Flame retardant composition

Abstract: A composition comprising: (i) a thermoplastic resin; and (ii) magnesium hydroxide, the surface of which has been treated with an organic aminosilane.

Description: This invention relates to flame retardant compositions containing certain thermoplastic resins or rubbers and a magnesium hydroxide filler. The compositions are particularly useful as insulation for wire and cable. Thermoplastic resins, which have good electrical insulation characteristics, are widely used to provide insulating jacketing or sheaths for wire and cable. Recently, there has been a demand for improved flame retardant properties, e.g., as high as V-1 to V-0 using Underwriters Laboratories standards. Thermoplastic resin can be made flame retardant by adding to the resin organic halides or antimony oxides, for example, or the resin itself can be halogenated such as polyvinyl chloride or chlorinated polyethylene. These thermoplastic resins, however, on burning, sag and emit large amounts of smoke and other harmful gases, and also corrode metals. In order to solve these problems, it has been proposed to add metal hydroxides to non-halogenated thermoplastic resins. Aluminum hydroxide was first used because of its low cost, but it has such a low decomposition temperature (170° to 190°C) that the aluminum hydroxide decomposes generating water, which, in turn, causes foaming on interior surfaces. Furthermore, to obtain a flame retardance of V-1 to V-0, aluminum hydroxide has to be added to the thermoplastic resin in large amounts, e.g., 60 to 65 percent by weight based on the weight of the total composition. Compared with aluminum hydroxide, magnesium hydroxide has a much higher decomposition temperature (about 360°C), and, thus, exhibits less foaming. For this reason, and others, magnesium hydroxide has been widely used as a flame retardant in resins. One disadvantage of a thermoplastic resin/magnesium hydroxide flame retardant composition, however, is that when it is applied to an electrical conductor as an outer jacket, the jacket exhibits blushing when it rubs against another jacket or other hard objects, is scratched, or bent. Blushing or "stress whitening" occurs when a resin, in jacket or molded form, is stressed or impacted and results in a white mark on the surface of the resin at the point of impact. These white marks not only detract from the appearance of the jacket, but also have a degrading effect insofar as arc resistance, insulation, mechanical, and other properties are concerned. EP-A-237 713 describes a flame-retardant olefinic resin composition comprising (1) 100 parts by weight of an ethylenic polymer resin mixture having an average density of 0.890 to 0.915 g/cm³, of (a) an ethylenic polymer consisting mainly of an ethylene-alpha-olefin copolymer and (b) a silane-grafted polymer obtained by grafting a silane to at least one component of said ethylenic polymer (a), and (2) 50 to 300 parts by weight of a hydrated metal compound, e.g., MgOH₂, which may be surface treated, among others, with a silane which has an alkoxy oligomer as the main chain skeleton of the molecule. Although reduced blushing is mentioned in said reference, said property is not attributed to the presence of the hydrated metal compound. An object of this invention, therefore, is to provide a composition, which is suitable as an insulating jacket for wire or cable, and, as a jacket, will not be susceptible to blushing. Other objects and advantages will become apparent hereinafter. According to the invention, a composition has been discovered which meets the above objective. The composition consists of (i) a certain thermoplastic resin or rubber as specified hereinbelow as resin component; (ii) magnesium hydroxide, the surface of which has been treated with an organic aminosilane and which has certain characteristics which will be specified below; and, optionally, (iii) one or more antioxidants and additives selected from those which also will be specified below. The thermoplastic resin or rubber can be any homopolymer or copolymer produced from two or more of the comonomers mentioned below, or a blend of two or more of these polymers. Generally, the monomers useful in the production of these homopolymers and copolymers will have 2 to 20 carbon atoms. Said monomers are alpha-olefins such as ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene; unsaturated esters such as vinyl acetate, ethyl acrylate, methyl acrylate, methyl methacrylate, t-butyl acrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, and other alkyl acrylates; diolefins such as 1,4-pentadiene, 1,3-hexadiene, 1,5-hexadiene, 1,4-octadiene, and ethylidene norbornene; other monomers such as styrene, p-methyl styrene, alphamethyl styrene, vinyl naphthalene, and similar aryl olefins; nitriles such as acrylonitrile and methacrylonitrile; vinyl methyl ketone, vinyl methyl ether, and maleic anhydride; and acrylic acid, methacrylic acid, and other similar unsaturated acids. In addition to polyolefins, included among the polymers can be polyesters, polycarbonates, and polyurethanes. The homopolymers and copolymers of ethylene are preferred. The resins are preferably non-halogenated. Examples of homopolymers and copolymers of ethylene are high pressure, low density polyethylene; polyethylenes of various densities (high, medium, linear low, very low, and ultra-low) wherein the comonomer is 1-butene, 1-hexene, 4-methyl-1-pentene, or 1-octene; ethylene/propylene rubber; ethylene/propylene/diene monomer rubber; ethylene/vinyl acetate copolymer; ethylene/ethyl acrylate copolymer; isobutylene/isoprene rubber; and polybutene-1. The magnesium hydroxide to be used herein and a method for its preparation are described in US-A-4,098,762. Characteristics for this magnesium hydroxide are (a) a strain in the <101> direction of no more than 3.0 x 10⁻³; (b) a crystallite size in the <101> direction of more than 80 nm (800 angstroms); and (c) a surface area, determined by the BET method, of less than 20 square meters per gram. The average particle diameter of the magnesium hydroxide can be in the range of 0.1 to 15 µm (microns) and is preferably in the range of 0.5 to 3 µm (microns). The surface area can be 1 to less than 20 square meters per gram and is preferably 3 to 8 square meters per gram. The amount of magnesum hydroxide incorporated into the composition can be in the range of 50 to 200 parts by weight based on 100 parts by weight of thermoplastic resin and is preferably present in an amount of 70 to 170 parts by weight. The magnesium hydroxide can also have been previously surface treated with various fatty acids or metallic salts of fatty acids such as stearic acid, sodium oleate, sodium stearate, sodium lauryl sulfonate, calcium stearate, or zinc stearate as described, for example, in US-A-4,255,303. The aminosilane with which the magnesium hydroxide is surface treated or coated can be any organic compound having an amino group and a silicon atom in its molecular structure. The aminosilane compound may be referred to as a coupling agent. It will generally contain 6 to 30 carbon atoms and a trialkoxy moiety, and can be aliphatic or aromatic, or a mixture of various aminosilanes. Examples of aminosilanes suitable for use in the invention follow: (1) gamma-aminopropyl triethoxy silane (H₂NCH₂CH₂CH₂Si(OC₂H₅)₃), (2) N-beta-(aminoethyl)-gamma-aminopropyl trimethoxy silane (H₂NCH₂CH₂NHCH₂CH₂CH₂Si(OCH₃)₃), (3) gamma-ureidopropyl triethoxy silane (H₂NCONHCH₂CH₂CH₂Si(OC₂H₅)₃), (4) gamma-anilinopropyl trimethoxy silane (5) aminobenzene trimethoxy silane (6) N-4,4′-methylene-bisbenzeneamino-2-hydroxypropyloxypropyl trimethoxy silane (7) N-4,4′-methylene-bisbenzeneaminopropyl trimethoxy silane hydrochloride (8) N-aminobenzenemethylene-p-phenylene-gamma-ureidopropyl trimethoxy silane (9) N-4,4′-oxybisbenzeneamino-2-hydroxypropyloxypropyl trimethoxy silane (10) N-4,4′-oxybisbenzeneaminopropyl trimethoxy silane hydrochloride (11) N-aminobenzeneoxy-p-phenylene-gamma-ureidopropyl trimethoxy silane (12) N-4,4′-sulfonylbisbenzeneamino-2-hydroxypropyloxypropyl trimethoxy silane (13) N-4,4′-sulfonylbisbenzeneamino-propyl trimethoxy silane hydrochloride (14) N-aminobenzenesulfonyl-p-phenylene-gamma-ureidopropyl trimethoxy silane (15) N-p-phenylenediamino-2-hydroxypropyloxypropyl trimethoxy silane (16) N-p-phenylenediaminopropyl trimethoxy silane hydrochloride and (17) N-p-phenylenediamino-gamma-ureidopropyl trimethoxy silane The amount of aminosilane coupling agent used in the surface treatment of the magnesium hydroxide is in the range of 0.1 to 3 parts by weight based on 100 parts by weight of resin and is preferably added in the range of 0.12 to 2.8 parts by weight. The surface treatment of the magnesium hydroxide with the aminosilane coupling agent can be carried out in any one of a number of conventional techniques for coating fillers. One technique is a slurry process in which the magnesium hydroxide is introduced into a solution of the aminosilane in ethyl or isopropyl alcohol, and then dried; another technique is by direct application of the aminosilane to a magnesium hydroxide in powder form. Commercial embodiments of the composition of the invention are generally obtained by kneading together the thermoplastic resin, the magnesium hydroxide surface treated with the aminosilane coupling agent, one or more antioxidants, and other additives in apparatus such as a Banbury mixer, a pressure kneader, a twin screw extruder, a Buss co-kneader, a Henschel mixer, or a roll kneader. The components can be added in any order and the components used in smaller amounts can be added via a masterbatch. The other useful and possible additives for the subject composition are surfactants, reinforcing filler, crosslinking agents, ultraviolet stabilizers, antistatic agents, pigments, dyes, slip agents, plasticizers, lubricants, viscosity control agents, extender oils, metal deactivators, water tree growth retardants, voltage stabilizers, flame retardant additives, and smoke suppressants. Examples of antioxidants are: hindered phenols such as tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]methane and thiodiethylene bis(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate; phosphites and phosphonites such as tris(2,4-di-tert-butylphenyl)phosphite and di-tert-butylphenylphosphonite; various amines such as polymerized 2,2,4-trimethyl-1,2-dihydroquinoline; and silica. Antioxidants are used in amounts of about 1 to about 5 parts by weight per hundred parts by weight of thermoplastic resin. The thermoplastic resin can be crosslinked by adding a crosslinking agent to the composition. Suitable crosslinking agents are organic peroxides such as dicumyl peroxide; 2,5-dimethyl-2,5-di(t-butylperoxy)hexane; t-butyl cumyl peroxide; and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane-3. Dicumyl peroxide is preferred. The composition of the invention can be extruded about, or coated on, an electrical conductor or subjected to injection, rotational, or compression molding. In addition to being useful in wire and cable applications, subject composition can be used as a sheath for a glass core in fiber optics applications. The invention is illustrated by the following examples. EXAMPLE 1 Test samples are made up by compression molding the composition into sheets, and cutting up the sheets into sample size. The composition is prepared as follows: 100 parts by weight of ethylene/ethyl acrylate copolymer (EEA) containing 19 percent by weight ethyl acrylate and having a melt index of 0.75 is prepared. 140 parts by weight magnesium hydroxide, surface treated with stearic acid, are added, in small increments, to 150 parts by weight of ethanol containing 0.07 parts by weight of amino silane number (1) (see above) and 3 parts by weight of water, and agitated to prepare a slurry. The slurry is dried and pulverized. The product is an aminosilane surface treated magnesium hydroxide. A mixture of 2.5 parts by weight carbon black and 0.5 parts by weight of pentaerythritoltetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], an antioxidant, is also prepared. The thermoplastic resin (EEA), the aminosilane coated magnesium hydroxide, and the carbon black/antioxidant mixture are kneaded together at 160°C for 10 minutes in a Banbury mixer. The mixture is then pre-heated in a thermopress forming machine for 5 minutes and pressed at 150°C and 100 kilograms per square centimeter for 3 minutes into a sheet having a thickness of 1 millimeter, a length of 150 millimeters, and a width of 180 millimeters. The sheet is punched into nine 20 millimeter wide, 150 millimeter long, samples for the blushing tests. The samples are subjected to scratch tests under a load of 500 grams by a needle abrasion testing machine in accordance with MIL Standards, W-22759D. Partial blushing of the impacted portion is observed. The samples are then bent twice to 180°C and observed visually. Partial blushing of the impacted portion is observed. EXAMPLES 2 TO 4 Example 1 is repeated except that aminosilane number (1) is added in amounts of 0.14 (Example 2), 1.4 (Example 3), and 2.8 (Example 4) parts by weight instead of 0.07 parts by weight as in Example 1. No blushing is observed. EXAMPLE 5 Example 1 is repeated except that an ethylene/1-butene copolymer is used instead of the ethylene/ethyl acrylate copolymer. No blushing is observed. EXAMPLES 6 TO 12 Example 1 is repeated except that instead of aminosilane number (1), aminosilanes numbered (2), (3), (4), (5), (8), (12), and (17), respectively, are used. No blushing is observed. EXAMPLES 13 AND 14 For example 13, example 1 is repeated except that no carbon black is used and, for example 14, example 5 is repeated except that 5 parts by weight of carbon black are used. No blushing is observed. EXAMPLE 15 Example 5 is repeated except that 1 part by weight of gamma-mercaptopropyl trimethoxy silane is added. No blushing is observed. EXAMPLES 16 TO 19 (comparative) Example 1 is repeated except that, instead of aminosilane number (1), the following silanes are used: Total blushing of the impacted portion is observed. EXAMPLES 20 TO 23 (comparative) Examples 16 to 19 are repeated except that an ethylene/l-butene copolymer is used instead of an ethylene/ethyl acrylate copolymer. Total blushing of the impacted portion is observed. It is also observed that the compositions of examples 2 to 15 display improved strength and moldability over the compositions of examples 1 and 16 to 23. Example 24 Example 1 is repeated except that 0.5 part of dicumyl peroxide is added to the composition. No blushing is observed and the samples show good heat durability and tensile strength.

Claims: A resin composition consisting of: (i) a thermoplastic resin selected from homopolymers and copolymers produced from at least one (co)monomer selected from alpha-olefins, unsaturated esters, diolefins, aryl olefins, nitriles, unsaturated acids, vinyl methyl ketone, vinyl methyl ether, and maleic anhydride, and furthermore from polyesters, polycarbonates, and polyurethanes; or a rubber selected from ethylene/propylene rubber, ethylene/propylene/diene monomer rubber and isobutylene/isoprene rubber as resin component; (ii) magnesium hydroxide, the surface of which has been treated with an organic aminosilane, said magnesium hydroxide having (a) a strain in the <101> direction of no more than 3.0·10⁻³; (b) a cristallite size in the <101> direction of more than 8·10⁻⁸ m (800 angstroms); and (c) a surface area, determined by the BET method, of less than 20 square meters per gram; and, optionally, (iii) one or more antioxidants and additives selected from the group consisting of surfactants, reinforcing filler, crosslinking agents, ultraviolet stabilizers, antistatic agents, pigments, dyes, slip agents, plasticizers, lubricants, viscosity control agents, extender oils, metal deactivators, water tree growth retardants, voltage stabilizers, flame retardant additives and smoke suppressants. The composition defined in claim 1, wherein the resin is not halogenated. The composition defined in one or both of the claims 1 and 2, wherein the resin is an ethylene homopolymer or copolymer. The composition defined in one or more of the claims 1 to 3, wherein the magnesium hydroxide is present in an amount of 50 to 200 parts by weight, based on 100 parts by weight of resin. The composition defined in one or more of the claims 1 to 4, wherein the magnesium hydroxide has an average particle diameter in the range of 0.1 to 15 µm (microns) and a surface area in the range of 1 to less than 20 square meters per gram. The composition defined in one or more of the claims 1 to 5, wherein the aminosilane is present in an amount of 0.1 to 3 parts by weight, based on 100 parts by weight of resin. The composition defined in one or more of the claims 1 to 6, wherein the aminosilane is present in an amount of 0.12 to 2.8 parts by weight, based on 100 parts by weight of resin. The composition defined in one or more of the claims 1 to 7, additionally containing an organic peroxide crosslinking agent. The composition defined in claim 8, wherein the organic peroxide crosslinking agent is dicumyl peroxide. The composition defined in one or more of the claims 1 to 7, coated on an electrical conductor. The composition defined in one or more of the claims 1 to 7, extruded about an electrical conductor. A molded article comprising the composition defined in one or more of the claims 1 to 7. An electrical conductor coated with the composition defined in one or more of the claims 1 to 7. A cable having an outer jacket comprising the composition defined in one or more of the claims 1 to 7.

Inventors: HASHIMOTO SATOSHI, HAYASHI SHOJI, HORITA KATSUHIRO, KOSHIYAMA TAKAO, SUYA HACHIRO, YOSHIDA MAMORU, HASHIMOTO, SATOSHI, HAYASHI, SHOJI, HORITA, KATSUHIRO, KOSHIYAMA, TAKAO, SUYA, HACHIRO, YOSHIDA, MAMORU
Applicants: NIPPON UNICAR CO LTD, NIPPON UNICAR COMPANY LIMITED
Application year: 1989
Main classification: H01B3
IPC codes: C08K9, H01B7, C09K21, H01B3, C08K3, C08L23