Patent Publication Number: US-2002013395-A1

Title: Flame-retardant polyolefin-based resin composition, method manufacturing, and flame-retardant cable therefrom

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to a flame-retardant polyolefin-based resin composition, a method for manufacturing the same, and a flame-retardant cable; and more particularly to a polyolefin-based resin composition that retains excellent flame retardance even without containing organic halide-based flame retardants, to a method for manufacturing the same, and to a flame-retardant cable.  
       BACKGROUND OF THE INVENTION  
       [0002] In conventional practice, highly extrudable and electrically insulating polyvinyl chloride resins and polyolefin-based resins such as polyethylene resins and ethylene-vinyl acetate copolymer resins are used as outer sheathing and insulating cores of electric wires and cables. In particular, polyvinyl chloride resins are widely used because of their superior characteristics. Polyolefin-based resins are rendered flame-retardant to prevent flames. In conventional practice, such flame retardance is commonly achieved by adopting methods in which organic compounds containing halogens such as chlorine and bromine (that is, organic halide-based flame retardants) are compounded with such thermoplastic polyolefin-based resins.  
       [0003] However, polyolefin-based resin compositions containing such organic halides produce large amounts of black smoke, biologically hazardous gases, and gases that corrode metals and the like during burning. Thermoplastic resins obtained by adding metal hydroxides such as aluminum hydroxide and magnesium hydroxide as flame retardants have been proposed for use in order to address this problem. However, large amounts of metal hydroxides must be added in order to achieve adequate flame retardance, creating problems such as impaired mechanical characteristics, reduced fluidity during melting, and the like. Research has therefore been conducted in order to develop flame-retardant aids capable of ensuring the necessary flame retardance while somewhat reducing the amount of added metal hydroxides. Silicone can be cited as a possible aid.  
       [0004] For example, Japanese Patent Application Laying-open (hereinafter called JP Kokai) No. Hei 1-141928 discloses a flame-retardant resin composition obtained by adding a metal hydroxide, a silicone rubber, and/or silicone gum (such as a highly polymerized polydimethyl silicone, polymethylvinyl silicone, or polymethylphenyl silicone) to a halogen-free polyolefin-based resin such as an ethylene-ethyl acrylate copolymer (EEA), and JP Kokai No. Hei 1-141929 discloses a flame-retardant resin composition obtained by adding a metal hydroxide and silicone oil (such as polydimethyl silicone or polymethylphenyl silicone) to a halogen-free polyolefin-based resin such as an ethylene-ethyl acrylate copolymer (EEA).  
       [0005] However, silicones are incompatible with polyethylene (PE), ethylene-vinyl acetate copolymers (EVA), ethylene-ethyl acrylate copolymers (EEA), and other polyolefin-based resins, and the components must therefore be compounded for a very long time in order to be adequately dispersed. Another drawback is that silicones, even when dispersed, tend to migrate to the surfaces of polyolefin-based resin moldings, adversely affecting the feel and appearance of the polyolefin-based resin moldings.  
       [0006] JP Kokai No. Hei 8-41256 discloses a method for manufacturing flame-retardant elastomers by the heat treatment of mixtures containing ethylene-α-olefin unconjugated diene copolymers, polyolefin-based resins, organopolysiloxanes having two or more SiH groups per molecule, hydrosilylation catalysts, epoxy-modified polyolefin-based resins, and magnesium hydroxide or aluminum hydroxide. However, elastomers resulting from the addition reaction and crosslinking of the SiH groups contained in the organopolysiloxanes with the unsaturated hydrocarbon groups contained in the ethylene-α-olefin unconjugated diene copolymers, prevents the polyolefin-based resins devoid of aliphatic unsaturated bonds from becoming less combustible.  
       [0007] An object of the present invention is to address the above-described problems by providing a polyolefin-based resin composition that is highly flame-retardant even without containing organic halide-based flame retardants or polyolefin-based resins having aliphatic unsaturated bonds, to provide a method for manufacturing the same, and to provide a flame-retardant cable.  
       [0008] As a result of thoroughgoing research aimed at attaining the stated object, the inventors perfected the present invention upon discovering that flame retardance can be markedly improved if a platinum-based catalyst, a metal hydroxide, and an organosilicon compound in which hydrogen atoms are bonded to silicon atoms are each added in a prescribed amount to a polyolefin-based resin.  
       SUMMARY OF THE INVENTION  
       [0009] The present invention is a flame-retardant polyolefin-based resin composition, a method for making the composition, and a flame retardant cable made from the composition. The flame-retardant polyolefin-based resin composition comprises (A) 100 weight parts polyolefin-based resin, (B) 10 to 200 weight parts particulate metal hydroxide, (C) 0.01 to 50 weight parts of an organosilicon compound having at least one hydrosilyl group, and (D) a platinum-based catalyst in an amount of 0.1 ppm to 10,000 ppm in terms of platinum metal per weight part of components (A) and (B) combined.  
       DESCRIPTION OF THE INVENTION  
       [0010] The present invention is a flame-retardant polyolefin-based resin composition, a method for making the composition, and a flame retardant cable made from the composition. The flame-retardant polyolefin-based resin composition comprises (A) 100 weight parts polyolefin-based resin, (B) 10 to 200 weight parts particulate metal hydroxide, (C) 0.01 to 50 weight parts of an organosilicon compound having at least one hydrosilyl group, and (D) a platinum-based catalyst in an amount of 0.1 ppm to 10,000 ppm in terms of platinum metal per weight part of components (A) and (B) combined. The invention also relates to a method for manufacturing a flame-retardant polyolefin-based resin composition characterized in that components (A) and (B) are mixed while heated, component (C) is admixed, and component (D) is then admixed. The invention further relates to a flame-retardant cable whose core wire is coated with the aforementioned flame-retardant polyolefin-based resin composition.  
       [0011] The polyolefin-based resin (component (A)) of the present flame-retardant polyolefin-based resin composition should be an olefin homopolymer or a copolymer of an olefin with another vinyl polymer, and is not subject to any particular limitations as long as it is devoid of aliphatic unsaturated bonds. Specific examples of such resins include high-density polyethylene, medium-density polyethylene, low-density polyethylene, and copolymers of ethylene with C 3 -C 12  α-olefins such as propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, and decene-1; polypropylene and copolymers of propylene with C 3 -C 12  α-olefins such as butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, and decene-1; copolymers of ethylene with vinyl-based monomers such as vinyl acetate, ethyl acrylate, methacrylic acid, ethyl methacrylate, maleic acid, and maleic anhydride; copolymers obtained by methods in which polyethylene or copolymers of ethylene with α-olefins are modified with acrylic acid, maleic acid, or another unsaturated carboxylic acid or derivative; and mixtures of two or more of the above-described polyolefin-based resins. The methods for manufacturing such polyolefin-based resins are not subject to any particular limitations, but because miscibility with other components is preferred, polymerization based on the use of metallocene-type catalysts is viewed as a preferred option.  
       [0012] Of these, polyethylene is preferred because of considerations related to the mechanical properties of the polyolefin-based resin composition, and ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, and mixtures thereof are preferred from the standpoint of enhanced flame retardance.  
       [0013] The particulate metal hydroxide (component (B)) should preferably be a hydroxide of a Group IIa, IIIa, or IVb metal of the Periodic Table. Hydroxides whose decomposition start temperatures fall within a range of 150-450° C. are preferred because they are the most effective in terms of achieving flame retardance. Specifically, particulate magnesium hydroxide, particulate aluminum hydroxide, and mixtures of the two are preferred, and particulate magnesium hydroxide is particularly preferred. The mean grain size thereof should be 0.01 to 30 μm, and preferably 0.05 to 10 μm. This is because a hydroxide of this size disperses better in the polyolefin-based resin and has no adverse effect on the moldability of the resin composition.  
       [0014] Whether used singly or as mixture of two or more ingredients, component (B) should be added in an amount of 10 to 200 weight parts, and preferably 30 to 150 weight parts, per 100 weight parts polyolefin-based resin. This is because adding less than 10 weight parts fails to provide the resulting polyolefin-based resin composition with the desired degree of flame retardance, while adding more than 200 weight parts has a markedly adverse effect on the mechanical strength of the polyolefin-based resin composition and on melt fluidity.  
       [0015] Component (B) can be dispersed in the polyolefin-based resin without being modified in any way. It is also possible to use a product surface-treated with a silane coupling agent, a titanium coupling agent, a higher fatty acid, or another surface treatment agent. Calcium carbonate, talc, clay, mica, silica, and other fillers may be used together with these flame retardants as long as there is no marked reduction in flame retardance.  
       [0016] The organosilicon compound having at least one hydrosilyl group (component (C)) undergoes dehydrocondensation, polymerization, or crosslinking under the action of component (D) in the presence of component (B), improving the flame retardance of component (A). Consequently, each molecule should preferably contain two or more hydrosilyl groups, and the presence of three or more groups is even more preferred. A compound that does not volatilize easily during heating and mixing with the polyolefin-based resin should preferably be used in order to obtain higher flame retardance. Organohydrogenpolysiloxanes are typical examples of such organosilicon compounds. The degree of polymerization thereof may be 2 or greater, and a degree of 3 or greater is preferred from the standpoint of volatility. No limitations are imposed on the molecular structure thereof, which may be straight, branched, cyclic, reticulated, cage-shaped, or the like. Such organohydrogenpolysiloxanes are described by the average molecular formula  
       (R 3 SiO ½ ) a (R 2 SiO 2/2 ) b (RSiO 3/2 )C(SiO 4/2 ) d    
       [0017] where R designates hydrogen atoms or monovalent hydrocarbon groups, of which at least one R is a hydrogen atom, and a, b, c, and d are each a number equal to or greater than 0, except that a, b, and c cannot all be zero at the same time.  
       [0018] The following are specific examples of such organohydrogenepolysiloxanes.  
       [0019] Chemical Formula 1  
                 
 
       [0020] (where m and n are such that m≧1, n≧0 and 5≦m+n≦5000)  
       [0021] Chemical Formula 2  
                 
 
       [0022] (where m is a number equal to or greater than 2)  
       [0023] Chemical Formula 3  
                 
 
       [0024] (where m and n are such that 0≦m, 1≦n, and 3≦m+n≦20)  
       [0025] Chemical Formula 4  
                 
 
       [0026] (where R is a C 1 -C 20  monovalent hydrocarbon group, and m is such that 2≦m≦5000).  
       [0027] Component (C) is not necessarily limited to an organopolysiloxane and may be, for example, a polymer containing residual hydrosilyl groups that is obtained by conducting a hydrosilylation reaction between an organic compound having two allyl groups per molecule and a methyl oligosiloxane having four or more hydrosilyl groups per molecule in accordance with JP Kokai No. Hei 3-95266. Component (C) may be used singly or as a combination of two or more ingredients. A compound diluted with an organosiloxane devoid of hydrosilyl groups may also be used.  
       [0028] Component (C) should be used in an amount of 0.01 to 50 weight parts, preferably 0.5 to 25 weight parts, and ideally 1.0 to 20 weight parts, per 100 weight parts component (A).  
       [0029] The platinum-based catalyst (component (D)) acts on the hydrosilyl groups of component (C) and brings about dehydrocondensation. Examples of component (C) include microparticulate platinum, chloroplatinic acid, alcohol-modified chloroplatinic acid, platinum diketone complexes, platinum olefin complexes, complexes of dialkenyl oligosiloxane and chloroplatinic acid or platinum, and products obtained by supporting microparticulate platinum on alumina, silica, carbon black, and other particulate carriers. Of these, complexes of dialkenyl oligosiloxane and chloroplatinic acid or platinum are preferred. Particularly preferred are the chloroplatinic acid complex of 1,3-divinyltetramethyldisiloxane disclosed in Japanese Patent Publication (hereinafter called JP Kokoku) No. Sho 42-22924, and the chloroplatinic acid complex of 1,3-divinyltetramethyldisiloxane or the platinum complex of 1,3-divinyltetramethyldisiloxane disclosed in JP Kokoku No. Sho 46-28795, Sho 46-29731, and Sho 47-23679. Such platinum complexes should preferably be used after being diluted with liquid methylvinylpolysiloxane.  
       [0030] The amount of component (D) in terms of platinum metal should be 0.1 to 10,000 ppm, preferably 1 to 5000 ppm, and ideally 5 to 1000 ppm, in relation to the total amount of components (A) and (B). This is because using less than 0.1 ppm is ineffective for improving flame retardance, whereas using more than 10,000 ppm has an adverse effect on the electric insulation properties of the resulting polyolefin-based resin composition and results in a blackened appearance.  
       [0031] Antioxidants, lubricants, organic pigments, inorganic pigments, colorants, UV absorbers, heat stabilizers, light stabilizers, dispersants, antifungal agents, antistatic agents, and other additives may also be added as needed to the present polyolefin-based resin composition as long as the merits of the present invention are not compromised. 
     
    
    
     WORKING EXAMPLES  
     [0032] The present invention will now be described through working examples.  
     [0033] Table 1 shows the average molecular formulas of the organopolysiloxanes used in the working and comparative examples. In Table 1, Me is a methyl group.  
     [0034] The following polyolefin-based resins were used in the working and comparative examples.  
     [0035] EEA (ethylene ethyl acrylate copolymer) resin: Jaylex® A1150, manufactured by Japan Polyolefin.  
     [0036] HDPE (high-density polyethylene): Hi-Zex® 5305E, manufactured by Mitsui Kagaku.  
     [0037] PP (polypropylene): Norbrene® Y101, manufactured by Sumitomo Chemical.  
     [0038] Particulate magnesium hydroxide: Kisuma® 5A, manufactured by Kyowa Kagaku, mean grain size: 0.8 μm.  
     [0039] Platinum catalyst solution: Vinyl-terminated polydimethylsiloxane solution of platinum/1,3-divinyltetramethyldisilbxane complex (platinum concentration: 0.5 wt %).  
     Working Examples 1-8,  
     Comparative Examples 1-5  
     [0040] Polyolefin-based resins, particulate magnesium hydroxide, and the hydrosilyl group-containing organopolysiloxanes SR1-SR5 shown in Table 1 were mixed in the ratios shown in Tables 2 and 3, yielding polyolefin-based resin compositions. The numbers in the tables indicate weight parts.  
     [0041] A Laboplastomill® (mixer manufactured by Toyo Seiki Seisakusho) was heated to 220° C., a polyolefin-based resin was introduced therein and melted, particulate magnesium hydroxide was then introduced, and the ingredients were compounded until a uniform dispersion was obtained. An organopolysiloxane containing hydrosilyl groups was subsequently added under stirring, the platinum catalyst solution was added, and the ingredients were mixed for 5 minutes at 220° C., yielding a polyolefin-based resin composition. The polyolefin-based resin composition thus obtained was injection-molded at a molding temperature of 220° C., and the oxygen index thereof was measured in accordance with JIS-K7201 “Combustion Test Methods for Plastics Based on Oxygen Index Techniques.” The results are shown in Tables 2 and 3.  
                   TABLE 1                       Organopolysiloxane   Average molecular formula                  SR1   HMe 2 SiO(Me 2 SiO) 60 SiMe 2 H       SR2   HMe 2 SiO(Me 2 SiO) 1700 SiMe 2 H       SR3   Me 3 SiO(Me 2 SiO) 30 SiMe 2 H       SR4   Me 3 SiO(Me 2 SiO) 540 (MeHSi) 10 SiMe 3         SR5   Me 3 SiO(Me 2 SiO) 300 SiMe 3                    
 
     [0042]                                           TABLE 2                                   Working   Working   Comparative   Comparative   Comparative   Comparative           Example 1   Example 2   Example 1   Example 2   Example 3   Example 4                                                                EEA   100   100   100   100   100   100       Magnesium   50   100   50   100   100   100       hydroxide       SR1   5   10           10       Platinum   0.4   0.4               0.4       catalyst       solution       Oxygen   30   40   25   27   35   26       index                    
     [0043]                                               TABLE 3                                   Working   Working   Working   Working   Working   Working   Comparative           Example   Example   Example   Example   Example   Example   Example           3   4   5   6   7   8   5                                                                    HDPE   100   100   100   100   100       100       PP                       100       Magnesium   100   100   100   120   100   100   100       hydroxide       SR2   10       SR3       10       SR4           10   10   10   10       SR5                           10       Platinum   0.4   0.4   0.4   0.4   0.4   0.4   0.4       catalyst       solution       Oxygen   37   41   41   44   41   37   35       index