Polypropylene-based resin foam particles and polypropylene-based resin foam molded articles

Abstract

The present invention addresses the problem of providing polypropylene resin foam particles that (a) can provide a polypropylene resin foam molded body having good fusion properties at a low molding pressure, and (b) can provide a polypropylene resin foam molded body having good compressive strength and almost no deformation. Provided are polypropylene foam particles that include a base material resin containing prescribed amounts of a polypropylene resin (A) and a polypropylene homopolymer (B), each having a specific melting point.

Description

[Technical Field]

[0001] This invention relates to polypropylene resin foam particles and polypropylene resin foam molded articles. [Background technology]

[0002] Polypropylene-based foamed molded products are used in a variety of applications, including automotive interior components, core materials for automotive bumpers, as well as insulation materials, cushioning packaging materials, and reusable containers (see, for example, Patent Documents 1-3).

[0003] In recent years, the amount of polypropylene-based foamed molded articles used per vehicle has increased, particularly in order to reduce the weight of automobiles. Therefore, there is a growing demand for polypropylene-based foamed particles that can efficiently produce polypropylene-based foamed molded articles during the molding process. Specifically, there is a need for polypropylene-based foamed particles that, compared to existing polypropylene-based foamed particles, can produce polypropylene-based foamed molded articles with good fusion properties using less water vapor, i.e., at lower molding pressures.

[0004] Furthermore, there is a demand for polypropylene-based foam particles that can provide polypropylene-based foam molded articles with minimal deformation. Additionally, when polypropylene-based foam molded articles are used in automotive applications, they are often used as shock absorbers. Therefore, compressive strength is also required for these polypropylene-based foam molded articles. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Public Publication WO2017 / 169260 [Patent Document 2] International Public Publication WO2016 / 060162 [Patent Document 3] Japanese Patent Publication No. 2018-162371

Summary of the Invention

Problems to be Solved by the Invention

[0006] In view of the above situation, an object of one embodiment of the present invention is to provide (a) polypropylene-based resin foam particles that can provide a polypropylene-based resin foam molded body having good fusion properties at a low molding pressure, and (b) a polypropylene-based resin foam molded body having good compressive strength and almost no deformation.

Means for Solving the Problems

[0007] As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.

[0008] That is, the polypropylene-based resin foam particles according to one embodiment of the present invention contain a base resin containing a polypropylene-based resin (A) having a melting point of 135°C to 150°C and a polypropylene homopolymer (B) having a melting point of 85°C or less. When the total amount of the polypropylene-based resin (A) and the polypropylene homopolymer (B) is 100 parts by weight, the base resin contains more than 80.0 parts by weight and 98.0 parts by weight or less of the polypropylene-based resin (A), and 2.0 parts by weight or more and less than 20.0 parts by weight of the polypropylene homopolymer (B).

Effects of the Invention

[0009] According to one embodiment of the present invention, there is an effect that (a) polypropylene-based resin foam particles that can provide a polypropylene-based resin foam molded body having good fusion properties at a low molding pressure, and (b) polypropylene-based resin foam particles that can provide a polypropylene-based resin foam molded body having good compressive strength and almost no deformation can be provided.

Modes for Carrying Out the Invention

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

[0011] Also, unless otherwise specified in this specification, as a structural unit, X 1 a structural unit derived from a monomer, and X 2 a structural unit derived from a monomer, and ··· and X n a copolymer containing monomers (n is an integer of 2 or more) is also referred to as "X 1 / X 2 / ··· / X n copolymer". X 1 / X 2 / ··· / X n Unless otherwise specified, the copolymerization mode of the X

[0012] / X

[0013] <First Embodiment> [1-1. Polypropylene-based resin foamed particles] The polypropylene resin foam particles according to the first embodiment of the present invention include a base resin containing a polypropylene resin (A) having a melting point of 135°C to 150°C and a polypropylene homopolymer (B) having a melting point of 85°C or less. The base resin contains, when the total amount of the polypropylene resin (A) and the polypropylene homopolymer (B) is 100 parts by weight, more than 80.0 parts by weight and 98.0 parts by weight or less of the polypropylene resin (A), and 2.0 parts by weight or more and less than 20.0 parts by weight of the polypropylene homopolymer (B).

[0014] Polypropylene-based resin foam particles according to the first embodiment of the present invention can be molded by known methods to provide a polypropylene-based resin foam molded article.

[0015] In this specification, "polypropylene resin foam particles according to the first embodiment of the present invention" may be referred to as "first foam particles."

[0016] Because the first foam particles have the above-described structure, they have the advantages of (a) being able to provide a polypropylene-based resin foam molded article with good fusion properties at a low molding pressure (in other words, a low heating vapor pressure), and (b) being able to provide a polypropylene-based resin foam molded article with good compressive strength and almost no deformation. Because the first foam particles have the above-described structure, they also have the advantage of being able to provide a polypropylene-based resin foam molded article with good surface beauty.

[0017] <Ingredients> (Base resin) The base resin contains, as resin components, at least a polypropylene resin (A) and a polypropylene homopolymer (B). In addition to the resin components, the base resin may optionally contain additives such as foaming nucleating agents. The base resin can also be said to be the components that substantially constitute the foamed particles. Therefore, the types and amounts of each component contained in the base resin can also be said to be the types and amounts of each component contained in the first foamed particles. The base resin can also be said to be the components that constitute the polypropylene resin particles.

[0018] In this specification, 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 also be referred to as "propylene units."

[0019] (Polypropylene resin (A)) The polypropylene resin (A) may be (a) a homopolymer of propylene, (b) a block copolymer, random copolymer or graft copolymer of propylene and a monomer other than propylene, or (c) a mixture of two or more of these.

[0020] Polypropylene resin (A) 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. The "monomers other than propylene monomers" used in the manufacture of polypropylene resin (A) are sometimes referred to as "comonomers." The "structural units derived from monomers other than propylene monomers" contained in polypropylene resin (A) are sometimes referred to as "comonomer units."

[0021] Examples of comonomers include α-olefins having 2 or 4 to 12 carbon atoms, such as ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene.

[0022] Specific examples of polypropylene resin (A) include polypropylene homopolymer, propylene / ethylene random copolymer, propylene / 1-butene random copolymer, propylene random / ethylene / 1-butene copolymer, propylene / ethylene block copolymer, propylene / 1-butene block copolymer, propylene / chlorinated vinyl copolymer, propylene / maleic anhydride copolymer, and styrene-modified polypropylene resin. One of these polypropylene resins (A) may be used alone, or two or more may be used in combination. Among these, propylene / ethylene random copolymer and propylene / ethylene / 1-butene random copolymer are preferred because the resulting foamed particles have good foaming properties and the molded article has good moldability. Note that 1-butene is synonymous with butene-1.

[0023] Let's consider the case where a polypropylene resin (A) is a propylene / ethylene random copolymer or a propylene / ethylene / 1-butene random copolymer (let's call this Case A). In Case A, the ethylene content in the propylene / ethylene random copolymer or propylene / ethylene / 1-butene random copolymer is preferably 0.2% to 10.0% by weight per 100% by weight of each copolymer. The ethylene content can also be said to be the content of constituent units (ethylene units) derived from ethylene. When the ethylene unit content in the propylene / ethylene random copolymer or propylene / ethylene / 1-butene random copolymer is (i) 0.2% by weight or more, the foaming properties of the foamed particles in the production of the first foamed particles and / or the moldability of the resulting foamed particles tend to be good, and when it is 10.0% by weight or less, there is no risk of the mechanical properties of the foamed molded article obtained from the first foamed particles deteriorating.

[0024] Furthermore, in case A, the 1-butene content in the propylene / ethylene / 1-butene random copolymer is preferably 0.2% to 10.0% by weight of 100% by weight of the copolymer. The 1-butene content can also be said to be the content of constituent units (1-butene units) derived from 1-butene. When the 1-butene unit content in the propylene / ethylene / 1-butene random copolymer is (i) 0.2% by weight or more, the foaming properties of the foamed particles in the production of the first foamed particles and / or the moldability of the resulting foamed particles tend to be good, and when it is 10.0% by weight or less, there is no risk of the mechanical properties of the foamed molded article obtained from the first foamed particles deteriorating.

[0025] Furthermore, in case A, the total content of ethylene units and 1-butene units in the propylene / ethylene / 1-butene random copolymer is preferably 0.5% to 10.0% by weight per 100% by weight of the propylene / ethylene / 1-butene random copolymer. When the total content of ethylene units and 1-butene units in the propylene / ethylene / 1-butene random copolymer is (i) 0.5% by weight or more, the foaming properties of the foamed particles in the production of the first foamed particles and / or the moldability of the resulting foamed particles tend to be good, and when it is 10.0% by weight or less, there is no risk of the mechanical properties of the foamed molded article obtained from the first foamed particles deteriorating.

[0026] The melting point of the polypropylene resin (A) according to the first embodiment of the present invention is preferably 135°C to 150°C, more preferably 137°C to 148°C, more preferably 139°C to 146°C, more preferably 140°C to 146°C, even more preferably 141°C to 145°C, and particularly preferably 142°C to 144°C. When the melting point of the polypropylene resin (A) is (i) 135°C or higher, the foamed molded article obtained from the first foamed particles has excellent heat resistance, and when it is 150°C or lower, it becomes easier to increase the foaming ratio of the foamed particles in the production of the first foamed particles.

[0027] In this specification, the melting point of polypropylene resin (A) is a value obtained by measurement using differential scanning calorimetry (hereinafter referred to as the "DSC method"). The specific operating procedure is as follows: (1) Melt the polypropylene resin (A) by raising the temperature of 5 mg to 6 mg of polypropylene resin (A) from 40°C to 220°C at a heating rate of 10°C / min; (2) Then, crystallize the polypropylene resin (A) by lowering the temperature of the molten polypropylene resin (A) 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 (A) 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 (A) obtained during the second heating (i.e., at (3)) can be determined as the melting point of the polypropylene resin (A). Furthermore, if multiple peaks (melting peaks) exist in the DSC curve of the polypropylene resin (A) 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 (A). As a differential scanning calorimeter, for example, the DSC6200 model manufactured by Seiko Instruments Inc. can be used.

[0028] The MFR at 230°C of the polypropylene resin (A) used in the first embodiment of the present invention is not particularly limited, but is preferably 3 g / 10 min to 30 g / 10 min, more preferably 4 g / 10 min to 20 g / 10 min, and even more preferably 5 g / 10 min to 18 g / 10 min.

[0029] When the MFR of the polypropylene resin (A) is 3 g / 10 min or more, it tends to be easier to increase the foaming ratio of the foamed particles in the production of the first foamed particles. When the MFR of the polypropylene resin is 30 g / 10 min or less, there is no risk of the bubbles in the resulting foamed particles becoming interconnected, and as a result, (i) the compressive strength of the foamed molded article obtained from the first foamed particles tends to be good, or (ii) the surface quality of the foamed molded article tends to be good.

[0030] Consider the case where the MFR of the polypropylene resin (A) is in the range of 3 g / 10 min to 30 g / 10 min. In this case, it is easy to obtain polypropylene resin foam particles with a relatively large foaming ratio. Furthermore, in this case, the foam molded product obtained from the first foam particles has the advantage of having excellent surface beauty and a small dimensional shrinkage rate.

[0031] In this specification, the MFR value of polypropylene resin (A) is the value obtained by measuring using the MFR measuring instrument described in JIS K7210:1999 under the following conditions: orifice diameter of 2.0959 ± 0.005 mmφ, orifice length of 8.000 ± 0.025 mm, load of 2.16 kgf, and temperature of 230 °C (230 ± 0.2 °C).

[0032] Polypropylene resin (A) can be obtained by known methods. There are no particular restrictions on the polymerization catalyst used when synthesizing polypropylene resin (A), and Ziegler catalysts and the like can be used.

[0033] The base resin contains, in 100 parts by weight of resin components, more than 80.0 parts by weight and 98.0 parts by weight or less of polypropylene resin (A), preferably between 82.5 and 98.0 parts by weight, more preferably between 85.0 and 95.0 parts by weight, and even more preferably between 90.0 and 95.0 parts by weight. When the base resin contains, in 100 parts by weight of resin components, (a) more than 80.0 parts by weight of polypropylene resin (A), it is possible to provide polypropylene resin foam particles that have good compressive strength and are hardly deformable, and (b) 98.0 parts by weight or less, it is possible to provide polypropylene resin foam particles that have excellent surface beauty and good fusion properties that can be provided at a low molding pressure.

[0034] (Polypropylene polymer (B)) The polypropylene homopolymer (B) according to the first embodiment of the present invention is a polypropylene homopolymer having a melting point of 85°C or lower. In the process of diligently studying the first embodiment of the present invention, the inventors have surprisingly made the following unique discoveries: By using foamed particles containing the above-mentioned polypropylene resin (A) and the polypropylene homopolymer (B) having a melting point of 85°C or lower, (a) a polypropylene resin foam molded article with good fusion properties can be provided at a low molding pressure, and (b) a polypropylene resin foam molded article with good compressive strength and almost no deformation can be provided.

[0035] Furthermore, in the process of diligently studying the first embodiment of the present invention, the inventors have surprisingly made the following discovery: By using foamed particles containing the above-mentioned polypropylene resin (A) and a polypropylene homopolymer (B) having a melting point of 85°C or lower, it is possible to provide a polypropylene resin foamed molded article with excellent surface beauty.

[0036] The melting point of the polypropylene homopolymer (B) is 85°C or lower, preferably 80°C or lower, more preferably less than 78°C, and even more preferably 75°C or lower. When the melting point of the polypropylene homopolymer (B) is 85°C or lower, the resulting foamed particles have the advantages of (a) being able to provide a polypropylene resin foam molded article with good fusion properties at a lower molding pressure, and (b) being able to provide a foam molded article with better compressive strength, minimal deformation, and excellent surface beauty. The reason for this is presumed to be as follows, but the present invention is not limited to this reason: when the melting point of the polypropylene homopolymer (B) is 85°C or lower, the polypropylene homopolymer (B) can easily penetrate the aggregate (non-crystalline portion) of the polypropylene resin (A) with almost no crystallization. The lower limit of the melting point of the polypropylene homopolymer (B) is not particularly limited, but it is preferably 40°C or higher. If the melting point of polypropylene homopolymer (B) is 40°C or higher, the polypropylene homopolymer (B) has the advantage of being easy to handle because it is not sticky at room temperature.

[0037] In this specification, the melting point of polypropylene homopolymer (B) is a value obtained by measurement using the DSC method. Specifically, the DSC curve of polypropylene homopolymer (B) can be obtained using the same method as for measuring the melting point of polypropylene resin (A), except that polypropylene homopolymer (B) is used instead of polypropylene resin (A). Similar to the melting point of polypropylene resin (A), the melting point of polypropylene homopolymer (B) can be determined from the DSC curve of polypropylene homopolymer (B).

[0038] The weight-average molecular weight of the polypropylene homopolymer (B) is preferably 40,000 to 140,000, more preferably greater than 40,000 and 140,000 or less, and particularly preferably between 75,000 and 140,000. A polypropylene homopolymer (B) with a weight-average molecular weight of 40,000 or more has sufficient viscosity. Therefore, when the weight-average molecular weight of the polypropylene homopolymer (B) is 40,000 or more, a blend containing the polypropylene resin (A) and the polypropylene homopolymer (B) can be easily melt-kneaded in the production of polypropylene resin particles containing the base resin. Furthermore, when the weight-average molecular weight of the polypropylene homopolymer (B) is 140,000 or less, the resulting foamed particles have the advantages of (a) providing a polypropylene resin foamed molded article with good fusion properties at a lower molding pressure, and (b) providing a foamed molded article with better compressive strength, minimal deformation, and superior surface beauty. The reason for this is presumed to be as follows, but the present invention is not limited to this reason: When the weight-average molecular weight of the polypropylene homopolymer (B) is 140,000 or less, the melting point of the polypropylene homopolymer (B) becomes moderately low, and it becomes difficult to crystallize. Therefore, the polypropylene homopolymer (B) can easily penetrate the aggregate (non-crystalline portion) of the polypropylene resin (A) with almost no crystallization.

[0039] In this specification, the weight-average molecular weight of polypropylene homopolymer (B) is the value obtained by converting the value obtained by gel permeation chromatography (GPC) to polystyrene.

[0040] The polypropylene homopolymer (B) preferably has low stereoregularity, that is, it is preferable to have a polypropylene homopolymer with low stereoregularity. In other words, a polypropylene homopolymer (B) with a melting point of 85°C or lower can be realized with a polypropylene homopolymer with low stereoregularity.

[0041] Polypropylene homopolymers with low stereoregularity can be obtained by polymerization reactions using propylene monomers and metallocene catalysts. In other words, it is preferable that polypropylene homopolymer (B) is polymerized using a metallocene catalyst. Polypropylene homopolymers polymerized using a metallocene catalyst tend to have lower stereoregularity of the polypropylene monomers in the polymer. Therefore, the melting point of the polypropylene homopolymer tends to be lower compared to those polymerized using a Ziegler catalyst or the like.

[0042] Examples of metallocene catalysts include catalysts that have a silylene 2-bridged indenyl complex as their basic structure and that have the activity to catalyze the polymerization reaction of propylene monomers.

[0043] The "stereoregularity" of polypropylene resins, including polypropylene homopolymers, can be expressed in terms of mesopentad fraction (mmmm). The mesopentad fraction of polypropylene homopolymer (B) is preferably 25 mol% to 65 mol%, more preferably 30 mol% to 60 mol%, even more preferably 35 mol% to 55 mol%, and particularly preferably 40 mol% to 50 mol% out of 100 mol% of the total constituent units of the polymer. When the mesopentad fraction of polypropylene homopolymer (B) is 25 mol% to 65 mol%, the resulting foamed particles have the advantages of (a) providing a foamed molded article with excellent fusion properties at a lower molding pressure, and (b) providing a polypropylene resin foamed molded article with better compressive strength, minimal deformation, and superior surface beauty. The reason for this is presumed to be as follows, but is not limited to this reason: When the mesopentade fraction is between 25 mol% and 65 mol%, the melting point of the polypropylene homopolymer (B) becomes moderately low, and it becomes less likely to crystallize. Therefore, the polypropylene homopolymer (B) can easily penetrate the aggregate (amorphous portion) of the polypropylene resin (A) with almost no crystallization.

[0044] In this specification, the mesopentade fraction of a polypropylene resin (e.g., polypropylene homopolymer (B)) is a value obtained by measuring it using the following methods (1) to (3): (1) A polypropylene resin (e.g., polypropylene homopolymer (B)) was dissolved in o-dichlorobenzene as a sample. The resulting solution was subjected to a JEOL JNM-GX270 instrument and measured at a resonance frequency of 67.93 MHz. 13 (1) Measure the 1C-NMR spectrum; (2) Assign each peak to the spectrum derived from the methyl group, setting the mmmm peak to 21.855 ppm, and determine the peak area; (3) Express the ratio of the mmmm peak to the total peak area derived from the methyl group as a percentage, and express it as the mesopentade fraction (mol%). The detailed measurement conditions are as follows. Solvent used for measurement: o-dichlorobenzene (90% by weight) / benzene-D6 (10% by weight) Sample concentration: 15% to 20% by weight Measurement temperature: 120℃~130℃ Resonance frequency: 67.93MHz Pulse width: 10 μsec (45° pulse) Pulse repetition time: 7.091 sec Data points: 32K Total count: 8168 Measurement mode: Noise decoupling In this specification, the assignment of the obtained spectra and the calculation of the pentad fraction are performed based on the method used by T. Hayashi et al. [Polymer, 29, 138-143 (1988)].

[0045] The base resin contains, in 100 parts by weight of the resin component, 2.0 parts by weight or more and less than 20.0 parts by weight of polypropylene homopolymer (B), preferably between 2.0 and 17.5 parts by weight, more preferably between 5.0 and 15.0 parts by weight, and even more preferably between 5.0 and 10.0 parts by weight. When the base resin contains, in 100 parts by weight of the resin component, (a) 2.0 parts by weight or more of polypropylene homopolymer (B), it is possible to provide polypropylene resin foam particles that can provide a polypropylene resin foam molded article with excellent surface beauty and good fusion properties at a low molding pressure, and (b) less than 20.0 parts by weight, it is possible to provide polypropylene resin foam particles that can provide a polypropylene resin foam molded article with good compressive strength and almost no deformation. Furthermore, by including polypropylene homopolymer (B) within the above range in the base resin, it is possible to provide polypropylene resin foam particles that can provide a polypropylene resin foam molded article with even better surface beauty.

[0046] The base resin preferably contains, when the total amount of polypropylene resin (A) and polypropylene homopolymer (B) is 100 parts by weight, (a) more than 80.0 parts by weight and 98.0 parts by weight or less of polypropylene resin (A), and 2.0 parts by weight or more and less than 20.0 parts by weight of polypropylene homopolymer (B); (b) 82.5 parts by weight to 98.0 parts by weight of polypropylene resin (A), and 2.0 parts by weight to 17.5 parts by weight of polypropylene homopolymer (B); (c) 85.5 parts by weight to 98.0 parts by weight of polypropylene resin (A), and 2.0 parts by weight to 14.5 parts by weight of polypropylene homopolymer (B); and (d) 87.5 parts by weight to 97.5 parts by weight of polypropylene resin (A), and 2.5 parts by weight to 12.5 parts by weight of polypropylene homopolymer (B). When the base resin contains, with respect to 100 parts by weight of the total amount of polypropylene resin (A) and polypropylene homopolymer (B), more than 80.0 parts by weight and 98.0 parts by weight or less, and 2.0 parts by weight or more and less than 20.0 parts by weight of polypropylene homopolymer (B), it is possible to provide (a) polypropylene resin foam particles that can provide a polypropylene resin foam molded article having good fusion properties at a low molding pressure, and (b) polypropylene resin foam particles that can provide a polypropylene resin foam molded article having good compressive strength, almost no deformation, and superior surface beauty.

[0047] (Other resins, etc.) The base resin may further contain resins other than the polypropylene resin (A) and the polypropylene homopolymer (B) (sometimes referred to as "other resins, etc.") as resin components, to the extent that the effects of the first embodiment of the present invention are not impaired. Examples of such other resins, etc. include (a) polypropylene resins other than the polypropylene resin (A) and the polypropylene homopolymer (B), (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, (c) styrene resins such as polystyrene, styrene / maleic anhydride copolymer, and styrene / ethylene copolymer, (d) polyolefin waxes such as propylene-α-olefin wax, and (e) olefin rubbers such as ethylene / propylene rubber, ethylene / butene rubber, ethylene / hexene rubber, and ethylene / octene rubber.

[0048] (Additives) In addition to the polypropylene resin (A) and polypropylene homopolymer (B) described above, the base resin may optionally contain additives. Examples of additives include colorants, water absorbents, foaming nucleating agents, antistatic agents, flame retardants, antioxidants, light stabilizers, crystal nucleating agents, conductive agents, and lubricants. Such additives may be added directly to the blend or polypropylene resin composition described later in the production of polypropylene resin particles.

[0049] Examples of colorants include carbon black, ultramarine, cyanine pigments, azo pigments, quinacridone pigments, cadmium yellow, chromium oxide, iron oxide, perylene pigments, and anthraquinone pigments. Among these, carbon black is preferred as a colorant because it yields molded articles with minimal color unevenness and excellent colorability. One of these colorants may be used alone, or two or more may be used in combination. When using a mixture of two or more colorants, the mixing ratio may be adjusted as appropriate depending on the purpose.

[0050] In the first embodiment of the present invention, the base resin may or may not contain carbon black. When the base resin contains carbon black, it is preferable that the carbon black content is less than 10 parts by weight when the total amount of polypropylene resin (A) and polypropylene homopolymer (B) is 100 parts by weight.

[0051] The water-absorbing substance is used in the production of the first foamed particles to increase the amount of water impregnated in the resin particles. By using the water-absorbing substance when producing the first foamed particles, foaming properties can be imparted to the resin particles. The effect of the water-absorbing substance on imparting foaming properties to the resin particles is particularly pronounced when water is used as the foaming agent.

[0052] Examples of absorbent substances that can be used in the first embodiment of the present invention include glycerin, diglycerin, polyethylene glycol, C12-C18 aliphatic alcohols (e.g., pentaerythritol, cetyl alcohol, stearyl alcohol), melamine, isocyanuric acid, melamine-isocyanuric acid condensate, zinc borate, and the like. One of these absorbent substances may be used alone, or two or more may be used in combination. When two or more absorbent substances are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0053] Among the water-absorbing substances mentioned above, glycerin and polyethylene glycol are preferred because (a) they do not promote the refinement of the average bubble diameter of the foamed particles, and (b) they have good affinity with polypropylene resin (A).

[0054] The amount of water-absorbing substance used in the production of the first foamed particles, in other words, the content of water-absorbing substance in the base resin, will now be explained. The content of water-absorbing substance in the base resin, per 100 parts by weight of the total amount of polypropylene resin (A) and polypropylene homopolymer (B), is preferably 0.01 to 1.00 parts by weight, more preferably 0.05 to 0.70 parts by weight, and even more preferably 0.10 to 0.60 parts by weight. When the content of water-absorbing substance is (i) 0.01 parts by weight or more, the foaming effect of the water-absorbing substance can be sufficiently obtained, and (ii) when it is 1.00 part by weight or less, there is no risk of the resulting foamed particles shrinking.

[0055] A foaming nucleating agent is a substance that can be used in the production of the first foamed particles and can act as a foaming nucleus when the resin particles foam. It is preferable to use a foaming nucleating agent in the production of the first foamed particles; in other words, it is preferable that the first foamed particles contain a foaming nucleating agent.

[0056] Examples of foaming nucleating agents that can be used in one first embodiment of the present invention include silica (silicon dioxide), silicates, alumina, diatomaceous earth, calcium carbonate, magnesium carbonate, calcium phosphate, feldspar apatite, and barium sulfate. Examples of silicates include talc, magnesium silicate, kaolin, halloysite, deckite, aluminum silicate, and zeolite. One of these foaming nucleating agents may be used alone, or two or more may be used in combination. When two or more foaming nucleating agents are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0057] The amount of foaming agent used in the production of the first foamed particles, in other words, the content of the foaming agent in the base resin, will now be explained. From the viewpoint of uniformity of the average bubble diameter, the content of the foaming agent in the base resin is preferably 0.005 parts by weight to 2.000 parts by weight, more preferably 0.010 parts by weight to 1.000 parts by weight, and even more preferably 0.030 parts by weight to 0.500 parts by weight, per 100 parts by weight of the total amount of polypropylene resin (A) and polypropylene homopolymer (B).

[0058] Examples of inorganic nucleating agents include feldspar, zeolite, talc, kaolin, mica, calcium stearate, calcium carbonate, silica, titanium dioxide, bentonite, and barium sulfate. These nucleating agents may be used alone or in combination of two or more. Among these nucleating agents, silicate compounds such as feldspar, zeolite, talc, kaolin, and mica are preferred, with talc being more preferred. When a silicate compound is used as the nucleating agent, a foamed molded article can be provided in which the foamed particles have high blackness and little to no intergranular space between them.

[0059] The amount of nucleating agent used in the production of the first foamed particles, in other words, the content of the nucleating agent in the base resin, will be explained. The content of the nucleating agent in the base resin, per 100 parts by weight of the total amount of polypropylene resin (A) and polypropylene homopolymer (B), is preferably 0.01 to 0.25 parts by weight, and more preferably 0.01 to 0.20 parts by weight. When the content of the nucleating agent in the base resin, per 100 parts by weight of the total amount of polypropylene resin (A) and polypropylene homopolymer (B), is (a) 0.01 parts by weight or more, the foamed molded article provided by the foamed particles tends to be a foamed molded article with a uniform color (black) with no color unevenness, or a foamed molded article with a substantially uniform color (black) with very little color unevenness, and (b) 0.25 parts by weight or less, the foamed molded article provided by the foamed particles tends to have a high degree of blackness, with no or very few gaps between particles.

[0060] <Physical properties> The following describes the physical properties of the first type of foamed particle.

[0061] (DSC ratio of foamed particles) The first foamed particle preferably has at least two melting peaks in the DSC curve obtained by differential scanning calorimetry described later. Of these melting peaks, the heat of fusion obtained from the high-temperature melting peak is defined as the "high-temperature side heat of fusion," and the heat of fusion obtained from the low-temperature melting peak is defined as the "low-temperature side heat of fusion." If there are three or more melting peaks, the heat of fusion obtained from the highest-temperature melting peak is defined as the "high-temperature side heat of fusion," and the heat of fusion obtained from the other melting peaks is defined as the "low-temperature side heat of fusion."

[0062] The DSC ratio of the first foamed particles is not particularly limited, but is preferably 10.0% to 50.0%, more preferably 20.0% to 40.0%, and even more preferably 22.0% to 30.0%. When the DSC ratio of the foamed particles is 10.0% or higher, the foamed particles have the advantage of being able to provide a foamed molded article with sufficient strength. On the other hand, when the DSC ratio of the foamed particles is 50.0% or lower, the foamed particles have the advantage of being able to be molded at a relatively low temperature (molding temperature) to provide a foamed molded article.

[0063] In this specification, the DSC ratio refers to the ratio of the heat of fusion on the high-temperature side to the total heat of fusion, calculated from the DSC curve of the first foamed particle. In this specification, the DSC curve is obtained using a differential scanning calorimeter (e.g., Seiko Instruments DSC6200). More specifically, in this specification, the method for measuring (calculating) the DSC ratio of foamed particles using a differential scanning calorimeter (e.g., Seiko Instruments DSC6200) is as follows (1) to (6): (1) Weigh out 5 mg to 6 mg of foamed particles; (2) Heat the foamed particles from 40°C to 220°C at a heating rate of 10°C / min to melt the foamed particles; (3) In the DSC curve of the foamed particles obtained in the process of (2), draw a straight line connecting the point representing the temperature before the start of melting and the point representing the temperature after the end of melting to create a baseline; (4) The melting peak on the high-temperature side or the highest temperature (5) Draw a straight line perpendicular to the X-axis that passes through the maximum point between the melting peak and the adjacent melting peak; (6) Define the heat amount calculated from the high-temperature region enclosed by the baseline, the straight line passing through the maximum point, and the DSC curve as the high-temperature side heat of fusion, define the heat amount calculated from the low-temperature region enclosed by the baseline, the straight line passing through the maximum point, and the DSC curve as the low-temperature side heat of fusion, and define the heat amount calculated from the region enclosed by the baseline and the DSC curve as the total heat of fusion (= high-temperature side heat of fusion + low-temperature side heat of fusion); (7) Calculate the DSC ratio from the following formula: DSC ratio (%) = (high-temperature side heat of fusion / total heat of fusion) × 100.

[0064] The DSC ratio of the first foamed particle is also an indicator of the amount of high-melting-point crystals contained in the foamed particle. In other words, a DSC ratio of 10.0% to 50.0% indicates that the foamed particle contains a relatively large amount of high-melting-point crystals. Furthermore, the DSC ratio of the foamed particle greatly influences the viscoelasticity of the resin particles and the foamed particles when foaming and expanding the resin particles. That is, when the DSC ratio of the foamed particle is 10.0% to 50.0%, the resin particles and the foamed particles can exhibit excellent foaming and expanding properties, respectively, when foaming and molding the resin particles. As a result, the foamed particle has the advantage of producing a foamed molded article with excellent internal bonding at low molding pressure and excellent mechanical strength such as compressive strength.

[0065] Methods for controlling the DSC ratio within a predetermined range in the first foamed particles include adjusting the manufacturing conditions of the first foamed particles (particularly the foaming temperature, foaming pressure, holding time, and the temperature of the region (space) where the dispersion is released). Because these adjustments are easy, adjusting the foaming temperature, foaming pressure, and / or holding time is preferred as a method for controlling the DSC ratio within a predetermined range.

[0066] For example, increasing the foaming temperature tends to decrease the DSC ratio, while decreasing the foaming temperature tends to increase it. This is because the amount of unmelted crystals changes depending on the foaming temperature. Similarly, increasing the foaming pressure tends to decrease the DSC ratio, while decreasing the foaming pressure tends to increase it. This is because the degree of plasticization changes depending on the foaming pressure, which in turn changes the amount of unmelted crystals. Furthermore, increasing the holding time tends to increase the DSC ratio. This is because the amount of unmelted crystal growth changes depending on the holding time.

[0067] (Average bubble diameter of foaming particles) The average bubble diameter of the first foam particles is not particularly limited, but is preferably 110 μm to 280 μm, more preferably 120 μm to 270 μm, more preferably 130 μm to 260 μm, even more preferably 140 μm to 250 μm, even more preferably 150 μm to 240 μm, and particularly preferably 160 μm to 230 μm. When the average bubble diameter of the first foam particles is (i) 110 μm or more, the foam particles can provide a polypropylene resin foam molded article that is free from color unevenness, has excellent colorability, and has excellent compressive strength, and (ii) when the average bubble diameter of the first foam particles is 280 μm or less, there is no risk of the molding cycle of the in-molded foam molded article becoming long, which has the advantage of good productivity. Here, the molding cycle refers to the time from the start of in-molded foam molding to the end of molding when the obtained molded article is released from the mold, when a foam molded article is obtained by in-molded foam molding using foam particles.

[0068] In this specification, the method for measuring the average bubble diameter of foamed particles is as follows (1) to (5): (1) Using a razor (Feather High Stainless Double-Edged), cut the foamed particle so as to pass through its center; (2) Observe the resulting cut surface of the foamed particle at 50x magnification using an optical microscope (Keyence VHX-100); (3) Draw a straight line through the center or approximate center of the cut surface of the foamed particle in the image obtained from the observation; (4) (4-1) Measure the number of bubbles n present on the straight line; (4-2) Measure the length of the line segment cut off from the straight line at the intersection of the straight line and the surface of the foamed particle, and define this as the foamed particle diameter L; (5) Calculate the average bubble diameter of the foamed particle using the following formula: Average bubble diameter (μm) = L / n.

[0069] (Foaming ratio of foaming particles) The first foamed particles preferably have an expansion ratio of 15 to 50 times, more preferably 18 to 40 times, and even more preferably 20 to 25 times. If the expansion ratio of the foamed particles is (i) 15 times or more, a lightweight foamed molded article can be obtained with production efficiency, and (ii) if it is 50 times or less, there is no risk of insufficient strength in the resulting foamed molded article.

[0070] In this specification, the foaming ratio of foaming particles is calculated by the following methods (1) to (4): (1) measure the weight w (g) of the foaming particles; (2) then immerse the foaming particles used to measure the weight in ethanol contained in a graduated cylinder, and calculate the volume v (cm³) of the foaming 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 (ρ2) to calculate the density ρ1 of the foamed particles; (5) Divide the density ρ2 of the polypropylene resin particles used in the production of the foamed particles by the density ρ1 of the foamed particles (ρ2 / ρ1), multiply the resulting value by 100, and the resulting value is taken as the foaming ratio of the foamed particles.

[0071] The first foamed particle has the advantage of being able to provide a polypropylene-based resin foam molded article with good fusion properties at a low molding pressure. This advantage can be evaluated by the minimum molding pressure during in-mold foam molding that can provide a foam molded article with an internal fusion rate of 60% or more. The minimum molding pressure will be described in detail in the section (Minimum Molding Pressure) of [1-2. Polypropylene-based Resin Foam Molded Article] below.

[0072] <Method for manufacturing polypropylene resin foam particles> The method for producing the first foamed particles is not particularly limited, and known production methods can be used as appropriate. One embodiment of the method for producing the first foamed particles will be described in detail below, but for matters other than those described in detail below, the above description (for example, the description in the <Components> section) should be referred to as appropriate. Note that the method for producing the first foamed particles is not limited to the method described below.

[0073] (granulation process) In manufacturing the first foamed particles, a process (granulation process) may be carried out to first manufacture polypropylene resin particles containing a base resin.

[0074] One method for producing resin particles is to use an extruder. Specifically, for example, resin particles can be produced by the following methods (1) to (5): (1) Blend one or more selected from the group consisting of a polypropylene resin (A), a polypropylene homopolymer (B), and other resins and additives as needed to produce a blend; (2) Put the blend into an extruder and melt-knead it to prepare a polypropylene resin composition; (3) Extrude the polypropylene resin composition through a die provided in the extruder; (4) Solidify the extruded polypropylene resin composition by cooling it by passing it through water, etc.; (5) Then, cut the solidified polypropylene resin composition with a cutter into desired shapes such as cylindrical, elliptical, spherical, cubic, or rectangular parallelepiped. Alternatively, in (3), the melt-kneaded polypropylene resin composition may be directly extruded into water through a die provided in the extruder, and immediately after extrusion, the polypropylene resin composition may be cut into particle shapes, cooled, and solidified. In this way, by melting and kneading the blended materials, more uniform resin particles can be obtained.

[0075] The weight per particle of the resin particles obtained as described above is preferably 0.2 mg / particle to 10.0 mg / particle, and more preferably 0.5 mg / particle to 6.0 mg / particle. When the weight per particle of the resin particles is (A) 0.2 mg / particle or more, the handling properties of the resin particles tend to improve, and the shrinkage rate of the foamed molded article obtained by molding the resulting foamed particles tends to be smaller. When the weight per particle is (B) 10.0 mg / particle or less, the mold filling properties tend to improve in the in-mold foaming molding process.

[0076] The melting point of the resin particles is preferably 139°C to 150°C, and more preferably 140°C to 146°C. If the melting point of the resin particles is (i) 139°C or higher, the foamed molded article obtained by molding the resulting foamed particles has excellent heat resistance. If the melting point is 150°C or lower, it becomes easier to increase the foaming ratio of the resulting foamed particles in the production of the first foamed particles.

[0077] In this specification, the melting point of resin particles is a value obtained by measurement using the DSC method. Specifically, the DSC curve of resin particles can be obtained using the same method as for measuring the melting point of polypropylene resin (A), except that resin particles are used instead of polypropylene resin (A). Similar to the melting point of polypropylene resin (A), the melting point of resin particles can be determined from the DSC curve of the resin particles.

[0078] (Foaming process) The foaming process in the method for producing foamed particles is not particularly limited, as long as it can foam the resin particles. In the first embodiment of the present invention, the foaming process is (a) A dispersion step of dispersing resin particles, an aqueous dispersion medium, a foaming agent, and, if necessary, a dispersant and / or a dispersion aid in a container, (b) A heating-pressure step in which the temperature inside the container is raised to a certain temperature and the pressure inside the container is raised to a certain pressure, (c) A holding step to maintain the temperature and pressure inside the container at a constant temperature and constant pressure, (d) Preferably includes a discharge step of opening one end of the container and releasing the dispersion inside the container into a region (space) with a pressure lower than the foaming pressure (i.e., the pressure inside the container).

[0079] The process of manufacturing foamed particles from resin particles in this manner is called the "single-stage foaming process," and the resulting foamed particles are called "single-stage foamed particles."

[0080] (Dispersion process) The dispersion process can also be described as the process of preparing a dispersion in which resin particles, a foaming agent, and, if necessary, a dispersant and / or a dispersion aid are dispersed in an aqueous dispersion medium.

[0081] The container is not particularly limited, but it is preferable that it be able to withstand the foaming temperature and pressure described later. For example, a pressure-resistant container is preferred, and an autoclave-type pressure-resistant container is more preferable.

[0082] The aqueous dispersion medium is not particularly limited, as long as it can uniformly disperse resin particles, foaming agents, etc. Examples of aqueous dispersion mediums include (a) dispersion mediums obtained by adding methanol, ethanol, ethylene glycol, glycerin, etc. to water, and (b) tap water and industrial water. In order to enable stable production of foaming particles, it is preferable to use pure water and ultrapure water such as RO water (water purified by reverse osmosis membrane method), distilled water, and deionized water (water purified by ion exchange resin) as the aqueous dispersion medium.

[0083] The amount of aqueous dispersion medium used is not particularly limited, but 100 to 400 parts by weight is preferred per 100 parts by weight of resin particles. (a) When the amount of aqueous dispersion medium used is 100 parts by weight or more, there is no risk of the stability of the dispersion being reduced (in other words, the dispersion of resin particles will be good), and (b) when the amount used is 400 parts by weight or less, there is no risk of productivity being reduced.

[0084] Examples of blowing agents include (a) (a-1) inorganic gases such as nitrogen, carbon dioxide, and air (a mixture of oxygen, nitrogen, and carbon dioxide), and (a-2) water; and (b) (b-1) saturated hydrocarbons having 3 to 5 carbon atoms such as propane, n-butane, isobutane, n-pentane, isopentane, and neopentane; (b-2) ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether; and (b-3) halogenated hydrocarbons such as monochloromethane, dichloromethane, and dichlorodifluoroethane. At least one type of blowing agent selected from the group consisting of the inorganic and organic blowing agents described above can be used. When using a mixture of two or more blowing agents, the mixing ratio may be adjusted as appropriate depending on the purpose. From the viewpoint of environmental impact and blowing power, inorganic blowing agents are preferred among the above-mentioned blowing agents. Furthermore, carbon dioxide is preferred among inorganic blowing agents because it has a moderately high plasticizing effect and easily improves the blowing properties of the blowing particles in the production of the first blowing particles. The blowing agent may consist of (i) carbon dioxide alone, (ii) water alone, or (iii) carbon dioxide and water alone.

[0085] The amount of foaming agent used is not particularly limited and should be used appropriately depending on (a) the type of foaming agent and / or (b) the desired foaming ratio of the foamed particles. The amount of foaming agent used is preferably 2.0 to 60.0 parts by weight, more preferably 2.0 to 50.0 parts by weight, more preferably 2.0 to 40.0 parts by weight, more preferably 2.0 to 30.0 parts by weight, even more preferably 2.0 to 20.0 parts by weight, and particularly preferably 2.0 to 10.0 parts by weight per 100 parts by weight of resin particles. When the amount of foaming agent used is 2.0 parts by weight or more per 100 parts by weight of resin particles, foamed particles with a suitable density can be obtained. On the other hand, when the amount of foaming agent used is 60.0 parts by weight or less per 100 parts by weight of resin particles, the effect corresponding to the amount of foaming agent used is obtained, so there is no economic waste.

[0086] When water is used as a foaming agent, the water in the dispersion in the container can be used as the foaming agent. Specifically, when using water in the dispersion as a foaming agent, it is preferable to include a water-absorbing substance in the resin particles beforehand. This makes it easier for the resin particles to absorb the water in the dispersion in the container, and as a result, it becomes easier to use water as a foaming agent.

[0087] In the first method for producing foamed particles, it is preferable to use a dispersant. Using a dispersant has the advantage of suppressing the fusion of resin particles (sometimes referred to as blocking) and enabling the stable production of foamed particles. Examples of dispersants include inorganic substances such as tricalcium phosphate, trimagnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, clay, aluminum oxide, titanium oxide, and aluminum hydroxide. One of these dispersants may be used alone, or two or more may be used in mixture. Furthermore, when using a mixture of two or more dispersants, the mixing ratio may be appropriately adjusted depending on the purpose.

[0088] The amount of dispersant used in the dispersion in the first embodiment of the present invention is preferably 0.01 to 3.00 parts by weight, and more preferably 0.10 to 3.00 parts by weight, per 100 parts by weight of resin particles. When the amount of dispersant used is (a) 0.01 parts by weight or more, the risk of poor dispersion of resin particles increases as the amount of dispersant used increases, and (b) when the amount is 3.00 parts by weight or less, the risk of poor fusion between foam particles during in-molding foam molding using the resulting foam particles is eliminated.

[0089] In the first method for producing foamed particles, it is preferable to use a dispersion aid to (a) improve the effect of suppressing the fusion of resin particles and / or to (b) improve the stability of the dispersion in the container. Examples of dispersion aids include anionic surfactants. Examples of anionic surfactants include sodium alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate, sodium alkanesulfonates, sodium alkylsulfonates, sodium alkyldiphenyl ether disulfonates, and sodium α-olefin sulfonates. One of these dispersion aids may be used alone, or two or more may be used in combination. When two or more dispersion aids are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0090] In the first embodiment of the present invention, the amount of dispersion aid used in the dispersion is preferably 0.001 to 0.500 parts by weight, more preferably 0.001 to 0.200 parts by weight, and even more preferably 0.010 to 0.200 parts by weight, per 100 parts by weight of resin particles. When the amount of dispersion aid used is within the above range, there is no risk of causing poor dispersion of the resin particles.

[0091] When the stability of the dispersion decreases, multiple resin particles may adhere to each other or form clumps in the container. As a result, (i) adhered foam particles may be obtained, (ii) clumps of resin particles may remain in the container, preventing the production of foam particles, or (iii) the productivity of foam particles may decrease.

[0092] (Heating-pressure boosting process and holding process) The heating-pressure step is preferably performed after the dispersion step, and the holding step is preferably performed after the heating-pressure step. In this specification, (a) a constant temperature in the heating-pressure step and the holding step may be referred to as the foaming temperature, and (b) a constant pressure may be referred to as the foaming pressure.

[0093] The foaming temperature cannot be specified in general, as it varies depending on the type of polypropylene resin (A) and polypropylene homopolymer (B), the type of foaming agent, the desired apparent density of the foamed particles, etc. Preferably, the foaming temperature is (i) -20°C to +10°C for the mixture of polypropylene resin (A) and polypropylene homopolymer (B), or -20°C to +10°C for the resin particles; (ii) -5°C to +4°C for the mixture of polypropylene resin (A) and polypropylene homopolymer (B), or -5°C to +4°C for the resin particles; and (iii) -5°C to +3°C for the mixture of polypropylene resin (A) and polypropylene homopolymer (B), or -5°C to +3°C for the resin particles.

[0094] The foaming pressure is preferably 1.0 MPa (gauge pressure) to 5.0 MPa (gauge pressure), more preferably 2.0 MPa (gauge pressure) to 5.0 MPa (gauge pressure), and even more preferably 2.5 MPa (gauge pressure) to 3.5 MPa (gauge pressure). If the foaming pressure is 1.0 MPa (gauge pressure) or higher, foamed particles with a suitable density can be obtained.

[0095] In the holding process, the time for holding the dispersion in the container at or near the foaming temperature and pressure (holding time) is not particularly limited. The holding time is preferably 10 to 60 minutes, more preferably 12 to 55 minutes, and even more preferably 15 to 50 minutes. When the holding time is 10 minutes or more, the amount of unmelted crystals (crystals of polypropylene resin) in the resin particles can be made sufficient during the foaming process from resin particles to foamed particles. As a result, foamed particles with a low open-cell ratio can be obtained, and the shrinkage of the resulting foamed particles can be reduced. On the other hand, when the holding time is 60 minutes or less, the amount of unmelted crystals in the resin particles does not become excessive during the foaming process from resin particles to foamed particles. Therefore, the resulting foamed particles can be molded at a relatively low temperature (molding temperature) to provide a foamed molded article.

[0096] (Release process) The release step is preferably performed (a) after the heating-pressure step if the holding step is not performed, or (b) after the holding step if the holding step is performed. The release step allows the resin particles to foam, resulting in foamed particles.

[0097] In the release process, the "region with a pressure lower than the foaming pressure" refers to the "region under a pressure lower than the foaming pressure" or the "space under a pressure lower than the foaming pressure," and can also be described as "an atmosphere with a pressure lower than the foaming pressure." The region with a pressure lower than the foaming pressure is not particularly limited as long as the pressure is lower than the foaming pressure; for example, it may be a region under atmospheric pressure.

[0098] In the discharge process, when discharging the dispersion into a region with a pressure lower than the foaming pressure, the dispersion can be discharged through an open orifice with a diameter of 1 mm to 5 mm for purposes such as adjusting the flow rate of the dispersion and reducing variations in the foaming ratio of the resulting foamed particles. Furthermore, to improve foaming properties, the low-pressure region (space) may be filled with saturated water vapor.

[0099] (Two-stage foaming process) Incidentally, in order to obtain foamed particles with a high foaming ratio, one method is to use a large amount of inorganic foaming agent in the first foaming process (hereinafter referred to as Method 1). Furthermore, as an alternative to Method 1, it is also possible to obtain foamed particles (first-stage foamed particles) with a relatively low foaming ratio (foaming ratio of about 2 to 35 times) in the first foaming process, and then foam the obtained first-stage foamed particles again to increase the foaming ratio (hereinafter referred to as Method 2).

[0100] As an example of Method 2, a method comprising the following steps in order is provided: (a1) producing single-stage foamed particles with a foaming ratio of 2 to 35 times in a single-stage foaming process; (a2) placing the single-stage foamed particles in a pressure vessel and pressurizing them with nitrogen, air, carbon dioxide, etc., at 0.2 MPa (gauge pressure) to 0.6 MPa (gauge pressure) to raise the pressure inside the single-stage foamed particles (hereinafter sometimes referred to as "internal pressure") above atmospheric pressure; (a3) ​​then heating the single-stage foamed particles with increased internal pressure using steam, etc., to further foam them. The process of increasing the foaming ratio of single-stage foamed particles, as in Method 2, is called the "double-stage foaming process," and the polyolefin resin foamed particles obtained by the method of Method 2 are called "double-stage foamed particles."

[0101] In step (a3) ​​of the two-stage foaming process, it is preferable to adjust the pressure of the steam used to heat the first-stage foamed particles to 0.03 MPa (gauge pressure) to 0.20 MPa (gauge pressure), taking into consideration the foaming ratio of the second-stage foamed particles. When the steam pressure in the two-stage foaming process is 0.03 MPa (gauge pressure) or higher, the foaming ratio tends to improve, and when it is 0.20 MPa (gauge pressure) or lower, the possibility of the resulting second-stage foamed particles adhering to each other decreases. If the second-stage foamed particles adhere to each other, the resulting second-stage foamed particles may not be usable for subsequent in-mold foaming.

[0102] The internal pressure of the first-stage foamed particles, obtained by impregnating the first-stage foamed particles with nitrogen, air, carbon dioxide, etc., should be appropriately varied considering the foaming ratio of the second-stage foamed particles and the water vapor pressure of the second-stage foaming process. The internal pressure of the first-stage foamed particles is preferably 0.15 MPa (absolute pressure) to 0.60 MPa (absolute pressure), more preferably 0.20 MPa (absolute pressure) to 0.60 MPa (absolute pressure), and even more preferably 0.30 MPa (absolute pressure) to 0.60 MPa (absolute pressure). When the internal pressure of the first-stage foamed particles is 0.15 MPa (absolute pressure) or higher, high-pressure water vapor is not required to improve the foaming ratio, thus reducing the possibility of the second-stage foamed particles adhering together. When the internal pressure of the first-stage foamed particles is 0.6 MPa (absolute pressure) or lower, the possibility of the second-stage foamed particles becoming interconnected decreases. As a result, the possibility of a decrease in rigidity, such as the compressive strength, of the final in-molded foamed article decreases. Note that "connecting bubbles" can also be called "connecting air bubbles".

[0103] [1-2. Polypropylene-based resin foam molded product] The polypropylene resin foam molded article according to the first embodiment of the present invention is a foam molded article obtained by molding polypropylene resin foam particles as described in section [1-1. Polypropylene Resin Foam Particles]. It can also be said that the polypropylene resin foam molded article according to the first embodiment of the present invention includes the polypropylene resin foam particles as described in section [1-1. Polypropylene Resin Foam Particles].

[0104] In this specification, the "polypropylene-based resin foamed molded article according to the first embodiment of the present invention" may be referred to as the "first foamed molded article."

[0105] The first foamed molded body, having the above-described structure, has the advantages of having good fusion properties and good compressive strength, and exhibiting almost no deformation.

[0106] Furthermore, the first foamed molded body has the advantage of having excellent surface aesthetics due to the above-described structure.

[0107] (Internal fusion properties) The first foamed molded article also has the advantage of excellent internal fusion properties. In this specification, the internal fusion properties of the first foamed molded article are evaluated by the internal fusion rate. The first foamed molded article preferably has an internal fusion rate of 60% or more, more preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, even more preferably 95% or more, and most preferably 100%. A foamed molded article with an internal fusion rate of 60% or more has the advantage of excellent impact resistance.

[0108] In this specification, the internal bonding rate is a value measured by the following methods (1) to (4): (1) Make a 5 mm cut perpendicular to any one surface of the foamed molded body with a cutter, perpendicular to the portion having that surface; (2) Then, break the foamed molded body by hand along the cut; (3) Visually observe the area of ​​the resulting fracture surface excluding the cut portion, and measure the number of foamed particles present in that area, and the number of foamed particles that have broken outside the particle interface in that area (i.e., foamed particles that have broken themselves); (4) Calculate the internal bonding rate based on the following formula; Internal bonding rate (%) = (Number of foamed particles fractured outside the particle interface in the region / Total number of foamed particles present in the region) × 100.

[0109] (Surface beauty) In this specification, the surface beauty of the first foamed molded article is evaluated by the degree of the gaps between foam particles on the surface of the foamed molded article (hereinafter sometimes referred to as "intergranular space"). The smaller the size of the intergranular space on the surface of the foamed molded article, and the fewer the number of intergranular spaces, the better the surface beauty of the foamed molded article is intended to be.

[0110] For example, in one embodiment of the foamed molded body, a 1.5 mm layer is applied to the surface of the foamed molded body. 2 Preferably, there should be no gaps between particles larger than 1.0 mm. 2 It is particularly preferable that there are no gaps between particles larger than a certain size.

[0111] (Transformation) In this specification, the deformation of the first foamed molded article is evaluated by the wrinkles on the surface of the foamed molded article. The fewer wrinkles on the surface of the foamed molded article, the less deformation the foamed molded article is intended to have.

[0112] (Compressive strength) The first foamed molded article also has the advantage of having excellent compressive strength. For example, the first foamed molded article preferably satisfies the following formula (2), and is particularly preferably satisfied with the following formula (1).

[0113] (Compressive strength of the foamed molded material at 50% strain (MPa)) ≥ 0.0069 × (Density of the foamed molded material (g / L)) + 0.018 ... Equation (1) (Compressive strength of the foamed molded material at 50% strain (MPa)) ≥ 0.0069 × (Density of the foamed molded material (g / L)) ... Equation (2) The methods for measuring the compressive strength (MPa) and density (g / L) of the foamed molded article at 50% strain will be described in detail in the following examples.

[0114] <Method for manufacturing foamed molded products> The method for manufacturing the first foamed molded article is not particularly limited, and known methods can be applied. An example of the method for manufacturing the first foamed molded article is a method for manufacturing a polypropylene resin foamed molded article having a molding step for molding polypropylene resin foam particles according to one embodiment of the present invention. Specific embodiments of the method for manufacturing the first foamed molded article include, for example, a manufacturing method (in-mold foaming method) that sequentially includes (b1) to (b6) below, but is not limited to such a manufacturing method: (b1) A mold consisting of a fixed mold that cannot be driven and a movable mold that can be driven is mounted on an in-mold foaming molding machine. Here, the fixed mold and the movable mold can be formed inside the fixed mold and the movable mold by driving the movable mold toward the fixed mold (this operation may be referred to as "mold closing"); (b2) Drive the movable mold toward the fixed mold so that a small gap (also called cracking) is formed between the fixed mold and the movable mold, so that the molds are not completely closed; (b3) Fill the molding space formed inside the fixed and mobile molds with foam particles, for example, through a filling machine; (b4) Drive the movable part so that the fixed part and the movable part are completely closed (i.e., completely closed); (b5) Preheat the mold with steam to expel the air from inside the mold, then heat the mold with steam on one side and the other side, and then heat the mold on both sides with steam to perform in-mold foam molding; (b6) The in-mold foamed product is removed from the mold and dried (for example, at 75°C) to obtain a foamed molded body.

[0115] In (b2) above, the cracking (mm) formed is not particularly limited and may be, for example, greater than 0.0 mm and less than or equal to 20.0 mm, or between 1.0 mm and 10.0 mm, or between 1.0 mm and 5.0 mm.

[0116] In (b3) above, the following methods (b3-1) to (b3-4) can be listed as methods for filling the molding space with foamed particles: (b3-1) A method of filling a molded space with foamed particles (including the two-stage foamed particles described above, the same applies hereinafter) after pressurizing them with an inorganic gas in a container to impregnate the foamed particles with the inorganic gas and applying a predetermined internal pressure to the foamed particles; (b3-2) A method of filling a molding space with foamed particles and then compressing the mold to reduce the volume inside the mold by 10% to 75%; (b3-3) A method of compressing foamed particles with gas pressure and filling them into the molding space; (b3-4) A method for filling a molding space with foamed particles without any special pretreatment.

[0117] In the first method for producing a foamed molded article, the inorganic gas used in method (b3-1) above can be at least one 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.

[0118] In the first method for manufacturing a foamed molded article, the internal pressure of the foamed particles in method (b3-1) is preferably 0.10 MPa (absolute pressure) to 0.30 MPa (absolute pressure), and preferably 0.11 MPa (absolute pressure) to 0.25 MPa (absolute pressure).

[0119] In the first method for manufacturing a foamed molded article, the temperature inside the container when impregnating the foamed particles with inorganic gas in method (b3-1) is preferably 10°C to 90°C, and more preferably 40°C to 90°C.

[0120] In the method described in (b3-3) above, the recovery force of the foamed particles compressed by gas pressure is used in the subsequent step (b5) to fuse the foamed particles together.

[0121] Here, in (b5) above, the steam pressure during one-sided heating and reverse one-sided heating is defined as "steam pressure A," and the steam pressure during double-sided heating is defined as "steam pressure B."

[0122] The water vapor pressure A is not particularly limited, but is preferably 0.02 MPa (gauge pressure) to 0.22 MPa (gauge pressure), more preferably 0.04 MPa (gauge pressure) to 0.20 MPa (gauge pressure), even more preferably 0.06 MPa (gauge pressure) to 0.19 MPa (gauge pressure), and particularly preferably 0.08 MPa (gauge pressure) to 0.18 MPa (gauge pressure). This configuration has the advantage that a foamed molded article with a high internal bonding rate tends to be obtained. In particular, setting the water vapor pressure A to about half the water vapor pressure B used during in-mold foaming is preferable because it does not require excessive pressurization, is economically advantageous, and provides a foamed molded article with a high internal bonding rate.

[0123] In this specification, the water vapor pressure B in the first foam molding method is defined as "molding pressure". The first foam molding method, by using the first foam particles, can provide a foam molding with excellent internal fusion properties at a lower molding pressure than the conventional method. In other words, the first foam molding method can provide a foam molding with excellent internal fusion properties at a lower minimum molding pressure than the conventional method.

[0124] (Minimum molding pressure) In this specification, "minimum molding pressure" refers to the value measured by the following methods (1) to (3): (1) The water vapor pressure B is varied in increments of 0.01 MPa between 0.20 MPa (gauge pressure) and 0.30 MPa (gauge pressure), and foam particles are foamed and molded in a mold at each water vapor pressure B to obtain a foamed molded body; (2) The internal bonding rate is measured for each foamed molded body; (3) The lowest water vapor pressure B at which a foamed molded body with an internal bonding rate of 60% or more is obtained is set as the minimum molding pressure. The method for measuring the internal bonding rate is as described above.

[0125] The steam pressure B is preferably 0.16 MPa (gauge pressure) to 0.38 MPa (gauge pressure), more preferably 0.18 MPa (gauge pressure) to 0.34 MPa (gauge pressure), even more preferably 0.19 MPa (gauge pressure) to 0.32 MPa (gauge pressure), particularly preferably 0.20 MPa (gauge pressure) to 0.30 MPa (gauge pressure), and most preferably 0.20 MPa (gauge pressure) to less than 0.26 MPa (gauge pressure). In other words, the molding process preferably includes a step of heating the polypropylene resin foam particles on both sides using steam at a pressure of less than 0.26 MPa (gauge pressure). The lower the steam pressure B, the lower the economic burden. When the steam pressure B is 0.16 MPa (gauge pressure) or higher, there is an advantage that a foamed molded article with a high internal bonding rate and good compressive strength tends to be obtained.

[0126] In the first embodiment of the present invention, the lower the minimum molding pressure, the better. For example, it is preferable that the minimum molding pressure be less than 0.26 MPa, more preferably 0.25 MPa (gauge pressure) or less, even more preferably 0.24 MPa (gauge pressure) or less, and still preferable 0.23 MPa (gauge pressure) or less. When the minimum molding pressure is within the above range, it can be said that the foamed molded article is economically less burdensome. A foamed molded article with a low minimum molding pressure (for example, a foamed molded article with a minimum molding pressure of less than 0.26 MPa) can also be said to be a foamed molded article that has achieved low molding pressure.

[0127] Generally, the higher the water vapor pressure A and / or water vapor pressure B, the higher the internal bonding rate of the resulting foamed molded body tends to be. However, once the pressure exceeds a certain value, the internal bonding rate stops changing. The higher the water vapor pressure A and / or water vapor pressure B, the higher the cost of pressurizing the water vapor. In other words, the lower the water vapor pressure A and / or water vapor pressure B, the more economically advantageous it is. Therefore, when manufacturing a foamed molded body, it is preferable that the water vapor pressure A and / or water vapor pressure B be the lowest pressures within the range that yields the foamed molded body with the highest possible internal bonding rate, and that water vapor pressure B be the lowest molding pressure. This makes it possible to achieve both a high internal bonding rate and economic efficiency in the resulting foamed molded body. Furthermore, if the water vapor pressure A and / or water vapor pressure B are excessively high (for example, if the molding pressure is 0.26 MPa or higher), only the surface of the foamed molded body will fuse preferentially, and water vapor will not be able to pass into the interior of the foamed molded body. As a result, not only will the internal bonding rate decrease, but the deformation of the resulting foamed molded body after molding may also become significantly larger.

[0128] <Second Embodiment> The second embodiment relates to polypropylene resin foam particles and polypropylene resin foam molded articles.

[0129] When foamed molded products are used in components for automobiles and the like, black foamed molded products are preferred for parts that are visible to the human eye, and there is a growing demand for polypropylene resin foam particles that can provide black foamed molded products. For example, Patent Document 3 discloses a method for producing polypropylene resin foam particles, which involves blending a predetermined amount of carbon black with a primary particle size greater than 0 nm and 50 nm or less.

[0130] Furthermore, from the standpoint of molding costs, there is a growing demand for polypropylene resin foam particles that can provide foamed molded products with a small amount of water vapor usage. To meet this demand, for example, Patent Document 1 discloses polypropylene resin foam particles composed of polypropylene resin particles with a polypropylene resin mixture consisting of a polypropylene resin and a polypropylene wax as the base resin.

[0131] However, the technologies described in Patent Documents 3 and 1 were insufficient in terms of achieving a balance between surface aesthetics (e.g., blackness, color unevenness, intergranularity and wrinkles), fusion properties, and molding costs, and there was room for further improvement.

[0132] A second embodiment of the present invention has been made in view of the above-mentioned problems, and its object is to provide polypropylene resin foam particles that (a) can provide a polypropylene resin foam molded article having good fusion properties at a low molding pressure, and (b) can provide a polypropylene resin foam molded article having excellent surface beauty.

[0133] As a result of diligent research to solve the aforementioned problems, the present inventors have completed a second embodiment of the present invention.

[0134] That is, the polypropylene resin foam particles according to the second embodiment of the present invention include a base resin containing a polypropylene resin (A) having a melting point of 135°C to 150°C, a polypropylene homopolymer (B) having a melting point of 85°C or less, and carbon black, wherein when the total amount of the polypropylene resin (A) and the polypropylene homopolymer (B) is 100 parts by weight, the base resin contains (i) more than 80.0 parts by weight and 98.0 parts by weight or less of the polypropylene resin (A), (ii) 2.0 parts by weight or more and less than 20.0 parts by weight of the polypropylene homopolymer (B), and (iii) 2 parts by weight or more and less than 10 parts by weight of the carbon black.

[0135] According to a second embodiment of the present invention, the following effects can be achieved: (a) polypropylene resin foam particles that can provide a polypropylene resin foam molded article having good fusion properties at a low molding pressure, and (b) polypropylene resin foam particles that can provide a polypropylene resin foam molded article having excellent surface beauty.

[0136] [2-1. Technical idea according to the second embodiment of the present invention] As described above, the technologies described in Patent Documents 3 and 1 were insufficient in terms of achieving a balance between surface aesthetics, fusion properties, and molding costs, and there was room for further improvement.

[0137] For example, the technology described in Patent Document 3 does not evaluate the molding cost, such as whether it is possible to provide a foamed molded body with good (desired) fusion properties at a low molding pressure. Therefore, when the inventors molded the foamed particles obtained by the technology in Patent Document 3 at a lower molding pressure than conventional methods to obtain a foamed molded body, they found that there was room for improvement in the fusion properties of the obtained foamed molded body. Furthermore, the inventors evaluated the intergranular spacing of the foamed molded body obtained by the technology in Patent Document 3 using stricter evaluation criteria than those described in Patent Document 3. As a result, it was found that there was room for improvement in the intergranular spacing of the foamed molded body obtained by the technology in Patent Document 3 (see Comparative Example B1). In other words, it was found that the technology in Patent Document 3 has room for further improvement in all aspects, including surface aesthetics (e.g., blackness, color unevenness, intergranular spacing and wrinkles), fusion properties, and molding cost.

[0138] Furthermore, the technology described in Patent Document 1 does not evaluate the molding cost, for example, whether it is possible to provide a foamed molded body with good (desired) fusion properties at a low molding pressure. When the inventors molded the foamed particles obtained by the technology in Patent Document 1 at a lower molding pressure than conventional methods to obtain a foamed molded body, they found that there was room for improvement in the fusion properties of the obtained foamed molded body. In addition, the inventors manufactured a foamed molded body by blending the foamed particles obtained by the technology in Patent Document 1 with carbon black with a small particle size as described in Patent Document 3, and examined the surface beauty of the obtained foamed molded body. As a result, it was found that there was room for improvement in the color unevenness of the obtained foamed molded body (see Comparative Example B2). In other words, it was found that the technology in Patent Document 1 has room for further improvement in terms of surface beauty, fusion properties, and molding cost.

[0139] In view of the above-mentioned problems, the inventors diligently conducted research with the aim of providing polypropylene resin foam particles that (a) can provide a polypropylene resin foam molded article having good fusion properties at a low molding pressure, and (b) can provide a polypropylene resin foam molded article having excellent surface beauty (e.g., blackness, color unevenness, intergranularity and wrinkles). As a result, the inventors independently obtained the following findings and completed a second embodiment of the present invention: By blending a polypropylene resin having a relatively high melting point, a polypropylene homopolymer having a relatively low melting point, and carbon black in specific amounts, it is possible to provide polypropylene resin foam particles that (a) can provide a polypropylene resin foam molded article having good fusion properties at a low molding pressure, and (b) can provide a polypropylene resin foam molded article having excellent surface beauty (e.g., blackness, color unevenness, intergranularity and wrinkles).

[0140] [2-2. Polypropylene-based foamed resin particles] The polypropylene resin foam particles according to the second embodiment of the present invention include a base resin containing a polypropylene resin (A) having a melting point of 135°C to 150°C, a polypropylene homopolymer (B) having a melting point of 85°C or less, and carbon black. The base resin contains, when the total amount of the polypropylene resin (A) and the polypropylene homopolymer (B) is 100 parts by weight, (i) more than 80.0 parts by weight and 98.0 parts by weight or less of the polypropylene resin (A), (ii) 2.0 parts by weight or more and less than 20.0 parts by weight of the polypropylene homopolymer (B), and (iii) 2 parts by weight or more and less than 10 parts by weight of the carbon black. In other words, the second embodiment of the present invention differs from the first embodiment in that it is essential to include carbon black.

[0141] Polypropylene-based resin foam particles according to the second embodiment of the present invention can be molded by known methods to provide a polypropylene-based resin foam molded article.

[0142] In this specification, "polypropylene resin foam particles according to the second embodiment of the present invention" may be referred to as "second foam particles."

[0143] The second foam particles, having the above-described structure, have the advantages of (a) being able to provide a polypropylene-based resin foam molded article with good fusion properties at a low molding pressure (in other words, a low heating vapor pressure), and (b) being able to provide a polypropylene-based resin foam molded article with excellent surface beauty. In the second embodiment of this specification, "polypropylene-based resin foam molded article with excellent surface beauty" means a polypropylene-based resin foam molded article that has at least (i) a high degree of blackness, (ii) a uniform color (black) with no color unevenness, or a substantially uniform color (black) with very little color unevenness, (iii) no or very few gaps between particles, and (iv) no or very few wrinkles.

[0144] (Carbon Black) In a second embodiment of the present invention, the base resin includes carbon black. The composition of the carbon black is not particularly limited, and known carbon blacks can be used. The primary particle size of the carbon black is not particularly limited, but is preferably greater than 0 nm and 100 nm or less, and more preferably between 20 nm and 100 nm. When the primary particle size of the carbon black is 100 nm or less, there is an advantage that the resulting polypropylene resin molded foam has excellent blackness. Examples of such carbon blacks include channel black, roller black, disc, gas furnace black, oil furnace black, thermal black, acetylene black, etc., and one or more of these can be used.

[0145] In this specification, the "primary particle size of carbon black" shall be the value obtained by the following measurement method: (1) Polypropylene resin foam particles are cut in half using a microtome; (2) The obtained cross section is imaged at 40,000 times magnification using a transmission electron microscope to obtain a cross-sectional photograph; (3) Fifty carbon black particles are arbitrarily selected from the obtained cross-sectional photograph, and the particle diameter (Ferret diameter) in the X and Y directions is measured for each primary particle of carbon black; (4) For each primary particle of carbon black, the arithmetic mean value of the particle diameter in the X direction and the particle diameter in the Y direction is calculated, and the obtained value is defined as the primary particle size of carbon black.

[0146] In a second embodiment of the present invention, when the total amount of polypropylene resin (A) and polypropylene homopolymer (B) of the base resin is 100 parts by weight, the base resin contains 2 parts by weight or more and less than 10 parts by weight of carbon black, preferably 2 to 8 parts by weight, and more preferably 2 to 6 parts by weight. When the total amount of polypropylene resin (A) and polypropylene homopolymer (B) of the base resin is 100 parts by weight, if the carbon black contains (a) 2 parts by weight or more, the blackness of the foamed molded article provided by the foamed particles tends to be higher, and if it contains less than 10 parts by weight, the spacing between particles in the foamed molded article provided by the foamed particles tends to be reduced or eliminated.

[0147] In a second embodiment of the present invention, the base resin may optionally further contain a colorant other than carbon black. Examples of colorants other than carbon black include ultramarine, cyanine pigments, azo pigments, quinacridone pigments, cadmium yellow, chromium oxide, iron oxide, perylene pigments, anthraquinone pigments, and the like. In a second embodiment of the present invention, one of these colorants other than carbon black may be used alone, or two or more may be used in mixture. Furthermore, in a second embodiment of the present invention, when two or more colorants other than carbon black are used in mixture, the mixing ratio may be appropriately adjusted depending on the purpose.

[0148] For aspects of the polypropylene resin foam particles of the second embodiment other than those described above, the description of the first embodiment shall be appropriately applied.

[0149] [2-3. Polypropylene-based resin foam molded product] The polypropylene resin foam molded article according to the second embodiment of the present invention is a foam molded article obtained by molding polypropylene resin foam particles as described in section [2-2. Polypropylene Resin Foam Particles]. It can also be said that the polypropylene resin foam molded article according to the second embodiment of the present invention includes the polypropylene resin foam particles as described in section [2-2. Polypropylene Resin Foam Particles].

[0150] In this specification, the "polypropylene-based resin foamed molded article according to the second embodiment of the present invention" may be referred to as the "second foamed molded article."

[0151] The second foamed molded body, having the above-described structure, has good fusion properties and excellent surface aesthetics, specifically having the advantages of (i) high blackness, (ii) uniform color (black) with no color unevenness, or nearly uniform color (black) with very little color unevenness, (iii) no or very few gaps between particles, and (iv) no or very few wrinkles.

[0152] (Internal fusion properties) The internal bonding rate in the second embodiment is the same as that described in the section on (internal bonding properties) in the first embodiment; therefore, we will refer to that description and omit the explanation here.

[0153] (Surface beauty) In this specification, the surface aesthetics of the second foamed molded article are evaluated by the degree of blackness, color unevenness, intergranularity, and wrinkles of the foamed molded article. In this specification, "intergranularity of the foamed molded article" refers to the gaps between foam particles on the surface of the foamed molded article. The smaller the size of the intergranularity between foam particles on the surface of the foamed molded article, and the fewer the number of intergranularity between foam particles, the better the surface aesthetics of the foamed molded article. The evaluation methods for blackness, color unevenness, and wrinkles of the foamed molded article are described in detail in [Example B] below.

[0154] <Method for manufacturing foamed molded products> The details of the method for manufacturing a foamed molded article in the second embodiment of the present invention are the same as those described in the section on "Method for Manufacturing a Foamed Molded Article" in the first embodiment; therefore, the same description will be used here, and the explanation will be omitted.

[0155] One embodiment of the present invention may have the following configuration:

[0156] [X1] Polypropylene resin foam particles comprising a base resin containing a polypropylene resin (A) having a melting point of 135°C to 150°C and a polypropylene homopolymer (B) having a melting point of 85°C or less, wherein the base resin contains, when the total amount of the polypropylene resin (A) and the polypropylene homopolymer (B) is 100 parts by weight, more than 80.0 parts by weight and 98.0 parts by weight or less of the polypropylene resin (A), and 2.0 parts by weight or more and less than 20.0 parts by weight of the polypropylene homopolymer (B).

[0157] [X2] Polypropylene resin foam particles according to [X1], wherein the base resin contains carbon black.

[0158] [X3] When the total amount of the polypropylene resin (A) and the polypropylene homopolymer (B) is 100 parts by weight, the polypropylene resin foam particles according to [X2] contain 2 parts by weight or more and less than 10 parts by weight of the carbon black.

[0159] [X4] Polypropylene resin foam particles according to any one of [X1] to [X3], wherein the weight-average molecular weight of the polypropylene homopolymer (B) is 40,000 to 140,000.

[0160] [X5] Polypropylene resin foam particles according to any one of [X1] to [X4], wherein the mesopentade fraction (mmmm) of the polypropylene homopolymer (B) is 25 mol% to 65 mol%.

[0161] [X6] Polypropylene resin foam particles according to any one of [X2] to [X5], wherein the primary particle size of the carbon black is 100 nm or less.

[0162] [X7] The polypropylene resin foam particle according to any one of [X1] to [X6], wherein the polypropylene resin (A) is at least one of a propylene / ethylene random copolymer and a propylene / ethylene / 1-butene random copolymer, and the ethylene content in the copolymer is 0.2% to 10.0% by weight per 100% by weight of each copolymer.

[0163] [X8] Polypropylene resin foam particles according to any one of [X1] to [X7], wherein the MFR of the polypropylene resin (A) at 230°C is 3 g / 10 min to 30 g / 10 min.

[0164] [X9] Polypropylene resin foam particles according to any one of [X1] to [X8], wherein the DSC ratio ((heat of fusion on the high temperature side / total heat of fusion) × 100) of the polypropylene resin foam particles is 10.0% to 50.0%.

[0165] [X10] Polypropylene resin foam particles according to any one of [X1] to [X9], wherein the average bubble diameter of the polypropylene resin foam particles is 110 μm to 280 μm.

[0166] [X11] Polypropylene resin foam particles according to any one of [X1] to [X10], wherein the foaming ratio of the polypropylene resin foam particles is 15 to 50 times.

[0167] [X12] Polypropylene homopolymer (B) has a melting point of 40°C or higher, and is a polypropylene resin foam particle according to any one of [X1] to [X11].

[0168] [X13] Polypropylene resin foam particles as described in any one of [X1] to [X12], wherein the lowest water vapor pressure (minimum molding pressure) at which a foamed molded article with an internal bonding rate of 60% or more can be obtained is less than 0.26 MPa (gauge pressure).

[0169] A polypropylene resin foam molded article obtained by molding polypropylene resin foam particles described in any one of [X14], [X1], to [X13].

[0170] [X15] 1.5 mm on the surface of the polypropylene resin foam molded body 2 A polypropylene resin foam molded article as described in [X14], in which there are no intergranular spaces larger than [X14].

[0171] [X16] The polypropylene resin foam molded article according to [X14] or [X15], wherein the polypropylene resin foam molded article satisfies the following formula (1).

[0172] (Compressive strength of the polypropylene-based foam molded article at 50% strain (MPa)) ≥ 0.0069 × (Density of the polypropylene-based foam molded article (g / L)) + 0.018... Equation (1).

[0173] [X17] A method for producing polypropylene resin foam particles, comprising: a dispersion step of dispersing polypropylene resin particles, an aqueous dispersion medium, and a foaming agent in a container; and a release step of opening one end of the container and releasing the dispersion liquid obtained in the dispersion step into a region with a pressure lower than the pressure inside the container, wherein the polypropylene resin particles include a base resin containing a polypropylene resin (A) having a melting point of 135°C to 150°C and a polypropylene homopolymer (B) having a melting point of 85°C or less, and the base resin contains, when the total amount of the polypropylene resin (A) and the polypropylene homopolymer (B) is 100 parts by weight, more than 80.0 parts by weight and 98.0 parts by weight or less, and 2.0 parts by weight or more and less than 20.0 parts by weight of the polypropylene homopolymer (B).

[0174] [X18] A method for producing polypropylene resin foam particles according to [X17], wherein the foaming agent comprises at least one of carbon dioxide and water.

[0175] [X19] A method for producing polypropylene resin foamed particles according to [X17] or [X18], wherein the amount of foaming agent used is 2.0 parts by weight to 60.0 parts by weight per 100 parts by weight of resin particles.

[0176] [X20] Further includes a heating-pressure step of raising the temperature inside the container to the foaming temperature and raising the pressure inside the container to the foaming pressure, The foaming temperature is such that the melting point of the mixture of polypropylene resin (A) and polypropylene homopolymer (B) is -20°C to +10°C, or the melting point of polypropylene resin particles is -20°C to +10°C. A method for producing polypropylene resin foam particles according to any one of [X17] to [X19], wherein the foaming pressure is 1.0 MPa (gauge pressure) to 5.0 MPa (gauge pressure).

[0177] [X21] A method for producing polypropylene resin foam particles according to any one of [X17] to [X20], wherein the base resin contains carbon black.

[0178] [X22] A method for producing polypropylene resin foam particles according to [X21], wherein the total amount of the polypropylene resin (A) and the polypropylene homopolymer (B) is 100 parts by weight, and the carbon black is contained in an amount of 2 parts by weight or more but less than 10 parts by weight.

[0179] [X23] A method for producing polypropylene resin foam particles according to any one of [X17] to [X22], wherein the weight-average molecular weight of the polypropylene homopolymer (B) is 40,000 to 140,000.

[0180] [X24] A method for producing polypropylene resin foam particles according to any one of [X17] to [X23], wherein the mesopentade fraction (mmmm) of the polypropylene homopolymer (B) is 25 mol% to 65 mol%.

[0181] [X25] A method for producing polypropylene resin foam particles according to any one of [X21] to [X24], wherein the primary particle size of the carbon black is 100 nm or less.

[0182] [X26] A method for producing foamed polypropylene resin particles according to any one of [X17] to [X25], wherein the polypropylene resin (A) is at least one of a propylene / ethylene random copolymer and a propylene / ethylene / 1-butene random copolymer, and the ethylene content in the copolymer is 0.2% to 10.0% by weight per 100% by weight of each copolymer.

[0183] [X27] A method for producing polypropylene resin foam particles according to any one of [X17] to [X26], wherein the MFR of the polypropylene resin (A) at 230°C is 3 g / 10 min to 30 g / 10 min.

[0184] [X28] A method for producing polypropylene resin foam particles according to any one of [X17] to [X27], wherein the DSC ratio ((heat of fusion on the high temperature side / total heat of fusion) × 100) of the polypropylene resin foam particles is 10.0% to 50.0%.

[0185] [X29] A method for producing polypropylene resin foam particles according to any one of [X17] to [X28], wherein the average bubble diameter of the polypropylene resin foam particles is 110 μm to 280 μm.

[0186] [X30] A method for producing polypropylene resin foam particles according to any one of [X17] to [X29], wherein the foaming ratio of the polypropylene resin foam particles is 15 to 50 times.

[0187] A method for producing polypropylene resin foam particles according to any one of [X17] to [X30], wherein the melting point of the polypropylene homopolymer (B) is 40°C or higher.

[0188] [X32] A method for producing polypropylene resin foam particles according to any one of [X17] to [X31], wherein the lowest water vapor pressure (minimum molding pressure) at which a foamed molded article with an internal bonding rate of 60% or more can be obtained is less than 0.26 MPa (gauge pressure).

[0189] A method for manufacturing a polypropylene resin foamed molded article, comprising a molding step of molding polypropylene resin foamed particles obtained by a method for manufacturing polypropylene resin foamed particles described in any one of [X33], [X17], to [X32].

[0190] [X34] 1.5 mm on the surface of the polypropylene resin foam molded body 2 A method for manufacturing a polypropylene resin foam molded article as described in [X33], wherein there are no gaps between particles larger than [X33].

[0191] [X35] A method for manufacturing a polypropylene-based resin foam molded article according to [X33] or [X34], wherein the polypropylene-based resin foam molded article satisfies the following formula (1).

[0192] (Compressive strength of the polypropylene-based foam molded article at 50% strain (MPa)) ≥ 0.0069 × (Density of the polypropylene-based foam molded article (g / L)) + 0.018... Equation (1).

[0193] [X36] A method for manufacturing a polypropylene resin foam molded article according to any one of [X33] to [X35], wherein the molding step comprises a step of heating the polypropylene resin foam particles on both sides at a pressure of less than 0.26 MPa (gauge pressure) using steam.

[0194] One embodiment of the present invention may have the following configuration:

[0195] [Y1] Polypropylene resin foam particles comprising a base resin containing a polypropylene resin (A) having a melting point of 135°C to 150°C and a polypropylene homopolymer (B) having a melting point of 85°C or less, wherein the base resin contains, when the total amount of the polypropylene resin (A) and the polypropylene homopolymer (B) is 100 parts by weight, more than 80.0 parts by weight and 98.0 parts by weight or less of the polypropylene resin (A), and 2.0 parts by weight or more and less than 20.0 parts by weight of the polypropylene homopolymer (B).

[0196] [Y2] The polypropylene resin foam particles according to [Y1], wherein the weight-average molecular weight of the polypropylene homopolymer (B) is 40,000 to 140,000.

[0197] [Y3] Polypropylene resin foam particles according to [Y1] or [Y2], wherein the mesopentade fraction (mmmm) of the polypropylene homopolymer (B) is 25 mol% to 65 mol%.

[0198] A polypropylene resin foam molded article obtained by molding polypropylene resin foam particles described in any one of [Y4], [Y1], to [Y3].

[0199] One embodiment of the present invention may have the following configuration:

[0200] [Z1] Polypropylene resin foam particles comprising a base resin containing a polypropylene resin (A) having a melting point of 135°C to 150°C, a polypropylene homopolymer (B) having a melting point of 85°C or less, and carbon black, wherein the base resin contains, when the total amount of the polypropylene resin (A) and the polypropylene homopolymer (B) is 100 parts by weight, (i) more than 80.0 parts by weight and 98.0 parts by weight or less of the polypropylene resin (A), (ii) 2.0 parts by weight or more and less than 20.0 parts by weight of the polypropylene homopolymer (B), and (iii) 2 parts by weight or more and less than 10 parts by weight of the carbon black.

[0201] [Z2] The polypropylene resin foam particles according to [Z1], wherein the weight-average molecular weight of the polypropylene homopolymer (B) is 40,000 to 140,000.

[0202] [Z3] Polypropylene resin foam particles according to [Z1] or [Z2], wherein the mesopentade fraction (mmmm) of the polypropylene homopolymer (B) is 25 mol% to 65 mol%.

[0203] [Z4] Polypropylene resin foam particles according to any one of [Z1] to [Z3], wherein the primary particle size of the carbon black is 100 nm or less.

[0204] A polypropylene resin foam molded article obtained by molding polypropylene resin foam particles described in any one of [Z5], [Z1], to [Z4]. [Examples]

[0205] [Example A] The first embodiment of the present invention will be specifically described below with reference to Example A, but the technical scope of the present invention is not limited by these Examples A.

[0206] 〔material〕 The substances (materials) used in Example A and Comparative Example A are shown below. <Polypropylene resin> (Polypropylene resin (A)) Polypropylene resin A-1: ​​Propylene / ethylene random copolymer (MFR 8g / 10 min, weight-average molecular weight 280,000, melting point 143°C, ethylene content 2.7% by weight) (Polypropylene polymer (B)) Polypropylene resin B-1: Propylene homopolymer (weight-average molecular weight 130,000, melting point 75°C, glass transition temperature -11°C, mesopentad fraction 45 mol%) [Manufactured by Idemitsu Kosan Co., Ltd., L-MODU S901] Polypropylene resin B-2: Propylene homopolymer (weight-average molecular weight 75,000, melting point 75°C, glass transition temperature -11°C, mesopentad fraction 45 mol%) [Manufactured by Idemitsu Kosan Co., Ltd., L-MODU S600] Polypropylene resin B-3: Propylene homopolymer (weight-average molecular weight 45,000, melting point 75°C, glass transition temperature -11°C, mesopentad fraction 45 mol%) [Manufactured by Idemitsu Kosan Co., Ltd., L-MODU S400] <Other resins> Polypropylene resin (C): Propylene / ethylene / 1-butene random copolymer (MFR 7g / 10 min, melting point 134℃) Wax: Propylene / ethylene random copolymer (weight-average molecular weight 6400, melting point 78°C, glass transition temperature -27°C) <Additives> Absorbent substance: Glycerin [Manufactured by Lion Corporation, refined glycerin D] Foaming nucleating agent: Talc [Hayashi Chemical Co., Ltd., Talc Powder PK-S].

[0207] [Measurement method] The evaluation methods used in Example A and Comparative Example A are described below.

[0208] (Melting point) The melting points of polypropylene resins (polypropylene resin (A), polypropylene homopolymer (B), polypropylene resin (C)), wax, and polypropylene resin particles were determined by DSC method using a differential scanning calorimeter (Seiko Instruments Inc., DSC6200 model). The specific operating procedure was as follows (1) to (3): (1) The sample (polypropylene resin, wax, or polypropylene resin particles) was melted by raising the temperature of 5 mg to 6 mg from 40 °C to 220 °C at a heating rate of 10 °C / min; (2) The molten sample was then crystallized by lowering the temperature from 220 °C to 40 °C at a cooling rate of 10 °C / min; (3) The crystallized sample was then further heated from 40 °C to 220 °C at a heating rate of 10 °C / min. The melting point of the sample was defined as the temperature of the peak (melting peak) in the DSC curve of the sample obtained during the second heating (i.e., when (3) is true). If, by the method described above, multiple peaks (melting peaks) were present in the DSC curve of the sample obtained during the second heating, the temperature of the peak with the largest heat of fusion was defined as the melting point of the sample.

[0209] (MFR) The MFR of polypropylene resins (polypropylene resin (A) and polypropylene resin (C)) was determined using an MFR measuring instrument described in JIS K7210:1999, under the following conditions: orifice diameter of 2.0959 ± 0.005 mmφ, orifice length of 8.000 ± 0.025 mm, load of 2.16 kgf, and temperature of 230 °C (230 ± 0.2 °C).

[0210] (Mesopentade fraction (mmmm) of polypropylene homopolymer (B)) The method for measuring the mesopentade fraction of polypropylene homopolymer (B) was as follows: (1) Polypropylene homopolymer (B) was dissolved in o-dichlorobenzene as a sample, and measured using a JEOL JNM-GX270 instrument at a resonance frequency of 67.93 MHz. 13(1) 13C-NMR was measured; (2) For the spectrum derived from the methyl group, each peak was assigned to a 21.855 ppm mmmm peak, and the peak area was determined; (3) The ratio of mmmm peaks to the total peak area derived from the methyl group was expressed as a percentage and expressed as the mesopentade fraction (mol%). The detailed measurement conditions were as follows. Solvent used for measurement: o-dichlorobenzene (90% by weight) / benzene-D6 (10% by weight) Sample concentration: 15% to 20% by weight Measurement temperature: 120℃~130℃ Resonance frequency: 67.93MHz Pulse width: 10 μsec (45° pulse) Pulse repetition time: 7.091 sec Data points: 32K Total count: 8168 Measurement mode: Noise decoupling The assignment of the obtained spectra and the calculation of the pentad fraction (mmmm) were performed based on the method used by T. Hayashi et al. [Polymer, 29, 138-143 (1988)].

[0211] (DSC ratio of foamed particles) For the measurement (calculation) of the DSC ratio of the foamed particles, a differential scanning calorimeter (Seiko Instruments DSC6200 model) was used. The method for measuring (calculating) the DSC ratio of the foamed particles using a differential scanning calorimeter was as follows (1) to (6): (1) 5 mg to 6 mg of foamed particles were weighed out; (2) The temperature of the foamed particles was increased from 40°C to 220°C at a heating rate of 10°C / min to melt the foamed particles; (3) In the DSC curve of the foamed particles obtained in the process of (2), a baseline was created by drawing a straight line connecting the point representing the temperature before the start of melting and the point representing the temperature after the end of melting; (4) The melting peak on the high temperature side or the hottest melting peak and adjacent to each other A straight line passing through the maximum point between the melting peak was drawn perpendicular to the X-axis; (5) The amount of heat calculated from the high-temperature region enclosed by the baseline, the straight line passing through the maximum point, and the DSC curve was defined as the high-temperature side heat of fusion, the amount of heat calculated from the low-temperature region enclosed by the baseline, the straight line passing through the maximum point, and the DSC curve was defined as the low-temperature side heat of fusion, and the amount of heat calculated from the region enclosed by the baseline and the DSC curve was defined as the total heat of fusion (= high-temperature side heat of fusion + low-temperature side heat of fusion); (6) The DSC ratio was calculated from the following formula: DSC ratio (%) = (heat of fusion on the high-temperature side / total heat of fusion) × 100.

[0212] (Average bubble diameter of foaming particles) The method for measuring the average bubble diameter of foam particles was as follows (1) to (5): (1) Using a razor (Feather High Stainless Double-Edged), the foam particle was cut so as to pass through its center; (2) The resulting cut surface of the foam particle was observed at 50x magnification using an optical microscope (Keyence VHX-100); (3) A straight line was drawn through the center or approximate center of the cut surface of the foam particle in the image obtained from the observation; (4) (4-1) The number of bubbles n present on the straight line was measured; (4-2) The length of the line segment cut off from the straight line at the intersection of the straight line and the surface of the foam particle was measured and defined as the foam particle diameter L; (5) The average bubble diameter of the foam particle was calculated using the following formula: Average bubble diameter (μm) = L / n.

[0213] (Foaming ratio of foaming particles) The method for measuring the expansion ratio of the foaming particles was as follows (1) to (4): (1) The weight w (g) of the foaming particles was measured; (2) Next, the foaming particles used for weight measurement were submerged in ethanol contained in a graduated cylinder, and the volume v (cm³) of the foaming particles was determined based on the rise in the liquid level of the graduated cylinder. 3 (3) measured the weight w (g) and the volume v (cm³). 3 (4) The density ρ1 of the foamed particles was calculated by dividing the density ρ2 of the polypropylene resin particles used in the production of the foamed particles by the density ρ1 of the foamed particles (ρ2 / ρ1) and multiplying the resulting value by 100. The resulting value was taken as the foaming ratio of the foamed particles.

[0214] (Measurement of internal bonding rate and minimum molding pressure of foamed molded products) The internal bonding rate was measured as follows (1) to (4): (1) A 5 mm cut was made perpendicular to any one surface of the foamed molded body using a cutter; (2) The foamed molded body was then broken by hand along the cut; (3) The area of ​​the resulting fracture surface excluding the cut portion was visually observed, and the number of all foamed particles present in that area, and the number of foamed particles that fractured outside the particle interface in that area (i.e., foamed particles that fractured themselves) were counted; (4) The internal bonding rate was calculated based on the following formula; Internal bonding rate (%) = (Number of foamed particles fractured outside the particle interface in the region / Total number of foamed particles present in the region) × 100.

[0215] The minimum molding pressure during in-mold foam molding was measured as follows (1) to (3): (1) The water vapor pressure was varied in increments of 0.01 MPa between 0.20 MPa (gauge pressure) and 0.30 MPa (gauge pressure), and foam particles were foam-molded in the mold at each water vapor pressure to obtain a foamed molded body; (2) The internal bonding rate was measured for each foamed molded body; (3) The lowest water vapor pressure at which a foamed molded body with an internal bonding rate of 60% or more was obtained was defined as the minimum molding pressure.

[0216] Based on the obtained minimum molding pressure, it was determined whether a foamed molded body with an internal bonding rate of 60% or more could be provided at a low molding pressure, i.e., whether a reduction in molding pressure had been achieved. ○ (Sufficient reduction in molding pressure has been achieved): Minimum molding pressure is less than 0.26 MPa (gauge pressure). × (Insufficient reduction of molding pressure (not achieved)): Minimum molding pressure is 0.26 MPa (gauge pressure) or higher.

[0217] (Density of foamed molded material) The methods for measuring and evaluating the density of the foamed molded body were as follows (1) to (3): (1) The length, width, and thickness of the foamed molded body (foamed molded body (A)) obtained in the [production of foamed molded body (A)] step described later were measured with calipers, and the volume V (cm³) of the foamed molded body was measured. 3 (1) The following was calculated; (2) The weight W (g) of the foamed molded body was then measured; (3) The density of the foamed molded body was calculated based on the following formula: Density of foamed molded material (g / cm³) 3 ) = Weight of foamed molded body W (g) / Volume of foamed molded body V (cm³) 3 ).

[0218] (Compressive strength of foamed molded material) The methods for measuring and evaluating the compressive strength of the foamed molded body were as follows (1) to (3): (1) A test piece measuring 50 mm in length, 50 mm in width, and 25 mm in thickness was cut from approximately the center of the foamed molded body (foamed molded body (A)) obtained in the [production of foamed molded body (A)] process described later; (2) The compressive stress (MPa) at 50% compression was measured on the test piece at a speed of 10 mm / min using a tensile-compression testing machine [Minebea, TG series] in accordance with NDZ-Z0504; (3) Based on the measurement results of the compressive strength at 50% strain (MPa), the compressive strength of the foamed molded body was evaluated according to the following criteria: ◎(Good): The following equation (1) is satisfied. ○ (Pass): Equation (1) below is not satisfied, and equation (2) below is satisfied. × (Poor): The following equations (1) and (2) are not satisfied. (Compressive strength of the foamed molded material at 50% strain (MPa)) ≥ 0.0069 × (Density of the foamed molded material (g / L)) + 0.018 ... Equation (1) (Compressive strength of the foamed molded material at 50% strain (MPa)) ≥ 0.0069 × (Density of the foamed molded material (g / L)) ... Equation (2) Here, the method for measuring the density of the foamed molded product is as described in the (Density of Foamed Molded Product) section above.

[0219] (Surface aesthetics of foamed molded products) In Example A, the method for evaluating the surface beauty of the foamed molded body was as follows: The surface of the foamed molded body (foamed molded body (B)) obtained in the [production of foamed molded body (B)] process described later was visually observed and evaluated on a 5-point scale from 1 to 5 based on the following criteria. 5: On the surface of the foamed molded body, 1.0 mm 2 There are no gaps between particles larger than this. 4: On the surface of the foamed molded body, 1.0 mm 2 There are gaps between particles larger than 1.5 mm. 2 There are no gaps between particles larger than this. 3: On the surface of the foamed molded body, 1.5 mm 2 There are gaps between particles larger than 2.0 mm. 2 There are no gaps between particles larger than this. 2: On the surface of the foamed molded body, 2.0 mm 2 There are gaps between particles that are larger than [a certain size]. 1: The foamed particles hardly expand, and the gaps between the particles are not filled at all. Furthermore, a higher rating indicates superior surface aesthetics.

[0220] (Deformation of foamed molded material) The method for evaluating whether or not the foamed molded body was deformed was as follows: The foamed molded body (foamed molded body (B)) obtained in the [production of foamed molded body (B)] process described later was visually observed and evaluated according to the following criteria. ○ (Good): There is almost no deformation of the foamed molded product, and there are no wrinkles on the surface of the foamed molded product. △ (Pass): The foamed molded body is slightly deformed, and there are small wrinkles on the surface of the foamed molded body. × (Fail): The foamed molded body is significantly deformed, and there are many wrinkles on the surface of the foamed molded body.

[0221] (Example A1) [Production of resin particles] A blend was prepared by combining 97.5 parts by weight of polypropylene resin A-1 as polypropylene resin (A), 2.5 parts by weight of polypropylene resin B-1 as propylene homopolymer (B), and 0.1 parts by weight of talc and 0.2 parts by weight of glycerin as additives.

[0222] Next, the blend was melt-kneaded in an extruder (resin temperature 225°C) to obtain a resin composition. The resin composition was extruded in strand form from the tip of the extruder and then granulated by cutting to produce resin particles (1.2 mg / particle). A twin-screw extruder [Toshiba Machine Co., Ltd., TEM26-SX] with two 26 mm diameter shafts (screws) was used as the extruder.

[0223] [Production of foamed particles] In a 10L pressure vessel, 100 parts by weight of the obtained resin particles, 200 parts by weight of water as an aqueous dispersion medium, 0.3 parts by weight of kaolin as a dispersant, 0.06 parts by weight of sodium dodecylbenzenesulfonate (DBS) as a dispersion aid, and 5.6 parts by weight of carbon dioxide as a blowing agent were charged to prepare a dispersion containing the blowing agent (dispersion step). While stirring the dispersion, the foaming temperature (temperature inside the pressure vessel) was set to 151°C and the foaming pressure (pressure inside the vessel) was set to 2.8 MPa (heating-pressure step). After the temperature and pressure inside the pressure vessel reached the predetermined foaming temperature and pressure, the temperature and pressure inside the pressure vessel were maintained at the predetermined foaming temperature and pressure for a further 30 minutes (holding step). Thereafter, while maintaining the foaming pressure inside the pressure vessel at the predetermined foaming pressure by supplying carbon dioxide, the dispersion was released to atmospheric pressure at 95°C through a 3.2 mmφ orifice provided at the bottom of the pressure vessel to obtain foamed polypropylene resin particles (release step). Subsequently, the polypropylene resin foam particles were dried at 75°C for 24 hours. The DSC ratio, average bubble diameter, and foaming ratio of the obtained foam particles were measured. The results are shown in Table 1.

[0224] The resulting foamed particles showed two peaks in the DSC curve obtained by DSC measurement.

[0225] Furthermore, using the foamed particles obtained in the [Preparation of Foamed Particles] step, the internal fusion rate and minimum molding pressure were measured as described in the section (Measurement of Internal Fusion Rate and Minimum Molding Pressure of Foamed Molded Body). The results are shown in Table 1.

[0226] [Preparation of foamed molded body (A)] A foamed molded body was produced by the following methods (1) to (6) in order: (1) The foamed particles obtained in the [production of foamed particles] step were placed in a pressure vessel, and air was injected into the pressure vessel to increase the pressure inside the vessel, thereby impregnating the foamed particles with pressurized air and making the internal pressure of the foamed particles 0.20 MPa (absolute pressure); (2) The foamed particles with internal pressure were filled into a mold installed in a molding machine. Here, a polyolefin foam molding machine [Daisen Kogyo Co., Ltd., EP-900] was used as the molding machine, and a mold capable of forming a molding space of 370 mm in length x 320 mm in width x 50 mm in thickness was used, with a cracking of 5 mm; (3) After filling with foam particles, with the drain valve of the molding machine's drain line open, the foam particles were heated for 10 seconds with steam at 0.1 MPa (gauge pressure) (steam pressure A) (one-sided heating and reverse one-sided heating) to expel the air from inside the mold; (4) Then, with the drain valve of the molding machine's drain line closed, the foam particles were heated for another 10 seconds with steam at the minimum molding pressure (steam pressure B) obtained by the method described above (double-sided heating); (5) This heating fused the foam particles together to obtain a foam molded body (A); (6) The obtained foam molded body (A) was removed from the mold, left at room temperature for 2 hours, and then cured and dried at 75°C for 16 hours. The density and compressive strength of the obtained foam molded body (A) were measured. The results are shown in Table 1.

[0227] [Preparation of foamed molded body (B)] A foamed molded body was produced by the following methods (1) to (6) in order: (1) The foamed particles obtained in the [production of foamed particles] step were placed in a pressure vessel, and pressurized air was injected into the pressure vessel to increase the pressure inside the vessel, thereby impregnating the foamed particles with pressurized air and setting the internal pressure of the foamed particles to 0.20 MPa (absolute pressure); (2) The foamed particles with internal pressure were filled into a mold installed in a molding machine without compression in the thickness direction. Here, a polyolefin foam molding machine [Daisen Kogyo Co., Ltd., EP-900] was used as the molding machine, and a mold capable of forming a molding space of 370 mm in length x 320 mm in width x 20 mm in thickness was used, with cracking set to 0 mm; (3) After filling with foam particles, with the drain valve of the molding machine's drain line open, the foam particles were heated for 10 seconds with steam at 0.1 MPa (gauge pressure) (steam pressure A) (one-sided heating and reverse one-sided heating) to expel the air from inside the mold; (4) Then, with the drain valve of the molding machine's drain line closed, the foam particles were heated for another 10 seconds with steam at 0.27 MPa (gauge pressure) (steam pressure B) (double-sided heating); (5) This heating fused the foam particles together to obtain a foam molded body (B); (6) The obtained foam molded body (B) was removed from the mold, left at room temperature for 2 hours, and then cured and dried at 75°C for 16 hours. The surface beauty and deformation of the obtained foam molded body (B) were evaluated. The results are shown in Table 1.

[0228] (Example A2) Foamed particles and foamed molded articles were prepared using the same method as in Example A1, except that 95.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), 5.0 parts by weight of polypropylene resin B-1 was used as the propylene homopolymer (B), the amount of foaming agent used was 5.4 parts by weight, and the foaming pressure was 2.7 MPa. The physical properties of each were then measured and evaluated. The results are shown in Table 1.

[0229] (Example A3) As the polypropylene resin (A), 90.0 parts by weight of polypropylene resin A-1 was used. As the propylene homopolymer (B), 10.0 parts by weight of polypropylene resin B-1 was used. The amount of the foaming agent used was 5.4 parts by weight, and the foaming pressure was 2.7 MPa. Except for these, foamed particles and a foamed molded body were produced in the same manner as in Example A1, and each physical property was measured and evaluated. The results are shown in Table 1.

[0230] (Example A4) As the polypropylene resin (A), 85.0 parts by weight of polypropylene resin A-1 was used. As the propylene homopolymer (B), 15.0 parts by weight of polypropylene resin B-1 was used. The amount of the foaming agent used was 5.4 parts by weight, and the foaming pressure was 2.7 MPa. Except for these, foamed particles and a foamed molded body were produced in the same manner as in Example A1, and each physical property was measured and evaluated. The results are shown in Table 1.

[0231] (Example A5) As the polypropylene resin (A), 95.0 parts by weight of polypropylene resin A-1 was used. As the propylene homopolymer (B), 5.0 parts by weight of polypropylene resin B-2 was used. The amount of the foaming agent used was 5.4 parts by weight, and the foaming pressure was 2.7 MPa. Except for these, foamed particles and a foamed molded body were produced in the same manner as in Example A1, and each physical property was measured and evaluated. The results are shown in Table 1.

[0232] (Example A6) As the polypropylene resin (A), 95.0 parts by weight of polypropylene resin A-1 was used. As the propylene homopolymer (B), 5.0 parts by weight of polypropylene resin B-3 was used. The amount of the foaming agent used was 5.4 parts by weight, and the foaming pressure was 2.7 MPa. Except for these, foamed particles and a foamed molded body were produced in the same manner as in Example A1, and each physical property was measured and evaluated. The results are shown in Table 1.

[0233]

Table 1

[0234] (Comparative Example A2) As the polypropylene-based resin (A), 98.5 parts by weight of the polypropylene-based resin A-1 was used, and as the propylene homopolymer (B), 1.5 parts by weight of the polypropylene-based resin B-1 was used. Foamed particles and a foamed molded article were produced in the same manner as in Example A1, and each physical property was measured and evaluated. The results are shown in Table 2.

[0235] (Comparative Example A3) As the polypropylene-based resin (A), 80.0 parts by weight of the polypropylene-based resin A-1 was used, and as the propylene homopolymer (B), 20.0 parts by weight of the polypropylene-based resin B-1 was used. The amount of the foaming agent used was 5.4 parts by weight, and the foaming pressure was 2.7 MPa. Foamed particles and a foamed molded article were produced in the same manner as in Example A1, and each physical property was measured and evaluated. The results are shown in Table 2.

[0236] (Comparative Example A4) As the polypropylene-based resin (A), 98.5 parts by weight of the polypropylene-based resin A-1 was used. Instead of the propylene homopolymer (B), 1.5 parts by weight of wax was used, and the foaming pressure was 2.9 MPa. Foamed particles and a foamed molded article were produced in the same manner as in Example A1, and each physical property was measured and evaluated. The results are shown in Table 2.

[0237] (Comparative Example A5) As the polypropylene-based resin (A), 95.0 parts by weight of the polypropylene-based resin A-1 was used. Instead of the propylene homopolymer (B), 5.0 parts by weight of wax was used, and the foaming pressure was 2.8 MPa. Foamed particles and a foamed molded article were produced in the same manner as in Example A1, and each physical property was measured and evaluated. The results are shown in Table 2.

[0238] (Comparative example A6) Foamed particles and foamed molded articles were prepared using the same method as in Example A1, except that 92.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), 8.0 parts by weight of wax was used instead of propylene homopolymer (B), the amount of foaming agent used was 5.4 parts by weight, the foaming temperature was 150°C, and the foaming pressure was 2.7 MPa. The physical properties of each were measured and evaluated. The results are shown in Table 2.

[0239] (Comparative example A7) In Example A1, foamed particles and foamed molded articles were prepared using the same method as in Example A1, except that 50.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), and 50.0 parts by weight of polypropylene resin (C) was used instead of propylene homopolymer (B), and the foaming temperature was set to 150°C and the foaming pressure to 2.9 MPa. The physical properties of each were then measured and evaluated. The results are shown in Table 2.

[0240] (Comparative example A8) In Example A1, foamed particles and foamed molded articles were prepared using the same method as in Example A1, except that 40.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), and 60.0 parts by weight of polypropylene resin (C) was used instead of propylene homopolymer (B). The foaming temperature was set to 150°C and the foaming pressure to 2.9 MPa. The physical properties of each were then measured and evaluated. The results are shown in Table 2.

[0241] (Comparative example A9) Foamed particles and foamed molded articles were prepared using the same method as in Example A1, except that 30.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), 70.0 parts by weight of polypropylene resin (C) was used instead of propylene homopolymer (B), and the foaming temperature was set to 150°C. The physical properties of each were then measured and evaluated. The results are shown in Table 2.

[0242] [Table 2] (summary) From Tables 1 and 2, the following is clear: (1) The foamed particles of Examples A1 to A6 can be molded at a low molding pressure, and the foamed molded articles obtained by molding these foamed particles have a compressive strength of a certain level or higher, excellent surface appearance, and suppressed deformation.

[0243] (2) Examples A1 to A6 are compared with Comparative Example A1. This shows that when polypropylene resin (A) is used alone (Comparative Example A1), the molding pressure of the foamed molded product is not sufficiently reduced, and 1.5 mm 2 ~2.0mm 2 It can be seen that gaps of a certain size occur between the particles, meaning that the resulting foamed molded product has inferior surface appearance.

[0244] (3) Examples A1 to A6 are compared with Comparative Example A2. This shows that when the amount of polypropylene homopolymer (B) used is insufficient (Comparative Example A2), the molding pressure of the foamed molded article is not reduced sufficiently, and 1.5 mm 2 ~2.0mm 2 It can be seen that gaps of a certain size occur between the particles, meaning that the resulting foamed molded product has inferior surface appearance.

[0245] (4) Examples A1 to A6 are compared with Comparative Example A3. This shows that when the amount of polypropylene homopolymer (B) used is excessive (Comparative Example A3), the foamed molded article is greatly deformed, has many wrinkles on the surface of the foamed molded article, and has poor compressive strength. (5) Examples A1 to A6 are compared with Comparative Examples A4 to A6. This shows that even if the melting point is 85°C or lower, when a wax other than polypropylene homopolymer (B) is used (Comparative Examples A4 to A6), the compressive strength of the foamed molded article is poor.

[0246] (6) Examples A1 to A6 are compared with Comparative Examples A7 to A9. This shows that when a polypropylene resin (C) that is not a polypropylene homopolymer and has a melting point above 85°C is used (Comparative Examples A7 to A9), 1.5 mm 2 ~2.0mm 2It can be seen that there are grain intervals of large size, that is, the foam molded body has poor surface beauty, is greatly deformed, and has many wrinkles on the surface.

[0247] 〔Example B〕 Hereinafter, the second embodiment of the present invention will be specifically described with reference to Example B. However, the technical scope of the present invention is not limited by these Example B.

[0248] 〔Materials〕 The substances (materials) used in Example B and Comparative Example B are shown below.

[0249] <Polypropylene resin> Regarding the polypropylene resin used in Example B, since it is the same as that described in the <Polypropylene resin> section in Example A, the description thereof is incorporated herein and omitted here.

[0250] <Carbon black> 40 parts by weight of carbon black A or B and 60 parts by weight of polypropylene resin (MFR = 7.5 g / 10 min) were mixed to prepare a masterbatch of carbon black A or B. That is, in any of the masterbatches, the concentration of carbon black in 100% by weight of the masterbatch was 40% by weight. In the following Example B and Comparative Example B, these carbon black masterbatches were used. In Tables 3 and 4, the average particle diameter of carbon black in the obtained foamed particles is also shown.

[0251] <Other resins and additives> Regarding the other resins and additives used in Example B, since they are the same as those described in the <Other resins> and <Additives> sections in Example A, respectively, the description thereof is incorporated herein and omitted here.

[0252] 〔Measurement method〕 Regarding the evaluation methods carried out in Example B and Comparative Example B, they will be described below.

[0253] (Primary particle size of carbon black) The primary particle size of carbon black was measured by performing the following steps (1) to (4): (1) Polypropylene resin foam particles were cut in half using a microtome; (2) The obtained cross-sections were imaged at 40,000x magnification using a transmission electron microscope to obtain cross-sectional images; (3) 50 carbon black particles were arbitrarily selected from the obtained cross-sectional images, and the particle diameter (Ferret diameter) in the X and Y directions was measured for each primary particle of carbon black; (4) For each primary particle of carbon black, the arithmetic mean of the particle diameter in the X direction and the particle diameter in the Y direction was calculated, and the obtained value was defined as the primary particle size of the carbon black.

[0254] (Fusing properties of foamed molded products) The fusion properties of the foamed molded article were evaluated by the internal fusion rate of the foamed molded article. The method for measuring the internal fusion rate is the same as that described in the section (Measurement of Internal Fusion Rate and Minimum Molding Pressure of Foamed Molded Article) in Example A, so that description is used and the explanation is omitted here.

[0255] Based on the obtained internal fusion rate, the fusion properties of the foamed molded article were evaluated according to the following evaluation criteria. ○ (Good): The internal bonding rate is 60% or higher. × (Defective): The internal bonding rate is less than 60%.

[0256] (Surface aesthetics of foamed molded products) In Example B, the surface beauty of the foamed molded article was evaluated by assessing the degree of blackness, color unevenness, intergranularity, and wrinkles of the foamed molded article. The evaluation methods and criteria for each were as follows.

[0257] (Blackness of foamed molded material) The method for evaluating the blackness of the foamed molded body was as follows (1) to (3): (1) The surface of the obtained foamed molded body (a 320mm x 370mm surface formed from the mold surface where the water vapor holes described later are drilled holes) was scanned using a printer / multifunction device (iR-ADVC5035, manufactured by Canon) to obtain a surface image of the foamed molded body; (2) The blackness of the entire surface (320mm x 370mm) of the foamed molded body in the obtained image was evaluated by RGB analysis performed using image processing software (DIBAS32); (3) Specifically, the mode (measured value) of the sum of RGB values ​​over the entire surface of the foamed molded body was quantified using the following formula, with black 0 (100%) and white 255 (0%) as the baseline, and judged according to the following criteria. Note that a higher blackness (%) value indicates a higher blackness. Blackness of foamed molded material (%) = (255 - measured value) / 255 × 100 ○ (Good): Blackness is 88% or higher. × (Defective): Blackness is less than 88%.

[0258] (Color unevenness in foamed molded products) The method for evaluating the color unevenness of the foamed molded body was as follows: For foamed molded bodies that received a rating of ○ (good) for the blackness of the foamed molded body, the foamed molded body was visually observed and evaluated according to the following criteria. ○ (Good): The black color of the foamed molded product is uniform or nearly uniform, and there is little to no color unevenness within or between the foam particles. △ (Pass): The black color of the foamed molded product is uneven, with a few grayish areas visible. × (Defective): The foamed molded product has uneven black coloration, with numerous grayish areas.

[0259] (between particles in foamed molded material) The evaluation method for the intergranular structure of the foamed molded product was as follows: The surface of the obtained foamed molded product was visually observed and evaluated according to the following criteria. ○ (Good): The surface of the foamed molded product has no intergranular spaces (gaps between foam particles), or if present, they are 1.0 mm. 2 The following particles are spaced very slightly apart, 1.0 mm in size.2 There are no gaps between particles larger than this. △ (Pass): 1.0 mm on the surface of the foamed molded product. 2 There are a few (not many) gaps between grains larger than 1.5mm, but the overall size is 1.5mm. 2 There are no gaps between particles larger than this. × (Defective): 1.0 mm on the surface of the foamed molded product. 2 There are many gaps between particles larger than 1.5 mm, and / or 1.5 mm 2 There are gaps between particles that are larger than [a certain size].

[0260] (Wrinkles in foamed molded material) The method for evaluating wrinkles in the foamed molded product was as follows: The surface of the obtained foamed molded product was visually observed and evaluated according to the following criteria. ○ (Good): The surface of the foamed molded product has no wrinkles, or very few. △ (Pass): There are some small wrinkles (but not many), and there are no large wrinkles, or if there are, very few. × (Defective): Numerous small wrinkles are present, as well as a number of larger wrinkles.

[0261] In the [Measurement Method] of Example B, the melting points of the polypropylene resin, wax, and polypropylene resin particles are the same as those described in (Melting Point) in Example A. Also, in the [Measurement Method] of Example B, the MFR of the polypropylene resin (A) and the mesopentad fraction of the polypropylene homopolymer (B) are the same as those described in (MFR) and (Mesopentad Fraction of Polypropylene Homopolymer (B) (mmmm)) in Example A, respectively. Furthermore, the DSC ratio of the foamed particles, the average bubble diameter of the foamed particles, and the foaming ratio of the foamed particles are the same as those described in (DSC ratio of foamed particles), (average bubble diameter of foamed particles), and (foaming ratio of foamed particles) in Example A, respectively.

[0262] (Example B1) [Production of resin particles] As the polypropylene resin (A), 97.5 parts by weight of polypropylene resin A-1 was blended with 2.5 parts by weight of polypropylene resin B-1 as the propylene homopolymer (B), 4 parts by weight of carbon black, and as additives, 0.1 parts by weight of talc and 0.2 parts by weight of glycerin.

[0263] Next, the blend was melt-kneaded in an extruder (resin temperature 225°C) to obtain a resin composition. The resin composition was extruded in strand form from the tip of the extruder and then granulated by cutting to produce resin particles (1.2 mg / particle). A twin-screw extruder [Toshiba Machine Co., Ltd., TEM26-SX] with two 26 mm diameter shafts (screws) was used as the extruder.

[0264] [Production of foamed particles] In a 10L pressure vessel, 100 parts by weight of the obtained resin particles, 200 parts by weight of water as an aqueous dispersion medium, 0.3 parts by weight of kaolin as a dispersant, 0.06 parts by weight of sodium dodecylbenzenesulfonate (DBS) as a dispersion aid, and 5.6 parts by weight of carbon dioxide as a blowing agent were charged to prepare a dispersion containing the blowing agent (dispersion step). While stirring the dispersion, the foaming temperature (temperature inside the pressure vessel) was set to 151°C and the foaming pressure (pressure inside the vessel) was set to 2.9 MPa (heating-pressure step). After the temperature and pressure inside the pressure vessel reached the predetermined foaming temperature and pressure, the temperature and pressure inside the pressure vessel were maintained at the predetermined foaming temperature and pressure for a further 30 minutes (holding step). Thereafter, while maintaining the foaming pressure inside the pressure vessel at the predetermined foaming pressure by supplying carbon dioxide, the dispersion was released to atmospheric pressure at 95°C through a 3.2 mmφ orifice provided at the bottom of the pressure vessel to obtain foamed polypropylene resin particles (release step). Subsequently, the polypropylene resin foam particles were dried at 75°C for 24 hours. The DSC ratio, average bubble diameter, and foaming ratio of the obtained foam particles were measured. The results are shown in Table 3.

[0265] [Production of foamed molded products] A foamed molded body was produced by the following methods (1) to (6) in order: (1) The foamed particles obtained in the [production of foamed particles] step were placed in a pressure vessel, and air was injected into the pressure vessel to increase the pressure inside the vessel, thereby impregnating the foamed particles with pressurized air and making the internal pressure of the foamed particles 0.20 MPa (absolute pressure); (2) The foamed particles with internal pressure were filled into a mold installed in a molding machine. Here, a polyolefin foam molding machine [Daisen Kogyo Co., Ltd., EP-900] was used as the molding machine, and a mold was used in which the steam holes were drilled holes and which could form a molding space of 370 mm in length x 320 mm in width x 50 mm in thickness, with a cracking of 5 mm; (3) After filling with foam particles, with the drain valve of the molding machine's drain line open, the foam particles were heated for 10 seconds with steam at 0.1 MPa (gauge pressure) (steam pressure A) (one-sided heating and reverse one-sided heating) to expel the air from inside the mold; (4) After that, with the drain valve of the molding machine's drain line closed, the foam particles were heated for another 10 seconds with steam at 0.24 MPa (gauge pressure) (steam pressure B) (both-sided heating); (5) This heating fused the foam particles together to obtain a foam molded body; (6) The obtained foam molded body was removed from the mold, left at room temperature for 2 hours, and then cured and dried at 75°C for 16 hours. The resulting foamed molded articles were measured and evaluated for their fusion properties and surface aesthetics (blackness, color unevenness, intergranularity, and wrinkles). The results are shown in Table 3.

[0266] (Example B2) Foamed particles and foamed molded articles were prepared using the same method as in Example B1, except that 95.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), 5.0 parts by weight of polypropylene resin B-1 was used as the propylene homopolymer (B), and the foaming pressure (gauge pressure) was changed to 2.8 MPa. The physical properties of each were then measured and evaluated. The results are shown in Table 3.

[0267] (Example B3) Foamed particles and foamed molded articles were prepared using the same method as in Example B1, except that 85.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), 15.0 parts by weight of polypropylene resin B-1 was used as the propylene homopolymer (B), and the foaming pressure (gauge pressure) was changed to 2.8 MPa. The physical properties of each were then measured and evaluated. The results are shown in Table 3.

[0268] (Example B4) Foamed particles and foamed molded articles were prepared using the same method as in Example B1, except that 95.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), 5.0 parts by weight of polypropylene resin B-1 was used as the propylene homopolymer (B), 6 parts by weight of carbon black B was used as the carbon black, and the foaming pressure (gauge pressure) was changed to 2.8 MPa. The physical properties of each were then measured and evaluated. The results are shown in Table 3.

[0269] (Example B5) Foamed particles and foamed molded articles were prepared using the same method as in Example B1, except that 95.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), 5.0 parts by weight of polypropylene resin B-2 was used as the propylene homopolymer (B), and the foaming pressure (gauge pressure) was changed to 2.8 MPa. The physical properties of each were then measured and evaluated. The results are shown in Table 3.

[0270] (Example B6) Foamed particles and foamed molded articles were prepared using the same method as in Example B1, except that 95.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), 5.0 parts by weight of polypropylene resin B-3 was used as the propylene homopolymer (B), 4 parts by weight of carbon black A was used as the carbon black, and the foaming pressure (gauge pressure) was changed to 2.7 MPa. The physical properties of each were then measured and evaluated. The results are shown in Table 3.

[0271] [Table 3] (Comparative Example B1) Foamed particles and foamed molded articles were prepared using the same method as in Example B1, except that 100.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), and propylene homopolymer (B) was not used. The physical properties of each were then measured and evaluated. The results are shown in Table 4.

[0272] (Comparative example B2) Foamed particles and foamed molded articles were prepared using the same method as in Example B1, except that 100.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), propylene homopolymer (B) was not used, and carbon black B was used instead of carbon black A. The physical properties of each were then measured and evaluated. The results are shown in Table 4.

[0273] (Comparative Example B3) Foamed particles and foamed molded articles were prepared using the same method as in Example B1, except that 95.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), 5.0 parts by weight of propylene-α-olefin wax was used instead of propylene homopolymer (B), and the foaming pressure (gauge pressure) was changed to 2.8 MPa. The physical properties of each were then measured and evaluated. The results are shown in Table 4.

[0274] (Comparative example B4) Foamed particles and foamed molded articles were prepared using the same method as in Example B1, except that 98.5 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A) and 1.5 parts by weight of polypropylene resin B-1 was used as the propylene homopolymer (B). The physical properties of each were then measured and evaluated. The results are shown in Table 4.

[0275] (Comparative Example B5) Foamed particles and foamed molded articles were prepared using the same method as in Example B1, except that 80.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A) and 20.0 parts by weight of polypropylene resin B-1 was used as the propylene homopolymer (B). The physical properties of each were then measured and evaluated. The results are shown in Table 4.

[0276] (Comparative example B6) Foamed particles and foamed molded articles were prepared using the same method as in Example B1, except that 95.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), 5.0 parts by weight of polypropylene resin B-1 was used as the propylene homopolymer (B), and 10 parts by weight of carbon black A was used, and the foaming pressure (gauge pressure) was changed to 3.0 MPa. The physical properties of each were then measured and evaluated. The results are shown in Table 4.

[0277] (Comparative Example B7) Foamed particles and foamed molded articles were prepared using the same method as in Example B1, except that 95.0 parts by weight of polypropylene resin A-1 was used as the polypropylene resin (A), 5.0 parts by weight of polypropylene resin B-1 was used as the propylene homopolymer (B), and 10 parts by weight of carbon black B was used, and the foaming pressure (gauge pressure) was changed to 3.0 MPa. The physical properties of each were then measured and evaluated. The results are shown in Table 4.

[0278] [Table 4] (summary) From Tables 3 and 4, the following is clearly evident.

[0279] (1) The foamed particles of Examples B1 to B6 provided foamed molded articles with excellent fusion properties even when molded at a low molding pressure (0.24 MPa (gauge pressure)). Furthermore, the foamed molded articles formed by molding the foamed particles of Examples B1 to B6 are intended to be polypropylene resin foamed molded articles that have excellent surface beauty, namely (i) high blackness, (ii) uniform color (black) with no color unevenness or nearly uniform color (black) with very little color unevenness, (iii) no or very few gaps between particles, and (iv) no or very few wrinkles.

[0280] (2) A comparison of Examples B1 to B6 with Comparative Examples B1 to B2 shows that when polypropylene resin (A) is used alone, the fusion properties and intergranular structure are poor.

[0281] (3) A comparison of Examples B1 to B6 with Comparative Example B3 shows that even if the melting point is 85°C or lower, if a polypropylene-based resin that is not a polypropylene homopolymer is used, the fusion properties and color uniformity will be poor.

[0282] (4) A comparison of Examples B1 to B6 with Comparative Example B4 shows that when less than 2 parts by weight of polypropylene homopolymer (B) is used, the fusion properties and intergranular structure become poor.

[0283] (5) A comparison of Examples B1 to B6 with Comparative Example B5 shows that when 20 parts by weight or more of polypropylene homopolymer (B) is used, a foamed molded article with many wrinkles is formed. [Industrial applicability]

[0284] According to one embodiment of the present invention, polypropylene resin foam particles can be provided that (a) provide a polypropylene resin foam molded article having good fusion properties at a low molding pressure, and (b-1) provide a polypropylene resin foam molded article having good compressive strength and being almost deformation-free.

[0285] According to another embodiment of the present invention, polypropylene resin foam particles can be provided that (a) provide a polypropylene resin foam molded article having good fusion properties at a low heating vapor pressure, and (b) provide a polypropylene resin foam molded article having good blackness, uniform color without color unevenness, and with almost no deformation. For this reason, one embodiment of the present invention can be used for a variety of applications, including automotive interior components, core materials for automotive bumpers, as well as thermal insulation materials, cushioning packaging materials, and reusable containers.

Claims

1. A polypropylene resin (A) having a melting point of 135°C to 150°C, The material contains a base resin containing a polypropylene homopolymer (B) having a melting point of 85°C or lower. The base resin is defined as the total amount of the polypropylene resin (A) and the polypropylene homopolymer (B) being 100 parts by weight. The aforementioned polypropylene resin (A) contains more than 80.0 parts by weight and 98.0 parts by weight or less, and Polypropylene resin foam particles containing 2.0 parts by weight or more and less than 20.0 parts by weight of the aforementioned polypropylene homopolymer (B).

2. The polypropylene resin foam particles according to claim 1, wherein the base resin contains carbon black.

3. The polypropylene resin foam particles according to claim 2, wherein when the total amount of the polypropylene resin (A) and the polypropylene homopolymer (B) is 100 parts by weight, the carbon black is contained in 2 parts by weight or more and less than 10 parts by weight.

4. The polypropylene resin foam particles according to any one of claims 1 to 3, wherein the weight-average molecular weight of the polypropylene homopolymer (B) is 40,000 to 140,000.

5. The polypropylene resin foam particle according to any one of claims 1 to 4, wherein the mesopentade fraction (mmmm) of the polypropylene homopolymer (B) is 25 mol% to 65 mol%.

6. Polypropylene resin foam particles according to any one of claims 2 to 5, wherein the primary particle size of the carbon black is 100 nm or less.

7. The polypropylene resin (A) is at least one of a propylene / ethylene random copolymer and a propylene / ethylene / 1-butene random copolymer, Polypropylene resin foam particles according to any one of claims 1 to 6, wherein the ethylene content in the copolymer is 0.2% by weight to 10.0% by weight per 100% by weight of each copolymer.

8. The polypropylene resin foamed particle according to any one of claims 1 to 7, wherein the MFR of the polypropylene resin (A) at 230°C is 3 g / 10 min to 30 g / 10 min.

9. The polypropylene resin foam particles according to any one of claims 1 to 8, wherein the DSC ratio ((heat of fusion on the high temperature side / total heat of fusion) × 100) of the polypropylene resin foam particles is 10.0% to 50.0%.

10. The polypropylene resin foam particles according to any one of claims 1 to 9, wherein the average bubble diameter of the polypropylene resin foam particles is 110 μm to 280 μm.

11. The polypropylene resin foam particles according to any one of claims 1 to 10, wherein the foaming ratio of the polypropylene resin foam particles is 15 to 50 times.

12. A polypropylene resin foam molded article obtained by molding polypropylene resin foam particles according to any one of claims 1 to 11.

13. A dispersion step in which polypropylene resin particles, an aqueous dispersion medium, and a foaming agent are dispersed in a container, The process includes a discharge step of opening one end of the container and releasing the dispersion liquid obtained in the dispersion step into a region with a pressure lower than the pressure inside the container, The polypropylene resin particles include a base resin containing a polypropylene resin (A) having a melting point of 135°C to 150°C and a polypropylene homopolymer (B) having a melting point of 85°C or less, wherein the base resin is composed of 100 parts by weight of the total amount of the polypropylene resin (A) and the polypropylene homopolymer (B). The aforementioned polypropylene resin (A) contains more than 80.0 parts by weight and 98.0 parts by weight or less, and A method for producing polypropylene resin foam particles, comprising 2.0 parts by weight or more and less than 20.0 parts by weight of the polypropylene homopolymer (B).

14. The method for producing polypropylene resin foam particles according to claim 13, wherein the foaming agent comprises at least one of carbon dioxide and water.

15. A method for producing polypropylene resin foamed particles according to claim 13 or 14, wherein the amount of foaming agent used is 2.0 parts by weight to 60.0 parts by weight per 100 parts by weight of resin particles.

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