Flame-proof thermoplastic moulding materials

Details Flame-proof thermoplastic moulding materials Flame-proof thermoplastic moulding materials

1999-03-10

2001-10-23

Hoke, Veronica P. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S117000, C524S425000, C524S426000

Reexamination Certificate

active

06306941

ABSTRACT:

The invention relates to thermoplastic molding compositions comprising
A) from 5 to 97% by weight of a thermoplastic polymer selected from the group consisting of polyamides, polyesters, polyphenylene ethers, vinylaromatic polymers and mixtures of these,
B) from 1 to 30% by weight of an alkylphosphonic acid compound of the formula I
 where R is alkyl having from 1 to 4 carbon atoms and x is 0 or
C) from 1 to 30% by weight of a synergist for B) selected from the group consisting of inorganic calcium and magnesium compounds and mixtures of these,
D) from 1 to 50% by weight of a fibrous filler and
E) from 0 to 40% by weight of other additives and processing aids,
where the sum of the percentages by weight of components A) to E) is always 100%.
The invention also relates to the use of the novel thermoplastic molding compositions for producing shaped articles of any type and to the shaped articles obtainable in this way.
One of the disadvantages of halogen-containing flame-retardant thermoplastics is that they are toxicologically questionable, and they are increasingly being replaced by halogen-free flame-retardant thermoplastics.
Important requirements for flame-retardant systems of this type are, in particular, a pale inherent color, adequate thermal stability when being incorporated into the thermoplastics and retention of efficacy when fibrous fillers are added; addition of such fillers adversely affects the flame-retardant action (“wicking” effect of glass fibers).
Besides thermoplastics which contain red phosphorus, there are four other halogen-free flame retardants.
1. Inorganic flame retardants based on hydroxides or carbonates, especially of magnesium, which must be employed in large amounts to give adequate efficacy;
2. Nitrogen-containing flame retardants, such as melamine cyanurate, which usually only give adequate flame retardancy in unreinforced thermoplastics;
3. Phosphorus compounds, such as triphenylphosphine oxide, which have an undesirable plasticizing side-effect in many thermoplastics;
4. Ammonium polyphosphates and melamine phosphate, which do not have adequate thermal stability at above 200° C.
Alkylphosphonic acid compounds and their efficacy as flame retardants in thermoplastics are known from U.S. Pat. No. 3,789,091, DE-A 44 41 022 and DE-A 44 06 857. From the two German applications it is clear to the person skilled in the art that addition of an alkylphosphonic acid compound gives good flame retardancy (class V-0 in UL 94) in unreinforced transparent (amorphous) polyamides or mixtures of these with partially crystalline polyamides, and that additives may be added to polyamides of this type.
However, it would be desirable to have a flame-retardant partially crystalline PA product without the addition of amorphous polyamides, since the latter reduce the chemical and heat resistance. For glass-fiber-reinforced polyamides, the efficacy of the alkylphosphonic acid compounds is inadequate, since the UL 94 classification is only V-2 with dripping of flaming particles from the specimens.
It is not advisable to increase the amount of phosphonic acid compound since the additive sweats out during processing (mold deposit) and the mechanical properties are very adversely affected (plasticizing property of the phosphorus compound).
It is an object of the present invention to provide a halogen-free flame retardant which is suitable for reinforced polyamides, polyesters, PPE and vinylaromatic polymers and which shows goods flame retardancy with adequate crust formation and without dripping flaming particles.
We have found that this object is achieved by the molding compositions defined at the outset. Preferred embodiments are given in the subclaims.
Surprisingly, addition of inorganic magnesium and/or calcium compounds and alkylphosphonic acid compounds gives a synergistic flame-retardant effect in reinforced thermoplastics, such as polyesters, polyamides, in particular partially crystalline polyamides, PPE and vinylaromatic polymers and mixtures of these. The UL 94 classification V-0 is achieved by the combination according to the invention and the specimens do not drip flaming particles.
The novel molding compositions comprise, as component A), from 5 to 97, preferably from 10 to 93 and in particular from 30 to 80% by weight, of a thermoplastic polymer selected from the group consisting of polyamides, polyesters, polyphenylene ethers, vinylaromatic polymers and mixtures of these.
1. Polycarbonates and polyesters
Suitable polycarbonates (frequently also called aromatic polyesters) are known per se. They can be prepared, for example, by the processes described in DE-B-1 300 266 by interfacial polycondensation or by the process described in DE-A-14 95 730 by reaction of biphenyl carbonate with bisphenols. The preferred bisphenol is 2,2-di(4-hydroxyphenyl)propane, referred to in general and below as bisphenol A.
Instead of bisphenol A, other aromatic dihydroxy compounds can also be used, in particular 2,2-di(4-hydroxyphenyl)pentane, 2,6-dihydroxynaphthalene, 4,4′-dihydroxydiphenyl sulfone, 4,4′-dihydroxydiphenyl ether, 4,4′-dihydroxydiphenyl sulfite, 4,4′-dihydroxydiphenylmethane, 1,1-di(4-hydroxyphenyl)ethane or 4,4-dihydroxydiphenyl, and mixtures of these.
Particularly preferred polycarbonates are those based on bisphenol A or bisphenol A together with up to 30 mol % of the abovementioned aromatic dihydroxy compounds.
The viscosity ratio of these polycarbonates is in general in the range 1.1 to 1.5, in particular from 1.28 to 1.4 (measured at 25° C. in a 0.5% strength by weight solution in dichloromethane).
Suitable polyesters are likewise known per se and are described in the literature. They contain, in their primary chain, an aromatic ring which derives from an aromatic dicarboxylic acid. The aromatic ring can also be substituted, eg. by halogen, such as chlorine or bromine, or by C
1
-C
4
-alkyl, such as methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl or tert-butyl.
The polyesters can be prepared by reaction of aromatic dicarboxylic acids or their esters or other ester-forming derivatives with aliphatic dihydroxy compounds in a manner known per se.
Preferred dicarboxylic acids which may be mentioned are naphthalenedicarboxylic acid, terephthalic acid and isophthalic acid and mixtures of these. Up to 10 mol % of the aromatic dicarboxylic acids may be replaced by aliphatic or cycloaliphatic dicarboxylic acids, such as adipic acid, azelaic acid, sebacic acid, dodecanedioic acids and cyclohexanedicarboxylic acids.
Preferred aliphatic dihydroxy compounds are diols with from 2 to 6 carbon atoms, in particular 1,2-ethanediol, 1,4-butanediol, 1,6-hexanediol, 1,4-hexanediol, 1,4-cyclohexanediol and neopentyl glycol, and mixtures of these.
Particularly preferred polyesters which may be mentioned are polyalkylene terephthalates which derive from alkanediols with from 2 to 6 carbon atoms. Polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate are particularly preferred.
The viscosity number of the polyesters is generally in the range from 60 to 200 ml/g (measured in a 0.5% strength by weight solution in a phenol/o-dichlorobenzene mixture (weight ratio 1:1 at 25° C.)).
2. Vinylaromatic polymers
The molecular weight of these polymers, which are known and commercially available, is generally in the range from 1500 to 2,000,000, preferably in the range from 70,000 to 1,000,000.
Vinylaromatic polymers of styrene, chlorostyrene, &agr;-methylstyrene and p-methylstyrene may be mentioned in a purely representative capacity; comonomers such as (meth)acrylonitrile or (meth)acrylates may be included in the structure of the polymer in subordinate amounts (preferably not more than 20, in particular not more than 8, % by weight). Particularly preferred vinylaromatic polymers are polystyrene and impact-modified polystyrene. Mixtures of these polymers may, of course, also be employed. Preparation is preferably by the process described in EP-A-302 485.
Preferred ASA polymers are constructed from a soft or elastomeric phase compri

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