Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-03-04
2001-02-06
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S101000, C524S413000, C524S514000, C524S496000
Reexamination Certificate
active
06184282
ABSTRACT:
The invention relates to flame-retardant thermoplastic molding compositions comprising
A) from 40 to 98% by weight of a thermoplastic polyamide
B) from 1 to 40% by weight of melamine cyanurate
C) from 1 to 50% by weight of a fibrous filler which is pretreated with a silane compound and whose arithmetic mean fiber length (d
50
) is from 70 to 200 &mgr;m, or of an acicular mineral filler or mixtures of these
D) from 0 to 30% by weight of other additives and processing aids
where the total of the percentages by weight of components A) to D) is 100%.
In addition, the invention relates to the use of the novel molding compositions to produce moldings of any type, and to the resultant moldings.
JP-A 53/051 250 discloses flame-retardant polyamide molding compositions which contain melamine cyanurate and fillers. These are prepared by carrying out the polymerization of the amide-forming monomers in the presence of the fillers and of the flame retardant. JP-A 54/016 565, furthermore, discloses polyamide molding compositions with melamine cyanurate and containing fillers, where the mineral fillers are preferably intended to have a L/D ratio of 4-¼. It is also known from JP-A/118 454 that mixtures of melamine with cyanuric acid show flame-retardant action in polyamide, and these mixtures may also contain fillers.
Such molding compositions have the disadvantage that their mechanical properties, such as stiffness and strength, are unsatisfactory. The addition of glass fibers to polyamide mixtures with melamine cyanurate improves their mechanical properties, but their flame retardancy is adversely effected, since glass fibers drastically reduce flame retardancy through the effect known as wicking.
Correspondingly, EP-A 241 702 discloses that the flame retardancy of polyamide mixtures made from glass fibers with melamine cyanurate can be improved by using unsized short glass fibers (fiber length on average from 100 to 250 &mgr;m) in the mixture.
EP-A 614 933 discloses mixtures of magnesium hydroxide and melamine cyanurate for polyamides.
The known molding compositions achieve the UL 94 classification V-0 only at high total contents of flame retardant, and in addition in many applications the times of continued burning in the glow-wire test are important. The French standard NF F 16-101 demands continued burning times which are less than or equal to 2 seconds. The known molding compositions are very far from fulfilling this requirement.
In all of the patents mentioned the glass fibers used, if any are used at all, are conventional continuous fibers (rovings) or chopped fibers (fiber bundles of from 4 to 6 mm length). The distribution of glass fiber lengths in the product then results from shearing in the extruder, and although this is not mentioned it is from about 250 to 300 &mgr;m for usual processing (based on a product with 25% glass fiber content). Account has to be taken here of the fact that the average fiber length (for any given processing) generally falls as the proportion of fiber increases, since there is increased interaction between fibers in the zone where they are incorporated and therefore more fiber breakage (F. Raumsteiner, R. Theysohn, Comp. Sci. Techn. 23 (1985) 231).
It is an object of the present invention, therefore, to provide flame-retardant thermoplastic molding compositions which have good mechanical properties and good flame retardancy. In particular, the addition of sized, very short glass fibers should make it possible to achieve a level of flame retardancy which permits very short continued burning times in the glow-wire test.
We have found that this object is achieved by means of the molding compositions defined at the outset. Preferred embodiments are given in the subclaims.
Surprisingly, it has been found that the use in the product of particularly short glass fibers, especially having a certain distribution of glass fiber lengths, results in only a small but acceptable decline in mechanical properties (stiffness and strength), but markedly improved processability and flame retardancy. This is in contradiction to normal injection molding, since practically no change either in mechanical properties or in flame retardancy is observed in this range of fiber length (only at >1 mm does flowability deteriorate). It is therefore usual in the case of injection-molded products to accept a compromise if necessary between mechanical properties (increasing with fiber length) and isotropy (falling with fiber length), but the fiber length asked for is usually as high as possible.
As well as using short glass fibers, it is also possible in principle to produce short fibers through high shear in the extruder.
The novel molding compositions contain, as component A), from 40 to 98% by weight, preferably from 40 to 87% by weight and in particular from 60 to 85% by weight of a thermoplastic polyamide.
The polyamides of the novel molding coompositions generally have a relative viscosity &eegr;
rel
, determined in a 1% strength by weight solution in 96% strength by weight sulfuric acid at 25° C., of from 1.7 to 5.0, corresponding to a K value (Fikentscher) of from 50 to 96. Preference is given to the use of polyamides having a relative viscosity of from 2.3 to 4.5, in particular from 2.5 to 4.0.
Preference is given to semicrystalline or amorphous resins having a molecular weight (weight-average) of at least 5,000, as described, for example, in the American patents 2 071 250, 2 071 251, 2 130 523, 2 130 948, 2 241 322, 2 312 966, 2 512 606 and 3 393 210.
Examples of these are polyamides derived from lactams having from 7 to 13 ring members, for example polycaprolactam, polycaprylolactam and polylaurolactam, and also polyamides obtained by reacting dicarboxylic acids with diamines.
Dicarboxylic acids which may be used are alkanedicarboxylic acids having from 6 to 12 carbon atoms, in particular from 6 to 10 carbon atoms, and aromatic dicarboxylic acids. Merely as examples, mention may be made of adipic acid, azelaic acid, sebacic acid, dodecanedioic acid and terephthalic and/or isophthalic acid.
Particularly suitable diamines are alkanediamines having from 6 to 12 carbon atoms, in particular from 6 to 8 carbon atoms, and also m-xylylenediamine, di(4-aminophenyl)methane, di(4-aminocyclohexyl)methane, 2,2-di(4-aminophenyl)propane and 2,2-di(4-aminocyclohexyl)propane.
Preferred polyamides are polyhexamethylene adipamide, polyhexamethylene sebacamide and polycaprolactam.
Other suitable polyamides are those obtainable, for example, by condensing 1,4-diaminobutane with adipic acid at elevated temperature (nylon-4,6). Preparation processes for polyamides of this structure are described, for example, in EP-A 38 094, EP-A 38 582 and EP-A 39 524.
Other suitable polyamides are those obtainable by copolymerizing two or more of the monomers mentioned above, or mixtures of more than one polyamide in any desired mixing ratio.
Such partly aromatic, semicrystalline copolyamides are built up from:
A
1
) from 20 to 90% by weight of units derived from terephthalic acid and hexamethylenediamine,
A
2
) from 0 to 50% by weight of units derived from &egr;-caprolactam,
A
3
) from 0 to 80% by weight of units derived from adipic acid and hexamethylenediamine and
A
4
) from 0 to 40% by weight of other polyamide-forming monomers,
where the proportion of components (A
2
) or (A
3
) or (A
4
) or mixtures of these is at least 10% by weight.
Component A
1
) contains from 20 to 90% by weight of units derived from terephthalic acid and hexamethylenediamine.
Besides the units derived from terephthalic acid and hexamethylenediamine, the copolyamides contain units derived from &egr;-caprolactam and/or units derived from adipic acid and hexamethylenediamine and/or units derived from other polyamide-forming monomers.
The proportion of units derived from &egr;-caprolactam is at most 50% by weight, preferably from 20 to 50% by weight, in particular from 25 to 40% by weight, while the proportion of units derived from adipic acid and hexamethylenediamine is up to 80% by weight, preferably from 30 to 75% by weight an
Gareiss Brigitte
Gorrissen Heiner
Lauke Harald
Ulmerich Karlheinz
BASF - Aktiengesellschaft
Keil & Weinkauf
Rajguru U. K.
Seidleck James J.
LandOfFree
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