Polypropylene-based resin foamed particles, method for producing polypropylene-based resin foamed particles, and automotive interior material

Abstract

To provide a resin product which enables effective utilization of polypropylene recovered from automobile shredder residue, is lightweight, and contains a small amount of TVOC.SOLUTION: There are provided polypropylene-based resin foamed particles and a method for producing the same, in which the foamed particles are formed from a polypropylene-based resin composition containing a polypropylene-based resin mainly composed of polypropylene derived from automobile shredder residue, the resin composition having a heat of fusion of 68 J / g or greater, the DSC curve of the foamed particles exhibiting a main endothermic peak having the largest peak area and a high-temperature peak that appears on the high-temperature side of the main endothermic peak, the heat of fusion of the high-temperature peak being between 10 J / g and 35 J / g inclusive, and the TVOC content in the foamed particles, measured according to VDA277:2011, being 10 μg / g or less (including 0).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to polypropylene-based resin foam particles having a low content of VOC components, a method for producing the same, and an automotive interior material.

Background Art

[0002] Conventionally, in order to more effectively utilize limited resources, after consumer goods such as automobiles and electric appliances are discarded, efforts have been made to recover useful parts, metals, etc. from the waste and recycle them.

[0003] As one of the materials for which such recycling is considered, for example, there is automobile shredder residue (hereinafter referred to as "ASR") generated during the process of discarding automobiles as described in Patent Document 1. The ASR contains thermoplastic resins such as polypropylene.

[0004] Polypropylene-based resins are used in various forms such as exterior parts such as bumpers and interior materials for automobiles such as instrument panels and door trims (for example, Patent Document 2).

[0005] In recent years, efforts have been made to recycle resins such as polypropylene contained in ASR, that is, to reuse them as raw materials for resin products. Specifically, it is desired to reuse the polypropylene obtained by recovering from ASR as a raw material for resin products such as interior materials for automobiles.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, the polypropylene-based resin mainly composed of polypropylene obtained from ASR had a large total amount of volatile organic compounds (TVOC) measured based on the VDA277 standard of the German Automobile Industry Association. Resin products manufactured from such polypropylene-based resins with a large amount of TVOC also had a large amount of TVOC in the products. Therefore, when used in applications such as automotive interior materials and building materials for housing, there was a problem that a process for separately removing TVOC in the products was required.

[0008] The present invention has been made in view of such a background, and aims to provide a resin product that can effectively utilize polypropylene recovered from automotive shredder residue, is lightweight, and has a low TVOC content.

Means for Solving the Problems

[0009] One aspect of the present invention is polypropylene-based resin foam particles according to the following [1] to [6]. [1] Polypropylene-based resin foam particles composed of a polypropylene-based resin composition containing a polypropylene-based resin mainly composed of polypropylene derived from automotive shredder residue, wherein the heat of fusion of the polypropylene-based resin composition is 68 J / g or more, the foam particles have a crystal structure in which a main endothermic peak with the largest peak area and a high-temperature peak, which is an endothermic peak appearing on the high-temperature side of the main endothermic peak, appear in the DSC curve obtained when the foam particles are heated from 23°C to 230°C at a heating rate of 10°C / min, the heat of fusion of the high-temperature peak of the foam particles is 10 J / g or more and 35 J / g or less, the apparent density of the foam particles is 10 kg / m 3 or more and 300 kg / m 3 or less, and the closed-cell ratio is 85% or more, The polypropylene-based resin foam particles, wherein the TVOC in the foam particles measured based on VDA277:2011 is 10 μg / g or less (including 0).

[0010] [2] The polypropylene-based resin foam particles according to [1], wherein the total content of linear alkanes having 12 to 18 carbon atoms in the foam particles measured based on VDA278:2016 is 100 μg / g or less (including 0). [3] The polypropylene-based resin foam particles according to [1] or [2], wherein the foam particles contain one or more metal elements selected from the group consisting of iron, copper, chromium, and nickel, and the content of the metal element is 100 mass ppm or more and 3000 mass ppm or less. [4] The polypropylene-based resin foam particles according to any one of [1] to [3], wherein the TVOC in the foam particles measured based on VDA277:2011 is 5 μg / g or less (including 0).

[0011] [5] The polypropylene-based resin foam particles according to any one of [1] to [4], wherein the heat of fusion of the high-temperature peak of the foam particles is 15 J / g or more. [6] The polypropylene-based resin foam particles according to any one of [1] to [5], wherein the ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the foam particles is 0.2 or more and 0.5 or less. [7] The polypropylene-based resin foam particles according to any one of [1] to [6], wherein the average bubble diameter of the foam particles is 10 μm or more and 80 μm or less. [8] The polypropylene-based resin foam particles according to any one of [1] to [7], wherein the content of the polypropylene-based resin containing polypropylene derived from automotive shredder residue as a main component is 3 mass% or more and 60 mass% or less.

[0012] Another aspect of the present invention lies in the automotive interior material according to the following [9]. [9] An automotive interior material composed of an in-mold formed body of the polypropylene-based resin foam particles according to any one of [1] to [8].

[0013] Still another aspect of the present invention relates to a method for producing polypropylene-based resin foamed particles according to the following

[10] to

[14] .

[10] A method for producing polypropylene-based resin foamed particles using a polypropylene-based resin having a TVOC of 300 μg / g or more as measured based on VDA277:2011, a dispersion step of dispersing resin particles composed of a polypropylene-based resin composition containing the polypropylene-based resin in an aqueous medium in a sealed container to obtain a dispersion; a foaming agent impregnation step of impregnating the resin particles with an inorganic physical foaming agent; a holding step of holding the temperature of the dispersion at a temperature of -15°C or higher and +10°C or lower than the melting point of the polypropylene-based resin composition for 10 minutes or more and 60 minutes or less; a foaming step of setting the temperature of the dispersion immediately before foaming to -15°C or higher and +10°C or lower than the melting point of the polypropylene-based resin composition, and releasing the resin particles together with the aqueous medium into an atmosphere at a pressure lower than the pressure in the sealed container by opening the sealed container, the method for producing polypropylene-based resin foamed particles comprising the above steps.

[0014]

[11] The method for producing polypropylene-based resin foamed particles according to

[10] , wherein the content of linear alkanes having 12 to 18 carbon atoms in the polypropylene-based resin as measured based on VDA278:2016 is 150 μg / g or more.

[12] The method for producing polypropylene-based resin foamed particles according to

[10] or

[11] , wherein the polypropylene-based resin contains one or more metal elements selected from the group consisting of iron, copper, chromium, and nickel, and the content of the metal element is 1000 mass ppm or more and 20000 mass ppm or less.

[13] The method for producing polypropylene-based resin foamed particles according to any one of

[10] to

[12] , wherein the polypropylene-based resin is a polypropylene-based resin mainly composed of polypropylene derived from automobile shredder residue.

[14] The difference [(TE)-(TH)] between the temperature (TE) of the dispersion immediately before foaming in the foaming step and the temperature (TH) of the dispersion in the holding step is more than 0°C and not more than 2°C, and the method for producing polypropylene-based resin foamed particles according to any one of

[10] to

[13] .

Advantages of the Invention

[0015] According to the polypropylene-based resin foamed particles and the method for producing the same, polypropylene recovered from automobile shredder residue can be effectively utilized. Specifically, although the polypropylene-based resin foamed particles use a polypropylene-based resin with a high VOC content mainly composed of polypropylene derived from automobile shredder residue, the TVOC in the foamed particles is low. Therefore, the foamed particles have little impact on the human body and a low environmental load. Further, according to the method for producing the polypropylene-based resin foamed particles, foamed particles with low TVOC in the foamed particles can be obtained. Therefore, the foamed particle molded body produced using the foamed particles is lightweight and can also be suitably used for applications such as automobile interior materials.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0017] In this specification, the alphabets and numerals enclosed in parentheses do not limit the present invention in any way. Also, "polypropylene-based resin particles" may be referred to as "resin particles", "polypropylene-based resin foam particles" may be referred to as "foam particles", "foam particle molded body" may be referred to as "molded body", and "polypropylene-based resin composition" may be referred to as "resin composition". Further, when the expression "~" is used in this specification, it shall be used in the sense of including the numerical values or physical values described before and after it. Also, the numerical values or physical values described as upper and lower limits shall be used in the sense of including those values.

[0018] · Foam particles The foam particles are composed of a polypropylene-based resin composition. The polypropylene-based resin composition contains a polypropylene-based resin as a main component. Specifically, the proportion of the polypropylene-based resin in the polypropylene-based resin composition is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more. The polypropylene-based resin composition may contain one or more polypropylene-based resins.

[0019] As used herein, the polypropylene-based resin refers to a homopolymer of propylene monomer (i.e., propylene homopolymer), a propylene-based copolymer containing 70% by mass or more of constitutional units derived from propylene, and a mixture of the propylene homopolymer and the propylene-based copolymer. Examples of the propylene-based copolymer include copolymers of propylene and ethylene and / or α-olefins having 4 or more carbon atoms. The propylene-based copolymer may be a random copolymer or a block copolymer. Further, the total content of the constitutional units derived from ethylene and the content of the constitutional units derived from α-olefins having 4 or more carbon atoms in the propylene-based copolymer are preferably 1 to 15% by mass, more preferably 2 to 12% by mass. As used herein, the polypropylene-based resin includes a polypropylene-based resin having a morphology in which a propylene polymer is used as a matrix (i.e., continuous phase) and a rubbery body containing the ethylene-propylene-based rubber is used as a domain (i.e., dispersed phase).

[0020] The polypropylene-based resin composition contains, for example, a polypropylene-based resin mainly composed of polypropylene derived from automotive shredder residue (i.e., ASR) recovered from automotive shredder residue. As used herein, ASR refers to "automotive shredder residue" as defined in Article 2-5 of the Act No. 87 of 2002, "Act on Recycling of End-of-Life Vehicles, etc.". More specifically, after removing recyclable parts such as engines and batteries from an end-of-life vehicle, the disassembled end-of-life vehicle is crushed, metals and other useful materials are separated from the crushed materials, and after these are recovered, the remaining material is called ASR. As an example of a method for obtaining ASR, there is a method including a disassembling step of removing reusable parts and non-reusable parts from an end-of-life vehicle, an accessory separating step of removing automotive accessories from the disassembled end-of-life vehicle that has undergone the disassembling step, and a crushing and sorting step of crushing the disassembled end-of-life vehicle and / or automotive accessories that have undergone the separating step and separating metals from the resulting crushed materials to recover ASR. More specifically, ASR can be obtained by the methods described in Patent No. 6609877, Patent No. 6627142, Patent No. 6762071, etc.

[0021] In addition to polypropylene derived from automotive components, ASR usually contains other plastics and rubbers derived from automotive components other than polypropylene-based resins such as polystyrene (PS) and acrylonitrile-butadiene-styrene resin (ABS), as well as various metals.

[0022] The method for recovering polypropylene from ASR is not particularly limited, and polypropylene can be recovered from ASR by appropriately combining known sorting methods. For the recovery of polypropylene-based resins, for example, the sorting steps shown in the following (α) to (δ) can be employed alone or in combination of two or more. (α) Magnetic separation step of separating metals and non-metals by magnetic force (β) Air classification step of separating light and heavy substances by air flow (γ) Wet specific gravity separation step of separating light and heavy specific gravity substances by a solvent (δ) Electrostatic separation step of separating resins according to their ease of charging

[0023] For example, in the wet specific gravity separation step (γ), as described in Japanese Patent No. 3711472, a method using water flow classification and sedimentation rate, or as described in Japanese Unexamined Patent Application Publication No. 2004-58032, a pulsating bubbling tank for intermittently discharging bubbles and a sedimentation tank, and a method using a device having a floating matter separation tank for separating substances lighter and heavier than water can be used to separate the polypropylene contained in ASR. Further, as described in Japanese Unexamined Patent Application Publication No. 2008-178846 and Japanese Patent No. 6762071, these sorting steps can be carried out in combination. For example, by combining the air classification step and the wet specific gravity separation step, separating the light and heavy substances contained in ASR by air flow, and then immersing each separately in a separation liquid for specific gravity separation, the polypropylene contained in ASR can be separated. The polypropylene-based resin mainly composed of polypropylene recovered from ASR obtained by performing such sorting steps can be obtained, for example, from Planic Co., Ltd.

[0024] In a polypropylene-based resin mainly composed of polypropylene derived from automotive shredder residue, the phrase "mainly composed of polypropylene derived from automotive shredder residue" means containing 50% by mass or more of polypropylene derived from automotive shredder residue, preferably 55% by mass or more, and more preferably 60% by mass or more. Examples of polypropylene other than that derived from automotive shredder residue that can be contained in the polypropylene-based resin mainly composed of polypropylene derived from automotive shredder residue include polypropylene derived from household electrical appliances. The polypropylene derived from automotive shredder residue can be, for example, the types of polypropylene described above as the polypropylene-based resin. Among them, the polypropylene derived from automotive shredder residue preferably has a morphology in which a propylene homopolymer is used as a matrix (i.e., continuous phase) and a rubbery body containing the ethylene-propylene rubber is used as a domain (i.e., dispersed phase).

[0025] In addition, a polypropylene-based resin mainly composed of polypropylene derived from ASR may contain metal components such as iron in addition to the resin component. Specifically, for example, a polypropylene-based resin mainly composed of polypropylene derived from ASR may contain one or more metal elements selected from the group consisting of iron, copper, chromium, and nickel. The content of the metal element in the polypropylene-based resin mainly composed of polypropylene derived from ASR is, for example, 1000 mass ppm or more and 20000 mass ppm or less, more specifically 2000 mass ppm or more and 10000 mass ppm or less, and even more specifically 3000 mass ppm or more and 8000 mass ppm or less. Such metal elements are considered to be metal elements derived from automotive members that could not be completely separated from the resin component in the process of obtaining the ASR or in the process of recovering polypropylene from the ASR, and metal elements generated from crushers when disassembled automobiles and / or automotive accessories are crushed in the process of obtaining the ASR. That is, the metal element in the polypropylene-based resin mainly composed of polypropylene derived from ASR is a component that is likely to be specifically contained due to the manufacturing method of polypropylene derived from ASR. The measurement method of the content of the metal element in the polypropylene-based resin mainly composed of polypropylene derived from ASR will be described in the examples. The polypropylene-based resin mainly composed of polypropylene derived from automotive shredder residue will be hereinafter referred to as "polypropylene-based resin A" as appropriate.

[0026] The polypropylene-based resin composition constituting the foam particles contains the polypropylene-based resin A mainly composed of polypropylene derived from the automotive shredder residue, and may further contain a polypropylene-based resin B other than the polypropylene-based resin A mainly composed of polypropylene derived from the automotive shredder residue. Details of the polypropylene-based resin B will be described later. For example, non-recycled polypropylene-based resins, that is, polypropylene-based resins that have not received a heat history due to molding processes such as molding for forming molded products (also referred to as "virgin polypropylene-based resins") can be mentioned.

[0027] 〔DSC Characteristics〕 When the foamed particles are heated from 23°C to 230°C at a heating rate of 10°C / min, the DSC curve obtained has a crystal structure in which, as shown in FIG. 1, the main endothermic peak Pa with the largest peak area and the high-temperature peak Pb that appears on the high-temperature side of the main endothermic peak Pa appear. The high-temperature peak Pb appears, for example, adjacent to the main endothermic peak Pa. Note that only two endothermic peaks, the main endothermic peak Pa and the high-temperature peak Pb, may appear as endothermic peaks in the DSC curve, or other endothermic peaks may appear in addition to the main endothermic peak Pa and the high-temperature peak Pb.

[0028] More specifically, the method for measuring the DSC curve and the method for determining the main endothermic peak Pa and the high-temperature peak Pb are as follows. First, in accordance with JIS K7122-1987, differential scanning calorimetry is performed under the condition of heating about 3 mg of foamed particles as a sample from 23°C to 230°C at a heating rate of 10°C / min to obtain a DSC curve. The flow rate of nitrogen gas in the measurement environment is 30 mL per minute. As described above, at least two endothermic peaks appear in the DSC curve of the foamed particles.

[0029] Next, as shown in FIG. 1, a straight line L1 is drawn connecting a point α corresponding to 80°C on the DSC curve and a point β corresponding to the melting end temperature T of the foamed particles. The melting end temperature T is the high-temperature side endpoint of the endothermic peak with the highest peak temperature, that is, the intersection of the endothermic peak with the highest peak temperature in the DSC curve and the baseline on the high-temperature side of the endothermic peak.

[0030] After drawing the straight line L1, a straight line L2 parallel to the vertical axis of the graph is drawn passing through the maximum point γ existing between adjacent endothermic peaks. By this straight line L2, adjacent endothermic peaks are divided into individual endothermic peaks. Then, the area surrounded by the portion constituting each endothermic peak in the DSC curve, the straight line L1, and the straight line L2 is taken as the peak area of the endothermic peak. Among the plurality of endothermic peaks, the endothermic peak with the largest peak area is the main endothermic peak Pa, and an endothermic peak adjacent to the main endothermic peak Pa, for example, on the high-temperature side of the main endothermic peak Pa, is the high-temperature peak Pb.

[0031] The main endothermic peak appearing in the DSC curve indicates a melting peak due to the melting of the resin component inherent to the resin, and can be referred to as the "resin inherent peak". The resin inherent peak appears due to the melting of the crystals that the resin component constituting the foamed particles usually has. On the other hand, the high-temperature peak appearing on the higher temperature side than the resin inherent peak is presumed to appear due to the melting of the secondary crystals formed in the resin component during the manufacturing process of the foamed particles. That is, when a high-temperature peak appears in the DSC curve of the foamed particles, it is presumed that secondary crystals are formed in the resin component constituting the foamed particles.

[0032] Whether the foamed particles have the crystal structure described above can be determined based on the DSC curve obtained by performing differential scanning calorimetry (DSC) under the conditions described above in accordance with JIS K7122:1987. Also, when performing DSC, 1 to 3 mg of the foamed particles may be used as a sample.

[0033] Specifically, in the DSC curve (i.e., the first DSC curve) obtained when heating from 23°C to 230°C at a heating rate of 10°C / min (i.e., the first heating) as described above, both the resin inherent peak of the resin component constituting the foamed particles and the high-temperature peak appear. In contrast, after the first heating, cooling is performed from 230°C to 23°C at a cooling rate of 10°C / min, and then heating from 23°C to 230°C is performed again at a heating rate of 10°C / min (i.e., the second heating). In the DSC curve obtained at this time (i.e., the second DSC curve), only the resin inherent peak of the resin component constituting the foamed particles can be seen. Therefore, by comparing the DSC curve obtained during the first heating with the DSC curve obtained during the second heating, the resin inherent peak and the high-temperature peak can be distinguished. The flow rate of nitrogen gas in the measurement environment shall be 30 mL per minute.

[0034] The heat of fusion of the high-temperature peak in the DSC curve is 10 J / g or more and 35 J / g or less. When the heat of fusion is less than 10 J / g, it may be difficult to sufficiently reduce the TVOC in the expanded particles measured based on VDA277:2011. Also, the in-mold formability of the expanded particles may be impaired. On the other hand, when the heat of fusion exceeds 35 J / g, the in-mold formability of the expanded particles may be impaired. From the above viewpoints, the heat of fusion of the high-temperature peak is preferably 12 J / g or more and 32 J / g or less, and more preferably 15 J / g or more and 30 J / g or less. The heat of fusion of the high-temperature peak is calculated based on the area of the high-temperature peak in the DSC curve. Specifically, the heat of fusion of the high-temperature peak can be calculated based on the area of the portion surrounded by the portion constituting the high-temperature peak Pb in the DSC curve, the straight line L1, and the straight line L2.

[0035] The heat of fusion of the polypropylene-based resin composition constituting the expanded particles is 68 J / g or more. The expanded particles of the present invention are expanded particles in which, while using a polypropylene-based resin composition having a relatively large heat of fusion as described above as the base resin, the heat of fusion of the high-temperature peak in the first DSC curve is within a predetermined range, whereby the TVOC in the expanded particles measured based on VDA277:2011 can be sufficiently reduced. Also, when the heat of fusion of the polypropylene-based resin composition is less than 68 J / g, the in-mold formability of the expanded particles and the mechanical properties of the molded article may decrease. From the above viewpoints, the heat of fusion of the polypropylene-based resin composition constituting the expanded particles is preferably 68 J / g or more and 95 J / g or less, and more preferably 69 J / g or more and 85 J / g or less.

[0036] The heat of fusion of the polypropylene-based resin composition can be determined based on the DSC curve obtained by performing differential scanning calorimetry (DSC) in accordance with JIS K7122-1987. Specifically, first, the polypropylene-based resin composition is used as a test piece, and the test piece is conditioned based on “(2) When measuring the melting temperature after performing a certain heat treatment” in “3. Conditioning of test pieces” in JIS K7122-1987. Both the heating rate and the cooling rate during conditioning are set to 10 °C / min, and the temperature range is from 23 °C to 230 °C. Then, the conditioned test piece is heated again from 23 °C to 230 °C at a rate of 10 °C / min to obtain a DSC curve (the DSC curve during the second heating). The flow rate of nitrogen gas in the measurement environment is set to 30 mL per minute. In this DSC curve, a straight line is drawn connecting the point corresponding to 80 °C and the end point on the high-temperature side of the melting peak with the highest peak temperature. The heat of fusion of the polypropylene-based resin composition can be calculated based on the area of the region enclosed by the straight line determined in this way and the melting peak of the DSC curve.

[0037] Conventionally, the polypropylene-based resin A mainly composed of polypropylene obtained from ASR had a large total amount of volatile organic compounds (TVOC) measured based on the German Automobile Industry Association standard VDA277:2011. Resin products such as injection-molded articles, extrusion-molded articles, and foam-molded articles manufactured from such polypropylene-based resin A with a large amount of TVOC also had a large amount of TVOC in the products. Therefore, in order to be used in applications such as automotive interior materials and building materials for housing, it was necessary to separately remove the TVOC in the products, which was troublesome.

[0038] The reason why the polypropylene-based resin A mainly composed of polypropylene obtained from ASR contains a large amount of TVOC measured based on VDA277:2011 is not clear, but for example, the following reasons can be considered. First, it is considered that volatile organic compounds are generated by the decomposition of a part of the resin due to the thermal history given when thermoforming or melt-kneading a polypropylene-based resin. Since the polypropylene-based resin A mainly composed of polypropylene derived from ASR has received a lot of thermal history in its manufacturing process, it is considered to contain a lot of TVOC. Second, as described above, the polypropylene-based resin A mainly composed of polypropylene derived from the ASR often contains a metal element, which is a component that is specifically likely to be contained in its manufacturing process. Specific examples of the metal element include one or more metal elements selected from the group consisting of iron, copper, chromium, and nickel. When the polypropylene-based resin A contains such a metal element, the decomposition of the resin due to the thermal history is more likely to occur. Therefore, the polypropylene-based resin A mainly composed of polypropylene derived from ASR is considered to be more likely to contain a lot of TVOC.

[0039] The polypropylene-based resin containing a lot of TVOC, such as the polypropylene-based resin A mainly composed of polypropylene derived from automotive shredder residue, is specifically a resin in which the TVOC measured based on VDA277:2011 is, for example, 300 μg / g or more, more specifically 500 μg / g or more, and even more specifically 800 μg / g or more. The upper limit of the TVOC is not particularly specified, but is generally 5000 μg / g. From the viewpoint of more effectively utilizing the effects of the present invention, the TVOC measured based on VDA277:2011 in the polypropylene-based resin containing a lot of TVOC, such as the polypropylene-based resin A mainly composed of polypropylene derived from automotive shredder residue, is preferably 300 μg / g or more and 5000 μg / g or less, more preferably 500 μg / g or more and 3000 μg / g or less, even more preferably 800 μg / g or more and 2500 μg / g or less, and particularly preferably 800 μg / g or more and 1500 μg / g or less. Incidentally, the TVOC measured based on VDA277:2011 in the virgin polypropylene-based resin commonly used as the polypropylene-based resin is usually less than 300 μg / g, and more generally less than 100 μg / g.

[0040] The foamed particles are composed of a polypropylene-based resin composition exhibiting a predetermined heat of fusion. When the foamed particles are heated from 23°C to 230°C at a heating rate of 10°C, a crystal structure appears in the DSC curve obtained, with a main endothermic peak having the largest peak area and a high-temperature peak appearing on the high-temperature side of the main endothermic peak. Since the heat of fusion of the high-temperature peak is within a predetermined range, although it is composed of a polypropylene-based resin composition containing a large amount of polypropylene-based resin A containing a lot of TVOC, the TVOC content in the foamed particles is reduced. The reason why the foamed particles of the present invention exhibit such an effect is not clear, but it is considered as follows.

[0041] First, as will be described later, the foamed particles are produced by a method called the "direct foaming method" in which resin particles impregnated with a foaming agent and dispersed in an aqueous medium in a container are discharged from the container together with the aqueous medium into an atmosphere at a pressure lower than the pressure inside the container at a predetermined foaming temperature. In such a direct foaming method, since a state is formed in which the resin particles are dispersed in a dispersion medium (such as an aqueous medium), it is considered that a part of the VOC components contained in the resin particles is discharged into the aqueous medium. Also, during foaming, the temperature inside the container is kept relatively high, and since it is rapidly discharged into an atmosphere at a pressure lower than the pressure inside the container, it is considered that a part of the VOC components contained in the resin particles is discharged at this time.

[0042] Second, the foamed particles are composed of a polypropylene-based resin composition that exhibits a predetermined heat of fusion, and have a crystal structure in which a main endothermic peak and a high-temperature peak appear, and the heat of fusion of the high-temperature peak is adjusted within a predetermined range. Such a crystal structure is formed by subjecting the polypropylene-based resin to secondary crystallization by providing a step of holding at a predetermined temperature for a predetermined time, which will be described later, in the direct foaming method. In the manufacturing process of the foamed particles, by crystallizing the polypropylene-based resin so that the heat of fusion of the high-temperature peak is within a predetermined range, it is considered that the VOC components are less likely to dissolve in the polypropylene-based resin, and the VOC components are more easily discharged from the resin particles. Note that among various manufacturing methods of foamed particles other than the direct foaming method, such as the extrusion foaming method and the impregnation foaming method, by adopting the direct foaming method, foamed particles having a heat of fusion of a desired high-temperature peak can be obtained more efficiently.

[0043] 〔VOC content〕 The TVOC (that is, the total amount of volatile organic compounds) in the foamed particles is 10 μg / g or less (including 0). Since such foamed particles and their in-mold molded articles have a low VOC content, they have a small impact on the human body and a small environmental load. Therefore, the molded article has a small environmental load and is lightweight, and can also be suitably used for applications such as automotive interior materials. From the above viewpoints, the TVOC in the foamed particles is preferably 5 μg / g or less (including 0), more preferably 3 μg / g or less (including 0), still more preferably 1 μg / g or less (including 0), and particularly preferably substantially free of volatile organic compounds. In this specification, being substantially free of volatile organic compounds means that in the measurement of the TVOC of the following foamed particles, the content of TVOC is less than the measurement lower limit value. The TVOC in the foamed particles is measured based on the measurement of organic compound emission by the headspace-GC method specified in VDA277:2011.

[0044] In addition, as a result of the study by the present inventors, it has been found that polypropylene-based resin A mainly composed of polypropylene derived from automobile shredder residue tends to contain a large amount of linear alkanes having 12 to 18 carbon atoms measured based on VDA278:2016 as VOC components. Such linear alkanes with a large number of carbon atoms have a longer molecular chain and a higher boiling point compared to, for example, toluene, xylene, ethylbenzene, hexane, etc., which have generally been focused on as conventional VOC components, and thus it has not been easy to remove them from the resin. The content of linear alkanes having 12 to 18 carbon atoms in polypropylene-based resin A mainly composed of polypropylene derived from automobile shredder residue is usually 150 μg / g or more, and from the viewpoint of being able to more effectively utilize the effects of the present invention, it is preferably 200 μg / g or more, more preferably 250 μg / g or more. On the other hand, in the case of the foamed particles being composed of a polypropylene-based resin composition containing polypropylene-based resin A containing a large amount of linear alkanes having 12 to 18 carbon atoms, the content of linear alkanes having 12 to 18 carbon atoms in the foamed particles is likely to be reduced. The foamed particles preferably have a total content of linear alkanes having 12 to 18 carbon atoms in the foamed particles measured based on VDA278:2016 of 100 μg / g or less. In this case, the foamed particles and their in-mold molded bodies have a smaller impact on the human body and a smaller environmental load. From such a viewpoint, the total content of linear alkanes having 12 to 18 carbon atoms in the foamed particles measured based on VDA278:2016 is more preferably 80 μg / g or less, further preferably 50 μg / g or less, still more preferably 30 μg / g or less, particularly preferably 25 μg / g or less, and most preferably 15 μg / g or less. The total content of linear alkanes having 12 to 18 carbon atoms in the foamed particles is measured based on the measurement of organic compound emission by the thermal desorption-GC / MS method specified in VDA278:2016.

[0045] The expanded particles contain one or more metal elements selected from the group consisting of iron, copper, chromium, and nickel, and the content of the metal element is preferably 100 mass ppm or more and 3000 mass ppm or less. As described above, according to the present invention, even when the metal element is contained in the expanded particles, the TVOC measured based on VDA277:2011 in the expanded particles is reduced. From the viewpoints of reducing the TVOC in the expanded particles and improving the in-mold formability of the expanded particles, and promoting the effective utilization of resources, the content of the metal element is more preferably 150 mass ppm or more and 2500 mass ppm or less, and even more preferably 200 mass ppm or more and 2000 mass ppm or less. Further, the expanded particles contain one or more metal elements selected from the group consisting of iron, copper, chromium, and nickel, and when the content of the metal element is within the above range, in the direct foaming method, moisture is likely to adhere to the surface of the expanded particles immediately after foaming, and it is considered that the occurrence of the phenomenon that the expanded particles fuse with each other immediately after foaming (also referred to as the blocking phenomenon) is easily suppressed.

[0046] The ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the expanded particles is preferably 0.2 to 0.5. In this case, the in-mold formability of the expanded particles and the mechanical properties of the obtained molded body can be improved in a well-balanced manner. Also, the VOC content of the expanded particles can be more reliably reduced. This is considered to be because, during the production of the expanded particles, due to the change in the crystal structure when a high-temperature peak that takes a more dense crystal state than the inherent crystals of the polypropylene-based resin is formed, the VOC components are more easily discharged outside the resin particles. From the above viewpoints, the ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the expanded particles is more preferably 0.2 to 0.4, and even more preferably 0.2 to 0.35.

[0047] The total heat of fusion of the expanded particles can be calculated based on the area of the portion surrounded by the portion constituting the main endothermic peak Pa in the first DSC curve, the portion constituting the high-temperature peak Pb, and the straight line L1 (see Fig. 1). That is, the total heat of fusion of the expanded particles is the sum of the heat of fusion of the main endothermic peak Pa and the heat of fusion of the high-temperature peak Pb. The heat of fusion of the main endothermic peak Pa can be calculated based on the area of the portion surrounded by the portion constituting the main endothermic peak Pa in the DSC curve, the straight line L1, and the straight line L2.

[0048] The temperature Tb of the apex of the high-temperature peak Pb (see Fig. 1), that is, the melting peak temperature of the high-temperature peak Pb, is preferably 155°C or higher and 175°C or lower, and more preferably 158°C or higher and 172°C or lower. In this case, the in-mold formability and mechanical properties of the expanded particles can be further improved.

[0049] The expanded particles may have a fusion layer on their surface to enhance the fusibility between the expanded particles during in-mold forming. The fusion layer may be present over the entire surface of the expanded particles or may be present on a part of the surface. Examples of the resin constituting the fusion layer include crystalline polyolefin resins having a melting point lower than the melting point of the polypropylene-based resin composition constituting the expanded particles, and amorphous polyolefin resins having a softening point lower than the melting point of the polypropylene-based resin composition constituting the expanded particles. Further, the fusion layer is preferably in a substantially non-expanded state. Note that the "non-expanded state" described above includes a state where the fusion layer does not foam and does not contain bubbles, and a state where the bubbles disappear after foaming, and means that there is almost no bubble structure in the fusion layer.

[0050] The method for forming a fused layer on the surface of the foamed particles is not particularly limited. For example, a method of foaming resin particles having a fused layer on the surface, a method of attaching a fused layer to the surface of the foamed particles after obtaining the foamed particles, etc. can be exemplified. When obtaining foamed particles by foaming resin particles having a fused layer on the surface, when manufacturing the resin particles, using an extrusion device capable of co-extrusion, a melt-kneaded product for forming the resin particle body and a resin melt for forming the fused layer are co-extruded. It is preferable to adopt a method of laminating a fused layer on the surface of the resin particles.

[0051] 〔Apparent density of foamed particles〕 The apparent density of the foamed particles is 10 kg / m 3 or more and 300 kg / m 3 or less. Thereby, it is lightweight and a molded body having good mechanical strength in a wide range of molding pressures can be easily obtained. From the viewpoint of improving this effect, the apparent density of the foamed particles is preferably 15 kg / m 3 or more and 200 kg / m 3 or less, more preferably 20 kg / m 3 or more and 100 kg / m 3 or less, and even more preferably 25 kg / m 3 or more and 80 kg / m 3 or less.

[0052] The calculation method of the apparent density of the foamed particles is as follows. First, the foamed particle group is left standing for 1 day in an environment of 50% relative humidity, 23 °C temperature, and 1 atm pressure to adjust the state of the foamed particles. After measuring the mass (unit: g) of this foamed particle group, it is submerged in a graduated cylinder filled with water at 23 °C using a wire mesh or the like, and the volume (unit: L) of the foamed particle group is obtained from the rise in the water surface. Then, the apparent density of the foamed particles (unit: kg / m 3 ) can be calculated by unit conversion of the value obtained by dividing the mass of the foamed particle group by the volume of the foamed particle group.

[0053] 〔Closed cell ratio of foamed particles〕 The closed cell ratio of the expanded particles is 85% or more. Thereby, the in-mold formability of the expanded particles can be further enhanced, and a good molded article can be easily obtained within a wide range of molding pressures. From the viewpoint of improving this effect, the closed cell ratio of the expanded particles is preferably 90% or more, and more preferably 92% or more. On the other hand, from the viewpoint of reducing the VOC components in the expanded particles, it is advantageous for the closed cell ratio to be small. However, in the above expanded particles, although the closed cell ratio is high, the TVOC is reduced. Therefore, excellent formability as described above is ensured.

[0054] The closed cell ratio of the expanded particles is a value measured using an air comparison pycnometer based on ASTM-D2856-70 Procedure C. The method for measuring the closed cell ratio of the expanded particles is specifically as follows. About 20 cm 3 of the expanded particles after conditioning the bulk volume are used as a measurement sample, and the apparent volume Va of the measurement sample is measured from the rise in the liquid level when the measurement sample is submerged in a graduated cylinder containing ethanol. After the measurement sample for which the apparent volume Va has been measured is sufficiently dried, in accordance with Procedure C described in ASTM-D2856-70, the true volume value Vx of the measurement sample measured by an air comparison pycnometer (manufactured by Tokyo Science Co., Ltd., "Beckman Model1000 Air Comparison Pycnometer") is measured. Then, using these volume values Va and Vx, the closed cell ratio of the measurement sample is calculated based on the following formula (1). The above operation is performed 5 times by changing the measurement sample, and the arithmetic mean value (N = 5) of the closed cell ratios in the 5 measurement samples is taken as the closed cell ratio of the expanded particles.

[0055] Closed cell ratio (%) = (Vx - W / ρ) × 100 / (Va - W / ρ) ··· (1) However, the meanings of the symbols in the above formula (1) are as follows. Vx: The true volume of the expanded particles measured by the above method, that is, the sum of the volume of the resin constituting the expanded particles and the total volume of the bubbles in the closed cell portion within the expanded particles (unit: cm 3 ) Va: The apparent volume of the expanded particles (unit: cm 3 ) W: The mass of the expanded particles (sample for measurement) (unit: g) ρ: The density of the resin constituting the expanded particles (unit: g / cm 3 )

[0056] [Average bubble diameter of expanded particles] The average bubble diameter of the expanded particles is preferably 10 μm or more and 150 μm or less, more preferably 20 μm or more and 120 μm or less, still more preferably 30 μm or more and 100 μm or less, and particularly preferably 50 μm or more and 80 μm or less. In this case, the in-mold formability of the expanded particles can be further enhanced, and a good molded body can be easily obtained in a wide range of molding pressures. Furthermore, when the average bubble diameter of the expanded particles is within the above range, the bubble structure constituting the expanded particles is controlled, the specific surface area of the resin can be made sufficiently large, and an independent bubble structure can be maintained. As a result, while maintaining the moldability of the expanded particles, the emission efficiency of VOC components from the resin constituting the expanded particles can be further increased.

[0057] The average bubble diameter of the expanded particles is a value calculated by the following method. First, the expanded particles are cut so as to be roughly bisected. Next, a magnified photograph is obtained so that the entire exposed cut surface is within the field of view. On the obtained magnified photograph, four line segments are drawn from the outermost surface of the expanded particles through the central part to the outermost surface on the opposite side so that the angles formed by adjacent line segments are equal (that is, the angles formed by adjacent line segments are 45°). The value obtained by dividing the total length of the four line segments thus obtained by the total number of bubbles intersecting the line segments is taken as the bubble diameter of each expanded particle.

[0058] The above operations are performed on 10 or more expanded particles randomly extracted, and the value obtained by arithmetically averaging the bubble diameters of the expanded particles obtained for each expanded particle is taken as the average bubble diameter of the expanded particles.

[0059] [Ash content of expanded particles] The ash content of the foamed particles is preferably 0.02% by mass or more and 4% by mass or less. In this case, while ensuring good in-mold formability of the foamed particles, the blending amount of polypropylene resin A mainly composed of polypropylene derived from automobile shredder residue can be increased, making it easier to utilize automobile shredder residue. From the above perspective, the ash content of the foamed particles is more preferably 0.1% by mass or more and 3% by mass or less, and even more preferably 0.2% by mass or more and 2% by mass or less.

[0060] The ash content of the foamed particles can be calculated from the mass of the residue remaining after burning the foamed particles in accordance with the direct ashing method (Method A) of JIS K7250-1:2006. The ash contained in the combustion residue of the foamed particles mainly originates from the components contained in polypropylene resin A, and specifically, it is composed of inorganic fillers, inorganic substances such as metals contained in polypropylene resin A.

[0061] · Foamed particle molded body After filling the foamed particles into a mold, a foamed particle molded body can be obtained by molding using a method called in-mold molding, in which a heating medium such as steam is supplied into the mold and heated. When steam is supplied into the mold in the in-mold molding method, the foamed particles undergo secondary foaming and their surfaces melt. As a result, the foamed particles in the mold fuse with each other, and a molded body having a desired shape corresponding to the shape of the cavity of the mold can be obtained. The density of the molded body is preferably 10 kg / m 3 or more and 300 kg / m 3 or less. In this case, the light weight and mechanical strength of the molded body can be improved in a well-balanced manner.

[0062] From the perspective of further enhancing the mechanical strength of the molded body, the density of the molded body is more preferably 15 kg / m 3 or more, even more preferably 20 kg / m 3 or more, and particularly preferably 25 kg / m 3 or more. From the perspective of further enhancing the light weight of the molded body, the density of the molded body is 200 kg / m 3More preferably, it is as follows: 100 kg / m 3 Even more preferably, it is as follows: 80 kg / m 3 Particularly preferably, it is as follows. From the above viewpoints, the density of the molded body is 15 kg / m 3 or more and 200 kg / m 3 or less. More preferably, it is 15 kg / m 3 or more and 100 kg / m 3 or less. Even more preferably, it is 20 kg / m 3 or more and 80 kg / m 3 or less. Particularly preferably, it is as follows. The density of the molded body is calculated by dividing the mass of the molded body (unit: g) by the volume (unit: L) obtained from the outer dimensions of the molded body and performing unit conversion. When it is not easy to obtain the volume from the outer dimensions of the molded body, the volume of the molded body can be obtained by the water immersion method.

[0063] Also, from the viewpoint of further improving the mechanical properties of the molded body, the closed cell ratio of the molded body is preferably 75% or more, more preferably 80% or more, and even more preferably 85% or more.

[0064] The closed cell ratio of the molded body is measured according to ASTM2865 - 70 Procedure C. Specifically, first, a test piece with a length of 25 mm × width of 25 mm × height of 30 mm is cut out from the center of the molded body, and the geometric volume Va of the test piece (unit: cm 3 ) is calculated, that is, the product of the longitudinal dimension (unit: cm), the transverse dimension (unit: cm), and the height dimension (unit: cm). Next, according to Procedure C described in ASTM - D2856 - 70, the true volume value Vx of the test piece is measured using an air comparison pycnometer (specifically, "Beckman Model1000 Air Comparison Pycnometer" manufactured by Tokyo Science Co., Ltd.). The true volume value Vx obtained by the air comparison pycnometer is the sum of the volume of the resin constituting the measurement sample and the total volume of the air bubbles in the closed cell part in the measurement sample (unit: cm 3 ).

[0065] The closed-cell ratio of the test piece (unit: %) is expressed by the following formula (2) using the mass W of the test piece (unit: g), the density ρ of the resin constituting the foamed particles (unit: g / cm 3 ), the geometric volume Va of the test piece obtained by the method described above, and the true volume Vx of the test piece. Closed-cell ratio = (Vx - W / ρ) × 100 / (Va - W / ρ) ··· (2)

[0066] The above operations are performed on 5 test pieces, and the closed-cell ratio of each test piece is calculated. Then, the arithmetic mean value of the closed-cell ratios of these 5 test pieces is taken as the closed-cell ratio of the molded body.

[0067] · Use of the foamed particle molded body The molded body is composed of foamed particles with a TVOC content of 10 μg / g or less measured based on VDA277:2011. Therefore, the TVOC content in the molded body measured based on VDA277:2011 is 10 μg / g or less. For this reason, the molded body is widely applicable to automotive members (specifically, automotive exterior materials, automotive interior materials), household electrical appliances, packaging materials, building materials for housing, etc. In particular, due to the reduction of VOC, the molded body is also preferably used as an automotive interior material, etc. Specifically, the process of removing VOC from the product is unnecessary, and it can be easily used for these applications.

[0068] · Manufacturing method of the foamed particles The manufacturing method of the foamed particles is a method for manufacturing polypropylene-based resin foamed particles in which foamed particles are manufactured using a polypropylene-based resin with a TVOC of 300 μg / g or more measured based on VDA277:2011. And despite using a polypropylene-based resin with a high VOC content, the TVOC in the foamed particles can be reduced, and foamed particles with little impact on the human body and low environmental load can be easily obtained. Also, the obtained foamed particles are excellent in moldability. Examples of the polypropylene-based resin with a TVOC of 300 μg / g or more measured based on VDA277:2011 include polypropylene-based resins mainly composed of polypropylene recovered from automotive crushed residues.

[0069] The foamed particles are produced, for example, from a dispersion step, a foaming agent impregnation step, a holding step, and a foaming step. In the dispersion step, resin particles composed of a polypropylene-based resin composition containing a polypropylene-based resin with a TVOC of 300 μg / g or more measured based on VDA277:2011 are dispersed in an aqueous medium in a sealed container to obtain a dispersion. In the foaming agent impregnation step, an inorganic physical foaming agent is impregnated into the resin particles. Note that the foaming agent impregnation step can also be performed simultaneously with the dispersion step and / or the holding step. In the holding step, the temperature of the dispersion is held at a temperature of not less than the melting point of the polypropylene-based resin composition - 15°C and not more than the melting point of the polypropylene-based resin composition + 10°C for 10 to 60 minutes. In the foaming step, the temperature of the dispersion immediately before foaming is set to not less than the melting point of the polypropylene-based resin composition - 15°C and not more than the melting point of the polypropylene-based resin composition + 10°C, and the sealed container is opened to release the resin particles together with the aqueous medium into an atmosphere at a pressure lower than the pressure in the sealed container. Such a foaming method is also called a direct foaming method.

[0070] 〔Polypropylene-based resin particles〕 In the method for producing foamed particles, first, resin particles composed of a polypropylene-based resin composition are prepared. The resin particles are composed of a polypropylene-based resin composition containing a polypropylene-based resin with a TVOC of 300 μg / g or more measured based on VDA277:2011, such as polypropylene-based resin A mainly composed of polypropylene recovered from automotive crushing residues. Further, the polypropylene-based resin composition can contain a polypropylene-based resin B such as a non-renewable polypropylene-based resin (i.e., virgin polypropylene-based resin).

[0071] · Polypropylene-based resin composition From the viewpoint of enhancing the mechanical strength and heat resistance of the molded article, the melting point of the polypropylene-based resin composition constituting the resin particles is preferably 140°C or higher. From the viewpoint of further enhancing the in-mold formability of the foamed particles and widening the range of molding pressures at which a good foamed particle molded article can be obtained, the melting point of the resin composition is preferably 165°C or lower. From the above viewpoints, the melting point of the polypropylene-based resin composition is preferably 140°C or higher and 165°C or lower, more preferably 142°C or higher and 160°C or lower, and even more preferably 145°C or higher and 155°C or lower. In the present specification, the polypropylene-based resin composition refers to a resin composition mainly composed of a polypropylene-based resin. The mass ratio of the polypropylene-based resin in the polypropylene-based resin composition is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0072] The melting point Tm of the polypropylene-based resin composition is determined based on JIS K7121:1987. Specifically, first, a test piece made of the resin composition is prepared, and the test piece is conditioned based on “(2) When measuring the melting temperature after performing a certain heat treatment” in “3. Conditioning of test pieces” in JIS K7121:1987. The heating rate and the cooling rate in the conditioning are both 10°C / min, and the temperature range is from 23°C to 230°C. The DSC curve is obtained by heating the conditioned test piece from 30°C to 230°C at a heating rate of 10°C / min, and the peak temperature of the melting peak appearing in the DSC curve is taken as the melting point. The flow rate of nitrogen gas in the measurement environment is 30 mL per minute. When a plurality of melting peaks appear in the DSC curve, the peak temperature of the melting peak with the highest height based on the baseline is taken as the melting point of the resin composition.

[0073] The resin composition contains at least a polypropylene-based resin A mainly composed of polypropylene derived from automotive shredder residue recovered from automotive shredder residue. From the viewpoint of promoting effective utilization of resources and material recycling while maintaining good in-mold formability of the expanded particles, the mass ratio of the polypropylene-based resin A mainly composed of polypropylene derived from automotive shredder residue in the resin composition is preferably 1% by mass or more and 60% by mass or less, more preferably 2% by mass or more and 50% by mass or less, and even more preferably 3% by mass to 45% by mass.

[0074] In addition to the polypropylene-based resin A mainly composed of polypropylene derived from automotive shredder residue, the resin composition may contain one or more other polypropylene-based resins B. The polypropylene-based resin A can be said to be a polypropylene-based resin containing a large amount of VOC such that the TVOC measured based on VDA277:2011 is, for example, 300 μg / g or more. The polypropylene-based resin B is a polypropylene-based resin other than the polypropylene-based resin A mainly composed of polypropylene derived from automotive shredder residue (that is, a polypropylene-based resin not mainly composed of polypropylene derived from automotive shredder residue), and examples thereof include a non-recycled polypropylene-based resin and a recycled polypropylene-based resin mainly composed of recycled polypropylene derived from sources other than automotive shredder residue. The non-recycled polypropylene-based resin is, for example, a polypropylene-based resin that has not received a heat history by molding or the like, and the recycled polypropylene-based resin is, for example, a polypropylene-based resin that has received a heat history by molding or the like. The polypropylene-based resin B can be said to be a polypropylene-based resin such that the TVOC measured based on VDA277:2011 is, for example, less than 300 μg / g. From the viewpoint of improving the in-mold formability and mechanical properties of the expanded particles in a well-balanced manner, the polypropylene-based resin composition preferably contains the polypropylene-based resin A mainly composed of polypropylene derived from automotive shredder residue and the polypropylene-based resin B. Also, from the same viewpoint, the polypropylene-based resin B is preferably a non-recycled polypropylene-based resin.

[0075] In the resin composition, the mass ratio of polypropylene resin A to polypropylene resin B is preferably polypropylene resin A: polypropylene resin B = 1:99 to 60:40, more preferably 2:98 to 50:50, and even more preferably 3:97 to 45:55. In this case, it is possible to more easily obtain foamed particles having excellent in-mold formability, and it is possible to further promote the effective use of recycled materials containing a large amount of VOC.

[0076] The melting point Tm of polypropylene resin A mainly composed of polypropylene derived from automobile shredder residue A is preferably 155°C or higher, more preferably 158°C or higher, even more preferably 160°C or higher, and particularly preferably 162°C or higher. In this case, when compressive strain is applied to the molded body, the compressive stress at a relatively small amount of compressive strain tends to be high. In addition, it is possible to more easily reduce the change in stress accompanying the increase in compressive strain. The melting point Tm of polypropylene resin A mainly composed of polypropylene derived from automobile shredder residue A is preferably 170°C or lower, more preferably 168°C or lower, and even more preferably 165°C or lower. In this case, the in-mold formability of the foamed particles can be further enhanced, and the range of molding pressure in which a good molded body can be obtained can be widened. From the above viewpoints, the melting point Tm of polypropylene resin A A is preferably 155°C or higher and 170°C or lower, more preferably 158°C or higher and 170°C or lower, even more preferably 160°C or higher and 168°C or lower, and even more preferably 162°C or higher and 165°C or lower.

[0077] The melting point Tm of polypropylene resin A mainly composed of polypropylene derived from automobile shredder residue AThe measurement method is the same as the measurement method of the melting point Tm of the polypropylene-based resin composition described above, except that a test piece made of polypropylene-based resin A mainly composed of polypropylene derived from automotive shredder residue is used instead of the polypropylene-based resin composition.

[0078] The melting point Tm of polypropylene-based resin B B is preferably 130°C or higher and less than 160°C, more preferably 135°C or higher and 158°C or lower, even more preferably 140°C or higher and 156°C or lower, and particularly preferably 142°C or higher and 155°C or lower. In this case, the foaming property in the production process of the foamed particles can be further enhanced, and the in-mold formability of the foamed particles can be further enhanced.

[0079] The melting point Tm of polypropylene-based resin B B The measurement method is the same as the measurement method of the melting point Tm of the polypropylene-based resin composition described above, except that a test piece made of polypropylene-based resin B is used instead of the polypropylene-based resin composition.

[0080] The melting point Tm of the polypropylene-based resin A A and the melting point Tm of the polypropylene-based resin B B The difference Tm A -Tm B is preferably 10°C or higher and 30°C or lower, and more preferably 15°C or higher and 25°C or lower. In this case, while the resin component derived from automotive shredder residue is contained in the foamed particles, the in-mold formability of the foamed particles can be further enhanced, and the range of molding pressure for obtaining a good foamed particle molded body can be made wider.

[0081] When measured under the conditions of a temperature of 230°C and a load of 2.16 kg, the melt flow rate (MFR) of the polypropylene-based resin A is preferably 10 g / 10 min or more and 40 g / 10 min or less, more preferably 15 g / 10 min or more and 35 g / 10 min or less, and even more preferably 20 g / 10 min or more and 30 g / 10 min or less. In this case, while containing the resin component derived from automotive shredder residue in the expanded particles, the in-mold formability of the expanded particles can be further enhanced, and the range of molding pressure in which a good expanded particle molded body can be obtained can be made wider.

[0082] Also, when measured under the conditions of a temperature of 230°C and a load of 2.16 kg, the melt flow rate (MFR) of the polypropylene-based resin B is preferably 5 g / 10 min or more and 10 g / 10 min or less, and more preferably 6 g / 10 min or more and 9 g / 10 min or less. In this case, expanded particles having good in-mold formability can be obtained more easily.

[0083] Also, the melt flow rate MFR of the polypropylene-based resin A A and the melt flow rate MFR of the polypropylene-based resin B B and the difference MFR A -MFR B is preferably 8 g / 10 min or more and 25 g / 10 min or less, more preferably 10 g / 10 min or more and 22 g / 10 min or less, and even more preferably 12 g / 10 min or more and 20 g / 10 min or less. In this case, the variation in the in-mold formability of the expanded particles can be further reduced, and expanded particles having excellent in-mold formability can be obtained more easily.

[0084] The MFRs of the above-mentioned polypropylene-based resin A and polypropylene-based resin B are values measured under the conditions of a test temperature of 230°C and a load of 2.16 kg in accordance with JIS K7210-1:2014.

[0085] The ash content of the polypropylene-based resin A mainly composed of polypropylene derived from automobile crushing residues is preferably 1% by mass or more and 25% by mass or less, more preferably 2% by mass or more and 20% by mass or less, still more preferably 3% by mass or more and 15% by mass or less, and particularly preferably 3% by mass or more and 10% by mass or less. In this case, even when the MFR of the polypropylene-based resin A is relatively high, the in-mold formability of the foamed particles can be further enhanced while maintaining the foamability of the resin particles, and the range of molding pressure in which a good foamed particle molded body can be obtained can be made wider.

[0086] The reasons for obtaining the above-described effects by using a polypropylene-based resin having an ash content within the specific range are considered to be, for example, the following reasons. From the viewpoint of enhancing the foamability of the resin particles, it is preferable to use a polypropylene-based resin having a relatively high MFR. However, the foamed particles obtained by using a polypropylene-based resin having a high MFR are liable to cause the resin to stretch excessively during in-mold molding. For example, when in-mold molding is performed at a high molding pressure, the molded body is liable to shrink. On the other hand, by using a polypropylene-based resin having an ash content within the specific range, the bubble diameter of the foamed particles can be made relatively small and the bubble film can be made thin. And such foamed particles are liable to be softened by heating, while it is considered that the resin is less likely to stretch excessively. Therefore, by using a polypropylene-based resin having an ash content within the specific range, even when in-mold molding is performed at a high molding pressure, shrinkage of the molded body is suppressed, and it is considered that the moldable range can be made wider while maintaining the foamability of the resin particles.

[0087] The ash content of the polypropylene-based resin A can be calculated from the mass of the residue remaining after burning the polypropylene-based resin A in accordance with the direct ashing method (Method A) of JIS K7250-1:2006. The ash contained in the combustion residue of the polypropylene-based resin A is mainly composed of inorganic substances contained in the polypropylene-based resin A such as inorganic fillers and metals.

[0088] Also, the ash content of the polypropylene-based resin B is preferably less than 1% by mass, more preferably less than 0.5% by mass, and even more preferably less than 0.1% by mass. In this case, during the production process of the foamed particles, while maintaining good foamability, the in-mold formability of the foamed particles can be further enhanced, and the range of molding pressure for obtaining a good molded body can be made wider.

[0089] The ash content of the polypropylene-based resin B can be calculated from the mass of the residue remaining after burning the polypropylene-based resin B in accordance with the direct ashing method (Method A) of JIS K7250-1:2006.

[0090] The polypropylene-based resin A mainly composed of polypropylene derived from the automotive shredder residue preferably contains an ethylene-propylene rubber, and more preferably contains an ethylene-propylene rubber derived from the automotive shredder residue. Also, in this case, the polypropylene-based resin A preferably exhibits a morphology in which the polypropylene-based resin forms a matrix (i.e., continuous phase) and the rubber-like body containing the ethylene-propylene rubber forms domains (i.e., dispersed phase). Further, the flexural modulus of the polypropylene-based resin A is preferably 800 MPa or more and 1200 MPa or less. In this case, even when the blending amount of the polypropylene-based resin A is relatively large, the in-mold formability of the foamed particles can be further enhanced, and the range of molding pressure for obtaining a good foamed particle molded body can be made wider. Also, in this case, the melting point of the polypropylene-based resin constituting the matrix is more preferably 160°C or higher. Furthermore, the rubber-like body domains in the polypropylene-based resin A may contain a polyethylene-based resin in addition to the ethylene-propylene rubber.

[0091] Note that ethylene-propylene rubber is a rubbery substance composed of an ethylene-propylene copolymer containing an ethylene component and a propylene component. That is, the ethylene-propylene rubber may be a copolymer of ethylene and propylene (i.e., EPM). Further, the ethylene-propylene rubber may be an ethylene-propylene copolymer (e.g., EPDM) containing components derived from monomers other than ethylene and propylene, such as diene, within a range that does not impair the above-described effects. The mass ratio of the component derived from ethylene to the component derived from propylene in the ethylene-propylene rubber (component derived from ethylene: component derived from propylene) is usually 30:70 to 80:20. The ethylene-propylene rubber is a substance different from polypropylene-based resins and polyethylene-based resins, and those skilled in the art can distinguish between the two.

[0092] The method for observing the morphology of the polypropylene-based resin A is as follows. First, an observation sample is cut out from the polypropylene-based resin A. The method of cutting out the observation sample is not particularly limited. For example, when the shape of the polypropylene-based resin A is a cylindrical pellet, the pellet may be cut perpendicularly to the height direction of the pellet so as to pass through the center of the pellet. In this way, an observation sample in which the cross section of the center of the pellet made of the polypropylene-based resin A is exposed can be obtained. Next, this observation sample is embedded in an epoxy resin, electron staining is performed with ruthenium tetroxide, and then a section is prepared from the sample using an ultramicrotome or the like. This section is placed on a grid of a transmission electron microscope (e.g., "JEM-1040Flash" manufactured by JEOL Ltd.), observed at a predetermined magnification (e.g., 5000 times), and a cross-sectional photograph (i.e., TEM photograph) of the polypropylene-based resin A is taken. From the cross-sectional photograph, the morphology of the polypropylene-based resin phase and the rubbery phase containing ethylene-propylene rubber in the polypropylene-based resin A is visually observed.

[0093] From the viewpoint of stably enhancing the in-mold formability of the foamed particles, the average diameter of the domains of the rubbery state containing the ethylene-propylene rubber in the polypropylene-based resin A is preferably 0.5 μm or more and 5 μm or less, more preferably 0.8 μm or more and 3 μm or less, and even more preferably 1 μm or more and 2 μm or less. The average diameter of the domains is calculated based on the TEM photograph. Specifically, after measuring the longest diameter and the shortest diameter of 50 domains randomly selected from the domains appearing in the TEM photograph, the arithmetic mean of these is calculated. The arithmetic mean value of the longest diameter and the shortest diameter thus obtained is taken as the average diameter of the domains of the rubbery state containing the ethylene-propylene rubber.

[0094] Also, from the viewpoint of stably enhancing the in-mold formability of the foamed particles, the area ratio of the domains in the morphology is preferably 20% or more and 40% or less, and more preferably 25% or more and 35% or less.

[0095] The area ratio of the domains is calculated based on the TEM photograph. More specifically, using image analysis software (for example, "WinROOF2013" manufactured by Mitani Corporation), a monotone process is performed to make the domain part in the TEM photograph black and the part other than the domain white for measurement. Then, the total area occupied by the domain part in the measurement target is calculated by the image analysis software, and the ratio of the total area occupied by the domain part to the total area of the entire measurement target is calculated. The ratio of the total area occupied by the domain part thus obtained is taken as the area ratio of the domains in the morphology of the polypropylene-based resin A. Note that the part other than the domains contains a matrix and inorganic substances such as talc.

[0096] The flexural modulus M of the polypropylene-based resin B B and the flexural modulus M of the polypropylene-based resin A A and the difference M B -M Ais preferably from -100 MPa to 500 MPa, more preferably from -50 MPa to 300 MPa, and even more preferably from -30 MPa to 100 MPa. In this case, it becomes easier to enhance the secondary foaming property of the foamed particles during in-mold forming. As a result, it is possible to further enhance the in-mold formability of the foamed particles under relatively low molding pressure conditions and widen the range of molding pressures in which a good foamed particle molded body can be obtained.

[0097] As reasons for obtaining the above-described effects, for example, the following reasons can be considered. Generally, in a polypropylene-based resin containing an ethylene-propylene-based rubber such as impact polypropylene, when the melting point increases, the flexural modulus also tends to increase. On the other hand, the polypropylene-based resin A mainly composed of polypropylene derived from the automobile crushing residue has a relatively low ratio of flexural modulus to melting point. By producing resin particles using such a polypropylene-based resin A having a relationship between melting point and flexural modulus and a polypropylene-based resin B, it is considered that the foaming property of the resin particles is good and it becomes easy to obtain foamed particles that can be well molded even under relatively low molding pressure conditions. Therefore, it is considered that foamed particles excellent in in-mold formability can be stably obtained while more effectively utilizing the resin component derived from the automobile crushing residue.

[0098] The flexural modulus M of the polypropylene-based resin A A and the flexural modulus M of the polypropylene-based resin B B can be determined based on JIS K7171:2008.

[0099] In the polypropylene-based resin composition, other polymers such as resins other than the polypropylene-based resin and elastomers other than ethylene-propylene rubber may be included as long as the above-described effects are not impaired. Examples of other resins that can be included in the polypropylene-based resin composition include thermoplastic resins such as polystyrene-based resins, polyamide-based resins, polyester-based resins, polyethylene-based resins, and acrylonitrile-butadiene-styrene resins. Examples of other elastomers include ethylene-butene rubber and ethylene-octene rubber. These other polymers may be derived from ASR. The content of the other polymer in the polypropylene-based resin composition is preferably 20% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less, and particularly preferably 3% by mass or less.

[0100] In the polypropylene-based resin composition, inorganic substances such as talc, silica, and glass fiber may be included as long as the above-described effects are not impaired. The main component of the inorganic substance contained in the resin composition is preferably talc. In this case, even when a resin composition having a relatively high melting point is used, the fusion property of the foamed particles can be further improved. As a result, the in-mold moldability of the foamed particles can be further improved. The reason for this is considered to be that the average bubble diameter of the foamed particles tends to be small.

[0101] In the polypropylene-based resin composition, additives such as a bubble regulator, a crystal nucleating agent, a flame retardant, a flame retardant aid, a plasticizer, an antistatic agent, an antioxidant, an ultraviolet absorber, a light stabilizer, an antibacterial agent, and a colorant may be included as long as the above-described effects are not impaired. The resin composition preferably contains carbon black as a colorant. In this case, for example, the content of carbon black in the resin composition may be 0.1% by mass or more and 5% by mass or less, may be 0.5% by mass or more and 4% by mass or less, or may be 1% by mass or more and 3% by mass or less.

[0102] Polypropylene-based resin B is preferably a polypropylene-based copolymer containing 70% by mass or more of constituent units derived from propylene, and more preferably a polypropylene-based copolymer containing 80% by mass or more of constituent units derived from propylene. Note that the polypropylene-based resin B may contain two or more types of polypropylene-based copolymers.

[0103] From the viewpoint of further enhancing the in-mold formability of the foamed particles and widening the range of molding pressures for obtaining a good foamed particle molded body, polypropylene-based resin B is preferably a copolymer of propylene and ethylene and / or an α-olefin having 4 or more carbon atoms. Further, the copolymer is more preferably a random copolymer (that is, a polypropylene-based random copolymer).

[0104] Examples of the α-olefin used in the polypropylene-based copolymer include 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-butene, and the like. The total content of the constituent units derived from ethylene and the constituent units derived from an α-olefin having 4 or more carbon atoms (that is, the content of the comonomer component) in the polypropylene-based copolymer is preferably 0.5% by mass or more and 15% by mass or less, more preferably 1% by mass or more and 10% by mass or less, and even more preferably 2% by mass or more and 5% by mass or less.

[0105] Polypropylene-based resin B is preferably a polypropylene-based resin containing a constituent unit derived from ethylene (that is, an ethylene component) as a copolymer component and / or a polypropylene-based resin containing constituent units derived from ethylene and 1-butene (that is, an ethylene component and a butene component) as a copolymer component. Examples of the polypropylene-based resin containing an ethylene component include propylene-ethylene random copolymers. Further, examples of the polypropylene-based resin containing an ethylene component and a butene component include propylene-ethylene-butene random copolymers.

[0106] [Preparation of Resin Particles] In the above manufacturing method, first, resin particles composed of a polypropylene resin composition containing the polypropylene resin A are prepared. The method for preparing the resin particles is not particularly limited. For example, when producing resin particles by the strand cut method, the polypropylene resin A and the polypropylene resin B compounded as necessary are supplied to an extruder, and kneaded while being heated in the extruder to obtain a kneaded product in a molten state. This molten kneaded product is extruded in a strand shape from small holes of a die attached to the downstream side of the extruder. By cutting the strand-shaped extrudate to a desired length while pulling it, resin particles composed of a polypropylene resin composition containing the polypropylene resin A can be obtained.

[0107] The operation of manufacturing the molten kneaded product of the polypropylene resin composition and the operation of manufacturing resin particles from the molten kneaded product may be carried out using the same extruder as described above. Also, for example, the above two operations may be carried out using separate extruders or the like.

[0108] In the above manufacturing method, the resin particles containing a foaming agent dispersed in an aqueous medium in a container are foamed by a method called the "direct foaming method" in which the resin particles are discharged together with the aqueous medium into an atmosphere at a pressure lower than the pressure in the container. Hereinafter, a preferred embodiment of the foaming method will be described.

[0109] In the above manufacturing method, resin particles are dispersed in an aqueous medium in a container to obtain a dispersion. The aqueous medium is a liquid such as water. Specifically, first, the resin particles are placed in a container such as a sealed container and dispersed in the aqueous medium. At this time, a dispersant, a dispersion aid, a surfactant, etc. for dispersing the resin particles in the aqueous medium in the container may be added as necessary.

[0110] As the dispersant, for example, inorganic fine particles such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, mica, etc. can be used. These inorganic fine particles may be used alone or two or more kinds of inorganic fine particles may be used in combination. As the dispersion aid, for example, aluminum sulfate etc. can be used. Further, as the surfactant, for example, anionic surfactants such as sodium alkylbenzene sulfonate, sodium dodecylbenzene sulfonate, sodium alkanesulfonate, etc. can be used. These surfactants may be used alone or two or more kinds of surfactants may be used in combination.

[0111] Next, a foaming agent is supplied into the container, and the pressure in the container is increased to impregnate the resin particles with the foaming agent. Thereby, resin particles containing the foaming agent can be obtained. At this time, by heating the resin particles in the container together with the aqueous medium, the impregnation of the foaming agent into the resin particles can be promoted.

[0112] As the foaming agent, from the viewpoints such as not being detected as a VOC component and having a small environmental load and excellent handleability, for example, inorganic physical foaming agents such as carbon dioxide, air, nitrogen, helium, argon, etc. can be used. Among them, carbon dioxide is preferably used. The addition amount of the foaming agent is preferably 0.1 part by mass or more and 30 parts by mass or less, and preferably 0.5 part by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the resin particles.

[0113] The pressure inside the container immediately before foaming is preferably 0.5 MPa(G) or more, more preferably 1.0 MPa(G) or more, and even more preferably 1.5 MPa(G) or more in terms of obtaining lighter foamed particles. Further, from the viewpoint of more easily adjusting the heat of fusion of the high-temperature peak of the obtained foamed particles within a desired range and further promoting the discharge of VOC components from the resin particles, the pressure inside the container immediately before foaming is preferably 1.8 MPa(G) or more, and more preferably 2.0 MPa(G) or more in terms of gauge pressure. On the other hand, the pressure inside the container is preferably 4.0 MPa(G) or less in terms of gauge pressure. Within the above range, there is no risk of container breakage, explosion, etc., and foamed particles with a desired apparent density can be safely produced. Note that the G in parentheses attached after the unit of pressure means that the pressure is gauge pressure.

[0114] After impregnating the resin particles with a foaming agent, the contents of the container are discharged into an atmosphere at a pressure lower than that of the container. As a result, the resin particles foam to form a cell structure, and are cooled by the outside air (i.e., the atmosphere) to stabilize the cell structure, and foamed particles are obtained.

[0115] In the above production method, a step of adjusting the crystal structure of the resin component constituting the resin particles is performed between the dispersion of the resin particles in an aqueous medium and the foaming of the resin particles. By foaming after adjusting the crystal structure of the resin component, the VOC content in the foamed particles can be lowered, and it becomes possible to produce foamed particles with a TVOC of 10 μg / g or less measured based on VDA277:2011. Further, foamed particles having excellent in-mold formability and excellent mechanical strength can be easily obtained.

[0116] Adjusting the crystal structure of the resin component is carried out by holding the temperature of the dispersion liquid in which the resin particles are dispersed at a temperature of Tm - 15°C or higher and Tm + 10°C or lower for 10 to 60 minutes (that is, the holding step). Here, Tm is the melting point of the polypropylene-based resin composition constituting the resin particles. By foaming the resin particles after this holding step, adhesion between the resin particles in the holding step can be suppressed, and foamed particles having a crystal structure in which a specific melting peak (high-temperature peak) appears can be obtained. From the viewpoint of easily adjusting the heat of fusion of the high-temperature peak of the obtained foamed particles within a desired range, the temperature of the dispersion liquid in the holding step is preferably held at a temperature of Tm - 10°C or higher and Tm + 10°C or lower for 10 to 60 minutes, more preferably held at a temperature of Tm - 5°C or higher and Tm + 10°C or lower for 10 to 60 minutes, and even more preferably held at a temperature of Tm or higher and Tm + 10°C or lower for 10 to 60 minutes.

[0117] From the viewpoint of easily adjusting the heat of fusion of the high-temperature peak of the obtained foamed particles within a desired range, in the foaming step, the temperature of the dispersion liquid immediately before foaming is set to Tm - 15°C or higher and Tm + 10°C or lower. From the same viewpoint, the temperature of the dispersion liquid during foaming is preferably Tm - 10°C or higher and Tm + 10°C or lower, more preferably Tm - 5°C or higher and Tm + 10°C or lower, and even more preferably Tm or higher and Tm + 10°C or lower.

[0118] Also, the difference [(TE) - (TH)] between the temperature (TE) of the dispersion liquid immediately before foaming in the foaming step and the temperature (TH) of the dispersion liquid in the holding step is preferably more than 0°C and 2°C or less. In this case, the heat of fusion of the high-temperature peak of the obtained foamed particles can be easily adjusted within a desired range, and the emission of VOC components from the resin particles can be further promoted. From such a viewpoint, [(TE) - (TH)] is more preferably 0.1°C or higher and 1.5°C or lower, and even more preferably 0.2°C or higher and 1.0°C or lower. Generally, the temperature of the dispersion liquid (TE) immediately before foaming in the foaming step and the temperature of the dispersion liquid (TH) in the holding step are set to be constant in each step. However, when the temperature TE and / or TH is not constant in each step, the temperature used for calculating the above difference [(TE)-(TH)] shall be the temperature set for the longest time in each step.

[0119] In the method for producing the foamed particles, resin particles that have undergone the holding step may be prepared in advance, and the foamed particles may be obtained by foaming these resin particles. From the perspective of enhancing the productivity of the foamed particles, in the presence of a foaming agent, the resin particles dispersed in the dispersion medium in the container are heated to perform the holding step, and then the content of the sealed container is discharged from the container into an atmosphere at a pressure lower than the pressure in the container to foam the resin particles, whereby it is preferable to obtain foamed particles having a crystal structure in which a specific melting peak described later appears.

[0120] In the method for producing the foamed particles, when foaming the resin particles, the resin particles may be foamed in one step as described above, or the resin particles may be foamed in two or more steps. When the resin particles are foamed in two steps, first, in the first foaming step, the resin particles are foamed by the direct foaming method to obtain first-stage foamed particles. In the second foaming step, for example, the first-stage foamed particles are pressure-treated with air or the like to increase the pressure (internal pressure) in the bubbles of the first-stage foamed particles, and then the first-stage foamed particles are heated with steam or the like to further foam them. By foaming the resin particles in multiple steps in this way, it is possible to easily obtain foamed particles with a higher foaming ratio (that is, a lower bulk density).

Examples

[0121] Examples of the method for producing the foamed particles will be described.

[0122] (Polypropylene-based resin) Table 1 shows the properties of the polypropylene-based resin used in the production of the foamed particles, etc. In the columns of the resin particles in Tables 2 and 3, the formulation of the polypropylene-based resin composition used in the production of the foamed particles and the properties of the polypropylene-based resin composition constituting the resin particles, etc. are shown. Note that the density of the polypropylene-based resin used in this example is 900 kg / m3 in all cases.

[0123] "rPP1" is an ethylene-propylene random copolymer. "rPP1" is a non-recycled polypropylene-based resin and corresponds to the aforementioned polypropylene-based resin B.

[0124] "Re-PP1" is a polypropylene-based resin mainly composed of polypropylene derived from ASR recovered from ASR and corresponds to the aforementioned polypropylene-based resin A. Specifically, it is "PLC-A02" manufactured by Planic Co., Ltd. Further, Re-PP1 contains inorganic substances such as metal elements and talc. Also, the shape of Re-PP1 is a cylindrical pellet, the average length in the height direction of the pellet (the average length in the extrusion direction during pellet production) is 3 mm, the diameter of the pellet is 3 mm, and the average mass of the pellet is 16 mg. When the morphology of Re-PP1 used in this example was observed by the method described later, a morphology was shown in which polypropylene was used as the matrix M and a rubber-like body containing an ethylene-propylene rubber was used as the domain D (see Figure 2).

[0125] Also, "HMS-PP1" is high melt strength propylene, specifically, MFX3 manufactured by Japan Polypropylene Corporation. "HMS-PP1" is a non-recycled polypropylene-based resin and corresponds to the aforementioned polypropylene-based resin B.

[0126]

Table 1

[0127] The measurement methods for the physical property values shown in Tables 1 to 3 are as follows.

[0128] 〔Melting point, heat of fusion〕 The melting point was determined based on JIS K7121:1987. Specifically, first, the state of the resin composition or the test piece made of resin was adjusted based on “3. Conditioning of test pieces” in JIS K7121:1987, “(2) When measuring the melting temperature after performing a certain heat treatment”. Both the heating rate and the cooling rate during conditioning were 10 °C / min, and the temperature range was from 23 °C to 230 °C. A DSC curve was obtained by heating the conditioned test piece from 30 °C to 230 °C at a heating rate of 10 °C / min. The flow rate of nitrogen gas in the measurement environment was 30 mL per minute. Then, the peak temperature of the melting peak appearing in the DSC curve was taken as the melting point. As the measuring device, a heat flux differential scanning calorimeter (manufactured by SII NanoTechnology Inc., model number: DSC7020) was used.

[0129] Also, the heat of fusion of the resin composition or the resin was determined from the DSC curve obtained by performing differential scanning calorimetry in accordance with JIS K 7122:1987. Specifically, a straight line was drawn on the DSC curve obtained in the above-mentioned measurement of the melting point, connecting the point corresponding to 80 °C on the DSC curve and the end point on the high-temperature side of the melting peak with the highest peak temperature. Then, the heat of fusion was calculated based on the area of the region surrounded by the straight line thus determined and the melting peak of the DSC curve.

[0130] 〔Melt flow rate MFR〕 In accordance with JIS K7210-1:2014, the melt flow rate (i.e., MFR) of the resin was measured under the conditions of a temperature of 230 °C and a load of 2.16 kg.

[0131] 〔Flexural modulus〕 The resin was heat-pressed at 230 °C to produce a 4-mm sheet, and a test piece with a length of 80 mm × width of 10 mm × thickness of 4 mm was cut out from this sheet. The flexural modulus of this test piece was determined in accordance with JIS K7171:2008. The radius R1 of the indenter and the radius R2 of the support base were both 5 mm, the distance between the fulcrums was 64 mm, and the test speed was 2 mm / min.

[0132] 〔Morphology of Polypropylene-based Resin A〕 The morphology of polypropylene-based resin A (i.e., "Re-PP1" in Table 1) mainly composed of the polypropylene derived from the ASR was observed by the following method. First, cylindrical pellets made of the polypropylene-based resin A derived from the ASR were cut perpendicularly to the height direction of the pellets so as to pass through the center thereof, and an observation sample with the cross-section of the center of the pellets exposed was prepared. Next, this observation sample was embedded in an epoxy resin, electron staining was performed with ruthenium tetroxide, and then a section including the center of the pellets was prepared from the sample using an ultramicrotome or the like. This section was placed on a grid of a transmission electron microscope (for example, "JEM-1040Flash" manufactured by JEOL Ltd.), observed at a magnification of 5000 times, and a cross-sectional photograph (i.e., TEM photograph) of the polypropylene-based resin A was taken.

[0133] From the cross-sectional photograph, the morphology of the polypropylene phase and the rubbery phase containing ethylene-propylene rubber in the polypropylene-based resin A was visually observed. As an example, a cross-sectional photograph of the polypropylene-based resin A is shown in FIG. 2. In FIG. 2, the domain D of the rubbery body containing ethylene-propylene rubber is shown in a relatively dark color tone, and the matrix M of polypropylene is shown in a lighter color tone than the domain D.

[0134] Also, the average diameter of the domain of the rubbery body containing ethylene-propylene rubber was calculated based on the TEM photograph. More specifically, the longest diameter and the shortest diameter of 50 domains randomly selected from the domains appearing in the TEM photograph were measured respectively. The arithmetic mean value of the longest diameter and the shortest diameter thus obtained was taken as the average diameter of the domain of the rubbery body containing ethylene-propylene rubber. As a result, the average diameter of the domain of the rubbery body containing ethylene-propylene rubber in the polypropylene-based resin A was 1.2 μm.

[0135] Also, the area ratio of the domain in the morphology was calculated based on the TEM photograph. More specifically, using image analysis software ("WinROOF2013" manufactured by Mitani Corporation), monotone processing was performed on the TEM photograph to make the domain part black and the part other than the domain white, and it was made the measurement target. Then, the total area occupied by the domain part in the measurement target was calculated by the image analysis software, and the ratio of the total area occupied by the domain part to the total area of the entire measurement target was calculated. As a result, the area ratio of the domain in the morphology of polypropylene-based resin A was 28%.

[0136] Next, the configuration and manufacturing method of the foamed particles of this example will be described.

[0137] (Example 1) Polypropylene-based resin B (specifically, rPP1 in Table 1), polypropylene-based resin A mainly composed of polypropylene derived from ASR (specifically, Re-PP1 in Table 1), and a foam regulator were charged into an extruder, and a molten kneaded product containing polypropylene-based resin A and polypropylene-based resin B was formed in the extruder. The blending ratio of polypropylene-based resin A and polypropylene-based resin B (where the total amount of both is 100% by mass) is shown in Table 2. Also, zinc borate was used as the foam regulator. The addition amount of zinc borate was 500 mass ppm with respect to the total of polypropylene-based resin A and polypropylene-based resin B. Note that "PP" in the specification means "polypropylene".

[0138] Thereafter, the molten kneaded product was extruded in a strand shape from the small holes of the die provided on the downstream side of the extruder. The resin temperature during extrusion was 220°C as shown in Table 2. This strand-shaped extrudate was taken up, cooled in water, and then cut into an appropriate length using a pelletizer to obtain resin particles. The average weight of the resin particles was 1.0 mg.

[0139] The resin particles obtained as described above were foamed by the direct foaming method. Specifically, first, 1 kg of resin particles were put into a container with an internal volume of 5 L together with 3 L of water as an aqueous medium. Next, 0.3 parts by mass of a dispersant and 0.02 parts by mass of sodium alkylbenzene sulfonate and 0.01 parts by mass of aluminum sulfate as a dispersion aid were added to the container per 100 parts by mass of the resin particles to disperse the resin particles in the aqueous medium. Kaolin was used as the dispersant.

[0140] Thereafter, while stirring the inside of the container, as shown in Table 2, when the temperature of the dispersion medium was 25°C, carbon dioxide as a foaming agent was supplied into the sealed container at the impregnation pressure shown in Table 2, and then the temperature inside the container was raised to 151.8°C. By holding this temperature for 15 minutes, the foaming agent was impregnated into the resin particles while promoting the secondary crystallization of the polypropylene-based resin (holding step). Thereafter, after adjusting the temperature inside the container to 152.3°C, the container was opened, and the resin particles were foamed by discharging the contents into an atmospheric pressure atmosphere (foaming step). The pressure inside the container at this time (that is, the foaming pressure) was 2.1 MPa(G). By the operations in these holding step and foaming step, the heat of fusion of the high-temperature peak of the foamed particles obtained was adjusted within the predetermined range, and the discharge of VOC components from the resin particles was promoted. These foamed particles were dried in an atmosphere at a temperature of 23°C and a relative humidity of 50% for 24 hours. Thus, the foamed particles of Example 1 were obtained.

[0141] (Example 2, Example 3) The manufacturing methods of the foamed particles of Example 2 and Example 3 are generally the same as the manufacturing method of the foamed particles of Example 1, except that the mass ratio of polypropylene-based resin A and polypropylene-based resin B and the manufacturing conditions were changed as shown in Table 2.

[0142] (Example 4) The manufacturing method of the foamed particles of Example 4 is generally the same as Example 3, except that the manufacturing conditions in the foaming step were changed as shown in Table 2.

[0143] (Comparative Example 1) This example is an example of manufacturing foamed particles by impregnation foaming. Specifically, first, resin particles were manufactured by the same method as in Example 2.

[0144] The obtained resin particles were foamed by the impregnation foaming method. Specifically, first, 1 kg of resin particles were put into a sealed container with a volume of 5 L. Next, carbon dioxide was supplied into the container under the conditions of a temperature of 25°C and a pressure of 4.0 MPa (G), and the temperature was maintained for 24 hours to impregnate the resin particles with carbon dioxide as a foaming agent. Then, steam at 0.4 MPa (G) was supplied into the container to heat the resin particles, and the resin particles were foamed under the condition of a temperature of 143°C to obtain foamed particles.

[0145] (Comparative Example 2) Comparative Example 2 is an example of manufacturing foamed particles by the extrusion foaming method. Specifically, first, polypropylene-based resin B (specifically, HMS-PP1 in Table 1), polypropylene-based resin A mainly composed of polypropylene derived from ASR (specifically, Re-PP1 in Table 1), and a cell regulator were put into an extruder, and a molten resin kneaded product containing polypropylene-based resin A and polypropylene-based resin B was formed in the extruder. The mass ratio of polypropylene-based resin A to polypropylene-based resin B is as shown in Table 3.

[0146] While heating the resin kneaded product in the extruder at a temperature of 220°C, carbon dioxide was supplied to the molten resin kneaded product under the condition of a pressure of 4.0 MPa (G) to produce a foaming molten resin kneaded product in the extruder. Then, the foaming molten resin was extruded in a strand shape from the small holes of the die provided on the downstream side of the extruder and foamed under the conditions of a temperature of 220°C and a pressure of 0.53 MPa (G), and at the same time, it was cut to an appropriate length using a pelletizer. In this way, extrusion foamed particles were obtained.

[0147] (Comparative Example 3) This example is about manufacturing foamed particles composed of a composite resin of a polypropylene-based resin and a polystyrene-based resin by the direct foaming method. Specifically, first, a polypropylene-based resin (manufactured by Prime Polymer Co., Ltd., trade name: F-794NV, melting point 134°C, virgin polypropylene) and zinc borate were melt-kneaded in an extruder. Then, the melt-kneaded material in the molten state was extruded in a strand form from small holes of a die provided on the downstream side of the extruder. The resin temperature during extrusion was 220°C. This strand-shaped extrudate was taken up, cooled in water, and then cut to an appropriate length using a pelletizer to obtain polypropylene-based resin seeds particles.

[0148] 1000 g of deionized water was put into an autoclave with an internal volume of 3 liters (L) equipped with a stirring device, and after adding 6.0 g of sodium pyrophosphate and dissolving it, 12.9 g of powdered magnesium nitrate hexahydrate was added, and it was stirred at room temperature for 30 minutes to synthesize a magnesium pyrophosphate slurry as a suspending agent. After synthesizing the magnesium pyrophosphate slurry, 1.0 g of sodium lauryl sulfonate (10% by mass aqueous solution) as a surfactant, 0.5 g of sodium nitrite as a water-soluble polymerization inhibitor, and 150 g of the polypropylene-based resin seeds particles were added to this reaction product slurry. Next, 1.675 g of benzoyl peroxide (manufactured by NOF Corporation, trade name: Niper BW) as a polymerization initiator, 0.26 g of t-butyl peroxy-2-ethylhexyl monocarbonate (manufactured by NOF Corporation, trade name: Perbutyl E), and 4.25 g of 1,1-di(tert-butylperoxy)cyclohexane (manufactured by Arkema Yoshitomi Co., Ltd., trade name: Lupersol 331M70) as a crosslinking agent were dissolved in 335 g of styrene and 15 g of butyl acrylate as styrene-based monomers, and were put into the autoclave being stirred at 500 rpm. After replacing the inside of the autoclave with nitrogen, the temperature increase was started, and the temperature was raised to 86°C over one and a half hours.

[0149] After maintaining at 86°C for 30 minutes, the stirring speed was reduced to 450 rpm, and it was cooled to 80°C over 30 minutes. After cooling to 80°C, it was maintained at 80°C for 5 hours, heated to 120°C over 2 hours, and then maintained at 120°C for 5 hours as it was. Thereafter, it was cooled to 30°C over about 6 hours. After cooling, the content was taken out, nitric acid was added to dissolve magnesium pyrophosphate adhering to the surface of the composite resin particles, then dehydrated and washed with a centrifuge, and the moisture adhering to the surface was removed with an air flow drying device to obtain composite resin particles with an average particle diameter of 1.5 mm.

[0150] 1 kg of the composite resin particles obtained as described above was charged into a 5 L pressure-resistant container equipped with a stirrer together with 3 liters (L) of water as a dispersion medium. Further, 5 g of kaolin as a dispersant and 0.6 g of sodium alkylbenzene sulfonate as a surfactant were added to the dispersion medium. Next, while stirring at 300 rpm, carbon dioxide as an inorganic physical foaming agent was supplied to the pressure-resistant container at a ratio of 4 parts by mass per 100 parts by mass of the composite resin particles under the condition of a pressure of 1.0 MPa(G), and the temperature in the pressure-resistant container was raised to 165°C under stirring and maintained at the same temperature for 15 minutes. Thereafter, the composite resin particles were foamed by discharging the content into an atmospheric pressure atmosphere under the conditions of a foaming temperature of 165°C and a foaming pressure of 0.4 MPa(G) to obtain composite resin foamed particles.

[0151] (Comparative Example 4) The method for producing the foamed particles of Comparative Example 4 is generally the same as the method for producing the foamed particles of Example 2 except that the production conditions in the foaming step were changed as shown in Table 3.

[0152] (Comparative Example 5) The method for producing the foamed particles of Comparative Example 5 is generally the same as the method for producing the foamed particles of Example 2 except that the production conditions in the foaming step were changed as shown in Table 3.

[0153] The evaluation methods for the resin particles and foamed particles obtained as above are as follows. The results are shown in Table 2 and Table 3.

[0154] 〔Content of TVOC in resin particles and foamed particles〕 The total VOC content of the resin particles and the foamed particles was measured based on VDA277:2011 "Measurement of Organic Compound Emission by Headspace-GC Method". The measurement method for the total VOC content of the resin raw materials in Table 1 is the same as that of the resin particles and the foamed particles.

[0155] 〔Content of linear alkane components with 12 to 18 carbon atoms in the foamed particles〕 The content of linear alkane components with 12 to 18 carbon atoms in the foamed particles was measured based on VDA278:2016 "Measurement of Organic Compound Emission by Thermal Desorption-GC / MS Method". Note that when the VOC component content is 2 μg / g or less, it cannot be detected, and in this case, the content was set to 0. The measurement method for the content of linear alkane components in the resin raw materials in Table 1 is the same as that of the foamed particles.

[0156] Since VDA277:2011 and VDA278:2016 are standards defined by different measurement methods and measurement conditions, the measurement results of the two do not necessarily match. Specifically, when the same object is used as the measurement sample, volatile organic compounds may be detected when measured based on VDA278:2016, while the total amount of volatile organic compounds (TVOC) measured based on VDA277:2011 may be 0.

[0157] 〔VOC Evaluation〕 For the foamed particles, the case where the TVOC measured based on the VDA277:2011 standard is 10 μg / g or less and the total content of linear alkanes with 12 to 18 carbon atoms measured based on the VDA278:2016 standard is 100 μg / g or less was evaluated as "A". Also, the case where either the TVOC measured based on the VDA277:2011 standard exceeds 10 μg / g or the total content of linear alkanes with 12 to 18 carbon atoms measured based on the VDA278:2016 standard exceeds 100 μg / g was evaluated as "B". Further, the case where the TVOC measured based on the VDA277:2011 standard exceeds 10 μg / g and the total content of linear alkanes with 12 to 18 carbon atoms measured based on the VDA278:2016 standard exceeds 100 μg / g was evaluated as "C".

[0158] 〔Apparent density of expanded particles〕 The expanded particles were left standing for 24 hours or more in an environment with a relative humidity of 50%, a temperature of 23°C, and an atmospheric pressure of 1 atm to adjust the state of the expanded particles. After measuring the mass (unit: g) of this group of expanded particles, they were submerged in a graduated cylinder filled with water at 23°C using a wire mesh or the like, and the volume (unit: L) of the group of expanded particles was determined from the rise in the water level. Then, the value obtained by dividing the mass of the group of expanded particles by the volume of the group of expanded particles was converted to the appropriate units to calculate the apparent density (unit: kg / m 3 ) of the expanded particles.

[0159] 〔Average bubble diameter of expanded particles〕 The expanded particles were cut approximately in half. Next, a magnified photograph was taken so that the entire exposed cut surface was within the field of view. On the obtained magnified photograph, four line segments were drawn from the outermost surface of the expanded particle through the central part to the outermost surface on the opposite side such that the angles formed by adjacent line segments were equal (that is, the angles formed by adjacent line segments were 45°). The value obtained by dividing the total length of the four line segments thus obtained by the total number of bubbles intersecting the line segments was taken as the bubble diameter of each expanded particle.

[0160] The above operations were performed on 10 or more randomly selected expanded particles, and the arithmetic mean of the bubble diameters of the expanded particles obtained for each expanded particle was taken as the average bubble diameter of the expanded particles.

[0161] 〔Independent bubble ratio of expanded particles〕 The independent bubble ratio of the expanded particles was measured using an air comparison pycnometer based on ASTM-D2856-70 Procedure C. Specifically, first, the bulk volume after conditioning was approximately 20 cm 3The foamed particles were used as a measurement sample, and the measurement sample was immersed in a graduated cylinder containing ethanol. The apparent volume Va of the measurement sample was measured from the amount of the liquid level rise at this time. After the measurement sample for which the apparent volume Va was measured was sufficiently dried, in accordance with Procedure C described in ASTM-D2856-70, the true volume value Vx of the measurement sample measured by an air comparison pycnometer (manufactured by Tokyo Science Co., Ltd., "Beckman Model1000 Air Comparison Pycnometer") was measured. Then, using these volume values Va and Vx, the independent bubble ratio of the measurement sample was calculated based on the following formula (1). The above operations were performed 5 times with the measurement sample changed, and the arithmetic mean value (N = 5) of the independent bubble ratios in the 5 measurement samples was taken as the independent bubble ratio of the foamed particles.

[0162] Independent bubble ratio (%) = (Vx - W / ρ) × 100 / (Va - W / ρ) ··· (1) However, the meanings of the symbols in the above formula (1) are as follows. Vx: The true volume of the foamed particles measured by the above method, that is, the sum of the volume of the resin constituting the foamed particles and the total bubble volume of the independent bubble portions in the foamed particles (unit: cm 3 ) Va: The apparent volume of the foamed particles measured from the amount of the liquid level rise when the foamed particles are immersed in a graduated cylinder containing ethanol (unit: cm 3 ) W: The mass of the foamed particles (measurement sample) (unit: g) ρ: The density of the resin constituting the foamed particles (unit: g / cm 3 )

[0163] 〔High-temperature peak heat quantity, total heat of fusion〕 The measurement methods for the total heat of fusion and the high-temperature peak heat quantity (that is, the heat of fusion of the high-temperature peak) are as described above.

[0164] 〔Content of metal element components in foamed particles〕 The content of the metal element component in the foamed particles is measured by measuring the ash content in the foamed particles and then performing fluorescence X-ray analysis (i.e., XRF) on the resin composition constituting the foamed particles as the measurement target to obtain the composition ratio of each metal element component among the inorganic components contained in the resin composition, and multiplying this composition ratio by the ash content of the foamed particles. Specifically, it was measured by the following method. The ash content of the foamed particles was calculated from the mass of the residue remaining after burning the foamed particles in accordance with the direct ashing method (Method A) of JIS K7250-1:2006. Specifically, first, the foamed particles were precisely weighed and then placed in a crucible. The foamed particles in the crucible were burned by heating them in an electric furnace with the ambient temperature set at 600 °C for 1 hour. After the heating was completed, the mass of the residue remaining in the crucible was measured. Then, the value obtained by expressing the ratio of the mass of the residue to the mass of the foamed particles before heating as a percentage was defined as the ash content A (unit: mass%) of the foamed particles. Next, in order to quantify the inorganic components such as metal elements that make up the ash of the foamed particles, a wavelength-dispersive fluorescence X-ray analyzer Supermini manufactured by Rigaku Corporation was used. As the sample used, resin particles (mini pellets) composed of the resin composition before foaming were used to prepare a disk-shaped sample with an outer diameter of φ44 mm and a thickness of 4 mm, and the inorganic elements present in the resin were analyzed. The mass ratio of the total amount of Fe, Cu, Cr, and Ni in the total amount of 100 mass% of the qualitatively determined inorganic elements was calculated. The obtained value was defined as the composition ratio M (mass%) of the metal element components (total of Fe, Cu, Cr, and Ni) in the ash. Then, the content (mass ppm) of the metal element components (i.e., the total amount of Fe, Cu, Cr, and Ni) in the foamed particles was obtained by calculating A×M of each foamed particle's ash content and performing unit conversion. In the fluorescence X-ray analysis, elements such as carbon and hydrogen that make up the resin are not detected. Also, the measurement method for the content of the metal element component in the raw material in Table 1 is the same as the above except that the measurement target is changed to the raw material.

[0165] 〔Moldability〕 The moldability of the foamed particles was examined by evaluating the moldable range of the foamed particles. In the evaluation of the formable range, foamed particle compacts were produced by performing in-mold forming of the foamed particles while changing the forming pressure during the main heating by 0.01 MPa at a time within the range of 0.10 to 0.38 MPa (G). The lower limit forming pressure and the formable range were determined based on the surface property, fusion property, and recovery property of the obtained compacts.

[0166] The method for manufacturing a foamed particle compact is as follows. First, the foamed particles are placed in a pressure-resistant container, and the inside of the pressure-resistant container is pressurized with an inorganic gas such as air or carbon dioxide to impregnate the foamed particles with the inorganic gas, and an internal pressure of 0.10 MPa (G) is applied to the foamed particles. Next, the foamed particles with the internal pressure applied are filled into the mold by the cracking filling method. In this example, a mold having a cavity capable of forming a flat plate-shaped foamed particle compact with a length of 250 mm, a width of 200 mm, and a thickness of 50 mm was used. In the cracking filling, the foamed particles were filled into the mold with a 5-mm cracking gap (that is, a 10% cracking amount) in the thickness direction of the compact, and then the mold was completely closed to mechanically compress the foamed particles in the mold.

[0167] Next, steam was supplied into the mold to perform in-mold forming. In the in-mold forming, first, preliminary heating was performed by supplying steam into the mold for 5 seconds with the drain valve of the mold open. Then, the drain valve was closed, and one-sided heating was performed by supplying steam from one surface side of the mold until a pressure 0.08 MPa (G) lower than the forming pressure during the main heating was reached. Next, one-sided heating was performed by supplying steam from the other surface side of the mold until a pressure 0.04 MPa (G) lower than the forming pressure during the main heating was reached. After that, main heating was performed by supplying steam from both surfaces of the mold until the forming pressure during the main heating was reached. After the main heating was completed, the pressure in the mold was released, and the compact was cooled in the mold until the surface pressure due to the foaming force of the compact reached 0.04 MPa (G).

[0168] Subsequently, the foamed particle molded body taken out from the mold was left standing in an oven at 80°C for 12 hours to perform a curing process. After the curing process, the foamed particle molded body was left standing for 24 hours under the conditions of a relative humidity of 50%, 23°C, and 1 atm to adjust the state of the foamed particle molded body. The surface property, fusion property, and recovery property of the foamed particle molded body after the state adjustment were evaluated, and the range of the molding pressure (that is, the molding pressure at which qualified products could be obtained) that passed all items according to the evaluation criteria described below was defined as the moldable range. In addition, when qualified products could not be molded at any molding pressure, the symbol "-" was indicated in the column of the moldable range. The wider the moldable range, the better the moldability can be judged. And when there are two or more points in the range (points) of the molding pressure at which qualified products can be molded, the moldability is evaluated as "EXCELLENT", when the range (points) of the molding pressure at which qualified products can be molded is one point, the moldability is evaluated as "GOOD", and when qualified products could not be molded at any molding pressure, the moldability was evaluated as "BAD".

[0169] The evaluation methods for the surface property, fusion property, and recovery property in the evaluation of the moldable range are as follows.

[0170] · Surface property A 100 mm × 100 mm square was drawn at the center of one skin surface in the thickness direction of the foamed particle molded body, and then a diagonal line was drawn from one of the corners of this square. Then, the number of voids existing on the diagonal line, that is, the voids having a size of 1 mm × 1 mm or more among the gaps formed between the foamed particles, was counted. And when the number of voids was two or less, it was judged as qualified, and when it was three or more, it was judged as unqualified.

[0171] · Fusion property The foamed particle molded body was broken so as to be roughly equally divided in the longitudinal direction. Among the foamed particles exposed on the fracture surface, 100 or more randomly selected foamed particles were visually observed to determine whether they were foamed particles broken inside the particles (i.e., foamed particles with material failure) or foamed particles broken at the interface between the foamed particles. Then, the value expressed as a percentage of the number of foamed particles broken inside the particles to the total number of observed foamed particles (i.e., the material failure rate) was calculated, and this value was used as the fusion rate. When the fusion rate was 80% or more, it was judged as qualified, and when it was less than 80%, it was judged as unqualified.

[0172] ·Recovery In a plan view of the foamed particle molded body seen from the thickness direction, the thickness of the foamed particle molded body at four positions 10 mm inside from each vertex toward the center and the thickness of the foamed particle molded body at the central part were measured respectively. Next, the ratio (unit: %) of the thickness of the thinnest part to the thickness of the thickest part among the measured parts was calculated. When the ratio of the thickness thus obtained was 95% or more, it was judged as qualified, and when it was less than 95%, it was judged as unqualified.

[0173]

Table 2

[0174]

Table 3

[0175] As shown in Table 2, the expanded particles of Examples 1 to 4 contain a polypropylene-based resin A mainly composed of polypropylene derived from ASR, and resources are effectively utilized. Also, as shown in Table 2, although the expanded particles of Examples 1 to 3 are produced using a polypropylene-based resin A mainly composed of polypropylene derived from ASR, which contains a large amount of VOC, the TVOC measured based on VDA277:2011 is reduced to below the detection lower limit. Further, in Examples 1 to 3, the content of linear alkanes having 12 to 18 carbon atoms measured based on VDA278:2016 is also reduced. The expanded particles of Example 4 are also produced using a polypropylene-based resin A mainly composed of polypropylene derived from ASR, which contains a large amount of VOC. In Example 4, although the TVOC measured based on VDA277:2011 and the content of linear alkanes having 12 to 18 carbon atoms measured based on VDA278:2016 are more than those in Examples 1 to 3, they are sufficiently reduced. Furthermore, the expanded particles of Examples 1 to 4 had good in-mold formability. Therefore, by performing in-mold forming using the expanded particles of Examples 1 to 4, an expanded particle molded body suitable for use in automotive interior materials and the like can be produced.

[0176] On the other hand, as shown in Table 3, in Comparative Example 1, expanded particles are produced by impregnation foaming, and in Comparative Example 2, expanded particles are produced by extrusion foaming. These production methods do not have a holding and foaming process under the predetermined conditions specified in the present invention, and no high-temperature peak was formed in the first DSC curve of the obtained expanded particles. As a result, in Comparative Example 1 and Comparative Example 2, the VOC reduction effect was insufficient, the TVOC was high, and a large amount of linear alkanes having 12 to 18 carbon atoms were contained. Also, the expanded particles of Comparative Example 1 and Comparative Example 2 had insufficient in-mold formability.

[0177] Comparative Example 3 is foamed particles composed of a composite resin. The temperature in the holding / foaming step in the direct foaming method was excessively high with respect to the melting point of the resin, and no high-temperature peak was formed in the first DSC curve of the obtained foamed particles. In Comparative Example 3, foamed particles were produced by the direct foaming method in the same manner as in the Examples, but VOC could not be sufficiently reduced. Note that the resin raw material used in Comparative Example 3 did not originally contain linear alkanes having 12 to 18 carbon atoms.

[0178] In Comparative Example 4, the holding temperature during the production of the foamed particles was set to a temperature sufficiently exceeding the melting point + 10°C. In this case, blocking occurred where the particles adhered to each other, and foamed particles could not be obtained.

[0179] In Comparative Example 5, the holding temperature during the production of the foamed particles was set to a temperature slightly exceeding the melting point + 10°C. The heat of fusion of the high-temperature peak of the foamed particles was less than 10 J / g. In this case, the TVOC of the foamed particles could not be sufficiently reduced.

[0180] As described above, specific embodiments of the foamed particles and the method for producing the same according to the present invention have been described based on the Examples. However, the specific embodiments of the foamed particles and the method for producing the same according to the present invention are not limited to the embodiments of the Examples, and the configuration can be appropriately changed without departing from the spirit of the present invention.

Claims

1. A polypropylene resin foam particle composed of a polypropylene resin composition containing a polypropylene resin mainly composed of polypropylene derived from automobile crushing residue, wherein the heat of fusion of the polypropylene resin composition is 68 J / g or more, when the foam particles are heated from 23°C to 230°C at a heating rate of 10°C / min, the DSC curve obtained has a crystal structure in which a main endothermic peak with the largest peak area and a high-temperature peak, which is an endothermic peak appearing on the high-temperature side of the main endothermic peak, appear, the heat of fusion of the high-temperature peak of the foam particles is 10 J / g or more and 35 J / g or less, The apparent density of the foamed particles is 10 kg / m ３ or more and 300 kg / m ３ or less, and the closed cell ratio is 85% or more, a polypropylene resin foam particle in which the TVOC in the foam particles measured based on VDA 277:2011 is 10 μg / g or less (including 0).

2. The polypropylene resin foam particle according to claim 1, wherein the total content of linear alkanes having 12 to 18 carbon atoms in the foam particles measured based on VDA 278:2016 is 100 μg / g or less (including 0).

3. The foam particles contain one or more metal elements selected from the group consisting of iron, copper, chromium, and nickel, and the content of the metal elements is 100 ppm by mass or more and 3000 ppm by mass or less. The polypropylene resin foam particle according to claim 1 or 2.

4. The polypropylene resin foam particle according to claim 1 or 2, wherein the TVOC in the foam particles measured based on VDA 277:2011 is 5 μg / g or less (including 0).

5. The polypropylene resin foam particle according to claim 1 or 2, wherein the heat of fusion of the high-temperature peak of the foam particles is 15 J / g or more.

6. The polypropylene resin foam particle according to claim 1 or 2, wherein the ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the foam particles is 0.2 or more and 0.5 or less.

7. The polypropylene resin foam particle according to claim 1 or 2, wherein the average bubble diameter of the foam particles is 10 μm or more and 80 μm or less.

8. The polypropylene resin foam particle according to claim 1 or 2, wherein the content of the polypropylene resin mainly composed of polypropylene derived from automobile crushing residue is 3% by mass or more and 60% by mass or less.

9. An automotive interior material composed of a molded article in a mold of the polypropylene resin foam particle according to claim 1 or 2.

10. A method for producing polypropylene-based resin foamed particles using a polypropylene-based resin in which TVOC measured based on VDA277:2011 is 300 μg / g or more, a dispersion step of dispersing resin particles composed of a polypropylene-based resin composition containing the polypropylene-based resin in an aqueous medium in a sealed container to obtain a dispersion; a foaming agent impregnation step of impregnating the resin particles with an inorganic physical foaming agent; a holding step of holding the temperature of the dispersion at a temperature of not less than the melting point of the polypropylene-based resin composition - 15°C and not more than the melting point of the polypropylene-based resin composition + 10°C for 10 minutes or more and 60 minutes or less; a foaming step of setting the temperature of the dispersion immediately before foaming to not less than the melting point of the polypropylene-based resin composition - 15°C and not more than the melting point of the polypropylene-based resin composition + 10°C, and opening the sealed container to discharge the resin particles together with the aqueous medium into an atmosphere at a pressure lower than the pressure in the sealed container. A method for producing polypropylene-based resin foamed particles.

11. The method for producing polypropylene-based resin foamed particles according to claim 10, wherein the content of linear alkanes having 12 to 18 carbon atoms in the polypropylene-based resin measured based on VDA278:2016 is 150 μg / g or more.

12. The method for producing polypropylene-based resin foamed particles according to claim 10 or 11, wherein the polypropylene-based resin contains one or more metal elements selected from the group consisting of iron, copper, chromium, and nickel, and the content of the metal elements is 1000 mass ppm or more and 20000 mass ppm or less.

13. The method for producing polypropylene-based resin foamed particles according to claim 10 or 11, wherein the polypropylene-based resin is a polypropylene-based resin mainly composed of polypropylene derived from automotive shredder residue.

14. The method for producing polypropylene-based resin foamed particles according to claim 10 or 11, wherein the difference [(TE) - (TH)] between the temperature (TE) of the dispersion immediately before foaming in the foaming step and the temperature (TH) of the dispersion in the holding step exceeds 0°C and is 2°C or less.

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