Method for producing a polypropylene resin having a branched structure, method for producing extruded foam particles, and method for producing a foamed molded article

Abstract

The present invention addresses the problem of providing: a branched polypropylene-based resin having a high melt tension; and a method for producing the branched polypropylene-based resin. Provided is a production method comprising a first melt-kneading step for melt-kneading a polypropylene-based resin, a conjugated diene compound and a radical polymerization initiator in a first melt-kneading section and an ejection step for ejecting a polypropylene-based resin having a branched structure which has been produced in the first melt-kneading step through a die, in which the specific energy E1 is 0.35 kWh / kg or more.

Description

Technical Field

[0001] The present invention relates to a method for producing a polypropylene-based resin having a branched structure, a method for producing extruded foam particles, and a method for producing a foamed molded body.

Background Art

[0002] A polypropylene-based resin in-mold foamed molded body obtained using polypropylene-based resin foam particles has features such as excellent arbitrariness of shape, cushioning property, light weight, and heat insulation property, which are advantages of in-mold foamed molded bodies.

[0003] Examples of methods for producing polypropylene-based resin foam particles include a batch foaming method, which is a discontinuous process, and an extrusion foaming method, which is a continuous process. The extrusion foaming method has many advantages in terms of efficiency and environmental aspects, etc., but there is a problem that it is difficult to obtain polypropylene-based resin foam particles with good moldability.

[0004] As a means for solving this problem, using a modified polypropylene resin with improved melt tension as a raw material has been studied.

[0005] For example, Patent Document 1 discloses a method for producing a modified polypropylene resin composition with improved melt tension by adding a specific thiuram sulfide-based compound to a polypropylene-based resin.

[0006] As a technique for obtaining polypropylene-based resin foam particles by an extrusion foaming method, the technique described in Patent Document 2 can be mentioned. Patent Document 2 discloses a method for producing polypropylene-based resin foam particles by melt-kneading a polypropylene-based resin and a foaming agent using an extruder, then cooling, and extruding the obtained molten resin into a low-pressure region and cutting it into pieces.

Prior Art Documents

Patent Documents

[0007]

【Patent Document Japanese Patent Publication No. 2011-153170 [Patent Document 2] International Public Gazette No. 2018 / 016399 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, prior art relating to modified polypropylene resin compositions, such as that described in Patent Document 1, is insufficient from the viewpoint of melt tension and there is room for further improvement.

[0009] One embodiment of the present invention has been made in view of the above-mentioned problems, and its object is to provide a branched polypropylene resin having high melt tension and a method for producing the same. [Means for solving the problem]

[0010] As a result of diligent research to solve the aforementioned problems, the inventors have independently discovered the following findings and completed the present invention: By introducing a specific energy of a predetermined value or higher into a resin mixture containing a polypropylene resin, a conjugated diene compound, and a radical polymerization initiator in specific weight ratios and melt-kneading it, it is possible to obtain a novel branched polypropylene resin with high melt tension.

[0011] In other words, a method for producing a polypropylene resin according to one embodiment of the present invention is a method for producing a polypropylene resin having a branched structure, and includes a first production apparatus equipped with a first melt-kneading section having a screw and a die, comprising: a first melt-kneading step of melt-kneading a polypropylene resin, a conjugated diene compound and a radical polymerization initiator in the first melt-kneading section; and a discharge step of dischargeing the polypropylene resin having a branched structure obtained in the first melt-kneading step through the die, wherein the amount of the conjugated diene compound used is 0.30 to 1.50 parts by weight per 100 parts by weight of the polypropylene resin, the amount of the radical polymerization initiator used is 0.50 to 2.00 parts by weight per 100 parts by weight of the polypropylene resin, and the specific energy E1 is 0.35 kWh / kg or more, where the specific energy E1 is the value obtained by dividing the power P1 required to drive the screw of the first melt-kneading section by the discharge amount Q1 of the polypropylene resin having a branched structure.

[0012] Furthermore, a method for producing polypropylene resin extruded foam particles according to another embodiment of the present invention uses a third manufacturing apparatus comprising a second melt-kneading section having a plurality of screws and a granulation section having a die, and includes a second melt-kneading step in which a branched polypropylene resin and a foaming agent are melt-kneaded in the second melt-kneading section, and an extrusion foaming step in which the composition obtained in the second melt-kneading step is discharged through the die into a region where the pressure is lower than the internal pressure of the third manufacturing apparatus, wherein the specific energy E2 is 0.190 kWh / kg or less, and the specific energy E2 is the value obtained by dividing the power P2 required to drive the plurality of screws in the second melt-kneading section by the discharge amount Q2 of the composition. [Effects of the Invention]

[0013] According to one embodiment of the present invention, a method for producing a polypropylene resin having a branched structure with high melt tension can be provided. [Modes for carrying out the invention]

[0014] One embodiment of the present invention is described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by appropriately combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Moreover, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic and patent documents mentioned herein are incorporated herein by reference. Furthermore, unless otherwise specified herein, "A to B" representing a numerical range means "A or greater (including A and greater than A) and B or less (including B and less than B)."

[0015] In this specification, "polypropylene resin having a branched structure" refers to (a) a polypropylene resin in which the molecules of a polypropylene resin without a branched structure are partially crosslinked intermolecularly, and (b) a polypropylene resin in which a diene compound other than (poly)propylene is introduced as a branched chain to a polypropylene resin without a branched structure. In this specification, "polypropylene resin without a branched structure" may be referred to as "linear polypropylene resin," and "polypropylene resin having a branched structure" may be referred to as "branched polypropylene resin," and "linear polypropylene resin" and "branched polypropylene resin" may be collectively referred to as "polypropylene resin." Linear polypropylene resin can also be considered a raw material for branched polypropylene resin.

[0016] In this specification, linear polypropylene resin refers to a resin containing 50 mol% or more of structural units derived from propylene monomers out of 100 mol% of the total structural units contained in the resin. In this specification, "structural units derived from propylene monomers" may be referred to as "propylene units."

[0017] In addition, in this specification, the branched polypropylene-based resin is intended to be a resin in which the main chain of the branched polypropylene-based resin contains 50 mol% or more of structural units derived from propylene monomers in 100 mol% of all structural units contained in the main chain. The "main chain" of the branched polypropylene-based resin is intended to be a structure derived from a linear polypropylene-based resin that is a raw material of the branched polypropylene-based resin.

[0018] <First Embodiment> [1-1. Technical Idea of the First Embodiment] As a result of the intensive studies by the present inventor, the following findings were newly discovered.

[0019] In order to produce polypropylene-based resin foam particles with good moldability by the extrusion foaming method, it was considered that one of the solutions is to improve the melt tension of the polypropylene-based resin used as a raw material.

[0020] The technique of Patent Document 1 aims to improve the melt tension by mixing a special raw material, a thiuram sulfide-based compound, into the polypropylene-based resin. However, the technique of Patent Document 1 has problems such as an increase in cost due to the use of a special raw material. In addition, the modified polypropylene resin produced by the technique of Patent Document 1 has room for further improvement in melt tension.

[0021] On the other hand, the present inventor first used a polypropylene-based resin, a conjugated diene compound, and a radical polymerization initiator as raw materials, and increased the amount of the radical polymerization initiator used with respect to the polypropylene-based resin to increase the branching points of the polypropylene-based resin, thereby improving the melt tension of the obtained branched polypropylene-based resin. However, simply increasing the amount of the radical polymerization initiator used could not achieve an improvement in melt tension to the intended level.

[0022] As a result of further diligent research by the inventors, the following findings were independently discovered, leading to the completion of the first embodiment of the present invention: By appropriately adjusting the weight ratio of each component in a resin mixture containing a polypropylene resin, a conjugated diene compound, and a radical polymerization initiator (the first resin mixture described later), and the specific energy introduced into the resin mixture during melt kneading, the melt tension of the resulting branched polypropylene resin can be significantly improved.

[0023] Furthermore, the inventors investigated the reason why adjusting the specific energy introduced into the resin mixture during melt kneading improved the melt tension of the branched polypropylene resin, and independently discovered the following: (i) When a resin mixture with an increased amount of radical polymerization initiator is melt-kneaded with a specific energy below a predetermined value, the gel fraction of the resulting branched polypropylene resin increases; and (ii) When the specific energy introduced into the melt kneading of the resin mixture exceeds a predetermined value, the gel fraction of the resulting branched polypropylene resin decreases rapidly.

[0024] [1-2. Method for producing polypropylene resin having a branched structure] A method for producing a branched polypropylene resin according to a first embodiment of the present invention includes a first production apparatus equipped with a first melt-kneading section having a screw and a die, comprising: a first melt-kneading step in which a polypropylene resin, a conjugated diene compound, and a radical polymerization initiator are melt-kneaded in the first melt-kneading section; and a discharge step in which the branched polypropylene resin obtained in the first melt-kneading step is discharged through the die, wherein the amount of the conjugated diene compound used is 0.30 to 1.50 parts by weight per 100 parts by weight of the polypropylene resin, the amount of the radical polymerization initiator used is 0.50 to 2.00 parts by weight per 100 parts by weight of the polypropylene resin, and the specific energy E1 is 0.35 kWh / kg or more.

[0025] In this specification, "specific energy E1" is the value obtained by dividing the power P1 required to drive the screw of the first melting and kneading section by the discharge rate Q1 of the polypropylene resin having a branched structure.

[0026] In this specification, the "method for producing a branched polypropylene resin according to the first embodiment of the present invention" may also be referred to as the "first manufacturing method."

[0027] According to the first manufacturing method, a branched polypropylene resin having high melt tension can be obtained. Furthermore, the branched polypropylene resin obtained by the first manufacturing method has a low gel fraction. That is, the first manufacturing method can provide a branched polypropylene resin having a melt tension of 8.0 cN or more at 200°C and a gel fraction of 10.0% by weight or less. The gel fraction will be discussed in more detail later. In addition, the branched polypropylene resin obtained by the first manufacturing method has the advantage of being able to provide polypropylene resin extruded foam particles with excellent moldability.

[0028] First, we will explain the raw materials (components) used in the first manufacturing method, and then we will explain each step of the process.

[0029] (First resin mixture) In the first manufacturing method, a mixture containing at least a polypropylene resin, a conjugated diene compound, and a radical polymerization initiator in the specific amounts described above is referred to as the first resin mixture.

[0030] (Polypropylene resin) The polypropylene resin used in the first manufacturing method may be (a) a polypropylene resin without a branched structure (i.e., a linear polypropylene resin), or (b) a mixture of a polypropylene resin without a branched structure and a branched polypropylene resin. The branched polypropylene resin used in (b) a mixture with a polypropylene resin without a branched structure may be (i) a branched polypropylene resin obtained by the first manufacturing method, (ii) a graft copolymer of propylene and a monomer other than propylene, (iii) a branched polypropylene resin obtained by introducing a branched structure to a polypropylene resin without a branched structure by irradiating the polypropylene resin without a branched structure with radiation, or (iv) a mixture thereof.

[0031] The linear polypropylene resin used in the first manufacturing method may be (a) a homopolymer of propylene, (b) a block copolymer, alternating copolymer, random copolymer or graft copolymer of propylene and a monomer other than propylene, or (c) a mixture thereof. Furthermore, the main chain of the branched polypropylene resin used in the first manufacturing method may be (a) a homopolymer of propylene, (b) a block copolymer, alternating copolymer, random copolymer or graft copolymer of propylene and a monomer other than propylene, or (c) a mixture thereof.

[0032] Polypropylene resins may have one or more structural units derived from monomers other than propylene monomers, in addition to propylene units, or may have one or more of these units. In this specification, monomers other than propylene monomers used in the manufacture of polypropylene resins (for example, in the manufacture of linear polypropylene resins) may be referred to as "comonomers," and "structural units derived from monomers other than propylene monomers" contained in polypropylene resins may be referred to as "comonomer units."

[0033] Examples of comonomers 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 (d) Dienes such as 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 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 monomers, vinyltoluene, divinylbenzene, etc.

[0034] 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.

[0035] Examples of methacrylate 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.

[0036] Examples of styrene monomers include styrene, methylstyrene, dimethylstyrene, alpha-methylstyrene, para-methylstyrene, ethylstyrene, diethylstyrene, isopropylstyrene, t-butylstyrene, bromostyrene, dibromostyrene, tribromostyrene, chlorostyrene, dichlorostyrene, and trichlorostyrene.

[0037] The polypropylene resin preferably has structural units derived from α-olefins having 2 or 4 to 12 carbon atoms as comonomer units, 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 most preferably structural units derived from ethylene and / or 1-butene. This configuration has the advantages of (a) obtaining a branched polypropylene resin having high melt tension and low gel fraction, and (b) providing polypropylene resin extruded foam particles with excellent moldability from the obtained branched polypropylene resin.

[0038] The polypropylene resin is preferably a propylene homopolymer, a polypropylene block copolymer, a polypropylene alternating copolymer, and / or a polypropylene random copolymer, and is preferably a propylene homopolymer and / or a polypropylene random copolymer. This configuration has the advantages of (a) obtaining a branched polypropylene resin having high melt tension and low gel fraction, and (b) providing polypropylene resin extruded foam particles with excellent moldability from the obtained branched polypropylene resin.

[0039] The polypropylene resin preferably contains 90 mol% or more of propylene units, more preferably 93 mol% or more, even more preferably 95 mol% or more, and particularly preferably 97 mol% or more, of the total structural units contained in the polypropylene resin. This configuration has the advantage of yielding a branched polypropylene resin with high melt tension and low gel fraction.

[0040] The melting point of polypropylene resin is not particularly limited. The melting point of polypropylene resin is preferably, for example, 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 polypropylene resin is (a) 130°C or higher, there is no risk of reduced dimensional stability of the in-molded foamed molded product, there is no risk of insufficient heat resistance of the in-molded foamed molded product, and the compressive strength of the in-molded foamed molded product tends to be increased. When the melting point is 165°C or lower, it is possible to mold extruded foamed particles at a relatively low vapor pressure, which has the advantage that extruded foamed particles can be molded using a general-purpose molding machine for polypropylene resin foamed particles.

[0041] In this specification, the melting point of polypropylene resins is measured by differential scanning calorimetry (hereinafter referred to as the "DSC method"). The specific procedure is as follows: (1) Melt the polypropylene resin by raising the temperature of 5-6 mg of polypropylene resin from 40°C to 220°C at a heating rate of 10°C / min; (2) Then, crystallize the polypropylene resin by lowering the temperature of the molten polypropylene resin from 220°C to 40°C at a cooling rate of 10°C / min; (3) Then, further raise the temperature of the crystallized polypropylene resin from 40°C to 220°C at a heating rate of 10°C / min. The temperature of the peak (melting peak) of the DSC curve of the polypropylene resin obtained during the second heating (i.e., at (3)) can be determined as the melting point of the polypropylene resin. Furthermore, if multiple peaks (melting peaks) exist in the DSC curve of the polypropylene resin obtained during the second heating cycle using the method described above, the temperature of the peak with the largest heat of fusion (melting peak) is defined as the melting point of the polypropylene resin. As a differential scanning calorimeter, for example, the DSC6200 model manufactured by Seiko Instruments Inc. can be used.

[0042] The melt flow rate (MFR) of the polypropylene resin at 230°C is not particularly limited, but is 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 at 230°C is (a) 0.5 g / 10 min or more, the resulting branched polypropylene resin has the advantage of providing an in-molded foamed molded article with less deformation and good (beautiful) surface properties, and (b) when it is 20.0 g / 10 min or less, it has the advantage of good foaming properties of the composition during extrusion foaming.

[0043] In this specification, the MFR value of polypropylene resin at 230°C is the value measured using an MFR measuring instrument described in JIS K7210, under the 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.

[0044] The first resin mixture in the first manufacturing method may further contain other resins other than polypropylene resins, to the extent that the effects of the first embodiment of the present invention are not impaired. Examples of other resins other than polypropylene resins include (a) ethylene resins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, and ethylene / methacrylic acid copolymer, and (b) styrene resins such as polystyrene, styrene / maleic anhydride copolymer, and styrene / ethylene copolymer.

[0045] (Conjugated diene compounds) Examples of conjugated diene compounds that can be used in the first embodiment of the present invention include butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, and 2,5-dimethyl-2,4-hexadiene. These conjugated diene compounds may be used individually or in combination of two or more. Among these conjugated diene compounds, butadiene and isoprene are particularly preferred because (a) they are inexpensive and easy to handle, and (b) the reaction proceeds uniformly. In other words, the conjugated diene compound that can be used in the first embodiment of the present invention is particularly preferably composed of isoprene and / or butadiene, and most preferably consists only of isoprene and / or butadiene.

[0046] The amount of conjugated diene compound used is 0.30 to 1.50 parts by weight per 100 parts by weight of polypropylene resin, preferably 0.30 to 0.80 parts by weight, and more preferably 0.30 to 0.60 parts by weight. If the amount of conjugated diene compound used is less than 0.30 parts by weight per 100 parts by weight of polypropylene resin, the degree of modification of the polypropylene resin (the number of crosslinks introduced into the polypropylene resin) will be insufficient, and as a result, the melt tension of the resulting branched polypropylene resin cannot be sufficiently increased (for example, to 8.0 cN or more). If the amount of conjugated diene compound used exceeds 1.50 parts by weight per 100 parts by weight of polypropylene resin, the crosslinking between polypropylene resins by the conjugated diene compound will be excessive, resulting in a high viscosity of the resulting branched polypropylene resin. As a result, it becomes difficult to obtain high-magnification polypropylene resin extruded foam particles from the resulting branched polypropylene resin.

[0047] Within the limits of not impairing the effects of the first embodiment of the present invention, in addition to the polypropylene resin, the conjugated diene compound, and the radical polymerization initiator, monomers copolymerizable with the conjugated diene compound may be used in combination. In other words, the first resin mixture in the first production method may further contain monomers copolymerizable with the conjugated diene compound. Examples of monomers copolymerizable with the conjugated diene compound include (a) acrylic acid esters such as vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, metal acrylate salts, metal methacrylate salts, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and stearyl acrylate, and (b) methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and stearyl methacrylate.

[0048] (Radical polymerization initiator) The radical polymerization initiator according to the first embodiment of the present invention is an organic peroxide having the ability to abstract hydrogen from polypropylene resins and conjugated diene compounds. Suitable radical polymerization initiators for use in the first embodiment of the present invention include organic peroxides such as ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxycarbonates, peroxydicarbonates, and peroxyesters.

[0049] Organic peroxides 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-butyl4,4-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, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane. Dialkyl peroxides such as t-peroxy-3-hexine; diacyl peroxides such as benzoyl peroxide; peroxyesters such as t-butyl peroxyoctate, t-butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy3,5,5-trimethylhexanoate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl peroxyacetate, t-butyl peroxybenzoate, and di-t-butyl peroxyisophthalate; peroxycarbonates such as t-butyl peroxyisopropyl carbonate; etc. are preferred. Among these, t-butyl peroxyisopropyl carbonate, t-butyl peroxybenzoate, and 2,2-bis(t-butylperoxy)butane are preferred. In other words, in the first embodiment of the present invention, the radical polymerization initiator preferably comprises one or more selected from the group consisting of peroxyketals, peroxyesters, and peroxycarbonates, and more preferably comprises only one or more selected from this group. In the first embodiment of the present invention, the radical polymerization initiator particularly preferably comprises one or more selected from peroxycarbonates, and may consist of only one or more selected from peroxycarbonates. These organic peroxides may be used individually or in combination of two or more.

[0050] The amount of radical polymerization initiator used is 0.50 to 2.00 parts by weight per 100 parts by weight of polypropylene resin, preferably 0.60 to 1.80 parts by weight, more preferably 0.70 to 1.60 parts by weight, even more preferably 0.90 to 1.50 parts by weight, and particularly preferably 1.10 to 1.50 parts by weight. If the amount of radical polymerization initiator used is less than 0.50 parts by weight per 100 parts by weight of polypropylene resin, the degree of modification of the polypropylene resin may be insufficient. As a result, when the resulting branched polypropylene resin is extruded and foamed, the strain-hardening properties of the branched polypropylene resin do not develop sufficiently, and there is a tendency to obtain only extruded foamed particles with a high open-cell ratio. If the amount of radical polymerization initiator used exceeds 2.00 parts by weight per 100 parts by weight of polypropylene resin, the amount of gel in the resulting branched polypropylene resin may increase due to increased hydrogen extraction from the polypropylene resin by the radical polymerization initiator. As a result, when using the branched polypropylene resin for extrusion foaming, there is a tendency to obtain only extruded foamed particles with a low foaming ratio and a high percentage of open cells.

[0051] (Other ingredients) In the first manufacturing method, in addition to the polypropylene resin, conjugated diene compound, and radical polymerization initiator described above, other components may be used as needed. In other words, the first resin mixture may further contain other components as needed. Examples of other components include (a) resins other than polypropylene resins (sometimes referred to as "other resins"), (b) stabilizers such as antioxidants, metal deactivators, phosphorus-based processing stabilizers, ultraviolet absorbers, ultraviolet stabilizers, fluorescent whitening agents, metal soaps, and antacid adsorbents, and / or (c) additives such as foam regulators, colorants, chain transfer agents, lubricants, plasticizers, fillers, reinforcing agents, flame retardants, and antistatic agents. Other resins include (a) polyolefin resins other than polypropylene resins, such as ethylene / propylene random copolymers, ethylene / propylene block copolymers, and ethylene / propylene alternating copolymers; (b) ethylene resins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene / vinyl acetate copolymers, ethylene / acrylic acid copolymers, and ethylene / methacrylic acid copolymers; and (c) styrene resins such as polystyrene, styrene / maleic anhydride copolymers, and styrene / ethylene copolymers. These other components may be used individually or in combination of two or more.

[0052] (1st manufacturing equipment) The first manufacturing apparatus used in the first manufacturing method comprises a first melt-kneading section having a screw and a die. Examples of the first melt-kneading section include a single-screw extruder having a single screw and a multi-screw extruder having multiple screws (for example, a twin-screw extruder having two screws). Of these, a multi-screw extruder is preferred as the first melt-kneading section, and a twin-screw extruder is more preferred, due to its ability to perform continuous kneading and its ease of scaling up.

[0053] The die of the first manufacturing apparatus used in the first manufacturing method is located at the end of the first manufacturing apparatus in the extrusion direction and has at least one hole (sometimes referred to as an extrusion hole) for discharging branched polypropylene resin. The number and diameter of the holes in the die, as well as the thickness of the die (length of the holes in the extrusion direction), are not particularly limited.

[0054] (First melting and mixing process) The first melt-kneading step involves supplying a "raw material for branched polypropylene resin," which includes a polypropylene resin, a conjugated diene compound, and a radical polymerization initiator, to the first melt-kneading section, and melt-kneading the first resin mixture containing these raw materials within the first melt-kneading section. Melt-kneading in the first melt-kneading step means kneading the polypropylene resin and the first resin mixture, which includes the polypropylene resin and the conjugated diene compound, with the radical polymerization initiator within the first melt-kneading section at a temperature at which the polypropylene resin can melt. The first melt-kneading step can also be described as a step in preparing (obtaining) a branched polypropylene resin by reacting the polypropylene resin with the conjugated diene compound and the radical polymerization initiator.

[0055] The first melt-mixing step refers to the period from when the unmelted polypropylene resin is introduced into the first melt-mixing section until the resulting branched polypropylene resin is introduced from the first melt-mixing section into the die.

[0056] In the first melt-kneading step, it is sufficient that a branched polypropylene resin is ultimately prepared. The specific manner in which the polypropylene resin, a conjugated diene compound, and a radical polymerization initiator are supplied to the raw material supply port of the first melt-kneading section in the first melt-kneading step, and these raw materials are melt-kneaded to prepare a polypropylene resin having a branched structure is not particularly limited, and examples include the following methods (a1) to (a4): (a1) A method for preparing a first resin mixture by simultaneously or in any order mixing an unmelted polypropylene resin, a conjugated diene compound, and a radical polymerization initiator; and then supplying the first resin mixture to a first melt-kneading section to melt-knead the first resin mixture and prepare a polypropylene resin having a branched structure; (a2) A method for preparing a polypropylene resin having a branched structure by supplying unmelted polypropylene resin to a first melt-kneading section and melt-kneading the polypropylene resin thereafter, supplying a conjugated diene compound and a radical polymerization initiator to the melt-kneaded polypropylene resin from the same or separate raw material supply ports located in the middle of the first melt-kneading section, and further melt-kneading the resulting first resin mixture; (a3) A method for preparing a polypropylene resin having a branched structure by supplying unmelted polypropylene resin and a radical polymerization initiator to the first melt-mixing section from the same or separate raw material supply ports, and melt-mixing the polypropylene resin and radical polymerization initiator. Then, supplying a conjugated diene compound to the melt-mixed mixture of polypropylene resin and radical polymerization initiator from a raw material supply port located in the middle of the first melt-mixing section, and further melt-mixing the resulting first resin mixture; (a4) A method for preparing a polypropylene resin having a branched structure by supplying unmelted polypropylene resin and a conjugated diene compound to the first melt-kneading section from the same or separate raw material supply ports, and melt-kneading the polypropylene resin and the conjugated diene compound. Subsequently, supplying a radical polymerization initiator to the melt-kneaded mixture of polypropylene resin and conjugated diene compound from a raw material supply port located in the middle of the first melt-kneading section, and further melt-kneading the resulting first resin mixture.

[0057] In the first manufacturing method, if other components are used as necessary, the timing of supplying the other components to the first melt-mixing section is not particularly limited. The other components may be added to the first resin mixture prepared in advance in (i)(a1), and may be supplied to the first melt-mixing section together with or separately from the unmelted polypropylene resin, conjugated diene compound, or radical polymerization initiator from the same or separate raw material supply port as these raw materials in (ii)(a2) to (a4).

[0058] Since the polypropylene resin in the first resin mixture becomes molten at the start of the reaction with the radical polymerization initiator, methods (a2) to (a4) are preferred. Depending on the properties of the radical polymerization initiator and conjugated diene compound used, method (a3) ​​is more preferred for raw material supply from a safety viewpoint.

[0059] (Discharge process) The first manufacturing method includes an extrusion step of extruding a branched polypropylene resin obtained by melt-kneading a first resin mixture from a die. The extrusion step refers to the period from when the branched polypropylene resin enters the die from the first melt-kneading section until the branched polypropylene resin is extruded from the die.

[0060] In the extrusion process, branched polypropylene resin is extruded from the die in strand form at a temperature at which it can be extruded from the die's holes. By cooling and shredding the extruded strand-shaped branched polypropylene resin (also simply called "strand"), branched polypropylene resin of the desired shape and size can be obtained. The method of cooling the strand is not particularly limited and includes water cooling using water. The strand may be shredded after cooling, or cooling and shredding may be performed simultaneously.

[0061] (Specific energy E1) The specific energy E1 [kWh / kg] is the value obtained by dividing the power P1 [kW] required to drive the screw of the first melting and mixing section, more specifically the power P1 [kW] required to drive the motor that rotates the screw of the first melting and mixing section, by the discharge rate Q1 [kg / h] of the branched polypropylene resin. In this specification, "power P1 required to drive the screw of the first melting and mixing section" may be referred to as "required power P1".

[0062] By setting the specific energy E1 to 0.35 kWh / kg or higher, the melt tension of the resulting branched polypropylene resin is improved and the gel fraction is reduced. The specific energy E1 is more preferably 0.38 kWh / kg or higher, and particularly preferably 0.40 kWh / kg or higher. The upper limit of the specific energy E1 is not particularly limited, but from the viewpoint of energy efficiency and resin degradation, it is preferably 0.60 kWh / kg or less, and more preferably 0.50 kWh / kg or less.

[0063] The specific energy E1 can be adjusted to a desired range by appropriately selecting the temperature of the first melt-mixing section, the temperature of the first resin mixture in the first melt-mixing section, the time of the first melt-mixing process (melt-mixing time), the rotational speed N1 of the screw in the first melt-mixing section, the discharge amount Q1 of the branched polypropylene resin, the ratio of the effective length L1 of the screw in the first melt-mixing section to the bore diameter D1 (L1 / D1), etc. Note that "bore diameter D1" is the inner diameter of the cylinder that houses the screw.

[0064] The required power P1 can be calculated from the motor capacity of the screw in the first melting and mixing section, the motor current value of the screw in the first melting and mixing section, the discharge volume Q1 of the branched polypropylene resin, the rotational speed N1 of the screw in the first melting and mixing section, and the maximum rotational speed of the screw in the first melting and mixing section. Note that in calculating the required power P1, the motor torque of the screw in the first melting and mixing section may be used instead of the motor current value.

[0065] The first melt-mixing step preferably further includes a specific energy E1 adjustment step that adjusts the specific energy E1 to 0.35 kWh / kg or more. The specific energy E1 adjustment step is a step of adjusting one or more selected from the group consisting of, for example, the temperature of the first melt-mixing section, the temperature of the first resin mixture, the melt-mixing time, the rotational speed N1 of the screw of the first melt-mixing section, the discharge amount Q1 of the branched polypropylene resin, and the ratio (L1 / D1) of the effective length L1 to the diameter D1 of the screw of the first melt-mixing section.

[0066] The temperature of the first melt-mixing section is not particularly limited, and should be a temperature at which the polypropylene resin can melt and the specific energy E1 is 0.35 kWh / kg or more. Such a temperature is preferably in the range of 160°C to 300°C, more preferably in the range of 160°C to 250°C, and even more preferably in the range of 160°C to 210°C. An example of the temperature of the first melt-mixing section is the temperature of the cylinder (barrel) that houses the screw inside. The above configuration of the temperature of the first melt-mixing section is preferable in that (a) the polypropylene resin melts and does not decompose thermally, and (b) the radical polymerization initiator decomposes sufficiently.

[0067] In the first melt-mixing step, the temperature of the first resin mixture is not particularly limited, and any temperature at which the specific energy E1 is 0.35 kWh / kg or higher is acceptable.

[0068] The melt-mixing time is not particularly limited and should be the time required for the specific energy E1 to reach 0.35 kWh / kg or more. The melt-mixing time may be, for example, 30 seconds to 10 minutes, 30 seconds to 5 minutes, 30 seconds to 2 minutes, or 30 seconds to 1 minute. The melt-mixing time refers to the time of the first melt-mixing process, that is, the time from when the polypropylene resin is supplied to the first melt-mixing section until the resulting branched polypropylene resin is extruded through the die, and can also be said to be the time that the polypropylene resin supplied to the first melt-mixing section is present in the first melt-mixing section.

[0069] The rotational speed N1 of the screw in the first melting and mixing section is not particularly limited and should be any rotational speed N1 necessary for the specific energy E1 to be 0.35 kWh / kg or more. The rotational speed N1 of the screw in the first melting and mixing section may be set appropriately depending on the size of the first melting and mixing section (for example, the ratio of the effective length L1 to the diameter D1 of the screw in the first melting and mixing section (L1 / D1)) and / or the discharge rate Q1, etc.

[0070] The discharge rate Q1 of the branched polypropylene resin is not particularly limited and should be any discharge rate Q1 necessary for the specific energy E1 to be 0.35 kWh / kg or more. The discharge rate Q1 of the branched polypropylene resin may be set appropriately depending on the size of the first melt-mixing section (for example, the ratio of the effective length L1 of the screw of the first melt-mixing section to the diameter D1 (L1 / D1)).

[0071] The ratio of the effective length L1 to the diameter D1 of the screw in the first melting and mixing section (L1 / D1) is a value that indicates the mixing efficiency of the screw. The larger the value of L1 / D1, the greater the amount of work done during melting and mixing, and the higher the specific energy E1. The value of L1 / D1 can be appropriately selected so that the specific energy E1 is 0.35 kWh / kg or more, but for example, it may be around 30 to 75 or around 35 to 65.

[0072] [1-3. Polypropylene resins with branched structures] The branched polypropylene resin produced by the manufacturing method described in section 1-2 above [Method for producing a branched polypropylene resin] is also a first embodiment of the present invention.

[0073] In this specification, the "branched polypropylene resin produced by the manufacturing method described in section 1-2. Method for producing a branched polypropylene resin," that is, the "branched polypropylene resin according to the first embodiment of the present invention," may also be referred to as "the branched polypropylene resin."

[0074] This branched polypropylene resin has the advantage of achieving both high melt tension and low gel fraction. Because this branched polypropylene resin has high melt tension and low gel fraction, applying this branched polypropylene resin to the extrusion foaming method makes it possible to provide polypropylene resin extruded foam particles with good moldability. This is presumed to be partly due to the fact that the cell membrane is sufficiently maintained in the polypropylene resin extruded foam particles obtained from this branched polypropylene resin by the extrusion foaming method, and thus these polypropylene resin extruded foam particles have a sufficiently low open-cell ratio. However, this presumption does not limit the present invention in any way.

[0075] The melt tension of this branched polypropylene resin at 200°C is not particularly limited, but is preferably 8.0 cN or higher, more preferably 8.5 cN or higher, more preferably 9.0 cN or higher, and even more preferably 9.5 cN or higher. The upper limit of the melt tension at 200°C is not particularly limited.

[0076] When the melt tension of the branched polypropylene resin is as described above, when polypropylene resin extruded foam particles are produced by an extrusion foaming method using the branched polypropylene resin, the melt tension of the branched polypropylene resin during foaming becomes sufficiently high. As a result, the obtained polypropylene resin extruded foam particles have the advantage of being able to sufficiently retain the cell membrane. With the first manufacturing method described in section [1-2. Method for manufacturing polypropylene resin having a branched structure], a branched polypropylene resin having the melt tension within the range described above can be obtained.

[0077] The method for measuring melt tension in this specification is described below. In this specification, melt tension is measured using a Capillograph 1D (manufactured by Toyo Seiki Seisakusho Co., Ltd., Japan). Specifically, the procedure is as follows (1) to (5): (1) A sample resin for measurement (branched polypropylene resin) 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 dispensed in a string-like form from a capillary die (1.0 mm diameter, 10 mm length) at a constant piston descent speed (10 mm / min), and this string-like material is passed through a tension-detecting pulley located 350 mm below the capillary die, after which winding using a winding roll is started; (4) After the winding of the string-like material stabilizes, 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 in 4 minutes; (5) The load on the load cell pulley when the string-like material breaks is measured as the melt tension.

[0078] The gel fraction of this branched polypropylene resin is not particularly limited, but a lower amount is preferable. The gel fraction is preferably 10.0% by weight or less, more preferably 9.0% by weight or less, more preferably 8.5% by weight or less, even more preferably 8.0% by weight or less, even more preferably 7.5% by weight or less, and particularly preferably 7.0% by weight or less.

[0079] When the gel fraction of the branched polypropylene resin has the above configuration, it is presumed that crosslinking in the branched polypropylene resin occurs at an appropriate frequency. Therefore, when producing polypropylene resin extruded foam particles by an extrusion foaming method using a branched polypropylene resin, there are advantages such as (a) the melt tension of the branched polypropylene resin during foaming being sufficiently high, and (b) the generation of gel in the resulting polypropylene resin extruded foam particles being suppressed. Here, "gel" refers to a gel-like (also called a gel-like) foreign substance that is locally generated in the polypropylene resin extruded foam particles due to excessive crosslinking. Gel can cause cell membrane rupture in polypropylene resin extruded foam particles. With the first manufacturing method described in section [1-2. Method for manufacturing polypropylene resin having a branched structure], a branched polypropylene resin having a gel fraction within the range described above can be obtained.

[0080] In this specification, "gel fraction" refers to the value calculated by the following formula (1) after treating a sample made of branched polypropylene resin in p-xylene at 130°C for 6 hours using a wire mesh with a mesh size of 37 μm (400 mesh), drying the residue remaining in the wire mesh, and measuring its weight: Gel fraction (weight %) = (weight of residue / weight of sample) × 100 (1).

[0081] The method for measuring gel fraction will be explained in detail. While the method for measuring gel fraction is not particularly limited, for example, the gel fraction can be determined by using a gel fraction measuring device and performing the following steps (1) to (10) in order: (1) Weigh 0.5 g of branched polypropylene resin accurately and use this as the sample; (2) Place the sample in a bag-shaped wire mesh with a mesh size of 37 μm (400 mesh) and pleated sides; (3) Place the stirrer piece and the wire mesh containing the sample from (2) into a 300 mL round-bottom flask, and then add 150 mL of p-xylene to the round-bottom flask; (4) Stir the solution in the round-bottom flask at 130°C and 80 rpm for 1 hour using an oil bath apparatus and a stirrer; (5) After completely replacing the p-xylene in the round-bottom flask, stir the solution in the round-bottom flask for 1 hour; (6) After completely replacing the p-xylene in the round-bottom flask, stir the solution in the round-bottom flask for 4 hours; (7) Remove the wire mesh from the round-bottom flask with tweezers, rinse the wire mesh with p-xylene to remove any deposits from the sides of the wire mesh; (8) Dry the residue (resin-insoluble material) inside the wire mesh in a vacuum dryer at 80°C for 8 hours; (9) After cooling, measure the weight of the residue with each 400-mesh wire mesh; (10) Calculate the gel fraction (weight %) based on the following formula; Gel fraction (weight %) = Residue weight (g) / Sample weight (0.5g) × 100 Here, the weight of the residue inside the wire mesh = the weight of the wire mesh after filtration and drying (including the residue) - the weight of the wire mesh only before filtration.

[0082] The MFR of this branched polypropylene resin at 230°C is not particularly limited, but for example, 0.5 g / 10 min to 20.0 g / 10 min is preferred, 1.0 g / 10 min to 15.0 g / 10 min is more preferred, 1.5 g / 10 min to 10.0 g / 10 min is even more preferred, 2.0 g / 10 min to 10.0 g / 10 min is even more preferred, and 2.0 g / 10 min to 5.0 g / 10 min is particularly preferred. When the MFR of this branched polypropylene resin at 230°C is (a) 0.5 g / 10 min or more, the branched polypropylene resin has the advantage of being able to provide an in-molded foamed molded article with little deformation and good (beautiful) surface properties, and (b) when it is 20 g / 10 min or less, the composition containing the branched polypropylene resin has the advantage of having good foaming properties when extruded foamed.

[0083] In this specification, the MFR of branched polypropylene resin at 230°C can be measured in the same manner as the MFR of polypropylene resin at 230°C, except that branched polypropylene resin is used instead of polypropylene resin.

[0084] This branched polypropylene resin contains structural units derived from polypropylene resins and structural units derived from conjugated diene compounds. If other resins are used in the manufacture of the branched polypropylene resin, this branched polypropylene resin contains components derived from the other resins and / or other resins. Furthermore, this branched polypropylene resin may contain structural units derived from radical polymerization initiators. Here, "structural units derived from radical polymerization initiators" refers to structural units derived from various substances produced by the decomposition of radical polymerization initiators in the manufacture of branched polypropylene resins. If other components are used in the manufacture of branched polypropylene resins, this branched polypropylene resin contains the other components. The descriptions in section 1-2. Method for manufacturing branched polypropylene resins may be appropriately referenced as examples of the forms of polypropylene resins, other resins, conjugated diene compounds, radical polymerization initiators, and other components.

[0085] The shape and size of the branched polypropylene resin are not particularly limited and may be, for example, pellets. In this specification, pellets refer to polymers (resin) granulated into small, lumpy molded materials having approximately constant length and thickness, such as cylindrical, spherical, elliptical, or polygonal prisms (e.g., triangular, square, pentagonal, or hexagonal prisms). The size of the pellets is not particularly limited as long as they can be handled, but examples include those with a length of approximately 2.5 mm to 3.5 mm and a thickness of approximately 2.5 mm to 3.5 mm.

[0086] (Application) Applications of this branched polypropylene resin include extruded foamed particles and extruded foamed sheets. Extruded foamed particles or extruded foamed sheets can be obtained by extruding a composition containing this branched polypropylene resin and a foaming agent. This branched polypropylene resin can be used in injection foam molding, such as core-back molding, by using this branched polypropylene resin and a foaming agent. Because this branched polypropylene resin has high melt tension, the film obtained by molding this branched polypropylene resin into a film has the advantage of being difficult to tear. Therefore, this branched polypropylene resin can also be used for non-foamed films and surface coatings for paper. Furthermore, this branched polypropylene resin can also be used in ordinary injection molding (non-foamed).

[0087] [1-4. Method for producing polypropylene resin extruded foam particles] A method for producing polypropylene resin extruded foam particles according to a first embodiment of the present invention includes a first step of melt-kneading (a) a polypropylene resin having a branched structure obtained by the manufacturing method described in section [1-2. Method for producing polypropylene resin having a branched structure] or a polypropylene resin having a branched structure described in section [1-3. Polypropylene resin having a branched structure] and (b) a foaming agent in a second manufacturing apparatus, and a second step of extruding the composition obtained in the first step through a die into a region where the pressure is lower than the internal pressure of the second manufacturing apparatus.

[0088] The method for producing polypropylene resin extruded foam particles according to the first embodiment of the present invention has the above-described configuration, and therefore can provide polypropylene resin extruded foam particles with good moldability.

[0089] (First step) The first step will now be explained in detail. A specific example of the first step is the process of melting the branched polypropylene resin in the second manufacturing apparatus and dissolving the foaming agent into the branched polypropylene resin. The first step can also be described as the process of preparing a molten and kneaded mixture of the branched polypropylene resin and the foaming agent.

[0090] The blowing agent used in one embodiment of the present invention is not particularly limited, and known organic and inorganic blowing agents can be used. Examples of organic blowing agents include aliphatic hydrocarbons such as propane and fluorinated hydrocarbons such as difluoroethane. Examples of inorganic blowing agents include carbon dioxide, air, nitrogen and other inorganic gases, and water. The blowing agents described above may be used individually or in combination of two or more. The amount of blowing agent used in the first step may be appropriately adjusted according to the type of blowing agent and the target foaming ratio of the polypropylene resin extruded foam particles.

[0091] In the first step, if necessary, further nucleating agents, stabilizers (e.g., antioxidants, metal deactivators, phosphorus-based processing stabilizers, UV absorbers, UV stabilizers, fluorescent whitening agents, metal soaps, and antacid adsorbents) and additives (e.g., colorants, crosslinking agents, chain transfer agents, lubricants, plasticizers, fillers, reinforcing agents, pigments, dyes, flame retardants, and antistatic agents) may be used.

[0092] In the first step, the branched polypropylene resin and the blowing agent, as well as any other optional components, may be mixed before being supplied to the second manufacturing apparatus, or they may be mixed within the second manufacturing apparatus. In other words, in the first step, the composition may be supplied to the second manufacturing apparatus, or the composition may be prepared (completed) within the second manufacturing apparatus. In the first step, (i) the method and sequence of mixing the branched polypropylene resin and the blowing agent, as well as any other optional components, or (ii) the method and sequence of supplying the branched polypropylene resin and the blowing agent, as well as any other optional components, to the second manufacturing apparatus is not particularly limited.

[0093] The composition obtained in the first step may be cooled before being extruded into a low-pressure region.

[0094] (Second step) The second step involves extruding the composition obtained in the first step, i.e., the melted and kneaded composition, through a die into a region with a pressure lower than the internal pressure of the second manufacturing apparatus, and then shredding the extruded composition. The second step yields extruded foam particles. Therefore, the second step can also be described as a granulation step for granulating polypropylene resin extruded foam particles.

[0095] In the second step, the region in which the composition obtained in the first step is extruded is not particularly limited, as long as the pressure is lower than the internal pressure of the second manufacturing apparatus. For example, in the second step, the composition obtained in the first step may be extruded into the gas phase or into the liquid phase.

[0096] In the second step, the composition extruded into a region with a pressure lower than the internal pressure of the second manufacturing apparatus immediately begins to foam. In the second step, the foaming composition may be shredded, or the foamed composition may be shredded. If the foaming composition is shredded, the shredded composition may complete foaming in the region to which it was extruded.

[0097] Depending on the region in which the composition obtained in the first step is extruded and the method of shredding the composition, the second step (granulation step) can be broadly classified into two types: the cold cut method and the die face cut method. An example of the cold cut method is a method in which the composition containing a foaming agent extruded from the die is foamed, and the strand-shaped foam is taken up while being cooled through a water tank and then shredded (strand cut method). The die face cut method is a method in which the composition extruded from the holes of the die is cut by a cutter that rotates while in contact with the surface of the die or while maintaining a small gap.

[0098] The die face cutting method can be further divided into the following three types based on differences in cooling methods: the underwater cut (UWC) method, the watering cut (WRC) method, and the hot cut (HC) method. The UWC method involves filling a chamber attached to the tip of the die with cooling water adjusted to a predetermined pressure so that it is in contact with the resin discharge surface of the die, and cutting the composition extruded from the hole in the die underwater. The WRC method involves placing a cooling drum downstream of the die through which cooling water flows along the inner circumference of the cooling drum connected to the die, and cooling the composition cut by the cutter in the air while foaming, or after foaming, in the cooling water. The HC method involves cutting the composition in the air with a cutter, and cooling the cut composition in the air while foaming, or after foaming. The HC method may also include the mist cut method, which further includes a step of spraying a mixed mist of water and air.

[0099] [1-5. Polypropylene resin extruded foam particles] Polypropylene resin extruded foam particles produced by the manufacturing method described in section [1-4. Method for producing polypropylene resin extruded foam particles] are also a first embodiment of the present invention. Polypropylene resin extruded foam particles according to the first embodiment of the present invention can also be said to be produced by foaming a branched polypropylene resin or branched polypropylene resin pellets described in section [1-3. Polypropylene resin having a branched structure]. Polypropylene resin extruded foam particles according to the first embodiment of the present invention can also be said to include a branched polypropylene resin or branched polypropylene resin pellets described in section [1-3. Polypropylene resin having a branched structure].

[0100] In this specification, "extruded foamed polypropylene resin particles" may also be referred to as "extruded foamed particles." In this specification, "extruded foamed polypropylene resin particles produced by the manufacturing method described in section 1-4. Method for producing extruded foamed polypropylene resin particles," that is, "extruded foamed polypropylene resin particles obtained by the manufacturing method for extruded foamed polypropylene resin particles according to the first embodiment of the present invention," may also be referred to as "first extruded foamed particles."

[0101] The first extruded foamed particle has the advantage of excellent moldability because it has the aforementioned structure.

[0102] [1-6. Method for manufacturing polypropylene resin foam molded articles] A method for producing a polypropylene resin foam molded article according to the first embodiment of the present invention includes a heating step of filling a molding space formed from at least two molds of a mold with polypropylene resin extruded foam particles obtained by the manufacturing method described in section [1-4. Method for producing polypropylene resin extruded foam particles] (i.e., first extruded foam particles) or polypropylene resin extruded foam particles described in section [1-5. Polypropylene resin extruded foam particles] (i.e., first extruded foam particles), and then heating the polypropylene resin extruded foam particles in the molding space.

[0103] In this specification, "polypropylene resin foamed molded article" may also be referred to as "foamed molded article." In this specification, "polypropylene resin foamed molded article according to the first embodiment of the present invention" may also be referred to as "first foamed molded article." Furthermore, a foamed molded article obtained by manufacturing using a mold may also be referred to as an in-mold foamed molded article.

[0104] The method for producing a polypropylene resin foamed molded article according to the first embodiment of the present invention has the above-described configuration, and therefore can provide a polypropylene resin molded article with a high foaming ratio and excellent fusion properties.

[0105] In the method for manufacturing a polypropylene resin foam molded article according to the first embodiment of the present invention, the mold used is not particularly limited. The mold may consist of at least two molds, for example, a fixed mold that cannot be driven and a movable mold that can be driven. As the movable mold approaches the fixed mold, a molding space is formed inside the fixed mold and the movable mold. When the extruded foam particles in the molding space are heated, the mold frame of the fixed mold and the mold frame of the movable mold may come into contact (i.e., the mold can be sealed). On the other hand, when filling the molding space with extruded foam particles, the mold frame of the fixed mold and the mold frame of the movable mold do not need to come into contact, and a small gap (also called cracking) may be formed between the mold frame of the fixed mold and the mold frame of the movable mold.

[0106] In the method for manufacturing a polypropylene resin foam molded article according to the first embodiment of the present invention, the method for filling the molding space with polypropylene resin extruded foam particles and the method for heating the polypropylene resin extruded foam particles in the mold are not particularly limited. Examples of these methods include the following (b1) to (b4).

[0107] (b1) A method in which extruded foam particles are pressurized with an inorganic gas in a container to impregnate the extruded foam particles with the inorganic gas and apply a predetermined internal particle pressure to the extruded foam particles. Subsequently, the extruded foam particles are filled into the molding space of a mold, and the extruded foam particles in the molding space are heated with steam; (b2) A method of filling the molding space of a mold with extruded foam particles, compressing the extruded foam particles in the molding space to reduce its volume by 10% to 75%, and then heating the extruded foam particles in the molding space with steam; (b3) A method in which extruded foam particles are compressed with gas pressure and filled into the molding space of a mold. Then, the extruded foam particles in the molding space are heated with steam, utilizing the recovery force of the extruded foam particles in the molding space; (b4) A method in which extruded foam particles are filled into the molding space of a mold without any special pretreatment, and then the extruded foam particles in the molding space are heated with steam.

[0108] In the manufacturing of this foamed molded product, the pressure of the steam used to heat the extruded foam particles (hereinafter sometimes referred to as vapor pressure) varies depending on the characteristics of the extruded foam particles used, and cannot be specified in general terms.

[0109] In the method described in (b1) above, at least one inorganic gas can be selected from the group consisting of air, nitrogen, oxygen, carbon dioxide, helium, neon, argon, etc. Among these inorganic gases, air and / or carbon dioxide are preferred.

[0110] In the method described in (b1), the internal pressure of the foamed particles is preferably 0.05 MPa to 0.30 MPa (absolute pressure), and preferably 0.06 MPa to 0.25 MPa (absolute pressure).

[0111] In the method described in (b1) above, the temperature inside the container when impregnating the foamed particles with inorganic gas is preferably 10°C to 90°C, and more preferably 40°C to 90°C.

[0112] <Second Embodiment> The second embodiment relates to a method for producing polypropylene resin extruded foam particles.

[0113] However, prior art relating to extruded foam particles, such as that described in Patent Document 2, is insufficient from the standpoint of moldability of polypropylene resin extruded foam particles, and there is room for further improvement.

[0114] The second embodiment was made in view of the above-mentioned problems, and its purpose is to provide polypropylene resin extruded foam particles with excellent moldability and a method for producing the same.

[0115] As a result of diligent research to solve the above problems, the inventors have independently discovered the following findings and have completed a second embodiment of the present invention: By melt-kneading a branched polypropylene resin and a foaming agent while controlling the specific energy introduced into the melt-kneading process to a predetermined value or less, it is surprisingly possible to widen the molding width when using the resulting polypropylene resin extruded foam particles, that is, to obtain polypropylene resin extruded foam particles with excellent moldability.

[0116] The technical concept of the second embodiment will be explained in more detail below.

[0117] [2-1. Technical Concept of the Second Embodiment] Polypropylene resin in-mold foam molded articles are manufactured by filling a mold with polypropylene resin foam particles and heating and fusing them with steam or the like. Polypropylene resin in-mold foam molded articles are required to possess good physical properties in terms of arbitrary shape, cushioning, lightness, compressive strength, and heat insulation.

[0118] The physical properties of polypropylene resin in-mold foam molded articles can be determined by various factors, but it has been found that they change significantly depending on the vapor pressure during molding (for example, during in-mold foam molding, and more specifically, during heat fusion). Therefore, in order to obtain polypropylene resin in-mold foam molded articles with desired physical properties, strict control of the vapor pressure during molding was required.

[0119] Therefore, the inventors diligently investigated ways to increase the degree of freedom of vapor pressure during molding. As a result, the inventors independently discovered that the degree of freedom of vapor pressure during molding increases when using polypropylene resin extruded foam particles manufactured by a specific manufacturing method. More specifically, the inventors independently discovered the following findings and completed a second embodiment of the present invention: In the production of polypropylene resin extruded foam particles, by controlling the specific energy introduced into the melt kneading of a branched polypropylene resin and a foaming agent to a predetermined value or less, it is surprisingly possible to widen the degree of freedom (molding range) of vapor pressure during molding using the resulting polypropylene resin extruded foam particles.

[0120] By using polypropylene resin extruded foam particles with a wide molding width during molding, it is possible to obtain polypropylene resin in-mold foam molded articles that exhibit excellent compressive strength, excellent fusion properties, and / or a beautiful surface, even when molding is performed at a vapor pressure lower or higher than the conventionally acceptable range.

[0121] A second embodiment of the present invention will be described below, but the present invention is not limited thereto. With regard to each aspect of the second embodiment of the present invention, the description of the first embodiment will be appropriately referenced except for the aspects described in detail below.

[0122] [2-2. Method for producing polypropylene resin extruded foam particles] A method for producing polypropylene resin extruded foam particles according to a second embodiment of the present invention uses a third manufacturing apparatus comprising a second melt-kneading section having a plurality of screws and a granulation section having a die, and includes a second melt-kneading step in which a branched polypropylene resin and a foaming agent are melt-kneaded in the second melt-kneading section, and an extrusion foaming step in which the composition obtained in the second melt-kneading step is discharged through the die into a region where the pressure is lower than the internal pressure of the third manufacturing apparatus, and the specific energy E2 is 0.190 kWh / kg or less. Here, the specific energy E2 is the value obtained by dividing the power P2 required to drive the plurality of screws in the second melt-kneading section by the discharge amount Q2 of the composition.

[0123] According to a second embodiment of the present invention, polypropylene resin extruded foam particles with excellent moldability and a method for producing the same can be provided.

[0124] In this specification, the "method for producing polypropylene resin extruded foam particles according to the second embodiment of the present invention" may be referred to as the "second manufacturing method." The extruded foam particles obtained by the second manufacturing method can be molded into a polypropylene resin foamed molded article by molding the extruded foam particles (for example, in-mold foaming).

[0125] The second manufacturing method has the advantage of being able to provide extruded foam particles with excellent moldability due to the configuration described above. The second manufacturing method also has the advantage of being able to provide extruded foam particles with a low open-cell ratio. In this specification, the moldability of extruded foam particles is evaluated by the molding width of the extruded foam particles. The molding width of extruded foam particles will be described later.

[0126] First, we will explain the raw materials (components) used in the second manufacturing method, and then we will explain each step of the process.

[0127] (2-2-1. Second resin mixture) In the second manufacturing method, raw materials (components) other than the foaming agent may be referred to as the "second resin mixture." The second resin mixture includes a polypropylene resin having a branched structure and may optionally include additives such as a bubble nucleating agent.

[0128] (Linear polypropylene resin) The linear polypropylene resin, which is a raw material for the branched polypropylene resin used in the second manufacturing method, will be described below. Each aspect of the linear polypropylene resin described in detail below may be interpreted as each aspect of the main chain of the branched polypropylene resin.

[0129] In the second embodiment, the linear polypropylene resin may be (a) a homopolymer of propylene, (b) a block copolymer, alternating copolymer, or random copolymer of propylene and a monomer other than propylene, or (c) a mixture of two or more of these.

[0130] In the second embodiment, the linear polypropylene resin may have one or more structural units derived from monomers other than propylene monomers (i.e., structural units derived from comonomers (comonomer units)) in addition to propylene units, or may have one or more of these units.

[0131] The comonomer in the second embodiment is the same as that described in the section on (polypropylene resin) in the first embodiment; therefore, we will refer to that description and omit further explanation here.

[0132] The linear polypropylene resin preferably has structural units derived from α-olefins having 2 or 4 to 12 carbon atoms as comonomer units, 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 most preferably structural units derived from ethylene and / or 1-butene. This configuration has the advantages of (a) obtaining a branched polypropylene resin having high melt tension and low gel fraction, and (b) providing polypropylene resin extruded foam particles with excellent moldability from the obtained branched polypropylene resin.

[0133] The linear polypropylene resin is preferably a propylene homopolymer, a polypropylene block copolymer, a polypropylene alternating copolymer, and / or a polypropylene random copolymer, and more preferably a propylene homopolymer and / or a polypropylene random copolymer. This configuration has the advantages of (a) obtaining a branched polypropylene resin having high melt tension and low gel fraction, and (b) providing polypropylene resin extruded foam particles with excellent moldability from the obtained branched polypropylene resin.

[0134] The linear polypropylene resin preferably contains 90 mol% or more of propylene units, more preferably 93 mol% or more, even more preferably 95 mol% or more, and particularly preferably 97 mol% or more, of the total structural units contained in the linear polypropylene resin. This configuration has the advantage of yielding a branched polypropylene resin with high melt tension and low gel fraction.

[0135] The melting point of the linear polypropylene resin is not particularly limited. The melting point of the linear polypropylene resin is preferably, for example, 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 linear polypropylene resin is within the above range, it has the advantages of (a) the obtained extruded foam particles having excellent moldability, and (b) the extruded foam particles being able to provide a foamed molded article with excellent fracture resistance. When the melting point of the linear polypropylene resin is (a) 130°C or higher, it has the advantages of not having a risk of reduced dimensional stability of the foamed molded article, not having a risk of insufficient heat resistance of the foamed molded article, and having a tendency for the compressive strength of the foamed molded article to be increased, and (b) 165°C or lower, it has the advantage that the extruded foam particles can be molded at a relatively low vapor pressure, and the extruded foam particles can be molded using a general-purpose molding machine for polypropylene resin foam particles.

[0136] In this specification, the melting point of linear polypropylene resin is determined by the same method as the method for measuring the melting point of polypropylene resin described in the (Polypropylene Resin) section above, except that "linear polypropylene resin" is used instead of "polypropylene resin". Furthermore, as with the melting point of polypropylene resin described above, if multiple peaks (melting peaks) exist in the DSC curve of the linear polypropylene resin obtained during the second heating, the temperature of the peak with the largest heat of fusion (melting peak) is defined as the melting point of the linear polypropylene resin.

[0137] The MFR of linear polypropylene resin at 230°C is not particularly limited. The MFR of linear polypropylene resin at 230°C is preferably, for example, 0.5 g / 10 min to 50.0 g / 10 min, more preferably 1.0 g / 10 min to 30.0 g / 10 min, even more preferably 2.0 g / 10 min to 20.0 g / 10 min, and particularly preferably 2.0 g / 10 min to 10.0 g / 10 min. When the MFR of linear polypropylene resin at 230°C falls within the above range, it has the advantage that branched polypropylene resin with an MFR of 0.5 g / 10 min to 20.0 g / 10 min at 230°C can be easily obtained.

[0138] In this specification, the MFR of linear polypropylene resin at 230°C is a value obtained by measuring it using the same method as the measurement method for the MFR of polypropylene resin at 230°C described in the (polypropylene resin) section above, except that "linear polypropylene resin" is used instead of "polypropylene resin".

[0139] (Polypropylene resin with a branched structure) The branched polypropylene resin (branched polypropylene resin) used in the second embodiment can be obtained by introducing a branched structure into a linear polypropylene resin. In the second embodiment, there are no particular limitations on the method for introducing a branched structure into a linear polypropylene resin, but examples include (c1) irradiating the linear polypropylene resin with radiation, and (c2) melt-kneading a mixture containing the linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator.

[0140] A specific example of the method described in (c1) above is the method described in Japanese Patent Publication No. 2002-542360.

[0141] The method described in (c2) above will be further explained. In the method described in (c2), for example, a branched polypropylene resin can be obtained by performing (i) to (iv) below in order: (i) a mixture containing a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator is melt-kneaded in an apparatus equipped with a die; (ii) the resulting molten mixture is extruded from the die; (iii) the extruded molten mixture (also called a strand) is cooled; (iv) the strand is shredded simultaneously with and after the cooling of the strand. Specific examples of the method described in (c2) above include, for example, the method described in WO2020 / 004429 and the first manufacturing method.

[0142] (i) A branched structure can be stably introduced into a linear polypropylene resin, and the reproducibility of introducing the branched structure is high, and / or (ii) a branched polypropylene resin can be obtained without requiring complex equipment and with high productivity, therefore, in the second embodiment, the branched polypropylene resin is preferably a branched polypropylene resin obtained by the method of (c2) described above, and is particularly preferably a branched polypropylene resin obtained by the first manufacturing method described above.

[0143] In the second embodiment, the melt tension of the branched polypropylene resin may be higher than that of the linear polypropylene resin. The melt tension of the branched polypropylene resin at 200°C is preferably 8.0 cN or higher, more preferably 9.0 cN or higher, and even more preferably 10.0 cN or higher. By using a branched polypropylene resin with high melt tension as a raw material, the molding width of the resulting polypropylene resin extruded foam particles can be widened.

[0144] The method for measuring the melt tension of the branched polypropylene resin in the second embodiment is the same as that described in section [1-3. Polypropylene resin having a branched structure] in the first embodiment, so we will refer to that description and omit the explanation here.

[0145] The MFR of the branched polypropylene resin in the second embodiment at 230°C is the same as that described in section [1-3. Polypropylene resin having a branched structure] in the first embodiment, so we will refer to that description and omit the explanation here.

[0146] (Other resins and rubbers) The second resin mixture may further contain resins other than branched polypropylene resins (sometimes referred to as "other resins") and / or rubber, to the extent that it does not impair the effects of the second embodiment of the present invention. Other resins and rubbers may be collectively referred to as "other resins, etc." Examples of other resins include (a) linear polypropylene resins such as ethylene / propylene random copolymer, ethylene / propylene block copolymer, ethylene / propylene alternating copolymer, and propylene homopolymer; (b) ethylene resins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, and ethylene / methacrylic acid copolymer; and (c) styrene resins such as polystyrene, styrene / maleic anhydride copolymer, and styrene / ethylene copolymer. Examples of rubbers include olefin rubbers such as ethylene / propylene rubber, ethylene / butene rubber, ethylene / hexene rubber, and ethylene / octene rubber.

[0147] The content of other resins, etc., in the second resin mixture is preferably 60 parts by weight or less, more preferably 40 parts by weight or less, and even more preferably 20 parts by weight or less, per 100 parts by weight of the second resin mixture. The lower limit of the content of other resins, etc., is not particularly limited and may be, for example, 0 parts by weight per 100 parts by weight of the second resin mixture.

[0148] (bubble nucleating agent) The second resin mixture may contain a nucleating agent for the purpose of controlling the number and shape of bubbles in the resulting extruded foam particles. Examples of nucleating agents include a sodium bicarbonate-citric acid mixture, monosodium citrate, talc, and calcium carbonate. These nucleating agents may be used individually or in combination of two or more.

[0149] The amount of nucleating agent used, in other words, the content of the nucleating agent in the second resin mixture, is not particularly limited. The amount of 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, per 100 parts by weight of branched polypropylene resin.

[0150] (Other ingredients) The second resin mixture may further contain, as optional, other components, (a) stabilizers such as antioxidants, metal deactivators, phosphorus-based processing stabilizers, UV absorbers, UV stabilizers, fluorescent whitening agents, metal soaps, and antacid adsorbents, and / or (b) additives such as crosslinking agents, chain transfer agents, lubricants, plasticizers, fillers, reinforcing agents, flame retardants, colorants, and antistatic agents. These other components may be used individually or in combination of two or more.

[0151] (2-2-2. Composition) In the second manufacturing method, the substance obtained by adding a foaming agent to the second resin mixture described above may be referred to as the "composition."

[0152] The blowing agent that can be used in the second manufacturing method is not particularly limited as long as it is a blowing agent that is commonly used in extrusion foaming. Examples of the blowing agent include (a) (a-1) aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, and hexane; (a-2) alicyclic hydrocarbons such as cyclopentane and cyclobutane; (a-3) ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether; (a-4) fluorinated hydrocarbons such as difluoroethane; (a-5) alcohols such as methanol and ethanol; (a-6) inorganic gases such as air, nitrogen, and carbon dioxide; and (a-7) physical blowing agents such as water; and (b) chemical blowing agents including thermal decomposition type blowing agents such as sodium bicarbonate, azodicarbonamide, and dinitrosopentamethylenetetramine.

[0153] In the second manufacturing method, inorganic gases are preferred as blowing agents, and carbon dioxide is more preferred, due to the lower production costs and environmental impact. Furthermore, due to the lower production costs and environmental impact, it is preferable to use only carbon dioxide as the blowing agent and to substantially not contain any blowing agents other than carbon dioxide, as mentioned above as examples of blowing agents. Specifically, the content of blowing agents other than carbon dioxide in the composition is preferably 0.01 parts by weight or less, more preferably 0.001 parts by weight or less, even more preferably 0.0001 parts by weight or less, and particularly preferably 0 parts by weight, per 100 parts by weight of the composition.

[0154] In the second manufacturing method, the amount of blowing agent used may be adjusted as appropriate depending on the type of blowing agent and the target foaming ratio of the foam. In the second manufacturing method, the total amount of blowing agent used is preferably 1 to 20 parts by weight, more preferably 1 to 15 parts by weight, even more preferably 1 to 10 parts by weight, and particularly preferably 2 to 10 parts by weight, per 100 parts by weight of the composition. "Amount of blowing agent used" can also be said to be "Content of blowing agent in the composition".

[0155] (2-2-3.Third manufacturing equipment) The third manufacturing apparatus used in the second manufacturing method comprises a second melt-kneading section having a plurality of screws and a granulation section having a die. The third manufacturing apparatus may further comprise a transport section and / or a cooling section. When the third manufacturing apparatus comprises a transport section and a cooling section, (a) the second melt-kneading section, the transport section, the cooling section, and the granulation section are connected, and (b) the second melt-kneading section, the transport section, the cooling section, and the granulation section are arranged in this order from the upstream side to the downstream side in the extrusion direction of the composition. When the third manufacturing apparatus comprises a transport section and a cooling section, (a) the order of the transport section and the cooling section may be reversed on the upstream and downstream sides, and (b) the transport section may be provided on both the upstream and downstream sides of the cooling section. The transport section can be omitted if the pressure of the composition in the piping from the second melt-kneading section to the granulation section is sufficiently low. Also, the cooling section can be omitted if the temperature of the composition has sufficiently decreased at the outlet of the second melt-kneading section.

[0156] As the second melt-mixing section having multiple screws, for example, a twin-screw extruder having two screws is preferred in order to have good mixing properties. Furthermore, it is preferable that the second melt-mixing section has a screw configuration that prevents the foaming agent injected into the second melt-mixing section from flowing back upstream. In other words, as the second melt-mixing section having multiple screws, a twin-screw extruder having a two-screw configuration with a backflow prevention function is more preferable.

[0157] The transport section consists of transport members for transporting the composition from the second melt-mixing section to the granulation section. These transport members may be any known transport members used in the extrusion foaming method, such as a gear pump. The gear pump is a useful component for maintaining or appropriately increasing the pressure of the composition flow.

[0158] The cooling section consists of a cooling member that cools the composition transported from the transport section (or the second melt-mixing section if the transport section is omitted). The cooling member can be any known cooling member used in the extrusion foaming method. Examples of such cooling members include a single-screw extruder or a static mixer. The composition is cooled to a predetermined temperature by slowly cooling it while mixing at a low shear rate using a single-screw extruder or a static mixer.

[0159] The die in the granulation section is provided with at least one hole (sometimes referred to as an discharge hole) for discharging the molten mixture. The shape of the die's hole in a cross-section perpendicular to the extrusion direction (hereinafter sometimes simply referred to as the "shape of the die's hole") is not particularly limited. Since extruded foam particles having a spherical or substantially spherical shape can be obtained, the shape of the die's hole is preferably circular, substantially circular, elliptical, square, etc. The number and diameter of the holes provided in the die are not particularly limited. From the viewpoint of appropriately maintaining the size of the foam particles in the in-mold foam molding process, the die preferably has holes with a diameter of 0.1 mm to 2.0 mm, and more preferably has holes with a diameter of 0.4 mm to 1.5 mm. It is more preferable for the die to have multiple holes (for example, two or more). In this specification, if the shape of the die's hole is not circular, the diameter of the die's hole refers to the diameter of the inscribed circle of the die's hole shape.

[0160] (2-2-4. Second melting and mixing process) The second melt-mixing step is a step in which the branched polypropylene resin is melted in the second melt-mixing section of the third manufacturing apparatus and a blowing agent is dissolved in the branched polypropylene resin. The second melt-mixing step can also be described as a step in preparing a melt-mixed product of a composition containing a second resin mixture having branched polypropylene resin and a blowing agent.

[0161] In the second melt-mixing step, it is sufficient that the blowing agent is ultimately dissolved in the branched polypropylene resin. The order and method of supplying the branched polypropylene resin and the blowing agent to the second melt-mixing section in the second melt-mixing step are not particularly limited, and examples include the following methods (d) or (e): (d)(d-1) A method of preparing a composition by mixing or blending a branched polypropylene resin with a foaming agent; (d-2) The composition is then supplied to a second melt-kneading section and melt-kneaded; (e)(e-1) A branched polypropylene resin is supplied to a second melt-mixing section and the branched polypropylene resin is melt-mixed; (e-2) A foaming agent is then supplied to the melt-mixed branched polypropylene resin from a raw material supply port located in the middle of the second melt-mixing section, that is, a composition is prepared (completed) in the second melt-mixing section, and the composition is further melt-mixed.

[0162] In the method described in (d) or (e) above, if other resins, nucleating agents, and other components are added to the composition as needed, the method and order in which these raw materials are supplied to the second melt-mixing section are not particularly limited. The other resins, nucleating agents, and other components may be added simultaneously with the branched polypropylene resin and / or the blowing agent, or they may be added separately and in no particular order. When a blowing agent that is liquid at room temperature (e.g., aliphatic hydrocarbons, alicyclic hydrocarbons, ethers, and alcohols) is used as the blowing agent, the methods described in (d) and (e) above can be used. When a blowing agent that is gaseous at room temperature, such as carbon dioxide, is used as the blowing agent, the method described in (e) above can be used.

[0163] The second melt-kneading step may further include, for example, a step of melt-kneading the composition by the method of (d) or (e) described above, and then lowering the temperature of the melt-kneaded composition within a temperature range in which the melt-kneaded composition does not solidify.

[0164] (2-2-5. Extrusion and Foaming Process) The extrusion foaming process involves extruding the composition obtained in the second melt-kneading process, i.e., the melt-kneaded composition, through a die into a region with a pressure lower than the internal pressure of the third manufacturing apparatus, and then shredding the extruded composition. Extruded foam particles are obtained through the extrusion foaming process. Therefore, the extrusion foaming process can also be described as a granulation process that granulates polypropylene resin extruded foam particles.

[0165] In the extrusion foaming process, the region in which the composition obtained in the second melt-kneading process is extruded is not particularly limited, as long as the pressure is lower than the internal pressure of the third manufacturing apparatus. For example, in the extrusion foaming process, the composition obtained in the second melt-kneading process may be extruded into the gas phase or into the liquid phase.

[0166] In the extrusion foaming process, the composition extruded into a region with a pressure lower than the internal pressure of the third manufacturing apparatus immediately begins to foam. In the extrusion foaming process, the composition may be shredded while foaming, or the composition may be shredded after foaming is complete. If the composition is shredded while foaming, the shredded composition may complete foaming in the region to which it was extruded.

[0167] Depending on the region in which the composition obtained in the second melt-kneading step is extruded and the method of shredding the composition, the extrusion foaming step (granulation step) can be broadly classified into two types: the cold-cut method and the die-face-cut method. The cold-cut method and the die-face-cut method are the same as those described in the section (second step) of the first embodiment, so that description will be used as a reference and the explanation will be omitted here.

[0168] In the extrusion foaming process of the second embodiment, the case in which the composition obtained in the second melt-kneading process is extruded into the liquid phase (e.g., UWC) will be described. The liquid phase is not particularly limited, but water is preferred because it can be manufactured inexpensively and safely. The temperature of the liquid phase is not particularly limited, but it is preferably 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, as it is easier to obtain extruded foam particles with fewer particles adhering to each other. In this specification, the temperature of the liquid phase can be measured by a thermometer placed in contact with the liquid phase. Within the specified region, the liquid phase pressure relative to the composition is not particularly limited, but it 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, as this makes it easier to keep the open-cell ratio of the resulting extruded foam particles low and to keep the adhesion between the resulting extruded foam particles low. In this specification, "MPa·G" is intended to mean that MPa represents gauge pressure.

[0169] (2-2-6. Specific Energy E2) In the second manufacturing method, the specific energy E2 is the value obtained by dividing the power P2 [kW] required to drive the multiple screws of the second melting and kneading section, more specifically the power P2 [kW] required to drive the motor that rotates the multiple screws of the second melting and kneading section, by the discharge rate of the composition Q2 [kg / h]. In this specification, "power P2 required to drive the multiple screws of the second melting and kneading section" may be referred to as "required power P2".

[0170] In the second manufacturing method, by setting the specific energy E2 to 0.190 kWh / kg or less, extruded foam particles with excellent moldability can be obtained. The specific energy E2 is more preferably 0.180 kWh / kg or less, and particularly preferably 0.170 kWh / kg or less. The lower limit of the specific energy E2 is not particularly limited, but for example, 0.050 kWh / kg or more is preferred.

[0171] The specific energy E2 can be adjusted to a desired range by appropriately selecting the temperature of the second melting and mixing section, the temperature of the composition within the second melting and mixing section, the time of the second melting and mixing process, the rotational speed N2 of the screw in the second melting and mixing section, the discharge volume Q2 of the melted and mixed composition, the ratio of the effective length L2 of the screw in the second melting and mixing section to the bore diameter D2 (L2 / D2), etc. Note that "bore diameter D2" is the inner diameter of the cylinder housing the screw.

[0172] The required power P2 can be calculated from the motor capacity of the screw in the second melting and mixing section, the motor current value of the screw in the second melting and mixing section, the discharge volume Q2 of the composition, the rotational speed N2 of the screw in the second melting and mixing section, and the maximum rotational speed of the screw in the second melting and mixing section. Note that in calculating the required power P2, the "motor torque" of the screw in the second melting and mixing section may be used instead of the "motor current value" of the screw in the second melting and mixing section.

[0173] The second manufacturing method (for example, the second melt-kneading step) preferably further includes a specific energy E2 adjustment step that adjusts the specific energy E2 to 0.190 kWh / kg or less. The specific energy E2 adjustment step is a step of adjusting one or more selected from the group consisting of, for example, the temperature of the second melt-kneading section, the temperature of the composition in the second melt-kneading section, the time of the second melt-kneading step, the rotational speed N2 of the screw in the second melt-kneading section, the discharge amount Q2 of the melt-kneaded composition, and the ratio (L2 / D2) of the effective length L2 to the diameter D2 of the screw in the second melt-kneading section.

[0174] In the second melt-mixing step, the temperature of the second melt-mixing section is not particularly limited, and any temperature at which the specific energy E2 is 0.190 kWh / kg or less is acceptable. Furthermore, it is preferable that the temperature of the second melt-mixing section be within a range that does not hinder the supply of the blowing agent to the raw materials. If the blowing agent is a gas, if the branched polypropylene resin is not melted at the blowing agent supply position in the second melt-mixing section, the blowing agent may escape to the upstream side of the second melt-mixing section. For this reason, it is preferable to set the barrel temperature so that the branched polypropylene resin is completely melted while preventing vaporization of the blowing agent due to high resin temperature. The temperature of the second melt-mixing section is preferably a temperature at which the branched polypropylene resin and other resins can melt, for example, preferably in the range of 170°C to 230°C, more preferably in the range of 180°C to 220°C, and even more preferably in the range of 180°C to 210°C. An example of the temperature of the second melt-mixing section is the temperature of the cylinder (barrel) that houses the screw inside. If the temperature of the second melt-mixing section is as described above, it is preferable in that the polypropylene resin and other resins having a branched structure melt and do not undergo thermal decomposition.

[0175] The temperature of the cooling section and the die are not particularly limited and may be set appropriately depending on the melting point of the branched polypropylene resin, the type and amount of foaming agent used, the manner of the extrusion foaming process, etc. When a single-screw extruder is used as the cooling section, the temperature of the cooling section may be, for example, the temperature of the cylinder (barrel) that houses the screw inside the single-screw extruder.

[0176] The melting and mixing time is not particularly limited and should be any time at which the specific energy E2 is 0.190 kWh / kg or less. The rotational speed N2 of the screw in the second melting and mixing section is not particularly limited and should be any rotational speed N2 at which the specific energy E2 is 0.190 kWh / kg or less. The rotational speed N2 of the screw in the second melting and mixing section may be set appropriately depending on the size of the second melting and mixing section (for example, the ratio of the effective length L2 of the screw in the second melting and mixing section to the diameter D2 (L2 / D2)) and / or the discharge rate Q2, etc.

[0177] The discharge rate Q2 of the molten and kneaded composition is not particularly limited and should be any discharge rate Q2 such that the specific energy E2 is 0.190 kWh / kg or less. The discharge rate Q2 of the molten and kneaded composition may be appropriately set depending on the size of the second molten and kneading section (for example, the ratio of the effective length L2 of the screw of the second molten and kneading section to the diameter D2 (L2 / D2)).

[0178] The ratio of the effective length L2 to the diameter D2 of the screw in the second melting and mixing section (L2 / D2) is a value that indicates the mixing efficiency of the screw. The larger this value, the greater the amount of work done during melting and mixing, and the higher the specific energy E2. L2 / D2 can be selected as appropriate, but for example, it may be around 20 to 45, and more preferably around 25 to 35.

[0179] [2-3. Polypropylene resin extruded foam particles] In this specification, "extruded polypropylene resin foam particles obtained by the second manufacturing method" may also be referred to as "second extruded foam particles."

[0180] (Moldability) The second type of extruded foamed particle has the advantage of excellent moldability, specifically a wide molding width (for example, 0.03 MPa or more).

[0181] In this specification, "molding width of polypropylene resin extruded foam particles" refers to the range of vapor pressure during in-mold foam molding that allows for the production of a polypropylene resin in-mold foam molded article that satisfies the following conditions: (x1) sufficient fusion between polypropylene resin extruded foam particles, (x2) sufficient filling of gaps between polypropylene resin extruded foam particles, (x3) a smooth surface, (x4) no melting of the surface, (x5) sufficient compressive strength, and (x6) the mold shape is transferred without shrinking by more than 5% relative to the dimensions of the 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 a polypropylene resin in-mold foam molded article cannot be obtained. In this specification, for example, when polypropylene resin extruded foam particles are in-mold foam molding, a polypropylene resin in-mold foam molded article satisfying the above-described conditions (x1) to (x6) can be obtained. If the vapor pressure during in-mold foam molding is P1 to P2, the "value" obtained by P2-P1 is defined as the "molding width of the polypropylene resin extruded foam particles." In this specification, "P1 to P2" is also referred to as the "feasible vapor pressure range."

[0182] If the vapor pressure is too low for the polypropylene resin extruded foam particles, the resulting polypropylene resin in-mold foamed molded article may have (a) insufficient fusion between the polypropylene resin extruded foam particles, (b) insufficient filling of gaps between the polypropylene resin extruded foam particles, (c) poor surface appearance, and / or (d) shrinkage resulting in the shape of the mold used for in-mold foaming not being transferred. If the vapor pressure is too high for the polypropylene resin extruded foam particles, the resulting polypropylene resin in-mold foamed molded article may have (a) a melted surface, and / or (b) insufficient compressive strength.

[0183] The molding width of the second extruded foam particles is not particularly limited. A wider molding width is preferable for the second extruded foam particles. Preferably, the molding width of the second extruded foam particles is 0.03 MPa or more, and more preferably 0.04 MPa or more. Extruded foam particles with a molding width within the above range have excellent moldability. Extruded foam particles with a molding width within the above range are particularly suitable for in-mold foam molding using molds with complex shapes. This is because, when extruded foam particles with a molding width within the above range are used in in-mold foam molding using molds with complex shapes, the steam hits the extruded foam particles in the mold evenly, and there is no risk of uneven steam contact with the extruded foam particles. Therefore, it is considered that there is no risk of areas with high and low steam pressure coexisting within a mold with a complex shape.

[0184] By molding the second extruded foam particles (e.g., in-mold foaming), a foamed molded article with excellent compressive strength, excellent fusion properties, and / or a beautiful surface can be obtained without the need to strictly control the vapor pressure.

[0185] (shape) The shape of the second extruded foam particles is preferably spherical or nearly spherical, considering the ease of filling the mold when molding the extruded foam particles, but is not limited to these. For example, in order to impart sound absorption and / or water permeability to the foamed molded body, foamed molded bodies with voids may be manufactured. In such cases, cylindrical, elliptical, rectangular parallelepiped, or tubular (straw-shaped) extruded foam particles may be used.

[0186] (diameter) The case where the shape of the second extruded foam particles is spherical or substantially spherical will be described. In this case, the average diameter (also called the average particle diameter) of the second extruded foam particles is not particularly limited. Furthermore, in this case, since the workability and moldability of the extruded foam particles are excellent, the average diameter of the second extruded foam particles is preferably, for example, 0.5 mm to 10.0 mm, more preferably 1.0 mm to 7.0 mm, and even more preferably 2.0 mm to 5.0 mm. Here, the average diameter of the polypropylene resin extruded foam particles is the arithmetic mean of the diameters measured using a caliper or the like for any 20 polypropylene resin extruded foam particles. The average diameter of the second extruded foam particles can be appropriately adjusted by the diameter of the holes provided in the die, etc.

[0187] (Open cell ratio) The open-cell ratio of the second extruded foam particles is preferably as low as possible. The open-cell ratio of the second extruded foam particles is preferably 15.0% or less, more preferably 10.0% or less, even more preferably 8.0% or less, and particularly preferably 5.0% or less. The lower limit of the open-cell ratio of the second extruded foam particles is not particularly limited, and is, for example, 0.0% or more. This configuration has the advantages of (a) that the extruded foam particles have excellent moldability because the cells hardly rupture and shrink during molding, and (b) that the foamed molded article obtained using the extruded foam particles exhibits characteristics such as arbitrariness of shape, cushioning properties, lightness, compressive strength, and heat insulation properties to a greater extent.

[0188] In this specification, the open-cell ratio of polypropylene resin extruded foam particles is a value obtained by measuring using an air-comparison hydrometer [Tokyo Science Co., Ltd., Model 1000] according to the method described in Procedure C (PROSEDURE C) of ASTM D2856-87. Specifically, the open-cell ratio of extruded foam particles is calculated by performing the following (1) to (3) in order: (1) Using an air-comparison hydrometer, the volume Vc (cm³) of the extruded foam particles 3(1) Measure the volume of the extruded foam particles after measuring Vc; (2) Submerge the entire volume of extruded foam particles in ethanol in a graduated cylinder; (3) Then, from the rise in the position of the ethanol in the graduated cylinder, determine the apparent volume of the extruded foam particles Va (cm³). 3 (4) Determine the open-cell ratio of the extruded foamed particles using the following formula: Open cell percentage (%) = ((Va - Vc) × 100) / Va. The method for measuring volume Va is also known as the immersion method.

[0189] (Expansion ratio) The foaming ratio of the second extruded foam particles is preferably 2 to 45 times, more preferably 3 to 40 times, even more preferably 3 to 30 times, and particularly preferably 3 to 25 times. The above configuration has the advantage that the polypropylene resin molded foam article obtained using the extruded foam particles exhibits characteristics such as arbitrary shape, cushioning, lightness, and heat insulation. If the foaming ratio of the extruded foam particles obtained by the production of the extruded foam particles does not reach the above range, a method of increasing the foaming ratio by pressurizing the inside of the extruded foam particles with an inert gas and then heating the extruded foam particles is also available (for example, the method described in Japanese Patent Application Publication No. 10-237212).

[0190] In this specification, the foaming ratio of polypropylene resin extruded foam particles is calculated by the following method: (1) measure the weight w (g) of the extruded foam particles; (2) then immerse the extruded foam particles used for weight measurement in ethanol contained in a graduated cylinder, and calculate the volume v (cm³) of the extruded foam particles based on the rise in the liquid level in the graduated cylinder. 3 (3) measure the weight w (g) and the volume v (cm³). 3 (4) Divide by (1) to calculate the density ρ1 of the extruded foam particles; (5) Perform the same operation as in (1) to (3) using the base resin instead of the extruded foam particles to calculate the density ρ2 of the base resin; (6) Divide the density ρ2 of the base resin of the extruded foam particles by the density ρ1 of the extruded foam particles (ρ2 / ρ1) and the resulting value is taken as the foaming ratio.

[0191] In this specification, the base resin can also be said to be the resin component that substantially constitutes the extruded foam particles. The density of the base resin of the extruded foam particles does not substantially change even when the extruded foam particles are melted under reduced pressure and returned to a resin mass. Therefore, the density of the resin mass obtained by melting the extruded foam particles under reduced pressure can be considered to be the density of the base resin of the extruded foam particles. In this specification, the process of melting the extruded foam particles under reduced pressure to obtain a resin mass may be referred to as "resin return," and the resin mass obtained by resin return may be referred to as "returned resin."

[0192] There are no particular limitations on the specific method of resin return, but for example, the following method can be performed in order: (f1) Place foamed particles into a dryer adjusted to the melting point of linear polypropylene resin + 10°C; (f2) Then, using a vacuum pump, reduce the pressure inside the dryer to -0.05 MPa (gauge pressure) to -0.10 MPa (gauge pressure) over 5 to 10 minutes; (f3) After that, leave the extruded foamed particles in the dryer for 30 minutes to prepare a resin mass (returned resin); (f4) Then, after cooling the temperature inside the dryer to room temperature, return the pressure inside the dryer to atmospheric pressure; (f5) After that, remove the resin mass from the dryer.

[0193] (Crystal peak) Polypropylene resin extruded foam particles obtained by the extrusion foaming method are characterized by having one crystal peak in the DSC curve obtained by DSC measurement. In other words, polypropylene resin foam particles with one crystal peak in the DSC curve obtained by DSC measurement are highly likely to have been obtained by the extrusion foaming method. The second type of extruded foam particle may also have one crystal peak in the DSC curve obtained by DSC measurement.

[0194] The DSC curve of polypropylene resin extruded foam particles used to calculate crystal peaks is the curve obtained by DSC measurement while heating 5-6 mg of polypropylene resin extruded foam particles from 40°C to 220°C at a heating rate of 10°C / min.

[0195] [2-4. Method for manufacturing polypropylene resin foam molded articles] A method for producing a polypropylene resin foam molded article according to a second embodiment of the present invention includes a heating step of filling a molding space formed from at least two molds of a mold with polypropylene resin extruded foam particles obtained by the manufacturing method described in section [2-2. Method for producing polypropylene resin extruded foam particles] (i.e., second extruded foam particles) or polypropylene resin extruded foam particles described in section [2-3. Polypropylene resin extruded foam particles] (i.e., second extruded foam particles), and then heating the polypropylene resin extruded foam particles in the molding space.

[0196] In this specification, the polypropylene-based resin foam molded article according to the second embodiment of the present invention may also be referred to as the "second foam molded article."

[0197] The method for producing a polypropylene resin foam molded article according to the second embodiment of the present invention has the advantage of providing a polypropylene resin in-mold foam molded article that has excellent compressive strength, excellent fusion properties, and / or a beautiful surface, even when molding is performed at a vapor pressure lower or higher than the conventional acceptable range.

[0198] In the method for producing a polypropylene resin foam molded article according to the second embodiment of the present invention, the heating step preferably includes a step of heating polypropylene resin extruded foam particles with steam.

[0199] Other aspects of the method for manufacturing a polypropylene-based resin foam molded article in the second embodiment are the same as those described in section 1-6. Method for manufacturing a polypropylene-based resin foam molded article in the first embodiment, so we will refer to that description and omit further explanation here.

[0200] In another embodiment of the present invention, it is most preferable to combine the first embodiment and the second embodiment. In other words, the branched polypropylene resin obtained by the first manufacturing method in the first embodiment may be used as the branched polypropylene resin used in the second manufacturing method in the second embodiment.

[0201] In other words, another embodiment of the present invention is a method for producing polypropylene resin extruded foam particles, using a third manufacturing apparatus comprising a second melt-kneading section having a plurality of screws and a granulation section having a die, and including a second melt-kneading step in which a branched polypropylene resin and a foaming agent obtained by the first manufacturing method are melt-kneaded in the second melt-kneading section, and an extrusion foaming step in which the composition obtained in the second melt-kneading step is discharged through the die into a region where the pressure is lower than the internal pressure of the third manufacturing apparatus, wherein the specific energy E2 is 0.190 kWh / kg or less, where the specific energy E2 is the value obtained by dividing the power P2 required to drive the plurality of screws in the second melt-kneading section by the discharge amount Q2 of the composition, and the branched polypropylene resin is obtained by the following manufacturing method.

[0202] One embodiment of the present invention may have the following configuration:

[0203] [X1] A method for producing a polypropylene resin having a branched structure, comprising: a first manufacturing apparatus comprising a first melt-kneading section having a screw and a die, wherein a polypropylene resin, a conjugated diene compound and a radical polymerization initiator are melt-kneaded in the first melt-kneading section; and a discharge step is performed to discharge the polypropylene resin having a branched structure obtained in the first melt-kneading section through the die, wherein the amount of the conjugated diene compound used is 0.30 to 1.50 parts by weight per 100 parts by weight of the polypropylene resin, the amount of the radical polymerization initiator used is 0.50 to 2.00 parts by weight per 100 parts by weight of the polypropylene resin, and the specific energy E1 is 0.35 kWh / kg or more, where the specific energy E1 is the value obtained by dividing the power P1 required to drive the screw of the first melt-kneading section by the discharge amount Q1 of the polypropylene resin having a branched structure.

[0204] [X2] The manufacturing method according to [X1], wherein the first melting and kneading section is a multi-screw extruder.

[0205] [X3] The manufacturing method according to [X1] or [X2], wherein the conjugated diene compound consists solely of isoprene and / or butadiene.

[0206] [X4] The manufacturing method according to any one of [X1] to [X3], wherein the radical polymerization initiator consists of only one or more selected from the group consisting of peroxyketal, peroxyester, and peroxycarbonate.

[0207] [X5] The manufacturing method according to any one of [X1] to [X4], wherein the melt flow rate of the polypropylene resin at 230°C is 0.5 g / 10 min to 20.0 g / 10 min.

[0208] [X6] The manufacturing method according to any one of [X1] to [X5], wherein the gel fraction of the polypropylene resin having the branched structure is 10.0% by weight or less.

[0209] [X7] The manufacturing method according to any one of [X1] to [X6], wherein the temperature of the first melt-kneading section is 160°C to 300°C.

[0210] [X8] The manufacturing method according to any one of [X1] to [X7], wherein the melting and mixing time of the first melting and mixing step is 30 seconds to 10 minutes.

[0211] [X9] The manufacturing method according to any one of [X1] to [X8], wherein the ratio (L1 / D1) of the effective length L1 to the diameter D1 of the screw in the first melting and kneading section is 30 to 75.

[0212] A method for producing polypropylene resin extruded foam particles, comprising: (a) a polypropylene resin having a branched structure obtained by a manufacturing method described in any one of (X1) to (X9), and (b) a foaming agent, in a second manufacturing apparatus; and a second step of discharging the composition obtained in the first step through a die into a region where the pressure is lower than the internal pressure of the second manufacturing apparatus.

[0213] [X11] A method for producing polypropylene resin extruded foam particles, comprising: a second melt-kneading step of melt-kneading a branched polypropylene resin and a foaming agent obtained by the manufacturing method described in any one of [X1] to [X9] using a third manufacturing apparatus comprising a second melt-kneading section having a plurality of screws and a granulation section having a die, in the second melt-kneading section; and an extrusion foaming step of discharging the composition obtained in the second melt-kneading step through the die into a region where the pressure is lower than the internal pressure of the third manufacturing apparatus, wherein the specific energy E2 is 0.190 kWh / kg or less, where the specific energy E2 is the value obtained by dividing the power P2 required to drive the plurality of screws in the second melt-kneading section by the discharge amount Q2 of the composition.

[0214] [X12] A method for producing polypropylene resin extruded foam particles, comprising: a second melt-kneading step of melt-kneading a branched polypropylene resin and a foaming agent in the second melt-kneading step, using a third manufacturing apparatus comprising a second melt-kneading section having a plurality of screws and a granulation section having a die; and an extrusion foaming step of extruding the composition obtained in the second melt-kneading step through the die into a region with a pressure lower than the internal pressure of the third manufacturing apparatus, wherein the specific energy E2 is 0.190 kWh / kg or less, where the specific energy E2 is the value obtained by dividing the power P2 required to drive the plurality of screws in the second melt-kneading section by the discharge amount Q2 of the composition.

[0215] [X13] A method for producing polypropylene resin extruded foam particles according to [X11] or [X12], further comprising the third manufacturing apparatus and a cooling unit.

[0216] [X14] A method for producing polypropylene resin extruded foam particles according to any one of [X11] to [X13], wherein the third manufacturing apparatus further comprises a transport unit.

[0217] [X15] The die has holes with a diameter of 0.1 mm to 2.0 mm, a method for producing polypropylene resin extruded foam particles according to any one of [X11] to [X14].

[0218] [X16] A method for producing polypropylene resin extruded foam particles according to any one of [X11] to [X15], wherein the melt flow rate of the polypropylene resin having the branched structure at 230°C is 0.5 g / 10 min to 20.0 g / 10 min, and the melt tension at 200°C is 8.0 cN or more.

[0219] [X17] A method for producing polypropylene resin extruded foam particles according to any one of [X11] to [X16], wherein the foaming agent consists solely of carbon dioxide.

[0220] [X18] A method for producing polypropylene resin extruded foam particles according to any one of [X11] to [X17], wherein the ratio (L2 / D2) of the effective length L2 to the diameter D2 of the screw in the second melt-mixing section is 20 to 45.

[0221] [X19] A method for producing polypropylene resin extruded foam particles according to any one of [X11] to [X18], wherein the open-cell ratio of the polypropylene resin extruded foam particles is 15.0% or less.

[0222] A method for manufacturing a polypropylene resin foamed molded article, comprising filling polypropylene resin extruded foam particles obtained by the method for manufacturing polypropylene resin extruded foam particles described in any one of items [X20], [X11] to [X19] into a molding space formed from at least two molds provided in a mold, and then heating the polypropylene resin extruded foam particles in the molding space.

[0223] [X21] The method for producing a polypropylene resin foam molded article according to [X20], wherein the heating step comprises a step of heating the polypropylene resin extruded foam particles with steam, and the molding width in the heating step is 0.03 MPa or more.

[0224] One embodiment of the present invention may have the following configuration:

[0225] [Y1] A method for producing a polypropylene resin having a branched structure, comprising: a first manufacturing apparatus equipped with a first melt-kneading section having a screw and a die, comprising: a first melt-kneading step of melt-kneading a polypropylene resin, a conjugated diene compound and a radical polymerization initiator in the first melt-kneading section; and a discharge step of dischargeing the polypropylene resin having a branched structure obtained in the first melt-kneading step through the die, wherein the amount of the conjugated diene compound used is 0.30 to 1.50 parts by weight per 100 parts by weight of the polypropylene resin, the amount of the radical polymerization initiator used is 0.50 to 2.00 parts by weight per 100 parts by weight of the polypropylene resin, and the specific energy E1 is 0.35 kWh / kg or more, where the specific energy E1 is the value obtained by dividing the power P1 required to drive the screw of the first melt-kneading section by the discharge amount Q1 of the polypropylene resin having a branched structure.

[0226] [Y2] The manufacturing method according to [Y1], wherein the first melting and kneading section is a multi-screw extruder.

[0227] A method for producing polypropylene resin extruded foam particles, comprising: (a) a polypropylene resin having a branched structure obtained by the manufacturing method described in [Y1] or [Y2], and (b) a foaming agent, in a second manufacturing apparatus; and a second step of discharging the composition obtained in the first step through a die into a region where the pressure is lower than the internal pressure of the second manufacturing apparatus.

[0228] A method for manufacturing a polypropylene resin foamed molded article, comprising filling polypropylene resin extruded foam particles obtained by the manufacturing method described in [Y4] and [Y3] into a molding space formed from at least two molds provided in a mold, and then heating the polypropylene resin extruded foam particles in the molding space.

[0229] One embodiment of the present invention may have the following configuration:

[0230] [Z1] A method for producing polypropylene resin extruded foam particles, comprising: a second melt-kneading step of melt-kneading a branched polypropylene resin and a foaming agent in the second melt-kneading step, using a third manufacturing apparatus comprising a second melt-kneading section having a plurality of screws and a granulation section having a die; and an extrusion foaming step of discharging the composition obtained in the second melt-kneading step through the die into a region with a pressure lower than the internal pressure of the third manufacturing apparatus, wherein the specific energy E2 is 0.19 kWh / kg or less, and the specific energy E2 is the value obtained by dividing the power P2 required to drive the plurality of screws in the second melt-kneading section by the discharge amount Q2 of the composition.

[0231] [Z2] The method for producing polypropylene resin extruded foam particles according to [Z1], further comprising the third manufacturing apparatus and a cooling unit.

[0232] [Z3] A method for producing polypropylene resin extruded foam particles according to [Z1] or [Z2], further comprising the third manufacturing apparatus and a transport unit.

[0233] [Z4] The die has holes with a diameter of 0.1 mm to 2.0 mm, a method for producing polypropylene resin extruded foam particles according to any one of [Z1] to [Z3].

[0234] [Z5] A method for producing polypropylene resin extruded foam particles according to any one of [Z1] to [Z4], wherein the melt flow rate of the polypropylene resin having the branched structure at 230°C is 0.5 g / 10 min to 20.0 g / 10 min, and the melt tension at 200°C is 8.0 cN or more.

[0235] A method for manufacturing a polypropylene resin foamed molded article, comprising filling polypropylene resin extruded foam particles obtained by a method for manufacturing polypropylene resin extruded foam particles described in any one of [Z6], [Z1], to [Z5] into a molding space formed from at least two molds provided in a mold, and then heating the polypropylene resin extruded foam particles in the molding space.

[0236] [Z7] The method for producing a polypropylene resin foam molded article according to [Z6], wherein the heating step comprises heating the polypropylene resin extruded foam particles with steam, and the molding width in the heating step is 0.03 MPa or more. [Examples]

[0237] [Example A] The first embodiment of the present invention will be described in more detail below with reference to Example A, but the present invention is not limited in any way by these Examples A.

[0238] (raw materials) As the polypropylene resin, we used product name F113G (propylene homopolymer, MFR 3.0g / 10min at 230°C, melting point 160°C) manufactured by Prime Polymer Co., Ltd. Only isoprene was used as the conjugated diene compound. Only t-butyl peroxyisopropyl carbonate was used as the radical polymerization initiator.

[0239] [Example A-1] As the first manufacturing apparatus, a device was used that included a first melt-mixing section with a screw and a die at the end in the extrusion direction. The first melt-mixing section was a twin-screw extruder that (a) had a twin-screw rotating in the same direction with a bore diameter of φ46 mm inside the cylinder, (b) had a raw material supply port (polypropylene resin supply feeder) at the upstream end in the extrusion direction, and (c) had two more raw material supply ports (radical polymerization initiator supply pump and conjugated diene compound supply pump) in the middle of the cylinder. The ratio L1 / D1 of the effective length L1 to the bore diameter D1 of the screw in the first melt-mixing section was 30.7.

[0240] Polypropylene resin was supplied from a polypropylene resin feeder to a twin-screw extruder. Then, 1.40 parts by weight of radical polymerization initiator per 100 parts by weight of polypropylene resin was supplied to the twin-screw extruder from a radical polymerization initiator supply pump. Subsequently, 0.50 parts by weight of conjugated diene compound per 100 parts by weight of polypropylene resin was supplied to the twin-screw extruder from a conjugated diene compound supply pump to the melt-kneaded polypropylene resin and radical polymerization initiator, thereby preparing the first resin mixture in the twin-screw extruder. The supply rate of the first resin mixture to the twin-screw extruder was 50 kg / h. Note that the supply rate of the first resin mixture refers to the amount of the first resin mixture prepared per unit time in the twin-screw extruder at the time the conjugated diene compound is supplied to the twin-screw extruder.

[0241] The first resin mixture prepared was melt-kneaded in a twin-screw extruder under the conditions of a cylinder temperature of 200°C (i.e., a temperature of 200°C in the first melt-kneading section) and a screw rotation speed (N1) of 258 rpm to obtain a branched polypropylene resin (first melt-kneading step). The obtained branched polypropylene resin was extruded from a die in strand form at an extrusion rate (Q1) of 50 kg / h (extrusion step). The extruded branched polypropylene resin (strands) was (a) water-cooled and then (b) shredded into pellet form (cylindrical form) to obtain branched polypropylene resin pellets.

[0242] The power P1 required to drive the motor that rotates the screw of the twin-screw extruder, which is the first melting and mixing section, was 20 kW, and the specific energy E1 was 0.40 kWh / kg. The manufacturing conditions and results are shown in Table 1.

[0243] [Examples A-2 to A-3, Comparative Examples A-1 to A-5] A branched polypropylene resin was obtained using the same method as in Example A-1, except that the composition of the first resin mixture, discharge volume Q1, screw rotation speed N1, power P1, and specific energy E1 were changed as shown in Table 1.

[0244] [Evaluation of polypropylene resins with branched structures] For the branched polypropylene resins obtained in Examples A-1 to A-3 and Comparative Examples A-1 to A-5, (a) melt tension, (b) gel fraction, and (c) MFR at 230°C were measured by the following methods. The results are shown in Table 1.

[0245] (a) Measurement of melt tension The melt tension was measured using a Capillograph 1D (manufactured by Toyo Seiki Seisakusho Co., Ltd., Japan). Specifically, the procedure was as follows (1) to (5): (1) A 9.55 mm diameter barrel heated to 200°C was filled with the branched polypropylene resin obtained in each Example A or Comparative Example A; (2) The branched polypropylene resin was then heated for 10 minutes in the barrel heated to the test temperature (200°C); (3) The branched polypropylene resin was then dispensed in a string-like manner from a capillary die (1.0 mm diameter, 10 mm length) at a constant piston descent speed (10 mm / min), and this string-like material was passed through a tension-sensing pulley located 350 mm below the capillary die, after which winding using a winding roll was started; (4) After the winding 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 on the load cell pulley when the string-like material broke was measured as the melt tension.

[0246] (b) Measurement of gel fraction The gel fraction was measured using a gel fraction analyzer. Specifically, the following steps (1) to (10) were performed in order: (1) 0.5 g of branched polypropylene resin obtained in each Example A or Comparative Example A was accurately weighed and used as the sample; (2) The sample was placed in a bag-shaped wire mesh with a mesh opening of 37 μm (400 mesh) and pleated sides; (3) A stirrer piece and the wire mesh containing the sample from (2) were placed in a 300 mL round-bottom flask, and 150 mL of p-xylene was added to the round-bottom flask; (4) The solution in the round-bottom flask was stirred for 1 hour at 130 °C and 80 rpm using an oil bath apparatus and a stirrer. (5) After completely replacing the p-xylene in the round-bottom flask, the solution in the round-bottom flask was stirred for another hour; (6) After completely replacing the p-xylene in the round-bottom flask, the solution in the round-bottom flask was stirred for four hours; (7) The wire mesh was removed from the round-bottom flask with tweezers, and the wire mesh was washed with p-xylene to remove any deposits from the sides of the wire mesh; (8) The residue (resin-insoluble matter) inside the wire mesh was dried in a vacuum dryer at 80°C for eight hours; (9) After cooling, the weight of the residue inside the 400-mesh wire mesh was measured; (10) The gel fraction (weight %) was calculated based on the following formula; Gel fraction (weight %) = weight of residue (g) / 0.5 (g) × 100. Here, the weight of the residue inside the wire mesh = the weight of the wire mesh after filtration and drying (including the residue) - the weight of the wire mesh alone before filtration.

[0247] (c) Measurement of MFR at 230°C The MFR values ​​at 230°C were measured using branched polypropylene resins obtained in each Example A or Comparative Example A as samples, with an MFR measuring instrument described in JIS K7210. The measurement conditions were 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.

[0248] [Table 1] The branched polypropylene resins of Examples A-1 to A-3, produced by the first manufacturing method, exhibited a melt tension exceeding 8.0 cN (80 mN), and in particular, the branched polypropylene resin of Example A-2 exhibited a melt tension exceeding 9.5 cN (95 mN). Furthermore, the gel fraction of the branched polypropylene resins of Examples A-1 to A-3, produced by the first manufacturing method, was 10.0% by weight or less in all cases. In contrast, the branched polypropylene resins of Comparative Examples A-1 to A-5, produced by a manufacturing method with a specific energy E1 of less than 0.35 kWh / kg, exhibited low melt tension and high gel fraction.

[0249] [Example B] A second embodiment of the present invention will be described in more detail below with reference to Example B, but the present invention is not limited in any way by these Examples B.

[0250] (Measurement and evaluation methods) [MFR of branched polypropylene resin at 230°C] The method for measuring the MFR of the branched polypropylene resin at 230°C in the second embodiment is the same as the method described in "(c) Measurement of MFR at 230°C" of [Example A], except that the branched polypropylene resin obtained in each Example B or Comparative Example B was used as the sample.

[0251] [Melting tension of branched polypropylene resins] The method for measuring the melt tension of the branched polypropylene resin in the second embodiment is the same as the method described in "(a) Measurement of melt tension" of [Example A], except that the branched polypropylene resin obtained in each Example B or Comparative Example B is filled into a 9.55 mm diameter barrel heated to 200°C.

[0252] [Expansion ratio] The expansion ratio of polypropylene resin extruded foam particles was calculated using the following method: (1) The weight w (g) of the extruded foam particles was measured; (2) Next, the extruded foam particles used for weight measurement were submerged in ethanol contained in a graduated cylinder, and the volume v (cm³) of the extruded foam particles was calculated based on the rise in the liquid level in the graduated cylinder. 3 (3) measured the weight w (g) and the volume v (cm³). 3 (4) The density ρ1 of the extruded foam particles was calculated by dividing by (1) and (2) by the density ρ1 of the extruded foam particles; (5) The density ρ2 of the base resin was calculated by performing the same operation as in (1) to (3) using the base resin (recycled resin) instead of the extruded foam particles; (6) The expansion ratio was obtained by dividing the density ρ2 of the base resin of the extruded foam particles by the density ρ1 of the extruded foam particles (ρ2 / ρ1).

[0253] In Example B and Comparative Example B, the density of the resin mass obtained by returning the extruded foam particles to the resin was considered to be the density of the base resin. The following steps (f1) to (f5) were performed in order, and the resulting resin mass was used as the return resin for the extruded foam particles: (f1) The extruded foam particles were placed in a dryer adjusted to a temperature of 160°C; (f2) Then, using a vacuum pump, the pressure inside the dryer was reduced to -0.05 MPa (gauge pressure) to -0.10 MPa (gauge pressure) over a period of 5 to 10 minutes; (f3) After that, the extruded foam particles were left in the dryer for 30 minutes to prepare the resin mass (return resin); (f4) Then, after the temperature inside the dryer was cooled to room temperature, the pressure inside the dryer was returned to atmospheric pressure; (f5) After that, the resin mass was removed from the dryer.

[0254] [Open cell ratio] The open-cell ratio of extruded foam particles was measured using an air-comparison hydrometer [Tokyo Science Co., Ltd., Model 1000] according to the method described in Procedure C (PROSEDURE C) of ASTM D2856-87. Specifically, the open-cell ratio of extruded foam particles was calculated by performing the following steps (1) to (3) in order: (1) Using an air-comparison hydrometer, the volume Vc (cm³) of the extruded foam particles was measured. 3(1) The volume of the extruded foam particles after measuring Vc was measured; (2) Then, the entire volume of the extruded foam particles was submerged in ethanol in a graduated cylinder; (3) After that, the apparent volume of the extruded foam particles Va (cm³) was determined from the rise in the position of the ethanol in the graduated cylinder. 3 (4) The open-cell ratio of the extruded foamed particles was calculated using the following formula: Open cell percentage (%) = ((Va - Vc) × 100) / Va.

[0255] [Molding width] In in-mold foam molding, polypropylene resin extruded foam particles were foam-molded in a mold while varying the vapor pressure by 0.02 MPa increments within a certain range of vapor pressure to obtain a polypropylene resin in-mold foam molded article. At this time, the range of vapor pressure during in-mold foam molding that can be obtained satisfying the following conditions was determined: (x1) sufficient fusion between polypropylene resin extruded foam particles, (x2) sufficient filling of gaps between polypropylene resin extruded foam particles, (x3) a beautiful surface, (x4) no melting of the surface, (x5) sufficient compressive strength, and (x6) the shape of the mold (die) used for in-mold foam molding is transferred without shrinkage.

[0256] Furthermore, for each item (x1) to (x6) in the measurement of the molding width, any arbitrary standard may be established as appropriate so as to maintain a consistent standard between each Example B and Comparative Example B.

[0257] When the vapor pressure range obtained by the method described above is denoted as P1 to P2, this "P1 to P2" is defined as the "feasible vapor pressure range," and the "value" obtained by P2-P1 is defined as the "molding width of polypropylene resin extruded foam particles." The "feasible vapor pressure range" and the "molding width of polypropylene resin extruded foam particles" are listed in the "vapor pressure range" and "molding width" columns of Table 2, respectively.

[0258] (1st manufacturing equipment) In the following Production Example B, as the first production apparatus used for producing a polypropylene-based resin having a branched structure, an apparatus including a first melt kneading section having a screw and a die at the end in the extrusion direction was used. As the first melt kneading section, (a) a co-rotating twin-screw with a diameter of φ46 mm was provided in the cylinder, (b) a raw material supply port (polypropylene-based resin supply feeder) was provided at the upstream end in the extrusion direction, and (c) a twin-screw extruder having two additional raw material supply ports (radical polymerization initiator supply pump and conjugated diene compound supply pump) in the middle of the cylinder was used. The ratio L₁ / D₁ of the effective length L₁ to the diameter D₁ of the screw in the first melt kneading section was 30.7.

[0259] (The third production apparatus) In the following Example B and Comparative Example B, as the third production apparatus used for producing polypropylene-based resin extrusion foamed particles, an apparatus in which a second melt kneading section, a cooling section, a transport section, a diverter valve, and a granulation section were connected in series was used. As the second melt kneading section, a twin-screw extruder having two screws, a raw material supply section at one end, and a foaming agent supply section in the middle of the screw was used. In the second melt kneading section, the diameter D of the screw was 26 mm, and the ratio (L / D) of the effective length L to the diameter D of the screw was 40.6. As the cooling section, a static mixer was used. The granulation section had a die having six holes with a pore diameter of 0.8 mm.

[0260] (Production Example B) (Production of polypropylene-based resin having a branched structure) The following (1) to (5) were carried out in order to produce a branched polypropylene-based resin: (1) 100 parts by weight of random polypropylene resin (manufactured by Prime Polymer Co., Ltd., F-724NPC) and 1.33 parts by weight of a mixture of t-butyl peroxyisopropyl monocarbonate and 2,2-di(t-butylperoxy)butane as a radical polymerization initiator were supplied at 70 kg / h to a twin-screw extruder (having a co-rotating twin-screw with a shaft diameter of φ46 mm) (the first melt-kneading section) provided in the first production apparatus; (2) 0.55 parts by weight of isoprene as a conjugated diene compound was supplied with respect to 100 parts by weight of the random polypropylene resin from an injection section provided in the middle of the twin-screw extruder; (3) The mixture in the twin-screw extruder was melt-kneaded under the conditions of a cylinder temperature of 200 °C (that is, the temperature of the first melt-kneading section was 200 °C) and a screw rotation speed (N1) of 258 rpm to obtain a melt-kneaded product (branched polypropylene-based resin) (the first melt-kneading step); (4) The obtained melt-kneaded product (branched polypropylene-based resin) was extruded (discharged) from a die provided at the end of the twin-screw extruder at a discharge rate (Q1) of 70 kg / h, and the extruded melt-kneaded product (strand) was cooled with water in a water tank; (5) The strand was cut into pellets by a pelletizer provided at the front of the water tank to obtain pelletized branched polypropylene-based resin. The MFR of the obtained branched polypropylene-based resin at 230 °C was 3.8 g / 10 min, and the melt tension was 10.6 cN. Here, the blending ratio (t-butyl peroxyisopropyl monocarbonate: 2,2-di(t-butylperoxy)butane) of each radical polymerization initiator in the mixture of radical polymerization initiators was 1:2. Also, the power P1 (required power P1) required for driving the motor that rotates the screw of the twin-screw extruder, which is the first melt-kneading section, was 27 kW, and the specific energy E1 was 0.39 kWh / kg.

[0261] As described above, the method for producing a polypropylene-based resin having a branched structure in Example B can be said to be an example of the method for producing a polypropylene-based resin having a branched structure of the first embodiment. That is, in Example B, the first embodiment was implemented.

[0262] (Preparation of Polypropylene-Based Resin Having No Branched Structure) A mixture was prepared by mixing 60% by weight of random polypropylene resin (manufactured by Borealis, trade name RD734MO) with 40% by weight of carbon black. The resulting mixture was used as a non-branched polypropylene resin (linear polypropylene resin) in the following examples and comparative examples.

[0263] Furthermore, in the following Example B and Comparative Example B, talc was used as a bubble nucleating agent.

[0264] (Example B-1) (Second melting and mixing process) A second resin mixture was prepared by blending 95.55 parts by weight of a branched polypropylene resin (branched polypropylene resin), 4.25 parts by weight of a non-branched polypropylene resin (linear polypropylene resin), and 0.2 parts by weight of talc as a bubble nucleating agent. The second resin mixture was then supplied from the raw material supply unit to a twin-screw extruder (second melt-mixing unit), and melt-mixing of the second resin mixture was started at a cylinder temperature of 210°C (i.e., the temperature of the first melt-mixing unit, 210°C) and a screw rotation speed (N2) of 120 rpm. The supply rate of the second resin mixture to the twin-screw extruder was 10 kg / h. During the melt-mixing of the second resin mixture, only carbon dioxide gas was injected into the twin-screw extruder from the foaming agent supply unit as a foaming agent, and the resulting composition was further melt-mixed. The supply rate of the foaming agent to the twin-screw extruder was 0.25 kg / h.

[0265] (Extrusion foaming process) The melt-kneaded composition obtained through the second melt-kneading process was passed through a die in the granulation section and discharged at a discharge rate (Q2) of 10.25 kg / h into a region filled with water as a liquid phase at a pressure lower than the internal pressure of the third manufacturing apparatus. The power P2 required to drive the motors that rotate the two screws of the twin-screw extruder, which is the second melt-kneading section, was 1.435 kW, and the specific energy E2 was 0.140 kWh / kg. In this region, the water pressure relative to the composition was 0.2 MPa. The extruded composition was shredded with a cutter in the region filled with water (liquid phase) to obtain spherical or substantially spherical polypropylene resin extruded foam particles. The obtained polypropylene resin extruded foam particles were recovered by subjecting them to a centrifugal dewatering machine. The manufacturing conditions and results for each manufacturing process are shown in Table 2.

[0266] The resulting polypropylene resin extruded foam particles were evaluated for foaming ratio, open cell ratio, and moldability using the method described above. The open cell ratio was 3.3%, and the other physical properties are shown in Table 2.

[0267] (In-mold foam molding) Using the obtained polypropylene resin extruded foam particles, in-mold foam molding was performed using a polyolefin foam molding machine and block-shaped mold (molding space: 381 mm long x 381 mm wide x 60 mm thick) manufactured by Teubert Maschinenbau GmbH. Specifically, the procedure was as follows: (1) A gap of 18 mm (30% cracking rate) was left between the molds (hereinafter referred to as cracking), and the polypropylene resin extruded foam particles were filled into the molding space of the mold; (2) The extruded foam particles were then compressed by completely closing the mold (i.e., the thickness of the molding space became 60 mm); (3) Next, the air in the molding space of the mold was expelled with steam at 0.15 MPa (gauge pressure); (4) Then, an in-mold foamed polypropylene resin body was obtained by double-sided heating molding for 5 seconds using steam at a predetermined pressure. At this time, the steam pressure was increased by 0.02 MPa increments starting from 0.20 MPa (gauge pressure) to produce the foamed molded body (in-mold foamed body). The steam pressure was increased to a maximum of 0.30 MPa (gauge pressure). The molded width of the obtained in-molded foamed articles was evaluated as described above. The manufacturing results are shown in Table 2.

[0268] (Example B-2) Polypropylene resin extruded foam particles and in-molded foam molded articles were obtained using the same method as in Example B-1, except that the screw rotation speed N2, foaming agent supply amount, required power P2, and specific energy E2 were changed as shown in Table 2. The foaming ratio, open cell ratio, and molded width of the obtained polypropylene resin extruded foam particles and in-molded foam molded articles were evaluated using the method described above. As a result, the open cell ratio was 3.6%, and the other physical properties were as shown in Table 2.

[0269] (Example B-3) Polypropylene resin extruded foam particles and in-molded foam molded articles were obtained using the same method as in Example B-1, except that the screw rotation speed N2, foaming agent supply amount, required power P2, and specific energy E2 were changed as shown in Table 2. The foaming ratio, open cell ratio, and molded width of the obtained polypropylene resin extruded foam particles and in-molded foam molded articles were evaluated using the method described above. As a result, the open cell ratio was 3.8%, and the other physical properties are as shown in Table 2.

[0270] (Example B-4) Polypropylene resin extruded foam particles and in-molded foam molded articles were obtained using the same method as in Example B-1, except that the screw rotation speed N2, foaming agent supply amount, required power P2, and specific energy E2 were changed as shown in Table 2. The foaming ratio, open cell ratio, and molded width of the obtained polypropylene resin extruded foam particles and in-molded foam molded articles were evaluated using the method described above. As a result, the open cell ratio was 4.8%, and the other physical properties are as shown in Table 2.

[0271] (Comparative example B-1) Polypropylene resin extruded foam particles and in-molded foam molded articles were obtained using the same manufacturing method as in Example B-1, except that the screw rotation speed N2, discharge volume Q2, foaming agent supply amount, required power P2, and specific energy E2 were changed as shown in Table 2. The foaming ratio, open cell ratio, and molded width of the obtained polypropylene resin extruded foam particles and in-molded foam molded articles were evaluated using the method described above. As a result, the open cell ratio was 9.8%, and the other physical properties are as shown in Table 2.

[0272] [Table 2] Table 2 shows that the polypropylene resin extruded foam particles of Examples B-1 to B-2, produced by the second manufacturing method, had a molding width of 0.04 MPa. Therefore, it was found that the second manufacturing method can provide polypropylene resin extruded foam particles with excellent moldability, that is, particles that can be molded in a wide range of vapor pressures. In contrast, the polypropylene resin extruded foam particles of Comparative Example B-1, produced by a manufacturing method with a specific energy E2 exceeding 0.190 kWh / kg, had a narrower molding width compared to Examples B-1 to B-2, and exhibited inferior moldability, requiring strict control of vapor pressure during molded foaming. [Industrial applicability]

[0273] According to the first embodiment of the present invention, a novel branched polypropylene resin with improved melt tension can be provided. Therefore, the first embodiment of the present invention can be suitably used to obtain polypropylene resin extruded foam particles with excellent moldability. Furthermore, according to the second embodiment of the present invention, polypropylene resin extruded foam particles with excellent moldability can be provided. Therefore, the second embodiment of the present invention can be suitably used to obtain a polypropylene resin in-molded foam molded article having good physical properties such as arbitrariness of shape, cushioning properties, lightness, compressive strength, and heat insulation properties. Therefore, the first and second embodiments of the present invention can be suitably used in fields such as automotive interior components, cushioning materials, packaging materials, and heat insulation materials, respectively.

Claims

1. A method for producing a polypropylene resin having a branched structure, Using a first manufacturing apparatus comprising a first melting and kneading section having a screw and a die, A first melt-kneading step in which a polypropylene resin, a conjugated diene compound, and a radical polymerization initiator are melt-kneaded in the first melt-kneading section, The process includes a dispensing step in which the branched polypropylene resin obtained in the first melt-kneading step is extruded through the die, The amount of the conjugated diene compound used is 0.30 to 1.50 parts by weight per 100 parts by weight of the polypropylene resin. The amount of radical polymerization initiator used is 0.50 to 2.00 parts by weight per 100 parts by weight of the polypropylene resin. Specific energy E １ It is 0.35 kWh / kg or more, Here, the specific energy E １ The power P required to drive the screw in the first melting and kneading section is １ The discharge volume Q of the polypropylene resin having the branched structure １ A method for producing a branched polypropylene resin, which is a value obtained by dividing by [a certain factor].

2. The manufacturing method according to claim 1, wherein the first melt-mixing section is a multi-screw extruder.

3. The method for producing the product according to claim 1 or 2, wherein the conjugated diene compound consists solely of isoprene and / or butadiene.

4. The manufacturing method according to any one of claims 1 to 3, wherein the radical polymerization initiator consists of only one or more selected from the group consisting of peroxyketal, peroxyester, and peroxycarbonate.

5. The manufacturing method according to any one of claims 1 to 4, wherein the melt flow rate of the polypropylene resin at 230°C is 0.5 g / 10 min to 20.0 g / 10 min.

6. (a) A polypropylene resin having a branched structure obtained by the manufacturing method described in any one of claims 1 to 5, and (b) a foaming agent, in a first step of melting and kneading these in a second manufacturing apparatus, A method for producing polypropylene resin extruded foam particles, comprising a second step of discharging the composition obtained in the first step through a die into a region where the pressure is lower than the internal pressure of the second manufacturing apparatus.

7. Using a third manufacturing apparatus comprising a second melting and kneading section having multiple screws and a granulation section having a die, A second melt-kneading step in which a polypropylene resin having a branched structure and a foaming agent obtained by the manufacturing method described in any one of claims 1 to 5 are melt-kneaded in the second melt-kneading section, The process includes an extrusion foaming step in which the composition obtained in the second melt-kneading step is discharged through the die into a region where the pressure is lower than the internal pressure of the third manufacturing apparatus, Specific energy E ２ It is 0.190 kWh / kg or less, Here, the specific energy E ２ The power P required to drive the plurality of screws in the second melting and kneading section is ２ The discharge volume Q of the composition ２ A method for producing polypropylene resin extruded foam particles, which is the value obtained by dividing by [a certain factor].

8. The method for producing polypropylene resin extruded foam particles according to claim 7, wherein the third manufacturing apparatus further comprises a cooling unit.

9. The method for producing polypropylene resin extruded foam particles according to claim 7 or 8, wherein the third manufacturing apparatus further comprises a transport unit.

10. The method for producing polypropylene resin extruded foam particles according to any one of claims 7 to 9, wherein the die has holes with a pore diameter of 0.1 mm to 2.0 mm.

11. A method for producing polypropylene resin extruded foam particles according to any one of claims 7 to 10, wherein the melt flow rate of the polypropylene resin having the branched structure at 230°C is 0.5 g / 10 min to 20.0 g / 10 min, and the melt tension at 200°C is 8.0 cN or more.

12. A method for producing polypropylene resin extruded foam particles according to any one of claims 7 to 11, wherein the foaming agent consists solely of carbon dioxide.

13. A method for producing a polypropylene resin foamed molded article, comprising filling polypropylene resin extruded foam particles obtained by the method for producing polypropylene resin extruded foam particles according to any one of claims 7 to 12 into a molding space formed from at least two molds provided in a mold, and then heating the polypropylene resin extruded foam particles in the molding space.

14. The heating step comprises heating the polypropylene resin extruded foam particles with steam, The method for producing a polypropylene-based resin foamed molded article according to claim 13, wherein the molding width in the heating step is 0.03 MPa or more.

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