Expanded beads of polypropylene-based resin, and expanded bead molded body

Abstract

The present invention pertains to expanded beads of a polypropylene-based resin. An expansion layer forming the expanded beads contains the polypropylene-based resin as a base resin and contains a cyclic phosphonate-based compound and an NOR-type hindered amine-based compound. The blended amount of the cyclic phosphonate-based compound in the expansion layer is not less than 5 parts by mass but less than 25 parts by mass with respect to 100 parts by mass of resins forming the expansion layer. The blended amount of the NOR-type hindered amine-based compound in the expansion layer is not less than 0.1 parts by mass but less than 5 parts by mass with respect to 100 parts by mass of resins forming the expansion layer. The expansion layer contains a phenol-based antioxidant. The blended amount of the phenol-based antioxidant in the expansion layer is not less than 0.01 parts by mass but less than 0.5 parts by mass with respect to 100 parts by mass of resins forming the expansion layer. The ratio of the blended amount of the phenol-based antioxidant with respect to the blended amount of the NOR-type hindered amine-based compound is 0.03-0.9. The present invention also pertains to an expanded bead molded body obtained through in-mold molding of the expanded beads.

Description

Polypropylene resin expanded beads and expanded bead molded products

[0001] The present invention relates to expanded polypropylene resin beads and expanded bead moldings.

[0002] Expanded bead moldings obtained by molding expanded polypropylene resin beads in a mold are lightweight and have excellent impact resistance and energy absorption properties, and have therefore been used for vehicle components such as automobile bumpers. In recent years, with the spread of electric vehicles, applications requiring high flame retardancy, such as protective materials for on-board batteries and electronic components, have been increasing. When high flame retardancy is required for expanded polypropylene resin beads, attempts have been made to impart flame retardancy to the molded product by adding a flame retardant to the expanded beads. For example, Patent Document 1 discloses expanded polypropylene beads containing specific amounts of a polypropylene resin, an organophosphorus compound, and a hindered amine, and an expanded molded product obtained by molding the expanded polypropylene beads, with the aim of obtaining an expanded molded product with excellent flame retardancy.

[0003] International Publication No. 2022 / 203035

[0004] In the technology of Patent Document 1, specific amounts of an organic phosphorus compound and a hindered amine are added to expanded polypropylene resin beads, but when expanded beads containing these specific amounts of compounds are molded in a mold, fusion between the expanded beads may be insufficient, and there is room for improvement in obtaining an expanded polypropylene resin bead molding that has high flame retardancy and excellent fusion properties. An object of the present invention is to provide expanded polypropylene resin beads that can be used to produce an expanded bead molding that has excellent flame retardancy and fusion properties, and an expanded polypropylene resin bead molding that has excellent flame retardancy and fusion properties.

[0005] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by blending a specific phosphonate compound, a specific hindered amine compound, and a specific antioxidant in specific amounts and specific ratios with expanded polypropylene resin beads and molded articles. One aspect of the present invention is as follows [1] to

[10] . [1] Expanded polypropylene resin beads, wherein a foamed layer constituting the expanded beads has a polypropylene resin as a base resin and contains a cyclic phosphonate compound and a NOR hindered amine compound, the amount of the cyclic phosphonate compound in the foamed layer being 5 parts by mass or more and less than 25 parts by mass per 100 parts by mass of the resin components constituting the foamed layer, the amount of the NOR hindered amine compound in the foamed layer being 0.1 parts by mass or more and less than 5 parts by mass per 100 parts by mass of the resin components constituting the foamed layer, the foamed layer containing a phenolic antioxidant, the amount of the phenolic antioxidant in the foamed layer being 0.01 parts by mass or more and less than 0.5 parts by mass per 100 parts by mass of the resin components constituting the foamed layer, and the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound being 0.03 to 0.9. [2] The expanded polypropylene resin beads according to the above [1], wherein the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound is 0.07 or more and 0.9 or less. [3] The expanded polypropylene resin beads according to the above [1], wherein the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound is 0.14 or more and 0.9 or less. [4] The expanded polypropylene resin beads according to any one of the above [1] to [3], wherein the amount of the NOR hindered amine compound in the foam layer is 0.1 parts by mass or more and 3.5 parts by mass or less per 100 parts by mass of the resin components constituting the foam layer. [5] The melting point Tm of the phenolic antioxidant A [6] The expanded polypropylene resin particles according to any one of [1] to [4], wherein the melting point Tm of the cyclic phosphonate compound is 200°C or more and less than 300°C. B is 200°C or more and less than 300°C, and the melting point Tm Aand the melting point Tm of the cyclic phosphonate compound B The melting point difference (Tm A -Tm B

[0023] The expanded polypropylene resin beads according to any one of [1] to [5] above, wherein the temperature (Tc) of the expanded polypropylene resin beads is -50°C or higher and 50°C or lower. [7] The expanded polypropylene resin beads according to any one of [1] to [6] above, wherein the cyclic phosphonate compound is pentaerythritol diphosphonate. [8] The expanded polypropylene resin beads according to any one of [1] to [7] above, wherein the foamed layer contains a sulfur-based antioxidant, and the amount of the sulfur-based antioxidant in the foamed layer is 0.01 parts by mass or higher and 0.5 parts by mass or lower per 100 parts by mass of the resin components constituting the foamed layer. [9] The expanded polypropylene resin beads according to [8] above, wherein the ratio of the amount of the NOR-type hindered amine compound to the amount of the sulfur-based antioxidant is 0.03 or higher and 0.9 or lower.

[10] An expanded bead molding obtained by molding the expanded polypropylene resin beads according to any one of [1] to [9] above in a mold.

[0006] According to the present invention, it is possible to provide expanded polypropylene resin beads from which expanded bead moldings excellent in flame retardancy and fusion properties can be produced, and expanded polypropylene resin bead moldings excellent in flame retardancy and fusion properties.

[0007] [Expanded Polypropylene Resin Beads] The expanded polypropylene resin beads of the present invention are polypropylene resin beads, wherein a foamed layer constituting the expanded beads has a polypropylene resin as a base resin and contains a cyclic phosphonate compound and a NOR hindered amine compound, the amount of the cyclic phosphonate compound in the foamed layer being 5 parts by mass or more and less than 25 parts by mass per 100 parts by mass of the resin components constituting the foamed layer, the amount of the NOR hindered amine compound in the foamed layer being 0.1 parts by mass or more and less than 5 parts by mass per 100 parts by mass of the resin components constituting the foamed layer, the foamed layer containing a phenolic antioxidant, the amount of the phenolic antioxidant in the foamed layer being 0.01 parts by mass or more and less than 0.5 parts by mass per 100 parts by mass of the foamed layer, and the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound being 0.03 to 0.9.

[0008] (Polypropylene Resin) The expanded polypropylene resin beads (hereinafter simply referred to as expanded beads) have a foam layer (hereinafter simply referred to as foam layer) made of a polypropylene resin as a base resin. When the expanded beads are not provided with a coating layer or the like, the entire expanded beads typically form the foam layer. When a coating layer made of an unexpanded resin is provided, the foam layer forms the core layer of the expanded beads. In this specification, the phrase "the foam layer has a polypropylene resin as a base resin" means that the content of the polypropylene resin in the resin components constituting the foam layer is 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 99% by mass or more. There is no particular upper limit, and it is 100% by mass or less. In the present invention, examples of the polypropylene resin include propylene homopolymers, propylene random copolymers, propylene block copolymers, and impact-resistant polypropylenes (block polypropylenes) composed of two or more phases including a continuous phase of a propylene polymer and a rubber phase such as an ethylene-α-olefin copolymer present as a dispersed phase in the continuous phase. These resins may be used alone or in combination of two or more.

[0009] The foam layer may contain other resins besides polypropylene-based resins as long as the objectives and effects of the present disclosure are not impaired. Examples of other resins include thermoplastic resins other than polypropylene-based resins, such as polyethylene-based resins and polystyrene-based resins, and elastomers. The content of other resin components in the resin components constituting the foam layer is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and even more preferably 0% by mass. In other words, it is particularly preferable that the foam layer substantially contains only polypropylene-based resins as resin components.

[0010] The content of the structural units derived from propylene in the polypropylene-based resin is preferably 80% by mass or more, more preferably 90% by mass or more, and is preferably 99% by mass or less, more preferably 98% by mass or less.

[0011] Examples of propylene-based random copolymers include copolymers of propylene and ethylene and / or an α-olefin having 4 to 20 carbon atoms. Examples of the α-olefin include 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-butene. The polypropylene-based resin preferably contains, as a main component, an ethylene-propylene random copolymer, a propylene-butene random copolymer, an ethylene-propylene-butene random copolymer, or a mixture of two or more of these. In this case, the proportion of these propylene-based random copolymers in the polypropylene-based resin is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. When the propylene-based random copolymer contains a component derived from ethylene (ethylene component) and / or a component derived from butene (butene component) as copolymerization components, from the viewpoint of further improving the in-mold moldability of the expanded beads under low molding pressure conditions, the total content of the ethylene component and the butene component in the propylene-based random copolymer is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more. Furthermore, from the viewpoint of stably obtaining expanded bead molded articles having good mechanical properties such as compressive strength, the total content of the ethylene component and the butene component in the propylene-based random copolymer is preferably 15% by mass or less. That is, the total content of the ethylene component and the butene component in the propylene-based random copolymer is preferably 1 to 15% by mass, more preferably 2 to 15% by mass, and even more preferably 3 to 15% by mass. The contents of the ethylene and α-olefin-derived components in the propylene-based random copolymer can be determined by IR spectroscopy.

[0012] The melting point of the polypropylene resin is preferably 130°C or higher, more preferably 135°C or higher, and even more preferably 140°C or higher, from the viewpoint of improving the mechanical properties of the resulting expanded bead molding. On the other hand, the melting point of the polypropylene resin is preferably 155°C or lower, more preferably 150°C or lower, and even more preferably 146°C or lower, from the viewpoint of improving the in-mold moldability of the expanded beads under conditions of low molding pressure. That is, the melting point of the polypropylene resin is preferably 130°C to 155°C, more preferably 135°C to 150°C, and even more preferably 140°C to 146°C. The melting point of the polypropylene resin is measured in accordance with JIS K 7121:2012 using the propylene resin or expanded beads as a test piece. Specifically, the test specimen was conditioned as described in "(2) Measuring the melting temperature after a certain heat treatment," in which the test specimen was heated from 23°C to 200°C at a heating rate of 10°C / min under conditions of a nitrogen inflow rate 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 at the second heating). Next, the apex temperature of the melting peak in the DSC curve was determined, and this value was taken as the melting point of the polypropylene-based resin. Note that when multiple melting peaks appear in the DSC curve, the apex temperature of the melting peak with the highest melting peak height relative to the baseline was used as the melting point.

[0013] The melt flow rate (MFR) of the polypropylene resin is preferably 2 g / 10 min or more, more preferably 5 g / 10 min or more, from the viewpoint of improving the expandability during expansion of the resin beads and the secondary expandability during in-mold molding of the expanded beads, and is preferably 15 g / 10 min or less, more preferably 10 g / 10 min or less, from the viewpoint of improving the uniformity of the cells in the expanded beads and the physical properties of the expanded bead molding. That is, the MFR of the polypropylene resin is preferably 2 to 15 g / 10 min, more preferably 5 to 10 g / 10 min. The MFR of the polypropylene resin is measured in accordance with JIS K 7210-1:2014 at a temperature of 230°C and a load of 2.16 kg.

[0014] The polydispersity (Mw / Mn) of the polypropylene resin is preferably 4.0 or more and 25 or less, and more preferably 4.1 or more and 15 or less.

[0015] The polydispersity (Mw / Mn) of a polypropylene resin is the value obtained by dividing the weight average molecular weight (Mw) by the number average molecular weight (Mn) measured by gel permeation chromatography (GPC) using polystyrene as the standard substance.

[0016] The polydispersity (Mw / Mn) of polypropylene resins is measured by gel permeation chromatography (GPC). First, a sample solution with a concentration of 2.2 mg / ml is prepared by dissolving the polypropylene resin in o-dichlorobenzene. A chromatogram is obtained using this sample solution under the following conditions: columns: two TSKgel® GMH6-HT and two TSKgel GMH6-HTL; eluent: o-chlorobenzene; flow rate: 1.0 ml / min; temperature: 140°C. Then, using polystyrene as a standard, the number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the polypropylene resin are calculated, and the polydispersity (Mw / Mn) is then determined. A high-temperature GPC system, HLC-8321GPC / HT, manufactured by Tosoh Corporation, can be used as the measurement device.

[0017] From the viewpoint of further improving the expandability during the production process of the expanded beads and the secondary expandability of the expanded beads during in-mold molding, it is more preferable that the MFR of the polypropylene-based resin contained in the base resin is 5 g / 10 min or more and 10 g / 10 min or less, and that the polydispersity (Mw / Mn) is 4.0 or more and 25 or less.

[0018] The expanded polypropylene resin beads of the present invention contain specific amounts of a cyclic phosphonate compound, a NOR hindered amine compound, and a phenolic antioxidant in the foam layer, and further, the ratio of the amount of the NOR hindered amine compound to the amount of the phenolic antioxidant is within a specific range. Therefore, by molding the expanded polypropylene resin beads of the present invention in a mold, an expanded bead molding having excellent flame retardancy and fusion-bonding properties can be obtained.

[0019] (Cyclic Phosphonate Compound) The cyclic phosphonate compound is a compound containing one or more cyclic phosphonate moieties in the molecule, and is preferably at least one selected from the group consisting of compounds represented by the following general formula (1), compounds represented by the following general formula (2), compounds represented by the following general formula (3), and compounds represented by the following general formula (4), and is more preferably pentaerythritol diphosphonate represented by the following general formula (1). The pentaerythritol diphosphonate of formula (1) is a spirocyclic compound containing two cyclic phosphonate moieties in the molecule. The cyclic phosphonate compounds may be used alone or in combination of two or more. (In the formula, R 1 and R 2 are each an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a benzyl group, a phenylethyl group, a phenyl group, or a naphthyl group, and R ３ is an alkyl group having 1 to 22 carbon atoms or an aryl group having 6 to 15 carbon atoms, and R ４ , R ８ , R ９ and R １２ are each an alkyl group having 1 to 4 carbon atoms, and R ５ , R ７ and R １１ are each a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ６ and R １０ are each an alkyl group having 1 to 22 carbon atoms, a cycloalkyl group having 9 to 22 carbon atoms, an aryl group having 9 to 22 carbon atoms, or an aralkyl group having 9 to 22 carbon atoms.

[0020] In formula (1), R １ and R ２ may be the same or different, and are preferably the same. １ R is an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a benzyl group, a phenylethyl group, a phenyl group, or a naphthyl group, preferably an alkyl group having 1 or 2 carbon atoms, and more preferably a methyl group. ２is an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a benzyl group, a phenylethyl group, a phenyl group, or a naphthyl group, preferably an alkyl group having 1 or 2 carbon atoms, and more preferably a methyl group. １ and R ２ are more preferably methyl groups.

[0021] In formula (2), R ３ is an alkyl group having 1 to 22 carbon atoms or an aryl group having 6 to 15 carbon atoms, and is preferably a phenyl group.

[0022] In formula (3), R ４ and R ８ may be the same or different, and are preferably the same. ４ is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. ８ is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. ５ and R ７ may be the same or different, and are preferably the same. ５ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably an ethyl group. ７ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably an ethyl group. ６ represents an alkyl group having 1 to 22 carbon atoms, a cycloalkyl group having 9 to 22 carbon atoms, an aryl group having 9 to 22 carbon atoms, or an aralkyl group having 9 to 22 carbon atoms, and is preferably a linear alkyl group having 1 to 12 carbon atoms.

[0023] In formula (4), R ９ and R １２ may be the same or different, and are preferably the same. ９ is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. １２ is an alkyl group having 1 to 4 carbon atoms, preferably a methyl group. １０R is an alkyl group having 1 to 22 carbon atoms, a cycloalkyl group having 9 to 22 carbon atoms, an aryl group having 9 to 22 carbon atoms, or an aralkyl group having 9 to 22 carbon atoms, and is preferably a linear alkyl group having 1 to 12 carbon atoms. １１ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably an ethyl group.

[0024] Melting point Tm of cyclic phosphonate compounds Ａ The melting point Tm of the cyclic phosphonate compound is preferably 80°C or higher and 350°C or lower, more preferably 150°C or higher and 330°C or lower, and even more preferably 200°C or higher and 300°C or lower. Ａ is measured based on JIS K 0064:1992.

[0025] The amount of the cyclic phosphonate compound in the foam layer of the expanded polypropylene resin beads of the present invention is 5 parts by mass or more and less than 25 parts by mass per 100 parts by mass of the resin components constituting the foam layer. If the amount of the cyclic phosphonate compound is too small, a foamed bead molding having high flame retardancy cannot be obtained. From the viewpoint of obtaining a foamed bead molding having higher flame retardancy, the amount of the cyclic phosphonate compound in the foam layer is preferably 6 parts by mass or more, more preferably 7 parts by mass or more, and even more preferably 8 parts by mass or more per 100 parts by mass of the resin components constituting the foam layer. On the other hand, if the amount is too large, a foamed bead molding having excellent fusion properties cannot be obtained. From the viewpoint of obtaining a foamed bead molding having excellent fusion properties, the amount of the cyclic phosphonate compound in the foam layer is preferably 22 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 17 parts by mass or less per 100 parts by mass of the resin components constituting the foam layer. That is, the amount of the cyclic phosphonate compound in the foam layer is preferably 6 parts by mass or more and 22 parts by mass or less, more preferably 7 parts by mass or more and 20 parts by mass or less, and even more preferably 8 parts by mass or more and 17 parts by mass or less, per 100 parts by mass of the resin component constituting the foam layer.

[0026] (NOR-Type Hindered Amine Compound) The NOR-type hindered amine compound has, in its structure, a 2,2,6,6-tetramethyl-4-piperidinamine moiety having a hydrocarbon group bonded to a nitrogen atom via an oxygen atom, as shown in the following formula (5), and thereby can improve the flame retardancy of a molded article. (In formula (I), R １３ represents a hydrocarbon group.)

[0027] In the general formula (5), R １３ represents a hydrocarbon group, and when a molecule of the hindered amine compound contains two or more hindered amine moieties represented by formula (5), a plurality of R １３ may be the same or different, but multiple R １３ are preferably the same. １３ is preferably at least one selected from the group consisting of an alkyl group and a cycloalkyl group, and more preferably a cycloalkyl group. １３ is an alkyl group, R １３ is more preferably an alkyl group having 1 to 20 carbon atoms, and even more preferably an undecyl group. １３ is a cycloalkyl group, R １３ is more preferably a cycloalkyl group having 4 to 10 carbon atoms, and even more preferably a cyclohexyl group. The NOR type hindered amine compounds may be used alone or in combination of two or more.

[0028] From the viewpoint of suppressing bleed-out from a molded article, the molecular weight of the NOR hindered amine compound is preferably 600 or more, more preferably 1500 or more. Furthermore, from the viewpoint of improving dispersion of the NOR hindered amine compound in a resin, the molecular weight of the NOR hindered amine compound is preferably 3000 or less, more preferably 2500 or less. In the NOR hindered amine compound, the number of 2,2,6,6-tetramethyl-4-piperidinamine moieties having a hydrocarbon group bonded to nitrogen via an oxygen bond, represented by general formula (5), is preferably 2 or more and 8 or less, more preferably 2 or more and 6 or less, and even more preferably 2 or 6.

[0029] The amount of the hindered amine compound in the foam layer of the expanded polypropylene resin beads of the present invention is 0.1 parts by mass or more and less than 5 parts by mass per 100 parts by mass of the resin components constituting the foam layer. If the amount of the hindered amine compound is too small, a foamed bead molding having high flame retardancy cannot be obtained. From the viewpoint of obtaining a foamed bead molding having higher flame retardancy, the amount of the hindered amine compound in the foam layer is preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.4 parts by mass or more per 100 parts by mass of the resin components constituting the foam layer. On the other hand, if the amount is too large, a foamed bead molding having excellent fusion properties cannot be obtained. From the viewpoint of obtaining a foamed bead molding having excellent fusion properties, the amount of the hindered amine compound in the foam layer is preferably 3.5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less per 100 parts by mass of the resin components constituting the foam layer. That is, the amount of the hindered amine compound in the foam layer is preferably 0.2 parts by mass or more and 3.5 parts by mass or less, more preferably 0.3 parts by mass or more and 3 parts by mass or less, even more preferably 0.4 parts by mass or more and 2 parts by mass or less, and still more preferably 0.4 parts by mass or more and 1 part by mass or less.

[0030] (Phenol-based antioxidant) The phenol-based antioxidant is an antioxidant having one or more phenol structures in the molecule, in which one or more hydroxyl groups are bonded to an aromatic ring, preferably two or more phenol structures in the molecule, more preferably three or more phenol structures in the molecule. At high temperatures (e.g., 180°C or higher) such as in a process of melt-kneading a resin, decomposition of the resin occurs in a relatively short time, and the phenol-based antioxidant is a compound that suppresses the decomposition of the resin at such high temperatures in a short time. Specific examples of the phenolic antioxidant include 1,3,5-trimethyl-2,4,6-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)benzene, 2,6-di-t-butyl-p-cresol, triethylene glycol bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 2,2-methylenebis(4-methyl-6-t-butylphenol), 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], etc. These may be used alone or in combination of two or more. Among these, from the viewpoint of further improving flame retardancy, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 1,3,5-trimethyl-2,4,6-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)benzene are preferred, and 1,3,5-trimethyl-2,4,6-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)benzene is particularly preferred.

[0031] The melting point Tm of the phenolic antioxidant Ｂ From the viewpoint of obtaining a foamed bead molding having higher flame retardancy, the melting point Tm of the phenolic antioxidant is preferably 50°C or higher and 350°C or lower, more preferably 80°C or higher and 330°C or lower, even more preferably 100°C or higher and 320°C or lower, still more preferably 150°C or higher and 310°C or lower, and even more preferably 200°C or higher and 300°C or lower. Ｂis measured based on JIS K 0064:1992.

[0032] The melting point Tm of the cyclic phosphonate compound Ａ and the melting point Tm of the phenolic antioxidant Ｂ The melting point difference (Tm Ａ -Tm Ｂ From the viewpoint of obtaining a foamed bead molding having higher flame retardancy, the melting point difference (Tm Ａ -Tm Ｂ ) is the melting point Tm of the cyclic phosphonate compound measured by the above-mentioned method. Ａ and the melting point Tm of the phenolic antioxidant Ｂ It can be found from

[0033] The amount of the phenolic antioxidant in the foam layer of the expanded polypropylene resin beads of the present invention is 0.01 parts by mass or more but less than 0.5 parts by mass per 100 parts by mass of the resin components constituting the foam layer. If the amount of the phenolic antioxidant is too small, an expanded bead molding having high flame retardancy and good fusion properties cannot be obtained. From the viewpoint of obtaining an expanded bead molding having higher flame retardancy, the amount of the phenolic antioxidant in the foam layer is preferably 0.02 parts by mass or more, more preferably 0.04 parts by mass or more, even more preferably 0.06 parts by mass or more, and even more preferably 0.08 parts by mass or more per 100 parts by mass of the resin components constituting the foam layer. If the amount is too large, an expanded bead molding having high flame retardancy and good fusion properties cannot be obtained. From the viewpoint of obtaining a foamed bead molding having better fusion properties, the blending amount of the phenolic compound in the foam layer is preferably 0.4 parts by mass or less, more preferably 0.3 parts by mass or less, even more preferably 0.2 parts by mass or less, and still more preferably 0.15 parts by mass or less, relative to 100 parts by mass of the resin component constituting the foam layer. That is, the blending amount of the phenolic antioxidant in the foam layer is preferably 0.02 parts by mass or more and 0.4 parts by mass or less, more preferably 0.04 parts by mass or more and 0.3 parts by mass or less, even more preferably 0.06 parts by mass or more and 0.2 parts by mass or less, and still more preferably 0.08 parts by mass or more and 0.15 parts by mass or less.

[0034] The ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound (phenolic antioxidant / NOR hindered amine compound) (compounding ratio) is 0.03 or more and 0.9 or less. If this blending ratio is too low, it is impossible to obtain an expanded bead molding that combines high flame retardancy and good fusion properties. From the viewpoint of obtaining expanded beads with higher flame retardancy and excellent fusion properties, the blending ratio is preferably 0.07 or more, more preferably 0.11 or more, and even more preferably 0.14 or more. On the other hand, if the blending ratio is too high, it is impossible to obtain an expanded bead molding with high flame retardancy. From the viewpoint of obtaining an expanded bead molding with higher flame retardancy, the blending ratio is preferably 0.8 or less, more preferably 0.7 or less, and even more preferably 0.6 or less. That is, the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound is preferably 0.07 or more and 0.8 or less, more preferably 0.11 or more and 0.7 or less, and even more preferably 0.14 or more and 0.6 or less. When the ratio of the amounts is within the above range, the expanded beads can be used to produce expanded bead molded articles with excellent flame retardancy and fusion properties. While the reason for this is unclear, it is thought to be as follows. As described above, the NOR hindered amine compound has a 2,2,6,6-tetramethyl-4-piperidinamine moiety having a hydrocarbon group bonded to a nitrogen atom via an oxygen atom, and therefore, when used in combination with a cyclic phosphonate compound, it is thought to impart high flame retardancy to expanded bead molded articles. However, if the expanded beads contain a large amount of the NOR hindered amine compound, the fusion properties of the molded articles will deteriorate. On the other hand, if the amount of the NOR hindered amine compound is too small, the expanded bead molded articles will not have high flame retardancy. In the present invention, by using a phenolic antioxidant in a specific amount and in a specific ratio in combination with a NOR hindered amine compound, high flame retardancy can be imparted to the expanded bead molding even when the blending amount of the NOR hindered amine compound is in a small range.As described above, by using a phenolic antioxidant in a specific amount and a specific ratio in combination with a NOR hindered amine, the phenolic antioxidant can contribute to improving flame retardancy without inhibiting the flame retardancy-improving effect of the NOR hindered amine compound. Therefore, it is believed that it is possible to impart high flame retardancy to an expanded bead molding even when the amount of NOR hindered amine compound is reduced. Furthermore, the phenolic antioxidant is unlikely to inhibit fusion between the expanded beads during in-mold molding, and it is possible to reduce the amount of NOR hindered amine compound added. Therefore, it is believed that it is possible to sufficiently fuse the expanded beads during in-mold molding. As a result, it is believed that by in-mold molding the expanded beads of the present invention, an expanded bead molding having high flame retardancy and excellent fusion properties can be obtained.

[0035] (Sulfur-Based Antioxidant) The foamed layer of the expanded polypropylene resin beads of the present invention preferably contains a sulfur-based antioxidant. Examples of the sulfur-based antioxidant include esters having a sulfide bond in the molecule. Specific examples of esters having a sulfide bond in the molecule include didodecyl-3,3'-thiodipropionate, ditridecyl-3,3'-thiodipropionate, ditetradecyl-3,3'-thiodipropionate, dioctadecyl-3,3'-thiodipropionate, pentaerythritol tetrakis(3-dodecylthiopropionate), pentaerythritol tetrakis(3-tridecylthiopropionate), pentaerythritol tetrakis(3-tetradecylthiopropionate), and pentaerythritol tetrakis(3-octadecylthiopropionate). These may be used alone or in combination of two or more.

[0036] The amount of the sulfur-based antioxidant in the foam layer of the expanded polypropylene resin beads of the present invention is preferably 0.02 parts by mass or more, more preferably 0.04 parts by mass or more, even more preferably 0.06 parts by mass or more, and even more preferably 0.08 parts by mass or more, relative to 100 parts by mass of the resin components constituting the foam layer, in order to provide an expanded bead molding with excellent mechanical properties such as compression properties even when placed in a high-temperature environment for a long period of time. Furthermore, the amount of the sulfur-based compound in the foam layer is preferably 0.4 parts by mass or less, more preferably 0.3 parts by mass or less, even more preferably 0.2 parts by mass or less, and even more preferably 0.15 parts by mass or less, relative to 100 parts by mass of the resin components constituting the foam layer, in order to provide an expanded bead molding with high flame retardancy.

[0037] The ratio of the amount of the sulfur-based antioxidant to the amount of the NOR hindered amine compound (sulfur-based antioxidant / NOR hindered amine compound) (compounding ratio) is preferably 0.03 or more, more preferably 0.07 or more, and even more preferably 0.14 or more, from the viewpoint of providing an expanded bead molding with excellent mechanical properties such as compression properties even when placed in a high-temperature environment for a long period of time. Furthermore, from the viewpoint of providing an expanded bead molding with high flame retardancy, the compounding ratio is preferably 0.9 or less, more preferably 0.8 or less, and even more preferably 0.7 or less. That is, the ratio of the amount of the sulfur-based antioxidant to the amount of the NOR hindered amine compound is preferably 0.03 or more and 0.9 or less, more preferably 0.07 or more and 0.8 or less, and even more preferably 0.14 or more and 0.7 or less.

[0038] (Characteristics and Composition of Expanded Polypropylene Resin Beads) As described above, the expanded polypropylene resin beads of the present invention contain specific amounts of a cyclic phosphonate compound, a NOR-type hindered amine compound, and a phenolic antioxidant, and preferably have the following characteristics.

[0039] The average cell diameter of the foamed layer of the expanded polypropylene resin beads of the present invention is preferably 50 μm or more and 250 μm or less. The average cell diameter of the foamed layer of the expanded polypropylene resin beads of the present invention is more preferably 60 μm or more, and even more preferably 65 μm or more. The average cell diameter of the foamed layer of the expanded polypropylene resin beads of the present invention is more preferably 200 μm or less, even more preferably 150 μm or less, and even more preferably 120 μm or less. That is, the average cell diameter of the foamed layer is more preferably 60 μm or more and 200 μm or less, even more preferably 65 μm or more and 150 μm or less, and even more preferably 65 μm or more and 120 μm or less. When the average cell diameter of the foamed layer is within the above range, the expanded beads have excellent in-mold moldability, and by in-mold molding of the expanded beads, an expanded bead molded article with excellent mechanical properties can be obtained. The average cell diameter is measured by drawing a line segment from the outer edge of a cell located on the outermost surface of an expanded bead through the center to the outer edge of a cell located on the outermost surface of the other expanded bead in an enlarged photograph of the cross section of the expanded bead divided into two, and dividing the number of cells intersecting the line segment by the length of the line segment. Specifically, it can be measured by the method described in the Examples. The average cell diameter of the foamed layer can be adjusted to the desired range by adjusting the type and amount of cell control agent added to the resin particles, the amount of cyclic phosphonate compound and hindered amine compound added, or the foaming pressure during foaming of the resin particles.

[0040] The bulk density of the expanded polypropylene resin beads of the present invention is preferably 10 g / L or more and 500 g / L or less. The bulk density of the expanded polypropylene resin beads of the present invention is more preferably 20 g / L or more, and even more preferably 30 g / L or more. The bulk density of the expanded polypropylene resin beads of the present invention is more preferably 100 g / L or less, even more preferably 70 g / L or less, and even more preferably 60 g / L or less. That is, the bulk density of the expanded polypropylene resin beads is more preferably 20 g / L or more and 100 g / L or less, even more preferably 30 g / L or more and 70 g / L or less, and even more preferably 30 g / L or more and 60 g / L or less. Having the bulk density of the expanded beads in the above range is preferable because it allows for the production of an expanded bead molding that is lightweight and has excellent fusion properties. The bulk density is measured by the method described in the examples.

[0041] The expanded polypropylene resin beads of the present invention preferably have one or more melting peaks (high-temperature peaks) on the high-temperature side of the resin-specific melting peak (resin-specific peak) of the polypropylene resin in a differential scanning calorimetry (DSC) curve measured in accordance with JIS K7122-2012. These melting peaks can be obtained by the following method. Specifically, a DSC curve is obtained by heating 1 to 3 mg of expanded beads from 23°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter, and the melting peaks (high-temperature peaks) can be confirmed from the DSC curve. The peak with the largest heat of fusion is the melting peak (resin-specific peak) specific to the polypropylene resin, and the melting peak appearing higher in temperature is the high-temperature peak. The DSC curve in this case refers to the DSC curve obtained by heating the expanded beads using the above-mentioned measurement method (DSC curve in the first heating). The resin-specific endothermic peak (resin-specific peak) refers to the endothermic peak due to the melting of crystals specific to the polypropylene resin constituting the expanded beads. The resin-specific peak is considered to be an endothermic peak that appears due to the endothermic heat caused by the melting of crystals typically found in the polypropylene-based resin constituting the expanded beads. On the other hand, the endothermic peak (high-temperature peak) on the higher temperature side of the resin-specific peak is an endothermic peak that appears higher in the first DSC curve than the resin-specific peak. When this high-temperature peak appears, it is presumed that secondary crystals exist in the resin. In the DSC curve (DSC curve in the second heating) obtained when the expanded beads are heated from 23°C to 200°C at a heating rate of 10°C / min (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 (second heating), only the endothermic peak due to the melting of crystals specific to the polypropylene-based resin constituting the expanded beads appears. This resin-specific peak appears in both the DSC curves obtained in the first and second heatings, and the peak apex temperatures may differ slightly between the first and second heatings, but the difference is usually less than 5° C. This makes it possible to identify which peak is the resin-specific peak.The expanded beads are preferably those in which only a melting peak (intrinsic peak) inherent to a polypropylene-based resin appears in a DSC curve obtained in a second heating cycle when the expanded beads are heated from 23°C to 200°C at a heating rate of 10°C / min, then cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated from 23°C to 200°C at a heating rate of 10°C / min.

[0042] The heat of fusion of the high-temperature peak of the expanded polypropylene resin beads of the present invention is preferably 5 to 40 J / g, more preferably 10 to 30 J / g, and even more preferably 15 to 25 J / g, because this broadens the range of molding conditions for obtaining a good expanded bead molded article when the expanded beads are molded in a mold. The heat of fusion of the high-temperature peak is measured by the method described above, but more specifically, it can be measured by the method described in the Examples.

[0043] The average mass of the expanded polypropylene resin beads of the present invention (the arithmetic mean value per particle obtained by measuring the masses of 200 randomly selected particles) is preferably 0.1 to 20 mg, more preferably 0.2 to 10 mg, even more preferably 0.3 to 5 mg, and still more preferably 0.4 to 2 mg.

[0044] The expanded polypropylene resin beads of the present invention may contain other additives in the foamed layer, as long as the additives do not impair the effects of the present invention. Examples of the additives include various conventional additives such as other antioxidants, ultraviolet absorbers, other light stabilizers, antistatic agents, pigments, dyes, fillers, conductive fillers, and cell regulators. These additives can be incorporated into the expanded beads by adding them, for example, during the process of producing the resin beads.

[0045] Examples of the cell regulator include metal borate, polyhydric alcohols such as glycerin, polyethylene glycol, and pentaerythritol, and aliphatic alcohols such as cetyl alcohol and stearyl alcohol. Metal borate such as zinc borate and magnesium borate is preferably used, and zinc borate is more preferred. The amount of metal borate contained in the resin portion for forming the foamed layer is preferably 0.005 to 0.5 parts by mass, more preferably 0.01 to 0.2 parts by mass, and even more preferably 0.015 to 0.15 parts by mass, per 100 parts by mass of the resin components for forming the foamed layer. That is, the amount of metal borate in the foamed layer of the obtained polypropylene resin expanded beads is preferably 0.005 to 0.5 parts by mass, more preferably 0.01 to 0.2 parts by mass, and even more preferably 0.015 to 0.15 parts by mass, per 100 parts by mass of the resin components constituting the foamed layer. Furthermore, when zinc borate is used, its number-based arithmetic mean particle diameter is preferably 0.5 μm or more and 15 μm or less, more preferably 1 μm or more and 10 μm or less.The number-based arithmetic mean particle diameter of zinc borate is obtained by converting the volume-based particle size distribution measured by laser diffraction scattering method into a number-based particle size distribution by assuming the particle shape to be spherical, and then arithmetically averaging the particle diameters based on this number-based particle size distribution.The above particle diameter means the diameter of a hypothetical sphere having the same volume as the particle.

[0046] The expanded polypropylene resin particles of the present invention may contain a pigment or dye as a colorant to impart colors such as chromatic, black, and gray. Chromatic pigments include red, blue, green, yellow, and purple pigments. The chromatic pigments may be inorganic or organic. Examples of inorganic pigments include chromates such as yellow lead, zinc yellow, and barium yellow; ferrocyanides such as Prussian blue; sulfides such as cadmium yellow and cadmium red; oxides such as red iron oxide; and silicates such as ultramarine. Examples of organic pigments include azo pigments such as monoazo pigments, disazo pigments, azo lakes, condensed azo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanines, anthraquinones, perylenes, perinones, thioindigo, quinacridones, dioxazines, isoindolinones, and quinophthalones.

[0047] From the viewpoint of uniformly imparting a black or gray appearance to the foamed bead molding, it is preferable to use iron oxide, titanium black, or carbon black as the pigment, such as channel black, roller black, furnace black, thermal black, or acetylene black.

[0048] When a pigment is blended into the expanded beads, the blending amount of the pigment in the foam layer is preferably 0.01 to 5 parts by mass per 100 parts by mass of the resin component constituting the foam layer from the viewpoint of uniform coloring without impairing flame retardancy. From the viewpoint of obtaining a more uniformly colored expanded bead molding, the blending amount is more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, and even more preferably 0.5 parts by mass or more. Furthermore, from the viewpoint of obtaining a expanded bead molding with higher flame retardancy, the blending amount is more preferably 4 parts by mass or less, even more preferably 3 parts by mass or less.

[0049] When the expanded bead molding is colored using the pigment, carbon black, titanium oxide, talc, calcium carbonate, magnesium hydroxide, or magnesium carbonate may be used in combination with the pigment to adjust the brightness of the color imparted to the molding or to make the appearance of the molding uniform.

[0050] The expanded polypropylene resin particles of the present invention may contain an ultraviolet absorber. Examples of ultraviolet absorbers include benzophenone compounds, benzotriazole compounds, triazine compounds, and benzoate compounds. Examples of benzophenone compounds include 2-hydroxy-4-octyloxybenzophenone, and examples of benzotriazole compounds include 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzylphenyl)]-2H-benzotriazole, 2-(3,5-di-t-butyl-2-hydroxyphenyl)benzotriazole, 2-(3-t-butyl-5-methyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di-t-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, and 2-(3,5-di-t-amyl-2- Examples of the ultraviolet absorber include 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole, 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole, etc.; examples of the triazine compound include 2-[4,6-diphenyl-1,3,5-triazin-2-yl]-5-(hexyloxy)phenol, 2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-(n-octyloxy)phenol, etc.; and examples of the benzoate compound include 2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate, hexadecyl-3,5-di-t-butyl-4-hydroxybenzoate, etc. The amount of the ultraviolet absorber in the foam layer is preferably 0.01 to 2 parts by mass, more preferably 0.05 to 1 part by mass, and even more preferably 0.1 to 0.8 parts by mass, per 100 parts by mass of the resin component constituting the foam layer. The ultraviolet absorber is a compound that has the property of absorbing ultraviolet rays, and is a compound that can mainly absorb light with a wavelength of 300 to 400 μm.

[0051] The expanded polypropylene resin beads of the present invention may contain other light stabilizers. Examples of light stabilizers include non-NOR hindered amine compounds. Non-NOR hindered amine compounds are compounds having a 2,2,6,6-tetramethyl-4-piperidineamine moiety in which the only atoms directly bonded to the nitrogen atom are hydrogen or carbon. The content of the other light stabilizers in the foamed layer is preferably 0.01 to 2 parts by mass, more preferably 0.05 to 1 part by mass, and even more preferably 0.1 to 0.8 parts by mass, per 100 parts by mass of the resin components constituting the foamed layer.

[0052] The polypropylene-based expanded beads of the present invention may be expanded beads having only a particulate foam layer, or may be expanded beads having a multilayer structure having a particulate foam layer serving as a core layer and a resin layer covering the foam layer. The foam layer may also have through-holes. In the case of expanded beads having a multilayer structure, the resin layer may cover the entire surface of the foam layer or a portion of the surface of the foam layer. Examples of resin components constituting the coating layer include polyethylene-based resins and polypropylene-based resins. The melting point of the resin component constituting the coating layer is preferably lower than the melting point of the resin component constituting the foam layer. Furthermore, the coating layer is preferably in an unfoamed state. The ratio of the mass of the resin component constituting the foam layer to the mass of the resin component constituting the coating layer (mass of foam layer:mass of coating layer) is preferably 99:1 to 80:20, more preferably 98:2 to 85:15, and particularly preferably 98:2 to 90:10. The coating layer may contain the cyclic phosphonate compound, NOR hindered amine compound, and phenolic antioxidant in the same blending ratio as in the foam layer, or in a different blending ratio from that in the foam layer, or none of them may be blended in. Alternatively, one or two of the cyclic phosphonate compound, NOR hindered amine compound, and phenolic antioxidant may be selected and blended in the coating layer.

[0053] [Method for Producing Expanded Polypropylene Resin Beads] As described above, the expanded polypropylene resin beads of the present invention are polypropylene resin expanded beads, and the method for producing the expanded polypropylene resin beads is not particularly limited, as long as the expanded layer constituting the expanded beads is a polypropylene resin base resin, and comprises a cyclic phosphonate compound and a NOR hindered amine compound, the amount of the cyclic phosphonate compound in the foamed layer being 5 parts by mass or more and less than 25 parts by mass per 100 parts by mass of the resin components constituting the foamed layer, the amount of the NOR hindered amine compound in the foamed layer being 0.1 parts by mass or more and less than 5 parts by mass per 100 parts by mass of the resin components constituting the foamed layer, the foamed layer containing a phenolic antioxidant, the amount of the phenolic antioxidant in the foamed layer being 0.01 parts by mass or more and less than 0.5 parts by mass per 100 parts by mass of the resin components constituting the foamed layer, and the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound being 0.03 to 0.9. Such expanded beads can be produced by a conventionally known method, for example, by releasing polypropylene resin particles containing a blowing agent, a cyclic phosphonate compound, a NOR-type hindered amine compound, and a phenolic antioxidant dispersed in an aqueous medium in a container, together with the aqueous medium, from the container into an atmosphere under a pressure lower than the pressure inside the container, thereby expanding the resin particles. An example of a suitable production method is shown below.

[0054] A preferred method for producing the expanded polypropylene-based resin beads of the present invention includes a dispersing step of dispersing polypropylene-based resin particles containing a cyclic phosphonate compound, a NOR-type hindered amine compound, and a phenol-based antioxidant in an aqueous medium containing an inorganic dispersant in a container; a blowing agent impregnation step of impregnating the polypropylene-based resin particles with a blowing agent in the container; and a foaming step of releasing the polypropylene-based resin particles containing the blowing agent together with the aqueous medium from the container to foam them.

[0055] (Production of Polypropylene-Based Resin Particles) The resin particles can be obtained by supplying the polypropylene-based resin, a cyclic phosphonate-based compound, a NOR-type hindered amine-based compound, a phenol-based antioxidant, and other additives such as a cell regulator, pigment, and ultraviolet absorber, which are blended as needed, into an extruder, heating and kneading the mixture to form a resin melt, and then extruding the resin melt from the extruder and pelletizing it by a strand cutting method, a hot cutting method, an underwater cutting method, or the like.

[0056] The average mass per resin particle (the arithmetic mean value per particle obtained by measuring the mass of 200 randomly selected 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. The external shape of the particles is not particularly limited as long as the intended object of the present invention can be achieved, but in the case of the strand cut method, the resin particles are 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 0.1 to 3.0 mm, more preferably 0.3 to 1.5 mm. The ratio (length / diameter ratio) of the length of the resin particles in the extrusion direction to the length of the resin particles in the direction perpendicular to the extrusion direction (diameter of the resin particles) is preferably 0.5 to 5.0, more preferably 1.0 to 3.0.

[0057] In the strand cutting method, the particle size, length / diameter ratio, and average mass of the resin particles can be adjusted by appropriately changing the extrusion speed, take-up speed, cutter speed, etc. when extruding the resin melt to cut the strands.

[0058] (Production of Expanded Polypropylene Resin Beads) A preferred method for producing expanded polypropylene resin beads of the present invention includes a dispersion step of dispersing polypropylene resin particles containing a cyclic phosphonate compound, a NOR-type hindered amine compound, and a phenolic antioxidant in an aqueous medium containing an inorganic dispersant in a container, a foaming agent impregnation step of impregnating the polypropylene resin particles with a foaming agent in the container, and a foaming step of releasing the polypropylene resin particles containing a foaming agent together with the aqueous medium from the container under a pressure lower than that of the container to foam them, and these steps are preferably included in this order. Hereinafter, each step of the preferred method for producing a polypropylene resin of the present invention will be described.

[0059] (Dispersion step) An aqueous dispersion medium is preferably used as the dispersion medium for dispersing the resin particles in a sealed container. The aqueous dispersion medium is a dispersion medium containing water as a main component. The proportion of water in the aqueous dispersion medium is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass. Examples of dispersion media other than water in the aqueous dispersion medium include ethylene glycol, glycerin, methanol, and ethanol.

[0060] In the dispersion step, a dispersant is preferably added to the dispersion medium to prevent the polypropylene-based resin particles heated in the container from fusing together. Any dispersant can be used as the dispersant as long as it prevents the polypropylene-based resin particles from fusing together in the container. While both organic and inorganic dispersants can be used, inorganic dispersants are preferred, and particulate inorganic dispersants are more preferred due to their ease of handling. Examples of dispersants include natural or synthetic clay minerals such as kaolin, mica, and clay, as well as aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, and iron oxide. These may be used alone or in combination of two or more. Of these, natural or synthetic clay minerals are preferred as the dispersant. The amount of dispersant added is preferably 0.001 to 5 parts by mass per 100 parts by mass of the resin particles.

[0061] When a dispersant is used, it is preferable to use an anionic surfactant such as sodium dodecylbenzenesulfonate, sodium alkylsulfonate, or sodium oleate as a dispersing aid in combination with the dispersant. It is preferable to add about 0.001 to 1 part by mass of the dispersing aid to the aqueous medium per 100 parts by mass of the resin particles.

[0062] (Foaming Agent Impregnation Step) A physical foaming agent is preferably used as the foaming agent for expanding the polypropylene-based resin particles. Examples of the physical foaming agent include inorganic and organic physical foaming agents. Examples of inorganic physical foaming agents include carbon dioxide, air, nitrogen, helium, and argon. Examples of organic physical foaming agents include aliphatic hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, hexane, cyclopentane, and cyclohexane, and halogenated hydrocarbons such as chlorofluoromethane, trifluoromethane, 1,1-difluoroethane, 1-chloro-1,1-difluoroethane, 1,1,1,2-tetrafluoroethane, methyl chloride, ethyl chloride, and methylene chloride. These physical foaming agents may be used alone or in combination. Alternatively, an inorganic physical foaming agent and an organic physical foaming agent may be used in combination. From the viewpoint of reducing the burden on the environment and further increasing the flame retardancy of the expanded bead molding, the blowing agent is preferably an inorganic physical blowing agent, more preferably carbon dioxide.

[0063] The amount of the foaming agent added is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 15 parts by mass, based on 100 parts by mass of the resin particles.

[0064] A preferred method for impregnating the resin particles with the blowing agent is to disperse the resin particles in an aqueous dispersion medium in a sealed container, then pressurize the blowing agent into the sealed container, and maintain the sealed container at a predetermined temperature and pressure, thereby impregnating the resin particles with the blowing agent.

[0065] (Expansion Step) The pressure (internal pressure) inside the sealed container during expansion, i.e., the pressure inside the container immediately before releasing the resin particles together with the aqueous medium, is preferably 0.5 MPa (G) or more, more preferably 0.8 MPa (G) or more. The upper limit is preferably 4 MPa (G) or less, more preferably 3 MPa (G) or less. Within the above range, the desired expanded particles can be safely produced without risk of damage or explosion of the sealed container. Preferably, the temperature is raised to 100 to 200°C, more preferably 130 to 160°C, and the resin particles containing the blowing agent are then preferably released from the sealed container into an atmosphere of a pressure lower than the pressure inside the sealed container (e.g., atmospheric pressure) to expand the resin particles.

[0066] The expanded polypropylene resin beads obtained as described above can be pressurized with air or the like to increase the pressure (internal pressure) within the cells of the foamed layer, and then heated with steam or the like to further expand (second-stage expansion) to produce expanded beads with a higher expansion ratio (lower bulk density).

[0067] [Expanded Bead Molded Article] The expanded bead molded article of the present invention is obtained by molding the expanded polypropylene resin beads in a mold. The expanded bead molded article of the present invention is an in-mold molded article of the expanded polypropylene resin beads. Specifically, the expanded bead molding of the present invention is an expanded bead molding obtained by in-mold molding of expanded polypropylene resin beads, the expanded layer of which comprises a polypropylene resin as a base resin and which contains a cyclic phosphonate compound and a NOR hindered amine compound, wherein the amount of the cyclic phosphonate compound in the foam layer is 5 parts by mass or more and less than 25 parts by mass per 100 parts by mass of the resin components constituting the foam layer, the amount of the NOR hindered amine compound in the foam layer is 0.1 parts by mass or more and less than 5 parts by mass per 100 parts by mass of the resin components constituting the foam layer, the foam layer contains a phenolic antioxidant, the amount of the phenolic antioxidant in the foam layer is 0.01 parts by mass or more and less than 0.5 parts by mass per 100 parts by mass of the resin components constituting the foam layer, and the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound is 0.03 to 0.9.

[0068] The in-mold molding method involves filling a mold with expanded beads and then heat-molding the expanded beads. Specifically, after filling the mold with the expanded beads, the expanded beads are heated to cause secondary expansion and fuse together to obtain an expanded bead molded article shaped to the molding space. Examples of methods for heating the expanded beads include a method in which a heating medium such as steam is introduced into the mold to heat the expanded beads with the heating medium, a method in which the expanded beads are heated by irradiating them with electromagnetic waves such as microwaves, and a combination of these methods. Known methods can be used to fill the mold with expanded beads. Examples include a method in which the expanded beads are pressurized with a pressurized gas to apply a predetermined internal pressure to the expanded beads before filling them into the mold (pressure filling method), a method in which the expanded beads are compressed with a pressurized gas and then filled into a pressurized mold, and then the pressure inside the mold is released (compression filling method), a method in which the mold is opened before filling with the expanded beads to expand the molding space, and then the mold is closed after filling to mechanically compress the expanded beads (cracking filling method), and a combination of these filling methods.

[0069] The density of the expanded bead molding of the present invention is preferably 10 g / L or more and 300 g / L or less, more preferably 20 g / L or more, even more preferably 30 g / L or more, still more preferably 40 g / L or more, and even more preferably 50 g / L or more. It is also more preferably 120 g / L or less, even more preferably 90 g / L or less, even more preferably 80 g / L or less, even more preferably 70 g / L or less, and even more preferably 63 g / L or less. That is, it is more preferably 20 g / L or more and 120 g / L or less, even more preferably 30 g / L or more and 90 g / L or less, even more preferably 40 g / L or more and 80 g / L or less, even more preferably 50 g / L or more and 90 g / L or less, and even more preferably 50 g / L or more and 63 g / L or less. The density of the expanded bead molding is calculated by dividing the mass of the expanded bead molding by the volume calculated based on its dimensions.

[0070] The foamed bead molding of the present invention has excellent fusion properties and excellent flame retardancy, and therefore can be suitably used in applications requiring high flame retardancy, such as protective materials for batteries and electronic components mounted in vehicles.

[0071] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples in any way.

[0072] [Measurements and Evaluations] The expanded beads and expanded bead molded articles of the Examples and Comparative Examples were subjected to the following measurements and evaluations. The expanded beads and expanded bead molded articles were evaluated after being left to stand for 2 days under conditions of 50% relative humidity, 23°C, and 1 atm to condition them.

[0073] <Bulk density of expanded particles> Approximately 500 cm 3 The expanded particles were filled into a measuring cylinder, and the bottom of the measuring cylinder was lightly tapped on the floor several times to stabilize the filling height of the expanded particles in the measuring cylinder. The bulk volume of the expanded particles indicated by the graduations on the measuring cylinder was read and designated as V1 (L). Next, the mass of the expanded particles was measured and designated as W1 [g]. The mass W1 [g] of the expanded particles was divided by the volume V1 (W1 / V1) and the unit was expressed as [kg / m 3 The bulk density of the expanded beads was calculated by converting the value into the value of the particle diameter.

[0074] <High-Temperature Peak Heat of Fusion of Expanded Beads> The high-temperature peak heat of fusion of the expanded beads was measured by heat flux differential scanning calorimetry based on JIS K7122-2012. Specifically, approximately 2 mg of expanded beads was sampled and heated from 23°C to 200°C at a rate of 10°C / min using a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Corporation), obtaining a DSC curve with one or more melting peaks. In the following description, the resin-specific peak is designated A, and the high-temperature peak appearing higher than A is designated B. A straight line (α-β) was drawn connecting point α corresponding to 80°C on the DSC curve and point β on the DSC curve corresponding to the melting end temperature T of the expanded beads. The melting end temperature T is the high-temperature end point of high-temperature peak B, and refers to the intersection of the high-temperature peak and the high-temperature baseline. Next, a line parallel to the vertical axis of the graph was drawn from point γ on the DSC curve, which corresponds to the valley between the resin-specific peak A and the high-temperature peak B, and the point where this line intersected with the line (α-β) was designated as δ. The area of ​​high-temperature peak B was the area enclosed by the curve of the high-temperature peak B portion of the DSC curve, the line segment (δ-β), and the line segment (γ-δ), and this was designated as the heat of fusion of the high-temperature peak.

[0075] <Evaluation of fusion bonding> The expanded bead molding was bent and broken, and the number of expanded beads present on the fracture surface (C1) and the number of broken expanded beads (C2) were determined. The ratio of broken expanded beads to the above-mentioned expanded beads (C2 / C1 x 100) was calculated as the material failure rate. The above measurement was carried out five times using different test pieces, and the material failure rate for each was determined and evaluated according to the following criteria. Evaluation criteria A: Material failure rate is 60% or more B: Material failure rate is 40% or more but less than 60% C: Material failure rate is less than 40%

[0076] <Flame Retardancy Evaluation (UL94 Flammability Judgment)> The flame retardancy of the expanded bead moldings was evaluated based on the results of a vertical flame test (20 mm vertical flame test) conducted in accordance with the UL94 standard. The specific test method is as follows. (Preparation of Measurement Samples) Five test pieces measuring 125 mm in length, 13 mm in width, and 13 mm in thickness were cut out from near the center of the expanded bead molding so that all surfaces of the test piece were cut out. (Evaluation Criteria) Evaluation was based on UL94 standards V-0, V-1, and V-2. Note that if the UL94 standards V-0, V-1, or V-2 was not met, the test piece was evaluated as failing.

[0077] <Density of Expanded Bead Molding> The expanded bead molding was left for 2 days under the conditions of 50% relative humidity, 23°C, and 1 atm. Then, its mass was measured and designated as W [g]. Next, the volume V [cm] of the expanded bead molding was calculated based on the dimensions of the expanded bead molding. 3 The mass W [g] of the expanded bead molding was divided by the volume V (W / V), and the unit was expressed as [kg / m 3 The density of the expanded bead molding was calculated by converting the density of the expanded bead molding into the mass fraction of the expanded bead molding.

[0078] [Raw Materials] The raw materials used in the Examples and Comparative Examples are as follows. (Polypropylene Resins) PP1: Ethylene-propylene random copolymer, melting point 143°C, ethylene content 2.1 mass%, MFR (load 2.16 kg, 230°C, JIS K7210-1:2014) 6 g / 10 min, polydispersity (Mw / Mn) 9.4 PP2: Ethylene-propylene random copolymer, melting point 134°C, ethylene content 3.5 mass%, MFR (load 2.16 kg, 230°C, JIS K7210-1:2014) 5 g / 10 min, polydispersity (Mw / Mn) 5.0 PP3: High melt tension polypropylene, melting point 159°C, MFR (load 2.16 kg, 230°C, JIS K7210-1:2014) 1.7 g / 10 min Melt tension: 390 mN (measurement temperature: 230°C, measurement device: Capillograph 1D manufactured by Toyo Seiki Seisaku-sho, Ltd., orifice nozzle diameter: 2.095 mm, orifice length: 8.0 mm, pulley diameter: 45 mm, take-up speed: initial speed 0 m / min, speed increased at a constant rate to reach 200 m / min in 4 minutes, and the maximum value immediately before the strand being taken up broke was recorded.)

[0079] (Polyethylene resin) PE1: Linear low-density polyethylene, melting point 120°C, density 0.923 cm / cm ３ , MFR (load 2.16 kg, 190 ° C, JIS K7210-1:2014) 1.5 g / 10 min

[0080] (Cyclic phosphonate compounds) PCO900: manufactured by Thor, trade name "Aflammit PCO900", melting point 240°C, compound represented by the following formula (6):

[0081] (NOR-type hindered amine compounds) NOR116: BASF Corporation, trade name "Flamestab NOR116", a compound represented by the following formula (7), molecular weight 2261

[0082] (Phenol-based antioxidant) 1330: BASF Corporation, trade name "Irganox 1330", melting point 245°C, compound represented by the following formula (8): 1010: BASF Corporation, trade name "Irganox 1010", melting point 120°C, compound represented by the following formula (9)

[0083] (Sulfur-based antioxidant) Dioctadecyl-3,3'-thiodipropionate: BASF, trade name "Irganox PS 802"

[0084] [Production of Expanded Polypropylene Resin Beads and Expanded Bead Moldings] (Example 1) An extruder with an inner diameter of 50 mm and a strand-forming die attached to the outlet side was prepared. PP1, zinc borate (arithmetic mean particle diameter based on number: 9 μm), PCO900, NOR116, 1330, and the sulfur-based antioxidant were fed into the extruder in the amounts shown in Table 1, and melt-kneaded to form a resin melt. The resulting resin melt was extruded as strands through the strand-forming die, and the extruded strands were water-cooled and cut with a pelletizer to obtain polypropylene resin particles with an average mass of 1.0 mg per particle.

[0085] A 100 L autoclave was charged with 20 kg of the polypropylene resin particles, 60 L of water as a dispersion medium, 80 g of a dispersant, 40 g of a surfactant, and 2 g of a dispersing aid. Next, carbon dioxide was injected into the autoclave as a blowing agent, and the autoclave was pressurized to a gauge pressure of 0.5 MPa (G). Next, the contents of the sealed container were heated to the foaming temperature shown in Table 1 at a temperature increase rate of 2°C / min while stirring. Next, carbon dioxide was injected into the sealed container to the gauge pressure (foaming pressure) shown in Table 1, and then the container was maintained at the same temperature and pressure for 15 minutes. The contents of the autoclave were then released under atmospheric pressure, and the polypropylene resin particles were expanded to obtain expanded polypropylene resin particles. Measurement results for the physical properties of the resulting expanded polypropylene resin particles are shown in Table 1.

[0086] The mold used was a split mold for flat molding, with internal dimensions of a rectangular parallelepiped (400 mm long, 300 mm wide, and 30 mm thick) when fully closed. After the evacuation step, the mold was opened 3 mm in the thickness direction from the fully closed state and then filled with foamed beads. After filling was complete, the mold was fully closed (cracking amount: 3 mm, 10%). Steam was then supplied into the mold to heat the foamed beads, resulting in a plate-shaped foamed bead molded article. The steam heating was performed as follows: First, steam was supplied into the mold with both drain valves open (evacuation step). Next, steam was supplied into the mold from one mold with the drain valve of the opposite mold open (one-sided heating step). Then, steam was supplied from the other mold with the drain valve of the opposite mold open (reverse one-sided heating step). Next, steam was supplied from both molds with the drain valves of both molds closed until the molding steam pressure in the mold reached the value listed in Table 1 (double-sided heating step). After the double-side heating step, the pressure was released, followed by water cooling for 20 seconds. The mold was then further water-cooled until the pressure (surface pressure) generated on the molding surface of the mold due to the secondary expansion force of the expanded bead molding reached 0.05 MPa (G). The split mold was then opened, and the molded article was removed from the mold. The molded article removed from the mold was cured in an oven at 80°C for 12 hours and then slowly cooled to room temperature. The density, fusion property, and flame retardancy of the resulting expanded bead molding were evaluated, and the results are shown in Table 1.

[0087] (Examples 2 to 7 and Comparative Examples 1 to 5) Expanded polypropylene resin beads were obtained in the same manner as in Example 1, except that the amount of each component was changed so that the blending amount of each component per 100 parts by mass of the resin component constituting the foam layer was as shown in Tables 1 and 3. Measurement results of the physical properties of the obtained expanded polypropylene resin beads are shown in Tables 1 and 3. Expanded bead moldings were obtained using the expanded polypropylene resin beads obtained here in the same manner as in Example 1, except that the molding vapor pressure was adjusted to the vapor pressure shown in Tables 1 and 3. The density, fusion property evaluation results, and flame retardancy evaluation results of the obtained expanded bead moldings are shown in Tables 1 and 3.

[0088] (Example 8) Expanded polypropylene resin beads were obtained in the same manner as in Example 6, except that the phenolic antioxidant 1330 was changed to 1010. Measurement results of the physical properties of the obtained expanded polypropylene resin beads are shown in Table 2. The expanded polypropylene resin beads thus obtained were used to obtain an expanded bead molding in the same manner as in Example 6. The results of the density, fusion property evaluation, and flame retardancy evaluation of the obtained expanded bead molding are shown in Table 2.

[0089] Example 9: A manufacturing apparatus was prepared, equipped with a core layer extruder with an inner diameter of 50 mm, a coating layer extruder with an inner diameter of 30 mm, and a co-extrusion die for forming a multilayer strand consisting of a cylindrical core layer and a coating layer covering the side of the core layer. PP1, zinc borate (arithmetic mean particle size based on number: 9 μm), PCO900, NOR116, 1330, and the sulfur-based antioxidant were fed to the core layer extruder in the amounts shown in Table 2, and melt-kneaded to form a resin melt for forming the core layer. Only PP2 was fed to the coating layer extruder and melt-kneaded to form a resin melt for forming the coating layer. The obtained resin melt for forming the core layer and the resin melt for forming the coating layer are introduced into a co-extrusion die for forming a multilayer strand and merged in the die, and a multilayer strand having a two-layer structure (coating layer / core layer structure) consisting of a cylindrical core layer and a coating layer covering the side of the core layer is extruded from the co-extrusion die.The ratio of the coating layer to the core layer is adjusted to be 3 / 97 by mass.The extruded strand is then water-cooled and cut with a pelletizer to obtain polypropylene-based resin particles having an average mass of 1.0 mg per particle, which have a two-layer structure consisting of a cylindrical core layer and a coating layer covering the side of the core layer.

[0090] The obtained polypropylene resin particles were treated in the same manner as in Example 1 to obtain expanded polypropylene resin particles having a multilayer structure having a foam layer and a coating layer. Here, the core layer of the resin particles was expanded to form a particulate foam layer, and the coating layer was an unexpanded resin layer. Measurement results of the physical properties of the obtained expanded polypropylene resin particles are shown in Table 2. The obtained expanded polypropylene resin particles were used to obtain an expanded bead molding in the same manner as in Example 1. The results of the density, fusion property evaluation, and flame retardancy evaluation of the obtained expanded bead molding are shown in Table 2.

[0091] (Example 10) Expanded polypropylene resin particles were obtained in the same manner as in Example 1, except that polypropylene resin PP1 and polypropylene resin PP3 were supplied in a mass ratio of 85 / 15 (PP1 / PP3) instead of polypropylene resin PP1. Measurement results of the physical properties of the obtained expanded polypropylene resin particles are shown in Table 2.

[0092] (Example 11) Expanded polypropylene resin particles were obtained in the same manner as in Example 1, except that polypropylene resin PP1 and polyethylene resin PE1 were supplied in a mass ratio of 85 / 15 (PP1 / PE1) instead of polypropylene resin PP1. Measurement results of the physical properties of the obtained expanded polypropylene resin particles are shown in Table 2.

[0093] (Example 12) Expanded polypropylene resin beads were obtained in the same manner as in Example 1, except that conductive carbon black (trade name: Ketjenblack EC300J, manufactured by Lion Corporation) was fed as the conductive filler to the extruder in the amount shown in Table 2. Measurement results of the physical properties of the expanded polypropylene resin beads obtained are shown in Table 2.

[0094] (Example 13) Expanded polypropylene resin beads were obtained in the same manner as in Example 1, except that PTFE powder (polytetrafluoroethylene fibril, manufactured by Mitsubishi Chemical Corporation, trade name Metablen A-3800) was fed as a filler to the extruder in the blending amount shown in Table 2. Measurement results of the physical properties of the obtained expanded polypropylene resin beads are shown in Table 2.

[0095]

[0096]

[0097]

[0098] From the results shown in Tables 1 and 2, it can be seen that the expanded bead moldings of the Examples have excellent fusion properties, and furthermore, their flammability according to the UL-94 standard is V-2 or higher, indicating excellent flammability. This shows that the expanded polypropylene resin beads of the present invention can be used to produce expanded bead moldings with excellent flame retardancy and fusion properties, and that the expanded polypropylene resin beads of the present invention have excellent flame retardancy and fusion properties.

Claims

1. Polypropylene-based resin foam particles, a foam layer constituting the foamed beads has a polypropylene-based resin as a base resin, and contains a cyclic phosphonate-based compound and a NOR-type hindered amine-based compound; the amount of the cyclic phosphonate compound in the foam layer is 5 parts by mass or more and less than 25 parts by mass per 100 parts by mass of a resin component constituting the foam layer, the amount of the NOR hindered amine compound in the foam layer is 0.1 parts by mass or more and less than 5 parts by mass per 100 parts by mass of a resin component constituting the foam layer, the foam layer contains a phenolic antioxidant; the amount of the phenolic antioxidant in the foamed layer is 0.01 parts by mass or more and less than 0.5 parts by mass per 100 parts by mass of a resin component constituting the foamed layer, The expanded polypropylene resin particles have a ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound of 0.03 or more and 0.9 or less.

2. 2. The expanded polypropylene resin beads according to claim 1, wherein the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound is 0.07 or more and 0.9 or less.

3. 2. The expanded polypropylene resin beads according to claim 1, wherein the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound is 0.14 or more and 0.9 or less.

4. The expanded polypropylene resin beads according to any one of claims 1 to 3, wherein the amount of the NOR hindered amine compound in the foamed layer is 0.1 parts by mass or more and 3.5 parts by mass or less per 100 parts by mass of the resin component constituting the foamed layer.

5. The melting point Tm of the phenolic antioxidant Ａ The expanded polypropylene resin particles according to any one of claims 1 to 3, wherein the temperature is 200°C or higher and lower than 300°C.

6. The melting point Tm of the cyclic phosphonate compound Ｂ is 200°C or more and less than 300°C, and the melting point Tm Ａ and the melting point Tm of the cyclic phosphonate compound Ｂ The melting point difference (Tm Ａ -Tm Ｂ 4. The expanded polypropylene resin particles according to claim 1, wherein the temperature is −50° C. or higher and 50° C. or lower.

7. The expanded polypropylene resin particles according to any one of claims 1 to 3, wherein the cyclic phosphonate compound is pentaerythritol diphosphonate.

8. The expanded polypropylene resin particles according to any one of claims 1 to 3, wherein the foamed layer contains a sulfur-based antioxidant, and the blending amount of the sulfur-based antioxidant in the foamed layer is 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the resin component constituting the foamed layer.

9. 9. The expanded polypropylene resin beads according to claim 8, wherein the ratio of the amount of the sulfur-based antioxidant to the amount of the NOR-type hindered amine compound is 0.03 or more and 0.9 or less.

10. A foamed bead molding obtained by molding the foamed polypropylene resin beads according to any one of claims 1 to 3 in a mold.

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