Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
124968S
"Ageing-resistant polyamide blends'i
This invention relates to moulding compositions of
polyamides and grafted acrylates.
Polyamide moulding compositions are distinguished by
the valuable technological properties thereof, such as
rigidity, toughness, resistance to stress corrosion and to
solvents. Unfortunately, the toughness and, in particular
the impact strength of the mouldings obtained from poly-
amide moulding compositions under multiaxial load are
inadequate for numerous applications.
It is known from DE-OS 2,742,176 that the notched
impact strength of polyamides may be considerably increased
by the addition of from 5 to 40%, by weight, of a cross-
linked graft polymer. Cross-linked polybutadienes grafted
with esters of methacrylic acid are recommended as the graft
polymers. The graft polymers are dispersed in the polyamide
moulding with a particle size of greater than 0.1 ~m,
preferably greater than 0.2 ~m.
Graft polymers of polybutadiene as the graft base
degrade on account of the reactive double bonds. Although
polyacrylate-based graft polymers do not have this disadvan-
tage, they are difficult to disperse. Polyamide mouldings
in which the graft polymers are present in particle sizes
of mainly greater than 3 ~m do not show adequate toughness.
Although better dispersion may be obtained by applying in-
tense shear forces, there is a risk in that case of partial
degradation of the polyamide which in turn leads to deter-
ioration of the properties.
In addition, it is known that a rubber homogenously
dispersed in a polyamide matrix tends to agglomerate during
thermoplastic processing, a phenomenon which is more pronoun-
ced in polyacrylate rubbers than in polybutadiene rubbers.
Accordingly, an object of the present invention is
not only to provide mixtures of substantially non-agglomer-
ating polyacrylates characterized by ready dispersibility
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in polyamides, but also to find graft products of which the
particles are capable of withstanding even relatively long
processing times at elevated temperature, as may occur, for
example, during compounding in extruders and in the injection-
moulding of glass-fibre-containing compositions, without an
increase in the size of the particles beyond 3 ~m. This
desirable property is hereinafter referred to in short as
"processing stability".
The mixtures of polyamide and elastomeric polyacrylate-
based graft polymers known from DE-OS 3,200,070 and DE-OS
2,144,528 do not show the desired range of properties.
It has now surprisingly been found that, by graft
polymerization of monomers in the absence of suspending
agents onto the completely broken latex of an acrylate rubber
suspended in water, a powder-form graft polymer is obtained
which may not only be dispersed extremely finely in poly-
amides in the conventional way without particle enlargement,
it also withstands even relatively long processing times at
elevated temperature without particle enlargement.
The expression "dispersed extremely finely or
extremely small particle size" means that the number, shape
and size of the graft polymer particles to be used are still
largely identical with the number, shape and size of the
graft polymer particles introduced into the molten polyamide,
even after homogenization.
Accordingly, the present invention relates to mixtures
comprising:
(A) from 55 to 99%, by weight, preferably from 70 to 98%,
by weight, more preferably from 75 to 97%, by weight,
p~r~,a~onctrh~ehs/ufm; of components (A) and (B) of a
B ~ polyamlde; an
tB) from 1 to 45%, by weight, preferably from 2 to 30%,
by weight, more preferably from 3 to 25%, by weight,
based on the sum of components ~A~ and ~B), of a
powder-form graft polymer comprising:
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(a) from 60 to 98%, by weight, preferably from 70
to 95%, by weight, based on (B), of an acrylate
rubber having a glass transition temperature
below 0C, as determined by shear modulus
measurements, as the graft base; and
(b) from 2 to 40%, by weight, preferably from 5 to
30%, by weight, based on (B), of at least one
ethylenically unsaturated monomer of which the
homo- or co-polymer(s) formed in the absence of
(a) have a glass transition temperature above
25C, as the graft monomer;
characterized in that the graft polymer (B) is obtained by
grafting graft monomers (b) onto the completely broken latex
of (a) suspended in water in the absence of suspending agents.
The powder-form graft polymer (B) obtained may then
be dried and homogenized in the desired ratio with polyamide
(A) in such a way that the average particle size of (B) in
(A) is from 0.05 to 3 ~m, preferably from 0.1 to 2 ~m, more
preferably from 0.1 to 1 ~m.
Suitable polyamides (A) are thermoplastic polyamides~
-partially crystalline polyamides. Particularly
suitable partially crystalline polyamides are polyamides of
which the acid component consists completely or partially of
terephthalic acid andJor isophthalic acid and/or suberic acid
andJor sebacic acid and/or azelaic acid and/or adipic acid
and/or cyclohexane dicarboxylic acid and of which the
diamine component consists completely or partially of m-
and/or p- xylylene diamine and/or hexamethylene diamine andJ
or 2,2,4-trimethylhexamethylene diamine andJor 2,4,4-trimethyl-
hexamethylene diàmine and/or isophorone diamine and of which
the composition is known.
Other suitable polyamides are polyamides produced
completely or partially from C6-C12 lactams, optionally
using one or more of the above-mentioned starting components.
Particularly preferred partially crystalline poly-
amides are polyamide-6, polyamide-66 and corresponding
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copolyamides.
The polyamides should preferably have a relative
viscosity (as measured using a 1%, by weight, solution in
_-cresol at 25C) of from 2.0 to 5.0, more preferably from
2.5 to 4.0
The acrylate rubbers (B) (a) are preferably polymers
of acrylates, optionallv containing up to 40%, by
weight, of other polymerizable, ethylenically unsaturated
monomers. If the acrylate rubbers used as the graft base
(a) are themselves graft products containing a diene rubber
core, the diene rubber core is not included in the calcul-
ation of that percentage. Preferred polymerizable
acrylates include C1-C8 alkyl esters, for example methyl,
ethyl, butyl, octyl and 2-ethyl hexyl esters; halogenated
alkyl esters, preferably halogen C1-C8 alkyl esters, such
as chloroethylacrylate, and aromatic esters, such as
benzylacrylate and phenylethylacrylate. They may be used
either individually or in admixture.
The acrylate rubbers (a) may be uncross-linked,
cross-linked and, preferably, partially cross-linked.
Monomers c.ontaining more than one polymerizable
double bond may be copolymerized for cross-linking.
Preferred examples of cross-linking monomers are esters
of unsaturated monocarboxylic acids containing from 3 to
8 carbon atoms and unsaturated monohydric alcohols
containing from 3 to 12 carbon atoms or saturated polyols
containing from 2 to 4 OH groups and from 2 to 20 carbon
atoms, such as ethylene glycol dimethacrylate, allyl
methacrylate; polyunsaturated heterocyclic compounds, such
as trivinyl and triallyl cyanurate and isocyanurate, tris-
acrylol-s-triazines, more especially triallyl cyanurate;
polyfunctional vinyl compounds, such as di- and tri-vinyl
benzenes; and also triallyl phosphate and diallyl phthalate.
Preferred cross-linking monomers are allyl meth-
acrylate, ethylene glycol dimethacrylate, diallyl phthalate
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and heterocyclic compounds containing at least three
ethylenically unsaturated groups.
Particularly preferred cross-linking monomers are the
cyclic monomers triallyl cyanurate, triallyl isocyanurate,
trivinyl cyanurate, triacryloyl hexahydro-s-triazine, tri-
allyl benzenes.
The cross-linking monomers are preferably used in
quantities of from 0.02 to 5%, by weight, more preferably
from 0.05 to 2%, by weight, based on the graft base (a).
Cyclic cross-linking monomers containing at least
three ethylenically unsaturated groups are advantageously
used in quantities of less than 1%, by weight, based on the
graft base (a).
Preferred "other" polymerizable ethylenically
unsaturated monomers which may optionally be used in
addition to the acrylates in the production of the graft
base (a) are, for example, acrylonitrile, styrene, a-
methylstyrene, acrylamides, vinyl C1-C6 alkyl ethers.
Preferred acrylate rubbers as the graft base (a) are
emulsion polymers which have a gel content of >,60%, by
weight.
The gel content of the graft base (a) is determined
in dimethyl formamide at 25C (M. Hoffmann, H. Kromer,
R. Kuhn, Polymeranalytik I and II, Georg Thieme Verlag,
Stuttgart 1977).
The graft base (a) may also be an acrylate rubber
which accumulates in the form of an aqueous emulsion (latex)
and of which the latex particles contain from 1 to 20%, by
weight, preferably from 1 to 10%, by weight, based on (a),
of monomers already grafted on in aqueous emulsion of which
the homo- or co-polymers have glass temperatures above 0C.
Preferred monomers such as these to be grafted on
are alkyl acrylates, alkyl methacrylates, styrene, acryl-
onitrile, a-methylstyrene and/or vinyl acetate.
The graft bases (a) are produced, for example, by
emulsion polymerization or emulsion graft polymerization.
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However, they may also be obtained by preparing an acrylate
rubber by solution or mass polymerization, subsequently
grafting on the graft monomers and then converting these
rubbers into an aqueous emulsion which is suitable for
further grafting processes.
Acrylate rubbers as the graft base (a) may also be
products which contain a cross-linked diene rubber of one or
more conjugated dienes, such as polybutadiene, or a
copolymer of a conjugated diene with an ethylenically
unsaturated monomer, such as styrene and/or acrylonitrile,
as core.
The graft base (a) may contain from 0.1 to 80%, by
weight, preferably from 10 to 50%, by weight, based on (a),
of the polybutadiene core. The shell and core of the graft
base, independently of one another, may be uncross-linked,
partially cross-linked or highly cross-lin~ed.
Accordingly, preferred graft bases (a) are acrylate
rubbers containing at least 20%, by weight, of acrylate
units which may be selected from the following:
20 (1) polyacrylate homo- and copolymers;
(2) polyacrylate homo- and copolymers containing a
diene rubber core;
(3) emulsion graft polymers of polyacrylate homo- or
copolymers optionally containing a diene rubber core
and ethylenically unsaturated polymerizable monomers.
The grafting yield, i.e. the quotient of the quantity
of monomer (b) grafted on and the quantity of graft monomer
(b) used, generally amounts to from 20 to 80%, by weight.
The grafting yield may be determined as described in M.
Hoffmann, H. Kromer, R. Kuhn, Polymeranalytik, Vol. 1,
Georg Thieme Verlag, Stuttgart 1977.
Preferred graft monomers (b) are ~-methyl styrene,
styrene, acrylonitrile, methyl methacrylate or mixtures of
these monomers. Preferred graft monomer mixtures are
mixtures of styrene and acrylonitrile in a ratio, by weight,
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of from 90:10 to 50:50. The preferred graft monomer is
methyl methacrylate.
The powder-form graft polymers (B) may be prepared
as follows:
First, the monomers of the graft base (a) are polymer-
ized in emulsion in known manner in the presence of radical-
forming initiators so that particles having an average
particle diameter d50 of from 0.05 to 3 ~m are formed. The
monomer mixture may be introduced into the polymerization
system continuously or semi-continuously at the beginning of
or during the polymerization process.
If a cross-linked acrylate rubber containing a cross-
linked diene rubber as core is to be used as the graft base
(a), the diene rubber is first prepared in latex form by
emulsion polymerization of a conjugated diene. The graft
monomers are then emulsified in the diene rubber latex,
again in aqueous emulsion, and the resulting emulsion
polymerized in known manner in the presence of radical-
forming initiators. The thus-formed acrylate rubber shell
may be cross-linked by using cross-linking monomers during
the actual production process.
In this production of a graft base (a) already
partially grafted in emulsion, the formation of new
particles must be prevented as far as possible. An emulsion
stabilizer must be present in a quantity sufficient to
cover the surface of the particles. The size of these
particles may be varied within wide limits according to the
conduct of the reaction. If an agglomerated latex is used
as the polydiene core to obtain large particles, the
acrylate rubber particles may contain several diene rubber
cores. Polymerization of the acrylate rubber may also be
controlled in such a way that acrylate rubber particles
with and without a diene rubber core are formed alongside
one another. In certain circumstances, mixtures of the
type in question may also be used as the graft base (a).
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If an already grafted rubber is to be used as the
graft base (a) an aqueous suspension of that graf`ted rubber
must first be prepared.
After preparation of the graft base (a), the emulsion
is completely broken or coagulated, i.e. by electrolytes,
acids, bases, mechanical forces or temperature. It is
preferred to use aqueous solutions of acids and/or salts at
elevated temperatures, more especially at temperatures of
from 30 to 100C. A heterogeneous suspension of the polymer
in the form of discrete polymer particles of different shape
and size in aqueous phase is obtained in this way. The
particle characteristics may be influenced in the coagulation
medium by variation of the precipitation parameters.
The process is favourably influenced by stirring the
suspensions.
After preparation of the polymer suspension in the
aqueous coagulation medium, the graft monomers (b), option-
ally in combination with regulators, radical initiators
(more especially water-soluble persulphates) or antioxidants
are introduced into the stirred polymer suspension,
preferably at temperatures of from 30 to 100C, and
radically polymerized. The addition of suspension media
should be avoided. The graft polymer (B) is then isolated,
for example by filtration or centrifugation, and subsequently
dried. The process is suitable for batch, semi-continuous
or fully continuous operation.
After isolation and drying, the graft polymers (B) are
storable, free-flowing, non-sticking powders which may
readily be metered by conventional powder metering units for
mixing with the polyamides (A). One particular advantage
lies in the fact that the graft products (B) may readily be
dispersed in the molten polyamide (A) without a need for
intense shear forces to be applied.
If the graft polymers (B) used in accordance with the
present invention contain fractions of polymer formed by
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polymerization of ungrafted parts of the graft monomers (b),
the expression "graft polymer (B)", irrespective of the
degree of grafting, is to be understood to ~ean the sum of
the reaction products formed by polymerization of the graft
monomers (b) in the presence of the graft base (a).
The average particle size d50 is the diameter above
which 50%, by weight, and below which 50%, by weight, of the
dispersed particles lie. It may be determined by ultra-
centrifuge measurements (W. Scholtan, H. Lange, Kolloid. Z.
and Z. Polymere 250 (1972), 782 - 796) or by electron
microscopy and subsequent particle counting (G. Kampf, H.
Schuster, Angew. Makromolekulare Chemie 14, (1970), 111 -
129) or by light scattering measurements.
The expression "in the absence of suspending agents"
used herein means the
absence of substances which are able, depending on quantity
and type, to suspend the graft monomers (b) in the aqueous
phase. This definition does not exclude the presence of
substances which may have had a suspend~nE effect, for
example in the production of a grafted graft base (a). In such
cases, the coagulant or precipitant used to break the latex
(a) has to be used in a quantity which compensates the
suspending effect of the substances used in the initial
stage. In other words, it is important in accordance with
the present invention to ensure that the graft monomers (b)
do not form a (stable) emulsion in the aqueous phase.
The moulding compositions according to the present
invention may contain conventional additives, such as
lubricants and mould release agents, nucleating agents,
stabilizers, fillers and reinforcing materials, flameproof-
ing agents and dyes.
The filled or reinforced moulding compositions may
contain up to 60%, by weight, based on the reinforced
moulding composition, of fillers and/or reinforcing materials.
Preferred reinforcing materials are glass fibres. Preferred
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fillers, which may also have a reinforcing effect, are
glass beads, mica, silicates, feldspar, quartz, talcum,
titanium dioxide, wollastonite.
The flameproofed moulding compositions contain
flameproofing agents in a concentration of generally less
than 30%, by weight, based on the flameproofed moulding
compositions.
The flameproofing agents used may be various known
flameproofing agents, such as cyclic chlorine compounds,
melamine and its salts, such as melamine cyanurate or
melamine sulphate, red phosphorus.
The mixtures of polyamide (A) and graft rubber (B)
may be prepared in conventional mixing units, such as
mixing rolls, kneaders, single-screw and multi-screw
extruders. The temperature prevailing during preparation
of the mixtures should be at least 10C and preferably at
most 90C above the melting point of the polyamide.
Even with low contents of graft polymer (B), the
mixtures according to the present invention are distin-
guished by a considerable improvement in impact strengthunder multiaxial load, even where polyamides of relatively
low molecular weight are used. Another surprising property
of the mixtures is the high flow line resistance thereof.
In addition, they are distinguished by high dimensional
stability under heat and by surprisingly high resistance
to ageing in hot air.
Commensurate with this range of properties, the
mixtures according to the present invention may be used
anywhere in the injection moulding and extrusion field
where high multiaxial toughness in combination with high
dimensional stability under heat and resistance to hot air
is required, as is the case for example with parts of
mechanical and electrical units in the engine compartment
of motor vehicles and with temperature-stressed domestic
appliances.
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In the following Examples, the parts are parts, by
weight, and the percentages percentages, by weight.
EXAMPLES
1. Production of the graft base (a)
1.1 Production of a polybutadiene latex
In a reactor, the following emulsion was polymerized
while stirring at 65C until the monomers had reacted almost
completely (approx. 22 hours):
100 parts of butadiene
1.8 parts of the sodium salt of disproportionated
abietic acid,
0.257 part of sodium hydroxide,
0.3 part of n-dodecyl mercaptan,
1.029 parts of sodium ethylene diamine tetraacetate,
0.023 part of potassium persulphate and
176 parts of water.
A latex is obtained which contains polybutadiene particles
having an average diameter (d50) of 0.1 ~m in a concen-
tration of approx. 36%.
1.2 Production of acrylate rubber containing polydiene cores
The following mixture is introduced into a reactor
with stirring at 63C:
200 parts of latex 1.1,
5000 parts of water,
14 parts of potassium persulphate,
0.0124 part of triallyl cyanurate and
30 399.09 part of n-butylacrylate.
The following mixtures are separately introduced
into the reactor over a period of 5 hours at 63C:
Mixture 1: 90 parts of sodium C14-C18 alkyl
sulphonate and
11900 parts of water.
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Mixture 2: 23.09 parts of triallyl cyanurate and
10101 parts of n-butylacrylate.
Polymerization is then completed over a period of 2 hours at
65C. The polymers formed have gel contents of from 85 to
95% and average particle diameters (d50) of 0.5 ~m (polymer
content in the latex: 38%).
2. Production of the graft polymers (B)
2.1 Graft polymer of 80% of acrylate rubber 1.2 and 20% of
methyl methacrylate
18800 parts of water and
245 parts of magnesium sulphate (MgS04 . xH20)
are introduced into a reactor at 70C. 11200 parts of latex
1.2 are then run into the reactor with stirring over a
period of 2 hours.
After this addition, 1 part of potassium persulphate
is introduced into the reactor. 1276 parts of methyl
methacrylate are then uniformly introduced with stirring
over a period a 1 hour. Thereafter, the suspension is
stirred for 1 hour at 90C. The polymer may then be
isolated (graft polymer K).
3. Production of the graft polymers (B) containing remains
of monomers (b) grafted both in emulsion and also in
suspension
3.1 Production of the emulsion graft polymers
3.1.1 Emulsion graft polymer of 80% of acrylate rubber 1.2
and 20% of methyl methacrylate.
30 2926 parts of latex 1.2,
1.5 parts of potassium persulphate and
90 parts of water
are introduced into a reactor. The following mixtures are
separately introduced into the reactor at 65C:
Mixture 1: 278 parts of methyl methacrylate
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Mixture 2: 150 parts of water and
4 parts of sodium C~4 C18 alkyl
sulphonate
Polymerization is then completed over a period of 4 hours
at 65C (graft polymer L). Polymer content in the
latex: 37.8%.
3.1. 2 Emulsion graft polymer of 80% of acrylate rubber 1.2,
14.4% of styrene and 5. 6% of acrylonitrile
The prodcedure is as in Example 3.1.1, except that a
mixture of 77 parts of acrylonitrile and 201 parts of
styrene is introduced as mixture 1 instead of methyl
methacrylate (graft polymer M)
3.2 Production of the graft polymers (B) from the emulsion
graft polymers
3. 2.1 Graft polymer of 70% of acrylate rubber and 30% of
methyl methacrylate
20 18800 parts of water and
240 parts of magnesium sulphate
are introduced into a reactor at 70C. 11200 parts of latex
3.1.1 (graft polymer L) are run into the reactor with
25 stirring over a period of 2 hours. After the addition,
1 part of potassium persulphate is introduced into the
reactor. 529 parts of methyl methacrylate are then
uniformly introduced with stirring over a period of 1 hour,
after which the suspension is stirred for 1 hour at 90~C.
30 The polymer is then isolated (graft polymer ~).
3.2.2 Graft product of 70% of acrylate rubber, 21.6% of
styrene and 8.4% of acrylonitrile
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The procedure is as in Example 3.2.1, except that latex
3.1.2 containing graft polymer ~ is used instead of latex
- 3.1.1 and a mixture of :
148 parts of acrylonitrile and
381 parts of styrene
is incorporated instead of methyl methacrylate (graft
polymer 0).
4. Production of comparison graft polymers
Graft polymer, type NP
A copolymer of a graft base of :
69.45 parts of n-butylacrylate,
0.35 part of 1,3-butylene diacrylate and
0.28 part of allyl methacrylate
and a graft shell of
19.95 parts of methyl methacrylate and
9.97 parts o~ allyl methacrylate
(corresponding to DE-OS 2,726,256).
5. Production of the mixtures
The following polyamides were melted in a Werner &
Pfleiderer continuous-action twin-screw extruder:
Type Q: polyamide-6 having a relative viscosity (as
measured using a 1%, by weight, solution in m-
cresol at 25C) of 3.5
Type R: polyamide-66 having a relative viscosity (as
measured using a 1%, by weight, solution in m-
cresol at 25C) of 3.5.
The graft polymer (B) was introduced into the polyamide
melt under nitrogen through a second feed inlet and homo-
geneously dispersed in the melt. (It may be advantageous
to degas the melt before it issues from the die.) The
barrel temperatures were selected in such a way that a melt
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temperature of 275 C was guaranteed. The melt strand of
the mixtures according to the present invention was cooled
in water, granulated and dried. Standard small test bars
tcorresponding to DIN 53 453) and plates measuring 3 x 60 x
60 mm were produced from the granulate in a conventional
injection moulding machine at mould temperatures of 80C.
The test specimens were used for testing impact
strength and notched impact strength (in accordance with
DIN 53 543), ball indentation hardness (in accordance with
DIN 53 456), Vicat dimensional stability under heat (in
accordance with DIN 53 460) and also impact strength under multi-
axial load using the so-called EFDR test (according to
DIN 53 443, page 2, penetration of a 3 x 60 x 60 mm plate
under a weight of 35 kg by a spherically tipped spike 20 mm
in diameter dropped from a height of 1 m). Flow line
resistance was tested in accordance with DIN 52 455 (tension
test) using tension bars injected at either end. The
results are shown in the following Table.
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