Method for producing polypropylene-based resin foamed particles

Abstract

A method for manufacturing polypropylene resin foamed particles involves foaming polypropylene resin particles to produce foamed particles. The resin particles are composed of a mixture of virgin raw materials and recycled polypropylene resin raw materials. The recycled raw materials include propylene copolymer as the base resin. The melting point MP1 of the virgin raw materials is above 130°C and below 150°C. The melting point MP2 (°C) of the recycled raw materials and the melting point MP1 (°C) of the virgin raw materials satisfy a specific relationship. The melt flow rate MFR2 (g / 10 min) of the recycled raw materials and the melt flow rate MFR1 (g / 10 min) of the virgin raw materials satisfy a specific relationship. The difference between the crystallization temperature CP2 (°C) of the recycled raw materials and the crystallization temperature CP1 (°C) of the virgin raw materials satisfies a specific relationship.

Description

Technical Field

[0001] This invention relates to a method for manufacturing polypropylene resin foam particles. Background Technology

[0002] Polypropylene resin foamed particle molded bodies, formed from polypropylene resin foamed particles, possess excellent lightweight, cushioning, and toughness. Therefore, polypropylene resin foamed particle molded bodies are widely used as transport containers for food, packaging or cushioning materials for electrical and electronic components, precision components, and vehicle parts, as well as impact-absorbing materials for building components such as residential insulation materials and vehicle parts.

[0003] Furthermore, in recent years, the trend of promoting the development of a circular society has not only included the reuse of waste products and the recycling of waste materials, but also the increasing demand from society for the use of waste materials used by end users as recycled materials (post-consumption materials).

[0004] Patent document 1 discloses a method for manufacturing polypropylene resin foam particles, which aims to achieve a black foam particle molded body with excellent appearance and physical properties by using a post-consumer material of polypropylene resin foam molded body containing carbon black. The method manufactures polypropylene resin foam particles with a specific range of bulk densities.

[0005] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2024-41662 Summary of the Invention The technical problem that the invention aims to solve In recent years, there has been a growing demand for environmentally friendly products that can further reduce environmental impact. One method for manufacturing such environmentally friendly products requires polypropylene resin foam particles that can be molded even at low molding pressures (molding pressures) when forming foam particles into molded bodies.

[0006] The present invention was made in view of the above-mentioned technical problems, and its object is to provide a method for manufacturing polypropylene resin foam particles, which can produce polypropylene resin foam particles that can be formed even with low molding pressure, even when using recycled raw materials of polypropylene resin molded bodies.

[0007] Solution to the above technical problems The inventors discovered that by using virgin raw materials that satisfy a specific relationship and recycled raw materials of polypropylene resin molded articles to manufacture polypropylene resin foam particles, the above-mentioned technical problems can be solved, thus completing the present invention.

[0008] That is, the present invention is as follows.

[0009] <1> A method for manufacturing polypropylene resin foamed particles involves foaming polypropylene resin particles to produce polypropylene resin foamed particles. The polypropylene resin particles are composed of a mixture of virgin raw materials and recycled polypropylene resin raw materials. The virgin raw materials include at least one propylene copolymer selected from ethylene-propylene copolymer, butene-propylene copolymer, and ethylene-butene-propylene copolymer as a base resin. The recycled raw materials include at least one propylene copolymer selected from ethylene-propylene copolymer, butene-propylene copolymer, and ethylene-butene-propylene copolymer as a base resin. The base resin has a melting point MP1 of virgin raw material that is above 130°C and below 150°C. The difference between the melting point MP2 (°C) of the recycled raw material and the melting point MP1 (°C) of the virgin raw material satisfies the following equation (1). The difference between the melt flow rate MFR2 (g / 10 min) of the recycled raw material and the melt flow rate MFR1 (g / 10 min) of the virgin raw material satisfies the following equation (2). The difference between the crystallization temperature CP2 (°C) of the recycled raw material and the crystallization temperature CP1 (°C) of the virgin raw material satisfies the following equation (3).

[0010] -10 <MP2-MP1<10･･･(1) 0≤MFR2-MFR1≤10･･･(2) 2 <CP2-CP1<12･･･(3)。

[0011] <2> like <1> In the method for manufacturing polypropylene resin foamed particles, the ash content of the recycled raw material is between 500 ppm and 2000 ppm by mass.

[0012] <3> like <1> or <2> In the method for manufacturing polypropylene resin foamed particles, the crystallization temperature CP2 of the recycled raw material is above 105℃ and below 115℃.

[0013] <4> like <1> ~ <3> The method for manufacturing polypropylene resin foamed particles according to any one of the claims, wherein the ratio of the flexural modulus of the virgin raw material to the flexural modulus of the recycled raw material is 0.5 or more and 2.0 or less.

[0014] <5> like <1> ~ <4> The method for manufacturing polypropylene resin foamed particles according to any one of the claims, wherein the blending ratio of the virgin raw material to the recycled raw material is: 10-90% by mass of the virgin raw material and 10-90% by mass of the recycled raw material (wherein, the total of the virgin raw material and the recycled raw material is 100% by mass).

[0015] <6> like <1> ~ <5> The method for manufacturing polypropylene resin foamed particles according to any one of the claims, wherein the recycled raw material is derived from the recycled raw material of the polypropylene resin foamed particle molded body.

[0016] <7> A method for manufacturing foamed particle molded articles, which involves... <1> ~ <6> The polypropylene resin foam particles obtained by any of the manufacturing methods described herein are formed by in-mold molding.

[0017] Invention Effects According to the present invention, a method for manufacturing polypropylene resin foam particles can be provided, which can produce polypropylene resin foam particles that can be formed even using low forming pressure. Attached Figure Description

[0018] Figure 1 This is a graph illustrating the DSC curve of polypropylene resin foam particles during the first heating. Detailed Implementation

[0019] [Manufacturing method of polypropylene resin foam particles] The present invention discloses a method for manufacturing polypropylene resin foamed particles (hereinafter also referred to as the method for manufacturing foamed particles of the present invention or the manufacturing method of the present invention), which manufactures polypropylene resin foamed particles (hereinafter also referred to as foamed particles) by foaming polypropylene resin particles (hereinafter also referred to as resin particles) with polypropylene resin as the base resin. The polypropylene resin particles are composed of a mixed resin of virgin raw materials and recycled raw materials of polypropylene resin molded bodies. The virgin raw materials include at least one propylene copolymer (B) selected from ethylene-propylene copolymer, butene-propylene copolymer, and ethylene-butene-propylene copolymer as the base resin. The recycled raw materials include ethylene-propylene copolymer... At least one propylene copolymer (R) selected from ethylene-butene-propylene copolymer and ethylene-butene-propylene copolymer is used as the base resin. The melting point MP1 of the virgin raw material is 130°C or higher and less than 150°C. The difference between the melting point MP2 (°C) of the recycled raw material and the melting point MP1 (°C) of the virgin raw material satisfies the following equation (1). The difference between the melt flow rate MFR2 (g / 10 min) of the recycled raw material and the melt flow rate MFR1 (g / 10 min) of the virgin raw material satisfies the following equation (2). The difference between the crystallization temperature CP2 (°C) of the recycled raw material and the crystallization temperature CP1 (°C) of the virgin raw material satisfies the following equation (3). In addition, in this specification, the base resin refers to the main component in the resin composition constituting the virgin raw material, the recycled raw material, the resin particles, or the foaming particles. Specifically, the content of the base resin in the resin composition is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. Furthermore, in this specification, the numerical range indicated by “~” refers to the range included by taking the values ​​recorded before and after “~” as the lower and upper limits.

[0020] -10 <MP2-MP1<10･･･(1) 0≤MFR2-MFR1≤10･･･(2) 2 <CP2-CP1<12･･･(3) In the method for manufacturing foamed particles of the present invention, by using virgin raw materials with a specific relationship and recycled raw materials of polypropylene resin molded bodies as raw materials for resin particles, it is possible to provide foamed particles with excellent formability that are not prone to problems such as dimensional shrinkage even under low molding pressure. Furthermore, especially when the polypropylene resin foamed particle molded body (hereinafter also simply referred to as foamed particle molded body or molded body) formed by the method for manufacturing foamed particles of the present invention is large, the molded body exhibits excellent dimensional stability even under low molding pressure. Moreover, when molding foamed particles obtained by the manufacturing method of the present invention, a good molded body can usually be obtained even without post-molding heat curing, thus further reducing environmental impact. In this specification, polypropylene resin refers to a polymer with a propylene-derived constituent unit content of 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more.

[0021] <Original Raw Materials> In this specification, virgin raw material refers to raw material that has not undergone heat treatment after sale. Furthermore, the propylene copolymer (B) of the base resin used as the virgin raw material includes at least one selected from ethylene-propylene copolymer, butene-propylene copolymer, and ethylene-butene-propylene copolymer, preferably including at least one selected from ethylene-propylene copolymer and ethylene-butene-propylene copolymer, and more preferably including ethylene-propylene copolymer. The base resin referred to herein is the main resin material constituting the raw material, and the propylene copolymer (B) of the base resin used as the virgin raw material means that the main resin material constituting the virgin raw material is the propylene copolymer (B). The content of propylene copolymer (B) in the resin of the virgin raw material is preferably 70% by mass or more, more preferably 90% by mass or more, and most preferably 95% by mass or more. Furthermore, other resins may be further blended into the base resin without hindering the effects of the present invention.

[0022] When the propylene copolymer (B) contains ethylene, from the viewpoint of further improving the formability of the foamed particle molded article under lower molding pressure, the content of ethylene in the propylene copolymer (B) is preferably 1% by mass or more, more preferably 2% by mass or more, and from the viewpoint of more easily and stably obtaining a good molded article, it is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. When the propylene copolymer (B) contains butene, from the viewpoint of further improving the formability of the foamed particle molded article under lower molding pressure, the content of butene in the propylene copolymer (B) is preferably 1% by mass or more, more preferably 2% by mass or more, and from the viewpoint of more easily and stably obtaining a good molded article, it is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0023] The monomer content (ethylene and butene content) of the propylene copolymer (B) was determined using a known method based on IR spectroscopy. Specifically, it was determined quantitatively using the method described in the Handbook of Polymer Analysis (edited by the Polymer Analysis Research Conference of the Japan Society for Analytical Chemistry, published January 1995, Kinokuniya Shoten, pages 615-616 "II.2.3 2.3.4 Propylene / Ethylene Copolymer", 618-619 "II.2.3 2.3.5 Propylene / Butene Copolymer"), i.e., by relating the values ​​obtained by correcting the absorbance of ethylene and butene with a specified coefficient to the thickness of a thin-film test piece. More specifically, the measurement was performed using the method described in the examples.

[0024] (Other polymers) The virgin raw material may include polymers other than propylene copolymer (B) to the extent that it does not impair the objective effect of the present invention. Examples of other polymers include thermoplastic resins such as polypropylene resins, polybutene resins, and polystyrene resins, as well as thermoplastic elastomers (e.g., polybutadiene elastomers; block copolymers of styrene-butadiene, styrene-isoprene, styrene-butadiene-styrene, and styrene-isoprene-styrene, and their hydrogenated products). The content of other polymers in the virgin raw material is preferably 10% by mass or less, more preferably 5% by mass or less.

[0025] (additive) Raw materials may contain additives, and further additives may be added as needed. Examples of additives include antioxidants, UV protectants, light stabilizers, antistatic agents, flame retardants, flame retardant auxiliaries, metal deactivators, conductive fillers, bubble conditioners, and colorants.

[0026] The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 100 parts by mass of propylene copolymer (B).

[0027] In cases where the virgin raw material contains multiple propylene copolymers (B), or contains other polymers or additives besides propylene copolymers (B), the measurements of the virgin raw material described below will be performed using the virgin raw material containing multiple propylene copolymers (B), or the virgin raw material containing other polymers or additives, as the sample.

[0028] (Melting point MP1) From the viewpoint of suppressing shrinkage after molding to improve formability, the melting point MP1 of the raw material is 130°C or higher, preferably 134°C or higher, more preferably 138°C or higher, and even more preferably 140°C or higher. From the viewpoint of further improving the formability of the foamed particle molded body under lower molding pressure, it is less than 150°C, preferably 148°C or lower, more preferably 146°C or lower, and even more preferably 144°C or lower.

[0029] The melting point MP1 was measured using the raw material as a test piece according to JIS K 7121:2012. Specifically, the test piece was conditioned using "(2) after a certain heat treatment, the melting temperature was measured". Under the condition of nitrogen inflow of 30 mL / min, the test piece was heated from 23°C to 200°C at a heating rate of 10°C / min, then held at that temperature for 10 minutes, then cooled to 23°C at a cooling rate of 10°C / min, and then heated to 200°C again at a heating rate of 10°C / min to obtain the DSC curve (the DSC curve during the second heating). Then, the peak temperature of the melting peak in the DSC curve was determined, and this value could be used as the melting point of the raw material. In the case of multiple melting peaks in the DSC curve, the peak temperature of the melting peak with the highest height relative to the baseline was used as the melting point MP1. At this point, by using the temperature at the valley of the DSC curve between the peak temperatures of each melting peak as the boundary, and comparing the area (heat of fusion) of each melting peak, it is possible to determine the melting peak with the largest area. The temperature at the valley of the DSC curve can be determined by referring to the differential curve of the DSC (DDSC) and based on the temperature at which the vertical axis of the differential curve is 0.

[0030] (Mel flow rate MFR1) The melt flow rate MFR1 of the raw material is not particularly limited as long as it satisfies the relationship of the above formula (2). However, from the viewpoint of obtaining foamed particles with excellent formability more easily and stably, it is preferable to have a flow rate of 1g / 10min or more, more preferably 3g / 10min or more, even more preferably 5g / 10min or more, and preferably 15g / 10min or less, more preferably 12g / 10min or less, and even more preferably 9g / 10min or less.

[0031] The melt flow rate MFR1 is a value measured for the virgin raw material, according to JIS K 7210-1:2014, at a temperature of 230°C and a load of 2.16 kg.

[0032] (Crystallization temperature CP1) The crystallization temperature CP1 of the raw material is not particularly limited as long as it satisfies the relationship of the above formula (3). However, from the viewpoint of obtaining foamed particles with excellent formability more easily and stably, it is preferred to be above 90°C, more preferably above 93°C, even more preferably above 95°C, and preferably below 125°C, more preferably below 120°C, even more preferably below 115°C, even more preferably below 110°C, and even more preferably below 105°C.

[0033] The crystallization temperature CP1 is determined using a differential scanning calorimeter (DSC) for the primary raw material, according to JIS K 7121:2012. In the case of multiple crystallization peaks in the DSC curve, the peak temperature of the crystallization peak with the largest area is taken as the crystallization temperature CP1.

[0034] (Heat of molten metal) From the viewpoint of further improving the formability of foamed particle molded articles under lower molding pressure, the melt heat of the raw material is preferably 30 J / g or more, more preferably 40 J / g or more, even more preferably 50 J / g or more, even more preferably 55 J / g or more, even more preferably 58 J / g or more, and preferably 100 J / g or less, more preferably 90 J / g or less, even more preferably 80 J / g or less, even more preferably 75 J / g or less, and even more preferably 74 J / g or less.

[0035] The heat of fusion is measured for the primary raw material using a differential scanning calorimeter (DSC) according to JIS K 7122:2012. In the case of multiple melting peaks in the DSC curve, the sum of the areas of the multiple melting peaks is taken as the heat of fusion.

[0036] (Flexural modulus of elasticity F1) From the viewpoint of further suppressing shrinkage after molding and improving formability, the flexural modulus F1 of the raw material is preferably 800 MPa or more, more preferably 850 MPa or more, even more preferably 900 MPa or more, even more preferably 950 MPa or more, and preferably 1600 MPa or less, more preferably 1500 MPa or less, even more preferably 1400 MPa or less, even more preferably 1300 MPa or less, and even more preferably 1200 MPa or less.

[0037] The flexural modulus F1 is measured for the virgin raw material according to JIS K 7171:2016.

[0038] <Recycled Polypropylene Resins> Recycled polypropylene resin raw materials (hereinafter also referred to as recycled raw materials) refer to used polypropylene resin raw materials, such as those recovered after the production of polypropylene resin molded bodies, etc. Compared with virgin raw materials, they refer to materials that have undergone at least one heat treatment. For example, recycled polypropylene resin molded bodies can be used as raw materials for resin particles by crushing and melting them, or by crushing, melting, and then granulating them. Furthermore, there are no particular restrictions on the use of recycled polypropylene resin as long as the above formulas (1) to (3) are satisfied, but it is preferable to use recycled raw materials derived from polypropylene resin foamed particle molded bodies.

[0039] Polypropylene resin molded articles refer to molded articles obtained by molding polypropylene resin. Polypropylene resin foamed particle molded articles refer to polypropylene resin molded articles obtained by using polypropylene resin foamed particles as raw materials. Furthermore, the polypropylene resin foamed particle molded article of the present invention, described later, is a polypropylene resin foamed particle molded article obtained by in-mold molding of polypropylene resin foamed particles obtained by the manufacturing method of the present invention.

[0040] (Preparation method of recycled raw materials) Recycled used polypropylene resin molded parts sometimes contain foreign objects other than the polypropylene resin molded parts, such as packaging bags or labels. Therefore, it is preferable to perform foreign object sorting. Foreign object sorting can be carried out by visual sorting by operators or by using sorting machines.

[0041] For crushing polypropylene resin molded parts, a pulverizer is preferred. Pulverizers include compression pulverizers, shear pulverizers, and impact pulverizers. As a pulverizing method, for example, coarse pulverization can be performed once using an impact pulverizer followed by fine pulverization using a shear pulverizer, or a one-step pulverization process can be used. In particular, using equipment with a perforated plate or screen installed at the outlet of a shear pulverizer or similar device, pulverizing in a single step while ensuring uniform particle size, is economically preferable. There are no particular limitations on the size of the pulverized material, but it is preferably between 1 mm and 30 mm.

[0042] The obtained pulverized material is preferably heated and reduced in volume to form a molten ingot. Heating and volume-reducing machines include extruders, presses, etc. There are no particular restrictions on the processing temperature during volume reduction, but to avoid thermal degradation of the polypropylene resin, it is preferable to perform the process at a low temperature, preferably below 220°C and above the resin melting point. The molten ingot is preferably pulverized again using the aforementioned pulverizer, then melted using an extruder, and finally granulated to produce polypropylene resin recycled raw material granules. The aforementioned pulverizer can be used as the pulverizer. A single-screw extruder, twin-screw extruder, etc., can be used as the extruder, but from the viewpoint of preventing resin deterioration, a single-screw extruder is preferred. There are no particular restrictions on the extruder temperature, but to avoid thermal degradation of the polypropylene resin, it is preferable to perform the process at a low temperature, preferably below 220°C and above the resin melting point. For the polypropylene resin melted by the extruder, it is preferable to first remove foreign matter through a filter. Metal mesh, sintered metal, etc., can be used as the filter, but using metal mesh is economically preferred. Granulation methods for molten polypropylene resins include underwater cutting, where molten resin is extruded from a mold into water or mist, while simultaneously being continuously cut and cured by a rotating blade mounted in front of the mold; and wire harness cutting, where the resin is continuously extruded from the mold into wire bundles, cooled and cured in a water bath, and then cut using a cutting machine. Wire harness cutting is economically preferred. There are no particular limitations on particle size, but an average mass of 1–30 mg per particle is preferred. Furthermore, according to the above recycling methods, the recycled raw material of this invention undergoes more than two heating operations relative to the virgin raw material.

[0043] (Base material resin) The propylene copolymer (R) of the base resin used as a recycled raw material includes at least one selected from ethylene-propylene copolymer, butene-propylene copolymer, and ethylene-butene-propylene copolymer, preferably including ethylene-propylene copolymer. The base resin referred to herein is the main resin material constituting the raw material, and the propylene copolymer (R) of the base resin used as a recycled raw material means that the main resin material constituting the recycled raw material is the propylene copolymer (R). The content of propylene copolymer (R) in the resin of the recycled raw material is preferably 80% by mass or more, more preferably 90% by mass or more, and most preferably 95% by mass or more. Furthermore, other resins may be further blended into the base resin without hindering the objective effect of the present invention. Moreover, the propylene copolymer (R) may be the same as or different from the propylene copolymer (B) described above.

[0044] The propylene copolymer (R) is preferably of the same type as the propylene copolymer (B). For example, if the propylene copolymer (R) contains an ethylene-propylene copolymer, the propylene copolymer (B) preferably contains an ethylene-propylene copolymer.

[0045] When the propylene copolymer (R) contains ethylene, from the viewpoint of further improving the formability of the foamed particle molded article under lower molding pressure, the content of ethylene in the propylene copolymer (R) is preferably 1% by mass or more, more preferably 2% by mass or more, and from the viewpoint of more easily and stably obtaining a good molded article, it is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. When the propylene copolymer (R) contains butene, from the viewpoint of further improving the formability of the foamed particle molded article under lower molding pressure, the content of butene in the propylene copolymer (R) is preferably 1% by mass or more, more preferably 2% by mass or more, and from the viewpoint of more easily and stably obtaining a good molded article, it is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0046] The monomer content (ethylene and butene content) of the propylene copolymer (R) is measured using the same method as that of the propylene copolymer (B) of the aforementioned virgin raw material.

[0047] The recycled raw material may contain polymers other than propylene copolymers (R) to the extent that it does not impair the effects of the present invention. Examples of other polymers include the aforementioned thermoplastic resins and thermoplastic elastomers that may be contained in the virgin raw material. Furthermore, the recycled raw material may contain or be added to additives exemplified as additives that may be added to the virgin raw material. Similar to the virgin raw material, in cases where the recycled raw material contains multiple propylene copolymers (R), or contains polymers or additives other than propylene copolymers (R), the measurements of the recycled raw material described below will be performed using a sample containing multiple propylene copolymers (R) or a sample containing other polymers or additives.

[0048] (Melting point MP2) The melting point MP2 of the recycled material is not particularly limited as long as it satisfies the relationship in equation (1) above. However, from the viewpoint of suppressing shrinkage after molding to improve formability, it is preferably 120°C or higher, more preferably 125°C or higher, even more preferably 130°C or higher, even more preferably 140°C or higher, even more preferably 142°C or higher, and even more preferably 144°C or higher. From the viewpoint of further improving the formability of the foamed particle molded body under lower molding pressure, it is preferably less than 160°C, more preferably less than 155°C, even more preferably less than 150°C, and even more preferably less than 148°C. The melting point MP2 is measured using the recycled material as a test piece in the same way as the melting point MP1.

[0049] (Mel flow rate MFR2) The melt flow rate MFR2 of the recycled raw material is not particularly limited as long as it satisfies the relationship in equation (2) above. However, from the viewpoint of more easily and stably obtaining foamed particles with excellent formability, it is preferable to have a melt flow rate of 3 g / 10 min or more, more preferably 5 g / 10 min or more, even more preferably 7 g / 10 min or more, and preferably 20 g / 10 min or less, more preferably 15 g / 10 min or less, and even more preferably 13 g / 10 min or less. The melt flow rate MFR2 is measured for the recycled raw material under the same conditions as the measurement method of MFR1, at a temperature of 230°C and a load of 2.16 kg.

[0050] (Crystallization temperature CP2) The crystallization temperature CP2 of the recycled raw material is not particularly limited as long as it satisfies the relationship in equation (3) above. However, from the viewpoint of more easily and stably obtaining foamed particles with excellent formability, it is preferable to be 95°C or higher, more preferably 100°C or higher, even more preferably 105°C or higher, and preferably 130°C or lower, more preferably 125°C or lower, even more preferably 120°C or lower, even more preferably 115°C or lower, and even more preferably 113°C or lower. The crystallization temperature CP2 is measured for the recycled raw material using the same method as the crystallization temperature CP1.

[0051] (Gray component) From the viewpoint of making it easier to adjust the crystallization temperature to the desired range, the ash content of the recycled raw material is preferably 300 ppm by mass or more, more preferably 400 ppm by mass or more, even more preferably 500 ppm by mass or more, and preferably 2000 ppm by mass or less, more preferably 1800 ppm by mass or less, even more preferably 1600 ppm by mass or less, and most preferably 1200 ppm by mass or less.

[0052] The ash content of the recycled raw material is measured according to JIS K 6226-2:2003. Furthermore, the recycled raw material is preferably derived from polypropylene resin foamed particle molded material. In this case, since it contains inorganic substances such as bubble nucleating agents derived from the foamed particle molded material, it is particularly important to set the ash content of the recycled raw material within the aforementioned specific range.

[0053] (Flexural modulus F2) From the viewpoint of further suppressing shrinkage after molding and further improving formability, the flexural modulus F2 of the recycled material is preferably 600 MPa or more, more preferably 700 MPa or more, further preferably 800 MPa or more, even more preferably 900 MPa or more, even more preferably 1000 MPa or more, and preferably 1600 MPa or less, more preferably 1500 MPa or less, and even more preferably 1400 MPa or less. The flexural modulus F2 is measured for the recycled material using the same method as the measurement of the flexural modulus F1.

[0054] (Heat of molten metal) From the viewpoint of further improving the formability of foamed particle molded articles under lower molding pressure, the heat of fusion of the recycled raw material is preferably 40 J / g or more, more preferably 50 J / g or more, further preferably 60 J / g or more, even more preferably 65 J / g or more, even more preferably 70 J / g or more, and preferably 100 J / g or less, more preferably 90 J / g or less, even more preferably 85 J / g or less, even more preferably 80 J / g or less, and even more preferably 78 J / g or less. The heat of fusion of the recycled raw material is measured using the same method as that used for measuring the heat of fusion of the virgin raw material.

[0055] (Equation (1): Difference (MP2-MP1)) The difference between the melting point MP2 (°C) of the recycled raw material and the melting point MP1 (°C) of the virgin raw material (MP2-MP1) satisfies the following relationship (1).

[0056] -10 <MP2-MP1<10･･･(1) By using raw materials that satisfy this relationship, foamed particles can be provided that can be molded into well-formed articles even under low forming pressure. Specifically, molded articles formed from foamed particles obtained by the manufacturing method of the present invention are less prone to problems such as dimensional shrinkage even under low forming pressure, especially when the molded article is large, the dimensional stability after molding is particularly excellent even under low forming pressure. From the above viewpoint, the temperature difference (MP2-MP1) is preferably -5°C or higher, more preferably -2°C or higher, further preferably 0°C or higher, even more preferably 2°C or higher, even more preferably 3°C or higher, and preferably 8°C or lower, more preferably 6°C or lower, and even more preferably 5°C or lower.

[0057] (Equation (2): Difference (MFR2-MFR1)) The difference between the melt flow rate MFR2 (g / 10 min) of the recycled feedstock and the melt flow rate MFR1 (g / 10 min) of the virgin feedstock (MFR2-MFR1) satisfies the following relationship (2).

[0058] 0≤MFR2-MFR1≤10･･･(2) By using raw materials that satisfy this relationship, the raw materials can be thoroughly mixed, the closed-cell ratio of the foamed particles obtained by the manufacturing method of the present invention is easily improved, and the molded articles formed from the foamed particles are less prone to problems such as dimensional shrinkage, even under low molding pressure. Furthermore, especially when the molded article is large, the dimensional stability after molding is particularly excellent, even under low molding pressure. From the above viewpoint, the difference (MFR2-MFR1) is preferably 8 g / 10 min or less, more preferably 6 g / 10 min or less, further preferably 4 g / 10 min or less, and preferably 1 g / 10 min or more, more preferably 2 g / 10 min or more.

[0059] (Equation (3): Difference (CP2-CP1)) The difference between the crystallization temperature CP2 of the recycled raw material and the crystallization temperature CP1 of the virgin raw material (CP2-CP1) satisfies the following relationship (3).

[0060] 2 <CP2-CP1<12･･･(3) By using raw materials that satisfy this relationship, foamed particles can be provided that can be molded into well-formed articles even under low forming pressure. Specifically, molded articles formed from foamed particles obtained by the manufacturing method of the present invention are less prone to problems such as dimensional shrinkage even under low forming pressure. Furthermore, especially when the molded article is large, the dimensional stability after molding is particularly excellent even under low forming pressure. From the above viewpoint, the temperature difference (CP2-CP1) is preferably 3°C or more, more preferably 5°C or more, further preferably 7°C or more, and preferably 11°C or less.

[0061] By using raw materials that satisfy equations (1) to (3), the melting point related to low-pressure molding, and the MFR and crystallization temperature related to post-molding shrinkage have specific relationships, and equations (1) to (3) are interrelated. Therefore, the molded body formed by the foamed particles obtained by the manufacturing method of the present invention is less prone to problems such as dimensional shrinkage even under low molding pressure. In addition, especially when the molded body is large, the dimensional stability after molding is particularly excellent even under low molding pressure. Furthermore, when molding the foamed particles obtained by the manufacturing method of the present invention, a good molded body can usually be obtained even without post-molding heating and curing, thus further reducing the environmental impact.

[0062] (Compared to (F1 / F2)) From the viewpoint of further suppressing shrinkage after molding and further improving formability, the ratio of the flexural modulus F1 of the virgin material to the flexural modulus F2 of the recycled material (F1 / F2) is preferably 0.5 or more, more preferably 0.7 or more, and preferably 2.0 or less, more preferably 1.7 or less, and even more preferably 1.5 or less.

[0063] <Polypropylene resin particles> Polypropylene resin particles are composed of a mixed resin of the aforementioned virgin raw materials and the aforementioned recycled raw materials. The resin particles obtained by the manufacturing method of the present invention can be single-layer resin particles composed of the mixed resin, or multi-layer resin particles with a coating layer on the surface of a core layer composed of the mixed resin. Since dimensional shrinkage after molding is mainly caused by the foam portion, it is important that the resin forming the foam portion is composed of a mixed resin of the aforementioned virgin raw materials and the aforementioned recycled raw materials, regardless of whether it is a single-layer or multi-layer foam particle.

[0064] (Mixed resin) For a mixed resin of virgin and recycled raw materials, it can be obtained by feeding the virgin and recycled raw materials, along with additives as needed, into an extruder, melting and kneading the supplied materials. Then, by extruding the molten and kneaded mixed resin from the extruder and granulating it into a predetermined shape and mass, polypropylene resin particles composed of the mixed resin can be obtained.

[0065] Regarding the content of virgin raw materials in the mixed resin, when the total of virgin and recycled raw materials is 100% by mass, from the viewpoint of the physical property stability of the obtained foamed particles and molded articles, it is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more. From the viewpoint of further reducing environmental impact, it is preferably 97% by mass or less, more preferably 95% by mass or less, even more preferably 93% by mass or less, even more preferably 90% by mass or less, and even more preferably 88% by mass or less.

[0066] Furthermore, in this invention, even when the blending ratio of recycled raw materials is increased to reduce environmental impact, a good foamed particle molded body can still be obtained. Moreover, the preferred blending ratio of the virgin raw material to the recycled raw material is: 10-90% by mass of the virgin raw material and 10-90% by mass of the recycled raw material (wherein the total of the virgin raw material and the recycled raw material is 100% by mass), more preferably: 10-50% by mass of the virgin raw material and 50-90% by mass of the recycled raw material. And even more preferably: 20-50% by mass of the virgin raw material and 50-80% by mass of the recycled raw material.

[0067] That is, when the total of the virgin raw material and the recycled raw material is 100% by mass, the proportion of the virgin raw material is preferably 10-90% by mass, more preferably 10-50% by mass, and even more preferably 20-50% by mass.

[0068] On the other hand, depending on the amount of recycled raw materials obtained, a good foamed particle molded body can be obtained by increasing the amount of virgin raw materials. In this case, the mixing ratio of the virgin raw materials to the recycled raw materials is preferably: 10-90% by mass of the virgin raw materials and 10-90% by mass of the recycled raw materials (wherein the total of the virgin raw materials and the recycled raw materials is 100% by mass), and more preferably: 50-90% by mass of the virgin raw materials and 50-10% by mass of the recycled raw materials.

[0069] That is, when the total of the virgin raw material and the recycled raw material is 100% by mass, the proportion of the virgin raw material is preferably 10 to 90% by mass, more preferably 50 to 90% by mass.

[0070] The mixed resin constituting the polypropylene resin particles may contain polymers other than propylene copolymer (B) or propylene copolymer (R), to the extent that it does not impair the objective effect of the present invention. Examples of other polymers include the aforementioned thermoplastic resins and thermoplastic elastomers that may be contained in the primary raw materials. Furthermore, the mixed resin may contain or be added to additives exemplified as additives that may be added to the primary raw materials.

[0071] When the resin particles are multilayer resin particles with a coating layer on their surface, multilayer resin particles having a resin particle body (core layer) composed of mixed resin and a coating layer covering the resin particle body (core layer) can be produced by co-extrusion, or by pre-producing a resin particle body composed of mixed resin and then coating it with a coating layer. Specifically, in the co-extrusion method, an extrusion apparatus equipped with the following devices can be used: a resin particle body (core layer) forming extruder for forming a resin particle body (core layer) composed of mixed resin; a coating layer forming extruder for forming a coating layer; and a co-extrusion die connected downstream of these extruders, such as a multilayer wire harness forming die. The resin particle body (core layer) forming extruder is supplied with virgin and recycled raw materials for forming the mixed resin, as well as additives added as needed, and the mixture is melt-kneaded to obtain a mixed resin melt. The coating layer forming extruder is supplied with resin (e.g., polyolefin resin) for forming the coating layer, as well as additives added as needed, and the mixture is melt-kneaded to obtain a coating layer forming resin melt. The mixed resin melt and the coating layer forming resin melt are introduced into a co-extrusion die and combined, extruded from an extrusion apparatus, and granulated into a predetermined shape and mass. This yields multi-layered resin particles with a coating layer on the surface of the resin particle body (core layer) composed of the mixed resin. Alternatively, as another method for coating the resin particle body (core layer) composed of the mixed resin, the resin particle body (core layer) and the material for forming the coating layer can be placed in a mixing apparatus with mixing and heating functions for heating and mixing. Furthermore, the coating layer can cover a portion of the resin particle body (core layer) or completely cover the entire outer surface of the resin particle body (core layer). Preferably, the coating layer covers 50% or more of the resin particle body (core layer), more preferably 70% or more, and even more preferably 80% or more. Furthermore, the resin particle body (core layer) is preferably in a foamed state, but the coating layer can be in a foamed state or a non-foamed state without bubbles. From the viewpoint of improving the strength of the resulting molded article, the coating layer is preferably in a non-foamed state.

[0072] When the resin particles and foamed particles obtained by the manufacturing method of the present invention are multilayer resin particles and foamed particles with a coating layer on the surface, the above-mentioned effects can be obtained by using a mixed raw material composed of the above-mentioned virgin raw material and recycled raw material as the raw material of the resin particle body (core layer) covered by the coating layer and satisfying the above formulas (1) to (3).

[0073] Furthermore, the polyolefin resin constituting the coating layer can adopt the same composition as the coating layer in multilayer foamed particles known in the prior art.

[0074] The resin constituting the coating layer is preferably composed of a polyolefin resin. Examples of polyolefin resins include polyethylene resins, polypropylene resins, and polybutene resins. From the viewpoint of excellent adhesion to the foamed core layer, the polyolefin resin constituting the coating layer preferably includes at least one selected from the group consisting of polyethylene resins and polypropylene resins, and more preferably includes a polypropylene resin. Examples of polyolefin resins include propylene-ethylene copolymers, ethylene-butene copolymers, ethylene-butene-propylene copolymers, and propylene homopolymers. Furthermore, examples of polypropylene resins include propylene-ethylene copolymers, ethylene-butene-propylene copolymers, and propylene homopolymers, preferably including at least one selected from the group consisting of propylene-ethylene copolymers and ethylene-butene-propylene copolymers, and more preferably including an ethylene-butene-propylene copolymer.

[0075] The resin constituting the coating layer may include polymers other than the aforementioned polyolefin resins, without hindering the objective effect of the present invention. Examples of other polymers include the aforementioned thermoplastic resins and thermoplastic elastomers that may be contained in the virgin raw materials. Furthermore, additives exemplified as additives that can be added to the resin constituting the coating layer may be added to the virgin raw materials.

[0076] (Melting point) When the resin constituting the coating layer is a polypropylene resin, from the viewpoint of facilitating better weldability between the foamed particles, its melting point is preferably lower than that of the mixed resin constituting the resin particle body (core layer). Specifically, from the viewpoint of further improving the formability of the foamed particle molded article under lower molding pressure, the melting point is preferably 100°C or higher, preferably 110°C or higher, more preferably 115°C or higher, and even more preferably 120°C or higher. Furthermore, from the viewpoint of facilitating better weldability between the foamed particles, it is preferably 150°C or lower, preferably 145°C or lower, more preferably 140°C or lower, and even more preferably 138°C or lower. The melting point is measured for the polypropylene resin constituting the coating layer using the same method as the measurement of the melting point MP1.

[0077] (Crystallization temperature) When the resin constituting the coating layer is a polypropylene resin, from the viewpoint of more easily and stably obtaining foamed particles with excellent formability, its crystallization temperature is preferably 90°C or higher, more preferably 93°C or higher, even more preferably 95°C or higher, and preferably 130°C or lower, more preferably 125°C or lower, even more preferably 120°C or lower, even more preferably 115°C or lower, even more preferably 110°C or lower, and even more preferably 105°C or lower. The crystallization temperature is measured for the polypropylene resin constituting the coating layer using the same method as the measurement of the crystallization temperature CP1.

[0078] (Heat of molten metal) When the resin constituting the coating layer is a polypropylene resin, from the viewpoint of further improving the formability of the foamed particle molded article under lower molding pressure, its heat of melt is preferably 30 J / g or more, more preferably 40 J / g or more, further preferably 50 J / g or more, even more preferably 55 J / g or more, even more preferably 57 J / g or more, and preferably 100 J / g or less, more preferably 90 J / g or less, even more preferably 80 J / g or less, even more preferably 70 J / g or less, and even more preferably 65 J / g or less. The heat of melt is measured for the polypropylene resin constituting the coating layer using the same method as for measuring the heat of melt of the virgin raw material.

[0079] (Mel flow rate) When the resin constituting the coating layer is a polypropylene resin, from the viewpoint of more easily and stably obtaining foamed particles with excellent formability, its melt flow rate is preferably 1 g / 10 min or more, more preferably 3 g / 10 min or more, even more preferably 4 g / 10 min or more, and preferably 15 g / 10 min or less, more preferably 10 g / 10 min or less, and even more preferably 8 g / 10 min or less. The melt flow rate is measured for the polypropylene resin constituting the coating layer using the same method as the melt flow rate MFR1.

[0080] (Mass ratio of resin particle bulk (core layer) to coating layer) From the perspective of balancing the improvement of the weldability between foamed particles and the reduction of environmental impact, the mass ratio of resin particle body (core layer) to coating layer (resin particle body (core layer): coating layer) is preferably 99.5:0.5 to 80:20, more preferably 99:1 to 90:10, and even more preferably 98:2 to 95:5.

[0081] The shape of the resin particles is not particularly limited as long as it achieves the intended purpose of this invention, but a cylindrical shape is preferred. When the resin particles are cylindrical, the particle size (length in the extrusion direction) is preferably 0.2 to 4 mm, more preferably 0.5 to 3 mm. Furthermore, the ratio (length / diameter ratio) of the length of the resin particle in the extrusion direction to its length in a direction orthogonal to the extrusion direction is preferably 0.5 to 5.0, more preferably 1.0 to 3.0.

[0082] The average mass of the resin particles is preferably adjusted to 0.1–20 mg, more preferably 0.2–10 mg, even more preferably 0.3–5 mg, and even more preferably 0.4–2 mg.

[0083] <Fogging of Polypropylene Resin Particles> By impregnating the resin particles obtained as described above with a foaming agent, the polypropylene resin particles impregnated with the foaming agent are foamed, thereby obtaining polypropylene resin foamed particles.

[0084] Specifically, for example, a dispersion medium and polypropylene resin particles are placed in a sealed container that can be sealed and is resistant to heat and pressure, such as an autoclave. The polypropylene resin particles are dispersed in the dispersion medium by a mixer or the like, while a foaming agent is added to the sealed container. The container is then kept under a predetermined temperature and pressure atmosphere, thereby impregnating the polypropylene resin particles with the foaming agent.

[0085] As a dispersion medium, there are no particular restrictions as long as it does not dissolve polypropylene resin particles. For example, alcohols such as water, ethylene glycol, glycerol, methanol, and ethanol can be used, with water being the preferred choice.

[0086] To more stably prevent the polypropylene resin particles from sticking together, it is preferable to further add a dispersant to the dispersion medium. Examples of dispersants include organic dispersants such as polyvinyl alcohol, polyvinylpyrrolidone, and methylcellulose; and insoluble inorganic salts such as alumina, zinc oxide, kaolin, mica, magnesium phosphate, and tricalcium phosphate. These can be used alone or in combination of two or more. From the perspective of ease of processing, insoluble inorganic salts are preferred as dispersants, and kaolin is more preferred. When adding a dispersant, it is preferable to add approximately 0.001 to 5 parts by weight relative to 100 parts by weight of the polypropylene resin particles.

[0087] When using a dispersant, it is preferable to add inorganic salts such as aluminum sulfate as a dispersing aid. When adding a dispersing aid, it is preferable to add about 0.001 to 1 part by weight relative to 100 parts by weight of polypropylene resin particles.

[0088] Surfactants may also be added to the dispersion medium. Examples of surfactants include sodium alkylbenzene sulfonate (such as sodium dodecylbenzene sulfonate), sodium alkyl sulfonate, sodium oleate, sodium lauryl sulfate, sodium polyoxyethylene alkyl ether phosphate, sodium polyoxyethylene alkyl ether sulfate, and other anionic and nonionic surfactants commonly used in suspension polymerization. When a surfactant is added, it is preferable to add approximately 0.001 to 1 part by weight relative to 100 parts by weight of the polypropylene resin particles.

[0089] There are no particular limitations on the foaming agent as long as it can foam polypropylene resin particles. Examples of foaming agents include inorganic physical foaming agents such as air, nitrogen, carbon dioxide, argon, helium, oxygen, and neon; aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, and n-hexane; alicyclic hydrocarbons such as cyclohexane and cyclopentane; halogenated hydrocarbons such as chloroethane, 2,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene, and trans-1-chloro-3,3,3-trifluoropropene; and organic physical foaming agents such as dialkyl ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether. From the viewpoint of minimizing environmental impact and being economical, inorganic physical foaming agents are preferred, more preferably one or more selected from the group consisting of nitrogen, air, and carbon dioxide, and even more preferably carbon dioxide. These can be used alone or in combination of two or more.

[0090] The amount of foaming agent added depends on the desired bulk density of the polypropylene resin foam particles, the type of polypropylene resin, and the type of foaming agent. However, for example, when using an inorganic physical foaming agent, the amount added is preferably 0.1 to 30 parts by mass relative to 100 parts by mass of polypropylene resin particles, and more preferably 0.5 to 15 parts by mass.

[0091] The heating temperature during impregnation of the foaming agent is preferably 100°C to 180°C, more preferably 130°C to 175°C. Furthermore, the holding time at this heating temperature is preferably 1 to 100 minutes, more preferably 10 to 60 minutes.

[0092] Then, the polypropylene resin particles impregnated with the foaming agent are released together with the dispersion medium from the sealed container into an atmosphere with a pressure lower than that inside the sealed container, causing the polypropylene resin particles to foam, thereby obtaining polypropylene resin foamed particles.

[0093] When polypropylene resin particles are released from a sealed container into an atmosphere with a pressure lower than that inside the sealed container for foaming, the foaming temperature is typically preferred to be between 110°C and 170°C. Furthermore, the pressure inside the sealed container is preferably between 0.5 MPa (G) and 5 MPa (G). The pressure marked (G) is gauge pressure, i.e., a pressure value based on atmospheric pressure.

[0094] It is also possible to pressurize the polypropylene resin foam particles obtained as described above using air or the like, increase the internal pressure inside the bubbles of the foam particles, and then heat the foam particles with steam or the like to make them foam (two-step foaming), thereby producing foam particles with a higher foaming ratio (lower bulk density).

[0095] [Polypropylene resin foam particles] <Bulk density> From the perspective of improving the strength of the molded body, the bulk density of polypropylene resin foam particles is preferably 10 kg / m³. 3 The above, preferably 15 kg / m 3 The above is further optimized to 20 kg / m 3 From the perspective of improving the lightweight nature of foamed particle molded articles, 200 kg / m³ is preferred. 3 The following is more preferably 100 kg / m 3 The following is a further preferred value: 60 kg / m 3 The following is a further preferred value: 50 kg / m 3 the following.

[0096] The bulk density of the foamed particles is calculated as follows. First, a mass W1 [g] of foamed particles is filled into a graduated cylinder. The filling height of the foamed particles is stabilized by gently tapping the bottom of the graduated cylinder on the ground several times. Next, the volume V1 [L] of the foamed particle group indicated by the graduated cylinder scale is read. The mass W1 of the foamed particle group is divided by the volume V1 (W1 / V1), and the unit is converted to [kg / m³]. 3 ], thereby determining the packing density of the bubbling particles.

[0097] <Temperature Peak> Polypropylene resin foamed particles preferably have the following crystal structure: in the DSC curve obtained by heating the foamed particles from 23°C to 200°C at a heating rate of 10°C / min, a melting peak caused by the inherent crystal melting of the polypropylene resin (i.e., the resin-inherent peak) and one or more melting peaks (i.e., high-temperature peaks) appearing on the high-temperature side of the resin appear. The DSC curve is obtained by performing differential scanning calorimetry (DSC) according to JIS K 7122:2012 using 1-3 mg of foamed particles as a test sample. The resin-inherent peak refers to the melting peak caused by the inherent crystal melting of the polypropylene resin constituting the foamed particles, which can be considered as an endothermic peak that occurs due to the endothermic melting of the crystals that is usually present in polypropylene resin. On the other hand, the melting peak on the high-temperature side of the resin-inherent peak (i.e., the high-temperature peak) refers to the melting peak that appears on the high-temperature side of the DSC curve, which is higher than the resin-inherent peak. In the presence of this high-temperature peak, it is presumed that secondary crystals exist in the resin. Furthermore, in the DSC curve obtained when the foamed particles are heated from 23°C to 200°C at a heating rate of 10°C / min (i.e., the first heating), cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated again from 23°C to 200°C at a heating rate of 10°C / min (i.e., the second heating), preferably only the melting peak caused by the melting of the crystals inherent in the polypropylene resin constituting the foamed particles appears. In this way, the inherent resin peaks and high-temperature peaks can be distinguished.

[0098] The adjustment of the high-temperature peak can be achieved, for example, after the resin particles are dispersed in the dispersion medium and / or when the resin particles are impregnated with a foaming agent, or after impregnation, by controlling the rate of temperature rise within the sealed container, or by maintaining the temperature within the sealed container at a predetermined temperature for a predetermined time. Specifically, for example, a holding process can be performed, where the temperature within the sealed container is maintained at a temperature above (the melting point of the resin particles - 20°C) and below (the melting point of the resin particles) for approximately 10 to 60 minutes. Subsequently, a second holding process can be performed, where the temperature within the sealed container is adjusted to a temperature below (the melting point of the resin particles - 15°C) and further maintained for approximately 10 to 60 minutes.

[0099] <Heat of fusion at the high temperature peak> From the viewpoint of improving the formability of foamed particles and obtaining a molded body with an excellent balance between cushioning and rigidity, the melting heat of polypropylene resin foamed particles at the high temperature peak is preferably 8 to 50 J / g, more preferably 10 to 40 J / g, and even more preferably 12 to 30 J / g.

[0100] Figure 1 An example of a DSC curve (the DSC curve for the first heating) is shown, in which the inherent resin peak P1 and a high-temperature peak P2, which is higher than the inherent resin peak, appear in the DSC curve obtained when polypropylene resin foam particles are heated from 23°C to 200°C at a heating rate of 10°C / min. Figure 1 In the case of the high-temperature peak P2 shown, its melting heat can be calculated as follows. First, set the point at 80°C on the DSC curve as α, and set the point on the DSC curve corresponding to the melting end temperature T as β, and draw a straight line L1 connecting them. Next, starting from the point γ on the DSC curve corresponding to the valley between the resin's inherent peak and the high-temperature peak, draw a straight line L2 parallel to the vertical axis of the graph, and set the point intersecting the straight line L1 as δ. The area (2) of the part enclosed by the curve, line segment (δ-β), and line segment L2 of the high-temperature peak portion of the DSC curve can be set as the area of ​​the high-temperature peak, and the melting heat of the high-temperature peak can be calculated from this area.

[0101] [Polypropylene Resin Foamed Particle Molding] By in-mold molding the polypropylene resin foam particles obtained by the manufacturing method of the present invention, a polypropylene resin foam particle molded body can be obtained.

[0102] In-mold forming can be performed by filling foamed particles into a molding mold and heating them using a heating medium such as steam. Specifically, after filling the foamed particles into the molding mold, a heating medium such as steam is introduced into the molding mold, thereby heating the foamed particles and causing them to foam and fuse together, thus obtaining a foamed particle molded body with a shape that has been given a forming space. In addition, the in-mold forming in this invention can be performed by the following pressure forming method (for example, Japanese Patent Publication No. 51-22951): the foamed particles are pre-pressurized using a pressurized gas such as air to increase the pressure inside the bubbles of the foamed particles, and after adjusting the pressure inside the foamed particles to a pressure 0.01 to 0.3 MPa higher than atmospheric pressure, the foamed particles are filled into the molding mold under atmospheric pressure or depressurization, and then a heating medium such as steam is supplied into the mold, thereby heating and fusing the foamed particles. In addition, molding can be performed using the following compression filling molding method (Japanese Patent Publication No. 4-46217): after filling a molding mold pressurized to atmospheric pressure or above with compressed gas, foamed particles pressurized to that pressure are supplied to the mold cavity, and a heating medium such as steam is supplied to heat the cavity, thereby causing the foamed particles to heat and fuse. Alternatively, molding can be performed using the following atmospheric pressure filling molding method (Japanese Patent Publication No. 6-49795): after filling the mold cavity of a molding mold with high secondary foaming power obtained under special conditions under atmospheric pressure or reduced pressure, a heating medium such as steam is supplied to heat the cavity, thereby causing the foamed particles to heat and fuse; or molding can be performed using a combination of the above methods (Japanese Patent Publication No. 6-22919), etc.

[0103] In particular, according to the present invention, even at low minimum forming pressures (vapor pressures), for example, below 0.3 MPa (G), good molded articles with excellent weldability, surface properties, and dimensional stability can be obtained. Excellent weldability generally refers to obtaining a molded article with a weld ratio of 70% or more, preferably 80% or more. Excellent surface properties refer to a smooth surface without obvious gaps or voids. Furthermore, in the present invention, based on the above characteristics, foamed particle molded articles with excellent dimensional stability can be obtained. Moreover, from the viewpoint of low-pressure formability, the minimum forming vapor pressure is preferably below 0.28 MPa (G).

[0104] <Density> From the viewpoint of easily obtaining molded articles with a good balance between strength and lightweight, the density of polypropylene resin foamed particle molded articles is preferably 10 kg / m³. 3 The above, preferably 15 kg / m 3 The above is further optimized to 20 kg / m 3 The above, and preferably 200 kg / m 3The following is more preferably 100 kg / m 3 The following is a further preferred value: 80 kg / m 3 The following is a further preferred value: 60 kg / m 3 the following.

[0105] The density of polypropylene resin foamed particle molded body is calculated by dividing the mass of the foamed particle molded body by the volume obtained based on the external dimensions of the molded body and then converting the units.

[0106]

Example

[0107] The resin raw materials, resin particles, foamed particles, and foamed particle molded articles of the Examples and Comparative Examples were measured and evaluated as follows. Furthermore, in the measurement of the physical properties of the resin particles, when the resin particles had a coating layer, only the resin particle body forming extruder described later was used, and no surface coating layer was formed. Otherwise, the resin particles were obtained under the same conditions as in the corresponding Examples and Comparative Examples, and the following measurements were performed using resin particles without a coating layer. Furthermore, the physical property measurements of the foamed particles were performed using foamed particles that had undergone state conditioning by standing for 24 hours at 50% RH, 23°C, and 1 atm. Furthermore, the physical property measurements and evaluations of the foamed particle molded articles were performed using molded articles that had undergone state conditioning by standing for 12 hours at 50% RH, 80°C, and 1 atm after demolding.

[0108] [Measurement Method] <Resin raw materials (virgin and recycled materials) and resin particles> (Melting point) The melting points of the resin raw materials and resin particles were measured by differential scanning calorimetry (DSC) according to JIS K 7121:2012. A high-sensitivity DSC calorimeter “EXSTAR DSC7020” (manufactured by Hitachi High Technology Co., Ltd.) was used as the measuring device. The condition of the test piece was adjusted by measuring the melting temperature after a certain heat treatment (2). About 2 mg of polypropylene resin was taken as the test piece. Under the condition of nitrogen flow rate of 30 mL / min, the test piece was heated from 23°C to 200°C at a heating rate of 10°C / min. Then, it was held at this temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and then heated to 200°C again at a heating rate of 10°C / min to obtain the DSC curve (DSC curve at the second heating). The peak temperature of the melting peak in the DSC curve was determined and taken as the melting point.

[0109] Furthermore, when multiple melting peaks appear in the DSC curve, the vertex temperature of the melting peak with the largest area is used as the melting point. In this case, by using the temperatures at the valleys of the DSC curves between the vertex temperatures of each melting peak as boundaries, and comparing the areas (heat of fusion) of each melting peak, the melting peak with the largest area can be identified. The temperatures at the valleys of the DSC curves correspond to the temperatures where the vertical axis of the differential curve of the DSC (DDSC) is 0, so this can also be determined from the differential curve of the DSC.

[0110] (Mel flow rate) The melt flow rate of the resin raw materials and resin particles was measured according to JIS K 7210-1:2014, under conditions of 230℃ and 2.16kg load.

[0111] (Crystallization temperature) The crystallization temperatures of the resin raw materials and resin particles were measured using a differential scanning calorimeter according to JIS K 7121:2012. In cases where multiple crystallization peaks appeared in the DSC curve, the peak temperature of the crystallization peak with the largest area was taken as the crystallization temperature.

[0112] (Heat of molten metal) The melting heat of the resin raw materials and resin particles was determined according to JIS K 7122:2012 by differential scanning calorimetry, as follows.

[0113] The measuring device used was a high-sensitivity differential scanning calorimeter "EXSTAR DSC7020" (manufactured by Hitachi High Technology Co., Ltd.). The condition of the test piece was adjusted by measuring the melting temperature after a certain heat treatment. About 2 mg of polypropylene resin was used as the test piece. Under the condition of nitrogen inflow rate of 30 mL / min, the test piece was heated from 23°C to 200°C at a heating rate of 10°C / min, and then held at that temperature for 10 minutes. After that, it was cooled to 23°C at a cooling rate of 10°C / min, and then heated to 200°C again at a heating rate of 10°C / min to obtain the DSC curve (the DSC curve at the second heating).

[0114] The point at 80°C on the DSC curve obtained during the second heating is designated as α, and the point on the DSC curve corresponding to the melting point is designated as β. The area enclosed by the DSC curve and the line segment (α-β) in the interval between points α and β is measured, and the heat of fusion of the polypropylene resin is calculated based on this area.

[0115] (Flexural modulus) The flexural modulus of the resin raw material was measured according to JIS K 7171:2016. First, polypropylene resin was hot-pressed at 230°C to prepare a sheet with a thickness of 4 mm. Standard test pieces with a length of 80 mm × width of 10 mm × thickness of 4 mm were cut from this sheet. Using these test pieces, with the radius of the indenter (R1) and the radius of the support platform (R2) both 5 mm, the distance between the support points 64 mm, and the test speed 2 mm / min, a bending test was conducted. Based on the bending test results, the flexural modulus of the polypropylene resin was measured.

[0116] (Gray component) The ash content of the recycled raw material was measured according to JIS K 6226-2:2003. The measuring apparatus used was a LECO TGA701 thermogravimetric analyzer manufactured by Japan Co., Ltd. Specifically, about 5g of the recycled raw material was taken as the measurement sample, its mass was measured, and it was placed in a crucible. The heating furnace was set to a nitrogen flow. Under the nitrogen atmosphere, the furnace temperature was increased from room temperature to 105°C at a rate of 10°C / min, and then held at 105°C until the measured mass reached equilibrium. The temperature was then increased from 105°C to 550°C at a rate of 10°C / min, and held at 550°C until the measured mass reached equilibrium. The furnace flow was then changed from nitrogen to air, and the temperature was increased from 550°C to 950°C at a rate of 10°C / min. After holding at 950°C for 10 minutes, the mass M1 of the combustion residue was determined, and the material was cooled to room temperature. Divide the mass M1 of the combustion residue by the mass of the sample measured in the crucible, then multiply by 100. Multiply the resulting value (mass%) by 10000 to calculate the ash content (mass ppm) of the recycled raw material. Perform the above operation twice and use the arithmetic mean as the ash content of the recycled raw material.

[0117] (Carbon black content) The carbon black content in the recycled raw material was measured according to JIS K 6226-2:2003. The measuring apparatus used was a differential thermal and thermogravimetric analyzer (TG / DTA6200) manufactured by Nippon Seiko Co., Ltd. Specifically, approximately 10 mg of the recycled raw material was taken as the measurement sample, its mass was measured, and it was placed in a platinum crucible. The furnace was set to a nitrogen flow, and under nitrogen atmosphere, the furnace temperature was increased from room temperature to 500°C at a rate of 10°C / min, and held at 500°C for 5 minutes. Then, the measuring atmosphere was changed to air, and the temperature was increased from 500°C to 1000°C at a rate of 10°C / min. The mass of the equilibrium portion held at 500°C was designated as M1, and the mass of the equilibrium portion at temperatures above 700°C was designated as M2. The carbon black content in the recycled raw material was determined by subtracting the mass M2 from the mass M1, dividing the result by the mass of the measured sample, and then multiplying by 100. The above operation was performed twice, and the arithmetic mean of the two operations was taken as the carbon black content in the recycled raw material.

[0118] <Foaming Particles> (Heat of melting at the high temperature peak) The melting heat of the high-temperature peak of the foamed particles was calculated according to JIS K 7122:2012 by differential scanning calorimetry, as follows.

[0119] Specifically, approximately 2 mg of foamed particles were used as a test piece and heated from 23°C to 200°C at a heating rate of 10°C / min using an EXSTAR DSC7020 differential scanning calorimeter (manufactured by Hitachi High Technology Co., Ltd.). A DSC curve with two or more melting peaks (DSC curve at the first heating) was obtained. Furthermore, the measurement was performed under a nitrogen inflow rate of 30 mL / min. Regarding the obtained DSC curve, the intrinsic peak of the polypropylene resin constituting the foamed particles was designated as P1, and the high-temperature peak appearing at a higher temperature was designated as P2.

[0120] Plot a straight line (α-β) connecting point α on the DSC curve corresponding to 80°C and point β on the DSC curve corresponding to the melting point T of the test piece. Furthermore, the melting point T refers to the endpoint of the high-temperature side of the high-temperature peak P2, specifically the intersection of the high-temperature peak and the high-temperature side baseline. Next, starting from point γ on the DSC curve corresponding to the valley between the inherent peak P1 and the high-temperature peak P2, draw a straight line parallel to the vertical axis of the graph, and designate the point intersecting this line as δ.

[0121] Calculate the area enclosed by the curve, line segment (δ-β), and line segment (γ-δ) of the high-temperature peak P2 portion of the DSC curve, and calculate the melting heat of each high-temperature peak based on this area. Measure the melting heat of the above high-temperature peaks for three different test pieces, and take the arithmetic mean of the obtained values ​​as the melting heat of the high-temperature peak of the foamed particles.

[0122] (Bulk density) The bulk density of the foamed particles is calculated as follows. First, a mass W1 [g] of foamed particles is filled into a graduated cylinder. The filling height of the foamed particles is stabilized by gently tapping the bottom of the graduated cylinder on the ground several times. Next, the volume V1 [L] of the foamed particles indicated by the graduated cylinder scale is read. The mass W1 [g] of the foamed particles is divided by the volume V1 [L] (W1 / V1), and the unit is converted to [kg / m³]. 3 ], thereby determining the packing density of the bubbling particles.

[0123] <Foamed Particle Molding Body> (Density of the molded body) To determine the density of the foamed particle molded body, the mass of the foamed particle molded body was divided by the volume calculated based on the molded body dimensions. The densities of three test pieces were then calculated, and their arithmetic mean was taken as the density of the foamed particle molded body. Furthermore, within the formable range described later, the density of foamed particle molded bodies obtained by in-mold forming with the lowest forming pressure was measured.

[0124] [Evaluation Method] <Toolbox-shaped foamed particle molding> (The lowest forming pressure to obtain a well-formed body) In the section on "Fabrication of Toolbox-Shaped Foamed Particle Moldings" described later, foamed particle moldings are fabricated by increasing the molding pressure (vapor pressure) in increments of 0.02 MPa (G) within the range of 0.20 to 0.40 MPa (G). The minimum molding pressure is determined to obtain a foamed particle molding that achieves an "A" rating in both appearance and dimensional stability.

[0125] (Appearance) In the section on "Making Toolbox-Shaped Foamed Particle Moldings" described later, after the molding is removed from the mold, it is cured or conditioned using the following methods.

[0126] Unripe After the molded body is removed from the mold, it is left to stand for 24 hours at 23°C, 50%RH, and 1 atm to adjust its condition.

[0127] 3-Hour Curing After removing the molded body from the mold, it is left to stand in an oven at 80°C for 3 hours for curing. Then, it is left to stand at 23°C, 50%RH, and 1 atm for 24 hours to adjust the condition of the molded body.

[0128] 24-Hour Curing After removing the molded body from the mold, it is left to stand in an oven at 80°C for 24 hours for curing. Then, it is left to stand at 23°C, 50%RH, and 1 atm for 24 hours to adjust the condition of the molded body.

[0129] The molded articles after maturation or condition adjustment by the above methods shall be evaluated according to the following criteria.

[0130] A: The foamed particles on the surface of the molded body have few gaps between each other, and the unevenness is not obvious.

[0131] B: The surface of the molded body has obvious unevenness caused by the gaps between the foamed particles.

[0132] (Dimensional stability) Similar to the above (appearance), in the "Making of Toolbox-Shaped Foamed Particle Moldings" described later, after the molded body is removed from the mold that can form a toolbox-shaped molding body with multiple concave and convex partitions of 80cm x 90cm x 15cm, the molded body after curing or condition adjustment is evaluated according to the following criteria.

[0133] A: The toolbox-shaped molded body does not have large dimensional changes, and the inner wall has almost no inward tilting.

[0134] B: The toolbox-shaped molded body has a small dimensional variation, which is within 5%.

[0135] C: The toolbox-shaped molded body exhibits significant dimensional changes (more than 5%), especially with inward tilting of the inner wall portion, which has not been reversed.

[0136] [raw material] The resins used in the examples and comparative examples are shown in Tables 1 and 2. Resin 1 is an ethylene-propylene copolymer (ethylene content: 3.1% by mass), and resin 2 is an ethylene-butene-propylene copolymer (ethylene content: 3.8% by mass, butene content: 3.8% by mass). Two melting peaks appear on the DSC curve, with the largest melting peak having a peak temperature of 125°C. Furthermore, recycled raw materials 1 through 7 are all ethylene-propylene copolymers.

[0137] Table 1

[0138] Table 2

[0139] Examples 1-4, Comparative Examples 2-6 <Preparation of Resin Particles> A manufacturing apparatus was prepared, comprising: an extruder for forming a resin particle body (core layer) with an inner diameter of 50 mm; a multilayer wire harness forming die attached downstream of the resin particle body (core layer) forming extruder; and an extruder for forming a coating layer with an inner diameter of 30 mm. Furthermore, in the manufacturing apparatus, the downstream side of the coating layer forming extruder is connected to the multilayer wire harness forming die. Moreover, the structure of the manufacturing apparatus enables the stacking of resin melts for forming each layer within the die and allows for co-extrusion.

[0140] As the polypropylene resin used to form the resin particle body (core layer), virgin and recycled raw materials as shown in Table 3 or Table 4 were used, with blending ratios as shown in Table 3 or Table 4. In addition to these materials, carbon black (furnace black) as a colorant and zinc borate (trade name "Firebrake ZB" manufactured by Borax) as a bubble regulator were supplied to the extruder for forming the resin particle body (core layer) at the blending ratios shown in Table 3 or Table 4, and melt-kneaded to obtain a mixed resin melt-knead. As the polypropylene resin used to form the coating layer, the polypropylene resin shown in Table 3 or Table 4 was supplied to the extruder for forming the coating layer, and melt-kneaded to obtain a resin melt-knead for forming the coating layer. The mixed resin melt-knead and the resin melt-knead for forming the coating layer were introduced into a die for forming a multilayer wire harness and merged within the die. A multilayer wire harness having a two-layer structure consisting of a resin particle body (core layer) and a coating layer, with a coating layer mass ratio as shown in Table 3 or Table 4, was extruded. The extruded wire bundle was water-cooled and cut by a granulator to obtain cylindrical multilayer resin particles with an average mass of 1.0 mg / particle and a length / diameter ratio of 2.0.

[0141] <Preparation of foamed particles> 100 kg of the obtained resin particles were fed together with 230 L of water as the dispersion medium into a sealed container with a capacity of 400 L. Additionally, relative to 100 parts by mass of the resin particles, 0.3 parts by mass of kaolin as an inorganic dispersant, 0.004 parts by mass of sodium alkylbenzene sulfonate (as the active ingredient) as a surfactant, and 0.01 parts by mass of aluminum sulfate were added to the sealed container. Next, carbon dioxide as a foaming agent was pressurized into the sealed container to a pressure 1 MPa lower than the gauge pressure shown in Table 3 or Table 4. Then, while stirring the sealed container, the temperature was raised to the temperature shown in Table 3 or Table 4 at a heating rate of 2 °C / min. Carbon dioxide was then injected again, and the pressure was raised to the gauge pressure shown in Table 3 or Table 4, and then maintained at this temperature for 15 minutes. This process was performed to ensure a high-temperature peak appeared in the endothermic curve obtained from the DSC measurement of the obtained foamed particles. Then, the contents (resin particles and water) in the sealed container are released to atmospheric pressure to obtain one-step foamed particles with the bulk density shown in Table 3 or Table 4.

[0142] Furthermore, the obtained one-step foamed particles were cured for 24 hours at an ambient temperature of 23°C, a relative humidity of 50%, and a pressure of 1 atm. Then, the cured one-step foamed particles were placed in a pressurized, sealed container, and the pressure inside the container was increased from atmospheric pressure to pressurize the particles. This pressurized state was maintained for a specified time, thereby impregnating the bubbles within the foamed particles with air. The one-step foamed particles were then removed from the sealed container, yielding one-step foamed particles with an internal bubble pressure of 0.5 MPa (G). These one-step foamed particles were then fed into a two-step foaming apparatus. Steam was supplied to this apparatus to foam the one-step foamed particles, thus obtaining two-step foamed particles.

[0143] The measurement results of the obtained foamed particles are shown in Table 3 or Table 4. Furthermore, the mass ratio of the resin particle body (core layer) to the coating layer in the foamed particles is the same as the mass ratio of the resin particle body (core layer) to the coating layer in the resin particles.

[0144] <Fabrication of Toolbox-Shaped Foamed Particle Moldings> The two-step foamed particles obtained as described above were cured for 24 hours at an air temperature of 23°C, a relative humidity of 50%, and a pressure of 1 atm. Then, they were placed in a pressurized, sealed container and pressurized with compressed air to impregnate the foamed particles with air, applying the internal pressure (bubble pressure) shown in Table 3 or Table 4. Next, the pressurized foamed particles were filled into a molding mold (mold) with a toolbox-shaped foamed particle molded body having multiple concave and convex partition sections, capable of forming a body with dimensions of 80cm x 90cm x 15cm. The cracking amount is shown in Table 3 or Table 4. Heating was then performed according to the following method: The heating method involves supplying steam to the mold with the exhaust valves on both sides open for preheating (exhaust process). Then, steam is supplied from one side of the mold for heating, followed by steam supply from the other side. Finally, steam is supplied from both sides of the mold at a predetermined forming steam pressure for heating. After heating, the pressure was released, and the foamed particle molded body was water-cooled until the surface pressure caused by the foaming force of the foamed particle molded body reached 0.05 MPa (G). Then, the mold was opened and the foamed particle molded body was removed. The measurement and evaluation results of the obtained foamed particle molded body are shown in Table 3 or Table 4.

[0145] Furthermore, when using the two-step foamed particles obtained above, and fabricating a flat foamed particle molded body with dimensions of 300mm (length) × 250mm (width) × 60mm (height) in the same manner as described above, the density of the molded body in Examples 1 to 4 was 33kg / m³. 3The minimum forming pressure at which a well-formed body can be obtained is 0.28 MPa (G), enabling forming at low forming pressures. Furthermore, in the evaluation of the minimum forming pressure at which a well-formed body can be obtained, the formable forming pressure range is 0.06 MPa (G). Within this range, foamed particle molded bodies that pass all evaluations of weldability, surface properties, and dimensional stability can be obtained, demonstrating a wide range of formability and excellent formability.

[0146] Comparative Example 1 In the above-described <Preparation of Resin Particles>, a manufacturing apparatus including an extruder with an inner diameter of 50 mm and a wire harness forming die attached to the downstream side of the extruder was prepared. As the polypropylene resin used to form the resin particles, the virgin raw materials shown in Table 4 were used. Carbon black (furnace black) as a colorant and zinc borate (trade name "Firebrake ZB" manufactured by Borax) as a bubble regulator were fed into the extruder at the blending ratios shown in Table 4, respectively, and were melt-kneaded and extruded to obtain resin particles. Otherwise, foamed particles and foamed particle molded articles were prepared in the same manner as in Example 1. The measurement and evaluation results of the obtained foamed particles and foamed particle molded articles are shown in Table 4.

[0147] Table 3

[0148] Table 4

[0149] As shown in Tables 3 and 4, the toolbox-shaped molded body formed by in-mold molding of foamed particles obtained by the manufacturing method of the present invention has excellent dimensional stability even under low molding pressure.

[0150] Industrial applicability The foamed particles obtained by the manufacturing method of this invention can be molded even with low forming pressure and help reduce environmental impact. The foamed particle molded bodies formed by in-mold molding of the foamed particles obtained by the manufacturing method of this invention can be widely used as impact-absorbing materials, heat-insulating materials, and various packaging materials, and are applied in food transport containers, electrical and electronic components, precision components, packaging or cushioning materials for vehicle components, building components such as residential heat insulation materials, and general merchandise.

Claims

1. A method for manufacturing polypropylene resin foamed particles, comprising foaming polypropylene resin particles to produce polypropylene resin foamed particles, characterized in that, The polypropylene resin particles are composed of a mixture of virgin raw materials and recycled polypropylene resin raw materials. The virgin raw materials include at least one propylene copolymer selected from ethylene-propylene copolymer, butene-propylene copolymer, and ethylene-butene-propylene copolymer as the base resin. The recycled raw material comprises at least one propylene copolymer selected from ethylene-propylene copolymer, butene-propylene copolymer, and ethylene-butene-propylene copolymer as the base resin. The melting point MP1 of the primary raw material is above 130°C and below 150°C. The melting point MP2 (°C) of the recycled raw material and the melting point MP1 (°C) of the virgin raw material satisfy the following relationship (1): The melt flow rate MFR2 (g / 10 min) of the recycled raw material and the melt flow rate MFR1 (g / 10 min) of the virgin raw material satisfy the following relationship (2): The difference between the crystallization temperature CP2 (°C) of the recycled raw material and the crystallization temperature CP1 (°C) of the virgin raw material satisfies the following relationship (3). -10 <MP2-MP1<10･･･(1) 0≤MFR2-MFR1≤10･･･(2) 2 <CP2-CP1<12･･･(3)。 2. The method for manufacturing polypropylene resin foamed particles as described in claim 1, characterized in that, The ash content of the recycled raw material is between 500 ppm and 2000 ppm by mass.

3. The method for manufacturing polypropylene resin foamed particles as described in claim 1 or 2, characterized in that, The crystallization temperature of the recycled raw material is above 105℃ and below 115℃.

4. The method for manufacturing polypropylene resin foamed particles as described in claim 1 or 2, characterized in that, The ratio of the flexural modulus of the virgin material to the flexural modulus of the recycled material is 0.5 to 2.

0.

5. The method for manufacturing polypropylene resin foamed particles as described in claim 1 or 2, characterized in that, The blending ratio of the virgin raw material to the recycled raw material is: 10-90% by mass of the virgin raw material and 10-90% by mass of the recycled raw material, wherein the total of the virgin raw material and the recycled raw material is 100% by mass.

6. The method for manufacturing polypropylene resin foamed particles as described in claim 1 or 2, characterized in that, The recycled raw material is derived from polypropylene resin foamed particle molding.

7. A method for manufacturing a foamed particle molded body, characterized in that, It is formed by in-mold molding of polypropylene resin foam particles obtained by the manufacturing method described in claim 1 or 2.

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