Method for manufacturing polypropylene resin foam particles

Abstract

The present invention provides a method for producing polypropylene-based resin foam particles that can be molded even at low molding pressures. [Solution] A method for producing foamed polypropylene resin particles by foaming polypropylene resin particles, wherein the resin particles consist of a mixed resin of virgin raw material and recycled polypropylene resin raw material, the recycled raw material contains a propylene copolymer as a base resin, the melting point MP1 of the virgin raw material is 130°C or higher and less than 150°C, the melting point MP2 (°C) of the recycled raw material and the melting point MP1 (°C) of the virgin raw material satisfy a specific relationship, 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 a specific relationship, and the crystallization temperature CP2 (°C) of the recycled raw material and the crystallization temperature CP1 (°C) of the virgin raw material satisfy a specific relationship.

Description

[Technical Field]

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

[0002] Polypropylene resin foam particle molded articles, which are formed by molding polypropylene resin foam particles, exhibit excellent lightness, cushioning properties, and toughness. For this reason, polypropylene resin foam particle molded articles are widely used as transport containers for food and other products, packaging or cushioning materials for electrical and electronic components, precision parts, and vehicle components, building materials such as insulation materials for houses, and shock absorbers for vehicle components, etc.

[0003] Furthermore, alongside the use of polypropylene-based foam particle molded products, in recent years, amidst the movement to promote a circular economy, there has been a growing social demand not only for recycling such as the reuse of scrap and the use of waste materials, but also for utilizing waste materials that have been used by end users as recycled materials (post-consumer materials).

[0004] Patent Document 1 discloses a method for producing polypropylene resin foam particles having a specific range of bulk density, with the aim of providing a black foam particle molded article with excellent appearance and physical properties using a post-consumer material of a polypropylene resin foam molded article containing carbon black. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2024-41662 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in recent years, there has been a demand for environmentally friendly products that can further reduce the burden on the environment. One method for manufacturing such environmentally friendly products is to produce polypropylene resin foam particles that can be molded even at low molding pressures when molding foam particles to produce foam particle molded products.

[0007] The present invention has been made in view of the above problems, and aims to provide a method for producing polypropylene resin foam particles that can be molded even at low molding pressure, even when using recycled materials from polypropylene resin molded articles. [Means for solving the problem]

[0008] The inventors of the present invention have found that the above problems can be solved by producing polypropylene resin foam particles using virgin raw materials and recycled raw materials of polypropylene resin molded articles that satisfy a specific relationship, and have completed the present invention. In other words, the present invention is as follows: <1> A method for producing polypropylene resin foam particles by foaming polypropylene resin particles, wherein the polypropylene resin particles consist of a mixed resin of a virgin raw material containing at least one propylene copolymer selected from ethylene-propylene copolymer, butene-propylene copolymer, and ethylene-butene-propylene copolymer as a base resin, and a recycled polypropylene resin raw material, wherein the recycled raw material is selected from at least one propylene copolymer selected from ethylene-propylene copolymer, butene-propylene copolymer, and ethylene-butene-propylene copolymer. A method for producing polypropylene resin foam particles, wherein both contain one type of propylene copolymer as a 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 relationship shown in 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 relationship shown in equation (2), and 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 relationship shown in equation (3). -10 <MP2-MP1<10 ···(1) 0 ≤ MFR2 - MFR1 ≤ 10 ···(2) 2 <CP2-CP1<12 ···(3) <2> The ash content of the recycled raw material is 500 ppm by mass or more and 2000 ppm by mass or less. <1> A method for producing polypropylene resin foam particles as described above. <3> The crystallization temperature CP2 of the recycled material is 105°C or higher and 115°C or lower. <1> or <2> A method for producing polypropylene resin foam particles as described above. <4> 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. <1> ~ <3> A method for producing polypropylene resin foam particles as described in any one of the following. <5> 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 (provided that the total of the virgin raw material and the recycled raw material is 100% by mass). <1> ~ <4> A method for producing polypropylene resin foam particles as described in any one of the following. <6> The recycled material is a recycled material derived from a polypropylene-based resin foam particle molded product. <1> ~ <5> A method for producing polypropylene resin foam particles as described in any one of the following. [Effects of the Invention]

[0009] According to the present invention, a method for producing polypropylene-based resin foam particles that can be molded even at low molding pressures is provided. [Brief explanation of the drawing]

[0010] [Figure 1] This figure illustrates the DSC curve of polypropylene resin foam particles after the first heating. [Modes for carrying out the invention]

[0011] [Method for manufacturing polypropylene resin foam particles] The method for producing polypropylene-based resin foamed particles of the present invention (hereinafter, simply referred to as the method for producing foamed particles of the present invention or the production method of the present invention) is a method for producing polypropylene-based resin foamed particles (hereinafter, simply referred to as foamed particles) by foaming polypropylene-based resin particles (hereinafter, simply referred to as resin particles) having a polypropylene-based resin as a base resin. The polypropylene-based resin particles are composed of a virgin raw material containing at least one propylene copolymer (B) selected from an ethylene-propylene copolymer, a butene-propylene copolymer, and an ethylene-butene-propylene copolymer as a base resin, and a recycled raw material of a polypropylene-based resin molded body. The recycled raw material contains at least one propylene copolymer (R) selected from an ethylene-propylene copolymer, a butene-propylene copolymer, and an ethylene-butene-propylene copolymer as a base resin. The melting point MP1 of the virgin raw material is 130°C or higher and lower 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 relationship of the following formula (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 relationship of the following formula (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 relationship of the following formula (3). In this specification, the base resin refers to the main component in the resin component constituting the virgin raw material, the recycled raw material, the resin particles, or the foamed particles. Specifically, the content of the base resin in the resin component is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more. Also, in this specification, the numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. -10 < MP2 - MP1 < 10 ···(1) 0 ≦ MFR2 - MFR1 ≦ 10 ···(2) 2 < CP2 - CP1 < 12 ···(3)

[0012] In the method for producing foamed particles of the present invention, by using a material in which virgin raw materials and recycled raw materials from polypropylene-based resin molded articles have a specific relationship as raw materials for resin particles, it is possible to provide foamed particles with excellent moldability that are less prone to defects such as dimensional shrinkage, even at low molding pressures. In particular, when the polypropylene-based resin foamed particle molded article (hereinafter simply referred to as a foamed particle molded article or molded article) produced by molding polypropylene-based resin foamed particles produced by the method for producing foamed particles of the present invention is large, it exhibits particularly excellent dimensional stability after molding, even at low molding pressures. Furthermore, when molding foamed particles obtained by the manufacturing method of the present invention, a good molded article can be obtained without performing the heat curing that is usually performed after molding, thus further reducing the burden on the environment. In this specification, polypropylene-based resin refers to a polymer in which the content of constituent units derived from propylene is 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more.

[0013] <Virgin 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) used as the base resin of the virgin raw material comprises at least one selected from ethylene-propylene copolymer, butene-propylene copolymer, and ethylene-butene-propylene copolymer, and preferably at least one selected from ethylene-propylene copolymer and ethylene-butene-propylene copolymer. The term "base resin" here 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. Other resins may be further blended into the base resin as long as they do not hinder the intended effects of the present invention. When the propylene copolymer (B) contains an ethylene component, the content of the ethylene component in the propylene copolymer (B) is preferably 1% by mass or more, more preferably 2% by mass or more, from the viewpoint of enhancing the moldability of the foamed particle molded body at a lower molding pressure, and is preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less, from the viewpoint of easily and stably obtaining a good molded body. When the propylene copolymer (B) contains a butene component, the content of the butene component in the propylene copolymer (B) is preferably 1% by mass or more, more preferably 2% by mass or more, from the viewpoint of enhancing the moldability of the foamed particle molded body at a lower molding pressure, and is preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less, from the viewpoint of easily and stably obtaining a good molded body. The content of the monomer components (ethylene component, butene component) of the propylene copolymer (B) is determined by a known method determined by IR spectrum. Specifically, it is determined by the method described in the Polymer Analysis Handbook (edited by the Polymer Analysis Research Group of the Japanese Society for Analytical Chemistry, publication date: January 1995, publisher: Kiyokawa Shoten, page numbers and item names: 615 - 616 "II.2.3 2.3.4 Propylene / Ethylene Copolymer", 618 - 619 "II.2.3 2.3.5 Propylene / Butene Copolymer"), that is, by the method of quantifying from the relationship between the value obtained by correcting the absorbance of ethylene and butene with a predetermined coefficient and the thickness of the film-like test piece, etc. More specifically, it is measured by the method described in the examples.

[0014] (Other polymers) The virgin raw material may contain other polymers besides propylene copolymer (B) as long as they do not hinder the desired effects of the present invention. Examples of other polymers include thermoplastic resins such as polypropylene resins, polybutene resins, and polystyrene resins other than the propylene copolymer (B) described above, and thermoplastic elastomers (e.g., polybutadiene elastomers; block copolymers of styrene-butadiene, styrene-isoprene, styrene-butadiene-styrene, styrene-isoprene-styrene, and their hydrogenated products). The content of other polymers in the virgin raw material is preferably 10% by mass or less, and more preferably 5% by mass or less.

[0015] (Additives) Virgin raw materials may contain additives, and further additives may be added as needed. Examples of additives include antioxidants, UV inhibitors, light stabilizers, antistatic agents, flame retardants, flame retardant enhancers, metal deactivators, conductive fillers, bubble regulators, and colorants. 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, per 100 parts by mass of propylene copolymer (B).

[0016] If the virgin raw material contains multiple types of propylene copolymer (B), or other polymers or additives other than propylene copolymer (B), the measurement of the virgin raw material described later will be performed using the virgin raw material containing multiple types of propylene copolymer (B) or the virgin raw material containing other polymers or additives as a sample.

[0017] (Melting point MP1) The melting point MP1 of the virgin 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 suppressing shrinkage after molding and improving moldability, and less than 150°C, preferably 148°C or lower, more preferably 146°C or lower, and even more preferably 144°C or lower, from the viewpoint of further improving the moldability of the foamed particle molded article at lower molding pressures. The melting point MP1 is measured using virgin raw material as a test specimen in accordance with JIS K 7121:2012. Specifically, for conditioning the test specimen, "(2) When measuring the melting temperature after performing a certain heat treatment" is adopted. The test specimen is heated from 23°C to 200°C at a heating rate of 10°C / min under a nitrogen inflow of 30 mL / min, then held at that temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and then heated again to 200°C at a heating rate of 10°C / min to obtain a DSC curve (DSC curve after the second heating). Next, the peak temperature of the melting peak in the DSC curve is determined, and this value can be taken as the melting point of the virgin raw material. If multiple melting peaks appear in the DSC curve, the peak temperature of the melting peak with the highest height relative to the baseline is adopted as the melting point MP1. In this process, by distinguishing each melting peak based on the temperature of the trough in the DSC curve located between the peak temperatures of each melting peak and comparing the area (heat of fusion) of each melting peak, the melting peak with the largest area can be determined. The temperature of the trough in the DSC curve can be determined by referring to the differential curve of the DSC (DDSC) and finding the temperature at which the value on the vertical axis of the differential curve becomes 0.

[0018] (Meltflow Rate MFR1) The melt flow rate MFR1 of the virgin raw material is not particularly limited as long as the relationship of formula (2) above is satisfied, but from the viewpoint of easily obtaining foamed particles with excellent moldability, it is preferably 1 g / 10 min or more, more preferably 3 g / 10 min or more, even more preferably 5 g / 10 min or more, and preferably 15 g / 10 min or less, more preferably 12 g / 10 min or less, and even more preferably 9 g / 10 min or less. The aforementioned melt flow rate MFR1 is a value measured for virgin raw materials under the conditions of a temperature of 230°C and a load of 2.16 kg, in accordance with JIS K 7210-1:2014.

[0019] (Crystallization temperature CP1) The crystallization temperature CP1 of the virgin raw material is not particularly limited as long as the relationship of formula (3) above is satisfied, but from the viewpoint of easily obtaining foamed particles with excellent moldability, it is preferably 90°C or higher, more preferably 93°C or higher, even more preferably 95°C or higher, and preferably 125°C or lower, 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 CP1 is measured for virgin raw materials using a differential scanning calorimeter in accordance with JIS K 7121:2012. If multiple crystallization peaks appear in the DSC curve, the peak temperature of the crystallization peak with the largest area is taken as the crystallization temperature CP1.

[0020] (Heat of fusion) From the viewpoint of further improving the moldability of the foamed particle molded body at lower molding pressures, the heat of fusion of the virgin 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. The heat of fusion is measured for virgin raw materials using a differential scanning calorimeter in accordance with JIS K 7122:2012. If multiple fusion peaks appear in the DSC curve, the sum of the areas of the multiple fusion peaks is taken as the heat of fusion.

[0021] (Flexural modulus F1) The flexural modulus F1 of the virgin raw material is preferably 800 MPa or higher, more preferably 850 MPa or higher, even more preferably 900 MPa or higher, and even more preferably 950 MPa or higher, and preferably 1600 MPa or lower, more preferably 1500 MPa or lower, even more preferably 1400 MPa or lower, even more preferably 1300 MPa or lower, and even more preferably 1200 MPa or lower, from the viewpoint of further suppressing shrinkage of the molded article after molding and improving moldability. The aforementioned flexural modulus F1 is measured for virgin raw materials in accordance with JIS K 7171:2016.

[0022] <Recycled polypropylene resin material> Polypropylene resin recycled raw materials (hereinafter also simply referred to as recycled raw materials) refer to polypropylene resin raw materials recovered after the manufacture of used polypropylene resin molded products, etc., and are virgin raw materials that have been subjected to heat treatment at least once. For example, recovered polypropylene resin molded products can be crushed, crushed and melted, and pelletized to be used as raw materials for resin particles. The use of the recovered polypropylene resin is not particularly limited as long as it satisfies the above formulas (1) to (3), but it is preferable to use recycled raw materials derived from polypropylene resin foam particle molded products, for example.

[0023] (Method for preparing recycled materials) Since collected used polypropylene resin molded products may contain items other than the polypropylene resin molded product itself, such as packaging bags and labels, it is preferable to perform foreign object sorting. Foreign object sorting may be performed by visual inspection by an operator, or it may be performed using a sorting machine or the like. For crushing polypropylene resin molded articles, it is preferable to use a crusher. Crushers include compression crushers, shear crushers, and impact crushers. For example, the crushing method may involve first coarse crushing using an impact crusher and then fine crushing again using a shear crusher, or crushing in one go using a shear crusher. In particular, it is economical and preferable to crush in one step while maintaining uniform particle size by using a shear crusher with a perforated metal or screen installed at the outlet of the shear crusher. There are no particular restrictions on the size of the crushed material, but it is preferable that it be between 1 mm and 30 mm in size. The obtained pulverized material is preferably heated and reduced in volume to form a molten ingot. Heating and volume reduction machines include extruders and presses. The processing temperature during volume reduction is not particularly limited, but to avoid thermal degradation of the polypropylene resin, it is preferable to perform the process at the lowest possible temperature, preferably 220°C or lower and above the resin melting point. The molten ingot is preferably pulverized again using the above-mentioned pulverizer, then melted using an extruder and pelletized to form polypropylene resin recycled raw material pellets. The above-mentioned pulverizer can be used. For the extruder, single-screw extruders, twin-screw extruders, etc., can be used, but the use of a single-screw extruder is preferred from the viewpoint of preventing resin degradation. 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 the lowest possible temperature, preferably 220°C or lower and above the resin melting point. It is preferable to pass the polypropylene resin melted in the extruder through a filter to remove foreign matter. Woven wire mesh, sintered metal, etc. can be used as filters, but woven wire mesh is economical and preferred. Methods for pelletizing molten polypropylene resin include the underwater cutting method, in which the molten resin is continuously cut and solidified by a rotating blade attached to the front of the die while being extruded from the die into water or mist, and the strand cutting method, in which the resin is continuously extruded from the die in a strand shape, cooled and solidified in a water tank, and then cut with a cutting machine. Among these, the strand cutting method is economical and preferred. There are no particular restrictions on the size of the pellets, but it is preferable that the average mass of each pellet be 1 to 30 mg. In addition, according to the above recovery method, the recycled raw material of the present invention undergoes two or more heating operations compared to the virgin raw material.

[0024] (Base resin) The propylene copolymer (R) used as the base resin for the recycled raw material includes at least one selected from ethylene-propylene copolymer, butene-propylene copolymer, and ethylene-butene-propylene copolymer. Here, "base resin" 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, to the extent that they do not hinder the desired effects of the present invention. The propylene copolymer (R) may be the same as or different from the propylene copolymer (B) described above. If the propylene copolymer (R) contains an ethylene component, the content of the ethylene component in the propylene copolymer (R) is preferably 1% by mass or more, more preferably 2% by mass or more, from the viewpoint of further improving the moldability of the foamed particle molded article at lower molding pressures, and preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, from the viewpoint of making it easier to stably obtain a good molded article. If the propylene copolymer (R) contains a butene component, the content of the butene component in the propylene copolymer (R) is preferably 1% by mass or more, more preferably 2% by mass or more, from the viewpoint of further improving the moldability of the foamed particle molded article at lower molding pressures, and preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, from the viewpoint of making it easier to stably obtain a good molded article. The monomer component (ethylene component, butene component) content of the propylene copolymer (R) is measured in the same manner as the measurement of the monomer component (ethylene component, butene component) content of the virgin raw material propylene copolymer (B) described above.

[0025] The recycled material may contain other polymers besides propylene copolymer(R), as long as they do not hinder the desired effects of the present invention. Examples of other polymers include the thermoplastic resins and thermoplastic elastomers mentioned above, which may be contained in the virgin material. Furthermore, the recycled material may contain, or may be added to, the additives exemplified as additives that can be added to the virgin material. Similar to the virgin material, if the recycled material contains multiple types of propylene copolymer(R) or other polymers and additives other than propylene copolymer(R), the measurement of the recycled material described later will be performed using the recycled material containing multiple types of propylene copolymer(R) or the recycled material containing other polymers and additives as samples.

[0026] (Melting point MP2) The melting point MP2 of the recycled material is not particularly limited as long as the relationship of formula (1) above is satisfied, but from the viewpoint of suppressing shrinkage after molding and improving moldability, 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. Furthermore, from the viewpoint of further improving the moldability of the foamed particle molded body at lower molding pressures, it is preferably less than 160°C, more preferably 155°C or lower, even more preferably 150°C or lower, and even more preferably 148°C or lower. The melting point MP2 is measured using the recycled material as a test piece in the same manner as the measurement of the melting point MP1.

[0027] (Meltflow Rate MFR2) The melt flow rate MFR2 of the recycled raw material is not particularly limited as long as the relationship of formula (2) above is satisfied, but from the viewpoint of easily obtaining foamed particles with excellent moldability, it is preferably 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 of the recycled raw material is measured under the same conditions as the measurement of MFR1, with a temperature of 230°C and a load of 2.16 kg.

[0028] (Crystallization temperature CP2) The crystallization temperature CP2 of the recycled material is not particularly limited as long as the relationship of formula (3) above is satisfied, but from the viewpoint of easily obtaining foamed particles with excellent moldability, it is preferably 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 of the recycled material is measured in the same manner as the measurement of the crystallization temperature CP1.

[0029] (ash content) 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, and even more preferably 1600 ppm by mass or less, from the viewpoint of making it easier to adjust the crystallization temperature to a desired range. The ash content of recycled materials is measured in accordance with JIS K 6226-2:2003. Preferably, the recycled material is derived from polypropylene-based foamed particle molded articles. In this case, since it contains inorganic substances such as bubble nucleating agents derived from the foamed particle molded articles, it is particularly important to keep the ash content of the recycled material within the specified range.

[0030] (Flexural modulus F2) The flexural modulus F2 of the recycled material is preferably 600 MPa or higher, more preferably 700 MPa or higher, even more preferably 800 MPa or higher, even more preferably 900 MPa or higher, even more preferably 1000 MPa or higher, and preferably 1600 MPa or lower, more preferably 1500 MPa or lower, and even more preferably 1400 MPa or lower, from the viewpoint of further suppressing shrinkage of the molded article after molding and further improving moldability. The flexural modulus F2 of the recycled material is measured in the same manner as the measurement of the flexural modulus F1.

[0031] The heat of fusion of the recycled material is preferably 40 J / g or more, more preferably 50 J / g or more, even more 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, from the viewpoint of further improving the moldability of the foam particle molded body at lower molding pressures.

[0032] (Formula (1): Difference (MP2-MP1)) The difference between the melting point MP2 (°C) of the recycled material and the melting point MP1 (°C) of the virgin material (MP2-MP1) satisfies the relationship given by equation (1) below. -10 <MP2-MP1<10···(1) By using raw materials that satisfy this relationship, it is possible to provide foamed particles that can form good molded articles even at low molding pressures. Specifically, molded articles formed by molding foamed particles obtained by the manufacturing method of the present invention are less prone to defects such as dimensional shrinkage even at low molding pressures, and especially when the molded article is large, it exhibits excellent dimensional stability after molding, even at low molding pressures. From the above viewpoint, the difference (MP2-MP1) is preferably -5°C or higher, more preferably -2°C or higher, even more 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.

[0033] (Formula (2): Difference (MFR2-MFR1)) The difference between the melt flow rate MFR2 (g / 10 min) of recycled raw materials and the melt flow rate MFR1 of virgin raw materials (MFR2-MFR1) satisfies the relationship shown in equation (2) below. 0 ≤ MFR2 - MFR1 ≤ 10 ···(2) By using raw materials that satisfy this relationship, the raw materials are thoroughly mixed, the closed-cell ratio of the foamed particles obtained by the manufacturing method of the present invention tends to be high, and the molded article formed by molding the foamed particles is less prone to defects such as dimensional shrinkage even at low molding pressures, and in particular when the molded article is large, it exhibits excellent dimensional stability after molding, even at low molding pressures. From the above viewpoint, the difference (MFR2-MFR1) is preferably 8 g / 10 min or less, more preferably 6 g / 10 min or less, even more preferably 4 g / 10 min or less, and preferably 1 g / 10 min or more, more preferably 2 g / 10 min or more.

[0034] (Formula (3): Difference (CP2-CP1)) The difference between the crystallization temperature CP2 of the recycled material and the crystallization temperature CP1 of the virgin material (CP2-CP1) satisfies the relationship shown in equation (3) below. 2 <CP2-CP1<12 ···(3) By using raw materials that satisfy this relationship, it is possible to provide foamed particles that can form good molded articles even at low molding pressures. Specifically, molded articles formed by molding foamed particles obtained by the manufacturing method of the present invention are less prone to defects such as dimensional shrinkage even at low molding pressures, and especially when the molded article is large, it exhibits excellent dimensional stability after molding, even at low molding pressures. From the above viewpoint, the difference (CP2-CP1) is preferably 3°C or more, more preferably 5°C or more, even more preferably 7°C or more, and preferably 11°C or less.

[0035] 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 shrinkage after molding have a specific relationship, and equations (1) to (3) are interrelated, resulting in molded articles formed by molding foam particles obtained by the manufacturing method of the present invention that are less prone to defects such as dimensional shrinkage even at low molding pressures, and especially when the molded article is large, it exhibits excellent dimensional stability after molding, even at low molding pressures. Furthermore, when molding foam particles obtained by the manufacturing method of the present invention, a good molded article can be obtained without performing the heat curing that is usually performed after molding, thus further reducing the environmental burden.

[0036] (Ratio (F1 / F2)) The ratio of the flexural modulus F1 of virgin raw materials to the flexural modulus F2 of recycled raw materials (F1 / F2) is preferably 0.5 or higher, more preferably 0.7 or higher, and preferably 2.0 or lower, more preferably 1.7 or lower, and even more preferably 1.5 or lower, from the viewpoint of further suppressing shrinkage of the molded article after molding and further improving moldability.

[0037] <Polypropylene resin particles> Polypropylene resin particles are composed of a mixed resin of the virgin raw material and the recycled raw material described above. The resin particles obtained by the manufacturing method of the present invention may be single-layer particles composed of the mixed resin, or multi-layer resin particles having a separate 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 in the portion forming the foam, regardless of whether it is a single-layer foam particle or a multi-layer foam particle, is composed of a mixed resin of the virgin raw material and the recycled raw material described above.

[0038] (mixed resin) A mixed resin of virgin and recycled raw materials can be obtained by supplying the virgin and recycled raw materials, along with additives as needed, to an extruder, and melting and kneading the supplied materials. Then, by extruding the molten and kneaded mixed resin from the extruder and pelletizing it to a predetermined shape and mass, polypropylene resin particles composed of the mixed resin can be obtained. The virgin raw material content in the mixed resin is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more, when the total of virgin raw materials and recycled raw materials is considered to be 100% by mass, from the viewpoint of the stability of the physical properties of the resulting foamed particles and molded articles. Furthermore, from the viewpoint of further reducing the burden on the environment, 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. Furthermore, in the present invention, even if the proportion of recycled materials is increased for the purpose of reducing environmental impact, it is possible to obtain a good foamed particle molded article. Preferably, the proportion of virgin materials and recycled materials is 10 to 90% by mass of virgin materials and 10 to 90% by mass of recycled materials (provided that the total of virgin materials and recycled materials is 100% by mass), and more preferably, 20 to 50% by mass of virgin materials and 50 to 80% by mass of recycled materials. On the other hand, depending on the amount of recycled material available, it is possible to increase the amount of virgin material used to obtain a good foamed particle molded body. In this case, it is preferable that the ratio of virgin material to recycled material be 10-90% by mass for virgin material and 10-90% by mass for recycled material (provided that the total of virgin material and recycled material is 100% by mass), and more preferably 50-90% by mass for virgin material and 50-10% by mass for recycled material.

[0039] The mixed resin constituting the polypropylene resin particles may contain other polymers other than propylene copolymer (B) or propylene copolymer (R), as long as they do not hinder the desired effects of the present invention. Examples of other polymers include the thermoplastic resins and thermoplastic elastomers mentioned above, which may be contained in the virgin raw material. Furthermore, the mixed resin may contain, or may contain, the additives exemplified as additives that can be added to the virgin raw material.

[0040] When the resin particles are multilayer resin particles having a coating layer on their surface, multilayer resin particles can be produced by co-extrusion, which involves methods such as producing a resin particle body (core layer) composed of a mixed resin and a coating layer that covers the resin particle body (core layer), or by coating a pre-made resin particle body composed of a mixed resin with a coating layer. Specifically, in the co-extrusion method, an extrusion apparatus can be used that includes an extruder for forming the resin particle body (core layer) composed of a mixed resin, an extruder for forming the coating layer, and a co-extrusion die such as a die for forming a multilayer strand connected downstream of these extruders. Virgin raw materials and recycled raw materials for forming the mixed resin, along with additives added as needed, are supplied to the extruder for forming the resin particle body (core layer) and melt-kneaded to form a mixed resin molten product. A resin for forming the coating layer (for example, a polyolefin resin) and additives added as needed are supplied to the extruder for forming the coating layer and melt-kneaded to form a resin molten product for forming the coating layer. By introducing a mixed resin molten material and a coating layer-forming resin molten material into a co-extrusion die and combining them, then extruding them from an extruder while pelletizing them to a predetermined shape and mass, multilayer resin particles can be obtained in which a coating layer is present on the surface of a resin particle body (core layer) composed of a mixed resin. As a method for coating the resin particle body (core layer) composed of a mixed resin with the coating layer, for example, a method can be employed in which the resin particle body (core layer) composed of a mixed resin and the material for forming the coating layer are placed in a mixing device having mixing and heating functions, and then heated and mixed. The coating layer may cover only a part of the resin particle body (core layer), or it may 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. Preferably, the resin particle body (core layer) is in a foamed state, but the coating layer may be in a foamed state or in a non-foamed state without a cellular structure. From the viewpoint of improving the strength of the resulting molded article, it is preferable that the coating layer be in a non-foamed state.

[0041] When the resin particles and foamed particles obtained by the manufacturing method of the present invention are multilayer resin particles and foamed particles having a coating layer on their surface, the above-mentioned effects can be obtained by using the above-mentioned mixed raw material consisting of virgin raw material and recycled raw material as the raw material for the resin particle body (core layer) coated with the coating layer, and by satisfying the above formulas (1) to (3). Furthermore, the polyolefin resin constituting the coating layer can have the same configuration as the coating layer in conventionally known multilayer foamed particles.

[0042] 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. Due to their excellent adhesion to the foamed core layer, the polyolefin resin constituting the coating layer preferably includes one or more selected from the group consisting of polyethylene resins and polypropylene resins, and more preferably includes a polypropylene resin. Examples of polypropylene resins include propylene-ethylene copolymers, ethylene-butene copolymers, propylene-ethylene-butene copolymers, and propylene homopolymers, and among these, it is preferable to include one or more selected from the group consisting of propylene-ethylene copolymers and propylene-ethylene-butene copolymers.

[0043] The resin constituting the coating layer may contain other polymers besides the polyolefin resins described above, as long as they do not hinder the desired effects of the present invention. Examples of other polymers include the thermoplastic resins and thermoplastic elastomers described above, which may be included in the virgin raw material. Furthermore, the resin constituting the coating layer may contain additives exemplified as additives that can be added to the virgin raw material.

[0044] (Melting point) When the resin constituting the coating layer is a polypropylene resin, its melting point is preferably lower than that of the mixed resin constituting the resin particle body (core layer) from the viewpoint of improving the fusion properties between the foam particles. Specifically, 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, from the viewpoint of improving the moldability of the foam particle molded article at lower molding pressures, and preferably 150°C or lower, preferably 145°C or lower, more preferably 140°C or lower, and even more preferably 138°C or lower, from the viewpoint of improving the fusion properties between the foam particles. The melting point of the polypropylene resin constituting the coating layer is measured in the same manner as the measurement of the melting point MP1.

[0045] (crystallization temperature) When the resin constituting the coating layer is a polypropylene resin, 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, from the viewpoint of easily obtaining foamed particles with excellent moldability. The crystallization temperature is measured for the polypropylene resin constituting the coating layer in the same manner as the measurement of the crystallization temperature CP1.

[0046] (Heat of fusion) When the resin constituting the coating layer is a polypropylene resin, its heat of fusion 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 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 fusion of the polypropylene resin constituting the coating layer is measured in the same manner as the heat of fusion of the virgin raw material.

[0047] (Meltflow rate) When the resin constituting the coating layer is a polypropylene-based resin, 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, 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, from the viewpoint of easily obtaining foamed particles with excellent moldability. The melt flow rate is measured for the polypropylene-based resin constituting the coating layer in the same manner as the measurement of the melt flow rate MFR1.

[0048] (Mass ratio of resin particle body (core layer) to coating layer) The mass ratio of the resin particle body (core layer):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, from the viewpoint of achieving both improved fusion properties between foamed particles and reduced environmental impact.

[0049] The external shape of the resin particles is not particularly limited as long as it can achieve the intended purpose of the present invention, but is preferably cylindrical. When the external shape of the resin particles is cylindrical, the particle diameter (length in the extrusion direction) of the resin particles is preferably 0.2 to 4 mm, and more preferably 0.5 to 3 mm. Furthermore, the ratio (length / diameter ratio) of the length of the resin particles in the extrusion direction to the length in the direction perpendicular to the extrusion direction (diameter of the resin particles) is preferably 0.5 to 5.0, and more preferably 1.0 to 3.0. The average mass of the resin particles is preferably adjusted to 0.1 to 20 mg, more preferably 0.2 to 10 mg, even more preferably 0.3 to 5 mg, and even more preferably 0.4 to 2 mg.

[0050] <Foaming of polypropylene resin particles> By impregnating the resin particles obtained as described above with a foaming agent, and foaming the polypropylene resin particles impregnated with the foaming agent, foamed polypropylene resin particles can be obtained. Specifically, for example, by placing a dispersion medium and polypropylene resin particles in a sealed container that can withstand heating and pressurization, such as an autoclave, and dispersing the polypropylene resin particles in the dispersion medium using a stirrer, and simultaneously adding a foaming agent to the sealed container and maintaining it under a predetermined temperature and pressure atmosphere, the foaming agent can be impregnated into the polypropylene resin particles. The dispersion medium is not particularly limited as long as it does not dissolve the polypropylene resin particles. For example, water, ethylene glycol, glycerin, methanol, ethanol, and other alcohols can be used, with water being preferred.

[0051] To more stably prevent adhesion between polypropylene resin particles, it is preferable to add a dispersant to the dispersion medium. Examples of dispersants include organic dispersants such as polyvinyl alcohol, polyvinylpyrrolidone, and methylcellulose; and sparingly soluble inorganic salts such as aluminum oxide, zinc oxide, kaolin, mica, magnesium phosphate, and tricalcium phosphate. These can be used individually or in combination of two or more. Among these, sparingly soluble inorganic salts are preferred as dispersants due to their ease of handling, and kaolin is more preferred. When adding a dispersant, it is preferable to add about 0.001 to 5 parts by mass of the dispersant per 100 parts by mass of polypropylene resin particles. When using a dispersant, it is preferable to add an inorganic salt such as aluminum sulfate as a dispersion aid. When adding a dispersion aid, it is preferable to add about 0.001 to 1 part by mass of the dispersion aid per 100 parts by mass of polypropylene resin particles.

[0052] Surfactants may be further added to the dispersion medium. Examples of surfactants include sodium alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate, sodium alkylsulfonates, 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 adding surfactants, it is preferable to add about 0.001 to 1 part by mass of the surfactant per 100 parts by mass of polypropylene resin particles.

[0053] The blowing agent is not particularly limited as long as it can foam polypropylene resin particles. Examples of blowing agents include inorganic physical blowing 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 ethyl chloride, 2,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene, and trans-1-chloro-3,3,3-trifluoropropene; and organic physical blowing agents such as dialkyl ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether. Among these, the blowing agent is preferably an inorganic physical blowing agent, 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 individually or in combination of two or more types.

[0054] The amount of foaming agent to be added is determined by considering the bulk density of the desired polypropylene resin foam particles, the type of polypropylene resin, the type of foaming agent, etc. For example, when using an inorganic physical foaming agent, the amount to be added is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 15 parts by mass, per 100 parts by mass of polypropylene resin particles.

[0055] The heating temperature when impregnating with the foaming agent is preferably 100°C to 180°C, and more preferably 130°C to 175°C. The holding time at this heating temperature is preferably 1 to 100 minutes, and more preferably 10 to 60 minutes.

[0056] Then, by releasing polypropylene resin particles impregnated with a foaming agent, along with a dispersion medium, from a sealed container into an atmosphere with a pressure lower than the pressure inside the sealed container, the polypropylene resin particles can be foamed to obtain foamed polypropylene resin particles. When polypropylene resin particles are released from a sealed container into an atmosphere with a pressure lower than the pressure inside the container to induce foaming, the foaming temperature is usually preferably 110°C to 170°C. The pressure inside the sealed container is preferably 0.5 MPa(G) to 5 MPa(G). The pressure indicated by (G) is the gauge pressure, i.e., the pressure value relative to atmospheric pressure.

[0057] By applying pressure with air or the like to the polypropylene resin foam particles obtained as described above to increase the internal pressure within the bubbles of the foam particles, and then heating the foam particles with steam or the like to further expand them (two-stage foaming), it is possible to obtain foam particles with an even higher expansion ratio (lower bulk density).

[0058] [Polypropylene resin foam particles] <Bulk density> From the viewpoint of increasing the strength of the molded article, the bulk density of the polypropylene resin foam particles is preferably 10 kg / m³. 3 The above is a more comfortable 15 kg / m 3 More preferably 20 kg / m 3 Therefore, from the viewpoint of improving the lightweight properties of the foamed particle molded body, a preferred weight is 200 kg / m³. 3 Below, a comfortable rate of 100 kg / m 3 More preferably 60 kg / m 3 More preferably, 50 kg / m 3 The following applies: The bulk density of foam particles can be determined as follows: First, a group of foam particles with mass W1 [g] is filled into a graduated cylinder, and the filling height of the foam particles in the graduated cylinder is stabilized by lightly tapping the floor several times with the bottom of the graduated cylinder. Next, the volume V1 [L] of the foam particles indicated by the scale on the graduated cylinder is read. The bulk density is obtained by dividing the mass W1 of the foam particles by the volume V1 (W1 / V1) and converting the unit to [kg / m³]. 3 The bulk density of the foamed particles can be determined by converting it to [ ].

[0059] <High temperature peak> It is preferable that polypropylene resin foam particles have a crystalline structure in which, when the foam particles are heated from 23°C to 200°C at a heating rate of 10°C / min, the DSC curve obtained shows a melting peak due to the melting of crystals unique to the polypropylene resin (i.e., a resin-specific peak) and one or more melting peaks on the higher temperature side (i.e., high-temperature peaks). The DSC curve is obtained by performing differential scanning calorimetry (DSC) in accordance with JIS K 7122:2012 using 1 to 3 mg of foam particles as a test sample. The resin-specific peak is a melting peak due to the melting of crystals unique to the polypropylene resin constituting the foam particles, and is considered to be an endothermic peak that appears due to the endothermic reaction during the melting of crystals that polypropylene resins normally possess. On the other hand, the melting peak on the higher temperature side of the resin-specific peak (i.e., high-temperature peak) is a melting peak that appears on the DSC curve at a higher temperature than the resin-specific peak. When this high-temperature peak appears, it is presumed that secondary crystals are present in the resin. Furthermore, when foamed particles are heated from 23°C to 200°C at a heating rate of 10°C / min (i.e., the first heating), then 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), it is preferable that only the melting peak due to the melting of crystals specific to the polypropylene resin constituting the foamed particles appears in the resulting DSC curve. In this way, the resin-specific peak and the high-temperature peak can be distinguished. The high-temperature peak can be controlled, for example, by controlling the rate at which the temperature inside the sealed container rises or by maintaining the temperature inside the sealed container at a predetermined temperature for a predetermined time, after the resin particles have been dispersed in the dispersion medium and / or when the resin particles have been impregnated with a foaming agent. Specifically, for example, a first-stage holding process is performed in which the temperature inside the sealed container is maintained at a temperature of (melting point of the resin particles - 20°C) or higher but below (melting end temperature of the resin particles) for about 10 to 60 minutes. After that, a second-stage holding process may be performed in which the temperature inside the sealed container is adjusted to a temperature between (melting point of the resin particles - 15°C) and below (melting end temperature of polypropylene resin), and maintained for another 10 to 60 minutes.

[0060] <Heat of fusion at high temperature peak> The heat of fusion of the high-temperature peak of polypropylene resin foam particles is preferably 8 to 50 J / g, more preferably 10 to 40 J / g, and even more preferably 12 to 30 J / g, from the viewpoint of improving the moldability of the foam particles and obtaining a molded article with an excellent balance of cushioning and rigidity. Figure 1 shows an example of a DSC curve (DSC curve during the first heating) when polypropylene resin foam particles are heated from 23°C to 200°C at a heating rate of 10°C / min, in which a resin-specific peak P1 and a high-temperature peak P2 appear on the higher side of the resin-specific peak. When a high-temperature peak P2 appears as shown in Figure 1, the heat of fusion can be determined as follows. First, let α be the point on the DSC curve at a temperature of 80°C, and let β be the point on the DSC curve corresponding to the melting end temperature T, and draw a straight line L1 connecting them. Next, draw a straight line L2 parallel to the vertical axis of the graph from point γ on the DSC curve, which is in the valley between the resin-specific peak and the high-temperature peak, and let δ be the point where it intersects with the straight line L1. The area (2) enclosed by the curve of the high-temperature peak portion of the DSC curve, the line segment (δ-β), and the line segment L2 is taken as the area of ​​the high-temperature peak, and the heat of fusion of the high-temperature peak can be determined from this area.

[0061] [Polypropylene-based resin foam particle molded product] A molded polypropylene resin foam particle body can be obtained by in-mold molding the polypropylene resin foam particles obtained by the manufacturing method of the present invention.

[0062] In-mold molding can be performed by filling a mold with foamed particles and then heating and molding them using a heating medium such as steam. Specifically, after filling the mold with foamed particles, a heating medium such as steam is introduced into the mold to heat and foam the foamed particles, and the foamed particles are fused together to obtain a foamed particle molded body in which the shape of the molded space is formed. Alternatively, in-mold molding in the present invention can be performed by a pressurized molding method (for example, Japanese Patent Publication No. 51-22951) in which the foamed particles are pre-pressurized with a pressurized gas such as air to increase the pressure inside the bubbles of the foamed particles, the pressure inside the foamed particles is adjusted to a pressure 0.01 to 0.3 MPa higher than atmospheric pressure, the foamed particles are filled into a mold under atmospheric pressure or reduced pressure, and then a heating medium such as steam is supplied into the mold to heat and fuse the foamed particles. Furthermore, molding can also be performed by a compression filling molding method (Japanese Patent Publication No. 4-46217), in which foam particles pressurized to a pressure exceeding atmospheric pressure are filled into a mold pressurized to a pressure exceeding atmospheric pressure using compressed gas, and then a heating medium such as steam is supplied into the cavity to heat and fuse the foam particles. In addition, molding can also be performed by an atmospheric pressure filling molding method (Japanese Patent Publication No. 6-49795), in which foam particles with high secondary foaming strength obtained under special conditions are filled into the cavity of a mold under atmospheric pressure or reduced pressure, and then a heating medium such as steam is supplied to heat and fuse the foam particles, or by a method combining the above methods (Japanese Patent Publication No. 6-22919).

[0063] In particular, according to the present invention, even when the minimum molding pressure (steam pressure) is low, for example, in the range of 0.3 MPa (G) or less, a good molded article with excellent fusion properties, surface properties, and dimensional stability can be obtained. Excellent fusion properties generally mean that a molded article with a fusion rate of 70% or more, preferably 80% or more, can be obtained, and excellent surface properties mean that the surface of the molded article is smooth with no noticeable gaps or voids. Furthermore, in the present invention, a foamed particle molded article with the above characteristics and excellent dimensional stability can be obtained. From the viewpoint of low-pressure moldability, the minimum molding steam pressure is preferably 0.28 (G) or less.

[0064] <Density> The density of the polypropylene-based resin foam particle molded body is preferably 10 kg / m 3 or more, more preferably 15 kg / m 3 or more, still more preferably 20 kg / m 3 or more, and preferably 200 kg / m 3 or less, more preferably 100 kg / m 3 or less, still more preferably 80 kg / m 3 or less, even more preferably 60 kg / m 3 or less. The density of the polypropylene-based resin foam particle molded body is calculated by dividing the mass of the foam particle molded body by the volume obtained from the outer dimensions of the molded body and performing unit conversion.

Examples

[0065] Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited thereto.

[0066] Regarding the resin raw materials, resin particles, foam particles, and foam particle molded bodies of the examples and comparative examples, the following measurements and evaluations were performed. In addition, for the physical property measurement of the resin particles, when the resin particles have a coating layer, resin particles were obtained under the same conditions as the corresponding examples and comparative examples except that only the extruder for forming the resin particle body described later was used and no coating layer was formed on the surface, and the following measurements were performed using the resin particles without the coating layer. Also, the physical property measurement of the foam particles was performed using foam particles that were conditioned by standing for 24 hours under the conditions of 50% RH, 23 °C, and 1 atm. Furthermore, the physical property measurement and evaluation of the foam particle molded body were performed using a molded body that was conditioned by standing for 12 hours under the conditions of 50% RH, 80 °C, and 1 atm after the foam particle molded body was脱模.

[0067] [Measurement method] <Resin raw materials (virgin raw materials and recycled raw materials) and resin particles> (Melting point) The melting points of the resin raw materials and resin particles were measured by differential scanning calorimetry (DSC) in accordance with JIS K 7121:2012. A high-sensitivity differential scanning calorimetry instrument, "EXSTAR DSC7020" (manufactured by Hitachi High-Tech Science Co., Ltd.), was used. For conditioning the test specimens, "(2) When measuring the melting temperature after performing a certain heat treatment" was adopted. Approximately 2 mg of polypropylene resin was taken as a test specimen, and the specimen was heated from 23°C to 200°C at a heating rate of 10°C / min under conditions of a nitrogen inflow of 30 mL / min. Then, it was maintained at that temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and then heated again to 200°C at a heating rate of 10°C / min to obtain a DSC curve (DSC curve after the second heating). The peak temperature of the melting peak in the DSC curve was determined, and this value was defined as the melting point. If multiple melting peaks appear in the DSC curve, the peak temperature of the melting peak with the largest area is adopted as the melting point. In this case, the melting peak with the largest area can be determined by distinguishing each melting peak at the temperature of the trough in the DSC curve located between the peak temperatures of each melting peak and comparing the area (heat of fusion) of each melting peak. The temperature of the trough in the DSC curve corresponds to the temperature at which the value on the vertical axis of the differential curve of the DSC curve (DDSC) becomes 0, so it can also be determined from the differential curve of the DSC.

[0068] (Meltflow rate) The melt flow rates of the resin raw materials and resin particles were measured in accordance with JIS K 7210-1:2014 under conditions of 230°C and 2.16 kg load.

[0069] (crystallization temperature) The crystallization temperatures of the resin raw materials and resin particles were measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121:2012. If multiple crystallization peaks appeared in the DSC curve, the peak temperature of the crystallization peak with the largest area was used as the crystallization temperature.

[0070] (Heat of fusion) The heat of fusion of the resin raw materials and resin particles was determined as follows, based on JIS K 7122:2012, using differential scanning calorimetry. A high-sensitivity differential scanning calorimeter "EXSTAR DSC7020" (manufactured by Hitachi High-Tech Science Co., Ltd.) was used as the measuring device. For conditioning the test specimen, "(2) When measuring the melting temperature after performing a certain heat treatment" was adopted. Approximately 2 mg of polypropylene resin was taken as a test specimen, and the specimen was heated from 23°C to 200°C at a heating rate of 10°C / min under conditions of a nitrogen inflow of 30 mL / min. Then it was maintained at that temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and heated again to 200°C at a heating rate of 10°C / min to obtain the DSC curve (DSC curve after the second heating). The point on the DSC curve obtained during the second heating, at a temperature of 80°C, was designated as α, and the point on the DSC curve corresponding to the melting end temperature was designated as β. The area of ​​the region enclosed by the DSC curve between points α and β and the line segment (α-β) was measured, and the heat of fusion of the polypropylene resin was calculated from this area.

[0071] (Flexural modulus) The flexural modulus of the resin material was measured in accordance with JIS K 7171:2016. First, a 4 mm thick sheet was prepared by heat-pressing polypropylene resin at 230°C, and a standard test specimen measuring 80 mm in length, 10 mm in width, and 4 mm in thickness was cut from this sheet. Using this test specimen, a bending test was performed with the indenter radius R1 and the support base radius R2 each set to 5 mm, the distance between supports being 64 mm, and the test speed being 2 mm / min. The flexural modulus of the polypropylene resin was measured from the results of the bending test.

[0072] (ash content) The ash content of the recycled material was measured in accordance with JIS K 6226-2:2003. The measuring instrument used was a thermogravimetric analyzer TGA701 manufactured by LECO Japan Co., Ltd. Specifically, approximately 5g of the recycled material sample was taken, its mass was measured, and it was placed in a crucible. The furnace was heated under a nitrogen atmosphere with a nitrogen flow, and the furnace temperature was increased from room temperature to 105°C at a rate of 10°C / min. The temperature was then held at 105°C until the measured mass was in equilibrium. The temperature was then increased from 105°C to 550°C at a rate of 10°C / min, and the temperature was held at 550°C until the measured mass was in equilibrium. The furnace airflow was 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 sample was cooled to room temperature. The ash content (mass ppm) of the recycled material was calculated by dividing the mass M1 of the combustion residue by the mass of the sample placed in the crucible, multiplying the result by 100, and then multiplying the result by 10000. This operation was performed twice, and the arithmetic mean of these results was taken as the ash content of the recycled material.

[0073] (Carbon black content) The carbon black content in the recycled material was measured according to JIS K 6226-2:2003. The measuring instrument used was a Seiko Instruments TG / DTA6200 differential thermogravimetric analyzer. Specifically, approximately 10 mg of the recycled material sample was taken, its mass was measured, and it was placed in a platinum pan. The furnace was heated under a nitrogen atmosphere with a nitrogen flow, and 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. After that, the measurement 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 at 500°C was defined as M1, and the mass of the equilibrium portion at temperatures above 700°C was defined as M2. The carbon black content in the recycled material was determined by subtracting the mass M2 from the mass M1 to obtain mass M3, dividing the result by the mass of the sample, and multiplying the result by 100. The above procedure was performed twice, and the arithmetic mean of these results was used as the carbon black content in the recycled material.

[0074] <Foaming particles> (Heat of fusion at high temperature peak) The heat of fusion of the high-temperature peak of the foamed particles was determined by differential scanning calorimetry in accordance with JIS K 7122:2012, as follows. Specifically, approximately 2 mg of foamed particles were taken as test specimens and heated from 23°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter "EXSTAR DSC7020" (manufactured by Hitachi High-Tech Science Corporation) to obtain a DSC curve (DSC curve for the first heating) with two or more melting peaks. The above measurement was performed under conditions of a nitrogen inflow of 30 mL / min. Regarding the obtained DSC curve, the intrinsic peak of the polypropylene resin constituting the foamed particles was defined as P1, and the high-temperature peak appearing at a higher temperature was defined as P2. A straight line (α-β) was drawn connecting point α on the DSC curve corresponding to 80°C and point β on the DSC curve corresponding to the melting termination temperature T of the test specimen. The melting termination temperature is the high-temperature endpoint of the high-temperature peak P2, and is the intersection point of the high-temperature peak and the high-temperature baseline. Next, a straight line parallel to the vertical axis of the graph was drawn from point γ on the DSC curve, which is in the valley between the intrinsic peak P1 and the high-temperature peak P2, and the point where this line intersects the curve was denoted as δ. The area of ​​the region enclosed by the curve of the high-temperature peak P2 portion of the DSC curve, the line segment (δ-β), and the line segment (γ-δ) was determined, and the heat of fusion for each high-temperature peak was calculated from this area. The heat of fusion for the above high-temperature peaks was measured for three different test specimens, and the arithmetic mean of the obtained values ​​was taken as the heat of fusion for the high-temperature peak of the foamed particle.

[0075] (Bulk density) The bulk density of the foamed particles was determined as follows: First, a group of foamed particles with mass W1 [g] was filled into a graduated cylinder, and the filling height of the foamed particles inside the cylinder was stabilized by lightly tapping the floor several times with the bottom of the graduated cylinder. Next, the volume V1 [L] of the foamed particles indicated by the scale on the graduated cylinder was read. The mass W1 [g] of the foamed particles was divided by the volume V1 [L] to obtain (W1 / V1), and the unit was changed to [kg / m³]. 3 The bulk density of the foamed particles was determined by converting it to [a specific value].

[0076] <Foam particle molded product> (Molded body density) The density of the foam particle molded body was determined by calculating the density of three test specimens by dividing the mass of the foam particle molded body by the volume calculated based on the dimensions of the molded body, and then calculating the arithmetic mean of these densities. The density was measured using a foam particle molded body obtained by in-mold molding at the lowest molding pressure within the moldable range described later.

[0077] [Evaluation Method] <Toolbox-shaped foam particle molded body> (Minimum molding pressure for obtaining a good molded product) In the <Preparation of Toolbox-Shaped Foamed Particle Molding> described later, foamed particle molding was produced by increasing the molding pressure (steam pressure) in increments of 0.02 MPa (G) within the range of 0.20 to 0.40 MPa (G), and the minimum molding pressure at which a foamed particle molding was obtained in which both the appearance and dimensional stability evaluations described below were "A" was determined.

[0078] (exterior) In the process of producing a toolbox-shaped foamed particle molded body, described later, after removing the molded body from the mold, curing or conditioning was performed using the following method. ≪No curing≫ After removing the molded body from the mold, the condition of the molded body was adjusted by letting it stand for 24 hours under conditions of 23°C, 50% RH, and 1 atm. <3 hours of rest / recuperation> After removing the molded body from the mold, it was cured by standing in an oven at 80°C for 3 hours. Subsequently, the molded body was conditioned by standing at 23°C, 50% RH, and 1 atm for 24 hours. ≪24-hour recovery period≫ After removing the molded body from the mold, it was cured by standing in an oven at 80°C for 24 hours. Subsequently, the molded body was conditioned by standing at 23°C, 50% RH, and 1 atm for 24 hours. The molded articles that had been cured or conditioned using the methods described above were evaluated according to the following criteria. A: The gaps between foam particles on the surface of the molded product are small, and the unevenness is not noticeable. B: On the surface of the molded product, irregularities caused by gaps between foam particles are noticeable.

[0079] (Dimensional stability) Similar to the (appearance) described above, in the <fabrication of a toolbox-shaped foam particle molded body> described later, after removing the molded body from a mold capable of forming a toolbox-shaped molded body having multiple uneven partition sections measuring 80 cm in length, 90 cm in width, and 15 cm in height, the molded body was cured or conditioned and evaluated according to the following criteria. A: The toolbox-shaped molded body shows no significant dimensional changes, and there is almost no inward tilting phenomenon in the inner wall portion. B: The toolbox-shaped molded body exhibits slight dimensional changes, but these changes are within 5%. C: The dimensional change of the toolbox-shaped molded body is significant (over 5%), and in particular, inward tilting is observed in the inner wall portion, and this inward tilting does not recover.

[0080] [Raw materials] Tables 1 and 2 show the resins used in the examples and comparative examples. 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). Recycled materials 1 to 7 are also ethylene-propylene copolymers.

[0081] [Table 1]

[0082] [Table 2]

[0083] Examples 1-4, Comparative Examples 2-6 <Preparation of resin particles> A manufacturing apparatus was prepared comprising an extruder for forming the resin particle body (core layer) with an inner diameter of 50 mm, a die for forming multilayer strands attached downstream of the resin particle body (core layer) extruder, and an extruder for forming the coating layer (coating layer) with an inner diameter of 30 mm. The manufacturing apparatus is connected to the multilayer strand forming die downstream of the coating layer (coating layer) extruder. Furthermore, the manufacturing apparatus was designed to allow for the lamination of molten resin for forming each layer within the die, as well as co-extrusion. For forming the resin particle body (core layer), virgin raw materials and recycled raw materials shown in Table 3 or Table 4 were used as polypropylene resins in the proportions shown in Table 3 or Table 4. In addition to these materials, carbon black (furnace black) as a coloring agent and zinc borate (product name "Firebrake ZB" from Borax) as a foam regulator were supplied to the extruder for forming the resin particle body (core layer) in the proportions shown in Table 3, and melt-kneaded to obtain a mixed resin molten compound. For forming the coating layer (coating layer), the polypropylene resins shown in Table 3 were supplied to the extruder for forming the coating layer (coating layer) and melt-kneaded to obtain a resin molten compound for forming the coating layer (coating layer). The mixed resin molten compound and the resin molten compound for forming the coating layer were introduced into a die for forming multilayer strands and merged within the die to extrude multilayer strands having a two-layer structure consisting of a resin particle body (core layer) and a coating layer, with the mass ratio of the coating layer being the value shown in Table 3 or Table 4. The extruded strands were water-cooled and cut with a pelletizer to obtain cylindrical multilayer resin particles with an average mass of 1.0 mg per particle and a length / diameter ratio of 2.0.

[0084] <Preparation of foaming particles> 100 kg of the obtained resin particles were supplied to a 400 L sealed container along with 230 L of water as a dispersion medium. Additionally, 0.3 parts by mass of kaolin as an inorganic dispersant, 0.004 parts by mass of surfactant (sodium alkylbenzene sulfonate) (as an active ingredient), and 0.01 parts by mass of aluminum sulfate were added to the sealed container per 100 parts by mass of the resin particles. Next, carbon dioxide was injected into the sealed container as a foaming agent, and the pressure was increased to 1 MPa lower than the gauge pressure shown in Table 3 or Table 4. Then, while stirring the contents of the sealed container, the contents were heated at a heating rate of 2°C / min until the temperature shown in Table 3 or Table 4 was reached. Carbon dioxide was then injected again, and the pressure was increased to the gauge pressure shown in Table 3 or Table 4, after which the temperature was maintained for 15 minutes. This adjusted the endothermic curve obtained by DSC measurement of the resulting foamed particles to show a high-temperature peak. Finally, the contents of the sealed container (resin particles and water) were released to atmospheric pressure to obtain single-stage foamed particles with the bulk density shown in Table 3 or Table 4. Furthermore, the obtained single-stage foamed particles were left to cure for 24 hours in an environment with a temperature of 23°C, relative humidity of 50%, and 1 atm. The cured single-stage foamed particles were then placed in a pressurized sealed container, and the pressure inside the sealed container was increased from atmospheric pressure to pressurize the foamed particles. The pressurized state of the foamed particles was maintained for a predetermined time to impregnate the bubbles of the foamed particles with air. After that, the single-stage foamed particles were removed from the sealed container, and single-stage foamed particles with an internal pressure of 0.5 MPa(G) in the bubbles were obtained. These single-stage foamed particles were then supplied to a two-stage foaming apparatus. Steam was supplied into the apparatus to foam the single-stage foamed particles, thereby obtaining two-stage foamed particles. The measurement results for the obtained foamed particles are shown in Table 3 or Table 4. The mass ratio of the resin particle body (core layer) to the coating layer (coating layer) in the foamed particles was the same as the mass ratio of the resin particle body (core layer) to the coating layer (coating layer) in the resin particles.

[0085] <Fabrication of a toolbox-shaped foam particle molded body> As described above, the obtained foam particles were left to cure for 24 hours in an environment of 23°C, 50% relative humidity, and 1 atm. Then, they were placed in a pressurized sealed container and pressurized with compressed air to impregnate the foam particles with air, thereby applying the internal pressure (bubble pressure) shown in Table 3 or Table 4 to the foam particles. Next, the foam particles with applied internal pressure were filled into a mold (die) having a molding cavity capable of forming a toolbox-shaped foam particle molded body with multiple uneven shapes measuring 80 cm long × 90 cm wide × 15 cm high, with the cracking amount shown in Table 3 or Table 4, and heated using the following heating method. The heating method involved preheating (exhaust process) by supplying steam to the mold with drain valves provided on both sides of the mold open. Then, steam was supplied from one side of the mold for heating, and then steam was supplied from the other side for further heating. Subsequently, steam was supplied from both sides of the mold at a predetermined molding steam pressure for heating. After heating was complete, the pressure was released, and the foamed particle molded body was water-cooled until the surface pressure due to the foaming force 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. Furthermore, even when using the foamed particles obtained as described above, and producing a flat foamed particle molded body measuring 300 mm in length, 250 mm in width, and 60 mm in height in the same manner as described above, the molded body density in Examples 1 to 4 was 33 kg / m³. 3 The minimum molding pressure at which a good molded product could be obtained was 0.28 MPa(G), demonstrating that molding was possible at low molding pressures. Furthermore, the range of moldable molding pressures in which a foamed particle molded product that passed all evaluations of fusion properties, surface properties, and dimensional stability was obtained was 0.06 MPa(G), indicating excellent moldability.

[0086] Comparative Example 1 In the <Preparation of Resin Particles> described above, a manufacturing apparatus was prepared that included an extruder with an inner diameter of 50 mm and a strand-forming die attached downstream of the extruder. Virgin raw materials shown in Table 4 were used as the polypropylene resin for forming the resin particles, and carbon black (furnace black) as a coloring agent and zinc borate (product name "Firebrake ZB" from Borax, Inc.) as a foam regulator were supplied to the extruder in the proportions shown in Table 4. The mixture was melt-kneaded and extruded to obtain the resin particles. In addition, foam particles and molded foam particle articles were produced in the same manner as in Example 1. The measurement and evaluation results of the obtained foam particles and molded foam particle articles are shown in Table 4.

[0087] [Table 3]

[0088] [Table 4]

[0089] As can be seen from Tables 3 and 4, the toolbox-shaped molded body obtained by in-mold molding of foamed particles obtained by the manufacturing method of the present invention exhibited excellent dimensional stability even at low molding pressures. [Industrial applicability]

[0090] The foamed particles obtained by the manufacturing method of the present invention can be molded even at low molding pressure and contribute to reducing environmental impact. The foamed particle molded body obtained by in-mold molding of the foamed particles obtained by the manufacturing method of the present invention can be applied to a wide range of fields, such as food transport containers, electrical and electronic components, precision parts, vehicle components, building components such as housing insulation materials, and general merchandise, as shock absorbers, heat insulating materials, and various packaging materials.

Claims

1. A method for producing polypropylene resin foam particles by foaming polypropylene resin particles, The polypropylene resin particles consist of a mixed resin of a virgin raw material containing at least one propylene copolymer selected from ethylene-propylene copolymer, butene-propylene copolymer, and ethylene-butene-propylene copolymer as a base resin, and a recycled polypropylene resin raw material. The recycled material contains at least one propylene copolymer selected from ethylene-propylene copolymer, butene-propylene copolymer, and ethylene-butene-propylene copolymer as a base resin. The melting point MP1 of the virgin raw material is 130°C or higher and less than 150°C. The melting point MP2 (°C) of the recycled material and the melting point MP1 (°C) of the virgin material satisfy the relationship shown in equation (1) below. 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 relationship shown in equation (2) below. A method for producing polypropylene resin foam particles, wherein 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 relationship shown in equation (3) below. -10<MP2-MP1<10...(1) 0 ≤ MFR2 - MFR1 ≤ 10 ... (2) 2<CP2-CP1<12...(3)

2. A method for producing polypropylene resin foam particles according to claim 1, wherein the ash content of the recycled raw material is 500 ppm by mass or more and 2000 ppm by mass or less.

3. A method for producing polypropylene resin foam particles according to claim 1 or 2, wherein the crystallization temperature of the recycled raw material is 105°C or higher and 115°C or lower.

4. A method for producing polypropylene resin foam particles according to claim 1 or 2, 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.

5. A method for producing polypropylene resin foam particles according to claim 1 or 2, wherein the blending ratio of the virgin raw material and the recycled raw material is 10 to 90% by mass of the virgin raw material and 10 to 90% by mass of the recycled raw material (provided that the total of the virgin raw material and the recycled raw material is 100% by mass).

6. The method for producing polypropylene resin foam particles according to claim 1 or 2, wherein the recycled material is a recycled material derived from a molded polypropylene resin foam particle body.

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