Polyolefin resin foam particles and polyolefin resin foam molded articles

Abstract

The present invention pertains to polyolefin-based resin foamed particles and the like. The polyolefin-based resin foamed particles according to the present invention each contain a polyolefin-based resin, a specific amount of an inorganic hypophosphite, and a specific amount of a melamine-based flame retardant. The present invention basically ensures fine moldability of a foam product, and can, while improving the oxygen index thereof and the level of incombustibility, further improve safety regarding incombustibility of a product, and suppress generation of hazardous gas when being combusted.

Description

[Technical Field]

[0001] The present invention relates to the field of polymer foam materials, and more particularly to expanded polyolefin resin beads, expanded polyolefin resin molded articles obtained by molding the expanded polyolefin resin beads in a mold, and uses thereof. [Background technology]

[0002] Expanded polyolefin resin beads, obtained by expanding polyolefin resin particles, are filled into a mold for in-mold foam molding, and the expanded polyolefin resin beads are heated and fused to obtain an in-mold foam molded article. Such in-mold foam molded articles are characterized by their flexibility in shape, light weight, and heat insulation properties. Furthermore, in-mold polyolefin resin foam molded articles are superior in chemical resistance, heat resistance, and strain recovery rate after compression compared to in-mold polystyrene resin foam molded articles obtained using expanded polystyrene resin beads. Therefore, in-mold polyolefin resin foam molded articles are used for a variety of purposes, such as cushioning materials, returnable boxes, heat insulation materials, and automotive components.

[0003] However, while polyolefin resin in-mold foam molded articles have the above-mentioned excellent properties, they have the drawback of being easily flammable. In particular, foam molded articles have the drawback of being more flammable and easily combustible than non-foam molded articles. In recent years, there has been a demand for automotive components, building materials, and electrical appliance components to be flame-retardant and self-extinguishing, and in order to meet these demands, research into obtaining foam molded articles imparted with flame retardancy has been widely conducted. A common method is to add a flame retardant, and various flame retardants such as halogen-containing compounds, hydrated metal oxides, phosphate esters, and nitrogen-containing compounds are used as flame retardants for polyolefin resins.

[0004] Patent Document 1 describes in its working examples an in-mold foamed molded article that meets HF-1 in the horizontal test for UL94 foams without problems such as a decrease in in-mold foamability, by adding a sterically hindered amine ether type flame retardant to polyolefin resin pre-expanded particles as a non-halogen type flame retardant.

[0005] Patent Document 2 also describes an in-mold foamed article that, by using the flame retardant, becomes self-extinguishing in a combustion test based on FMVSS302 and has a desired black color tone.

[0006] Patent Document 3 describes flame-retardant pre-expanded polyolefin resin particles containing a pentavalent phosphate compound containing a halogen.

[0007] Patent Document 4 describes that by using a polyolefin resin composition containing a sterically hindered amine ether flame retardant and a non-halogen phosphate ester as pre-expanded polyolefin resin particles, the resulting pre-expanded polyolefin resin particles have excellent in-mold foaming properties and exhibit flame retardancy superior to conventional products.

[0008] Patent Document 5 describes that by using a specific phosphorus-based flame retardant, good flame retardancy is achieved in the FMVSS302 combustion test method even when no or only a small amount of sterically hindered amine ether compounds are used.

[0009] Patent Document 6 discloses pre-expanded polyolefin resin particles in which a hindered amine and an organic phosphorus compound are mixed at a specific weight ratio.

[0010] Much research is currently being conducted on the flame retardancy of non-foamed polyolefin materials. For example, Patent Document 7 discloses that a highly flame-retardant polyolefin composition can pass the UL94V-2 test by adding predetermined amounts of polypropylene, hypophosphite, melamine hydrobromide, a flame retardant synergist, etc. to a high-speed mixer, stirring the raw materials uniformly, extruding the resulting mixture in a twin-screw extruder to form pellets, and finally injection-molding the resulting pellets in an injection molding machine. However, achieving flame retardancy in polyolefin-based foamed materials is more difficult than achieving flame retardancy in the form of polyolefin films, tubes, or non-foamed materials. Methods suitable for non-foamed polyolefin materials are not necessarily suitable for the foamed form of the same polymer. The manufacturing process for polyolefin-based resin foam beads and their in-mold foamed articles involves steps such as impregnation with a blowing agent, heating, sudden pressure release, and steam heating, which raise concerns about decomposition of the flame retardant and / or reactions due to the flame retardant mixture. Also, the moldability of the foamed material may be affected by the presence of further additives such that the final product may not meet the foamed product requirements in the relevant sector of industry. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] WO2003 / 048239A1 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-263033 [Patent Document 3] Japanese Patent Application Publication No. 9-227711 [Patent Document 4] WO2010 / 119670A1 [Patent Document 5] WO2013 / 022049A1 [Patent Document 6] WO2016 / 052739A1 [Patent Document 7] CN105694221A Summary of the Invention [Problem to be solved by the invention]

[0012] However, the above-mentioned conventional techniques are not sufficient from the viewpoint of flame retardancy, and there is room for further improvement.

[0013] One embodiment of the present invention has been made in consideration of the above-mentioned problems, and its object is to provide novel expanded polyolefin resin beads and novel expanded polyolefin resin molded articles that are excellent in flame retardancy.

[0014] Another embodiment of the present invention has an object to provide an interior material for public transportation using the above-mentioned polyolefin resin foam molded article. [Means for solving the problem]

[0015] That is, the expanded polyolefin resin particles according to one embodiment of the present invention contain a polyolefin resin, 1.60 to 10.00 parts by weight of an inorganic hypophosphite, and 0.01 to 2.00 parts by weight of a melamine flame retardant, per 100 parts by weight of the polyolefin resin.

[0016] Furthermore, a method for producing expanded polyolefin resin beads according to one embodiment of the present invention includes the steps of dispersing polyolefin resin particles in an aqueous dispersion medium in a sealed container and adding a blowing agent to the resulting dispersion; heating the sealed container to a temperature equal to or higher than the softening temperature of the polyolefin resin particles; and releasing the resulting mixture from the sealed container into a low-pressure atmosphere to expand the polyolefin resin particles, thereby obtaining expanded polyolefin resin beads. The polyolefin resin particles contain a polyolefin resin, and 1.60 to 10.00 parts by weight of an inorganic hypophosphite and 0.01 to 2.00 parts by weight of a melamine-based flame retardant per 100 parts by weight of the polyolefin resin. [Effects of the Invention]

[0017] According to one embodiment of the present invention, it is possible to provide novel expanded polyolefin resin beads and novel expanded polyolefin resin molded articles that are excellent in flame retardancy. DETAILED DESCRIPTION OF THE INVENTION

[0018] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments and examples obtained by combining the configurations disclosed in each embodiment and example are also included in the scope of the present invention. Furthermore, all documents described in this specification are incorporated herein by reference.

[0019] Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0020] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

[0021] In this specification, "foam material" refers to a material obtained through a foaming process. In particular, a foam obtained by in-mold foam molding is called an "in-mold foam molded product." An "in-mold foam molded product" is sometimes simply called a "foam molded product." A material obtained through a foaming process prior to in-mold foam molding, etc., is called a "pre-foam material." Furthermore, particulate pre-foam material is called "resin foam particles" or "pre-foam particles." "Foam" and "foamed product" refer to products manufactured from foam materials and / or foam molded products.

[0022] As used in this specification (particularly the appended claims), the terms "a," "an," "the," and similar terms include singular and plural referents unless the context clearly dictates otherwise and is inconsistent.

[0023] In this specification, a numerical range expressed as "numeric value A to numerical value B" includes the endpoints A and B. In other words, "numeric value A to numerical value B" means "numerical value A or more (including numerical value A and greater than numerical value A) and numerical value B or less (including numerical value B and less than numerical value B)."

[0024] As used herein, the term "may" includes both the implementation and non-implementation of the treatment. As used herein, the term "optionally" or "optionally" means that the following event or situation may or may not occur, and includes both the occurrence and non-occurrence of the event or situation.

[0025] As used herein, the terms "some (preferred) embodiments," "another (preferred) embodiment," "some (preferred) examples," "another (preferred) example," etc., mean that a particular element (e.g., a feature, structure, property, and / or characteristic) associated with this embodiment is included in at least one embodiment described herein and may or may not be present in other embodiments. Also, the elements may be combined in any suitable manner in each embodiment.

[0026] The term "comprises" and variations thereof in the present specification and claims are intended to cover a non-exclusive inclusion, for example, a process, method, system, product, or apparatus comprising a series of steps or units is not limited to the listed steps or units, but may optionally include unlisted steps or units, or may optionally include other steps or units inherent to those processes, methods, products, or apparatus.

[0027] [Polyolefin resin expanded particles] The expanded polyolefin resin particles according to one embodiment of the present invention comprise a polyolefin resin, an inorganic hypophosphite, and a melamine-based flame retardant. In some embodiments of the present invention, the expanded polyolefin resin particles are obtained by expanding polyolefin resin particles. That is, in some embodiments of the present invention, the polyolefin resin particles comprise a polyolefin resin, an inorganic hypophosphite, and a melamine-based flame retardant. In the expanded polyolefin resin particles according to one embodiment of the present invention, the content of the inorganic hypophosphite is 1.60 to 10.00 parts by weight and the content of the melamine-based flame retardant is 0.01 to 2.00 parts by weight, per 100 parts by weight of the polyolefin resin.

[0028] The expanded polyolefin resin beads according to one embodiment of the present invention have the above-described structure and therefore have excellent flame retardancy, and can provide a polyolefin resin foam molded article having excellent flame retardancy.

[0029] The flame retardancy grade required for in-mold foamed articles varies depending on the application. In-mold foamed articles obtained from the polyolefin resin foam beads described in the above-mentioned patent documents can be suitably used in various fields requiring flame retardancy or self-extinguishing properties, such as transportation, buildings, structures, furniture, electrical and electronic equipment, etc. However, increasingly stringent flame retardancy standards are being required in these and other fields (e.g., public transportation), creating a growing need for further improvements in the flame retardancy of polyolefin foamed materials. For example, high-speed public transportation has experienced rapid development in recent years, and to meet the needs of social and economic development, not only are transportation speeds increasing but comfort and reliability are also improving. As public transportation, high-speed transportation modes such as high-speed trains and airplanes are characterized by high speeds, heavy passenger flows, and heavy traffic. Therefore, to ensure passenger safety, interior materials such as seat fillings for these high-speed transportation modes must meet stricter requirements, such as fire resistance, flame retardancy, low smoke, and low toxicity, than many other industries. As a result, interior materials for these high-speed transportation vehicles require, for example, higher flame retardant ratings and higher oxygen indexes, because fires in such vehicles can cause significant casualties and / or property loss.

[0030] The oxygen index refers to the concentration of oxygen required for a material to reach its ignition point. The UL94 flame retardant rating is used to evaluate a material's ability to extinguish a fire after it has ignited. The oxygen index and UL94 flame retardant rating are methods for determining the flame retardant performance of a material from different perspectives. Some materials may have a high oxygen index but may not pass a high grade in the UL94 test.

[0031] In a preferred embodiment of the present invention, an object is to provide polyolefin resin foamed beads that ensure good moldability of the foamed product while further improving flame retardancy and safety, specifically improving both the oxygen index and UL94 flame retardancy rating, and suppressing the generation of harmful gases during combustion, and a polyolefin resin foamed molded article obtained by molding the polyolefin resin foamed beads in a mold.

[0032] According to a preferred embodiment of the present invention, polyolefin resin foamed beads can be used to produce in-mold foamed molded articles that exhibit excellent in-mold foamability and surface appearance comparable to conventional products while also exhibiting excellent flame retardancy. The in-mold foamed molded articles achieve an HF-1 grade in the UL94 horizontal flammability test for foamed materials (UL94HF) and have a good oxygen index. In some embodiments of the present invention, the oxygen index is preferably 27.0% or higher. In other embodiments of the present invention, the oxygen index is more preferably 28.0% or higher, and even more preferably 29.0% or higher. The polyolefin resin foamed molded articles obtained from the polyolefin resin foamed beads according to a preferred embodiment of the present invention can suppress the generation of harmful gases during combustion and are particularly suitable for use in the field of interior materials for public transportation, especially high-speed transportation.

[0033] The present inventors have unexpectedly discovered that by incorporating specific amounts of inorganic hypophosphite and melamine flame retardant into a polyolefin resin, it is possible to obtain polyolefin resin foam particles and in-mold molded articles that exhibit high flame retardancy, exhibit good fusion of the foam particles during in-mold molding, and have excellent surface properties. The resulting in-mold molded articles also have a high oxygen index (e.g., 27.0% or higher) and meet the UL94 HF-1 grade. In this specification, "reaching HF-1 grade" means that the polyolefin resin foam molded article meets the HF-1 flame retardancy standard in the UL94 "Horizontal Flammability Test for Foam Materials." In this specification, "reaching HF-1 grade" does not imply that the polyolefin resin foam molded article requires UL94 HF-1 certification.

[0034] Each component will be described in detail below.

[0035] [Polyolefin resin] Polyolefin resins are polymers obtained by homopolymerization of one monomer selected from the group consisting of α-olefin monomers and some cyclic olefin monomers, or copolymerization of two or more monomers selected from the group. In this specification, polystyrene resins are not included in the polyolefin resins. Examples of the α-olefin monomers include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-pentene, i.e., monoolefins with a double bond at the end of the molecular chain. The α-olefin monomers are represented by the molecular formula R-CH=CH2 (where R is alkyl).

[0036] The polyolefin resin used in one embodiment of the present invention is a polymer containing 75% by weight or more of structural units derived from α-olefin monomers, relative to 100% by weight of all structural units of the polyolefin resin. In the polyolefin resin according to one embodiment of the present invention, the content of structural units derived from α-olefin monomers relative to 100% by weight of all structural units of the polyolefin resin is preferably 80% by weight or more. Furthermore, the polyolefin resin according to one embodiment of the present invention may contain, relative to 100% by weight of all structural units of the polyolefin resin, structural units derived from other monomers copolymerizable with α-olefin monomers, in an amount of, for example, 25% by weight or less, preferably 20% by weight or less.

[0037] In this specification, a "structural unit derived from an X monomer" may be referred to as an "X unit."

[0038] Specific examples of the α-olefin monomer include α-olefins having 2 to 12 carbon atoms, such as ethylene, propylene, 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. These may be used alone or in combination of two or more.

[0039] Specific examples of other monomers copolymerizable with the above-mentioned α-olefin monomers include (a) cyclic olefins such as cyclopentene, norbornene, and 1,4,5,8-dimethano-1,2,3,4,4a,8,8a,6-octahydronaphthalene, and (b) dienes such as 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, and 7-methyl-1,6-octadiene. These may be used alone or in combination of two or more.

[0040] Specific examples of polyolefin-based resins used in one embodiment of the present invention include (a) polyethylene-based resins primarily composed of ethylene units, such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene, and (b) polypropylene-based resins primarily composed of propylene units. These polyolefin-based resins may be used alone or in combination of two or more. Among these, it is preferable to use a polypropylene-based resin as the polyolefin-based resin from the viewpoints of mechanical strength, heat resistance, and the like. In other words, the polyolefin-based resin preferably contains a polypropylene-based resin, and more preferably is a polypropylene-based resin.

[0041] Here, the "polypropylene-based resin" used in one embodiment of the present invention refers to a polymer obtained by polymerization using propylene as at least a portion of the monomer, and is a polymer in which the content of propylene units exceeds 50% by weight in 100% by weight of all structural units of the polymer. The polypropylene-based resin is not particularly limited as long as it contains propylene as the main component of the monomer units, and examples thereof include propylene homopolymer, propylene / α-olefin random copolymer, and propylene / α-olefin block copolymer. These may be used alone or in combination of two or more. Examples of copolymers of propylene and α-olefins include copolymers of propylene and α-olefins having 4 to 10 carbon atoms. Examples of the α-olefins having 4 to 10 carbon atoms include 1-butene, 1-pentene, 1-hexene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, and 1-octene.

[0042] Among the above-mentioned polymers, the polypropylene-based resin is preferably a propylene / ethylene random copolymer or a propylene / ethylene / 1-butene random copolymer, because of its good expandability and moldability. The ethylene unit content in the polypropylene-based resin is preferably 1% by weight or more and 10% by weight or less, more preferably 2% by weight or more and 7% by weight or less, even more preferably 3.5% by weight or more and 6% by weight or less, and particularly preferably 3.5% by weight or more and 5% by weight or less, relative to 100% by weight of all constituent units of the polypropylene-based resin. The ethylene content of the copolymerization monomer component in the polypropylene-based resin (the ethylene unit content in all constituent units of the polypropylene-based resin) is 13 It can be measured using C-NMR.

[0043] The melting point of the polypropylene resin used in one embodiment of the present invention is preferably 130°C or higher and 165°C or lower, and more preferably 135°C or higher and 155°C or lower. A polypropylene resin with a melting point of 130°C or higher has the advantage of providing sufficient heat resistance and mechanical strength for the in-mold foam-molded article. A melting point of 165°C or lower has the advantage of easily ensuring fusion during in-mold foam-molding. The melting point refers to the peak temperature of the endothermic peak in the DSC curve obtained during the heating step (3) using a differential scanning calorimeter, following steps (1) to (3): (1) heating 1 to 10 mg of polypropylene resin from 40°C to 220°C at a heating rate of 10°C / min; (2) subsequently cooling the polypropylene resin to 40°C at a heating rate of 10°C / min; (3) subsequently heating the polypropylene resin again to 220°C at a heating rate of 10°C / min.

[0044] The melt flow rate (hereinafter referred to as "MFR value") of the polypropylene resin used in one embodiment of the present invention is preferably 0.5 g / 10 min or more and 30 g / 10 min or less, and more preferably 2 g / 10 min or more and 20 g / 10 min or less. When the MFR value is (a) 0.5 g / 10 min or more, there is an advantage that expanded polypropylene resin beads with a high expansion ratio can be easily obtained, and when it is (b) 30 g / 10 min or less, there is an advantage that the cells of the expanded polypropylene resin beads are difficult to break, and the open cell ratio of the expanded polypropylene resin beads is low.

[0045] The MFR value of the polypropylene resin is a value measured in accordance with JIS K7210 under conditions of a temperature of 230°C and a load of 2.16 kg.

[0046] The ratio (Mw / Mn) of the weight average molecular weight (hereinafter sometimes referred to as "Mw") to the number average molecular weight (hereinafter sometimes referred to as "Mn") of the polypropylene-based resin used in one embodiment of the present invention is not particularly limited, but is preferably 3.0 or more, and particularly preferably 3.0 or more and 6.0 or less. The Mw and Mn of the polypropylene-based resin are measured by general gel permeation chromatography (GPC).

[0047] Raw materials for producing polyolefin-based resins (e.g., polypropylene-based resin particles) may contain other types of polyolefin-based resins, such as polyethylene-based resins, other than polypropylene-based resins. Examples of such other types of polyolefin-based resins include high-density polyethylene-based resins, medium-density polyethylene-based resins, low-density polyethylene-based resins, and linear low-density polyethylene-based resins. The other type of polyolefin-based resin is preferably linear low-density polyethylene (also known as "linear low-density polyethylene" and sometimes abbreviated as "LLDPE") to increase the expansion ratio. One type of such other type of polyolefin-based resin may be used alone, or two or more types may be used in combination. When using such other type of polyolefin-based resin in one embodiment of the present invention, the content of the polypropylene-based resin is preferably 80% by weight or more, more preferably 90% by weight or more, and even more preferably 95% by weight or more, based on the total weight (100% by weight) of the polyolefin-based resins.

[0048] In another embodiment of the present invention, the polyolefin resin may contain a polyethylene resin or may be a polyethylene resin. When the polyolefin resin contains a polyethylene resin or is a polyethylene resin, there is an advantage that a foam molded article that is flexible, not easily cracked, and can withstand repeated use can be obtained.

[0049] Here, the "polyethylene resin" used in another embodiment of the present invention is a polymer obtained by polymerization using ethylene as at least a portion of the monomer, and is a polymer in which the content of ethylene units in 100% by weight of all structural units of the polymer exceeds 50% by weight.

[0050] Examples of polyethylene-based resins used in another embodiment of the present invention include ethylene homopolymers, ethylene / α-olefin random copolymers, ethylene / α-olefin block copolymers, low-density polyethylene, high-density polyethylene, and linear low-density polyethylene. The α-olefins referred to here include α-olefins having 3 to 15 carbon atoms, and these α-olefins may be used alone or in combination of two or more. Among these polyethylene-based resins, (a) ethylene / α-olefin block copolymers, in which the content of comonomer units other than ethylene units is 1 to 10 wt % based on 100 wt % of all structural units of the copolymer, or linear low-density polyethylene are preferred. This configuration offers the advantage that the polyethylene-based resin exhibits good foamability.

[0051] The melting point of the polyethylene resin used in another embodiment of the present invention is preferably 110°C or higher and 140°C or lower, and more preferably 120°C or higher and 130°C or lower. Polyethylene resins having a melting point within the above range have excellent foamability and moldability, and are advantageous in that they can produce expanded particles with excellent mechanical strength and heat resistance when formed into polyolefin resin in-mold foamed articles. The melting point refers to the peak temperature of the endothermic peak in the DSC curve obtained during the heating step (3) using a differential scanning calorimeter, following steps (1) to (3): (1) heating 1 to 10 mg of polyethylene resin from 40°C to 200°C at a heating rate of 10°C / min; (2) subsequently cooling the polyethylene resin to 40°C at a heating rate of 10°C / min; (3) subsequently heating the polyethylene resin again to 200°C at a heating rate of 10°C / min.

[0052] In another embodiment of the present invention, the polyethylene resin preferably has an MFR value of 0.5 g / 10 min to 30 g / 10 min, more preferably 1 g / 10 min to 5 g / 10 min, and particularly preferably 1.5 g / 10 min to 2.5 g / 10 min. A polyethylene resin with an MFR value of 0.5 g / 10 min or higher has the advantages of easily obtaining expanded beads with a high expansion ratio and tending to have uniform cell diameters. A polyethylene resin with an MFR value of 30 g / 10 min or lower has the advantages of easy foaming, a low open cell ratio due to less cell breakage, and a tendency to have uniform cell diameters. The MFR value of the polyethylene resin is measured in accordance with JIS K7210 at a temperature of 190°C and a load of 2.16 kg.

[0053] The polyolefin resin used in one embodiment of the present invention can be obtained using a catalyst such as a Ziegler catalyst, a metallocene catalyst, or a post-metallocene catalyst. The use of a Ziegler catalyst tends to result in a polyolefin resin (polymer) with a high Mw / Mn ratio. Furthermore, by subjecting the polyolefin resin (polymer) obtained using these catalysts to oxidative decomposition with an organic peroxide, it is possible to adjust the molecular weight and / or properties of the polyolefin resin (polymer), such as the melt flow rate.

[0054] The polyolefin resin used in one embodiment of the present invention is preferably in a non-crosslinked state, but may be crosslinked by treatment with an organic peroxide, radiation, or the like.

[0055] [Inorganic hypophosphite] Inorganic hypophosphites are inorganic phosphorus-based flame retardants and are used as the primary flame retardant in one embodiment of the present invention. Inorganic hypophosphites (a) have a high phosphorus content, (b) are effective radical traps and carbonizers with both vapor and condensed phase flame retardant mechanisms, (c) have excellent thermal stability and water resistance, and (d) have minimal impact on the mechanical properties of polymers. Therefore, inorganic hypophosphites are suitable for use in foamable plastics. In one embodiment of the present invention, the use of inorganic hypophosphites as the primary flame retardant significantly reduces toxicity and production costs compared to using organic phosphinates with organic groups as the primary flame retardant.

[0056] In one embodiment of the present invention, specific examples of inorganic hypophosphites include aluminum hypophosphite (abbreviated as "ALHP" and having the chemical formula Al(H2PO2)3), sodium hypophosphite, magnesium hypophosphite, zinc hypophosphite, and calcium hypophosphite. These compounds may be used alone or in combination of two or more. The present inventors independently discovered that when aluminum hypophosphite was used as the main flame retardant in one embodiment of the present invention, superior flame retardancy and thermal stability were exhibited. Therefore, aluminum hypophosphite is preferred as the inorganic hypophosphite.

[0057] According to one embodiment of the present invention, the content of inorganic hypophosphite in the expanded polyolefin resin beads is 1.60 to 10.00 parts by weight per 100 parts by weight of polyolefin resin. In this case, a polyolefin resin foam molded article produced from the expanded polyolefin resin beads exhibits excellent flame retardancy and moldability, passing the HF-1 grade in the UL94 "Horizontal Flammability Test for Foamed Materials" (i.e., the UL94HF test method), and achieving an oxygen index of 27.0% or higher. If the content of inorganic hypophosphite is less than 1.60 parts by weight, the flame retardancy is insufficient and the UL94 HF-1 grade cannot be achieved. On the other hand, if the content of inorganic hypophosphite is greater than 10.00 parts by weight, it may adversely affect dispersion stability and cell size during supercritical foaming, and the inorganic components may adhere to the surface of the expanded beads, further affecting moldability. In some embodiments of the present invention, the content of the inorganic hypophosphite is preferably 1.80 to 4.00 parts by weight to simultaneously achieve HF-1 grade and an oxygen index of 28.0% or more. In another embodiment of the present invention, the content of the inorganic hypophosphite may be 1.80 to 3.80 parts by weight, or even 2.00 to 3.70 parts by weight, since the carbonization resistance of the resulting foamed molded article during combustion is improved and the foamed molded article can achieve HF-1 grade and a higher oxygen index.

[0058] [Melamine-based flame retardants] Melamine-based flame retardants, also known as melamine flame retardants, are flame retardants containing a melamine structure, and have excellent thermal stability and good flame retardant and smoke-reducing effects. In one embodiment of the present invention, the melamine-based flame retardant is selected from melamine sulfate (C3H8N6O4S, CAS: 84962-53-8), melamine polyphosphate (C3H6N6(H3PO4)), and the like, because the resulting foamed molded article has excellent thermal stability, flame retardant, and smoke-reducing effects. n , CAS: 218768-84-4), Melamine cyanurate (C6H9N9O3, CAS: 37640-57-6), Melamine pyrophosphate (C3H 10 N6O7P2, CAS: 15541-60-3), Melamine Hydrobromide (C3H6N6 (HBr)x , CAS: 29305-12-2). Note that "melamine hydrobromide" may also be referred to as "melamine hydrobromide salt." In some embodiments of the present invention, the melamine-based flame retardant is preferably melamine hydrobromide (hereinafter, sometimes referred to as "MHB"), which combines the advantages of both nitrogen-based and bromine-based flame retardants. When melamine hydrobromide is used as the melamine-based flame retardant, it has the advantage that high flame retardancy can be obtained with a small amount of use. Melamine hydrobromide (C3H6N6(HBr) x ) where X=1, the molecular formula is:

[0059] [ka] The present inventors have surprisingly independently discovered the following: by using only a small amount of a melamine-based flame retardant, a flame-retardant synergistic effect between the inorganic hypophosphite and the melamine-based flame retardant is generated, and the polyolefin-based resin foam molded article according to one embodiment of the present invention has good flame retardancy while also satisfying safety and environmental protection requirements.

[0060] In the expanded polyolefin resin beads according to one embodiment of the present invention, the content of the melamine-based flame retardant is 0.01 to 2.00 parts by weight per 100 parts by weight of the polyolefin resin. In some embodiments of the present invention, the content of the melamine-based flame retardant is preferably 0.01 to 1.00 parts by weight per 100 parts by weight of the polyolefin resin, because this allows for high flame retardancy, a reduced halogen content in the final product (a foam-molded article), and low production costs. To further reduce the halogen content in the final product, the content of the melamine-based flame retardant is more preferably 0.30 parts by weight or less. In another embodiment of the present invention, the content of the melamine-based flame retardant may be 0.02 to 0.16 parts by weight, because this allows for high flame retardancy, a significant reduction in the halogen content in the final product (a foam-molded article), and low production costs.

[0061] In the expanded polyolefin resin particles according to some embodiments of the present invention, the weight ratio of the inorganic hypophosphite to the melamine flame retardant (content of inorganic hypophosphite (parts by weight) / content of melamine flame retardant (parts by weight)) is preferably more than 20, more preferably 25 to 27. When the weight ratio of the inorganic hypophosphite to the melamine flame retardant is within the above range, there are advantages in that there is no risk of environmental problems occurring and the flame retardancy rating and / or oxygen index of the foam are not adversely affected.

[0062] [Other flame retardant ingredients] In order to further increase the oxygen index and stability, in a preferred embodiment of the present invention, the polyolefin-based resin particles may optionally be a polyolefin-based resin having a structure represented by the general formula (1): R 1 NHCH2CH2CH2NR 2 CH2CH2NR 3 CH2CH2CH2NHR 4 (1) (In the formula, R 1 and R 2 is represented by the general formula (2):

[0063] [ka] (In the formula, R 5 is an alkyl group having 1 to 12 carbon atoms, and R 6 is a methyl group, a cyclohexyl group, or an octyl group), the dashed line above the triazine ring shown in general formula (2) represents the linkage with the nitrogen atom of general formula (1), and R 3 and R 4 is a group represented by general formula (2), the dashed line above the triazine ring represented by general formula (2) represents the linkage with the nitrogen atom of general formula (1), and R 3 and R 4 and the other represents a hydrogen atom).

[0064] In other words, in a preferred embodiment of the present invention, the expanded polyolefin resin beads further contain a compound represented by the general formula (1) as desired.

[0065] In general formula (2), R 5 represents an alkyl having 1 to 12 carbon atoms, such as methyl, ethyl, propyl, butyl, n-pentyl, n-hexyl, n-heptyl, nonyl, decyl, undecyl, dodecyl, isopropyl, isobutyl, sec-butyl, tert-butyl, 2-ethylbutyl, isopentyl, 1-methylpentyl, 1,3-dimethylbutyl, 1-methylhexyl, isoheptyl, 1,1,3,3-tetramethylpentyl, 1-methylundecyl, or 1,1,3,3,5,5-hexamethylhexyl. 6 represents a methyl group, a cyclohexyl group, or an octyl group. Specific examples of the group represented by the general formula (2) include groups derived from 2,4-bis[(1-methoxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazine, 2,4-bis[(1-oxocyclohexyl-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazine, 2,4-bis[(1-octyloxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazine, etc.

[0066] The compound represented by the above general formula (1) is a sterically hindered amine ether compound. Specific examples of the compound represented by the general formula (1) include N,N',N'''-tris{2,4-bis[(1-oxocyclohexyl-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazin-6-yl}-3,3'-ethylenediiminopropylamine, N,N',N''-tris{2,4-bis[(1-oxocyclohexyl-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazin-6-yl}-3,3'-ethylenediiminodipropylamine, N,N',N'''-tris{2,4-bis[(1-oxocyclohexyl-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazin-6-yl}-3,3'-ethylenediiminodipropylamine, and N,N',N'''-tris{2,4-bis[(1-octyloxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazin-6-yl}-3,3'-ethylenediiminodipropylamine. Examples thereof include ethylenediiminodipropylamine, N,N',N''-tris{2,4-bis[(1-octyloxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazin-6-yl}-3,3'-ethylenediiminopropylamine, N,N',N'''-tris{2,4-bis[(1-methoxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazin-6-yl}-3,3'-ethylenediiminopropylamine, and N,N',N''-tris{2,4-bis[(1-methoxy-2,2,6,6-tetramethylpiperidin-4-yl)n-butylamino]-s-triazin-6-yl}-3,3'-ethylenediiminopropylamine. These may be used alone or in combination of two or more.

[0067] In one embodiment of the present invention, the addition or non-addition of the compound represented by general formula (1) can be determined depending on the requirements of the actual field of application. In the expanded polyolefin resin beads according to some embodiments of the present invention, considering flame retardancy and cost, the content of the compound represented by general formula (1) is preferably 0.01 to 2.00 parts by weight, more preferably 0.10 to 1.50 parts by weight, and even more preferably 0.20 to 1.00 parts by weight, per 100 parts by weight of the polyolefin resin particles. When the compound represented by general formula (1) is used within the above-mentioned range, there is an advantage in that there is no risk of excessively high costs and no risk of adversely affecting the oxygen index of the foam.

[0068] In another preferred embodiment of the present invention, the polyolefin resin particles further comprise one or more brominated flame retardants (excluding the aforementioned melamine-based flame retardants) selected from the group consisting of brominated bisphenol A flame retardants, brominated bisphenol S flame retardants, brominated butadiene-styrene block copolymer flame retardants, and brominated polyphenylene ether flame retardants. In other words, in another preferred embodiment of the present invention, the expanded polyolefin resin particles further comprise one or more brominated flame retardants (excluding the aforementioned melamine-based flame retardants) selected from the group consisting of brominated bisphenol A flame retardants, brominated bisphenol S flame retardants, brominated butadiene-styrene block copolymer flame retardants, and brominated polyphenylene ether flame retardants. Among the above-mentioned brominated flame retardants, from the viewpoint of achieving a higher oxygen index, brominated bisphenol A flame retardants and / or brominated bisphenol S flame retardants such as bis(alkyl ether)tetrabromobisphenol A flame retardants and / or bis(alkyl ether)tetrabromobisphenol S flame retardants are preferred, and brominated bisphenol S flame retardants are more preferred. In other words, the brominated flame retardant preferably includes at least one selected from brominated bisphenol A flame retardants and brominated bisphenol S flame retardants. In some embodiments of the present invention, the polyolefin resin particles and the expanded polyolefin resin particles may include a brominated flame retardant other than the above-mentioned brominated flame retardants (other brominated flame retardants). Specific examples of brominated bisphenol A flame retardants and brominated bisphenol S flame retardants include one or more selected from the group consisting of tetrabromobisphenol A, tetrabromobisphenol S, tetrabromobisphenol A-bis(2,3-dibromopropyl ether) (hereinafter may be referred to as "TBAB" and also called "octabromoether"), tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol A-diglycidyl ether, and tetrabromobisphenol S-bis(2,3-dibromo-2-methylpropyl ether) (hereinafter may be referred to as "TBSB").

[0069] In the expanded polyolefin resin beads according to one embodiment of the present invention, the content of the brominated flame retardant is preferably 0.10 to 5.00 parts by weight, more preferably 0.20 to 3.00 parts by weight, and even more preferably 0.20 to 1.50 parts by weight, relative to 100 parts by weight of the polyolefin resin. This configuration has the advantage that a foamable product with superior flame retardancy (e.g., a higher oxygen index) can be obtained.

[0070] In another preferred embodiment of the present invention, the polyolefin resin particles further contain a radical generator to further enhance the flame retardancy of the polyolefin resin in-mold foamed article. In other words, in another preferred embodiment of the present invention, the expanded polyolefin resin particles further contain a radical generator.

[0071] Examples of radical generators used in one embodiment of the present invention include 2,3-dimethyl-2,3-diphenylbutane, poly-1,4-diisopropylbenzene, 2,3-diethyl-2,3-diphenylbutane, 3,4-dimethyl-3,4-diphenylhexane, 3,4-diethyl-3,4-diphenylhexane, 2,4-diphenyl-4-methyl-1-pentene, and 2,4-diphenyl-4-ethyl-1-pentene. Peroxides such as dicumyl peroxide can also be used as radical generators in one embodiment of the present invention. Among these radical generators, those that are stable at the processing temperature of the resin are preferred, specifically at least one selected from the group consisting of 2,3-dimethyl-2,3-diphenylbutane and poly-1,4-diisopropylbenzene are preferred. In other words, the radical generator preferably includes at least one selected from the group consisting of 2,3-dimethyl-2,3-diphenylbutane and poly-1,4-diisopropylbenzene. In some embodiments of the present invention, the radical generator is preferably 2,3-dimethyl-2,3-diphenylbutane (hereinafter, may be referred to as "DMDPB").

[0072] In some embodiments of the present invention, the content of the radical generator in the expanded polyolefin resin particles is preferably 0.01 to 0.50 parts by weight relative to 100 parts by weight of the polyolefin resin. In another embodiment of the present invention, the content of the radical generator may be 0.02 to 0.20 parts by weight relative to 100 parts by weight of the polyolefin resin. In another embodiment of the present invention, the content of the radical generator may be 0.03 to 0.15 parts by weight relative to 100 parts by weight of the polyolefin resin.

[0073] [Other ingredients] In order to obtain a black molded article, carbon black may be contained in the polyolefin resin particles for forming the expanded polyolefin resin beads according to one embodiment of the present invention.

[0074] Specific examples of carbon black used in one embodiment of the present invention include channel black, roller black, disc black, gas furnace black, oil furnace black, thermal black, acetylene black, etc. These carbon blacks may be used alone or in combination of two or more.

[0075] In the polyolefin resin particles and expanded polyolefin resin particles according to one embodiment of the present invention, the carbon black content is preferably 0.5 to 20.0 parts by weight per 100 parts by weight of the polyolefin resin particles. In some embodiments of the present invention, the carbon black content is more preferably 0.50 to 2.00 parts by weight. When the carbon black content is 0.50 parts by weight or more, the expanded polyolefin resin particles and the in-mold foamed articles tend to be sufficiently blackened. When the carbon black content is 20.00 parts by weight or less, there is no risk of the cell size of the resulting expanded polypropylene resin particles becoming smaller, and not only do they tend to have good in-mold foaming properties (particularly surface appearance), but they also tend to have sufficient flame retardancy.

[0076] In one embodiment of the present invention, the carbon black and the polyolefin resin may be directly mixed, or may be melt-kneaded with the polyolefin resin to form a carbon black master batch in which the carbon black is dispersed in the polyolefin resin. Examples of polyolefin resins used in the carbon black master batch include polyethylene resins and polypropylene resins.

[0077] The polyolefin resin particles may contain a foam nucleating agent (hereinafter referred to as "nucleating agent") capable of acting as foam nuclei. Nucleating agents used in one embodiment of the present invention include, for example, inorganic nucleating agents such as talc, calcium stearate, calcium carbonate, silica, kaolin, titanium oxide, bentonite, barium sulfate, and zinc borate. These may be used alone or in combination of two or more. Among these nucleating agents, talc, calcium carbonate, and calcium stearate are preferred because they are inexpensive and produce uniform cells. The amount of nucleating agent added in one embodiment of the present invention varies depending on the type of foaming agent used. The amount of nucleating agent added in one embodiment of the present invention is generally 0.005 to 2 parts by weight, more preferably 0.01 to 1 part by weight, per 100 parts by weight of the polyolefin resin. When the amount of nucleating agent added is 0.005 parts by weight or more, sufficient foaming tends to occur easily. When the amount of the nucleating agent added is 2 parts by weight or less, there is no risk of the average cell diameter of the expanded polyolefin resin beads becoming too small, and in-mold foaming moldability tends to be good.

[0078] If necessary, the polyolefin resin particles may contain a heat stabilizer, a light stabilizer, a colorant, an antistatic agent, a radiation heat transfer inhibitor, other flame retardants, a lubricant, a filler, etc., within a range that does not impair the effects of one embodiment of the present invention. In other words, the expanded polyolefin resin particles according to one embodiment of the present invention may contain a heat stabilizer, a light stabilizer, a colorant, an antistatic agent, a radiation heat transfer inhibitor, other flame retardants, a lubricant, a filler, etc.

[0079] In one embodiment of the present invention, the heat stabilizer may be a hindered amine compound, a phosphorus compound, or an epoxy compound. Specific examples of the light stabilizer may include a hindered amine, a phosphorus stabilizer, an epoxy compound, a phenolic antioxidant, a nitrogen-containing stabilizer, a sulfur stabilizer, and benzotriazole.

[0080] Specific examples of colorants used in one embodiment of the present invention include inorganic pigments such as carbon black, ketjen black, iron black, cadmium yellow, cadmium red, cobalt violet, cobalt blue, Prussian, ultramarine, chrome yellow, zinc yellow, and barium yellow; and organic pigments such as polyazo, quinacridone, phthalocyanine, Perlon, anthraquinone, thioindigo, diquinazine, isoindolinone, and quinophthalone.

[0081] The antistatic agent used in one embodiment of the present invention is not particularly limited, and examples thereof include (a) low-molecular-weight antistatic agents such as fatty acid ester compounds, aliphatic ethanolamine compounds, and aliphatic ethanolamide compounds, and (b) polymeric antistatic agents. These antistatic agents may be used alone or in combination. Commercially available antistatic agents may also be used. For example, ElectroStripper TS-11B is a commercially available mixture of octadecyldiethanolamine monostearate and octadecyldiethanolamine, and ElectroStripper TS-15B is a commercially available mixture of octadecyldiethanolamine monostearate, octadecyldiethanolamine, and an aliphatic alcohol. The content of the antistatic agent in the expanded polyolefin resin particles according to one embodiment of the present invention is preferably 0.1 to 3 parts by weight, and more preferably 0.2 to 2 parts by weight, per 100 parts by weight of the polyolefin resin. When the content of the antistatic agent is 0.1 part by weight or more, the antistatic effect tends to be easily exhibited. When the content of the antistatic agent is 3 parts by weight or less, the deformation shrinkage rate of the obtained foamed molded article tends to be small, and the surface elongation of the molded article tends to be good.

[0082] Examples of the radiation heat transfer inhibitor (a substance having the property of reflecting, scattering, or absorbing light in the near-infrared or infrared region (e.g., a wavelength region of about 800 to 3000 nm)) used in one embodiment of the present invention include graphite, graphene, activated carbon, carbon black, titanium dioxide, and metallic aluminum.

[0083] [Method for producing polyolefin resin particles] The polyolefin resin particles used in one embodiment of the present invention are obtained using raw materials such as (a) a polyolefin resin, (b) an inorganic hypophosphite, (c) a melamine-based flame retardant, and (d) other optional flame-retardant components or optional additives such as carbon black, a nucleating agent, and a compound represented by general formula (1). The polyolefin resin particles used in one embodiment of the present invention are obtained as polyolefin resin particles having shapes such as cylindrical, ellipsoidal, spherical, cubic, and rectangular prism shapes after melt-kneading these raw materials using an extruder, kneader, Banbury mixer, roll, etc. In some embodiments of the present invention, the inorganic hypophosphite, the melamine-based flame retardant, and other flame retardants may be mixed with a polyolefin resin to form a flame-retardant masterbatch, and then the flame-retardant masterbatch may be melt-kneaded with a large amount of polyolefin resin and other components. In another embodiment of the present invention, a flame retardant such as an inorganic hypophosphite or a melamine-based flame retardant and a radical generator may be mixed and dispersed in a polyolefin-based resin to prepare a composite flame-retardant masterbatch, and then the composite flame-retardant masterbatch may be melt-kneaded with the polyolefin-based resin and other components.

[0084] In order to obtain expanded particles having an appropriate average maximum diameter, the weight of a single polyolefin resin particle according to one embodiment of the present invention is preferably 0.1 mg to 30 mg, more preferably 0.3 mg to 10 mg, where the weight of a single polyolefin resin particle is the average resin particle weight for 100 particles randomly selected from the polyolefin resin particles.

[0085] [Method for producing expanded polyolefin resin beads] A method for producing expanded polyolefin resin beads according to one embodiment of the present invention includes the steps of dispersing polyolefin resin particles in an aqueous dispersion medium in a sealed container and adding a blowing agent to the resulting dispersion; heating the sealed container to a temperature equal to or higher than the softening temperature of the polyolefin resin particles; and releasing the resulting mixture from the sealed container into a low-pressure atmosphere to expand the polyolefin resin particles, thereby obtaining expanded polyolefin resin beads. The polyolefin resin particles contain a polyolefin resin, and 1.60 to 10.00 parts by weight of an inorganic hypophosphite and 0.01 to 2.00 parts by weight of a melamine-based flame retardant per 100 parts by weight of the polyolefin resin.

[0086] The method for producing expanded polyolefin resin beads according to one embodiment of the present invention includes the above-described configuration, and therefore can provide expanded polyolefin resin beads that can provide in-mold foamed articles that exhibit excellent flame retardancy while having the same good in-mold foam moldability and surface appearance as conventional ones.

[0087] In some embodiments of the present invention, the blowing agent is (a) water and / or (b) an inorganic gas such as carbon dioxide, air, or nitrogen. These blowing agents may be used alone or in combination. These blowing agents have a low environmental impact and are not flammable, with carbon dioxide being the most preferred.

[0088] Although it is preferable to use only water as the aqueous dispersion medium used in one embodiment of the present invention, a dispersion medium in which methanol, ethanol, ethylene glycol, glycerin, etc. have been added to water can also be used. In one embodiment of the present invention, when a hydrophilic compound is contained, the water in the aqueous dispersion medium also functions as a foaming agent, which is useful for increasing the foaming ratio.

[0089] To prevent the polyolefin resin particles from adhering to each other, it is preferable to use a dispersant in the aqueous dispersion medium. Examples of dispersants that can be used in one embodiment of the present invention include inorganic dispersants such as calcium phosphate, magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay. These dispersants may be used alone or in combination of two or more. In one embodiment of the present invention, it is more preferable to use a dispersing aid in combination with a dispersing agent. Examples of dispersing aids that can be used in one embodiment of the present invention include (a) carboxylate-type polymeric surfactants such as N-acylamino acid salts, (b) sulfonate-type polymeric surfactants such as alkylbenzene sulfonates, (c) sulfate-type polymeric surfactants such as alkyl allyl ether sulfates, and (d) polycarboxylic acid-type polymeric surfactants such as maleic acid copolymer salts and polyacrylates. These dispersing aids may be used alone or in combination of two or more. Among these, it is preferable to use at least one selected from the group consisting of calcium phosphate, magnesium phosphate, barium sulfate, and kaolin as the dispersant in combination with at least one selected from the group consisting of sodium n-alkanesulfonate and sodium alkylbenzenesulfonate (such as DBS) as the dispersing aid.

[0090] The amounts of dispersant and dispersion aid used in one embodiment of the present invention vary depending on their types and the types and amounts of polyolefin resin particles used. Regarding the amounts of dispersant and dispersion aid used in one embodiment of the present invention, it is generally preferable to blend 0.2 to 2.5 parts by weight of dispersant and 0.005 to 0.08 parts by weight of dispersion aid per 100 parts by weight of aqueous dispersion medium. To improve the dispersibility of polyolefin resin particles in the aqueous dispersion medium, it is preferable to add 25 to 90 parts by weight of polyolefin resin particles per 100 parts by weight of aqueous dispersion medium.

[0091] In some embodiments of the present invention, the heating temperature inside the sealed container (sometimes referred to as the "foaming temperature") is preferably at least 25°C below the melting point of the polyolefin-based resin particles and 25°C below the melting point of the polyolefin-based resin particles, and more preferably at least 15°C below the melting point of the polyolefin-based resin particles and 15°C below the melting point of the polyolefin-based resin particles. The inside of the sealed container is heated to this temperature and further pressurized to impregnate the polyolefin-based resin particles with a foaming agent. In some embodiments of the present invention, the foaming temperature is preferably 150 to 160°C, and more preferably 154 to 160°C.

[0092] In some embodiments of the present invention, the foaming pressure is preferably 1.3 MPa to 2.2 MPa, more preferably 1.3 MPa to 1.8 MPa, and even more preferably 1.4 MPa to 1.7 MPa. When the foaming temperature and foaming pressure are within the above-mentioned ranges, the resulting expanded beads have the advantage of excellent moldability, and the resulting foamed molded article has the advantage of excellent appearance and molded article strength.

[0093] There are no particular limitations on the closed container for dispersing the polyolefin resin particles, and any container can be used as long as it can withstand the pressure and temperature inside the container during the production of the polyolefin resin particles, and examples thereof include autoclave-type containers.

[0094] The expansion ratio of the expanded polyolefin resin beads obtained by the above-mentioned production method is, for example, 5 times or more and 45 times or less. The expansion ratio of the expanded polyolefin resin beads affects the density of the molded article (the higher the expansion ratio, the lower the density of the molded article), and also affects the flame retardancy (particularly the oxygen index) of the molded article to some extent. In some embodiments of the present invention, the expansion ratio of the expanded polyolefin resin beads is preferably 8 to 45 times, more preferably 9 to 40 times, and even more preferably 10 to 38 times. The expansion ratio of the expanded polyolefin resin beads is calculated by dividing the weight w (g) of the expanded polyolefin resin beads and the volume v (cm) of the expanded polyolefin resin beads when submerged in ethanol by the weight w (g) of the expanded polyolefin resin beads. 3) was calculated, and the weight w, volume v, and density d (g / cm 3 ) of the polyolefin resin particles before foaming were calculated. 3 ) was calculated using the following formula:

[0095] Expansion ratio = d × v / w.

[0096] The volume (v) of polyolefin resin foam particles submerged in ethanol is the value (cm) obtained by submerging the polyolefin resin foam particles in ethanol in a measuring cylinder containing ethanol and reading the rise in the ethanol liquid level from the scale of the measuring cylinder. 3 ) is intended.

[0097] Alternatively, expanded polyolefin resin beads with a high expansion ratio may be obtained by a two-stage expansion method in which expanded polyolefin resin beads with an expansion ratio of 5 to 35 times are first produced and then further expanded by the following methods (1) and (2): (1) the expanded polyolefin resin beads are placed in a sealed container and subjected to a pressure treatment in which nitrogen, air, etc. are impregnated into the expanded polyolefin resin beads; (2) the pressure inside the expanded polyolefin resin beads is increased above atmospheric pressure by such pressure treatment, and then the expanded polyolefin resin beads are heated with steam, etc., and further expanded.

[0098] The expanded polyolefin resin particles according to one embodiment of the present invention may be obtained, for example, by the following method: the polyolefin resin particles according to one embodiment of the present invention are dispersed in an aqueous dispersion medium in a sealed container, and the sealed container is heated in the presence of a foaming agent to a temperature equal to or higher than the softening temperature of the polyolefin resin particles. The resulting mixture is then released from the sealed container into a low-pressure atmosphere to be foamed.

[0099] [Polyolefin resin foam molded article] A polyolefin resin foam molded article according to one embodiment of the present invention is obtained by in-mold foam molding of the polyolefin resin foam beads described in the section [Polyolefin Resin Foam Beads] above or the polyolefin resin foam beads obtained by the production method described in the section [Production Method of Polyolefin Resin Foam Beads] above.

[0100] The polyolefin resin foam molded article according to one embodiment of the present invention has the above-described configuration, and therefore has the advantage of exhibiting excellent flame retardancy while maintaining good in-mold foam moldability and surface appearance equivalent to conventional products.

[0101] A polyolefin resin foam molded article according to one embodiment of the present invention can be obtained by filling a mold with the polyolefin resin foam beads described in the section [Polyolefin Resin Foam Beads] above or the polyolefin resin foam beads obtained by the manufacturing method described in the section [Method for Manufacturing Polyolefin Resin Foam Beads] above, and heating the polyolefin resin foam beads with steam or the like to perform in-mold foam molding in which the polyolefin resin foam beads are fused together.

[0102] When the expanded polyolefin resin beads according to one embodiment of the present invention are used for in-mold foam molding, (a) A method of molding the expanded polyolefin resin beads as they are, (b) A method in which an inorganic gas such as air is injected into the expanded polyolefin resin beads in advance to impart expandability to the expanded polyolefin resin beads, and the expanded polyolefin resin beads are then filled into a mold and molded; and (c) A method in which expanded beads are filled in a mold in a compressed state and molded, and other conventionally known methods can be applied.

[0103] In one embodiment of the present invention, a method of imparting expandability to expanded polyolefin resin beads by injecting inorganic gas such as air into the expanded polyolefin resin beads in advance (hereinafter sometimes referred to as the "internal pressure imparting method") will be described. When the internal pressure imparting method is used, an internal pressure of 3.0 atm or less is preferably imparted to the expanded polyolefin resin beads, more preferably an internal pressure of 1.3 atm to 3.0 atm, and even more preferably an internal pressure of 1.5 atm to 2.5 atm. When the internal pressure imparted to the expanded polyolefin resin beads is 3.0 atm or less, not only is the time required to impart internal pressure in a pressure vessel shortened, but also the cooling time required during in-mold molding is shortened, thereby shortening the molding cycle and tending to improve productivity. Furthermore, when the applied internal pressure is 1.3 atm or more, after molding in the mold, (a) there is no risk of gaps between particles occurring on the surface of the polyolefin resin foam molded article, (b) there is no risk of surface irregularities occurring on the surface of the polyolefin resin foam molded article, (c) there is no risk of the polyolefin resin foam molded article shrinking and causing wrinkles on the surface of the polyolefin resin foam molded article, and (d) in polyolefin resin foam molded articles having ridges, the polyolefin resin foam particles have good packing properties and there is no risk of voids occurring.

[0104] For example, the method of applying internal pressure to the expanded polyolefin resin beads can be carried out by filling a pressure-resistant container with the expanded polyolefin resin beads and applying pressure with an inorganic gas. If necessary, the interior of the pressure-resistant container may be heated. The pressure-resistant container is not particularly limited, and examples thereof include autoclave-type pressure-resistant containers. Examples of the inorganic gas include air, nitrogen, argon, and helium, with air and / or nitrogen being preferred because of their low cost.

[0105] A specific method for producing a polyolefin resin foamed molded article (sometimes referred to as an "in-mold polyolefin resin foamed article") from expanded polyolefin resin beads according to one embodiment of the present invention by in-mold foam molding will now be described. Examples of such methods include the following (1) to (7): (1) preliminarily subjecting the expanded polyolefin resin beads to air pressure treatment in a pressure-resistant vessel (also known as air impregnation treatment), (2) imparting expandability to the expanded polyolefin resin beads by forcing air into the expanded polyolefin resin beads, (3) filling the expanded polyolefin resin beads into a closable but non-hermetically sealed molding space consisting of two molds (a fixed mold and a movable mold), (4) molding using steam or the like as a heating medium at a heated water vapor pressure of about 0.10 MPa to 0.40 MPa for about 3 to 30 seconds, (5) fusing the expanded polyolefin resin beads together, (6) water-cooling the mold, and (7) opening the mold to obtain an in-mold polyolefin resin foamed article. In a preferred embodiment of the present invention, (a) the air impregnation treatment applies a pressure of 0.19 MPa to 0.23 MPa to the expanded polyolefin resin particles, (b) the heated water vapor pressure is slightly different between the fixed mold and the movable mold (for example, 0.30 MPa for the fixed mold and 0.31 MPa for the movable mold), and (c) the heating time is 20 to 25 seconds. In this specification, when the heated water vapor pressure is different between the fixed mold and the movable mold, the heated water vapor pressure may be expressed as follows: heated water vapor pressure of the fixed mold / heated water vapor pressure of the movable mold.

[0106] The density of the polyolefin resin in-mold foamed article obtained using the expanded polyolefin resin beads according to one embodiment of the present invention is preferably 10 g / L to 150 g / L, more preferably 20 g / L to 100 g / L, and even more preferably 25 g / L to 95 g / L, from the viewpoint of obtaining a highly flame-retardant product.

[0107] [Application] The polyolefin resin foam molded article obtained in this manner has excellent moldability and flame retardancy, and a good molded article appearance. Furthermore, the polyolefin resin foam molded article obtained in this manner has a high fusion rate, conforms to HF-1 in the UL94 horizontal foam test (also referred to as "reaching UL94 HF-1 grade," "passing the UL94 HF-1 test," or "being UL94 HF-1 grade"), and can have a high oxygen index. In some preferred embodiments of the present invention, the oxygen index of the polyolefin resin foam molded article is 27.0% or higher, more preferably 28.0% or higher, and even more preferably 30.0% or higher. Therefore, the polyolefin resin foam beads and polyolefin resin foam molded article according to one embodiment of the present invention can meet the requirements for interior materials for public transportation. Therefore, the polyolefin resin foam beads and polyolefin resin foam molded article according to one embodiment of the present invention are particularly suitable for producing cushioning materials such as seat fillings for high-speed public transportation (high-speed trains, airplanes, etc.). According to international standards, tracks with speeds of over 200 km / h, and new lines reaching 250 km / h, are considered high-speed railways (also known as "gaotie"). In China, "gaotie" refers to a railway system that can travel at a maximum speed of 200 km / h or more.

[0108] Therefore, one embodiment of the present invention further provides an interior material for public transportation, such as a cushioning material for high-speed trains, using the polyolefin resin foam molded article. In other words, the interior material for public transportation according to one embodiment of the present invention includes the polyolefin resin foam molded article described in the section entitled "Polyolefin Resin Foam Molded Article." In one embodiment of the present invention, a high-speed train seat filling material manufactured from the polyolefin resin in-mold foam molded article according to one embodiment of the present invention passes the flame retardancy rating, oxygen index, smoke density, and smoke toxicity test in a horizontal flammability test, and satisfies the flame retardancy technical requirements of TB / T3237-2010 for interior materials for high-speed vehicles. Furthermore, one embodiment of the present invention may also include a public transportation vehicle equipped with the interior material. Furthermore, one embodiment of the present invention may also include the use of the interior material in public transportation (or, in other words, a method for manufacturing an interior material for public transportation using the interior material).

[0109] An embodiment of the present invention may have the following configuration.

[0110] [X1] Expanded polyolefin resin particles containing a polyolefin resin, 1.60 to 10.00 parts by weight of an inorganic hypophosphite, and 0.01 to 2.00 parts by weight of a melamine flame retardant, relative to 100 parts by weight of the polyolefin resin.

[0111] [X2] Expanded polyolefin resin particles according to [X1], containing 1.80 to 4.00 parts by weight of the inorganic hypophosphite per 100 parts by weight of the polyolefin resin.

[0112] [X3] General formula (1): R 1 NHCH2CH2CH2NR 2 CH2CH2NR 3 CH2CH2CH2NHR 4 (1) (In the formula, R 1 and R 2 is represented by the general formula (2):

[0113] [ka] (In the formula, R 5 is an alkyl group having 1 to 12 carbon atoms, and R 6 is a methyl group, a cyclohexyl group, or an octyl group), and the dashed line above the triazine ring shown in general formula (2) represents a linking point with the nitrogen atom of general formula (1), R 3 and R 4 is a group represented by the general formula (2), the broken line above the triazine ring represented by the general formula (2) represents a linking point with the nitrogen atom of the general formula (1), and R 3 and R 4 and the other represents a hydrogen atom, The expanded polyolefin resin particles according to [X1] or [X2] contain 0.01 to 2.00 parts by weight of the compound represented by the general formula (1) per 100 parts by weight of the polyolefin resin.

[0114] [X4] Expanded polyolefin resin particles according to any one of [X1] to [X3], further comprising one or more brominated flame retardants selected from the group consisting of brominated bisphenol A flame retardants, brominated bisphenol S flame retardants, brominated butadiene-styrene block copolymer flame retardants, and brominated polyphenylene ether flame retardants.

[0115] [X5] Expanded polyolefin resin particles according to [X4], wherein the brominated flame retardant comprises at least one selected from a brominated bisphenol A flame retardant and a brominated bisphenol S flame retardant.

[0116] [X6] Expanded polyolefin resin particles according to [X4] or [X5], containing 0.10 to 5.00 parts by weight of the bromine-based flame retardant per 100 parts by weight of the polyolefin resin.

[0117] [X7] Expanded polyolefin resin particles according to any one of [X1] to [X6], further comprising a radical generator.

[0118] [X8] Expanded polyolefin resin particles according to [X7], wherein the radical generator comprises at least one selected from the group consisting of 2,3-dimethyl-2,3-diphenylbutane and poly-1,4-diisopropylbenzene.

[0119] [X9] Expanded polyolefin resin particles according to [X7] or [X8], containing 0.01 to 0.50 parts by weight of the radical generator per 100 parts by weight of the polyolefin resin.

[0120] [X10] Expanded polyolefin resin particles according to any one of [X1] to [X9], wherein the polyolefin resin includes a polypropylene resin.

[0121] [X11] Expanded polyolefin resin particles according to any one of [X1] to [X10], having an expansion ratio of 5 to 45 times.

[0122] [X12] A method for producing expanded polyolefin resin particles, comprising the steps of dispersing polyolefin resin particles in an aqueous dispersion medium in a sealed container and adding a blowing agent to the resulting dispersion; heating the sealed container to a temperature equal to or higher than the softening temperature of the polyolefin resin particles; and releasing the resulting mixture from the sealed container into a low-pressure atmosphere to expand the polyolefin resin particles, thereby obtaining expanded polyolefin resin particles, wherein the polyolefin resin particles contain a polyolefin resin, and 1.60 to 10.00 parts by weight of an inorganic hypophosphite and 0.01 to 2.00 parts by weight of a melamine flame retardant per 100 parts by weight of the polyolefin resin.

[0123] [X13] A polyolefin resin foamed molded article obtained by in-mold foaming of expanded polyolefin resin beads according to any one of [X1] to [X11] or expanded polyolefin resin beads obtained by the method for producing expanded polyolefin resin beads according to [X12].

[0124] [X14] A polyolefin resin foam molded article according to [X13], which is UL94 HF-1 grade and has an oxygen index of 27.0% or more.

[0125] [X15] An interior material for public transportation, comprising the polyolefin resin foam molded article according to [X13] or [X14].

[0126] Another embodiment of the present invention may have the following configuration.

[0127] [Y1] Expanded polyolefin resin particles characterized by containing a polyolefin resin, 1.6 to 10.0 parts by weight of an inorganic hypophosphite, and 0.01 to 2.0 parts by weight of a melamine-based flame retardant, per 100 parts by weight of the polyolefin resin.

[0128] [Y2] Expanded polyolefin resin particles according to [Y1], characterized in that the inorganic hypophosphite is contained in an amount of 1.8 to 4.0 parts by weight per 100 parts by weight of the polyolefin resin.

[0129] [Y3] General formula (1): R 1 NHCH2CH2CH2NR 2 CH2CH2NR 3 CH2CH2CH2NHR 4 (1) (In the formula, R 1 and R 2 is represented by the general formula (2):

[0130] [ka] (In the formula, R 5 is an alkyl group having 1 to 12 carbon atoms, R 6 is a methyl group, a cyclohexyl group, or an octyl group), the dashed line above the triazine ring shown in general formula (2) represents the linkage with the nitrogen atom of general formula (1), and R 3 and R 4is a group represented by general formula (2), the dashed line above the triazine ring represented by general formula (2) represents the linkage with the nitrogen atom of general formula (1), and R 3 and R 4 and the other represents a hydrogen atom, The expanded polyolefin resin particles according to [Y1] or [Y2], characterized in that the compound represented by the general formula (1) is contained in an amount of 0.01 to 2.0 parts by weight per 100 parts by weight of the polyolefin resin.

[0131] [Y4] Expanded polyolefin resin particles according to any one of [Y1] to [Y3], further comprising one or more brominated flame retardants selected from the group consisting of brominated bisphenol A flame retardants, brominated bisphenol S flame retardants, brominated butadiene-styrene block copolymer flame retardants, and brominated polyphenylene ether flame retardants.

[0132] [Y5] The expanded polyolefin resin particles according to [Y4], characterized in that the brominated flame retardant contains at least one selected from brominated bisphenol A flame retardants and brominated bisphenol S flame retardants, and the amount of the brominated flame retardant is 0.1 to 5.0 parts by weight per 100 parts by weight of the polyolefin resin.

[0133] [Y6] Expanded polyolefin resin particles according to any one of [Y1] to [Y5], further comprising a radical generator.

[0134] [Y7] The expanded polyolefin resin particles according to [Y6], characterized in that the radical generator contains at least one of 2,3-dimethyl-2,3-diphenylbutane and poly-1,4-diisopropylbenzene, and the amount of the radical generator is 0.01 to 0.5 parts by weight per 100 parts by weight of the polyolefin resin.

[0135] [Y8] Expanded polyolefin resin particles according to any one of [Y1] to [Y7], characterized in that the polyolefin resin is a polypropylene resin.

[0136] [Y9] Expanded polyolefin resin particles according to any one of [Y1] to [Y8], characterized in that the expansion ratio is 5 to 45 times.

[0137] [Y10] A method for producing expanded polyolefin resin beads, comprising dispersing polyolefin resin particles in an aqueous dispersion medium in a sealed container, heating the mixture in the presence of a foaming agent to a temperature equal to or higher than the softening temperature of the polyolefin resin particles, and then releasing the resulting mixture from the sealed container into a low-pressure atmosphere to expand the polyolefin resin particles, thereby obtaining expanded polyolefin resin beads, The polyolefin resin particles contain a polyolefin resin, 1.6 to 10.0 parts by weight of an inorganic hypophosphite, and 0.01 to 2.0 parts by weight of a melamine-based flame retardant, per 100 parts by weight of the polyolefin resin.

[0138] [Y11] A polyolefin resin foam molded article, characterized by being obtained by in-mold foam molding of the expanded polyolefin resin beads according to any one of [Y1] to [Y9] or the expanded polyolefin resin beads obtained by the production method of [Y10].

[0139] [Y12] The polyolefin resin foam molded article according to [Y11], which is of UL94 HF-1 grade and has an oxygen index of 27% or more.

[0140] [Y13] An interior material for public transportation, characterized by containing the polyolefin resin foam molded article according to [Y11] or [Y12]. [Example]

[0141] The present invention will be further explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0142] Example 1 [Preparation of polypropylene resin particles] A flame-retardant aluminum hypophosphite masterbatch (mass fraction of ALHP: 25 wt%) was obtained by mixing 1.60 parts by weight of aluminum hypophosphite (ALHP) and 4.80 parts by weight of polypropylene resin (propylene / ethylene random copolymer, ethylene content: 2.2 wt%, MFR: 8.0 g / 10 min). A flame-retardant melamine hydrobromide masterbatch (mass fraction of MHB: 20 ​​wt%) was obtained by mixing 0.06 parts by weight of melamine hydrobromide (MHB) and 0.24 parts by weight of polypropylene resin (propylene / ethylene random copolymer, ethylene content: 2.2 wt%, MFR: 8.0 g / 10 min).

[0143] 94.96 parts by weight of polypropylene-based resin (propylene / ethylene random copolymer, ethylene content: 2.2 wt%, MFR: 8.0 g / 10 min) was mixed with the obtained aluminum hypophosphite flame-retardant masterbatch, melamine hydrobromide flame-retardant masterbatch, 0.06 parts by weight of 2,3-dimethyl-2,3-diphenylbutane (radical generator, DMDPB), 0.63 parts by weight of carbon black, and 0.87 parts by weight of talc to obtain a mixture. The resulting mixture was kneaded in a twin-screw extruder (maximum extrusion temperature setting: 200 °C) to obtain polypropylene-based resin particles. Each polypropylene-based resin particle weighed 1.0 mg. The amount of polypropylene-based resin used was 100 parts by weight, calculated by adding the amount of polypropylene-based resin contained in each masterbatch and the amount of polypropylene-based resin mixed with the masterbatch.

[0144] [Preparation of polypropylene resin foam particles] As a sealed container, the capacity is 0.01 m 3A 10 L autoclave was used. 100 parts by weight of the resulting polypropylene resin particles, 200 parts by weight of water, 0.6 parts by weight of powdered basic tricalcium phosphate (dispersant), and 0.04 parts by weight of sodium n-alkanesulfonate (dispersion aid) were added to the autoclave, and the polyolefin resin particles were dispersed in water in the autoclave. While stirring the resulting aqueous dispersion, carbon dioxide, a foaming agent, was introduced (added) to the aqueous dispersion. The autoclave, i.e., the resulting aqueous dispersion, was heated to a foaming temperature of 155°C, which is a temperature above the softening temperature of the polyolefin resin particles, and the pressure inside the autoclave was increased to a foaming pressure of 1.55 MPa by introducing additional carbon dioxide into the autoclave. Then, while maintaining the pressure inside the vessel by introducing nitrogen gas, a valve located at the bottom of the pressure vessel was opened, and the mixture (aqueous dispersion) inside the autoclave was released into the atmosphere, which was under a low pressure, through an orifice plate with an opening of 3.2 mm in diameter, thereby obtaining expanded polypropylene resin beads. The expansion ratio of the resulting expanded polypropylene resin beads was measured and found to be 15 times. The results are shown in Table 1.

[0145] [Production of in-mold foamed molded body] After removing moisture from the resulting polypropylene-based resin foamed beads, an internal pressure of 0.21 MPa (gauge pressure) was applied to the polypropylene-based resin foamed beads by air impregnation. The pressurized polypropylene-based resin foamed beads were then packed into a mold measuring 450 mm long, 350 mm wide, and 60 mm thick. The polypropylene-based resin foamed beads in the mold were then heated for 22 seconds at a steam pressure of 0.30 MPa (gauge pressure) / 0.31 MPa (gauge pressure) using steam as a heating medium to fuse the polypropylene-based resin foamed beads together, yielding a flat-shaped polypropylene-based resin foamed molded article (flat-shaped molded article). Evaluation of the resulting polypropylene-based resin foamed molded article revealed no surface irregularities and almost no gaps between the particles. When the resulting in-mold foamed molded article was folded and its cross section was observed, more than 60% of the particles were fully fused to other particles, demonstrating an excellent fusion rate.

[0146] The density, flame retardancy grade, and oxygen index of the obtained in-mold foamed articles were measured and evaluated. The results are shown in Table 2.

[0147] (Examples 2 to 14 and Comparative Examples 1 to 7) [Preparation of polypropylene resin particles] The amounts of ALHP and MHB used were changed as shown in Table 1 to produce an aluminum hypophosphite flame-retardant masterbatch (aluminum hypophosphite mass fraction: 25 wt%) and a melamine hydrogen bromide flame-retardant masterbatch (MHB mass fraction: 20 wt%). The production method was the same as in Example 1.

[0148] A mixture was obtained by mixing a polypropylene resin (propylene / ethylene random copolymer, ethylene content: 2.2 wt%, MFR: 8.0 g / 10 min) with the resulting aluminum hypophosphite flame-retardant masterbatch, the melamine hydrogen bromide flame-retardant masterbatch, DMDPB, and optionally a sterically hindered amine ether flame retardant compound corresponding to the compound represented by general formula (1) of the present invention [BASF FLAMESTAB NOR116FF, abbreviated as "NOR116FF"], an optional brominated flame retardant (tetrabromobisphenol A-bis(2,3-dibromopropyl)ether (TBAB) or tetrabromobisphenol S-bis(2,3-dibromopropyl)ether (TBSB)], carbon black, and talc. The resulting mixture was kneaded in a twin-screw extruder at a maximum extrusion temperature of 200°C to obtain polypropylene resin particles. Each polypropylene resin particle weighed 1.0 mg. Here, to better disperse TBAB and TBSB in the polypropylene resin (propylene / ethylene random copolymer), they may be mixed with a small amount of polypropylene resin (propylene / ethylene random copolymer, ethylene content: 2.2 wt%, MFR: 8.0 g / 10 min) to form a flame-retardant masterbatch (mass fraction: 20 wt%), which is then added to the system. The amount of each component used is shown in Table 1. The amount of polypropylene resin used to mix with the masterbatch was such that the total amount of polypropylene resin contained in each masterbatch and the amount of polypropylene resin mixed with the masterbatch was 100 parts by weight.

[0149] [Preparation of polypropylene resin foam particles] As a sealed container, the capacity is 0.01 m 3A 10 L autoclave was used. 100 parts by weight of the resulting polypropylene resin particles, 200 parts by weight of water, 0.6 parts by weight of powdered basic tricalcium phosphate (dispersant), and 0.04 parts by weight of sodium n-alkanesulfonate (dispersing aid) were added to the autoclave, and the polyolefin resin particles were dispersed in water in the autoclave. While stirring the resulting aqueous dispersion, carbon dioxide, a foaming agent, was introduced (added) into the aqueous dispersion. The autoclave, i.e., the resulting aqueous dispersion, was heated to a foaming temperature of 154°C to 160°C, which is a temperature above the softening temperature of the polyolefin resin particles, and the pressure inside the autoclave was increased to a foaming pressure of 1.3 MPa to 2.2 MPa by introducing additional carbon dioxide into the autoclave. Then, while maintaining the pressure inside the vessel by introducing nitrogen gas, a valve installed in the lower part of the pressure vessel was opened, and the mixture (aqueous dispersion) inside the autoclave was released from the autoclave into the atmosphere under a low pressure atmosphere through an orifice plate with an opening of 3.2 mm in diameter, thereby obtaining expanded polypropylene resin beads. The expansion ratio of the obtained expanded polypropylene resin beads was measured. The results are shown in Table 1.

[0150] [Production of in-mold foamed molded body] After removing moisture from the resulting polypropylene-based resin foamed beads, an internal pressure of 0.21 MPa (gauge pressure) was applied to the polypropylene-based resin foamed beads by air impregnation. The pressurized polypropylene-based resin foamed beads were then packed into a mold measuring 450 mm long, 350 mm wide, and 60 mm thick. The polypropylene-based resin foamed beads in the mold were then heated for 22 seconds at a steam pressure of 0.30 MPa (gauge pressure) / 0.31 MPa (gauge pressure) using steam as a heating medium to fuse the polypropylene-based resin foamed beads together, yielding a flat-shaped polypropylene-based resin foamed molded article (flat-shaped molded article). Evaluation of the resulting polypropylene-based resin foamed molded article revealed no surface irregularities and almost no gaps between the particles. When the resulting in-mold foamed molded article was folded and its cross section was observed, more than 60% of the particles were fully fused to other particles, demonstrating an excellent fusion rate.

[0151] The density, flame retardancy grade, and oxygen index of the obtained in-mold foamed articles were measured and evaluated. The results are shown in Table 2.

[0152] (Comparative Examples 8 and 9) [Preparation of polypropylene resin particles] A mixture was obtained by mixing 100 parts by weight of a polypropylene resin (propylene / ethylene random copolymer, ethylene content: 2.2% by weight, MFR: 8.0 g / 10 min) with the weight parts shown in Table 1 of a sterically hindered amine ether flame retardant compound (NOR116FF) corresponding to the compound represented by general formula (1) of the present invention, ammonium polyphosphate (APP), carbon black, and talc. The resulting mixture was kneaded in a twin-screw extruder, with the maximum extrusion temperature set to 200°C, to obtain polypropylene resin particles. Each polypropylene resin particle weighed 1.0 mg.

[0153] [Preparation of polypropylene resin foam particles] Expanded polypropylene resin beads were obtained in the same manner as in the above Examples. The expansion ratio was measured, and the results are shown in Table 1.

[0154] [Production of in-mold foamed molded body] A flat polypropylene resin foam molded article (flat molded article) was obtained by the same method as in the above examples. Evaluation of the obtained polypropylene resin foam molded article revealed no irregularities on the surface and almost no gaps between particles. When the obtained in-mold foam molded article was folded and the cross section was observed, it was found that 60% or more of the particles were sufficiently fused with other particles, indicating an excellent fusion rate.

[0155] The density, flame retardancy grade, and oxygen index of the obtained in-mold foamed articles were measured and evaluated. The results are shown in Table 2.

[0156] The evaluations in the examples and comparative examples were carried out as follows.

[0157] (Fusion rate) A 5mm deep cut was made on the surface of the foam molded article with a cutter. The foam molded article was then split along the cut near the cut. The fracture surface of the obtained foam molded article was visually observed, and the ratio (B / A x 100) of the number of foam particles (B) that were broken internally, rather than at the foam particle interface, on the fracture surface to the total number of foam particles (A) on the fracture surface was calculated, and the obtained value was taken as the fusion rate. The fusion property was judged from the fusion rate. Specifically, a fusion rate of 60% or more was considered acceptable.

[0158] (Expansion ratio) The weight of the polyolefin resin foam particles W (g) and the volume V (cm) of the ethanol submerged particles 3 ) and the density d (g / cm 3 ) was calculated using the following formula:

[0159] Foaming ratio = d × V / W (Density of in-mold foamed body) The apparent density MD (g / L) of the in-mold foam molded article was calculated by dividing the weight W2 (g) of the foam molded article by the volume V2 (L) of the foam molded article.

[0160] MD=W2 / V2 (Flame retardant grade) Measurements and evaluations were carried out in accordance with UL94 "Horizontal Flammability Test for Foam Materials," and then the evaluation was carried out according to the following criteria. In Table 2, the results of the flame retardancy grade are shown in the "HF-1 Test" column.

[0161] ◎ (Excellent): Passed HF-1 ○(Good): Passed HF-2 ×(defective):HF NG (oxygen index) The measurement was carried out in accordance with GB / T 2406.2-2009. The skin of the in-mold foamed article was peeled off and 15 to 30 samples measuring 80 to 150 mm x 10 mm x 10 mm were cut out. These samples were then conditioned at 23°C and 50% RH for at least 88 hours, after which the oxygen index was measured and the final results were obtained using the up-and-down method. The oxygen index results are listed in the "OI" column in Table 2.

[0162] As shown in Tables 1 and 2, Comparative Example 1 failed the HF-1 test because the content of aluminum hypophosphite was too low. Comparative Examples 2 and 3 passed the HF-1 test, but had low oxygen indices because the aluminum hypophosphite content was below the range specified in the present invention. Comparative Example 4, compared to Comparative Example 1, did not reach HF-1 grade and had a slightly lower oxygen index despite the addition of the compound represented by general formula (1) of the present invention. Comparative Examples 5 to 7 did not add MHB. Comparative Example 5 did not reach HF-1 grade and also had a low oxygen index. Comparative Examples 6 and 7 reached HF-1 grade, but did not achieve an oxygen index of 27.0%. Comparative Examples 8 and 9 incorporated an ammonium polyphosphate flame retardant and a compound represented by general formula (1). Plate-shaped molded articles with surface appearance and fusion rate that met the specified requirements were obtained, but they did not pass the UF94 "Horizontal Flammability Test for Foamed Materials." From Examples 1 to 14, it is clear that the flame retardant composition mixed at the specific ratio specified in one embodiment of the present invention can provide a polyolefin resin in-mold foamed article having a flame retardancy rating of HF-1 and a high oxygen index while maintaining moldability. [Table 1] [Table 2] [Industrial Applicability]

[0163] According to one embodiment of the present invention, novel expanded polyolefin resin beads and novel expanded polyolefin resin molded articles having excellent flame retardancy can be provided. Therefore, the expanded polyolefin resin beads and expanded polyolefin resin molded articles according to one embodiment of the present invention can be particularly suitably used as interior materials for public transportation (e.g., high-speed public transportation (high-speed trains, airplanes, etc.)).

Claims

1. A polyolefin resin, The composition contains 1.60 to 10.00 parts by weight of an inorganic hypophosphite and 0.01 to 2.00 parts by weight of a melamine-based flame retardant relative to 100 parts by weight of the polyolefin-based resin, The weight ratio of the inorganic hypophosphite to the melamine flame retardant (content (parts by weight) of the inorganic hypophosphite / content (parts by weight) of the melamine flame retardant) is 25 or more.

2. 2. The expanded polyolefin resin particles according to claim 1, wherein the inorganic hypophosphite is contained in an amount of 1.80 to 4.00 parts by weight per 100 parts by weight of the polyolefin resin.

3. General formula (1): R １ NHCH ２ CH ２ CH ２ NR ２ CH ２ CH ２ NR ３ CH ２ CH ２ CH ２ NHR ４ (1) (In the formula, R １ and R ２ is represented by the general formula (2): 【Chemistry 1】 (In the formula, R ５ is an alkyl group having 1 to 12 carbon atoms, and R ６ is a methyl group, a cyclohexyl group, or an octyl group), and the dashed line above the triazine ring in general formula (2) represents a linking point with the nitrogen atom in general formula (1), R ３ and R ４ is a group represented by the general formula (2), the broken line above the triazine ring represented by the general formula (2) represents a linking point with the nitrogen atom of the general formula (1), and R ３ and R ４ and the other represents a hydrogen atom, 3. The expanded polyolefin resin particles according to claim 1, comprising 0.01 to 2.00 parts by weight of the compound represented by general formula (1) relative to 100 parts by weight of the polyolefin resin.

4. The expanded polyolefin resin particles according to any one of claims 1 to 3, further comprising one or more brominated flame retardants selected from the group consisting of brominated bisphenol A flame retardants, brominated bisphenol S flame retardants, brominated butadiene-styrene block copolymer flame retardants, and brominated polyphenylene ether flame retardants.

5. The expanded polyolefin resin particles according to claim 4, wherein the brominated flame retardant comprises at least one selected from the group consisting of a brominated bisphenol A flame retardant and a brominated bisphenol S flame retardant.

6. 6. The expanded polyolefin resin particles according to claim 4, wherein the bromine-based flame retardant is contained in an amount of 0.10 to 5.00 parts by weight per 100 parts by weight of the polyolefin resin.

7. The expanded polyolefin resin particles according to any one of claims 1 to 6, further comprising a radical generator.

8. 8. The expanded polyolefin resin particles according to claim 7, wherein the radical generator comprises at least one selected from the group consisting of 2,3-dimethyl-2,3-diphenylbutane and poly-1,4-diisopropylbenzene.

9. 9. The expanded polyolefin resin particles according to claim 7, wherein the radical generator is contained in an amount of 0.01 to 0.50 parts by weight per 100 parts by weight of the polyolefin resin.

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

11. The expanded polyolefin resin particles according to any one of claims 1 to 10, having an expansion ratio of 5 to 45 times.

12. The method includes the steps of dispersing polyolefin resin particles in an aqueous dispersion medium in a sealed container and adding a foaming agent to the resulting dispersion; heating the sealed container to a temperature equal to or higher than the softening temperature of the polyolefin resin particles; and releasing the resulting mixture from the sealed container into a low-pressure atmosphere to foam the polyolefin resin particles, thereby obtaining expanded polyolefin resin particles. The polyolefin-based resin particles contain a polyolefin-based resin, 1.60 to 10.00 parts by weight of an inorganic hypophosphite, and 0.01 to 2.00 parts by weight of a melamine-based flame retardant, relative to 100 parts by weight of the polyolefin-based resin, and the weight ratio of the inorganic hypophosphite to the melamine-based flame retardant (content (parts by weight) of the inorganic hypophosphite / content (parts by weight) of the melamine-based flame retardant) is 25 or more.

13. A polyolefin resin foam molded article obtained by in-mold foam molding of the expanded polyolefin resin beads according to any one of claims 1 to 11.

14. The polyolefin resin foam molded article according to claim 13, which is of UL94 HF-1 grade and has an oxygen index of 27.0% or more.

15. An interior material for public transportation, comprising the polyolefin resin foam molded article according to claim 13 or 14.

Images