Polypropylene resin foam particles, polypropylene resin foam molded body, and method for manufacturing polypropylene resin foam particles

Abstract

The present invention addresses the problem of providing polypropylene resin foam particles capable of providing a foam molded body in a short molding cycle. Provided are foamed particles obtained by foaming resin particles, wherein: the resin particles contain a polypropylene-based random copolymer and a specific amount of a propylene homopolymer and / or a polypropylene-based block copolymer, and have a specific MFR; and when the propylene homopolymer is included, the heat quantity ratio of a high-temperature-side melting peak of the resin particles is within a specific range.

Description

Polypropylene-based resin expanded beads, polypropylene-based resin expanded molded article, and method for producing polypropylene-based resin expanded beads

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

[0002] Polypropylene resin foam molded articles are used in a variety of applications, such as cushioning packaging materials and automotive components (see, for example, Patent Documents 1 to 3).

[0003] International Publication No. WO2006 / 054727 Japanese Patent Application Laid-Open No. 2012-184303 International Publication No. WO2009 / 001626

[0004] However, the above-mentioned conventional techniques are not sufficient from the viewpoint of the molding cycle in the production of foamed molded articles using foamed beads, and there is room for further improvement.

[0005] One embodiment of the present invention has been made in consideration of the above-mentioned problems, and its object is to provide novel expanded polypropylene-based resin beads that can provide expanded polypropylene-based resin molded articles in a short molding cycle, expanded polypropylene-based resin molded articles obtained by molding the expanded polypropylene-based resin beads, and a novel method for producing expanded polypropylene-based resin beads.

[0006] The present inventors have conducted extensive research to solve the above problems and have completed the present invention.

[0007] That is, the expanded polypropylene resin particles according to one embodiment of the present invention are polypropylene resin particles obtained by expanding polypropylene resin particles, the polypropylene resin particles containing a polypropylene random copolymer (A), a propylene homopolymer (B1) and / or a polypropylene block copolymer (B2), the polypropylene resin particles having a melt flow rate (MFR) of 20.0 g / 10 min or more at 230° C. under a load of 2160 g, and the polypropylene resin particles containing the propylene homopolymer (B1) and / or a polypropylene block copolymer (B2) When the polypropylene-based resin particles contain 1), (i) the content of the propylene homopolymer (B1) is less than 95 parts by weight based on 100 parts by weight of the total of the polypropylene random copolymer (A) and the propylene homopolymer (B1), and (ii) the polypropylene-based resin particles have, in a DSC curve obtained by measurement using a differential scanning calorimeter, (ii-1) only one melting peak or (ii-2) two or more melting peaks, and the heat ratio of the melting peak on the highest temperature side is 95% or more and less than 100% of the total heat of fusion (100%).

[0008] Furthermore, a method for producing expanded polypropylene-based resin beads according to one embodiment of the present invention comprises: an extrusion step of melt-kneading a mixed resin containing a polypropylene-based random copolymer (A) and a propylene homopolymer (B1) and / or a polypropylene-based block copolymer (B2) to obtain polypropylene-based resin beads; and an expansion step of expanding the polypropylene-based resin beads obtained in the extrusion step, wherein the polypropylene-based resin beads have a melt flow rate (MFR) of 20.0 g / 10 min or more at 230°C under a load of 2160 g, and when the mixed resin contains the propylene homopolymer (B1), (i) in the mixed resin, the propylene homopolymer (B1) is less than 95 parts by weight per 100 parts by weight of the total of the polypropylene random copolymer (A) and the propylene homopolymer (B1), and (ii) In a DSC curve obtained by measurement using a differential scanning calorimeter, the polypropylene resin particles (ii-1) have only one melting peak, or (ii-2) have two or more melting peaks, and the heat ratio of the melting peak on the highest temperature side to the total heat of fusion (100%) is 95% or more but less than 100%.

[0009] According to one embodiment of the present invention, it is possible to provide novel expanded polypropylene-based resin beads that can provide expanded polypropylene-based resin molded articles in a short molding cycle, and a novel method for producing the expanded polypropylene-based resin beads.

[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 the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0011] In this specification, a "structural unit derived from an X monomer" contained in a polymer, copolymer, or resin may be referred to as an "X unit."

[0012] Unless otherwise specified in this specification, the structural unit is X １ Unit, X ２ Units, ... and X ｎ A copolymer containing units (n is an integer of 2 or more) is referred to as "X １ / X ２ / ・・・ / X ｎ Also referred to as "copolymer". X １ / X ２ / ・・・ / X ｎ Unless otherwise specified, the polymerization mode of the copolymer is not particularly limited, and the copolymer may be a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer.

[0013] In this specification, "polypropylene-based resin particles" may be referred to as "resin particles," "expanded polypropylene-based resin particles" may be referred to as "expanded particles," "expanded polypropylene-based resin particles according to one embodiment of the present invention" may be referred to as "the present expanded particles," "polypropylene-based resin foam molded body" may be referred to as "foam molded body," and "polypropylene-based resin foam molded body according to one embodiment of the present invention" may be referred to as "the present foam molded body." In this specification, "method for producing expanded polypropylene-based resin particles" may be referred to as "production method," and "method for producing expanded polypropylene-based resin particles according to one embodiment of the present invention" may be referred to as "the present production method."

[0014] [1. Technical Concept of One Embodiment of the Present Invention] A polypropylene-based random copolymer can generally be used as a raw material for a polypropylene-based resin foam molded article. On the other hand, a polypropylene-based block copolymer can also be used as a raw material for a polypropylene-based resin foam molded article. For example, this can be done when the impact resistance of the polypropylene-based resin foam molded article is to be increased or when recycled resin is used to reduce the environmental impact.

[0015] As a recycled polypropylene resin, polypropylene block copolymers are distributed in much larger quantities than polypropylene random copolymers.

[0016] Propylene homopolymers may also be used as a raw material for polypropylene-based resin foam molded articles, for example, when the purpose is to improve the dimensional stability of the polypropylene-based resin foam molded articles.

[0017] Motivated by the above, the present inventors have conducted extensive research into the following: providing expanded polypropylene resin particles, which are a raw material for polypropylene resin expansion moldings, by using a combination of a polypropylene random copolymer and a propylene homopolymer and / or a polypropylene block copolymer.

[0018] Through intensive research, the present inventors independently obtained the following novel finding: when resin particles obtained by using a combination of a polypropylene random copolymer and a propylene homopolymer and / or a polypropylene block copolymer are expanded, and the expanded particles are then molded to obtain a foamed molded article, the molding cycle may be lengthened in some cases.

[0019] Therefore, the present inventors have conducted further intensive research with the following objective: to provide expanded beads that can provide expanded molded articles in a short molding cycle even when a polypropylene random copolymer is used in combination with a propylene homopolymer and / or a polypropylene block copolymer.

[0020] As a result, the present inventors independently found the following novel finding, which led to the completion of the present invention: the finding that the following expanded beads, or expanded beads obtained by the following production method, can surprisingly provide an expanded molded article in a short molding cycle: Expanded polypropylene-based resin beads obtained by expanding polypropylene-based resin beads, wherein the polypropylene-based resin beads contain a polypropylene-based random copolymer (A) and a propylene homopolymer (B1) and / or a polypropylene block copolymer (B2), and the polypropylene-based resin beads have a melt flow rate (MFR) of 20.0 g / 10 min or more at 230°C under a load of 2160 g, and when the polypropylene-based resin particles contain the propylene homopolymer (B1), (i) the content of the propylene homopolymer (B1) in the polypropylene-based resin particles is less than 95 parts by weight based on 100 parts by weight of the total of the polypropylene-based random copolymer (A) and the propylene homopolymer (B1), and (ii) The polypropylene resin particles are expanded polypropylene resin particles, which have (ii-1) only one melting peak or (ii-2) two or more melting peaks in a DSC curve obtained by measurement using a differential scanning calorimeter, and the heat ratio of the melting peak on the highest temperature side to the total heat of fusion (100%) is 95% or more and less than 100%;The present invention relates to a method for producing a polypropylene-based resin particle production process, the method comprising: an extrusion step of melt-kneading a mixed resin containing a polypropylene-based random copolymer (A) and a propylene homopolymer (B1) and / or a polypropylene-based block copolymer (B2) to obtain polypropylene-based resin particles; and an expansion step of expanding the polypropylene-based resin particles obtained in the extrusion step, wherein the polypropylene-based resin particles have a melt flow rate (MFR) of 20.0 g / 10 min or more at 230°C under a load of 2160 g, and when the mixed resin contains the propylene homopolymer (B1), (i) in the mixed resin, the propylene homopolymer (B1) is less than 95 parts by weight per 100 parts by weight of the total of the polypropylene-based random copolymer (A) and the propylene homopolymer (B1), and (ii) A method for producing expanded polypropylene resin particles, wherein the polypropylene resin particles have (ii-1) only one melting peak or (ii-2) two or more melting peaks in a DSC curve obtained by measurement using a differential scanning calorimeter, and the heat ratio of the melting peak on the highest temperature side to the total heat of fusion (100%) is 95% or more but less than 100%;

[0021] [2. Expanded Polypropylene Resin Beads] Expanded polypropylene resin beads according to one embodiment of the present invention are polypropylene resin beads obtained by expanding polypropylene resin beads, the polypropylene resin beads containing a polypropylene random copolymer (A) and a propylene homopolymer (B1) and / or a polypropylene block copolymer (B2), the polypropylene resin particles having a melt flow rate (MFR) of 20.0 g / 10 min or more at 230°C under a load of 2160 g, and the polypropylene resin particles containing the propylene homopolymer (B1) and / or a polypropylene block copolymer (B2). (i) in the polypropylene-based resin particles, the content of the propylene homopolymer (B1) is less than 95 parts by weight based on 100 parts by weight of the total of the polypropylene-based random copolymer (A) and the propylene homopolymer (B1), and (ii) in a DSC curve obtained by measurement by a differential scanning calorimeter, the polypropylene-based resin particles (ii-1) have only one melting peak or (ii-2) have two or more melting peaks, and the heat ratio of the melting peak on the highest temperature side to the total heat of fusion (100%) is 95% or more and less than 100%.

[0022] The present expanded beads have the above-mentioned structure, which is advantageous in that they can provide expanded molded articles in a short molding cycle. Furthermore, the present expanded beads have the above-mentioned structure, which is advantageous in that they can provide expanded molded articles with excellent internal fusion properties and / or surface aesthetics. The molding cycle, and methods for measuring and evaluating the internal fusion properties and surface aesthetics of expanded molded articles will be described in detail in the Examples below.

[0023] <Components> (Polypropylene Resin Particles) (Resin Components) The polypropylene random copolymer (A), propylene homopolymer (B1), and polypropylene block copolymer (B2) can also be considered as resin components in the resin particles and expanded beads. In other words, the resin particles and the present expanded beads contain at least the polypropylene random copolymer (A) and the propylene homopolymer (B1) and / or the polypropylene block copolymer (B2) as resin components. In this specification, "components that substantially constitute the expanded beads" and "components that substantially constitute the resin particles" are also referred to as "base resin." In other words, the resin particles contain a base resin, and the base resin contains the polypropylene random copolymer (A) and the propylene homopolymer (B1) and / or the polypropylene block copolymer (B2). In other words, the present expanded beads contain a base resin, and the base resin contains the polypropylene random copolymer (A) and the propylene homopolymer (B1) and / or the polypropylene block copolymer (B2).

[0024] The polypropylene random copolymer (A), the propylene homopolymer (B1) and the polypropylene block copolymer (B2) are all polypropylene resins.

[0025] In this specification, the term "polypropylene resin" refers to a resin having the highest content of propylene units among all the structural units constituting the resin. For example, the polypropylene resin contains 50 mol % or more of propylene units out of 100 mol % of all structural units.

[0026] (Polypropylene Random Copolymer (A)) The polypropylene random copolymer (A) has, in addition to propylene units, one or more constituent units derived from a monomer other than a propylene monomer.

[0027] In this specification, the "structural units other than propylene units" contained in the polypropylene resin may be referred to as "comonomer units." In other words, the polypropylene random copolymer (A) contains at least propylene units and comonomer units. In the polypropylene random copolymer (A), the bonding order of the propylene units and the comonomer units is random.

[0028] 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.

[0029] The heating temperature of the expanded beads when they are molded (for example, in-mold foam molding) is sometimes referred to as the "molding temperature." From the viewpoint of lowering the molding temperature, the polypropylene random copolymer (A) preferably contains an ethylene unit as a comonomer unit. For example, the polypropylene random copolymer (A) is preferably a propylene / ethylene random copolymer containing a propylene unit and an ethylene unit.

[0030] The polypropylene random copolymer (A) is not limited to a propylene / ethylene random copolymer. Examples of the polypropylene random copolymer (A) other than a propylene / ethylene random copolymer include a propylene / 1-butene random copolymer, a propylene / ethylene / 1-butene random copolymer, a propylene / chlorinated vinyl random copolymer, and a propylene / maleic anhydride random copolymer. Note that the 1-butene is synonymous with butene-1.

[0031] The polypropylene random copolymer (A) may be a combination of a propylene / ethylene random copolymer and one or more polypropylene random copolymers other than the propylene / ethylene random copolymer.

[0032] The melting point of the polypropylene random copolymer (A) is not particularly limited, but is preferably 130° C. or higher, more preferably 130° C. to 160° C., more preferably 135° C. to 155° C., and even more preferably 140° C. to 150° C. When the polypropylene random copolymer (A) has a melting point of (i) 130° C. or higher, the expanded molded article obtained from the expanded beads has excellent heat resistance, and (ii) when the melting point is 160° C. or lower, it is advantageous in that it becomes easy to increase the expansion ratio of the expanded beads in the production of the expanded beads.

[0033] In this specification, the melting points of the polypropylene random copolymer (A), the propylene homopolymer (B1), the polypropylene block copolymer (B2) and the mixture of the propylene homopolymer (B1) and the polypropylene block copolymer (B2) described below are values ​​measured by differential scanning calorimetry (hereinafter referred to as "DSC method").Specific operating procedures are as described in the examples described below.As the differential scanning calorimeter, for example, a DSC7020 model manufactured by Seiko Instruments Inc. can be used.

[0034] The melt flow rate (MFR) of the polypropylene random copolymer (A) at 230°C and a load of 2160 g is not particularly limited, as long as the MFR of the polypropylene resin particles is 20.0 g / 10 min or more. The MFR of the polypropylene random copolymer (A) at 230°C and a load of 2160 g is preferably 3.0 g / 10 min to 30.0 g / 10 min, more preferably 4.0 g / 10 min to 20.0 g / 10 min, and even more preferably 5.0 g / 10 min to 18.0 g / 10 min. When the MFR of the polypropylene random copolymer (A) at 230°C and a load of 2160 g is within the above range, it has the advantage of easily obtaining expanded beads having a relatively high expansion ratio. Furthermore, in this case, there are also the advantages that the surface beauty of the expanded molded articles obtained from the expanded beads is excellent and the shrinkage rate of the expanded molded articles is low.

[0035] In this specification, the MFR at 230°C and a load of 2160 g of the polypropylene random copolymer (A), the propylene homopolymer (B1), the polypropylene block copolymer (B2), the mixture of the propylene homopolymer (B1) and the polypropylene block copolymer (B2), and the polypropylene resin particles is a value determined using a melt mass-flow rate measuring device as specified in JIS-K 7210. Specific operating procedures are as described in the Examples below.

[0036] The polypropylene random copolymer (A) may be a newly produced one (non-recycled polypropylene random copolymer) produced by a known method, or a recycled polypropylene random copolymer derived from recycled materials. In other words, a recycled material containing a recycled polypropylene random copolymer may be used as the polypropylene random copolymer (A). The polypropylene random copolymer (A) may contain a recycled polypropylene random copolymer. When only recycled materials are used as the polypropylene random copolymer (A), the content of the polypropylene random copolymer (A) in the expanded beads is the product obtained by multiplying the amount of recycled material used (blended amount) by the content ratio of the recycled polypropylene random copolymer in the recycled material. The polypropylene random copolymer (A) may be a mixture of a recycled polypropylene random copolymer and a non-recycled polypropylene random copolymer.

[0037] The proportion of polypropylene random copolymers derived from recycled materials (i.e., recycled polypropylene random copolymers) in 100% by weight of the polypropylene random copolymer (A) may be 50% or more, 70% or more, 80% or more, or even 100%. The polypropylene random copolymer (A) may be composed solely of recycled polypropylene random copolymers. The higher the proportion of polypropylene random copolymers derived from recycled materials (i.e., recycled polypropylene random copolymers) in the polypropylene random copolymer (A), the more advantageously the environmental load can be reduced.

[0038] As used herein, the term "recycled material" refers to (a) a resin composition (or pellets) obtained by reusing a resin product that has been used and / or discarded after being converted into a resin composition (or pellets) by any means (e.g., crushing, shredding, melting, or a combination thereof) from a resin product (e.g., foam particles; foam molded products; films; food trays; packaging containers such as bags and bottles; medical containers such as IV drip packs and syringes; clothing cases; miscellaneous goods such as clear files; home appliances; automobile parts; fishing gear such as fishing nets, ropes, and floats); and (b) a resin composition obtained by reusing waste generated during the production of a resin product after being reusable into a resin composition (or pellets) by any means (e.g., crushing, shredding, melting, or a combination thereof). Resin product recovery is often performed by collecting resin products for each intended use and / or by collecting the raw materials used for the resin product. Therefore, recycled materials may primarily contain resins of the same or substantially the same composition (e.g., polypropylene-based resins and polyethylene-based resins). On the other hand, in the recovery of resin products, the resin product to be recovered may be mixed with other resin products for different purposes and / or made from different raw materials. Therefore, the recycled material may contain, in addition to the resin that is the main component, resins with compositions other than the resin in question.

[0039] In this specification, the resin contained in the recycled material may be referred to as a "recycled resin." For example, a recycled material obtained by (a) converting a resin product obtained primarily from a polypropylene-based resin into a resin composition by any means, and / or (b) converting waste generated during the production process of a resin product using a polypropylene-based resin as a primary raw material into a resin composition by any means, contains a recycled polypropylene-based resin as the recycled resin. A recycled material containing primarily recycled polypropylene-based resin as the resin may contain recycled polyethylene-based resin as the recycled resin in an amount less than the amount of recycled polypropylene-based resin.

[0040] The recycled material may contain additives used in the manufacturing process of the resin product (for example, various additives described in the section (Additives) below, such as foam nucleating agents (e.g., talc, calcium carbonate, silica, kaolin, barium sulfate, calcium hydroxide, aluminum hydroxide, aluminum oxide, titanium oxide, zinc borate, etc.) and colorants).

[0041] In this specification, the origin of the recycled material is not particularly limited. The recycled material may be derived from a foam such as foam particles and foam molded products. The recycled material may also be derived from a non-foamed material (for example, films; food trays; packaging containers such as bags and bottle containers; medical containers such as intravenous packs and syringes; clothing cases; miscellaneous goods such as clear files; home appliances; automobile parts; fishing gear such as fishing nets, ropes, and floats).

[0042] In this specification, a resin that has never been in the form of a resin product may also be referred to as a “non-recycled resin.” For example, a polypropylene-based resin that has never been in the form of a resin product is also referred to as a “non-recycled polypropylene-based resin.”

[0043] The following describes a case where resin particles contain multiple polypropylene random copolymers with different compositions, physical properties, and / or origins (whether recycled or not, etc.). In this case, the mixture of all polypropylene random copolymers contained in the resin particles is considered to be "polypropylene random copolymer (A)." Furthermore, the physical properties (e.g., melting point, MFR, etc.) of the mixture of all polypropylene random copolymers contained in the resin particles are considered to be the physical properties (e.g., melting point, MFR, etc.) of the polypropylene random copolymer (A).

[0044] (Propylene homopolymer (B1)) The melting point of the propylene homopolymer (B1) is not particularly limited, but is preferably from 150° C. to 167° C., more preferably from 153° C. to 166° C., and even more preferably from 155° C. to 165° C. When the propylene homopolymer (B1) has a melting point of (i) 150° C. or higher, it has the effect of providing excellent heat resistance, and when it has a melting point of (ii) 167° C. or lower, it has the advantage of being able to lower the foaming temperature and molding temperature.

[0045] The MFR of the propylene homopolymer (B1) at 230°C and a load of 2160 g is not particularly limited, as long as the MFR of the polypropylene resin particles is 20.0 g / 10 min or more. The MFR of the propylene homopolymer (B1) at 230°C and a load of 2160 g is preferably 1 g / 10 min to 350 g / 10 min, more preferably 5 g / 10 min to 300 g / 10 min, and even more preferably 10 g / 10 min to 290 g / 10 min. When the MFR of the propylene homopolymer (B1) at 230°C and a load of 2160 g is within the above range, it has the advantage of easily obtaining expanded beads having a relatively high expansion ratio. Furthermore, in this case, there are also the advantages that the surface beauty of the expanded molded articles obtained from the expanded beads is excellent and the shrinkage rate of the expanded molded articles is low.

[0046] When the resin particles contain a polypropylene random copolymer (A) and a propylene homopolymer (B1), the propylene homopolymer (B1) is present in an amount of less than 95 parts by weight, preferably 10 to 50 parts by weight, more preferably 10 to 40 parts by weight, and even more preferably 10 to 30 parts by weight, per 100 parts by weight of the total of the polypropylene random copolymer (A) and the propylene homopolymer (B1). This configuration has the advantage of lowering the foaming temperature and molding temperature. When the resin particles contain a polypropylene random copolymer (A) and a propylene homopolymer (B1), the expanded particles obtained by expanding the resin particles may also contain a polypropylene random copolymer (A) and a propylene homopolymer (B1).

[0047] When the resin particles contain a propylene homopolymer (B1), the ratio of the content of the polypropylene random copolymer (A) to the content of the propylene homopolymer (B1) in the resin particles (content (parts by weight) of the polypropylene random copolymer (A):content (parts by weight) of the propylene homopolymer (B1)) is preferably 90:10 to 50:50, more preferably 85:15 to 50:50, even more preferably 80:20 to 60:40, and particularly preferably 75:25 to 70:30. This configuration has the advantages of (i) being able to lower the foaming temperature and molding temperature, and (ii) the resulting foamed molded article having excellent heat resistance.

[0048] The propylene homopolymer (B1) may be a newly produced propylene homopolymer (non-recycled propylene homopolymer) produced by a known method, or a recycled propylene homopolymer derived from a recycled material. In other words, a recycled material containing a recycled propylene homopolymer may be used as the propylene homopolymer (B1). The propylene homopolymer (B1) may contain a recycled propylene homopolymer. When a recycled material is used, the content of the propylene homopolymer (B1) in the expanded beads is the product obtained by multiplying the amount (blended amount) of the recycled material used by the content ratio of the propylene homopolymer (B1) in the recycled material. The propylene homopolymer (B1) may be a mixture of a recycled propylene homopolymer and a non-recycled propylene homopolymer.

[0049] From the viewpoint of reducing the environmental load, the proportion of propylene homopolymers derived from recycled materials (i.e., recycled propylene homopolymers) in 100% by weight of the propylene homopolymer (B1) is preferably 50% or more, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 100%. That is, it is particularly preferable that the propylene homopolymer (B1) is composed solely of recycled propylene homopolymers.

[0050] The propylene homopolymer (B1) may contain structural units derived from isoprene and structural units derived from conjugated dienes, but preferably does not contain any of them. The total content of structural units derived from isoprene and structural units derived from conjugated dienes in 100% by weight of the propylene homopolymer (B1) is preferably 20% by weight or less, more preferably 10% by weight or less, even more preferably 5% by weight or less, and most preferably 0% by weight.

[0051] The case where the resin particles contain multiple types of propylene homopolymers that differ in composition, physical properties, and / or origin (whether recycled or not, etc.) will be described. In this case, the mixture of all propylene homopolymers contained in the resin particles is regarded as "propylene homopolymer (B1)." Furthermore, the physical properties (e.g., melting point, MFR, etc.) of the mixture of all propylene homopolymers contained in the resin particles are regarded as the physical properties (e.g., melting point, MFR, etc.) of the propylene homopolymer (B1).

[0052] (Polypropylene Block Copolymer (B2)) The polypropylene block copolymer (B2) has, in addition to propylene units, one or more structural units derived from a monomer other than a propylene monomer. In other words, the polypropylene block copolymer (B2) contains at least propylene units and comonomer units. More specifically, the polypropylene block copolymer (B2) contains a propylene block composed of propylene units and a comonomer block composed of comonomer units. Specific examples of the comonomer units are the same as those explained above in the section (Polypropylene Random Copolymer (A)), and therefore, the explanation therefor is omitted here.

[0053] From the viewpoint of lowering the molding temperature, the polypropylene-based block copolymer (B2) preferably contains an ethylene unit as a comonomer unit, for example, the polypropylene-based block copolymer (B2) is preferably a propylene / ethylene block copolymer containing a propylene block composed of propylene units and an ethylene block composed of ethylene units.

[0054] The polypropylene-based block copolymer (B2) is not limited to a propylene / ethylene block copolymer. Examples of the polypropylene-based block copolymer (B2) other than a propylene / ethylene block copolymer include a propylene / 1-butene block copolymer, a propylene / ethylene / 1-butene block copolymer, a propylene / vinyl chloride block copolymer, and a propylene / maleic anhydride block copolymer.

[0055] The polypropylene-based block copolymer (B2) includes substances that are considered to be polypropylene-based block copolymers in the technical field of polypropylene-based resins. For example, a propylene / ethylene block copolymer includes a homopolypropylene matrix and a polyethylene layer covered with an ethylene / propylene elastic copolymer as a domain, and is sometimes called an impact copolymer.

[0056] The polypropylene-based block copolymer (B2) may be a combination of a propylene / ethylene block copolymer and one or more polypropylene-based block copolymers (B2) other than a propylene / ethylene block copolymer.

[0057] The melting point of the polypropylene-based block copolymer (B2) is not particularly limited, but is preferably from 150° C. to 167° C., and more preferably from 155° C. to 165° C. When the polypropylene-based block copolymer (B2) has a melting point of (i) 150° C. or higher, it has the effect of providing excellent heat resistance, and when it has a melting point of (ii) 167° C. or lower, it has the effect of providing excellent moldability.

[0058] In this specification, the MFR of the polypropylene block copolymer (B2) at 230°C and a load of 2160 g is not particularly limited, as long as the MFR of the polypropylene resin particles is 20.0 g / 10 min or more. The MFR of the polypropylene block copolymer (B2) at 230°C and a load of 2160 g is preferably 1 g / 10 min to 350 g / 10 min, more preferably 5 g / 10 min to 300 g / 10 min, more preferably 10 g / 10 min to 295 g / 10 min, and even more preferably 10 g / 10 min to 290 g / 10 min. When the MFR of the polypropylene block copolymer (B2) at 230°C and a load of 2160 g falls within the above range, it has the advantage of easily obtaining expanded beads having a relatively high expansion ratio. Furthermore, in this case, it also has the advantage that the surface beauty of the expanded molded articles obtained from the expanded beads is excellent and the shrinkage rate of the expanded molded articles is low.

[0059] When the resin particles contain a polypropylene block copolymer (B2), the ratio of the content of the polypropylene random copolymer (A) in the resin particles to the content of the polypropylene block copolymer (B2) (content (parts by weight) of the polypropylene random copolymer (A):content (parts by weight) of the polypropylene block copolymer (B2)) is preferably 90:10 to 40:60, more preferably 85:15 to 55:45, even more preferably 80:20 to 60:40, and particularly preferably 75:25 to 65:35. This configuration has the advantages of (i) being able to lower the foaming temperature and molding temperature, and (ii) the resulting foamed molded article having excellent heat resistance.

[0060] The polypropylene-based block copolymer (B2) may be a newly produced polypropylene-based block copolymer (non-recycled polypropylene-based block copolymer) produced by a known method, or a recycled polypropylene-based block copolymer derived from a recycled material. In other words, a recycled material containing a recycled polypropylene-based block copolymer may be used as the polypropylene-based block copolymer (B2). The polypropylene-based block copolymer (B2) may contain a recycled polypropylene-based block copolymer. When a recycled material is used, the content of the polypropylene-based block copolymer (B2) in the expanded beads is the product obtained by multiplying the amount (blended amount) of the recycled material used by the content ratio of the polypropylene-based block copolymer (B2) in the recycled material. The polypropylene-based block copolymer (B2) may be a mixture of a recycled polypropylene-based block copolymer and a non-recycled polypropylene-based block copolymer. The polypropylene-based block copolymer (B2) preferably contains a recycled polypropylene-based block copolymer derived from a recycled material. As described above, the circulation volume of polypropylene-based block copolymers as recycled polypropylene-based resins is greater than the circulation volume of polypropylene-based random copolymers. Therefore, recycled polypropylene-based block copolymer resins are relatively easy to obtain.

[0061] From the viewpoint of reducing the environmental load, the proportion of recycled polypropylene block copolymers derived from recycled materials (i.e., recycled polypropylene block copolymers) in 100% by weight of the polypropylene block copolymer (B2) is preferably 50% or more, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 100%. That is, it is particularly preferred that the polypropylene block copolymer (B2) is composed solely of recycled polypropylene block copolymers.

[0062] The polypropylene block copolymer (B2) may contain, but preferably does not contain, structural units derived from isoprene and structural units derived from conjugated dienes. In 100% by weight of the polypropylene block copolymer (B2), the total content of structural units derived from isoprene and structural units derived from conjugated dienes is preferably 20% by weight or less, more preferably 10% by weight or less, even more preferably 5% by weight or less, and most preferably 0% by weight.

[0063] The following describes a case where resin particles contain multiple polypropylene-based block copolymers with different compositions, physical properties, and / or origins (e.g., whether recycled or not). In this case, the mixture of all polypropylene-based block copolymers contained in the resin particles is considered to be the "polypropylene-based block copolymer (B2)." Furthermore, the physical properties (e.g., melting point, MFR, etc.) of the mixture of all polypropylene-based block copolymers contained in the resin particles are considered to be the physical properties (e.g., melting point, MFR, etc.) of the polypropylene-based block copolymer (B2).

[0064] At least one of the polypropylene random copolymer (A), the propylene homopolymer (B1), and the polypropylene block copolymer (B2) preferably contains a recycled resin derived from recycled materials. Using recycled resin not only reduces environmental pollution, but also significantly reduces the amount of plastic waste generated and the amount of plastic used in production. Therefore, embodiments using recycled resin as all or part of the resin have the advantage of contributing to the achievement of Sustainable Development Goals (SDGs), such as Goal 12 "Ensure sustainable consumption and production patterns" and Goal 14 "Conserve and sustainably use the oceans and marine resources for sustainable development."

[0065] (Mixture of Propylene Homopolymer (B1) and Polypropylene-Based Block Copolymer (B2)) The melting point of the mixture of the propylene homopolymer (B1) and the polypropylene-based block copolymer (B2) is not particularly limited, but is preferably 150° C. or higher and 167° C. or lower, and more preferably 155° C. to 167° C. When the melting point of the mixture of the propylene homopolymer (B1) and the polypropylene-based block copolymer (B2) is (i) 150° C. or higher, the effect of excellent heat resistance is obtained, and (ii) when it is 167° C. or lower, the effect of excellent moldability is obtained.

[0066] The MFR of the mixture of propylene homopolymer (B1) and polypropylene block copolymer (B2) at 230°C and a load of 2160 g is not particularly limited, as long as the MFR of the polypropylene resin particles is 20.0 g / 10 min or more. The MFR of the mixture of propylene homopolymer (B1) and polypropylene block copolymer (B2) at 230°C and a load of 2160 g is preferably 1 g / 10 min to 350 g / 10 min, more preferably 5 g / 10 min to 300 g / 10 min, more preferably 8 g / 10 min to 300 g / 10 min, and even more preferably 10 g / 10 min to 290 g / 10 min. If the MFR of the mixture of propylene homopolymer (B1) and polypropylene block copolymer (B2) at 230°C and a load of 2160 g is within the above range, it has the advantage of easily obtaining expanded particles having a relatively high expansion ratio. Furthermore, in this case, there are also advantages that the surface of the foamed molded article obtained from the present expanded beads is excellent and the shrinkage rate of the foamed molded article is small.

[0067] In one embodiment of the present invention, the resin particles may (i) contain a propylene homopolymer (B1) and not contain a polypropylene-based block copolymer (B2), (ii) contain a polypropylene-based block copolymer (B2) and not contain a propylene homopolymer (B1), or (iii) contain both a propylene homopolymer (B1) and a polypropylene-based block copolymer (B2). Therefore, the "melting point and MFR of the mixture of the propylene homopolymer (B1) and the polypropylene-based block copolymer (B2)" respectively mean (i) the melting point and MFR of the propylene homopolymer (B1) when the resin particles contain the propylene homopolymer (B1) but not the polypropylene-based block copolymer (B2), (ii) the melting point and MFR of the polypropylene-based block copolymer (B2) when the resin particles contain the polypropylene-based block copolymer (B2) but not the propylene homopolymer (B1), and (iii) the melting point and MFR of the mixture of the propylene homopolymer (B1) and the polypropylene-based block copolymer (B2) when the resin particles contain both the propylene homopolymer (B1) and the polypropylene-based block copolymer (B2).

[0068] In the resin particles, it is preferred that, based on a total of 100 parts by weight of the polypropylene random copolymer (A), the propylene homopolymer (B1), and the polypropylene block copolymer (B2), (a) the content of the polypropylene random copolymer (A) is 45 to 95 parts by weight, and the total content of the propylene homopolymer (B1) and the polypropylene block copolymer (B2) is 5 to 55 parts by weight; (b) the content of the polypropylene random copolymer (A) is 50 to 90 parts by weight, and the total content of the propylene homopolymer (B1) and the polypropylene block copolymer (B2) is 10 to 50 parts by weight; and (c) the content of the polypropylene random copolymer (A) is 70 to 80 parts by weight, and the total content of the propylene homopolymer (B1) and the polypropylene block copolymer (B2) is 20 to 30 parts by weight. When the contents of the polypropylene random copolymer (A), propylene homopolymer (B1), and polypropylene block copolymer (B2) contained in the resin particles are within the above-mentioned ranges, the expanded beads have the advantage of being superior in productivity for producing polypropylene resin foamed molded articles. The term "total content of propylene homopolymer (B1) and polypropylene block copolymer (B2)" refers to (i) the content of propylene homopolymer (B1) when the resin particles contain propylene homopolymer (B1) but not polypropylene block copolymer (B2), (ii) the content of polypropylene block copolymer (B2) when the resin particles contain polypropylene block copolymer (B2) but not propylene homopolymer (B1), and (iii) the total content of propylene homopolymer (B1) and polypropylene block copolymer (B2) when the resin particles contain both propylene homopolymer (B1) and polypropylene block copolymer (B2).

[0069] The resin particles may further contain, as a resin component, a resin other than the polypropylene random copolymer (A), the propylene homopolymer (B1), and the polypropylene block copolymer (B2) (sometimes referred to as "other resins, etc.") to the extent that the effects of one embodiment of the present invention are not impaired. Examples of the other resins include: (a) polypropylene resins other than polypropylene random copolymers, propylene homopolymers, and polypropylene block copolymers; (b) ethylene resins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear very low-density polyethylene, ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, and ethylene / methacrylic acid copolymer; (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. The content of other resins in the resin particles is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, per 100 parts by weight of the total of the polypropylene random copolymer (A), the propylene homopolymer (B1), and the polypropylene block copolymer (B2).

[0070] (Additives) In addition to the resin components described above, the resin particles may further contain optional additives. Examples of the additives include colorants, water-absorbing substances (e.g., (i) polyols such as glycerin and diglycerin, (ii) polyethers such as polyethylene glycol and polyethylene oxide, and (iii) metal borates such as borax and zinc borate), foam nucleating agents (e.g., inorganic substances such as talc, calcium carbonate, silica, kaolin, barium sulfate, calcium hydroxide, aluminum hydroxide, aluminum oxide, and titanium oxide), antistatic agents (e.g., glycerin monostearate, glycerin monodistearate), and flame retardants (e.g., hydroxybenzoates). Examples of suitable additives include hindered amine flame retardants, bromine flame retardants, phosphate ester flame retardants, and melamine flame retardants, antioxidants (e.g., hindered phenol antioxidants), heat stabilizers (e.g., phosphorus-based heat stabilizers and sulfur-based heat stabilizers), light stabilizers (e.g., benzotriazole UV absorbers, triazine UV absorbers, HALS and / or hindered amine light stabilizers), nucleating agents, conductive agents (e.g., carbon, carbon nanotubes, and metal fillers), lubricants, acid scavengers, antiblocking agents, metal chelating agents (e.g., IRGANOX® MD1024 and ADK STAB® CDA-1), lubricants, antibacterial agents, organic peroxides, and MFR adjusters. The resin particles may also contain an additive for recycled materials containing any one or a combination of two or more of these additives. A "metal chelating agent" is sometimes referred to as a "metal deactivator." Such additives may be added directly to the mixed resin or polypropylene resin composition described below in the production of polypropylene resin particles.

[0071] Examples of colorants include chromatic pigments and carbon black. Chromatic pigments include (i) blue pigments such as copper phthalocyanine blue, ultramarine, cobalt blue, and Prussian blue; (ii) red pigments such as perylene red, quinacridone red, and cadmium red; (iii) yellow pigments such as condensed azo yellow, cadmium yellow, and barium chromate; (iv) green pigments obtained by blending blue and yellow pigments; (v) orange pigments obtained by blending red and yellow pigments; and (vi) purple pigments such as cobalt violet and pigments obtained by blending blue and red pigments. The resin particles may contain carbon black.

[0072] <Physical Properties> The physical properties of the present resin particles and the present expanded particles will be described below.

[0073] (MFR of polypropylene-based resin particles) The MFR of the polypropylene-based resin particles at 230°C and a load of 2160 g is 20.0 g / 10 min or more, preferably 20.0 g / 10 min or more and 150.0 g / 10 min or less, more preferably 23.0 g / 10 min or more and 100.0 g / 10 min or less, and even more preferably 23.0 g / 10 min or more and 50.0 g / 10 min or less. This configuration has the advantage that the expanded beads can provide a foamed molded article in a short molding cycle. This configuration also has the advantage that a foamed molded article having excellent internal fusion properties and / or surface beauty can be provided.

[0074] (Heat ratio of melting peak on the high-temperature side of polypropylene-based resin particles) When the resin particles contain a propylene homopolymer (B1), the polypropylene-based resin particles have (ii-1) only one melting peak or (ii-2) two or more melting peaks in a DSC curve obtained by measurement using a differential scanning calorimeter. When the resin particles contain a propylene homopolymer (B1) and have two or more melting peaks in a DSC curve obtained by measurement using a differential scanning calorimeter, the heat ratio of the melting peak on the high-temperature side of 100% of the total heat of fusion is preferably 95% or more but less than 100%, more preferably 96% or more but 99%. This configuration has the advantage that internal fusion properties are easily improved due to the influence of a low-melting point resin component (for example, a polypropylene-based random copolymer having a melting point of 160°C or less, such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear very low-density polyethylene, etc.). The method for measuring the calorific value ratio of the melting peak on the high temperature side of the resin particles will be described in detail in the examples below.

[0075] (DSC Ratio of Expanded Polypropylene Resin Beads) The expanded beads preferably have at least two melting peaks in a DSC curve obtained by differential scanning calorimetry (DSC) described below. The heat of fusion determined from the higher-temperature peak among the melting peaks is referred to as the "high-temperature heat of fusion (Q ｈ ) and the heat of fusion calculated from the melting peak on the low temperature side is called the "low temperature heat of fusion (Q ｌ In addition, when there are three or more melting peaks, the heat of fusion calculated from the highest melting peak is called the "high-temperature heat of fusion (Q ｈ ) and the heat of fusion calculated from the other melting peaks is called the "low-temperature heat of fusion (Q ｌ The ratio of the heat of fusion on the higher temperature side to the total heat of fusion is also called the "DSC ratio." The DSC ratio can be calculated using the following formula: DSC ratio (%) = Q ｈ / (Q ｌ +Q ｈ ) x 100.

[0076] The DSC ratio of the expanded beads is not particularly limited. The DSC ratio of the expanded beads is preferably 10.0% to 50.0%, more preferably 15.0% to 45.0%, even more preferably 20.0% to 40.0%, and particularly preferably 30.0% to 40.0%. When the DSC ratio of the expanded beads is 10.0% or more, the expanded beads 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 expanded beads is 50% or less, the expanded beads have the advantage of being able to be molded at a relatively low temperature (molding temperature) to provide a foamed molded article. The method for measuring the DSC ratio of the expanded beads will be described in detail in the Examples below.

[0077] The DSC ratio of the expanded beads is also a measure of the amount of high-melting-point crystals contained in the expanded beads. That is, a DSC ratio of 10.0% to 50.0% indicates that the expanded beads contain a relatively large amount of high-melting-point crystals. Furthermore, the DSC ratio of the expanded beads is significantly related to the viscoelasticity of the resin beads and the expanded beads when they are foamed and expanded. That is, when the DSC ratio of the expanded beads is 10.0% to 50.0%, the resin beads and the expanded beads can exhibit excellent foamability and expansion properties, respectively, when they are foamed and when they are molded. As a result, the expanded beads have the advantage that they can produce foamed molded articles with excellent internal fusion properties and excellent mechanical strength, such as compressive strength, even at low molding pressures.

[0078] In the present expanded beads, examples of a method for controlling the DSC ratio within a predetermined range include a method for adjusting the conditions during production of the present expanded beads (particularly, the foaming temperature, foaming pressure, holding time, and the temperature of the region (space) from which the dispersion is released, etc.) In terms of ease of adjustment, a method for controlling the DSC ratio within a predetermined range by adjusting the foaming temperature, foaming pressure, and / or holding time is preferred.

[0079] For example, increasing the foaming temperature tends to decrease the DSC ratio, while decreasing the foaming temperature tends to increase the DSC ratio. This is because the amount of unmelted crystals varies depending on the foaming temperature. Increasing the foaming pressure also tends to decrease the DSC ratio, while decreasing the foaming pressure also tends to increase the DSC ratio. This is because the degree of plasticization varies depending on the foaming pressure, thereby changing the amount of unmelted crystals. In addition, the DSC ratio tends to increase as the holding time increases. This is because the amount of growth of unmelted crystals varies depending on the holding time.

[0080] (Expansion Ratio of Expanded Polypropylene Resin Beads) The expanded beads preferably have an expansion ratio of 10 to 50, more preferably 18 to 40, and even more preferably 18 to 30. If the expansion ratio of the expanded beads is (i) 10 or more, a lightweight expanded molded article can be obtained efficiently, and if (ii) 50 or less, there is no risk of the strength of the resulting expanded molded article being insufficient. The method for calculating the expansion ratio of the expanded beads will be described in detail in the Examples below.

[0081] (Average Cell Diameter of Expanded Polypropylene Resin Beads) The average cell diameter of the expanded beads is not particularly limited. The average cell diameter of the expanded beads is preferably 80 μm to 500 μm, more preferably 85 μm to 400 μm, even more preferably 90 μm to 300 μm, and particularly preferably 95 μm to 250 μm. When the average cell diameter of the expanded beads is (i) 80 μm or more, the expanded beads can provide a polypropylene resin foam molded article having excellent compressive strength, and (ii) when the average cell diameter is 500 μm or less, there is no risk of the molding cycle becoming longer, which has the advantage of improving productivity. The method for measuring the average cell diameter of the expanded beads will be described in detail in the Examples below.

[0082] The expanded polypropylene resin beads according to one embodiment of the present invention may have the following configuration: Expanded polypropylene resin beads obtained by expanding polypropylene resin particles, wherein the polypropylene resin particles have a melt flow rate (MFR) of 20.0 g / 10 min or more at 230°C under a load of 2160 g, and the polypropylene resin particles contain a polypropylene random copolymer (A), and the expanded polypropylene resin beads satisfy at least one of the following (a) or (b): (a) the polypropylene resin particles further contain a propylene homopolymer (B1), and (i) in the polypropylene resin particles, the content of the propylene homopolymer (B1) is less than 95 parts by weight based on 100 parts by weight of the total of the polypropylene random copolymer (A) and the propylene homopolymer (B1), and (ii) The polypropylene-based resin particles have, in a DSC curve obtained by measurement using a differential scanning calorimeter, (ii-1) only one melting peak or (ii-2) two or more melting peaks, and the heat ratio of the melting peak on the highest temperature side to the total heat of fusion (100%) is 95% or more but less than 100%; (b) The polypropylene-based resin particles further contain a polypropylene-based block copolymer (B2).

[0083] [3. Method for producing expanded polypropylene-based resin beads] A method for producing expanded polypropylene-based resin beads according to one embodiment of the present invention comprises an extrusion step of melt-kneading a mixed resin containing a polypropylene-based random copolymer (A) and a propylene homopolymer (B1) and / or a polypropylene-based block copolymer (B2) to obtain polypropylene-based resin beads, and an expansion step of expanding the polypropylene-based resin beads obtained in the extrusion step, wherein the polypropylene-based resin beads have a melt flow rate (MFR) of 20.0 g / 10 min or more at 230°C under a load of 2160 g, and the mixed resin is When the polypropylene homopolymer (B1) is contained, (i) in the mixed resin, the amount of the propylene homopolymer (B1) is less than 95 parts by weight per 100 parts by weight of the total of the polypropylene random copolymer (A) and the propylene homopolymer (B1), and (ii) the polypropylene resin particles have, in a DSC curve obtained by measurement by a differential scanning calorimeter, (ii-1) only one melting peak or (ii-2) two or more melting peaks, and the heat ratio of the melting peak on the highest temperature side is 95% or more and less than 100% of the total heat of fusion (100%).

[0084] Because the present production method includes the above-described configuration, it has the advantage of being able to provide expanded beads that can provide expanded molded articles in a short molding cycle. Furthermore, because the present production method includes the above-described configuration, it has the advantage of being able to provide expanded beads that can provide expanded molded articles with excellent internal fusion properties and / or surface aesthetics. Furthermore, because the present production method includes the above-described configuration, it is possible to provide expanded beads that can provide expanded molded articles with excellent internal fusion properties and / or surface aesthetics using a smaller amount of steam than conventional methods, despite the use of a propylene homopolymer (B1) and / or a polypropylene-based block copolymer (B2). That is, because the present production method includes the above-described configuration, it also has the advantage of low energy consumption (energy saving).

[0085] (Extrusion Step) In the extrusion step, a mixed resin containing the polypropylene random copolymer (A) and the propylene homopolymer (B1) and / or the polypropylene block copolymer (B2) is melt-kneaded.

[0086] The specific embodiment of the extrusion step is not particularly limited. For example, a method for obtaining resin particles can be a method using an extruder. Specifically, for example, resin particles can be produced by the following methods (1) to (5): (1) blending a polypropylene random copolymer (A), a propylene homopolymer (B1), and / or a polypropylene block copolymer (B2), and, if necessary, one or more selected from the group consisting of other resins and additives to produce a mixed resin; (2) feeding the mixed resin into an extruder and melt-kneading the mixed resin to prepare a polypropylene resin composition; (3) extruding the polypropylene resin composition through a die equipped in the extruder; (4) solidifying the extruded polypropylene resin composition by cooling it, for example, by passing it through water; (5) then cutting the solidified polypropylene resin composition into desired shapes such as a cylindrical, elliptical, spherical, cubic, rectangular, hollow cylinder, polygonal prism, etc., using a cutter. Alternatively, in (3), the melt-kneaded polypropylene resin composition may be directly extruded into water through a die provided in an extruder, and immediately after extrusion, the polypropylene resin composition may be cut into particles, cooled, and solidified. By melt-kneading the mixed resin in this manner, more uniform resin particles can be obtained.

[0087] The weight per particle of the resin particles obtained as described above is preferably 0.2 mg / particle to 10.0 mg / particle, 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 handleability of the resin particles tends to be improved and the shrinkage rate of the foamed molded article obtained by molding the obtained foamed beads tends to be small. When the weight per particle of the resin particles is (b) 10.0 mg / particle or less, the mold filling property in the in-mold foam molding step tends to be improved.

[0088] In the present production method, it is preferable that (i) the extrusion step includes a peroxide treatment step of treating the mixed resin with a peroxide, or (ii) the extrusion step includes a peroxide treatment step of treating the propylene homopolymer (B1) and / or the polypropylene-based block copolymer (B2) with a peroxide prior to the extrusion step. Herein, for convenience, the peroxide treatment step included in the extrusion step may be referred to as the "peroxide treatment step A," and the peroxide treatment step included prior to the extrusion step may be referred to as the "peroxide treatment step B." The present production method may include a peroxide treatment step A of treating the propylene homopolymer (B1) and / or the polypropylene-based block copolymer (B2) with a peroxide prior to the extrusion step, and the extrusion step may include a peroxide treatment step B of treating the mixed resin with a peroxide.

[0089] In this production method, a case where the extrusion step includes a peroxide treatment step A in which the mixed resin is treated with a peroxide (hereinafter also referred to as "Case A") will be described. In Case A, for example, the mixed resin to which an organic peroxide has been added can be treated with a peroxide by melt-kneading the mixed resin in an extruder. By carrying out such peroxide treatment step A, polypropylene-based resin particles having an MFR of 20.0 g / 10 min or more at 230°C and a load of 2160 g can be obtained. In other words, a specific embodiment of the peroxide treatment step A in Case A is preferably such that the resulting resin particles have an MFR of 20.0 g / 10 min or more at 230°C and a load of 2160 g.

[0090] In the peroxide treatment step A of Case A, the amount of peroxide used is preferably 0.01 to 1.00 parts by weight, more preferably 0.05 to 0.50 parts by weight, even more preferably 0.10 to 0.40 parts by weight, and particularly preferably 0.10 to 0.30 parts by weight, relative to 100 parts by weight of the mixed resin.

[0091]

[0033] The present production method will be described below with reference to a case where the method includes a peroxide treatment step B in which the propylene homopolymer (B1) and / or polypropylene block copolymer (B2) is treated with a peroxide prior to the extrusion step (hereinafter also referred to as "Case B"). In Case B, the peroxide treatment step B in which the propylene homopolymer (B1) and / or polypropylene block copolymer (B2) is treated with a peroxide is carried out prior to the extrusion step, specifically, prior to preparing a mixed resin containing the polypropylene random copolymer (A) and the propylene homopolymer (B1) and / or polypropylene block copolymer (B2). In Case B, for example, the propylene homopolymer (B1) and / or polypropylene block copolymer (B2) can be treated with a peroxide by melt-kneading a mixture of an organic peroxide and the propylene homopolymer (B1) and / or polypropylene block copolymer (B2) in an extruder. By carrying out the peroxide treatment step B, polypropylene resin particles having an MFR of 20.0 g / 10 min or more at 230° C. and a load of 2160 g can be obtained in Case B. In other words, a specific embodiment of the peroxide treatment step B in Case B is preferably an embodiment in which the obtained resin particles have an MFR of 20.0 g / 10 min or more at 230° C. and a load of 2160 g. In the case of Case B, when both the propylene homopolymer (B1) and the polypropylene block copolymer (B2) are used, (i) only the propylene homopolymer (B1) may be treated with a peroxide without treating the polypropylene block copolymer (B2) with a peroxide, (ii) only the polypropylene block copolymer (B2) may be treated with a peroxide without treating the propylene homopolymer (B1) with a peroxide, or (iii) both the propylene homopolymer (B1) and the polypropylene block copolymer (B2) may be treated with a peroxide, so that the MFR of the resulting resin particles at 230°C and a load of 2,160 g is 20.0 g / 10 min or more.

[0092] In the peroxide treatment step B of Case B, the amount of peroxide used is preferably 0.01 to 1.00 parts by weight, more preferably 0.05 to 0.50 parts by weight, and even more preferably 0.10 to 0.40 parts by weight, per 100 parts by weight of the propylene homopolymer (B1) and / or the polypropylene block copolymer (B2) in total.

[0093] Examples of peroxides that can be used in the peroxide treatment step A and the peroxide treatment step B include 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, t-butylperoxylaurate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxybenzoate, dicumyl peroxide, 1,3-bis(t-butylperoxyisopropyl)benzene, t-butylperoxyisopropyl monocarbonate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 1,1-di(t-butylperoxy)cyclohexane, n-butyl-4,4-di(t-butylperoxy)valerate, α,α'-di(t-butylperoxy)diisopropylbenzene, and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3.

[0094] (Foaming step) The foaming step in the present production method is not particularly limited, but may include, for example, an embodiment having: (i) a dispersing step of dispersing polypropylene-based resin particles, an aqueous dispersion medium, and a foaming agent in a container to obtain a dispersion, (ii) a heating step of heating the dispersion to a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles, (iii) a pressurizing step of increasing the pressure in the container, and (iv) a releasing step of opening one end of the container and releasing the dispersion in the container into a region with a pressure lower than the pressure in the container. Hereinafter, an example of the foaming step will be described using an example in which the foaming step includes the dispersing step, the heating step, the pressurizing step, and the releasing step.

[0095] (Dispersion step) The container used in the dispersion step is not particularly limited. Examples of the container include a pressure-resistant container and an autoclave-type pressure-resistant container (pressure-resistant autoclave). The container may be equipped with a stirrer inside the container.

[0096] The aqueous dispersion medium is not particularly limited as long as it contains water. In terms of enabling stable production of expanded beads, it is preferable to use pure water such as RO water (water purified by a reverse osmosis membrane method), distilled water, deionized water (water purified by an ion exchange resin), or ultrapure water as the aqueous dispersion medium.

[0097] Examples of blowing agents include (a) (a-1) inorganic blowing agents such as inorganic gases such as nitrogen, carbon dioxide, and air (a mixture of oxygen, nitrogen, and carbon dioxide), and (a-2) water; and (b) organic blowing agents. From the viewpoint of reducing the environmental load and reducing the risk of combustion, the blowing agent is preferably an inorganic blowing agent, more preferably an inorganic gas and / or water, and even more preferably carbon dioxide and / or water. The water used as the aqueous dispersion medium can also be used as the blowing agent. In this case, both the aqueous dispersion medium and the blowing agent in the dispersion step can be water.

[0098] In this production method, it is preferable to use a dispersant (e.g., inorganic dispersant such as tricalcium phosphate, trimagnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, clay, etc.) and a dispersing aid (e.g., sodium dodecylbenzenesulfonate, sodium alkanesulfonate, sodium alkylsulfonate, sodium alkyldiphenyletherdisulfonate, sodium α-olefinsulfonate, etc.). This configuration can reduce adhesion of resin particles (sometimes referred to as blocking) and improve the stability of the dispersion in the container. As a result, it has the advantage of enabling stable production of expanded beads.

[0099] (Heating step) In this specification, the "softening temperature of the polypropylene-based resin particles" means the melting point of the resin with the highest melting point among the non-recycled polypropylene-based resin contained in the base resin constituting the polypropylene-based resin particles and the resin components contained in the recycled material, minus 10°C.

[0100] In this specification, "a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles" may be referred to as "foaming temperature." In other words, the heating step can be said to be a step of heating the temperature of the dispersion to the foaming temperature. The foaming temperature in the heating step is not particularly limited as long as it is equal to or higher than the softening temperature of the polypropylene-based resin particles. In the heating step, the temperature to which the dispersion is heated, i.e., the upper limit of the foaming temperature, is not particularly limited. The foaming temperature is preferably equal to or lower than the softening temperature of the polypropylene-based resin particles + 20.0°C, more preferably equal to or lower than the softening temperature of the polypropylene-based resin particles + 15.0°C, and even more preferably equal to or lower than the softening temperature of the polypropylene-based resin particles + 10.0°C. This configuration has the advantage that there is no risk of the polypropylene-based resin particles adhering to each other in the container.

[0101] (Pressurizing Step) In this specification, the pressure (constant pressure) after being pressurized in the pressurizing step may be referred to as the “foaming pressure.” In other words, in the pressurizing step, the pressure inside the container is increased to the foaming pressure.

[0102] In the pressurizing step, the pressure inside the container, i.e., the expansion pressure, is not particularly limited. The expansion pressure in the pressurizing step is preferably (i) 1.0 MPa (gauge pressure) to 10.0 MPa (gauge pressure), more preferably (ii) 1.5 MPa (gauge pressure) to 5.0 MPa (gauge pressure), and even more preferably (iii) 1.5 MPa (gauge pressure) to 3.5 MPa (gauge pressure). When the expansion pressure is 1.0 MPa (gauge pressure) or more, expanded beads with a suitable density can be obtained.

[0103] The heating step and the pressure applying step may be carried out in any order, or may be carried out simultaneously.

[0104] (Holding Step) The present production method may further include a holding step, after the heating step and the pressurizing step and before the releasing step, of holding the temperature inside the container at the foaming temperature and the pressure inside the container at (or near) the foaming pressure.

[0105] In the holding step, the time (holding time) for holding the temperature of the dispersion at the foaming temperature and the pressure inside the container at (near) the foaming pressure 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. A holding time of 10 minutes or longer has the advantage that a sufficient amount of unmelted crystals (crystals of the base resin) are present, thereby reducing shrinkage and / or an increase in the open cell ratio of the resulting expanded beads. On the other hand, a holding time of 60 minutes or shorter has the advantage that an excessive amount of unmelted crystals are not present, allowing the expanded beads to be molded at a low molding temperature.

[0106] (Releasing Step) The releasing step can be carried out (a) after the heating step and the pressurizing step when the holding step is not carried out, or (b) after the holding step when the holding step is carried out. The releasing step can expand the resin particles, resulting in expanded particles.

[0107] In the releasing step, the "region under a pressure lower than the pressure inside the container" refers to a "region under a pressure lower than the pressure inside the container" or a "space under a pressure lower than the pressure inside the container", and can also be referred to as "an atmosphere under a pressure lower than the pressure inside the container". The region under a pressure lower than the pressure inside the container can also be referred to as a region under a pressure lower than the foaming pressure, and may be, for example, a region under atmospheric pressure. The low-pressure region is, for example, a gas phase. Furthermore, in order to improve foaming properties, the low-pressure region (space) may be filled with saturated water vapor.

[0108] In the discharging step, when the dispersion is discharged into a region having a pressure lower than the pressure inside the container, the dispersion can also be discharged through an orifice having a diameter of 1 mm to 5 mm for the purposes of adjusting the flow rate of the dispersion and reducing variation in the expansion ratio of the resulting expanded beads.

[0109] As described above, the process of producing expanded beads from resin beads is called the "first-stage expansion process," and the resulting expanded beads are called "first-stage expanded beads." In order to obtain expanded beads with a high expansion ratio, the first-stage expanded beads obtained in the first-stage expansion process may be expanded again. The process of increasing the expansion ratio of the first-stage expanded beads is called the "second-stage expansion process," and the polypropylene resin expanded beads obtained by the second-stage expansion process are called "second-stage expanded beads." The specific method for the second-stage expansion process is not particularly limited, and any known method can be used.

[0110] [4. Polypropylene-based resin foam molded article] A polypropylene-based resin foam molded article according to one embodiment of the present invention is a foam molded article obtained by molding the polypropylene-based resin foam beads described in Section [2. Polypropylene-based resin foam beads]. The polypropylene-based resin foam molded article according to one embodiment of the present invention may be a foam molded article obtained by molding the polypropylene-based resin foam beads obtained by the production method described in Section [3. Production method for polypropylene-based resin foam beads]. It can also be said that the polypropylene-based resin foam molded article according to one embodiment of the present invention comprises the polypropylene-based resin foam beads described in Section [2. Polypropylene-based resin foam beads] or the polypropylene-based resin foam beads obtained by the production method described in Section [3. Production method for polypropylene-based resin foam beads].

[0111] In this specification, the "polypropylene resin foam molded article according to one embodiment of the present invention" may be referred to as the "present foam molded article."

[0112] The foamed molded article of the present invention has the above-mentioned structure and therefore has the advantage of excellent internal fusion and / or surface beauty.

[0113] (Internal fusion property) In this specification, the internal fusion property of the present foamed molded article is evaluated by the number of all foamed beads present and the number of foamed beads broken at places other than the particle interfaces on the fracture surface of the foamed molded article. The higher the number of foamed beads broken at places other than the particle interfaces among all foamed beads present, in other words, the higher the internal fusion rate, the better the internal fusion property.

[0114] The internal fusion rate of the foamed molded article is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more.

[0115] (Surface aesthetics) In this specification, the surface aesthetics of the present foamed molded article is evaluated based on the degree of gaps between the foam particles (hereinafter sometimes referred to as "intergranular gaps") on the surface of the foamed molded article and the wrinkles on the surface of the foamed molded article. The smaller the size and number of intergranular gaps on the surface of the foamed molded article, the better the surface aesthetics of the foamed molded article. Furthermore, the fewer wrinkles on the surface of the foamed molded article, the better the surface aesthetics of the foamed molded article.

[0116] (Molding cycle) In this specification, the length of the molding cycle of the present foam molded article is evaluated by the time (seconds) until the cooling (water cooling) of the molded article is completed. The time when the cooling (water cooling) of the molded article is completed is the time when the mold is opened and demolding is completed when the surface pressure measured by a surface pressure gauge attached to the surface of the Planck mold has dropped to 0.01 MPa (gauge pressure). The time for the cooling process alone, excluding the time for the heating process, is preferably 0 to 150 seconds, more preferably 0 to 110 seconds.

[0117] An embodiment of the present invention may have the following configuration.

[0118] [1] Expanded polypropylene resin particles obtained by expanding polypropylene resin particles, wherein the polypropylene resin particles contain a polypropylene random copolymer (A) and a propylene homopolymer (B1) and / or a polypropylene block copolymer (B2), and the polypropylene resin particles have a melt flow rate (MFR) of 20.0 g / 10 min or more at 230°C under a load of 2160 g, and when the polypropylene resin particles contain the propylene homopolymer (B1), (i) in the polypropylene resin particles, the content of the propylene homopolymer (B1) is less than 95 parts by weight per 100 parts by weight of the total of the polypropylene random copolymer (A) and the propylene homopolymer (B1), and (ii) The polypropylene resin particles are expanded polypropylene resin particles, which have (ii-1) only one melting peak or (ii-2) two or more melting peaks in a DSC curve obtained by measurement using a differential scanning calorimeter, and the heat ratio of the melting peak on the highest temperature side to the total heat of fusion (100%) is 95% or more but less than 100%.

[0119] [2] The expanded polypropylene resin particles according to [1], wherein the polypropylene resin particles contain the propylene homopolymer (B1), and the ratio of the content of the polypropylene random copolymer (A) to the content of the propylene homopolymer (B1) in the polypropylene resin particles (content of the polypropylene random copolymer (A):content of the propylene homopolymer (B1)) is 90:10 to 50:50.

[0120] [3] The expanded polypropylene resin particles according to [1] or [2], wherein the polypropylene resin particles contain the polypropylene block copolymer (B2), and the ratio of the polypropylene random copolymer (A) to the polypropylene block copolymer (B2) in the polypropylene resin particles (content of the polypropylene random copolymer (A):content of the polypropylene block copolymer (B2)) is 90:10 to 40:60.

[0121] [4] The expanded polypropylene resin particles according to any one of [1] to [3], wherein at least one of the polypropylene random copolymer (A), the propylene homopolymer (B1), and the polypropylene block copolymer (B2) contains a recycled resin.

[0122] [5] The expanded polypropylene resin particles according to any one of [1] to [4], wherein, in the polypropylene resin particles, the content of the polypropylene random copolymer (A) is 45 to 95 parts by weight, and the total content of the propylene homopolymer (B1) and the polypropylene block copolymer (B2) is 5 to 55 parts by weight, based on 100 parts by weight of the polypropylene random copolymer (A), the propylene homopolymer (B1), and the polypropylene block copolymer (B2).

[0123] [6] The expanded polypropylene resin particles according to any one of [1] to [5], wherein when the polypropylene resin particles contain the polypropylene block copolymer (B2), the polypropylene resin particles have, in a DSC curve obtained by measurement with a differential scanning calorimeter, (i) only one melting peak, or (ii) two or more melting peaks, and the heat ratio of the melting peak on the highest temperature side to the total heat of fusion (100%) is 95% or more but less than 100%.

[0124] [7] The expanded polypropylene resin particles according to any one of [1] to [6], wherein the polypropylene random copolymer (A) is at least one selected from the group consisting of a propylene / ethylene random copolymer, a propylene / 1-butene random copolymer, a propylene / ethylene / 1-butene random copolymer, a propylene / vinyl chloride random copolymer, and a propylene / maleic anhydride random copolymer.

[0125] [8] The expanded polypropylene resin particles according to any one of [1] to [7], wherein the melting point of the polypropylene random copolymer (A) is 130°C to 160°C.

[0126] [9] The polypropylene-based random copolymer (A) has a melt flow rate of 3.0 g / 10 min to 30.0 g / 10 min at 230°C under a load of 2160 g.

[10] The expanded polypropylene-based resin particles according to any one of [1] to [8].

[0127]

[10] The expanded polypropylene resin particles according to any one of [1] to [9], wherein the polypropylene random copolymer (A) includes a recycled polypropylene random copolymer.

[0128]

[11] The expanded polypropylene resin particles according to

[10] , wherein the proportion of the recycled polypropylene random copolymer in 100% by weight of the polypropylene random copolymer (A) is 50% or more.

[0129]

[12] The expanded polypropylene resin particles according to any one of [1] to

[11] , wherein the melting point of the propylene homopolymer (B1) is 150.0°C or higher and lower than 167.0°C.

[0130]

[13] The expanded polypropylene resin particles according to any one of [1] to

[12] , wherein the propylene homopolymer (B1) has a melt flow rate of 1 g / 10 min to 350 g / 10 min at 230°C under a load of 2160 g.

[0131]

[14] The expanded polypropylene resin particles according to any one of [1] to

[13] , wherein the propylene homopolymer (B1) includes a recycled propylene homopolymer.

[0132]

[15] The expanded polypropylene resin particles according to

[14] , wherein the proportion of the recycled propylene homopolymer in 100% by weight of the propylene homopolymer (B1) is 50% or more.

[0133]

[16] The expanded polypropylene resin particles according to any one of [1] to

[15] , wherein the total content of structural units derived from isoprene and structural units derived from conjugated dienes is 20% by weight or less, based on 100% by weight of the propylene homopolymer (B1).

[0134]

[17] The expanded polypropylene resin particles according to any one of [1] to

[16] , wherein the polypropylene block copolymer (B2) is at least one selected from the group consisting of a propylene / ethylene block copolymer, a propylene / 1-butene block copolymer, a propylene / ethylene / 1-butene block copolymer, a propylene / vinyl chloride block copolymer, and a propylene / maleic anhydride block copolymer.

[0135]

[18] The expanded polypropylene resin particles according to any one of [1] to

[17] , wherein the melting point of the polypropylene block copolymer (B2) is 150.0°C or higher and 167.0°C or lower.

[0136]

[19] The expanded polypropylene resin particles according to any one of [1] to

[18] , wherein the polypropylene block copolymer (B2) has a melt flow rate of 1 g / 10 min to 350 g / 10 min at 230°C under a load of 2160 g.

[0137]

[20] The expanded polypropylene resin particles according to any one of [1] to

[19] , wherein the polypropylene block copolymer (B2) includes a recycled polypropylene block copolymer.

[0138]

[21] The expanded polypropylene resin particles according to

[20] , wherein the proportion of the recycled polypropylene block copolymer in 100% by weight of the polypropylene block copolymer (B2) is 50% or more.

[0139]

[22] The expanded polypropylene resin particles according to any one of [1] to

[21] , wherein the total content of structural units derived from isoprene and structural units derived from conjugated dienes is 20% by weight or less in 100% by weight of the polypropylene block copolymer (B2).

[0140]

[23] The expanded polypropylene resin particles according to any one of [1] to

[22] , wherein the melting point of the mixture of the propylene homopolymer (B1) and the polypropylene block copolymer (B2) is 150.0°C or higher and 167.0°C or lower.

[0141]

[24] The expanded polypropylene resin particles according to any one of [1] to

[23] , wherein the melt flow rate of the mixture of the propylene homopolymer (B1) and the polypropylene block copolymer (B2) at 230°C under a load of 2160 g is 1 g / 10 min to 350 g / 10 min.

[0142]

[25] The expanded polypropylene resin particles according to any one of [1] to

[24] , wherein the polypropylene resin particles contain carbon black.

[0143]

[26] The expanded polypropylene resin particles according to any one of [1] to

[25] , wherein the expansion ratio is 10 to 50 times.

[0144]

[27] The expanded polypropylene resin particles according to any one of [1] to

[26] , wherein the average cell diameter is 80 μm to 500 μm.

[0145]

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

[27] .

[0146]

[29] The polypropylene resin foam molded article according to

[26] , wherein the internal fusion rate is 60% or more.

[0147]

[30] A method for producing polypropylene-based resin particles, comprising: an extrusion step of melt-kneading a mixed resin containing a polypropylene-based random copolymer (A) and a propylene homopolymer (B1) and / or a polypropylene-based block copolymer (B2) to obtain polypropylene-based resin particles; and an expansion step of expanding the polypropylene-based resin particles obtained in the extrusion step, wherein the polypropylene-based resin particles have a melt flow rate (MFR) of 20.0 g / 10 min or more at 230°C under a load of 2160 g, and when the mixed resin contains the propylene homopolymer (B1), (i) in the mixed resin, the propylene homopolymer (B1) is less than 95 parts by weight per 100 parts by weight of the total of the polypropylene-based random copolymer (A) and the propylene homopolymer (B1), and (ii) The method for producing expanded polypropylene resin particles, wherein the polypropylene resin particles have (ii-1) only one melting peak or (ii-2) two or more melting peaks in a DSC curve obtained by measurement using a differential scanning calorimeter, and the heat ratio of the melting peak on the highest temperature side is 95% or more and less than 100% of the total heat of fusion (100%).

[0148]

[31] The method for producing expanded polypropylene resin beads according to

[30] , wherein the extrusion step includes a peroxide treatment step A in which the mixed resin is treated with a peroxide.

[0149]

[32] The method for producing expanded polypropylene-based resin beads according to

[31] , wherein the amount of the peroxide used in the peroxide treatment step A is 0.01 to 1.00 parts by weight per 100 parts by weight of the propylene homopolymer (B1) and the polypropylene block copolymer (B2) combined.

[0150]

[33] The method for producing expanded polypropylene-based resin beads according to any one of

[30] to

[32] , further comprising a peroxide treatment step B of treating the propylene homopolymer (B1) and / or the polypropylene-based block copolymer (B2) with a peroxide before the extrusion step.

[0151]

[34] The method for producing expanded polypropylene-based resin beads according to

[33] , wherein the amount of the peroxide used in the peroxide treatment step B is 0.01 to 1.00 parts by weight per 100 parts by weight of the propylene homopolymer (B1) and the polypropylene block copolymer (B2) combined.

[0152]

[35] The method for producing expanded polypropylene-based resin beads according to any one of

[30] to

[34] , wherein the mixed resin contains the propylene homopolymer (B1), and the ratio of the content of the polypropylene-based random copolymer (A) to the content of the propylene homopolymer (B1) in the mixed resin (content of the polypropylene-based random copolymer (A):content of the propylene homopolymer (B1)) is 90:10 to 50:50.

[0153]

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

[30] to

[35] , wherein the mixed resin contains the polypropylene block copolymer (B2), and the ratio of the polypropylene random copolymer (A) to the polypropylene block copolymer (B2) in the mixed resin (content of the polypropylene random copolymer (A):content of the polypropylene block copolymer (B2)) is 90:10 to 40:60.

[0154]

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

[30] to

[36] , wherein at least one of the polypropylene random copolymer (A), the propylene homopolymer (B1), and the polypropylene block copolymer (B2) contains a recycled resin.

[0155]

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

[30] to

[37] , wherein, in the mixed resin, the content of the polypropylene random copolymer (A) is 45 to 95 parts by weight, and the total content of the propylene homopolymer (B1) and the polypropylene block copolymer (B2) is 5 to 55 parts by weight, based on a total of 100 parts by weight of the polypropylene random copolymer (A), the propylene homopolymer (B1), and the polypropylene block copolymer (B2).

[0156]

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

[30] to

[38] , wherein when the mixed resin contains the polypropylene block copolymer (B2), the polypropylene resin particles have, in a DSC curve obtained by measurement with a differential scanning calorimeter, (i) only one melting peak, or (ii) two or more melting peaks, and the heat ratio of the melting peak on the highest temperature side to the total heat of fusion (100%) is 95% or more and less than 100%.

[0157]

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

[30] to

[39] , wherein the polypropylene random copolymer (A) is at least one selected from the group consisting of a propylene / ethylene random copolymer, a propylene / 1-butene random copolymer, a propylene / ethylene / 1-butene random copolymer, a propylene / vinyl chloride random copolymer, and a propylene / maleic anhydride random copolymer.

[0158]

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

[30] to

[40] , wherein the melting point of the polypropylene random copolymer (A) is 130°C to 160°C.

[0159]

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

[30] to

[41] , wherein the polypropylene random copolymer (A) has a melt flow rate of 3.0 g / 10 min to 30.0 g / 10 min at 230°C and a load of 2160 g.

[0160]

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

[30] to

[42] , wherein the polypropylene random copolymer (A) includes a recycled polypropylene random copolymer.

[0161]

[44] The method for producing expanded polypropylene resin beads according to

[43] , wherein the proportion of the recycled polypropylene random copolymer in 100% by weight of the polypropylene random copolymer (A) is 50% or more.

[0162]

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

[30] to

[44] , wherein the melting point of the propylene homopolymer (B1) is 150.0°C or higher and lower than 167.0°C.

[0163]

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

[30] to

[45] , wherein the propylene homopolymer (B1) has a melt flow rate of 1 g / 10 min to 350 g / 10 min at 230°C under a load of 2160 g.

[0164]

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

[30] to

[46] , wherein the propylene homopolymer (B1) includes a recycled propylene homopolymer.

[0165]

[48] ​​The method for producing expanded polypropylene resin beads according to any one of

[30] to

[47] , wherein the proportion of the recycled propylene homopolymer in 100% by weight of the propylene homopolymer (B1) is 50% or more.

[0166]

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

[30] to

[48] , wherein the total content of structural units derived from isoprene and structural units derived from conjugated dienes is 20% by weight or less, based on 100% by weight of the propylene homopolymer (B1).

[0167]

[50] The method for producing expanded polypropylene-based resin beads according to any one of

[30] to

[49] , wherein the polypropylene-based block copolymer (B2) is at least one selected from the group consisting of a propylene / ethylene block copolymer, a propylene / 1-butene block copolymer, a propylene / ethylene / 1-butene block copolymer, a propylene / chlorinated vinyl block copolymer, and a propylene / maleic anhydride block copolymer.

[0168]

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

[30] to

[50] , wherein the melting point of the polypropylene block copolymer (B2) is 150.0°C or higher and 167.0°C or lower.

[0169]

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

[30] to

[51] , wherein the polypropylene block copolymer (B2) has a melt flow rate of 1 g / 10 min to 350 g / 10 min at 230°C and a load of 2160 g.

[0170]

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

[30] to

[52] , wherein the polypropylene block copolymer (B2) includes a recycled polypropylene block copolymer.

[0171]

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

[30] to

[53] , wherein the proportion of the recycled polypropylene block copolymer in 100% by weight of the polypropylene block copolymer (B2) is 50% or more.

[0172]

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

[30] to

[54] , wherein the total content of structural units derived from isoprene and structural units derived from conjugated diene is 20% by weight or less in 100% by weight of the polypropylene block copolymer (B2).

[0173]

[56] The method for producing expanded polypropylene-based resin beads according to any one of

[30] to

[55] , wherein the melting point of the mixture of the propylene homopolymer (B1) and the polypropylene-based block copolymer (B2) is 150.0°C or higher and 167.0°C or lower.

[0174]

[57] The method for producing expanded polypropylene-based resin beads according to any one of

[30] to

[56] , wherein the melt flow rate of the mixture of the propylene homopolymer (B1) and the polypropylene-based block copolymer (B2) at 230°C under a load of 2160 g is 1 g / 10 min to 350 g / 10 min.

[0175]

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

[30] to

[57] , wherein the mixed resin contains carbon black.

[0176]

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

[30] to

[58] , wherein the expansion ratio of the expanded polypropylene resin beads is 10 to 50 times.

[0177]

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

[30] to

[59] , wherein the expanded polypropylene resin beads have an average cell diameter of 80 μm to 500 μm.

[0178]

[61] A method for producing a polypropylene-based resin foam molded article, comprising a step of molding expanded polypropylene-based resin beads produced by the method for producing expanded polypropylene-based resin beads according to any one of

[30] to

[60] .

[0179]

[62] The method for producing a polypropylene-based resin foam molded article according to

[61] , wherein the polypropylene-based resin foam molded article has an internal fusion rate of 60% or more.

[0180]

[63] The method for producing a polypropylene-based resin foam molded body according to

[60] or

[61] , further comprising a cooling step of cooling the polypropylene-based resin foam molded body, wherein the cooling step is carried out for a time period of 0 to 110 seconds.

[0181] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0182] [Materials] <Base resin> (Polypropylene-based random copolymer (A)) A-1 [non-recycled resin; manufactured by Prime Polymer Co., Ltd., propylene / ethylene random copolymer] A-2 [non-recycled resin; manufactured by Prime Polymer Co., Ltd., propylene / ethylene / 1-butene random copolymer] A-3 [recycled material; a foamed molded article containing A-2 as the base resin was pulverized, and the pulverized material was melt-kneaded to obtain a resin composition in the form of pellets. The obtained resin composition in pellet form was used as a recycled material] - A-4 [Non-recycled resin; propylene / ethylene random copolymer manufactured by Prime Polymer Co., Ltd.] (propylene homopolymer (B1)) - B1-1 [Recycled material; recycled material obtained by recycling a resin product made of propylene homopolymer] - B1-2 [Recycled material; material obtained by treating B1-1 with peroxide] (polypropylene block copolymer (B2)) - B2-1 [Non-recycled resin; propylene / ethylene block copolymer manufactured by Prime Polymer Co., Ltd.] - B2-2 [Non-recycled resin; resin obtained by treating B2-1 with peroxide] - B2-3 [Recycled material; an automobile part containing a propylene / ethylene block copolymer as a base resin was pulverized, and the pulverized material was melt-kneaded to obtain a resin composition in pellet form. The obtained resin composition in pellet form was used as a recycled material.] B2-4 [Recycled material: Material obtained by treating B2-3 with peroxide] B2-5 [Recycled material: A foamed sheet containing a propylene / ethylene block copolymer as a base resin was pulverized, and the pulverized material was melt-kneaded to obtain a resin composition in pellet form. The resulting pellet-shaped resin composition was used as a recycled material.] B2-6, B2-7 [recycled material; material obtained by treating B2-5 with peroxide] (a mixture of propylene homopolymer (B1) and polypropylene block copolymer (B2)) (B1+B2)-1 [recycled material; material obtained by mixing B2-5 and B1-1 in a weight ratio of 1:1] (B1+B2)-2 [recycled material; material obtained by treating (B1+B2)-1 with peroxide] (peroxide) Peroxide [manufactured by NOF Corp., Perbutyl I] Peroxide [manufactured by NOF Corp., Perhexa 25B-40].

[0183] (Adjustment of MFR of Polypropylene Resin and Recycled Material (Peroxide Treatment Step)) B2-2 was obtained by dry-blending B2-1 with the peroxide shown in Table 1 using a blender, melt-kneading the mixture at a resin temperature of 220°C using a twin-screw extruder (TEM26-SX, manufactured by Toshiba Machine Co., Ltd.), water-cooling the extruded strand in a 2-m-long water tank, and then cutting it (approximately 5 mg / grain). Similarly, B2-4 was obtained by treating B2-3, B2-6 by treating B2-5, and B1-2 by treating B1-1 with the peroxide shown in Table 1, respectively. (B1+B2)-1 was obtained by dry-blending B2-5 and B1-1 at a weight ratio of 1:1. (B1+B2)-2 was obtained by treating B1+B2-1 with the peroxide shown in Table 1. The amount of peroxide (parts by weight) in Table 1 is the amount of peroxide used per 100 parts by weight of non-recycled resin or recycled material.

[0184] The composition of the non-recycled resin used, the composition of the recycled polypropylene resin contained in the recycled material, and the peroxide treatment are shown in Table 1. The melting point, MFR, number average molecular weight (Mn), weight average molecular weight (Mw), and z-average molecular weight (Mz) of the non-recycled resin and recycled material used were measured by the methods described below. The carbon black content and ash content in the recycled material used were measured by the methods described below. The results are shown in Table 2. The content of recycled polypropylene resin contained in the recycled material is the amount obtained by subtracting the carbon black content and ash content listed in Table 2 from 100% by weight of the recycled material.

[0185] <Resin particle additives> Talc [Talc Powder PK-S, manufactured by Hayashi Kasei Co., Ltd.] Glycerin [Purified Glycerin D, manufactured by Lion Corporation] Zinc borate [Zinc borate 2335, manufactured by Tomita Pharmaceutical Co., Ltd.] Carbon black masterbatch [a mixture obtained by mixing 40 parts by weight of carbon black and 60 parts by weight of polypropylene resin (MFR at 230°C = 7.5 g / 10 min)].

[0186] [Measurement Methods] The evaluation methods used in the examples and comparative examples are described below.

[0187] <Measurement of Melting Point of Polypropylene-Based Resin and Recycled Material> The melting points of the polypropylene-based resin and recycled material were measured using a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Corporation). The specific measurement method was as follows (1) to (3): (1) 5 to 6 mg of the sample to be measured was heated from 40°C to 220°C at a heating rate of 10°C / min to melt; (2) Then, the temperature was lowered from 220°C to 40°C at a heating rate of 10°C / min to crystallize; (3) The temperature was further increased 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 obtained during the second heating (i.e., during (3)) was taken as the melting point of the polypropylene-based resin and recycled material. In addition, when there are multiple peaks (melting peaks) in the DSC curves of the polypropylene-based resin and the recycled material obtained by the second temperature increase using the above-mentioned method, the temperature of the peak (melting peak) with the largest heat of fusion was taken as the melting point of the polypropylene-based resin and the recycled material.

[0188] <Measurement of MFR of Polypropylene Resin and Recycled Material> The MFR of the polypropylene resin and recycled material was measured using a melt mass-flow rate measuring device described in JIS K7210 under the following conditions: orifice 2.0959±0.005 mmφ, orifice length 8.000±0.025 mm, load 2160 g, and temperature 230±0.2°C.

[0189] <GPC Measurement of Polypropylene Resin and Recycled Material> The number average molecular weight (Mn), weight average molecular weight (Mw) and z average molecular weight (Mz) of the polypropylene resin and recycled material were measured as polystyrene equivalent values ​​by gel permeation chromatography (GPC). The GPC measurement conditions for measuring the molecular weights of the polypropylene resin and recycled material were as follows.

[0190] 20 mg of the polypropylene resin and recycled material to be measured were completely dissolved in 20 mL of o-dichlorobenzene at 145 ° C., and the resulting solution was hot-filtered through a sintered filter with a pore size of 1.0 μm, and the filtrate was used as an analytical sample. Measurement equipment: HLC-8321 GPC / HT type high-temperature gel permeation chromatograph (manufactured by Tosoh Corporation) Analysis equipment: Data processing software Empower 3 (manufactured by Waters Japan) Columns: 2 TSKgel GMH6-HT, 2 TSKgel GMH6-HTL (inner diameter 7.5 mm x length 300 mm, manufactured by Tosoh Corporation) Mobile phase: o-dichlorobenzene (containing 0.025% BHT) Column temperature: 140 ° C Detector: differential refractometer Flow rate: 1.0 mL / min Injection volume: 1.0 mL / min.

[0191] The recycled materials used in the examples and comparative examples did not contain any resins other than the polypropylene-based resins listed in the "Composition of Recycled Polypropylene-Based Resins Contained in the Recycled Material" column, but only contained carbon black and ash. Carbon black and ash do not affect the melting point, MFR, number-average molecular weight (Mn), weight-average molecular weight (Mw), and z-average molecular weight (Mz). Therefore, the melting point, MFR, number-average molecular weight (Mn), weight-average molecular weight (Mw), and z-average molecular weight (Mz) of the recycled materials can be considered to be the melting point, MFR, number-average molecular weight (Mn), weight-average molecular weight (Mw), and z-average molecular weight (Mz) of the polypropylene-based resins listed in the "Composition of Recycled Polypropylene-Based Resins Contained in the Recycled Material" column, respectively.

[0192] <Quantitative Determination of Carbon Black in Recycled Materials> The carbon black content in recycled materials was measured using a thermogravimetric and differential thermal analyzer (STA200RV, manufactured by Hitachi High-Tech Science Corp.). The specific operating procedures were as follows: (1) 6 to 8 mg of the sample to be measured was weighed into a Pt measuring vessel; (2) The temperature of the sample was increased to 600°C at 10°C / min in a nitrogen atmosphere, then cooled to 400°C at 10°C / min, and then the sample was placed in a simulated air (oxygen:nitrogen = 21%:79%) atmosphere and heated to 800°C at 10°C / min; (3) In the TG weight loss curve obtained in step (2), the weight loss rate (wt%) at 400°C in the step of increasing the temperature from 400°C to 800°C and the weight loss rate (wt%) at 800°C were used to calculate the weight ratio (wt%) of carbon black.

[0193] <Quantitative Determination of Ash Content in Recycled Materials> The ash content in the recycled materials was determined from the weight of the recycled materials and the weight of the residue after burning the recycled materials. The specific operating procedures were as follows: (1) The recycled materials were heated at 150°C for 1 hour to completely remove moisture from the recycled materials; (2) 1 g to 2 g of recycled materials were placed in a crucible and held at 300°C in an electric furnace for 30 minutes or more, and then burned at 750°C for 1 hour or more; (3) The crucible was removed from the electric furnace and cooled in a desiccator at 23°C for 1 hour; (4) The ash content in the recycled materials was calculated using the following formula: W1: weight of crucible (g); W2: weight of crucible + recycled materials before burning (g); W3: weight of crucible + recycled materials after burning (g); Ash content in recycled materials (wt%) = {(W3 - W1) * 100} / (W2 - W1).

[0194] <Measurement of MFR of Polypropylene-Based Resin Particles> The method for measuring the MFR of polypropylene-based resin particles is the same as the method described in the section <Measurement of MFR of Polypropylene-Based Resin> above, so that description is incorporated herein and the description is omitted here.

[0195] <Measurement of the calorific value ratio of the higher temperature peak of the DSC melting peak of polypropylene-based resin particles> The calorific value ratio of the higher temperature peak of the DSC melting peak was measured using a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Corporation). The specific measurement method was as follows (1) to (3): (1) 5 to 6 mg of the sample to be measured was heated from 40°C to 220°C at a heating rate of 10°C / min to melt; (2) Then, the temperature was lowered from 220°C to 40°C at a heating rate of 10°C / min to crystallize; (3) The temperature was further increased from 40°C to 220°C at a heating rate of 10°C / min. The melting peak area on the lower temperature side of the peak (melting peak) of the DSC curve obtained during the second heating (i.e., during (3)) was designated Q1, and the total area of ​​the melting peak was designated Q2, and the calorific value ratio was calculated using the following formula. High temperature peak heat rate (%) = (Q2 - Q1) / Q2 x 100.

[0196] Strictly speaking, the measurement was performed as follows: A line segment was drawn from the low-temperature melting peak and the maximum point between the low-temperature melting peak and the high-temperature melting peak to the melting initiation baseline, and this line segment was designated as line segment L. The area enclosed by the low-temperature melting peak and line segment L was designated as Q1. A line segment AB was also drawn connecting the endotherm point at 80°C (point A) and the endotherm at the temperature at which the high-temperature melting ends (point B), and the area enclosed by line segment AB and the DSC curve was designated as Q2.

[0197] <Measurement of DSC Ratio of Expanded Polypropylene Resin Beads> The DSC ratio was measured using a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Corporation). Specifically, the area of ​​the melting peak on the low-temperature side of the DSC curve obtained during the first temperature rise when 5 to 6 mg of expanded polypropylene resin beads was heated from 40°C to 220°C at a heating rate of 10°C / min was determined as Q ｌ The melting peak area on the high temperature side is Q ｈ The DSC ratio (%) was calculated using the following formula: ｈ / (Q ｌ +Q ｈ ) x 100.

[0198] Strictly speaking, the procedure was as follows: A line segment was drawn connecting the maximum point between the low-temperature melting peak and the high-temperature melting peak and the point on the curve at a temperature of 100°C.Ｌ The melting peak and line segment on the low temperature side Ｌ The area enclosed by and is Q ｌ In addition, a line was drawn from the maximum point between the melting peak on the low temperature side and the melting peak on the high temperature side to the melting end baseline. Ｈ The melting peak and line segment on the high temperature side Ｈ The area enclosed by and is Q ｈ In addition, the temperature at the top of the melting peak on the higher side and the temperature at the top of the melting peak on the lower side were read.

[0199] <Measurement of Expansion Ratio of Expanded Polypropylene Resin Beads> The expansion ratio of expanded beads was measured by the following methods (1) to (4): (1) Approximately 3 g to 10 g of expanded polypropylene resin beads were taken, dried at 60°C for 6 hours, and then conditioned in a room at 23°C and 50% humidity, and the weight w １ (2) The expanded particles used for the weight measurement were submerged in a measuring cylinder containing ethanol, and the volume v (cm) was measured by the amount of rise in the water level in the measuring cylinder (submersion method). ３ (3) The true specific gravity ρ of the expanded polypropylene resin particles was measured. ｂ =w １ / v was calculated; (4) Density ρ of polypropylene resin particles before foaming ｒ The true specific gravity ρ of the polypropylene resin foam particles ｂ The value obtained was used as the expansion ratio of the expanded polypropylene resin beads. In the examples and comparative examples shown below, the density ρ of the polypropylene resin beads before expansion (polypropylene resin beads) was ｒ are all 0.9 g / cm ３ It was.

[0200] <Average Cell Diameter of Expanded Polypropylene Resin Beads> The average cell diameter of expanded polypropylene resin beads was measured by the following methods (1) to (5): (1) Using a razor (high-stainless double-edged blade, manufactured by Feather Corporation), the expanded beads were cut so as to pass through the center of the expanded beads, while being careful not to destroy the cell membranes (cell membranes) of the expanded beads; (2) The cut surface of the expanded beads obtained was observed using a microscope (manufactured by Hirox Co., Ltd., RH-2000), and an image of the observed surface was taken; (3) On the obtained image, a line segment corresponding to a length of 2000 μm was drawn at any part of the expanded beads except for the surface layer part; (4) The number n of cells through which the line segment passed was measured, and the cell diameter was calculated from the formula (cell diameter = 2000 / n (μm)); (5) The same procedure was performed on 10 expanded beads, and the arithmetic mean value of the calculated cell diameters was taken as the average cell diameter of the expanded polypropylene resin beads.

[0201] <Internal Fusion Property of Polypropylene-Based Resin Foam Molded Articles> The internal fusion property of polypropylene-based resin foam molded articles was evaluated by determining the internal fusion rate of the molded article. The internal fusion rate of polypropylene-based resin foam molded articles was measured as follows (1) to (4): (1) A cutter was used to make a 5 mm long incision on any one surface of the foam molded article in a direction perpendicular to the surface; (2) The foam molded article was then manually broken along the incision; (3) The area of ​​the resulting fracture surface excluding the incision was visually observed to count the total number of foamed beads present in the area and the number of foamed beads that had broken in the area other than at the particle interface (i.e., the foamed beads that had broken themselves); (4) The internal fusion rate was calculated according to the following formula: Internal fusion rate (%) = (number of foamed beads that had broken in the area other than at the particle interface / total number of foamed beads present in the area) × 100. The values ​​listed in the "Internal Fusion Property" column of Tables 3 to 5 are the internal fusion rate (%) values.

[0202] <Surface Beauty of Polypropylene-Based Resin Foam Molded Article> A 350 mm long x 450 mm wide surface of the obtained polypropylene-based resin foam molded article was visually observed, and the surface beauty was judged according to the following criteria. Interparticle gaps (gaps between polypropylene-based resin foam particles), which are one of the evaluation indices for surface beauty, were judged by visually counting the number of gaps present in a 50 mm square area at the center of the surface of the molded article. 4 (Beautiful surface appearance): No wrinkles and 0 to 1 interparticle gap. 3 (Good surface appearance): No wrinkles and 2 to 3 interparticle gaps. 2 (Acceptable surface appearance): Wrinkles are observed or 4 to 5 interparticle gaps are present. 1 (Failure in surface appearance): Wrinkles are observed or 6 or more interparticle gaps are present.

[0203] <Molding Cycle of Polypropylene-Based Resin Foam Molded Articles> The molding cycle in the manufacturing method for polypropylene-based resin foam molded articles was measured from the start of molding to the end of molding, when the molded article was demolded. The start of molding was the point at which the polypropylene-based resin foam beads began to be filled into the mold. A mold capable of forming a molding space measuring 370 mm long, 320 mm wide, and 50 mm thick was used. Next, with the drain valve of the drain line of the molding machine open, steam at 0.10 MPa (gauge pressure) was pumped into the mold for 3 seconds to heat the foamed beads and expel air from the mold (preheating step). Next, steam was flowed from the fixed mold side to the movable mold side for 6 seconds (one-way heating step), and then steam was flowed from the movable mold side to the process mold side for 3 seconds (reverse one-way heating step) to expel air and heat the foamed beads. Next, with the drain valve of the drain line of the molding machine closed, steam at 0.30 MPa (gauge pressure) was pumped into the mold for 9 seconds to heat the foamed beads (double-sided heating step), fusing them to form a foam molded article. Next, the foam molded article in the mold was water-cooled. Subsequently, the mold was opened when the surface pressure measured by a surface pressure gauge attached to the surface of the Planck mold had dropped to 0.01 MPa (gauge pressure), and molding was completed when the mold was released. The evaluation criteria for molding cycle (productivity) were as follows: 3 (excellent): molding cycle was 180 seconds or less. 2 (poor): molding cycle was more than 180 seconds and less than 210 seconds. 1 (very poor): molding cycle was more than 210 seconds.

[0204] The methods for producing polypropylene resin particles, expanded polypropylene resin particles, and expanded molded polypropylene resin articles in Examples and Comparative Examples will be described below.

[0205] Example 1 [Preparation of Polypropylene-Based Resin Particles] 75 parts by weight of A-2 as the polypropylene-based random copolymer (A), 25 parts by weight of B2-2 as the polypropylene-based block copolymer (B), 0.2 parts by weight of talc, and 0.2 parts by weight of glycerin were weighed and dry-blended using a blender to obtain a mixed resin. The obtained mixed resin was melt-kneaded at a resin temperature of 220°C using a twin-screw extruder (TEM26-SX, manufactured by Toshiba Machine Co., Ltd.), and the extruded strand was water-cooled in a 2-m-long water tank and then cut to produce polypropylene-based resin particles (1.2 mg / particle) (extrusion step).

[0206] [Preparation of Expanded Polypropylene Resin Particles] A 10 L pressure-resistant autoclave was charged with 100 parts by weight (2.4 kg) of the polypropylene resin particles obtained as described above, 200 parts by weight of water, 0.3 parts by weight of kaolin (manufactured by BASF, ASP170) as a water-insoluble inorganic compound, and 0.06 parts by weight of sodium dodecylbenzenesulfonate (manufactured by Kao Corporation, Neopelex G-15) as a surfactant, and then 5 parts by weight of carbon dioxide was added as a foaming agent under stirring (dispersion step). The contents of the autoclave were heated to a foaming temperature of 160°C (heating step), and maintained for 10 minutes. After that, carbon dioxide was additionally injected to increase the internal pressure of the autoclave to a foaming pressure of 2.80 MPa (gauge pressure) (pressurization step). After maintaining the foaming temperature and foaming pressure for 20 minutes (maintaining step), the valve at the bottom of the autoclave was opened, and the foam was released through an orifice with a diameter of 3.6 mm to atmospheric pressure (releasing step), to obtain expanded polypropylene resin beads with an expansion ratio of 13. During this release, carbon dioxide was injected to maintain the pressure in the container so as not to decrease the pressure.

[0207] [Preparation of Polypropylene-Based Resin Foam Molded Article] The obtained polypropylene-based resin foamed beads were dried at 80°C. The dried polypropylene-based resin foamed beads were placed in a pressure-resistant container and impregnated with pressurized air to adjust the internal pressure of the polypropylene-based resin foamed beads to 0.20 MPa (absolute pressure). Next, the pressurized polypropylene-based resin foamed beads were filled into a mold measuring 370 mm in length, 320 mm in width, and 50 mm in thickness. The mold chamber was then heated with steam at 0.30 MPa (gauge pressure) (molding pressure) to fuse the foamed beads together. After water-cooling the inside of the mold and the surface of the molded article, the molded article was released from the mold to obtain a polypropylene-based resin foamed molded article. The obtained foamed molded article was left to stand at 23°C for 2 hours and then aged at 75°C for 16 hours.

[0208] (Examples 2 to 11, 13, and 15, and Comparative Examples 1 to 3 and 5) In [Preparation of Polypropylene-Based Resin Particles], polypropylene-based resin particles were prepared by the same procedure as in Example 1, except that the formulation of the base resin was changed as shown in Tables 3 to 5. For example, in Example 4, polypropylene-based resin particles were prepared by the same procedure as in Example 1, except for the following: 75 parts by weight of A-2 as the polypropylene-based random copolymer (A), 25 parts by weight of B2-4 as the polypropylene-based block copolymer (B-2), 0.2 parts by weight of talc, 0.2 parts by weight of glycerin, and 8.2 parts by weight of the carbon black masterbatch were weighed out and dry-blended using a blender to obtain a mixed resin. For example, in Example 5, polypropylene-based resin particles were prepared in the same manner as in Example 1, except for the following: 75 parts by weight of A-2 as the polypropylene-based random copolymer (A), 25 parts by weight of B2-4 as the polypropylene-based block copolymer (B-2), 0.05 parts by weight of zinc borate, and 8.2 parts by weight of a carbon black masterbatch were weighed and dry-blended using a blender to obtain a mixed resin. Next, polypropylene-based resin expanded beads and polypropylene-based resin foam molded articles were prepared in the same manner as in Example 1, except that in the [Preparation of Expanded Polypropylene-Based Resin Beads], the foaming conditions were changed as shown in Tables 3 to 5. The formulation conditions of the base resin, the foaming conditions, and the evaluation results of the obtained expanded polypropylene-based resin beads and expanded polypropylene-based resin foam molded articles are shown in Tables 3 to 5.

[0209] (Examples 12, 14, 18, 19 and Comparative Example 4) Polypropylene-based resin particles, expanded polypropylene-based resin particles, and polypropylene-based resin foam molded articles were prepared in the same manner as in Example 1, except that in [Preparation of Polypropylene-Based Resin Particles], the polypropylene-based random copolymer (A), the propylene homopolymer (B1) and / or the polypropylene-based block copolymer (B2), various additives, and 0.3 part by weight of Perhexa 25B-40 were dry-blended as shown in Tables 4 and 5. The formulation conditions of the base resin, the foaming conditions, and the evaluation results of the obtained expanded polypropylene-based resin particles and expanded polypropylene-based resin molded articles are shown in Tables 4 and 5.

[0210] (Examples 16 and 17) Polypropylene-based resin particles, expanded polypropylene-based resin particles, and polypropylene-based resin foam molded articles were prepared in the same manner as in Example 1, except that in [Preparation of Polypropylene-Based Resin Particles], the polypropylene-based random copolymer (A), the propylene homopolymer (B1) and / or the polypropylene-based block copolymer (B2), various additives, and 0.3 part by weight of Perbutyl I were dry-blended as shown in Table 4. Table 4 shows the formulation conditions of the base resin, the foaming conditions, and the evaluation results of the obtained expanded polypropylene-based resin particles and expanded polypropylene-based resin foam molded articles.

[0211] In Examples 1 to 19, it was found that, as long as the polypropylene-based resin particles contain a polypropylene-based random copolymer (A), a propylene homopolymer (B1) and / or a polypropylene-based block copolymer (B2) and have an MFR of 20.0 g / 10 min or more, even when recycled polypropylene-based random copolymer (A), or propylene homopolymer (B1) and / or polypropylene block copolymer (B2) is used as in Examples 2 to 15, foamed molded articles can be obtained in a short molding cycle, and the obtained foamed molded articles are excellent in both internal fusion properties and surface beauty.

[0212] In Comparative Examples 1 to 5, when the MFR of the polypropylene resin particles was less than 20 g / 10 min, there was room for improvement in the internal fusion property, surface aesthetics, and molding cycle.

[0213] According to one embodiment of the present invention, it is possible to provide novel expanded polypropylene resin particles that can provide expanded polypropylene resin molded articles in a short molding cycle, and therefore, this embodiment of the present invention can be used in a variety of applications, including automotive interior components, core materials for automotive bumpers, heat insulating materials, cushioning packaging materials, and returnable containers.

Claims

1. Polypropylene-based resin expanded particles obtained by expanding polypropylene-based resin particles, wherein the polypropylene-based resin particles contain a polypropylene-based random copolymer (A) and a propylene homopolymer (B1) and / or a polypropylene-based block copolymer (B2), and the polypropylene-based resin particles have a melt flow rate (MFR) of 20.0 g / 10 min or more at 230°C under a load of 2160 g, and when the polypropylene-based resin particles contain the propylene homopolymer (B1), (i) in the polypropylene-based resin particles, the content of the propylene homopolymer (B1) is less than 95 parts by weight per 100 parts by weight of the total of the polypropylene-based random copolymer (A) and the propylene homopolymer (B1), and (ii) The polypropylene resin particles are expanded polypropylene resin particles, which have (ii-1) only one melting peak or (ii-2) two or more melting peaks in a DSC curve obtained by measurement using a differential scanning calorimeter, and the heat ratio of the melting peak on the highest temperature side to the total heat of fusion (100%) is 95% or more but less than 100%.

2. The expanded polypropylene resin particles according to claim 1, wherein the polypropylene resin particles contain the propylene homopolymer (B1), and the ratio of the content of the polypropylene random copolymer (A) to the content of the propylene homopolymer (B1) in the polypropylene resin particles (content of the polypropylene random copolymer (A):content of the propylene homopolymer (B1)) is 90:10 to 50:

50.

3. The expanded polypropylene resin particles according to claim 1, wherein the polypropylene resin particles contain the polypropylene block copolymer (B2), and the ratio of the polypropylene random copolymer (A) to the polypropylene block copolymer (B2) in the polypropylene resin particles (content of the polypropylene random copolymer (A):content of the polypropylene block copolymer (B2)) is 90:10 to 40:

60.

4. The polypropylene-based resin expanded particles according to claim 1, wherein at least one of the polypropylene-based random copolymer (A), the propylene homopolymer (B1), and the polypropylene-based block copolymer (B2) contains a recycled resin.

5. The expanded polypropylene resin particles according to claim 1, wherein the polypropylene resin particles contain carbon black.

6. A polypropylene resin foam molded article obtained by molding the polypropylene resin foam beads according to any one of claims 1 to 5.

7. A method for producing polypropylene-based resin particles, comprising: an extrusion step of melt-kneading a mixed resin containing a polypropylene-based random copolymer (A) and a propylene homopolymer (B1) and / or a polypropylene-based block copolymer (B2) to obtain polypropylene-based resin particles; and an expansion step of expanding the polypropylene-based resin particles obtained in the extrusion step, wherein the polypropylene-based resin particles have a melt flow rate (MFR) of 20.0 g / 10 min or more at 230°C under a load of 2160 g, and when the mixed resin contains the propylene homopolymer (B1), (i) in the mixed resin, the propylene homopolymer (B1) is less than 95 parts by weight per 100 parts by weight of the total of the polypropylene-based random copolymer (A) and the propylene homopolymer (B1), and (ii) The method for producing expanded polypropylene resin particles, wherein the polypropylene resin particles have (ii-1) only one melting peak or (ii-2) two or more melting peaks in a DSC curve obtained by measurement using a differential scanning calorimeter, and the heat ratio of the melting peak on the highest temperature side is 95% or more and less than 100% of the total heat of fusion (100%).

8. The method for producing expanded polypropylene resin beads according to claim 7, wherein the extrusion step includes a peroxide treatment step A in which the mixed resin is treated with a peroxide.

9. A method for producing expanded polypropylene resin beads according to claim 7 or 8, comprising a peroxide treatment step B of treating the propylene homopolymer (B1) and / or the polypropylene block copolymer (B2) with a peroxide before the extrusion step.

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