Impact polypropylene

An impact polypropylene composition comprising: PA1 (i) isotactic polypropylene; and PA1 (ii) a copolymer of ethylene and an alpha-olefin comonomer having 3 to 8 carbon atoms, said copolymer (a) having a density of about 0.87 to about 0.90 gram per cubic centimeter and a crystallinity in the range of about 20 to about 35 percent by weight based on the weight of the copolymer and (b) being present in the composition in the range of about 20 to about 50 percent by weight based on the weight of the polypropylene.

TECHNICAL FIELD 
This invention relates to an improved version of impact polypropylene. 
BACKGROUND ART 
Impact polypropylene is widely used in such applications as appliances, 
automobiles, furniture, and luggage. It is generally a blend of isotactic 
polypropylene with ethylene/propylene or ethylene/propylene/diene rubbers 
or a similar combination prepared in situ. The rubber modifier overcomes 
the low temperature brittleness and the lack of impact resistance of the 
isotactic polypropylene. However, when the polypropylene is modified with 
an amorphous rubber, it experiences a severe stress whitening or blush on 
impact, e.g., when an object made of this impact polypropylene is struck, 
a white discoloration appears. This is obviously undesirable as it limits 
the applications of the impact polypropylene. 
DISCLOSURE OF THE INVENTION 
An object of this invention, therefore, is to provide a polypropylene, 
which exhibits much reduced blushing together with high impact resistance. 
Other objects and advantages will become apparent hereinafter. 
According to the present invention, the above object is met by a 
composition comprising the following components: 
(1) isotactic polypropylene; and 
(ii) a copolymer of ethylene and an 
alpha-olefin comonomer having 3 to 8 carbon atoms, said copolymer (a) 
having a density of about 0.87 to about 0.90 gram per cubic centimeter and 
a crystallinity in the range of about 10 to about 30 percent by weight 
based on the weight of the copolymer and (b) being present in the 
composition in a range of about 20 to about 50 percent by weight based on 
the weight of the polypropylene.

DETAILED DESCRIPTION 
Isotactic polypropylene homopolymer can be prepared by the process 
described in U.S. Pat. No. 4,304,891, issued on Dec. 8, 1981, which is 
incorporated by reference herein. The homopolymer preferably has a melt 
flow in the range of about 1 to about 20 and xylene solubles in the range 
of about 2 to about 6. 
The ethylene/alpha-olefin copolymer is the result of the copolymerization 
of ethylene and an alpha-olefin comonomer having 3 to 8 carbon atoms. It 
can be prepared by the processes described in European Patent Applications 
No. 0, 120 501 and 0 120 503, both published on Oct. 3, 1984 and 
incoporated by reference herein. The density of the copolymer is in the 
range of about 0.87 to about 0.90 gram per cubic entimeter. The portion of 
the copolymer attributed to the alpha-olefin comonomer is in the range of 
up to about 40 mole percent based on the total number of moles in the 
copolymer and is preferably in the range of about 7 to about 30 mole 
percent. The balance of the copolymer is based on ethylene. The preferred 
comonomers are propylene, 1-butene, 1-hexene, and 1-octene. The portion of 
the copolymer based on comonomer is in the range of about 15 to about 60 
percent by weight based on the weight of the copolymer, and is preferably 
in the range of about 20 to about 45 percent by weight. These 
ethylene/alpha-olefin copolymers are considered to be soft polymers 
because they are semi-crystalline. The crystallinity is in the range of 
about 20 to about 35 percent by weight. The copolymer has a melt index in 
the range of about 0.1 to about 10 grams per 10 minutes and preferably in 
the range of about 0.3 to about 1.0 gram per 10 minutes. Melt index is 
determined by ASTM D-1238, Condition E. It is measured at 190.degree. C. 
The isotactic polyproplylene and the ethylene/alpha-olefin copolymers are, 
of course, not reactive with one another. 
Subject composition can be prepared either by physical blending or in situ 
incorporation of the copolymer in a polypropylene matrix. The proportion 
of ethylene/alpha-olefin copolymer can be in the range of about 20 percent 
by weight to about 50 percent by weight based on the weight of the 
isotactic polypropylene. 
A typical blending technique is described as follows: isotactic 
polypropylene is mixed (dry) with the ethylene/propylene copolymer and the 
dry mixture is extruded at about 200.degree. C. and pelleted. Conventional 
stabilizers for the isotactic polypropylene and the ethylene/propylene 
copolymers are used. 
A typical in-situ method is carried out in the following manner: isotactic 
polypropylene homopolymer is prepared in one reactor and is transferred to 
another reactor (or reactors) where the ethylene/propylene copolymer is 
produced in the presence of the polypropylene homopolymer. The in-situ 
mixture is taken out of the reactor(s), stabilized, and extruded at about 
200.degree. C. and pelleted. 
Various conventional additives can be added in conventional amounts to 
subject compositions such as antioxidants, ultraviolet absorbers, 
antistatic agents, pigments, dyes, fillers including carbon black, slip 
agents, fire retardants, stabilizers and smoke inhibitors. 
The invention is illustrated by the following examples: 
EXAMPLES 1 to 6 
A polypropylene homopolyer having a melt flow of 4.0 and xylene solubles of 
3.5 is blended with an ethylene/propylene copolymer or an ethylene/-butene 
copolymer wherein the portion of the copolymer based on comonomer, 
propylene or 1-butene, is present in amounts of 25 and 15 percent by 
weight, respectively, based on the weight of the copolymer. The copolymer 
is present in the blend in an amount of 15 to 50 percent by weight based 
on the weight of the polypropylene. The blend is extruded and pelletized 
with the following stabilizers: 0.125 weight percent calcium stearate and 
0.125 weight percent antioxdiant. The pellets are injection molded into 
125 mil specimens for evaluation. 
The Table sets forth the variables, i.e., the weight percent of the 
copolymer based on the weight of the polypropylene; the density of the 
copolymer in gram per cubic centimeter; and the crystallinity in percent 
by weight, and the results. 
The tests used to obtain the results are as follows: 
1. The Gardner Impact (-30.degree. C.) test is carried out according to 
ASTM D-3029. This test involves dropping a weight from a defined height 
onto an injection molded disk, 125 mil thick, which has been 
preconditioned at -30.degree. C. The results are given in inch-pounds 
(inch-lbs). 
2. The 1% SFM (Secant Flexural Modulus) test is carried out according to 
ASTM D-790. The results are given in pounds per square inch (psi). 
3. The blushing (10 lbs) test is carried out as follows: An injection 
molded disk is used. The apparatus is the same as for the Gardner Impact 
test except that the falling weight (a steel bar) is 10 pounds. The steel 
bar is dropped on the disk. The disk is then aged at room temperature for 
24 hours. Stress-whitening or blushing appears on the disk in the form a 
circle. The extent of stresswhitening is defined by the diameter of the 
circle measured in fractions of an inch (in). 
4. Crystallinity is measured by Differential Scanning Colorimeter (DSC) 
using a Dupont 990 analyzer with a pressure DSC cell. 
TABLE 
__________________________________________________________________________ 
% Co- 
Density 
Crystallinity 
Gardner Impact 
1% SFM 
Blushing 
Examples 
Comonomer 
Polymer 
(g/cc) 
(% by wt.) 
(inch-lbs) 
(psi) 
(10 lb)(in) 
__________________________________________________________________________ 
1 propylene 
30 0.86 &lt;2 &gt;320 110,000 
0.63 
2 propylene 
15 0.87 20 20 160,000 
0.5 
3 1-butene 
30 0.87 20 &gt;300 125,000 
0.4 
4 1-butene 
50 0.87 20 &gt;320 86,000 
0.0 
5 1-butene 
30 0.90 35 175 120,000 
0.26 
6 1-butene 
30 0.92 45 20 130,000 
&lt;0.1 
7. 1-butene 
30 0.96 89 &lt;10 186,000 
0.0 
__________________________________________________________________________ 
Melt flow is determined in accordance with ASTM-1638. 
Xylene solubles are defined as the fraction that stays in solution after 
the polypropylene sample is dissolved in hot xylene and the solution is 
allowed to cool to 23.degree. C.