JP2024144291A - Polyolefin resin expanded particles and method for producing same - Google Patents

Abstract

[Problem] To provide a polyolefin resin foamed molded article having excellent moldability and flame retardancy with a small environmental impact. [Solution] To provide a polyolefin resin foamed particle containing a polyolefin resin (A), a specific calcium compound, a phenolic antioxidant (D), and a phosphorus-based processing stabilizer (E), and a method for producing the same. [Selected Figures] None

Description

The present invention relates to polyolefin resin foam particles and a method for producing the same.

Polyolefin resin foam molded articles obtained using polyolefin resin foam particles are used in a variety of applications, including automobile interior components and/or core materials for automobile bumpers, as well as heat insulation materials, cushioning packaging materials, and returnable boxes. In addition, a technique for adding a flame retardant and a metal salt hydrate to a polyolefin resin to improve the flame retardancy of a polyolefin resin foam molded article is known (for example, Patent Document 1).

JP 2013-35949 A

However, in the above-mentioned conventional technology, the substance added to the polyolefin resin (contained in the resin composition) contains elemental sulfur, and there is room for improvement in terms of balancing the environmental impact with the moldability and burning rate of the resulting foamed molded product.

One embodiment of the present invention has been developed in consideration of the above problems, and its purpose is to provide expanded polyolefin resin particles that can provide expanded molded articles with excellent moldability and flame retardancy while imposing a small environmental burden.

The inventors conducted extensive research to solve the above problems and have now completed the present invention.

That is, one embodiment of the present invention includes the following configuration.
[1] A polyolefin resin foam comprising (A), a calcium compound (C1), a phenol-based antioxidant (D) and a phosphorus-based processing stabilizer (E), wherein the calcium compound (C1) is a compound that does not contain elemental sulfur or halogen, and the content of the calcium compound (C1) is 0.10% by weight to 3.00% by weight based on 100% by weight of expanded polyolefin resin particles, and the calcium compound (C1) is dispersed inside a film constituting bubbles of the expanded polyolefin resin particles.
[2] The expanded polyolefin resin particles according to [1], wherein the calcium compound (C1) comprises at least one selected from the group consisting of calcium oxide, calcium hydroxide, calcium carbonate and fatty acid calcium.
[3] The expanded polyolefin resin particles according to [1] or [2], wherein the polyolefin resin (A) includes a recycled polyolefin resin.
[4] The expanded polyolefin resin particles according to any one of [1] to [3], further comprising a hindered amine (B).
[5] The expanded polyolefin resin particles according to any one of [1] to [4], further comprising carbon black and/or graphite.
[6] The expanded polyolefin resin particles according to any one of [1] to [5], further comprising a metal deactivator.
[7] A polyolefin resin foamed molded article obtained by molding the expanded polyolefin resin beads according to any one of [1] to [6].
[8] A method for producing expanded polyolefin resin particles, comprising: a dispersing step of dispersing polyolefin resin particles made of a polyolefin resin composition containing a polyolefin resin (A), a calcium compound (C2), a phenolic antioxidant (D) and a phosphorus-based process stabilizer (E) in an aqueous dispersion medium in a container; and a releasing step of releasing the dispersion obtained in the dispersing step into a region having a lower pressure than the pressure in the container, wherein the calcium compound (C2) is a compound containing neither elemental sulfur nor elemental halogen, and the content of the calcium compound (C2) is 0.10% by weight to 3.00% by weight in 100% by weight of the expanded polyolefin resin particles.
[9] The method for producing expanded polyolefin resin particles according to [8], wherein the calcium compound (C2) comprises at least one selected from the group consisting of calcium oxide, calcium hydroxide, calcium carbonate and fatty acid calcium.
[10] The method for producing expanded polyolefin resin particles according to [8] or [9], wherein the calcium compound (C2) comprises at least one selected from the group consisting of calcium oxide and fatty acid calcium.
[11] The method for producing expanded polyolefin resin beads according to any one of [8] to [10], wherein the polyolefin resin (A) includes a recycled polyolefin resin.
[12] A method for producing expanded polyolefin resin beads comprising a polyolefin resin (A), a calcium compound (C1), a phenolic antioxidant (D) and a phosphorus-based processing stabilizer (E), comprising:
In the container,
(i) a dispersing step of dispersing polyolefin-based resin particles made of a polyolefin-based resin composition containing a polyolefin-based resin (A), (ii) a calcium compound (C1) and/or a precursor of the calcium compound (C1), (iii) a phenol-based antioxidant (D), and (iv) a phosphorus-based process stabilizer (E) in an aqueous dispersion medium, and a blowing agent;
A discharging step of discharging the dispersion obtained in the dispersing step into a region with a lower pressure than the pressure inside the container,
The calcium compound (C1) is a compound that does not contain a sulfur element or a halogen element,
The precursor of the calcium compound (C1) is a compound that does not contain a sulfur element or a halogen element,
In the expanded polyolefin resin beads, the content of the calcium compound (C1) is 0.10% by weight to 3.00% by weight based on 100% by weight of the expanded polyolefin resin beads.
[13] The precursor of the calcium compound (C1) is
The method for producing expanded polyolefin resin particles according to [12], which contains at least one selected from the group consisting of calcium oxide, calcium hydroxide, calcium carbonate and calcium fatty acid.
[14] The precursor of the calcium compound (C1) is
The method for producing expanded polyolefin resin particles according to [12] or [13], which contains at least one selected from the group consisting of calcium oxide and fatty acid calcium salts.
[15] The method for producing expanded polyolefin resin beads according to any one of [12] to [14], wherein the polyolefin resin (A) includes a recycled polyolefin resin.

According to one embodiment of the present invention, it is possible to provide polyolefin resin foam particles that can provide foamed molded articles with excellent moldability and flame retardancy with a small environmental impact.

One embodiment of the present invention will be described below, but the present invention is not limited to this. The present invention is not limited to each of the configurations described below, and various modifications are possible within the scope of the claims. In addition, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. In addition, unless otherwise specified in this specification, "A to B" representing a numerical range intends "A or more (including A and greater than A) and B or less (including B and smaller than B)."

In this specification, a structural unit derived from an X monomer contained in a polymer or copolymer may be referred to as an "X unit."

Unless otherwise specified in this specification, a copolymer containing ^X1 units, ^X2 units, ..., and ^Xn units (n is an integer of 2 or more) as constituent units is also referred to as an " ^X1 / ^X2 /.../ ^Xn copolymer". Unless otherwise specified, the polymerization mode of ^{the X1} / ^X2 /.../ ^Xn copolymer is not particularly limited, and it may be a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer.

[1. Polyolefin resin expanded particles]
The expanded polyolefin resin beads according to one embodiment of the present invention comprise a polyolefin resin (A), a calcium compound (C1), a phenol-based antioxidant (D), and a phosphorus-based process stabilizer (E), wherein the calcium compound (C1) is a compound that does not contain elemental sulfur or halogen, the content of the calcium compound (C1) is 0.10% by weight to 3.00% by weight relative to 100% by weight of the expanded polyolefin resin beads, and the calcium compound (C1) is dispersed within a film constituting air bubbles of the expanded polyolefin resin beads.

The polyolefin resin foam particles according to one embodiment of the present invention have the above-mentioned configuration, and therefore have the advantage of being able to provide foamed molded articles with excellent moldability and flame retardancy with a small environmental impact.

In addition, the above-mentioned configuration can reduce contamination of water, soil, etc. Such an effect also contributes to the achievement of Goal 14 of the Sustainable Development Goals (SDGs) advocated by the United Nations, "Conserve and sustainably use the oceans and marine resources for sustainable development."

In this specification, "polyolefin resin particles" may be referred to as "resin particles", "polyolefin expanded particles" may be referred to as "expanded particles", "polyolefin expanded particles according to one embodiment of the present invention" may be referred to as "the present expanded particles", and "polyolefin resin expanded molded body" may be referred to as "expanded molded body".

In this specification, moldability refers to the surface beauty of the foam molded product.

In this specification, flame retardancy is evaluated based on the burning rate of the foam molded article. In this specification, if at least one of the maximum burning rate or the average burning rate of the foam molded article is excellent, the flame retardancy is evaluated as excellent. The evaluation method will be described in detail later.

<Polyolefin Resin (A)>
In this specification, the term "polyolefin resin" refers to a resin that contains 50 mol % or more of olefin units out of 100 mol % of all structural units constituting the resin.

The polyolefin resin (A) is not particularly limited, but examples thereof include polyethylene resins and polypropylene resins. These polyolefin resins may be used alone or in combination of two or more.

(Polyethylene resin)
In this specification, the term "polyethylene resin" refers to a resin that contains more than 50 mol % of ethylene units, based on 100 mol % of all structural units constituting the resin.

Examples of polyethylene resins include, but are not limited to, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, styrene modified polyethylene resins, ethylene/vinyl acetate copolymers, ethylene/propylene copolymers, ethylene/1-butene copolymers, ethylene/1-butene/propylene copolymers, ethylene/hexene copolymers, and ethylene/4-methyl-1-pentene copolymers.

The above-mentioned ethylene-based resins may be used alone or in combination of two or more.

(Polypropylene resin)
In this specification, the term "polypropylene resin" refers to a resin that contains 50 mol % or more of propylene units in 100 mol % of all structural units constituting the resin.

The polypropylene-based resin may be (i) a homopolymer of propylene, (ii) a block copolymer, alternating copolymer, random copolymer, or graft copolymer of propylene and a monomer other than propylene, or (iii) a mixture of two or more of these. A block copolymer of propylene and a monomer other than propylene is sometimes called an impact copolymer. A homopolymer of propylene, a block copolymer of propylene and a monomer other than propylene, an alternating copolymer, and a random copolymer are all linear polymers. It is preferable that the polypropylene-based resin is a linear polymer.

The polypropylene-based resin is preferably a random copolymer of propylene and a monomer other than propylene, since the resin particles and expanded particles can be processed at a low heating temperature in the foaming process and foam molding process described below.

In addition to propylene units, polypropylene-based resins may have one or more units, or may have one or more types, of structural units derived from monomers other than propylene monomers. The "monomers other than propylene monomers" used in the production of polypropylene-based resins may be referred to as "comonomers." The "structural units derived from monomers other than propylene monomers" contained in polypropylene-based resins may be referred to as "comonomer units."

Comonomers include α-olefins having 2 or 4 to 12 carbon atoms, such as ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene.

Specific examples of polypropylene-based resins include polypropylene homopolymers, ethylene/propylene random copolymers, 1-butene/propylene random copolymers, 1-butene/ethylene/propylene random copolymers, ethylene/propylene block copolymers, 1-butene/propylene block copolymers, 1-butene/ethylene/propylene block copolymers, ethylene/propylene block alternating polymers, 1-butene/propylene block alternating polymers, 1-butene/ethylene/propylene block alternating polymers, propylene/chlorinated vinyl copolymers, propylene/maleic anhydride copolymers, and styrene-modified polypropylene-based resins.

As the polypropylene-based resin, one of the above-mentioned specific examples may be used alone, or two or more of them may be used in combination. Among the above-mentioned specific examples, it is preferable that the polypropylene-based resin contains an ethylene/propylene random copolymer and/or a 1-butene/ethylene/propylene random copolymer, because the resin particles obtained have good expandability and the expanded particles obtained have good moldability. Furthermore, among the above-mentioned specific examples, it is preferable that the polypropylene-based resin contains an ethylene/propylene random copolymer and/or a 1-butene/ethylene/propylene random copolymer, because it is possible to obtain an expanded molded product with excellent moldability and flame retardancy.

When the polypropylene-based resin is a mixture of an ethylene/propylene random copolymer and a 1-butene/ethylene/propylene random copolymer, the preferred ratio of the ethylene/propylene random copolymer in the polypropylene-based resin is not particularly limited.

The polyolefin resin (A) preferably contains 70% by weight or more of polypropylene resin, more preferably 80% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, and even more preferably 98% by weight or more, based on 100% by weight of the polyolefin resin (A). It is particularly preferable that the polyolefin resin (A) contains 100% by weight of polypropylene resin, based on 100% by weight of the polyolefin resin (A). In other words, it is preferable that the polyolefin resin (A) is composed only of polypropylene resin. When the amount of polypropylene resin contained in the polyolefin resin (A) is within the above-mentioned range, it has the advantage that a foamed molded product with excellent flame retardancy can be obtained.

The content of polyolefin resin (A) in the present expanded beads is not particularly limited, but is preferably 93.00% by weight to 98.00% by weight, more preferably 94.00% by weight to 97.50% by weight, even more preferably 95.50% by weight to 97.00% by weight, and particularly preferably 95.00% by weight to 96.50% by weight, based on 100% by weight of the present expanded beads. This configuration has the advantages of (i) small reduction in strength of the expanded molded article, and (ii) large cell diameters, resulting in an expanded molded article with excellent moldability and beautiful appearance.

The polyolefin resin (A) preferably contains recycled polyolefin resin.

The present inventors have newly discovered that, when the polyolefin resin contains recycled polyolefin resin, (I) the polyolefin resin is easily thermally decomposed in the granulation process, so that the MFR of the resulting resin particles increases and many intergranular spaces are observed in the foamed molded article made of the foamed beads obtained from the resin particles, and (II) the flame retardancy of the resulting foamed molded article made of the foamed beads is deteriorated, compared to when the polyolefin resin does not contain recycled polyolefin resin.

Here, it is speculated that the flame retardancy of the foamed molded article obtained when the polyolefin resin contains a recycled polyolefin resin is deteriorated because (i) the recycled polyolefin resin is repeatedly heated in the recycling process, which reduces its molecular weight and makes it susceptible to decomposition and volatilization, and (ii) impurities contained in the recycled material containing the recycled polyolefin resin promote the decomposition of the recycled polyolefin resin and negate the effect of the flame retardant. However, one embodiment of the present invention is in no way limited to such speculation.

Therefore, in the course of intensive research, the inventors attempted to suppress an increase in the MFR of the resulting resin particles by using an antioxidant when producing polyolefin-based resin particles containing recycled polyolefin-based resin, but no sufficient improvement was observed. In addition, in the course of intensive research, the inventors attempted to improve the flame retardancy of the resulting foamed molded product by increasing the amount of an existing flame retardant and using two or more existing flame retardants in combination when producing expanded particles made of polyolefin-based resin containing recycled polyolefin-based resin, but no improvement was observed.

In addition, recycled materials (recycled materials containing recycled polyolefin resins) available on the market may contain carbon black. On the other hand, it is generally known that polyolefin resin foam particles that contain carbon black have poor flame retardancy.

As a result of intensive research, the present inventors have found that even when the polyolefin resin (A) contains recycled polyolefin resin, if the polyolefin resin foam particles contain a calcium compound (C1), a phenol-based antioxidant (D) and a phosphorus-based processing stabilizer (E), the calcium compound (C1) is a compound that does not contain sulfur or halogen elements, the content of the calcium compound (C1) is 0.10% by weight to 3.00% by weight based on 100% by weight of the polyolefin resin foam particles, and the calcium compound (C1) is dispersed inside the membrane that constitutes the bubbles, the polyolefin resin is prevented from thermally decomposing in the granulation process and the MFR is increased, and the resulting foamed molded article has excellent moldability and flame retardancy.

The inventors have also discovered that even when the expanded particles contain carbon black, the polyolefin resin expanded particles contain a calcium compound (C1), a phenol-based antioxidant (D), and a phosphorus-based processing stabilizer (E), the calcium compound (C1) is a compound that does not contain sulfur or halogen elements, the content of the calcium compound (C1) is 0.10% by weight to 3.00% by weight based on 100% by weight of the polyolefin resin expanded particles, the calcium compound (C1) is dispersed inside the film that constitutes the bubbles, and the expanded particles contain a hindered amine (B), so that the resulting foamed molded article has excellent moldability and flame retardancy.

In addition, when the polyolefin resin (A) contains recycled polyolefin resin, the amount of plastic waste generated and the amount of plastic used in production can be reduced. This effect contributes to the achievement of, for example, Goal 12 of the Sustainable Development Goals (SDGs) advocated by the United Nations, "Ensure sustainable consumption and production patterns."

In this specification, the term "recycled polyolefin resin" refers to polyolefin resin that has been used and/or discarded after being in the form of a polyolefin resin product (e.g., foam particles; foam molded products; films; food trays; packaging containers such as bags and bottles; medical containers such as IV packs and syringes; clothing cases; miscellaneous goods such as clear files; home appliances; automobile parts; etc.), and that has been re-formed into polyolefin resin (or polyolefin resin pellets) by any means (e.g., crushing, shredding, melting, and combinations thereof), and (ii) polyolefin resin that has been re-formed into polyolefin resin (or polyolefin resin pellets) by any means (e.g., crushing, shredding, melting, and combinations thereof) from waste generated during the production process of polyolefin resin products.

In this specification, "non-recycled polyolefin resin" refers to polyolefin resin that has never been in the form of a polyolefin resin product.

When the polyolefin resin (A) contains a recycled polyolefin resin, the content of the recycled polyolefin resin in the present expanded beads is not particularly limited, but is preferably 10% by weight to 100% by weight, more preferably 20% by weight to 70% by weight, and even more preferably 25% by weight to 50% by weight, relative to the weight percent of the polyolefin resin (A). This configuration has the advantage of further reducing the burden on the environment.

(Other resins)
In one embodiment of the present invention, the expanded beads may further contain a resin other than the polyolefin resin (A) (sometimes referred to as "other resins" in this specification) within a range that does not impair the effect of one embodiment of the present invention. Examples of the other resins include styrene resins (polystyrene, styrene/maleic anhydride copolymers, styrene/ethylene copolymers, etc.).

When the present foamed particles contain other resins, the content of the other resins in the present foamed particles is not particularly limited, but is preferably 1 to 10 parts by weight, and more preferably 2 to 5 parts by weight, per 100 parts by weight of the polyolefin resin (A). Since a polyolefin resin foamed molded product having better flame retardancy can be provided, the content of the other resins in the foamed particles is preferably 5 parts by weight or less per 100 parts by weight of the polyolefin resin (A). In other words, the polyolefin resin particles further have a resin other than the polyolefin resin (A), and the content of the other resins is preferably 5 parts by weight or less per 100 parts by weight of the polyolefin resin (A). Since a polyolefin resin foamed molded product having better flame retardancy can be provided, the content of the other resins in the foamed particles is more preferably 4 parts by weight or less, more preferably 3 parts by weight or less, more preferably 2 parts by weight or less, even more preferably 1 part by weight or less, and particularly preferably 0.1 parts by weight or less, per 100 parts by weight of the polyolefin resin (A). The content of other resins in the resin particles is 0.1 weight or less per 100 weight parts of polyolefin resin (A), which means that the expanded particles (resin particles) do not substantially contain other resins.

(Physical Properties)
The melt flow rate (MFR) of the polyolefin resin (A) at 230±0.2°C is not particularly limited, but is preferably 1g/10min to 40g/10min, more preferably 2g/10min to 35g/10min, even more preferably 3g/10min to 30g/10min, and particularly preferably 3g/10min to 10g/10min. MFR may also be referred to as "melt index (MI)". When the MFR of the polyolefin resin (A) is 1g/10min or more, it has the advantage that it is easy to increase the expansion ratio of the expanded beads in the production of the expanded beads. When the MFR of the polyolefin resin (A) is 30g/10min or less, there is no risk of the bubbles of the resulting expanded beads becoming interconnected, and as a result, there is the advantage that (i) the compressive strength of the expanded molded article obtained from the expanded beads tends to be good, or (ii) the surface beauty of the expanded molded article tends to be good. The method for measuring the MFR of the polyolefin resin will be described in detail in the Examples below.

The melting point of the polyolefin resin (A) is not particularly limited, but is preferably 135°C to 160°C, more preferably 137°C to 155°C, and even more preferably 139°C to 153°C. When the melting point of the polyolefin resin (A) is (i) 135°C or higher, the foamed molded article obtained from the resulting foamed beads has the advantage of having excellent heat resistance, and (ii) when it is 160°C or lower, it has the advantage that it is easy to increase the expansion ratio of the foamed beads in the production of the foamed beads. The method for measuring the melting point of the polyolefin resin (A) will be described in detail in the Examples below.

<Hindered amine (B)>
The expanded polyolefin resin beads according to one embodiment of the present invention preferably contain a hindered amine (B).

(Hindered amine)
In this specification, the term "hindered amine" refers to a hindered amine having an OR group (wherein R is a saturated or unsaturated monovalent hydrocarbon group) directly substituted on an N atom (hereinafter, may be referred to as an N-substituted hindered amine). The hindered amine is not particularly limited as long as it is a hindered amine having an OR group directly substituted on an N atom, and known hindered amines may be used. As the hindered amine, one type of hindered amine may be used alone, or two or more types of hindered amines may be used in combination.

As the hindered amine can exert a flame retardant effect over a wide temperature range, an N-substituted hindered amine containing a triazine component (hereinafter, sometimes referred to as a "triazine skeleton-containing hindered amine") is preferable. The triazine skeleton-containing hindered amine is not particularly limited, but (i) a compound having CAS number 191680-81-6 ((i-1) a reaction product of a product obtained by reacting a reaction product of peroxidized N-butyl-2,2,6,6-tetramethyl-4-piperidinamine and 2,4,6-trichloro-1,3,5-triazine with cyclohexane, and N,N'-bis(3-aminopropyl)ethylenediamine, (i-2) 2,4-bis((1-cyclohexyloxy-2,2,6,6-tetramethylpiperidin-4-yl)butyl (i-3) N,N',N'''-tris{2,4-bis[(1-hydrocarbyloxy-2,2,6,6-tetramethylpiperidin-4-yl)alkylamino]-s-triazin-6-yl}-3,3'-ethylenediiminodipropylamine) and/or (ii) bis(1-undecaneoxy-2,2,6,6-tetramethylpiperidin-4-yl)carbonate are preferred. Also, isomers of the above-mentioned triazine skeleton-containing hindered amines and crosslinked derivatives of the above-mentioned triazine skeleton-containing hindered amines can be used. More details about triazine skeleton-containing hindered amines are disclosed in European Patent No. 0889085, page 2, line 32 to page 4, line 6.

Commercially available products can also be suitably used as the triazine skeleton-containing hindered amine. Commercially available products of triazine skeleton-containing hindered amine include FLAMESTAB (registered trademark) NOR116 (a compound with CAS number 191680-81-6) manufactured by BASF, HOSTAVIN (registered trademark) NOW XP manufactured by CLARIANT, and Adeka STAB LA-81 (bis(1-undecaneoxy-2,2,6,6-tetramethylpiperidin-4-yl) carbonate) manufactured by Adeka Corporation.

In one embodiment of the present invention, the hindered amine may be a compound represented by the following structural formula (iv):

In the above structural formula (iv), G ¹ and G ² are independently a C _1-8 alkyl group, or pentamethylene; Z ¹ and Z ² are each a methyl group, or Z ¹ and Z ² together form a linking moiety which may be additionally substituted with an ester group, an ether group, an amide group, an amino group, a carboxy group, or a urethane group; and E is a C _1-8 alkoxy group, a C _5-12 cycloalkoxy group, a C _7-15 aralkoxy group, a -O-C(O)-C _1-18 alkyl group, or a -O-T-(OH) _b group; where T is (i) a C _1-18 alkylene chain, (ii) a C _5-18 cycloalkylene chain, (iii) a C _5-18 cycloalkenylene chain, or (iv) a C _1-4 alkyl substituted phenyl group. a _1-4 alkylene chain; b is 1 to 3 and is not greater than the number of carbon atoms in T, and when b is 2 or 3, each hydroxyl group is linked to a different carbon atom in T.

More details about the compound represented by the above structural formula (iv) are disclosed in EP 2225318, more specifically, from page 5, line 35 to page 25, line 48 of EP 2225318.

In one embodiment of the present invention, the hindered amine may be a compound represented by the following structural formula (v):

In the above structural formula (v), R is hydrogen or a methyl group, and R ¹ is a C _1-18 alkyl group, a C _2-18 alkenyl group, a C _2-18 alkynyl group, a C _5-12 cycloalkyl group, a C _5-8 cycloalkenyl group, a C _6-10 aryl group, or a C _7-9 aralkyl group.

More details about the compound represented by the above structural formula (v) are disclosed in European Patent No. 0309402, page 3, line 33 to page 8, line 58.

In one embodiment of the present invention, the hindered amine may be a compound represented by the following structural formula (vi):

In the above structural formula (vi), E, k, Y, W, R ₁ to R ₇ , and G ₁ to G ₄ are as defined in the specification of US Pat. No. 8,598,369.

More details about the compound represented by the above structural formula (vi) are disclosed in Examples 1 to 12 and Tables 1 to 5 of U.S. Patent No. 8,598,369.

The content of the hindered amine (B) in the expanded beads is not particularly limited, but is preferably 0.01% by weight to 3.00% by weight, more preferably 0.03% by weight to 1.00% by weight, even more preferably 0.05% by weight to 0.75% by weight, even more preferably 0.07% by weight to 0.50% by weight, and particularly preferably 0.10% by weight to 0.25% by weight, based on 100% by weight of the expanded beads. This configuration has the advantage that it is possible to obtain a foamed molded product with excellent flame retardancy.

<Calcium Compound (C1)>
The expanded polyolefin resin particles according to one embodiment of the present invention contain a calcium compound (C1) (the calcium compound (C1) is a compound that does not contain sulfur element and halogen element). This constitution has an advantage that it is possible to obtain an expanded molded product having excellent flame retardancy.

Calcium compound (C1) refers to a compound that contains calcium but does not contain sulfur or halogen elements.

Calcium compound (C1) may be a compound derived from calcium compound (C2) described later. Calcium compound (C1) may be (I) the same compound as calcium compound (C2) described later, or (II) a compound obtained by reacting calcium compound (C2) described later with water or a blowing agent present in a pressure vessel during the manufacturing process of the expanded beads.

Therefore, it is preferred that calcium compound (C1) is either (i) the same compound as calcium compound (C2), (ii) a hydrate of calcium compound (C2), or (iii) a carbonate of calcium compound (C2).

The calcium compound (C2) will be described later in the section <Calcium compound (C2)> in [2. Method for producing expanded polyolefin resin beads], so the description therein will be incorporated by reference and will not be described here.

The calcium compound (C1) is, for example, a compound that does not contain sulfur element and halogen element, and is preferably one or more compounds selected from the group consisting of calcium salts (e.g., anhydrous inorganic salts containing calcium, hydrates of inorganic salts containing calcium, organic salts containing calcium, hydrates of organic salts containing calcium, etc.), calcium hydroxide, calcium oxide, calcium peroxide, and calcium carbide.

The "anhydride of an inorganic salt containing calcium" and "hydrate of an inorganic salt containing calcium" contained in the calcium compound (C1) are preferably at least one selected from the group consisting of calcium carbonate, calcium hydrogen carbonate, calcium phosphite, monocalcium aluminosilicate, dicalcium aluminosilicate, monocalcium aluminate, tricalcium aluminate, dicalcium silicate, tricalcium silicate, calcium hypophosphite, calcium hydroxide phosphate, magnesium calcium carbonate, calcium diphosphate, pentacalcium hexasilicate, hexacalcium hexasilicate, calcium hexafluorosilicate, calcium metasilicate, magnesium calcium metasilicate, calcium metaphosphate, tricalcium phosphate, tetracalcium phosphate, octacalcium phosphate, calcium monohydrogen phosphate, calcium dihydrogen phosphate, and hydrates thereof.

The "anhydride of an organic salt containing calcium" and the "hydrate of an organic salt containing calcium" contained in the calcium compound (C1) are preferably, for example, one or more selected from the group consisting of fatty acid calcium and hydrates thereof.

The fatty acid calcium that may be contained in the calcium compound (C1) is preferably one or more selected from the group consisting of calcium acetate, calcium citrate, calcium oxalate, and calcium stearate.

The expanded particles may contain only one type of calcium compound described above, or may contain two or more types.

The calcium compound (C1) preferably contains one or more selected from the group consisting of calcium oxide, calcium hydroxide, calcium carbonate, and calcium fatty acid. In other words, the resin particles that are the raw material for the expanded particles preferably contain the calcium compound (C2) described below. This configuration has the advantages that the thermal decomposition of the polyolefin resin is suppressed in the granulation process for producing the resin particles, the MFR of the resin particles is less likely to increase, and an expanded molded product with excellent long-term thermal stability and flame retardancy can be obtained.

The content of calcium compound (C1) in the expanded beads is 0.10% by weight to 3.00% by weight, more preferably 0.12% by weight to 3.00% by weight, even more preferably 0.14% by weight to 3.00% by weight, even more preferably 0.16% by weight to 3.00% by weight, and particularly preferably 0.18% by weight to 3.00% by weight, based on 100% by weight of the expanded beads. This configuration has the advantage of being able to produce a foamed molded product with excellent flame retardancy.

When the calcium compound (C1) contains one or more selected from the group consisting of calcium oxide, calcium hydroxide, and calcium carbonate, the total content of calcium oxide, calcium hydroxide, and calcium carbonate in 100% by weight of the expanded beads is preferably 0.03% by weight or more, more preferably 0.05% by weight or more, more preferably 0.10% by weight or more, more preferably 0.12% by weight or more, even more preferably 0.14% by weight or more, and particularly preferably 0.15% by weight or more. This configuration has the advantages that in the granulation process for producing the resin particles, thermal decomposition of the polyolefin resin is suppressed, the MFR of the resin particles is less likely to increase, and an expanded molded product having excellent long-term thermal stability, flame retardancy, and surface beauty can be obtained.

When the calcium compound (C1) contains fatty acid calcium (containing neither sulfur nor halogen), the content of fatty acid calcium (containing neither sulfur nor halogen) is not particularly limited, but is preferably 0.01% by weight or more, more preferably 0.02% by weight or more, even more preferably 0.03% by weight or more, and particularly preferably 0.04% by weight or more, based on 100% by weight of the expanded particles. This configuration has the advantages of suppressing thermal decomposition of the polyolefin resin in the granulation process for producing the resin particles, making it difficult for the MFR of the resin particles to increase, and enabling the production of an expanded molded product with excellent long-term thermal stability, flame retardancy, and surface beauty.

In one embodiment of the present invention, the calcium compound (C1) is dispersed inside the film that constitutes the bubbles (the film itself). In other words, the calcium compound (C1) is intended not to be present on the surface and/or periphery of the film that constitutes the bubbles. This configuration has the advantage that it is possible to obtain a foamed molded product that is excellent in flame retardancy and surface beauty. In addition, as in the granulation process described below, when a resin composition containing a polyolefin resin (A) and a calcium compound (C2) is melt-kneaded to obtain resin particles, and the resin particles are used to perform, for example, a dispersion process and a release process described below to obtain foamed particles, the calcium compound (C1) is dispersed inside the film that constitutes the bubbles of the foamed particles in the obtained foamed particles. In addition, by analyzing a cross section of the film that constitutes the bubbles of the foamed particles using a scanning electron microscope energy dispersive X-ray spectroscopy [SEM-EDX], it is possible to confirm whether or not the calcium compound is dispersed inside the film that constitutes the bubbles of the foamed particles.

<Phenol-based antioxidant (D)>
The expanded polyolefin resin particles contain a phenol-based antioxidant (D). This configuration has the advantages that, in the granulation step for producing the resin particles, thermal decomposition of the polyolefin resin is suppressed, the MFR of the resin particles is less likely to increase, and an expanded molded product having excellent long-term thermal stability, surface beauty, and flame retardancy can be obtained.

The phenol-based antioxidant is not particularly limited, but is preferably at least one selected from the group consisting of tetrakis[methylene-3-(3',5'-di-t-butyl-4-hydroxyphenyl)propionate]methane, tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane. Among these, tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]pentaerythritol is more preferable. This configuration has the advantage that the thermal decomposition of the polyolefin resin is suppressed in the granulation process for producing the resin particles, the MFR of the resin particles is less likely to increase, and a foamed molded product with excellent long-term thermal stability, surface beauty, and flame retardancy can be obtained.

As the phenol-based antioxidant (D), commercially available products can also be suitably used. As commercially available products of the phenol-based antioxidant (D), it is preferable to use one or more selected from the group consisting of "Irganox 1010" manufactured by BASF (tetrakis [methylene-3-(3',5'-di-t-butyl-4-hydroxyphenyl) propionate] methane), "Irganox 1076" manufactured by BASF (octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate), as well as "Irganox 3114" manufactured by BASF and "Adekastab AO-20" manufactured by ADEKA (1,3,5-tris (3,5-di-t-butyl-4-hydroxybenzyl) 1,3,5-triazine-2,4,6 (1H,3H,5H)-trione). This configuration has the advantage of being able to produce foamed molded products with excellent flame retardancy.

In the present expanded beads, the above-mentioned phenol-based antioxidant (D) may be contained alone or in combination of two or more kinds.

The content of the phenolic antioxidant (D) in the expanded beads is not particularly limited, but is preferably 0.01% by weight to 1.00% by weight, more preferably 0.03% by weight to 0.50% by weight, more preferably 0.05% by weight to 0.30% by weight, and even more preferably 0.05% by weight to 0.20% by weight, based on 100% by weight of the expanded beads. This configuration has the advantage that thermal decomposition of the polyolefin resin is suppressed in the granulation process for producing the resin beads, making it difficult for the MFR of the resin beads to increase, and it is possible to obtain an expanded molded product that has excellent long-term thermal stability, surface beauty, and flame retardancy.

<Phosphorus-based processing stabilizer (E)>
The expanded polyolefin resin particles contain a phosphorus-based processing stabilizer (E). This configuration has the advantages that in the granulation process for producing the resin particles, thermal decomposition of the polyolefin resin is suppressed, the MFR of the resin particles is less likely to increase, and an expanded molded product having excellent long-term thermal stability, surface beauty, and flame retardancy can be obtained.

The phosphorus-based processing stabilizer is not particularly limited, but is preferably a trivalent phosphorus compound, for example, one or more selected from the group consisting of tris(2,4-di-t-butylphenyl)phosphite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, and tris(mono,dinonylphenyl)phosphite. Among these, tris(2,4-di-t-butylphenyl)phosphite is more preferable. This configuration has the advantage that in the granulation process for producing resin particles, thermal decomposition of the polyolefin resin is suppressed, the MFR of the resin particles is less likely to increase, and a foamed molded product with excellent long-term thermal stability, surface beauty, and flame retardancy can be obtained.

As the phosphorus-based processing stabilizer (E), commercially available products can also be suitably used. As commercially available phosphorus-based processing stabilizer (E), it is preferable to use one or more selected from the group consisting of "Irgafos 168" (tris(2,4-di-t-butylphenyl)phosphite) manufactured by BASF and "Adekastab PEP-24G" (bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite) manufactured by ADEKA. This configuration has the advantage that in the granulation process for producing resin particles, thermal decomposition of the polyolefin resin is suppressed, the MFR of the resin particles is less likely to increase, and a foamed molded product with excellent long-term thermal stability, surface beauty, and flame retardancy can be obtained.

The expanded particles may contain only one type of phosphorus-based processing stabilizer (E), or may contain a combination of two or more types.

The content of the phosphorus-based processing stabilizer (E) in the present expanded beads is not particularly limited, but is preferably 0.01% by weight to 1.00% by weight, more preferably 0.03% by weight to 0.50% by weight, more preferably 0.05% by weight to 0.30% by weight, and even more preferably 0.07% by weight to 0.20% by weight, based on 100% by weight of the expanded beads. This configuration has the advantage that thermal decomposition of the polyolefin resin is suppressed in the granulation process for producing the resin beads, making it difficult for the MFR of the resin beads to increase, and it is possible to obtain an expanded molded product that has excellent long-term thermal stability, surface beauty, and flame retardancy.

<Other additives>
In one embodiment of the present invention, the expanded particles may contain other additives in addition to the polyolefin resin (A), the hindered amine (B), the calcium compound (C1), the phenolic antioxidant (D), and the phosphorus-based processing stabilizer (E), as long as the effect of one embodiment of the present invention is not impaired. Examples of additives include colorants, hydrophilic compounds, crystal nucleating agents, antistatic agents, flame retardants, antioxidants, light stabilizers, conductive agents, lubricants, carbon black, powdered activated carbon, metal deactivators, etc. Such additives may be added to the resin particles obtained by adding them to the resin composition, or may be added directly to the dispersion when the resin particles are expanded.

Hydrophilic compounds are substances used for the purpose of increasing the amount of water impregnated in resin particles. When a resin composition contains a hydrophilic compound, it is possible to impart foamability to the resin particles. The effect of the hydrophilic compound in imparting foamability to the resin particles is particularly noticeable when water is used as the foaming agent.

Examples of hydrophilic compounds that can be used in one embodiment of the present invention include glycerin, polyethylene glycol, C12 to C18 aliphatic alcohols (e.g., pentaerythritol, cetyl alcohol, stearyl alcohol), melamine, isocyanuric acid, melamine-isocyanuric acid condensates, borax, zinc borate, and the like. One of these hydrophilic compounds may be used alone, or two or more may be mixed and used. When two or more hydrophilic compounds are mixed and used, the mixing ratio may be appropriately adjusted depending on the purpose.

The content of the hydrophilic compound in the expanded beads is preferably 0.01% by weight to 1.00% by weight, more preferably 0.05% by weight to 0.70% by weight, and even more preferably 0.10% by weight to 0.60% by weight, relative to 100% by weight of the expanded beads. When the content of the hydrophilic compound is (i) 0.01% by weight or more, the foaming effect of the hydrophilic compound can be sufficiently obtained, and (ii) when it is 1.00% by weight or less, there is no risk of the resulting expanded beads shrinking excessively.

The crystal nucleating agent blended into the resin composition is a substance that can become a foaming nucleus when the resin particles are foamed. It is preferable that the foamed particles contain a crystal nucleating agent.

Examples of crystal nucleating agents that can be used in one embodiment of the present invention include talc, feldspar, zeolite, mica, silica, kaolin, barium sulfate, aluminum hydroxide, aluminum oxide, titanium oxide, bentonite, zinc borate, and the like. These crystal nucleating agents may be used alone or in combination of two or more. When two or more crystal nucleating agents are used in combination, the mixing ratio may be adjusted as appropriate depending on the purpose.

From the viewpoint of uniformity of the average bubble diameter, the content of the crystal nucleating agent in the expanded beads is preferably 0.01% by weight to 2.00% by weight, more preferably 0.02% by weight to 1.00% by weight, and even more preferably 0.03% by weight to 0.50% by weight, relative to 100% by weight of the expanded beads.

The foamed particles preferably contain carbon black and/or graphite to color the resulting foamed molded article gray or black.

In the present expanded beads, the average particle size of the primary particles of the carbon black is preferably 10 nm to 200 nm, more preferably 15 nm to 150 nm, even more preferably 20 nm to 100 nm, and particularly preferably 20 nm to 50 nm. With this configuration, even when the amount of carbon black added is small, a foamed molded product with a high degree of blackness can be obtained, and the foamed molded product also has the advantage of having excellent flame retardancy.

The carbon black content in the expanded beads is not particularly limited, but is preferably 2.00% by weight to 5.00% by weight, more preferably 2.00% by weight to 4.00% by weight, and even more preferably 2.50% by weight to 3.50% by weight, based on 100% by weight of the expanded beads. When the carbon black content in 100% by weight of the expanded beads is 2.00% by weight or more, the blackness of the resulting expanded molded article tends to be good. When the carbon black content in 100% by weight of the expanded beads is 5.00% by weight or less, the flame retardancy of the resulting expanded molded article tends to be good.

The term "metal deactivator" refers to a substance capable of capturing metal ions. Specifically, the term "metal deactivator" refers to a substance capable of forming an ionic bond with a metal ion or a complex with a metal ion.

It is preferable that the present expanded beads further contain a metal deactivator. When the present expanded beads contain a metal deactivator, it has the advantage of being able to reduce accelerated deterioration due to oxidation of the expanded beads or the expanded molded article caused by metal ions. The recycled polyolefin resin may contain metal ions. Therefore, when the present expanded beads contain a recycled polyolefin resin as the polyolefin resin (A), it is particularly preferable that the expanded beads further contain a metal deactivator.

There are no particular limitations on the metal deactivator as long as it is capable of capturing metal ions, but examples include 2-hydroxy-N-1H-1,2,4-triazol-3-ylbenzamide, N'1,N'12-bis(2-hydroxybenzoyl)dodecane dihydrazide, N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, 1,3,5-triazine-2,4,6-triamine, 2',3-bis[[3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionyl]]propionohydrazide, EDTA, and EDTA-2Na. Commercially available products may be used as the metal deactivator. Commercially available products that can be used as metal deactivators include IRGANOX (registered trademark) MD1024 manufactured by BASF, and Adeka STAB (registered trademark) CDA-1, Adeka STAB (registered trademark) CDA-1M, Adeka STAB (registered trademark) CDA-6S, Adeka STAB (registered trademark) CDA-10, and Adeka STAB (registered trademark) ZS series manufactured by ADEKA.

<Physical Properties>
(MFR of polyolefin resin particles)
The MFR of the polyolefin resin particles according to one embodiment of the present invention is not particularly limited, but is more preferably 3 g/10 min to 35 g/10 min, even more preferably 5 g/10 min to 25 g/10 min, and particularly preferably 7 g/10 min to 15 g/10 min. When the MFR of the polyolefin resin particles is 3 g/10 min or more, there is an advantage that it is easy to increase the expansion ratio of the expanded beads in the production of the expanded beads. When the MFR of the polyolefin resin particles is 35 g/10 min or less, there is no risk of the cells of the resulting expanded beads becoming interconnected, and as a result, (i) the compressive strength of the expanded molded article obtained from the expanded beads tends to be good, or (ii) the surface beauty of the expanded molded article tends to be good. The method for measuring the MFR of the polyolefin resin particles will be described in detail in the examples below.

(Oxygen Index of Polyolefin Resin Particles)
The oxygen index of the polyolefin-based resin particles according to one embodiment of the present invention is not particularly limited, but is preferably 18.7% or more, more preferably 19.0% or more, even more preferably 19.1% or more, and particularly preferably 19.2% or more.The higher the oxygen index of the resin particles, the higher the flame retardancy of the foamed molded product tends to be.The method for measuring the oxygen index of the polyolefin-based resin particles will be described in detail in the examples below.

(DSC ratio of polyolefin resin expanded particles)
The DSC ratio of the expanded beads is not particularly limited, but is preferably 10.0% to 50.0%, more preferably 15.0% to 40.0%, even more preferably 18.0% to 30.0%, and particularly preferably 20.0% to 25.0%. When the DSC ratio of the expanded beads is 10.0% or more, the expanded beads have the advantage of being able to provide a foamed molded article having sufficient strength. On the other hand, when the DSC ratio of the expanded beads is 40.0% or less, the expanded beads have the advantage of being able to be molded at a relatively low temperature (molding temperature) to provide a foamed molded article. The method for measuring the DSC ratio of the expanded beads will be described in detail in the examples below.

(Bulk density of expanded polyolefin resin particles)
The bulk density of the present expanded beads is not particularly limited, but is preferably 15.0 g/L to 55.0 g/L, more preferably 20.0 g/L to 40.0 g/L, and even more preferably 20.0 g/L to 30.0 g/L. In addition, within the range of 20.0 g/L to 30.0 g/L, the greater the bulk density, the slower the burning rate of the foam tends to be. If the bulk density is less than 15.0 g/L, the resulting foamed molded product of the polyolefin resin tends to shrink or deform easily, and mechanical performance tends to decrease. In this specification, the foamed molded product tends to shrink or deform easily, meaning that the dimensional shrinkage rate or deformation shrinkage rate of the molded product tends to be large. If the bulk density exceeds 55.0 g/L, the mechanical strength of the resulting in-mold expanded molded product tends to be high, but the advantage of reducing the weight of the in-mold expanded molded product is not obtained, and the flexibility and cushioning properties of the resulting in-mold expanded molded product tend to be insufficient. In this specification, the mechanical strength of the in-mold foam tends to be high, which means that the dimensional shrinkage of the in-mold foam tends to be suppressed. The method for measuring the bulk density of the expanded beads will be described in detail in the Examples below.

2. Method for producing expanded polyolefin resin particles
A method for producing expanded polyolefin resin beads according to one embodiment of the present invention includes a dispersing step of dispersing polyolefin resin particles made of a polyolefin resin composition containing a polyolefin resin (A), a calcium compound (C2), a phenolic antioxidant (D) and a phosphorus-based process stabilizer (E) and a blowing agent in an aqueous dispersion medium in a container, and a releasing step of releasing the dispersion obtained in the dispersing step into a region having a lower pressure than the pressure in the container, wherein the calcium compound (C2) is a compound that does not contain elemental sulfur or elemental halogen, and the content of the calcium compound (C2) is 0.10% by weight to 3.00% by weight in 100% by weight of the expanded polyolefin resin beads.

Another embodiment of the present invention relates to a method for producing expanded polyolefin resin particles comprising a polyolefin resin (A), a calcium compound (C1), a phenol-based antioxidant (D) and a phosphorus-based process stabilizer (E), and the method comprises the steps of: (i) producing a polyolefin resin (A), (ii) producing a polyolefin resin composition comprising a calcium compound (C1) and/or a precursor of the calcium compound (C1), (iii) producing a phenol-based antioxidant (D) and (iv) producing a phosphorus-based process stabilizer (E) in a container; The method includes a dispersion step of dispersing polyolefin resin particles and a blowing agent in an aqueous dispersion medium, and a release step of releasing the dispersion liquid obtained in the dispersion step into a region with a lower pressure than the pressure inside the container, the calcium compound (C1) is a compound that does not contain sulfur element and halogen element, the precursor of the calcium compound (C1) is a compound that does not contain sulfur element and halogen element, and the content of the calcium compound (C1) in the polyolefin resin expanded particles is 0.10 weight % to 3.00 weight % in 100 weight % of the polyolefin resin expanded particles.

In this specification, the "polyolefin resin composition" may be referred to as the "resin composition," and the "method for producing expanded polyolefin resin particles according to one embodiment of the present invention" may be referred to as the "present production method."

The present manufacturing method has the above-mentioned configuration, and therefore has the advantage that it is possible to provide polyolefin resin foam particles that can provide foamed molded articles with excellent long-term thermal stability, surface beauty, and flame retardancy with a small environmental impact by suppressing thermal decomposition of the polyolefin resin in the granulation process for producing the resin particles, making it difficult for the MFR of the resin particles to increase.

In this manufacturing method, the polyolefin resin (A) may contain a recycled polyolefin resin. According to this manufacturing method, even when the polyolefin resin (A) contains a recycled polyolefin resin, the thermal decomposition of the polyolefin resin is suppressed in the granulation process for producing the resin particles, making it difficult for the MFR of the resin particles to increase, and the obtained foamed molded article has the advantages of being excellent in long-term thermal stability, surface beauty, and flame retardancy.

<Calcium Compound (C2)>
In the present production method, the polyolefin resin composition contains a calcium compound (C2), and the calcium compound (C2) is dispersed within the resin composition.

Calcium compound (C2) refers to a compound that contains calcium but does not contain sulfur or halogen elements. In this specification, "calcium compound (C2)" may also be referred to as "precursor of calcium compound (C1)", and the terms "calcium compound (C2)" and "precursor of calcium compound (C1)" are interchangeable. In other words, in this specification, the explanation of "calcium compound (C2)" can be replaced with the explanation of "precursor of calcium compound (C1)".

The calcium compound (C2) is preferably a compound that does not contain sulfur or halogen elements, and is, for example, one or more compounds selected from the group consisting of calcium salts (e.g., anhydrous inorganic salts containing calcium, hydrates of inorganic salts containing calcium, organic salts containing calcium, hydrates of organic salts containing calcium, etc.), calcium hydroxide, calcium oxide, calcium peroxide, and calcium carbide.

The "anhydride of an inorganic salt containing calcium" and "hydrate of an inorganic salt containing calcium" contained in the calcium compound (C2) are preferably at least one selected from the group consisting of calcium carbonate, calcium hydrogen carbonate, calcium phosphite, monocalcium aluminosilicate, dicalcium aluminosilicate, monocalcium aluminate, tricalcium aluminate, dicalcium silicate, tricalcium silicate, calcium hypophosphite, calcium hydroxide phosphate, magnesium calcium carbonate, calcium diphosphate, pentacalcium hexasilicate, hexacalcium hexasilicate, calcium hexafluorosilicate, calcium metasilicate, magnesium calcium metasilicate, calcium metaphosphate, tricalcium phosphate, tetracalcium phosphate, octacalcium phosphate, calcium monohydrogen phosphate, calcium dihydrogen phosphate, and hydrates thereof.

The "anhydride of an organic salt containing calcium" and the "hydrate of an organic salt containing calcium" contained in the calcium compound (C2) are preferably, for example, one or more selected from the group consisting of fatty acid calcium and hydrates thereof.

In the heating step of this manufacturing method, the resin particles are dispersed in an aqueous dispersant. Therefore, the calcium compound (C2) contained in the resin particles may change to a hydrate of the calcium compound (C2) during the manufacturing process. As a result, the expanded particles obtained by this manufacturing method (the expanded particles) may contain a hydrate of the calcium compound (C2) used as the calcium compound (C1). In addition, when carbon dioxide is used as a blowing agent in the heating step of this manufacturing method, the calcium compound (C2) contained in the resin particles may change to a carbonate of the calcium compound (C2) during the manufacturing process. As a result, the expanded particles obtained by this manufacturing method (the expanded particles) may contain a carbonate of the calcium compound (C2) used as the calcium compound (C1).

The calcium compounds (C2) described above may be used alone or in combination of two or more.

The calcium compound (C2) preferably contains one or more selected from the group consisting of calcium oxide, calcium hydroxide, calcium carbonate, and calcium fatty acid. This configuration has the advantage of producing a foamed molded product with excellent flame retardancy.

The calcium compound (C2) is preferably calcium oxide and/or fatty acid calcium. That is, the calcium compound (C2) preferably contains one or more compounds selected from the group consisting of calcium oxide and fatty acid calcium. This configuration has the advantage that a foamed molded product with excellent flame retardancy can be obtained.

The amount of each component used in the resin composition is preferably in the same numerical range as the content of each component described in [1. Expanded polyolefin resin particles]. The amount of calcium compound (C2) used is preferably in the same numerical range as the content of calcium compound (C1).

Each aspect (e.g., each step) of this manufacturing method will be described below, but for matters other than those described in detail below, the description in [1. Expanded polyolefin resin particles] will be used as appropriate.

(Granulation process)
The present production method preferably includes a granulation step of preparing resin particles prior to the expansion step.

The granulation step in this manufacturing method is not particularly limited as long as resin particles can be obtained, and known methods can be used. One example of the granulation step is a method in which the following steps (S1) to (S3) are carried out in order: (S1) A resin composition containing a predetermined amount of polyolefin resin (A), a calcium compound (C2), a phenolic antioxidant (D), and a phosphorus-based processing stabilizer (E), and optionally a hindered amine (B) and other additives, is melt-kneaded using an extruder to prepare a molten kneaded product; (S2) The molten kneaded product is extruded through a die provided in the extruder; (S3) The extruded molten kneaded product is chopped into a desired shape (e.g., cylindrical, spherical, etc.) to obtain polyolefin resin particles.

In the above (S1), a resin composition containing a predetermined amount of polyolefin resin (A), calcium compound (C2), phenolic antioxidant (D), and phosphorus-based processing stabilizer (E), and optionally hindered amine (B) and other additives, may be prepared in advance, and then fed to an extruder for melt-kneading to prepare a melt-kneaded product.

In the above (S3), before the molten mixture is chopped, the extruded molten mixture may be cooled and solidified using a cooling medium such as water.

(Dispersion process)
Examples of the vessel include a pressure vessel and an autoclave type pressure vessel. The vessel may be equipped with a stirrer therein.

Examples of aqueous dispersion media include (a) dispersion media obtained by adding methanol, ethanol, ethylene glycol, glycerin, or the like to water, (b) water such as tap water and industrial water, and (c) solutions (aqueous solutions) containing salts such as sodium chloride or sodium sulfate. In terms of enabling stable production of expanded particles, it is preferable to use pure water such as RO water (water purified by reverse osmosis membrane method), distilled water, deionized water (water purified by ion exchange resin), and ultrapure water as the aqueous dispersion medium.

Examples of blowing agents include (a) (a-1) inorganic gases such as nitrogen, carbon dioxide, and air (a mixture of oxygen, nitrogen, and carbon dioxide), and (a-2) water; and (b) organic blowing agents such as (b-1) saturated hydrocarbons having 3 to 5 carbon atoms such as propane, normal butane, isobutane, normal pentane, isopentane, and neopentane, (b-2) ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether, and (b-3) halogenated hydrocarbons such as monochloromethane, chloroethane, and hydrofluoroolefins.

In the present method for producing expanded beads, it is preferable to use a dispersant (e.g., a poorly water-soluble inorganic compound such as kaolin or talc) and a dispersion aid (e.g., an anionic surfactant such as sodium dodecylbenzenesulfonate). This configuration can reduce adhesion between resin particles (sometimes called blocking) and can increase the stability of the dispersion in the container. As a result, it has the advantage of being able to stably produce expanded beads.

The above-mentioned aqueous dispersion medium and foaming agent may each be used alone or in combination of two or more.

The amounts of the aqueous dispersion medium, blowing agent, dispersant, and dispersion aid used are not particularly limited, and can be appropriately set taking into consideration (i) the stability of the dispersion (dispersibility of the resin particles), (ii) the density of the resulting expanded beads, (iii) the fusion properties of the expanded molded article obtained by molding the resulting expanded beads, (iv) productivity, and (v) economic efficiency.

The method for dispersing the polyolefin resin particles and the blowing agent in the aqueous dispersion medium in the container, i.e., the specific method for the dispersion process, is not particularly limited. For example, a method may be used in which the aqueous dispersion medium, the polyolefin resin particles, and the blowing agent are supplied to the container, and the mixture in the container is stirred with a stirrer provided in the container.

(Temperature increase-pressure increase step and holding step)
It is preferable that the present production method further includes, in this order, after the dispersion step and before the release step, (1) a temperature-pressure increase step in which the temperature inside the container is increased to a constant temperature and the pressure inside the container is increased to a constant pressure, and (2) a holding step in which the temperature and pressure inside the container are held at constant temperature and constant pressure. In this specification, the (a) constant temperature in the temperature-pressure increase step and the holding step may be referred to as the foaming temperature, and the (b) constant pressure in the (a) constant pressure step may be referred to as the foaming pressure.

The foaming temperature is not particularly limited, but is preferably 130°C to 165°C, more preferably 135°C to 160°C, more preferably 140°C to 158°C, and even more preferably 150°C to 158°C. The DSC ratio of the foamed particles can be adjusted by the foaming temperature, and with this configuration, the DSC ratio is 10% to 50%.

The foaming pressure is not particularly limited, but is preferably 0.5 MPa (gauge pressure) to 10.0 MPa (gauge pressure), more preferably 1.0 MPa (gauge pressure) to 5.0 MPa (gauge pressure), more preferably 2.0 MPa (gauge pressure) to 3.0 MPa (gauge pressure), and even more preferably 2.2 MPa (gauge pressure) to 2.5 MPa (gauge pressure). If the foaming pressure is 0.5 MPa (gauge pressure) or more, foamed particles with a suitable density can be obtained.

In the holding step, the time (holding time) for which the dispersion in the container is held near the foaming temperature and foaming pressure is not particularly limited, but is preferably 10 to 60 minutes, more preferably 12 to 50 minutes, and even more preferably 15 to 40 minutes.

(Release process)
In the releasing step, the dispersion obtained after the heating step is released under low pressure. The releasing step allows the resin particles to expand, resulting in expanded particles. The releasing step can also be said to be a step of opening one end of the container and releasing the dispersion (dispersion) in the container into a region (space) with a pressure lower than the expansion pressure (i.e., the pressure inside the container).

In the release process, the "region under pressure lower than the foaming pressure" refers to the "region under pressure lower than the foaming pressure" or the "space under pressure lower than the foaming pressure", and can also be referred to as "an atmosphere under pressure lower than the foaming pressure". The region under pressure lower than the foaming pressure may be, for example, a region under atmospheric pressure.

In the release step, the temperature of the release area (atmosphere) is not particularly limited, but is preferably 20°C to 110°C, more preferably 50°C to 105°C, more preferably 80°C to 100°C, and even more preferably 90°C to 100°C. This configuration has the advantage that expanded particles with a relatively low bulk density can be obtained even at low expansion pressure, and there is no risk of the expanded particles sticking to each other in the release area.

(Foaming process)
The process from the dispersing step to the releasing step may be referred to as an expansion step. The process of producing expanded beads from resin beads in this manner is referred to as a "first-stage expansion step," and the expanded beads thus obtained are referred to as "first-stage expanded beads."

(Two-stage foaming process)
In order to obtain expanded beads with a high expansion ratio, the first-stage expanded beads obtained in the first-stage expansion step may be expanded again. The step of increasing the expansion ratio of the first-stage expanded beads is called the "second-stage expansion step", and the polyolefin resin expanded beads obtained in the second-stage expansion step are called "second-stage expanded beads". The specific method of the second-stage expansion step is not particularly limited, and a known method can be used.

[3. Polyolefin resin foam molding]
The polyolefin resin foam molded article according to one embodiment of the present invention is a foam molded article obtained by foam molding the polyolefin foam beads described in the section [1. Polyolefin foam beads]. In this specification, the "polyolefin resin foam molded article according to one embodiment of the present invention" may be referred to as the "present foam molded article".

Because this foamed molded product has the above-mentioned structure, it has the advantages of excellent long-term thermal stability, beautiful surface, and flame retardancy.

<Physical Properties>
(Burning rate of polyolefin resin foam molded body)
The maximum burning rate of the present foamed molded article is preferably less than 100 mm/min, more preferably less than 95 mm/min, more preferably less than 90 mm/min, more preferably 89 mm/min or less, more preferably 87 mm/min or less, even more preferably 80 mm/min or less, and particularly preferably 75 mm/min or less.

The average burning rate of the foamed molded article is preferably less than 95 mm/min, more preferably less than 90 mm/min, more preferably 88 mm/min or less, more preferably 87 mm/min or less, more preferably 85 mm/min or less, more preferably 80 mm/min or less, even more preferably 75 mm/min or less, and particularly preferably 70 mm/min or less.

In this specification, the foam molded product is "excellent in flame retardancy" means that the foam molded product has either a maximum burning rate of less than 100 mm/min or an average burning rate of less than 95 mm/min. In this specification, the foam molded product is also considered to have "excellent in flame retardancy" when it has non-flammability.

The method for measuring the maximum burning rate and average burning rate of foamed molded products will be described in detail in the examples below.

(Density of polyolefin resin foam molded body)
The density of the foamed molded article is not particularly limited, but is preferably 20.0 g/L to 60.0 g/L, preferably 26.5 g/L to 50.0 g/L, preferably 25.0 g/L to 45.0 g/L, preferably 30.0 g/L to 45.0 g/L, and preferably 35.0 g/L to 40.0 g/L. If the density of the foamed molded article is 26.5 g/L or more, there is an advantage that the foamed molded article has no sink marks on the surface of the foamed molded article, is smooth, and has better surface beauty, and if it is 50.0 g/L or less, a sufficiently lightweight foamed molded article can be obtained. In addition, according to the above-mentioned configuration, there is an advantage that a foamed molded article having excellent moldability and flame retardancy can be obtained. The method for measuring the density of the foamed molded article will be described in detail in the examples described later.

<Method of manufacturing foamed molded article>
The method for producing the present foamed molded article is not particularly limited as long as the present foamed beads can be molded (preferably in-mold foam molding), and a known method can be applied. As the method for producing the present foamed molded article, for example, the method described in the section <Method for producing foamed molded article> of International Publication WO2022/149538 can be suitably adopted.

Below, one embodiment of the present invention will be explained in more detail using examples and comparative examples, but the present invention is not limited to these examples.

〔material〕
The materials used in the examples and comparative examples are described below. The materials used in the examples and comparative examples were not particularly purified before use.

<Polyolefin Resin (A)>
Polypropylene resin 1: Ethylene/propylene random copolymer [recycled polyolefin resin, propylene unit content: 91 mol%, MFR = 7.1 g/10 min, melting point 153°C]
Polypropylene resin 2: 1-butene/ethylene/propylene random copolymer [non-recycled polyolefin resin, propylene unit content: 96 mol%, MFR = 10 g/10 min, melting point 148°C]
Polypropylene resin 3: ethylene/propylene random copolymer [recycled polyolefin resin, propylene unit content: 91 mol%, MFR = 12 g/10 min, melting point 152°C].

<Additives>
(Hindered amine (B))
Hindered amine [FLAMESTAB (registered trademark) NOR116 (compound with CAS number 191680-81-6), manufactured by BASF]
(Calcium compound (C2))
Calcium oxide [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.]
Calcium stearate [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.]
(Phenol-based antioxidant (D))
Phenolic antioxidant (manufactured by BASF, IRGANOX (registered trademark) 1010 (tetrakis [3- (3', 5'-di-t-butyl-4'-hydroxyphenyl) propionic acid] pentaerythritol)
(Phosphorus-based processing stabilizer (E))
Phosphorus-based processing stabilizer [Irgafos 168 (tris(2,4-di-t-butylphenyl)phosphite), manufactured by BASF]
(Calcium oxide mixture)
Calcium oxide mixture (manufactured by BASF, PS032G (a mixture containing at least calcium oxide, calcium stearate, a phenolic antioxidant, and a phosphorus-based processing stabilizer. In the mixture, the only compounds containing calcium are calcium oxide and calcium stearate, and the total content of calcium oxide and calcium stearate is 45% by weight in 100% by weight of the product)
(Other flame retardants)
Phosphate ester flame retardant [PX-200 (tetrakis(2,6-dimethylphenyl)-m-phenylene bisphosphate), manufactured by Daihachi Chemical Industry Co., Ltd.]
(Other additives)
Talc [Talc Powder PK-S, manufactured by Hayashi Kasei Co., Ltd.]
Glycerin [Refined glycerin D, manufactured by Lion Corporation]
Carbon black (average primary particle size: 30 nm)
Calcium sulfate dihydrate [Wako Pure Chemical Industries, Ltd.]
Metal deactivator [IRGANOX (registered trademark) MD1024, manufactured by BASF].

[Measurement method]
The measurement and evaluation methods for various items carried out in the examples and comparative examples will be described below.

(MFR of polyolefin resin (A) and polyolefin resin particles)
The MFR of the polyolefin resin (A) and the polyolefin resin particles was measured using an MFR measuring device described in JIS K7210-1: 2014. The measurement conditions were an orifice diameter of 2.0959±0.005 mmφ, an orifice length of 8.000±0.025 mm, a load of 2160 g, and a temperature of 230±0.2°C.

<Melting point of polyolefin resin (A)>
The melting point of the polyolefin resin (A) was measured using a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Corporation). Specific operation procedures were as follows (1) to (4): (1) the temperature of 5 mg to 6 mg of polyolefin resin (A) was raised from 40.0°C to 220.0°C at a heating rate of 10.0°C/min to melt the polyolefin resin (A); (2) the temperature of the molten polyolefin resin (A) was then lowered from 220.0°C to 40.0°C at a heating rate of 10.0°C/min to crystallize the polyolefin resin (A); (3) the temperature of the crystallized polyolefin resin (A) was then further raised from 40.0°C to 220.0°C at a heating rate of 10.0°C/min; (4) the temperature of the peak (melting peak) of the DSC curve of the polyolefin resin (A) obtained during the second heating (i.e., during (3)) was taken as the melting point of the polyolefin resin (A). In addition, when a plurality of peaks (melting peaks) are present in the DSC curve of the polyolefin resin (A) obtained during the second heating by the above-mentioned method, the temperature of the peak (melting peak) having the maximum heat of fusion was determined as the melting point of the polyolefin resin (A).

(Average particle size of primary particles of carbon black)
A cross section of the membrane constituting the bubbles of the obtained polyolefin resin foamed beads was photographed at a magnification of 40,000 times using a transmission electron microscope. In the obtained transmission electron microscope photograph, the particle diameters (Ferret diameters) of 50 randomly selected primary carbon black particles were measured in the X and Y directions, respectively, and the average value was calculated to be the average particle diameter of the primary carbon black particles.

(Oxygen Index of Polyolefin Resin Particles)
The oxygen index of the polyolefin-based resin particles was measured by the following methods (1) to (3): (1) the polyolefin-based resin particles were heat-pressed at 200° C. for 1 minute using a spacer having dimensions of 150 mm length×150 mm width×1 mm thickness to obtain a resin plate made of the polyolefin-based resin particles; (2) a sample having a length of 100 mm×width of 6.5 mm was cut out from the resin plate made of the polyolefin-based resin particles; (3) the oxygen index of the cut out sample was measured in accordance with JIS K7201 (test method for flammability based on oxygen index).

(Measurement of DSC ratio of expanded polyolefin resin particles)
The DSC ratio of the expanded polyolefin resin particles was measured using a differential scanning calorimeter [DSC7020, Hitachi High-Tech Science Corporation]. Specifically, the DSC ratio was calculated by [Qh/(Ql+Qh)×100], where the melting peak area on the low-temperature side of the DSC curve obtained when 5 mg to 6 mg of expanded polyolefin resin particles were heated from 40° C. to 220° C. at a heating rate of 10° C./min was taken as Ql, and the melting peak area on the high-temperature side was taken as Qh. Strictly speaking, the area surrounded by the melting peak on the low-temperature side and the tangent line from the maximum point between the melting peak on the low-temperature side and the melting peak on the high-temperature side to the melting start baseline was taken as Ql. In addition, the melting peak heat quantity on the high-temperature side, which is the heat quantity surrounded by the melting peak on the high-temperature side and the tangent line from the maximum point between the melting peak on the low-temperature side and the melting peak on the high-temperature side to the melting end baseline, was taken as Qh.

(Bulk density of expanded polyolefin resin particles)
The weight w (g) of the expanded polyolefin resin particles was weighed, and the volume v (L) was measured using a measuring cylinder at 23°C under atmospheric pressure (standard atmospheric pressure 0.1 MPa), to determine the bulk density in terms of w/v (g/L).

(Density of foamed molded body)
The density of the foam molded article was measured by the following methods (1) to (3): (1) the length (mm) of the foam molded article in the length direction, width direction, and thickness direction (mm) were measured, and the volume V (L) of the foam molded article was calculated; (2) the weight W (g) of the foam molded article was measured; and (3) the density of the foam molded article was calculated based on the following formula:
Density of foamed molded body (g/L) = W/V.

(Evaluation of surface aesthetics of polyolefin resin foam molded products)
The side surface of the obtained foamed molded article was visually observed and the surface aesthetics was judged according to the following criteria, where a larger number means a more excellent surface aesthetics.
2 (Good): There are almost no gaps between particles (between the polyolefin resin foam particles), the surface irregularities are not noticeable, and there are no wrinkles, shrinkage, or uneven coloring, making the surface beautiful.
1 (Fair): Some intergranular or surface irregularities, shrinkage, wrinkles or color unevenness are observed.
0 (unacceptable): Clearly noticeable gaps, surface irregularities, shrinkage, wrinkles or color unevenness across the entire observation surface.

(Burning rate of polyolefin resin foam molded body)
From the obtained polyolefin resin foam molded article, a flame retardancy test sample having a length of 350 mm, a width of 100 mm, and a thickness of 12 mm was cut out, and an A mark was provided at a position 38 mm from one end of the sample in the longitudinal direction, and a B mark was provided at a position 292 mm from the other end. Ten test samples were prepared, and tests were carried out on all of them. Using an FMVSS flammability tester [manufactured by Suga Test Instruments Co., Ltd.], a flame from a burner adjusted to a height of 38 mm was applied to the one end of the sample in the longitudinal direction for 15 seconds so that the end of the sample was the center of the flame, and the burning rate of the test pieces that did not have "non-flammability" was calculated based on the criteria shown in (i) to (iii) below, and the maximum burning rate and the average burning rate were calculated from the results.

(i) Those whose flames were extinguished before reaching the A-marked line were deemed to have "non-combustible properties." (ii) Those whose flames burned beyond the A-marked line and were extinguished before reaching the B-marked line: The burning speed {(L1)/T1} (mm/min) was calculated from the time T1 (min) from when the flames passed the A-marked line until they were extinguished and the burning distance L1 (mm) from the A-marked line. (iii) Those whose flames burned beyond the A-marked line and were burning until they reached the B-marked line: The burning speed 254/T2 (mm/min) was calculated from the time T2 (min) from when the flames passed the A-marked line until they reached the B-marked line and the distance 254 mm from the A-marked line to the B-marked line. Based on these results, the highest burning speed among the burning speeds of the 10 sample samples was determined as the "maximum burning speed." In addition, the average value of the burning speeds of the 10 sample samples was determined as the "average burning speed."

The methods for producing polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin in-mold foamed articles in the examples and comparative examples are described below.

(Examples 1 to 8 and Comparative Examples 1 to 6)
[Preparation of polyolefin-based resin particles]
The polyolefin resin and the materials shown in Table 1 or Table 2 were hand-blended to obtain the weight ratios shown in Table 1 or Table 2, and melt-kneaded using a twin-screw extruder at a resin temperature of 220° C. Thereafter, the resulting melt-kneaded product was extruded from the extruder in the form of strands, and the resulting strands were water-cooled and cut to obtain polyolefin resin particles with an average weight of 1.2 mg.

[Preparation of polyolefin resin foam particles]
In a 10L pressure-resistant autoclave, 100 parts by weight (2.4 kg) of the polyolefin resin particles obtained by the above method, 200 parts by weight of water, 0.3 parts by weight of kaolin [ASP170, manufactured by BASF] as a poorly water-soluble inorganic compound, and 0.38 parts by weight of an aqueous solution of sodium dodecylbenzenesulfonate [Neopelex G-15, manufactured by Kao Corporation] as a surfactant were charged. Then, while stirring the charged raw materials, 4 parts by weight of carbon dioxide was added to the autoclave as a foaming agent to prepare a dispersion (dispersion process). Next, the contents of the autoclave were heated to the foaming temperature shown in Table 1 or Table 2, and held for 10 minutes, and then carbon dioxide was additionally injected to increase the internal pressure of the autoclave to the foaming pressure shown in Table 1 or Table 2 (heating-pressure increase process). After maintaining the foaming temperature and foaming pressure for 20 minutes (maintaining step), the valve at the bottom of the autoclave was opened, and the foamed particles were discharged through an opening orifice having a diameter of 3.6 mm into an atmosphere at 97° C. under atmospheric pressure to obtain polyolefin-based resin foamed particles (discharging step). During the discharging step, carbon dioxide was injected to maintain the pressure in the container so that the pressure would not decrease.

[Preparation of second-stage expanded beads]
In all the cases except for Example 2, the obtained polyolefin resin expanded beads were dried at 80° C., impregnated with pressurized air in a pressure vessel to adjust the internal pressure to 0.3 MPa (absolute pressure), and then contacted with water vapor at 0.07 MPa (gauge pressure) to perform second-stage expansion. The bulk density of the obtained second-stage expanded beads was approximately 21 g/L.

[Preparation of polyolefin resin in-mold foamed article]
The obtained two-stage expanded particles were put into a pressure-resistant container, impregnated with pressurized air, and the polyolefin resin expanded particles, which had been adjusted in advance to have an internal pressure of 0.20 MPa (absolute pressure), were filled into a mold having a length of 370 mm, a width of 320 mm, and a thickness of 50 mm. The inside of the mold chamber was then heated with steam at 0.32 MPa (gauge pressure) to fuse the expanded particles together. After the inside of the mold and the surface of the molded body were cooled with water, the molded body was taken out to obtain a polyolefin resin in-mold expanded molded body. The obtained in-mold expanded molded body was left to stand at 23°C for 2 hours, and then aged at 75°C for 16 hours.

(Example 9 and Comparative Example 8)
The polyolefin resin and the materials shown in Table 1 or Table 2 were hand-blended to the weight ratios shown in Table 1 or Table 2, and melt-kneaded using a twin-screw extruder at a resin temperature of 220°C. The resulting melt-kneaded product was then extruded from the extruder in the form of a strand, and the resulting strand was water-cooled and cut to obtain polyolefin resin particles with an average weight of 1.2 mg. The resulting polyolefin resin particles were fed into a twin-screw extruder, and polyolefin resin particles with an average weight of 1.2 mg were obtained in the same manner. This process was repeated four times to obtain polyolefin resin particles that had been melt-kneaded four times.

The evaluation results for the obtained polyolefin resin particles, polyolefin resin foam particles, and polyolefin resin in-mold foamed articles are shown in Tables 1 and 2.

In Examples 1 to 4 and 6, calcium oxide was used as the calcium compound (C2). The amount used was 0.15% by weight based on 100% by weight of the expanded beads. Therefore, the expanded beads obtained in Examples 1 to 4 and 6 contain at least one calcium compound (C1) selected from the group consisting of calcium oxide, calcium oxide hydrate and calcium carbonate, and the total content of calcium oxide, calcium oxide hydrate and calcium carbonate in the expanded beads is at least in the range of 0.10% by weight to 3.00% by weight based on 100% by weight of the expanded beads, and is approximately 0.15% by weight to 0.27% by weight.

In addition, in Examples 1 to 3, calcium stearate was used as the calcium compound (C2). The amount used was 0.04% by weight based on 100% by weight of the expanded beads. Therefore, the expanded beads obtained in Examples 1 to 3 contain 0.04% by weight of calcium stearate as the calcium compound (C1) based on 100% by weight of the expanded beads.

In Example 5, a calcium oxide mixture was used as the calcium compound (C2). As described above, the calcium oxide mixture is a mixture containing at least calcium oxide, calcium stearate, a phenolic antioxidant, and a phosphorus-based processing stabilizer. In addition, the only compounds containing calcium in the mixture are calcium oxide and calcium stearate, and the total content of calcium oxide and calcium stearate is 45% by weight in 100% by weight of the product. Therefore, the expanded particles obtained in Example 5 contain at least one of calcium oxide, calcium oxide hydrate, and calcium carbonate as the calcium compound (C1), and calcium stearate. The total content of calcium oxide, calcium oxide hydrate, calcium carbonate, and calcium stearate in the expanded particles is at least in the range of 0.10% by weight to 3.00% by weight in 100% by weight of the expanded particles, and can be said to be approximately 0.225% by weight to 0.400% by weight.

In Examples 1 to 6, the evaluation results of polyolefin resin particles, polyolefin resin expanded particles, and polyolefin resin in-mold foamed molded products according to one embodiment of the present invention are shown. In Examples 1 to 5, the in-mold foamed molded products obtained were excellent in flame retardancy, even though the expanded particles contained carbon black. In Example 6, in which the expanded particles did not contain carbon black, the in-mold foamed molded products obtained had "non-flammability." Thus, the in-mold foamed molded products made of polyolefin resin expanded particles obtained by the manufacturing method of the present invention were excellent in flame retardancy. As shown in Comparative Examples 1 to 4, when the expanded particles did not contain a calcium compound (C2), the resulting foamed molded products did not have excellent flame retardancy, and even when the amount of hindered amine (B) was increased as in Comparative Example 2, there was still room for improvement in flame retardancy.

The polyolefin resin particles of Examples 3 to 6, which contain calcium compound (C2), had a lower MFR than the polyolefin resin particles of Comparative Examples 1 to 3, which do not contain calcium compound (C2). That is, the polyolefin resin particles contain calcium compound (C2), which suppresses the increase in MFR. The polyolefin resin particles obtained in Comparative Example 4 contained a phenol-based antioxidant (D) and a phosphorus-based processing stabilizer (E), so the MFR value was lower than that of Comparative Examples 1 to 3, but the MFR was not equivalent to that of Examples 3 to 6. Comparative Examples 5 to 6 show the results when the calcium compound (C2) was contained, but the content of calcium compound (C2) was low, or the content of calcium compound (C2) was high. In Comparative Examples 5 to 6, the MFR value of the polyolefin resin particles was also lower than that of Comparative Examples 1 to 3, but the MFR of the polyolefin resin particles was not equivalent to that of Examples 3 to 6. Furthermore, in Reference Example 2, which contained a calcium oxide mixture containing calcium oxide, calcium stearate, a phenolic antioxidant, and a phosphorus-based processing stabilizer, the increase in MFR was suppressed compared to Reference Example 1. Therefore, it was shown that in order to suppress the increase in MFR, a calcium compound (C2) with a content of 0.10 wt% to 3.00 wt% based on 100 wt% of polyolefin resin particles, a phenolic antioxidant (D), and a phosphorus-based processing stabilizer (E) are necessary.

In one embodiment of the present invention, the thermal decomposition of the polyolefin resin in the granulation process is not easily accelerated, thereby suppressing an increase in the MFR of the resin particles, and the polyolefin foam particles obtained from the resin particles are foamed to provide a polyolefin resin foam molded product having excellent moldability and flame retardancy. In one embodiment of the present invention, even when the polyolefin resin contains recycled polyolefin resin and/or carbon black, a polyolefin resin foam molded product having excellent moldability and flame retardancy can be provided. The polyolefin resin foam molded product having excellent flame retardancy can be used for various applications such as cushioning packaging materials, logistics materials, insulation materials, civil engineering and construction materials, and automotive parts, and can be particularly used in various fields that require strict flame retardancy standards to be met, such as transportation, buildings, structures, furniture, electrical equipment, and electronic equipment.

Claims (15)

The present invention comprises a polyolefin resin (A), a calcium compound (C1), a phenolic antioxidant (D) and a phosphorus-based processing stabilizer (E),
The calcium compound (C1) is a compound that does not contain a sulfur element or a halogen element,
The content of the calcium compound (C1) is 0.10% by weight to 3.00% by weight based on 100% by weight of the expanded polyolefin resin beads,
The calcium compound (C1) is a polyolefin resin foam particle dispersed inside the membrane constituting the air bubbles. The calcium compound (C1) is
2. The expanded polyolefin resin particles according to claim 1, comprising at least one selected from the group consisting of calcium oxide, calcium hydroxide, calcium carbonate and calcium fatty acid. The polyolefin resin foam particles according to claim 1, wherein the polyolefin resin (A) includes a recycled polyolefin resin. The expanded polyolefin resin particles according to claim 1, further comprising a hindered amine (B). The expanded polyolefin resin particles according to claim 4, further comprising carbon black and/or graphite. The polyolefin resin foam particles according to claim 1, further comprising a metal deactivator. A polyolefin resin foam molded product obtained by molding the polyolefin resin foam particles according to any one of claims 1 to 6. In the container,
a dispersing step of dispersing polyolefin resin particles made of a polyolefin resin composition containing a polyolefin resin (A), a calcium compound (C2), a phenol-based antioxidant (D) and a phosphorus-based process stabilizer (E) in an aqueous dispersion medium, and a foaming agent;
A discharging step of discharging the dispersion obtained in the dispersing step into a region with a lower pressure than the pressure inside the container,
The calcium compound (C2) is a compound that does not contain a sulfur element or a halogen element,
The content of the calcium compound (C2) is 0.10% by weight to 3.00% by weight based on 100% by weight of the expanded polyolefin resin beads. The calcium compound (C2) is
The method for producing expanded polyolefin resin beads according to claim 8, which contains at least one selected from the group consisting of calcium oxide, calcium hydroxide, calcium carbonate and calcium fatty acid. The calcium compound (C2) is
The method for producing expanded polyolefin resin beads according to claim 8, which contains at least one selected from the group consisting of calcium oxide and fatty acid calcium salts. The method for producing expanded polyolefin resin particles according to any one of claims 8 to 10, wherein the polyolefin resin (A) includes a recycled polyolefin resin. A method for producing expanded polyolefin resin beads, comprising: a polyolefin resin (A), a calcium compound (C1), a phenol-based antioxidant (D), and a phosphorus-based process stabilizer (E), the method comprising the steps of:
In the container,
(i) a dispersing step of dispersing polyolefin-based resin particles made of a polyolefin-based resin composition containing a polyolefin-based resin (A), (ii) a calcium compound (C1) and/or a precursor of the calcium compound (C1), (iii) a phenol-based antioxidant (D), and (iv) a phosphorus-based process stabilizer (E) in an aqueous dispersion medium, and a blowing agent;
A discharging step of discharging the dispersion obtained in the dispersing step into a region with a lower pressure than the pressure inside the container,
The calcium compound (C1) is a compound that does not contain a sulfur element or a halogen element,
The precursor of the calcium compound (C1) is a compound that does not contain a sulfur element or a halogen element,
In the expanded polyolefin resin beads, the content of the calcium compound (C1) is 0.10% by weight to 3.00% by weight based on 100% by weight of the expanded polyolefin resin beads. The precursor of the calcium compound (C1) is
The method for producing expanded polyolefin resin beads according to claim 12, comprising at least one selected from the group consisting of calcium oxide, calcium hydroxide, calcium carbonate and calcium fatty acid. The precursor of the calcium compound (C1) is
The method for producing expanded polyolefin resin beads according to claim 12, which contains at least one selected from the group consisting of calcium oxide and fatty acid calcium salts. The method for producing expanded polyolefin resin particles according to any one of claims 12 to 14, wherein the polyolefin resin (A) includes a recycled polyolefin resin.