Polyolefin-based resin foam particle, foam particle molded body obtained by in-mold molding of said foam particle, method for producing said foam particle, and method for assessing flame retardancy of said foam particle

Abstract

The present invention relates to: a polyolefin-based resin foam particle; a foam particle molded body obtained by in-mold molding of said foam particle; a method for producing said foam particle; and a method for determining the flame retardancy of said foam particle The polyolefin-based resin foam particle contains a polyolefin-based resin and a phosphonic acid ester compound. The phosphorus content P in the foam particle is 0.1-6 mass%. The foam particle satisfies formula (1): {(m215-m235) / m215}×100 / Ptot≤35 (1). In formula (1), m215 is the mass of a foam particle measured in thermogravimetric measurements at 215ºC, m235 is the mass of a foam particle measured in thermogravimetric measurements at 235ºC, and P to t is a numerical value that indicates the mass percentage of phosphorus in the foam particle, and falls within the range 0.001-0.06.

Description

Expanded polyolefin resin beads, expanded bead molded article obtained by molding the expanded beads in a mold, method for producing the expanded beads, and method for determining flame retardancy of the expanded beads

[0001] The present invention relates to expanded polyolefin resin beads, an expanded bead molding obtained by molding the expanded beads in a mold, and a method for producing the expanded beads.

[0002] Expanded polyolefin resin particles containing a phosphonate ester compound are generally known. The phosphonate ester compound can typically impart specific functions to the expanded polyolefin resin particles. The phosphonate ester compound can typically impart flame retardant properties to the expanded polyolefin resin particles. Therefore, the phosphonate ester compound can be a flame retardant material that imparts flame retardancy to the expanded polyolefin resin particles, or can form a part of the flame retardant material.

[0003] Various parts and technical components molded from the respective expanded polyolefin resin beads may require different flame retardancy. As a non-limiting example, foamed bead moldings molded in a mold for vehicles, particularly automobiles, from the respective expanded polyolefin resin beads are usually required to have good flame retardancy. More specific, non-limiting examples of the respective vehicle components molded in a mold from the respective expanded polyolefin resin beads that require good flame retardancy include housing elements and protective elements for battery systems, electrical devices, electronic devices, etc.

[0004] Thus, when producing expanded polyolefin resin beads, it is very important that the phosphonate ester compound is not substantially altered or decomposed to ensure that the resulting expanded polyolefin resin beads still have the desired properties due to a sufficient amount of unaltered or undecomposed phosphonate ester compound. The pressure and temperature conditions for producing expanded polyolefin resin beads, when combined with the presence of heated water for a long period of time, as in the case of producing expanded polyolefin resin beads by a conventional autoclave process, can cause undesirable alteration or decomposition of the phosphonate ester compound, resulting in the expanded polyolefin resin beads not exhibiting the desired properties with respect to flame retardancy.

[0005] Experiments have shown that hydrolysis of the phosphonate ester compound, which may occur in the presence of water during the autoclave-based process for producing the respective expanded polyolefin resin beads, can adversely affect the properties of the expanded polyolefin resin beads. If the phosphonate ester compound undergoes decomposition, such as hydrolysis, during the process for producing the respective expanded polyolefin resin beads, it becomes difficult to achieve the desired flame retardancy.

[0006] Therefore, an object of the present invention is to provide expanded polyolefin resin beads having improved properties, which are based on the fact that the deterioration and decomposition of the phosphonate ester compound is suppressed after the production process of the expanded polyolefin resin beads, and that a sufficient amount of the undegraded and undecomposed phosphonate ester compound is present in the expanded beads.

[0007] Another object of the present invention is to provide an expanded bead molding obtained by molding expanded polyolefin resin beads having improved properties in a mold, and a method for producing expanded polyolefin resin beads having improved properties.

[0008] A first aspect of the present invention is a polyolefin resin expanded bead, characterized in that the expanded bead contains a polyolefin resin and a phosphonate ester compound, the phosphorus content P of the expanded bead is 0.1 to 6 mass %, and the expanded bead satisfies the following formula (1): {(m ２１５ -m ２３５ ) / m ２１５}×100 / P ｔｏｔ ≦35 (1) In formula (1), m ２１５ is the mass of the expanded beads measured by thermogravimetry at 215 ° C; m ２３５ is the mass of the expanded beads measured by thermogravimetry at 235°C; P ｔｏｔ is a numerical value indicating the mass fraction of phosphorus in the expanded beads, and is in the range of 0.001 to 0.06.

[0009] Conducted on resin particles ３１ 1 is a diagram illustrating the principle of P-NMR analysis, showing the presence of altered / decomposed phosphonate ester compounds. ３１1 is a diagram showing the principle of P-NMR analysis, illustrating the presence of a modified / decomposed phosphonate ester compound; and FIG. 2 is a diagram showing the principle of TGA curves before and after the modification / decomposition of a phosphonate ester compound.

[0010] A first aspect of the present invention relates to expanded polyolefin resin beads. Hereinafter, simply referred to as "expanded beads." Expanded beads typically have an expanded cell structure, and more specifically, an expandable expanded cell structure. The cell structure of each expanded bead typically consists of cell walls defining one or more cell spaces. When an expanded bead is not provided with an additional covering layer, the entire bead typically becomes or represents a foamed layer. When an expanded bead is provided with a covering layer, the foamed layer becomes or represents a core layer of each expanded bead. Expanded beads can also be considered "cellular beads" and "expanded beads," respectively.

[0011] The foam layer is generally based on a polyolefin resin, where "polyolefin resin" refers to a polypropylene resin, a polyethylene resin, or a mixture of two or more of these.

[0012] In order to allow the expanded beads to fully exhibit the mechanical properties and other characteristics derived from the polypropylene-based resin, the proportion of the polypropylene-based resin in the polyolefin-based resin is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0013] Furthermore, when it is desired to allow the expanded beads to fully exhibit the mechanical properties and other characteristics derived from the polyethylene-based resin, the proportion of the polyethylene-based resin in the polyolefin-based resin is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0014] The polypropylene-based resin means a polypropylene homopolymer or a propylene-based copolymer containing 50% by mass or more of a component derived from a propylene monomer.

[0015] Non-limiting examples of propylene homopolymers include propylene-based resins such as isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene, etc. These resins exemplified as propylene homopolymers may be used alone or in combination of two or more.

[0016] In the propylene-based copolymer, the content of the component derived from the propylene monomer in the polypropylene-based resin is preferably 80% by mass or more, more preferably 90% by mass or more, and the content of the component derived from the propylene monomer in the polypropylene-based copolymer is preferably 99% by mass or less, more preferably 98% by mass or less.

[0017] Examples of propylene-based copolymers are copolymers of propylene with ethylene and / or at least one 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. These propylene-based copolymers may be, for example, random copolymers or block copolymers, with random copolymers being preferred. Preferred are ethylene-propylene random copolymers, propylene-butene random copolymers, and ethylene-propylene-butene random copolymers.

[0018] Further, examples of the propylene-based copolymer include impact-resistant polypropylene (block polypropylene) composed of two or more phases including a continuous phase of a propylene-based polymer and a rubber phase such as an ethylene-α-olefin copolymer present as a dispersed phase in the continuous phase.

[0019] A mixture of two or more of these propylene copolymers can also be the main polymer component of the foamed layer. In this case, the total content of the propylene copolymers in the polypropylene resin is preferably 60% by mass or more, 70% by mass or more, or even 80% by mass or more.

[0020] When the propylene-based random copolymer contains a component derived from ethylene (ethylene component) and / or a component derived from butene (butene component) as a comonomer, the moldability of the expanded beads in a mold under low molding pressure conditions can be further improved.

[0021] When the polypropylene-based resin is a propylene-ethylene-butene random copolymer, the total amount of the ethylene component and the butene component is preferably 1 to 15% by mass, more preferably 2 to 15% by mass, and even more preferably 3 to 15% by mass. In this embodiment, by molding the expanded beads in a mold, it is possible to obtain a component that has good mechanical properties such as compressive strength while maintaining good moldability of the expanded beads under low molding pressure conditions. The contents of the ethylene component and the butene component in each propylene-based random copolymer can be determined by IR spectroscopy.

[0022] The polypropylene-based resin may be a linear polypropylene resin, a branched polypropylene resin, or a combination of both.

[0023] The polyethylene-based resin refers to a polyethylene homopolymer or an ethylene-based copolymer containing 50% by mass or more of a component derived from an ethylene monomer. Specific examples of the polyethylene-based resin include high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), linear ethylene-based copolymers such as ethylene-vinyl acetate (EVA) copolymer and ethylene-methyl acrylate (EMA) copolymer. Among these, linear low-density polyethylene is preferred. Linear low-density polyethylene is a copolymer of ethylene and an α-olefin exhibiting a linear molecular structure. Examples of suitable linear low-density polyethylene include ethylene-1-butene copolymer, ethylene-1-pentene copolymer, ethylene-1-hexene copolymer, ethylene-4-methyl-1-pentene copolymer, and ethylene-1-octene copolymer. The linear low-density polyethylene is preferably a random copolymer. The content of components derived from ethylene monomers in such ethylene-based copolymers is preferably 80% by mass or more, 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more.

[0024] The method for producing the polyolefin resin is not limited. For example, the polyolefin resin can be produced by polymerizing an olefin monomer in the presence of a polymerization catalyst. Examples of the polymerization catalyst include a Ziegler-Natta polymerization catalyst and a metallocene polymerization catalyst.

[0025] The foam layer of the present invention may contain other polymeric materials besides the polyolefin-based resins, provided that the objects and effects of the present invention are not impaired. Examples of such other polymers include thermoplastic polymers, such as polystyrene-based resins, polyamide-based resins, polyester-based resins, polycarbonate-based resins, and polyphenylene ether-based resins. Examples of such other polymers include thermoplastic elastomers such as olefin-based thermoplastic elastomers (TPOs) and urethane-based thermoplastic elastomers (TPUs). Mixtures of at least two of these other polymeric materials are also contemplated.

[0026] The content of thermoplastic polymers other than the polyolefin-based resin in 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 particularly preferably 0% by mass. That is, it is particularly preferable that the foam layer contains substantially only polyolefin-based resin as the thermoplastic polymer.

[0027] Polyolefin resins typically exhibit a flexural modulus of 100 MPa or more. From the viewpoint of improving the moldability of the expanded beads, the flexural modulus of the polyolefin resin is preferably 3000 MPa or less, more preferably 2000 MPa or less, even more preferably 1500 MPa or less, and particularly preferably 1200 MPa or less. Thermoplastic elastomers exhibit rubber elasticity at room temperature and typically exhibit a flexural modulus of less than 100 MPa. The flexural modulus of thermoplastic resins is measured in accordance with JIS K7171:2008.

[0028] The foam layer of the present invention may contain a non-thermoplastic polymer, such as a thermosetting resin or rubber, as long as the non-thermoplastic polymer does not impair the object and effect of the present invention.

[0029] When a non-thermoplastic polymer is contained in the foam layer, the content of the non-thermoplastic polymer in 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 particularly preferably 0% by mass.

[0030] When the polyolefin resin is a polypropylene resin, 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. By producing expanded beads using a polypropylene resin having a melting point within the above range, it is typically possible to obtain a molded article having good mechanical properties, such as compressive strength, by molding the expanded beads in a mold. 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 148°C or lower. By producing expanded beads using a polypropylene resin having a melting point within the above range, it is possible to mold the expanded beads under low molding pressure conditions. That is, the melting point of the polypropylene resin is preferably 130°C or higher and 155°C or lower, more preferably 135°C or higher and 150°C or lower, and even more preferably 140°C or higher and 148°C or lower.

[0031] When the polyolefin resin is a polyethylene resin, the melting point of the polyethylene resin is preferably 110°C or higher. By producing expanded beads using a polyethylene resin having a melting point within the above range, the molded body obtained by molding the expanded beads in a mold is less likely to shrink, and the shape recovery after molding is good. From the viewpoint of further improving moldability, the melting point of the polyethylene resin is preferably 112°C or higher, more preferably 115°C or higher. On the other hand, the melting point of the polyethylene resin is preferably 130°C or lower. By producing expanded beads using a polyethylene resin having a melting point within the above range, a molded body with good fusion properties can be obtained even when molded at a low molding temperature, and expanded beads with good moldability are easily obtained. From the viewpoint of further improving moldability, the melting point of the polyethylene resin is preferably 128°C or lower, more preferably 125°C or lower. That is, the melting point of the polyethylene resin is preferably 110°C or higher and 130°C or lower, more preferably 112°C or higher and 128°C or lower, and even more preferably 115°C or higher and 125°C or lower.

[0032] The melting point of a polyolefin resin can be measured in accordance with JIS K 7121:2012 using a polyolefin resin, resin particles, or expanded particles as a test sample. Under conditions of a nitrogen inflow rate of 30 mL / min, the test sample is heated from 23°C to 200°C at a heating rate of 10°C / min, held at that temperature for 10 minutes, then 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 a differential scanning calorimetry (DSC curve) (DSC curve of the second heating). The apex temperature of the melting peak in the DSC curve is then determined, and this value is taken as the melting point of the polyolefin resin. When multiple melting peaks appear in the DSC curve, the apex temperature of the melting peak with the highest height relative to the baseline is used as the melting point.

[0033] The melt mass-flow rate (MFR) of the polypropylene-based resin measured at a temperature of 230°C and a load of 2.16 kg is preferably 3 g / 10 min or more, more preferably 4 g / 10 min or more. Having an MFR within the above range improves the expandability of the expanded beads during expansion and the secondary expandability of the expanded beads during in-mold molding. On the other hand, the MFR of the polypropylene-based resin is preferably 15 g / 10 min or less, more preferably 10 g / 10 min or less. Having an MFR within the above range facilitates the formation of uniform cells in the expanded beads, which in turn facilitates the improvement of the physical properties of the molded article obtained by molding the expanded beads. That is, the MFR of the polypropylene-based resin is preferably 3 to 15 g / 10 min, more preferably 4 to 10 g / 10 min.

[0034] The melt mass-flow rate (MFR) of the polyethylene resin measured at a temperature of 190°C and a load of 2.16 kg is preferably 0.5 g / 10 min or more, more preferably 0.8 g / 10 min or more. Having an MFR within the above range improves the expandability of the expanded beads during expansion and the secondary expandability of the expanded beads during in-mold molding. On the other hand, the MFR of the polyolefin resin is preferably 4 g / 10 min or less, more preferably 3 g / 10 min or less. These values ​​facilitate uniform cell formation in the expanded beads, which facilitates improved physical properties of the molded articles obtained by molding them. That is, the MFR of the polyethylene resin is preferably 0.5 to 4 g / 10 min, more preferably 0.8 to 3 g / 10 min.

[0035] The MFR of polyolefin resins such as polypropylene resins and polyethylene resins can be measured in accordance with JIS K 7210-1:2014. Alternatively, resin particles (expanded particles) can be used as test specimens. The MFR can be measured, for example, using an MFR measuring device available from Dynisco (38 Forge Parkway, Franklin, MA 02038, USA) under the name "LMI400."

[0036] The polydispersity (Mw / Mn) of the polypropylene-based resin can be 4.0 or more and 25 or less, or 4.1 or more and 15 or less. The polydispersity (Mw / Mn) of the polypropylene-based 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.

[0037] The polydispersity (Mw / Mn) of a polypropylene-based resin can be measured by gel permeation chromatography (GPC). According to an exemplary method, a polypropylene-based resin is first dissolved in o-dichlorobenzene to prepare a sample solution with a concentration of 2.2 mg / ml. Using this sample solution, GPC measurement is performed under the following conditions: GPC columns: two TSKgel® GM H6-HT columns and two TSKgel GMH6-HTL columns; eluent: o-chlorobenzene; flow rate: 1.0 ml / min; temperature: 140°C. Next, the number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the polypropylene-based resin are calculated from a calibration curve created using polystyrene as a standard substance, and then the polydispersity (Mw / Mn) is calculated. A high-temperature GPC system HLC-8321GPC / HT available from Tosoh Biosciences can be used as the measurement device.

[0038] The expanded beads are preferably (substantially) spherical. The average particle size of the expanded beads is preferably 0.3 to 8 mm, more preferably 0.5 to 5 mm, and even more preferably 0.8 to 4.5 mm. The arithmetic mean particle size of the expanded beads can be determined by the following method. First, the volume-based particle size distribution of the expanded beads is measured. The volume-based particle size distribution of the expanded beads can be measured using a particle size distribution measuring device (e.g., Millitrac JPA manufactured by Nikkiso Co., Ltd.). The number of expanded beads used in the measurement is, for example, 2,000 or more. Next, based on the volume-based particle size distribution of the expanded beads, the shape of the expanded beads is assumed to be spherical, and the number-based particle size distribution of the expanded beads is calculated by converting the particle size distribution to a number-based particle size distribution. In this case, the particle size is defined as the diameter of a hypothetical sphere having the same volume as the particle. The arithmetic mean particle size based on the number of expanded beads can then be calculated by calculating the arithmetic mean of the particle sizes based on this particle size distribution.

[0039] The average diameter of the bubbles in the expanded polyolefin beads is, for example, preferably 50 μm to 250 μm, more preferably 60 μm to 200 μm, and even more preferably 65 μm to 150 μm. When the average diameter of the bubbles in the expanded polyolefin beads is within the above range, the expandability of the expanded beads in a mold is improved when the expanded beads are molded into a molded article. The average diameter of the bubbles can be measured, for example, by drawing a line from the outer edge of the bubble located on the outermost surface of the expanded beads to the outer edge of the bubble located on the opposite outermost surface of the expanded beads in an image of the cross section of the expanded beads, which is roughly halved, observed under a microscope, and counting the number of bubbles that intersect with the line, passing through the center of the expanded beads. The average diameter of the bubbles can then be calculated by dividing the measured number of bubbles by the length of the line. The average diameter of the bubbles can be adjusted to the desired range by adjusting the type and amount of bubble control agent added to the resin beads used to form the expanded beads and the pressure used to expand the resin beads.

[0040] Therefore, expanded particles generally refer to a polyolefin-based resin particulate material composed of expanded polyolefin-based resin particles having an expanded cellular structure, particularly an expandable expanded cellular structure. In this specification, the expressions "expanded polyolefin-based resin particles" and "polyolefin-based resin particulate material" can be used interchangeably.

[0041] The expanded beads contain a polyolefin resin and a phosphonate ester compound, particularly a cyclic phosphonate ester compound. The polyolefin resin can be based on, for example, a polyethylene resin, a polypropylene resin, or a combination of a polyethylene resin and a polypropylene resin. The polyolefin resin serves as the base material for the expanded beads containing the phosphonate ester compound. In particular, the polyolefin resin can contain a phosphonate ester compound. This applies to the individual particles that make up the expanded beads. That is, the individual particles are made of a polyolefin resin and contain a phosphonate ester compound, and in particular, the polyolefin resin serves as the base material for the expanded beads containing the phosphonate ester compound. Examples of the respective phosphonate ester compounds are provided further below.

[0042] The phosphonate ester compound can have a specific function and therefore can impart specific properties to the expanded beads, particularly, the phosphonate ester compound can have a flame retardant function and therefore can impart flame retardancy to the expanded beads.

[0043] Thus, the phosphonate ester compound can form a flame retardant or part of a flame retardant. Particularly preferred phosphonate ester compounds are cyclic phosphonate ester compounds.

[0044] Because the expanded beads contain only small amounts of altered or decomposed phosphonate ester compounds, their properties are improved compared to expanded beads containing conventional phosphonate ester compounds. The alteration or decomposition of each phosphonate ester compound refers specifically to a change in the chemical structure of the phosphonate ester compound. For example, the chemical structure of the phosphonate ester compound is converted to phosphonic acid by hydrolysis. Experiments have shown that expanded beads exhibit desired properties, particularly good flame retardancy, when they comply with the following formula (1): This formula is a reliable indicator of whether the amount of altered or decomposed phosphonate ester compounds in the expanded beads is below a threshold. A value below this threshold indicates that the expanded beads have desirable properties, particularly flame retardancy. On the other hand, a value above the threshold indicates that the expanded beads do not have the desired properties, particularly flame retardancy.

[0045] Therefore, the expanded beads having improved properties are characterized by satisfying the following formula (1): {(m ２１５ -m ２３５ ) / m ２１５}×100 / P ｔｏｔ ≦35...(1) In formula (1), m ２１５ is the mass of the expanded beads measured by thermogravimetry at 215 ° C; m ２３５ is the mass of the expanded beads measured by thermogravimetry at 235°C; P ｔｏｔ is a numerical value indicating the mass fraction of phosphorus in the expanded beads, and is in the range of 0.001 to 0.06.

[0046] The inventors have found that by mathematically relating the results obtained from thermogravimetric analysis of expanded beads to a specific phosphorus content P of the expanded beads in the range of 0.1 to 6% by weight (0.001 to 0.06 as a mass fraction, which is the ratio of the mass of phosphorus to the mass of the expanded beads) and determining whether this relationship is equal to or less than 35, expanded beads exhibiting the desired properties, and in particular good flame retardancy, can be obtained.

[0047] As is clear from the above formula (1), the mass (m ２１５ ) is the mass (m) of the expanded beads at 235 ° C. measured by thermogravimetry. ２３５ ) and subtract this difference (m ２１５ -m ２３５ ) is the mass (m ２１５ ) and take the quotient {(m ２１５ -m ２３５ ) / m ２１５} 100 / P ｔｏｔ Then, it is confirmed whether the product is equal to or less than 35. ｔｏｔ is a numerical value indicating the mass fraction of phosphorus in the expanded beads, and is in the range of 0.001 to 0.06. ｔｏｔ is determined taking into account the phosphorus content of the unaltered phosphonate ester compounds contained in the expanded beads, the phosphorus content of the altered / decomposed phosphonate ester compounds, and the phosphorus content of all phosphorus substances resulting therefrom.

[0048] The temperature range of 215°C to 235°C is a temperature range in which the denatured / decomposed phosphonate ester compound experiences a large loss in mass, while the polyolefin resin and the undenatured / decomposed phosphonate ester compound are less likely to experience a loss in mass. Therefore, the value obtained by dividing the change in mass within this temperature range by the amount of phosphorus derived from the phosphonate ester compound serves as an index representing the proportion of denatured / decomposed phosphonate ester compound. Therefore, it is believed that the smaller the value of the left side of the above formula (1), the lower the proportion of denatured / decomposed phosphonate ester compound present in the expanded beads.

[0049] The reason for using mass values ​​at temperatures of 215°C and 235°C in the thermogravimetric analysis is that if a lower temperature is used as the lower measurement temperature, the influence of moisture remaining in the expanded beads becomes greater, while if a higher temperature is used as the upper measurement temperature, the influence of the phosphonate ester becoming more likely to decompose becomes greater. In either case, the potential additional influence of different decomposition mechanisms and / or thermodynamic mechanisms occurring in parallel may be a factor that reduces the accuracy of the thermogravimetric measurement.

[0050] Experimental results surprisingly and reliably show that when expanded beads satisfy formula (1), i.e., when the result is 35 or less, the expanded beads exhibit good flame retardancy, particularly improved flame retardancy compared to conventional expanded beads. The value of the left side of formula (1) is preferably 34 or less, more preferably 33 or less, more preferably 32 or less, more preferably 31 or less, more preferably 30 or less, more preferably 29 or less, more preferably 28 or less, more preferably 27 or less, more preferably 26 or less, more preferably 25 or less, more preferably 24 or less, more preferably 23 or less, more preferably 22 or less, more preferably 21 or less, more preferably 20 or less, more preferably 19 or less, more preferably 18 or less, more preferably 17 or less, more preferably 16 or less, more preferably 15 or less, more preferably 14 or less, more preferably 13, more preferably 12 or less, more preferably 11 or less, more preferably 10 or less, more preferably 9 or less, more preferably 8 or less, more preferably 7 or less, more preferably 6 or less, and more preferably 5 or less. Meanwhile, the value of the left side of formula (1) may be 0 or 1. Therefore, the range of the value on the left side can be, for example, between 0 and 35, or between 1 and 34. The aforementioned ranges can also represent interval thresholds. For example, the value can be between 5 and 35, or between 7 and 29, or between 16 and 24, etc. In general, experimental results surprisingly show that when the value is in the range of 1 to 35, the expanded beads exhibit good flame retardancy.

[0051] Expanded particles satisfying the above formula (1) can satisfy at least one of the following UL94 rating classifications: HBF, HF-2, HF-1, V-2, V-1, and V-0. Expanded particles satisfying formula (1) can also exhibit good flammability according to other flammability standards.

[0052] Thermogravimetric measurements to determine the mass of the expanded beads measured in thermogravimetric measurements at 215°C and 235°C, respectively, can be carried out using approximately 15 mg of ground sample in an inert gas atmosphere, for example, 100% nitrogen, at a heating rate of 10°C / min, using a single measurement program with controlled temperature gradient starting at 40°C and ending at 800°C. Thermogravimetric measurements to determine the mass of the expanded beads measured in thermogravimetric measurements at 215°C and 235°C, respectively, can be carried out using a thermogravimetric analyzer available from Mettler-Toledo GmbH (35396 Giessen, Germany) under the designation "TGA 2" or a "Microbalance XP5" also available from Mettler-Toledo GmbH. Similar thermogravimetric analyzers can also be generally used. Grinding of the sample prior to analysis can be carried out using a cryogenic centrifugal grinder available under the designation "Ultra Centrifugal Mill ZM 200" from Retsch GmbH, Retsch-Allee 1-5, 42781 Haan, Germany.

[0053] Measurements to determine the phosphorus content (P) of the expanded beads can be performed using an ICP-OES spectrometer by inductively coupled plasma atomic emission spectroscopy. Measurements to determine the phosphorus content (P) of the expanded beads can be performed using a test sample with a mass of 0.1 g ± 0.1 mg. First, a solution of the test sample in 6 ml of concentrated nitric acid is placed in a sealed fluororesin (tetrafluoromethoxyl: TFM®) reactor placed in a microwave oven for sample mineralization. The microwave mineralization equipment is operated under the following conditions: the test sample solution is heated from room temperature to 220°C over 30 minutes, and then maintained at that temperature for 20 minutes. After mineralization, the reactor is rinsed with Milli-Q® water, and the homogenized solution is transferred to a 50 ml volumetric flask by increasing the volume. Depending on the phosphorus content of the sample, the resulting solution is diluted to different volumes and then transferred to an ICP-OES spectrometer to measure the amount of phosphorus contained in the solution. The phosphorus content P of the expanded beads is calculated from the relationship between the measured amount of phosphorus and the mass of the expanded beads used as the measurement sample. As the ICP-OES spectrometer, a spectrometer sold under the name "Activa M" by HORIBA Europe GmbH (61440 Oberursel, Germany) can be used. Similar ICP-OES spectrometers can also be generally used.

[0054] Optionally, when the phosphorus content P of the expanded beads is very low, for example, when the phosphorus content P of the expanded beads is less than 1% by mass, the above formula (1) can take into account an offset coefficient OC. This offset coefficient takes into account that when heated from 215°C to 235°C, a portion of the polyolefin resin is thermally decomposed during measurement. As an example, research has shown that when a polyolefin resin is heated from 215°C to 235°C, it loses approximately 0.03% by mass of its mass during measurement. Therefore, an exemplary offset coefficient can be numerically set to 0.0001 to 0.0005, preferably 0.0002 to 0.0004, and more preferably 0.0003. When the phosphorus content P of the expanded beads is less than 1% by mass, it is preferable to apply the offset coefficient OC. In this case, in the above formula (1), {(m ２１５ -m２３５ ) / m ２１５} value by OC, and add 100 / P to that value. ｔｏｔ It is preferable to use the value obtained by multiplying by the above formula (1) as the left side of the formula (1).

[0055] Generally, when the phosphorus content P of the expanded beads is 1% by mass or more, it is not necessary to use the offset coefficient OC, because the mass loss due to thermal decomposition of the polyolefin resin is small compared to the mass loss due to the phosphonate ester compound that has been altered or decomposed, and such an offset coefficient can be ignored.

[0056] The phosphorus content P of the expanded beads is preferably in the range of 1 to 4.8 mass%, more preferably in the range of 1.5 to 4.8 mass%, and even more preferably in the range of 1.8 to 4.8 mass%, and preferably in the range of 1.8 to 4.4 mass%, and even more preferably in the range of 1.8 to 3.6 mass%.

[0057] When the phosphorus content P is within the aforementioned range, the expanded beads have good properties, particularly the desired flame retardancy. In particular, by setting the phosphorus content P to a predetermined value or more, the flame retardancy of the molded body can be stably improved. Furthermore, by setting the phosphorus content P to a predetermined value or less, the in-mold moldability of the expanded beads can be easily improved. Furthermore, from the viewpoint of easily obtaining expanded beads that have good fusion properties between the expanded beads and can be used to produce expanded bead molded bodies with good flame retardancy, the phosphorus content P of the expanded beads is preferably in the range of 1% by mass or more and 3.2% by mass or less, and more preferably 1.5% by mass or more and less than 3.0% by mass.

[0058] In an exemplary embodiment, the expanded beads may further contain a NOR hindered amine compound. The NOR hindered amine compound may form a flame retardant or a part of the flame retardant, and therefore may affect the flame retardancy of the expanded beads. The amount of the NOR hindered amine compound in the expanded beads is preferably 0.1 to 5 mass %, more preferably 0.3 to 4 mass %, and even more preferably 0.5 to 3 mass %. When the expanded beads contain a NOR hindered amine compound and the amount of the NOR hindered amine compound in the expanded beads is 3 mass % or less, the expanded beads can have good fusion properties while improving the flame retardancy of the resulting molded article.

[0059] In particular, the phosphorus content P of the expanded beads can be in the range of 1 to 4.8% by mass, and the blending amount of the NOR type hindered amine compound can be in the range of 0.1 to 5% by mass.

[0060] In an exemplary embodiment, the total amount of polyolefin-based resin in the expanded beads is at least 80% by weight. It is particularly preferred that the total amount of polyolefin-based resin in the expanded beads is greater than 82% by weight, and even more preferably greater than 85% by weight. When the total amount of polyolefin-based resin is equal to or greater than this threshold, expanded beads with excellent flame retardancy and good fusion properties can be produced with a relatively small amount of flame retardant.

[0061] In a further exemplary embodiment, the expanded beads further comprise a phenolic antioxidant. The amount of the phenolic antioxidant in the expanded bead compound can be in the range of 0.01 to 0.5 wt %, particularly 0.02 to 0.3 wt %, and more preferably 0.03 to 0.2 wt %. In particular, the phosphorus content P of the expanded beads can be in the range of 1 to 4.8 wt %, and the amount of the phenolic antioxidant can be in the range of 0.01 to 0.5 wt %.

[0062] The amount of the phosphonate ester compound in the expanded beads is preferably 1% by mass or more and 15% by mass or less, more preferably 2% by mass or more and 13% by mass or less, and even more preferably 3% by mass or more and 12% by mass or less. In this case, the density of the expanded beads is 120 kg / m ３Even in the case of expanded beads having a low bulk density, such as those described below, it is possible to obtain expanded beads that exhibit good fusion between the expanded beads and that can be used to produce expanded bead moldings having good flame retardancy. Furthermore, from the viewpoint of further improving fusion between the expanded beads during in-mold molding, the total amount of the phosphonate ester compound and the NOR hindered amine compound in the expanded beads is preferably 15% by mass or less, and more preferably 14% by mass or less. The lower limit of the total amount of the phosphonate ester compound and the NOR hindered amine compound in the expanded beads is preferably 1% by mass, more preferably 3% by mass, and even more preferably 5% by mass. Furthermore, the melting point of the phosphonate ester compound is preferably in the range of 200 to 300°C. The melting point of the phosphonate ester compound can be measured in accordance with JIS K 0064:1992.

[0063] In an exemplary embodiment, the phosphonate ester compound preferably comprises a cyclic phosphonate ester compound represented by the following general formula (1):

[0064] In general formula (1), R １ and R ２ each represents a hydrocarbon group, and R １ and R ２ Preferably, each represents a methyl group.

[0065] A specific, non-limiting example of a cyclic phosphonate ester compound is the flame retardant available under the name "Aflammit® PCO 900" from Thor GmbH, 67329 Speyer, Germany.

[0066] In general formula (1), R １ and R ２ may be the same or different, and are preferably the same. １ is preferably an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a benzyl group, a phenylethyl group, or a naphthyl group, more preferably an alkyl group having 1 or 2 carbon atoms, and more preferably a methyl group. ２is preferably 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, more preferably an alkyl group having 1 or 2 carbon atoms, and even more preferably a methyl group.

[0067] Generally, the cyclic phosphonate ester compound may be any compound containing one or more cyclic phosphonic acid moieties in the molecule, and is preferably selected from the group consisting of compounds represented by the above 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). The amount of the cyclic phosphonate ester compound in the expanded beads is preferably 1% by mass or more and 15% by mass or less, more preferably 2% by mass or more and 13% by mass or less, and even more preferably 3% by mass or more and 12% by mass or less. The pentaerythritol diphosphonate represented by the above general 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.

[0068] In general formula (3) or (4), R ４ , R ８ , R ９ and R １２ represents an alkyl group having 1 to 4 carbon atoms, and R ５ and R ７ each represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ６ and R １０ respectively represent 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.

[0069] In general formula (2), R ３ is preferably an alkyl group having 1 to 22 carbon atoms or an aryl group having 6 to 15 carbon atoms, and more preferably a phenyl group.

[0070] In general formula (3), R ４ and R ８may be the same or different, and are preferably the same. ４ is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably a methyl group. ８ is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably a methyl group. ５ and R ７ may be the same or different, and are preferably the same. ５ is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and more preferably an ethyl group. ７ is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and more preferably an ethyl group. ６ is preferably 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 more preferably a linear alkyl group having 1 to 12 carbon atoms.

[0071] In general formula (4), R ９ and R １２ may be the same or different, and are preferably the same. ９ is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably a methyl group. １２ is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably a methyl group. １０ is preferably 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 more preferably a linear alkyl group having 1 to 12 carbon atoms. １１ is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and more preferably an ethyl group.

[0072] Furthermore, the NOR-type hindered amine compound preferably has 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 general formula (5). In this case, the flame retardancy of the expanded beads can be further improved:

[0073] In general formula (5), R １３ represents a hydrocarbon group.

[0074] When one molecule of the NOR-type hindered amine contains two or more hindered amine moieties represented by the general formula (5), the plurality of R １３ may be the same or different, but multiple R １３ are preferably the same.

[0075] R 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.

[0076] R １３ When R is a cycloalkyl group, １３ is more preferably a cycloalkyl group having 4 to 10 carbon atoms, and more preferably a cyclohexyl group.

[0077] The NOR type hindered amine compounds may be used alone or in combination of two or more.

[0078] The molecular weight of the NOR hindered amine compound is preferably 600 or more, more preferably 1500 or more. This makes it easier to suppress so-called bleed-out from a molded article produced by molding the expanded beads. In order to improve the dispersibility of the NOR hindered amine compound in a polyolefin resin, the molecular weight of the NOR hindered amine compound is preferably 3000 or less, more preferably 2500 or less.

[0079] The number of 2,2,6,6-tetramethyl-4-piperidinamine moieties represented by the general formula (5) in the NOR type hindered amine compound is preferably 2 to 8, more preferably 2 to 6, and even more preferably 2 or 6.

[0080] A specific example of the NOR type hindered amine compound is available from BASF Japan Ltd. (Tokyo, Japan) under the name "Flamestab NOR 116."

[0081] The phenol-based antioxidant includes an antioxidant having one or more phenol structures in the molecule, each of which has one or more hydroxyl groups bonded to an aromatic ring. The phenol-based antioxidant is preferably an antioxidant having two or more phenol structures in the molecule, and more preferably an antioxidant having three or more phenol structures in the molecule.

[0082] At high temperatures (e.g., 180°C or higher) such as in the process of melt-kneading a polyolefin resin, decomposition of the polyolefin resin can occur in a relatively short time. The phenolic antioxidant is a compound that can inhibit the decomposition of the polyolefin resin in a short time at such high temperatures.

[0083] Specific examples of phenolic antioxidants include 1,3,5-trimethyl-2,4,6-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)benzene, 2,6-di-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.

[0084] The melting point of the phenolic antioxidant is preferably 50° C. to 350° C. in order to obtain a molded article having higher flame retardancy by molding the expanded beads. More preferably, the melting point of the phenolic antioxidant is 80° C. or higher and 330° C. or lower, even more preferably 100° C. or higher and 320° C. or lower, even more preferably 150° C. or higher and 310° C. or lower, and still more preferably 200° C. or higher and 300° C. or lower. The melting point of the phenolic antioxidant can be measured in accordance with JIS K 0064:1992.

[0085] The difference between the melting point of the phenolic antioxidant and the melting point of the phosphonate ester compound can be −150° C. or higher and 150° C. or lower, preferably −100° C. or higher and +100° C. or lower, and more preferably −50° C. or higher and +50° C. or lower. When the difference between the melting point of the phenolic antioxidant and the melting point of the phosphonate ester compound is within the above range, expanded beads with improved flame retardancy can be obtained.

[0086] In an embodiment in which the expanded beads further contain a NOR hindered amine and a phenolic antioxidant, the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound in the expanded beads is preferably 0.03 to 0.9, more preferably 0.04 to 0.9, more preferably 0.06 to 0.9, more preferably 0.07 to 0.9, and even more preferably 0.14 to 0.9. The ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound in the expanded beads is more preferably 0.04 to 0.5, and even more preferably 0.06 to 0.3.

[0087] Specifically, the aforementioned ratio is believed to be beneficial for the following reasons. It is believed that the NOR hindered amine compound exhibits high flame retardancy when used in combination with a phosphonic acid ester compound. However, if the expanded beads contain a large amount of the NOR hindered amine compound, the fusion strength of the molded article obtained by in-mold molding of the expanded beads tends to decrease. On the other hand, if the amount of the NOR hindered amine compound is too small, it becomes difficult to impart high flame retardancy to the molded article obtained by in-mold molding of the expanded beads. Therefore, by using a phenolic antioxidant and a NOR hindered amine compound in combination in specific amounts and specific ratios, it is possible to impart high flame retardancy to the molded article even when the amount of the NOR hindered amine compound is low. As described above, by using a phenolic antioxidant and a NOR hindered amine compound in combination in specific amounts and specific ratios, 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 possible to impart high flame retardancy to the molded article even when the amount of the NOR hindered amine compound is reduced. Furthermore, since phenolic antioxidants do not inhibit the fusion of the expanded beads during molding, the incorporation of a phenolic antioxidant can enhance the flame retardancy of the molded article while reducing the amount of NOR-type hindered amine compound added. Therefore, it is believed that the expanded beads can be sufficiently fused together during molding. As a result, it is believed that molding the expanded beads can produce a molded article with high flame retardancy, excellent fusion properties, and excellent structural properties.

[0088] In a further exemplary embodiment, the expanded beads may further comprise at least one sulfur-based antioxidant. The sulfur-based antioxidant may have a positive effect on the thermal stability of the expanded beads. The amount of the sulfur-based antioxidant is preferably 0.01 to 0.5% by weight, more preferably 0.02 to 0.3% by weight, and even more preferably 0.03 to 0.2% by weight. In particular, the phosphorus content P of the expanded beads may be in the range of 0.8 to 4.8% by weight, and the amount of the sulfur-based antioxidant may be in the range of 0.01 to 0.5% by weight.

[0089] In an exemplary embodiment in which the expanded beads further contain a sulfur-based antioxidant and a NOR hindered amine compound, the ratio of the amount of sulfur-based antioxidant to the amount of NOR hindered amine compound can be 0.03 to 0.9. When this ratio is 0.03 or greater, molded articles with excellent mechanical properties, such as compressibility, are more likely to be obtained, even when placed in a high-temperature environment for a long period of time. Preferably, the ratio of the amount of sulfur-based antioxidant to the amount of NOR hindered amine compound is 0.07 or greater, particularly 0.11 or greater, and more particularly 0.14 or greater. On the other hand, when the ratio is 0.9 or less, molded articles with high flame retardancy are more likely to be obtained while improving the fusion properties of the expanded beads themselves. From this perspective, the ratio is preferably 0.07 to 0.8, more preferably 0.11 to 0.7, and even more preferably 0.14 to 0.6.

[0090] Examples of sulfur-based antioxidants 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.

[0091] The expanded particles are 10 to 500 kg / m ３ In an exemplary embodiment, the expanded particles may have a bulk density of 10 to 200 kg / m ３ In particular, the expanded particles may have a bulk density of 20 kg / m ３ or more, 30 kg / m ３ or more, 40 kg / m ３ or more, 50 kg / m ３or more, 60 kg / m ３ or more, and 70 kg / m ３ or more, and ３ or more, and ３ or more, 100 kg / m ３ or more, 110 kg / m ３ The bulk density of the expanded beads may be 180 kg / m or more. ３ may be less than 150 kg / m ３ may be less than 130 kg / m ３ may be less than 120 kg / m ３ The above-mentioned numerical examples are also examples of preferred bulk density values, since they enable the molding of lightweight molded articles with good flame retardancy and fusion properties. The above-mentioned ranges can also represent interval thresholds. For example, the bulk density is 20 to 200 kg / m ３ , 30-150kg / m ３ , or 80 to 130 kg / m ３ The range can be:

[0092] The bulk density of expanded beads can be measured by the following method. First, the expanded beads to be used for measurement are allowed to stand for 24 hours or more in an environment of 23°C, 50% relative humidity, and 1 atmosphere to condition the expanded beads. After conditioning, a sample of expanded beads with a mass W (g) is packed into a cylinder so as to naturally pile up, and the bottom of the cylinder is lightly struck against a horizontal surface several times to stabilize the packed height of the expanded beads in the cylinder. The bulk volume V (L) of the expanded beads indicated by the scale on the cylinder is read, and the mass W of the expanded beads is divided by the bulk volume V of the expanded beads (W / V) to obtain the bulk density (kg / m) of the expanded beads by unit conversion. ３ ) is required.

[0093] In an exemplary embodiment, the expanded beads defined herein preferably have a melting peak specific to the polyolefin resin (resin-specific peak) and one or more melting peaks (high-temperature peaks) on the high-temperature side of the resin-specific peak in a differential scanning calorimetry (DSC) curve measured in accordance with JIS K7122-2012. These melting peaks can be obtained by the following method.

[0094] 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. The peak with the largest heat of fusion is the melting peak specific to the polyolefin resin, i.e., the resin-specific peak, and one or more melting peaks appearing at higher temperatures are high-temperature peaks. The DSC curve refers to the curve obtained by heating the expanded beads using the above measurement method (the DSC curve in the first heating). The resin-specific peak refers to an endothermic peak that occurs due to the melting of crystals specific to the polyolefin resin that constitutes the expanded beads. In other words, the resin-specific peak is considered to be an endothermic peak that appears due to the melting of crystals that the polyolefin resin that constitutes the expanded beads normally has.

[0095] The following method can be used to determine the peak corresponding to the resin-specific peak or the high-temperature peak: After heating the expanded beads from 23°C to 200°C at a heating rate of 10°C / min (first heating), the expanded beads are cooled from 200°C to 23°C at a heating 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). The DSC curve obtained from the second heating only shows an endothermic peak due to the melting of crystals specific to the polyolefin resin constituting the expanded beads, and no high-temperature peak appears in the DSC curve from the second heating.

[0096] The resin-specific peak appears in both the DSC curve after the first heating and the DSC curve after the second heating, and although the peak apex temperatures may differ slightly between the first and second heatings, it is possible to identify which peak is the resin-specific peak. On the other hand, the high-temperature peak is one or more endothermic peaks that appear on the higher temperature side of the resin-specific peak in the DSC curve after the first heating. When this high-temperature peak appears, it is estimated that secondary crystals exist in the polyolefin-based resin.

[0097] The heat of fusion of the high-temperature peak of the expanded beads is preferably in the range of 5 to 40 J / g, more preferably 6 to 30 J / g, and even more preferably 7 to 25 J / g. When the heat of fusion of the high-temperature peak of the expanded beads is in this range, expanded beads with a wide processing window can be easily obtained, and a good molded article can be obtained by molding. The heat of fusion of the high-temperature peak can be measured by the following method. On the DSC curve of the first heating, a straight line (α-β) is drawn connecting point α corresponding to 80°C on the DSC curve and point β on the DSC curve corresponding to the end temperature T of the melting of the expanded beads. The end temperature T of the melting is the high-temperature end point of the high-temperature peak, or, if multiple high-temperature peaks are present, the end point of the highest high-temperature peak, and a point on the baseline. Next, a straight line is drawn from point γ on the DSC curve parallel to the vertical axis of the graph. Point γ corresponds to the lowest heat point in the valley between the resin-specific peak and the high-temperature peak, or, if multiple high-temperature peaks are present, the lowest heat point in the valley between the resin-specific peak and the lowest high-temperature peak. The intersection of the line (α-β) and the line parallel to the vertical axis of the graph from the point γ is designated as δ. The heat of fusion of the high-temperature peak expressed in J / g corresponds to the heat of fusion calculated based on the area of ​​the high-temperature peak enclosed by the curve of the high-temperature peak portion of the DSC curve, the line segment (δ-β), and the line segment (γ-δ), divided by the mass of the expanded beads used in the experiment.

[0098] The expanded beads may have an average mass per particle (arithmetic mean mass per particle measured from 200 randomly selected particles) of 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.

[0099] In any embodiment, the expanded beads may contain one or more additional additives. Examples of such additional additives include various conventionally known additives such as other antioxidants, ultraviolet absorbers that absorb ultraviolet light, light stabilizers that absorb light with a wavelength of 300 to 400 μm, antistatic agents, colorants such as pigments and dyes, fillers, conductive fillers, and cell regulators. These additives can be incorporated into the expanded beads by adding them, for example, during the production process of the expanded beads.

[0100] Specific examples of the cell regulator include talc, 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 as the cell regulator, and zinc borate is more preferably used. The amount of metal borate in the resin particles used to form the expanded particles is preferably 0.005 to 0.5% by mass, more preferably 0.01 to 0.2% by mass, and even more preferably 0.015 to 0.15% by mass.

[0101] When zinc borate is used or present, it is desirable that the number-based arithmetic mean particle size is 0.5 to 15 μm, preferably 1 to 10 μm. The average particle size of zinc borate can be determined by converting the volume-based particle size distribution measured by laser diffraction scattering to a number-based particle size distribution assuming the particle shape is spherical, and then arithmetically averaging the particle sizes based on this number-based particle size distribution. The particle size is determined by arithmetically averaging the particle sizes based on this number-based particle size distribution. The particle size refers to the diameter of a hypothetical sphere having the same volume as the particle.

[0102] When the expanded particles contain a colorant, red, blue, green, yellow, or purple pigments or dyes can be used. The pigments or dyes can be inorganic or organic. Examples of inorganic pigments or dyes 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 flagellum; and silicates such as blue. Examples of organic pigments include azo pigments such as monoazo pigments, diazo pigments, azo lakes, condensed azo pigments, and chelated azo pigments, as well as polycyclic pigments such as phthalocyanines, anthraquinones, perylenes, perinones, thioindigo, quinacridones, dioxazines, isoindolinones, and quinophthalones.

[0103] When a uniform black or gray appearance of the expanded beads is desired, iron oxide, titanium black, or carbon particles are preferably used as the pigment. Carbon particles are particles made of carbon, and examples thereof include one or more materials selected from carbon black, conductive carbon, carbon nanotubes, graphene, graphite, activated carbon, etc. Among these, carbon black is preferred from the viewpoints of excellent dispersibility in polyolefin resins and cost balance. Specific examples of carbon black include channel black, roller black, furnace black, thermal black, acetylene black, and ketjen black.

[0104] When a colorant is blended, the amount of the colorant blended in the expanded beads is preferably 0.01 to 6% by mass, more preferably 0.1 to 5% by mass, and even more preferably 0.5 to 4% by mass, in order to maintain uniform coloring without impairing flame retardancy.

[0105] When the molded article formed from the expanded beads is colored using the above-mentioned coloring agents, carbon black, titanium oxide, talc, calcium carbonate, magnesium hydroxide, magnesium carbonate, or a combination thereof can be added to adjust the brightness of the color and make the appearance of the molded article uniform.

[0106] When an ultraviolet absorber is used or present, examples of the ultraviolet absorber include benzophenone compounds, benzotriazole compounds, triazine compounds, and benzoic acid compounds. Benzophenone compounds include 2-hydroxy-4-octyloxybenzophenone, and 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, and 2-(3,5-di-t-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole. Examples of triazine compounds include 2-(3,5-di-t-amyl-2-hydroxyphenyl)benzol, 2-(3,5-di-amyl-2-hydroxyphenyl)benzotriazole, 2-(2'-hydroxy-5'-octylphenyl)benzotriazole, etc. Examples of triazine compounds include 2-[4,6-diphenyl-1,3,5-triazin-2-yl]-5-(hexyloxy)phenol, and 2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-benzoic acid ester compounds include 2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoic acid ester and hexadecyl-3,5-di-t-butyl-4-hydroxybenzoic acid ester. The amount of the ultraviolet absorber in the expanded beads can be in the range of 0.01 to 2% by mass, preferably 0.05 to 1.5% by mass, and more preferably 0.1 to 1% by mass.

[0107] Examples of light stabilizers include hindered amine compounds (HALS). Examples of hindered amine compounds include compounds having a 2,2,6,6-tetramethyl-4-piperidinamine moiety in which the only atom directly bonded to the nitrogen atom is hydrogen or carbon. The amount of light stabilizer in the expanded beads is preferably 0.01 to 2% by mass, more preferably 0.05 to 1.5% by mass, and more preferably 0.1 to 1% by mass.

[0108] As further described above, the expanded beads are composed of a foam layer. Alternatively, the expanded beads may be composed of a foam layer and at least one covering layer disposed on the foam layer. Such expanded beads can be considered multi-layer expanded beads consisting of a foam layer as a core layer and at least one covering layer covering the core layer. The covering layer can be a resin layer, particularly a polyolefin-based resin layer such as a polyethylene-based resin layer or a polypropylene-based resin layer. In each multi-layer expanded bead, the at least one covering layer may cover a portion of the foam layer or the entire foam layer.

[0109] When the coating layer is a resin layer such as a polyolefin-based resin layer, the melting point of the resin component constituting the coating layer is preferably lower than the melting point of the resin component constituting the foamed layer. It is also preferable that the coating layer is a substantially non-foamed resin layer. In this case, a molded article having good mechanical strength can be stably provided.

[0110] The at least one coating layer may contain a phosphonate ester compound, a NOR hindered amine compound, a phenolic antioxidant, and a sulfuric acid antioxidant in the same proportion as in the foamed layer, in a proportion different from that in the foamed layer, or none of them may be used. At least one of the cyclic phosphonate ester compound, the NOR hindered amine compound, the phenolic antioxidant, and the sulfuric acid antioxidant may be selected and blended in the at least one coating layer.

[0111] It is preferable that the sum of the amount of the phosphonate ester compound and the amount of the NOR hindered amine compound in the coating layer is smaller than the sum of the amount of the phosphonate ester compound and the amount of the NOR hindered amine compound in the foam layer. It is also preferable that the amount of the phosphonate ester compound in the coating layer is smaller than the amount of the phosphonate ester compound in the foam layer, and it is more preferable that the amount of the NOR hindered amine compound in the coating layer is smaller than the amount of the NOR hindered amine compound in the foam layer. When the amounts of both the phosphonate ester compound and the NOR hindered amine compound in the coating layer are small, the fusion properties of the expanded beads during molding are improved, and moldability can be further enhanced. It is preferable that at least one coating layer does not contain either a phosphonate ester compound or a NOR hindered amine compound.

[0112] The ratio of the mass of the components constituting the foam layer to the mass of the components constituting the coating layer is preferably 99:1 to 70:30, more preferably 98:2 to 80:20, and even more preferably 97:3 to 85:15.

[0113] A second aspect of the present invention relates to a molded article formed from the expanded beads according to the first aspect of the present invention. The molded article can therefore be a foamed article. The molded article can be a vehicle part, i.e., a part to be placed in a vehicle, such as a part for an automobile, an aircraft, a personal watercraft, etc. More specific, but non-limiting, examples include molded articles formed by in-mold molding of the expanded beads, which are casing elements, housing elements, and protective elements for battery devices, electrical devices, electronic devices, etc.

[0114] The molded article is a molded article of the expanded beads obtained by molding the expanded beads in a mold. The molded article is composed of a foam structure having a polyolefin-based resin as a base resin. As explained in the section on expanded beads, examples of polyolefin-based resins include polypropylene-based resins, polyethylene-based resins, and blended resins of polypropylene-based resins and polyethylene-based resins. By molding expanded beads having the aforementioned bulk density in a mold, it is possible to obtain a foam having a density of, for example, 10 to 500 kg / m. ３The density of the compact can be 20 kg / m ３ or more, 30 kg / m ３ The density of the compact may be 200 kg / m or more. ３ or less, 150 kg / m ３ or less, 130 kg / m ３ or less, 120 kg / m ３ It may be the following:

[0115] The molding process for producing a molded article can be carried out by filling a mold with expanded beads and heat-molding them. Specifically, after filling the mold with expanded beads, the expanded beads are heated to cause secondary expansion of the expanded beads and to fuse the expanded beads together, thereby obtaining a molded article having the shape of the cavity of the mold. Examples of methods for heating the expanded beads include a method of introducing a heating medium such as steam into the mold and heating the expanded beads with the heating medium, a method of irradiating the expanded beads with electromagnetic waves such as high frequency waves, a method of introducing a specific adhesive (e.g., ATECARMA (trademark)) to bond the particles, a method of conductively heating the mold without introducing steam into the cavity to fuse the particles in the mold, and a combination of these methods.

[0116] The method for filling the foamed beads into the mold can be any known method. For example, there is a method in which the foamed beads are directly compressed into a pressurized mold with pressurized gas and then the pressure inside the mold is released (pressure filling method), and there is a method in which the foamed beads are mechanically compressed by first opening the mold to expand the molding space, then filling the mold with the foamed beads, and then closing the mold after filling (cracking filling method). It is also possible to pressurize the foamed beads with pressurized gas before filling, thereby applying a predetermined internal pressure to the cells of the foamed beads and imparting a certain degree of additional expandability to the foamed beads.

[0117] A third aspect of the present invention relates to a method for producing expanded polyolefin resin beads. This method generally includes the following steps: preparing a component (A) containing a polyolefin resin; and preparing a component (B) containing a phosphonate ester compound. This production method includes treating a mixture of the components (A) and (B) in the presence of a blowing agent at a specific temperature and / or a specific pressure for a specific period of time, thereby producing expanded polyolefin resin beads. The expanded polyolefin resin beads satisfy the following formula (1): {(m ２１５ -m ２３５ ) / m ２１５}×100 / P ｔｏｔ ≦35 (1) In formula (1), m ２１５ is the mass of the expanded beads measured by thermogravimetry at 215 ° C; m ２３５ is the mass of the expanded beads measured by thermogravimetry at 235°C; P ｔｏｔ is a numerical value indicating the mass fraction of phosphorus in the expanded beads, and is in the range of 0.001 to 0.06.

[0118] Component (A) is preferably a polyolefin resin. Also, component (B) is preferably a phosphonate ester compound. For the polyolefin resin and the phosphonate ester compound, the explanations regarding the polyolefin resin and the phosphonate ester compound in the first embodiment can be referred to as appropriate. The method for mixing components (A) and (B) to obtain a mixture of components (A) and (B) is not particularly limited, but a known extrusion molding method can typically be referred to. The mixture of components (A) and (B) can be produced separately, for example, in the first step of producing polyolefin resin particles. Then, in a subsequent step such as an autoclave step, the produced mixture (polyolefin resin particles) is treated in the presence of a blowing agent under a specific temperature and / or pressure to produce expanded polyolefin resin particles.

[0119] Alternatively, for example, as in the extrusion foaming method described below, a mixture of component (A) and component (B) is formed in the same process, a foaming agent is added to the mixture, and the mixture is treated under a specific temperature and / or pressure, thereby producing expanded polyolefin resin beads.

[0120] In particular, the blending amount of component (B) in the mixture is preferably 3 to 20 mass%, more preferably 5 to 18 mass%, and even more preferably 7.5 to 15 mass%. When the content of component (B) is within the above range, the expanded beads produced by this method have good properties, particularly with regard to the desired flame retardancy. Furthermore, the blending amount of component (A) in the mixture is preferably 80 mass% or more, preferably 82 mass% or more, and even more preferably 85 mass% or more.

[0121] In general, the mixture of components (A) and (B) can also include one or more other additives, examples of each of which are further disclosed in the exemplary embodiments above.

[0122] Generally, when processing polyolefin resins and phosphonate ester compounds to produce expanded beads, the raw materials are melt-mixed in an extruder, extruded into strands, and cut to a predetermined length to produce resin particles. These resin particles are then placed in a pressure vessel together with an aqueous dispersion medium such as water, heated appropriately, and released into a relatively low-pressure environment for expansion. During this series of steps, the polyolefin resin is melt-mixed with the hygroscopic phosphonate ester compound, resulting in a significant increase in the hygroscopicity of the resin particles themselves. This increased hygroscopicity of the polyolefin resin reduces the proportion of closed cells in the resulting expanded beads, which in turn reduces the fusion properties of the expanded beads when molded, resulting in poor surface quality of the resulting expanded bead moldings. Surprisingly, the present inventors have discovered that when the method of treating a mixture of components (A) and (B) with a blowing agent according to the present invention at a specific temperature and / or pressure for a specific period of time is carried out using an aqueous liquid dispersion medium, the effects of moisture absorption on the expanded beads are reduced, as will be apparent from the examples of the present invention. The reduced moisture absorption effect of the expanded beads is believed to be related to milder temperature and / or pressure and / or residence time conditions when treating the resin particles for a specific period of time under a specific temperature and / or pressure, compared to prior art processes. Similarly, the inventors have surprisingly discovered that when the method of treating a mixture of components (A) and (B) containing a blowing agent for a specific period of time under a specific temperature and / or pressure according to the present invention is carried out in a process involving the use of an aqueous liquid dispersion medium, a larger amount of the phosphorus compound initially introduced when mixing components (A) and (B) remains in the resulting expanded beads with less degradation or decomposition, as is evident from the examples of the present invention. The milder temperature and / or pressure and / or residence time conditions during treatment of the resin particles under a specific temperature and / or pressure and / or period of time are believed to further reduce the leaching of hygroscopic phosphorus compounds from the resin particles into the aqueous liquid dispersion medium, compared to prior art processes.

[0123] In particular, the method of treating a mixture of components (A) and (B) in the presence of a blowing agent under application of a specific temperature for a specific time comprises heating the mixture of components (A) and (B) in the presence of a blowing agent to a specific temperature of at least 80°C, more preferably 100°C, and holding the mixture at this specific temperature for preferably 60 minutes or less, more preferably 50 minutes or less, more preferably 45 minutes or less, more preferably 40 minutes or less, and more preferably 35 minutes or less. In other words, application of the specific temperature can comprise application of a temperature of at least 80°C, preferably 100°C, for preferably 60 minutes or less, more preferably 50 minutes or less, more preferably 45 minutes or less, more preferably 40 minutes or less, and more preferably 35 minutes or less. The specific temperature can be applied in the range of 80 to 180°C, particularly 80 to 160°C.

[0124] The temperature of at least 80°C in the above-mentioned production method is selected taking into consideration the decomposition temperature of the phosphonate ester compound and / or the melting of the crystals of the polyolefin resin (crystalline polyolefin resin). Test results have shown that the decomposition of the phosphonate ester compound is significantly more likely to occur at temperatures of 80°C or higher. Furthermore, although this depends on the type of polyolefin resin, at this temperature, the low-melting-point crystalline component of the polyolefin resin also tends to begin to melt. Therefore, the desired results can be obtained by selecting 80°C as the specific temperature for heating the mixture of components (A) and (B) in the presence of a blowing agent and treating it for the time range described below.

[0125] The temperature in the production method can be applied for a period of preferably 10 to 60 minutes, more preferably 20 to 50 minutes, even more preferably 25 to 45 minutes, and even more preferably 25 to 35 minutes. When the time is within the above range, the phosphonate ester compound contained in component (B) is exposed to severe degradation conditions for a short period of time, which is believed to enable the mixture to be foamed well while reducing degradation of the phosphonate ester compound contained in component (B). The temperature and time in the production method are particularly applicable when the mixture of components (A) and (B) and the blowing agent are in an autoclave, particularly in the presence of an aqueous or non-aqueous liquid dispersion medium, such as water or (silicone) oil, respectively. The temperature and time in the production method are also applicable to the mixture containing the blowing agent, for example, when the mixture of components (A) and (B) containing the blowing agent is heated in the absence of a liquid dispersion medium.

[0126] In particular, the method comprises treating a mixture of components (A) and (B) in the presence of a blowing agent under application of a specific temperature for a specific period of time, including heating the mixture of components (A) and (B) in the presence of the blowing agent to a specific foaming temperature of at least 100°C and holding the mixture at the specific foaming temperature for a specific period of time. During heating and holding the mixture at the specific foaming temperature, the mixture is exposed to a temperature of at least 80°C for a period of 60 minutes or less. Thus, when treating by heating the mixture in the presence of a blowing agent to and holding the specific foaming temperature, the mixture is exposed to a temperature of at least 80°C for a period of 60 minutes or less.

[0127] The specific pressure (gauge pressure) applied in the production method is preferably in the range of 0.1 to 10 MPa (G), more preferably in the range of 0.2 to 7.5 MPa (G), even more preferably in the range of 0.3 to 5 MPa (G), still more preferably in the range of 0.4 to 5 MPa (G), and even more preferably in the range of 0.5 to 4.5 MPa (G). The pressure is preferably applied for a period in the range of 10 to 60 minutes, more preferably in the range of 20 to 50 minutes, even more preferably in the range of 25 to 45 minutes, and still more preferably in the range of 25 to 35 minutes. When the time for which the pressure is applied is within the above range, the phosphonate ester compound contained in component (B) is exposed to severe degradation conditions for a short period of time, and it is therefore believed that the mixture can be well foamed while reducing degradation of the phosphonate ester compound contained in component (B). The pressure and time in the above-mentioned manufacturing method can be applied to the mixture of components (A) and (B) and the blowing agent when the mixture is in an autoclave, particularly in the presence of an aqueous or non-aqueous liquid dispersion medium, such as water or (silicone) oil.The pressure and time in the above-mentioned manufacturing method can also be applied to the mixture in a pressure vessel, for example, when the mixture of components (A) and (B) and the blowing agent is in a pressure vessel in the absence of a liquid dispersion medium.

[0128] The mixture of components (A) and (B) can be treated in a liquid dispersion medium composed of a non-aqueous liquid. The mixture can be treated, for example, in an autoclave. Alternatively, the mixture can be treated without a liquid dispersion medium, for example, in a pressure vessel. When the mixture is treated in a non-aqueous liquid or without a liquid dispersion medium, the phosphonate ester compound contained in component (B) is thought to be less degraded because substantial water does not degrade the phosphonate ester compound.

[0129] An exemplary method for producing expanded beads includes a dispersing step of dispersing a mixture containing at least components (A) and (B) and, optionally, a NOR-type hindered amine compound and / or a phenolic antioxidant and / or a sulfur-based antioxidant and / or any of the respective further additives in an aqueous dispersion medium containing an inorganic solid dispersant in a container. This method also includes a foaming step of impregnating the mixture with a blowing agent under the influence of pressure and temperature, and a foaming step of releasing the mixture (resin particles) containing the blowing agent together with the aqueous medium from the container into a pressure atmosphere lower than the pressure in the container to foam the mixture.

[0130] Another exemplary method for producing expanded beads is a method for producing expanded beads by extrusion foaming using an extruder. Specifically, the method includes feeding component (A), component (B), and a blowing agent into an extruder and kneading them, extruding a resin melt containing the blowing agent from the downstream side of the extruder to foam, and cutting the extruded foam into particles to obtain expanded beads. This process is a non-limiting example of a one-stage process for producing expanded beads.

[0131] The two-stage process for producing polyolefin resin particles can be explained as follows. First, a mixture containing a polyolefin resin (component (A)), a phosphonate ester compound (component B), an optional NOR-type hindered amine compound, an optional phenolic antioxidant and / or a sulfur-based antioxidant, and optional additives is fed into an extruder and heated and kneaded to obtain a resin melt. Next, the resin melt is extruded from the extruder and pelletized by a method such as strand cutting, hot cutting, or underwater cutting to produce polyolefin resin particles. When producing multilayer polyolefin resin particles, a production apparatus including a core layer extruder, a multilayer strand forming die attached downstream of the core layer extruder, and a coating layer extruder can be used. The coating layer extruder is connected downstream to a multilayer strand forming die, allowing the resin melts formed by each extruder to be stacked within the die.

[0132] The average mass of the resin particles (average mass of additives per particle measured from the masses of 200 randomly selected particles) is adjusted to preferably 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.

[0133] In particular, the strand cutting method forms cylindrical resin particles. When the resin particles have a cylindrical outer shape, the particle length of the polyolefin resin particles in the extrusion direction is preferably 0.1 to 4.0 mm, more preferably 0.3 to 3 mm, and even more preferably 0.5 to 2.5 mm. The length-to-diameter ratio (length / diameter ratio) is preferably 0.5 to 5.0, more preferably 1.0 to 3.0. In the strand cutting method, the particle size, major axis / diameter ratio, and average mass of the resin particles can be adjusted by appropriately changing the extrusion speed, take-up speed, and cutter speed by cutting the strand during extrusion of the molten material.

[0134] A preferred method for producing expanded polyolefin-based beads is to disperse polyolefin-based resin particles composed of a mixture containing a phosphonate ester compound, particularly a cyclic phosphonate ester compound, a NOR-type hindered amine compound, a phenolic antioxidant, and a sulfur-based antioxidant in an aqueous dispersion medium containing a solid dispersant in a container, impregnate the polyolefin-based resin particles with a blowing agent in the container, and release the polyolefin-based resin particles containing the blowing agent together with the aqueous dispersion medium in an atmosphere under pressure lower than the pressure in the container, thereby producing expanded polyolefin-based resin beads.

[0135] As the dispersion medium for dispersing the resin particles in the container, an aqueous dispersion medium is preferably used. As the aqueous dispersion medium, an aqueous dispersion medium having a water content of preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more can be used. The aqueous dispersion medium may have a water content of 100% by mass. Examples of dispersion mediums other than water include ethylene glycol, glycerin, methanol, ethanol, and silicone oil. Examples of silicone oil include polydimethylsiloxane (PDMS).

[0136] In the dispersion step, a solid dispersant is preferably added to the dispersion medium to prevent fusion between polyolefin resin particles heated in the container. As the solid dispersant, either organic or inorganic solid dispersants can be used as long as they prevent fusion between polyolefin resin particles in the container. However, inorganic solid dispersants are preferred, and fine inorganic solid dispersants are more preferred due to ease of handling. Examples of inorganic solid dispersants include natural or synthetic clay minerals such as kaolin, mica, and clay, 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 clay minerals or synthetic clay minerals are preferred as solid dispersants. The amount of solid dispersant in the container is preferably in the range of 0.001 to 5% by mass relative to 100% by mass of the polyolefin resin particles introduced into the container.

[0137] When a solid dispersant is used, it is preferable to use an anionic surfactant such as sodium dodecylbenzenesulfonate, sodium alkylsulfonate, sodium oleate, etc. as a dispersing aid in combination. The dispersing aid is preferably added in an amount of about 0.001 to 1 part by mass per 100 parts by mass of polyolefin resin particles in the aqueous dispersion medium.

[0138] A physical blowing agent is preferably used as the blowing agent for expanding the polyolefin resin particles. The physical blowing agent may be either inorganic or organic. Examples of inorganic physical blowing agents include carbon dioxide, air, nitrogen, helium, and argon. Examples of organic physical blowing 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 blowing agents can be used alone. Alternatively, two or more types of blowing agents can be used in combination. Alternatively, inorganic and organic physical blowing agents can be used in combination. The blowing agent is preferably an inorganic physical blowing agent, which can improve the environmental impact and flame retardancy of molded articles formed from the expanded beads. As the inorganic physical foaming agent, for example, carbon dioxide can be used.

[0139] The amount of the foaming agent added is preferably in the range of 0.1 to 30% by mass, more preferably 0.5 to 15% by mass, based on 100% by mass of the polyolefin resin particles.

[0140] The method of impregnating the resin particles with the blowing agent is preferably carried out by dispersing the resin particles in an aqueous dispersion medium in a sealed container, for example, an autoclave, adding the blowing agent to the sealed container, pressurizing the inside of the container, and maintaining the sealed container at a predetermined temperature and pressure.

[0141] During the expansion step, the internal pressure in the container, i.e., the internal pressure in the container immediately before the resin particles are released together with the aqueous dispersion medium, is preferably 0.1 MPa (G) or more, more preferably 0.2 MPa (G) or more, and even more preferably 0.5 MPa (G) or more. The upper limit is preferably 5 MPa (G) or less, more preferably 4 MPa (G) or less. Within the above range, there is no risk of damage or explosion to the sealed container, and the desired expanded particles can be produced safely.

[0142] The expansion temperature is selected based on the polyolefin resin contained in the polyolefin resin particles. The temperature inside the container is raised to a set expansion temperature, and the temperature is maintained for 1 to 30 minutes. After that, the resin particles containing the blowing agent are released from the sealed container into an atmosphere (e.g., atmospheric pressure) at a pressure lower than the pressure inside the container, thereby producing expanded particles.

[0143] When the polyolefin resin particles are based on a polypropylene resin, the foaming temperature is preferably 160°C or lower, more preferably 155°C or lower, and even more preferably 150°C or lower.

[0144] When the polyolefin resin particles are based on a polyethylene resin, the foaming temperature is preferably 140° C. or lower, more preferably 135° C. or lower, and even more preferably 130° C. or lower.

[0145] By selecting a relatively low expansion temperature during the production of expanded beads, the resin particles are less likely to be exposed to an environment in which the phosphonate ester compound contained in component (B) is likely to deteriorate, thereby suppressing deterioration of the phosphonate ester compound contained in component (B). In other words, by selecting a polyolefin resin that allows for a (relatively) low expansion temperature, expanded beads that satisfy the following formula (1) are more likely to be obtained. When an aqueous liquid dispersion medium is used, it is preferable to select a relatively high expansion pressure, a relatively low expansion temperature, and a short time for exposure to water at 80°C or higher in the expansion step, in order to suppress deterioration of the phosphonate ester compound contained in component (B) and obtain expanded beads that satisfy the following formula (1). It is also preferable to perform the expansion step using a non-aqueous liquid dispersion medium or to perform the expansion step in the absence of an aqueous liquid dispersion medium, such as by infrared heating, in order to obtain expanded beads that satisfy the following formula (1). {(m ２１５ -m ２３５ ) / m ２１５}×100 / P ｔｏｔ ≦35 (1) In formula (1), m ２１５ is the mass of the expanded beads measured by thermogravimetry at 215 ° C; m ２３５ is the mass of the expanded beads measured by thermogravimetry at 235°C; Pｔｏｔ is a numerical value indicating the mass fraction of phosphorus in the expanded beads, and is in the range of 0.001 to 0.06.

[0146] The expanded polyolefin resin beads obtained as described above can be made into expanded beads with a high expansion ratio (low bulk density) in a secondary step. In the secondary step, the expanded polyolefin resin beads obtained as described above are pressurized with a pressurized fluid such as air or carbon dioxide to increase the pressure (internal pressure) within the cells of the foam layer, and then the pressurized expanded beads are heated with steam, high frequency, infrared heating, or the like to further expand (second-stage expansion).

[0147] A fourth aspect of the present invention relates to a method for at least qualitatively determining the flame retardant behavior of expanded beads according to the first aspect of the present invention, which method further comprises providing and determining the mass of each expanded bead in thermogravimetry at 215°C and 235°C and the phosphorus content P of the expanded bead based in particular on the respective TGA and spectroscopy measurements (inductively coupled plasma atomic emission spectroscopy) defined above, determining whether the phosphorus content P of the expanded bead is in the range of 0.1 to 6% by weight, and determining whether the expanded bead satisfies the following formula (1) when the phosphorus content P of the expanded bead is in the range of 0.1 to 6% by weight: {(m ２１５ -m ２３５ ) / m ２１５}×100 / P ｔｏｔ ≦35 (1) In formula (1), m ２１５ is the mass of the expanded beads measured by thermogravimetry at 215 ° C; m ２３５ is the mass of the expanded beads measured by thermogravimetry at 235°C; P ｔｏｔ is a numerical value indicating the mass fraction of phosphorus in the expanded beads, and is in the range of 0.001 to 0.06.

[0148] If the expanded beads satisfy the above formula (1), the expanded beads are determined to have sufficiently high flame retardant behavior; if not, the expanded beads are determined to not have sufficiently high flame retardant behavior. Sufficiently high flame retardant behavior can mean satisfying at least one of the following UL94 standard classifications: HB-F, HF-2, HF-1, V-2, V-1, and V-0. Thus, if the expanded beads satisfy formula (1), the expanded beads can satisfy at least one of the following UL94 standard classifications: HB-F, HF-2, HF-1, V-2, V-1, and V-0.

[0149] This method uses the aforementioned parameter m ２１５ , m ２３５ and P ｔｏｔ The method may be performed, at least in part, under the control of a hardware and / or software-implemented controller that uses input parameters such as the above to determine whether equation (1) above is satisfied. The results of the determination may be output to a user and / or another hardware and / or software-implemented functional device.

[0150] All comments relating to the expanded particles of the first aspect of the invention also apply to the components of the second aspect of the invention and / or the process of the third aspect of the invention and / or the process of the fourth aspect of the invention, and vice versa.

[0151] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0152] Tables 1A, 1B, 2A, and 2B below show 11 examples of expanded particles according to various embodiments of the present invention, which vary in the parameters of the original (compact) polyolefin-based resin particles that are processed to produce the expanded particles and the parameters of the process for producing the expanded particles from the resin particles. By way of example, different liquid dispersion media, such as water, polydimethylsiloxane (PDMS, silicone oil), and different temperatures, pressures, and heating times are used throughout the examples.

[0153] The polypropylene resin of PP1 is an ethylene-propylene copolymer having a melting point of 143°C, an ethylene content of 2.1 mass%, and an MFR of 6 g / 10 min (measured under a load of 2.16 kg, at 230°C, in accordance with JIS K7210-1:2014).

[0154] The polypropylene resin of PP2 is an ethylene-propylene copolymer having a melting point of 133°C, an ethylene content of 3.5 mass%, and an MFR of 6 g / 10 min (measured under a load of 2.16 kg, at 230°C, in accordance with JIS K7210-1:2014).

[0155] The polyethylene resin made of PE is a linear low-density polyethylene (LLDPE) having a melting point of 120°C and an MFR of 1.5g / 10min (measured at 190°C under a load of 2.16kg in accordance with JIS K7210-1:2014).

[0156] The term "single layer" indicates that the resin particles are composed of only a foamed layer without a coating layer, whereas the term "multilayer" indicates that the resin particles have a foamed core layer and a substantially non-foamed resin layer as a coating layer covering the core layer.

[0157] The phosphonate ester compound used in the examples is "Aflammit® PCO 900" available from Thor GmbH, 67329 Speyer, Germany. It has a melting point of 240°C and is a cyclic phosphonate ester compound represented by the following general formula (1), where R １ , R ２ is a methyl group.

[0158] The NOR type hindered amine compound used in the examples is "Flamestab (registered trademark) NOR 116" available from BASF Japan Ltd. (Tokyo), represented by the following chemical formula, and has a molecular weight of 2261.

[0159] Phenolic antioxidant: trade name "Irganox (registered trademark) 1330", manufactured by BASF, melting point 245°C, compound represented by the following chemical formula:

[0160] Sulfur-based antioxidant: dioctadecyl-3,3′-thiodipropionate: manufactured by BASF, trade name “Irganox PS 802”, a compound represented by the following chemical formula:

[0161] Example 1: An extruder with an inner diameter of 50 mm and equipped with a strand-forming die downstream of the extruder was prepared. PP1, zinc borate (arithmetic mean particle size based on number: 9 μm), Aflammit PCO 900, Flamestab NOR 116, Irganox 1330, and Irganox PS 802 were fed into the extruder in the blending ratios shown in Table 1A and melt-kneaded to form a resin melt. The resulting resin melt was extruded as strands through the strand-forming die. The extruded strands were water-cooled and then cut with a pelletizer to obtain polypropylene resin particles (average mass per resin particle: 1.0 mg).

[0162] A 100 L sealed vessel was charged with 2 kg of the polypropylene resin particles, 75 L of water as a liquid dispersion medium, 65 g of kaolin, and 43 g of sodium dodecylbenzenesulfonate.

[0163] Next, carbon dioxide as a blowing agent was added to the sealed container until a gauge pressure of 0.5 MPa (G) was reached, and the container was pressurized. The contents of the sealed container were then heated to the foaming temperature shown in Table 1A. Next, carbon dioxide was pressurized into the sealed container to the gauge pressure (foaming pressure) shown in Table 1B, and the container was maintained at the same temperature and pressure for 9 minutes. The total time the polypropylene resin particles were exposed to a temperature of 80°C or higher is detailed in Table 1B.

[0164] The contents of the sealed container were then released under atmospheric pressure to expand the polypropylene resin particles, yielding expanded polypropylene resin particles. The measurement results for the physical properties of the expanded polypropylene resin particles are shown in Table 1B.

[0165] Examples 2 to 6 and Comparative Examples 1 to 7: Expanded polypropylene resin beads were obtained in the same manner as in Example 1, except that the blending amounts of each component and the process conditions were changed. The blending amounts of each component and the related process conditions are shown in Tables 1A, 1B, 3A, and 3B. Measurement results of the physical properties of the obtained expanded polypropylene resin beads are shown in Tables 1B and 3B. In Examples 2 to 7 and 11 and Comparative Examples 2 to 6 and 8, resin beads were produced using an extrusion device capable of producing multilayered polyolefin resin beads, and the resin beads were expanded to obtain multilayered expanded beads having a foamed core layer and a resin layer coating the core layer. To produce the resin beads, a production device equipped with a core layer-forming extruder, a multilayer strand-forming die attached downstream of the core layer-forming extruder, and a coating layer-forming extruder was used to produce multilayered resin beads using the blending amounts of each component and the related process conditions shown in Tables 1A, 1B, 3A, and 3B. The extruder for forming the coating layer is connected to a die for forming a multilayer strand on its downstream side, and the resin melts formed by the extruders can be laminated in the die.

[0166] Example 7 Expanded polyolefin resin particles (expanded polyethylene resin particles) were obtained in the same manner as in Examples 1 to 6, except that the blending amounts of each component and the process conditions were changed and a polyethylene resin was used as the polyolefin resin. The blending amounts of each component and the related process conditions are shown in Tables 2A and 2B.

[0167] Examples 8 to 10: Except for changing the amount of each component and the process conditions, and using polydimethylsiloxane (PDMS) as the liquid dispersion medium, polyolefin-based resin expanded beads (polypropylene-based resin expanded beads) were obtained in the same manner as in Examples 1 to 6. The amount of each component and the related process conditions are shown in Tables 2A and 2B.

[0168] Before measuring the density, the expanded beads obtained in Examples 8 to 10 were carefully washed with a solvent to remove any remaining PDMS oil, and the solvent was dried and removed. The expanded beads were then subjected to the molding process described below, and the fusion rate of the resulting molded body was evaluated. A split mold for molding a flat plate was prepared, having a molding space measuring 400 mm in length, 300 mm in width, and 30 mm in thickness. The expanded beads were filled into the molding space and clamped. Steam was then supplied into the mold to heat the expanded beads, resulting in a plate-shaped expanded bead molded body.

[0169] First, steam was supplied into the molds with the drain valves of both molds open (exhaust step). Next, steam was supplied into the molds from one mold with the drain valve of the other mold open to heat them (one-sided heating step). Next, steam was supplied from one mold with the drain valve of the other mold open (reverse one-sided heating step). Subsequently, with the drain valves of both molds closed, steam was supplied from both molds until the molding steam pressure inside the mold reached 0.32 MPa (G) (double-sided heating step). After the double-sided heating step was completed, the pressure inside the molds was released, and the molds were water-cooled until the pressure (surface pressure) generated on the molding surface of the mold due to the secondary foaming force of foamed bead molding reached 0.05 MPa (G).

[0170] The mold was then opened, and the molded article made of expanded particles 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.

[0171] The foamed bead molding thus obtained was subjected to bending and fracture, and the number of foamed beads present on the fractured surface (C1) and the number of foamed beads that had been fractured (C2) were counted.

[0172] The ratio of the number of foamed particles that were broken to the number of foamed particles (C2 / C1 x 100) was calculated as the material breakage rate.

[0173] The above measurements were performed on three molded articles, and the arithmetic mean value of the material failure rates was taken as the fusion rate. The obtained fusion rates were evaluated according to the following criteria. Note that a higher fusion rate indicates better fusion between the expanded beads.

[0174] As a result of measuring the fusion rate, Example 8 was evaluated to have a fusion rate of 60% or more, and Examples 9 and 10 were evaluated to have a fusion rate of 30% or more but less than 60%.

[0175] Example 11 An extruder having an inner diameter of 50 mm and equipped with a die for forming strands on the downstream side of the extruder was prepared.

[0176] PP1, zinc borate (arithmetic mean particle size based on number: 9 μm), Aflammit PCO 900, Flamestab NOR 116, Irganox 1330 and Irganox PS 802 were fed to an extruder in the blending ratios shown in Table 1 and melt-kneaded to form a resin melt.

[0177] The resulting resin melt was extruded as a strand from a strand-forming die, and the extruded strand was cooled with water and then cut with a pelletizer to obtain polypropylene-based resin particles (average mass per resin particle: 1.0 mg).

[0178] Carbon dioxide as a blowing agent was supported on the polypropylene-based resin particles at a pressure of about 5.0 MPa (G) for 1000 hours without heating or temperature control, to obtain compressed polypropylene-based resin particles.

[0179] The pressurized polypropylene resin particles were then expanded by being transported through a continuous infrared oven comprising a plurality of infrared emitters to obtain expanded polypropylene resin particles. The results of measurement of the physical properties of the obtained expanded polypropylene resin particles are shown in Table 2B.

[0180] Tables 1A, 1B, 2A, and 2B show that all 11 Examples satisfy the above formula (1) (see the values ​​listed in the last lines of Tables 1B and 2B). Therefore, all 11 Examples exhibit good flame retardancy. Tables 3A and 3B show eight Comparative Examples ("C1 to C8"), with Comparative Example 1 corresponding to Example 1, Comparative Example 2 corresponding to Example 2, Comparative Example 3 corresponding to Example 3, Comparative Example 4 corresponding to Example 4, Comparative Example 5 corresponding to Example 5, Comparative Example 6 corresponding to Example 6, Comparative Example 7 corresponding to Example 10, and Comparative Example 8 corresponding to Example 11.

[0181] In contrast to the Examples, the Comparative Examples do not satisfy the above formula (1) (see the values ​​shown in the last row of Table 3B), which is believed to be due to the presence of a larger amount of altered / decomposed phosphonate ester compound in the expanded beads of the Comparative Examples.

[0182] The examples provided in Tables 1A, 1B, 2A and 2B should not be considered exhaustive measures for mitigating the decomposition of phosphonate ester compounds, and other measures that affect the chemical reactions involved in the decomposition, such as altering pH, pressure, etc., are contemplated.

[0183] The presence of such altered / decomposed phosphonate compounds can be shown, for example, by solid-state phosphorus NMR analysis. ３１ The P-NMR analysis results show additional peaks relative to the original resin particles used to make the expanded beads, which additional peaks represent altered / decomposed phosphonate compounds.

[0184]

[0185] Molded articles obtained by molding the expanded beads of Examples 4 and 11 and Comparative Examples 4 and 8 in a mold were subjected to UL94 test evaluation. Examples 4 and 4, and Examples 11 and 8 were produced using the same polyolefin resin beads under different process conditions as shown in the table.

[0186] In Example 4, three out of five test pieces were evaluated as "V-0" according to the UL94 standard, whereas none of the five test pieces in Comparative Example 4 were evaluated as "V-0." In Example 11, five out of five test pieces were evaluated as "V-0" according to the UL94 standard, whereas none of the five test pieces in Comparative Example 8 were evaluated as "V-0."

[0187] In Example 12, single-layer expanded particles were produced by the extrusion foaming method as follows. First, an extrusion foaming apparatus equipped with an extruder (manufactured by IKG Corporation) with an inner diameter of 50 mm and an underwater cutter (manufactured by ECON) was prepared. The following polyolefin resins were fed into the extruder feed port of the extruder: 48 parts by mass of branched homopolypropylene (WB140 manufactured by Borealis, melting point 161°C); 38 parts by mass of ethylene-propylene random copolymer (ethylene content 3.1% by mass, MFR 7 g / 10 min, melting point 143°C); 11 parts by mass of Aflammit PCO 900; 3 parts by mass of Flamestab NOR 116; and 1 part by mass of a sodium bicarbonate-citric acid-based chemical foaming agent (FineCell Master PO217K manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.) as a foam adjuster. Next, the raw materials were melt-kneaded in an extruder, and isobutane was added as a foaming agent midway through the extruder and further kneaded to prepare a foamable resin melt. At this time, the amount of isobutane added to the foamable resin melt was 6% by mass. The foamable resin melt was then extruded through a die plate installed downstream of the extruder to foam, and the extruded foam was cut with a four-blade cutter to produce foamed particles. The die plate had five 2.3 mm diameter holes as extrusion ports. During extrusion, the resin temperature (foaming temperature) at the diverter section was 162°C, the foaming pressure was 3.4 MPa (G), and the total time the mixture was exposed to temperatures of 80°C or higher during the foaming process was 7 minutes. The resin melt was discharged at a rate of 13 kg / h, and the cutter rotation speed was 1,000 rpm.

[0188] The expanded beads obtained in Example 12 had an average mass of 11 mg / bead and a density of 122 kg / m ３ The phosphorus content P is 2.7 mass %, and {(m ２１５ -m ２３５ ) / m ２１５} × 100 is 2.9, and {(m ２１５ -m ２３５ ) / m ２１５}×100 / P ｔｏｔThe expanded beads obtained in Example 12 were molded in a mold to obtain a 200 kg / m3 foam having external dimensions of 400 mm length x 300 mm width x 20 mm thickness. ３ The obtained molded body was subjected to a UL94 vertical test evaluation, and the molded body was evaluated as "V-0" according to the UL94 standard.

[0189] Further exemplary aspects of the present invention will be apparent from the accompanying drawings in which:

[0190] FIG. 1A was performed on resin particles (Graph 1). ３１ 1B is a diagram showing the principle of P-NMR analysis, which was performed on expanded particles obtained by a conventional expansion process (Graph 2). ３１ This is a diagram illustrating the principle of P-NMR analysis. Graph 2, which shows the expanded particles, shows a second peak due to phosphorus, indicating the presence of a modified / decomposed phosphonate ester compound in the expanded particles. This second peak is not present in Graph 1, which shows resin particles before undergoing the expansion step in which a predetermined temperature and / or pressure is applied. This indicates that, in this example, the state-of-the-art autoclave-based expansion process produces modified / decomposed species of the phosphonate ester compound. As is clear from the above comparative example, if a large amount of such modified / decomposed species is present, the expanded particles do not satisfy formula (1).

[0191] 2 is a principle diagram of TGA curves in the temperature range of 215°C to 235°C of the phosphonate ester compounds used in the examples before and after alteration / decomposition. The upper graph shows the unaltered / undecomposed phosphonate ester compound, and the lower graph shows the altered / decomposed phosphonate ester compound, which exhibits different thermal behavior. In particular, the altered / decomposed phosphonate ester compound loses more mass due to heat than the non-altered / non-decomposed phosphonate ester compound, which is thought to have an adverse effect on the flame retardancy inherent to the phosphonate ester compound.

[0192] This application claims priority from European Patent Application No. 23315445.9, filed November 30, 2023.

Claims

1. A polyolefin resin expanded particle, comprising a polyolefin resin and a phosphonic acid ester compound, a phosphorus content P of the expanded particle being 0.1 to 6 mass %, and satisfying the following formula (1): {(m ２１５ -m ２３５ ) / m ２１５ }×100 / P ｔｏｔ ≦35 (1) In formula (1), m ２１５ is the mass of the expanded beads measured by thermogravimetry at 215 ° C; m ２３５ is the mass of the expanded beads measured by thermogravimetry at 235°C; P ｔｏｔ is a numerical value indicating the mass fraction of phosphorus in the expanded beads, and is in the range of 0.001 to 0.

06.

2. The polyolefin resin expanded beads according to claim 1, wherein the expanded beads contain a NOR type hindered amine compound, and the amount of the NOR type hindered amine compound in the expanded beads is 0.1% by mass or more and 5% by mass or less.

3. The expanded polyolefin resin beads according to claim 1 or 2, wherein the total amount of the phosphonic acid ester compound and the NOR hindered amine compound in the expanded beads is 15 mass % or less.

4. The expanded polyolefin resin beads according to any one of claims 1 to 3, wherein the phosphorus content P of the expanded beads is 1 to 4.8 mass %.

5. The expanded polyolefin resin beads according to any one of claims 1 to 4, wherein the expanded beads contain a phenolic antioxidant, and the amount of the phenolic antioxidant in the expanded beads is 0.01 to 0.5 mass %.

6. The expanded polyolefin resin beads according to any one of claims 1 to 5, wherein the expanded beads contain a NOR hindered amine compound and a phenolic antioxidant, and the ratio of the amount of the phenolic antioxidant to the amount of the NOR hindered amine compound in the expanded beads is 0.03 to 0.

9.

7. The expanded polyolefin resin particles according to any one of claims 1 to 6, wherein the phosphonate ester compound contains a cyclic phosphonate ester compound represented by any one of the following general formulas (1) to (4): In general formula (1), R １ and R ２ Each represents a hydrocarbon group. In general formula (2), R ３ represents an alkyl group having 1 to 22 carbon atoms or an aryl group having 6 to 15 carbon atoms. In general formula (3), R ４ and R ８ each represents an alkyl group having 1 to 4 carbon atoms; R ５ and R ７ each represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R 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. In general formula (4), R ９ and R １２ each represents an alkyl group having 1 to 4 carbon atoms; R １０ 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. １１ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

8. The expanded beads according to any one of claims 1 to 7, wherein the expanded beads contain a sulfur-based antioxidant, and the amount of the sulfur-based antioxidant in the expanded beads is 0.01 to 0.5 mass %.

9. The expanded beads according to any one of claims 1 to 8, wherein the expanded beads contain a NOR type hindered amine compound and a sulfur-based antioxidant, and the ratio of the amount of the NOR type hindered amine compound to the amount of the sulfur-based antioxidant in the expanded beads is 0.03 to 0.

9.

10. The expanded beads according to any one of claims 1 to 9, wherein the polyolefin resin comprises a polypropylene resin.

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

12. A method for producing expanded polyolefin resin particles, comprising the steps of: preparing a component (A) containing a polyolefin resin; and preparing a component (B) containing a phosphonic acid ester compound, and treating a mixture of the component (A) and the component (B) in the presence of a blowing agent at a specific temperature and / or a specific pressure for a specific period of time, wherein the expanded polyolefin resin particles satisfy the following formula (1): {(m ２１５ -m ２３５ ) / m ２１５ }×100 / P ｔｏｔ ≦35 (1) In formula (1), m ２１５ is the mass of the expanded beads measured by thermogravimetry at 215 ° C; m ２３５ is the mass of the expanded beads measured by thermogravimetry at 235°C; P ｔｏｔ is a numerical value indicating the mass fraction of phosphorus in the expanded beads, and is in the range of 0.001 to 0.

06.

13. The method for producing expanded polyolefin resin particles according to claim 12, wherein treating the mixture and the foaming agent at the specific temperature for the specific time comprises heating the mixture to a specific foaming temperature of at least 100°C and holding the mixture at the specific foaming temperature for the specific time, and during heating and holding the mixture at the specific foaming temperature, the mixture is exposed to a temperature of at least 80°C for 60 minutes or less.

14. The method for producing expanded polyolefin resin particles according to claim 12 or 13, wherein the mixture is treated in a non-aqueous liquid or the mixture is treated in the absence of a liquid dispersion medium.

15. The method for producing expanded polyolefin resin beads according to any one of claims 12 to 14, wherein the amount of said component (B) in said mixture is 3 to 20 mass %.

16. A method for at least qualitatively determining the flame retardant behavior of an expanded bead according to claim 1, comprising measuring the mass of the expanded bead in thermogravimetry at 215°C and 235°C and the phosphorus content P of the expanded bead, and determining whether the expanded bead satisfies the following formula (1) when the phosphorus content P of the expanded bead is in the range of 0.1 to 6% by mass: ２１５ -m ２３５ ) / m ２１５ }×100 / P ｔｏｔ ≦35 (1) In formula (1), m ２１５ is the mass of the expanded beads measured by thermogravimetry at 215 ° C; m ２３５ is the mass of the expanded beads measured by thermogravimetry at 235°C; P ｔｏｔ is a numerical value indicating the mass fraction of phosphorus in the expanded beads, and is in the range of 0.001 to 0.06.

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