Polypropylene-based resin foamed particles, method for producing same, and

Abstract

The foamed polypropylene resin particles contain an inorganic hypophosphite and a melamine flame retardant. The amount of the inorganic hypophosphite blended in the foamed particles is 0.5% by mass or more, the amount of the melamine-based flame retardant blended in the foamed particles is 0.05% by mass or more, and the total of the amount of the inorganic hypophosphite blended in the foamed particles and the amount of the melamine-based flame retardant blended in the foamed particles is 5% by mass or less. The foamed particles further comprise a first antioxidant comprising a phenolic antioxidant and a second antioxidant comprising a phosphorus-based antioxidant and / or a sulfur-based antioxidant. The total of the blending amount of the first antioxidant and the blending amount of the second antioxidant in the foamed particles is 0.05% by mass or more and 0.6% by mass or less, and the ratio of the blending amount of the second antioxidant to the blending amount of the first antioxidant is 0.5-10.

Description

Technical Field

[0001] The present invention relates to polypropylene resin foamed particles, a method for manufacturing the same, and a polypropylene resin foamed particle molded body. Background Art

[0002] Since polypropylene resin foamed particle molded bodies are lightweight and have excellent cushioning properties, rigidity, etc., they are used for various purposes such as packaging materials, containers, and cushioning materials. In the polypropylene resin foamed particles that make up the polypropylene resin foamed particle molded body, inorganic hypophosphates and melamine-based flame retardants are sometimes added for the purpose of improving flame retardancy (for example, Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: International Publication No. 2022 / 039076 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In the foamed particles of Patent Document 1, in order to obtain the desired flame retardancy, it is necessary to add a relatively large amount of flame retardant, resulting in a decrease in in-mold formability. On the other hand, if the amount of flame retardant added is reduced in order to improve in-mold formability, there is a problem that it is difficult to obtain the desired flame retardancy.

[0008] The present invention has been completed in view of the above background, and an object thereof is to provide polypropylene resin foamed particles and a method for manufacturing the same that can achieve both excellent flame retardancy and in-mold formability. In addition, the present invention provides a polypropylene resin foamed particle molded body that can achieve both excellent flame retardancy and compression physical properties.

[0009] Means for Solving the Problems

[0010] One aspect of the present invention relates to polypropylene resin foamed particles according to the following [1] to [5].

[0011] 〔1〕A polypropylene resin foamed particle, the polypropylene resin foamed particle containing an inorganic hypophosphate and a melamine-based flame retardant, wherein,

[0012] the compounding amount of the inorganic hypophosphate in the foamed particle is 0.5% by mass or more,

[0013] the compounding amount of the melamine-based flame retardant in the foamed particle is 0.05% by mass or more,

[0014] the total of the compounding amount of the inorganic hypophosphate and the compounding amount of the melamine-based flame retardant in the foamed particle is 5% by mass or less,

[0015] The foamed particles further contain a first antioxidant composed of a phenolic antioxidant and a second antioxidant composed of a phosphorus-based antioxidant and / or a sulfur-based antioxidant.

[0016] The total of the compounding amount of the first antioxidant and the compounding amount of the second antioxidant in the foamed particles is 0.05% by mass or more and 0.6% by mass or less.

[0017] The ratio of the compounding amount of the second antioxidant in the foamed particles to the compounding amount of the first antioxidant is 0.5 or more and 10 or less.

[0018] 〔2〕The polypropylene-based resin foamed particles according to 〔1〕, wherein the compounding amount of the inorganic hypophosphite in the foamed particles is 0.5% by mass or more and 1.5% by mass or less.

[0019] 〔3〕The polypropylene-based resin foamed particles according to 〔1〕 or 〔2〕, wherein the ratio of the compounding amount of the inorganic hypophosphite in the foamed particles to the compounding amount of the melamine-based flame retardant is 0.05 or more and 10 or less.

[0020] 〔4〕The polypropylene-based resin foamed particles according to any one of 〔1〕 to 〔3〕, wherein the ratio of the total of the compounding amount of the first antioxidant and the compounding amount of the second antioxidant in the foamed particles to the compounding amount of the inorganic hypophosphite is 0.05 or more and 0.5 or less.

[0021] 〔5〕The polypropylene-based resin foamed particles according to any one of 〔1〕 to 〔4〕, wherein the bulk density of the foamed particles is 20 kg / m 3 or more and 90 kg / m 3 or less.

[0022] Another aspect of the present invention relates to a polypropylene-based resin foamed particle molded body according to the following 〔6〕.

[0023] 〔6〕A polypropylene-based resin foamed particle molded body, which is obtained by in-mold molding of the polypropylene-based resin foamed particles according to any one of 〔1〕 to 〔5〕.

[0024] Another aspect of the present invention relates to a method for manufacturing polypropylene-based resin foamed particles according to the following 〔7〕.

[0025] 〔7〕A method for manufacturing polypropylene-based resin foamed particles, in which polypropylene-based resin particles are foamed to obtain polypropylene-based resin foamed particles, wherein,

[0026] The resin particles contain an inorganic hypophosphite, a melamine-based flame retardant, a first antioxidant composed of a phenolic antioxidant, and a second antioxidant composed of a phosphorus-based antioxidant and / or a sulfur-based antioxidant.

[0027] The compounding amount of the inorganic hypophosphite in the resin particles is 0.5% by mass or more.

[0028] The compounding amount of the melamine-based flame retardant in the resin particles is 0.05% by mass or more.

[0029] The total of the compounding amount of the inorganic hypophosphite and the compounding amount of the melamine-based flame retardant in the resin particles is 5% by mass or less.

[0030] The total of the compounding amount of the first antioxidant and the compounding amount of the second antioxidant in the resin particles is 0.05% by mass or more and 0.6% by mass or less.

[0031] The ratio of the compounding amount of the second antioxidant to the compounding amount of the first antioxidant in the resin particles is 0.5 or more and 10 or less.

[0032] Advantages of the Invention

[0033] According to the above method, it is possible to provide polypropylene-based resin foamed particles and a method for manufacturing the same that can achieve both excellent flame retardancy and in-mold formability. In addition, according to the above method, it is possible to provide a polypropylene-based resin foamed particle molded body that can achieve both excellent flame retardancy and compression physical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is an explanatory diagram showing an example of a DSC curve of the foamed particles. DETAILED DESCRIPTION

[0035] (Polypropylene-based resin foamed particles)

[0036] [Polypropylene-based resin]

[0037] The polypropylene-based resin foamed particles (hereinafter referred to as "foamed particles") are composed of a polypropylene-based resin. In this specification, the polypropylene-based resin refers to a homopolymer of propylene monomer and a propylene-based copolymer containing 50% by mass or more of structural units derived from propylene. As the propylene-based copolymer, copolymers of propylene and α-olefins having 4 to 10 carbon atoms such as ethylene-propylene copolymer, butene-propylene copolymer, hexene-propylene copolymer, and ethylene-propylene-butene copolymer can be preferably exemplified. These copolymers can be, for example, random copolymers or block copolymers, etc., and random copolymers are preferred. In addition, the foamed particles can be composed of one polypropylene-based resin or two or more polypropylene-based resins.

[0038] The melting point of the polypropylene resin constituting the foamed particles is preferably 125°C or higher and 160°C or lower, more preferably 125°C or higher and 155°C or lower, further preferably 130°C or higher and 150°C or lower, and particularly preferably 135°C or higher and 145°C or lower. In this case, good in-mold formability of the foamed particles and good compression physical properties of a polypropylene resin foamed particle molded body (hereinafter referred to as "foamed particle molded body" or "molded body") formed by in-mold molding of the foamed particles can be exhibited in a well-balanced manner.

[0039] The melting point of the polypropylene resin constituting the foamed particles is measured based on JIS K7121:2012. Specifically, a test piece composed of foamed particles is prepared, and the test piece is conditioned based on "(2) When measuring the melting temperature after a certain heat treatment" in "3. Conditioning of test pieces" in JIS K 7121:2012. In the conditioning, under the condition that the nitrogen inflow rate is 30 mL / min, the test piece is heated from 23°C to 200°C at a heating rate of 10°C / min, the temperature of 200°C is maintained for 10 minutes, and then cooled to 23°C at a cooling rate of 10°C / min. After conditioning the test piece in this way, the test piece is heated to 200°C again at a heating rate of 10°C / min to obtain a DSC curve. The peak temperature of the melting peak appearing in the DSC curve obtained above is taken as the melting point of the polypropylene resin constituting the foamed particles. In addition, when multiple melting peaks appear in the DSC curve, the peak temperature of the melting peak with the highest height based on the baseline is taken as the melting point of the polypropylene resin constituting the foamed particles.

[0040] [Inorganic hypophosphite]

[0041] The foamed particles contain an inorganic hypophosphite. In this specification, inorganic hypophosphite refers to a salt of hypophosphorous acid and a metal represented by the chemical formula M(H 2 PO 2 ) m (where M is a metal element and m is an integer of 1 or more and 3 or less). The inorganic hypophosphite contained in the foamed particles is preferably selected from sodium hypophosphite (Na(H 2 PO 2 ), magnesium hypophosphite (Mg(H 2 PO 2 ) 2 ), aluminum hypophosphite (Al(H 2 PO 2 ) 3 ), calcium hypophosphite (Ca(H 2 PO 2 ) 2) and one or more salts selected from the group consisting of zinc hypophosphite (Zn(H 2 PO 2 )) 2 ), more preferably aluminum hypophosphite and / or calcium hypophosphite, and still more preferably aluminum hypophosphite.

[0042] The content (A) of the inorganic hypophosphite in the foamed particles is 0.5% by mass or more. By setting the content (A) of the inorganic hypophosphite in the foamed particles to 0.5% by mass or more, the flame retardancy of the molded body can be easily improved. From this viewpoint, the content (A) of the inorganic hypophosphite is preferably 0.6% by mass or more, and more preferably 0.8% by mass or more. When the content (A) of the inorganic hypophosphite is too small, there is a risk of reducing the flame retardancy of the molded body.

[0043] On the other hand, if the total (A)+(B) of the content (A) of the inorganic hypophosphite and the content (B) of the melamine-based flame retardant in the foamed particles is too large, there is a risk of reducing the moldability during in-mold forming. By setting the content (A) of the inorganic hypophosphite within the range where the total (A)+(B) of the content (A) of the inorganic hypophosphite and the content (B) of the melamine-based flame retardant is 5% by mass or less, the flame retardancy of the molded body can be improved while avoiding a reduction in moldability. From the viewpoint of more reliably avoiding a reduction in moldability, the total (A)+(B) of the content (A) of the inorganic hypophosphite and the content (B) of the melamine-based flame retardant is preferably 3% by mass or less, and more preferably 1.5% by mass or less.

[0044] In addition, from the viewpoint of more easily improving the moldability of the foamed particles, the content (A) of the inorganic hypophosphite in the foamed particles is preferably 4% by mass or less, more preferably 3% by mass or less, still more preferably 2% by mass or less, particularly preferably 1.5% by mass or less, and most preferably 1.3% by mass or less.

[0045] When determining the preferred range of the content (A) of the inorganic hypophosphite in the foamed particles, the upper and lower limits of the content (A) of the inorganic hypophosphite described above can be arbitrarily combined. For example, the preferred range of the content (A) of the inorganic hypophosphite can be 0.5% by mass or more and 4% by mass or less, or 0.5% by mass or more and 3% by mass or less, or 0.5% by mass or more and 2% by mass or less, or 0.5% by mass or more and 1.5% by mass or less, or 0.6% by mass or more and 1.5% by mass or less.

[0046] From the viewpoint of uniformly improving the flame retardancy of the molded article and the formability during in-mold forming, the compounding amount (A) of the inorganic hypophosphite in the expanded particles is preferably 0.5% by mass or more and 1.5% by mass or less, more preferably 0.6% by mass or more and 1.3% by mass or less. From the same viewpoint, the ratio (A) / (B) of the compounding amount (A) of the inorganic hypophosphite to the compounding amount (B) of the melamine-based flame retardant is preferably 0.05 or more and 10 or less, more preferably 0.1 or more and 8 or less, further preferably 0.5 or more and 6 or less, and particularly preferably 1 or more and 5 or less.

[0047] [Melamine-based flame retardant]

[0048] The expanded particles contain a melamine-based flame retardant. In this specification, the melamine-based flame retardant refers to a flame retardant containing melamine represented by the following structural formula (1) as a partial structure.

[0049] [Chemical formula 1]

[0050]

[0051] As the melamine-based flame retardant, for example, salts of melamine with acids showing flame retardancy such as sulfuric acid, polyphosphoric acid, cyanuric acid, pyrophosphoric acid, and hydrobromic acid are used. The melamine-based flame retardant contained in the expanded particles is preferably one or more salts selected from the group consisting of melamine sulfate, melamine polyphosphate, melamine cyanurate, melamine pyrophosphate, and melamine hydrobromide, more preferably melamine hydrobromide. In addition, melamine hydrobromide is particularly preferably a compound represented by the following structural formula (2).

[0052] [Chemical formula 2]

[0053]

[0054] The compounding amount (B) of the melamine-based flame retardant in the expanded particles is 0.05% by mass or more. By making the compounding amount (B) of the melamine-based flame retardant in the expanded particles 0.05% by mass or more, the flame retardancy of the molded article can be easily improved. From this viewpoint, the compounding amount (B) of the melamine-based flame retardant is preferably 0.1% by mass or more, more preferably 0.2% by mass or more.

[0055] On the other hand, if the total amount (A) + (B) of the inorganic hypophosphite and the amount (B) of the melamine-based flame retardant in the foamed particles is excessive, there is a risk of reducing the formability during in-mold forming as described above. By setting the amount (B) of the melamine-based flame retardant in the foamed particles within the range where the total amount (A) + (B) of the inorganic hypophosphite and the amount (B) of the melamine-based flame retardant is 5% by mass or less, preferably 3% by mass or less, and more preferably 1.5% by mass or less, as described above, it is possible to improve the flame retardancy of the molded body while improving the formability during in-mold forming. From the viewpoint of more easily improving the formability of the foamed particles, the amount (B) of the melamine-based flame retardant in the foamed particles is preferably 2% by mass or less, more preferably 1% by mass or less, further preferably 0.5% by mass or less, and particularly preferably 0.4% by mass or less.

[0056] When determining the preferred range of the amount (B) of the melamine-based flame retardant in the foamed particles, the upper and lower limits of the amount (B) of the melamine-based flame retardant described above can be arbitrarily combined. For example, the preferred range of the amount (B) of the melamine-based flame retardant can be 0.05% by mass or more and 2% by mass or less, can also be 0.05% by mass or more and 1% by mass or less, can also be 0.05% by mass or more and 0.5% by mass or less, can also be 0.05% by mass or more and 0.4% by mass or less, and can also be 0.2% by mass or more and 0.4% by mass or less.

[0057] 〔Antioxidant〕

[0058] The foamed particles further contain a first antioxidant composed of a phenolic antioxidant and a second antioxidant composed of a phosphorus-based antioxidant and / or a sulfur-based antioxidant. In addition, the total amount of the amount (C) of the first antioxidant and the amount (D) of the second antioxidant in the foamed particles is 0.05% by mass or more and 0.6% by mass or less, and the ratio (D) / (C) of the amount (D) of the second antioxidant to the amount (C) of the first antioxidant is 0.5 or more and 10 or less.

[0059] By containing the first antioxidant and the second antioxidant in the foamed particles at the specific ratio based on the inorganic hypophosphite and the melamine-based flame retardant, it is possible to reduce the amount (A) of the inorganic hypophosphite and the amount (B) of the melamine-based flame retardant while ensuring excellent flame retardancy. In addition, since the foamed particles can easily reduce the amount (A) of the inorganic hypophosphite and the amount (B) of the melamine-based flame retardant, it is possible to balance excellent flame retardancy and in-mold formability.

[0060] The reason for improving the flame retardancy by the first antioxidant and the second antioxidant is not necessarily clear at present. However, for example, the following reasons are considered. As one of the evaluation methods for flame retardancy, there is a horizontal burning test specified in UL 94. In this evaluation, whether there is ignition caused by the drips generated during the combustion of the molded body is one of the evaluation indicators. Therefore, if the generation of drips during the combustion of the molded body can be suppressed, the flame retardancy can be improved.

[0061] The first antioxidant added to the foamed particles is also called a primary antioxidant and is considered to be able to suppress the generation of free radicals during the combustion of the molded body. In addition, the second antioxidant added to the foamed particles is also called a secondary antioxidant and can react with the free radicals generated during the combustion of the molded body to inactivate the free radicals. It is considered that the foamed particles act synergistically with the first antioxidant and the second antioxidant by using two antioxidants with different functions in this way, so that even when the blending amount (A) of the inorganic hypophosphite and the blending amount (B) of the melamine-based flame retardant are relatively small, the generation of drips generated during the combustion of the molded body can be suppressed.

[0062] When the total (C)+(D) of the blending amount (C) of the first antioxidant and the blending amount (D) of the second antioxidant is too small, there is a risk of reducing the flame retardancy of the molded body. From the viewpoint of fully obtaining the effect of improving the flame retardancy of the molded body, the total (C)+(D) of the blending amount (C) of the first antioxidant and the blending amount (D) of the second antioxidant is 0.05% by mass or more based on the mass of the foamed particles. From the viewpoint of further improving the effect of improving the flame retardancy of the molded body, the total (C)+(D) of the blending amount (C) of the first antioxidant and the blending amount (D) of the second antioxidant is preferably 0.06% by mass or more, more preferably 0.07% by mass or more, and further preferably 0.1% by mass or more based on the mass of the foamed particles.

[0063] On the other hand, when the total (C)+(D) of the blending amount (C) of the first antioxidant and the blending amount (D) of the second antioxidant is too large, there is also a risk of reducing the flame retardancy of the molded body. As the reason, it is considered that the excessive antioxidant reacts with the inorganic hypophosphite and the melamine-based flame retardant, reducing the effect of the flame retardant, etc. From the viewpoint of avoiding this problem, the total (C)+(D) of the blending amount (C) of the first antioxidant and the blending amount (D) of the second antioxidant is set to 0.6% by mass or less based on the mass of the foamed particles. From the viewpoint of more reliably obtaining the effect of improving the flame retardancy of the molded body, the total (C)+(D) of the blending amount (C) of the first antioxidant and the blending amount (D) of the second antioxidant is preferably 0.5% by mass or less, more preferably 0.4% by mass or less, and further preferably 0.3% by mass or less based on the mass of the foamed particles.

[0064] When determining the preferred range of the total amount (C) + (D) of the compounding amount (C) of the first antioxidant and the compounding amount (D) of the second antioxidant, the upper and lower limits of the total amount (C) + (D) of the compounding amount (C) of the first antioxidant and the compounding amount (D) of the second antioxidant described above can be arbitrarily combined. For example, the total amount (C) + (D) of the compounding amount (C) of the first antioxidant and the compounding amount (D) of the second antioxidant in the foamed particles can be 0.05% by mass or more and 0.5% by mass or less, can also be 0.06% by mass or more and 0.4% by mass or less, and can also be 0.07% by mass or more and 0.3% by mass or less.

[0065] In addition, by making the ratio (D) / (C) of the compounding amount (D) of the second antioxidant to the compounding amount (C) of the first antioxidant within the specific range, the first antioxidant and the second antioxidant can act synergistically, and the effect of improving the flame retardancy of the molded body can be obtained. When either the first antioxidant or the second antioxidant is in excess relative to the other, it is difficult for the first antioxidant and the second antioxidant to act synergistically, and there is a risk of reducing the flame retardancy of the molded body.

[0066] The ratio (D) / (C) of the compounding amount (D) of the second antioxidant to the compounding amount (C) of the first antioxidant is preferably 0.6 or more and 8 or less, more preferably 1 or more and 6 or less, and further preferably 2 or more and 5 or less. In this case, the effect of improving the flame retardancy of the molded body can be obtained more reliably, and a molded body with good compression physical properties can be obtained more easily.

[0067] The ratio {(C)+(D)} / (A) of the total amount (C) + (D) of the compounding amount (C) of the first antioxidant and the compounding amount (D) of the second antioxidant to the compounding amount (A) of the inorganic hypophosphite is preferably 0.05 or more and 0.5 or less, more preferably 0.06 or more and 0.4 or less. In this case, the formable range of the foamed particles can be further expanded. In addition, in this case, the effect of improving the flame retardancy of the molded body can be obtained more reliably, and a molded body with good compression physical properties can be obtained more easily.

[0068] Specifically, as the first antioxidant, a phenolic antioxidant, that is, an antioxidant having at least one substituted or unsubstituted phenol in the molecular structure as a partial structure, can be used. The foamed particles can contain one kind of the first antioxidant or two or more kinds of the first antioxidants.

[0069] The phenolic antioxidant is preferably one having a group relative to the phenolic group (HO-C 6 H 4-) The OH group in becomes a meta-position, and a hindered phenol antioxidant having a partial structure with a large molecular weight substituent such as a tert-butyl group or a long-chain hydrocarbon group bonded thereto. More preferably, it is a hindered phenol antioxidant having tert-butyl groups at two positions that are meta to the OH group in the phenol group (HO-C 6 H 4 -). Examples of the hindered phenol antioxidant include Irganox 1010 (pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]), Irganox 1330 (3,3′,3″,5,5′,5″-hexatert-butyl-α,α′,α″-(mesitylene-2,4,6-tolyl)tri-p-cresol), Irganox 1035 (thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxy-phenyl)propionate], Irganox 1076 (octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), Irganox 1135 (benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-C7-C9 branched alkyl ester) (manufactured by BASF Corporation above), Sumilizer GA-80 (bis[3-[3-(tert-butyl)-4-hydroxy-5-methylphenyl]propionic acid] 2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diylbis(2-methylpropane-2,1-diyl))) and Sumilizer WX-R (4,4′-thiobis(6-tert-butyl-m-cresol) (manufactured by Sumitomo Chemical Co., Ltd. above), etc. In addition, "Irganox" is a registered trademark of BASF Societas Europaea, and "Sumilizer" is a registered trademark of Sumitomo Chemical Co., Ltd.

[0070] As the second antioxidant, a phosphorus-based antioxidant and / or a sulfur-based antioxidant can be used. In the foamed particles, as the second antioxidant, an antioxidant containing either a phosphorus-based antioxidant or a sulfur-based antioxidant can be included, or an antioxidant containing both can be included. In addition, the foamed particles can contain one second antioxidant or two or more second antioxidants.

[0071] As a phosphorus-based antioxidant, an antioxidant containing at least one phosphorus atom in its molecular structure can be used. The phosphorus-based antioxidant is preferably selected from phosphonates and phosphites, more preferably phosphites, and further preferably a phosphite structure containing at least one phenyl group in its molecular structure. Additionally, it is preferred that a substituent with a large molecular weight such as a tert-butyl group or a long-chain hydrocarbon group is bonded to the phenyl group contained in the phosphite structure. As the phosphorus-based antioxidant, for example, Irgafos 168 (tris(2,4-di-tert-butylphenyl) phosphite), Irgafos 168FF (tris(2,4-di-tert-butylphenyl) phosphite) (manufactured by BASF Corporation), NONFLEX TNP (tris(nonylphenyl) phosphite, manufactured by Seiko Chemical Co., Ltd.), K-NOX 168 (tris(2,4-di-tert-butylphenyl) phosphite, manufactured by SUNKO INK CO., LTD.), HOSTANOX P-EPQ (tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenyldiphosphonite, manufactured by Clariant Chemicals Ltd.) etc. can be cited. In addition, "NONFLEX" is a registered trademark of Seiko Chemical Co., Ltd., and "HOSTANOX" is a registered trademark of Hoechst Gesellschaft mit Haftung (Hoechst AG, Germany).

[0072] As a sulfur-based antioxidant, an antioxidant containing at least one sulfur atom in its molecular structure can be used. The form of existence of the sulfur atom in the sulfur-based antioxidant is not particularly limited. For example, the sulfur atom in the sulfur-based antioxidant can exist in the form of a thioether group (-S-), a thiocarbonylthio group (-N(=S)-S-), etc. As the sulfur-based antioxidant, for example, sulfur ether-based antioxidants having a thioether group such as dioctadecyl 3,3'-thiodipropionate (DSTDP), dilauryl 3,3'-thiodipropionate (DLTDP), pentaerythritol tetrakis[3-laurylthiopropionate], and antioxidants having a thiocarbonylthio group such as nickel(II) dibutyldithiocarbamate can be used. The sulfur-based antioxidant is preferably a sulfur ether-based antioxidant, and more preferably dioctadecyl 3,3'-thiodipropionate.

[0073] [Fatty acid amide]

[0074] The foamed particles may further contain one or more fatty acid amides. Fatty acid amides have the effect of improving the dispersibility of inorganic hypophosphites, melamine-based flame retardants, the first antioxidant, and the second antioxidant in the foamed particles. Therefore, by using fatty acid amides, it is easier to obtain the above effects. When the foamed particles contain fatty acid amides, the blending amount (E) of the fatty acid amide relative to the total of the blending amount (C) of the first antioxidant and the blending amount (D) of the second antioxidant, (E) / {(C)+(D)}, is preferably 0.05 or more and 1 or less.

[0075] In addition, a fatty acid amide is a compound having a hydrocarbon group and an amide group in its molecular structure. The hydrocarbon group in the fatty acid amide is preferably a long-chain fatty acid group. Further, as the fatty acid amide, ethylene bisstearamide and erucamide can be preferably used.

[0076] 〔Carbon black〕

[0077] For the purpose of coloring the foamed particles, etc., the foamed particles may further contain carbon black. The blending amount of carbon black in the foamed particles is preferably 0.1% by mass or more and 1% by mass or less. In this case, it is possible to color the molded body while ensuring excellent flame retardancy.

[0078] 〔Other components〕

[0079] In the foamed particles, other polymers other than polypropylene-based resins may be contained within a range that does not impair the above effects. Examples of other polymers include thermoplastic resins other than polypropylene-based resins such as polyethylene-based resins and polystyrene-based resins, and elastomers. The content of other polymers in the foamed particles is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, further preferably 5 parts by mass or less, and particularly preferably 0 parts by mass, that is, the foamed particles substantially contain only polypropylene-based resins as the polymer.

[0080] In addition, in the polypropylene-based resin constituting the foamed particles, other flame retardants other than the inorganic hypophosphite and the melamine-based flame retardant may be contained within a range that does not impair the above effects. In this case, the blending amount of the flame retardant other than the inorganic hypophosphite and the melamine-based flame retardant in the foamed particles is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, further preferably 10 parts by mass or less, relative to 100 parts by mass of the total of the inorganic hypophosphite and the melamine-based flame retardant.

[0081] In addition, in the polypropylene resin constituting the foamed particles, other antioxidants other than the first antioxidant and the second antioxidant may be included within a range not impairing the above-described effects. In this case, the blending amount of the antioxidant other than the first antioxidant and the second antioxidant in the foamed particles is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, still more preferably 5 parts by mass or less, and particularly preferably 0 part by mass, that is, the foamed particles substantially contain only the first antioxidant and the second antioxidant as antioxidants.

[0082] In addition, in the polypropylene resin constituting the foamed particles, a NOR type hindered amine having a partial structure represented by the following structural formula (3) may be included. Further, examples of R in the following structural formula (3) include an alkyl group, a cycloalkyl group, an aralkyl group, an aryl group, etc. In addition, an arbitrary structure is bonded to * in the following structural formula (3). The NOR type hindered amine only needs to contain at least one partial structure represented by the following structural formula (3).

[0083] [Chemical formula 3]

[0084]

[0085] Examples of the NOR type hindered amine include NOR116 (manufactured by BASF), FP-T80 (manufactured by ADEKA Corporation), Tinuvin123 (manufactured by BASF), etc. In addition, "Tinuvin" is a registered trademark of BASF Societas Europaea.

[0086] The blending amount of the NOR type hindered amine in the foamed particles is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, still more preferably 10 parts by mass or less with respect to the total 100 parts by mass of the inorganic hypophosphite and the melamine-based flame retardant.

[0087] In addition to the above, in the polypropylene resin constituting the foamed particles, additives such as a bubble regulator, a crystal nucleating agent, a plasticizer, an antistatic agent, an ultraviolet absorber, etc. may be included within a range not impairing the above-described effects.

[0088] 〔Bulk density of foamed particles〕

[0089] The bulk density of the foamed particles is preferably 20 kg / m 3 or more and 90 kg / m 3 or less. In this case, it is possible to more easily obtain a foamed particle molded body having excellent flame retardancy and a good balance between light weight and compression physical properties.

[0090] The foamed particles contain an inorganic hypophosphite and a melamine-based flame retardant. Further, by using two antioxidants, namely a first antioxidant and a second antioxidant, a molded article having excellent flame retardancy can be easily obtained even when the packing ratio of the foamed particles is low. From the viewpoint of further improving the lightness of the molded article and easily and stably exhibiting excellent flame retardancy, the packing density of the foamed particles is more preferably 70 kg / m 3 Hereinafter, it is further preferably 65 kg / m 3 Hereinafter, it is particularly preferably 60 kg / m 3 Hereinafter. In addition, from the viewpoint of further improving the compression physical properties of the molded article and easily and stably exhibiting excellent flame retardancy, the packing density of the foamed particles is more preferably 25 kg / m 3 or more, further preferably 30 kg / m 3 or more, particularly preferably 35 kg / m 3 or more.

[0091] When constituting the preferred range of the packing density of the foamed particles, the upper limit and the lower limit of the packing density of the above-mentioned foamed particles can be arbitrarily combined. For example, the packing density of the foamed particles can be 25 kg / m 3 or more and 70 kg / m 3 or less, or can be 30 kg / m 3 or more and 65 kg / m 3 or less, or can be 35 kg / m 3 or more and 60 kg / m 3 or less.

[0092] 〔High-temperature peak〕

[0093] The foamed particles preferably have the following crystal structure: in the DSC curve obtained when heating from 23°C to 200°C at a heating rate of 10°C / minute, an endothermic peak generated by the melting inherent to the polypropylene-based resin constituting the foamed particles appears, and one or more melting peaks are located on the high-temperature side of this endothermic peak. The foamed particles having such a crystal structure have excellent mechanical strength and excellent moldability. In addition, hereinafter, the endothermic peak generated by the melting inherent to the polypropylene-based resin that appears in the DSC curve is referred to as the "resin inherent peak", and the melting peak that appears on the high-temperature side of the resin inherent peak is referred to as the "high-temperature peak". The resin inherent peak is generated by the endotherm during the melting of the crystal originally possessed by the polypropylene-based resin constituting the foamed particles. On the other hand, it is presumed that the high-temperature peak is generated due to the melting of the secondary crystals formed in the polypropylene-based resin constituting the foamed particles during the manufacturing process of the foamed particles. That is, when a high-temperature peak appears in the DSC curve, it is presumed that secondary crystals are formed in the polypropylene-based resin.

[0094] Whether the foamed particles have the above-described crystal structure can be determined based on the DSC curve obtained by differential scanning calorimetry (DSC) using the above conditions in accordance with JIS K7122:1987. In addition, when performing DSC, 1 to 3 mg of the foamed particles may be used as the sample.

[0095] Specifically, as described above, in the DSC curve obtained when heating from 23°C to 200°C at a heating rate of 10°C / min (i.e., the first heating), as Figure 1 shown, both a high-temperature peak ΔH2 and a resin-intrinsic peak ΔH1 of the polypropylene-based resin constituting the foamed particles appear. In contrast, after the first heating, when cooling from 200°C to 23°C at a cooling rate of 10°C / min and then heating from 23°C to 200°C again at a heating rate of 10°C / min (i.e., the second heating), only the resin-intrinsic peak of the polypropylene-based resin constituting the foamed particles appears. Therefore, by comparing the DSC curve obtained during the first heating with the DSC curve obtained during the second heating, the resin-intrinsic peak and the high-temperature peak can be distinguished.

[0096] From the viewpoint of further expanding the range of forming conditions for obtaining a good foamed particle molded body, the heat of fusion of the high-temperature peak of the foamed particles is preferably 5 J / g or more and 40 J / g or less, more preferably 10 J / g or more and 30 J / g or less.

[0097] The heat of fusion of the above-described high-temperature peak is a value obtained as follows. First, 1 to 3 mg of the foamed particles after conditioning is used as the sample, and differential scanning calorimetry is performed under the condition of heating from 23°C to 200°C at a heating rate of 10°C / min to obtain a DSC curve. Then, as Figure 1 shown, a straight line L1 connecting a point α corresponding to 80°C on the DSC curve and a point β corresponding to the melting end temperature T of the foamed particles is drawn. In addition, the melting end temperature T is the end point on the high-temperature side of the high-temperature peak ΔH2, that is, the intersection of the high-temperature peak ΔH2 and the baseline on the higher-temperature side than the high-temperature peak ΔH2 in the DSC curve.

[0098] After drawing the straight line L2, a straight line L2 passing through the maximum point γ existing between the resin-intrinsic peak ΔH1 and the high-temperature peak ΔH2 and parallel to the vertical axis of the graph is drawn. The resin-intrinsic peak ΔH1 and the high-temperature peak ΔH2 are divided by this straight line L2. The heat of fusion of the high-temperature peak ΔH2 can be calculated based on the area of the portion surrounded by the portion of the DSC curve constituting the high-temperature peak ΔH2, the straight line L1, and the straight line L2.

[0099] 〔Welding layer〕

[0100] In addition, the foamed particles may have a welding layer on their surfaces for improving the weldability of the foamed particles with each other during in-mold forming. The welding layer may exist on the entire surface of the foamed particles or on a part of the surface. Examples of the resin constituting the welding layer include crystalline polyolefin resins having a melting point lower than the melting point of the polypropylene-based resin constituting the foamed particles, and amorphous polyolefin resins having a softening point lower than the melting point of the polypropylene-based resin constituting the foamed particles, etc.

[0101] The method for forming the welding layer on the surface of the foamed particles is not particularly limited. For example, examples thereof include a method of foaming resin particles having a welding layer, and a method of attaching the welding layer to the foamed particles after obtaining the foamed particles. In the case of obtaining foamed particles by foaming resin particles having a welding layer, when manufacturing the resin particles, it is preferable to adopt a method of laminating the welding layer on the surface layer of the resin particles by co-extrusion.

[0102] (Method for manufacturing polypropylene-based resin foamed particles)

[0103] As the method for manufacturing the foamed particles, the following method can be adopted: After preparing polypropylene-based resin particles (hereinafter referred to as "resin particles") containing an inorganic hypophosphite, a melamine-based flame retardant, a first antioxidant composed of a phenolic antioxidant, and a second antioxidant composed of a phosphorus-based antioxidant and / or a sulfur-based antioxidant, the resin particles are foamed.

[0104] When manufacturing the polypropylene-based resin foamed particles, it is preferable to obtain foamed particles by foaming resin particles in which the blending amount (A) of the inorganic hypophosphite in the resin particles is 0.5% by mass or more, the blending amount (B) of the melamine-based flame retardant in the resin particles is 0.05% by mass or more, the total (A)+(B) of the blending amount (A) of the inorganic hypophosphite and the blending amount (B) of the melamine-based flame retardant in the resin particles is 5% by mass or less, the total (C)+(D) of the blending amount (C) of the first antioxidant and the blending amount (D) of the second antioxidant in the resin particles is 0.05% by mass or more and 0.6% by mass or less, and the ratio (D) / (C) of the blending amount (D) of the second antioxidant to the blending amount (C) of the first antioxidant in the resin particles is 0.5 or more and 10 or less. In addition, in this case, the blending amounts of the inorganic hypophosphite, the melamine-based flame retardant, the antioxidant, etc. in the resin particles are the blending amounts of the inorganic hypophosphite, the melamine-based flame retardant, the antioxidant, etc. in the foamed particles.

[0105] [Preparation of resin particles]

[0106] When manufacturing the foamed particles, first, the resin particles are prepared. The method for preparing the resin particles is not particularly limited. For example, in the case of producing resin particles by the strand cutting method, a resin melt-kneaded product containing a polypropylene-based resin, an inorganic hypophosphite, a melamine-based flame retardant, a first antioxidant, and a second antioxidant that constitute the foamed particles is extruded from small holes of a die attached to the downstream side of an extruder into a strand shape. At this time, the compounding amounts of the inorganic hypophosphite, the melamine-based flame retardant, the first antioxidant, and the second antioxidant are respectively set within the above ranges. In addition, additives such as carbon black and bubble adjusters can be added to the resin melt-kneaded product as needed. By pulling the strand-shaped extrudate while cutting it into a desired length, resin particles can be obtained.

[0107] When producing the above resin melt-kneaded product, the above components can be directly melt-kneaded with a heated melt of the polypropylene-based resin, but it is preferable to prepare a flame retardant masterbatch containing a polypropylene-based resin, an inorganic hypophosphite, a melamine-based flame retardant, a first antioxidant, and a second antioxidant in advance, and heat and melt-knead the flame retardant masterbatch and the polypropylene-based resin to produce the resin melt-kneaded product. In this way, by melt-kneading the pre-prepared flame retardant masterbatch and the polypropylene-based resin, the inorganic hypophosphite and the like can be uniformly dispersed in the resin melt-kneaded product, and the compounding amount of the inorganic hypophosphite and the like in the resin melt-kneaded product can be adjusted with higher precision.

[0108] In the case of producing the flame retardant masterbatch, the polypropylene-based resin used in the flame retardant masterbatch can be the same polypropylene-based resin as the polypropylene-based resin that constitutes the resin particles, or a different polypropylene-based resin. In addition, when using the flame retardant masterbatch, it is preferable that the total (a)+(b) of the compounding amount (a) of the inorganic hypophosphite and the compounding amount (b) of the melamine-based flame retardant in the flame retardant masterbatch is 20% by mass or more and 50% by mass or less, and the total (c)+(d) of the compounding amount (c) of the first antioxidant and the compounding amount (d) of the second antioxidant is 0.5% by mass or more and 10% by mass or less, and the ratio (d) / (c) of the compounding amount (d) of the second antioxidant to the compounding amount (c) of the first antioxidant is 0.5 or more and 10 or less. In addition, the flame retardant masterbatch preferably contains a fatty acid amide. In this case, the ratio (e) / {(c)+(d)} of the compounding amount (e) of the fatty acid amide to the total (c)+(d) of the compounding amount (c) of the first antioxidant and the compounding amount (d) of the second antioxidant is preferably 0.01 or more and 1 or less.

[0109] When using the flame retardant masterbatch to produce resin particles, the ratio of the flame retardant masterbatch to the polypropylene-based resin mixed with the flame retardant masterbatch is preferably polypropylene-based resin∶flame retardant masterbatch = 99∶1 to 90∶10.

[0110] In addition, in the case of producing resin particles using a flame retardant masterbatch, the melt flow rate of the polypropylene-based resin mixed with the flame retardant masterbatch is preferably 6 g / 10 min or more and 9 g / 10 min or less, and the ratio of the melt flow rate of the flame retardant masterbatch to the melt flow rate of the polypropylene-based resin is preferably 2 or more and 5 or less. In this case, it is possible to disperse inorganic hypophosphates and the like more uniformly in the resin melt-kneaded product.

[0111] When preparing the flame retardant masterbatch, the same method as the above-described method for producing resin particles can be employed, that is, a method of supplying a polypropylene-based resin and inorganic hypophosphates and the like to an extruder and melt-kneading them in the extruder.

[0112] 〔Foaming of resin particles〕

[0113] By foaming the resin particles, foamed particles can be obtained. The method of foaming the resin particles is not particularly limited. For example, the resin particles containing a foaming agent dispersed in an aqueous medium in a container can be foamed by a method called the "direct foaming method" in an atmosphere at a pressure lower than the pressure in the container together with the aqueous medium.

[0114] In the direct foaming method, first, the resin particles are placed in a container and dispersed in an aqueous medium. At this time, a dispersant, a dispersion aid, a surfactant, etc. for dispersing the resin particles in the aqueous medium in the container can be added as needed.

[0115] As the dispersant, for example, inorganic fine particles such as alumina, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, and mica can be used. These inorganic fine particles can be used alone or in combination of two or more. As the dispersion aid, for example, aluminum sulfate etc. can be used. In addition, as the surfactant, for example, anionic surfactants such as sodium alkylbenzenesulfonate, sodium dodecylbenzenesulfonate, and sodium alkanesulfonate can be used. These surfactants can be used alone or in combination of two or more.

[0116] Next, a foaming agent is supplied to the container, and the foaming agent is impregnated into the resin particles by increasing the pressure in the container. Thus, resin particles containing the foaming agent can be obtained. At this time, by heating the resin particles in the container together with the aqueous medium, the impregnation of the foaming agent into the resin particles can be promoted.

[0117] As a foaming agent used in the foaming process, for example, inorganic physical foaming agents such as carbon dioxide, air, nitrogen, helium, and argon, hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, and hexane, and organic physical foaming agents such as chloroethane, 2,3,3-trifluoropropene, trans-1,3,3,3-tetrafluoropropene, and trans-1-chloro-3,3,3-trifluoropropene can be used. From the viewpoints of environmental load and operability, carbon dioxide is preferably used as the foaming agent. The addition amount of the foaming agent is preferably 0.1 part by mass or more and 30 parts by mass or less, more preferably 0.5 part by mass or more and 15 parts by mass or less, relative to 100 parts by mass of the resin particles.

[0118] The pressure inside the container immediately before foaming is preferably 0.5 MPa(G) or more in terms of gauge pressure. On the other hand, the pressure inside the container is preferably 4.0 MPa(G) or less in terms of gauge pressure. If it is within the above range, there is no risk of container breakage, explosion, etc., and foamed particles can be safely manufactured.

[0119] After impregnating the resin particles with the foaming agent, the content of the container is released into an atmosphere at a pressure lower than that of the container. As a result, the resin particles foam to form a bubble structure and are cooled by the external gas (i.e., the atmosphere) to stabilize the bubble structure, and foamed particles are obtained.

[0120] In the method for manufacturing the resin particles, a step of adjusting the crystal structure of the resin component constituting the resin particles can be performed during the period from dispersing the resin particles in the aqueous medium to foaming the resin particles. By foaming after adjusting the crystal structure of the resin component, foamed particles having excellent in-mold formability and excellent mechanical strength can be easily obtained.

[0121] The method for adjusting the crystal structure of the resin component is as follows, for example. First, a holding step is performed at a temperature of (the melting point of the polypropylene-based resin constituting the resin particles - 15°C) or higher and (the melting point of the polypropylene-based resin constituting the resin particles + 15°C) or lower for a sufficient time, preferably about 10 to 60 minutes. By performing this holding step, crystals that generate a high-temperature peak during melting are easily formed in the polypropylene-based resin constituting the foamed particles, and foamed particles having a crystal structure with a high-temperature peak can be more easily obtained. In addition, the temperature inside the container during foaming is preferably (the melting point of the polypropylene-based resin constituting the resin particles) or higher and (the melting point of the polypropylene-based resin constituting the resin particles + 15°C) or lower.

[0122] In the method for manufacturing the foamed particles, resin particles after the holding step may also be prepared in advance, and the foamed particles are obtained by foaming the resin particles. From the viewpoint of improving the productivity of the foamed particles, it is preferable to heat the resin particles dispersed in a dispersion medium in a container in the presence of a foaming agent to perform the above-mentioned holding step, and then release the content of the closed container from the container into an atmosphere at a pressure lower than the pressure in the container to foam the resin particles, thereby obtaining foamed particles having a crystal structure with a high-temperature peak.

[0123] In the method for manufacturing the foamed particles, when foaming the resin particles, as described above, the resin particles can be foamed in one stage, or can be foamed in two or more stages. In the case of foaming the resin particles in two stages, first, in the foaming step of the first stage, the resin particles are foamed by the direct foaming method to obtain primary foamed particles. In the foaming step of the second stage, for example, the primary foamed particles can be pressurized using air or the like to increase the pressure (internal pressure) inside the bubbles of the primary foamed particles, and then the primary foamed particles are heated using steam or the like to further foam them. By foaming the resin particles in multiple stages in this way, it is possible to easily obtain foamed particles with a higher foaming ratio (i.e., a lower bulk density).

[0124] (Polypropylene-based resin foamed particle molded body)

[0125] By performing in-mold forming on the foamed particles, a molded body can be obtained. The molded body is manufactured as follows. First, the foamed particles are filled in a mold having a cavity corresponding to the shape of the desired molded body, and the multiple foamed particles are heated in the mold using a heating medium such as steam. The foamed particles in the cavity are further foamed by heating and are welded to each other. As a result, the multiple foamed particles are integrated to obtain a molded body corresponding to the shape of the cavity.

[0126] 〔Density of the molded body〕

[0127] The density of the molded body is preferably 20 kg / m 3 or more and 100 kg / m 3 or less, and more preferably 30 kg / m 3 or more and 90 kg / m 3 or less. In this case, it is possible to more easily obtain a foamed particle molded body having excellent flame retardancy and a good balance between light weight and compression physical properties. The density of the molded body is calculated by dividing the mass (unit: g) of the molded body by the volume (unit: L) obtained from the outer dimensions of the molded body and performing unit conversion.

[0128] 〔Flame retardancy of the molded body〕

[0129] The flame retardancy of the molded article can be evaluated by the results of the "Horizontal Burning Test for Foamed Materials" specified in UL 94 and the oxygen index measured based on JIS K 7201-2:2007.

[0130] The method of the horizontal burning test specified in UL 94 is as follows. First, prepare the test apparatus. The test apparatus has: a wire mesh that is horizontally arranged at a height of 175 mm ± 25 mm from the reference surface; a burner with fins that is arranged below the wire mesh; and absorbent cotton that is arranged below the area of the wire mesh where the test specimen is to be arranged. The burner is arranged such that the height from the tip of the fin to the wire mesh is 13 mm ± 1 mm.

[0131] Next, after in-mold forming the foamed particles, cut out a plate-shaped test specimen with a length of 150 mm, a width of 50 mm, and a thickness of 13 mm from the obtained molded article. In addition, the test specimen may have a skin surface, that is, the surface that contacts the inner wall surface of the molding die during in-mold forming, or may not have a skin surface.

[0132] Next, place the test specimen cut out from the molded article in an environment of a temperature of 21°C and a relative humidity of 50% for 24 hours to adjust the state of the test specimen. Mark lines at positions 25 mm, 60 mm, and 125 mm away from the proximal end in the longitudinal direction of the test specimen after the state has been adjusted.

[0133] Place the test specimen prepared in this way on the wire mesh of the test apparatus. At this time, when one of the two surfaces surrounded by the 150-mm side and the 50-mm side of the length of the test specimen is the skin surface, place the test specimen on the wire mesh with the skin surface facing downward. Then, ignite the burner and adjust the gas volume, air volume, etc. so that the height of the flame is 38 mm ± 1 mm. In this state, move the burner so that the flame of the burner contacts the proximal end of the test specimen for 60 seconds. Then, move the flame of the burner away from the test specimen and let it stand until the combustion of the test specimen ends. Perform the above operations on five test specimens, and the flame retardancy can be evaluated based on their afterflame time, afterglow time, the presence or absence of ignition of the absorbent cotton caused by the dripping of the ignited substance, and the length at the time of breakage of the test specimen.

[0134] The molded article preferably has a flame retardancy evaluated as HF-1 in the "Horizontal Burning Test of Foamed Materials" specified in UL 94. More specifically, it preferably satisfies the following four requirements: (1) The afterflame time of four out of five test specimens is 2 seconds or less, and the afterflame time of the remaining one is 10 seconds or less; (2) The afterglow time of any one of the five test specimens is 30 seconds or less; (3) Ignition of absorbent cotton caused by dripping of the igniting substance does not occur in any one of the five test specimens; and (4) The length at the time of breakage of any one of the five test specimens is less than 60 mm. Such a molded article has excellent flame retardancy, and thus can also be suitably used for applications requiring particularly high flame retardancy.

[0135] In addition, the method for measuring the oxygen index based on JIS K 7201-2:2007 is as described below. First, after in-mold forming of the foamed particles, a rod-shaped test specimen with a length of 150 mm, a width of 10 mm, and a thickness of 10 mm is cut out from the obtained molded article. This test specimen is installed in a predetermined measuring device. Then, with a mixed gas of oxygen and nitrogen filled in the measuring device, a flame is brought into contact with the upper end of the test piece. In addition, the maximum flame contact time with the test piece is 30 seconds.

[0136] The above operation is carried out by variously changing the oxygen concentration of the mixed gas filled in the measuring device. And the lowest oxygen concentration at which the combustion time is 180 seconds or more or the length of the burned test specimen is 50 mm or more is taken as the oxygen index.

[0137] The oxygen index of the molded article is preferably 27% or more. Such a molded article has excellent flame retardancy, and thus can also be suitably used for applications requiring particularly high flame retardancy.

[0138] Examples

[0139] Examples of the foamed particles and their manufacturing method will be described below. The inorganic hypophosphite, melamine-based flame retardant, first antioxidant, second antioxidant, and fatty acid amide used in this example are as described below.

[0140] 〔Inorganic hypophosphite〕

[0141] A1: Aluminum hypophosphite

[0142] A2: Calcium hypophosphite

[0143] 〔Melamine-based flame retardant〕

[0144] B1: Melamine hydrobromide

[0145] 〔First antioxidant〕

[0146] C1: Phenolic antioxidant ("Irganox 1010" manufactured by BASF Corporation)

[0147] C2: Phenolic antioxidant ("Irganox 1330" manufactured by BASF Corporation)

[0148] [Second antioxidant]

[0149] D1: Phosphorus-based antioxidant ("Irgafos 168" manufactured by BASF Corporation)

[0150] D2: Sulfur-based antioxidant (dioctadecyl 3,3'-thiodipropionate)

[0151] [Fatty acid amide]

[0152] E1: Ethylene bisstearamide

[0153] In this example, first, a flame retardant masterbatch containing a polypropylene resin, an inorganic hypophosphite, a melamine-based flame retardant, a first antioxidant, and a second antioxidant is produced. Then, resin pellets are produced using this flame retardant masterbatch, and the obtained resin pellets are foamed to obtain foamed pellets. Hereinafter, each process will be described in more detail.

[0154] [Production of flame retardant masterbatch]

[0155] In the production of the flame retardant masterbatch, an extruder having an inner diameter of 20 mm and equipped with a die for forming a strand on the outlet side is used. First, the polypropylene resin, the inorganic hypophosphite, the melamine-based flame retardant, the first antioxidant, the second antioxidant, and the fatty acid amide shown in Table 1 and Table 2 are supplied to the extruder, and they are kneaded while being heated in the extruder to produce a molten kneaded product.

[0156] Next, the molten kneaded product is introduced into the die for forming a strand, and the molten kneaded product is extruded into a strand shape from the die orifice at the front end of the die. The extruded product in the form of a strand is taken out, cooled, and cut into an appropriate length using a granulator to obtain the flame retardant masterbatches MB1 to MB8 shown in Table 1 and the flame retardant masterbatches MB9 to MB16 shown in Table 2. In addition, the average mass of each flame retardant masterbatch is 15 mg.

[0157] The compounding amount (a) of the inorganic hypophosphite, the compounding amount (b) of the melamine-based flame retardant, the compounding amount (c) of the first antioxidant, the compounding amount (d) of the second antioxidant, and the compounding amount (e) of the fatty acid amide in each flame retardant masterbatch are as shown in Table 1 and Table 2. In addition, the melt flow rate (i.e., MFR) of each flame retardant masterbatch is as shown in Table 1 and Table 2. Furthermore, the melt flow rate of the flame retardant masterbatch is a value measured under the conditions of a temperature of 230°C and a load of 2.16 kg in accordance with JIS K7210-1:2014.

[0158] [Production of Resin Particles]

[0159] In the production of resin particles, an extruder with an inner diameter of 26 mm and a die for forming a wire material attached to the outlet side is used. First, an ethylene-propylene random copolymer as a polypropylene-based resin, a flame retardant masterbatch, a bubble regulator, and carbon black in the types and amounts shown in Tables 3 and 4 are supplied to the extruder, and they are kneaded while being heated in the extruder to produce a resin melt-kneaded product. In addition, the melting point of the ethylene-propylene random copolymer used in this example is 143°C, and the MFR is 8 g / 10 minutes. The MFR of the ethylene-propylene random copolymer is a value measured under the conditions of a temperature of 230°C and a load of 2.16 kg in accordance with JIS K7210-1:2014.

[0160] The resin melt-kneaded product is introduced into the die for forming a wire material, and the resin melt-kneaded product is extruded into a wire shape from the die orifice at the front end of the die. The extruded product in the form of a wire is taken out, cooled, and cut into an appropriate length using a granulator to obtain resin particles. In addition, zinc borate is used as the bubble regulator, and the compounding amount of zinc borate is 500 mass ppm with respect to the mass of the ethylene-propylene random copolymer. In addition, the compounding amount of carbon black is 0.4 mass% with respect to the mass of the ethylene-propylene random copolymer. The average mass of each resin particle is 1.0 mg. The compounding amounts (A) of inorganic hypophosphite, (B) of melamine-based flame retardant, (C) of the first antioxidant, (D) of the second antioxidant, and (E) of fatty acid amide in each resin particle are as shown in Tables 3 and 4.

[0161] [Foaming of Resin Particles]

[0162] The resin particles thus obtained are foamed by the direct foaming method to obtain the foamed particles shown in Table 2. More specifically, first, 500 g of resin particles and 3.5 L of water as an aqueous medium are put into a container with an internal volume of 5 L. Then, 3 g of a dispersant and 0.2 g of a surfactant are added to the container to disperse the resin particles in the aqueous medium. In addition, kaolin is used as the dispersant, and sodium dodecylbenzenesulfonate is used as the surfactant.

[0163] Thereafter, while stirring the inside of the container, carbon dioxide as a foaming agent was supplied into the closed container, and the temperature inside the container was raised to approximately 154°C. The pressure inside the container at this time was 2.0 MPa(G). After the temperature of the container reached the desired temperature, the temperature inside the container was maintained for 15 minutes, whereby the foaming agent was impregnated into the resin particles and the crystal structure of the polypropylene-based resin constituting the resin particles was adjusted. Thereafter, the container was opened and the content was released into the atmospheric pressure atmosphere, whereby the resin particles were foamed. The foamed particles were dried for 24 hours in an atmosphere at a temperature of 23°C and a relative humidity of 50%. Through the above, the foamed particles of Examples 1 to 8 shown in Table 3 and the foamed particles of Comparative Examples 1 to 8 shown in Table 4 were obtained.

[0164] Using the resin particles, foamed particles, and molded articles obtained by in-mold forming of the foamed particles in this way, evaluations were made for each evaluation item shown in Table 3 and Table 4. The evaluation methods for these evaluation items are as described below.

[0165] 〔Bulk density of foamed particles〕

[0166] A set of foamed particles of 3 g or more and 10 g or less was used in the measurement of the bulk density of the foamed particles. First, the set of foamed particles was dried for 2 hours in an environment at a temperature of 60°C and an atmospheric pressure of 1 atm, and then the weight of the foamed particles was measured. The set of foamed particles was filled into a graduated cylinder, and the bottom surface of the graduated cylinder was gently tapped on the ground several times to stabilize the height of the foamed particles filled in the graduated cylinder. Thereafter, the bulk volume (unit: L) of the set of foamed particles was read according to the scale of the graduated cylinder. Then, the mass (unit: g) of the set of foamed particles in the graduated cylinder was divided by the above-mentioned bulk volume, and the unit was converted to calculate the bulk density of the foamed particles (unit: kg / m 3 )

[0167] 〔Melting heat of high-temperature peak〕

[0168] By the above method, the melting heat of the high-temperature peak of the foamed particles was measured.

[0169] 〔Formable range〕

[0170] In the evaluation of the formable range, in-mold forming was carried out while changing the forming pressure during formal heating between 0.30 and 0.38 MPa(G) by 0.01 MPa each time to produce a molded article, and the formable range was determined based on the surface property, weldability, and recoverability of the obtained molded article.

[0171] The manufacturing method of the molded body is as described below. First, the foam particles are put into a pressure-resistant container, and the inside of the pressure-resistant container is pressurized with air so that the air is impregnated into the foam particles, and an internal pressure of 0.10 MPa(G) is imparted to the foam particles. Next, the foam particles imparted with the internal pressure are filled into a molding die having a cavity capable of molding a flat-plate-shaped foam particle molded body with a length of 250 mm, a width of 200 mm, and a thickness of 50 mm.

[0172] Next, steam is supplied into the molding die for in-mold forming. In the in-mold forming, first, steam is supplied into the molding die for 5 seconds for preheating in a state where the discharge valve of the molding die is open. Next, the discharge valve is closed, and steam is supplied from one surface side of the molding die for one-side heating until the pressure reaches 0.08 MPa(G) lower than the molding pressure during the formal heating. Next, steam is supplied from the other surface side of the molding die for one-side heating until the pressure reaches 0.04 MPa(G) lower than the molding pressure during the formal heating. After that, steam is supplied from both surfaces of the molding die for formal heating until the formal heating molding pressure is reached. After the formal heating is completed, the pressure inside the molding die is released, and the molded body inside the molding die is cooled until the surface pressure generated by the foaming force of the molded body reaches 0.04 MPa(G).

[0173] After that, the foam particle molded body taken out from the molding die is left standing in an oven at 80 °C for 12 hours for a curing process. After the curing process, the foam particle molded body is left standing for 24 hours under the conditions of a relative humidity of 50%, a temperature of 23 °C, and an atmospheric pressure of 1 atm, thereby performing the condition adjustment of the foam particle molded body. The surface property, weldability, and recoverability of the condition-adjusted foam particle molded body are evaluated, and the range of the molding pressure (i.e., the molding pressure capable of obtaining qualified products) that meets any item in the evaluation criteria described below is taken as the formable range. The wider the formable range, the better the formability can be judged.

[0174] In addition, regarding the foam particles of Comparative Example 8 shown in Table 4, since qualified products cannot be obtained within the above-mentioned molding pressure range, "none" is recorded in the "formable range" column of Table 4. In addition, for Comparative Example 8, the evaluation of other molded bodies was not carried out. Therefore, a mark "-" is recorded in the evaluation items of the molded body in Comparative Example 8.

[0175] The evaluation methods for the surface property, weldability, and recoverability in the evaluation of the formable range are as described below.

[0176] · Surface property

[0177] Draw a square of 100 mm × 100 mm at the center of one skin surface in the thickness direction of the foamed particle molded body, and then draw a diagonal line from any corner of this square. Then, count the number of voids existing on the diagonal line, that is, the number of voids with a size of 1 mm × 1 mm or more in the gaps formed between the foamed particles. Then, when the number of voids is 2 or less, it is judged as qualified, and when the number of voids is 3 or more, it is judged as unqualified.

[0178] ·Weldability

[0179] Break the foamed particle molded body so as to be roughly equally divided in the length direction. By visually observing more than 100 randomly selected foamed particles exposed on the fracture surface, determine whether the foamed particles are fractured inside the particles (that is, the foamed particles that have undergone material failure) or the foamed particles that are fractured at the interface between the foamed particles. Then, calculate the ratio value (that is, the material failure rate) of the number of foamed particles fractured inside the particles to the total number of observed foamed particles expressed as a percentage, and use this value as the welding rate. Then, when the welding rate is 80% or more, it is judged as qualified, and when the welding rate is less than 80%, it is judged as unqualified.

[0180] ·Recovery

[0181] When observing the foamed particle molded body from the thickness direction in a top view, measure the thickness of the foamed particle molded body at four positions 10 mm inside from each vertex toward the center direction and the thickness of the foamed particle molded body at the center part, respectively. Then, calculate the ratio of the thickness of the thinnest part among the measured parts to the thickness of the thickest part (unit: %). When the thickness ratio obtained in this way is 95% or more, it is judged as qualified, and when the thickness ratio is less than 95%, it is judged as unqualified.

[0182] 〔Density of the molded body〕

[0183] Perform in-mold forming with the lowest forming pressure in the above-mentioned formable range to obtain a molded body. After drying this molded body in an environment of 80 °C for 24 hours, measure the mass of the molded body (unit: g). Then, divide the mass of the molded body by the volume (unit: L) calculated based on the external dimensions of the molded body and convert the unit, thereby calculating the density of the molded body (unit: kg / m 3 )

[0184] 〔Oxygen index〕

[0185] Perform in-mold forming using the lowest forming pressure within the above-described formable range to obtain a formed body. From the obtained formed body, cut out a rod-shaped test piece with a length of 150 mm, a width of 10 mm, and a thickness of 10 mm in a manner that does not include the skin surface, i.e., the surface that contacts the inner surface of the forming die during in-mold forming. Using this test piece, measure the oxygen index based on JIS K7201-2:2007. Record the oxygen index obtained in this way in Table 3 and Table 4.

[0186] 〔UL 94 Horizontal Burning Test〕

[0187] Perform in-mold forming using the lowest forming pressure within the above-described formable range to obtain a formed body. From the obtained formed body, cut out a plate-shaped test piece with dimensions of length 150 mm, width 50 mm, and thickness 13 mm in a manner that one of the two surfaces surrounded by the 150-mm side and the 50-mm side becomes the skin surface. Place this test piece on the wire mesh of the measuring device according to UL 94 with the skin surface facing downwards. Then, conduct a horizontal burning test by the method according to UL 94.

[0188] Record the distinctions of the test results specified in UL 94 and ISO 3582 in Table 3 and Table 4. More specifically, when the test results meet the following four requirements: (1) The afterflame time of four out of five test pieces is 2 seconds or less, and the afterflame time of the remaining one is 10 seconds or less; (2) The afterglow time of any one of the five test pieces is 30 seconds or less; (3) Ignition of the absorbent cotton caused by the dripping of the igniting substance does not occur in any one of the five test pieces; and (4) The length at the time of breakage of any one of the five test pieces is less than 60 mm, it is judged that the test results correspond to HF-1 in the UL 94 horizontal burning test, and record it as "HF-1" in Table 3 and Table 4. In addition, when the test results meet the following four requirements: (1) The afterflame time of four out of five test pieces is 2 seconds or less, and the afterflame time of the remaining one is 10 seconds or less; (2) The afterglow time of any one of the five test pieces is 30 seconds or less; (3) Ignition of the absorbent cotton caused by the dripping of the igniting substance exists in at least one of the five test pieces; and (4) The length at the time of breakage of any one of the five test pieces is less than 60 mm, it is judged that the test results correspond to HF-2 in the UL 94 horizontal burning test, and record it as "HF-2" in Table 3 and Table 4. In addition, since ignition of the absorbent cotton caused by the dripping of the igniting substance exists in at least one of the five test pieces in the comparative example, it is evaluated as "HF-2".

[0189]

[0190]

[0191]

[0192]

[0193] As shown in Table 3, the foamed particles of Examples 1 to 8 contain inorganic hypophosphite and a melamine-based flame retardant, and also contain two antioxidants, a first antioxidant and a second antioxidant. Therefore, the foamed particles of Examples 1 to 8 can ensure excellent flame retardancy while reducing the compounding amounts of inorganic hypophosphorous acid and the melamine-based flame retardant. In addition, the foamed particles of Examples 1 to 8 have excellent in-mold formability because the compounding amounts of inorganic hypophosphorous acid and the melamine-based flame retardant are reduced.

[0194] Among them, the foamed particles of Example 1 and Examples 4 to 8 with less compounding amount (A) of inorganic hypophosphorous acid and compounding amount (B) of the melamine-based flame retardant can further improve the in-mold formability.

[0195] On the other hand, the foamed particles of Comparative Example 1 shown in Table 4 have poor flame retardancy because they do not contain the first antioxidant and the second antioxidant. In addition, the foamed particles of Comparative Examples 2 to 4 do not contain either the first antioxidant or the second antioxidant, and the first antioxidant and the second antioxidant cannot act synergistically, so the flame retardancy is poor.

[0196] In the foamed particles of Comparative Examples 5 and 6, the balance between the compounding amount (C) of the first antioxidant and the compounding amount (D) of the second antioxidant is poor, and either the first antioxidant or the second antioxidant is excessively contained. Therefore, the foamed particles of these comparative examples cannot make the first antioxidant and the second antioxidant act synergistically, and the flame retardancy is poor.

[0197] The total (C)+(D) of the compounding amount (C) of the first antioxidant and the compounding amount (D) of the second antioxidant of the foamed particles of Comparative Example 7 is excessive. Therefore, the effects of the inorganic hypophosphite and the melamine-based flame retardant of the foamed particles of Comparative Example 7 are reduced by the antioxidant, and the flame retardancy is poor.

[0198] The total (A)+(B) of the compounding amount (A) of the inorganic hypophosphite and the compounding amount (B) of the melamine-based flame retardant of the foamed particles of Comparative Example 8 is excessive. Therefore, the in-mold formability of the foamed particles of Comparative Example 8 is poor.

[0199] As described above, the polypropylene-based resin foamed particles, the method for producing the same, and the polypropylene-based resin foamed particle molded body according to the present invention have been described based on the embodiments. However, the specific embodiments of the polypropylene-based resin foamed particles, the method for producing the same, and the polypropylene-based resin foamed particle molded body according to the present invention are not limited to the embodiments, and the configuration can be appropriately changed within the scope not impairing the gist of the present invention.

Claims

1. A polypropylene-based resin foamed particle, wherein the polypropylene-based resin foamed particle contains an inorganic hypophosphite and a melamine-based flame retardant, wherein, the compounding amount of the inorganic hypophosphite in the foamed particle is 0.5% by mass or more, the compounding amount of the melamine-based flame retardant in the foamed particle is 0.05% by mass or more, the total of the compounding amount of the inorganic hypophosphite and the compounding amount of the melamine-based flame retardant in the foamed particle is 5% by mass or less, the foamed particle further contains a first antioxidant composed of a phenolic antioxidant and a second antioxidant composed of a phosphorus-based antioxidant and / or a sulfur-based antioxidant, the total of the compounding amount of the first antioxidant and the compounding amount of the second antioxidant in the foamed particle is 0.05% by mass or more and 0.6% by mass or less, the ratio of the compounding amount of the second antioxidant to the compounding amount of the first antioxidant in the foamed particle is 0.5 or more and 10 or less.

2. The polypropylene-based resin foamed particle according to claim 1, wherein, the compounding amount of the inorganic hypophosphite in the foamed particle is 0.5% by mass or more and 1.5% by mass or less.

3. The polypropylene-based resin foamed particle according to claim 1 or 2, wherein, the ratio of the compounding amount of the inorganic hypophosphite to the compounding amount of the melamine-based flame retardant in the foamed particle is 0.05 or more and 10 or less.

4. The polypropylene-based resin foamed particle according to any one of claims 1 to 3, wherein, the ratio of the total of the compounding amount of the first antioxidant and the compounding amount of the second antioxidant to the compounding amount of the inorganic hypophosphite in the foamed particle is 0.05 or more and 0.5 or less.

5. The polypropylene-based resin foamed particle according to any one of claims 1 to 4, wherein, The bulk density of the foamed particles is 20 kg / m 3 or more and 90 kg / m 3 or less.

6. A molded article of a polypropylene-based resin foamed particle, which is obtained by in-mold molding of the polypropylene-based resin foamed particle according to any one of claims 1 to 5.

7. A method for manufacturing a polypropylene-based resin foamed particle, which foams polypropylene-based resin particles to obtain polypropylene-based resin foamed particles, wherein, the resin particles contain an inorganic hypophosphite, a melamine-based flame retardant, a first antioxidant composed of a phenolic antioxidant, and a second antioxidant composed of a phosphorus-based antioxidant and / or a sulfur-based antioxidant, the compounding amount of the inorganic hypophosphite in the resin particles is 0.5% by mass or more, the compounding amount of the melamine-based flame retardant in the resin particles is 0.05% by mass or more, the total of the compounding amount of the inorganic hypophosphite and the compounding amount of the melamine-based flame retardant in the resin particles is 5% by mass or less, the total of the compounding amount of the first antioxidant and the compounding amount of the second antioxidant in the resin particles is 0.05% by mass or more and 0.6% by mass or less, the ratio of the compounding amount of the second antioxidant to the compounding amount of the first antioxidant in the resin particles is 0.5 or more and 10 or less.

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