Flame-retardant, thermoplastic molding materials containing A) at least one polyphenylene ether, B) at least one vinylaromatic polymer and C) at least one flameproofing agent, comprise D) an amount of expandable graphite which increases the resistance of the molding material to dripping and are used for the production of flame-retardant moldings, fibers and films.
The present invention relates to flame-retardant thermoplastic molding materials having improved resistance to dripping, their use for the production of fibers, films and moldings, and the fibers, films and moldings produced therefrom.
Polymer blends comprising polyethylene ether (PPE) and styrene polymers are disclosed, for example, in U.S. Pat. Nos. 3,383,435, 4,128,602 and 4,128,603. Such molding materials are suitable for the production of shaped articles which are distinguished by a better heat distortion resistance compared with high impact polystyrene (HIPS) which is not blended with polyphenylene ethers. A detailed description of the properties of these polymer blends is also to be found in L. Bottenbruch, Technische Polymer-Blends, Kunststoff Handbuch 3/2, Hanser Verlag, Munich, 1993.
An important advantage of the polymer blends comprising a polyphenylene ether and styrene polymers is that molding materials which are flame-retardant and are therefore used for many applications in the area of electrical engineering can be prepared by adding halogen-free flameproofing agents, phosphorus-containing compounds being mentioned in particular. With regard to the use in the area of electrical engineering, in particular the testing of the flame-retardancy according to UL 94 (in J. Troitzsch, International Plastics Flammability Handbook, page 346 et seq., Hanser Verlag, Munich, 1990) is critical. In this test, a flame is repeatedly applied to vertically fastened test specimens. The test specimen heats up to a very great extent, resulting in many cases in the dripping of burning polymer material which ignites the cotton wool pad mounted under the rod. This undesired behavior is observed particularly when large amounts of flameproofing agents have to be used to achieve short combustion times.
The problem of the dripping of burning particles in the UL 94 test has long been known and is solved in the industry generally by adding small amounts of Teflon as an antidrip agent (U.S. Pat. No. 4,107,232). However, attempts have recently been made completely to avoid the use of halogen-containing compounds in thermoplastic molding materials. However, suitable alternative antidrip agents have not been found to date.
EP 0 297 868 discloses the use of expandable graphite in combination with carbon black of a certain specification for establishing the conductivity of thermoplastic or heat-curable resins. The resins obtained according to EP 0 297 888 are suitable in particular for the production of electrically conductive materials, such as electrodes, and for shielding electromagnetic waves. However the problem of improving the resistance to dripping is not tackled therein.
JO 3181 532 likewise disclosed the use of expandable graphite for thermoplastic molding materials. However, no flame-retardant molding materials are described therein. The purpose of adding graphite according to JO 3181 532 was to improve the electrical conductivity as well as the thermal conduction and frictional properties.
It is an object of the present invention to provide flameproofed thermoplastic molding materials, in particular molding materials based on polyphenylene ethers and styrene polymers, with resistance to dripping has been improved by the addition of a halogen-free antidrip agent.
We have found that this object is achieved and that, surprisingly, the addition of an amount of expandable graphite which increases the resistance to dripping, in particular of from about 0.5 to about 10% by weight of expandable graphite, can reduce the dripping of flame-retardant molding materials. According to the invention, it is possible in particular to obtain molding materials based on PPE and HIPS whose resistance to dripping has been substantially increased. In the fire test according to UL 94, these novel molding materials can achieve the classification V 0.
This result is all the more surprising since neither EP 0 297 888 nor JO 31 81 532 gives any indication that the fire behavior and in particular the dripping behavior of thermoplastic molding materials, for example molding materials comprising polyphenylene ethers and high impact polystyrene, can be improved simply by means of expanded graphite.
The present invention therefore relates to flame-retardant, thermoplastic molding materials containing a thermoplastic resin based on one or more polyphenylene ethers and at least one vinylaromatic polymer, a flameproofing agent and an amount of expandable graphite which increases the resistance to dripping of the molding material. Preferably, the expandable graphite is present in an amount of from about 0.5 to about 10, preferably from about 0.5 to about 9, in particular from about 0.5 to about 7.5, % by weight, based on the total weight of the molding material.
An advantageous embodiment of the invention provides a thermoplastic, flame-retardant molding material which contains, based in each case on the total weight of the molding material
A) from about 5 to about 97.5% by weight of polyphenylene ether,
B) from about 1 to about 93.5% by weight of styrene polymer,
C) from about 1 to about 20% by weight of flame-proofing agent,
D) from about 0.5 to about 10% by weight of expandable graphite,
E) from about 0 to about 50% by weight of impact modifier and
F) from about 0 to about 60% by weight of conventional additives.
The preferably provided molding material is one which contains, based in each case on the total weight of the molding material,
A) from about 15 to about 87.5% by weight of polyphenylene ether,
B) from about 10 to about 82.5% by weight of styrene polymer,
C) from about 2 to about 19% by weight of flame-proofing agent,
D) from about 0.5 to about 9% by weight of expandable graphite,
E) from about 0 to about 25% by weight of impact modifier and
F) from about 0 to about 50% by weight of conventional additives.
A particularly preferred molding material is one which contains, based on the total weight of the molding material,
A) from about 20 to about 82% by weight of polyphenylene ether,
B) from about 15 to about 77% by weight of styrene polymer,
C) from about 2.5 to about 18% by weight of flame-proofing agent,
D) from about 0.5 to 7.5% by weight of expandable graphite,
E) from about 0 to about 20% by weight of impact modifier and
F) from about 0 to about 30% by weight of conventional additives.
According to the invention, at least one polyphenylene ether known per se is used as component A). These are in particular compounds based on substituted, in particular disubstituted, polyphenylene ethers, the ether oxygen of one unit being bonded to the benzene nucleus of the neighboring unit. Polyphenylene ethers substituted in the 2- and/or 6-position relative to the oxygen atom are preferably used. Examples of substituents are halogen, such as chlorine or bromine, and alkyl of 1 to 4 carbon atoms which preferably has no a tertiary hydrogen atom, e.g. methyl, ethyl, propyl or butyl. The alkyl radicals may in turn be substituted by halogen, such as chlorine or bromine, or by hydroxyl. Further examples of possible substituents are alkoxy, preferably of up to 4 carbon atoms, such as methoxy, ethoxy, n-propoxy and n-butoxy, or phenyl which is unsubstituted or substituted by halogen and/or by alkyl. Also suitable are copolymers of various phenols, for example copolymers of 2,6-dimethylphenol and 2,3,6-trimethylphenol. Mixtures of different polyphenylene ethers can of course also be used.
Examples of polyphenylene ethers are poly(2,6-dilauryl-1,4-phenylene ether), poly(2,6-diphenyl-1,4-phenylene ether), poly(2,6-dimethoxy-1,4-phenylene ether), poly(2,6-diethoxy-1,4-phenylene ether), poly(2-methoxy-6-ethoxy-1,4-phenylene ether), poly(2-ethyl-6-stearyloxy-1,4-phenylene ether), poly-(2,6-dichloro-1,4-phenylene ether), poly(2-methyl-6-phenyl-1,4-phenylene ether), poly(2,6-dibenzyl-1,4-phenylene ether), poly(2-ethoxy-1,4-phenylene ether), poly-(2-chloro-1,4-phenylene ether) and poly(2,5-dibromo-1,4-phenylene ether). Preferably used polyphenylene ethers are those in which the substituents are alkyl of 1 to 4 carbon atoms, such as poly(2,6-dimethyl-1,4-phenylene ether), poly(2,6-diethyl-1,4-phenylene ether), poly(2-methyl-6-ethyl-1,4-phenylene ether), poly(2-methyl-6-propyl-1,4-phenylene ether), poly(2,6-dipropyl-1,4-phenylene ether) and poly(2-ethyl-6-propyl-1,4-phenylene ether).
For the purposes of the present invention, polyphenylene ethers are also to be understood as meaning those which are modified with monomers, such as fumaric acid, maleic acid or maleic anhydride.
Such polyphenylene ethers are described, inter alia, in WO 87/00540.
Regarding the physical properties of the polyphenylene ethers, those which have a weight average molecular weight Mw of from about 8000 to about 70,000, preferably from about 12,000 to about 60,000, in particular from about 25,000 to about 50,000, are used in the compositions. This corresponds to an intrinsic viscosity of about 0.18 to about 0.7, preferably from about 0.25 to about 0.62 and in particular from about 0.39 to about 0.55 dl/g, measured in chloroform at 25.degree. C.
The molecular weight distribution is determined in general by means of gel permation chromatography (0.8.times.50 cm Shodex separation column of the type A 803, A 804 and A 805 with THF as eluent at room temperature). The PPE samples are dissolved in THF under pressure at 110.degree. C., 0.16 ml of a 0.25% by weight solution being injected. Detection is effected in general using a UV detector. The calibration of the columns was carried out using PPE samples whose absolute molecular weight distributions were determined by a GPC/laser light scattering combination.
The component B) is preferably a toughened vinylaromatic polymer which is advantageously compatible with the polyphenylene ether used.
Examples of preferred vinylaromatic polymers compatible with polyphenylene ethers are stated in the monograph by O.Olabisi, Polymer-Polymer Miscibility, 1979, pages 224 to 230 and 245.
Both homopolymers and copolymers of vinylaromatic monomers of 8 to 12 carbon atoms, which are prepared in the presence of a rubber, are suitable. The rubber content is from about 5 to about 25, preferably from about 8 to about 17, % by weight, based on the weight of the component B).
Suitable high impact polystyrenes are for the most part commercially available and have a viscosity number (VN) of the hard matrix of from about 50 to about 130, preferably from about 60 to about 90, ml/g (0.5% strength in toluene at 23.degree. C.).
Particularly suitable monovinylaromatic compounds are styrene and the styrenes substituted on the nucleus and on the side chain. Preferred substituents are halogen, in particular chlorine and bromine, hydroxyl, and C.sub.1-4 alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl and tert-butyl. Examples of these compounds are chlorostyrene, a-methylstyrene, styrene, p-methylstyrene, vinyltoluene and p-tert-butylstyrene. However, styrene alone is preferably used.
The homopolymers are generally prepared by the known mass, solution or suspension processes (cf. Ullmanns Enzyklopadie der techn. Chemie, Volume 19, pages 265 to 272, Verlag Chemie, Weinheim 1980). The homopolymers may have weight average molecular weights Mw of from about 3000 to about 300,000, which can be determined by conventional methods.
Examples of suitable comonomers for the preparation of copolymers are (meth)acrylic acid, alkyl (meth)acrylates where the alkyl radical is of 1 to 4 carbon atoms, acrylonitrile and maleic anhydride as well as maleimides, acrylamide and methacrylamides and their N,N- or N-alkyl-substituted derivatives in which the alkyl radical is of 1 to 10 carbon atoms. Examples of C.sub.1 -C.sub.10 -alkyl radicals include C.sub.1 -C.sub.4 -alkyl of the above definition and n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl and their branched analogs.
The comonomers are contained in the styrene polymers in different amounts depending on their chemical structure. The miscibility of the copolymer with the polyphenylene ether is critical with regard to the content of comonomers in the copolymer. Such miscibility limits are known and are described, for example, in U.S. Pat. Nos. 4,360,618 and 4,405,753 and in the publication by J. R. Fried and G. A. Hanna, Polymer Eng. Sci. 22 (1982), 705 et seq. The copolymers are prepared by known processes which are described, for example, in Ullmanns Enzyklopadie der technischen Chemie, Volume 19, page 273 et seq., Verlag Chemie, Weinheim (1980). The copolymers have in general weight average molecular weights (Mw) of from about 10,000 to about 300,000, which can be determined by conventional methods.
The component B) is particularly preferably high impact polystyrene.
The generally used processes for the preparation of high impact polystyrenes are mass or solution polymerization in the presence of a rubber, as described, for example, in U.S. Pat. No. 2,694,692, and mass suspension polymerization processes, as described, for example, in U.S. Pat. No. 2,862,906. Other processes can of course also be used provided that the desired particle size of the rubber phase is established.
The natural or synthetic rubbers usually used for toughening styrene polymers are used as the rubber. Suitable rubbers for the purposes of the present invention in addition to natural rubber are, for example, polybutadiene, polyisoprene and copolymers of butadiene and/or of isoprene with styrene and other comonomers, which have a glass transition temperature, determined according to K. H. Illers and H. Breuer, Kolloidzeitschrift 190 (1) (1963) 16-34, of less than -20.degree. C. According to the invention, mixtures of different toughened polymers of the above definition may also be used.
The novel molding materials may contain, as component C), the following compounds C1, C2 and C3 individually or as a mixture:
C1) Phosphine oxide of the formula (I) ##STR1##
where R.sup.a, R.sup.b and R.sup.c are identical or different and are selected from hydrogen and straight-chain or branched, unsubstituted or substituted alkyl, aryl, alkylaryl or cycloalkyl groups of up to 40 carbon atoms.
Preferred alkyl radicals here are C.sub.1 -C.sub.20 -alkyl, in particular C.sub.1 -C.sub.12 -alkyl, e.g. methyl, ethyl, n-propyl, n-butyl, neopentyl, n-hexyl, n-octyl, n-nonyl, n-dodecyl, 2-ethylhexyl, 3,5,5-tri-methylhexyl and substituted alkyl radicals, such as cyanoethyl.
Preferred aryl radicals are phenyl and naphthyl as well as monosubstituted or polysubstituted radicals, such as tolyl, xylyl, mesityl and cresyl.
Preferred alkylaryl radicals are C.sub.1 -C.sub.20 -alkylaryl, in particular C.sub.1 -C.sub.12 -alkylaryl, the alkyl moiety and aryl moiety being as defined above.
Preferred cycloalkyl groups include C.sub.3 -C.sub.10 -cycloalkyl, such as cyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl.
Suitable substituents are cyano, hydroxy, C.sub.1 -C.sub.4 -alkyl and halogen, such as F, Cl, Br and I.
C2) Phosphate of the formula (II) ##STR2##
in which the substituents R.sup.a, R.sup.b and R.sup.c are identical or different and have the abovementioned meanings, and
C3) a boron compound.
Examples of phosphine oxides C1) are triphenylphosphine oxide, tritolylphosphine oxide, trisnonylphenylphosphine oxide, tricyclohexylphosphine oxide, tris(n-butyl)phosphine oxide, tris(n-hexyl)phosphine oxide, tris(n-octyl)phosphine oxide, tris(cyanoethyl)phosphine oxide, benzylbis(cyclohexyl)phosphine oxide, benzylbisphenylphosphine oxide and phenylbis(n-hexyl)-phosphine oxide. Triphenylphosphine oxide, tricyclohexylphosphine oxide, tris(n-octyl)phosine oxide and tris(cyanoethyl)phosphine oxide are particularly preferably used.
Particularly suitable phosphates C2) are alkyl- and aryl-substituted phosphates. Examples are phenyl bisdodecyl phosphate, phenyl bisneopentyl phosphate, phenyl ethyl hydrogen phosphate, phenyl bis(3,5,5-trimethylhexyl) phosphate, ethyl diphenyl phosphate, bis(2-ethylhexyl) p-tolyl phosphate, tritolyl phosphate, trixylyl phosphate, trimesityl phosphate, bis(2-ethylhexyl) phenyl phosphate, tris(nonylphenyl) phosphate, bis(dodecyl) p-tolyl phosphate, tricresyl phosphate, triphenyl phosphate, dibutyl phenyl phosphate, p-tolyl bis(2,5,5-trimethylhexyl) phosphate and 2-ethylhexyl diphenyl phosphate. Phosphorus compounds in which each of the radicals R.sup.a, R.sup.b and R.sup.c is an aryl radical are particularly suitable. Triphenyl phosphate, trixylyl phosphate and trimesityl phosphate are very particularly suitable. Cyclic phosphates may also be used. Particularly suitable here is diphenyl pentaerythrityl diphosphate.
Particularly preferred mixtures of the following phosphine oxide C1) and phosphate C2) combinations are: triphenylphosphine oxide/triphenyl phosphate or trixylyl phosphate, tricyclohexylphosphine oxide and triphenyl phosphate, tris(cyanoethyl)phosphine oxide and triphenyl phosphate, and tris(n-octyl)phosphine oxide and triphenyl phosphate. Mixtures of a plurality of phosphine oxides and phosphates may also be used, for example the mixture comprising triphenylphosphine oxide, triphenyl phosphate and trixylyl phosphate.
The molecular weight is in general not more than about 1000, preferably from about 150 to about 800.
According to the invention, boron compounds C3) are to be understood as meaning both inorganic and organic boron compounds.
Examples of inorganic boron compounds are boric acid, B.sub.2 O.sub.3 and salts of boric acid, preferably with alkali metals or alkaline earth metals. Boric acid, sodium borate and boron oxide are particularly preferred.
Organic boron compounds C3) are, for example, tetraphenyl borates, such as sodium tetraphenylborate, and tribenzyl borate.
In the case of a mixture of C1, C2 and C3, the composition of the component C) is in general, based on the content of the total component C):
C1) from 1 to 98.9, preferably from 10 to 85, in particular from 20 to 70, % by weight
C2) from 1 to 98.9, preferably from 10 to 85, in particular from 20 to 70, % by weight
C3) from 0.1 to 70, preferably from 5 to 50, in particular from 10 to 30, % by weight.
Other suitable components C) are organophosphorus compounds of the formulae (IV), (V) and (VI) ##STR3##
where
R.sup.1 and R.sup.4, independently of one another, are each unsubstituted or substituted alkyl or aryl;
R.sup.2, R.sup.3, R.sup.7 and R.sup.8, independently of one another, are each unsubstituted or substituted alkyl, aryl, alkoxy or aryloxy,
R.sup.5 is alkylene, --SO.sub.2 --, --CO--, --N.dbd.N-- or --(R.sup.6)P(O)--, where R.sup.6 is unsubstituted or substituted alkyl, aryl or alkylaryl, and n and p, independently of one another, are each from 1 to 30.
Suitable substituents in compounds of the formulae (IV), (V) and (VI)
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