High impact resistant polyamide

High impact resistant polyamide resins containing a polyamide matrix comprising at least one amorphous polyamide and dispersed particles of a toughener formed of a blend of ethylene, propylene, diene monomer rubber containing grafted succinic anhydride groups and an ionomer derived from ethylene, an alkyl acrylate and acrylic acid or methacrylic acid. The toughener has a particle size of less than about 360 nm, as determined by a small angle x-ray scattering technique. The toughener is present in the resin in the amount of at least 15% by weight.

FIELD OF THE INVENTION 
This invention relates to polyamide resins that have high impact resistance 
at low temperatures. More particularly, this invention relates to 
amorphous polyamides that contain at least a particular amount of 
dispersed toughener particles of two particular groups of chemical 
compositions and have a particle size of less than about 360 nm as 
determined by the small angle X-ray scattering technique disclosed. 
BACKGROUND 
Toughened nylon compositions are commercial high volume products. Such 
compositions contain a continuous nylon phase and a dispersed toughener 
phase. Such compositions are disclosed in Epstein, U.S. Pat. No. 4,174,358 
dated Nov. 13, 1979. 
The present invention is an improvement over the compositions disclosed in 
the Epstein patent, in that it has been found that certain amorphous 
nylons, when toughened with a combination of certain specific tougheners, 
in certain specific amounts, and the tougheners exist in the amorphous 
nylon as particles having a particle size of less than about 360 nm, yield 
fabricated parts having higher impact resistance at room temperature than 
those previously known. 
SUMMARY OF THE INVENTION 
The present invention is a thermoplastic composition consisting essentially 
of an amorphous polyamide matrix resin and a blend of ionomer and 
copolymer particles dispersed in the polyamide matrix resin. The polyamide 
must be of high molecular weight and have an apparent melt viscosity of 
3000 poise or more, when measured on a sample that contains no more than 
0.15% by weight water, the measurement being made at 280.degree. C. and at 
a shear ratio of about 100 sec.sup.-1. The amorphous polyamide must be 
present in the composition in the amount of about 75% to 85% by weight of 
the composition. The blend of ionomer and copolymer particles that are 
dispersed (substantially uniformly throughout the amorphous polyamide) 
have a particle size such that when the small angle X-ray procedure 
described herein is applied to a sample of the polymer a particle diameter 
less than about 360 nm is obtained. The implications of the procedure are 
that this represents a log-normal distribution where one-half the mass of 
the particles have a diameter less than about 360 nm. The copolymer in the 
copolymer particles has a Mooney viscosity of between about 40 and about 
66. The composition of the copolymer particles is either (a) 63 to 73% by 
weight ethylene, 24 to 30% by weight propylene, 3.0 to 6.5% by weight 
hexadiene, and 0 to 0.5% by weight norbornadiene containing succinic 
anhydride groups grafted thereto in the amount of 0.25 to 2.25% by weight 
of the copolymer, or (b) mixtures of at least 35 weight percent (a) and up 
to 65 weight percent of the copolymers of (a) which do not have succinic 
anhydride groups grafted thereto. The copolymer is present in the 
composition in the amount of from 4 to 20% by weight of the composition. 
The ionomers useful in the present invention are terpolymers containing 
from 40 to 93 wt. % ethylene, from 5 to 60 wt. % of an acrylate of the 
formula 
##STR1## 
wherein --R is an alkyl group containing 2 to 10 carbon atoms, --R' is --H 
or --CH.sub.3 and from 2 to 20 wt. % acrylic acid or methacrylic acid. The 
preferred ionomers contain from 70 to 85 wt. % ethylene, 10 to 20 wt. % of 
the above defined acrylate and 5 to 15 wt. % acrylic acid or methacrylic 
acid. The ionomer particles are present in the amount of from 5 to 21% by 
weight of the composition. The copolymer and ionomer particles in some of 
the compositions of the invention are present in amounts such that their 
weight plus the weight of the amorphous polyamide polymer combine to make 
100% of the thermoplastic components of the compositions of the invention. 
The compositions of the invention may contain various fillers, reinforcing 
ingredients such as glass fibers, pigments, stabilizers, mold release 
agents, antistatic agents and the like all of which are known to those 
skilled in the art. 
DETAILED DESCRIPTION 
The thermoplastic amorphous polyamides are obtained from at least one 
aromatic dicarboxylic acid containing 8-18 carbon atoms and at least one 
diamine selected from the class consisting of (i) 4-12 carbon normal 
aliphatic straight-chained diamine, and (ii) 8-20 carbon cycloaliphatic 
diamines containing at least one cycloaliphatic ring. 
Preferred diacids are isophthalic and terephthalic acids. Especially 
preferred are mixtures containing 60 to 70 mole % isophthalic acid and 40 
to 30 mole % terephthalic acid. 
Preferred diamines are hexamethylenediamine and 
bis(p-aminocyclohexyl)methane (M, hereinafter). M is available as a 
mixture of three stereoisomers--cis, cis; cis, trans; and trans, trans. 
Any isomer mixture can be used. Especially preferred are mixtures 
containing up to 10 mole % M isomers and 90 to 100 mole % 
hexamethylenediamine. 
Amorphous polyamides prepared from the especially preferred mixtures of 
diacids and the especially preferred mixtures of diamines have glass 
transition temperatures above 120.degree. C. 
Amorphous polyamides will generally have no distinct melting point and a 
heat of fusion of less than 1 cal/gram. The heat of fusion is conveniently 
determined by use of a differential scanning calorimeter (DSC). A suitable 
calorimeter is The Du Pont Company's 990 thermal analyzer, Part No. 990000 
with cell base II, Part No. 990315, and DSC cell, Part No. 900600. With 
this instrument, heat of fusion can be measured at a heating rate of 
20.degree. C. per minute. The sample is alternately heated to a 
temperature above the anticipated melting point and cooled rapidly by 
cooling the sample jacket with liquid nitrogen. The heat of fusion is 
determined on any heating cycle after the first and should be a constant 
value, within experimental error. 
The apparent melt viscosity of the polyamides at 280.degree. C. was 
determined by standard techniques with a capillary rheometer (typically 
with 0.0205 inch orifice diameter, 14.68/1 L/D ratio, and 0.3747 inch 
piston diameter). 
The toughened products claimed in this patent may be obtained from 
amorphous polyamides with an apparent melt viscosity of 3000 poise or more 
at 280.degree. C. and a shear rate of 100 sec.sup.-1 when the polyamides 
contain 0.15% or less water. 
The toughened products of this invention may be obtained from amorphous 
polyamides with quite high melt viscosity, for example, a melt viscosity 
of 20,000 poise at 280.degree. C., 100 sec.sup.-1 shear rate, and 0.05% 
water. The upper limit of the polyamide melt viscosity is dictated by the 
ability of the final processing equipment to fabricate articles from high 
viscosity melts. Those skilled in the art will recognize that materials 
with comparatively high melt viscosity are desirable in extrusion and blow 
molding applications while products with lower melt viscosities might be 
desirable for the injection molding of complicated parts. 
The copolymers present in the dispersed particles in the composition of the 
present invention are either (a) copolymers containing 63 to 73% by weight 
ethylene, 24 to 30% by weight propylene, 3.0 to 6.5% by weight hexadiene, 
and 0 to 0.5% by weight norbornadiene having a Mooney viscosity of 40 to 
60, and grafted with succinic anhydride groups so that the copolymer 
contains 1.5 to 2.0% by weight succinic anhydride groups, or (b) mixtures 
of (a) with ungrafted copolymers of (a), such mixtures containing at least 
about 35% by weight of (a). Processes for the preparation of such grafted 
copolymers are known in the art. A suitable process is disclosed in 
Caywood, U.S. Pat. No. 3,884,882. 
The ionomers useful in the present invention are terpolymers containing 
from 40 to 90 wt. % ethylene, from 8 to 60 wt. % of an acrylate of the 
formula 
##STR2## 
wherein --R is an alkyl group containing 2 to 10 carbon atoms, --R' is --H 
or --CH.sub.3 and from 2 to 20 wt. % acrylic acid or methacrylic acid. The 
acid groups are from 0 to 100% neutralized with metal ions. (As used 
herein the term "ionomer" includes the unneutralized acid copolymer.) The 
preferred metal ions are Zn.sup.++, Mg.sup.++, Al.sup.+++, Ca.sup.++, 
K.sup.+, Na.sup.+ and Li.sup.+. Especially preferred is Zn.sup.++ or 
Zn.sup.++ containing up to 50% based on Zn.sup.++ of Na+. The base 
terpolymer prior to neutralization with metal ions should have a melt 
index of 1.0 to 100 g/10 min. as determined by ASTM-D-1238-52T. The 
ionomers are prepared as described in Rees U.S. Pat. No. 3,264,272. The 
ionomer particles generally will comprise from 5 to 21% by weight of the 
composition. 
The compositions of this invention may be prepared by mixing preweighed, 
blended quantities of the amorphous polyamides, the ionomer and the 
copolymers (tougheners) in the molten state under high shear. Such mixing 
can be accomplished in commercially available equipment such as a 53 mm 
twin-screw extruder manufactured by Werner & Pfleiderer Corporation. A 
satisfactory screw design for an 1860 mm long screw includes mixing 
elements 750 mm and 1390 mm from the feed end of the screw. Barrel heaters 
may be set at 260.degree.-275.degree. C. A vacuum port may be used near 
the die. Screw speeds of 200-250 rpm and extrusion rates of 120-230 pph 
afford the compositions of this invention with melt temperatures of 
310.degree. to 340.degree. C. measured on the molten strand exiting the 
die. The strands are quenched in water and pelletized. The pellets are 
dried to a moisture content of 0.15% by weight or less prior to final 
processing (e.g., injection molding, blow molding, extrusion). 
The copolymer and ionomer particles in the compositions of this invention 
must have a particle size such that when the small angle x-ray procedure 
described herein is applied to a sample of the polymer a particle diameter 
less than about 360 nm is obtained. The implications of the procedure are 
that this represents a log-normal distribution where one-half the mass of 
the particles have a diameter less than about 360 nm. The particle size 
distribution in the compositions of the invention is affected by the 
following factors: the viscosity of the polyamide, the viscosity of the 
copolymer, the amount of shear applied in mixing the polyamide and the 
copolymer, and the mixing temperature. Thus, by using a high viscosity 
polyamide, low viscosity copolymer and ionomer coupled with a large amount 
of shear during mixing and a low mixing temperature, the desired particle 
size distribution can be readily achieved. 
The concentrations for the ingredients in toughened amorphous polyamides 
are from 4-20 weight % copolymer 5-21 weight % ionomer (tougheners) and 
85-75 weight % amorphous polyamide. Lower concentrations of the copolymer 
and ionomer (tougheners) afford products with inadequate low temperature 
toughness. Higher loadings of copolymer and ionomer (toughener) give 
products with inadequate tensile strength and stiffness for most uses. 
Especially preferred concentrations of the ingredients in the toughened 
products are 8-12 weight % copolymer 6-12 weight % ionomer (tougheners) 
and 85-78 weight % amorphous polyamide. 
The particle size is determined by small-angle x-ray scattering, according 
to the following technique: The small-angle x-ray scattering (SAXS) data 
should be acquired on a high-resolution instrument such as the one 
originally designed by Bonse and Hart Zeit. fur Physik, 189, 151 (1966), 
and subsequently manufactured commercially by Advanced Metals Research 
Corporation, Burlington, Mass., as the AMR Model 6-220 X-Ray Low Angle 
Scattering Goniometer. A suitable sample of amorphous polyamide containing 
dispersed copolymer particles consists of a molding (generally an 
injection-molded tensile or flex bar) of such thickness as to transmit 
about 1/e (1/2.71828 or 0.368) of a CuK.alpha. (wavelength=0.1542 nm) 
x-ray beam. This is the optimum thickness for transmission data (data 
acquired when the x-ray beam passes through the thickness of the sample 
along the surface normal), and is generally of the order of 80 mils (0.08 
inches or about 2 mm) for a typical sample. A typical molding is usually 
too thick (1/8 inch or greater) but can be thinned by sawing or milling. 
Scattered x-ray intensity data are acquired in the range from 8 to 600 
seconds of arc (2-theta). The AMR instrument is calibrated in seconds; 
this corresponds to 0.002.degree. to 0.16.degree. or 4.times.10.sup.-5 to 
3.times.10.sup.-3 radians. Appropriate step sizes range upwards from 2 
seconds of arc as the scattering angle increases; 20 points each at 
step-sizes of 2, 4, 8, and 16 seconds will cover the angular range in 81 
points. These are "slit-smeared" results, and, after smoothing and 
subtraction of instrumental background, should be "desmeared" before 
interpretation. For this work, the data are desmeared by the method of 
Schmidt and Hight, Acta Cryst., 13,480 (1960); P. W. Schmidt, Acta Cryst., 
19,938 (1965) to cover the range from 0.005.degree. to 0.07.degree. 
2-theta. (The experimental angular range from 0.07.degree. to 0.16.degree. 
of the observed data is required only to desmear the retained results 
below 0.07.degree.). The desmeared intensity results can be represented as 
I(h), where (h=4.pi. sin .theta.)/.lambda.=.times.2.theta.. Here, 
.theta.=(2.theta.)/2 and sin .theta.)=.theta. in radians at these small 
angles) and .lambda.=the wavelength of CUK.alpha. radiation. These 
intensity results are converted to the "Invariant" argument, h.sup.2 I(h), 
by multiplying each desmeared intensity by the square of the angle of 
observation for that point. 
A plot of the invariant argument will be characterized by having a maximum 
at an angle below 0.04.degree. 2-theta if the dispersed particles causing 
the scattering have diameters of the order of hundreds of nanometers. If 
the particle-size distribution is narrow (nearly monodisperse), the 
particle diameter is inversely proportional to the position of this 
maximum: diameter=4.87/2.theta..degree..sub.max nm. If there is finite 
breadth to the distribution, the peak position will be shifted to lower 
angles and the breadth of the distribution must be taken into account. For 
the results cited here, the observed invariant-argument curves were 
matched to calculated curves derived assuming a model of a log-normal 
particle-size distribution. For typical distributions, the most probable 
particle size is of the order of 2/3 to 3/4 that calculated on the basis 
of the peak position of the invariant argument alone. 
In order to characterize a particle-size distribution in the manner 
employed here, two measurements are made on the invariant-argument curve. 
The angular position (2-theta), h.sub.m, of the maximum is determined and 
the angular position of the "half-height" h.sub..lambda., is determined. 
The half-height is that point on the invariant-argument curve which has an 
ordinate one-half that of the maximum and is on the high-angle side of the 
maximum. Given a log-normal model, the breadth of the distribution, 
expressed in relative terms, is a function only of the ratio, R.sub.h, of 
these two angles: R.sub.h =h.sub.h /h.sub.m. (R.sub.h should have a value 
greater than about 1.57. If it is significantly less than this, the 
position of the maximum of the curve has probably been displaced to higher 
angles by interparticle interference arising from close, regular packing 
of the particles.) 
A log-normal distribution can be characterized by R.sub.S, the ratio of the 
size at one-sigma of the distribution to the size at the center. For this 
work, an expression for R.sub.S was determined from R.sub.h, by a third 
order polynomial regression fit to computer-generated data. This equation 
is: R.sub.S =1.19056+1.84535R.sub.h -0.33524R.sub.h.sup.2 
+0.030186R.sub.h.sup.3 (Note that when R.sub.h =1.5728+, R.sub.s =1.00 and 
the distribution is monodisperse. An R.sub.s of less than 1.0 has no 
physical meaning.) 
For each distribution ratio, R.sub.S, there is a factor, F, which can be 
used to correct the apparent size derived from the position of the 
invariant maximum corresponding to a monodisperse "distribution". Again, a 
third order polynomial fit was determined from a computer-generated model: 
F=1.48725-0.42839R.sub.S -0.062415R.sub.S.sup.2 +0.022482R.sub.S.sup.3. 
The scattering curve from monodisperse spherical particles can be 
approximated at a very low angles by I(h)=K exp (-h.sup.2 
R.sub.o.sup.2)/3. (See A. Guinier & G. Fournet, Small-Angle Scattering of 
X-Rays, John Wiley & Sons, Inc., New York (1955) page 25), where R.sub.o 
is the radius of gyration. The invariant argument is then k h.sup.2 exp 
(-h.sup.2 R.sub.o.sup.2)/3. From the differentiation of this expression, 
the condition for the maximum, h.sub.m, is: 
##EQU1## 
Substituting for h.sub.m =(2.pi..multidot.2.theta..sub.m)/.lambda., 
##EQU2## 
where .lambda.(CuK.alpha.)=0.15418 nm, R.sub.o =0.042502/2.theta..sub.max 
if 2.theta. is in radians, R.sub.o =2.4352/2.theta..sub.max if 2.theta. is 
in degrees. For the approximation used in this work, the exponential 
(Gaussian) fit does not extend to angles as high as represented by the 
maximum of the invariant argument, and a better approximation is given by: 
R.sub.o =2.182/2.theta..sub.max where 2.theta. is in degrees. Since the 
diameter of a sphere, D, as a function of the radius of gyration, R.sub.o, 
is: 
##EQU3## 
then D.sub.m (nm)=5.6339/2.theta..sub.max (deg)D.sub.m is the diameter of 
a particle in a monodisperse "distribution", where all the particles are 
the same size. When there is a finite distribution of sizes modeled as 
described above, then the characteristic diameter, D.sub.c, is derived 
from D.sub.m as: D.sub.c =F*D.sub.m. 
In the compounds of the present invention the characteristic diameter, 
D.sub.c, is no greater than about 360 nm. 
The composition of the invention may be fabricated into high impact parts 
such as automobile body parts, for example bumpers, fender extensions and 
the like by injection molding, blow molding, extrusion and other similar 
techniques. 
The composition of the invention include blends of two or more different 
amorphous polyamides or blends of crystalline polyamide and amorphous 
polyamide with the tougheners disclosed. 
In the Examples which follow yield strength and elongation at break were 
determined according to ASTM D-638. Flexural modulus was determined 
(1/4-inch specimens) according to ASTM D-790. Notched Izod impact 
(1/4-inch specimens) was determined according to ASTM D-256. The type of 
specimen break is noted in the examples and conforms to definitions in 
ASTM D-256, namely: 
C=complete break--wherein the specimen separates into two or more pieces 
P=partial break--an incomplete break that is not a hinge break but has 
fractured at least 90 percent of the distance between the vertex of the 
notch and the opposite side 
N=non-break--an incomplete break where the fracture extends less than 90 
percent of the distance between the vertex of the notch and the opposite 
side 
M=mixed breaks--some of the samples have complete breaks and some of the 
samples have partial breaks.