Polypropylene-based resin extruded foam particles, method for producing same, and foam molded body

Abstract

The present invention provides: extruded foam particles which are capable of achieving a low open cell ratio even in cases where the expansion ratio is high, and which enable the achievement of a foam molded body having a low open cell ratio in cases where the foam particles are subjected to foam molding; a method for producing the same; and a foam molded body which is formed of the same.　The present invention uses polypropylene-based resin extruded foam particles that satisfy the following requirements (i)-(iii). (i) The loss tangent tanδ0.1 at ω = 0.1 rad / sec of a base material resin that constitutes the extruded foam particles is 0.6 to 1.4 inclusive, the loss tangent being determined by dynamic viscoelasticity measurement at 180°C and an angular frequency ω of 0.1-100 rad / sec. (ii) The expansion ratio is 15 to 35 times inclusive. (iii) The open cell ratio is 10% or less.

Description

Extruded polypropylene resin foam particles, their production method, and foam molded articles

[0001] The present invention relates to extruded polypropylene resin foam beads, foamed molded articles, and a method for producing extruded polypropylene resin foam beads.

[0002] BACKGROUND ART Extruded foamed bead moldings obtained using extruded polypropylene resin foamed beads are used mainly as automobile interior components and core materials for automobile bumpers, as well as in various other applications such as heat insulating materials and cushioning packaging materials.

[0003] As a method for producing extruded polypropylene resin foam particles, Patent Document 1 discloses a method for producing extruded polypropylene resin foam particles by extruding and foaming a modified polypropylene resin obtained by melt-kneading a polypropylene resin, a monomer selected from aromatic vinyl and isoprene, and a radical generator, to obtain a foam having an expansion ratio of about 30 times (density 30 kg / m ３ Patent Document 2 describes that expanded beads with an expansion ratio of about 24 times can be obtained by extrusion-foaming a resin composition at least partially containing a polypropylene resin obtained by melt-kneading a polypropylene resin, isoprene, and a radical polymerization initiator, and that the expanded beads obtained can be made into a foam-molded product by in-mold foam molding. Patent Document 3 further describes that expanded beads with an expansion ratio of about 18 times can be obtained by extrusion-foaming a polypropylene resin having specific melt viscoelastic properties, and that the obtained expanded beads have good moldability when molded into a foam-molded product.

[0004] Japanese Patent Application Laid-Open No. 9-302131 Japanese Patent Application Laid-Open No. 2009-256460 International Publication No. 2018 / 016399

[0005] In this way, the extruded polypropylene resin foam beads can be molded to obtain a foamed molded article. However, the extruded polypropylene resin foam beads often have large shrinkage after heating, or poor surface properties of the molded article, particularly in the high expansion ratio range possible by the depressurization foaming method, making it difficult to obtain a satisfactory molded article, and even if molded, they may not exhibit sufficient compressive strength, leaving room for further improvement.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide extruded foam beads which can have a low open cell ratio (hereinafter, may be referred to as "open cell ratio") even when they are made into expanded beads with a high expansion ratio, and which can also give foamed molded articles with a low open cell ratio when the expanded beads are foam-molded; a method for producing the same; and a foamed molded article made from the same.

[0007]

[0006] In the course of addressing the above-mentioned problems, the present inventors have found that the cell membranes of expanded beads are stretched not only in the process of producing expanded beads by extrusion foaming but also in the process of molding the expanded beads, and as a result, the cell membranes are broken, i.e., open cells are formed as a result of stretching. Therefore, the inventors have further investigated the melt elasticity properties of the base resin and found that expanded beads made of a base resin in which the loss tangent tanδ, an index showing the ratio of melt viscosity to melt elasticity, is within a specific range in which the melt elasticity is stronger than that of conventional resins, can have a low open cell ratio even at a high expansion ratio of 15 times or more, and further that expanded molded articles having a low open cell ratio can be obtained when the expanded beads are foam-molded, thereby completing the present invention.

[0008] Aspects of the present disclosure relate to the following extruded polypropylene resin foam beads, a production method thereof, and a foam molded article.

[0009] [1] Extruded polypropylene resin foam particles satisfying the following (i) to (iii): (i) a loss tangent tanδ at ω=0.1 rad / sec of the base resin constituting the extruded foam particles, as measured in a dynamic viscoelasticity measurement at 180°C and an angular frequency ω of 0.1 to 100 rad / sec; ０．１ (ii) The expansion ratio is 15 times or more and 35 times or less. (iii) The open cell ratio is 10% or less. [2] The loss tangent tanδ ０．１The extruded polypropylene resin foam beads according to [1], wherein the value of the structural unit derived from the other monomer is 0.6 or more and 1.2 or less. [3] The extruded polypropylene resin foam beads according to [1] or [2], wherein the polypropylene resin contained in the base resin comprises a random copolymer of a propylene monomer and a monomer other than the propylene monomer, and the content of structural units derived from the other monomer is 3.0% by weight or less based on the total amount of structural units derived from the monomers constituting the random copolymer. [4] The extruded polypropylene resin foam beads according to [3], wherein the content of structural units derived from the other monomer is 2.8% by weight or less. [5] The extruded polypropylene resin foam beads according to [3] or [4], wherein the structural units derived from the other monomer include structural units derived from an α-olefin having 2 or 4 to 12 carbon atoms. [6] The extruded, foamed polypropylene resin beads according to any one of [3] to [5], wherein the structural units derived from the other monomers are derived from one or more monomers selected from the group consisting of ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene. [7] The extruded, foamed polypropylene resin beads according to any one of [3] to [5], wherein the structural units derived from the other monomers are derived from one or more monomers selected from the group consisting of ethylene, 1-butene, isobutene, and 1-pentene. [8] The extruded, foamed polypropylene resin beads according to any one of [1] to [7], further satisfying the following (iv): (iv) In dynamic viscoelasticity measurement of the base resin at 180°C and an angular frequency ω of 0.1 to 100 rad / sec, the complex viscosity η at ω = 100 rad / sec ＊ １００ [9] The complex viscosity η is 700 Pa·sec or less. ＊ １００

[10] The extruded polypropylene resin foam beads according to any one of [1] to [9], wherein the base resin of the extruded foam beads has a melting point (Tm) of 130.0°C to 165.0°C.

[11] A polypropylene resin foam molded article obtained by molding the extruded polypropylene resin foam beads according to any one of [1] to

[10] .

[12] The polypropylene resin foam molded article according to

[11] , wherein the expansion ratio is 15 to 50 times and the open cell ratio is 30% or less.

[13] The polypropylene resin foam molded article according to

[11] or

[12] , wherein the compressive strength is 0.100 MPa or more.

[14] A method for producing extruded polypropylene resin foam beads according to any one of [1] to

[10] , comprising melt-kneading a mixture containing a polypropylene resin composition containing a branched polypropylene resin (A) and a blowing agent under pressure, cooling the mixture, and then extruding the mixture into a lower-pressure atmosphere to foam and cut it.

[15] A method for producing extruded polypropylene resin foam beads according to

[14] , wherein the branched polypropylene resin (A) is obtained by melt-kneading a mixture containing a linear polypropylene resin (a), one or more monomers (b) selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and a radical polymerization initiator (c). [16 ... loss tangent tanδ at ω = 0.1 rad / sec of the branched polypropylene resin (A), as measured in dynamic viscoelasticity measurement at 180°C and an angular frequency ω of 0.1 to 100 rad / sec. ０．１

[17] The method for producing extruded polypropylene resin foam beads according to

[14] or

[15] , wherein the melt flow rate (MFR) of the polypropylene resin (A) having a branched structure is 0.05 g / 10 min or more and 10 g / 10 min or less.

[18] The method for producing extruded polypropylene resin foam beads according to any of

[15] to

[17] , wherein the conjugated diene is at least one selected from the group consisting of butadiene and isoprene.

[19] The method for producing extruded polypropylene resin foam beads according to any of

[15] to

[18] , wherein the radical polymerization initiator (c) is at least one organic peroxide selected from the group consisting of ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, and peroxyesters.

[20] The method for producing extruded expanded polypropylene resin beads according to any one of

[14] to

[19] , wherein the blowing agent is at least one selected from the group consisting of carbon dioxide gas, normal butane, and isobutane.

[21] The method for producing extruded expanded polypropylene resin beads according to any one of

[14] to

[20] , wherein the amount of the blowing agent used is 0.5 to 7.0 parts by weight per 100.0 parts by weight of the polypropylene resin composition.

[0010] According to the present invention, it is possible to provide extruded foam beads which can have a low open cell ratio even when a high expansion ratio is achieved, and which can give foamed molded articles having a low open cell ratio when the foamed beads are foam-molded, a method for producing the same, and foamed molded articles made from the same.

[0011] <<Extruded Polypropylene Resin Foamed Beads>> The extruded polypropylene resin foamed beads of this embodiment satisfy the following (i) to (iii): (i) The loss tangent tanδ at ω=0.1 rad / sec of the base resin constituting the extruded foamed beads, as measured in a dynamic viscoelasticity measurement at 180°C and an angular frequency ω of 0.1 to 100 rad / sec. ０．１(ii) The expansion ratio is 15 times or more and 35 times or less. (iii) The open cell ratio is 10% or less.

[0012] According to the extruded polypropylene resin foam beads of the present embodiment, a low open cell ratio can be achieved even when the expansion ratio is high, and further, when the foam beads are foam-molded, a foamed molded article having a low open cell ratio can be obtained.

[0013] The above conditions (i) to (iii) will be explained below.

[0014] <Condition (i)> The loss tangent (tan δ) is an index of melt elasticity, and the smaller the tan δ, the stronger the melt elasticity. ０．１ means the loss tangent at an angular frequency ω of 0.1 rad / sec. The loss tangent tanδ at ω = 0.1 rad / sec is measured in dynamic viscoelasticity measurement of the base resin constituting the extruded polypropylene resin foamed beads at 180°C and an angular frequency ω of 0.1 to 100 rad / sec. ０．１ is 0.6 or more and 1.4 or less, preferably 0.6 or more and 1.3 or less, more preferably 0.6 or more and 1.2 or less, even more preferably 0.6 or more and 1.1 or less, even more preferably 0.6 or more and 1.0 or less, and particularly preferably 0.6 or more and 0.95 or less. ０．１ When the ratio is 1.4 or less, the extruded foamed beads can have a low open cell ratio even when the extruded foamed beads are expanded to a high expansion ratio.

[0015] <Condition (ii)> From the viewpoint of weight reduction, the higher the expansion ratio of the extruded polypropylene resin foamed beads, the better. The expansion ratio of the extruded polypropylene resin foamed beads is 15 to 35 times, preferably 16 to 35 times, more preferably 17 to 35 times, and even more preferably 18 to 35 times.

[0016] <Condition (iii)> The lower the open cell rate of the extruded polypropylene resin foamed beads, the better. The open cell rate of the extruded foamed beads is 10% or less, preferably 9% or less, more preferably 8% or less, and even more preferably 7% or less. The lower limit of the open cell rate of the extruded foamed beads is not particularly limited, and is, for example, 0.0% or more. This configuration has the advantage that the cells are less likely to break during molding of the extruded foamed beads, resulting in excellent moldability of the extruded foamed beads, and the extruded foamed beads obtained using the extruded foamed beads exhibit more advantageous features such as shape flexibility, cushioning properties, light weight, compressive strength, and heat insulation properties.

[0017] In this specification, the open cell ratio of extruded polypropylene resin foamed beads is a value determined by measurement using an air-comparison type hydrometer [Tokyo Science Co., Ltd., Model 1000] in accordance with the method described in Procedure C of ASTM D2856-87. Specifically, the open cell ratio of extruded foamed beads is calculated by carrying out the following steps (1) to (3) in order: (1) The volume Vc (cm) of the extruded foamed beads is measured using an air-comparison type hydrometer. ３ (2) Next, the entire amount of the extruded foamed particles after measuring Vc is submerged in ethanol contained in a measuring cylinder; (3) After that, the apparent volume Va (cm 3 ) of the extruded foamed particles is calculated from the amount of rise in the position of the ethanol in the measuring cylinder. ３ (4) The open cell ratio of the extruded foamed beads is calculated using the following formula: Open cell ratio (%) = ((Va - Vc) x 100) / Va. The method for measuring the volume Va is also called the submersion method.

[0018] <Other Conditions> The extruded polypropylene resin foam particles may satisfy conditions (hereinafter also referred to as "other conditions") other than the above-mentioned conditions (i), (ii), and (iii) as long as the effects of the present invention are not impaired. The other conditions include complex viscosity η ＊ , melt flow rate (MFR), etc.

[0019] <Condition (iv): Complex viscosity η ＊The extruded polypropylene resin foam particles preferably satisfy the following (iv): (iv) In dynamic viscoelasticity measurement of the base resin at 180°C and an angular frequency ω of 0.1 to 100 rad / sec, the complex viscosity η at ω=100 rad / sec is ＊ １００ When the extruded foamed beads satisfy the condition (iv), the open cell ratio of the extruded foamed beads becomes lower. ＊ １００ The lower the complex viscosity η of the extruded foam particles, the more preferable. ＊ １００ is more preferably 300 Pa·sec or more and 650 Pa·sec or less, and even more preferably 300 Pa·sec or more and 600 Pa·sec or less.

[0020] <MFR> The melt flow rate (MFR) of the extruded polypropylene resin foam particles is not particularly limited, and is preferably 0.05 g / 10 min or more and 10 g / 10 min or less, more preferably 0.05 g / 10 min or more and 5.0 g / 10 min or less, and even more preferably 0.1 g / 10 min or more and 2.0 g / 10 min or less.

[0021] <Base Resin> The extruded polypropylene resin foam beads of this embodiment contain a polypropylene resin as the base resin. The polypropylene resin preferably contains a random copolymer of a propylene monomer and a monomer other than the propylene monomer. The content of the structural units derived from the other monomers relative to the total amount of structural units derived from the monomers constituting the random copolymer is preferably 0.5% by weight or more and 3.0% by weight or less. By including the specific random copolymer as the base resin, the open cell ratio of the extruded foam beads can be further reduced. In this specification, "structural units derived from a propylene monomer" may also be referred to as "propylene units." In this specification, "structural units derived from a monomer other than a propylene monomer" may also be referred to as "comonomer units." Furthermore, "the random copolymer" may also be referred to as "random polypropylene resin."

[0022] (Random Copolymer) Examples of other monomers (comonomers) besides propylene monomer include α-olefins having 2 or 4 to 12 carbon atoms, such as ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene; cyclic olefins such as cyclopentene, norbornene, and tetracyclo[6,2,11,8,13,6]-4-dodecene; 5- Examples thereof include dienes such as methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, and 7-methyl-1,6-octadiene; and vinyl monomers such as vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, vinyl acetate, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, maleic acid, maleic anhydride, styrene-based monomers, vinyltoluene, and divinylbenzene.

[0023] Examples of acrylic acid esters include methyl acrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and glycidyl acrylate.

[0024] Examples of methacrylic acid esters include methyl methacrylate, ethyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and glycidyl methacrylate.

[0025] Styrenic monomers include styrene, methylstyrene, dimethylstyrene, alpha-methylstyrene, para-methylstyrene, ethylstyrene, diethylstyrene, isopropylstyrene, t-butylstyrene, bromostyrene, dibromostyrene, tribromostyrene, chlorostyrene, dichlorostyrene, and trichlorostyrene.

[0026] The random copolymer preferably has, as a comonomer unit, a structural unit derived from an α-olefin having 2 or 4 to 12 carbon atoms, more preferably a structural unit derived from ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and / or 1-decene, more preferably a structural unit derived from ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, and / or 4-methyl-1-pentene, even more preferably a structural unit derived from ethylene, 1-butene, isobutene, and / or 1-pentene, and particularly preferably a structural unit derived from ethylene and / or 1-butene.

[0027] The content of the comonomer unit is preferably 2.8% by weight or less, more preferably 2.5% by weight or less, based on the total amount of structural units derived from the monomers constituting the random copolymer. The lower limit of the content of the comonomer unit is not particularly limited, and is, for example, 0.1% by weight or more, based on the total amount of structural units derived from the monomers constituting the random copolymer.

[0028] <<Method for producing extruded polypropylene resin foam beads>> The method for producing the extruded polypropylene resin foam beads described above will be described. The method for producing the extruded polypropylene resin foam beads of this embodiment includes melt-kneading a mixture containing a polypropylene resin composition containing a polypropylene resin (A) having a branched structure and a blowing agent under pressure, cooling the mixture, and then extruding the mixture under a lower pressure atmosphere to foam and cut it.

[0029] The polypropylene resin composition and the foaming agent used as raw materials will be described below, and then a specific embodiment of the method for producing extruded polypropylene resin foam beads will be described.

[0030] <Polypropylene Resin Composition> The polypropylene resin composition contains a polypropylene resin (A) having a branched structure (hereinafter also referred to as "branched polypropylene resin (A)"), and may further contain a polypropylene resin (B) into which no branched structure has been introduced (hereinafter also referred to as "linear polypropylene resin (B)"). These components will be described below.

[0031] [Branched Polypropylene Resin (A)] The branched polypropylene resin (A) is a modified polypropylene resin obtained by introducing a branched structure into the linear polypropylene resin (a). The linear polypropylene resin (a) refers to a resin containing 50 mol% or more of structural units derived from propylene monomers, based on 100 mol% of all structural units contained in the resin.

[0032] The method for introducing a branched structure into the linear polypropylene-based resin (a) is not particularly limited, and examples thereof include (1) a method of irradiating the linear polypropylene-based resin (a) with radiation, and (2) a method of melt-kneading a mixture containing the linear polypropylene-based resin (a), one or more monomers (b) selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and a radical polymerization initiator (c).

[0033] A specific example of the method (1) above is the method described in JP-A-2002-542360.

[0034] A specific example of the method (2) above is a method in which a linear polypropylene resin (a), one or more monomers (b) selected from a conjugated diene and a vinyl aromatic compound, and a radical polymerization initiator (c) are melt-kneaded at a temperature at which the linear polypropylene resin (a) melts and the radical polymerization initiator (c) decomposes.

[0035] [Linear Polypropylene Resin (a)] Examples of the linear polypropylene resin (a) include homopolypropylene resin (a1), random polypropylene resin (a2), and block polypropylene resin (a3). Among these, random polypropylene resin (a2) is preferred.

[0036] (Homopolypropylene Resin (a1)) The homopolypropylene resin (a1) refers to a homopolymer of a propylene monomer.

[0037] (Random Polypropylene Resin (a2)) Random polypropylene resin (a2) refers to a random copolymer of a propylene monomer and a monomer other than propylene. Random polypropylene resin (a2) contains 50 mol% or more of structural units derived from propylene monomers and less than 50 mol% of structural units derived from monomers other than propylene monomers, out of 100 mol% of all structural units contained in the resin. In this specification, a "structural unit derived from a propylene monomer" may also be referred to as a "propylene unit". In this specification, a "structural unit derived from a monomer other than a propylene monomer" may also be referred to as a "comonomer unit".

[0038] Examples of the comonomer include α-olefins having 2 or 4 to 12 carbon atoms, such as ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene; cyclic olefins such as cyclopentene, norbornene, and tetracyclo[6,2,11,8,13,6]-4-dodecene; and 5-methylene-2-norbornene. Examples of the vinyl monomer include dienes such as bornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, and 7-methyl-1,6-octadiene; and vinyl monomers such as vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, vinyl acetate, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, maleic acid, maleic anhydride, styrene-based monomers, vinyltoluene, and divinylbenzene.

[0039] Examples of acrylic acid esters include methyl acrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and glycidyl acrylate.

[0040] Examples of methacrylic acid esters include methyl methacrylate, ethyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and glycidyl methacrylate.

[0041] Styrenic monomers include styrene, methylstyrene, dimethylstyrene, alpha-methylstyrene, para-methylstyrene, ethylstyrene, diethylstyrene, isopropylstyrene, t-butylstyrene, bromostyrene, dibromostyrene, tribromostyrene, chlorostyrene, dichlorostyrene, and trichlorostyrene.

[0042] The random polypropylene resin (a2) preferably has, as a comonomer unit, a structural unit derived from an α-olefin having 2 or 4 to 12 carbon atoms, more preferably a structural unit derived from ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and / or 1-decene, more preferably a structural unit derived from ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, and / or 4-methyl-1-pentene, even more preferably a structural unit derived from ethylene, 1-butene, isobutene, and / or 1-pentene, and particularly preferably a structural unit derived from ethylene and / or 1-butene.

[0043] The random polypropylene resin (a2) preferably contains propylene units in an amount of 96 mol% or more, more preferably 96.5 mol% or more, and even more preferably 97 mol% or more, of all structural units (100 mol%) contained in the random polypropylene resin (a2).

[0044] (Block polypropylene resin (a3)) Examples of the block polypropylene resin (a3) ​​include an ethylene-propylene block copolymer, a propylene-butene block copolymer, and an ethylene-propylene-butene block copolymer. The propylene-ethylene block copolymer is a propylene-based polymer in which a polymer mainly composed of ethylene and an ethylene-propylene rubbery copolymer are dispersed in a linear polymer mainly composed of propylene, forming an islands-in-a-sea structure.

[0045] [Monomer (b) Selected from Conjugated Dienes and Vinyl Aromatic Compounds] Examples of conjugated dienes include butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, and 2,5-dimethyl-2,4-hexadiene. These conjugated diene compounds may be used alone or in combination of two or more. Among these conjugated diene compounds, butadiene and isoprene are particularly preferred because they are inexpensive, easy to handle, and the reaction proceeds uniformly.

[0046] Examples of vinyl aromatic compounds include styrene; methylstyrenes such as o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, β-methylstyrene, dimethylstyrene, and trimethylstyrene; chlorostyrenes such as α-chlorostyrene, β-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, dichlorostyrene, and trichlorostyrene; bromostyrenes such as o-bromostyrene, m-bromostyrene, p-bromostyrene, dibromostyrene, and tribromostyrene; o-fluorostyrene, m-fluorostyrene, p-fluorostyrene, and difluorostyrene; Examples of the vinyl aromatic compound include fluorostyrenes such as fluorostyrene and trifluorostyrene; nitrostyrenes such as o-nitrostyrene, m-nitrostyrene, p-nitrostyrene, dinitrostyrene and trinitrostyrene; vinylphenols such as o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, dihydroxystyrene and trihydroxystyrene; divinylbenzenes such as o-divinylbenzene, m-divinylbenzene and p-divinylbenzene; isopropenylstyrenes such as o-diisopropenylbenzene, m-diisopropenylbenzene and p-diisopropenylbenzene, etc. Among the above-mentioned vinyl aromatic compounds, styrene and / or methylstyrene are preferred in terms of low cost, ease of handling, and the tendency for the reaction to proceed uniformly.

[0047] The amount of the conjugated diene or the like (b) used is preferably 0.01 to 5.00 parts by weight, more preferably 0.20 to 3.00 parts by weight, and even more preferably 0.30 to 2.00 parts by weight, relative to 100 parts by weight of the linear polypropylene resin (a).

[0048] [Radical Polymerization Initiator (c)] The radical polymerization initiator (c) is an organic peroxide capable of abstracting hydrogen from the linear polypropylene resin (a) and the conjugated diene compound (b). Examples of the radical polymerization initiator (c) include organic peroxides such as ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, and peroxyesters.

[0049] As the organic peroxide, those with particularly high hydrogen abstraction ability are preferred. Examples of organic peroxides with high hydrogen abstraction ability include peroxyketals such as 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, n-butyl 4,4-bis(t-butylperoxy)valerate, and 2,2-bis(t-butylperoxy)butane; dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, t-butylcumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5- Suitable examples of organic peroxides include dialkyl peroxides such as di(t-butylperoxy)-3-hexyne; diacyl peroxides such as benzoyl peroxide; and peroxyesters such as t-butylperoxyoctate, t-butylperoxyisobutyrate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxyisopropylcarbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate. Among these, t-butylperoxyisopropylcarbonate and / or t-butylperoxybenzoate are preferred. These organic peroxides may be used alone or in combination of two or more.

[0050] The amount of the radical polymerization initiator (c) used is preferably 0.01 to 5.00 parts by weight, more preferably 0.10 to 3.00 parts by weight, more preferably 0.10 to 2.00 parts by weight, and particularly preferably 0.10 to 1.50 parts by weight, relative to 100 parts by weight of the linear polypropylene resin (a).

[0051] In the above method (2), examples of the apparatus for melt-kneading the linear polypropylene-based resin (a), the monomer (b) such as a conjugated diene, and the radical polymerization initiator (c) include kneaders such as rolls, co-kneaders, Banbury mixers, Brabenders, single-screw extruders, and twin-screw extruders; horizontal mixers such as twin-screw surface regenerators and twin-screw multi-disc devices; and vertical mixers such as double helical ribbon mixers. Among these, it is preferable to use a kneader, and extruders such as single-screw extruders and twin-screw extruders are particularly preferable from the viewpoint of productivity.

[0052] The order and method of mixing and kneading the linear polypropylene resin (a), the monomer (b) such as a conjugated diene, and the radical polymerization initiator (c) are not particularly limited. The linear polypropylene resin (a), the monomer (b) such as a conjugated diene, and the radical polymerization initiator (c) may be mixed and then melt-kneaded. Alternatively, the linear polypropylene resin (a) may be melt-kneaded, and then the monomer (b) such as a conjugated diene or the radical polymerization initiator (c) may be mixed simultaneously or separately, all at once, or in portions. The temperature of the kneader is preferably 130°C or higher and 300°C or lower. The melt-kneading time is generally preferably 1 minute or higher and 60 minutes or lower.

[0053] [Physical Properties of Branched Chain Polypropylene Resin (A)] (Melting Point) The melting point (Tm) of the branched chain polypropylene resin (A) is not particularly limited, but is preferably 130.0° C. to 165.0° C., and more preferably 135.0° C. to 163.0° C. In this specification, the melting point is a value determined by measurement using differential scanning calorimetry.

[0054] (MFR) The melt flow rate (MFR) of the branched polypropylene resin (A) is not particularly limited, but is preferably 0.05 g / 10 min or more and 10 g / 10 min or less, more preferably 0.05 g / 10 min or more and 5 g / 10 min or less, and even more preferably 0.1 g / 10 min or more and 2 g / 10 min or less. In this specification, MFR is a value determined by measurement at a temperature of 230°C in accordance with ISO 1133.

[0055] (tanδ ０．１Loss tangent tanδ at ω=0.1 rad / sec of the branched polypropylene resin (A) measured in dynamic viscoelasticity measurement at 180°C and an angular frequency ω of 0.1 to 100 rad / sec ０．１ is not particularly limited, but is preferably 0.2 or more but less than 1.0, more preferably 0.3 or more but 0.9, and even more preferably 0.3 or more but 0.85. ０．１ is less than 1.0, so that tan δ ０．１ Therefore, it becomes easier to obtain extruded polypropylene resin foam particles having a value of 1.4 or less.

[0056] tan δ ０．１ In order to obtain a branched polypropylene-based resin (A) that satisfies the above range, the amounts of the production raw materials used may be appropriately determined. For example, a method of increasing the amount of the monomer (b) used or a method of increasing the amount of the radical polymerization initiator (c) used may be mentioned.

[0057] (complex viscosity η ＊ In dynamic viscoelasticity measurement of the branched chain polypropylene resin (A) at 180°C and an angular frequency ω of 0.1 to 100 rad / sec, the complex viscosity η at ω = 100 rad / sec ＊ １００ is not particularly limited, but is preferably 700 Pa·sec or less.

[0058] (Linear Polypropylene Resin (B)) The linear polypropylene resin (B) is a linear resin that contains 50 mol% or more of structural units derived from propylene monomers, out of 100 mol% of all structural units contained in the resin, and has no branched structure. Examples of the linear polypropylene resin (B) include a propylene homopolymer, a block polypropylene resin, and a random polypropylene resin, with a propylene homopolymer and a random polypropylene resin being preferred, and a random polypropylene resin being more preferred. The random polypropylene resin is the same as the embodiment described above in the section [(Random Polypropylene Resin (a2))].

[0059] (Physical Properties of Linear Polypropylene Resin (B)) The melting point (Tm) of the linear polypropylene resin (B) is not particularly limited, but is preferably 130.0°C to 165.0°C, and more preferably 135.0°C to 163.0°C.

[0060] The upper limit of the melt flow rate (MFR) of the linear polypropylene resin (B) is preferably 5 g / 10 min or less, more preferably 1 g / 10 min or less, from the viewpoint of obtaining an extruded foamed bead molding having good surface properties and high compressive strength. The lower limit of the MFR of the linear polypropylene resin (B) is not particularly limited, but is preferably 0.1 g / 10 min or more, more preferably 0.2 g / 10 min or more.

[0061] In the extruded polypropylene resin foam beads of this embodiment, the weight ratio of the branched polypropylene resin (A) to the linear polypropylene resin (B) is 70:30 to 100:0, preferably 75:25 to 98:2, and more preferably 80:20 to 95:5, from the viewpoint of obtaining a foamed molded article having high compressive strength.

[0062] (Other Components) The polypropylene resin composition may contain components (hereinafter also referred to as "other components") other than the branched polypropylene resin (A) and linear polypropylene resin (B) described above, as long as the effects of the present invention are not impaired. Examples of other components include resins or rubbers other than the resins (A) and (B) (hereinafter also referred to as "other resins, etc."), bubble nucleating agents, stabilizers such as antioxidants, metal deactivators, phosphorus-based processing stabilizers, UV absorbers, UV stabilizers, fluorescent brighteners, metal soaps, and antacid adsorbents, and / or additives such as crosslinkers, chain transfer agents, lubricants, plasticizers, fillers, reinforcing agents, flame retardants, colorants, and antistatic agents. These other components may be used alone or in combination of two or more. The total content of the other components in the polypropylene resin composition is not particularly limited. The total content of the other components in the polypropylene-based resin composition is, for example, preferably 0.01 to 50.00 parts by weight, and more preferably 0.05 to 30.00 parts by weight, relative to 100 parts by weight of the total of the polypropylene-based resin (A) and the polypropylene-based resin (B).

[0063] (Other Resins, etc.) Examples of other resins include ethylene-based resins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear very low-density polyethylene, ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, and ethylene / methacrylic acid copolymer; and styrene-based resins such as polystyrene, styrene / maleic anhydride copolymer, and styrene / ethylene copolymer. Examples of the rubber include olefin-based rubbers such as ethylene / propylene rubber, ethylene / butene rubber, ethylene / hexene rubber, and ethylene / octene rubber. The total content of the other resins and rubbers in the base resin is not particularly limited. The total content of the other resins and rubbers in the polypropylene-based resin composition is, for example, preferably 1 to 30 parts by weight, more preferably 2 to 15 parts by weight, per 100 parts by weight of the total of the polypropylene-based resin (A) and the polypropylene-based resin (B).

[0064] (Gas nucleating agent) Examples of the gas nucleating agent include sodium bicarbonate-citric acid mixture, monosodium citrate, talc, calcium carbonate, etc. These gas nucleating agents may be used alone or in combination of two or more.

[0065] The content of the bubble nucleating agent in the polypropylene resin composition is not particularly limited. For example, the content of the bubble nucleating agent is preferably 0.01 to 5.00 parts by weight, more preferably 0.01 to 3.50 parts by weight, even more preferably 0.01 to 1.00 parts by weight, and particularly preferably 0.01 to 0.50 parts by weight, relative to 100 parts by weight of the total of the polypropylene resin (A) and the polypropylene resin (B). This configuration has the advantage that the average cell diameter and cell shape of the extruded foamed beads become uniform, and as a result, the foamability during extrusion foaming tends to be more stable.

[0066] <Blowing Agent> The blowing agent used in the production method of this embodiment is not particularly limited as long as it is a blowing agent commonly used in extrusion foaming. Examples of blowing agents include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane; alicyclic hydrocarbons such as cyclopentane and cyclobutane; ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether; alcohols such as methanol and ethanol; inorganic gases such as air, nitrogen, and carbon dioxide; physical blowing agents such as water; and chemical blowing agents including thermal decomposition blowing agents such as sodium bicarbonate, azodicarbonamide, and dinitrosopentamethylenetetramine. Among these, inorganic gases and physical blowing agents are preferred from the standpoint of environmental impact.

[0067] The amount of the foaming agent used is preferably 0.5 to 7.0 parts by weight, more preferably 1.0 to 6.0 parts by weight, and even more preferably 1.5 to 5.0 parts by weight, per 100.0 parts by weight of the polypropylene resin composition.

[0068] <Step of Obtaining Melt-Kneaded Product> Examples of extruders used to obtain the melt-kneaded product include single-screw extruders and twin-screw extruders. Among these, twin-screw extruders are preferred because of their excellent melt-kneading properties.

[0069] The cylinder temperature of the extruder is not particularly limited and can be appropriately set depending on the melting point of the polypropylene resin composition used, the type and amount of the blowing agent used, etc., from the viewpoint of sufficiently melt-kneading the polypropylene resin composition and the blowing agent. For example, the cylinder temperature of the extruder is preferably 150°C or higher and 250°C or lower, more preferably 170°C or higher and 230°C or lower.

[0070] <Step of cooling the melt-kneaded product and then extruding it under a lower pressure atmosphere to foam> Examples of cooling devices used to cool the obtained melt-kneaded product include a single-screw extruder, a static mixer, and a melt cooler. In the cooling device, a die for extruding the cooled melt-kneaded product is provided at the tip of the extrusion direction of the melt-kneaded product. The temperature of the cooling device is not particularly limited as long as it is a temperature suitable for foaming the obtained melt-kneaded product. For example, the temperature of the cooling device is preferably 120°C or higher and 180°C or lower, and more preferably 130°C or higher and 170°C or lower.

[0071] The cooled molten mixture is extruded through holes provided in the die into a region where the pressure is lower than the internal pressure of the cooling device (hereinafter also referred to as the "low-pressure region"). The molten mixture may be extruded into a gas phase or a liquid phase. The pressure in the low-pressure region is not particularly limited, but is preferably 5 MPa or less, and more preferably 1 MPa or less. The extruded molten mixture immediately begins to foam, and when foaming is completed, an extruded polypropylene resin foam is obtained.

[0072] The foaming step may further include a shredding step of cutting the extruded molten kneaded material into particles. In the shredding step, the molten kneaded material (extruded foam) may be shredded during foaming, or the molten kneaded material (extruded foam) may be shredded after foaming has finished. The method for shredding the extruded molten kneaded material is not particularly limited. For example, the molten kneaded material may be shredded along the extrusion direction using a cutter or the like provided next to the die. Through the above steps, extruded polypropylene resin foam particles are obtained.

[0073] The low-pressure region may be a gas phase or a liquid phase, but is preferably a gas phase because it is easier to obtain expanded beads with a relatively high expansion ratio. Water or the like may be sprayed onto the surface of the expanded beads cut in the gas phase to cool them.

[0074] [Physical Properties of Extruded Foamed Beads] The melting point, MFR, and tan δ of the base resin of the extruded foamed beads ０．１、 Complex viscosity η ＊ is measured by removing the air from the extruded foam particles and returning them to the resin, as described in the Examples.

[0075] (Melting Point) The melting point (Tm) of the base resin of the extruded foamed beads is not particularly limited, but is preferably 130.0° C. to 165.0° C., and more preferably 135.0° C. to 163.0° C. In this specification, the melting point is a value determined by measurement using differential scanning calorimetry.

[0076] (MFR) The melt flow rate (MFR) of the base resin is not particularly limited, but is preferably 0.05 g / 10 min or more and 10 g / 10 min or less, more preferably 0.05 g / 10 min or more and 5.0 g / 10 min or less, and even more preferably 0.1 g / 10 min or more and 2.0 g / 10 min or less. In this specification, MFR is a value determined by measurement in accordance with ISO 1133 under conditions of a temperature of 230°C and a load of 2.16 kg.

[0077] (tanδ ０．１ Loss tangent tanδ at ω=0.1 rad / sec, measured by dynamic viscoelasticity measurement of the base resin at 180°C and an angular frequency ω of 0.1 to 100 rad / sec ０．１is not particularly limited, but is 0.6 or more and 1.4 or less, preferably 0.6 or more and 1.3 or less, more preferably 0.6 or more and 1.2 or less, even more preferably 0.6 or more and 1.1 or less, even more preferably 0.6 or more and 1.0 or less, and particularly preferably 0.6 or more and 0.95 or less. ０．１ In order to obtain a base resin in which the amount of the monomer (b) satisfies the above range, the amounts of the raw materials used for production may be appropriately set. For example, a method of increasing the amount of the monomer (b) used or a method of increasing the amount of the radical polymerization initiator (c) used may be mentioned.

[0078] (complex viscosity η ＊ In dynamic viscoelasticity measurement of the base resin at 180°C and an angular frequency ω of 0.1 to 100 rad / sec, the complex viscosity η at ω = 100 rad / sec ＊ １００ is not particularly limited, but is more preferably 300 Pa·sec or more and 650 Pa·sec or less, and even more preferably 300 Pa·sec or more and 600 Pa·sec or less.

[0079] <<Foam Molded Article>> The polypropylene-based resin foam molded article of this embodiment is an in-mold molded article made from the extruded polypropylene-based resin foam beads described above. The polypropylene-based resin foam molded article can be obtained by filling the extruded foam beads into a mold that can be closed but not hermetically sealed, and then heating and molding with steam or the like. Examples of methods for producing the foam molded article include: (a) a method in which the foam beads are pressurized with an inorganic gas to impregnate the particles with the inorganic gas and apply a predetermined internal particle pressure, and then the particles are filled into a mold and heat-sealed with steam or the like (e.g., JP-B-51-22951); (b) a method in which the foam beads are compressed with gas pressure, filled into a mold, and heat-sealed with steam or the like by utilizing the recovery force of the particles (e.g., JP-B-53-33996); and (c) a method in which the foam beads are filled into a mold with an expanded gap, the mold is closed to a predetermined gap, the filled foam beads are compressed, and then heat-sealed with steam or the like.

[0080] <Physical Properties of Foam Molded Article> (Expansion Ratio) The expansion ratio of the polypropylene resin foam molded article is not particularly limited, but is preferably 15 to 50 times, and more preferably 15 to 30 times.

[0081] (Open Cell Ratio) The lower the open cell ratio of the polypropylene resin foam molded product, the better. From the viewpoint of obtaining an extruded foam bead molded product with high compressive strength, the open cell ratio of the foam molded product is preferably 30% or less, more preferably 25% or less, even more preferably 20% or less, and even more preferably 15% or less. The lower limit of the open cell ratio of the extruded foam bead molded product is not particularly limited, and is, for example, 0.0% or more, preferably 2% or more.

[0082] (Compression Strength) The compression strength of the polypropylene resin foam molded article is not particularly limited, but is preferably 0.100 MPa or more, more preferably 0.120 MPa or more, and even more preferably 0.150 MPa or more.

[0083] In this specification, the compressive strength of a foam molded article is the value of compressive stress at 50% strain when compressed at a compression rate of 10 mm / min using a tension and compression testing machine.

[0084] The foamed molded article is suitably used for automobile interior parts, core materials for automobile bumpers, heat insulating materials, cushioning packaging materials, etc.

[0085] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0086] Examples 1 to 8, Comparative Examples 1 to 4 (Branched Random Polypropylene Resin (A)) In the examples and comparative examples, the following MP-1 was produced as the branched random polypropylene resin (A).

[0087] (Production Example of MP-1) The raw resin F724NPC (manufactured by Prime Polymer Co., Ltd., linear random polypropylene resin, MFR: 7 g / 10 min) was fed to a twin-screw extruder at 70 kg / h, and then 1.0 part by weight of the radical polymerization initiator t-butylperoxyisopropyl carbonate (manufactured by NOF Corporation, Perbutyl (registered trademark) I) was fed to the twin-screw extruder per 100 parts by weight of the raw resin. Thereafter, 0.78 parts by weight of the conjugated diene compound isoprene (manufactured by Kuraray Co., Ltd., isoprene monomer) was fed to the twin-screw extruder containing the melt-kneaded raw resin and radical polymerization initiator, per 100 parts by weight of the raw resin, to prepare a resin mixture in the twin-screw extruder. The feed rate of the resin mixture to the twin-screw extruder was 70 kg / h. The prepared resin mixture was melt-kneaded in a twin-screw extruder at a cylinder temperature of 200°C and a screw rotation speed of 230 rpm, and the extruded strand was water-cooled and then chopped into pellets (cylindrical) to obtain MP-1.

[0088] (Production Examples of MP-2 to MP-9) In the Examples and Comparative Examples, MP-2 to MP-9 were produced as the branched random polypropylene resin (A). Specifically, MP-2 to MP-9 were produced under the same conditions as in the Production Example of MP-1, except that the raw materials shown in Table 1 were used in the amounts shown in Table 1.

[0089] (Linear Polypropylene Resin (B)) In the Examples and Comparative Examples, the following resin (B) was used as the linear polypropylene resin (B). Resin B: Linear random polypropylene resin (B221WC, melting point 149°C, MFR: 0.5 g / 10 min) manufactured by Prime Polymer Co., Ltd.

[0090] (Production Examples of Extruded Foamed Beads: Examples 1-7, Comparative Examples 1-4) The extruded foamed beads were produced using a twin-screw extruder with a shaft diameter of 15 mm, a melt cooler, a diverter valve, and a die connected in series. 0.02 parts by weight of talc (Talc Powder PK-S (registered trademark), manufactured by Hayashi Kasei Co., Ltd.) as a bubble nucleating agent was dry-blended with 100 parts by weight of the resin shown in Table 2 to prepare a polypropylene resin composition for extrusion foaming. The resin composition was then fed at 0.75 kg / h into a twin-screw extruder set to the cylinder temperature shown in Table 2, and melt-kneaded at a screw rotation speed of 40 rpm. Furthermore, 4.0 parts by weight of carbon dioxide gas, the foaming agent, per 100 parts by weight of the resin composition was fed using a metering pump through an injection port installed midway through the extruder, and the resulting composition was further melt-kneaded. The resulting melt-kneaded product was cooled by passing it through a melt cooler connected to the tip of the twin-screw extruder and set to the temperature shown in Table 2. The product was then extruded into the atmosphere through a die (φ0.7 mm × 2 holes) attached to the tip of the melt cooler to cause foaming, and the foam was quickly cut with a cutter (4 blades, 750 rpm) to obtain extruded foam particles weighing 2.1 mg / particle. The granulation method used here was the watering cut method (hereinafter also referred to as the WRC method), in which water was run along the wall so that the foamed particles after cutting would come into contact with water and be discharged outside the system. The temperature of the water used in the WRC was 15 to 35°C.

[0091] (Production Example of Extruded Foamed Beads: Example 8) The extruded polypropylene resin foamed beads obtained in Example 1 were placed in a pressure-resistant vessel, and the pressure was increased with air at a pressure increase rate of 0.05 MPa / h to 0.15 MPa G, and maintained at that pressure for 20 hours. Thereafter, the pressure of the pressure-resistant vessel was adjusted, if necessary, so that the internal pressure of the expanded beads was 0.18 MPa (absolute pressure). The pressurized polypropylene resin foamed beads were placed in the pressure-resistant vessel and heated at a water vapor pressure of 0.12 MPa G for 20 seconds to expand, thereby obtaining two-stage expanded beads of Example 8.

[0092] (Example of Production of Foam Molded Articles) Using each of the obtained extruded polypropylene resin beads, extruded polypropylene resin beads were produced by the following method. Each extruded polypropylene resin beads was placed in a pressure-resistant container, and the pressure was increased to 0.20 MPa·G with air at a pressure increase rate of 0.05 MPa / h and maintained at that pressure for 20 hours. Thereafter, the pressure of the pressure-resistant container was adjusted, if necessary, so that the internal pressure of the foamed beads was 0.20 MPa (absolute pressure). A block-shaped mold (molding space: length 381 mm × width 320 mm × thickness variable) was adjusted to a molding space thickness of 44 mm (cracking rate 10%). Next, the molding space of the mold was filled with the extruded polypropylene resin beads to which internal pressure had been applied. The mold was then moved so that the molding space thickness within the mold was 40 mm, and the molding space was compressed. Next, the air in the mold was expelled with steam at 0.10 MPa G, and then the mold was heated and molded for 7 seconds using steam with a vapor pressure of 0.26 MPa G to fuse the foamed particles together and produce a foamed molded article. Next, the steam in the mold was removed through the drain valve over 10 seconds, and the mold was water-cooled until the surface pressure gauge attached to the mold reached 0.05 MPa G, yielding a foamed molded article. The obtained polypropylene resin foamed molded article was dried at 75°C for 16 hours or more and allowed to stand at 23°C for 24 hours or more, after which various evaluations were performed.

[0093] <Evaluation> The resin (A) was evaluated for MFR and tanδ according to the following methods. ０．１ , complex viscosity η ＊ １００ The results are shown in Table 1. The extruded polypropylene resin foam particles were measured for MFR, expansion ratio, open cell ratio, and tanδ according to the following methods. ０．１ , complex viscosity η ＊ １００ The amount of comonomer was measured. ０．１ , complex viscosity η ＊ １００The comonomer content was measured by returning the extruded foamed beads to a resin using the following method. The results are shown in Table 2. The expansion ratio and open cell ratio of the foamed molded articles were measured using the following method. In addition, a compression test was conducted on the extruded foamed beads to measure the compressive strength at 50% strain. The results are shown in Table 2.

[0094] [Resin (A)] (MFR) was determined in accordance with the provisions of Method B of ISO 1133 (1997) using a Melt Indexer S-01 (manufactured by Toyo Seiki Seisakusho) under conditions of 230°C and 2.16 kg, converting the amount of resin extruded from a die in a certain time into the amount extruded in 10 minutes. Note that the certain time is 120 seconds when the melt flow rate is 1.0 g / 10 min or less; 60 seconds when it is greater than 1.0 g / 10 min and 3.5 g / 10 min or less; and 30 seconds when it is greater than 3.5 g / 10 min and 10 g / 10 min or less.

[0095] (tanδ ０．１ , complex viscosity η ＊ １００ ) Using a 1.5 mm thick spacer, a 1.5 mm thick press plate was prepared by hot pressing at 190°C for 5 minutes, and a 25 mm diameter punch was used to punch out a plate to serve as a test specimen. The measurement device used was an Anton Paar MCR viscoelasticity measuring device. The measurement conditions were a 25 mm diameter parallel plate jig, a measurement temperature of 180°C, a plate spacing of 1.0 mm, and a strain of 5%. The procedure involved preheating the jig to the measurement temperature, then sandwiching the test specimen between the parallel plates of the jig, and adjusting the plate spacing to a predetermined value while melting the test specimen. Furthermore, any resin that protruded from the plates was scraped off and removed, and the specimen was again preheated for 5 minutes to stabilize the temperature. After confirming that the temperature had stabilized sufficiently in air, dynamic viscoelasticity measurement was initiated. The measurement was performed at an angular frequency ω ranging from 0.1 rad / s to 100 rad / s. After obtaining the measured values ​​of the storage modulus G' and loss modulus G" at the measured angular frequency, the loss tangent tanδ and complex viscosity η* were calculated according to the following formulas: tanδ = G" / G' η* = √(G'^2 + G"^2) / ω where tanδ ０．１is tan δ at ω = 0.1 rad / s, η ＊ １００ is η at ω = 100 rad / s ＊ is.

[0096] [Extruded Foamed Beads] (Expansion Ratio) The expansion ratio of extruded polypropylene resin foamed beads was determined by measuring the mass w1 (g) of the foamed beads, then immersing the foamed beads in a measuring cylinder containing ethanol, and measuring the volume v1 (cm) by the amount of rise in the water level in the measuring cylinder (submersion method). ３ ) is measured, and the true specific gravity ρb = w1 / v1 of the expanded beads is calculated, and further, the ratio (ρr / ρb) to the resin density ρr before expansion can be calculated. The resin density ρr before expansion is measured using a resin obtained by melt-kneading a resin with the same composition as the expanded beads in the absence of a blowing agent. After measuring the mass w2 (g) of the resin, the resin is submerged in a measuring cylinder containing ethanol, and the volume v2 (cm ３ ) is measured and calculated as ρr = w2 / v2.

[0097] (Open Cell Ratio) This was calculated according to the method described in Procedure C of ASTM D2856-87 by carrying out the following steps (1) to (3) in order: (1) The volume Vc (cm) of the extruded foam particles was measured using an air comparison type hydrometer. ３ (2) Next, the entire amount of the extruded foamed particles after measuring Vc was submerged in ethanol contained in a measuring cylinder. (3) After that, the apparent volume Va (cm) of the extruded foamed particles was calculated from the amount of rise in the position of the ethanol in the measuring cylinder. ３ (4) The open cell ratio of the extruded foamed beads was calculated using the following formula: Open cell ratio (%) = ((Va - Vc) x 100) / Va

[0098] The melting point of the extruded foam particles was measured according to the following method. If foam particles are not available, the melting point of a foamed molded product may be measured and used as the melting point of the foam particles. (Melting Point) Using a Seiko Instruments Inc. DSC6200 differential scanning calorimeter, the following steps (1) to (3) were carried out. (1) The sample was melted by increasing the temperature from 40°C to 220°C at a heating rate of 10°C / min. (2) The sample was then crystallized by decreasing the temperature from 220°C to 40°C at a heating rate of 10°C / min. (3) The crystallized sample was then further increased in temperature from 40°C to 220°C at a heating rate of 10°C / min. The peak temperature (melting peak) of the DSC curve of the sample obtained during the second heating (i.e., during step (3)) was taken as the melting point Tm.

[0099] Comonomer amount, MFR, tanδ ０．１ , complex viscosity η ＊ １００ Since the value of β-glucan cannot be measured using expanded beads, it was measured after returning the expanded beads to resin by the following method. If expanded beads are not available, the expanded molded article may be returned to resin and used.

[0100] (Sample Preparation: Method of Returning to Resin) Based on the melting point Tm of the extruded foam particles measured with a differential scanning calorimeter, the extruded foam particles were placed in a dryer set at Tm + 10°C, and the pressure inside the dryer was reduced to -0.05 MPa·G to -0.10 MPa·G over 5 to 10 minutes using a vacuum pump. The foam particles were then left to stand in the dryer for 30 minutes to remove the air from the foam particles and form a resin block. If the resin particles stuck together and the block was large, the resin block was cut into small pieces with scissors or crushed in a mixer. When the foamed product was returned to a resin block, pieces of the foamed product cut into small pieces with scissors or a slicer, or pieces crushed in a mixer, were used and returned to a resin block in the same manner as above using a vacuum dryer.

[0101] (Amount of Comonomer) Approximately 90 mg of resin collected from the resin mass obtained in the above (Sample Preparation: Method of Returning to Resin) was used as a measurement sample. The measurement sample was dissolved in deuterated orthodichlorobenzene (ODCB-d4) at 150°C, and then 13C-NMR measurement was performed at 120°C using a Bruker NMR measurement device AVANCE NEO 700. Each peak appearing in the obtained NMR chart was assigned according to Macromolecules; 17, 1950 (1984) and assigned to six types of triads: PPP, PPE, EPE, PEP, EEP, and EEE. In addition, the abundance ratio of each triad was calculated in weight fraction from each area. Furthermore, the content, expressed as weight fraction, of monomers other than propylene monomer among the monomers constituting the random copolymer was calculated according to the following formula:

[0102] Content (wt%) of monomers other than propylene monomer expressed as weight fraction = ([PEP] + [EEP]) / ([PPP] + [PPE] + [EPE] + [PEP] + [EEP]) *In the formula, [PEP] is the abundance ratio of triad PEP expressed as weight fraction (%).

[0103] (MFR, tanδ ０．１ , complex viscosity η ＊ １００ ) MFR and tanδ of resin (A) ０．１ , complex viscosity η ＊ １００ Using the same method as in Example 1, the MFR and tanδ of the extruded polypropylene resin foam particles were ０．１ , complex viscosity η ＊ １００ was measured.

[0104] [Expansion Molded Article] (Expansion Ratio) A sample piece having a length / width / thickness of 25 / 25 / 25 mm (no skin layer on the entire surface) was cut out from an extruded polypropylene resin foamed bead molded article. After standing at 23° C. for 24 hours or more, the weight of the sample piece was measured, and the volume of the sample piece was measured by the water immersion method in the same manner as for the expansion ratio of the foamed beads, and the expansion ratio was calculated.

[0105] (Open Cell Ratio) A sample piece having a length / width / thickness of 25 / 25 / 25 mm (no skin layer on the entire surface) was cut out from an extruded polypropylene resin foamed bead molding. After standing at 23° C. for 24 hours or more, the open cell ratio of the extruded polypropylene resin foamed bead molding was measured using the same method as that for measuring the open cell ratio of foamed beads.

[0106] (Compression Test) A rectangular parallelepiped with a length / width / thickness of 50 / 50 / 25 mm (no skin layer on the entire surface) was cut out from the obtained extruded polypropylene resin foam beads to prepare a test specimen. The test specimen was left standing for 24 hours or more in an environment of 23°C and 50% humidity, after which the weight and dimensions were measured, and the density of the test specimen was calculated and converted into an expansion ratio. The test specimen was then compressed at a compression rate of 10 mm / min using a tension / compression tester (e.g., TG-50kN, manufactured by MinebeaMitsumi Inc.), and the compressive stress value at 50% strain was measured. The obtained value was taken as the compressive strength of the foam molded product.

[0107]

[0108]

[0109] From Table 2, tan δ ０．１ It has been found that expanded beads made of a base resin having a ρ of 1.4 or less can have a low open cell ratio even when expanded to a high expansion ratio of 15 times or more, and further that when these expanded beads are foam-molded, foamed molded articles having a low open cell ratio can be obtained.

Claims

1. Extruded polypropylene resin foamed beads satisfying the following (i) to (iii): (i) a loss tangent tanδ at ω=0.1 rad / sec of the base resin constituting the extruded foamed beads, as measured in a dynamic viscoelasticity measurement at 180°C and an angular frequency ω of 0.1 to 100 rad / sec; ０．１ (ii) The expansion ratio is 15 times or more and 35 times or less. (iii) The open cell ratio is 10% or less.

2. The loss tangent tanδ ０．１ The extruded polypropylene resin foam particles according to claim 1, wherein the value of the ρ is 0.6 or more and 1.2 or less.

3. The extruded polypropylene resin foam particles according to claim 1, wherein the polypropylene resin contained in the base resin comprises a random copolymer of a propylene monomer and a monomer other than the propylene monomer, and the content of structural units derived from the other monomers relative to the total amount of structural units derived from the monomers constituting the random copolymer is 3.0% by weight or less.

4. The extruded polypropylene resin foam particles according to claim 3, wherein the content of structural units derived from the other monomers is 2.8% by weight or less.

5. The extruded polypropylene resin foam particles according to claim 3 or 4, wherein the structural units derived from the other monomers include structural units derived from an α-olefin having 2 or 4 to 12 carbon atoms.

6. The extruded polypropylene resin foam particles according to claim 3 or 4, wherein the structural units derived from the other monomers include structural units derived from one or more monomers selected from the group consisting of ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene.

7. The extruded polypropylene resin foam particles according to claim 3 or 4, wherein the structural units derived from the other monomers include structural units derived from one or more monomers selected from the group consisting of ethylene, 1-butene, isobutene, and 1-pentene.

8. The extruded polypropylene resin foam beads according to claim 1 or 2, further satisfying the following (iv): (iv) When the base resin is subjected to dynamic viscoelasticity measurement at 180°C and an angular frequency ω of 0.1 to 100 rad / sec, the complex viscosity η at ω = 100 rad / sec is ＊ １００ is 700 Pa·sec or less.

9. The complex viscosity η ＊ １００ The extruded polypropylene resin foam particles according to claim 8, wherein the viscosity is 300 Pa·sec or more and 650 Pa·sec or less.

10. A polypropylene resin foam molded article obtained by molding the extruded polypropylene resin foam beads according to claim 1 or 2.

11. The polypropylene resin foam molded article according to claim 10, having an expansion ratio of 15 to 50 times and an open cell ratio of 30% or less.

12. A method for producing extruded polypropylene resin foam beads according to claim 1 or 2, comprising melt-kneading a mixture containing a polypropylene resin composition containing a polypropylene resin (A) having a branched structure and a foaming agent under pressure, cooling the mixture, and then extruding the mixture under a lower pressure atmosphere to foam the mixture and cut it.

13. A method for producing extruded polypropylene resin foam beads according to claim 12, wherein the polypropylene resin (A) having a branched structure is obtained by melt-kneading a mixture containing a linear polypropylene resin (a), one or more monomers (b) selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and a radical polymerization initiator (c).

14. The loss tangent tanδ at ω = 0.1 rad / sec of the polypropylene resin (A) having a branched structure, measured in dynamic viscoelasticity measurement at 180°C and an angular frequency ω of 0.1 to 100 rad / sec. ０．１ The method for producing extruded polypropylene resin foam beads according to claim 12, wherein the value of the ρ is 0.2 or more and less than 1.

0.

15. The method for producing extruded polypropylene resin foam beads according to claim 12, wherein the polypropylene resin (A) having a branched structure has a melt flow rate (MFR) of 0.05 g / 10 min or more and 10 g / 10 min or less.