JP6023529B2 - Non-halogen flame retardant resin composition and electric wire / cable using the same - Google Patents

Description

  The present invention relates to a non-halogen flame retardant resin composition excellent in flexibility and heat resistance, and an electric wire / cable using the same.

  In recent years, interest in environmental problems has increased worldwide, and electric wires and cables using non-halogen compositions that do not generate harmful halogen gas during incineration are becoming widespread. Various proposals have been made for electric wires and cables using non-halogen compositions.

  Non-halogen compositions used for electric wires and cables include polyolefin resins. And when heat resistance and a flame retardance are provided with respect to polyolefin resin, the method of aiming at the heat resistance improvement by silane bridge | crosslinking and the flame retardance improvement by the mixing | blending of a metal hydroxide is considered common.

  For example, Patent Document 1 proposes a non-halogen flame retardant resin composition using an ethylene vinyl acetate copolymer crosslinked with silane as a dispersed phase and an ethylene ethyl acrylate copolymer as a continuous phase in an olefin resin matrix. Has been. Further, Patent Document 1 proposes an electric wire / cable covered with this non-halogen flame retardant resin composition. And in patent document 1, the flame retardance is improved by highly filling a metal hydroxide as a flame retardant in the ethylene vinyl acetate copolymer and ethylene ethyl acrylate copolymer which carried out the silane bridge | crosslinking.

  Patent Document 2 proposes a flame retardant composition for covering electric wires and cables containing a metal hydroxide in a base resin composed of an ethylene polymer having a melting point of 120 ° C. or lower and high-density polyethylene. .

JP2011-1495A JP 2011-54283 A

  However, when a metal hydroxide is blended, an increase in density and a decrease in mechanical properties typified by flexibility become problems. In addition, flexibility can be improved by using ethylene ethyl acrylate copolymer (EEA) or ethylene vinyl acetate copolymer (EVA) as the base resin, but sufficient heat resistance even with silane crosslinking due to low melting point Cannot be secured.

  The present invention has been made in view of the problems of such conventional techniques. And the objective of this invention provides the non-halogen flame-retardant resin composition excellent in the softness | flexibility and heat resistance, suppressing the increase in a density, and the electric wire and cable using the said non-halogen flame-retardant resin composition. There is.

The halogen-free flame retardant resin composition according to the first aspect of the present invention comprises (A) 60 to 80 parts by mass of polyethylene and (B) metallocene polyethylene 40 to 20 having a lower density than the polyethylene of the above component (A). 100 parts by mass of (C) phosphorus-based flame retardant and 100 parts by mass of (A) component and (B) component with respect to 100 parts by mass of total part of (A) component and (B) component In contrast, (D) 5 to 20 parts by mass of a nitrogen-based flame retardant , and (C) a phosphorus-based flame retardant is a phosphate compound, a polyphosphate compound, red phosphorus, an organic phosphate ester A compound, a phosphazene compound, a phosphonic acid compound, a phosphinic acid compound, a phosphine oxide compound, a phosphorane compound and a phosphoramide compound, and (D) a nitrogen-based flame retardant is a tria A non-halogen flame retardant resin composition as defined in JIS K7112, which is at least one selected from the group consisting of a cyanide compound, a cyanuric acid compound, an isocyanuric acid compound, a triazole compound, a tetrazole compound, a diazo compound, and urea. density of the 1.000 g / cm ³ or less, hardness prescribed in JIS K7215 is not more HDD55 less, heat deformation of the prescribed in JIS C3005 is summarized as der Rukoto than 20%.

In the non-halogen flame retardant resin composition according to the second aspect of the present invention, in the composition of the first aspect, the component (A) polyethylene has a density of 0.915 to 0.930 g / cm ³ ( The gist of the metallocene polyethylene of component B) is that the density is 0.850 to 0.880 g / cm ³ .

The third non-halogen flame retardant resin composition according to an aspect of the present invention, in the composition of the first or second aspect, the silane coupling agent, by the crosslinking agent and crosslinking catalyst is further compounded, (A ) Polyethylene and (B) metallocene polyethylene are silane-crosslinked.

  The summary of the electric wire / cable according to the fourth aspect of the present invention is that the non-halogen flame retardant resin composition according to the first to third aspects is provided as a covering material.

  According to the present invention, there are provided a halogen-free flame retardant resin composition excellent in flexibility and heat resistance while suppressing an increase in density, and an electric wire / cable using the halogen-free flame retardant resin composition. Can do.

FIG. 1 is a cross-sectional view of an electric wire according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the cable according to the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in light of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  As shown in FIG. 1, the electric wire 1 in the present embodiment includes a core 3 such as a copper wire, and an insulator 4 as a covering material that covers the periphery of the core 3. As shown in FIG. 2, the cable 5 includes a plurality of bundled electric wires 1 (1 a, 1 b, 1 c) and a sheath 6 as a covering material that covers the peripheral edges of the bundled plural wires 1. . The insulator 4 and the sheath 6 contain a non-halogen flame retardant resin composition. Note that the cable 5 does not necessarily have to bundle a plurality of electric wires 1, and a single electric wire 1 may be covered with a sheath 6.

  The non-halogen flame retardant resin composition of the present embodiment includes (A) polyethylene and (B) a base resin in which an ultra-low density metallocene polyethylene having a density lower than that of the polyethylene is mixed, and (C) a phosphorus flame retardant. (D) Nitrogen-type flame retardant is contained, It is characterized by the above-mentioned. By using polyethylene and ultra-low-density metallocene polyethylene as the base resin for non-halogen flame retardant resin compositions, the same flexibility is ensured for ethylene ethyl acrylate copolymer (EEA) and ethylene vinyl acetate copolymer (EVA). can do. Furthermore, it is possible to ensure heat resistance higher than those of these resins without adding a metal hydroxide as in the prior art.

  Furthermore, the non-halogen flame retardant resin composition contains (C) a phosphorus flame retardant and (D) a nitrogen flame retardant in addition to the base resin. The phosphorus-based flame retardant and the nitrogen-based flame retardant can exhibit flame retardancy without being mixed in a large amount like a metal hydroxide. Therefore, by including both a phosphorus flame retardant and a nitrogen flame retardant as the flame retardant, it becomes possible to impart flame retardancy while suppressing an increase in density and a decrease in flexibility in the resin composition.

  Thus, the non-halogen flame retardant resin composition of this embodiment can achieve both flexibility and heat resistance by containing the components (A) to (D). Furthermore, it becomes possible to aim at the further improvement of heat resistance by using a phosphorus-type flame retardant and a nitrogen-type flame retardant instead of the metal hydroxide which causes the mass increase of a resin composition.

  Furthermore, it is preferable that the non-halogen flame retardant resin composition of this embodiment contains a silane coupling agent, a crosslinking agent, and a crosslinking catalyst in addition to the components (A) to (D). Specifically, it is preferable to introduce a silane coupling agent into polyethylene and ultra-low density metallocene polyethylene using a crosslinking agent, and then silane cross-link polyethylene and ultra-low density metallocene polyethylene with each other using a crosslinking catalyst. More specifically, it is preferable to form a crosslinked structure by grafting a silane coupling agent to the main chains of polyethylene and ultra-low density metallocene polyethylene and then condensing the silane coupling agent. Thus, by producing a siloxane bond as a cross-linked structure, durability can be imparted to polyethylene without impairing flexibility.

The polyethylene as the component (A) preferably has a density of 0.915 to 0.930 g / cm ³ . Moreover, it is preferable that the density of the ultra-low density metallocene polyethylene as the component (B) is 0.850 to 0.880 g / cm ³ . By using polyethylene and metallocene polyethylene having such a density, a resin composition having further excellent heat resistance and flexibility can be obtained.

  Here, the blending ratio of the component (A) and the component (B) is 60 to 80 parts by mass of the polyethylene of the component (A), and 40 to 20 parts by mass of the metallocene polyethylene of the component (B). It is necessary to be 100 parts by mass. If the blending ratio of the component (A) is less than 60 parts by mass, the high melting point component is small and the heat resistance may be reduced, and if it exceeds 80 parts by mass, the hardness is increased and the flexibility may be reduced. . Further, if the blending ratio of the component (B) is less than 20 parts, the flexibility may be lowered, and if it exceeds 40 parts by mass, the low melting point component is excessively increased and the heat resistance may be lowered.

  Moreover, the compounding ratio of the phosphorus flame retardant of the component (C) needs to be 50 to 100 parts by mass with respect to 100 parts by mass in total of the component (A) and the component (B). If the amount is less than 50 parts by mass, the flame retardancy may be reduced. If the amount exceeds 100 parts by mass, the hardness increases and the flexibility may decrease. Furthermore, the blending ratio of the nitrogen-based flame retardant of the component (D) needs to be 5 to 20 parts by mass with respect to 100 parts by mass in total of the component (A) and the component (B). If the amount is less than 5 parts by mass, the flame retardancy may decrease, and if it exceeds 20 parts by mass, the hardness increases, and thus flexibility may decrease.

  Examples of the phosphorus-based flame retardant include, but are not limited to, polyphosphate compounds such as melamine polyphosphate, aromatic phosphate esters, and aromatic condensed phosphate esters. Specifically, examples of the phosphoric flame retardant include melamine phosphate, melamine polyphosphate, guanidine phosphate, guanidine polyphosphate, ammonium phosphate, ammonium polyphosphate, ammonium amidophosphate, ammonium polyphosphate, and carbamate phosphate. , Phosphate compounds such as polyphosphate carbamates, polyphosphate compounds, red phosphorus, organophosphate compounds, phosphazene compounds, phosphonic acid compounds, phosphinic acid compounds, phosphine oxide compounds, phosphorane compounds, phosphoramide compounds, etc. can do.

  Nitrogen flame retardants include, but are not limited to, melamine compounds such as melamine cyanurate, triazine compounds, and guanidine compounds. Specifically, as nitrogen-based flame retardants, triazine compounds such as melamine, melam, melem, melon, melamine cyanurate, cyanuric acid compounds, isocyanuric acid compounds, triazole compounds, tetrazole compounds, diazo compounds, urea, etc. are used. can do. In addition, a phosphorus flame retardant and a nitrogen flame retardant can be used 1 type or in combination of 2 or more types.

  And when forming a silane bridge | crosslinking, as a silane coupling agent, vinyl silane compounds, such as vinyl trimethoxysilane, vinyl triethoxysilane, vinyl tris ((beta) -methoxyethoxy) silane, (gamma) -aminopropyl trimethoxysilane, (gamma) -amino Aminosilane compounds such as propyltriethoxysilane, N-β- (aminoethyl) γ-aminopropyltrimethoxysilane, β- (aminoethyl) γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane , Β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, and other epoxysilane compounds, γ-methacryloxypropyltrimethoxysilane Acrylic silane compounds such as bis (3- (triethoxysilyl) propyl) disulfide, polysulfide silane compounds such as bis (3- (triethoxysilyl) propyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercapto Examples thereof include mercaptosilane compounds such as propyltriethoxysilane. However, the silane coupling agent is not limited to these. Moreover, these can be used 1 type or in combination of 2 or more types. Furthermore, it is preferable that the mixture ratio of a silane coupling agent is 1.0-2.0 mass parts with respect to 100 mass parts of base resins.

  Examples of the crosslinking agent (radical generator) include organic peroxides, but are not limited thereto. Specifically, as the crosslinking agent, dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di- (tert-butylperoxy) hexane, 2,5-dimethyl- 2,5-di- (tert-butylperoxy) hexyne-3, 1,3-bis (tert-butylperoxyisopropyl) benzene, 1,1-bis (tert-butylperoxy) -3,3,5 -Trimethylcyclohexane, n-butyl-4,4-bis (tert-butylperoxy) valerate, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, tert-butylperoxybenzoate, tert-butylperoxyisopropyl carbonate, Diacetyl peroxide, lauroyl peroxide, tert- Such as chill cumyl peroxide and the like. Moreover, these can be used 1 type or in combination of 2 or more types. Furthermore, it is preferable that the mixture ratio of a crosslinking agent is 0.05-0.10 weight part with respect to 100 mass parts of base resins.

  Examples of the crosslinking catalyst include, but are not limited to, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctate, stannous acetate, stannous caprylate, zinc caprylate, lead naphthenate, and cobalt naphthenate. It is not a thing. Furthermore, the blending ratio of the crosslinking catalyst is preferably 0.1 to 0.2 parts by mass with respect to 100 parts by mass of the base resin in the case of dibutyltin dilaurate.

  In addition, you may mix | blend an appropriate quantity of antioxidant, a lubricant, etc. with a halogen-free flame-retardant resin composition as needed. Examples of the antioxidant include a phenolic antioxidant, an amine antioxidant, and a phosphorus antioxidant. Examples of the lubricant include hydrocarbon, fatty acid, fatty acid amide, ester, and alcohol.

The mechanical properties of the halogen-free flame retardant resin composition of the present embodiment are as follows: density is 1.000 g / cm ³ or less (based on JIS K7112), tensile strength is 10 MPa or more (based on JIS C3005), and tensile elongation is 350%. It is preferable that the above (conforms to JIS C3005). Further, it is preferable that the non-halogen flame-retardant resin composition has a hardness of HDD55 or less (based on JIS K7215) and a flame retardance of oxygen index of 25 or higher (based on JIS K7201). Further, the heat resistance is preferably 20% or less (conforming to JIS C3005) when heated at 120 ° C. By satisfying such mechanical characteristics, flexibility, flame retardancy, and heat resistance, it is possible to ensure insulation for a long period of time even when used as an insulator or sheath for electric wires and cables.

  This non-halogen flame retardant resin composition can be prepared by uniformly mixing the components (A) to (D) with a kneader. Examples of the kneader include Banbury mixers, tumblers, pressure kneaders, kneading extruders, mixing rollers, and the like, but other kneaders may be used.

  In the case of forming a silane crosslink, first, a polyethylene and / or ultra-low density metallocene polyethylene is grafted to a silane coupling agent using a crosslinker. Next, silane crosslinking can be formed by kneading polyethylene and / or ultra-low density metallocene polyethylene into which a silane coupling agent is introduced and a crosslinking catalyst. In this case, the phosphorus-based flame retardant and the nitrogen-based flame retardant may be added before the silane crosslinking is formed, or may be added after the formation.

  Thus, according to the present embodiment, the base resin is a mixture of polyethylene and ultra-low density metallocene polyethylene, so that a non-halogen flame retardant resin composition having excellent flexibility can be provided. Moreover, according to the present embodiment, by using a phosphorus-based flame retardant and a nitrogen-based flame retardant as a flame retardant, it is possible to provide a non-halogen flame retardant resin composition having excellent heat resistance while maintaining flexibility.

  And by using this non-halogen flame retardant resin composition as a coating for an insulator or a sheath, an electric wire / cable excellent in heat resistance and flexibility can be provided.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.

[Preparation of resin composition]
First, about Examples 1-8 and Comparative Examples 1-10, the resin composition was prepared with the material and compounding quantity which are shown in Table 1 and Table 2. Specifically, in Examples 1 to 8 and Comparative Examples 1 to 7, the components (A) to (D) were blended in the proportions shown in Tables 1 and 2, and mixed uniformly with a kneader, and then silane. A test sample was obtained by blending a coupling agent, a crosslinking agent and a crosslinking catalyst to form a silane bridge. A tumbler was used as the kneader. Further, in Comparative Examples 8 to 10, an ethylene vinyl acetate copolymer was used as a base resin, a flame retardant was blended and mixed therewith, and then a test sample was obtained by forming a silane crosslink.

  Here, in Examples 1-8 and Comparative Examples 1-7, SP2320 manufactured by Prime Polymer Co., Ltd. was used as the polyethylene (A) component. Moreover, KS240T manufactured by Nippon Polyethylene Co., Ltd. was used as the ultra-low density metallocene polyethylene of component (B). (P) Melapur 200 which is a melamine polyphosphate manufactured by BASF Japan Ltd. was used as the phosphorus-based flame retardant for the component (C). As the nitrogen-based flame retardant of component (D), STABIACE MC-5S, which is a melamine cyanurate manufactured by Sakai Chemical Industry Co., Ltd., was used.

  Moreover, P1205 by Mitsui DuPont Polychemical Co., Ltd. was used for the ethylene vinyl acetate copolymer (EVA) of Comparative Examples 8-10. As the metal hydroxides of Comparative Examples 7, 9, and 10, Maglux ST, which is magnesium hydroxide manufactured by Shin Mining Co., Ltd., was used.

  As the silane coupling agent, KBA-1003 which is vinyltriethoxysilane manufactured by Shin-Etsu Chemical Co., Ltd. was used. As a crosslinking agent, dicumyl peroxide (DCP) which is an organic peroxide manufactured by Mitsui Chemicals Fine Co., Ltd. was used. As a crosslinking catalyst, L-101 which is dibutyl tin laurate manufactured by Tokyo Fine Chemical Co., Ltd. was used.

  In Examples 1-8, the conditions of the compounding ratio of (A) component are 60-80 mass parts, and the conditions of the compounding ratio of (B) component are 40-20 mass parts. Moreover, in Examples 1-8, the conditions of the compounding ratio of (C) component are 50-100 mass parts with respect to 100 mass parts of base resins, The conditions of the compounding ratio of (D) component are base resin 100. It is 5-20 mass parts with respect to a mass part. Moreover, the compounding ratio of the silane coupling agent is 1.0 to 2.0 parts by mass with respect to 100 parts by mass of the base resin, and the compounding ratio of the crosslinking agent is 0.05 to 100 parts by mass with respect to 100 parts by mass of the base resin. 0.10 parts by mass. Furthermore, the compounding ratio of the crosslinking catalyst is 0.1 to 0.2 parts by mass with respect to 100 parts by mass of the base resin.

[Evaluation of resin composition]
For the resin compositions obtained in Examples 1 to 8 and Comparative Examples 1 to 10, mechanical properties (density, tensile strength, tensile elongation), flexibility (hardness), flame retardancy (oxygen index), and heat resistance ( Heat deformation) was measured. The measurement results of each example are shown in Table 3, and the measurement results of each comparative example are shown in Table 4.

The density was measured according to JIS K7112. Since the density is preferably 1.000 g / cm ³ or less, this value was used as a criterion. The tensile strength was measured according to JIS C3005. Since the tensile strength is preferably 10 MPa or more, this value was used as a criterion. The tensile elongation was measured according to JIS C3005. Since the tensile elongation is preferably 350% or more, this value was used as a criterion. The flexibility was measured by measuring the hardness according to JIS K7215. Since the hardness is preferably 55 or less for HDD, this value was used as a criterion. The flame retardancy was measured by measuring the oxygen index according to JIS K7201. Since the oxygen index is preferably 25 or more, this value was used as a criterion. The heat resistance was measured according to JIS C3005 by measuring the heat deformation at a heating temperature of 120 ° C. Since heat deformation is preferably 20% or less, this value was used as a criterion.

  As shown in Table 1 and Table 3, it can be seen that the resin compositions of Examples 1 to 8 satisfy all the above-mentioned conditions, and thereby satisfy the determination criteria for all characteristics.

  As shown in Table 2 and Table 4, in Comparative Example 1, the blending ratio of the component (A) in the base resin is set lower than the condition, and the blending ratio of the component (B) is set higher than the condition. From Comparative Example 1, it can be seen that when the blending ratio of the component (A) is less than 60 parts by mass and the blending ratio of the component (B) exceeds 40 parts by mass, the heat resistance is below the criterion.

  In Comparative Example 2, the blending ratio of the component (A) in the base resin is set higher than the condition, and the blending ratio of the component (B) is set lower than the condition. From Comparative Example 2, when the blending ratio of the component (A) exceeds 80 parts by mass and the blending ratio of the component (B) is less than 20 parts by mass, the hardness exceeds the criterion, and there is a problem in flexibility. You can see that it happens.

  In Comparative Example 3, the blending ratio of component (C) is lower than the conditions, and in Comparative Example 4, the blending ratio of component (C) is higher than the conditions. From Comparative Example 3, it can be seen that when the blending ratio of the component (C) is less than 50 parts by mass, the oxygen index does not satisfy the criterion and a problem occurs in flame retardancy. Moreover, from the comparative example 4, when (C) component exceeds 100 mass parts, it turns out that hardness exceeds a criterion and a problem arises in a softness | flexibility.

  In Comparative Example 5, the blending ratio of component (D) is lower than the conditions, and in Comparative Example 6, the blending ratio of component (D) is higher than the conditions. From Comparative Example 5, it can be seen that when the blending ratio of the component (D) is less than 5 parts by mass, the oxygen index does not satisfy the criterion, and there is a problem in flame retardancy. Moreover, from the comparative example 6, when (D) component exceeds 20 mass parts, it turns out that hardness exceeds a criterion and a problem arises in a softness | flexibility.

  In Comparative Example 7, only metal hydroxide is used as a flame retardant. From Comparative Example 7, it can be seen that when only the metal hydroxide is used as the flame retardant, the density exceeds the criterion, and thus the hardness also exceeds the conditions, causing a problem in flexibility. In addition, it can be seen from Comparative Example 7 that when only a metal hydroxide is used as a flame retardant, the determination criteria are not satisfied even with tensile strength and tensile elongation.

  In Comparative Examples 8 to 10, the base resin is composed only of EVA. In this case, it turns out that a problem arises in heat resistance.

  From these results, the blending ratio of component (A) is 60 to 80 parts by weight, the blending ratio of component (B) is 40 to 20 parts by weight, and the blending ratio of component (C) is 50 with respect to 100 parts by weight of base resin. ~ 100 parts by mass, when the blending ratio of component (D) satisfies all the conditions of 5 to 20 parts by mass with respect to 100 parts by mass of the base resin, a resin composition excellent in heat resistance and flexibility can be obtained. I understand.

  As mentioned above, although this invention was demonstrated by the Example, this invention is not limited to these, A various deformation | transformation is possible within the range of the summary of this invention.

1 Electric wire 3 Core 4 Insulator 5 Cable 6 Sheath

Claims (4)

(A) 60 to 80 parts by mass of polyethylene,
(B) 40 to 20 parts by mass of metallocene polyethylene having a lower density than the polyethylene of component (A),
(C) Phosphorus flame retardant 50 to 100 parts by mass with respect to 100 parts by mass in total of component (A) and component (B),
(D) 5-20 parts by mass of a nitrogen-based flame retardant,
A halogen-free flame retardant resin composition comprising:
(C) Phosphorus flame retardants are phosphate compounds, polyphosphate compounds, red phosphorus, organic phosphate ester compounds, phosphazene compounds, phosphonic acid compounds, phosphinic acid compounds, phosphine oxide compounds, phosphorane compounds and phosphoramide compounds. At least one selected from the group consisting of:
(D) The nitrogen flame retardant is at least one selected from the group consisting of a triazine compound, a cyanuric acid compound, an isocyanuric acid compound, a triazole compound, a tetrazole compound, a diazo compound, and urea,
The non-halogen flame retardant resin composition has a density specified in JIS K7112 of 1.000 g / cm ³ or less, a hardness specified in JIS K7215 of HDD55 or less, and a heat deformation specified in JIS C3005 of 20% or less. non-halogen flame retardant resin composition characterized in that it. The component (A) polyethylene has a density of 0.915 to 0.930 g / cm ³ , and the component (B) metallocene polyethylene has a density of 0.850 to 0.880 g / cm ^3. The non-halogen flame retardant resin composition according to claim 1. The non-halogen-free flame according to claim 1 or 2, wherein (A) polyethylene and (B) metallocene polyethylene are silane-crosslinked by further blending a silane coupling agent, a crosslinking agent, and a crosslinking catalyst. A flammable resin composition.   An electric wire / cable comprising the non-halogen flame retardant resin composition according to any one of claims 1 to 3 as a covering material.

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