US20170218158A1 - Polypropylene resin foamed particles, in-mold foam molded body of polypropylene resin, and method for manufacturing same - Google Patents

Polypropylene resin foamed particles, in-mold foam molded body of polypropylene resin, and method for manufacturing same Download PDF

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US20170218158A1
US20170218158A1 US15/487,122 US201715487122A US2017218158A1 US 20170218158 A1 US20170218158 A1 US 20170218158A1 US 201715487122 A US201715487122 A US 201715487122A US 2017218158 A1 US2017218158 A1 US 2017218158A1
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polypropylene resin
expanded
pressure
weight
mold
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Toru Yoshida
Shintaro Miura
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Kaneka Corp
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Kaneka Corp
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Publication of US20170218158A1 publication Critical patent/US20170218158A1/en
Priority to US15/910,652 priority Critical patent/US10221292B2/en
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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
    • C08J9/16—Making expandable particles
    • C08J9/18—Making expandable particles by impregnating polymer particles with the blowing agent
    • 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
    • C08J9/0061—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof characterized by the use of several polymeric components
    • 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
    • C08J9/224—Surface treatment
    • 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
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
    • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
    • C08L23/10—Homopolymers or copolymers of propene
    • C08L23/14—Copolymers of propene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
    • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
    • C08L23/16—Elastomeric ethene-propene or ethene-propene-diene copolymers, e.g. EPR and EPDM rubbers
    • 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
    • B29C44/02—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete 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
    • B29C44/3461—Making or treating 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
    • 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
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
    • B29K2023/10—Polymers of propylene
    • B29K2023/12—PP, i.e. polypropylene
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
    • B29K2105/0005—Condition, form or state of moulded material or of the material to be shaped containing compounding ingredients
    • B29K2105/0014—Catalysts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
    • B29K2105/04—Condition, form or state of moulded material or of the material to be shaped cellular or porous
    • B29K2105/041—Microporous
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
    • B29K2105/04—Condition, form or state of moulded material or of the material to be shaped cellular or porous
    • B29K2105/048—Expandable particles, beads or granules
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2995/00—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds
    • B29K2995/0037—Other properties
    • B29K2995/0063—Density
    • 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
    • C08J2201/03—Extrusion of the foamable blend
    • 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
    • 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
    • C08J2323/10—Homopolymers or copolymers of propene
    • C08J2323/14—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
    • C08J2423/10—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
    • C08J2423/16—Ethene-propene or ethene-propene-diene copolymers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L2314/00—Polymer mixtures characterised by way of preparation
    • C08L2314/02—Ziegler natta catalyst

Definitions

  • One or more embodiments of the present invention relate to (i) an expanded polypropylene resin particle, (ii) a polypropylene resin in-mold expanded molded product obtained from expanded polypropylene resin particles, (iii) a method of producing the expanded polypropylene resin particle, and (iv) a method of producing the polypropylene resin in-mold expanded molded product.
  • a polypropylene resin in-mold expanded molded product which is obtained with the use of expanded polypropylene resin particles obtained from a polypropylene resin, has characteristics such as being easily shaped, being light in weight, and being heat insulating, which are advantages of an in-mold expanded molded product.
  • a polypropylene resin in-mold expanded molded product is superior in terms of chemical resistance, heat resistance, strain recovery rate after compression, and the like.
  • a polypropylene resin in-mold expanded molded product is superior in terms of dimension accuracy, heat resistance, compressive strength, and the like. Because of these characteristics, a polypropylene resin in-mold expanded molded product is put to a wide range of use such as not only automobile interior materials and automobile bumper core materials but also heat insulating materials, shock-absorbing packing materials, and returnable containers.
  • a polypropylene resin in-mold expanded molded product is superior to a polyethylene resin in-mold expanded molded product in terms of heat resistance and compressive strength.
  • a molding temperature during in-mold foaming molding becomes high. Therefore, a high steam pressure is necessary during, for example, in-mold foaming molding with the use of steam. This tends to cause utility costs to be high.
  • Patent Literature 1 techniques in which a low-melting polypropylene resin having a melting point of 140° C. or lower is used (e.g. Patent Literature 1), (ii) techniques in which a mixture of a low-melting polypropylene resin and a high-melting polypropylene resin is used (e.g. Patent Literatures 2 and 4-8), and (iii) techniques in which a low-melting metallocene polypropylene resin, which is polymerized by use of a metallocene catalyst, is used (e.g. Patent Literature 3).
  • Patent Literatures 1 and 12 can be listed as literatures each of which discloses a technique for producing an expanded polypropylene resin particle that is excellent in characteristics such as heat resistance.
  • a molding temperature can be reduced with these techniques, the amount of decrease in compressive strength is excessively large in comparison with conventional in-mold expanded molded products.
  • a strength of approximately 0.23 MPa is required as compressive strength when the polypropylene resin in-mold expanded molded product is strained by 50% (hereinafter referred to as “50%-strained compressive strength”).
  • a pressure of 0.26 MPa (gage pressure) or more (i.e. high molding temperature) as in-mold foaming molding pressure is necessary in order to obtain polypropylene resin in-mold expanded molded product having the strength above.
  • a metallocene polypropylene resin poses a high production costs in comparison with a Ziegler polypropylene resin which is polymerized with the use of a Ziegler catalyst. Therefore, even if utility costs of in-mold foaming molding can be reduced as a result of a low molding temperature, material costs are still high. This is not necessarily advantageous from an industrial perspective.
  • One or more embodiments of the present invention provide a high-compressive-strength polypropylene resin in-mold expanded molded product while a molding temperature (steam pressure) during in-mold foaming molding is reduced.
  • the inventors of the present invention found that with the use of expanded polypropylene resin particles obtained from a base material resin including (i) a low-melting polypropylene resin having a structure in which a certain amount of certain comonomers is contained and (ii) a polypropylene resin having a melting point higher than that of the low-melting polypropylene resin, it may be possible to reduce a molding temperature during in-mold foaming molding to a low temperature and it may also be possible to maintain, at a level not inferior to those of conventional molded products, a compressive strength of a polypropylene resin in-mold expanded molded product to be obtained.
  • An expanded polypropylene resin particle which has an average cell diameter of 100 ⁇ m or more to 340 ⁇ m or less and which is obtained from a base material resin, the base material resin having a melting point of 140° C. or higher to 150° C. or lower and including a polypropylene resin A satisfying the following condition (a) and having a melting point of 130° C. or higher to 140° C. or lower and a polypropylene resin B having a melting point of 145° C. or higher to 165° C. or lower:
  • a structural unit of 1-butene is present in an amount of 3 weight % or more to 15 weight % or less with respect to 100 weight % entire structural units.
  • a structural unit of ethylene is present in amount of 2 weight % or more to 10 weight % or less with respect to 100 weight % entire structural units.
  • ⁇ 4> The expanded polypropylene resin particle as set forth in any one of ⁇ 1> through ⁇ 3>, configured such that the average cell diameter is 120 ⁇ m or more to 250 ⁇ m or less.
  • ⁇ 5> The expanded polypropylene resin particle as set forth in any one of ⁇ 1> through ⁇ 4>, configured such that the melting point of the base material resin is 145° C. or higher to 150° C. or lower.
  • ⁇ 6> The expanded polypropylene resin particle as set forth in any one of ⁇ 1> through ⁇ 5>, configured such that the melting point of the base material resin is 146° C. or higher to 148° C. or lower.
  • the expanded polypropylene resin particle is an expanded composite particle in which an expanded polypropylene resin core layer is covered with a polypropylene resin covering layer
  • the expanded polypropylene resin core layer is obtained from a base material resin including the polypropylene resin A and the polypropylene resin B; and the polypropylene resin covering layer includes the polypropylene resin A.
  • a polypropylene resin in-mold expanded molded product obtained by subjecting, to in-mold foaming molding, expanded polypropylene resin particles recited in any one of ⁇ 1> through ⁇ 9>.
  • a method of producing a polypropylene resin in-mold expanded molded product including the steps of:
  • a structural unit of ethylene is present in amount of 2 weight % or more to 10 weight % or less with respect to 100 weight % entire structural units.
  • ⁇ 15> The method as set forth in ⁇ 13> or ⁇ 14>, further including the step of: melting and kneading the polypropylene resin A and the polypropylene resin B in an extruder and then obtaining the polypropylene resin particles.
  • ⁇ 16> The method as set forth in any one of ⁇ 13> through ⁇ 15>, further including the step of: obtaining the polypropylene resin A by carrying out polymerization with use of a Ziegler catalyst.
  • the expanded polypropylene resin particles are each an expanded composite particle in which an expanded polypropylene resin core layer is covered with a polypropylene resin covering layer;
  • the expanded polypropylene resin core layer is obtained from a base material resin including
  • the polypropylene resin covering layer includes the polypropylene resin A.
  • FIG. 1 is a view illustrating a DSC curve of second temperature rise obtained when, in differential scanning calorimetry (DSC), (i) a temperature of a polypropylene resin is raised from 40° C. to 220° C. at a heating rate of 10° C./min., (ii) the temperature is cooled from 220° C. to 40° C. at a rate of 10° C./min., and (iii) the temperature is raised again from 40° C. to 220° C. at a rate of 10° C./min. t m is a melting point.
  • DSC differential scanning calorimetry
  • FIG. 2 is a view illustrating a DSC curve (temperature vs heat absorption quantity) obtained by a differential scanning calorimetry (DSC) in which a temperature of an expanded polypropylene resin particle is raised from 40° C. to 220° C. at a heating rate of 10° C./min.
  • the DSC curve shows two melting peaks and two melting heat quantity regions.
  • the two melting heat quantity regions are a low temperature-side melting heat quantity region Ql and a high temperature-side melting heat quantity region Qh.
  • the expanded polypropylene resin particles is obtained from a base material resin containing a polypropylene resin A and a polypropylene resin B.
  • the polypropylene resin A used in one or more embodiments of the present invention is a polypropylene resin which satisfies the following condition (a) and which has a melting point in a range of 130° C. or higher to 140° C. or lower: (a) a structural unit(s) of 1-butene is present in an amount of 3 weight % or more to 15 weight % or less with respect to 100 weight % entire structural units.
  • the polypropylene resin A used in one or more embodiments of the present invention has a structural unit(s) of 1-butene in an amount of 3 weight % or more to 15 weight % or less with respect to 100 weight % entire structural units. If a structural unit of 1-butene is less than 3 weight %, then a molding temperature during in-mold foaming molding tends not to decrease. If a structural unit of 1-butene is more than 15 weight %, then a compressive strength of an in-mold expanded molded product to be obtained tends to decrease.
  • the polypropylene resin A can contain, in addition to 1-butene, a structural unit of a comonomer which is copolymerizable with propylene.
  • a comonomer encompass at least one type of ⁇ -olefin, such as ethylene, 1-pentene, 1-hexene, and 4-methyl-1-butene, any of which has 2 carbon atoms or any of 4 carbon atoms through 12 carbon atoms.
  • the comonomer may be ethylene.
  • the polypropylene resin A may further satisfy the following condition (b) in regard to ethylene.
  • a structural unit of ethylene is present in amount of 2 weight % or more to 10 weight % or less with respect to 100 weight % entire structural units.
  • the polypropylene resin A may satisfy both the condition (a) and condition (b), because, with such a polypropylene resin A, (i) a molding temperature during in-mold foaming molding can be easily made low and (ii) compressive strength of an in-mold expanded molded product to be obtained does not decrease but can be kept high.
  • “100 weight % entire structural units” means that the sum of a structural unit obtained from propylene, a structural unit obtained from 1-butene, and a structural unit obtained from another/other comonomer(s) such as ethylene accounts for 100 weight %.
  • the polypropylene resin A may be at least one selected from the group consisting of (i) a propylene-1-butene random copolymer and (ii) a propylene-ethylene-1-butene random copolymer.
  • the polypropylene resin A may (i) have a structural unit obtained from 1-butene in an amount of 4 weight % or more to 9 weight % or less and/or (ii) have a structural unit obtained from ethylene in an amount of 2.5 weight % or more to 6 weight % or less.
  • the polypropylene resin A may have a melting point of 130° C. or higher to 140° C. or lower, such as 132° C. or higher to 138° C. or lower, or such as 134° C. or higher to 138° C. or lower. If the melting point of the polypropylene resin A is lower than 130° C., then compressive strength of an in-mold expanded molded product to be obtained tends to decrease. If the melting point is more than 140° C., then a molding temperature during in-mold foaming molding tends not to decrease.
  • a catalyst for use in polymerization of the polypropylene resin A in accordance with one or more embodiments of the present invention is not limited to any particular one.
  • the catalyst encompass a Ziegler catalyst and metallocene catalyst.
  • a polypropylene resin polymerized with the use of a metallocene catalyst (hereinafter also referred to as “metallocene polypropylene resin”)
  • a polypropylene resin polymerized with the use of a Ziegler catalyst (hereinafter also referred to as “Ziegler polypropylene resin”) has lower rigidity by melting point matching.
  • Ziegler polypropylene resin has lower rigidity by melting point matching.
  • a comparison of rigidity of a Ziegler polypropylene resin and rigidity of a metallocene polypropylene resin having an identical melting point shows that the rigidity of the Ziegler polypropylene resin is lower.
  • the use of a Ziegler catalyst may conventionally be disadvantageous in order to obtain (i) reducing a molding temperature during in-mold foaming molding to a low temperature and (ii) maintaining compressive strength of a polypropylene resin in-mold expanded molded product to be obtained.
  • a Ziegler catalyst in which not only the condition (a) but also the condition (b) are defined, it may be possible to easily obtain the product according to one or more embodiments of the present invention, even in a case where a polypropylene resin polymerized with the use of a Ziegler catalyst is used.
  • a polypropylene resin A which is polymerized with the use of a Ziegler catalyst may also be used in view of the fact that (i) such a polypropylene resin is industrially more available than a polypropylene resin polymerized with the use of a metallocene catalyst and (ii) such a polypropylene resin can be put to a wider range of use.
  • a polypropylene resin polymerized with the use of a Ziegler catalyst may be used in one or more embodiments of the present invention by being used as a polypropylene resin A.
  • Examples of the polypropylene resin B used in one or more embodiments of the present invention encompass (i) a propylene homopolymer and (ii) a copolymer including: propylene; and a comonomer which is copolymerizable with propylene.
  • the polypropylene resin B may be a copolymer including propylene and a comonomer copolymerizable with the propylene in view of the fact that such a polypropylene resin B allows a molding temperature during in-mold foaming molding to be easily made low.
  • a comonomer which is copolymerizable with propylene encompass ⁇ -olefin, such as ethylene, 1-butene, 1-pentene, 1-hexene, and 4-methyl-1-butene, any of which has 2 carbon atoms or any of 4 carbon atoms through 12 carbon atoms.
  • ethylene may be used.
  • These comonomers can be individually copolymerized with propylene, or these comonomers in combination can be copolymerized with propylene.
  • the polypropylene resin B may be a propylene-ethylene random copolymer or a propylene-ethylene-1-butene random copolymer in view of the fact that such a polypropylene resin B allows a molding temperature during in-mold foaming molding to be easily made low and makes it possible to maintain high compressive strength of an in-mold expanded molded product to be obtained without causing the compressive strength to decrease.
  • a melting point of the polypropylene resin B in accordance with one or more embodiments of the present invention may be 145° C. or higher to 165° C. or lower, such as 147° C. or higher to 160° C. or lower, or such as 148° C. or higher to 153° C. or lower. If the melting point of the polypropylene resin B is lower than 145° C., then compressive strength of an in-mold expanded molded product to be obtained tends to decrease. If the melting point is more than 165° C., then a molding temperature during in-mold foaming molding tends to be high.
  • a catalyst for use in polymerization of the polypropylene resin B is not limited to any particular one.
  • the catalyst encompass a Ziegler catalyst and metallocene catalyst. Note, however, that a polypropylene resin B polymerized with the use of a Ziegler catalyst may be used in view of the fact that such as polypropylene resin B is easily available industrially and can be put to a wider range of use.
  • a melt flow rate (hereinafter referred to as “MFR”) of each of the polypropylene resin A and the polypropylene resin B is not particularly limited, but may be more than 3 g/10 min. and less than 10 g/10 min., such as 5 g/10 min. or more to 9 g/10 min. or less.
  • the MFR of each of the polypropylene resin A and polypropylene resin B is more than 3 g/10 min. and less than 10 g/10 min., then (i) an in-mold expanded molded product tends to have a good surface appearance and (ii) a molding cycle during molding tends to be short.
  • the MFR of the polypropylene resin according to one or more embodiments of the present invention is measured with the use of an MFR measuring instrument described in JIS-K7210 and under conditions involving (i) an orifice having a diameter of 2.0959 ⁇ 0.005 mm and a length of 8.000 ⁇ 0.025 mm, (ii) a load of 2160 g, and (iii) a temperature of 230° C. ⁇ 0.2° C.
  • a ratio at which the polypropylene resin A and the polypropylene resin B are mixed is not particularly limited. Note, however, that in view of allowing a molding temperature during in-mold foaming molding to be easily made low and maintaining high compressive strength of an in-mold expanded molded product to be obtained without causing the compressive strength to decrease, it may be possible to mix the polypropylene resin A and the polypropylene resin B such that the polypropylene resin A accounts for 50 weight % or more to 70 weight % or less and the polypropylene resin B accounts for 30 weight % or more to 50 weight % or less with respect to a total amount of both the polypropylene resins as 100 weight %.
  • an additive as necessary in addition to the polypropylene resin A and the polypropylene resin B.
  • the additive encompass: a resin other than a polypropylene resin (described later); an expansion nucleating agent; a hydrophilic compound; a colorant; an antistatic agent; a flame retarder; an antioxidant; and electrically conductive agent.
  • a base material resin is constituted by a mixture of the polypropylene resin A, the polypropylene resin B, and the additive.
  • Examples of other resins which can be mixed encompass polyethylene resins such as a high-density polyethylene resin, a medium-density polyethylene resin, a low-density polyethylene resin, and a linear low-density polyethylene resin.
  • polyethylene resins such as a high-density polyethylene resin, a medium-density polyethylene resin, a low-density polyethylene resin, and a linear low-density polyethylene resin.
  • mixing equal to or less than 20 parts by weight of the polyethylene resin in 100 parts by weight of the polypropylene resin A and the polypropylene resin B combined may (i) allow an expansion ratio to easily increase or (ii) allow a molding temperature during in-mold foaming molding to be easily made low.
  • an expansion nucleating agent which is to become an expansion nucleus during expansion of the base material resin.
  • the expansion nucleating agent for use in one or more embodiments of the present invention encompass silica (silicon dioxide), silicate, alumina, diatomaceous earth, calcium carbonate, magnesium carbonate, calcium phosphate, feldspar, apatite, and barium sulfate.
  • silicate encompass talc, magnesium silicate, kaolin, halloysite, dickite, aluminum silicate, and zeolite.
  • an amount of the expansion nucleating agent contained in the base material resin used in one or more embodiments of the present invention may be equal to or greater than 0.005 parts by weight and equal to or less than 2 parts by weight, such as equal to or greater than 0.01 parts by weight and equal to or less than 1 part by weight, or such as equal to or greater than 0.03 parts by weight and equal to or less than 0.5 parts by weight with respect to 100 parts by weight of the polypropylene resin A and the polypropylene resin B combined.
  • Adding a hydrophilic compound to a base material resin may bring about the effect of promoting an increase in expansion ratio of expanded polypropylene resin particles.
  • hydrophilic compound for use in one or more embodiments of the present invention encompass water-absorbing organic matters such as glycerin, polyethylene glycol, glycerin fatty acid ester, melamine, isocyanuric acid, and a melamine-isocyanuric acid condensate.
  • An amount of the hydrophilic compound contained in the base material resin in accordance with one or more embodiments of the present invention may be equal to or greater than 0.01 parts by weight and equal to or less than 5 parts by weight, such as equal to or greater than 0.1 parts by weight and equal to or less than 2 parts by weight with respect to 100 parts by weight of the polypropylene resin A and the polypropylene resin B combined. If the amount of the hydrophilic compound contained is less than 0.01 parts by weight, then the effect of increasing an expansion ratio and the effect of enlarging a cell diameter are difficult to be obtained. If the amount of the hydrophilic compound contained is more than 5 parts by weight, then the hydrophilic compound becomes unlikely to be uniformly dispersed in a polypropylene resin.
  • colorant examples include carbon black, ultramarine blue, cyanine pigment, azo pigment, quinacridone pigment cadmium yellow, chrome oxide, iron oxide, perylene pigment, and Anthraquinone pigment. These colorants can be used individually or in combination.
  • An amount of the colorant contained in the base material resin may be equal to or greater than 0.001 parts by weight and equal to or less than 10 parts by weight, such as equal to or greater than 0.01 parts by weight and equal to or less than 8 parts by weight with respect to 100 parts by weight of the polypropylene resin A and the polypropylene resin B combined.
  • the carbon black may be equal to or greater than 1 part by weight and equal to or less than 10 parts by weight with respect to 100 parts by weight of the polypropylene resin A and the polypropylene resin B combined.
  • a melting point of the base material resin including the polypropylene resin A and the polypropylene resin B is approximately 130° C. or higher to 165° C. or lower, based on the respective melting points of the polypropylene resin A and of the polypropylene resin B.
  • the melting point of the base material resin may be 140° C. or higher to 150° C. or lower, such as 145° C. or higher to 150° C. or lower, such as 145° C. or higher to 149° C. or lower, such as 145° C. or higher to 148° C. or lower, or such as 146° C. or higher to 148° C. or lower.
  • a melting point t m of a polypropylene resin is a melting peak temperature in a second temperature rise (t m in FIG. 1 ) in a DSC curve which is obtained when, in differential scanning calorimetry (DSC), 1 mg or more to 10 mg or less of polypropylene resin is (i) heated from 40° C. to 220° C. at a heating rate of 10° C./min., (ii) cooled from 220° C. to 40° C. at a cooling rate of 10° C./min., and then (iii) heated again from 40° C. to 220° C. at a heating rate of 10° C./min.
  • DSC differential scanning calorimetry
  • FIG. 1 shows an example in which a single melting peak appears. Note, however, that in a case where a plurality of resins are mixed, a plurality of melting peaks may appear.
  • a resin other than a polypropylene resin can be mixed in one or more embodiments of the present invention.
  • a polyethylene resin is mixed in a high-melting polypropylene resin such as the polypropylene resin B
  • a melting peak (or shoulder) based on the polyethylene resin may appear around, for example, 130° C. That is, the total of two melting peaks may appear.
  • a temperature of a melting peak having a largest heat absorption quantity may be used as a melting point tin.
  • Examples of a method of mixing the polypropylene resin A and the polypropylene resin B encompass (i) a method in which the polypropylene resin A and the polypropylene resin B are mixed with the use of a blender or an extruder and (ii) a method in which the polypropylene resin A and the polypropylene resin B are blended by multi-stage polymerization during polymerization.
  • the method in which a blender or an extruder is used can also be used as a method of mixing the additive in the polypropylene resin.
  • the additive can be directly added to the polypropylene resin.
  • a resin to be used for production of a masterbatch may be a polyolefin resin, such as the polypropylene resin A and/or the polypropylene resin B, or such as a mixture of the polypropylene resin A and the polypropylene resin B.
  • expanded polypropylene resin particles may be expanded composite particles obtained by covering an expanded polypropylene resin core layer with a polypropylene resin covering layer because, with such expanded polypropylene resin particles, (i) a molding temperature in a case of obtaining a polypropylene resin in-mold expanded molded product to can be made lower and (ii) high compressive strength of the polypropylene resin in-mold expanded molded product can be maintained.
  • a resin of an expanded polypropylene resin core layer is made of a base material resin containing a polypropylene resin A and a polypropylene resin B and (ii) a polypropylene resin covering layer is made of a polypropylene resin A may be used.
  • adhesiveness of an interface between the expanded polypropylene resin core layer and the polypropylene resin covering layer can increase and (ii) fusibility of an in-mold expanded molded product can easily be good.
  • Such a characteristic is assumed to be derived from the following considerations: (i) Since a polypropylene resin A included in the expanded polypropylene resin core layer and a polypropylene resin A included in the polypropylene resin covering layer are identical polypropylene resins, adhesive strength of an interface between the expanded polypropylene resin core layer and the polypropylene resin covering layer becomes strong; and (ii) Since the polypropylene resin covering layer is made of a low-melting polypropylene resin A, expanded composite particles can be fused to each other at a lower molding temperature.
  • a step (granulation step) of producing polypropylene resin particles, which are made of a base material resin can be first carried out.
  • Examples of the method of producing polypropylene resin particles encompass a method in which an extruder is used. Specifically, it is possible, for example, that (i) a polypropylene resin A, a polypropylene resin B, and, as necessary, an additive (e.g.
  • a blended product is obtained, (ii) the blended product is introduced into an extruder and is melted and kneaded, (iii) a resultant product is extruded through a die provided at a tip of the extruder, and is then allowed to pass through water so as to be cooled, and (iv) the resultant product is chopped with the use of a cutter, so that polypropylene resin particles each having a desired shape, such as a columnar shape, an ellipsoidal shape, a spherical shape, a cubic shape, and a rectangular parallelepiped shape, are obtained.
  • a desired shape such as a columnar shape, an ellipsoidal shape, a spherical shape, a cubic shape, and a rectangular parallelepiped shape
  • an expansion nucleating agent a hydrophilic compound, a colorant
  • a middle part of the extruder so as to be mixed in the extruder, and (iii) melt and knead a resultant mixture in the extruder.
  • a weight of each of the polypropylene resin particles thus obtained may be 0.2 mg per particle or more to 10 mg per particle or less, such as 0.5 mg per particle or more to 5 mg per particle or less. If the weight of each of the polypropylene resin particles is less than 0.2 mg per particle, then handleability tends to decrease. If the weight is more than 10 mg per particle, then a mold-filling property during an in-mold foaming molding step tends to decrease.
  • the expanded polypropylene resin particles in accordance with one or more embodiments of the present invention may be expanded composite particles obtained by covering an expanded polypropylene resin core layer with a polypropylene resin covering layer.
  • Examples of a method of producing the expanded polypropylene resin particles encompass a method in which composite resin particles are first produced, the composite resin particles including a non-expanded polypropylene resin core layer and a non-expanded polypropylene resin covering layer.
  • Examples of a method of producing such composite resin particles encompass a method in which a die provided at a tip of an extruder is a core-sheath coextrusion die such as those disclosed in Japanese Examined Patent Application Publication, Tokukosho, No.
  • two extruders are used such that (i) a polypropylene resin for forming a polypropylene resin core layer is melted and kneaded in one of the two extruders, (ii) a polypropylene resin for constituting a polypropylene resin covering layer is melted and kneaded in the other one of the two extruders, (iii) molten resins thus obtained are introduced into a coextrusion die which is connected to the two extruders, and (iv) a sheath-core composite, which includes the polypropylene resin core layer and the polypropylene resin covering layer, is discharged in a strand shape.
  • the discharged substance in a strand shape is cooled by, for example, being allowed to pass through water
  • the discharged substance is cut so as to have a certain weight or size by use of a cutting machine including a drawing machine.
  • a cutting machine including a drawing machine.
  • This makes it possible to obtain composite resin particles each including a polypropylene resin core layer and a polypropylene resin covering layer.
  • a polypropylene resin covering layer which is less in thickness causes foaming of a polypropylene resin covering layer to be less likely to occur during foaming of composite resin particles.
  • a polypropylene resin covering layer is excessively thin, then sufficient covering is difficult. Therefore, a thickness of a polypropylene resin covering layer before being produced into expanded polypropylene resin particles (expanded composite particles) may be 0.1 ⁇ m or more to 300 ⁇ m or less, and a thickness of a polypropylene resin covering layer after being produced into the expanded polypropylene resin particles (expanded composite particles) may be 0.1 ⁇ m or more to 250 ⁇ m or less.
  • a weight ratio between the polypropylene resin core layer and the polypropylene resin covering layer may be 99.5:0.5 to 65:35, such as 99:1 to 70:30, or such as 97:3 to 80:20.
  • the weight ratio between the polypropylene resin core layer and the polypropylene resin covering layer can be adjusted by adjusting respective discharge quantities the two extruders.
  • an expansion nucleating agent, a hydrophilic compound, and/or an antioxidant for example, is/are added to the polypropylene resin for forming a polypropylene resin core layer and (ii) an antistatic agent, a flame retarder, and/or an electrically conductive agent, for example, is/are added to the polypropylene resin for constituting a polypropylene resin covering layer.
  • an antistatic agent, a flame retarder, and/or an electrically conductive agent for example, is/are added to the polypropylene resin for constituting a polypropylene resin covering layer.
  • one or more embodiments of the present invention is not limited to such a configuration, and such additives can be adjusted as appropriate.
  • Expanded polypropylene resin particles may be produced with the use of polypropylene resin particles (or composite resin particles) thus obtained.
  • Examples of a method of producing the expanded polypropylene resin particles in accordance with one or more embodiments of the present invention encompass a method of producing expanded polypropylene resin particles in an aqueous dispersion system by carrying out the following foaming step: (i) polypropylene resin particles along with a foaming agent such as carbon dioxide are dispersed into an aqueous dispersion medium in a pressure-resistant container, (ii) a resultant dispersion liquid is heated to a temperature equal to or higher than a softening temperature of the polypropylene resin particles and is subjected to pressure, (iii) the temperature and the pressure are retained for a certain period of time, (iv) the dispersion liquid is released to a region having a pressure lower than an internal pressure of the pressure-resistant container, so that the expanded polypropylene resin particles are obtained.
  • foaming agent such as carbon dioxide
  • the expanded polypropylene resin particles can also be obtained by (i) further adding, as necessary, a foaming agent around a foaming temperature to adjust a foaming pressure to a desired pressure, (ii) further adjusting a temperature, (iii) retaining adjusted temperature and the adjusted pressure for a certain period of time, (iv) releasing, into a region having a pressure lower than the internal pressure of the pressure-resistant container, the dispersion liquid in the pressure-resistant container.
  • the following aspect is possible: (2) Polypropylene resin particles, an aqueous dispersion medium, and, as necessary, a dispersing agent, for example, are placed into the pressure-resistant container. Then, while a resultant mixture is stirred, the inside of the pressure-resistant container is vacuumed as necessary. Then, while the mixture is heated to a temperature equal to or higher than the softening temperature of the polypropylene resin, a foaming agent is introduced into the dispersion liquid in the pressure-resistant container.
  • the following aspect is possible: (3) Polypropylene resin particles, an aqueous dispersion medium, and, as necessary, a dispersing agent, for example, are placed into the pressure-resistant container. Then, a resultant mixture is heated to a temperature around a foaming temperature. Then, a foaming agent is further introduced into the dispersion liquid in the pressure-resistant container, and a resultant mixture is at foaming temperature. Then, the foaming temperature is retained for a certain period of time. Then, the dispersion liquid in the pressure-resistant container is released into a region having a pressure lower than an internal pressure of the pressure-resistant container, so that expanded polyolefin resin particles are obtained.
  • the expansion ratio can be adjusted by (i) adjusting a pressure-releasing speed during foaming by increasing the internal pressure of the pressure-resistant container through injecting carbon dioxide, nitrogen, air, or a substance used as a foaming agent, into the pressure-resistant container before the dispersion liquid in the pressure-resistant container is released into the low-pressure region and (ii) controlling the pressure through introducing carbon dioxide, nitrogen, air, or a substance used as a foaming agent, into the pressure-resistant container also while the dispersion liquid in the pressure-resistant container is being released into the low-pressure region.
  • the pressure-resistant container into which the polypropylene resin particles are dispersed is not limited to any particular one, provided that the pressure-resistant container is capable of resisting a pressure and temperature inside the container during production of the expanded particles.
  • the pressure-resistant container encompass an autoclave-type pressure-resistant container.
  • An aqueous dispersion medium for use in one or more embodiments of the present invention may be water.
  • the aqueous dispersion medium can also be a dispersion medium obtained by adding methanol, ethanol, ethylene glycol, glycerin, or the like to water.
  • water in the aqueous dispersion medium serves also as a foaming agent. This contributes to an increase in expansion ratio.
  • foaming agent for use in one or more embodiments of the present invention encompass: saturated hydrocarbons such as propane, butane, and pentane; ethers such as dimethyl ether, alcohols such as methanol and ethanol; and inorganic gas such as air, nitrogen, carbon dioxide, and water.
  • saturated hydrocarbons such as propane, butane, and pentane
  • ethers such as dimethyl ether, alcohols such as methanol and ethanol
  • inorganic gas such as air, nitrogen, carbon dioxide, and water.
  • an inorganic gas foaming agent has particularly small environmental impact and has no dangerous inflammability, and is therefore may be used. It may also be possible to use at least one foaming agent selected from the group consisting of carbon dioxide and water.
  • a dispersing agent and/or a dispersion auxiliary agent in order to prevent polypropylene resin particles in an aqueous dispersion medium from adhering to each other.
  • dispersing agent examples include inorganic dispersion agents such as tertiary calcium phosphate, tertiary magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay. These inorganic dispersion agents can be used individually, or two or more of these inorganic dispersion agents can be used in combination.
  • inorganic dispersion agents such as tertiary calcium phosphate, tertiary magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay.
  • dispersion auxiliary agent encompass: (i) anionic surfactants of carboxylate type, (ii) anionic surfactants of sulfonate type such as alkylsulfonic acid salt, n-paraffin sulfonate salt, alkyl benzene sulfonate, alkyl naphthalene sulfonate, and sulfosuccinate, (iii) anionic surfactants of sulfate ester type such as sulfonated oil, alkyl sulfate salt, alkyl ether sulfate, and alkyl amide sulfate, and (iv) anionic surfactants of phosphate ester type such as alkyl phosphate, polyoxyethylene phosphate, and alkyl allyl ether sulfate.
  • anionic surfactants of carboxylate type such as alkylsulfonic acid salt, n-paraffin sulfonate salt, alkyl
  • At least one dispersing agent selected from the group consisting of tertiary calcium phosphate, tertiary magnesium phosphate, barium sulfate, and kaolin; and (ii) a dispersion auxiliary agent which is n-paraffin sulfonic acid soda.
  • an aqueous dispersion medium in an amount of equal to or greater than 100 parts by weight and equal to or less than 500 parts by weight with respect to 100 parts by weight of polypropylene resin particles so that dispensability of the polypropylene resin particles in the aqueous dispersion medium is good.
  • the respective amounts of dispersing agent and dispersion auxiliary agent vary, depending on (i) the types of the dispersing agent and the dispersion auxiliary agent and (ii) the type of and amount of polypropylene resin particles used.
  • the dispersing agent may be used in an amount of 0.2 parts by weight or more to 3 parts by weight or less, and the dispersion auxiliary agent may be used in an amount of 0.001 parts by weight or more to 0.1 parts by weight or less.
  • first-stage foaming step The step of thus obtaining expanded polypropylene resin particles from polypropylene resin particles may be referred to as “first-stage foaming step”, and the expanded polypropylene resin particles thus obtained may be referred to as “first-stage expanded particles”.
  • An expansion ratio of first-stage expanded particles may not reach 10 times, depending on foaming conditions such as foaming temperature, foaming pressure, and the type of foaming agent.
  • expanded polypropylene resin particles whose expansion ratio is increased in comparison with that of first-stage expanded particles can be obtained by (i) applying an internal pressure to the first-stage expanded particles by impregnation of inorganic gas (e.g. air, nitrogen, carbon dioxide) and then (ii) causing the first-stage expanded particles to come into contact with steam having a certain pressure.
  • inorganic gas e.g. air, nitrogen, carbon dioxide
  • the step of thus further foaming the expanded polypropylene resin particles so as to obtain expanded polypropylene resin particles having a high expansion ratio may be referred to as “second-stage foaming step”.
  • Expanded polypropylene resin particles thus obtained through the second-stage foaming step may be referred to as “second-stage expanded particles”.
  • a pressure of steam in the second-stage foaming step may be adjusted 0.04 MPa (gage pressure) or more to 0.25 MPa (gage pressure) or less, such as 0.05 MPa (gage pressure) or more to 0.15 MPa (gage pressure) or less, in view of the expansion ratio of the second-stage expanded particles.
  • the pressure of steam in the second-stage foaming step is less than 0.04 MPa (gage pressure)
  • the expansion ratio is less likely to increase. If the pressure is more than 0.25 MPa (gage pressure), then second-stage expanded particles to be obtained tend to adhere to each other, so that it becomes impossible to use the second-stage expanded particles for subsequent in-mold foaming molding.
  • An internal pressure of air to be impregnated into the first-stage expanded particles may be (i) made to change as appropriate in view of (a) the expansion ratio of the second-stage expanded particles and (b) steam pressure in the second-stage foaming step and (ii) 0.2 MPa or more (absolute pressure) or more to 0.6 MPa or less (absolute pressure).
  • the internal pressure of air to be impregnated into the first-stage expanded particles is less than 0.2 MPa (absolute pressure)
  • steam having a high pressure is necessary to increase the expansion ratio, so that the second-stage expanded particles tend to adhere to each other.
  • the internal pressure of air to be impregnated into the first-stage expanded particles is more than 0.6 MPa (absolute pressure)
  • the second-stage expanded particles tend to become an open-cell foam. In such a case, rigidity, such as compressive strength, of an in-mold expanded molded product tends to decrease.
  • the expansion ratio of the expanded polypropylene resin particles is not particularly limited, and may be 5 times or more to 60 times or less. If the expansion ratio of the expanded polypropylene resin particles is less than 5 times, then reductions in weights of expanded polypropylene resin particles and of a polypropylene resin in-mold expanded molded product tend to be insufficient. If the expansion ratio of the expanded polypropylene resin particles is more than 60 times, then mechanical strengths of expanded polypropylene resin particles and of a polypropylene resin in-mold expanded molded product tend to be impractical.
  • An average cell diameter of the expanded polypropylene resin particles may be 100 ⁇ m or more to 340 ⁇ m or less, such as 110 ⁇ m or more to 330 ⁇ m or less, or such as 120 ⁇ m or more to 250 ⁇ m or less. If the average cell diameter falls within these ranges, then the polypropylene resin in-mold expanded molded product tends to (i) have a good surface appearance and (ii) have a high compressive strength.
  • the average cell diameter of the expanded polypropylene resin particles can be controlled by adjusting the amount of an expansion nucleating agent to add.
  • the average cell diameter can be controlled by, for example, adjusting a high-temperature heat quantity ratio described later. If the high-temperature heat quantity ratio is less than 15%, then the average cell diameter tends to become large. If the high-temperature heat quantity ratio is more than 50%, then the average cell diameter tends to become small.
  • expanded polypropylene resin particles have (i) at least two melting peaks and (ii) at least two melting heat quantities of a low temperature-side melting heat quantity (Ql) and a high temperature-side melting heat quantity (Qh).
  • a resin other than a polypropylene resin can be mixed.
  • a polyethylene resin if a polyethylene resin is mixed, then not only the two melting peaks in FIG. 2 but a melting peak (or shoulder) based on the polyethylene resin may appear in a DSC curve obtained. That is, the total of three melting peaks may appear in the DSC curve.
  • Expanded polypropylene resin particles having at least two melting peaks can be easily obtained by, in the earlier-described method of producing expanded polypropylene resin particles in an aqueous dispersion system, (i) controlling, as appropriate, a temperature in the pressure-resistant container during foaming to a proper value and (ii) retaining the temperature for a certain period of time.
  • the temperature in the pressure-resistant container during foaming may be t m ⁇ 8 (° C.) or higher, such as t m ⁇ 5 (° C.) or high and t m +4 (° C.) or lower, or such as t m ⁇ 5 (° C.) or higher and t m +3 (° C.) or lower.
  • a period of time during which the polypropylene resin particles are retained at the temperature controlled in the pressure-resistant container during foaming may be 1 min. or more to 120 min. or less, such as 5 min. or more to 60 min. or less.
  • an entire melting heat quantity (Q), a low temperature-side melting heat quantity (Ql), and a high temperature-side melting heat quantity (Qh) of expanded polypropylene resin particles are defined as follows by use of FIG. 2 .
  • the low temperature-side melting heat quantity (Ql) is indicated by a part surrounded by a line segment A-D, a line segment C-D, and the DSC curve
  • the high temperature-side melting heat quantity (Qh) is indicated by a part surrounded by a line segment B-D, the line segment C-D, and the DSC curve
  • a point C is a point at which a heat absorption quantity between two melting heat quantity regions in the DSC curve is the smallest, the two melting heat quantity regions being a region of the low temperature-side melting heat quantity and a region of the high temperature-side melting heat quantity
  • a point D is a point at which the line segment A-B intersects a line that is drawn so as to extend, parallel to a Y-axis (axis indicating the heat absorption quantity), from the point C toward the line segment A-B.
  • the high-temperature heat quantity ratio of the expanded polypropylene resin particles can be adjusted as appropriate by, for example, (i) a retention time at the temperature in the pressure-resistant container (i.e. a retention time that (a) starts from a time point at which the polypropylene resin particles reach a desired temperature in the pressure-resistant container and (b) ends at time point at which the polypropylene resin particles foam, (ii) a foaming temperature (which is a temperature during foaming and which may or may not be identical to the temperature in the pressure-resistant container), and (iii) foaming pressure (pressure during foaming).
  • a retention time at the temperature in the pressure-resistant container i.e. a retention time that (a) starts from a time point at which the polypropylene resin particles reach a desired temperature in the pressure-resistant container and (b) ends at time point at which the polypropylene resin particles foam
  • a foaming temperature which is a temperature during foaming and which may or may not be identical to the temperature in the pressure-
  • a high-temperature heat quantity ratio or a heat quantity at the high temperature-side melting peak tends to become large by extending a retention time, decreasing a foaming temperature, or decreasing foaming pressure. Because of these factors, conditions to obtain a desired high-temperature heat quantity ratio can be easily found by conducting several experiments in which a retention time, a foaming temperature, or a foaming pressure is systematically changed. Note that the foaming pressure can be adjusted by adjusting the amount of a foaming agent.
  • PCT International Publication No. WO2009/001626 discloses an expanded polypropylene resin particle which has such a crystal structure that a DSC curve, which is obtained in a first temperature rise when a temperature of an expanded polypropylene resin particle is raised from room temperature to 200° C. at a heating rate of 2° C./min. in heat flux differential scanning calorimetry, shows (i) a main endothermic peak of 100° C. to 140° C. endothermic peak apex temperature exhibiting 70% to 95% endothermic peak heat quantity with respect to an entire endothermic peak heat quantity and (ii) two or more endothermic peaks appearing on a high-temperature side with respect to the main endothermic peak.
  • the expanded polypropylene resin particles are not limited to any number of endothermic peaks on a high-temperature side with respect to a main endothermic peak in heat flux differential scanning calorimetry at a heating rate of 2° C./min., but may have such a crystal structure that one endothermic peak appears.
  • the expanded polypropylene resin particles having such a crystal structure that one endothermic peak appears can be easily obtained by use of a base material resin including (i) a polypropylene resin A having a melting point of 130° C. or higher to 140° C. or lower and (ii) a polypropylene resin B having a melting point higher than that of the polypropylene resin A by less than 25° C.
  • a base material resin including (i) a polypropylene resin A having a melting point of 130° C. or higher to 140° C. or lower and (ii) a polypropylene resin B having a melting point higher than that of the polypropylene resin A by less than 25° C.
  • the expanded polypropylene resin particles having such a crystal structure that one endothermic peak may appear because, with such expanded polypropylene resin particles, (i) compatibility between both resins (polypropylene resin A and polypropylene resin B) when melted and kneaded is good, (ii) a variance in cell diameter of expanded polypropylene resin particles becomes small, and (iii) an in-mold expanded molded product has a good surface appearance.
  • the expanded polypropylene resin particles may be made into a polypropylene resin in-mold expanded molded product by a conventionally known in-mold foaming molding method.
  • Examples of an in-mold foaming molding method encompass:
  • a method of (a) subjecting expanded polypropylene resin particles to a pressure treatment with the use of inorganic gas (e.g. air, nitrogen, carbon dioxide) so that the expanded polypropylene resin particles, into which the inorganic gas is impregnated, has a certain internal pressure and (b) filling a mold with the expanded polypropylene resin particles, and (c) heating the mold by steam so that the expanded polypropylene resin particles are fused to each other.
  • inorganic gas e.g. air, nitrogen, carbon dioxide
  • the polypropylene resin in-mold expanded molded product may be obtained as a high-compressive-strength polypropylene resin in-mold expanded molded product by subjecting expanded polypropylene resin particles to in-mold foaming molding while a molding temperature (steam pressure) is reduced.
  • the polypropylene resin in-mold expanded molded product may be used in that a relationship particularly between a density of the molded product and a 50%-strained compressive strength satisfies the following Formula (1):
  • polypropylene resin in-mold expanded molded products satisfying Formula (1) have conventionally been used as highly strong polypropylene resin in-mold expanded molded products for automobile interior materials and automobile bumper core materials.
  • such conventional polypropylene resin in-mold expanded molded products require a high molding temperature during in-mold foaming molding.
  • a high steam pressure as 0.24 MPa (gage pressure) or more was necessary.
  • the polypropylene resin in-mold expanded molded product in accordance with one or more embodiments of the present invention is not limited to any particular density.
  • a decrease in compressive strength in a case where molding is possible with a low steam pressure (molding temperature) tends to be remarkable in a case where a density of molded product is 40 g/L or less.
  • the density of the molded product may be 40 g/L or less.
  • the density of the molded product may be 20 g/L or more to 40 g/L or less, such as 20 g/L or more to 35 g/L or less.
  • a polypropylene resin in-mold expanded molded product thus obtained can be put to various applications such as heat insulating materials, shock-absorbing packing materials, and returnable containers in addition to automobile interior materials and automobile bumper core materials.
  • the polypropylene resin in-mold expanded molded product may be used for automobile materials such as automobile interior materials and automobile bumper core materials because such automobile materials obtained from the polypropylene resin in-mold expanded molded product, which can be molded with a lower molding temperature (steam pressure), exhibit a compressive strength similar to those obtained from conventional molded products molded with a high molding temperature (steam pressure).
  • a structural unit of 1-butene is present in an amount of 3 weight % or more to 15 weight % or less with respect to 100 weight % entire structural units.
  • polypropylene resin in-mold expanded molded product as set forth in any one of [1] through [5], configured such that the polypropylene resin B is a propylene-ethylene random copolymer or a propylene-ethylene-1-butene random copolymer.
  • the expanded polypropylene resin particles are each an expanded composite particle in which an expanded polypropylene resin core layer is covered with a polypropylene resin covering layer
  • the expanded polypropylene resin core layer is obtained from a base material resin including
  • the polypropylene resin covering layer includes the polypropylene resin A.
  • polypropylene resin in-mold expanded molded product as set forth in any one of [1] through [8], configured such that the polypropylene resin in-mold expanded molded product has a density of 20 g/L or more to 40 g/L or less.
  • a method of producing a polypropylene resin in-mold expanded molded product including the steps of:
  • a structural unit of ethylene is present in amount of 2 weight % or more to 10 weight % or less with respect to 100 weight % entire structural units.
  • the expanded polypropylene resin particles are each an expanded composite particle in which an expanded polypropylene resin core layer is covered with a polypropylene resin covering layer.
  • the expanded polypropylene resin core layer is obtained from a base material resin including
  • the polypropylene resin covering layer includes the polypropylene resin A.
  • Table 1 shows polypropylene resins A-1 through A-8, polypropylene resins B-1 through B-5, and a polypropylene resin C which were used. Note that a Polypropylene resin B-4 is a propylene homopolymer, whereas the other polypropylene resins are random copolymers.
  • Polypropylene resin B-4 is a propylene homopolymer, and the other polypropylene resin is a random copolymer.
  • Talc manufactured by Hayashi-Kasei Co., Ltd., Talcan Powder PK-S
  • Polyethylene glycol manufactured by Lion Corporation, PEG#300
  • Carbon black manufactured by Mitsubishi Chemical Corporation, MCF88 (average particle size: 18 nm)
  • a polypropylene resin having a known comonomer content was hot pressed at 180° C., so that a film having a thickness of approximately 100 ⁇ m was produced.
  • the film thus produced was subjected to IR spectrum measurement so that a propylene-derived absorbance (I 810 ) at 810 cm ⁇ 1 , an ethylene comonomer-derived absorbance (I 733 ) at 733 cm ⁇ 1 , and a butene comonomer-derived absorbance (I 766 ) at 766 cm ⁇ 1 were read.
  • an absorbance ratio (I 733 /I 810 ) is shown in a horizontal axis, and an ethylene comonomer content is shown in a vertical axis, so that a calibration curve indicative of the ethylene comonomer content was obtained.
  • an absorbance ratio (I 766 /I 810 ) is shown in a horizontal axis, and a butene comonomer content is shown in a vertical axis, so that a calibration curve indicative of the butene comonomer content was obtained.
  • a melting point t m of the polypropylene resin was measured with the use of a differential scanning calorimeter DSC (manufactured by Seiko Instruments Inc., model: DSC6200). Specifically, the melting point t m was found as a melting peak temperature in a second temperature rise on a DSC curve obtained by (i) raising a temperature of 5 mg to 6 mg of the polypropylene resin (polypropylene resin particles) from 40° C. to 220° C. at a heating rate of 10° C./min. so as to melt the polypropylene resin, (ii) lowering the temperature from 220° C. to 40° C. at a cooling rate of 10° C./min.
  • a differential scanning calorimeter manufactured by Seiko Instruments Inc., model: DSC6200
  • the low temperature-side melting heat quantity (Ql) is indicated by a part surrounded by a line segment A-D, a line segment C-D, and the DSC curve and the high temperature-side melting heat quantity (Qh) is indicated by a part surrounded by a line segment B-D, the line segment C-D, and the DSC curve
  • a point C is a point at which a heat absorption quantity between two melting heat quantity regions in the DSC curve is the smallest, the two melting heat quantity regions being a region of the low temperature-side melting heat quantity and a region of the high temperature-side melting heat quantity
  • a point D is a point at which the line segment A-B intersects a line that is drawn so as to extend, parallel to a Y-axis (axis indicating the heat absorption quantity), from the point C toward the line segment A-B.
  • DSC measurement was carried out with the use of a differential scanning calorimeter (manufactured by Seiko Instruments Inc., model: DSC6200) by raising a temperature of 1 mg to 3 mg of expanded polypropylene resin particles from 40° C. to 200° C. at a heating rate of 2° C./min.
  • a differential scanning calorimeter manufactured by Seiko Instruments Inc., model: DSC6200
  • the polypropylene resin in-mold expanded molded product obtained was (i) left at room temperature for 1 hour, (ii) cured and dried in a thermostatic chamber at 75° C. for 3 hours, and (iii) extracted again and left at room temperature for 24 hours. Then, fusibility and a surface property were evaluated. Note that during in-mold foaming molding, the in-mold expanded molded product was molded while the molding pressure (steam pressure) in the both-surface heating step was changed in increments of 0.01 MPa. The lowest molding pressure, at which an in-mold expanded molded product whose fusibility was evaluated as “good” or “excellent” in fusibility evaluation (see below) was obtained, was regarded as a minimum molding pressure. An in-mold expanded molded product molded with the minimum molding pressure was subjected to (i) surface appearance evaluation, (ii) molded product density measurement, and (iii) 50%-strained compressive strength measurement.
  • the in-mold expanded molded product thus obtained was (i) notched by 5 mm in a thickness-wise direction with the use of a cutter and (ii) cleaved by hand. A cleaved surface was observed by visual inspection, and a percentage of clefts in expanded particles and not clefts in the interfaces of the expanded particles was obtained. Then, fusibility was judged by the following criteria:
  • the percentage of clefts in the expanded particles was 80% or more.
  • a surface of having a length of 300 mm and a width of 400 mm of the in-mold expanded molded product obtained was obtained by visual inspection, and a surface property was judged by the following criteria:
  • E Excellent: There is hardly any inter-particle space (spaces between expanded polypropylene resin particles); there is no noticeable surface unevenness; there is no wrinkle or shrinkage and the surface is therefore beautiful.
  • G Good: Some inter-particle spaces, surface unevenness, shrinkage, or wrinkles are observed.
  • F failed: Inter-particle spaces, surface unevenness, shrinkage, or wrinkles are noticeable throughout the surface observed.
  • E An edge part (ridge part), at which two surfaces of the in-mold expanded molded product obtained intersect, had no unevenness resulting from the expanded polypropylene resin particles and had a clear ridge formed; mold transferability is good. Even if the edge part was rubbed with a finger, the expanded particles were not peeled off.
  • F failed: Unevenness resulting from the expanded polypropylene resin particles was noticeable at an edge part (ridge part): mold transferability was poor. If the edge part was rubbed with a finger, then the expanded particles were easily peeled off.
  • test piece which had a size of length 50 mm ⁇ width 50 mm ⁇ thickness 25 mm, was cut out from substantially a center part of the in-mold expanded molded product obtained. Note that the test piece had a thickness of 25 mm by cutting off, by approximately 12.5 mm, each of parts containing respective surface layers of the in-mold expanded molded product.
  • a weight W(g) of the test piece was measured, and the length, width, and thickness of the test piece were measured with the use of a caliper, so that a volume V(cm 3 ) of the test piece was calculated. Then, a molded product density was obtained by W/V. A conversion was made so that the unit was g/L.
  • the test piece whose molded product density was measured, was subjected to a compressive strength test. Specifically, a compressive stress of the test piece when the test piece was compressed by 50% at a rate of 10 mm/min. was measured with the use of a tension and compression testing machine (manufactured by Minebea Co., Ltd., TG series) in conformity with NDS Z 0504. In addition, the 50%-strained compressive strength was evaluated as follows.
  • Polypropylene resins and additives were mixed in amounts shown in Tables 2 and 3 with the use of a blender. Each of the mixtures obtained was melted and kneaded at a resin temperature of 220° C. and extruded in a strand shape with the use of a twin-screw extruder (manufactured by O. N. Machinery Co., Ltd., TEK45). The strand thus extruded was water-cooled in a water tank having a length of 2 m, and was then cut. This resulted in polypropylene resin particles (1.2 mg per particle).
  • a DSC curve of a first temperature rise showed (i) one main endothermic peak and (ii) one high temperature peak on a high temperature-side of the main endothermic peak.
  • An apex temperature of the main endothermic peak of the second-stage expanded particles was identical to that of corresponding first-stage expanded particles.
  • a shoulder which was supposedly derived from heating during second-stage foaming, appeared around 110° C. on the DSC curve.
  • Example 7 the DSC curve showed the total of three endothermic peaks which are (i) one main endothermic peak at 145° C. or lower and (ii) two high temperature peaks on a high temperature-side of the main endothermic peak.
  • the first-stage expanded particles obtained (or second-stage expanded particles in Example 9, Comparative Examples 1 through 3, and Comparative Example 8) were introduced into a pressure-resistant container. Then, pressurized air was impregnated so that internal pressure of the expanded particles was adjusted in advance as shown in a corresponding part of Table 2 or 3.
  • Tables 2 and 3 show the results of moldability evaluation, molded product density measurement, and 50%-strained compressive strength measurement.
  • Comparisons between the molded products having substantially identical molded product densities indicate that (i) those in Examples can be molded with a low molding pressure and exhibit higher 50%-strained compressive strength and (ii) those in Comparative Examples exhibit decreased 50%-strained compressive strength with a low molding pressure and demand a higher molding pressure for high 50%-strained compressive strength.
  • a polypropylene resin A-8 (which is an ethylene-propylene random copolymer), a polypropylene resin B-4 (which is a homopolypropylene), and talc were mixed in amounts shown in Table 3 with the use of a blender.
  • the mixture obtained was melted and kneaded at a resin temperature of 220° C. and extruded in a strand shape with the use of a twin-screw extruder (manufactured by O. N. Machinery Co., Ltd., TEK45).
  • the strand thus extruded was water-cooled in a water tank having a length of 2 m, and was then cut. This resulted in polypropylene resin particles (1.3 mg per particle).
  • Example 3 shows the results of moldability evaluation, molded product density measurement, and 50%-strained compressive strength measurement.
  • core layer base material resins polypropylene resins and additives were mixed in amounts shown in Table 4 with the use of a blender so that mixtures serve as core layer base material resins.
  • a polypropylene resin A-1 was prepared in Example 16
  • a polypropylene resin A-2 was prepared in Example 17
  • a polypropylene resin A-6 was prepared in Comparative Example 9
  • a polypropylene resin A-1 was prepared in Comparative Example 10.
  • a co-extrusion die On outlet sides of the 50 mm single-screw extruder and the 30 mm twin-screw extruder, a co-extrusion die was provided. The molten resins were supplied from the extruders to the die, so that the molten resins were joined in the die. Then, a multi-layer strand, in which the core layer base material resin was covered with the covering layer resin, was extruded. Note that a ratio of a discharge quantity of the core layer base material resin extruded from the 50 mm single-screw extruder to a discharge quantity of the covering layer resin extruded from the 30 mm twin-screw extruder was adjusted to 95/5.
  • the strand thus extruded was water-cooled in a water tank having a length of 2 m, and was then cut. This resulted in composite resin particles (1.2 mg per particle).
  • Example 4 Subsequent production of first-stage expanded particles and of an in-mold expanded molded product was carried out as in Example 1 except the conditions shown in Table 4 were met.
  • Table 4 shows the results of moldability evaluation, molded product density measurement, and 50%-strained compressive strength measurement. Note that expanded polypropylene resin particles were subjected to DSC measurement at a heating rate of 2° C./min.
  • the DSC curve showed the total of two endothermic peaks which are (i) one main endothermic peak at 145° C. or lower and (ii) one high temperature peak on a high temperature-side of the main endothermic peak.
  • Any of a comparison between Example 1 and Example 16 and a comparison between Example 2 and Example 17 indicates that expanded composite particles may be molded with a low molding pressure. Any of a comparison between Example 16 and Comparative Example 10 and a comparison between Example 17 and Comparative Example 10 indicates that one or more embodiments of the present invention may be molded with a low molding pressure and exhibits high 50%-strained compressive strength.
  • a comparison of Example 16 or Example 17 with Comparative Example 11 indicates that adhesiveness of an interface between an expanded polypropylene resin core layer and a polypropylene resin covering layer is increased in each expanded composite particle.
  • One or more embodiments of the present invention can be used for various purposes such as automobile interior materials, automobile bumper core materials, heat insulating materials, shock-absorbing packing materials, and returnable containers.
  • Point A Heat absorption quantity of expanded polypropylene resin particles at 80° C. in DSC curve of first temperature rise
  • Point B Heat absorption quantity of expanded polypropylene resin particles at temperature at which melting on high temperature side ends in DSC curve of first temperature rise
  • Point C Point at which heat absorption quantity of expanded polypropylene resin particles becomes small between two melting heat quantity regions in DSC curve of first temperature rise, the two melting heat quantity regions being region of low temperature-side melting heat quantity and region of high temperature-side melting heat quantity
  • Point D Point at which line segment A-B intersects line that is drawn so as to extend, parallel to Y-axis, from point C toward line segment A-B in DSC curve of first temperature rise of expanded polypropylene resin particles

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