Method for reducing melt fracture during extrusion of ethylene polymers

A method for reducing the melt fracture during extrusion of a molten narrow molecular weight distribution ethylene polymer which comprises extruding said polymer through a die having a die gap greater than about 50 mils and wherein at least a portion of one surface of the die lip and/or die land in contact with the molten polymer is at an angle of divergence or convergence relative to the axis of flow of the molten polymer through the die.

FIELD OF THE INVENTION 
This invention relates to a method for reducing melt fracture, particularly 
sharkskin melt fracture, during extrusion of a molten narrow molecular 
weight distribution ethylene polymer, under conditions of flow rate and 
melt temperature which would otherwise produce such melt fracture, which 
method comprises extruding said polymer through a die having a die gap 
greater than about 50 mils and wherein at least a portion of one surface 
of the die lip and/or die land in contact with the molten polymer is at an 
angle of divergence or convergence, relative to the axis of flow of the 
molten polymer through the die. 
BACKGROUND OF THE INVENTION 
Most commercial low density polyethylenes are polymerized in heavy walled 
autoclaves or tubular reactors at pressures as high as 50,000 psi and 
temperatures up to 300.degree. C. The molecular structure of high pressure 
low density polyethylene is highly complex. The permutations in the 
arrangement of its simple building blocks are essentially infinite. High 
pressure resins are characterized by an intricate long chain branched 
molecular architecture. These long chain branches have a dramatic effect 
on the melt rheology of the resins. High pressure low density polyethylene 
resins also possess a spectrum of short chain branches generally 1 to 6 
carbon atoms in length which control resin crystallinity (density). The 
frequency distribution of these short chain branches is such that, on the 
average, most chains possess the same average number of branches. The 
short chain branching distribution characterizing high pressure low 
density polyethylene can be considered narrow. 
Low density polyethylene can exhibit a multitude of properties. It is 
flexible and has a good balance of mechanical properties such as tensile 
strength, impact resistance, burst strength, and tear strength. In 
addition, it retains its strength down to relatively low temperatures. 
Certain resins do not embrittle at temperatures as low as -70.degree. C. 
Low density polyethylene has good chemical resistance, and it is 
relatively inert to acids, alkalis, and inorganic solutions. It is, 
however, sensitive to hydrocarbons, halogenated hydrocarbons, and to oils 
and greases. Low density polyethylene has excellent dielectric strength. 
More than 50% of all low density polyethylene is processed into film. This 
film is primarily utilized in packaging applications such as for meat, 
produce, frozen food, ice bags, boilable pouches, textile and paper 
products, rack merchandise, industrial liners, shipping sacks, pallet 
stretch and shrink wrap. Large quantities of wide heavy gage film are used 
in construction and agriculture. 
Most low density polyethylene film is produced by the tubular blown film 
extrusion process. Products range from 2 in. diameter or smaller tubes of 
film to be used as sleeves or pouches, to huge bubbles that provide a lay 
flat of 20 ft. (when slit along an edge and opened up will measure 40 ft. 
wide). 
Polyethylene can also be produced at low to medium pressures by 
polymerizing ethylene or copolymerizing ethylene with various 
alpha-olefins using heterogeneous catalysts based on transition metal 
compounds of variable valence. These resins generally possess little, if 
any, long chain branching and the only branching to speak of is short 
chain branching. Branch length is controlled by comonomer type. Branch 
frequency is controlled by the concentration of comonomer(s) used during 
copolymerization. Branch frequency distribution is influenced by the 
nature of the transition metal catalyst used during the copolymerization 
process. The short chain branching distribution characterizing transition 
metal catalyzed low density polyethylene can be very broad. 
U.S. patent application Ser. No. 892,325 filed Mar. 3, 1978, and refiled as 
Ser. No. 014,414 on Feb. 27, 1979 in the names of F. J. Karol et al and 
entitled Preparation of Ethylene Copolymers In Fluid Bed Reactor, 
discloses that ethylene copolymers, having a density of 0.91 to 0.96, a 
melt flow ratio of .gtoreq.22 to .ltoreq.32 and a relatively low residual 
catalyst content can be produced in granular form, at relatively high 
productivities if the monomer(s) are polymerized in a gas phase process 
with a specific high activity Mg-Ti containing complex catalyst which is 
blended with an inert carrier material. 
U.S. patent application Ser. No. 892,322 filed Mar. 31, 1978, and refiled 
as Ser. No. 012,720 on Feb. 16, 1979 in the names of G. L. Goeke et al and 
entitled Impregnated Polymerization Catalyst, Process For Preparing, and 
Use For Ethylene Copolymerization discloses that ethylene copolymers, 
having a density of 0.91 to 0.96, a melt flow ratio of .gtoreq.22 to 
.ltoreq.32 and a relatively low residual catalyst content can be produced 
in granular form, at relatively high productivities, if the monomer(s) are 
polymerized in a gas phase process with a specific high-activity 
Mg-Ti-containing complex catalyst which is impregnated in a porous inert 
carrier material. 
U.S. patent application Ser. No. 892,037 filed Mar. 31, 1978 and refiled as 
Ser. No. 014,412 on Feb. 27, 1979 in the names of B. E. Wagner et al and 
entitled Polymerization Catalyst, Process for Preparing And Use For 
Ethylene Homopolymerization discloses that ethylene homopolymers having a 
density of about .gtoreq.0.958 to .ltoreq.0.972 and a melt flow ratio of 
about .gtoreq.22 to about .ltoreq.32 which have a relatively low residual 
catalyst residue can be produced at relatively high productivities for 
commercial purposes by a low pressure gas phase process if the ethylene is 
homopolymerized in the presence of a high-activity Mg-Ti-containing 
complex catalyst which is blended with an inert carrier material. The 
granular polymers thus produced are useful for a variety of end-use 
applications. 
The polymers as produced, for example, by the processes of said 
applications using the Mg-Ti containing complex catalyst possess a narrow 
molecular weight distribution, Mw/Mn, of about .gtoreq.2.7 to .ltoreq.3.6, 
and preferably, of about .gtoreq.2.8 to .ltoreq.3.4. 
LOW DENSITY POLYETHYLENE:RHEOLOGY 
The rheology of polymeric materials depends to a large extent on molecular 
weight and molecular weight distribution. 
In film extrusion, two aspects of rheological behavior are important: shear 
and extension. Within a film extruder and extrusion die, a polymeric melt 
undergoes severe shearing deformation. As the extrusion screw pumps the 
melt to, and through, the film die, the melt experiences a wide range of 
shear rates. Most film extrusion processes are thought to expose the melt 
to shear at rates in the 100-5000 sec.sup.-1 range. Polymeric melts are 
known to exhibit what is commonly termed shear thinning behavior, i.e., 
non-Newtonian flow behavior. As shear rate is increased, viscosity (the 
ratio of shear stress, .tau., to shear rate, .gamma.) decreases. The 
degree of viscosity decrease depends upon the molecular weight, its 
distribution, and molecular configuration, i.e., long chain branching of 
the polymeric material. Short chain branching has little effect on shear 
viscosity. In general high pressure low density polyethylenes have a broad 
molecular weight distribution and show enhanced shear thinning behavior in 
the shear rate range common to film extrusion. Narrow molecular weight 
distribution resins of the present invention exhibit reduced shear 
thinning behavior at extrusion grade shear rates. The consequences of 
these differences are that the present narrow distribution resins require 
higher power and develop higher pressures during extrusion than the high 
pressure low density polyethylene resins of broad molecular weight 
distribution and of equivalent average molecular weight. 
The rheology of polymeric materials is customarily studied in shear 
deformation. In simple shear the velocity gradient of the deforming resin 
is perpendicular to the flow direction. The mode of deformation is 
experimentally convenient but does not convey the essential information 
for understanding material response in film fabrication processes. As one 
can define a shear viscosity in terms of shear stress and shear rate, 
i.e.: 
.zeta. shear=.tau.12/.gamma. 
where 
.zeta. shear=shear viscosity (poise) 
.tau.12=shear stress (dynes/cm.sup.2) 
.gamma.=shear rate (sec.sup.-1) an extensional viscosity can be defined in 
terms of normal stress and strain rate, i.e.,: 
.zeta. ext=.pi./.epsilon. 
.zeta.ext=extensional viscosity (poise) 
.pi.=normal stress (dynes/cm.sup.2) 
.epsilon.=strain rate (sec.sup.-1) 
Due to the high shear stress developed during extrusion of a high molecular 
weight ethylene polymer having a narrow molecular weight distribution melt 
fracture, particularly sharkskin melt fracture, occurs. Sharkskin melt 
fracture has been described in the literature for a number of polymers. 
"Sharkskin" is a term used to describe a particular type of surface 
irregularity which occurs during extrusion of some thermoplastic materials 
under certain conditions. It is characterized by a series of ridges 
perpendicular to the flow direction and is described by J. A. Brydson Flow 
Properties of Polymer Melts, Van Nostrand-Reinhold Company (1970), pages 
78-81. 
In the present process, the onset of sharkskin melt fracture is determined 
by visual observation of the surface of an extrudate formed without 
take-off tension from a capillary die. Specifically this procedure for 
determining sharkskin melt fracture is as follows: a 40.times. 
magnification microscope is used. The extrudate is lighted from the side. 
The microscope shows the transition from a low-shear, glossy surface of 
the extrudate to a critical-shear, matted surface (the onset of sharskin 
melt fracture) to a high-shear, deep ridge, sharkskin melt fracture. This 
method is generally reproducible to .+-.10 percent in shear stress. 
The narrow molecular weight distribution ethylene polymers as described 
herein exhibit the characteristics of sharkskin melt fracture upon 
extruding. These characteristics include a pattern of wave distortion 
perpendicular to the flow direction; occurrence at low extrusion rates 
(less than expected for elastic turbulance); no effect of common die 
material; and less melt fracture with increasing temperature. 
There are several known methods for eliminating sharkskin melt fracture in 
polymers. These methods include increasing the resin temperature. However, 
in film formation this method is not useful since increasing resin 
temperature generally causes lower rates, due to bubble instability or 
heat transfer limitations. Another method for eliminating sharkskin is 
described in U.S. Pat. No. 3,920,782. In this method sharkskin formed 
during extrusion of polymeric materials is controlled or eliminated by 
cooling an outer layer of the material so that it emerges from the die 
with a reduced temperature while maintaining the bulk of the melt at the 
optimum working temperature. However, this method is difficult to employ 
and control. 
In the present method melt fracture, particularly sharkskin melt fracture, 
can be virtually eliminated by geometric changes in the die, i.e., by 
extruding the narrow molecular weight distribution ethylene polymer, at 
normal film extrusion temperatures, through a die having a die gap greater 
than about 50 mils and wherein at least a portion of one surface of the 
die lip and/or die land in contact with the molten polymer is at an angle 
of divergence or convergence relative to the axis of flow of the molten 
polymer through the die. The method of this invention is only possible due 
to the observation that the stress field at the exit of the die determines 
the creation of sharkskin melt fracture. This is, sharkskin melt fracture 
can be controlled or eliminated by the geometry at the exit of the die and 
is independent of die entrance or die land conditions. 
Films suitable for packaging applications must possess a balance of key 
properties for broad end-use utility and wide commercial acceptance. These 
properties include film optical quality, for example, haze, gloss, and 
see-through characteristics. Mechanical strength properties such as 
puncture resistance, tensile strength, impact strength, stiffness, and 
tear resistance are important. Vapor transmission and gas permeability 
characteristics are important considerations in perishable goods 
packaging. Performance in film converting and packaging equipment is 
influenced by film properties such as coefficient of friction, blocking, 
heat sealability and flex resistance. High pressure low density 
polyethylene has a wide range of utility such as in food packaging and 
non-food packaging applications. Bags commonly produced from low density 
polyethylene include shipping sacks, textile bags, laundry and dry 
cleaning bags and trash bags. Low density polyethylene film can be used as 
drum liners for a number of liquid and solid chemicals and as protective 
wrap inside wooden crates. Low density polyethylene film can be used in a 
variety of agricultural and horticultural applications such as protecting 
plants and crops, as mulching, for storing of fruits and vegetables. 
Additionally, low density polyethylene film can be used in building 
applications such as a moisture or moisture vapor barrier. Further, low 
density polyethylene film can be coated and printed for use in newspapers, 
books, etc. 
Possessing a unique combination of the aforedescribed properties, high 
pressure low density polyethylene is the most important of the 
thermoplastic packaging films. It accounts for about 50% of the total 
usage of such films in packaging. Films made from the polymers of the 
present invention preferably the ethylene hydrocarbon copolymers, offer an 
improved combination of end-use properties and are especially suited for 
many of the applications already served by high pressure low density 
polyethylene. 
An improvement in any one of the properties of a film such as elimination 
or reduction of melt fracture or an improvement in the extrusion 
characteristics of the resin or an improvement in the film extrusion 
process itself is of the utmost importance regarding the acceptance of the 
film as a substitute for high pressure low density polyethylene in many 
end use applications.

SUMMARY OF THE INVENTION 
It has now been found that melt fracture, particularly sharkskin melt 
fracture formed during extrusion of a molten narrow molecular weight 
distribution ethylene polymer, can be reduced by extruding said polymer 
through a die having a die gap greater than about 50 mils and wherein at 
least a portion of one surface of the die lip and/or die land in contact 
with the molten polymer is at an angle of divergence or convergence 
relative to the axis of flow of the molten polymer through the die. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
Dies 
The molten ethylene polymer is extruded through a die, preferably an 
annular die, having a die gap greater than about 50 mils to less than 
about 200 mils. Extruding a molten ethylene polymer through a die having a 
die gap of greater than about 50 mils to less than about 120 mils, is 
described in U.S. patent application Ser. No. 892,324 filed Mar. 31, 1978, 
and refiled as Ser. No. 012,795 on Feb. 16, 1979 in the names of W. A. 
Fraser et al. and entitled A Process for Making Film From Low Density 
Ethylene Hydrocarbon Copolymer. 
The die which may be used in the present invention may be a spiral annulus 
die, rod die, etc. 
FIG. 1 is a cross sectional view of a spiral/spider annulus die through 
which the molten thermoplastic ethylene polymer is extruded. Die block, 2, 
contains channels, 3. As the molten thermoplastic ethylene polymer is 
extruded it spreads out as it passes into the die channels. Dimension, b, 
is about 140 mils and dimension, a, is about 40 mils. The diameter of the 
die, d, is about 1 to 72 inches and preferably, from 6 to 32 inches. The 
die gap, c, is about 100 mils. 
FIG. 2 is a cross section of a spiral die showing the spiral section, j, 
land entry section, h, die land, g, and die lip, e and f. Dimensions e and 
f are about 0.5 inches, g is about 2 inches, h is about 4 inches and j is 
about 6 inches. 
FIG. 3 shows four different designs of die lips. 3i shows a die wherein the 
die lip is divergent. Angle .alpha. is from about 1.degree. to about 
45.degree.. Dimension k is from about 50 to about 200 mils; dimension, m, 
is from about 0.050 to 1.5 inches, while dimension, n, is from about 0.010 
to 0.110 inches. Die 3ii has one convergent die lip. Angle .beta. is from 
about 5.degree. to about 50.degree.. Die 3iii has both die lips 
convergent, and die 3iv has both die lips divergent. 
In the practice of this invention, the angle of divergence or convergence 
is in the area defined by the die land g, and/or die lip l and f, as 
illustrated in FIG. 2. The polymer melt entering the die is distributed 
around the die in the spiral distribution (or other distributing system 
such as is found in a spider die, for example) and land entry area to form 
an annular flow to the die land. 
The use of a die as illustrated in FIG. 2 allows improvement in flow 
uniformity by using length, g, as a constriction; by combining a proper 
constriction and a die lip and/or die land geometry, uniform polymer melt, 
free of sharkskin melt fracture, and of good flow uniformity, can be 
obtained. 
When at least a portion of one surface of the die lip and/or die land is at 
a convergent angle, the area after the die l and may be divergent, 
preceeding the final converging section. 
It is preferable to have an entry angle into the die land. This angle may 
be about 5.degree. to about 20.degree.. 
FILM EXTRUSION 
I. Blown Film Extrusion 
The films herein may be extruded by tubular blown film extrusion process. 
In this process a narrow molecular weight distribution polymer is melt 
extruded through an extruder. This extruder may have an extrusion screw 
therein with a length to diameter ratio of between 15:1 to 21:1, as 
described in U.S. patent application Ser. No. 940,005, filed Sept. 6, 1978 
in the names of John C. Miller et al and entitled "A Process For Extruding 
Ethylene Polymers". This application describes that this extrusion screw 
contains a feed, transition and metering section. Optionally, the 
extrusion screw can contain a mixing section such as that described in 
U.S. Pat. Nos. 3,486,192; 3,730,492 and 3,756,574, which are incorporated 
herein by reference. Preferably, the mixing section is placed at the screw 
tip. 
The extruder which may be used herein is a 24:1. The extrusion screw of the 
present invention may be substituted directly for the 24/1 length to 
diameter extrusion screw. Alternatively, when, for example, an extrusion 
screw of a length to diameter ratio of 18/1 is used in place of the 24/1 
extrusion screw, the remaining space in the extrusion barrel can be 
partially filled with various types of plugs, torpedoes, or static mixers 
to reduce residence time of the polymer melt. Also, the barrel of the 
extruder can be such so as to accomodate the 18/1 length to diameter 
extrusion screw directly. 
The molten polymer is then extruded through a die, as will hereinafter be 
described. 
The polymer is extruded at a temperature of about 325.degree. to about 
500.degree. F. The polymer is extruded in an upward vertical direction in 
the form of a tube although it can be extruded downward or even sideways. 
After extrusion of the molten polymer through the annular die, the tubular 
film is expanded to the desired extent, cooled, or allowed to cool and 
flattened. The tubular film is flattened by passing the film through a 
collapsing frame and a set of nip rolls. These nip rolls are driven, 
thereby providing means for withdrawing the tubular film away from the 
annular die. 
A positive pressure of gas, for example, air or nitrogen, is maintained 
inside the tubular bubble. As is known in the operation of conventional 
film processes, the pressure of the gas is controlled to give the desired 
degree of expansion of the tubular film. The degree of expansion, as 
measured by the ratio of the fully expanded tube circumference to the 
circumference of the die annulus, is in the range 1/1 to 6/1 and 
preferably, 1/1 to 4/1. The tubular extrudate is cooled by conventional 
techniques such as, by air cooling, water quench or mandrel. 
The drawdown characteristics of the polymers herein are excellent. 
Drawdown, defined as the ratio of the die gap to the product of film gauge 
and blow up ratio, is kept greater than about 2 to less than about 250 and 
preferably greater than about 25 to less than about 150. Very thin gauge 
films can be produced at high drawdown from these polymers even when said 
polymer is highly contaminated with foreign particles and/or gel. Thin 
gauge films greater than about 0.5 mils can be processed to exhibit 
ultimate elongations MD greater than about 400% to about 700% and TD 
greater than about 500% to about 700%. Furthermore, these films are not 
perceived as "splitty". "Splittiness" is a qualitative term which 
describes the notched tear response of a film at high deformation rates. 
"Splittiness" reflects crack propagation rate. It is an end-use 
characteristic of certain types of film and is not well understood from a 
fundamentals perspective. 
As the polymer exits the annular die, the extrudate cools and its 
temperature falls below its melting point and it solidifies. The optical 
properties of the extrudate change as crystallization occurs and a frost 
line is formed. The position of this frost line above the annular die is a 
measure of the cooling rate of the film. This cooling rate has a very 
marked effect on the optical properties of the film produced herein. 
The ethylene polymer can also be extruded in the shape of a rod or other 
solid cross section using the same die geometry for only the external 
surface. Additionally, the ethylene polymer can also be extruded into pipe 
through annular dies. 
II. Slot Cast Film Extrusion 
The films herein may also be extruded by slot cast film extrusion. This 
film extrusion method is well known in the art and comprises extruding a 
sheet of molten polymer through a slot die and then quenching the 
extrudate using, for example, a chilled casting roll or water bath. The 
die will hereinafter be described. In the chill roll process, film may be 
extruded horizontally and layed on top of the chill roll or it may be 
extruded downward and drawn under the chill roll. Extrudate cooling rates 
in the slot cast process are very high. Chill roll or water batch 
quenching is so fast that as the extrudate cools below its melting point, 
crystallites nucleate very rapidly, supramolecular structures have little 
time to grow and spherulites are held to a very small size. The optical 
properties of slot cast film are vastly improved over those characterizing 
films using the slower cooling rate, tubular blown film extrusion process. 
Compound temperatures in the slot cast film extrusion process generally 
run much higher than those typifying the tubular blown film process. Melt 
strength is not a process limitation in this film extrusion method. Both 
shear viscosity and extensional viscosity are lowered. Film can generally 
be extruded at higher output rate than practiced in the blown film 
process. The higher temperatures reduce shear stresses in the die and 
raise the output threshold for melt fracture. 
FILM 
The film produced by the method of the present invention has a thickness of 
greater than about 0.10 mils to about 20 mils, preferably greater than 
about 0.10 to 10 mils, most preferably greater than about 0.10 to 4.0 
mils. The 0.10 to 4.0 mil film is characterized by the following 
properties: a puncture resistance value of greater than about 7.0 
in-lbs/mil; an ultimate elongation of greater than about 400%; a thermal 
shrinkage of less than 3% after heating to 105.degree.-110.degree. C. and 
cooling to room temperature; tensile impact strength of greater than about 
500 to about 2000 ft-lbs/in.sup.3 and tensile strength greater than about 
2000 to about 7000 psi. 
Various conventional additives such as slip agents, antiblocking agents, 
and antioxidants can be incorporated in the film in accordance with 
conventional practice. 
THE ETHYLENE POLYMERS 
The copolymers which may be prepared in the process of the present 
invention are copolymers of a major mol percent (.gtoreq.90%) of ethylene, 
and a minor mol percent (.ltoreq.10%) of one or more C.sub.3 to C.sub.6 
alpha olefins. The C.sub.3 to C.sub.6 alpha olefins should not contain any 
branching on any of their carbon atoms which is closer than the fourth 
carbon atom. The preferred C.sub.3 to C.sub.6 alpha olefins are propylene, 
butene-1, pentene-1 and hexene-1. 
The ethylene polymers have a melt flow ratio of .gtoreq.18 to .ltoreq.32, 
and preferably of .gtoreq.22 to .ltoreq.32. The melt flow ratio value is 
another means of indicating the molecular weight distribution of a 
polymer. The melt flow ratio (MFR) range of .gtoreq.22 to .ltoreq.32 thus 
corresponds to a Mw/Mn value range of about 2.7 to 4.1. The polymers 
herein include a Mw/Mn value in the range of about 2.2 to 4.1. 
The homopolymers have a density of about .gtoreq.0.958 to .ltoreq.0.972 and 
preferably of about .gtoreq.0.961 to .ltoreq.0.968. 
The copolymers have a density of about .gtoreq.0.91 to .ltoreq.0.96 and 
preferably .gtoreq.0.917 to .ltoreq.0.955, and most preferably, of about 
.gtoreq.0.917 to .ltoreq.0.935. The density of the copolymer, at a given 
melt index level for the copolymer, is primarily regulated by the amount 
of the C.sub.3 to C.sub.6 comonomer which is copolymerized with the 
ethylene. In the absence of the comonomer, the ethylene would 
homopolymerize with the catalyst of the present invention to provide 
homopolymers having a density of about .gtoreq.0.96. Thus, the addition of 
progressively larger amounts of the comonomers to the copolymers results 
in a progressive lowering of the density of the copolymer. The amount of 
each of the various C.sub.3 to C.sub.6 comonomers needed to achieve the 
same result will vary from monomer to monomer, under the same reaction 
conditions. 
Thus, to achieve the same results, in the copolymers, in terms of a given 
density, at a given melt index level, larger molar amounts of the 
different comonomers would be needed in the order of C.sub.3 &gt;C.sub.4 
&gt;C.sub.5 &gt;C.sub.6. 
The ethylene polymers of the present invention have an unsaturated group 
content of .ltoreq.1, and usually .gtoreq.0.1 to .ltoreq.0.3, C=C/1000 
carbon atoms, and a cyclohexane extractables content of less than about 3, 
and preferably less than about 2, weight percent. 
The homopolymers of the present invention are granular materials which have 
an average particle size of the order of about 0.005 to about 0.06 inches, 
and preferably of about 0.02 to about 0.04 inches, in diameter. The 
particle size is important for the purposes of readily fluidizing the 
polymer particles in the fluid bed reactor, as described below. The 
homopolymers of the present invention have a settled bulk density of about 
15 to 32 pounds per cubic foot. 
The homopolymers and copolymers of the present invention are useful for 
making film. 
For film making purposes the preferred copolymers of the present invention 
are those having a density of about .gtoreq.0.917 to .ltoreq.0.924; a 
molecular weight distribution (Mw/Mn) of .gtoreq.2.7 to .ltoreq.3.6, and 
preferably of about .gtoreq.2.8 to 3.1; and a standard melt index of 
.gtoreq.0.5 to .ltoreq.5.0 and preferably of about .gtoreq.1.0 to 
.ltoreq.4.0. The films have a thickness of &gt;0 to .ltoreq.10 mils and 
preferably of &gt;0 to .ltoreq.5 mils. 
HIGH ACTIVITY CATALYST 
The compounds used to form the high activity catalyst used in the present 
invention comprise at least one titanium compound, at least one magnesium 
compound, at least one electron donor compound, at least one activator 
compound and at least one inert carrier material, as defined below. 
The titanium compound has the structure 
EQU Ti(OR).sub.a X.sub.b 
wherein R is a C.sub.1 to C.sub.14 aliphatic or aromatic hydrocarbon 
radical, or COR' where R' is a C.sub.1 to C.sub.14 aliphatic or aromatic 
hydrocarbon radical, X is Cl, Br or I, a is 0 or 1, b is 2 to 4 inclusive 
and a+b=3 or 4. 
The titanium compounds can be used individually or in combinations thereof, 
and would include TiCl.sub.3, TiCl.sub.4, Ti(OCH.sub.3)Cl.sub.3, 
Ti(OC.sub.6 H.sub.5)Cl.sub.3, Ti(OCOCH.sub.3)Cl.sub.3 and Ti(OCOC.sub.6 
H.sub.5)Cl.sub.3. 
The magnesium compound has the structure 
EQU MgX.sub.2 
wherein X is Cl, Br or I. Such magnesium compounds can be used individually 
or in combinations thereof and would include MgCl.sub.2, MgBr.sub.2 and 
MgI.sub.2. Anhydrous MgCl.sub.2 is the particularly preferred magnesium 
compound. 
About 0.5 to 56, and preferably about 1 to 10, mols of the magnesium 
compound are used per mol of the titanium compound in preparing the 
catalysts employed in the present invention. 
The titanium compound and the magnesium compound should be used in a form 
which will facilitate their dissolution in the electron donor compound, as 
described herein below. 
The electron donor compound is an organic compound which is liquid at 
25.degree. C. and in which the titanium compound and the magnesium 
compound are partially or completely soluble. The electron donor compounds 
are known, as such, or as Lewis bases. 
The electron donor compounds would include such compounds as alkyl esters 
of aliphatic and aromatic carboxylic acids, aliphatic ethers, cyclic 
ethers and aliphatic ketones. Among these electron donor compounds the 
preferable ones are alkyl esters of C.sub.1 to C.sub.4 saturated aliphatic 
carboxylic acids; alkyl esters of C.sub.7 to C.sub.8 aromatic carboxylic 
acids; C.sub.2 to C.sub.8, and preferably C.sub.3 to C.sub.4, aliphatic 
ethers; C.sub.3 to C.sub.4 cyclic ethers, and preferably C.sub.4 cyclic 
mono- or di-ether; C.sub.3 to C.sub.6, and preferably C.sub.3 to C.sub.4, 
aliphatic ketones; The most preferred of these electron donor compounds 
would include methyl formate, ethyl acetate, butyl acetate, ethyl ether, 
hexyl ether, tetrahydrofuran, dioxane, acetone and methyl isobutyl ketone. 
The electron donor compounds can be used individually or in combinations 
thereof. 
About 2 to 85, and preferably about 3 to 10 mols of the electron donor 
compound are used per mol of Ti. 
The activator compound has the structure 
EQU Al(R").sub.c X'.sub.d H.sub.e 
wherein X' is Cl or OR"', R" and R"' are the same or different and are 
C.sub.1 to C.sub.14 saturated hydrocarbon radicals, d is 0 to 1.5, e is 1 
or 0 and c+d+e=3. 
Such activator compounds can be used individually or in combinations 
thereof and would include Al(C.sub.2 H.sub.5).sub.3, Al(C.sub.2 
H.sub.5).sub.2 Cl, Al(i-C.sub.4 H.sub.9).sub.3, Al.sub.2 (C.sub.2 
H.sub.5).sub.3 Cl.sub.3, Al(i-C.sub.4 H.sub.9).sub.2 H, Al(C.sub.6 
H.sub.13).sub.3, Al(C.sub.2 H.sub.5).sub.2 H and Al(C.sub.2 H.sub.5).sub.2 
(OC.sub.2 H.sub.5). 
About 10 to 400, and preferably about 10 to 100, mols of the activator 
compound are used per mol of the titanium compound in activating the 
catalyst employed in the present invention. 
The carrier materials are solid, particulate materials which are inert to 
the other components of the catalyst composition, and to the other active 
components of the reaction system. These carrier materials would include 
inorganic materials such as oxides of silicon and aluminum and molecular 
sieves, and organic materials such as olefin polymers such as 
polyethylene. The carrier materials are used in the form of dry powders 
having an average particle size of about 10 to 250, and preferably of 
about 50 to 150 microns. These materials are also preferably porous and 
have a surface area of .gtoreq.3, and preferably of .gtoreq.50, square 
meters per gram. The carrier material should be dry, that is, free of 
absorbed water. This is normally done by heating or pre-drying the carrier 
material with a dry inert gas prior to use. The inorganic carrier may also 
be treated with about 1 to 8 percent by weight of one or more of the 
aluminum alkyl compounds described above to further activate the carrier. 
CATALYST PREATION 
The catalyst used in the present invention is prepared by first preparing a 
precursor composition from the titanium compound, the magnesium compound, 
and the electron donor compound, as described below. The carrier material 
can then be impregnated with precursor composition and then treated with 
the activator compound in one or more steps as described below. 
Alternatively the precursor composition can be treated with the carrier 
material and the activator compound in one or more steps as described 
below. 
The precursor composition is formed by dissolving the titanium compound and 
the magnesium compound in the electron donor compound at a temperature of 
about 20.degree. C. up to the boiling point of the electron donor 
compound. The titanium compound can be added to the electron donor 
compound before or after the addition of the magnesium compound, or 
concurrent therewith. The dissolution of the titanium compound and the 
magnesium compound can be facilitated by stirring, and in some instances 
by refluxing, these two compounds in the electron donor compound. After 
the titanium compound and the magnesium compound are dissolved, the 
precursor composition may be isolated by crystallization or by 
precipitation with a C.sub.5 to C.sub.8 aliphatic or aromatic hydrocarbon 
such as hexane, isopentane or benzene. 
The crystallized or precipitated precursor composition may be isolated, in 
the form of fine, free flowing particles having an average particle size 
of about 10 to 100 microns and a settled bulk density of about 18 to 33 
pounds per cubic foot. 
When thus made as disclosed above the precursor composition has the formula 
EQU Mg.sub.m Ti.sub.1 (OR).sub.n X.sub.p [ED].sub.q 
wherein 
ED is the electron donor compound, 
m is .gtoreq.0.5 to .ltoreq.56, and preferably .gtoreq.1.5 to .ltoreq.5, 
n is 0.1 or 2 
p is .gtoreq.2 to .ltoreq.116, and preferably .gtoreq.6 to .ltoreq.14, 
q is .gtoreq.2 to .ltoreq.85, and preferably .gtoreq.4 to .ltoreq.11, 
R is a C.sub.1 to C.sub.14 aliphatic or aromatic hydrocarbon radical, or 
COR' wherein R' is a C.sub.1 to C.sub.14 aliphatic or aromatic hydrocarbon 
radical and, 
X is Cl, Br or I. 
The precursor composition may then be impregnated, in a weight ratio of 
about 0.033 to 1, and preferably about 0.1 to 0.33, parts of the precursor 
composition into one part by weight of the carrier material. 
The impregnation of the dried (activated) support with the precursor 
composition may be accomplished by dissolving the precursor composition in 
the electron donor compound, and by then admixing the support with the 
dissolved precursor composition so as to allow the precursor composition 
to impregnate the support. The solvent is then removed by drying at 
temperatures of .ltoreq.70.degree. C. 
The support may also be impregnated with the precursor composition by 
adding the support to a solution of the chemical raw materials used to 
form the precursor composition in the electron donor compound, without 
isolating the precursor composition from such solution. The excess 
electron donor compound is then removed by drying at temperatures of 
.ltoreq.70.degree. C. 
Alternatively, the precursor composition can be diluted with the carrier 
material. The dilution of the precursor composition can be accomplished 
before the precursor composition is partially or completely activated, as 
disclosed below, or concurrent with such activation. The dilution of the 
precursor composition is accomplished by mechanically mixing or blending 
about 0.033 to 1, and preferably about 0.1 to 0.33, parts of the precursor 
composition with one part by weight of the carrier material. 
ACTIVATION OF PRECURSOR COMPOSITION 
In order to be used in the process of the present invention the precursor 
composition must be fully or completely activated, that is, it must be 
treated with sufficient activator compound to transform the Ti atoms in 
the precursor composition to an active state. 
It has been found that, in order to prepare a useful catalyst it is 
necessary to conduct the activation in such a way that, at least, the 
final activation stage must be conducted in the absence of solvent so as 
to avoid the need for drying the fully active catalyst to remove solvent 
therefrom. The activation procedure is hereafter described as to the 
impregnated precursor composition (A) and wherein the precursor 
composition is diluted with the carrier material (B). 
A. Activation of Impregnated Precursor Composition 
The activation is conducted in at least two stages. In the first stage the 
precursor composition, impregnated in the silica, is reacted with, and 
partially reduced by, enough activator compound so as to provide a 
partially activated precursor composition which has an activator 
compound/Ti molar ratio of about &gt;0 to &lt;10:1 and preferably of about 4 to 
about 8:1. This partial reduction reaction is preferably carried out in a 
hydrocarbon solvent slurry followed by drying of the resulting mixture, to 
remove the solvent, at temperatures between 20 to 80, and preferably of 
50.degree. to 70.degree. C. In this partial activation procedure the 
activator compound may be used while absorbed on the carrier material used 
as the support for the precursor composition. The resulting product is a 
free-flowing solid particulate material which can be readily fed to the 
polymerization reactor. The partially activated and impregnated precursor 
composition, however, is at best, weakly active, as a polymerization 
catalyst in the process of the present invention. In order to render the 
partially activated and impregnated precursor composition active for 
ethylene polymerization purposes, additional activator compound must also 
be added to the polymerization reactor to complete, in the reactor, the 
activation of the precursor composition. The additional activator compound 
and the partially activated impregnated precursor composition are 
preferably fed to the reactor through separate feed lines. The additional 
activator compound may be sprayed into the reactor in the form of a 
solution thereof in a hydrocarbon solvent such as isopentane, hexane, or 
mineral oil. This solution usually contains about 2 to 30 weight percent 
of the activator compound. The additional activator compound is added to 
the reactor in such amounts as to provide, in the reactor, with the 
amounts of activator compound and titanium compound fed with the partially 
activated and impregnated precursor compositiion, a total Al/Ti molar 
ratio of .gtoreq.10 to 400 and preferable of about 15 to 60. The 
additional amounts of activator compound added to the reactor, react with, 
and complete the activation of, the titanium compound in the reactor. 
B. Activation where Precursor is Diluted with Carrier Material 
Two procedures have been developed to accomplish this result. In one 
procedure, the precursor composition is completely activated, outside the 
reactor, in the absence of solvent, by dry blending the precursor 
composition with the activator compound. In this dry blending procedure 
the activator compound is preferably used while absorbed on a carrier 
material. This procedure has a disadvantage, however, in that the 
resulting dry, fully activated catalyst is pyrophoric where it contains 
&gt;10 weight percent of the activator compound. 
In the second, and preferred, of such catalyst activation procedures, the 
precursor composition is partially activated outside the polymerization 
reactor with activator compound in a hydrocarbon slurry, the hydrocarbon 
solvent is removed by drying and the partially activated precursor 
composition is fed to the polymerization reactor where the activation is 
completed with additional activator compound. 
Thus, in the dry blending catalyst making procedure the solid particulate 
precursor composition is added to and evenly blended with solid particles 
of porous carrier material wherein the activator compound is absorbed. The 
activator compound is absorbed on the carrier material, from a hydrocarbon 
solvent solution of the activator compound, so as to provide a loading of 
about 10 to 50 weight percent of activator compound on 90 to 50 weight 
percent of carrier material. The amounts of the precursor composition, 
activator compound and carrier material that are employed are such as to 
provide the desired Al/Ti molar ratios and to provide a final composition 
having a weight ratio of precursor composition to carrier material of less 
than about 0.50, and preferably of less than about 0.33. This amount of 
carrier material thus provides the necessary dilution therewith of the 
activated catalyst so as to provide the desired control of the 
polymerization activity of the catalyst in the reactor. Where the final 
compositions contain about .gtoreq.10 weight percent of the activator 
compound, they will be pyrophoric, During the dry blending operation, 
which may be conducted at ambient (25.degree. C.) or lower temperatures, 
the dry mixture is well agitated to avoid any heat build-up during the 
ensuing reduction reaction which is exothermic, initially. The resulting 
catalyst is thus completely reduced and activated and can be fed to, and 
used as such in, the polymerization reactor. It is a free-flowing 
particulate material. 
In the second, and preferred catalyst activation procedure, the activation 
is conducted in at least two stages. In the first stage the solid 
particulate precursor composition, diluted with carrier material, is 
reacted with and partially reduced by enough activator compound so as to 
provide a partially activated precursor composition which has an activator 
compound/Ti molar ratio of about 1 to 10:1 and preferably of about 4 to 
8:1. This partial reduction reaction is preferably carried out in a 
hydrocarbon solvent slurry followed by drying of the resulting mixture to 
remove the solvent, at temperatures between 20 to 80, and preferably of 
50.degree. to 70.degree. C. In this partial activation procedure the 
activator compound may be used while absorbed on the carrier material used 
to dilute the activator compound. The resulting product is a free-flowing 
solid particulate material which can be readily fed to the polymerization 
reactor. The partially activated precursor composition, however, is, at 
best, weakly active as a polymerization catalyst in the process of the 
present invention. In order to render the partially activated precursor 
composition active for ethylene polymerization purposes, additional 
activator compound must also be added to the polymerization reactor to 
complete, in the reactor, the activation of the percursor composition. The 
additional activator compound and the partially activated precursor 
composition are preferably fed to the reactor through separate feed lines. 
The additional activator compound may be sprayed into the reactor in the 
form of a solution thereof in a hydrocarbon solvent such as isopentane, 
hexane, or mineral oil. This solution usually contains about 2 to 30 
weight percent of the activator compound. The activator compound may also 
be added to the reactor in solid form, by being absorbed on a carrier 
material. The carrier material usually contains 10 to 50 weight percent of 
the activator for this purpose. The additional activator compound is added 
to the reactor in such amounts as to provide, in the reactor, with the 
amounts of activator compound and titanium compound fed with the partially 
activated precursor composition, a total A1/Ti molar ratio of about 10 to 
400 and preferably of about 15 to 60. The additional amounts of activator 
compound added to the reactor, react with, and complete the activation of, 
the titanium compound in the reactor. 
In a continuous gas phase process, such as the fluid bed process disclosed 
below, discrete portions of the partially or completely activated 
precursor composition or discrete portions of the partially activated 
precursor composition impregnated on the support are continuously fed to 
the reactor, with discrete portions of any additional activation of the 
partially activated precursor composition, during the continuing 
polymerization process in order to replace active catalyst sites that are 
expended during the course of the reaction. 
The Polymerization Reaction 
The polymerization reaction is conducted by contacting a stream of the 
monomer(s), in a gas phase process, such as in the fluid bed process 
described below, and substantially in the absence of catalyst poisons such 
as moisture, oxygen, CO, CO.sub.2, and acetylene with a catalytically 
effective amount of the completely activated precursor composition (the 
catalyst) which may be impregnated on a support at a temperature and at a 
pressure sufficient to initiate the polymerization reaction. 
In order to achieve the desired density ranges in the copolymers it is 
necessary to copolymerize enough of the .gtoreq.C.sub.3 comonomers with 
ethylene to achieve a level of .gtoreq.0 to 10 mol percent of the C.sub.3 
to C.sub.6 comonomer in the copolymer. The amount of comonomer needed to 
achieve this result will depend on the particular comonomer(s) employed. 
There is provided below a listing of the amounts, in mols, of various 
comonomers that must be copolymerized with ethylene in order to provide 
polymers having the desired density range at any given melt index. The 
listing also indicates the relative molar concentration, of such comonomer 
to ethylene, which must be present in the gas stream of monomers which is 
fed to the reactor. 
______________________________________ 
Gas Stream 
mol % needed Comonomer/Ethylene 
Comonomer in copolymer molar ratio 
______________________________________ 
propylene &gt;0 to 10 &gt;0 to 0.9 
butene-1 &gt;0 to 7.0 &gt;0 to 0.7 
pentene-1 &gt;0 to 6.0 &gt;0 to 0.45 
hexene-1 &gt;0 to 5.0 &gt;0 to 0.4 
______________________________________ 
A fluidized bed reaction system which can be used in the practice of the 
process of the present invention is illustrated in FIG. 4. With reference 
thereto the reactor 10 consists of a reaction zone 12 and a velocity 
reduction zone 14. 
The reaction zone 12 comprises a bed of growing polymer particles, formed 
polymer particles and a minor amount of catalyst particles fluidized by 
the continuous flow of polymerizable and modifying gaseous components in 
the form of make-up feed and recycle gas through the reaction zone. To 
maintain a viable fluidized bed, the mass gas flow rate through the bed 
must be above the minimum flow required for fluidization, and preferably 
from about 1.5 to about 10 times G.sub.mf and more preferably from about 3 
to about 6 times G.sub.mf. G.sub.mf is used in the accepted form as the 
abbreviation for the minimum mass gas flow required to achieve 
fluidization, C. Y. Wen and Y. H. Yu, "Mechanics of Fluidization", 
Chemical Engineering Progress Symposium Series, Vol. 62, p. 100-111 
(1966). 
It is essential that the bed always contains particles to prevent the 
formation of localized "hot spots" and to entrap and distribute the 
particulate catalyst throughout the reaction zone. On start up, the 
reaction zone is usually charged with a base of particulate polymer 
particles before gas flow is initiated. Such particles may be identical in 
nature to the polymer to be formed or different therefrom. When different, 
they are withdrawn with the desired formed polymer particles as the first 
product. Eventually, a fluidized bed of the desired polymer particles 
supplants the start-up bed. 
The partially or completely activated precursor compound (the catalyst) 
used in the fluidized bed is preferably stored for service in a reservoir 
32 under a blanket of a gas which is inert to the stored material, such as 
nitrogen and argon. 
Fluidization is achieved by a high rate of gas recycle to and through the 
bed, typically in the order of about 50 times the rate of feed of make-up 
gas. The fluidized bed has the general appearance of a dense mass of 
viable particles in possible free-vortex flow as created by the 
percolation of gas through the bed. The pressure drop through the bed is 
equal to or slightly greater than the mass of the bed divided by the 
cross-sectional area. It is thus dependent on the geometry of the reactor. 
Make-up gas is fed to the bed at a rate equal to the rate at which 
particulate polymer product is withdrawn. The composition of the make-up 
gas is determined by a gas analyzer 16 positioned above the bed. The gas 
analyzer determines the composition of the gas being recycled and the 
composition of the make-up gas is adjusted accordingly to maintain an 
essentially steady state gaseous composition within the reaction zone. 
To insure complete fluidization, the recycle gas and, where desired, part 
of the make-up gas are returned to the reactor at point 18 below the bed. 
There exists a gas distribution plate 20 above the point of return to aid 
fluidizing the bed. 
The portion of the gas stream which does not react in the bed constitutes 
the recycle gas which is removed from the polymerization zone, preferably 
by passing it into a velocity reduction zone 14 above the bed where 
entrained particles are given an opportunity to drop back into the bed. 
Particle return may be aided by a cyclone 22 which may be part of the 
velocity reduction zone or exterior thereto. Where desired, the recycle 
gas may then be passed through a filter 24 designed to remove small 
particles at high gas flow rates to prevent dust from contacting heat 
transfer surfaces and compressor blades. 
The recycle gas is then compressed in a compressor 25 and then passed 
through a heat exchanger 26 wherein it is stripped of heat of reaction 
before it is returned to the bed. By constantly removing heat of reaction, 
no noticeable temperature gradient appears to exist within the upper 
portion of the bed. A temperature gradient will exist in the bottom of the 
bed in a layer of about 6 to 12 inches, between the temperature of the 
inlet gas and the temperature of the remainder of the bed. Thus, it has 
been observed that the bed acts to almost immediately adjust the 
temperature of the recycle gas above this bottom layer of the bed zone to 
make it conform to the temperature of the remainder of the bed thereby 
maintaining itself at an essentially constant temperature under steady 
state conditions. The recycle is then returned to the reactor at its base 
18 and to the fluidized bed through distribution plate 20. The compressor 
25 can also be placed upstream of the heat exchanger 26. 
The distribution plate 20 plays an important role in the operation of the 
reactor. The fluidized bed contains growing and formed particulate polymer 
particles as well as catalyst particles. As the polymer particles are hot 
and possible active, they must be prevented from settling, for if a 
quiescent mass is allowed to exist, any active catalyst contained therein 
may continue to react and cause fusion. Diffusing recycle gas through the 
bed at a rate sufficient to maintain fluidization at the base of the bed 
is, therefore, important. The distribution plate 20 serves this purpose 
and may be a screen, slotted plate, perforated plate, a plate of the 
bubble cap type, and the like. The elements of the plate may all be 
stationary, or the plate may be of the mobile type disclosed in U.S. Pat. 
No. 3,298,792. Whatever its design, it must diffuse the recycle gas 
through the particles at the base of the bed to keep them in a fluidized 
condition, and also serve to support a quiescent bed of resin particles 
when the reactor is not in operation. The mobile elements to the plate may 
be used to dislodge any polymer particles entrapped in or on the plate. 
Hydrogen may be used as a chain transfer agent in the polymerization 
reaction of the present invention. The ratio of hydrogen/ethylene employed 
will vary between about 0 to about 2.0 moles of hydrogen per mole of the 
monomer in the gas stream. 
Any gas inert to the catalyst and reactants can also be present in the gas 
stream. The activator compound is preferably added to the reaction system 
at the hottest portion of the gas which is usually downstream from heat 
exchanger 26. Thus, the activator may be fed into the gas recycle system 
from dispenser 27 thru line 27A. 
Compounds of the structure Zn(R.sub.a)(R.sub.b), wherein R.sub.a and 
R.sub.b are the same or different C.sub.1 to C.sub.14 aliphatic or 
aromatic hydrocarbon radicals, may be used in conjunction with hydrogen, 
with the catalysts of the present invention as molecular weight control or 
chain transfer agents, that is, to increase the melt index values of the 
copolymers that are produced. About 0 to 50, and preferably about 20 to 
30, mols of the Zn compound (as Zn) would be used in the gas stream in the 
reactor per mol of titanium compound (as Ti) in the reactor. The zinc 
compound would be introduced into the reactor preferably in the form of a 
dilute solution (2 to 30 weight percent) in hydrocarbon solvent or 
absorbed on a solid diluent material, such as silica, of the types 
described above, in amounts of about 10 to 50 weight percent. These 
compositions tend to be pyrophoric. The zinc compound may be added alone, 
or with any additional portions of the activator compound that are to be 
added to the reactor from a feeder, not shown, which could be positioned 
adjacent dispenser 27, near the hottest portion of the gas recycle system. 
It is essential to operate the fluid bed reactor at a temperature below the 
sintering temperature of the polymer particles. To insure that sintering 
will not occur, operating temperatures below the sintering temperature are 
desired. For the production of ethylene copolymers in the process of the 
present invention an operating temperature of about 30 to 115.degree. C. 
is preferred, and a temperature of about 75 to 95.degree. C. is most 
preferred. Temperatures of about 75 to 95.degree. C. are used to prepare 
products having a density of about 0.91 to 0.92, and temperatures of about 
80 to 100.degree. C. are used to prepare products having a density of 
about &gt;0.92 to 0.94, and temperatures of about 90 to 115.degree. C. are 
used to prepare products having a density of about &gt;0.94 to 0.96. 
The fluid bed reactor is operated at pressures of up to about 1000 psi, and 
is preferably operated at a pressure of from about 150 to 350 psi, with 
operation at the higher pressures in such ranges favoring heat transfer 
since an increase in pressure increases the unit volume heat capacity of 
the gas. 
The partially or completely activated precursor composition is injected 
into the bed at a rate equal to its consumption at a point 30 which is 
above the distribution plate 20. Preferably, the catalyst is injected at a 
point located about 1/4 to 3/4 up the side of the bed. Injecting the 
catalyst at a point above the distribution plate is an important feature 
of this invention. Since the catalysts used in the practice of the 
invention are highly active, injection of the fully activated catalyst 
into the area below the distribution plate may cause polymerization to 
begin there and eventually cause plugging of the distribution plate. 
Injection into the viable bed, instead, aids in distributing the catalyst 
throughout the bed and tends to preclude the formation of localized spots 
of high catalyst concentration which may result in the formation of "hot 
spots". 
A gas which is inert to the catalyst such as nitrogen or argon is used to 
carry the partially or completely reduced precursor composition, and any 
additional activator compound or non-gaseous chain transfer agent that is 
needed, into the bed. 
The production rate of the bed is controlled by the rate of catalyst 
injection. The production rate may be increased by simply increasing the 
rate of catalyst injection and decreased by reducing the rate of catalyst 
injection. 
Since any change in the rate of catalyst injection will change the rate of 
generation of the heat of reaction, the temperature of the recycle gas is 
adjusted upwards or downwards to accomodate the change in rate of heat 
generation. This insures the maintenance of an essentially constant 
temperature in the bed. Complete instrumentation of both the fluidized bed 
and the recycle gas cooling system, is, of course, necessary to detect any 
temperature change in the bed so as to enable the operator to make a 
suitable adjustment in the temperature of the recycle gas. 
Under a given set of operating conditions, the fluidized bed is maintained 
at essentially a constant height by withdrawing a portion of the bed as 
product at a rate equal to the rate of formation of the particulate 
polymer product. Since the rate of heat generation is directly related to 
product formation, a measurement of the temperature rise of the gas across 
the reactor (the difference between inlet gas temperature and exit gas 
temperature) is determinative of the rate of particulate polymer formation 
at a constant gas velocity. 
The particulate polymer product is preferably continuously withdrawn at a 
point 34 at or close to the distribution plate 20 and in suspension with a 
portion of the gas stream which is vented before the particles settle to 
preclude further polymerization and sintering when the particles reach 
their ultimate collection zone. The suspending gas may also be used, as 
mentioned above, to drive the product of one reactor to another reactor. 
The particulate polymer product is conveniently and preferably withdrawn 
through the sequential operation of a pair of timed valves 36 and 38 
defining a segregation zone 40. While valve 38 is closed, valve 36 is 
opened to emit a plug of gas and product to the zone 40 between it and 
valve 36 which is then closed. Valve 38 is then opened to deliver the 
product to an external recovery zone. Valve 38 is then closed to await the 
next product recovery operation. 
Finally, the fluidized bed reactor is equipped with an adequate venting 
system to allow venting the bed during start up and shut down. The reactor 
does not require the use of stirring means and/or wall scraping means. 
The catalyst system of this invention appears to yield a fluid bed product 
having an average particle size between about 0.005 to about 0.06 inches 
and preferably about 0.02 to about 0.04 inches. 
The properties of the polymers produced in the Examples were determined by 
the following test methods: 
Density 
For materials having a density &lt;0.940, ASTM-1505 procedure is used and 
plaque is conditioned for one hour at 100.degree. C. to approach 
equilibrium crystallinity. 
For materials having a density of .gtoreq.0.940, a modified procedure is 
used wherein the test plaque is conditioned for one hour at 120.degree. C. 
to approach equilibrium crystallinity and is then quickly cooled to room 
temperature. All density values are reported as grams/cm.sup.3. All 
density measurements are made in a density gradient column. 
Melt Index (MI) 
ASTM D-1238--Condition E--Measured at 190.degree. C.--reported as grams per 
10 minutes. 
Flow Rate (HLMI) 
ASTM D-1238--Condition F--Measured at 10 times the weight used in the melt 
index test above. 
##EQU1## 
productivity 
a sample of the resin product is ashed, and the weight % of ash is 
determined; since the ash is essentially composed of the catalyst, the 
productivity is thus the pounds of polmer produced per pound of total 
catalyst consumed. The amount of Ti, Mg and Cl in the ash are determined 
by elemental analysis. 
n-hexane extractables 
(FDA test used for polyethylene film intended for food contact 
applications). 
A 200 square inch sample of 1.5 mil gauge film is cut into strips measuring 
1".times.6" and weighted to the nearest 0.1 mg. The strips are placed in a 
vessel and extracted with 300 ml of n-hexane at 50.degree..+-.1.degree. C. 
for 2 hours. The extract is then decanted into tared culture dishes. After 
drying the extract in a vacuum desiccator, the culture dish is weighed to 
the nearest 0.1 mg. The extractables, normalized with respect to the 
original sample weight, is then reported as the weight fraction of 
n-hexane extractables. 
bulk density 
The resin is poured via 3/8" diameter funnel into a 100 ml graduated 
cylinder to 100 ml line without shaking the cylinder, and weighed by 
difference. 
Molecular Weight Distribution (Mw/Mn) 
Gel Permeation Chromatography For resins with density &lt;0.94: Styrogel 
Packing: (Pore Size Sequence is 10.sup.7, 10.sup.5, 10.sup.4, 10.sup.3, 60 
A.degree.) Solvent is Perchloroethylene at 117.degree. C. For resins with 
density 24 0.94: Styrogel Packing: (Pore Size Sequence is 10.sup.7, 
10.sup.6, 10.sup.5, 10.sup.4, 60 A.degree.) Solvent is ortho dichloro 
benzene at 135.degree. C. 
Detection for all resins; Infra red at 3.45 
The following Examples are designed to illustrate the process of the 
present invention and are not intended as a limitation upon the scope 
thereof. 
I. PREATION OF IMPREGNATED PRECURSOR 
In a 12 1 flask equipped with a mechanical stirrer are placed 41.8 g (0.439 
mol) anhydrous MgCl.sub.2 and 2.5 1 tetrahydrofuran (THF). To this 
mixture, 27.7 g (0.184 mol) TiCl.sub.4 is added dropwise over 1/2 hour. It 
may be necessary to heat the mixture to 60.degree. C. for about 1/2 hour 
in order to completely dissolve the material. 
500 g of porous silica is added and the mixture stirred for 1/4 hour. The 
mixture is dried with a N.sub.2 purge at 60.degree. C. for about 3-5 hours 
to provide a dry free flowing powder having the particle size of the 
silica. The absorbed precursor composition has the formula 
EQU TiMg.sub.3.0 Cl.sub.10 (THF).sub.6.7 
Ib. Preparation of Impregnated Precursor from Preformed Precursor 
Composition 
In a 12 liter flask equipped with a mechanical stirrer, 146 g of precursor 
composition is dissolved in 2.5 liters dry THF. The solution may be heated 
to 60.degree. C. in order to facilitate dissolution. 500 g of porous 
silica is added and the mixture is stirred for 1/4 hour. The mixture is 
dried with a N.sub.2 purge at .ltoreq.60.degree. C. for about 3-5 hours to 
provide a dry free flowing powder having the particle size of the silica. 
The precursor composition employed in this Procedure Ib. is formed as in 
Procdure Ia. except that it is recovered from the solution thereof in THF 
by crystallization or precipitation. 
The precursor composition may be analyzed at this point for Mg and Ti 
content since some of the Mg and/or Ti compound may have been lost during 
the isolation of the precursor composition. The empirical formulas used 
herein in reporting the precursor compositions are derived by assuming 
that the Mg and Ti still exist in the form of the compounds in which they 
were first added to the electron donor compound. The amount of electron 
donor is determined by chromatography. 
II. ACTIVATION PROCEDURE 
The desired weights of impregnated, precursor composition and activator 
compound are added to a mixing tank with sufficient amounts of anhydrous 
aliphatic hydrocarbon diluent such as isopentane to provide a slurry 
system. 
The activator compound and precursor compound are used in such amounts as 
to provide a partially activated precursor composition which as an Al/Ti 
ratio of &lt;0 to .ltoreq.10:1 and preferably of 4 to 8:1. 
The contents of the slurry system are then thoroughly mixed at room 
temperature and at a atmospheric pressure for about 1/4 to 1/2 hour. The 
resulting slurry is then dried under a purge of dry inert gas such as 
nitrogen or argon, at a atmospheric pressure and at a temperature of 
65.degree..+-.10.degree. C. to remove the hydrocarbon diuluent. This 
process usually requires about 3 to 5 hours. The resulting catalyst is in 
the form of a partially activated precursor composition which is 
impregnated within the pores of the silica. The material is a free flowing 
particulate material having the size and shape of the silica. It is not 
pyrophoric unless the aluminum alkyl content exceeds a loading of 10 
weight percent. It is stored under a dry inert gas such as nitrogen or 
argon prior to future use. It is now ready for use by being injected into, 
and fully activated within, the polymerization reactor. 
When additional activator compound is fed to the polymerization reactor for 
the purpose of completing the activation of the precursor composition, it 
is fed into the reactor as a dilute solution in a hydrocarbon solvent such 
as isopentane. These dilute solutions contain about 5 to 30% by volume of 
the activator compound. 
The activator compound is added to the polymerization reactor so as to 
maintain the Al/Ti ratio in the reactor at a level of about .gtoreq.10 to 
400:1 and preferably of 15 to 60:1. 
EXAMPLE 1 
Preparation of Copolymer 
Ethylene was copolymerized with propylene or butene-1 (propylene in Runs 1 
and 2 and butene-1 in Runs 3 to 14) in each of this series with catalyst 
formed as described above and as activated by Activation Procedure A to 
produce polymers having a density of .ltoreq.0.940. In each case, the 
partially activated precursor composition had an Al/Ti mol ratio of 4.4 to 
5.8. The completion of the activation of the precursor composition in the 
polymerization reactor was accomplished with triethyl aluminum (as a 5 
weight % solution in isopentane in Runs 1 to 3 and 4 to 14, and adsorbed 
in silica, 50/50 weight %, in Runs 4 and 5 so as to provide the completely 
activated catalyst in the reactor with an Al/Ti mol ratio of about 29 to 
140. 
Each of the polymerization reaction was continuously conducted for &gt;1 hour 
after equilibrium was reached and under a pressure of about 300 psia and a 
gas velocity of about 5 to 6 times G.sub.mf in a fluid bed reactor system 
at a space time yield of about 3 to 6 lbs/hr/ft.sup.3 of bed space. The 
reaction system was as described in the drawing above. It has a lower 
section 10 feet high and 131/2 inches in (inner) diameter, and an upper 
section which was 16 feet high and 231/2 inches in (inner) diameter. 
In several of the Runs zinc diethyl was added during the reaction (as a 2.6 
weight % solution in isopentane) to maintain a constant Zn/Ti mol ratio 
where the zinc diethyl was used, the triethyl aluminum was also added as a 
2.6 weight percent in isopentane. 
Table A below lists, with respect to Runs 1 to 14 various operating 
conditions employed in such examples i.e., the weight percent of precursor 
composition in the blend of silica and precursor composition; Al/Ti ratio 
in the partially activated precursor composition; Al/Ti ratio maintained 
in the reactor; polymerization temperature; percent by volume of ethylene 
in reactor; H.sub.2 /ethylene mol ratio; comonomer (C.sub.x)/C.sub.2 mol 
ratio in reactor; catalyst productivity and Zn/Ti mol ratio. Table B below 
lists properties of the granular virgin resins made in runs 1 to 14, i.e., 
density, melt index (M.I.); melt flow ratio (MFR); weight percent ash; Ti 
content (ppm), bulk density and average particle size. 
TABLE A 
______________________________________ 
Reaction Conditions For Runs 1 to 14 
Al/ti 
ratio 
Weight in part. 
Al/Ti 
% act ratio H.sub.2 /C.sub.2 
C/C.sub.2 
Run pre- pre- in Temp Vol % mol mol 
No cursor cursor reactor 
C. C.sub.2 
ratio ratio 
______________________________________ 
1 8.3 5.8 40.5 90 41.7 0.492 0.486 
2 8.3 5.8 50.8 90 39.7 0.566 0.534 
3 20.1 4.50 88.3 85 56.3 0.148 0.450 
4 19.8 4.40 26.7 85 50.2 0.350 0.350 
5 19.8 4.40 26.7 80 54.1 0.157 0.407 
6 6.9 5.08 42.0 85 49.2 0.209 0.480 
7 6.9 5.08 33.6 85 46.5 0.208 0.482 
8 6.9 5.08 28.8 85 42.1 0.206 0.515 
10 8.3 5.8 124.6 90 45.1 0.456 0.390 
11 8.3 5.8 80.8 90 42.7 0.365 0.396 
12 8.3 5.8 52.0 90 48.4 0.350 0.397 
13 8.3 5.8 140.1 90 42.6 0.518 0.393 
14 8.3 5.8 63.5 90 40.8 0.556 0.391 
______________________________________ 
TABLE B 
______________________________________ 
Properties of Polymers Made in Runs 1 to 14 
average 
bulk particle 
Run No Density M.I. MFR density 
size, inches 
______________________________________ 
1 0.927 22.0 24.4 16.8 0.0230 
2 0.929 24.0 23.4 17.5 0.0230 
3 0.925 0.61 27.1 16.8 0.0300 
4 0.931 12.0 26.7 16.8 0.0275 
5 0.923 1.47 28.2 15.6 0.0404 
6 0.919 3.41 25.9 16.8 0.0550 
7 0.925 2.90 24.5 17.5 0.0590 
8 0.919 3.10 24.6 16.2 0.0570 
10 0.929 16.0 24.1 17.3 0.0230 
11 9.929 15.3 24.0 16.6 0.0234 
12 0.928 11.5 24.1 16.7 0.0248 
13 0.929 20.7 24.3 17.3 0.0258 
14 0.929 29.2 26.1 16.8 0.0206 
______________________________________ 
EXAMPLE 2 
An ethylene-butene copolymer prepared as in Example 1 and having a density 
of 0.924 and a melt index of 2.0 was formed into a film of 1.5 mil gauge 
by blown film extrusion using a 21/2 inch diameter 18:1 L/D extrusion 
screw in a 24/1 extruder. The extrusion screw had a feed section of 12.5 
inches, transition section of 7.5 inches, a metering section of 20 inches, 
and a mixing section of 5 inches. The mixing section was a fluted mixing 
section with the following characteristics: a diameter of 2.5 inches; 3.0 
inch channels; channel radius of 0.541 inches; mixing barrier land width 
of 0.25 inches; cleaning barrier land width of 0.20 inches; and a mixing 
barrier length of 4.5 inches. The void in the barrel was filled by a plug 
2.496 inches in diameter, 11.0 inches long which contained a static mixer 
9.0 inches long and 1.0 inch in diameter. Also, a 20/60/20 mesh screen 
pack and a three inch diameter die were used. The die had a gap of 40 
mils. The sides of the die were parallel with the flow axis of the polymer 
melt. The melt temperature of the copolymer was about 400.degree. F. Nip 
roll height was approximately 15 ft. Cooling was accomplished with a 
Venturi type air ring. All films were prepared at a 2:1 blow-up ratio 
(ratio of bubble circumference to die circumference). The rate of 
production of the film was 7.27 lbs/hour/inch of die. Sharkskin melt 
fracture was measured using a 40.times. magnification microscope. In this 
procedure, the extrudate is lighted from the side. The microscope shows 
the transition from a low-shear glossy surface of the extrudate to a 
critical-shear, matted surface (the onset of sharkskin melt fracture) to 
high-shear, deep-ridge, sharkskin melt fracture. A high level of sharkskin 
melt fracture was observed during production of the film. 
EXAMPLE 3 
The procedure of Example 2 was exactly repeated except that melt 
temperature was about 380.degree. F. and the rate of production of the 
film was 4.14 pounds/hour/inch of die. A high level of sharkskin melt 
fracture was observed during production of the film. 
EXAMPLE 4 
The procedure of Example 2 was exactly repeated except that the die had a 
gap of 80 mils, melt temperature was about 390.degree. F. and the rate of 
production of the film was 7.38 pounds/hour/inch of die. A low level of 
sharkskin melt fracture was observed during production of the film. 
EXAMPLE 5 
The procedure of Example 2 was exactly repeated except that a die had the 
configuration as in FIG. 3i was used with angle .alpha.=4.57.degree., and 
dimensions k=80 mils, m=50 mils, and n=40 mils in FIG. 3i. Melt 
temperature was about 398.degree. F. and the rate of production of the 
film was 7.22 pounds/hour/inch of die. No melt fracture was observed 
during production of the film. 
EXAMPLE 6 
The procedure of Example 2 was exactly repeated except that the die 
described in Example 5 was used, melt temperature was about 410.degree. F. 
and the rate of production of the film was 8.38 pounds/hour/inch of die. A 
low level of sharkskin melt fracture was observed during production of the 
film. 
The results of Examples 2 to 6 are summarized in Table I. 
TABLE I 
______________________________________ 
Die 
Ex- Die Rate Die 
am- gap Die (lb/hr/in 
temp Melt 
ple (mils) design of die) 
(.degree.F.) 
Fracture 
______________________________________ 
2 40 Parallel surfaces 
7.27 400 High level 
3 40 Parallel surfaces 
4.14 380 High level 
4 80 Parallel surfaces 
7.38 390 Low level 
5 80 One side divergent 
7.22 398 None 
6 80 One side divergent 
8.38 410 Low level 
______________________________________ 
The data of Table I show that the final die gap opening is the primary 
geometric factor controlling sharkskin melt fracture. Examples 2 and 3 in 
which the sides of the die are parallel and which have a die gap of 40 
mils produce film with a high level of melt fracture. This high level of 
melt fracture occurs in Example 3 with the much lower rate of formation of 
film. A comparison of a die having one surface of the die lip at a 
divergent angle from the flow axis of the melt through the die (a die of 
the present invention, Example 5) with a die having parallel sides 
(Example 4), with the die gap of each die=80 mils, no melt fracture occurs 
with the die of the present invention. Even at a higher production rate 
and higher die temperature, the die of the present invention (Example 6) 
produces a low level of melt fracture. 
EXAMPLE 7 
An ethylene-butene copolymer prepared as in Example 1 and having a density 
of 0.924 and a melt index of 2.0 was formed into a film of 1.5 mil gauge 
by blown film extrusion using a 21/2 inch diameter screw extruder as 
described in Example 2. 
The die with the configuration as shown in FIG. 3i was used. Angle 
.alpha.=5.7.degree., the die gap (dimension k)=100 mils, m=500 mils, and 
n=60 mils. The melt temperature of the copolymer was about 400.degree. F. 
Nip roll height was approximately 15 ft. Cooling was accomplished with a 
Venturi type air ring. Blow up ratio was 2:1. The rate of production of 
the film was 7.0 lbs/hour/inch. Sharkskin melt fracture was determined as 
in Example 2. No melt fracture was observed during production of the film. 
EXAMPLE 8 
The procedure of Example 7 was exactly repeated except that the angle 
.alpha. of the die was 20.degree. and m=0.110 inches. No melt fracture was 
observed during production of the film. 
EXAMPLE 9 
The procedure of Example 7 was exactly repeated except that the angle of 
the die was 40.degree. and m=0.050 inches. No melt fracture was observed 
during production of the film. 
EXAMPLE 10 
The procedure of Example 7 was exactly repeated except that the angle 
.alpha. of the die was 0.degree., and m=0 inches, i.e., the sides of the 
die were parallel. A high level of melt fracture was observed during 
production of the film. 
These Examples 7 to 10 demonstrate that when using the die of the present 
invention (Examples 7 to 9), no melt fracture was observed even when the 
angle of divergence was as high as 40.degree. (Example 9). When the die 
sides were parallel, a high level of melt fracture was observed for a die 
gap equivalent to the upstream land separation before the divergent 
section. 
EXAMPLE 11 
An ethylene-butene copolymer prepared as in Example 1 and having a density 
of 0.919 and a melt index of 2.0 was formed into a rod using a capillary 
rheometer. 
The rod die was 2.40 cm long with parallel sides and a constant internal 
diameter of 0.123 cm. The melt temperature of the copolymer was 
180.degree. C. The polymer was extruded at a volumetric flow rate of 0.011 
cm.sup.3 /sec. 
The apparent shear rate .gamma..sub..alpha. was determined according to the 
following equation: 
EQU apparent shear rate .gamma..sub..alpha. =(4Q/.pi.r.sup.3), sec.sup.-1 
Q=volumetric flow rate, cm.sup.3 /sec 
r=internal radius of the die, cm. 
The apparent shear rate at the onset of melt fracture was 60 sec.sup.-1 
(with r in the equation=radius of the die at the exit). Also, the channel 
shear rate was 60 sec (with r in the equation=radius of the channel.) 
EXAMPLE 12 
The procedure of Example 11 was exactly repeated except that the rod die 
was 2.54 cm. long with entry section 0.337 cm in diameter and die gap of 
0.126 cm. The die lip was convergent with the same cross section as shown 
in FIG. 3iii with the angle of convergence=10.degree.. 
The melt temperature of the copolymer was 180.degree. C. The polymer was 
extruded at a volumetric flow rate of 0.0244 cm.sup.3 /sec. The apparent 
shear rate was determined as in Example II. The apparent shear rate at the 
onset of melt fracture was 125 sec.sup.-1 (with r in the equation=radius 
of the die at the exit). Also, the channel shear rate was 7 sec.sup.-1 
(with r in the equation=radius of the channel) 
The data of Examples 11 and 12 show that at approximately the same exit 
diameter, using the die of the present invention (Example 12) about twice 
the flow rate of polymer through the die is possible before the onset of 
melt fracture as compared to a die, with parallel sides.