • B29C44/44—Feeding the material to be shaped into a closed space, i.e. to make articles of definite length in solid form
    • B29C44/445—Feeding the material to be shaped into a closed space, i.e. to make articles of definite length in solid form in the form of expandable granules, particles or beads
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/3461—Making or treating expandable particles
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2201/00—Foams characterised by the foaming process
    • C08J2201/02—Foams characterised by the foaming process characterised by mechanical pre- or post-treatments
    • C08J2201/034—Post-expanding of foam beads or sheets
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2203/00—Foams characterized by the expanding agent
    • C08J2203/06—CO2, N2 or noble gases
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2205/00—Foams characterised by their properties
    • C08J2205/04—Foams characterised by their properties characterised by the foam pores
    • C08J2205/052—Closed cells, i.e. more than 50% of the pores are closed
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C08J2323/16—Ethene-propene or ethene-propene-diene copolymers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2423/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2423/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C08J2423/10—Homopolymers or copolymers of propene
    • C08J2423/14—Copolymers of propene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2423/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2423/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C08J2423/18—Homopolymers or copolymers of hydrocarbons having four or more carbon atoms
    • C08J2423/20—Homopolymers or copolymers of hydrocarbons having four or more carbon atoms having four to nine carbon atoms
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/16—Making expandable particles
    • C08J9/18—Making expandable particles by impregnating polymer particles with the blowing agent

Definitions

  • the present disclosure relates to a polypropylene-based resin foamed bead molded body formed by mutually fusing cylindrical foamed beads having through holes, and a method for manufacturing the same.
  • Polypropylene-based resin expanded particle moldings are lightweight and have excellent cushioning properties, rigidity, etc., and are used in a variety of applications.
  • Polypropylene-based resin foamed beads are produced by, for example, filling a mold with polypropylene-based resin foamed beads and heating with steam to cause secondary foaming of the foamed beads and melt the surfaces of the foamed beads to fuse them together. It is manufactured by an in-mold molding method in which the material is molded into a desired shape.
  • the expanded bead molded article immediately after molding tends to swell due to secondary foaming, in order to obtain an expanded bead molded article having a desired shape, the expanded bead molded article is cooled in the mold with water or air, etc., and then released from the mold. do.
  • the steam that has flowed into the cells of the expanded bead molded product during the in-mold molding condenses in the cells, creating a negative pressure inside the cells, resulting in an expanded bead molded product.
  • volumetric shrinkage may occur in the molded product, resulting in large deformation of the molded product. Therefore, after releasing the expanded bead molded article from the mold, a curing step is usually required in which the expanded bead molded article is allowed to stand for a predetermined period of time in a high-temperature atmosphere adjusted to a temperature of about 60 to 80° C. to restore the shape of the expanded bead molded article. is.
  • Patent Document 1 discloses a technique of fusing foamed particles composed of a foam layer and a fusion layer while maintaining gaps between the particles. According to Patent Document 1, the curing step can be omitted.
  • Patent Document 2 discloses a technique for in-mold molding of foamed beads using a polypropylene-based resin whose melting point, melt flow index, Z-average molecular weight, etc. are adjusted to specific ranges. According to the company, the curing time can be shortened.
  • the present invention has been made in view of such a background. Expanded polypropylene resin beads that can obtain an expanded bead molded article having a desired shape and excellent appearance and rigidity even if the curing step is omitted.
  • An object of the present invention is to provide a method for manufacturing a molded article.
  • Another object of the present invention is to provide an expanded bead molded article excellent in appearance and rigidity.
  • a molding die is filled with cylindrical polypropylene resin foamed particles having through holes, and a heating medium is supplied to fuse the foamed particles to each other to form a polypropylene resin foamed particle molded article.
  • a method of manufacturing a The foamed particles have a foamed layer made of a polypropylene-based resin, The foamed beads have a closed cell rate of 90% or more, The average pore diameter d of the through holes in the expanded beads is less than 1 mm, The method for producing a polypropylene-based resin expanded bead molded article, wherein the expanded bead molded article has an open cell rate of 2.5% or more and 12% or less.
  • Another aspect of the present invention is a polypropylene-based resin expanded bead molded article in which cylindrical polypropylene-based resin expanded particles having through holes are fused to each other,
  • the expanded bead molded product has a closed cell ratio of 90% or more,
  • the polypropylene-based resin expanded bead molded article has an open cell rate of 2.5% or more and 12% or less.
  • a polypropylene-based resin foamed particle molded article having a desired shape and excellent appearance and rigidity can be obtained. Therefore, according to the above manufacturing method, it is possible to remarkably improve the efficiency of manufacturing an expanded bead molded article excellent in rigidity and appearance.
  • FIG. 1 is a schematic diagram of the appearance of expanded beads.
  • FIG. 2 is a schematic diagram of a cross section of a foamed bead in a direction parallel to the penetration direction of the through holes of the foamed bead composed of the foamed layer.
  • FIG. 3 is a schematic diagram of a cross section of a foamed bead having a foamed layer and a fusion layer in a direction parallel to the penetration direction of through-holes of the foamed bead.
  • FIG. 4 is an explanatory diagram showing a method of calculating the area of the high temperature peak.
  • a to B representing a numerical range is synonymous with “A or more and B or less”, and is used to include the values of A and B, which are the endpoints of the numerical range.
  • a numerical value or physical property value when expressed as a lower limit, it means that it is greater than or equal to the numerical value or physical property value, and when a numerical value or physical property value is expressed as an upper limit, it means that it is equal to or less than that numerical value or physical property value.
  • “% by weight” and “% by mass”, and “parts by weight” and “parts by mass” are substantially synonymous.
  • expanded polypropylene resin particles are arbitrarily referred to as “expanded particles”, and expanded particle molded articles are arbitrarily referred to as “molded articles”.
  • Expanded beads having a foamed layer made of polypropylene resin are generally called polypropylene resin expanded beads.
  • the foamed bead molded article is manufactured by performing a molding process in which a large number of foamed particles are filled in a mold and a heating medium such as steam is supplied to fuse the foamed particles to each other. That is, a molded article can be obtained by in-mold molding the expanded beads.
  • the expanded beads have a cylindrical shape with through holes, and the average hole diameter d of the through holes is less than 1 mm, and the ratio d/D of the average hole diameter d to the average outer diameter D of the expanded beads is 0.4 or less.
  • the foamed beads have a foamed layer made of a polypropylene-based resin and have a closed cell ratio of 90% or more.
  • the shape of the molded article can be stabilized by, for example, leaving the molded article after release from the mold in an environment of 23° C. for 12 hours or longer.
  • pretreatment pressurization may be performed in which internal pressure is applied in advance to the foamed particles before being filled in the mold, or pretreatment pressurization may not be performed. It is possible to produce an expanded bead molded article having a desired shape, excellent appearance and rigidity, while omitting the curing step without performing pretreatment pressurization.
  • the expanded bead 1 is cylindrical and has a through hole 11 .
  • the foamed bead 1 has a foamed layer 2 made of a polypropylene-based resin. Furthermore, as shown in FIG. 3, the foamed beads 1 preferably have a fusion layer 3 covering the foamed layer 2 .
  • the foam layer is composed of polypropylene resin.
  • a polypropylene-based resin refers to a homopolymer of a propylene monomer and a propylene-based copolymer containing 50% by mass or more of structural units derived from propylene.
  • the polypropylene-based resin is preferably a propylene-based copolymer obtained by copolymerizing propylene and other monomers.
  • Propylene-based copolymers include propylene and ⁇ -olefins having 4 to 10 carbon atoms, such as ethylene-propylene copolymers, butene-propylene copolymers, hexene-propylene copolymers, and ethylene-propylene-butene copolymers.
  • a copolymer with is preferably exemplified. These copolymers are, for example, random copolymers, block copolymers, etc., and are preferably random copolymers.
  • the polypropylene-based resin may contain a plurality of types of polypropylene-based resins.
  • the polypropylene-based resin that constitutes the foam layer may contain a polymer other than the polypropylene-based resin within a range that does not impair the object and effect of the present disclosure.
  • examples of other polymers include thermoplastic resins other than polypropylene-based resins, such as polyethylene-based resins and polystyrene-based resins, and elastomers.
  • the content of the other polymer in the polypropylene-based resin constituting the foam layer is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. , 0, that is, it is particularly preferable that the foamed layer contains substantially only a polypropylene-based resin as a polymer.
  • the polypropylene resin constituting the foam layer is an ethylene-propylene random copolymer, and the content of the ethylene component in the copolymer is preferably 0.5% by mass or more and 10% by mass or less.
  • the total amount of ethylene component and propylene component in the ethylene-propylene random copolymer is 100% by mass. In this case, it is possible to mold a good molded article having excellent rigidity at a lower molding heating temperature (that is, a lower molding pressure). From the viewpoint of further improving this effect, the content of the ethylene component in the copolymer is more preferably more than 2.0% by mass and 5.0% by mass or less, and more preferably 2.5% by mass or more and 4.0% by mass.
  • the content of the monomer component in the copolymer can be determined by IR spectrum measurement.
  • the ethylene component and the propylene component of the ethylene-propylene copolymer mean the structural units derived from ethylene and the structural units derived from propylene in the ethylene-propylene copolymer, respectively.
  • the content of each monomer component in the copolymer means the content of structural units derived from each monomer in the copolymer.
  • the melting point Tmc of the polypropylene-based resin forming the foam layer is preferably 155°C or less.
  • a molded article having excellent appearance and rigidity can be molded at a lower molding temperature (that is, a lower molding pressure).
  • the melting point Tmc of the polypropylene-based resin forming the foam layer is preferably 150° C. or lower, more preferably 145° C. or lower.
  • the melting point Tmc of the polypropylene resin constituting the foam layer is preferably 135° C. or higher, more preferably 138° C. or higher. More preferably, the temperature is 140° C. or higher.
  • the melting point of polypropylene-based resin is determined based on JIS K7121:1987. Specifically, as the conditioning, "(2) When measuring the melting temperature after performing a constant heat treatment" is adopted, and the conditioned test piece is heated from 30 ° C. at a heating rate of 10 ° C./min. A DSC curve is obtained by raising the temperature to 200° C., and the apex temperature of the melting peak is taken as the melting point. When a plurality of melting peaks appear in the DSC curve, the apex temperature of the melting peak with the largest area is taken as the melting point.
  • the melt mass flow rate (that is, MFR) of the polypropylene-based resin constituting the foam layer is preferably 5 g/10 minutes or more, more preferably 6 g/10 minutes or more. Preferably, it is more preferably 7 g/10 minutes or more.
  • the MFR is preferably 12 g/10 minutes or less, more preferably 10 g/10 minutes or less, from the viewpoint of further increasing the rigidity of the molded article.
  • the MFR of a polypropylene resin is a value measured under conditions of a test temperature of 230°C and a load of 2.16 kg based on JIS K7210-1:2014.
  • the bending elastic modulus of the polypropylene-based resin forming the foam layer is preferably 800 MPa or more and 1600 MPa or less. From the viewpoint of increasing the rigidity of the molded body and from the viewpoint of more reliably suppressing dimensional changes when the curing step is omitted, the flexural modulus of the polypropylene-based resin constituting the foam layer is preferably 800 MPa or more. It is more preferably 850 MPa or higher, and even more preferably 900 MPa or higher.
  • the polypropylene constituting the foam layer The flexural modulus of the system resin is preferably less than 1200 MPa, more preferably 1100 MPa or less, and even more preferably 1000 MPa or less.
  • the flexural modulus of polypropylene resin can be determined according to JIS K7171:2008.
  • the resistance to shrinkage and deformation after release from the mold is small, and when the curing step is omitted, , there was a tendency for the molded body to shrink and deform remarkably.
  • the curing step can be omitted even when foamed particles made of a polypropylene-based resin having a flexural modulus of less than 1200 MPa are used.
  • the foamed particles have a closed cell rate of 90% or more.
  • the closed cell ratio of the foam layer is preferably 92% or more, and preferably 95% or more. is more preferable.
  • I the average value of five samples
  • Closed cell ratio (%) (Vx-W/ ⁇ ) x 100/(Va-W/ ⁇ ) (I) however, Vx: The true volume of the expanded bead measured by the above method, that is, the sum of the volume of the resin constituting the expanded bead and the total volume of the closed cells in the expanded bead (unit: cm 3 ) Va: Apparent volume of expanded beads measured from the increase in water level when the expanded beads are submerged in a graduated cylinder containing ethanol (unit: cm 3 ) W: Weight of sample for measurement of foamed particles (unit: g) ⁇ : Density of resin constituting expanded beads (unit: g/cm 3 )
  • the molded body has an open cell structure.
  • the open-cell structure is a minute space portion communicating with the outside of the molded article.
  • the open-cell structure includes voids formed by interconnecting through-holes of a plurality of expanded particles, voids formed by through-holes of expanded particles communicating with voids formed between expanded particles, and voids formed between expanded particles. Voids formed by interconnecting voids, open-cell portions of foamed particles constituting the molded article, and the like are formed by connecting intricately.
  • a molded product having an open cell ratio of 2.5% or more and 12% or less is manufactured.
  • the curing step is omitted, significant shrinkage, deformation, etc. can be suppressed, and a molded article having a desired shape and excellent appearance and rigidity can be produced.
  • the molded article has an open cell structure at the above-mentioned predetermined ratio, so that air can flow into the air bubbles inside the molded article immediately after releasing the mold, and the internal pressure of the entire molded article is increased.
  • the open cell ratio of the molded article is less than 2.5%, if the curing step is omitted, the molded article may significantly shrink and deform, making it impossible to obtain a molded article having a desired shape. Even if the curing step is omitted, the open cell ratio of the molded body is preferably 3% or more, more preferably 4% or more, from the viewpoint of further preventing significant shrinkage, deformation, etc. of the molded body. More preferably, it is 4.5% or more. On the other hand, if the open cell ratio of the molded article exceeds 12%, the appearance of the molded article may deteriorate and the rigidity may decrease. From the viewpoint of further improving the appearance and rigidity of the molded article, the open cell ratio of the molded article is preferably 10% or less, more preferably 8% or less, and 7.5% or less. 6% or less is more preferable.
  • the open cell content of the molded body is measured according to ASTM 2856-70 Procedure B. In other words, it is a corrected open cell ratio measured by a method of calculating by taking account of the closed cells that are broken when cutting out the measurement sample.
  • a dry automatic density meter specifically, Accupic II1340 manufactured by Shimadzu Corporation
  • the open cell ratio is measured as follows. First, the compact is left to stand at 23° C. for 12 hours for conditioning. Next, a first cubic test piece measuring 2.5 cm long, 2.5 cm wide, and 2.5 cm high is cut out from the center of the compact, and its geometric volume Va [unit: cm 3 ] is measured. .
  • Va is a value determined by vertical dimension [cm] ⁇ horizontal dimension [cm] ⁇ height dimension [cm].
  • the true volume V1 [unit: cm 3 ] of the first test piece is measured using a dry automatic densitometer.
  • the first test piece is divided into 8 equal parts to obtain a cubic second test piece measuring 1.25 cm long ⁇ 1.25 cm wide ⁇ 1.25 cm high.
  • the true volume V2 [unit: cm 3 ] of the second test piece is measured with a dry automatic densitometer.
  • the true volume V2 of the second test piece is the sum of the true volumes of the eight pieces cut out from the first test piece.
  • the open cell ratio Co [unit: %] is calculated by the following formula (II).
  • the open cell ratio Co in this specification is a physical property value measured according to ASTM2856-70 procedure B as described above, and an independent molded body measured according to ASTM2856-70 procedure C described later. It is a physical property value that cannot be calculated based on the void ratio.
  • the open cell ratio Co of the molded body measured according to ASTM 2856-70 procedure B is the closed cell ratio Bp of the molded body measured according to ASTM 2856-70 procedure C and the following formula ( III).
  • the open cell fraction Co measured according to ASTM 2856-70 Procedure B is corrected to account for closed cells that are destroyed when the test piece is cut, whereas the ASTM 2856-70 Procedure C describes The two methods are conceptually different because closed cells that are destroyed when the test piece is cut are not taken into account in the above method.
  • the ratio of closed cells that are destroyed when the test piece is cut out depends on the shape of the expanded beads (that is, the presence or absence of through holes, the hole diameter of the through holes, etc.) and the closed cell ratio of the expanded beads. greatly affected by Furthermore, it is affected by the molding conditions of the expanded bead molded article (that is, the molding pressure, the internal pressure of the expanded bead, the filling method, etc.).
  • the open cell ratio Co in this specification is conceptually different from the porosity of the compact.
  • the porosity of the compact is measured and calculated, for example, as follows. Specifically, first, a rectangular parallelepiped test piece (20 mm long x 100 mm wide x 20 mm high) is cut out from the central portion of the compact.
  • the porosity of the molded body can be obtained by (IV).Therefore, even in the measurement of the porosity of the molded body, the closed cells that are destroyed when the test piece is cut out are not considered.
  • This method differs from the method for measuring the open cell ratio Co in that a liquid such as ethanol is used as a medium for the molding, and the porosity of the molded product is always larger than the open cell ratio Co of the molded product.
  • Porosity (%) [(Vd-Vc) / Vd] ⁇ 100 (IV)
  • a molded product having an open cell ratio of 2.5% or more and 12% or less is produced by in-mold molding foamed particles satisfying the following (1) to (3).
  • the expanded beads have through holes. If the foamed particles do not have through-holes, it is difficult to set the open cell ratio of the molded article to 2.5% or more.
  • the average pore diameter d of the through-holes of the foamed particles is less than 1 mm. By decreasing the average pore size, the open cell ratio tends to decrease, and by increasing the average pore size, the open cell ratio tends to increase. When the average hole diameter of the through holes is 1 mm or more, it tends to be difficult to make the value of the open cell ratio of the molded body 12% or less.
  • the ratio [d/D] of the average pore diameter d of the through-holes to the average outer diameter D of the expanded beads is 0.4 or less.
  • the open cell ratio tends to decrease, and by increasing the ratio [d/D], the open cell ratio tends to increase.
  • the ratio [d/D] exceeds 0.4, it tends to be difficult to make the value of the open cell ratio of the molded article 12% or less.
  • a molded body In addition to in-mold molding using expanded particles satisfying the above (1) to (3), for example, by controlling the following conditions (4) to (6) in in-mold molding, a molded body
  • the open cell ratio can be easily adjusted within the range of 2.5% or more and 12% or less.
  • the internal pressure of the particles is preferably 0.05 MPa (G) (G: gauge pressure) or less, more preferably 0.03 MPa (G) or less, and further preferably 0.01 MPa (G) or less. It is particularly preferable to mold at 0 MPa (G), that is, without applying an internal pressure to the expanded beads.
  • the lower limit of the internal pressure is 0 MPa (G) from the viewpoint of forming a good expanded bead molded article.
  • the cracking amount is generally preferably in the range of 5% to 35%, more preferably in the range of 10% to 30%, even more preferably in the range of 15% to 25%.
  • the cracking filling method is a molding method in which the mold is not completely closed in order to efficiently fill the amount of foamed particles that exceeds the volume of the mold when filling the mold with foamed particles. This is a method of providing an opening portion of the mold.
  • This open portion is called cracking, and the ratio (%) of the volume of the open portion to the volume inside the mold is expressed as the amount of cracking (%).
  • the cracking is finally closed when steam is introduced after the mold is filled with foamed particles, and as a result, the filled foamed particles are mechanically compressed.
  • (6) When the molding temperature (specifically, the molding pressure) is increased, the open cell ratio tends to decrease, and when the molding temperature (specifically, the molding pressure) is decreased, the open cell ratio tends to increase. There is however, from the viewpoint of production efficiency of the molded body, it is preferable to perform molding at a low molding pressure.
  • the molding pressure is preferably in the range of, for example, 0.20 MPa (G) (G: gauge pressure) to 0.30 MPa (G), and 0.20 MPa (G) to 0.26 MPa (G).
  • the range is more preferable, and the range of 0.22 MPa (G) to 0.24 MPa (G) is even more preferable.
  • the conditions for adjusting the open cell ratio of the molded article are not necessarily limited to (4) to (6). In other words, by molding the foamed particles so that the open cell ratio of the molded body is 2.5% or more and 12% or less, the molded body has a desired shape and is excellent in appearance and rigidity while being uncured. can be manufactured.
  • the foamed beads are preferably foamed beads with a multi-layer structure having a foam layer and a fusion layer covering the foam layer.
  • the fusion layer is made of, for example, a polyolefin resin.
  • Polyolefin-based resins include, for example, polyethylene-based resins, polypropylene-based resins, polybutene-based resins, and the like. From the viewpoint of adhesion to the foam layer, the polyolefin resin is preferably a polyethylene resin or a polypropylene resin, more preferably a polypropylene resin.
  • polypropylene-based resins examples include ethylene-propylene copolymers, ethylene-butene copolymers, ethylene-propylene-butene copolymers, and propylene homopolymers. Among them, ethylene-propylene copolymers or ethylene-propylene- Butene copolymers are preferred.
  • the melting point Tms of the polyolefin resin forming the fusion layer is preferably lower than the melting point Tmc of the polypropylene resin forming the foam layer. That is, it is preferable that Tms ⁇ Tmc. In this case, the meltability of the foamed particles is improved, and molding at a lower temperature becomes possible. Furthermore, in this case, it becomes easier to suppress significant shrinkage/deformation when the curing step is omitted. The reason for this is not clear, but by molding at a low molding heating temperature, the amount of heat received by the foamed particles from a heating medium such as steam during molding in the mold can be suppressed to a lower level, and the dimensional change due to thermal shrinkage of the molded product can be reduced.
  • Tmc ⁇ Tms ⁇ 5 is preferable, Tmc ⁇ Tms ⁇ 6 is more preferable, and Tmc ⁇ Tms ⁇ 8 is further preferable.
  • Tmc ⁇ Tms ⁇ 35 is preferable, Tmc ⁇ Tms ⁇ 20 is more preferable, and Tmc More preferably, -Tms ⁇ 15.
  • the melting point Tms of the polyolefin resin constituting the fusion layer is preferably 120° C. or more and 145° C. or less, and is 125° C. or more and 140° C. or less. is more preferable.
  • the melting point of the polyolefin resin that constitutes the fusion layer is obtained based on JIS K7121:1987. Specifically, it is determined by the same conditions and method as those for the polypropylene-based resin that constitutes the foamed layer.
  • the MFR of the polyolefin resin that constitutes the fusion layer is preferably about the same as the MFR of the polypropylene resin that constitutes the foam layer. Specifically, it is preferably 2 to 15 g/10 minutes, more preferably 3 to 12 g/10 minutes, even more preferably 4 to 10 g/10 minutes.
  • the polyolefin resin is a polypropylene resin
  • its MFR is a value measured under conditions of a test temperature of 230°C and a load of 2.16 kg based on JIS K7210-1:2014.
  • When is a polyethylene resin its MFR is a value measured under conditions of a test temperature of 190°C and a load of 2.16 kg based on JIS K7210-1:2014.
  • the foamed layer is made of a foamed polypropylene resin, and the fusion layer is in a foamed state.
  • the fusing layer is substantially non-foamed.
  • substantially non-foamed includes a state in which the fusion layer is not foamed and contains no cells, and a state in which the cells disappear after foaming, and means that there is almost no cell structure.
  • the thickness of the fusion layer is, for example, 0.5 to 100 ⁇ m.
  • an intermediate layer may be provided between the foam layer and the fusion layer.
  • the mass ratio (% by mass) of the resin forming the foam layer and the resin forming the fusion layer is preferably 99.5:0.5 from the viewpoint of improving moldability while maintaining the rigidity of the molded body. 5 to 80:20, more preferably 99:1 to 85:15, still more preferably 97:3 to 90:10.
  • the mass ratio is represented by the ratio of the resin forming the foam layer to the resin forming the fusion layer.
  • the foamed particles show an endothermic peak (that is, resin-specific peak) due to melting specific to polypropylene resin and 1 It is preferable to have a crystal structure in which the above melting peaks (that is, high temperature peaks) appear.
  • a DSC curve is obtained by differential scanning calorimetry (DSC) according to JIS K7121:1987 using 1 to 3 mg of foamed particles as a test sample.
  • the resin-specific peak is an endothermic peak due to the melting of the polypropylene-based resin that constitutes the expanded beads, and is considered to be due to the endothermic peak during the melting of the crystals inherent in the polypropylene-based resin.
  • the endothermic peak on the high-temperature side of the resin-specific peak is an endothermic peak that appears on the high-temperature side of the resin-specific peak in the DSC curve.
  • this high temperature peak appears, it is presumed that secondary crystals are present in the resin.
  • the temperature is cooled from 200 ° C. to 23 ° C. at a cooling rate of 10 ° C./min. In the DSC curve obtained when cooling and then heating again from 23 ° C. to 200 ° C.
  • the polypropylene resin constituting the expanded beads Since only the endothermic peak due to the melting specific to .sup.2 is seen, the resin specific peak and the high temperature peak can be distinguished.
  • the temperature at the top of this resin-specific peak may slightly differ between the first heating and the second heating, but the difference is usually within 5°C.
  • the amount of heat of fusion at the high-temperature peak of the expanded beads is preferably 5 to 40 J/g, more preferably 7 to 30 J/g, from the viewpoints of further improving the moldability of the expanded beads and obtaining a molded article having excellent rigidity. More preferably 10 to 20 J/g.
  • the ratio of the heat of fusion of the high-temperature peak to the heat of fusion of all the melting peaks of the DSC curve is preferably 0.05 to 0.3, more preferably 0.1 to 0.25, more preferably 0.15 to 0.2.
  • the amount of heat of fusion of all melting peaks means the total amount of heat of fusion determined from the areas of all the melting peaks of the DSC curve.
  • the amount of heat of fusion at each peak of the DSC curve of the expanded beads is a value obtained as follows. First, one expanded bead is sampled from the expanded bead group after condition adjustment.
  • a DSC curve is obtained when the test piece is heated from 23° C. to 200° C. at a heating rate of 10° C./min with a differential thermal scanning calorimeter.
  • An example of a DSC curve is shown in FIG.
  • the DSC curve has a resin-specific peak ⁇ H1 and a high-temperature peak ⁇ H2 having an apex on the high-temperature side of the apex of the resin-specific peak ⁇ H1.
  • a straight line L1 is obtained by connecting the point ⁇ on the DSC curve at a temperature of 80° C. and the point ⁇ at the melting end temperature T of the expanded beads.
  • a straight line L2 parallel to the vertical axis of the graph is drawn from a point ⁇ on the DSC curve corresponding to the valley between the resin-specific peak ⁇ H1 and the high-temperature peak ⁇ H2, and the intersection of the straight lines L1 and L2 is ⁇ and
  • the point ⁇ can also be said to be a maximum point existing between the resin-specific peak ⁇ H1 and the high-temperature peak ⁇ H2.
  • the area of the resin-specific peak ⁇ H1 is the area of the portion surrounded by the curve of the resin-specific peak ⁇ H1 portion of the DSC curve, the line segment ⁇ - ⁇ , and the line segment ⁇ - ⁇ .
  • the area of the high temperature peak ⁇ H2 is the area of the portion surrounded by the curve of the high temperature peak ⁇ H2 portion of the DSC curve, the line segment ⁇ - ⁇ , and the line segment ⁇ - ⁇ , which is the heat of fusion of the high temperature peak (that is, high temperature peak heat quantity).
  • the area of the total melting peak is the area of the portion surrounded by the curve of the resin-specific peak ⁇ H1 portion of the DSC curve, the curve of the high temperature peak ⁇ H2 portion, and the line segment ⁇ - ⁇ (that is, the straight line L1). It is defined as the heat of fusion at the melting peak.
  • the expanded particles have through holes as described above. It is preferable that the cylindrical expanded beads having through-holes have at least one cylindrical hole passing through the columnar expanded beads such as cylinders and prisms in the axial direction. It is more preferable that the expanded beads have a columnar shape and have a cylindrical hole passing through them in the axial direction.
  • the open cell ratio of the molded article tends to be as low as, for example, less than 2.5%. As a result, if the curing step is omitted, there is a possibility that significant shrinkage/deformation of the compact cannot be suppressed.
  • the molding pressure is lowered to positively form the voids between the particles. Rigidity may be significantly reduced.
  • the open cell ratio of the molded product tends to increase, for example, to more than 12%.
  • the appearance and rigidity of the molded product may deteriorate.
  • the average pore diameter d of the expanded beads is less than 1 mm as described above.
  • the average pore diameter d of the expanded particles should be 0.95 mm or less from the viewpoint that a molded article having a desired shape can be obtained even if the curing step is omitted, and a molded article having excellent appearance and rigidity can be obtained. is preferred, 0.92 mm or less is more preferred, and 0.90 mm or less is even more preferred.
  • the lower limit of the average pore diameter d of the expanded particles is preferably 0.2 mm or more, more preferably 0.4 mm or more.
  • the average pore diameter d of the expanded beads can be adjusted not only by adjusting the pore diameter dr of through holes in the resin particles described later, but also by adjusting the apparent density and high-temperature peak heat quantity of the expanded beads.
  • the average pore diameter d can be more easily adjusted to a small value.
  • the average pore diameter d of the through-holes of the expanded particles is obtained as follows. 50 or more foamed beads randomly selected from the group of foamed beads are cut perpendicularly to the penetration direction of the through-hole at the position where the area of the cut surface is maximized. Take a photograph of the cut surface of each expanded particle, determine the cross-sectional area (specifically, the opening area) of the through-hole portion, calculate the diameter of an imaginary perfect circle having the same area as that area, and calculate the arithmetic mean. The obtained value is defined as the average pore diameter d of the through-holes of the foamed particles. Even if the size of the through-hole of each expanded bead is not uniform in the through-hole direction, the through-hole diameter of each expanded bead should be the maximum area of the cut surface of the expanded bead as described above. determined by the pore size at
  • the average outer diameter D of the expanded beads is preferably 2 mm or more, more preferably 2 mm or more, from the viewpoint that the thickness of the cylindrical expanded beads increases to improve the secondary foamability of the expanded beads and the rigidity of the molded article. 5 mm or more, more preferably 3 mm or more. On the other hand, it is preferably 5 mm or less, more preferably 4.5 mm or less, and even more preferably 4.3 mm or less, from the viewpoint of improving filling properties into the mold during molding.
  • the ratio d/D of the average pore diameter d to the average outer diameter D of the expanded beads is 0.4 or less. If the ratio d/D is too large, the open cell ratio of the molded product tends to increase, for example, to over 12%. As a result, the appearance and rigidity of the molded product may deteriorate.
  • d/D is preferably 0.35 or less, and preferably 0.3, from the viewpoint of improving the appearance of the molded body, further improving the rigidity, and further improving the secondary foamability. It is more preferably 0.25 or less, more preferably 0.25 or less.
  • the ratio d/D is preferably 0.1 or more from the viewpoint that the value of the open cell ratio of the molded article can be adjusted more easily.
  • the average outer diameter D of the expanded beads is obtained as follows. 50 or more foamed beads randomly selected from the group of foamed beads are cut perpendicularly to the penetration direction of the through-hole at the position where the area of the cut surface is maximized. Take a picture of the cut surface of each foamed bead, find the cross-sectional area of the foamed bead (specifically, the cross-sectional area including the opening of the through hole), and calculate the diameter of an imaginary perfect circle having the same area as that area. and the average outer diameter D of the expanded beads is obtained by arithmetically averaging these values.
  • the outer diameter of each expanded bead should be such that the area of the cut surface of the expanded bead in the direction perpendicular to the penetration direction is the maximum as described above. is determined by the outer diameter at the position where
  • the average thickness t of the cylindrical foamed particles is preferably 1.2 mm or more and 2 mm or less. If the average value of the thickness t is within this range, the thickness of the expanded beads is sufficiently thick, so that the secondary foamability during in-mold molding is further improved. In addition, the foamed particles are less likely to be crushed by an external force, and the rigidity of the molded article is further improved. From this point of view, the average thickness t of the expanded beads is more preferably 1.3 mm or more, and still more preferably 1.5 mm or more.
  • the ratio t/D of the average wall thickness t to the average outer diameter D of the expanded beads is preferably 0.35 or more and 0.5 or less.
  • t/D is within the above range, the filling property of the expanded beads is good and the secondary foamability is further improved in the in-mold molding of the expanded beads. Therefore, a molded article having excellent appearance and rigidity can be produced at a lower molding heating temperature.
  • the apparent density of the expanded particles is preferably 10 kg/m 3 or more and 150 kg/m 3 or less, more preferably 15 kg/m 3 or more and 100 kg/m 3 or less. , more preferably 20 kg/m 3 or more and 80 kg/m 3 or less, and particularly preferably 25 kg/m 3 or more and 45 kg/m 3 or less.
  • the curing step can be omitted, and a compact with a good appearance can be produced without curing.
  • the apparent density of the expanded particles is determined by leaving the expanded particles in a graduated cylinder filled with alcohol (e.g., ethanol) at 23°C under the conditions of 50% relative humidity, 23°C, and 1 atm for one day (the weight of the expanded particles W (g)) is submerged using a wire mesh or the like, the volume V (L) of the expanded bead group is obtained from the rise in the water level, and the weight of the expanded bead group is divided by the volume of the expanded bead group (W/V), It can be obtained by converting the unit to [kg/m 3 ].
  • alcohol e.g., ethanol
  • the ratio of the apparent density of the expanded beads to the bulk density of the expanded beads is preferably 1.7. or more, more preferably 1.75 or more.
  • the apparent density/bulk density is preferably 2.3 or less, more preferably 2.1 or less, and still more preferably 1.9. It is below.
  • the bulk density of expanded particles is determined as follows. Expanded particles are randomly taken out from the group of expanded particles and placed in a graduated cylinder with a volume of 1 L. A large number of expanded particles are accommodated up to the scale of 1 L so as to be in a state of natural accumulation, and the mass of the accommodated expanded particles is W2 [g]. is divided by the storage volume V2 (1 L) (W2/V2), and the unit is converted to [kg/m 3 ] to obtain the bulk density of the expanded particles.
  • the foamed beads are produced, for example, by dispersing polypropylene-based resin particles having a polypropylene-based resin as a base resin in a dispersion medium (e.g., liquid), impregnating the resin particles with a foaming agent, and adding the resin particles containing the foaming agent together with the dispersion medium. It can be produced by a method of releasing under low pressure (that is, a dispersion medium releasing foaming method). Specifically, it is preferable to disperse the resin particles in a dispersion medium in an airtight container, and after heating, inject the foaming agent into the resin particles to impregnate the resin particles with the foaming agent.
  • a dispersion medium e.g., liquid
  • the fusion layer by foaming resin particles having a multi-layer structure having a core layer and a fusion layer covering the core layer, the foam layer and the fusion layer covering the foam layer are formed. It is possible to obtain foamed particles having a multilayer structure.
  • resin particles are manufactured as follows. First, a polypropylene-based resin serving as a base resin and additives such as a cell nucleating agent supplied as necessary are fed into an extruder, heated and kneaded to obtain a resin melt-kneaded product. Thereafter, the resin particles are obtained by extruding the resin melt-kneaded material into a cylindrical strand having through holes through a small hole of a die attached to the tip of the extruder, cooling it, and cutting it. The extrudate is cut, for example with a pelletizer. A cutting method can be selected from a strand cutting method, a hot cutting method, an underwater cutting method, and the like. In this manner, cylindrical resin particles having through holes can be obtained.
  • a core layer forming extruder and a fusion layer forming extruder are used to obtain a resin melt-kneaded material of each raw material, and each melt-kneaded material is extruded and placed in a die. They are combined to form a shell-and-core composite composed of a non-foamed cylindrical core layer and a non-foamed fusion layer covering the outer surface of the cylindrical core layer. Multilayered resin particles can be obtained by cooling and cutting the composite while extruding it in the form of a strand through the pores of a spinneret attached to the nozzle.
  • the particle diameter of the resin particles is preferably 0.1-3.0 mm, more preferably 0.3-1.5 mm.
  • the length/outer diameter ratio of the resin particles is preferably 0.5 to 5.0, more preferably 1.0 to 3.0.
  • the average mass per particle (determined from the mass of 200 randomly selected particles) is preferably prepared to be 0.1 to 20 mg, more preferably 0.2 to 10 mg, More preferably 0.3 to 5 mg, particularly preferably 0.4 to 2 mg.
  • the mass ratio of the core layer and the fusion layer in the case of multilayer resin particles is preferably 99.5:0.5 to 80:20, more preferably 99:1 to 85:15, and still more preferably 97:3. ⁇ 90:10.
  • the mass ratio is represented by core layer:bonding layer.
  • the average hole diameter d of the through-holes in the expanded beads can be adjusted within the desired range.
  • the hole diameter dr of the through holes in the core layer of the resin particles can be adjusted, for example, by adjusting the hole diameter of the small holes of the die for forming the through holes (that is, the inner diameter of the die).
  • the average outer diameter and average wall thickness of the expanded particles can be adjusted within the above desired ranges.
  • the through-holes of the resin particles are improved.
  • the average pore diameter dr is preferably less than 0.25 mm, more preferably less than 0.24 mm, even more preferably 0.22 mm or less.
  • the average hole diameter dr of the through holes of the resin particles is preferably 0.1 mm or more.
  • the ratio dr/Dr of the average pore diameter dr to the average outer diameter Dr of the resin particles is preferably 0.4 or less, more preferably 0.3 or less, and 0.25 or less. It is more preferably 0.2 or less, particularly preferably 0.2 or less. From the viewpoint of production stability of resin particles having through holes, the ratio dr/Dr of the average pore diameter dr to the average outer diameter Dr of the resin particles is preferably 0.1 or more.
  • the average pore diameter dr of the through-holes of the resin particles is obtained as follows. 50 or more resin particles randomly selected from the resin particle group are cut perpendicularly to the penetrating direction of the through hole at the position where the area of the cut surface is maximized. A photograph of the cut surface of each resin particle is taken, the cross-sectional area (specifically, the opening area) of the through-hole portion is obtained, the diameter of a virtual perfect circle having the same area as that area is calculated, and the arithmetic mean is calculated. The obtained value is taken as the average pore diameter dr of the through holes of the resin particles. Even if the size of the through-hole of each resin particle is not uniform in the through-hole diameter in the through-hole direction, the through-hole diameter of each resin particle will be the maximum area of the cross section of the resin particle as described above. determined by the pore size at
  • the average outer diameter Dr of the resin particles is obtained as follows. 50 or more resin particles randomly selected from the resin particle group are cut perpendicularly to the penetrating direction of the through hole at the position where the area of the cut surface is maximized. Take a picture of the cut surface of each resin particle, find the cross-sectional area of the resin particle (specifically, the cross-sectional area including the opening of the through hole), and calculate the diameter of a virtual perfect circle having the same area as that area. The arithmetic mean value of these is taken as the average outer diameter Dr of the resin particles.
  • the outer diameter of each resin particle is such that the area of the cross section of the resin particle in the direction perpendicular to the penetration direction is the maximum as described above. is determined by the outer diameter at the position where
  • the particle diameter, length/outer diameter ratio and average mass of the resin particles are adjusted by appropriately changing the extrusion speed, take-up speed, cutter speed, etc. when extruding the resin melt-kneaded product. It can be done by
  • An aqueous dispersion medium is used as a dispersion medium (specifically, a liquid) for dispersing the resin particles obtained as described above in a closed container.
  • the aqueous dispersion medium is a dispersion medium (specifically liquid) containing water as a main component.
  • the proportion of water in the aqueous dispersion medium is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.
  • Examples of the dispersion medium other than water in the aqueous dispersion medium include ethylene glycol, glycerin, methanol, and ethanol.
  • the core layer of the resin particles may contain a foam modifier, a crystal nucleating agent, a coloring agent, a flame retardant, a flame retardant aid, a plasticizer, an antistatic agent, an antioxidant, an ultraviolet inhibitor, and a light stabilizer.
  • conductive fillers, antibacterial agents and the like can be added.
  • Inorganic powders such as talc, mica, zinc borate, calcium carbonate, silica, titanium oxide, gypsum, zeolite, borax, aluminum hydroxide, and carbon; phosphoric acid nucleating agents, phenolic nucleating agents. , an amine-based nucleating agent, and an organic powder such as a polyfluoroethylene-based resin powder.
  • the content of the cell control agent is preferably 0.01 to 1 part by mass with respect to 100 parts by mass of the polypropylene resin.
  • dispersant any agent that prevents fusion of the resin particles in the container can be used, and it can be used regardless of whether it is organic or inorganic. However, fine inorganic particles are preferable because of ease of handling.
  • dispersants include clay minerals such as amsnite, kaolin, mica and clay. Clay minerals may be natural or synthetic. Dispersants include aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, iron oxide and the like. One or two or more dispersants are used. Among these, it is preferable to use a clay mineral as a dispersant. It is preferable to add about 0.001 to 5 parts by mass of the dispersant per 100 parts by mass of the resin particles.
  • an anionic surfactant such as sodium dodecylbenzenesulfonate, sodium alkylbenzenesulfonate, sodium laurylsulfate, and sodium oleate together as a dispersing aid.
  • the amount of the dispersing aid added is preferably 0.001 to 1 part by mass per 100 parts by mass of the resin particles.
  • a physical foaming agent is preferably used as the foaming agent for foaming the resin particles.
  • Physical blowing agents include inorganic physical blowing agents and organic physical blowing agents. Examples of inorganic physical blowing agents include carbon dioxide, air, nitrogen, helium, argon, and the like. Examples of organic physical blowing agents include aliphatic hydrocarbons such as propane, butane and hexane; cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; Halogenated hydrocarbons such as chloro-1,1-dichloroethane, 1,2,2,2-tetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride, and the like are included.
  • the physical foaming agents may be used alone or in combination of two or more.
  • an inorganic physical foaming agent and an organic physical foaming agent can be mixed and used.
  • inorganic physical blowing agents are preferably used, and carbon dioxide is more preferably used.
  • carbon dioxide is more preferably used.
  • n-butane, i-butane, n-pentane, and i-pentane are preferably used from the viewpoint of solubility in polypropylene resin and foamability.
  • the amount of foaming agent added to 100 parts by mass of resin particles is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 15 parts by mass.
  • a method for impregnating the resin particles with the blowing agent includes dispersing the resin particles in an aqueous dispersion medium in a closed vessel, and pressurizing the blowing agent into the resin particles while heating.
  • a method of impregnation is preferably used.
  • the internal pressure of the closed container during foaming is preferably 0.5 MPa (G: gauge pressure) or more.
  • the internal pressure of the closed container is preferably 4.0 MPa (G) or less.
  • the temperature during expansion can be kept within an appropriate range.
  • Foaming is preferably carried out in a sealed container at (melting point of polypropylene resin ⁇ 10° C.) or higher, more preferably at (melting point of polypropylene resin) or higher (melting point of polypropylene resin +20° C.) or lower. .
  • the expanded beads are put into a pressurizable sealed container, and pressurized by pressurizing a pressurized gas such as air into the container.
  • a pressurized gas such as air
  • the molded product can be obtained by in-mold molding of the foamed particles as described above (that is, in-mold molding method).
  • the in-mold molding method is carried out by filling a mold with expanded particles and heating and molding using a heating medium such as steam. Specifically, after the foamed particles are filled in the mold, a heating medium such as steam is introduced into the mold to heat the foamed particles for secondary foaming, and the foamed particles are mutually fused and molded.
  • a molded body in which the shape of the space is shaped can be obtained.
  • the molded body is formed by molding foamed particles in a mold, and is composed of a large number of foamed particles that are fused together.
  • the molded body has an open cell structure.
  • the open cell structure is a minute space portion communicating with the outside of the molded article.
  • the open-cell structure includes voids formed by interconnecting through-holes of a plurality of expanded particles, voids formed by through-holes of expanded particles communicating with voids formed between expanded particles, and voids formed between expanded particles.
  • Voids formed by interconnecting voids, open-cell portions of foamed particles constituting the molded article, and the like are formed by connecting intricately.
  • the open cell rate of the molded body is 2.5% or more and 12% or less.
  • the open cell ratio of the molded article may shrink or deform significantly if the curing step is omitted.
  • the open cell ratio of the molded article exceeds 12%, the appearance and rigidity of the molded article may deteriorate.
  • the open cell ratio of the molded body is preferably 3% or more, more preferably 4% or more, and 4.5% or more. is more preferable.
  • the open cell ratio of the molded article is preferably 10% or less, more preferably 8% or less, and 7.5% or less. 6% or less is more preferable.
  • the porosity of the molded body is preferably 4% or more, more preferably 4.5% or more, and more preferably 5%. It is more preferable that it is above.
  • the porosity of the molded body is preferably 12% or less, more preferably 10% or less, and even more preferably 8% or less. The porosity of the molded body can be measured by the measuring method described above.
  • the closed cell ratio of the molded body is 90% or more. If it is less than 90%, the appearance and rigidity of the molded product may be impaired. From the viewpoint of further improving the appearance and rigidity of the molded article, the closed cell ratio of the molded article is preferably 91% or more, more preferably 92% or more.
  • the closed cell content of the molded body is measured according to ASTM 2865-70 Procedure C. Specifically, the closed cell content of the molded article is measured as follows. First, a measurement sample measuring 2.5 cm long, 2.5 cm wide, and 2.5 cm high is cut out from the center of the compact, and the geometric volume Va is obtained. Specifically, Va is a value determined by vertical dimension [cm] ⁇ horizontal dimension [cm] ⁇ height dimension [cm]. Next, according to procedure C described in ASTM-D2856-70, the true volume value Vx of the measurement sample is measured using an air comparison type hydrometer (specifically, Accupic II 1340 manufactured by Shimadzu Corporation). Measure. The closed cell ratio is calculated by the following formula (VII).
  • Vx The true volume of the measurement sample measured by the above method, that is, the sum of the volume of the resin constituting the measurement sample and the total volume of the closed cells in the measurement sample (unit: cm 3 ).
  • Va Geometric volume of measurement sample (unit: cm 3 )
  • W Weight of measurement sample (unit: g)
  • the density of the compact is preferably 10 kg/m 3 or more and 100 kg/m 3 or less. In this case, it is possible to improve the lightness and rigidity of the molded body in a well-balanced manner. From the viewpoint of further improving the rigidity of the molded article, the density of the molded article is more preferably 20 kg/m 3 or more, further preferably 25 kg/m 3 or more. From the viewpoint of further improving the lightness of the molded article, the density of the molded article is more preferably 80 kg/m 3 or less, and even more preferably 50 kg/m 3 or less.
  • the density of the molded body is calculated by dividing the weight (g) of the molded body by the volume (L) obtained from the outer dimensions of the molded body and converting the result into units.
  • the volume of the molded body can be determined by the submersion method.
  • the volume of the molded body can be determined by the submersion method.
  • it has been particularly difficult to omit the curing step because the molded article tends to be remarkably deformed after being released from the mold.
  • the expanded bead molded article of the present disclosure even if the apparent density is low, the curing process can be omitted, and even without curing, the desired shape, appearance and rigidity can be obtained. become a body. Also from the viewpoint of effectively exhibiting this effect, it is preferable to set the density of the molded body within the above range.
  • the maximum bending strength of the compact is preferably 250 kPa or more, more preferably 300 kPa or more, and even more preferably 320 kPa or more.
  • the maximum bending strength conforms to JIS K7221-2:2006, and the maximum bending strength of the molded body can be measured as the maximum bending strength.
  • the ratio [S/DE] of the maximum bending strength S of the molded body to the density DE of the molded body is preferably 9 kPa ⁇ m 3 /kg or more and 15 kPa ⁇ m 3 /kg or less. In this case, it is possible to obtain an effect that the expanded bead molded article has excellent rigidity. From the viewpoint of further improving the rigidity of the molded body, the ratio [S/DE] of the maximum bending strength S of the molded body to the density DE of the molded body is more preferably 9.5 kPa ⁇ m 3 /kg or more. , 10 kPa ⁇ m 3 /kg or more.
  • the density DE of the compact used in the above calculation means the density of the test piece used for measuring the maximum bending strength.
  • Molded bodies are also used as sound absorbing materials, shock absorbing materials, cushioning materials, etc. in various fields such as the field of vehicles such as automobiles and the field of construction.
  • the following physical properties were measured and evaluated for the resins, expanded particles, and molded bodies used in Examples and Comparative Examples.
  • the measurement and evaluation of the physical properties of the expanded beads were carried out after the expanded beads were allowed to stand for 24 hours under the conditions of 50% relative humidity, 23° C., and 1 atm.
  • the physical properties of the molded body were measured and evaluated using a molded body that was not subjected to the curing process. Specifically, in the production of the molded body described later, the physical properties are measured and measured using the molded body that has been conditioned by allowing the molded body after release to stand for 12 hours under the conditions of 50% relative humidity, 23 ° C., and 1 atm. made an evaluation.
  • Table 1 shows the properties and the like of the polypropylene-based resin used for producing the expanded beads.
  • Both the ethylene-propylene copolymer and the ethylene-propylene-butene copolymer used in this example are random copolymers.
  • the density of the polypropylene-based resin is 900 kg/m 3 .
  • the monomer component content of the polypropylene-based resin (specifically, ethylene-propylene copolymer, ethylene-propylene-butene copolymer) was obtained by a known method of determining by IR spectrum. Specifically, Polymer Analysis Handbook (Edited by Japan Society for Analytical Chemistry Polymer Analysis Research Round-table Conference, publication date: January 1995, publisher: Kinokuniya Bookstore, page numbers and item names: 615-616 "II. 2.3 2.3.4 Propylene/Ethylene Copolymers”, 618-619 “II.2.3 2.3.5 Propylene/Butene Copolymers”), i.e.
  • ethylene and butene It was obtained by a method of quantifying from the relationship between the absorbance corrected by a predetermined coefficient and the thickness of the film-like test piece. More specifically, first, a polypropylene resin was hot-pressed in an environment of 180° C. to form a film, and a plurality of test pieces having different thicknesses were produced. Next, by measuring the IR spectrum of each test piece, the absorbance at 722 cm -1 and 733 cm -1 derived from ethylene (A 722 , A 733 ) and the absorbance at 766 cm -1 derived from butene (A 766 ) were read. rice field. Next, for each test piece, the ethylene component content in the polypropylene resin was calculated using the following formulas (1) to (3).
  • the above formulas (1) to (3) can be applied to random copolymers.
  • the content of the butene component in the polypropylene resin was calculated using the following formula (4).
  • the value obtained by arithmetically averaging the butene component contents obtained for each test piece was defined as the butene component content (%) in the polypropylene resin.
  • Butene component content (%) 12.3 ( A766 /L) (4)
  • A means the absorbance
  • L means the thickness (mm) of the film-like test piece.
  • the melting point of the polypropylene resin was obtained based on JIS K7121:1987. Specifically, "(2) When measuring the melting temperature after performing a constant heat treatment" is adopted as the condition adjustment, and the condition-adjusted test piece is heated from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min. A DSC curve was obtained by heating up to °C, and the apex temperature of the melting peak was defined as the melting point. A heat flux differential scanning calorimeter (manufactured by SII Nanotechnology Co., Ltd., model number: DSC7020) was used as the measurement device.
  • melt flow rate of polypropylene resin The melt flow rate (that is, MFR) of the polypropylene resin was measured according to JIS K7210-1:2014 under the conditions of a temperature of 230° C. and a load of 2.16 kg.
  • Table 2 shows the properties of the multilayered resin particles and foamed particles.
  • the average pore size of the through-holes of the expanded beads was determined as follows. 100 expanded beads randomly selected from the group of expanded beads after conditioning were cut perpendicularly to the penetration direction of the through-hole at the position where the area of the cut surface was approximately maximum. A photograph of the cut surface of each expanded bead was taken, and the cross-sectional area (opening area) of the through-hole portion in the cross-sectional photograph was determined. The diameter of an imaginary perfect circle having the same area as the cross-sectional area was calculated, and the value obtained by arithmetically averaging these values was taken as the average pore diameter (d) of the through-holes of the expanded beads.
  • the average outer diameter of the expanded beads was determined as follows. 100 expanded beads randomly selected from the group of expanded beads after conditioning were cut perpendicularly to the penetration direction of the through-hole at the position where the area of the cut surface was approximately maximum. A photograph of the cut surface of each expanded bead was taken, and the cross-sectional area of the expanded bead (including the opening of the through hole) was determined. The diameter of an imaginary perfect circle having the same area as the cross-sectional area was calculated, and the value obtained by arithmetically averaging these values was taken as the average outer diameter (D) of the expanded beads.
  • Average wall thickness t (average outer diameter D-average pore diameter d)/2 (5)
  • the bulk density of the expanded beads was determined as follows. Expanded particles are randomly taken out from the group of expanded particles after conditioning, placed in a graduated cylinder with a capacity of 1 L, and a large number of expanded particles are accommodated up to the 1 L scale so as to be in a state of natural accumulation.
  • the bulk density of the expanded beads was obtained by dividing W2 [g] by the storage volume V2 (1 [L]) (W2/V2) and converting the unit into [kg/m 3 ].
  • the bulk ratio [times] of the expanded beads was obtained by dividing the density [kg/m 3 ] of the resin forming the foamed layer of the expanded beads by the bulk density [kg/m 3 ] of the expanded beads.
  • the apparent density of the expanded beads was determined as follows. First, a graduated cylinder containing ethanol at a temperature of 23°C was prepared, and an arbitrary amount of expanded particles (mass of expanded particles W1 [g]) after conditioning was placed in the ethanol in the graduated cylinder using a wire mesh. and sank. Then, considering the volume of the wire mesh, the volume V1 [L] of the foamed particles read from the water level rise was measured. The apparent density of the expanded particles was obtained by dividing the mass W1 [g] of the group of expanded particles placed in the graduated cylinder by the volume V1 [L] (W1/V1) and converting the unit to [kg/m 3 ]. asked.
  • the closed cell content of the foamed beads was measured according to ASTM-D2856-70 procedure C using an air-comparative hydrometer. Specifically, it was obtained as follows. The foamed particles having a bulk volume of about 20 cm 3 after conditioning were used as a measurement sample, and the apparent volume Va was accurately measured by the ethanol soaking method as described below. After sufficiently drying the measurement sample whose apparent volume Va was measured, according to the procedure C described in ASTM-D2856-70, the true volume of the measurement sample measured by Accupic II 1340 manufactured by Shimadzu Corporation was measured.
  • Tables 3 and 4 show the properties of the molded bodies.
  • Pretreatment pressurization step When the pretreatment pressurization step was performed before molding of the expanded beads, the pretreatment pressurization was performed as follows. Specifically, the expanded beads were placed in an airtight container, and the expanded beads were pressurized with compressed air to apply the internal pressures shown in Tables 3 and 4 in advance to the expanded beads before molding. The internal pressure of the expanded beads is a value measured as follows.
  • Q (g) be the weight of the expanded bead group under increased internal pressure immediately before filling the mold
  • U (g) be the weight of the expanded bead group after 48 hours
  • the weight Q (g ) and U (g) was defined as the increased air amount W (g)
  • M is the molecular weight of air
  • R is the gas constant
  • T is the absolute temperature
  • V is the volume (L) obtained by subtracting the volume of the base resin occupying the expanded bead group from the apparent volume of the expanded bead group.
  • Open cell rate Open cell content (ie, corrected open cell content) was measured according to ASTM 2856-70 Procedure B.
  • a dry automatic density meter specifically, Accupic II1340 manufactured by Shimadzu Corporation
  • Va was a value determined by vertical dimension [cm] ⁇ horizontal dimension [cm] ⁇ height dimension [cm].
  • a true volume value V1 [unit: cm 3 ] of the first test piece was measured using a dry automatic densitometer.
  • the first test piece was divided into 8 equal parts to obtain a cubic second test piece measuring 1.25 cm long ⁇ 1.25 cm wide ⁇ 1.25 cm high.
  • the true volume value V2 [unit: cm 3 ] of the second test piece was measured using a dry automatic densitometer.
  • the true volume V2 of the second test piece is the sum of the true volumes of the eight pieces cut out from the first test piece.
  • the closed cell content of the molded body was measured according to ASTM 2865-70 Procedure C. Specifically, it was measured as follows. First, a measurement sample of 2.5 cm long ⁇ 2.5 cm wide ⁇ 2.5 cm high was cut out from the central part of the compact, and the geometric volume Va was obtained. Specifically, Va is a value determined by vertical dimension [cm] ⁇ horizontal dimension [cm] ⁇ height dimension [cm]. Next, according to procedure C described in ASTM-D2856-70, the true volume value Vx of the measurement sample is measured using an air comparison type hydrometer (specifically, Accupic II 1340 manufactured by Shimadzu Corporation). It was measured. The closed cell ratio was calculated by the following formula (7).
  • Closed cell ratio (%) (Vx-W/ ⁇ ) x 100/(Va-W/ ⁇ ) (7)
  • Vx The true volume of the measurement sample measured by the above method, that is, the sum of the volume of the resin constituting the measurement sample and the total volume of the closed cells in the measurement sample (unit: cm 3 ).
  • Va Geometric volume of measurement sample (unit: cm 3 )
  • W Weight of measurement sample (unit: g)
  • the molded body density (kg/m 3 ) was calculated by dividing the weight (g) of the molded body by the volume (L) determined from the outer dimensions of the molded body and converting the unit.
  • the molded body is bent and broken, and the number C1 of expanded particles present on the fracture surface and the number C2 of broken expanded particles are determined, and the ratio of the number of broken expanded particles to the number of expanded particles present on the broken surface ( That is, the material destruction rate) was calculated.
  • the material destruction rate is calculated from the formula C2/C1 ⁇ 100. The above measurement was performed 5 times using different test pieces, and the material destruction rate was determined for each. When the arithmetic mean value of the material destruction rate was 90% or more, it was judged as acceptable.
  • maximum bending strength It was measured in accordance with JIS K7221-2:2006, and the maximum bending strength was determined as the maximum bending strength of the molded article. Specifically, a test piece having a length of 120 mm, a width of 25 mm, and a thickness of 20 mm was cut out from the molded product after removing the surface skin layer. Using this test piece, the descent speed of the pressure wedge was 10 mm / min, the distance between the fulcrums was 100 mm, the radius of the tip of the support base was 5 mm, and the radius of the tip of the pressure wedge was 5 mm. Based on this, the bending strength was measured. The density of the test piece used for measuring the maximum bending strength was obtained by the same method as the measurement of the density of the molded body, and is shown in Tables 3 and 4 as "cut-out molded body density (bending)".
  • Example 1 ⁇ Production of expanded polypropylene beads (expanded beads A)> Polypropylene resin 1 (abbreviated as PP1) was melt-kneaded in a core layer-forming extruder at a maximum set temperature of 245° C. to obtain a resin melt-kneaded product.
  • PP1 is an ethylene-propylene random copolymer and has an ethylene component content of 3.1% by mass. Table 1 shows the properties of PP1.
  • a polypropylene resin 4 (abbreviated as PP4) was melt-kneaded in a fusion layer-forming extruder at a maximum set temperature of 245° C. to obtain a resin melt-kneaded product.
  • PP4 polypropylene resin 4
  • each resin melt-kneaded product was extruded from the core layer forming extruder and the fusion layer forming extruder from the tip of a coextrusion die provided with small holes for forming through holes.
  • the melted and kneaded resins are combined in the die to form a sheath consisting of a non-foamed cylindrical core layer and a non-foamed fusion layer covering the outer surface of the cylindrical core layer.
  • a core-shaped composite was formed.
  • the composite is extruded into a cylindrical strand having a through hole through the pores of the mouthpiece attached to the tip of the extruder. It was cut so that the mass was approximately 1.5 mg.
  • a multilayer resin particle comprising a cylindrical core layer having through holes and a fusion layer covering the core layer was obtained.
  • zinc borate as a cell regulator was supplied to the extruder for forming the core layer, and 500 ppm by mass of zinc borate was contained in the polypropylene resin.
  • the foamed particles were placed in a pressure vessel, and air was injected into the pressure vessel to increase the pressure inside the vessel, impregnating the air into the cells to increase the internal pressure of the foamed particles.
  • steam was supplied to the expanded beads (single-stage expanded beads) taken out of the pressure vessel so that the pressure in the pressure vessel (that is, the drum pressure) became the pressure shown in Table 2, and the particles were heated under atmospheric pressure.
  • the values shown in Table 2 were the pressures inside the cells (that is, the internal pressure) in the single-stage expanded beads taken out of the pressure-resistant container.
  • the apparent density of the single-stage expanded beads was lowered to obtain expanded beads (two-stage expanded beads).
  • expanded beads having a bulk ratio of 37.5 were obtained. These are called expanded particles A.
  • the predetermined molding pressure was set as the lowest pressure among the molding pressures at which acceptable products can be obtained in the evaluation of fusion bondability described above.
  • Example 2 Expanded beads having a bulk ratio of 38.3 (that is, expanded beads B ).
  • a molded article was obtained in the same manner as in Example 1, except that expanded particles B were used.
  • the open cell rate of the molded article thus produced was 5.3%.
  • Example 3 Expanded beads having a bulk ratio of 36.0 times (that is, expanded beads C ). Further, a molded article was obtained in the same manner as in Example 1 except that the expanded particles C were used. The open cell rate of the molded article thus produced was 5.3%.
  • Example 4 As the polypropylene-based resin forming the foamed layer, a mixed resin PP3 in which PP1 and PP2 were mixed at a mixing ratio of 80% by weight: 20% by weight was used, and the foaming temperature was changed to the value shown in Table 2. Expanded beads having a bulk ratio of 37.7 times (that is, expanded beads D) were obtained in the same manner as in . Further, a molded article was obtained in the same manner as in Example 1 except that the expanded particles D were used. The open cell ratio of the molded article thus produced was 4.1%.
  • Example 5 Expanded beads having a bulk ratio of 18.0 (that is, expanded beads G) were obtained in the same manner as for the production of expanded beads A, except that the expansion temperature was changed to the value shown in Table 2 and the two-stage expansion was not performed. . A molded article was obtained in the same manner as in Example 1, except that the expanded particles G were used. The open cell rate of the molded article thus produced was 5.1%.
  • Example 6 In the molding process, pretreatment pressure was applied so that the internal pressure of the expanded particles before filling into the mold became the value shown in Table 4, and the amount of cracking was changed to the value shown in Table 4. A compact was obtained in the same manner as in Example 1. The open cell ratio of the molded article thus produced was 3.5%.
  • the foamed particles having no through-holes as in this example are poor in passage of steam at the time of molding, and therefore the appearance and rigidity of the molded product are remarkably inferior unless the pretreatment pressurization is carried out. Therefore, in this example, pretreatment pressurization was performed as described above.
  • Comparative Example 3 A molded article was obtained in the same manner as in Comparative Example 2, except that in the molding step, the pretreatment pressure was applied so that the internal pressure of the expanded particles before filling into the mold became the value shown in Table 4. .
  • the open cell rate of the molded article thus produced was 17.4%.
  • Comparative Example 1 since the molded article was produced using expanded particles having no through holes, the open cell ratio of the molded article was too low. As a result, in the non-cured molding, significant shrinkage/deformation of the molded body occurred (that is, the recoverability was unsatisfactory), and a good molded body could not be obtained.
  • Comparative Example 2 the molded article was produced using foamed particles having through holes with an excessively large average pore diameter, so that the open cell ratio of the molded article was too high. As a result, the appearance of the molded body was poor, and the rigidity was also lowered. Comparative Example 3 is an example of molding so that the open cell ratio is smaller than that of Comparative Example 2. In Comparative Example 3, although the open cell ratio was able to be reduced, the reduction was insufficient, and as a result, a molded article with good appearance and rigidity could not be obtained.
  • Comparative Example 4 is an example in which the same foamed particles as in Example 1 were used and a molded article was produced under different molding conditions. In Comparative Example 4, since the open cell ratio of the molded article was too low, the uncured molded article caused significant shrinkage/deformation (that is, the recoverability failed), and a good molded article could not be obtained. rice field. Similarly to Comparative Example 4, Comparative Example 5 is also an example in which the expanded beads similar to those in Example 1 were used and a molded article was produced under different molding conditions. In Comparative Example 5, although the open cell rate of the molded body was higher than that of Comparative Example 4, the open cell rate was still too low. pass), and a good compact could not be obtained.
  • Comparative Example 6 is also an example in which the expanded beads similar to those in Example 1 were used and a molded article was produced under different molding conditions.
  • the open cell ratio of the molded article is even lower than in Comparative Example 4.
  • Comparative Example 6 since the open cell ratio of the molded article was too low, significant shrinkage/deformation of the molded article occurred in the uncured molded article (that is, the recoverability failed), and a good molded article could not be obtained. rice field.
  • Comparative Example 7 although the average pore diameter of the through-holes of the expanded particles was smaller than that of Comparative Example 2, the molded article was produced using the expanded particles whose average pore diameter of the through-holes was still too large. I became too much. As a result, the appearance of the molded body was poor, and the rigidity was also lowered.

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