GB2290547A

GB2290547A - Thermoplastic molding materials

Info

Publication number: GB2290547A
Application number: GB9510913A
Authority: GB
Inventors: Hans Hoenl; Norbert Moedersheim; Hubert Meyer; Heinz-Dieter Vondenhagen; Holger Wantzelius
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1994-05-31
Filing date: 1995-05-30
Publication date: 1996-01-03
Also published as: FR2720403B1; ITMI951043A0; IT1274545B; ITMI951043A1; GB9510913D0; JPH07331004A; FR2720403A1

Abstract

Thermoplastic molding materials contain from 20 to 95% by weight of a polystyrene or high-impact polystyrene A, as obtained by free radical or anionic polymerization of styrene in the presence or absence of a rubber, from 2 to 40% by weight of at least one polyphenylene ether B, from 0 to 30% by weight of a phosphorus-containing fireproofing agent C, from 0.05 to 1% by weight of Ca or Zn stearate D and from 1 to 30% by weight of a styrene/diene block copolymer E.

Description

Thermoplastic molding materials The present invention relates to flame-retardant thermoplastic molding materials based on a polyphenylene ether (PPE) and a styrene polymer. Such blends are known per se and are suitable for the production of moldings which have lower flammability than pure, toughened styrene polymers. The material properties of such moldings are generally satisfactory; however, particularly the fire characteristics are often unsatisfactory.

It is an object of the present invention to prepare improved fireproofed thermoplastic molding materials based on blends of toughened styrene polymers and polyphenylene ethers, which contain, inter alia, phosphorus-containing fireproofing agents.

We have found that the flammability of PS/PPE blends and their dripping behavior in a fire are substantially reduced by the addition of styrene/butadiene block polymers to blends of toughened styrene polymers and polyphenylene ethers, which are treated with phosphorus-containing flameproofing agents.

We have found that this object is achieved, according to the invention, by a molding material which contains at least one toughened styrene polymer, at least one polyphenylene ether, if required at least one phosphorus-containing fireproofing agent as well as at least one styrene/butadiene block copolymer.

The present invention directly relates to a thermoplastic molding material containing, in each case roughly, based on the sum of A to E, A: from 20 to 95, preferably from 20 to 60, % by weight of at least one polystyrene or high-impact polystyrene A, as obtained by free radical or anionic polymerization of styrene in the presence or absence of a rubber, B: from 2 to 40, preferably from 10 to 40, % by weight of at least one polyphenylene ether B, C: from 0 to 30, preferably from 1 to 30, % by weight of one or more phosphorus-containing fireproofing agents C, D: from 0.05 to 1% by weight of a metal stearate D, selected from calcium stearate and zinc stearate, and E: from 1 to 30, preferably from 1 to 10, % by weight of at least one block copolymer E, containing in each case one or more styrene and butadiene or isoprene blocks.

The addition of elastomers to blends of styrene polymers and polyphenylene ethers which contain organic phosphites is known (J 58 021444). However, hydrogenated styrene/butadiene/isoprene copolymers are preferred. A further additive is titanium oxide.

Such blends are said to be particularly pale and dimensionally stable.

Blends of polyphenylene ethers, aromatic phosphates, polystyrene and glass fibers, which are described in DE 3038-551, likewise contain hydrogenated block copolymers having an A-B-(A) structure. These self-extinguishing molding materials have the advantage of being readily processable to give impact-resistant, glossy finished articles.

High-impact polystyrene A A is a toughened styrene polymer which was prepared by polymerization of styrene and possibly styrene alkylated in the nucleus or sidechain, in the presence of rubber. Preferably, exclusively styrene is used for the polymerization in the presence of the rubber. The rubber content should be from 3 to 25, preferably from 5 to 15, % by weight.

Suitable rubbers used for toughening styrene polymers are natural or synthetic rubbers. 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 isoprene with styrene and other comonomers, which have a glass transition temperature below -20 C (according to K.H. Illers and H. Breuer, Kolloidzeitschrift 176 (1961), 110). Butadiene polymers having a 1,4-cis content of from 25 to 99% by weight are particularly suitable. However, acrylate rubbers, EPDM rubbers, polybutylene rubbers and polysiloxane rubbers may also be used.

The rubber grafted with styrene (flexible phase) is finely distributed in the polystyrene phase, which is referred to as the rigid matrix. The average particle diameter (d50 value of the integral mass distribution) is from 0.2 to 7 pm. The processes for the preparation of styrene polymers are known and are described, for example, in Ullmanns Encyklopädie der technischen Chemie, 4thEdition, Volume 19, pages 265 to 295, Verlag Chemie, Weinheim, or H. Gerrens, Chem. Ing. Tech. 52 (1980), 477.

Suitable toughened polystyrene grades are for the most part commercially available and their rigid matrix has a viscosity number of, for example, from 50 to 130 [ml/g, measured using a 0.5% strength solution in toluene at 23 C].

Polyphenylene ether B The suitable polyphenylene ethers B are known and are preferably prepared by oxidative coupling of phenols disubstituted in the oposition (cf. U.S. Patents 3,661,848, 3,378,505, 3,306,874, 3,306,875 and 3,639,656). Examples of substituents are halogen, such as chlorine or bromine, and alkyl or alkoxy. The alkyl or alkoxy groups, which preferably contain 1 to 4 carbon atoms but no a tertiary hydrogen atom, may in turn be substituted by chlorine or bromine.

Examples of such polyphenylene ethers are: poly-2, 6-dilauryl-1,4-phenylene ether, poly-2,6-diphenyl-l,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-2,6-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.

Poly-2,6-dimethyl-1,4-phenylene ether is particularly preferred.

Copolymers of different phenols, for example those which contain 2,6-dimethylphenol and 2,3,6-trimethylphenol, are also suitable.

Mixtures of different polyphenylene ethers can of course also be used.

Graft copolymers of polyphenylene ethers and vinyl aromatic monomers, such as styrene, a-methylstyrene, vinyltoluene or chlorotoluene, are also possible. For the calculation of the novel amount of polyphenylene ether, the grafting base and grafted shell are considered separately in this case.

The polyphenylene ethers generally have a limiting viscosity of from 0.2.to 0.7 dl/g, measured in 0.5% strength solution in chloroform at 25 C. This corresponds to an average molecular weight Mw of from 10000 to 60000.

Phosphorus compounds C A phosphorus compound can optionally be added, preferably in an amount of from 1 to 30% by weight The amount of C is particularly preferably from 1 to 10% by weight.

Suitable phosphorus compounds C are all substances conventionally employed for mixing with plastics to render them flameproof, eg.

phosphoric esters, phosphinic esters, phosphine oxides, phosphonic acid salts, phosphonic esters and red phosphorus or mixtures of these compounds. Triphenylphosphine oxide, triphenyl phosphate or a mixture thereof is preferably used.

As described in European Patent 311,909, phosphorus-containing compounds can also be used in combination with a triazine compound. A preferably used triazine compound is melamine.

Stearate D The novel molding materials contain from 0.05 to 1.00% by weight of calcium stearate or zinc stearate D.

Block copolymer E E is a block copolymer or a mixture of such block copolymers, containing in each case one or more blocks of styrene and diene (butadiene or isoprene). The novel component E should preferably have a styrene/butadiene/styrene block copolymer and a molecular weight (Mn) of from 50 000 to 150 000. The butadiene content should be from 20 to 80% by weight. The S-B-S structure can be asymmetrical; it is preferably symmetrical. Radial S-B block copolymers are also possible. The S-B transition may be well defined or tapered, and the block copolymer may be elastomeric or tough and resilient in its macroscopic behavior, ie. the glass transition temperature Tg may be below or above room temperature.

Additives F The novel molding materials may contain conventional additives F, such as pigments, fillers, reinforcing materials, oligomers and polymers, antistatic agents, antioxidants and other stabilizers and further lubricants (except for aromatic sulfonamides).

The novel thermoplastic molding materials are obtained by mixing their components at from 200 to 350 C, preferably from 250 to 300 C, in a conventional mixing apparatus, for example a kneader, a Banbury mixer or a single-screw extruder, preferably a twin-screw extruder. Thorough mixing is necessary in order to obtain n a very homogeneous molding material. The mixing times are in general from 30 seconds to 30 minutes, preferably from 1 to 5 minutes. The order in which the components are mixed may vary; selected components may be premixed or components may be mixed together.

The novel molding materials are suitable for the production of moldings of all types, for example by injection molding or extrusion. They may furthermore be used for the production of films and semifinished products by the deep drawing or blowmolding processes.

The novel molding materials have good flow, high heat distortion resistance, good mechanical properties and excellent fireproof properties.

In order to evaluate the property profile of the polymer blends, the following properties were determined: Vicat softening temperature VST/B/50 according to ISO 306 ( C) Melt volume rate MVR 200/5 according to ISO 1133 (ml/10 min) Elongation at break according to ISO 527 (%) Tensile modulus of elasticity according to ISO 527 (MPa) Fire behavior according to UL 948 (class) Burning rate according to IEC 65 Fire behavior was investigated in the vertical fire test according to UL 94, using 2.4 mm test bars, according to the specifications of the Underwriter Laboratories, with the aim of classification in one of the fire classes UL 94 V-0, UL 94 V-1, UL 94 V-2 or UL 94 V-3. If the fire test according to UL 94 is not passed, the sample is classified under HB.

The burning rate according to IEC 65 was measured using test specimens sawn from injection molded rear panels of television sets.

Examples The following components were prepared for the examples and comparative experiments: Component A: A(1) High-impact polystyrene containing 8% by weight of polybutadiene and having an average particle size of the flexible component of 2.8 Fm. The viscosity number of the rigid matrix is 70 ml/g (0.5% strength in toluene at 23 C).

A(2) As for A(1), except that the polybutadiene content is 6% by weight, and 8.4% by weight of a medical white oil are added.

Component B: Poly-2,6-dimethyl-1,4-phenylene ether having an average molecular weight Mw of 25000.

Component C: C(1) Triphenylphosphine oxide C(2) Triphenyl phosphate Component D: Zinc stearate Component E: E(1) Commercial product FinaclearE 520 from Fina SBS block copolymer Mn = 100 103, polybutadiene content: 26% by weight E(2) Commercial product StyroluxE KR 2691 from BASF SBS block copolymer Mn = 80 103, polybutadiene content: 24% by weight In addition, a commercial, sterically hindered phenol was used as an antioxidant (KerobitE TBK from BASF).

A comparison of Example (1) with Comparative Experiment V1 in the table below shows that the addition of 10% by weight of component E(1) increases the fire class from V-2 to V-i. In addition to this improvement, the toughness is also substantially increased without the rigidity decreasing greatly.

A comparison of Examples (2) and (3) with the comparison (2) shows that, even in the absence of phosphorus-containing flameproofing agents, the fire behavior, in this case measured according to IEC 65, is clearly improved by adding 5% by weight of component E(1) or E(2).

Table: Examples/Comparative Experiments

1 V1 2 1 3 4 Component A(1) 35.30 45.30 0 0 0 Component A(2) 0 0 87.00 87.00 92.00 Component B 40.00 40.00 7.50 7.50 7.50 Component C(1) 7,00 7.00 0 0 0 Component C(2) 7.00 7.00 0 0 Component D 0.50 0.50 0.50 ~ 0.50 0.50 Component E(1) 10.00 5.00 0 Component E(2) 0 0 0 5.00 0 Component F 0.20 0.20 0 0 0 VST/B/50 82 84 86 85 84 MVR 200/5 6.4 6.1 11 13 13 Elongation at 29 17 46 32 31 break Tensile modulus 2100 2200 1800 1900 1900 of elasticity UL 94 2.4 mm V-1 V-2 - - - test specimen

1 vi 2 3 4 IEC, 2.3 mm - - passed passed not (television passed rear panels) Burning rate - - 35 36 > 40

Claims

Claims 1. A thermoplastic molding material based on styrene polymer and comprising A: from 20 to 95% by weight of at least one styrene polymer or high-impact styrene polymer, as obtained by free radical or anionic polymerization in the presence or absence of a rubber, B: from 2 to 40% by weight of at least one polyphenylene ether polymer, C: from 0 to 30% by weight of a phosphorus-containing fireproofing agent or a mixture of phosphorus containing fireproofing agents, D: from 0.05 to 1% by weight of at least one metal stearate selected from calcium stearate and zinc stearate, E: from 1 to 30% by weight of at least one block copolymer containing in each case one or more blocks of styrene and diene, and F: if required, one or more further additives.
2. A molding material as claimed in claim 1, containing, as component C, from 1 to 30% by weight of a compound selected from triphenyl phosphate, triphenylphosphine oxide and mixtures thereof.
3. A molding material as claimed in claim 1 or 2, containing, as component E, a styrene/butadiene/styrene block copolymer having a molecular weight (N4) of from 50,000 to 150,000 and a butadiene content of from 20 to 80% by weight.
4. A molding material as claimed in any of claims 1 to 3, containing, as component A, toughened styrene polymer obtained by polymerization of exclusively styrene in the presence of a rubber.
5. A molding material as claimed in any of claims 1 to 4, containing, as component B, poly-2,6-dimethyl-1,4-phenylene ether.
6. A molding material substantially as exemplified in any of the foregoing Examples 1 to 4.