Polymer Mixture comprising polybutylene terephthala tbemoplastle elastomer, and aa halograaated flame retardant additive; articles formed therefrom

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T e invention relates to a polymer mixture wbi comprises the following constituents:

A. a polybutylene terephthalate;

B. a thermoplastic elastomer; C. an halogenated flame retardant additive.

The invention also relates to articles forme the polymer mixture according to the Invention. Pol; mixtures which comprise a polybutylene terephthalate a thermoplastic elastomer, for example, a polyether* ester block copolymer, ere known, for example, from DB-C-2338615 and DB-B-24602S7. The addition of flan* rβtardants is not mentioned in these publications.

The addition of flame-retarding, halogen-conti. edditives to polybutylene terephthalates is disc-low BP-A-0045777. A large number of compounds are mentϋ as suitable lame-ratardants, including, for βxampJ polycarbonate oligomers prepared starting from broαi: nated bispfaenol A and brominated polystyrene.

Polymer mixtures which eoeprise a polybutylene ^' terephthalate a balogenated flame retardant additive such as a broninated polystyrene, an aromatic polycar¬ bonate end an agent to improve the Impact strength are disclosed in KP-A-0322934. The polymer mixtures just mentioned have a good tracking index and good flase- retarding properties.

Polymer mixtures which comprise a polybutylene terephthalate, a thermoplastic elastomer and a baloge¬ nated flame retardant additive such am a bro lnatad polystyrene as a flame-retardant ere described in nαn-prepublisbed BP-A-0392190. These known polymer mix¬ tures have a good combination of properties: a good flexibility, e good flow of their melt, good flame- retarding properties and a high tracking index. According to the general teaching of EP-A-0392X90, conventional additives, for example, reinforcing fibres, may be added to the polymer mixtures. For example, if a polymer mixture having a greater rigidity is to be obtained, conventional glass fibres will be added. However, Applicants* experiments have demonstrated that, although the addition of conventional glass fibres leads to an increase of the rigidity, it also results in a strong decrease of the flow properties and a remarkable reduction of the tracking index.

The invention is based on the discovery that the rigidity can be Improved without too strong a reduction of the flow and/or of the tracking index occurring by using a given type of glass fibres.

The polymer mixture according to the invention is characterised in that the polymer mixture comprises in addition (D) glass fibres having a length of less than 200 s-lcrometres and a diameter of less than 25 micro¬ metres.

The polymer mixture according to the invention preferably conprises as constituent B a polyether eβter block copolymer, or a polyester-ester urethane or a polyether imlde ester.

The composition of the polymer mixture according to the invention is preferably such that the polymer mix- ture comprises

45-70 parts by weight of constituent A, 5-25 parts by weight of constituent B,

10-30 parts by weight of constituent C, and 5-15 parts by weight of constituent o per loo parts by weight of the sum of the constituents

A, B, c and D.

The polymer mixture according to the invention comprises as constituent A a polymer or a copolymer which Is built up for more than 70 mol% from units derived from terephthallc acid and butane-l,4-diol.

It is possible to use a metal compound (for example, antimony oxide) which cooperates synβrglstlcally with the halσgenated flame retardant additive in the polymer mixtures according to the invention.

The polymer mixture according to the invention may comprise 1-100 parts by weight of conventional additives per 100 parts by weight of A. plus B. plus C. plus D.

The polymer mixture according to the invention comprises at any rate the following constituents:

A. a polybutylene terephthalate,

B. a thermoplastic elastomer.

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c. a halogenated flame retardant additive, and D. a special type of glass fibres.

A. polylyitylene terephthalate Polybutylene terephthalate is a polymer known per se. It is derived from butane-l,4-diol and terephthalic acid. It is possible to use in the polymer mixtures copolyesters in which a part of the diol compound and/or a part αf the terephthalic acid has been replaced by another diol and/or carboxylic acid. For the polymer mixtures according to the Invention it is to be pre¬ erred to use a polybutylene terephthalate which is built up for more than 70 mol% from units derived from butane-l,4-diol and terephthalic acid.

It is possible to use a polybutylene terephthalate in which a branching agent, for example, a glycol having three or more hydroxyl groups or a trifunctional or polyfunctional carboxylic acid has been incorporated.

B. Thermoplastic elastomer

Various types of -thermoplastic elastomers may be used in the polymer mixture according to the Invention. Examples are the polyether-ester block copolymers, polyester-ester urethanes and polyether imlde esters known pqr se.

Polyether-ester block copolymers are generally obtained by condensation polymerisation of one or more dicarboxylic acids, one or more long-chain glycols and one or more short-chain glycols. Examples of suitable polyether-ester block copolymers are described in DE-C-2338615 and DE-B-2460258, as well as in the litera¬ ture references cited therein.

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As a polyester-ester urethane is preferably ujsed a block copolymer which is built up from polyester-ester units which are bonded by means of groups of the formula Rl [NBC(0)]p, wherein SI is a polyfunctional group having at most 30 carbon atoms and p has a value of 2 or 3, and In which the polyester-ester units ere built up from blocks having a number of ester units of the for¬ mula - OG0C(O)R2C(O) - and blocks having a number of ester units which are capable of forming a bifunctiional polyester or polyester amide having,a melting-point ^* of less than 100 oc, which blocks are bonded together by ester bonds, at least βo mol% of the R2 groups being 1,4-phenylene radicals and at least 80 mol% of the o- groups being a tetramethylene group _*

SUch polymers and their methods of preparation are disclosed, for example, in BP-A-0102115, us-A-4,180,257 and US-A-4,228,245.

AS a polyether imlde ester is preferably used a block copolymer obtained by reaction of a diol having a low molecular weight, a dicarboxylic acid, a poly(oxyaUylene)diamine and a tricarboxylic acid or a derivative thereof. Such polymers are described, for example, in US-A-4,544,734, US-A-4,556,705 and US-A-4,556,688.

C. Halogenated flame retardant additive.

Any known halogenated flame retardant suitable for blending with polybutylenβtβrβphtalatβs nay be used. Preferred are bromlnated polystyrenes and brominated epoxy resins.

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Brominated polystyrenes are flame-retardants 'known per se for synthetic resins.They are commercially available. They may comprise, for example, approximately 40-70% by weight of bromine.

examples of suitable brαninated epoxyresins are the tetrabromo blsphenol A-diglycidyl ethers with a mole¬ cular weight of about 2,000 to 20,000.

D. Glass; fibres

The polymer mixture according to the invention must comprise glass fibres having a length of less than 200 micrometres and a diameter of less than 25 micrometres. Such types of glass fibres are generally available.

In addition to the constituents mentioned herein¬ before the polymer mixture according to the invention may moreover comprise conventional additives. Suitable edditives are pigments and dyes, stabilisers, tcan- sesterification inhibitors, flame-reterdants, mould- release agents, etc.

The polymer mixture according to the invention can be obtained according to the conventional methods of preparing polymer mixtures, for example, by melt extru¬ sion.

Example I, comparative examples A and B The following constituents were used in the examples: PBT: a polyester derived from butanediol and terephthalic acid having an intrinsic visco¬ sity of 1.18 dl/g, measured in a 60/40 mJjxture of phenol/tetrachlσroethane at 25*C.

TPE: a polyether imlde ester commercially available as L0MOD* J10

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FR: a bromlnated polystyrene having a bromine content of approximately 65% by weight.

Glass glas fibres having an average length of fibres-1: approximately 4-5 millimetres and an average diameter of approximately 10 micrometres*

Glass glass fibres having an average length of fibres-2: approximately 70 micrometres and an average diameter of 12 micrometres.

AOC: a mixture of 85% by weight of Sb203 and 15% of a carrier polymer.

T: a polytetrafluoroethylene compound.

O: a mixture of remaining conventionally used additives (stabiliser + mould release agent).

The constituents mentioned hereinbefore in the quantities es indicated in the table hereinafter were compounded in an extruder and pelletlsed. Standardised test pieces were injection-moulded from the resulting pellets to determine the combustibility class according to UL-94/ to determine the "comparative tracking index" according to IEC, 1979 (3rd edition), and to determine a few mechanical properties, in addition the melt visco¬ sity index (MVI) was determined.

The results obtained are also recorded in the table hereinafter.

T A B L E

Example no. B Con ositiαn (parts by weight) o PBT 50 53 53 o TPE 25 15 15 o glass fibres-l 7 o glass fibres-2 7 o FR 17.5 17.5 17.5

O AOC 7 7 7 o T 0.25 0.25 0.25 o 0 0.45 0.45 0.45

Properties o Tensile module 1500 2100 2190 o Bending module 1450 2045 2110 o comparative tracking index (V) 325 275 325 o UL-94 (1.6 mm rod) V-0 V-0 V-0 o HVI (250*C; 2.16 kg) 22.4 14.5 17.5

Zt will be obvious from the results recorded in the above table that the addition of conventional glass fibres {comparative example B) results in an Increase of the rigidity and in a considerable deterioration of the flow properties. Moreover the tracking index decreases.

By using special fibres (example I) a further Improvement of the rigidity can even be obtained, while in addition the flow properties are deteriorated to a much lesser extent. The tracking index is βlso kept up.