Extruded foam particles and method for producing the same

Abstract

The present invention addresses the problem of inexpensively providing polypropylene resin extruded foam particles that exhibit an excellent moldability. A method for producing polypropylene resin extruded foam particles has a T of 10-25 and a step for passing a composition that has been melt-kneaded with an extruder through a die in the liquid phase region and extruding the same. The composition contains a foaming agent and a resin mixture that contains a polypropylene resin, and T = (temperature A of the composition immediately after introduction into the die) - (melting point of the resin mixture) + (amount of foaming agent used) x 2.5 - {(temperature A - liquid phase temperature) x 0.08}.

Description

[Technical Field]

[0001] The present invention relates to extruded foam particles and a method for producing the same. [Background technology]

[0002] The polypropylene resin in-mold foamed articles obtained using the expanded polypropylene resin beads have the advantages of in-mold foamed articles, such as flexibility in shape, excellent shock-absorbing properties, light weight, and heat insulation.

[0003] An example of a technique for obtaining expanded polypropylene resin beads by extrusion foaming is the technique described in Patent Document 1. Patent Document 1 discloses a method for producing pre-expanded beads of a thermoplastic resin, which comprises melting a thermoplastic resin using an extruder, mixing a foaming agent therein, followed by cooling and extruding the melted thermoplastic resin, and then cutting the extruded foam into pre-expanded beads while foaming the resin to a diameter 1.5 to 10.5 times the diameter of the nozzle of the extrusion die, or after completing the foaming, and then cutting the extruded foam into pre-expanded beads.

[0004] An example of an apparatus used to obtain expanded polypropylene resin particles by the extrusion foaming method is the apparatus described in Patent Document 2. Patent Document 2 discloses an extrusion method for producing foam pellets, which includes the steps of extruding a polymer melt through an extrusion die into a shredding chamber having a fluid inlet, a pellet suspension outlet, and a cutter assembly having a plurality of cutter blades, and shredding the extruded melt to produce one or more pellets. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-011041 [Patent Document 2] International Publication No. WO2018 / 006040 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above-mentioned conventional techniques are not sufficient from the viewpoint of inexpensively obtaining polypropylene resin foam particles having excellent moldability by the extrusion foaming method.

[0007] One embodiment of the present invention has been made in view of the above-mentioned problems, and its object is to provide extruded polypropylene resin foam beads which are excellent in moldability at low cost. [Means for solving the problem]

[0008] That is, a method for producing extruded polypropylene resin foam beads according to one embodiment of the present invention comprises a melt-kneading step of melt-kneading a composition containing a resin mixture containing a polypropylene resin having a branched structure and a blowing agent using an extruder equipped with a die, an extrusion step of extruding the composition through the die into a region that is under a lower pressure than the extruder and is in a liquid phase, a chopping step of chopping the composition in the region, and a step of obtaining extruded polypropylene resin foam beads, wherein the blowing agent is carbon dioxide gas, and the use of the blowing agent The amount of the composition is 0.5 to 7.0 parts by weight relative to 100.0 parts by weight of the resin mixture, the temperature A of the composition immediately after entering the die is the melting point of the resin mixture + 0°C to the melting point + 30°C, the temperature B of the liquid phase is 20°C to 90°C, and the value T calculated by the following formula (1) is 10 to 25: T = (the temperature A) - (the melting point) + (the amount of the blowing agent used) x 2.5 - {(the temperature A - the temperature B) x 0.08} formula (1). [Effects of the Invention]

[0009] According to one embodiment of the present invention, it is possible to provide extruded polypropylene resin foam beads having excellent moldability at low cost. DETAILED DESCRIPTION OF THE INVENTION

[0010] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0011] Unless otherwise specified in this specification, the structural unit is X 1 The structural units derived from the monomer and X 2 Structural units derived from monomers and X n A copolymer containing a monomer (n is an integer of 2 or more) is referred to as "X 1 / X 2 / ··· / X n Also called "copolymer". X 1 / X 2 / ··· / X n Unless otherwise specified, the copolymer is not particularly limited in terms of the polymerization mode, and may be a random copolymer, a block copolymer, or a graft copolymer.

[0012] 1. Technical Concept of One Embodiment of the Present Invention The present inventors decided to use only carbon dioxide gas as a blowing agent in order to produce extruded polypropylene resin foam particles at low cost. Compared with using organic blowing agents such as butane and pentane, using only carbon dioxide gas as a blowing agent has the advantage of lower production costs and a smaller environmental impact because there is no need to make the production equipment explosion-proof.

[0013] When an organic blowing agent is used as the blowing agent, it is relatively easy to control the manufacturing process, and it has been easy to obtain extruded polypropylene resin foamed beads with excellent moldability. However, when extruded polypropylene resin foamed beads are manufactured using only carbon dioxide gas as the blowing agent and by a conventional method except for using carbon dioxide gas, the resulting extruded polypropylene resin foamed beads have poor moldability. The reason for this is unclear, but it is thought to be as follows.

[0014] Carbon dioxide gas is an inorganic gas and therefore does not mix well with polypropylene-based resins. Therefore, when carbon dioxide gas is used, conventional knowledge (e.g., manufacturing conditions) regarding the effect of organic blowing agents on the physical properties (e.g., plasticity, viscosity, etc.) of molten resins cannot be utilized. As a result, when carbon dioxide gas is used, conventional manufacturing conditions for obtaining extruded polypropylene-based resin foamed particles with excellent moldability using organic blowing agents cannot be utilized with only slight modifications.

[0015] Therefore, the present inventors have investigated various production conditions in order to obtain extruded polypropylene resin foam particles that are excellent in moldability even when carbon dioxide gas is used.

[0016] As a result, the present inventors independently discovered that, in order to obtain extruded polypropylene resin foam particles having excellent moldability using carbon dioxide gas, it is important to adjust the temperature of the molten resin immediately after entering the die and the amount of foaming agent used.

[0017] Next, the present inventors decided to adopt the underwater cut (UWC) method among the techniques for obtaining expanded polypropylene resin particles by extrusion foaming. The UWC method is a method in which a composition (also referred to as a molten resin) obtained by melt-kneading in an extruder is extruded through a die into a liquid phase (e.g., underwater), and the composition is shredded by a shredding unit (e.g., a cutter) provided immediately after the die in the liquid phase. On the other hand, there is also a method in which a composition obtained by melt-kneading in an extruder is extruded through a die into a gas phase such as air, and the composition is shredded by a shredding unit provided immediately after the die in the gas phase. In this specification, for convenience, the "method of extruding a molten resin into a gas phase such as air and shredding the molten resin" will hereinafter be referred to as the "gas-phase cutting method."

[0018] Compared to the gas-phase cutting method, when using the UWC method, it is not easy to control the temperature of the molten resin immediately after entering the die, and controlling this temperature becomes increasingly important. This is because the thermal conductivity of the liquid phase is higher than that of the gas phase. Therefore, when using the UWC method with a liquid phase set at a temperature lower than the die temperature, the temperature of the die in contact with the liquid phase may decrease compared to when using the gas-phase cutting method. As a result, compared to when using the gas-phase cutting method, when using the UWC method, the molten resin immediately after entering the die may cool and solidify while passing through the die, which may cause the resin to clog in the die.

[0019] Therefore, the present inventors further investigated various production conditions in order to obtain extruded polypropylene resin foamed beads having excellent moldability even when the UWC method using carbon dioxide gas is carried out.

[0020] As a result, the inventors independently obtained the following new findings, which led to the completion of the present invention: The temperature of the molten resin immediately after entering the die, the amount of blowing agent used, and the temperature of the liquid phase (e.g., water) are adjusted so that the value T calculated by the above formula (1) becomes a specific value in accordance with the melting point of the resin mixture containing the polypropylene-based resin. This makes it possible to provide extruded polypropylene-based resin foamed beads with excellent moldability, even when using the UWC method that uses carbon dioxide gas.

[0021] 2. Method for producing extruded polypropylene resin foam particles A method for producing extruded polypropylene-based resin foamed beads according to one embodiment of the present invention comprises the steps of: a melt-kneading step of melt-kneading a composition containing a resin mixture containing a polypropylene-based resin having a branched structure and a blowing agent using an extruder equipped with a die; an extrusion step of extruding the composition through the die into a region where the pressure is lower than that of the extruder and the region is a liquid phase; a chopping step of chopping the composition in the region; and a step of obtaining extruded polypropylene-based resin foamed beads, wherein the blowing agent is carbon dioxide gas, the amount of the blowing agent used is 0.5 to 7.0 parts by weight per 100.0 parts by weight of the resin mixture, the temperature A of the composition immediately after entering the die is the melting point of the resin mixture + 0°C to the melting point + 30°C, the temperature B of the liquid phase is 20 to 90°C, and the value T calculated by the following formula (1) is 10 to 25: T=(the temperature A)−(the melting point)+(the amount of the foaming agent used)×2.5−{(the temperature A−the temperature B)×0.08}···Equation (1).

[0022] In this specification, "polypropylene-based resin having a branched structure" may be referred to as "polypropylene-based resin," "extruded polypropylene-based resin beads" may be referred to as "extruded foam beads," "method for producing extruded polypropylene-based resin beads" may be referred to as "production method," and "method for producing extruded polypropylene-based resin beads according to one embodiment of the present invention" may be referred to as "the present production method."

[0023] The present production method has the above-mentioned configuration, and therefore has the advantage of being able to provide extruded polypropylene resin foamed beads with excellent moldability at low cost.

[0024] In this specification, the moldability of extruded polypropylene resin beads is evaluated by (a) the molding width of the extruded polypropylene resin beads, and (b) the compressive strength of the polypropylene resin in-mold foamed article obtained from the extruded polypropylene resin beads.

[0025] The extruded polypropylene resin beads obtained by this production method can be foamed in a mold to form an in-mold polypropylene resin foamed article. In this specification, the "in-mold polypropylene resin foamed article" may also be referred to as the "foamed article."

[0026] First, the raw materials used in this production method will be described, and then each step of this production method will be described.

[0027] (2-1.Resin mixture) In this production method, the resin mixture can also be said to be the components in the composition other than the foaming agent.

[0028] (2-1-1. Polypropylene resin having a branched structure) In this specification, "polypropylene resin having a branched structure" refers to a linear polypropylene resin in which some of the molecules are crosslinked, and a polypropylene resin in which a diene compound other than polypropylene has been introduced as a branched chain into a linear polypropylene resin. In this specification, "polypropylene resin having a branched structure" may also be simply referred to as "polypropylene resin."

[0029] In this specification, a polypropylene-based resin refers to a resin that contains 50 mol % or more of structural units derived from propylene monomers, based on 100 mol % of all structural units contained in the resin. In this specification, "structural units derived from propylene monomers" may also be referred to as "propylene units."

[0030] The polypropylene-based resin may be a block copolymer, a random copolymer, or a graft copolymer, and may be composed solely of propylene units other than the structural units forming the branched structure.

[0031] The polypropylene resin may have, in addition to the propylene unit, one or more structural units derived from a monomer other than the propylene monomer, or may have one or more types. Examples of the monomer other than the propylene monomer include the following monomers: (a) 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; (b) cyclic olefins such as cyclopentene, norbornene, and tetracyclo[6,2,11,8,13,6]-4-dodecene; (c) dienes such as 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, and 7-methyl-1,6-octadiene; and (d) 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.

[0032] 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.

[0033] 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.

[0034] Styrenic monomers include styrene, methylstyrene, dimethylstyrene, alpha-methylstyrene, para-methylstyrene, ethylstyrene, diethylstyrene, isopropylstyrene, t-butylstyrene, bromostyrene, dibromostyrene, tribromostyrene, chlorostyrene, dichlorostyrene, and trichlorostyrene.

[0035] The polypropylene-based resin preferably has, in addition to propylene units, structural units derived from a monomer other than propylene monomers, structural units derived from an α-olefin having 2 or 4 to 12 carbon atoms; more preferably structural units 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 structural units derived from ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, and / or 4-methyl-1-pentene; even more preferably structural units derived from ethylene, 1-butene, isobutene, and / or 1-pentene; and even more preferably structural units derived from ethylene and / or 1-butene.

[0036] The polypropylene resin preferably contains structural units derived from propylene monomers in an amount of 90 mol % or more, more preferably 93 mol % or more, even more preferably 95 mol % or more, and particularly preferably 97 mol % or more, based on 100 mol % of all structural units contained in the polypropylene resin. This configuration has the advantage that the compressive strength of the foamed molded article obtained from the extruded foamed beads is likely to be high.

[0037] The melting point of the polypropylene-based resin is not particularly limited. For example, the melting point of the polypropylene-based resin is preferably 130°C to 165°C, more preferably 135°C to 164°C, even more preferably 138°C to 163°C, and particularly preferably 140°C to 162°C. When the polypropylene-based resin has a melting point of (a) 130°C or higher, there is an advantage that the compressive strength of the foamed molded article tends to be high, and when (b) 165°C or lower, there is an advantage that the extruded foamed beads can be molded at a relatively low vapor pressure, and therefore the extruded foamed beads can be molded using a general-purpose molding machine for polypropylene-based resin foamed beads.

[0038] In this specification, the melting point of a polypropylene-based resin is a value determined by differential scanning calorimetry (hereinafter referred to as the "DSC method"). The specific procedure is as follows: (1) 5 to 6 mg of polypropylene-based resin is melted by increasing the temperature from 40°C to 220°C at a heating rate of 10°C / min; (2) The temperature of the molten polypropylene-based resin is then decreased from 220°C to 40°C at a heating rate of 10°C / min to crystallize the polypropylene-based resin; (3) The temperature of the crystallized polypropylene-based resin is then increased 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 polypropylene-based resin obtained during the second heating (i.e., during (3)) can be determined as the melting point of the polypropylene-based resin. The differential scanning calorimeter used may be, for example, a DSC6200 model manufactured by Seiko Instruments Inc.

[0039] The melt flow rate (MFR) of the polypropylene resin is not particularly limited. The MFR of the polypropylene resin is, for example, preferably 0.5 g / 10 min to 20.0 g / 10 min, more preferably 1.0 g / 10 min to 15.0 g / 10 min, even more preferably 2.0 g / 10 min to 12.0 g / 10 min, and particularly preferably 2.0 g / 10 min to 10.0 g / 10 min. When the MFR of the polypropylene resin is (a) 0.5 g / 10 min or more, there is an advantage that the surface properties of the foamed molded article tend to be good (beautiful), and when it is (b) 20.0 g / 10 min or less, there is an advantage that the foamability of the composition during extrusion foaming is good.

[0040] In this specification, the MFR of a polypropylene-based resin is a value obtained by measurement using an MFR measuring device specified in JIS K7210 under conditions of an orifice diameter of 2.0959±0.0050 mmφ, an orifice length of 8.000±0.025 mm, a load of 2160 g, and a temperature of 230±0.2°C.

[0041] A polypropylene resin having a branched structure can be obtained by introducing a branched structure into a polypropylene resin that does not have a branched structure introduced. The method for introducing a branched structure into a polypropylene resin that does not have a branched structure introduced is not particularly limited, and examples thereof include (a) a method of irradiating a polypropylene resin that does not have a branched structure introduced with radiation, and (b) a method of melt-kneading a polypropylene resin that does not have a branched structure introduced with a conjugated diene compound and a radical polymerization initiator.

[0042] A specific method for obtaining a polypropylene resin having a branched structure by irradiating a polypropylene resin not having a branched structure with radiation includes, for example, the method described in JP-A-2002-542360.

[0043] A method of melt-kneading a polypropylene resin not having a branched structure, a conjugated diene compound, and a radical polymerization initiator (hereinafter also referred to as Method A) will be further described. In Method A, for example, the following steps (i) to (iv) are carried out in order to obtain a polypropylene resin having a branched structure: (i) a polypropylene resin not having a branched structure, a conjugated diene compound, and a radical polymerization initiator are melt-kneaded in an extruder equipped with a die; (ii) the resulting melt-kneaded mixture is extruded from the die; (iii) the extruded melt-kneaded mixture (also referred to as strands) is cooled; (iv) the strands are chopped simultaneously with or after cooling. Specific methods for obtaining a polypropylene resin having a branched structure by Method A include, for example, the method described in WO2020 / 004429.

[0044] In one embodiment of the present invention, the polypropylene-based resin is preferably a polypropylene-based resin having a branched structure obtained by the above-mentioned Method A, for the following reasons (i) and / or (ii): (i) a branched structure can be stably introduced into a polypropylene-based resin that does not have a branched structure introduced therein, and the introduction of the branched structure can be highly reproducible; and (ii) a polypropylene-based resin having a branched structure can be obtained with high productivity without requiring complex equipment.

[0045] In other words, in one embodiment of the present invention, the polypropylene-based resin having a branched structure is preferably obtained by a method of melt-kneading a polypropylene-based resin to which a branched structure has not been introduced, a conjugated diene compound, and a radical polymerization initiator.

[0046] The melt tension of the polypropylene resin having a branched structure is not particularly limited. The melt tension of the polypropylene resin having a branched structure is, for example, preferably 3 cN to 20 cN, more preferably 3 cN to 15 cN, and particularly preferably 3 cN to 10 cN. This configuration has the advantage that extruded polypropylene resin foamed beads having a low open cell ratio can be obtained.

[0047] In this specification, the melt tension of the polypropylene resin having a branched structure is measured using a Capillograph 1D (manufactured by Toyo Seiki Seisakusho, Japan). Specifically, the procedure is as follows: (1) A sample resin (a polypropylene resin having a branched structure) for measurement is filled into a 9.55 mm diameter barrel heated to the test temperature (200°C); (2) The sample resin is then heated for 10 minutes in the barrel heated to the test temperature (200°C); (3) The sample resin is then extruded in a string-like form from a capillary die (diameter 1.0 mm, length 10 mm) at a constant piston descending speed (10 mm / min), and this string-like material is passed through a tension detection pulley located 350 mm below the capillary die, after which winding using a winding roll begins; (4) After the take-up of the string-like material has stabilized, the winding speed of the string-like material is increased at a constant rate from an initial speed of 1.0 m / min to a speed of 200 m / min over 4 minutes; (5) The load applied to the pulley with the load cell when the string-like material breaks is measured as the melt tension.

[0048] The melt flow rate (MFR) of the branched polypropylene resin at 230°C is not particularly limited. The MFR of the branched polypropylene resin at 230°C is, for example, preferably 0.5 g / 10 min to 20.0 g / 10 min, more preferably 1.0 g / 10 min to 15.0 g / 10 min, even more preferably 2.0 g / 10 min to 12.0 g / 10 min, and particularly preferably 2.0 g / 10 min to 10.0 g / 10 min. When the branched polypropylene resin has an MFR of (a) 0.5 g / 10 min or more, there is an advantage that the surface properties of the foamed molded article tend to be good (beautiful), and when it is (b) 20.0 g / 10 min or less, there is an advantage that the foamability of the composition during extrusion foaming is good. In this specification, the MFR of a polypropylene resin having a branched structure is a value obtained by measurement using an MFR measuring device specified in JIS K7210 under conditions of an orifice diameter of 2.0959±0.0050 mmφ, an orifice length of 8.000±0.025 mm, a load of 2160 g, and a temperature of 230±0.2°C.

[0049] The amount of the polypropylene resin having a branched structure used, in other words, the content of the polypropylene resin having a branched structure in the resin mixture, is not particularly limited. The content of the polypropylene resin having a branched structure is, for example, preferably 20 to 100 parts by weight, more preferably 40 to 100 parts by weight, even more preferably 50 to 100 parts by weight, and particularly preferably 60 to 100 parts by weight, relative to 100 parts by weight of the resin mixture.

[0050] (2-1-2. Other resins or rubbers) The resin mixture may further contain a resin other than the polypropylene-based resin (sometimes referred to as "other resin") or rubber, provided that the effect of one embodiment of the present invention is not impaired. Examples of other resins other than the polypropylene-based resin include (a) polypropylene-based resins without branched structures (e.g., ethylene / propylene random copolymers, ethylene / propylene block copolymers, propylene homopolymers, etc.), (b) 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 copolymers, ethylene / acrylic acid copolymers, and ethylene / methacrylic acid copolymers, and (c) styrene-based resins such as polystyrene, styrene / maleic anhydride copolymers, and styrene / ethylene copolymers. Examples of the rubber include olefin-based rubbers such as ethylene / propylene rubber, ethylene / butene rubber, ethylene / hexene rubber, and ethylene / octene rubber.

[0051] The amount of the other resin or rubber used, in other words, the content of the other resin or rubber in the resin mixture, is not particularly limited. The content of the other resin or rubber is, for example, preferably 0.01 to 20.00 parts by weight, more preferably 0.05 to 15.00 parts by weight, even more preferably 0.10 to 10.00 parts by weight, and particularly preferably 0.10 to 5.00 parts by weight, relative to 100 parts by weight of the resin mixture.

[0052] (2-1-3. Bubble nucleating agent) The resin mixture may contain a bubble nucleating agent to control the number and shape of bubbles in the resulting extruded polypropylene resin beads. Examples of bubble nucleating agents include sodium bicarbonate-citric acid mixtures, monosodium citrate, talc, and calcium carbonate. These bubble nucleating agents may be used alone or in combination of two or more.

[0053] The amount of the bubble nucleating agent used, in other words, the content of the bubble nucleating agent in the resin mixture, is not particularly limited. For example, the amount of the bubble nucleating agent used 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 polypropylene resin.

[0054] (2-1-4. Coloring agents) The resin mixture may or may not contain a colorant. When the resin mixture does not contain a colorant, extruded foam particles can be obtained in a natural color (e.g., a color derived from the resin mixture). When the resin mixture contains a colorant, extruded foam particles can be obtained in a desired color (i.e., a color derived from the colorant). Examples of colorants include perylene-based organic pigments, azo-based organic pigments, quinacridone-based organic pigments, phthalocyanine-based organic pigments, threne-based organic pigments, dioxazine-based organic pigments, isoindoline-based organic pigments, and carbon black. These colorants may be used alone or in combination of two or more. The amount of colorant used, i.e., the content of colorant in the resin mixture, is not particularly limited.

[0055] The amount of the colorant used, in other words, the content of the colorant in the resin mixture, is not particularly limited. The content of the colorant is, for example, preferably 0.01 to 20.00 parts by weight, more preferably 0.05 to 15.00 parts by weight, even more preferably 0.10 to 10.00 parts by weight, and particularly preferably 0.10 to 5.00 parts by weight, relative to 100 parts by weight of the resin mixture.

[0056] (2-1-5. Other ingredients) The resin mixture may further contain, as necessary, other components such as (a) stabilizers such as antioxidants, metal deactivators, phosphorus-based processing stabilizers, UV absorbers, UV stabilizers, fluorescent brighteners, metal soaps, and antacid adsorbents, and / or (b) additives such as crosslinkers, chain transfer agents, lubricants, plasticizers, fillers, reinforcing agents, flame retardants, and antistatic agents. These other components may be used singly or in combination of two or more.

[0057] (2-1-6. Melting point of resin mixture) The melting point of the resin mixture is not particularly limited. In this specification, the melting point of the resin mixture can be determined by the same method as the method for measuring the melting point of the polypropylene resin described above, except that the polypropylene resin is replaced with a resin mixture. In this specification, since the resin composition of the resin mixture and the resin composition of the resulting extruded polypropylene resin beads are the same, the melting point of the extruded polypropylene resin beads can be considered to be the melting point of the resin mixture. The melting point of the extruded polypropylene resin beads can be determined by the same method as the method for measuring the melting point of the polypropylene resin described above, except that the polypropylene resin is replaced with an extruded polypropylene resin beads.

[0058] The melting point of the resin mixture is not particularly limited, but is preferably 130° C. to 165° C., more preferably 135° C. to 164° C., even more preferably 138° C. to 163° C., and particularly preferably 140° C. to 162° C. When the melting point of the resin mixture is (a) 130° C. or higher, there is an advantage that the compressive strength of the foamed molded article tends to be high, and when (b) 165° C. or lower, there is an advantage that the extruded foamed beads can be molded at a relatively low vapor pressure, and therefore the extruded foamed beads can be molded using a general-purpose molding machine for polypropylene-based resin foamed beads.

[0059] (2-2. Composition) In this manufacturing method, the resin mixture to which the foaming agent is added is referred to as a composition.

[0060] (2-2-1. Foaming Agent) In this production method, carbon dioxide gas is used as the blowing agent, which has the advantages of lower production costs and a smaller environmental impact than when organic blowing agents are used.

[0061] In the present production method, a substance other than carbon dioxide gas that can function as a foaming agent may be used in combination with carbon dioxide gas, as long as the effect according to one embodiment of the present invention is not impaired.

[0062] The composition preferably contains substantially no substances other than carbon dioxide gas that can function as a foaming agent. Specifically, the content of substances other than carbon dioxide gas that can function as a foaming agent in the composition is preferably 0.01 part by weight or less, more preferably 0.001 part by weight or less, even more preferably 0.0001 part by weight or less, and particularly preferably 0 part by weight, per 100 parts by weight of the composition.

[0063] Examples of substances other than carbon dioxide gas that can function as a blowing agent include: (a) aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane; (b) aliphatic cyclic hydrogens such as cyclopentane and cyclobutane; (c) inorganic gases such as air and nitrogen; and (d) water.

[0064] The amount of foaming agent used is 0.5 to 7.0 parts by weight, preferably 0.5 to 6.0 parts by weight, more preferably 0.5 to 5.0 parts by weight, even more preferably 0.5 to 4.0 parts by weight, and particularly preferably 0.5 to 3.5 parts by weight, relative to 100.0 parts by weight of the resin mixture. The "amount of foaming agent used" can also be referred to as the "amount of carbon dioxide gas used" or the "content of foaming agent (carbon dioxide gas) in the composition."

[0065] (2-3. Melt-kneading process) The melt-kneading step can also be said to be a step of obtaining a melt-kneaded composition in which a resin mixture containing a polypropylene-based resin having a branched structure and a composition containing a blowing agent are melt-kneaded. In the melt-kneading step, it is sufficient that a resin mixture containing a polypropylene-based resin having a branched structure and a composition containing a blowing agent are finally melt-kneaded. Specific examples of the melt-kneading step include the following methods (a) to (c): (a) A method in which a polypropylene resin having a branched structure, a foaming agent, and, if necessary, other resins, a bubble nucleating agent, a colorant, and other components are mixed or blended to prepare a composition, and then the composition is melt-kneaded; (b) A method in which a polypropylene resin having a branched structure and a foaming agent are mixed or blended, the resulting composition is melt-kneaded, and then other resins, bubble nucleating agents, colorants and other components are added to the composition as needed, and the resulting composition is further melt-kneaded; (c) (c-1) A method in which a polypropylene resin having a branched structure is mixed or blended with other resins, bubble nucleating agents, colorants and other components as necessary to prepare a resin mixture, and the crude resin mixture is melt-kneaded; (c-2) A method in which a foaming agent is added to the obtained resin mixture to prepare a composition, and the composition is further melt-kneaded.

[0066] In any of the above methods (a) to (c), the method and order of adding other resins, bubble nucleating agents, colorants, and other components that are used as needed are not particularly limited. The other resins, bubble nucleating agents, colorants, and other components that are used as needed may be added simultaneously or separately and in any order.

[0067] The melt-kneading step may further include a step of melt-kneading the composition by, for example, the above-described methods (a) to (c), and then lowering the temperature of the melt-kneaded composition within a temperature range in which the melt-kneaded composition does not solidify.

[0068] The extruder used in the melt-kneading step is not particularly limited as long as it is equipped with a die at its end. The extruder is equipped, for example, with a kneading device for melt-kneading a composition containing a resin mixture and a foaming agent, and with a die at its end. The extruder may further be equipped with a cooling device to lower the temperature of the composition melt-kneaded in the kneading device.

[0069] As the kneading device, for example, a twin-screw extruder is preferred because it has good mixing properties. Furthermore, the kneading device preferably has a screw configuration so that the blowing agent injected into the kneading device does not flow back upstream of the kneading device. That is, as the kneading device, a twin-screw extruder with a screw configuration is more preferred. In the step of lowering the temperature of the melt-kneaded composition, a cooling device such as a single-screw extruder and / or a melt cooler, which is installed downstream of the kneading device, can be used to lower the temperature of the composition. A gear pump may be installed between the kneading device (e.g., a twin-screw extruder) and the cooling device to improve the extrusion stability of the composition. Furthermore, a diverter valve may be installed between the cooling device and the die.

[0070] (2-4. Extrusion process) The extrusion process includes a step of forcing the melt-kneaded composition into a die, and a step of extruding the composition through the die into a region where the pressure is lower than that of the extruder and where the composition is in a liquid phase.

[0071] In this production method, the temperature A of the composition immediately after entering the die is adjusted to within the range of the melting point of the resin mixture +0°C to the melting point +30°C. Temperature A is preferably the melting point of the resin mixture +1°C to the melting point +25°C, more preferably the melting point of the resin mixture +2°C to the melting point +23°C, more preferably the melting point of the resin mixture +3°C to the melting point +20°C, and even more preferably the melting point of the resin mixture +5°C to the melting point +15°C. This configuration has the advantage that the extruded foam beads, described below, tend to have a wider molding width, and the resulting foamed molded article tends to have a higher compressive strength.

[0072] Methods for adjusting the temperature A of the composition immediately after entering the die to within a range of the melting point of the resin mixture + 0°C to the melting point + 30°C include adjusting various conditions that can affect temperature A. The various conditions that can affect temperature A include (a) the temperature of the melt-kneaded composition immediately after leaving the kneading device, (b) the temperature and heat transfer area of ​​the single-screw extruder or melt cooler that is the cooling section, and the residence time of the composition in the single-screw extruder or melt cooler, (c) the temperature of the diverter valve, (d) the set temperature of the die provided at the end of the extruder, the length of the die in the extrusion direction (sometimes referred to as the thickness of the die), the contact area between the die and the liquid phase, and (e) the temperature of the liquid phase, which will be described later.

[0073] Temperature A can be measured by (a) a thermometer installed so as to protrude into the die hole and installed near the die entrance, or (b) a thermometer installed so as to be in contact with the composition just before entering the die, for example, near the exit of a diverter valve. The temperature of the composition may change as the composition passes through the die. The thermometer for measuring Temperature A is preferably installed, for example, within 20 mm upstream or downstream from the die entrance along the extrusion direction.

[0074] The liquid phase is not particularly limited, but is preferably water because it can be produced cheaply and safely.

[0075] The temperature B of the liquid phase is 20°C to 90°C, preferably 25°C to 85°C, more preferably 30°C to 80°C, even more preferably 35°C to 80°C, and particularly preferably 40°C to 80°C. This configuration has the advantages of making it possible to stably control the temperature A of the composition immediately after it enters the die, and of easily obtaining extruded foamed beads with little adhesion between the extruded foamed beads. In this specification, the temperature B of the liquid phase can be measured by a thermometer installed so as to be in contact with the liquid phase.

[0076] Within this range, the liquid phase pressure for the composition is preferably 0.05 MPa·G to 0.60 MPa·G, more preferably 0.07 MPa·G to 0.55 MPa·G, even more preferably 0.10 MPa·G to 0.50 MPa·G, even more preferably 0.10 MPa·G to 0.45 MPa·G, and particularly preferably 0.10 MPa·G to 0.40 MPa·G. This configuration has the advantage that it is easy to keep the open cell content of the resulting extruded foamed beads low and to keep the mutual adhesion of the resulting extruded foamed beads low. In this specification, "MPa·G" is intended to refer to gauge pressure.

[0077] (2-5. Shredding process) The composition extruded through the die into a region where the pressure is lower than that of the extruder and where the liquid phase is present immediately begins to foam. In the chopping step, the composition may be chopped while foaming, or after foaming has finished. When the composition is chopped while foaming, the chopped composition can complete foaming in the region. The chopping step can also be said to be a step of chopping the composition into particles to prepare extruded polypropylene resin foam particles.

[0078] The method for shredding the composition extruded from the die is not particularly limited. For example, the composition may be shredded along the extrusion direction using a cutter provided next to the die. The number of cutter blades and the number of rotations of the cutter are not particularly limited.

[0079] (2-6. Step of obtaining extruded polypropylene resin foam particles) The step of obtaining extruded polypropylene resin beads can also be said to be a step of recovering the extruded polypropylene resin beads (chopped) prepared in the chopping step.

[0080] The method for recovering the extruded polypropylene resin foam particles is not particularly limited, and examples of the method for recovering the extruded polypropylene resin foam particles include centrifugal dehydration.

[0081] (2-10.T) In the present production method, the value T calculated by formula (1) is 10 to 25, preferably 10 to 20, more preferably 10 to 19, still more preferably 10 to 18, even more preferably 10 to 17, and particularly preferably 11 to 16. This method has the advantage that extruded polypropylene resin foamed beads having excellent moldability can be obtained.

[0082] [3. Extruded polypropylene resin foam particles] The extruded polypropylene resin foam particles obtained by the present production method, in other words, the extruded polypropylene resin foam particles according to one embodiment of the present invention, will be described. In this specification, the "extruded polypropylene resin foam particles according to one embodiment of the present invention" may also be referred to as the "extruded polypropylene resin foam particles of the present invention."

[0083] The present extruded polypropylene resin foam particles are produced by the present production method having the above-mentioned configuration, and therefore have the advantage of excellent moldability.

[0084] (3-1. Crystalline peak) The extruded polypropylene resin foamed beads obtained by the extrusion foaming method are characterized by having one crystalline peak in the DSC curve X obtained by DSC measurement. In other words, the expanded polypropylene resin beads having one crystalline peak in the DSC curve X obtained by DSC measurement are highly likely to have been obtained by the extrusion foaming method. The extruded polypropylene resin foamed beads also have one crystalline peak in the DSC curve X obtained by DSC measurement.

[0085] In this specification, the DSC curve X of the extruded polypropylene resin foamed beads is a curve obtained by DSC measurement when 5 to 6 mg of the extruded polypropylene resin foamed beads are heated from 40°C to 220°C at a heating rate of 10°C / min. In other words, the DSC curve X of the extruded polypropylene resin foamed beads is a DSC curve obtained during the first heating.

[0086] (3-2. Bulk density) The bulk density of the extruded polypropylene resin foamed beads is preferably 40 g / L to 300 g / L, more preferably 50 g / L to 250 g / L, even more preferably 60 g / L to 200 g / L, and particularly preferably 70 g / L to 150 g / L. This configuration has the advantage that the in-mold polypropylene resin foamed article obtained using the extruded polypropylene resin foamed beads exhibits characteristics such as flexibility in shape, cushioning properties, light weight, and heat insulation. If the expansion ratio of the extruded polypropylene resin foamed beads does not reach the above range, a method of increasing the expansion ratio by pressurizing the inside of the extruded polypropylene resin foamed beads with an inert gas and then heating them (e.g., the method described in JP-A-10-237212) can also be used.

[0087] In this specification, the bulk density of the extruded polypropylene resin foam particles is calculated by carrying out the following steps (1) to (3) in order: (1) The extruded polypropylene resin foam particles are divided into a volume V (cm 3 (2) The powder surface (top) of the container is scraped off, and the weight W (g) of the extruded polypropylene resin foam particles in the container is measured. (3) The bulk density of the extruded polypropylene resin foam particles is calculated using the following formula: Bulk density (g / L) = Weight W (g) of foam particles / {Volume V (cm) of container} 3 ) / 1000}.

[0088] (3-3. Open cell ratio) The lower the open cell ratio of the extruded polypropylene resin foamed beads, the better. The open cell ratio of the extruded polypropylene resin foamed beads is preferably 10.0% or less, more preferably 9.0% or less, more preferably 8.0% or less, more preferably 7.0% or less, even more preferably 6.0% or less, and particularly preferably 5.0% or less. The lower limit of the open cell ratio of the extruded polypropylene resin foamed beads is not particularly limited, and is, for example, 0.0% or more. This configuration has the advantage that the in-mold polypropylene resin foamed article obtained using the extruded polypropylene resin foamed beads exhibits characteristics such as shape flexibility, cushioning properties, light weight, compressive strength, and heat insulation properties.

[0089] In this specification, the open cell ratio of the extruded polypropylene resin foamed beads can be determined by measuring using an air comparison type hydrometer (Tokyo Science Co., Ltd., Model 1000) in accordance with the method described in ASTM D2856-87, Procedure C. The method for measuring the open cell ratio will be described in detail in the examples described later.

[0090] (3-4. Molding width) The extruded polypropylene resin beads have the advantage of a wide molding width (e.g., exceeding 0). In this specification, the "molding width of the extruded polypropylene resin beads" refers to the range of vapor pressures during in-mold foam molding that can produce a polypropylene resin in-mold foam molded article that satisfies the following criteria when the extruded polypropylene resin beads are foamed in-mold: (x1) sufficient fusion between the extruded polypropylene resin beads, (x2) sufficient filling of gaps between the extruded polypropylene resin beads, (x3) a clean surface, (x4) no melting of the surface, (x5) sufficient compressive strength, and (x6) a mold shape transfer without shrinking by 5% or more relative to the dimensions of the mold (metal mold) used for in-mold foam molding. Furthermore, if the polypropylene resin in-mold foam molded article sticks to the mold and cannot be removed, it is determined that the polypropylene resin in-mold foam molded article cannot be obtained. In this specification, for example, when extruded polypropylene resin beads are foamed in-mold to obtain an in-mold foamed polypropylene resin article satisfying the above-mentioned (x1) to (x6), if the vapor pressure during in-mold foaming is P1 to P2, the "value" obtained by P2 - P1 is defined as the "molding width of extruded polypropylene resin beads." In addition, in this specification, "P1 to P2" is also referred to as the "workable vapor pressure width."

[0091] If the vapor pressure is too low for the extruded polypropylene resin particles, (a) the fusion between the extruded polypropylene resin particles is insufficient, (b) the gaps between the extruded polypropylene resin particles are not filled sufficiently, (c) the surface appearance is poor, and / or (d) shrinkage occurs, resulting in a polypropylene resin in-mold foamed product in which the shape of the mold (metal mold) used for in-mold foaming is not transferred.If the vapor pressure is too high for the extruded polypropylene resin particles, (a) the surface is melted, and / or (b) the compressive strength of the in-mold foamed polypropylene resin may be insufficient.

[0092] The usable vapor pressure range of the extruded polypropylene resin foam beads is not particularly limited. The wider the molding width of the extruded polypropylene resin foam beads, the better. The molding width of the extruded polypropylene resin foam beads is preferably greater than 0 MPa, more preferably 0.01 MPa or more, more preferably 0.02 MPa or more, more preferably greater than 0.02 MPa, more preferably 0.03 MPa or more, even more preferably 0.04 MPa or more, particularly preferably 0.05 MPa or more, and most preferably 0.06 MPa or more.

[0093] By molding the present extruded polypropylene resin beads, it is possible to obtain a polypropylene resin foam molded article having excellent compressive strength, excellent fusion bonding, and / or a beautiful surface. More specifically, by in-mold foam molding the present extruded polypropylene resin beads, it is possible to obtain a polypropylene resin foam molded article having excellent compressive strength, excellent fusion bonding, and / or a beautiful surface.

[0094] 4. Method for producing polypropylene resin foam molded body A method for producing a polypropylene-based resin foam molded article according to one embodiment of the present invention includes a step of molding extruded polypropylene-based resin beads produced by the present production method described in the above section [2. Method for producing extruded polypropylene-based resin beads]. Also, a method for producing a polypropylene-based resin foam molded article by molding the extruded polypropylene-based resin beads produced by the present production method described in the above section [2. Method for producing extruded polypropylene-based resin beads] is also one embodiment of the present invention.

[0095] The method for producing a polypropylene-based resin foam molded article according to one embodiment of the present invention has the above-mentioned configuration, and therefore has the advantage of being able to provide a polypropylene-based resin foam molded article having excellent compressive strength. The compressive strength of the polypropylene-based resin foam molded article produced by the method for producing a polypropylene-based resin foam molded article according to one embodiment of the present invention is, for example, at least the following numerical value (compressive strength (MPa)): Compressive strength (MPa) = {0.0000056 × D 3 +0.062×D 2 -0.0302×D+168} / 1000. Here, D in the formula is the density (g / L) of the polypropylene resin foam molded article.

[0096] The molding method for extruded polypropylene resin foam beads is not particularly limited, and may be, for example, in-mold foam molding using a mold. A method for producing a polypropylene resin foam molded article, which comprises a step of in-mold foam molding the extruded polypropylene resin foam beads produced by the present production method described in the above section [2. Production method for extruded polypropylene resin foam beads], is also one embodiment of the present invention.

[0097] [1] A method for producing extruded polypropylene resin particles, comprising: a melt-kneading step in which a resin mixture containing a polypropylene resin having a branched structure and a composition containing a blowing agent is melt-kneaded using an extruder equipped with a die; an extrusion step in which the composition is extruded through the die into a region that is under a lower pressure than the extruder and is in a liquid phase; a shredding step in which the composition is shredded in the region; and a step in which the extruded polypropylene resin particles are obtained, wherein the blowing agent is carbon dioxide gas, and the amount of the blowing agent used is 100% by weight of the resin mixture. a temperature A of the composition immediately after entering the die is from the melting point of the resin mixture + 0°C to the melting point + 30°C, a temperature B of the liquid phase is from 20°C to 90°C, and a value T calculated by the following formula (1) is from 10 to 25: T=(the temperature A)-(the melting point)+(the amount of the blowing agent used)×2.5-{(the temperature A-the temperature B)×0.08}... formula (1).

[0098] [2] The method for producing extruded polypropylene resin foam beads according to [1], wherein the pressure of the liquid phase against the composition in the region is 0.05 MPa·G to 0.60 MPa·G.

[0099] [3] The method for producing extruded polypropylene resin foam beads according to [1] or [2], wherein the extruded polypropylene resin foam beads have a bulk density of 40 g / L to 300 g / L.

[0100] [4] The method for producing extruded polypropylene resin foam beads according to any one of [1] to [3], wherein the extruded polypropylene resin foam beads have an open cell ratio of 10.0% or less.

[0101] [5] The method for producing extruded polypropylene resin foam beads according to any one of [1] to [4], wherein the melting point of the resin mixture is 130°C to 165°C.

[0102] [6] The method for producing extruded polypropylene resin foam beads according to any one of [1] to [5], wherein the polypropylene resin having a branched structure has a melt tension of 3 cN to 20 cN.

[0103] [7] The method for producing extruded expanded polypropylene resin beads according to any one of [1] to [6], wherein the polypropylene resin having a branched structure is obtained by melt-kneading a polypropylene resin not having a branched structure, a conjugated diene compound, and a radical polymerization initiator.

[0104] [8] The method for producing extruded polypropylene resin foam beads according to any one of [1] to [7], wherein the melt flow rate at 230°C of the polypropylene resin having a branched structure is 0.5 g / 10 min to 20.0 g / 10 min.

[0105] [9] A method for producing a polypropylene resin foamed article, comprising a step of molding extruded polypropylene resin beads produced by the method for producing extruded polypropylene resin foamed beads according to any one of [1] to [8]. [Example]

[0106] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0107] (Measurement and evaluation methods) [MFR] Using a polypropylene resin having a branched structure as a sample, the MFR of the polypropylene resin having a branched structure was measured using an MFR measuring device specified in JIS K7210 under the following conditions: orifice diameter 2.0959±0.0050 mmφ, orifice length 8.000±0.025 mm, load 2160 g, and temperature 230±0.2°C.

[0108] [Melt tension] The melt tension of the polypropylene resin having a branched structure was measured using a Capillograph 1D (manufactured by Toyo Seiki Seisakusho, Japan). Specifically, the procedure was as follows: (1) A sample resin (a polypropylene resin having a branched structure) for measurement was filled into a 9.55 mm diameter barrel heated to 200°C; (2) The sample resin was then heated for 10 minutes in the barrel heated to 200°C; (3) The sample resin was then extruded in a string-like form from a capillary die (diameter 1.0 mm, length 10 mm) at a constant piston descending speed (10 mm / min), and this string-like material was passed through a tension detection pulley located 350 mm below the capillary die, after which winding using a winding roll was initiated; (4) After the take-up of the string-like material stabilized, the winding speed of the string-like material was increased at a constant rate from an initial speed of 1.0 m / min to a speed of 200 m / min in 4 minutes; (5) The load applied to the pulley with a load cell when the string-like material broke was measured, and the obtained value was taken as the melt tension.

[0109] [Melting point] Using a differential scanning calorimeter (Seiko Instruments Inc., DSC6200), the melting points of the extruded polypropylene resin beads obtained by the following method were measured. These were regarded as the melting points of the resin mixture and are shown in Tables 1 and 2: (1) The temperature of 5 to 6 mg of extruded polypropylene resin beads was increased from 40°C to 220°C at a rate of 10°C / min to melt the extruded polypropylene resin beads; (2) The temperature of the melted extruded polypropylene resin beads was then increased from 40°C to 220°C. (3) The temperature of the crystallized extruded polypropylene resin beads was then increased from 40°C to 220°C at a rate of 10°C / min; (4) the peak temperature (melting peak) of the DSC curve of the extruded polypropylene resin beads obtained during the second temperature increase (i.e., during (3)) was taken as the melting point of the extruded polypropylene resin beads.

[0110] [DSC curve X] Using a differential scanning calorimeter (Seiko Instruments Inc., DSC6200 model), 5 to 6 mg of extruded polypropylene resin foam particles were heated from 40°C to 220°C at a heating rate of 10°C / min, thereby obtaining a DSC curve X of the extruded polypropylene resin foam particles.

[0111] [Bulk density] The bulk density of the extruded polypropylene resin foam particles was calculated by carrying out the following steps (1) to (3) in order: (1) The extruded polypropylene resin foam particles were divided into 2 groups, each having a volume V (cm 3 (2) The powder surface (top) of the container was scraped off, and the weight W (g) of the extruded polypropylene resin foam particles in the container was measured. (3) The bulk density of the extruded polypropylene resin foam particles was calculated using the following formula: Bulk density (g / L) = Weight of foam particles W (g) / Volume of container V (cm 3 ) / 1000}. The values ​​obtained are shown in Tables 1 and 2.

[0112] [Open cell ratio] The open cell ratio of the extruded polypropylene resin foam particles was measured by the following method. Using an air comparison type hydrometer [Tokyo Science Co., Ltd., Model 1000], the volume Vc (cm) of the obtained extruded polypropylene resin foam particles was measured in accordance with the method described in Procedure C of ASTM D2856-87. 3 ) was measured. Next, the entire amount of the extruded polypropylene resin foamed beads after measuring Vc was submerged in ethanol contained in a measuring cylinder. After that, the apparent volume Va (cm ) of the extruded polypropylene resin foamed beads was calculated from the amount of rise in the position (liquid level) of the ethanol in the measuring cylinder. 3 The open cell ratio of the extruded polypropylene resin foam beads was calculated using the following formula: Open cell rate (%) = (Va - Vc) × 100 / Va. The values ​​obtained are listed in Tables 1 and 2.

[0113] [Molding width] First, a block-shaped mold (molding space: 381 mm long x 381 mm wide x variable thickness) was prepared so that the thickness of the molding space was 78 mm (cracking rate: 30%). Next, the molding space of the mold was filled with extruded polypropylene resin foam particles. The mold was then moved so that the thickness of the molding space in the mold was 60 mm, and the molding space was compressed. Next, the air in the mold was expelled with steam at 0.10 MPa (gauge pressure). After that, the mold was heated for 10 seconds using steam with a vapor pressure of 0.20 to 0.44 MPa (gauge pressure) and foam-molded in-mold to obtain a polypropylene resin foam molded article. Here, foam-molding in-mold was performed while changing the vapor pressure in increments of 0.02 MPa. In this case, a polypropylene resin in-mold foamed product satisfying the following (x1) to (x5) can be obtained. The range of vapor pressure during in-mold foaming was determined, and the obtained range of vapor pressure was designated as P1 to P2: (x1) the polypropylene resin extruded particles are sufficiently fused together (fusion rate), (x2) the gaps between the polypropylene resin extruded particles are sufficiently filled, (x3) the surface is beautiful, (x4) the surface is not melted, and (x5) there is no shrinkage and the shape of the mold (metal mold) used for in-mold foaming is transferred to the polypropylene resin in-mold foamed product.

[0114] Here, the evaluation of the fusion rate (x1), the gaps between particles (x2), the surface aesthetics (x3), the surface melt state (x4), and the shrinkage rate (x5) were carried out as follows: The evaluations of (x1) to (x5) were carried out using polypropylene resin foam molded articles obtained by the above-mentioned method, which were dried in a drying chamber at 75°C for 16 hours or more, and then left to stand at 23°C for 24 hours or more.

[0115] (Evaluation of fusion rate) A 5mm cut was made with a knife or similar tool from about 100mm from one corner of a polypropylene resin foam molded article to a point about 100mm from the opposite corner, and the area surrounded by the cut and the corner was struck with a hammer or similar tool to break the cut. The fracture surface was visually inspected, and the total number of extruded foam particles present on the fracture surface and the number of extruded foam particles that had broken within the extruded foam particles at the fracture surface were counted. The ratio (%) of the number of extruded foam particles that had broken within the extruded foam particles at the fracture surface to the total number of extruded foam particles present on the fracture surface was calculated, and a ratio of 60% or more was deemed acceptable, and a ratio of less than 60% was deemed unacceptable.

[0116] (Evaluation of particle spacing) The extruded foam particles were visually observed in a 100 mm x 100 mm area near the center of both sides (surfaces perpendicular to the thickness direction) of the surface of the polypropylene resin foam molded article, and the number of gaps between the extruded foam particles (areas recessed from the surface) was counted. A sample with 20 or fewer gaps between the extruded foam particles was considered to be acceptable, and a sample with 21 or more gaps was considered to be unacceptable.

[0117] (Evaluation of surface aesthetics) For the polypropylene resin foam molded article, the gaps between the extruded foam particles were visually observed at the longest end, and the number of gaps (recesses relative to the surface) between the extruded foam particles was counted. A sample with three or fewer gaps between the extruded foam particles was rated as passing, and a sample with four or more gaps was rated as failing.

[0118] (Evaluation of surface melt state) The surface melt state of the polypropylene resin foam molded article was evaluated immediately after molding without drying or leaving the obtained polypropylene resin foam molded article. Specifically, the polypropylene resin foam molded article immediately after molding was deemed to have failed if (a) the foam molded article stuck to the mold and could not be released, or (b) the foam molded article could be released from the mold but a part of the foam molded article surface, such as a steam slit portion on the foam molded article surface, remained on the mold side, and all other cases were deemed to have passed.

[0119] (Evaluation of shrinkage rate) The length, width, and thickness of the polypropylene resin foam molded article were measured. Using the obtained results, the shrinkage rate (%) of each of the length, width, and thickness of the polypropylene resin foam molded article was evaluated using the following formula: {(dimension of molding space in mold) - (dimension of molded product)} x 100 / dimension of molding space in mold. A product was deemed to have passed if the shrinkage rates of its length, width, and thickness were all 5% or less, and was deemed to have failed if any of them exceeded 5%. The dimensions of the molding space in the mold were 381mm length, 381mm width, and 60mm thickness.

[0120] The vapor pressure range "P1 to P2" was defined as the "workable vapor pressure range," and the "value" obtained from P2-P1 was defined as the "molding range of extruded polypropylene resin foam beads." The "workable vapor pressure range" and "molding range of extruded polypropylene resin foam beads" are listed in the "vapor pressure range" and "molding range" columns of Tables 1 and 2, respectively.

[0121] [Compression strength] Test pieces measuring 50 mm in length, width, and thickness were cut from the polypropylene-based resin in-mold foam molded articles obtained in the Examples and Comparative Examples. Only one surface perpendicular to the thickness direction of the polypropylene-based resin in-mold foam molded article was cut. That is, the uncut surface perpendicular to the thickness direction of the polypropylene-based resin in-mold foam molded article was the surface that was in contact with the mold during in-mold foam molding (also referred to as the skin layer). The test pieces were compressed at a rate of 10% of their thickness (approximately 5 mm / min) using a tension-compression tester (e.g., TG-50kN, manufactured by MinebeaMitsumi Inc.) in accordance with ISO 844 to measure the compressive stress at 50% compression. The obtained value was taken as the compressive strength of the polypropylene-based resin in-mold foam molded article.

[0122] [Moldability] The moldability was evaluated based on the following criteria, and the evaluation results are shown in Tables 1 and 2. ⊚ (Excellent): The molding width is 0.06 MPa or more, and the compressive strength is equal to or greater than the value (compressive strength (MPa)) calculated by the following formula. ◯ (Good): The molding width is 0.04 MPa or more and less than 0.06 MPa, and the compressive strength is equal to or greater than the value (compressive strength (MPa)) calculated by the following formula. △ (standard): The molding width is 0.04 MPa or more and less than 0.06 MPa, and the compressive strength is less than the value (compressive strength (MPa)) calculated by the following formula. × (bad): The molding width is greater than 0.02 MPa and less than 0.04 MPa, and the compressive strength is less than the value (compressive strength (MPa)) calculated by the following formula. ×× (very bad): The molding width is 0.02 MPa or less. Compressive strength (MPa) = {0.0000056 × D 3 +0.062×D 2 -0.0302×D+168} / 1000. Here, D in the formula is the density of the test piece (g / L).

[0123] (Polypropylene resin having a branched structure) (Preparation of Resin A) A branched polypropylene resin (Resin A) was produced by carrying out the following steps (1) to (5) in order: (1) 100 parts by weight of random polypropylene resin (F-724NPC, manufactured by Prime Polymer Co., Ltd.) and 1.0 part by weight of a radical polymerization initiator were fed into a twin-screw extruder with a shaft diameter of φ45 mm at 70 kg / h; (2) 0.45 parts by weight of isoprene was fed as a conjugated diene compound relative to 100 parts by weight of random polypropylene resin through an injection port provided midway through the twin-screw extruder; (3) The mixture in the twin-screw extruder was melt-kneaded at a cylinder temperature of 200 °C and a screw rotation speed of 230 rpm; (4) The molten mixture was extruded through a die provided at the end of the twin-screw extruder, and the extruded molten mixture (strands) was water-cooled in a water bath; (5) The strands were chopped using a pelletizer provided at the end of the water bath to obtain a branched polypropylene resin. The MFR of the obtained polypropylene resin having a branched structure (resin A) was 2.3 g / 10 min. The melt tension of the obtained polypropylene resin having a branched structure (resin A) was 12 cN.

[0124] As described above, Resin A was a polypropylene-based resin having a branched structure obtained by melt-kneading a polypropylene-based resin not having a branched structure, a conjugated diene compound (isoprene), and a radical polymerization initiator.

[0125] (Resin B) A high melt tension polypropylene resin (WB140HMS, manufactured by Borealis) was used as the branched polypropylene resin (Resin B). The MFR of the branched polypropylene resin (Resin B) was 2.1 g / 10 min. The melt tension of the resulting branched polypropylene resin (Resin B) was 14 cN.

[0126] Resin B was a polypropylene resin having a branched structure obtained by melt-kneading a polypropylene resin not having a branched structure, a conjugated diene compound, and a radical polymerization initiator.

[0127] Examples and Comparative Examples are described below. In the Examples and Comparative Examples, the extruder used to produce the extruded polypropylene resin foamed beads was a twin-screw extruder (kneading device) with a shaft diameter of 26 mm, a melt cooler (cooling device), a diverter valve, and a die connected in series in this order. The die used had three holes with a diameter of 0.8 mm. A thermometer for measuring temperature A was installed near the outlet of the diverter valve, specifically, 10 mm upstream from the inlet of the die along the extrusion direction, so as to be in contact with the composition.

[0128] Example 1 The polypropylene-based resin extrusion foam beads of Example 1 were produced by the following method: (1) 99.8 parts by weight of a branched polypropylene resin (resin A) and 0.2 parts by weight of talc as a bubble nucleating agent were blended to prepare a resin mixture; (2) The resin mixture was fed into a twin-screw extruder equipped with an extruder, and melt-kneading of the resin mixture was started; (3) During the melt-kneading of the resin mixture, 3 parts by weight of carbon dioxide gas per 100 parts by weight of the resin mixture was pressurized into the twin-screw extruder as a blowing agent to prepare a composition; (4) The composition was melt-kneaded at 200 ° C; (5) The composition was fed into a die at the end of the extruder; (6) The composition that had passed through the die was extruded into a region filled with water as a liquid phase at a lower pressure than the extruder; (7) In the region filled with water (liquid phase), the composition was chopped with a cutter immediately after passing through the die; (8) The chopped composition was subjected to a centrifugal dehydrator to obtain extruded polypropylene-based resin foam beads. The weight of each of the extruded polypropylene resin foam particles obtained was 2 mg.

[0129] In Example 1, (a) the temperature B of the liquid phase (water) and (b) the pressure of water on the composition in the water-filled region (water pressure) were set to the temperatures shown in Table 1. In Example 1, the temperature A of the composition immediately after entering the die was adjusted to the temperature shown in Table 1 by adjusting various conditions.

[0130] Example 2 Extruded polypropylene resin foamed beads were obtained in the same manner as in Example 1, except that the temperature A of the composition immediately after entering the die was adjusted to the temperature shown in Table 1 by adjusting various conditions. The weight per particle of the obtained extruded polypropylene resin foamed beads was 2 mg / particle.

[0131] (Comparative Example 1) An attempt was made to obtain extruded polypropylene resin foam beads in the same manner as in Example 1, except that the temperature A of the composition immediately after entering the die was adjusted to the temperature shown in Table 1 by adjusting various conditions. However, the composition solidified in the die, causing the composition to clog at the die outlet, making it impossible to extrude the composition and resulting in failure to obtain extruded polypropylene resin foam beads. Therefore, the "steam pressure range" and "molding width" columns in Table 2 are marked with "die clogging."

[0132] (Comparative Example 2) Extruded polypropylene resin foamed beads were obtained in the same manner as in Example 1, except that the temperature A of the composition immediately after entering the die was adjusted to the temperature shown in Table 1 by adjusting various conditions. The weight per particle of the obtained extruded polypropylene resin foamed beads was 2 mg / particle.

[0133] Example 3 The extruded polypropylene resin foam particles of Example 3 were produced by the following method: (1) 95.55 parts by weight of a polypropylene resin having a branched structure (resin A), 4.25% by weight of a carbon masterbatch having a carbon concentration of 40%, and 0.2 parts by weight of talc as a bubble nucleating agent were blended to prepare a resin mixture; (2) The resin mixture was fed into a twin-screw extruder equipped with an extruder, and melt-kneading of the resin mixture was started; (3) During the melt-kneading of the resin mixture, 3 parts by weight of carbon dioxide gas was added to 100 parts by weight of the resin mixture. (4) The composition was melt-kneaded at 200°C; (5) the composition was passed through a die at the end of the extruder, and the temperature A of the composition immediately after entering the die was measured; (6) the composition was extruded through the die into a region filled with water as a liquid phase at a lower pressure than the extruder; (7) in the region filled with water, the composition was chopped with a cutter immediately after passing through the die; (8) the chopped composition was subjected to a centrifugal dehydrator to obtain extruded polypropylene resin foam particles. The weight of the resulting extruded polypropylene resin foam particles per particle was 2 mg.

[0134] A carbon masterbatch with a carbon concentration of 40% was prepared as follows: Carbon black was blended into a polypropylene resin (WB140HMS, manufactured by Borealis) to a concentration of 40%, the resulting mixture was melt-kneaded in an extruder, and the resulting molten mixture was extruded into water and cut to produce a carbon masterbatch. The carbon masterbatch with a carbon concentration of 40% is referred to as "Carbon MB" in Tables 1 and 2.

[0135] In Example 3, (a) the temperature B of the liquid phase (water) and (b) the water pressure (water pressure) on the composition in the water-filled region were set to the temperatures shown in Table 1. In Example 3, the temperature A of the composition immediately after entering the die was adjusted to the temperature shown in Table 1 by adjusting various conditions.

[0136] (Examples 4 to 9 and Comparative Example 3) Extruded polypropylene resin foamed beads were obtained in the same manner as in Example 3, except that (a) the amount of carbon dioxide gas injected into the twin-screw extruder during melt-kneading of the resin mixture per 100 parts by weight of the resin mixture was changed to the amount shown in Table 1, (b) the temperature B of the liquid phase (water) was changed to a temperature shown in Table 1, (c) the water pressure was changed to a temperature shown in Table 1, and / or (d) various conditions were adjusted to adjust the temperature A of the composition immediately after entering the die to a temperature shown in Table 1. The weight per particle of the obtained extruded polypropylene resin foamed beads was 2 mg.

[0137] (Comparative Examples 4 and 5) An attempt was made to obtain extruded polypropylene resin foam beads using the same method as in Example 3, except that (a) the temperature B of the liquid phase (water) was changed to a temperature listed in Table 1, (b) the water pressure was changed to a temperature listed in Table 1, and / or (c) various conditions were adjusted to adjust the temperature A of the composition immediately after entering the die to a temperature listed in Table 1. However, the composition solidified in the die, causing the composition to clog at the die outlet, making it impossible to extrude the composition and resulting in failure to obtain extruded polypropylene resin foam beads. Therefore, the columns for "steam pressure range" and "molding width" in Table 2 state "die clogging."

[0138] (Example 10 and Comparative Example 6) Extruded polypropylene resin foam beads were obtained in the same manner as in Example 3, except that (a) Resin B was used instead of Resin A as the polypropylene resin having a branched structure, (b) the water pressure (hydraulic pressure) on the composition in the water-filled region was changed to the pressure shown in Table 1, and (c) various conditions were adjusted to adjust the temperature A of the composition immediately after entering the die to the temperature shown in Table 1. The weight per particle of the obtained extruded polypropylene resin foam beads was 2 mg / particle.

[0139] For the extruded polypropylene resin beads obtained in each of the Examples and Comparative Examples, except for Comparative Examples 1, 4, and 5, where die clogging occurred, the DSC curve X was measured by the method described above. As a result, all of the extruded polypropylene resin beads had one crystalline peak. Furthermore, for the extruded polypropylene resin beads obtained in each of the Examples and Comparative Examples, except for Comparative Examples 1, 4, and 5, where die clogging occurred, the melting point (melting point of the resin mixture), bulk density, open cell ratio, molding width, and moldability were measured and evaluated by the method described above. The results are shown in Tables 1 and 2.

[0140] (Production of polypropylene resin foam molded products) The extruded polypropylene resin beads obtained in Example 1 were used to produce a polypropylene resin foam molded article by the following method.

[0141] First, a block-shaped mold (molding space: 381 mm long x 381 mm wide x variable thickness) was prepared so that the thickness of the molding space was 78 mm (cracking rate: 30%). Next, the molding space of the mold was filled with extruded polypropylene resin foam particles. The mold was then moved so that the thickness of the molding space in the mold was 60 mm, and the molding space was compressed. Next, the air in the mold was expelled with steam at 0.10 MPa (gauge pressure). After that, the product was heated and molded for 10 seconds using steam with a vapor pressure of 0.24 MPa (gauge pressure) to 0.30 MPa (gauge pressure), to obtain a polypropylene resin foam molded article.

[0142] The obtained polypropylene resin foam molded article passed all of the evaluations (x1) to (x5) described above, and the compressive strength measured by the method described in the above [Compressive strength] satisfied the following formula: Compressive strength (MPa) = {0.0000056 × D 3 +0.062×D 2 -0.0302×D+168} / 1000.

[0143] That is, the polypropylene resin foam molded article obtained by molding the extruded polypropylene resin beads obtained in Example 1 had the advantage of exhibiting sufficient compressive strength. [Table 1]

[0144] [Table 2] Tables 1 and 2 show that the method for producing extruded polypropylene resin foam beads according to one embodiment of the present invention can provide extruded polypropylene resin foam beads with excellent moldability at low cost. Furthermore, the extruded polypropylene resin foam beads of Comparative Examples 3 and 6 had molding widths of 0 MPa and 0.02 MPa or less. It is estimated that when extruded polypropylene resin foam beads with a molding width of 0.02 MPa or less are used in in-mold foam molding using a mold with a complex shape, it is highly likely that an in-mold foam molded product in which the shape of the mold is transferred will not be obtained. This is because, when in-mold foam molding is used in a mold with a complex shape, the extruded polypropylene resin foam beads in the mold may differ in their susceptibility to steam exposure. Therefore, it is thought that areas of high and low steam pressure on the extruded polypropylene resin foam beads coexist within the mold. [Industrial Applicability]

[0145] According to one embodiment of the present invention, extruded polypropylene resin beads having excellent moldability can be provided at low cost. Therefore, one embodiment of the present invention can be suitably used to obtain in-mold foamed polypropylene resin articles having excellent shape flexibility, cushioning properties, light weight, heat insulation properties, etc. Therefore, one embodiment of the present invention can be suitably used in fields such as automotive interior materials, cushioning materials, packaging materials, and heat insulation materials.

Claims

1. a melt-kneading step of melt-kneading a resin mixture containing a polypropylene-based resin having a branched structure and a composition containing a foaming agent using an extruder equipped with a die; an extrusion step of extruding the composition through the die into a region where the pressure is lower than that of the extruder and the region is in a liquid phase; shredding the composition in the region; and a step of obtaining extruded polypropylene resin foam particles, The foaming agent is carbon dioxide gas, the amount of the foaming agent used is 0.5 parts by weight to 7.0 parts by weight per 100.0 parts by weight of the resin mixture; the temperature A of the composition immediately after entering the die is the melting point of the resin mixture + 0°C to the melting point + 30°C; The temperature B of the liquid phase is 20°C to 90°C, A method for producing extruded polypropylene resin foamed beads, wherein the value T calculated by the following formula (1) is 10 to 25: T=(the temperature A)−(the melting point)+(the amount of the foaming agent used)×2.5−{(the temperature A−the temperature B)×0.08}...Equation (1).

2. 2. The method for producing extruded polypropylene resin foam beads according to claim 1, wherein the pressure of the liquid phase against the composition in the region is 0.05 MPa·G to 0.60 MPa·G.

3. 3. The method for producing extruded polypropylene resin foam beads according to claim 1, wherein the extruded polypropylene resin foam beads have a bulk density of 40 g / L to 300 g / L.

4. 4. The method for producing extruded polypropylene resin foam beads according to claim 1, wherein the extruded polypropylene resin foam beads have an open cell rate of 10.0% or less.

5. The method for producing extruded polypropylene resin foam beads according to any one of claims 1 to 4, wherein the melting point of the resin mixture is 130°C to 165°C.

6. 6. The method for producing extruded polypropylene resin foam beads according to claim 1, wherein the polypropylene resin having a branched structure has a melt tension of 3 cN to 20 cN.

7. The method for producing extruded polypropylene resin foam beads according to any one of claims 1 to 6, wherein the polypropylene resin having a branched structure is obtained by melt-kneading a polypropylene resin not having a branched structure, a conjugated diene compound, and a radical polymerization initiator.

8. The method for producing extruded polypropylene resin foam beads according to any one of claims 1 to 7, wherein the melt flow rate at 230 ° C. of the polypropylene resin having a branched structure is 0.5 g / 10 min to 20.0 g / 10 min.

9. A method for producing a polypropylene resin foamed article, comprising a step of molding the extruded polypropylene resin foamed beads produced by the method for producing extruded polypropylene resin foamed beads according to any one of claims 1 to 8.

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