Polypropylene resin foam particles

Abstract

The present invention addresses the problem of providing polypropylene resin foam particles that contain two types of recycled resins and can provide a foam molded body having a good appearance. Polypropylene resin foam particles contain a base resin containing a virgin resin (A) that is a polypropylene random copolymer, a recycled resin (X), and a recycled resin (Y). The MFR of (X) and the MFR of (Y) are greater than 1, are different from each other, and satisfy a predetermined calculation formula.

Description

Polypropylene resin foam particles

[0001] This invention relates to polypropylene resin foam particles.

[0002] Polypropylene resin foam molded products are used in a variety of applications, including automotive interior components, bumper core materials, insulation materials, cushioning packaging materials, and reusable containers. In recent years, from the perspective of environmental considerations, various technologies have been investigated for recovering polypropylene resin from the aforementioned foam molded products and reusing it as recycled polypropylene resin (for example, Patent Documents 1 to 3).

[0003] Japanese Patent Publication No. 2024-041662, Japanese Patent Publication No. 2024-115423, Japanese Patent Publication No. 2024-055630

[0004] However, the conventional technologies described above were not sufficient from the standpoint of the appearance of the foamed molded product, and there was room for further improvement.

[0005] One embodiment of the present invention has been made in view of the above-mentioned problems, and aims to provide polypropylene resin foam particles that contain two types of recycled resins with different MFRs, and that can provide a foam molded article with a good appearance.

[0006] The inventors of this invention have diligently studied and conducted research to solve the aforementioned problems, and as a result, have completed this invention.

[0007] Polypropylene resin foam particles according to one embodiment of the present invention include a base resin containing virgin polypropylene resin (A), recycled polypropylene resin (X), and recycled polypropylene resin (Y), and satisfy the following requirements (1) to (5): (where MFR Ｘ This is the melt flow rate (g / 10 min) of recycled polypropylene resin (X), and MFR Ｙis the melt flow rate (g / 10 minutes) of the recycled polypropylene-based resin (Y). When the total amount of the weight of the recycled polypropylene-based resin (X) and the weight of the recycled polypropylene-based resin (Y) is taken as 100% by weight, p is the weight percentage of the recycled polypropylene-based resin (X), and q is the weight percentage of the recycled polypropylene-based resin (Y).) (1) 1 < MFR Ｘ ; (2) 1 < MFR Ｙ ; (3) MFR Ｘ ≠ MFR Ｙ ; (4) 4.0 < exp{(p / 100)×ln(MFR Ｘ ) + (q / 100)×ln(MFR Ｙ )} < 20.0; (5) The virgin polypropylene-based resin (A) is a polypropylene-based random copolymer.

[0008] A method for producing polypropylene-based resin expanded beads according to another embodiment of the present invention is a method for producing polypropylene-based resin expanded beads, comprising: a step of preparing a base resin by mixing a virgin polypropylene-based resin (A), a recycled polypropylene-based resin (X) and a recycled polypropylene-based resin (Y); and a step of preparing expanded beads from the base resin, wherein the polypropylene-based resin expanded beads satisfy the following requirements from (1) to (5): (Wherein, MFR Ｘ is the melt flow rate (g / 10 minutes) of the recycled polypropylene-based resin (X), and MFR Ｙ is the melt flow rate (g / 10 minutes) of the recycled polypropylene-based resin (Y). When the total amount of the weight of the recycled polypropylene-based resin (X) and the weight of the recycled polypropylene-based resin (Y) is taken as 100% by weight, p is the weight percentage of the recycled polypropylene-based resin (X), and q is the weight percentage of the recycled polypropylene-based resin (Y).) (1) 1 < MFR Ｘ ; (2) 1 < MFR Ｙ ; (3) MFR Ｘ ≠ MFR Ｙ ; (4) 4.0 < exp{(p / 100)×ln(MFR Ｘ) + (q / 100) × ln(MFR Ｙ )} < 20.0; (5) The virgin polypropylene-based resin (A) is a polypropylene-based random copolymer.

[0009] According to one embodiment of the present invention, there can be provided expanded polypropylene-based resin particles containing two types of recycled resins having different MFRs, which are capable of providing an expanded molded article having a good appearance.

[0010] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to each configuration described below, and various modifications can be made within the scope shown in the claims. In addition, embodiments or examples obtained by combining technical means respectively disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means respectively disclosed in each embodiment. All academic documents and patent documents described in the present specification are incorporated herein by reference.

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

[0012] Unless otherwise specified in the present specification, as a structural unit, X １ unit, X ２ unit, ... and X ｎ unit (n is an integer of 2 or more), and the copolymer containing these units is also referred to as "X １ / X ２ / ... / X ｎ copolymer". Except as explicitly stated, the polymerization mode of X １ / X ２ / ... / X ｎ copolymer is not particularly limited, and it may be a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer.

[0013] In this specification, "polypropylene resin particles" may be referred to as "resin particles," "polypropylene resin foam particles" may be referred to as "foamed particles," "polypropylene resin foam particles according to one embodiment of the present invention" may be referred to as "the foamed particles," and "polypropylene resin foam molded article" may be referred to as "foamed article." In addition, in this specification, "a method for producing polypropylene resin foam particles according to one embodiment of the present invention" may be referred to as "the manufacturing method."

[0014] [1. Polypropylene Resin Foam Particles] These foam particles contain a base resin containing virgin polypropylene resin (A), recycled polypropylene resin (X), and recycled polypropylene resin (Y), and satisfy the following requirements (1) to (5): (where MFR Ｘ This is the melt flow rate (g / 10 min) of recycled polypropylene resin (X), and MFR Ｙ is the melt flow rate (g / 10 min) of recycled polypropylene resin (Y), and when the total amount of recycled polypropylene resin (X) and recycled polypropylene resin (Y) is taken as 100% by weight, p is the weight % of recycled polypropylene resin (X) and q is the weight % of recycled polypropylene resin (Y). ) (1) 1 < MFR Ｘ (2) 1 < MFR Ｙ (3) MFR Ｘ ≠MFR Ｙ ; (4) 4.0<exp{(p / 100)×ln(MFR Ｘ )+(q / 100)×ln(MFR Ｙ )} < 20.0; (5) The virgin polypropylene resin (A) is a polypropylene random copolymer.

[0015] (1) Technical concept of one embodiment of the present invention: Because the foamed particles have the above configuration, they have the advantage of being able to provide a foamed molded article with a good appearance while containing two types of recycled resins with different MFRs.

[0016] The aforementioned recycled resins typically have different MFRs depending on their form, original use, etc., so the MFR of one type of recycled resin is usually different from that of another. Therefore, when blending virgin resin with one type of recycled resin, the MFR of the resulting polypropylene resin particles is easily affected by the differences in MFR of each recycled resin. Consequently, trial and error is required to stably produce polypropylene resin particles with an MFR suitable for foaming.

[0017] The aforementioned "one type of recycled resin" refers to a recycled resin having the same copolymer structural units, melting point, MFR, ash content, and carbon black content. In this specification, even if resins have the same structural units, resins with different MFRs, for example, are treated as different types of recycled resins.

[0018] These foamed particles contain a base resin containing recycled polypropylene resin (X) and recycled polypropylene resin (Y). This configuration involves blending two types of recycled resins. While the MFRs of the two recycled resins typically differ, by selecting an appropriate blending ratio of the two recycled resins in anticipation of this difference, the MFR of the mixture of the two recycled resins can be kept within a desired range. In this case, since the MFR of the mixture combined with the virgin resin is already within a desired range, the MFR of the polypropylene resin particles can be stably made suitable for foaming.

[0019] However, as mentioned above, when foamed particles were manufactured using polypropylene resin particles containing two types of recycled resins with different MFRs, and a foamed molded product was manufactured from these foamed particles, the appearance of the foamed molded product sometimes became unsatisfactory.

[0020] The inventors diligently investigated the causes of the aforementioned appearance defects. As a result, they found that simply mixing the two types of recycled resins in a blending ratio that stabilizes the MFR of the polypropylene resin particles is not always sufficient to prevent the aforementioned appearance defects. The inventors then conducted further investigations and found that if the components constituting the foamed particles satisfy the requirements (1) to (5) above, the aforementioned appearance defects can be sufficiently prevented while containing the two types of recycled resins.

[0021] These foamed particles contain a base resin containing two types of recycled resins, and are therefore formed by foaming polypropylene resin particles that have an MFR suitable for foaming. As a result, they exhibit excellent foaming properties. Furthermore, since these foamed particles satisfy the requirements (1) to (5) above, they can provide foamed molded articles with a good appearance.

[0022] (2) Base resin The foamed particles contain a base resin comprising virgin polypropylene resin (A), recycled polypropylene resin (X), and recycled polypropylene resin (Y). Hereinafter, virgin polypropylene resin (A) will also be referred to as component (A), recycled polypropylene resin (X) as component (X), and recycled polypropylene resin (Y) as component (Y).

[0023] (2-1) Virgin polypropylene resin (A) (Component (A)) In this specification, "polypropylene resin" means a resin in which the content of propylene-derived constituent units (propylene units) is the largest among all constituent units of the resin. Preferably, the polypropylene resin contains 50 mol% or more of propylene units in 100 mol% of all constituent units of the resin.

[0024] Virgin polypropylene resin is a polypropylene resin that does not use recycled materials. In other words, it is a polypropylene resin that has never been used as a material for resin products. Virgin polypropylene resin may be a commercially available product or may be newly manufactured by methods such as suspension polymerization.

[0025] The aforementioned component (A) is a polypropylene random copolymer (requirement (5)). Requirement (5) is that the virgin resin is a polypropylene random copolymer so that the resin particles and foam particles can be processed at a low heating temperature in the foaming process and foam molding process described later.

[0026] In this specification, "random copolymer" refers to a copolymer composed of constituent units derived from two or more monomers, wherein each constituent unit is arranged randomly. Furthermore, "block copolymer" refers to a copolymer composed of constituent units derived from two or more monomers, wherein each constituent unit is arranged continuously, forming a block structure.

[0027] The aforementioned component (A) is not particularly limited as long as it is a copolymer in which 50 mol% or more of the total constituent units of the copolymer are derived from propylene, and each constituent unit is arranged randomly. Examples of such copolymers include ethylene / propylene random copolymer, ethylene / propylene / butene random copolymer, propylene / butene random copolymer, propylene / chlorinated vinyl random copolymer, and propylene / maleic anhydride random copolymer.

[0028] The component (A) may be one of these copolymers used alone, or a mixture thereof may be used. In particular, because it is readily available, it is preferable to use an ethylene / propylene random copolymer or an ethylene / propylene / butene random copolymer, or a mixture thereof, as the component (A).

[0029] The ratio of each constituent unit of component (A) is not particularly limited as long as it contains 50 mol% or more of constituent units derived from propylene, and can be appropriately set by a person skilled in the art according to the desired application. Furthermore, when a mixture of multiple polypropylene-based random copolymers, for example, a mixture of ethylene / propylene random copolymer and ethylene / propylene / butene random copolymer, is used as component (A), the mixing ratio is not particularly limited and can be appropriately set by a person skilled in the art according to the desired application.

[0030] The melting point of component (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 melting point of component (A) is (i) 130°C or higher, it is possible to provide a foamed molded article with excellent heat resistance, and when it is 160°C or lower, it has the advantage that it is easy to increase the foaming ratio of the foamed particles in the production of these foamed particles. In this specification, the melting points of each polypropylene resin (components (A), (X), and (Y)) are measured by differential scanning calorimetry (also referred to as the "DSC method"). More specifically, the melting points are measured by the procedure described in the examples.

[0031] The MFR of component (A) is not particularly limited, but 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.

[0032] If the MFR of component (A) is within the range described above, it becomes easier to provide foamed particles with a high expansion ratio, and as a result, it becomes easier to provide a foamed molded article with a beautiful surface and low shrinkage rate. In this specification, the MFR of each polypropylene resin is a value obtained using a melt mass flow rate measuring instrument described in JIS-K7210 under the conditions of a temperature of 230°C and a load of 2160 g, and more specifically, it is a value measured by the procedure described in the examples.

[0033] (2-2) Recycled polypropylene resin (X) and recycled polypropylene resin (Y) (components (X) and (Y)) Recycled polypropylene resin (recycled resin) refers to (i) polypropylene resin that has been used and / or discarded once or more in the form of polypropylene resin products (e.g., foamed particles; foamed molded bodies; films; food trays; packaging containers such as bags and bottles; medical containers such as drip bags and syringes; clothing cases; miscellaneous goods such as clear files; home appliances; automobile parts), and then returned to the form of polypropylene resin (or polypropylene resin pellets) by any means (e.g., crushing, shredding, melting, and combinations thereof), and (ii) polypropylene resin that has been returned to the form of polypropylene resin (or polypropylene resin pellets) by any means (e.g., crushing, shredding, melting, and combinations thereof) of waste discharged during the manufacturing process of polypropylene resin products. The above (i) is also referred to as PCR material, and the above (ii) is also referred to as PIR material.

[0034] "PCR material" is an abbreviation for post-consumer recycled, meaning that the resin is recycled from resin that has been used and discarded by consumers. "PIR material" is an abbreviation for post-industrial recycled, meaning that the resin is recycled from waste generated during the manufacturing process.

[0035] The (X) component and the (Y) component may be any resin corresponding to either (i) or (ii). From the viewpoint of promoting the recycling of polypropylene resins, it is preferable that at least one of the (X) component and the (Y) component is a resin corresponding to (i), and it is more preferable that both the (X) component and the (Y) component are resins corresponding to (i).

[0036] In particular, it is preferable that component (X) and / or component (Y) are derived from used automobile parts, given the high demand for recycling and the ability to meet advanced environmental standards, such as the draft regulations on end-of-life vehicles announced by the European Commission in July 2023.

[0037] The aforementioned components (X) and (Y) are both recycled resins, but they are different types of recycled resins. As stated above, in this specification, "one type of recycled resin" means a recycled resin having the same copolymer constituent units, melting point, MFR, ash content and carbon black content. The aforementioned components (X) and (Y) are at least the requirements of (3) above (MFR Ｘ ≠MFR Ｙ To satisfy the requirements, each component is a different type of resin. In other words, these foamed particles contain two types of recycled resins.

[0038] The (X) and (Y) components may each be polypropylene random copolymers or polypropylene block copolymers, as long as they satisfy the requirements of (1) to (4) above.

[0039] The polypropylene random copolymers are as described in (2-1) above. The polypropylene block copolymers are not particularly limited and include ethylene / propylene block copolymers, ethylene / propylene / butene block copolymers, propylene / butene block copolymers, propylene / chlorinated vinyl block copolymers, propylene / maleic anhydride block copolymers, and the like.

[0040] Polypropylene block copolymers include substances that are considered polypropylene block copolymers in the field of polypropylene resin technology. For example, ethylene / propylene block copolymers contain a polyethylene layer covered with homopolypropylene as the matrix and ethylene / propylene elastic copolymer as the domains, and are sometimes referred to as impact copolymers.

[0041] The components (X) and (Y) may both be polypropylene random copolymers or polypropylene block copolymers, as long as they are different types of resins. Alternatively, one of the components (X) and (Y) may be a polypropylene random copolymer and the other a polypropylene block copolymer.

[0042] For example, in Example 1 described later, ethylene / propylene random copolymer C-1 is used as component (X), and ethylene / propylene block copolymer D-1 is used as component (Y). On the other hand, in Example 18 described later, ethylene / propylene block copolymer D-1 is used as component (X), and ethylene / propylene block copolymer D-2 is used as component (Y). Thus, ethylene / propylene block copolymer D-1 is used as both component (X) and component (Y). Component (X) and component (Y) only need to satisfy the requirements of (1) to (4) above. As long as the requirements are satisfied, as in the above examples, one type of recycled resin may, in combination with another recycled resin, correspond to component (X) in some combinations and to component (Y) in other combinations.

[0043] The ratio of each component (X) and (Y) is not particularly limited, as long as they contain at least 50 mol% of propylene-derived components out of 100 mol% of the total constituent units of the copolymer.

[0044] Because using a single material has the advantage of facilitating recycling, component (X) is preferably an ethylene / propylene random copolymer, an ethylene / propylene / butene random copolymer, an ethylene / propylene block copolymer, or an ethylene / propylene / butene block copolymer. From a similar viewpoint, component (Y) is preferably an ethylene / propylene random copolymer, an ethylene / propylene / butene random copolymer, an ethylene / propylene block copolymer, or an ethylene / propylene / butene block copolymer.

[0045] The melting points of component (X) and component (Y) are not particularly limited, but are preferably 135°C to 170°C and more preferably 135°C to 165°C, respectively. When the melting point is (i) 135°C or higher, the foamed molded article obtained from the resulting foamed particles has the advantage of having excellent heat resistance, and when it is 170°C or lower, it has the advantage of allowing the foaming temperature and molding temperature to be lowered.

[0046] The aforementioned components (X) and (Y) satisfy requirements (1) to (4) with respect to MFR. Requirements (1) and (2) are intended to select resins with good fluidity and processability during melting. Requirement (3) is required that the MFRs of the two resins are different, since, when two types of recycled resins are used and requirement (3) is satisfied, the MFR of the mixture can be kept within a desired range by selecting an appropriate blending ratio of the two types of recycled resins. Requirement (4) is required that, when two types of recycled resins are used and requirement (4) is satisfied, the foaming properties of the foamed particles are excellent and the appearance of the foamed molded article is excellent, so the formula described in (4) is satisfied. The formula described in (4) is a formula for determining the estimated value of the MFR of the mixture of component (X) and component (Y).

[0047] MFR Ｘ and MFR Ｙ The range is not particularly limited as long as it satisfies requirements (1) to (4) above, but independently, 2.0 g / 10 min to 50.0 g / 10 min is preferred, 3.0 g / 10 min to 35.0 g / 10 min is more preferred, and 4.0 g / 10 min to 30.0 g / 10 min is even more preferred. MFR Ｘ and MFR Ｙ If the range is as described above, the kneadability between component (A) and components (X) and (Y) is improved, resulting in a more uniform cell structure of the resulting foamed particles and making it possible to provide a foamed molded article with a superior appearance.

[0048] In the formula defining requirement (4) above, p and q are not particularly limited, but when the sum of the weights of component (X) and component (Y) is 100% by weight, p:q is preferably between 10:90 and 90:10, more preferably between 20:80 and 80:20, and even more preferably between 25:75 and 75:25. If p:q is within the above range, MFR Ｘ and MFR Ｙ When the range is as described above, it becomes easier to satisfy the relationship defined in the above formula.

[0049] The foamed particles preferably satisfy requirement (4-1) below, more preferably satisfy requirement (4-2), even more preferably satisfy requirement (4-3), and particularly preferably satisfy requirement (4-4). This configuration has the advantage of having superior foaming properties of the foamed particles and superior aesthetic appearance of the foamed molded article.

[0050] (4-1) 5.0<exp{(p / 100)×ln(MFR Ｘ )+(q / 100)×ln(MFR Ｙ )}<19.0; (4-2)6.0<exp{(p / 100)×ln(MFR Ｘ )+(q / 100)×ln(MFR Ｙ )}<18.0; (4-3)8.0<exp{(p / 100)×ln(MFR Ｘ )+(q / 100)×ln(MFR Ｙ )}<17.0; (4-4)9.0<exp{(p / 100)×ln(MFR Ｘ )+(q / 100)×ln(MFR Ｙ )} < 15.0.

[0051] The amount of ash in component (X) and component (Y) (hereinafter sometimes referred to as "ash content") is not particularly limited, but is preferably 0 ppm or more and 70,000 ppm or less, and more preferably 0 ppm or more and 50,000 ppm or less, respectively. If the ash content is within the above range, it has the advantage that the cells of the resulting foamed particles are less likely to become fine. The ash content of component (X) and component (Y) is measured by the method described in the examples.

[0052] The carbon black concentrations in component (X) and component (Y) are not particularly limited, but are preferably 0% by weight or more and 10% by weight or less, and more preferably 0% by weight or more and 5% by weight or less, respectively. When the carbon black concentrations are within the above range, there is an advantage that the flammability of the foamed molded article is not easily deteriorated. The carbon black concentrations of component (X) and component (Y) are measured by the method described in the examples.

[0053] (2-3) Composition of base resin The base resin of the foamed particles preferably contains 40% to 95% by weight of component (A) and 5% to 60% by weight of component (X) and component (Y) in total, based on a total amount of component (A), component (X), and component (Y) of 100% by weight. The aforementioned ratio may include 45% to 90% by weight of component (A) and a total of 10% to 55% by weight of component (X) and component (Y); or it may include 50% to 85% by weight of component (A) and a total of 15% to 50% by weight of component (X) and component (Y); or it may include 55% to 80% by weight of component (A) and a total of 20% to 45% by weight of component (X) and component (Y). The content ratio of component (X) and component (Y) is as described in (2-2) above.

[0054] Since the aforementioned components (X) and (Y) are recycled resins, when the base resin has the aforementioned ratio, the amount of plastic waste generated and the amount of plastic used in manufacturing can be reduced. Such effects contribute, for example, to achieving Goal 12 of the United Nations' Sustainable Development Goals (SDGs), "Ensure sustainable consumption and production patterns."

[0055] From the standpoint of meeting advanced environmental standards, as outlined in the draft regulations published by the European Commission in July 2023, it is preferable that the base resin of these foamed particles contains at least 25% by weight of component (X) and component (Y) in total, based on a total amount of 100% by weight of component (A), component (X), and component (Y). For example, it is preferable that component (A) is contained at least 40% by weight and component (X) and component (Y) are contained at least 25% by weight and component (Y) are contained at least 60% by weight in total; it is more preferable that component (A) is contained at least 45% by weight and component (X) and component (Y) are contained at least 70% by weight and component (Y) are contained at least 30% by weight and component (Y) are contained at least 55% by weight and component (A) is contained at least 50% by weight and component (X) and component (Y) are contained at least 50% by weight in total.

[0056] (3) Additives The foamed particles may optionally contain additives in addition to the base resin described above. Such additives include: colorants; water absorbents (e.g., (i) polyols such as glycerin and diglycerin, (ii) polyethers such as polyethylene glycol and polyethylene oxide, and (iii) metal borate salts such as borax and zinc borate); foaming nucleating agents (e.g., inorganic substances such as talc, calcium carbonate, silica, kaolin, barium sulfate, calcium hydroxide, aluminum hydroxide, aluminum oxide, and titanium dioxide); antistatic agents (e.g., glycerin monostearate, glycerin monodistearate); flame retardants (e.g., hinda Examples of additives include: bromine-based flame retardants, phosphate ester-based flame retardants, melamine-based flame retardants, etc.; antioxidants (e.g., hindered phenol-based antioxidants); heat stabilizers (e.g., phosphorus-based and sulfur-based heat stabilizers); light stabilizers (e.g., benzotriazole-based UV absorbers, triazine-based UV absorbers, HALS and / or hindered amine-based light stabilizers); nucleating agents; conductive agents (e.g., carbon, carbon nanotubes, metal fillers); lubricants; acid scavenging agents; antiblocking agents; metal chelating agents (e.g., IRGANOX® MD1024, Adekastab® CDA-1); lubricants; antibacterial agents, etc. These additives can be used individually or in combination of two or more, depending on the purpose.

[0057] These foamed particles may contain additives that are intentionally mixed in during the manufacturing process, as well as additives that are unintentionally mixed in, such as those derived from recycled materials or those mixed in during the recycling process of recycled materials (for example, colorants such as carbon black).

[0058] (4) Other physical properties and bulk density of the foamed particles The bulk density of the foamed particles may be 10.0 g / L or more and 200.0 g / L or less. Because the foamed particles have such a bulk density, they have the advantage of being applicable to foamed molded articles of various uses and shapes. The bulk density is not particularly limited as long as it is within the above range, and may be, for example, 15.0 g / L or more and 150.0 g / L or less, or 20.0 g / L or more and 100.0 g / L or less. The bulk density may be appropriately adjusted within the above range according to the use and desired physical properties, etc. For example, when applied to automotive component use, from the viewpoint of reducing vehicle weight, a relatively low density is preferable, specifically, 10.0 g / L or more and 40.0 g / L or less is preferable, 15.0 g / L or more and 35.0 g / L or less is more preferable, and 20.0 g / L or more and 33.0 g / L or less is even more preferable. On the other hand, when applied to energy absorbing members, the density is relatively high, specifically, it is preferable to have a density of more than 40 g / L and 200 g / L or less, more preferably 45.0 g / L or more and 150.0 g / L or less, and even more preferably 50.0 g / L or more and 100.0 g / L or less. The bulk density of these foamed particles is a value measured under atmospheric pressure, and more specifically, a value measured by the procedure described in the examples.

[0059] [2. Method for Producing Polypropylene Resin Foam Particles] A method for producing polypropylene resin foam particles according to one embodiment of the present invention is a method for producing polypropylene resin foam particles comprising the steps of: preparing a base resin by mixing virgin polypropylene resin (A), recycled polypropylene resin (X), and recycled polypropylene resin (Y); and preparing foam particles from the base resin, wherein the polypropylene resin foam particles satisfy the following requirements (1) to (5): (where MFR Ｘ This is the melt flow rate (g / 10 min) of recycled polypropylene resin (X), and MFR Ｙis the melt flow rate (g / 10 min) of recycled polypropylene resin (Y), and when the total amount of recycled polypropylene resin (X) and recycled polypropylene resin (Y) is taken as 100% by weight, p is the weight % of recycled polypropylene resin (X) and q is the weight % of recycled polypropylene resin (Y). ) (1) 1 < MFR Ｘ (2) 1 < MFR Ｙ (3) MFR Ｘ ≠MFR Ｙ ; (4) 4.0<exp{(p / 100)×ln(MFR Ｘ )+(q / 100)×ln(MFR Ｙ )} < 20.0; (5) The virgin polypropylene resin (A) is a polypropylene random copolymer.

[0060] Because this manufacturing method has the aforementioned configuration, it is possible to obtain these foamed particles. In other words, this manufacturing method has the advantage of being able to provide polypropylene-based resin foamed particles that contain two types of recycled resins with different MFRs and that can provide foamed molded articles with a good appearance.

[0061] As for component (A), component (X), and component (Y), and requirements (1) to (5), they have already been explained, so their explanation will be omitted here. The content of each component in the base resin is preferably the preferred content of each component as described in "(2-3) Composition of the base resin".

[0062] (1) Steps for preparing the base resin The base resin is prepared by mixing component (A), component (X), and component (Y). The method of mixing is not particularly limited. For example, component (A), component (X), and component (Y) are weighed to the content ratios described in (2-2) and (2-3) of 1. and mixed by known methods such as dry blending and hand blending. In the above step, the various additives described above may be further mixed during the mixing process.

[0063] (2) Granulation step The step of preparing the base resin may further include a step of producing polypropylene resin particles (sometimes simply referred to as "resin particles") containing the base resin (granulation step).

[0064] In the granulation process, there are no particular limitations on the method for producing resin particles, but one example is the use of an extruder. Specifically, for example, resin particles can be produced by the following methods (1) to (4): (1) The base resin is put into an extruder and the base resin is melt-kneaded to prepare a polypropylene resin composition; (2) The obtained polypropylene resin composition is extruded from a die provided in the extruder; (3) The extruded polypropylene resin composition is solidified by cooling it by passing it through water, etc.; (4) The solidified polypropylene resin composition is then cut with a cutter into desired shapes such as cylindrical, elliptical, spherical, cubic, rectangular parallelepiped, hollow cylindrical, polygonal prism, etc. Alternatively, in (2), the melt-kneaded polypropylene resin composition may be directly extruded into water from a die provided in the extruder, and immediately after extrusion, the polypropylene resin composition may be cut into particle shapes, cooled, and solidified. In this way, more uniform resin particles can be obtained by melt-kneading the base resin. Furthermore, in this manufacturing method, the resin particles containing the base resin obtained by this operation can also be used as a base resin for the foamed particles in the subsequent foamed particle preparation step.

[0065] The average weight per particle of the resin particles obtained as described above is preferably 0.5 mg / particle or more and 3.5 mg / particle or less, and more preferably 0.7 mg / particle or more and 2.0 mg / particle or less. By setting the average weight of the resin particles within the above range, it is possible to provide foamed particles with excellent filling properties during in-mold foam molding, which has the advantage of making it easier to manufacture foamed molded articles with complex shapes.

[0066] (3) Step for preparing foamed particles The present manufacturing method includes a step for preparing foamed particles from the base resin (preferably resin particles) (foamed particle preparation step). In the foamed particle preparation step, the method for preparing foamed particles from the base resin is not particularly limited, but a method including a dispersion step and a foaming step including a heating-pressure step, a holding step and a release step can be preferably mentioned. That is, the foamed particle preparation step in the present manufacturing method preferably includes a dispersion step and a foaming step.

[0067] (3-1) Dispersion process The foam particle preparation process preferably includes a dispersion process in which a base resin (resin particles), an aqueous dispersion medium, a foaming agent, and, if necessary, a dispersant and / or a dispersion aid are dispersed in a container before the foaming process. The dispersion process can also be described as a process of preparing a dispersion in which the base resin (resin particles), a foaming agent, and, if necessary, a dispersant and / or a dispersion aid are dispersed in an aqueous dispersion medium.

[0068] The container is not particularly limited, but it is preferably a container that can withstand the foaming temperature and foaming pressure described later. For example, it is preferably a pressure-resistant container, and more preferably an autoclave-type pressure-resistant container. The container may be equipped with a stirrer inside.

[0069] The aqueous dispersion medium is not particularly limited, as long as it can uniformly disperse the base resin, foaming agent, etc.

[0070] Examples of the aqueous dispersion medium include (a) a dispersion medium obtained by adding methanol, ethanol, ethylene glycol, and glycerin to water, (b) water such as ultrapure water, pure water, tap water, and industrial water, and (c) a solution (aqueous solution) containing a salt such as sodium chloride or sodium sulfate.

[0071] In order to enable stable production of foamed particles, it is preferable to use pure water and ultrapure water such as RO water (water purified by reverse osmosis), distilled water, and deionized water (water purified by ion exchange resin) as the aqueous dispersion medium.

[0072] Examples of the blowing agents include (a) (a-1) inorganic gases such as nitrogen, carbon dioxide, and air (a mixture of oxygen, nitrogen, and carbon dioxide), and (a-2) water; and (b) (b-1) saturated hydrocarbons having 3 to 5 carbon atoms such as propane, n-butane, isobutane, n-pentane, isopentane, and neopentane; (b-2) ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether; and (b-3) halogenated hydrocarbons such as monocormethane, chloroethane, and hydrofluoroolefin.

[0073] As the blowing agent, at least one selected from the group consisting of the inorganic and organic blowing agents described above can be used. When using a mixture of two or more blowing agents, the mixing ratio may be appropriately adjusted depending on the purpose. From the viewpoint of environmental impact and blowing power, inorganic blowing agents are preferred among those described above. Furthermore, carbon dioxide is preferred among inorganic blowing agents because it has a moderately high plasticizing effect and easily improves the blowing properties of the foamed particles in the production of these foamed particles.

[0074] The aqueous dispersion medium and foaming agent described above may be used individually or in combination of two or more types.

[0075] In this manufacturing method, it is preferable to use dispersants (e.g., inorganic substances such as tricalcium phosphate, kaolin, and talc) and dispersion aids (e.g., anionic surfactants such as sodium alkanesulfonate and sodium dodecylbenzenesulfonate). This configuration reduces adhesion between resin particles (sometimes referred to as blocking) and improves the stability of the dispersion in the container. As a result, it has the advantage of being able to stably produce foamed particles.

[0076] (3-2) Foaming Process The process for preparing foamed particles preferably includes a foaming process, which follows the dispersion process, in which the base resin (resin particles) is foamed in the dispersion obtained in the dispersion process. The method for foaming the base resin (resin particles) in the foaming process is not particularly limited, but a method including (a) a heating-pressure-raising process in which the temperature inside the container of the dispersion is raised to a certain temperature and the pressure inside the container is raised to a certain pressure, (b) a holding process in which the temperature and pressure inside the container are maintained at a constant temperature and a constant pressure, and (c) a release process in which one end of the container is opened and the dispersion inside the container is released into a region (space) with a pressure lower than the foaming pressure (i.e., the pressure inside the container). In other words, the foaming process according to this manufacturing method preferably includes a heating-pressure-raising process, a holding process and a release process.

[0077] (3-2-a) Heating and Pressurizing Process The heating and pressurizing process is a process in which the temperature inside the container holding the dispersion is raised to a certain temperature and the pressure inside the container is raised to a certain pressure. The heating and pressurizing process can also be described as a process in which the temperature inside the container holding the dispersion and the pressure inside the container are adjusted to a temperature suitable for depressurization foaming of the base resin.

[0078] The temperature inside the container (hereinafter also referred to as the foaming temperature) is not particularly limited as long as it is a temperature suitable for depressurizing and foaming the base resin, but for example, it may be 145.0°C or higher and 165.0°C or lower, or 150.0°C or higher and 160.0°C or lower.

[0079] The internal pressure of the container (hereinafter also referred to as the foaming pressure) is not particularly limited as long as it is a pressure suitable for depressurizing and foaming the base resin, but for example, it may be 1.0 MPa or more and 4.0 MPa or less, or 1.5 MPa or more and 3.5 MPa or less.

[0080] (3-2-b) Holding process The holding process is a process of maintaining the foaming temperature and foaming pressure for a certain period of time. In the holding process, the time for which the foaming temperature and foaming pressure are maintained (holding time) is not particularly limited, but may be, for example, 10 minutes or more and 60 minutes or 15 minutes or more and 40 minutes or less.

[0081] (3-2-c) Release Process The release process involves opening one end of the container that has undergone the heating-pressure and holding processes, and releasing the dispersion liquid inside the container into a region (space) with a pressure lower than the foaming pressure (i.e., the pressure inside the container). This operation (pressure release operation) allows the base resin to foam, and as a result, foamed particles can be obtained.

[0082] The aforementioned "region with a pressure lower than the foaming pressure" refers to "a region under a pressure lower than the foaming pressure" or "a space under a pressure lower than the foaming pressure," and can also be described as "an atmosphere under a pressure lower than the foaming pressure." The pressure in the region with a pressure lower than the foaming pressure is not particularly limited as long as it is lower than the foaming pressure, and may be atmospheric pressure, for example. In other words, the release step may be a step of releasing the dispersion under atmospheric pressure.

[0083] In the discharge process, when discharging the dispersion into a region with a pressure lower than the foaming pressure, the dispersion may be discharged through an open orifice with a diameter of 1 mm to 5 mm in order to adjust the flow rate of the dispersion and reduce variations in the foaming ratio of the resulting foamed particles. Furthermore, the low-pressure region (space) may be filled with saturated water vapor to improve foaming properties.

[0084] (3-2-d) Two-stage foaming process The present manufacturing method may include a two-stage foaming process in which the foamed particles obtained in the foaming process are foamed again. By carrying out a two-stage foaming process, it is possible to obtain foamed particles with a higher foaming ratio. In this specification, foamed particles obtained through such a two-stage foaming process are referred to as two-stage foamed particles, and foamed particles obtained in a single foaming process (single-stage foaming process) (in other words, foamed particles made by foaming a base resin (resin particles) that have not gone through a two-stage foaming process) are referred to as single-stage foamed particles.

[0085] These foamed particles may be single-stage foamed particles or double-stage foamed particles. If these foamed particles are double-stage foamed particles, the bulk density is intended to be the value measured for such double-stage foamed particles.

[0086] In the two-stage foaming process, the method for re-foaming the foamed particles (first-stage foamed particles) is not particularly limited, and known methods can be employed.

[0087] [3. Polypropylene Resin Foam Molded Article] In one embodiment of the present invention, a polypropylene resin foam molded article is provided, which is obtained by foam molding the foam particles. The polypropylene resin foam molded article according to one embodiment of the present invention (hereinafter also referred to as "the foam molded article") is a foam molded article that contains two types of recycled resins with different MFRs, because it uses the foam particles as a raw material, and therefore exhibits an excellent appearance.

[0088] (1) Appearance of the Foamed Molded Article In this specification, "good appearance of the foamed molded article" means that when the side surface of the foamed molded article is observed visually, there are almost no irregularities on the surface of the foamed molded article and no voids between foam particles, and there are no wrinkles or shrinkage, i.e., it is beautiful. In this specification, the voids between foam particles are also called "intergranular spaces". "Almost no intergranular spaces" means that when the intergranular spaces between foam particles are observed visually in a 100 mm x 100 mm area near the center of both sides (planes perpendicular to the thickness direction) of the surface of the molded article, the number of locations where there are gaps between foam particles is 20 or less. Furthermore, "poor appearance of the foamed molded article" means that when the side surface of the foamed molded article is observed visually, one or more properties selected from the group consisting of surface irregularities, intergranular spaces, shrinkage, and wrinkles are clearly visible. "Clearly visible intergranular spaces" means that there are more than 20 of the aforementioned gaps.

[0089] (2) Method for manufacturing the foamed molded article The method for manufacturing the foamed molded article is not particularly limited, and known molding methods can be applied. For example, such a method includes, but is not limited to, the following steps in order: (b1) supplying foamed particles to be used as raw material into a mold having a molding space; (b2) heating the inside of the mold with steam at a predetermined pressure (molding pressure) to fuse the foamed particles together; (b3) water-cooling the inside of the mold and the surface of the foamed molded article, and then drying the foamed molded article.

[0090] (b1) In step (b), the foam particles may be supplied into the mold under conditions in which a predetermined internal pressure (foam particle internal pressure) is applied to the foam particles.

[0091] The internal pressure of the foamed particles is not particularly limited, but is preferably between 0.10 MPa (absolute pressure) and 0.30 MPa (absolute pressure), and preferably between 0.15 MPa (absolute pressure) and 0.25 MPa (absolute pressure). Methods for applying internal pressure to the foamed particles include pressurizing with air and impregnating with inorganic gas.

[0092] One embodiment of the present invention may include the following configuration:

[0093] [1] Polypropylene resin foam particles containing a base resin containing virgin polypropylene resin (A), recycled polypropylene resin (X), and recycled polypropylene resin (Y), and satisfying the following requirements (1) to (5): (where MFR Ｘ This is the melt flow rate (g / 10 min) of recycled polypropylene resin (X), and MFR Ｙ is the melt flow rate (g / 10 min) of recycled polypropylene resin (Y), and when the total amount of recycled polypropylene resin (X) and recycled polypropylene resin (Y) is taken as 100% by weight, p is the weight % of recycled polypropylene resin (X) and q is the weight % of recycled polypropylene resin (Y). ) (1) 1 < MFR Ｘ (2) 1 < MFR Ｙ (3) MFR Ｘ ≠MFR Ｙ ; (4) 4.0<exp{(p / 100)×ln(MFR Ｘ )+(q / 100)×ln(MFR Ｙ )} < 20.0; (5) The virgin polypropylene resin (A) is a polypropylene random copolymer.

[0094] [2] The polypropylene resin foam particles according to [1], wherein the virgin polypropylene resin (A) is an ethylene / propylene random copolymer, an ethylene / propylene / butene random copolymer, or a mixture thereof.

[0095] [3] The base resin is polypropylene resin foam particles according to [1] or [2], wherein the base resin contains 40% to 95% by weight of the virgin polypropylene resin (A) and the recycled polypropylene resin (Y) in total, based on a total amount of 100% by weight of the virgin polypropylene resin (A), the recycled polypropylene resin (X), and the recycled polypropylene resin (Y).

[0096] [4] The polypropylene resin foam particles according to any one of [1] to [3], wherein the recycled polypropylene resin (X) is an ethylene / propylene random copolymer, an ethylene / propylene / butene random copolymer, an ethylene / propylene block copolymer, or an ethylene / propylene / butene block copolymer.

[0097] [5] Polypropylene resin foam particles according to any one of [1] to [4], wherein the recycled polypropylene resin (Y) is an ethylene / propylene random copolymer, an ethylene / propylene / butene random copolymer, an ethylene / propylene block copolymer, or an ethylene / propylene / butene block copolymer.

[0098] [6] Polypropylene resin foam particles according to any one of [1] to [5], wherein the recycled polypropylene resin (X) and / or the recycled polypropylene resin (Y) are derived from used automobile parts.

[0099] [7] The polypropylene resin foam particles according to any one of [1] to [6], wherein the melting point of the virgin polypropylene resin (A) is 130°C or higher.

[0100] [8] The polypropylene resin foam particles according to any one of [1] to [7], wherein the melt flow rate of the virgin polypropylene resin (A) is 3.0 g / 10 min or more and 30.0 g / 10 min or less.

[0101] [9] The polypropylene resin foam particles according to any one of [1] to [8], wherein the melting point of the recycled polypropylene resin (X) is 135°C or higher and 170°C or lower.

[0102]

[10] The polypropylene resin foam particles according to any one of [1] to [9], wherein the melt flow rate of the recycled polypropylene resin (X) is 2.0 g / 10 min or more and 50.0 g / 10 min or less.

[0103]

[11] The polypropylene resin foam particles according to any one of [1] to

[10] , wherein the melting point of the recycled polypropylene resin (Y) is 135°C or higher and 170°C or lower.

[0104]

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

[11] , wherein the melt flow rate of the recycled polypropylene resin (Y) is 2.0 g / 10 min or more and 50.0 g / 10 min or less.

[0105]

[13] Polypropylene resin foam particles according to any one of [1] to

[12] , further containing carbon black.

[0106]

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

[13] , wherein the melting point of the virgin polypropylene resin (A) is 160°C or lower.

[0107] A polypropylene resin foam molded article obtained by molding polypropylene resin foam particles described in any one of [1] to

[14] .

[0108]

[16] A method for producing polypropylene resin foam particles, comprising the steps of: preparing a base resin by mixing virgin polypropylene resin (A), recycled polypropylene resin (X), and recycled polypropylene resin (Y); and preparing foam particles from the base resin, wherein the polypropylene resin foam particles satisfy the following requirements (1) to (5): (where MFR ＸThis is the melt flow rate (g / 10 min) of recycled polypropylene resin (X), and MFR Ｙ is the melt flow rate (g / 10 min) of recycled polypropylene resin (Y), and when the total amount of recycled polypropylene resin (X) and recycled polypropylene resin (Y) is taken as 100% by weight, p is the weight % of recycled polypropylene resin (X) and q is the weight % of recycled polypropylene resin (Y). ) (1) 1 < MFR Ｘ (2) 1 < MFR Ｙ (3) MFR Ｘ ≠MFR Ｙ ; (4) 4.0<exp{(p / 100)×ln(MFR Ｘ )+(q / 100)×ln(MFR Ｙ )} < 20.0; (5) The virgin polypropylene resin (A) is a polypropylene random copolymer.

[0109]

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

[16] , wherein the virgin polypropylene resin (A) is an ethylene / propylene random copolymer, an ethylene / propylene / butene random copolymer, or a mixture thereof.

[0110]

[18] The method for producing polypropylene resin foam particles according to

[16] or

[17] , wherein the base resin contains 40% to 95% by weight of the virgin polypropylene resin (A) and the recycled polypropylene resin (Y) in total, based on a total amount of 100% by weight of the virgin polypropylene resin (A), the recycled polypropylene resin (X), and the recycled polypropylene resin (Y).

[0111]

[19] A method for producing foamed polypropylene resin particles according to any one of

[16] to

[18] , wherein the recycled polypropylene resin (X) is an ethylene / propylene random copolymer, an ethylene / propylene / butene random copolymer, an ethylene / propylene block copolymer, or an ethylene / propylene / butene block copolymer.

[0112]

[20] A method for producing polypropylene resin foam particles according to any one of

[16] to

[19] , wherein the recycled polypropylene resin (Y) is an ethylene / propylene random copolymer, an ethylene / propylene / butene random copolymer, an ethylene / propylene block copolymer, or an ethylene / propylene / butene block copolymer.

[0113]

[21] A method for producing polypropylene resin foam particles according to any one of

[16] to

[20] , wherein the recycled polypropylene resin (X) and / or the recycled polypropylene resin (Y) are derived from used automobile parts.

[0114]

[22] The method for producing polypropylene resin foam particles according to any one of

[16] to

[21] , wherein the melting point of the virgin polypropylene resin (A) is 130°C or higher.

[0115]

[23] A method for producing polypropylene resin foam particles according to any one of

[16] to

[22] , wherein the melt flow rate of the virgin polypropylene resin (A) is 3.0 g / 10 min or more and 30.0 g / 10 min or less.

[0116]

[24] The method for producing polypropylene resin foam particles according to any one of

[16] to

[23] , wherein the melting point of the recycled polypropylene resin (X) is 135°C or higher and 170°C or lower.

[0117]

[25] A method for producing polypropylene resin foam particles according to any one of

[16] to

[24] , wherein the melt flow rate of the recycled polypropylene resin (X) is 2.0 g / 10 min or more and 50.0 g / 10 min or less.

[0118]

[26] The method for producing polypropylene resin foam particles according to any one of

[16] to

[25] , wherein the melting point of the recycled polypropylene resin (Y) is 135°C or higher and 170°C or lower.

[0119]

[27] A method for producing polypropylene resin foam particles according to any one of

[16] to

[26] , wherein the melt flow rate of the recycled polypropylene resin (Y) is 2.0 g / 10 min or more and 50.0 g / 10 min or less.

[0120]

[28] A method for producing polypropylene resin foam particles according to any one of

[16] to

[27] , further comprising carbon black.

[0121]

[29] The method for producing polypropylene resin foam particles according to any one of

[16] to

[28] , wherein the melting point of the virgin polypropylene resin (A) is 160°C or lower.

[0122] A method for producing a polypropylene resin foamed molded article, comprising the step of foam molding polypropylene resin foamed particles described in any one of

[30] [1] to

[14] , or polypropylene resin foamed particles obtained by a method for producing polypropylene resin foamed particles described in any one of

[16] to

[29] .

[0123] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples, comparative examples and tables, "parts" and "%" refer to weight-based units (parts by weight and weight %) unless otherwise specified.

[0124] [Materials] <Base Resin> (Polypropylene Resin) Table 1 shows the resin number, polymer composition, melting point, and MFR of each polypropylene resin used. For recycled polypropylene resins (also called "recycled resins"), the ash content, carbon black content, and the main origin of each polypropylene resin are also shown.

[0125] As already stated in (2-2) of Section 1 above, in Example 1, which will be described later, ethylene / propylene random copolymer C-1 is used as component (X), and ethylene / propylene block copolymer D-1 is used as component (Y). On the other hand, in Example 18, which will be described later, ethylene / propylene block copolymer D-1 is used as component (X), and ethylene / propylene block copolymer D-2 is used as component (Y). The description "Recycled polypropylene resin (X) or (Y)" in Table 1 is based on the fact that resin number D-1 corresponds to component (Y) in the combination of Example 1, and to component (X) in the combination of Example 18.

[0126] The "Recycled Material" column in Table 1 shows the main origins of recycled resins. "Foam" means that the recycled resin is derived from foamed molded products, and "Non-foam" means that the recycled resin is derived from uses other than foamed molded products. "ASR material" is an abbreviation for Automobile Shredder Residue, meaning the residue remaining after a scrapped automobile has been shredded. "Automotive recovery material" means that the resin is derived from automotive parts extracted from a scrapped automobile. "50% automotive recovery material" means that the recycled resin is a mixture of 50% by weight of automotive recovery material and 50% by weight of PCR material. ASR material may contain small amounts of impurities such as metals and pigments, but since automotive recovery material is a resin, it contains less of these impurities than ASR material.

[0127] <Quantitative Determination of Carbon Black in Recycled Resin> The carbon black content in recycled resin was measured using a differential thermogravimetric analyzer (STA200RV, manufactured by Hitachi High-Tech Science Co., Ltd.). The specific operating procedure was as follows (1) to (3): (1) A sample of 6 mg to 8 mg was weighed into a Pt measuring container: (2) The sample temperature was raised to 600°C at a rate of 10°C / min under a nitrogen atmosphere, then cooled to 400°C at a rate of 10°C / min, and then raised to 800°C at a rate of 10°C / min under a simulated air atmosphere (oxygen:nitrogen = mixed gas with a volume ratio of 21%:79%): (3) In the TG weight loss rate curve obtained in the process of (2) above, the weight ratio (weight %) of carbon black was calculated from the difference between the weight loss rate (weight %) at 400°C and the weight loss rate (weight %) at 800°C during the process of raising the temperature from 400°C to 800°C.

[0128] <Determination of Ash Content in Recycled Resin> The ash content in recycled resin was determined from the weight of the recycled resin and the weight of the residue after combustion. The specific procedure was as follows (1) to (4): (1) The recycled resin was heated at 150°C for 1 hour to completely remove moisture from the recycled resin; (2) 1 g to 2 g of recycled resin was placed in a crucible and held at 300°C for 30 minutes or more using an electric furnace, 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 amount of ash (ppm) in the recycled resin was calculated using the following formula. The results are shown in the "Ash Content (ppm)" column of Table 1. W1: Crucible weight (g) W2: Weight of crucible + recycled resin before combustion (g) W3: Weight of crucible + recycled resin after combustion (g) Ash content in recycled resin (ppm) = {(W3 - W1) × 1,000,000} / (W2 - W1).

[0129] <Additives> The following additives were used in the amounts shown in Tables 2 to 4: ・Talc [Hayashi Chemical Co., Ltd., Talc Powder PK-S] ・Glycerin [Lion Corporation, Purified Glycerin D] [Measurement Method] The measurement and evaluation methods for various items performed in the examples and comparative examples are described below.

[0130] (MFR of virgin and recycled resins) The MFR of virgin and recycled resins was measured using an MFR measuring instrument described in JIS K7210-1:2014. The measurement conditions were an orifice diameter of 2.0959 ± 0.005 mmφ, an orifice length of 8.000 ± 0.025 mm, a load of 2160 g, and a temperature of 230 ± 0.2 °C.

[0131] (Melting points of virgin and recycled resins) The melting points of virgin and recycled resins were measured using a differential scanning calorimeter [Hitachi High-Tech Science Corporation, DSC7020]. The specific operating procedure was as follows (1) to (4): (1) A sample of 5 mg to 6 mg of the material (virgin or recycled resin) was heated from 40.0°C to 220.0°C at a heating rate of 10.0°C / min to melt the material; (2) The molten material was then cooled from 220.0°C to 40.0°C at a cooling rate of 10.0°C / min to crystallize the material; (3) The crystallized material was then heated from 40.0°C to 220.0°C at a heating rate of 10.0°C / min; (4) The temperature of the peak (melting peak) of the DSC curve of the material obtained during the second heating (i.e., at (3)) was taken as the melting point of the material. Furthermore, if multiple peaks (melting peaks) exist in the DSC curve of the object obtained during the second heating step using the method described above, the temperature of the peak with the largest heat of fusion (melting peak) was defined as the melting point of the object.

[0132] (Bulk density of foamed particles) The bulk density of the foamed particles was measured as follows: The weight w (g) of the foamed particles was weighed, and its volume V (L) was measured using a graduated cylinder at 23°C under atmospheric pressure. The bulk density (BD) of the foamed particles was calculated as w / V (g / L).

[0133] (Appearance of the foamed molded body) The side surface of the foamed molded body was visually inspected and its appearance was judged according to the following criteria. A higher number indicates a better appearance: 1 (Good): There is almost no surface irregularity or voids between foam particles (sometimes referred to as intergranular space), and there are no wrinkles or shrinkage; i.e., it is beautiful; 0 (Poor): One or more properties selected from the group consisting of surface irregularity, intergranular space, shrinkage, and wrinkles are clearly visible.

[0134] [Examples 1 to 18 and Comparative Examples 1 to 3] (1) Process for preparing the base resin (resin particles) Virgin resin, recycled resin, and additives of the types and amounts described in Tables 2 to 4 were hand-blended and melt-kneaded at a resin temperature of 220°C using a twin-screw extruder. The resulting melt-kneaded material was then extruded from the extruder in the form of strands, and the resulting strands were water-cooled and cut to obtain resin particles containing a base resin with an average weight of 1.2 mg.

[0135] (2) Preparation of foamed particles In a 10 L container (pressure-resistant autoclave), 100 parts by weight (2.4 kg) of resin particles obtained by the method described above, 200 parts by weight of water, 0.3 parts by weight of kaolin [BASF ASP170] as a dispersant, and 0.030 parts by weight of aqueous solution of sodium dodecylbenzenesulfonate [Kao Corporation Neoperex G-15] as a dispersion aid were charged. Then, while stirring the charged raw materials, 5 parts by weight of carbon dioxide was added to the autoclave as a foaming agent to prepare a dispersion (dispersion step). Next, the contents of the autoclave were heated to the foaming temperature shown in Table 2, Table 3, or Table 4, held for 10 minutes, and then carbon dioxide was added under pressure to increase the internal pressure of the autoclave to the foaming pressure shown in Table 2, Table 3, or Table 4 (heating-pressure step). After holding the foaming temperature and pressure for 20 minutes (holding step), the valve at the bottom of the autoclave was opened, and the foamed particles were released through a 3.6 mm diameter open orifice to atmospheric pressure (release step). During this process, carbon dioxide was injected to maintain the pressure inside the autoclave and prevent a drop in pressure. The obtained foamed particles were dried at 75°C and cured at 23°C for 24 hours or more. The bulk density of these foamed particles is shown in the "Single-Stage Foamed Particles" column of Tables 2 to 4.

[0136] (3) Two-stage foaming of foamed particles In Examples 2 and 10, the foamed particles obtained in (2) above were subjected to two-stage foaming. The foamed particles were placed in a pressure vessel and pressurized with air to adjust the internal pressure (absolute pressure) to the level described in the "Two-stage foaming conditions" column in Table 2 or Table 3. The foamed particles with internal pressure were placed in a pressure vessel, heated for 30 seconds at the vapor pressure described in Table 2 or Table 3, and then released to atmospheric pressure to obtain two-stage foamed particles. The obtained two-stage foamed particles were dried at 75°C and cured at 23°C for 24 hours or more. The bulk density of these two-stage foamed particles is shown in the "Two-stage foamed particles" column in Tables 2 and 3.

[0137] (4) Preparation of Foamed Molded Body The foamed particles obtained in (2) above, or the two-stage foamed particles obtained in (3) above, were placed in a pressure vessel and pressurized with air to adjust the internal pressure of the foamed particles to the internal pressure (absolute pressure) specified in the "Molding" column of Tables 2 to 4. The foamed particles with internal pressure were filled into a mold having a molding space of 370 mm in length x 320 mm in width x 50 mm in thickness. Then, the inside of the mold was heated with steam at the molding pressure (gauge pressure) specified in Tables 2 to 4 to fuse the foamed particles together and obtain a foamed molded body. After water cooling the inside of the mold and the surface of the foamed molded body, the foamed molded body was removed. The obtained foamed molded body was left to stand at 23°C for 1 hour, dried at 75°C for 16 hours, and cured at 23°C for 24 hours, after which its appearance was observed. The results are shown in Tables 2 to 4.

[0138] In Tables 2 to 4, the "ratio p of recycled polypropylene resin (X)" and the "ratio q of recycled polypropylene resin (Y)" correspond to the p and q of requirement (4) for the foamed particles, respectively. Furthermore, the "value of formula exp" indicates the calculation result of the formula shown in requirement (4).

[0139] As shown in Tables 1 to 3, the foamed particles prepared in the examples all satisfied requirements (1) to (5) above for these foamed particles, and the foamed molded articles prepared using these foamed particles all had a good appearance. Therefore, it can be seen that by satisfying requirements (1) to (5) above, these foamed particles can provide foamed molded articles with a good appearance while containing two types of recycled resins with different MFRs.

[0140] On the other hand, the foamed particles prepared in Comparative Examples 1 and 2 did not satisfy requirement (2) of the foamed particles (Table 1) and did not satisfy requirement (4) (Table 4). The foamed particles prepared in Comparative Example 3 did not satisfy requirement (4) (Table 4). The foamed particles prepared in Comparative Examples 1 to 3 all contained two types of recycled resin with different MFRs (Table 1), but the appearance of the foamed molded articles prepared using these foamed particles was poor (Table 4).

[0141] From the results of the examples and comparative examples, it can be seen that these foamed particles satisfy all of the above requirements, and that they can provide a foamed molded article with a good appearance while containing two types of recycled resins with different MFRs.

[0142] One embodiment of the present invention can provide a foamed molded body with a good appearance. This foamed molded body can be used in a variety of applications, such as cushioning packaging materials, logistics materials, heat insulation materials, civil engineering and construction components, and automotive components. In particular, it can be suitably used in parts of these components that are easily visible to the human eye and require a beautiful surface.

Claims

1. Polypropylene resin foam particles containing a base resin containing virgin polypropylene resin (A), recycled polypropylene resin (X), and recycled polypropylene resin (Y), satisfying the following requirements (1) to (5): (where MFR Ｘ This is the melt flow rate (g / 10 min) of recycled polypropylene resin (X), and MFR Ｙ is the melt flow rate (g / 10 min) of recycled polypropylene resin (Y), and when the total amount of recycled polypropylene resin (X) and recycled polypropylene resin (Y) is taken as 100% by weight, p is the weight % of recycled polypropylene resin (X) and q is the weight % of recycled polypropylene resin (Y). ) (1) 1 < MFR Ｘ (2) 1 < MFR Ｙ (3) MFR Ｘ ≠MFR Ｙ ; (4) 4.0<exp{(p / 100)×ln(MFR Ｘ )+(q / 100)×ln(MFR Ｙ )} < 20.0; (5) The virgin polypropylene resin (A) is a polypropylene random copolymer.

2. The polypropylene resin foam particles according to claim 1, wherein the virgin polypropylene resin (A) is an ethylene / propylene random copolymer, an ethylene / propylene / butene random copolymer, or a mixture thereof.

3. The polypropylene resin foam particles according to claim 1, wherein the base resin contains 40% to 95% by weight of the virgin polypropylene resin (A) and the recycled polypropylene resin (Y) in total, based on a total amount of 100% by weight of the virgin polypropylene resin (A), the recycled polypropylene resin (X), and the recycled polypropylene resin (Y).

4. The polypropylene resin foam particles according to claim 1, wherein the recycled polypropylene resin (X) is an ethylene / propylene random copolymer, an ethylene / propylene / butene random copolymer, an ethylene / propylene block copolymer, or an ethylene / propylene / butene block copolymer.

5. The polypropylene resin foam particles according to claim 1, wherein the recycled polypropylene resin (Y) is an ethylene / propylene random copolymer, an ethylene / propylene / butene random copolymer, an ethylene / propylene block copolymer, or an ethylene / propylene / butene block copolymer.

6. The polypropylene resin foam particles according to claim 1, wherein the recycled polypropylene resin (X) and / or the recycled polypropylene resin (Y) are derived from used automobile parts.

7. The polypropylene resin foam particles according to claim 1, wherein the melting point of the virgin polypropylene resin (A) is 130°C or higher.

8. The polypropylene resin foam particles according to claim 1, wherein the melt flow rate of the virgin polypropylene resin (A) is 3.0 g / 10 min or more and 30.0 g / 10 min or less.

9. The polypropylene resin foam particles according to claim 1, wherein the melting point of the recycled polypropylene resin (X) is 135°C or higher and 170°C or lower.

10. The polypropylene resin foam particles according to claim 1, wherein the melt flow rate of the recycled polypropylene resin (X) is 2.0 g / 10 min or more and 50.0 g / 10 min or less.

11. The polypropylene resin foam particles according to claim 1, wherein the melting point of the recycled polypropylene resin (Y) is 135°C or higher and 170°C or lower.

12. The polypropylene resin foam particles according to claim 1, wherein the melt flow rate of the recycled polypropylene resin (Y) is 2.0 g / 10 min or more and 50.0 g / 10 min or less.

13. Polypropylene resin foam particles according to claim 1, further comprising carbon black.

14. A polypropylene resin foam molded article obtained by molding polypropylene resin foam particles according to any one of claims 1 to 13.

15. A method for producing expanded polypropylene resin particles, comprising: a step of preparing a base resin by mixing a virgin polypropylene resin (A), a recycled polypropylene resin (X), and a recycled polypropylene resin (Y); and a step of preparing expanded particles from the base resin, wherein the expanded polypropylene resin particles satisfy the following requirements (1) to (5): (wherein, MFR Ｘ is the melt flow rate (g / 10 min) of the recycled polypropylene resin (X), MFR Ｙ is the melt flow rate (g / 10 min) of the recycled polypropylene resin (Y), when the total amount of the weight of the recycled polypropylene resin (X) and the weight of the recycled polypropylene resin (Y) is 100% by weight, p is the weight percentage of the recycled polypropylene resin (X), and q is the weight percentage of the recycled polypropylene resin (Y).) (1) 1 < MFR Ｘ ; (2) 1 < MFR Ｙ ; (3) MFR Ｘ ≠ MFR Ｙ ; (4) 4.0 < exp{(p / 100)×ln(MFR Ｘ ) + (q / 100)×ln(MFR Ｙ )} < 20.0; (5) the virgin polypropylene resin (A) is a polypropylene random copolymer.

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