Process for cold forming propylene copolymers

A process for the solid phase forming of an impact polypropylene copolymer comprising (a) providing an impact polypropylene copolymer comprising (i) a matrix, which is either a homopolymer of propylene or a copolymer of propylene and up to about 5 percent by weight of at least one other alpha-olefin based on the weight of the copolymer, and, incorporated into said matrix, (ii) a copolymer of ethylene and at least one other alpha-olefin, said copolymer having a crystallinity of at least about 20 percent and being present in the impact copolymer in an amount of at least about 10 percent by weight based on the total weight of the impact copolymer; and (b) forming the impact polypropylene copolymer at a temperature above the melting point of component (ii) but below the melting point of component (i).

TECHNICAL FIELD 
This invention relates to a process for cold forming propylene copolymers. 
BACKGROUND INFORMATION 
Cold forming (or solid phase forming) is commonly used to fabricate 
finished articles from sheet or other fabricated preforms at temperatures 
below the melting point of the preform material. A common example is the 
stamping of steel sheet to produce automobile body components. The same 
process is used commercially to finish polymers such as polypropylene 
and/or impact polypropylene copolymers. 
The major problem associated with the cold forming or stamping of polymers 
is the tendency of a formed part to return to its original shape over 
time, especially when subjected to elevated temperatures. This is 
obviously undesirable since the desired part geometry is altered. Two 
other problems associated with the cold forming of polymers is (i) uneven 
deformation during forming resulting in variations in wall thickness or, 
in severe instances, tearing of the preform material, and (ii) poor 
definition of formed part details. 
These problems may be alleviated by performing the forming operation at 
elevated temperatures just below the melting point of the polymer. 
However, at these high temperatures, the polymer often becomes difficult 
to handle. In the case of sheet, sagging or deformation under its own 
weight is a problem. A further drawback is that precise temperature 
control is required at the higher temperatures. Use of high temperatures 
also necessitates longer cycle times. Thus, it is desirable to form 
polymer well below its melting point. 
DISCLOSURE OF THE INVENTION 
An object of this invention, therefore, is to provide a process for the 
forming of impact polypropylene copolymer at temperatures below its 
melting point, which gives rise to a dimensionally stable and evenly 
formed product of good definition. Other objects and advantages will 
become apparent hereinafter. 
According to the present invention, the above object is met by a process 
for the manufacture of a shaped article which comprises cold forming an 
impact copolymer composition comprised of: 
a. at least ten percent (10%) by weight of the total composition of an 
interpolymer of ethylene and one or more other alpha-olefins, having a 
crystallinity of at least about twenty percent (20%), incorporated into: 
b. a matrix which is either a homopolymer of propylene or an interpolymer 
of propylene and one or more other alpha olefins; 
at a temperature above the melting point of said interpolymer of ethylene 
and below the melting point of said homopolymer or interpolymer of 
propylene.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
For applications requiring a high level of low temperature impact strength, 
so-called "impact polypropylene copolymers" are used. These polypropylene 
copolymers are usually manufactured by the incorporation of an elastomeric 
impact modifier, e.g., an ethylene/propylene copolymer rubber (EPR), into 
a homopolymer matrix either by blending the homopolymer with the EPR or by 
producing the copolymer in-situ. 
A typical process for the preparation of impact polypropylene copolymers 
comprises the following steps: 
(a) contacting a sufficient amount of propylene or propylene and at least 
one other alpha-olefin, preferably having 2 or 4 to 8 carbon atoms, to 
provide a copolymer having up to about 5 percent by weight of the other 
alpha-olefin based on the weight of the copolymer, and hydrogen, under 
polymerization conditions, with a catalyst comprising (i) a catalyst 
precursor, which includes titanium, magnesium, chlorine, and an electron 
donor; (ii) a hydrocarbylaluminum cocatalyst; and (iii) a selectivity 
control agent, which is different from the electron donor, in a first 
reactor in such a manner that a mixture of a homopolymer of propylene or a 
copolymer of propylene and alpha-olefin together with active catalyst is 
produced; 
(b) passing the mixture from step (a) into a second reactor; and 
(c) adding to the second reactor: 
a sufficient amount of ethylene and at least one other alpha-olefin, 
preferably alpha-olefins having 3 to 8 carbon atoms, to provide an 
ethylene/alpha-olefin copolymer having an ethylene content of at least 
about 85 percent by weight based on the weight of the copolymer, and 
hydrogen. 
The process steps and conditions and the catalyst used in each reactor can 
be the same as those described in U.S. Pat. No. 4,414,132 or U.S. patent 
application Ser. No. 051,853 filed on May 19, 1987, and the reactors are 
preferably gas phase reactors such as the fluidized bed reactor described 
in U.S. Pat. No. 4,482,687. 
The atomic or mole ratios of catalyst components are generally as follows: 
______________________________________ 
Ratio Broad Range 
Preferred Range 
______________________________________ 
Mg to Ti 1:1 to 50:1 
3:1 to 30:1 
Cl to Mg 1:1 to 5:1 2:1 to 3:1 
Mg to electron donor 
0.1:1 to 100:1 
1:1 to 60:1 
Cocatalyst to Ti 
5:1 to 300:1 
20:1 to 100:1 
Cocatalyst to selec- 
0.1:1 to 100:1 
0.2:1 to 50:1 
tivity control agent 
______________________________________ 
The polymerization can be conducted using gas phase, slurry, or solution 
processes; however, the polymerization in the second reactor is preferably 
carried out in the gas phase. For gas phase polymerizations, fluidized bed 
reactors are the reactors of choice. With respect to fluidized bed 
reactors, U.S. Pat. No. 4,482,687 is mentioned above. 
The fluidized bed reactors are generally operated at a temperature in the 
range of about 40.degree. C. to about 150.degree. C. and preferably about 
60.degree. C. to about 120.degree. C. and a pressure of about 50 psig to 
about 700 psig and preferably about 250 psig to about 550 psig. The 
velocity of the fluidizing gas can be in the range of about 0.1 to about 
3.0 feet per second and is preferably about 0.5 to about 2.0 feet per 
second. The weight flow ratio of monomer to catalyst in the first reactor 
can be about 1000:1 to about 100,000:1 and is preferably about 10,000:1 to 
about 100,000:1. 
As noted above, propylene or a mixture of propylene and at least one 
alpha-olefin are introduced together with hydrogen and catalyst into the 
first reactor. The alpha-olefin components can be, for example, ethylene, 
1-butene, 1-hexene, 4-methyl-1-pentene, or 1-octene, or various mixtures 
of alpha-olefins. The mole ratio of alpha-olefin to propylene can be about 
0.01 to about 0.06 and, preferably, is about 0.015 to about 0.04. The mole 
ratio of hydrogen to propylene alone or combined propylene and 
alpha-olefin can be in the range of about 0.001 to about 0.45 and is 
preferably about 0.004 to about 0.1. In the case of propylene and 
alpha-olefin, sufficient amounts of comonomers are used to provide a 
copolymer having up to about 5 percent by weight alpha-olefin based on 
the weight of the copolymer, and preferably about 0.1 to about 2 percent 
by weight alpha-olefin. 
The combination of components and conditions, previously mentioned, leads 
to a mixture of homopolymer or copolymer of propylene together with active 
catalyst embedded in the polymer matrix. This mixture from the first 
reactor is transferred to the second reactor to which additional catalyst, 
cocatalyst, and selectivity control agent can be added although it is 
preferred that only cocatalyst be added to the second reactor. For some 
catalysts, none of these three components need be added. 
In the second reactor, ethylene and alpha-olefin, usually propylene can be 
introduced in a mole ratio of about 10 to about 100 moles of ethylene per 
mole of alpha-olefin, i.e., total alpha-olefin other than ethylene. A 
preferred ratio is in the range of about 10 to about 50 moles of ethylene 
per mole of alpha-olefin. The goal is to provide a copolymer of ethylene 
containing at least about 85 percent by weight ethylene based on the 
weight of the copolymer and preferably about 90 to about 99 percent 
ethylene, and having a crystallinity in the range of about 20 to about 60 
percent, preferably about 35 to about 50 percent. The percent 
crystallinity attributed to the copolymer fraction can be calculated from 
the weight fraction of second reactor product and the measured heat of 
fusion required to melt the copolymer fraction as determined by 
differential scanning calorimetry (DSC). The combined 
ethylene/alpha-olefin addition is preferably sufficient to provide a 
copolymer fraction of about 10 to about 50 percent by weight of copolymer 
based on the weight of the product, and most preferably a copolymer 
fraction of about 20 to about 35 percent by weight. Hydrogen is also 
introduced into the second reactor together with the ethylene and 
alpha-olefin. The mole ratio of hydrogen to combined ethylene and 
alpha-olefin is about 0.1 to about 1.0 and is preferably about 0.1 to 
about 0.4. It should be noted that some or all of the alpha-olefin in the 
second reactor can come from the first reactor. The two reactors are 
operated continuously, in series. The product is an ethylene/alpha-olefin 
copolymer incorporated into a matrix of propylene homopolymer or 
copolymer. 
The introduction of alpha-olefin comonomer into the first reactor results 
in final products with somewhat lower stiffness (flexural modulus), but 
with some gain in Izod impact strength. 
The impact polypropylene copolymer product can be processed into suitable 
preforms by any of the widely known polymer processing methods including 
injection molding, extrusion, and compression molding. The preform can 
have any suitable geometry dictated by the finished part. As an example, 
cups or trays may be fabricated from sheet stock prepared by the extrusion 
process. The polymer processing methods are widely known and described by 
the literature. A summary of injection molding, extrusion, and compression 
molding processes can be found in the Modern Plastics Encyclopedia-1988 
published by McGraw-Hill (1987), pages 226 to 250. 
Subject process can be, alternatively, described as the solid phase forming 
of an impact polypropylene copolymer comprising (a) providing an impact 
polypropylene copolymer comprising (i) a matrix, which is either a 
homopolymer of propylene or a copolymer of propylene and up to about 5 
percent by weight at least one other alpha-olefin based on the weight of 
the copolymer and, incorporated into said matrix, (ii) a copolymer of 
ethylene and at least one other alpha-olefin, said copolymer having a 
crystallinity of at least about 20 percent and being present in the impact 
copolymer in an amount of at least about 10 percent by weight based on the 
weight of the impact copolymer; and (b) forming said impact polypropylene 
copolymer at a temperature above the melting point of component (ii) but 
below the melting point of component (i). 
The terms "cold forming" or "solid phase forming" are meant to be generic 
and to include widely known and used manufacturing methods whose common 
denominator is that polymer deformation or shaping into a finished part is 
accomplished below the polymer melting point. These processes include 
solid phase pressure forming, forging, stamping, roll forming, and 
coining. Process descriptions and typical forming temperatures of a 
variety of thermoplastic materials can be found in the SPE Journal, 
October 1969, Volume 25, pages 46 to 52. 
The cold forming is carried out at a temperature above the melting point of 
the ethylene/alpha-olefin copolymer prepared in the second reactor and 
below the melting point of the matrix, i.e., the homopolymer or copolymer 
of propylene prepared in the first reactor. A typical low temperature is 
the range of about 130.degree. to about 135.degree. C. and a typical high 
temperature is in the range of about 145.degree. to about 155.degree. C. 
The patents, patent application and other publications mentioned in this 
specification are incorporated by reference herein. 
The invention is illustrated by the following examples. 
EXAMPLES 1 TO 3 
ASTM Type I tensile bars are prepared from the following polymers: 
Example 1: a homopolymer of propylene 
Example 2: a conventional impact polypropylene copolymer 
Example 3: an impact polypropylene copolymer for use in the invention 
In examples 2 and 3 the matrix is a homopolymer of propylene and the 
copolymer incorporated into the matrix is an ethylene/ propylene 
copolymer. A typical process for preparing the impact copolymers is 
described above. 
The tensile bars are prepared by injection molding the polypropylene at a 
melt temperature of 440.degree. to 460.degree. F. The bars measure 8 
inches in length, 1/8 inch in thickness, and 3/4 inch in maximum width. 
They are heated in a circulatory air oven at 140.degree. C. and are then 
manually wrapped around a 1.5 inch steel mandrel to simulate a forming 
operation. 
After one day of aging, the coil diameter (inside measurement) is examined. 
The example 1 and example 2 polymers distort significantly from the formed 
dimension. The example 3 polymer has nearly the same configuration as when 
originally formed attesting to the superior dimensional stability of the 
so formed polymer. 
Variables and results are shown in the following table. 
TABLE 
______________________________________ 
Example 1 2 3 
______________________________________ 
Melt Flow (dg/min) 3.6 1.8 3.4 
Secant Flexural Modulus (psi) 
207,000 110,000 150,000 
Tensile Yield Strength (psi) 
4,400 2,910 4,300 
Copolymer Fraction (%) 
0 25 23 
Ethylene in Copolymer Fraction (%) 
-- 60 95 
DSC Melting Point 
PE (.degree.C.) none 118 128 
PP (.degree.C.) 160 159 153 
DSC Delta H (Heat of Fusion) 
PE (cal/g) 0 0.05 6.6 
PP (cal/g) 23.0 17.3 14.7 
PE Delta H Fusion (% of Total) 
0 2.8 31 
Crystallinity of Copolymer Fraction 
0 0.3 40 
(%) 
Diameter of formed part (Inches) 
2.3 2.9 1.6 
Recovery % 53 93 7 
______________________________________ 
Notes to Table: 
1. Melt flow is determined under ASTM D1238, Condition L 
at 230.degree. C. and 2.16 kilogram load. The results are given in 
decigrams per minute. 
2. Secant Flexural modulus is determined under ASTM D790, 
Method A. The results are given in pounds per square inch. 
3. Tensile yield strength is determined under ASTM D638; 
draw rate = 2 inches per minute. The results are given in 
pounds per square inch. 
4. Copolymer fraction is the percentage of ethylene/propylene 
copolymer incorporated into the matrix based on the total 
weight of copolymer and matrix. 
5. Ethylene in copolymer fraction is the percentage of ethylene 
in the ethylene/propylene copolymer incorporated into the matrix 
based on the weight of the ethylene/propylene copolymer. 
6/7. The DSC melting point for the polyethylene crystalline 
fraction of the ethylene/propylene copolymer (PE) and the 
polypropylene crystalline fraction of the same copolymer (PP) 
is given in degrees Centigrade. The DSC delta H (Heat of Fusion) 
for PE and PP is given in calories per gram. The PE value stands 
for the endotherm peak associated with the melting of the 
polyethylene crystalline fraction. The PP value stands for the 
endotherm peak associated with the melting of the polypropylene 
crystalline fraction. The DSC delta H PE represents the energy 
required to melt the polyethylene crystalline fraction and the 
DSC delta H PP represents the energy required to melt the 
polypropylene crystalline fraction. The values are determined 
under ASTM D3417 and D3418. 
8. The PE delta H fusion (% of total) is the heat of fusion 
due to ethylene crystallinity as measured by Differential 
Scanning Colorimetry (DSC). The value is given as a percentage 
of the total heat of fusion. It is noted that polyethylene 
crystallinity melts in the 100.degree. C. to 135.degree. C. region. 
Propylene crystallinity, on the other hand, melts in the 
150.degree. C. to 170.degree. C. region. The selected temperature 
of 140.degree. C. is above the melting point of the ethylene/ 
propylene copolymer, but below the melting point of the 
polypropylene matrix. The Delta H of Fusion of the ethylene/ 
propylene copolymer is proportional to the polyethylene 
crystallinity and the Delta H of Fusion of the matrix is 
proportional to the melting point of the polypropylene 
crystallinity. 
9. The diameter of the formed part is measured in inches. 
10. The recovery represents the percentage of change in 
diameter from the original diameter of the part as formed to 
the present diameter of the formed part after aging for 24 
hours. The percentage is based on the original diameter.