Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Flame- retardant polyamide mouldincr eom~ositions
The invention relates to flame-retardant polyamide
compositions based on magnesium hydroxide with very good
mechanical and electrical properties and high surface
quality.
Polyamides are engineerings thermoplasticSwith the
characteristic features
- good processability
- very good mechanical properties
- very good electrical properties
- high deflection temperature
- good chemical resistance
- very high surface quality.
If polyamides of proven value are reinforced with glass
fibres, glass spheres, mineral fillers or mixtures of
these, their properties may be appreciably enhanced.
Elastomeric modification improves the impact strength of
the reinforced polyamides. Novel products tailor-made for
specific fields of application axe constantly being
developed as a result of the many possible permutations.
However, the utilisation of mineral fillers and/or glass
fibres is detrimental to surface quality.
Polyamides have long proved valuable in the electrical
sector. The polyamides used in this field of application
are mainly flame-retardant typs.
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The following flame-retardant additives are well known and
are used in polyamides since long time.
R~d 8hos~hoxus (eg DE-A-3 713 746 (= US-4 877 823) and
EP-A 299 444 (= US-5 081 222)) is a flame-retardant agent
normally supplied only in glass fibre-reinforced PA 66 and
6/6T. Such compounds are supplied only in dark colours due
to the reddish brown colour inherent in the phosphorus, and
its pigment-like character. They also have a tendency to
form phosphine and phosphates under the influence of
humidity and heat (as a result of a disproportionation
reaction of the phosphorus). Phosphine causes toxicology
problems and also corrodes the copper-containing contacts
in electrical equipment. Phosphates form conductive
deposits between the electrical contacts. Suitable
stabilisers can retard the disproportionation reaction of
the phosphorus but not suppress it completely.
~) Oryamic hslogen c~~ounds
Brominated diphenyls or diphenylethers combined with
antimony trioxide have long been utilised. Tncreasingly,
use is made of the following halogen compounds:
- chlorinated cycloaliphatic hydrocarbons
(Dechlorane~ plus, ex Occidental Chemical Co)
- brominated styrene oligomers (DE-A-2703419)
- polystyrenes brominated in the nucleus (PYRO-CHEK~
68, ex FERRO Chemicals)
Zinc salts or iron oxides are today utilised as synergist.
The majority of halogen-based flame-retardant agents
themselves begin to undergo decomposition at the
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temperatures of polyamides. Corrosive gases form,
resulting in destruction of the electrical contacts. The
electrical properties of polyamides are, moreover, impaired
by the ion-forming dissociation products.
These disadvantages are an accepted fact when preparing
light-coloured components.
3) NitroQga coaaoounds
Melamine salts have proved to be of value as flame-
retardant agents only where unreinforced polyamides are
involved. Such products are inherently light-coloured and
are possessed of good electrical properties. The
relatively low decomposition temperature of melamine salts
is a disadvantage.
4) Ma~nesiuxn by oxi~d~
Magnesium hydroxide is a known flame-retardant agent for
use with polyolefines and elastomers. Compared with
aluminium hydroxide, used hitherto, it has the advantage of
a higher water dissociation temperature (> 340° C). The
literature contains references describing the utilisation
of magnesium hydroxide in polyamides. However, a quantity
in excess of 55~ is required to achieve a flame-retardancy
rating of V 0 using the Underwrites Laboratories Test
Standard UL 94, at a thickness of 1.6 mm. Processing such
products presents due to the high fillers content lot of
problems. Impact strength, especially in the case of PA 66
are at low level. Beside that very poor surface quality are
obtained.
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CA 02099479 2003-04-08
23189-7523
4
In EP-A-0 335 165
(= US-4 963 610) from 0.1 to 20 wt-% of a functionalised
olefine homopolymer or copolymer and from 3 to 30 wt-% of a
reinforcing fibre are added to polyamide to produce flame-
retardant compounds having from 40 to 70 wt-% of certain
magnesium hydroxide species (specific surface area less
than l8 m2/g). According to this publication, at a
thickness of l.6 mm, a rating of V 0 in accordance with
UL 94 is not achieved with magnesium hydroxide of any other
type and not having olefineic additives. As a result of
coupling of certain polyolefines with polyamide, and the
high content levels; such compounds are very difficult to
process.
The invention provides polyamide moulding compositions which
are free of phosphorus (red) and halogen, but which are
readily workable, and moulded components. therefrom, having,
at a thickness of 1.6 mm, the classification V 0 in
accordance with UL 94, and which additionally exhibit good
mechanical properties and good surfaces.
It has now been found that the properties indicated are
obtained by combining:
from 5 to 30 wt-% of a thermoplastic
polyamide,
from 10 to 30 wt-% of a thermoplastic
partly aromatic
copolyamide,
from 0 to 25 wt-% reinforcements,
CA 02099479 2003-04-08
23189-7523
from 40 to 60 wt-~ magnesium hydroxide,
5 from 0 to 2.0 wt-~ additives, such as
lubricants,
stabilisers and
nucleating agents.
The invention provides flame-resistant polyamide moulding
compositions of
A) from 5 to 30 wt-~, and preferably from 10 to 25 wt-~,
of a thermoplastic, partially crystalline polyamide,
B) from 10 to 30 wt-~, and preferably from 15 to 28 wt -~,
of a thermoplastic, partially crystalline, partly
aromatic copolyamide,
C) from 40 to 60 wt-~ of magnesium hydroxide,
D) from 0 to 25 wt-~, and preferably from 5 to 23 wt-~, of
reinforcements,
E) from 0 to 2 wt-~ workability additives,
the use of the polyamide moulding compositions for the
preparation of moulded bodies and moulded bodies froiri the
moulding compositions according to the invention.
The compositions according to the invention are prepared on
commercial single- or twin-screw extruders or kneaders.
The magnesium hydroxide is dosed into the granulate in the
feed hopper and/or into the polyamide melt through a side
screw. The reinforcements D) (eg glass fibres) are
dispensed into the glass fibre orifice a short distance
upstream of the extruder head, in accordance with prior
art. The temperature of the composition is matched to the
polyamides used and is between 220 and 340° C.
Partly crystalline polyamides (PA), in particular PA 6, PA
66, PA 46, PA 610, PA 6/6T or partially crystalline
copolyamides or mixtures based on these components, are
suitable as thermoplastic polyamide A) of the moulding
compositions according to the invention.
Compounds which are suitable as partly aromatic copolyamide
B) of the moulding compositions according to the invention
are preferably copolyamides of isophthalic acid
hexamethylenediamine and/or terephthalic acid
hexamethylenediamine and caprolactam.
Commercial glass fibres and/or carbon fibres and/or mineral
fibres, optionally with surface treatment for polyamides,
and preferably glass fibres, are used as the reinforcements
D) for the moulding compositions according to the
invention.
Commercial magnesium hydroxide, with or without surface
treatment, is used as magnesium hydroxide C) according to
the present invention. A marked improvement in the
mechanical properties results from surface-treating the
magnesium hydroxide with aminosilanes. Finely-particulate
(diameter: 0.4-l0u) Mg hydroxides may preferably be used
according to the present invention.
The workability additives E) comprise commercial
lubricants, heat stabilisers and/or nucleating agents.
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After premixing, the ingredients were extruded at a
temperature of 290° C in a twin--screw continuous kneader and
compounder, and then granulated. The granulate obtained
was dried at 70° C in a vacuum drying cabinet for
4 h. and then injection-moulded in an Arburg injection
moulding machine at a material temperature of 290° C to form
test pieces.
The mechanical and electrical properties, fire retardancy
in accordance with UL 94 and surface quality were
determined (cf. Tables 1 and 2).
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Table 1
Test 1 2 3 4 5
Compa- Compa-
rative rative
Polyamide 45.4 40.2 19.2 17.0 16.9
6
Copolyamide 0.0~ 0.0~ 26.2 23.2 22.9
of 85 wt-$
polyamide
6
and 15 wt-~
polyamide
6,I
Mg(OA)2 54.5 51.7 54.5 51.7 45.1
Glass fibres 0.0~ 8.0~ 0.0~ 8.0~ 15.0
Amide wax 0.1~ 0.1~ 0.1~ 0.1~ 0.1~
Izod
an[kJ/m2] 23 25 25 25 26
Surface + -- +++ ++ ++
quality
Fireproofing
rating to
Testing Standard
UL 94
at 3.2 mm V 0 V O V O V O V O
1.6 mm V 2 V 0 V 0 V 0 V 0
0.8 mm V 2 V 2 V 2 V 2 V 0
Resistance
4o to glowing
wire ( C) 960 960 960 960 960
Tracking > 600 > 600 > 600 > 600 > 600
resistance
(to IEC 112
or
VDO 303 T1)
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Test 6 7 8 9 10
Compa- Compa-
rative rative
Polyamide 45.4 40.2 19.2 17.0 16.9
66
Copolyamide 0.0~ 0.0~ 26.2 23.25 22.9
of 85 wt-~
polyamide
6
10and 15 wt-~
polyamide
6,I
Mg(OH)2 54.5 51.7 54.5 51.7 45.1
15Glass fibres 0.0~ 8.0~ 0.0~ 8.0~ 15.0
Amide wax 0.1~ 0.1~ 0.1~ 0.1~ 0.1~
Izod
20an[kJ/m2] 16 19 23 26 27
Surface -- -- +++ ++ ++
quality
25Fireproofing
rating to
Testing Standard
UL 94
at 3.2 mm V 0 V 0 V 0 V 0 V 0
30
1.6 mm V 2 V 0 V 0 V 0 V 0
0.8 mm V 2 V 2 V 2 V 2 V 0
35
Resistance
to glowing
wire ( C) 960 960 960 960 960
40Tracking > 600 > 600 > 600 > 600 > 600
resistance
(to IEC 112
or
VDO 303 T1)
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Surface quality was classified as follows:
-- unsatisfactory (discoloured, rough, etc.)
- imperfect
+ satisfactory
++ good
+++ excellent (smooth, uniform colour)
If test pieces from prior art moulding compositions and
those from the special mixtures according to the invention
are compared (Examples 1 with 3, 2 with 4, 6 with 8 and 7
with 9), it will be noted that surface quality increases
markedly in each case. Whereas resistance to a glowing
wire and tracking resistance remain constant, the moulded
pieces according to the invention are placed in the higher
flame-retardant classification, V 0, rather than V 2, in -
accordance with Test Standard UL 94, at a thickness of
1.6 mm.
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