Extrudable compositions comprising a thermoplastic polyester continuous phase, a thermoplastic polyolefin discrete phase, and a polyester-polyether, diblock, compatibilizer are disclosed. Voided films made from the composition are also disclosed. The voided films have paper-like texture and appearance.

This invention relates to compositions comprising a polyester continuous 
phase, a polyolefin discrete phase, and a third component. This invention 
also relates to voided films made from the compositions of this invention 
and to methods of making such voided films. 
Polyester compositions, in particular, polyester films, are well-known 
important materials with many uses. Sometimes a minor amount of a second 
polymer is blended with the polyester to improve selected properties, for 
example, U.S. Pat. No. 3,579,609 (Sevenich) describes modified 
poly(ethylene terephthalate) film prepared from compositions comprising 
minor amounts of fusible, heat-stable homopolymers or copolymers of 
mono-alpha olefin blended with poly(ethylene-terephthalate) polymer. 
A second component can be added to help prepare voided films. For example, 
U.S. Pat. No. 3,944,699 (Mathews et al.) discloses opaque voided films 
made from blends of a polyester with 3 to 27% of an ethylene or propylene 
polymer. See also, for example, European Patent Publication 451,797 
(Hamano et al.). Other examples of voided films are described, for 
example, in U.S. Pat. No. 4,377,616 (Ashcraft et al.). 
Sometimes a third component is added to the polymer blend. For example, 
U.S. Pat. No. 4,368,295 (Newton et al.) discloses film prepared from a 
composition comprising polyester, polyolefin, and carboxylated polyolefin 
additive. Such additive is said to allow more uniformly opaque or 
translucent films to be produced. See also U.S. Pat. No. 4,771,108 
(Mackenzie). 
U.S. Pat. No. 4,871,784 (Otonari et al.) discloses certain voided film 
comprising a polyester continuous phase, a polypropylene minor phase, and 
certain surface active agents. 
U.S. Pat. No. 5,194,468 (Abu-Isa et al.) discloses certain thermoplastic 
blends comprising polyester and high density polyethylene. In one example, 
a thermoplastic elastomer was added but it was concluded that the addition 
of the elastomer did not enhance the compatibility of the blend. 
Sometimes the polyester is the minor component in a polymer blend, with 
polyolefin as the major component, with or without a third component. See, 
for example, U.S. Pat. Nos. 4,615,941 (Lu) and 4,615,942 (Lu). 
U.S. Pat. No. 4,968,464 (Kojoh et al.) discloses a process for producing a 
porous film containing a polyolefin resin as a main component, comprising 
melting a mixture of polyolefin, polyester-polyether thermoplastic 
elastomer, and thermoplastic polyester. 
Briefly, in one aspect, the present invention provides an extrudable 
thermoplastic composition comprising a thermoplastic polyester continuous 
phase, a thermoplastic polyolefin discrete phase, and a 
polyester-polyether, diblock, compatibilizer stable at the extrusion 
temperature of the composition. Preferably, the ratio of the viscosity of 
said polyolefin to said polyester is close enough to 1.0 that the 
composition will not fibrillate during extrusion. 
In another aspect, the present invention provides voided film comprising 
the composition of this invention. 
This invention also provides a method for preparing a voided film 
comprising the steps of A) preparing the composition of this invention, B) 
extruding said composition into a film or sheet, and C) orienting said 
film or sheet to produce voids. Said preparation step can comprise mixing 
in an extruder utilizing conventional shear rates. Preferably, said 
compatibilizer is present at 1% or less by weight based on the total 
weight of said polyester and said polyolefin. More preferably, said 
compatibilizer is present at an amount sufficient to narrow the size 
distribution of the thermoplastic olefin phase, but less than that amount 
which would substantially decrease the amount of voids or voiding in the 
oriented article, e.g., film or sheet. 
The resulting films of this invention are opaque films which exhibit a 
remarkable paper-like texture and appearance and are therefore suitable 
for use as a paper substitute, in applications such as photographic 
printing papers, release liners, paper-backed adhesive products, etc. The 
films of this invention are generally more glossy or pearlescent than 
typical papers. 
The thermoplastic polyester continuous phase generally comprises linear 
homopolyesters or copolyesters, such as homopolymers and copolymers of 
terephthalic acid and isophthalic acid. The linear polyesters may be 
produced by condensing one or more dicarboxylic acids or a lower alkyl 
diester thereof, e.g., dimethylterephthalate, terephthalic acid, 
isophthalic acid, phthalic acid, 2,5-, 2,6-, or 2,7-naphthalene 
dicarboxylic acid, succinic acid, sebacic acid, adipic acid, azelaic acid, 
bibenzoic acid and hexahydroterephthalic acid, or 
bis-p-carboxyphenoxyethane, with one or more glycols, e.g., ethylene 
glycol, pentyl glycol, and 1,4-cyclohexanedimethanol. The particularly 
preferred polyester is polyethylene terephthalate. 
Sufficient intrinsic viscosity is required in the continuous phase to yield 
a finished film with adequate physical properties to be useful in the 
desired applications, such as adhesive tapes, abrasive article substrates, 
and the like. Generally, the intrinsic viscosity should be greater than 
about 0.5 in the case of polyethylene terephthalate when measured at 
30.degree. C. using a solvent consisting of 60% phenol and 40% 
o-dichlorobenzene (ASTM D4603). 
Polymers suitable for the discrete phase include polyolefins such as 
polypropylene. The preferred polyolefins are those with melt flow index 
(MFI), or viscosity, close to the MFI, or viscosity, of the polyester 
matrix (continuous phase) at the processing conditions used (for example, 
temperature and shear rate). Preferably, the viscosity ratio of the 
polyolefin to the polyester at the processing conditions is from 0.5 to 
2.0. The desired morphology consists of roughly spherical polyolefin 
domains smaller than approximately 30 microns in diameter, preferably 
smaller than 15 microns in diameter. If the viscosity of the polyolefin is 
too high (i.e., the polyolefin MFI is too low) relative to the polyester, 
large polyolefin domains are formed under normal processing conditions in 
the extruder. Large polyolefin domains are undesirable because they give 
rise to large voids during film orientation which, in turn, can cause web 
breaks during processing. If the polyolefin viscosity is too low, relative 
to the polyester, adequate dispersion of the polyolefin is obtained in the 
extruder; however, under normal operating conditions, the low viscosity 
polyolefin domains tend to elongate in the flow direction near the surface 
of the web adjacent to the die during extrusion. Fibrillar polyolefin 
domains in the flow direction can cause the film to be very weak in the 
transverse direction, making orientation in the transverse direction 
difficult. 
The amount of added polyolefin will affect final film properties. In 
general, as the amount of added polyolefin increases, the amount of 
voiding in the final film also increases. As a result, properties that are 
affected by the amount of voiding in the film, such as mechanical 
properties, density, light transmission, etc., will depend upon the amount 
of added polyolefin. As the amount of polyolefin in the blend is 
increased, a composition range will be reached at which the olefin can no 
longer be easily identified as the dispersed, or discrete, phase. Further 
increase in the amount of polyolefin in the blend will result in a phase 
inversion wherein the polyolefin becomes the continuous, phase. 
Preferably, the amount of the polyolefin in the composition is from 15% by 
weight to 45% by weight, more preferably from 20% by weight to 35% by 
weight, most preferably from 25% by weight to 30% by weight. 
Additionally, the selected polyolefin must be incompatible with the matrix 
or continuous phase selected. In this context, incompatibility means that 
the discrete phase does not dissolve into the continuous phase in a 
substantial fashion, i.e., the discrete phase must form separate, 
identifiable domains within the matrix provided by the continuous phase. 
The polyester-polyether copolymers useful as compatibilizers in this 
invention may change the size distribution of the discrete phase during 
the extrusion process. Suitable compatibilizers are those which tend to 
reduce the domain size of the discrete phase. The primary benefit appears 
to be achieved by reducing the size of the largest domains of the discrete 
phase. This size distribution change can be observed by comparing solid 
samples of different compositions. A technique which is useful in 
preparing samples for observation of the phases is forming or selecting a 
solid sample, cooling the sample in liquid nitrogen or other suitable 
quenching medium, and fracturing the sample. This technique should expose 
a fresh fracture surface which exhibits the morphology of the phases as 
illustrated in the attached electron micrographs. 
The compatibilizer must also withstand the thermal exposure encountered 
during the process of extrusion of the blend, i.e., the temperature 
required to process the highest melting component or the blend, which will 
normally be the processing temperature required of the continuous phase. 
Representative examples of polyester-polyether block copolymers useful in 
this invention include Ecdel.TM. 9965, 9966, and 9967 elastomeric 
copolymers, available from Eastman Chemical Co. and thought to be block 
copolymers consisting of hard and soft segments of cyclohexane-based 
(1,4-cyclohexanedimethanol and 1,4-cyclohexanedicarboxylic acid) with 
polytetramethylene oxide segments. The different grades are said to 
represent varying molecular weights of approximately the same ratios of 
hard and soft segments. Polyester-ether block copolymers based on 
polybutylene terephthalate and polytetramethylene oxide are also useful in 
this invention, as are similar polyester-ether copolymers in which another 
acid group, such as isophthalic acid, is substituted all or in part for 
the acid group of the polyester, or another glycol component is 
substituted all or in part for the glycol portion of either the polyester 
or polyether blocks. Hytrel.TM. thermoplastic elastomers such as G4074 and 
G5544, available from DuPont, both thought to be such polyester-ether 
block copolymers, are also suitable compatibilizer materials. Other 
examples of trade names of commercially available polyester-ether block 
copolymers are RITEFLEX.TM. (available from Hoechst-Celanese Corp.), 
PELPRENE.TM. (available from Toyobo Co., Ltd.) and LOMOD.TM. (available 
from General Electric Co.). 
Films made using ethylene-acrylic acid copolymers as proposed 
compatibilizers result in brittle films. Such compatibilizers may 
separately form a third phase or fail to reduce the size distribution of 
the discrete phase. Unacceptable changes in the morphology of the blend 
from an unacceptable compatibilizer include the formation of a second 
co-continuous phase of the discrete component instead of the formation of 
discrete droplets. 
Materials not suitable as compatibilizers may be unable to alter the size 
distribution of the discrete phase or may tend to make the discrete phase 
too miscible with the continuous phase and thereby lose the ability of the 
discrete phase to separate into discrete droplets. In some applications, 
where the goal is a finished film with lower overall density, excessive 
compatibility to the point of not allowing voiding to occur during 
orientation will also be unacceptable. Addition of amounts of the 
compatibilizer component must be controlled, as too much may cause the 
over-compatibilization of the discrete phase resulting in no voiding. 
The process by which the finished articles are made may also have an effect 
on the finished morphology and finished physical properties. Generally 
speaking, a film of the invention may be made by using conventional 
film-making technology. This includes a means of drying, blending, and 
supplying resins to an extruder, a means of extruding the blended 
materials in a manner to properly melt and adequately mix the components, 
an optional means of filtering the melt, a means of casting or of forming 
a sheet (in the case of a flat film) or forming a tube or bubble (in the 
case of tubular extrusion or blown films), a means of orienting or 
stretching the sheet or tube (either sequentially or simultaneously), an 
optional means of heat setting or stabilizing the oriented film or tube 
(bubble), and an optional means of converting the finished film or 
slitting the tube or bubble. 
A process of dry blending the polyolefin and compatibilizer has been found 
to be useful. For instance, blending may be accomplished by mixing the 
finely divided, e.g., powdered or granular, thermoplastic olefin discrete 
phase component and the compatibilizer and tumbling them together in a 
container. The dry blend is then fed to the extruder in a conventional 
manner. 
Blending dry components may also be accomplished by separately feeding 
measured quantities of each component into an extruder hopper or throat at 
a rate corresponding to the ratio of the components desired in the 
finished article. The use of recycle materials may also be accomplished at 
this point. When feeding previously blended or extruded polyester, 
polyolefin, and compatibilizer materials, such as in a recycle feedstock, 
an appropriate adjustment in the feed rate of all other components is 
required to result in the final film containing the desired ratio of all 
components. 
Alternatively, blending of the components may be affected by combining melt 
streams of the continuous component, e.g., polyester, and the other 
polymeric additives during the extrusion process. A common means to 
accomplish this is to add the minor components by extruding them as a melt 
stream at the desired ratio into the extruder barrel containing the major 
component. The ratio of the components may then be controlled by the 
separate rates of the separate extruders. 
If filtration of the melt stream(s) is desired, this is generally 
accomplished by including a filtration device between the outlet or gate 
of the extruder and the slot or tube die. Tubular filter elements or 
folded fabric filter elements are commercially available and their use is 
common in the polymer extrusion industry. 
The extrusion, quenching and stretching or orientation of the film may be 
effected by any process which is known in the art for producing oriented 
film, e.g., by a flat film process or a bubble or tubular process. The 
flat film process is preferred for making film according to this invention 
and involves extruding the blend through a slot die and rapidly quenching 
the extruded web upon a chilled casting drum so that the continuous phase 
of the film is quenched into the amorphous state. The quenched film is 
then biaxially oriented by stretching in mutually perpendicular directions 
at a temperature above the glass transition temperature of the 
thermoplastic polyester continuous phase. Generally, the film is stretched 
in one direction first and then in a second direction perpendicular to the 
first. However, stretching may be effected in both directions 
simultaneously if desired. In a typical process, the film is stretched 
firstly in the direction of extrusion over a set of rotating rollers or 
between two pairs of nip rollers and is then stretched in the direction 
transverse thereto by means of a tenter apparatus. Films may be stretched 
in each direction up to 3 to 5 times their original dimension in the 
direction of stretching. 
The temperature of the first orientation (or stretching) affects film 
properties. Generally, the first orientation step is in the machine 
direction. Orientation temperature control may be achieved by controlling 
the temperature of heated rolls or by controlling the addition of radiant 
energy, e.g., by infrared lamps, as is known in the art of making 
polyethylene terephthalate films. A combination of temperature control 
methods may be utilized. 
Too low an orientation temperature may result in a film with an uneven 
appearance. Increasing the first orientation temperature may reduce the 
uneven stretching, giving the stretched film a more uniform appearance. 
The first orientation temperature also affects the amount of voiding that 
occurs during orientation. In the temperature range in which voiding 
occurs, the lower the orientation temperature, generally the greater the 
amount of voiding that occurs during orientation. As the first orientation 
temperature is raised, the degree of voiding decreases to the point of 
elimination. Electron micrographs of samples show that at temperatures at 
which no voiding occurs, the polyolefin domains often deform during 
stretching. This is in contrast to highly voided oriented samples; 
electron micrographs of highly voided samples show that the polyolefin 
domains in general retain their approximately spherical shape during 
orientation. 
Generally, a second orientation, or stretching, in a direction 
perpendicular to the first orientation is desired. The temperature of such 
second orientation is generally similar to or higher than the temperature 
of the first orientation. 
After the film has been stretched it may be further processed. For example, 
the film may be annealed or heat-set by subjecting the film to a 
temperature sufficient to further crystallize the thermoplastic polyester 
continuous phase while restraining the film against retraction in both 
directions of stretching. 
The film may, if desired, conveniently contain additives conventionally 
employed in the manufacture of thermoplastics polyester films. Thus, 
agents such as dyes, pigments, fillers, inorganic voiding agents, 
lubricants, anti-oxidants, anti-blocking agents, surface active agents, 
slip aids, gloss-improvers, ultraviolet light stabilizers, viscosity 
modifiers and dispersion stabilizers may be incorporated, as appropriate. 
Films of this invention may be used without further treatment or they may 
be further treated, for example, by the application of a coating. This 
coating may provide enhanced functions such as adhesion, release, barrier, 
antistatic, abrasion resistance, or heat sealability, and can be applied 
by any conventional coating means. A further method of producing a coated 
film is to apply the coating to the film at some stage before orientation, 
or preferably, in the case of biaxially oriented film, between the two 
stages of biaxial orientation of the film. Suitable coatings which may be 
applied in this way include, for example, coatings of vinylidene chloride 
copolymers, for example, vinylidene chloride/acrylonitrile copolymers 
containing from 4 to 20% of acrylonitrile. 
The films may be used in any of the applications for which polyethylene 
terephthalate is used except, of course, those where a high degree of 
transparency is required. For example, the film may be used as a paper 
substitute, as a base for carbon paper and carbon ribbon for use in 
typewriters, in applications in which very high speed printing machines 
are used in conjunction with computers, textile threads where the 
decorative appearance of the films is useful, magnetic recording tape, 
cable wrapping and as a thermal barrier, for example, in protective 
clothing. The films of this invention may be part of multi-layer 
compositions comprising layers of non-voided films or other materials. 
The films of this invention exhibit a remarkable paper-like texture and 
appearance and are therefore suitable for use as a paper substitute, in 
applications such as photographic printing papers, release liners, 
paper-backed adhesive products, etc. The films of this invention are 
generally more glossy or pearlescent than typical papers.

EXAMPLES 
In the following Examples and Comparative Examples a variety of extrudable 
compositions were prepared with a polyester continuous phase and a 
polypropylene discrete phase. Some of these compositions were extruded 
into film. 
Example 1 
An additive blend of materials was made by dry blending 30 parts (30% by 
wt) FINA 3374X polypropylene (available from Fina Oil and Chemical Co.) 
having a melt flow index (mfi) of 2.5 (determined by ASTM D1238-90b) and a 
compatibilizer consisting of 0.25 parts (0.25% by wt.) of pre-dried 
HYTREL.TM. G4074 engineering thermoplastic elastomer (available from E. I. 
DuPont deNemours & Co., Inc.). This blend was then fed to the input of a 
2.5 inch (6.35 cm) extruder using a volumetric solids feeder to control 
the rate of addition. An additional feed stream of 69.75 parts (69.75% by 
wt.) dried, extrusion grade polyethylene terephthalate (PET), with an 
intrinsic viscosity (I.V.) of 0.58 to 0.64 and a melt point of about 
253.degree. C. (determined as the maximum in the melting peak of the 2nd 
heating scan taken @ 20.degree. C./Min. using a Perkin-Elmer DSC7), was 
fed to the input of the extruder. The total feed rate was about 100 
lbs/hr. The extruder had a 24:1 L/D barrel and was equipped with a mixing 
screw to provide enhanced mixing of the components. A filter for 
particulate control and a gear pump for flow rate control were installed 
between the extruder gate and a 14.5 inch (36.8 cm) wide sheeting die with 
a die gap of about 0.040 inches (0.10 cm). The extruder temperatures were 
approximately: zone 1 455.degree. F. (235.degree. C.), zone 2 499.degree. 
F. (259.degree. C.), zone 3 500.degree. F. (260.degree. C.), zone 4 
510.degree. F. (266.degree. C.), gate 510.degree. F. (266.degree. C.), 
filter, gear pump and necktube 530.degree. F. (277.degree. C.), and die 
525.degree. F. (274.degree. C.). A static mixer was used in the necktube, 
close to the die, in order to minimize thermal gradients in the melt. The 
sheet formed by the die was cast onto a temperature controlled casting 
wheel maintained at a temperature of about 110.degree. F. (43.degree. C.) 
and the cast sheet was held in place by electrostatic pinning. A finished 
film was then made using conventional polyester film biaxial orientation 
equipment to stretch the film in the machine direction (MD) about 3.4 
times by preheating the cast web to about 200.degree. F. (93.degree. C.) 
and then stretching at a temperature of about 225.degree. F. (107.degree. 
C.) and then to stretch the film in the transverse direction (TD) about 
3.0 times at a temperature of about 245.degree. F. (118.degree. C.). The 
stretched film was then subjected to a heat set temperature of about 
420.degree. F. (216.degree. C.) for about 20 sec. while the film was 
restrained. 
Examples 2-6 
In Example 2, film was made as in Example 1 except the compatibilizer and 
PET percentages were varied as shown in Table 1. In Examples 3-6, films 
were made as in Example 1 except the compatibilizer and PET percentages 
were varied as shown in Table 1 and the MD stretch temperature was about 
240.degree. F. (116.degree. C.). The polypropylene percentage remained at 
30 wt %. Because the thickness of the finished film will vary with changes 
in compatibilizer level, changes in casting wheel speed were made to keep 
the finished film thickness within the range of about 3.5 to 4.5 mils 
(0.089 to 0.11 mm) where necessary. The finished film thickness was 
measured using a contact micrometer with a foot size of about 1.25 cm in 
diameter to allow a reading to be taken without "denting" the film as 
would result from a stylus-type foot. The compositions and densities of 
the resulting films are summarized in Table 1. 
Comparative Example C1 
In Comparative Example C1, film was made as in Example 1 except no 
HYTREL.TM. G4074 thermoplastic elastomer was added as a compatibilizer. 
The polypropylene percentage remained at 30 wt %. The resulting film 
density and composition are also included in Table 1. 
The film density was calculated by using a calculated sample weight per 
sample volume as follows. Five disks 1.971 inches (5 cm) in diameter were 
stamped out using a circular die and the sample density was calculated as 
follows: 
##EQU1## 
TABLE 1 
______________________________________ 
PET, Compatibilizer, 
Density, 
Ex. Wt % Wt % g/cc 
______________________________________ 
C1 70 0 0.58 
1 69.75 0.25 0.78 
2 69.5 0.5 1.01 
3 69 1 1.05 
4 68 2 1.07 
5 65 5 1.08 
6 60 10 1.04 
______________________________________ 
The data in Table 1 show that low density films can be made at low levels 
of compatibilizer addition. 
Comparative Example C2 and Examples 7 and 8 
Comparative Example C2 and Examples 7 and 8, films were made as in 
Comparative Example C1, and Examples 1, and 2 respectively except FINA 
3230 polypropylene (mfi of 1.6) was used instead of FINA 3374X 
polypropylene (mfi of 2.5) and the MD preheat temperatures were about 
205.degree. F. (95.degree. C.). TD stretch temperatures were varied in a 
range of 250.degree. F. (121.degree. C.) to 315.degree. F. (157.degree. 
C.) in an attempt to locate an appropriate temperature at which to TD 
orient Comparative Example C2. A suitable temperature was not found and 
numerous web breaks resulted. When 0.25 lbs/hr of Hytrel.TM. G4074 
thermoplastic elastomer was added to the extruder to produce Example 7, 
the TD stretch temperature was lowered to about 275.degree. F. 
(135.degree. C.) and the frequency of web breaks was substantially 
reduced. Example 8 was also produced at a TD stretch temperature of about 
275.degree. F. (135.degree. C.) without web breaks. In each case, the 
heatset temperature was about 420.degree. F. (216.degree. C.). 
FIG. 1 is an SEM micrograph of the unoriented cast web sample of the 
composition described in Comparative Example C2 (without compatibilizer). 
FIG. 1 shows the approximate center of the cast web cross-section. The 
machine direction is shown by the arrows in the micrograph. Note the 
numerous larger (about 15-20 microns) polypropylene domains seen in the 
micrograph. 
FIG. 2 is an SEM micrograph of the unoriented cast web sample of the 
composition described in Example 8. FIG. 2 shows the approximate center of 
the cast web cross-section. The machine direction is shown by the arrows 
in the micrograph. Note the absence of the larger (about 15-20 microns) 
polypropylene domains in the compatibilized sample of FIG. 2 when compared 
to the uncompatibilized sample in FIG. 1. 
FIG. 3 is an SEM micrograph of the machine direction oriented (MDO) web 
sample of the composition described in Example 8. FIG. 3 shows the 
approximate center of the MDO web cross-section. The machine direction is 
shown by the arrows in the micrograph. The voids that form around the 
polypropylene domains as a result of stretching the film are easily seen 
in FIG. 3. 
In Examples 9-11, films were produced as in Example 8 except the MD stretch 
temperature was about 240.degree. F. (116.degree. C.). The compositions 
and results of density testing are summarized in Table 2. 
TABLE 2 
______________________________________ 
PET, Compatibilizer, 
Density, 
Thickness, 
Ex. Wt % Wt % g/cc mils 
______________________________________ 
C2 70 0 0.60 4.0 
7 69.25 0.25 0.69 4.3 
8 69.5 0.5 0.80 3.7 
9 69.0 1.0 0.95 3.0 
10 68.0 2.0 1.01 2.7 
11 65.0 5.0 1.08 3.6 
______________________________________ 
During the processing of Comparative Example C2, numerous web breaks and 
processing problems were encountered. The larger polypropylene domains 
observed in Comparative Example C2 (see FIG. 1) may cause large voids to 
be generated during stretching. These large voids may be the source of the 
processing problems and web breaks resulting from large voids generated 
during stretching. Examples 7-11 were produced with substantially fewer 
web breaks. The data in Table 2 show that low levels of compatibilizer 
produce acceptable, low density films. 
The films from the above Examples and Comparative Examples were tested for 
the following physical properties. 
Light transmission values were obtained using a Gardner Hazemeter Model 
UX10 in accordance with ASTM D1003. 
Heat shrinkage data in (MD) were obtained by cutting a sample strip 1 inch 
wide, about 12 inches long, placing marks on the sample strip 10 inches 
apart, fastening one end of the sample strip to a rack designed to hold 
multiple sample strips, inserting the rack with the sample strip(s) into a 
convection oven set at 150.degree. C., heating the sample to 150.degree. 
C. for 15 minutes, cooling the sample to room temperature and measuring 
the change in length between the 10 inch marks. This change was reported 
as a percent shrinkage. The designation "left/center/right" refers to the 
location in the film from which the test sample was cut. 
Physical properties such as modulus, break strength, and break elongation 
were determined by ASTM D882 with 1 inch sample width, 4 inch jaw gap, 2 
inch/min jaw speed on a Model 4502 Instron.TM. tensile tester. A sample 
for MD testing was cut parallel to the MD direction. 
Roughness was obtained by testing on a Rodenstock Model RM 600, which 
utilizes a non-contacting, dynamically focused laser beam. Vapor coated 
samples were tested using the following conditions, a range of 30 microns, 
a table speed of 10 mm/min, 8000 points, a scan length of 5 mm, a low 
frequency cutoff of 0.10 and a high frequency cutoff of 10.0. The two 
R.sub.q values (defined as the geometric average from the test center 
line) were obtained by testing both sides of the samples. 
The test results are summarized in Table 3. 
TABLE 3 
__________________________________________________________________________ 
Break Break 
Light MD Shrinkage 
Modulus 
Strength 
Elongation 
Density, 
Transmission, 
Left/Center/Right, 
MD .times. TD, 
MD .times. TD, 
MD .times. TD, 
Roughness 
Ex. 
g/cc 
% % ksi ksi % R.sub.q, microns 
__________________________________________________________________________ 
C1 0.58 
18.3 1.3/1.2/1.3 
208 .times. 183 
6.29 .times. 4.93 
28.6 .times. 12.8 
1.03 .times. 0.859 
1 0.78 
22.9 1.4/1.4/1.5 
283 .times. 262 
9.86 .times. 8.42 
39.3 .times. 23.9 
0.982 .times. 0.792 
2 1.01 
44.6 1.2/1.0/1.1 
335 .times. 367 
9.30 .times. 11.3 
28.6 .times. 33.8 
0.997 .times. 0.774 
3 1.05 
51.9 1.1/1.0/1.2 
326 .times. 378 
7.77 .times. 10.2 
14.4 .times. 26.7 
0.832 .times. 0.765 
4 1.07 
63.3 1.2/1.0/1.1 
297 .times. 366 
6.32 .times. 9.21 
5.6 .times. 17.2 
0.933 .times. 1.070 
5 1.08 
75.1 1.2/1.0/1.2 
286 .times. 351 
6.01 .times. 9.08 
5.5 .times. 19.6 
0.764 .times. 0.909 
6 1.04 
69.9 1.1/1.0/1.1 
255 .times. 310 
5.10 .times. 7.48 
3.9 .times. 10.3 
0.997 .times. 0.897 
C2 0.60 
17.8 1.5/1.3/1.2 
230 .times. 228 
7.16 .times. 6.93 
28.5 .times. 15.2 
0.598 .times. 0.452 
7 0.69 
9.7 1.4/1.2/1.3 
224 .times. 213 
8.08 .times. 6.78 
35.4 .times. 18.6 
0.842 .times. 0.768 
8 0.80 
12.8 1.5/1.3/1.3 
252 .times. 244 
8.65 .times. 7.74 
33.2 .times. 19.7 
0.942 .times. 0.975 
9 0.95 
24.7 13./1.2/1.3 
312 .times. 328 
9.06 .times. 9.97 
31.0 .times. 26.6 
0.942 .times. 0.633 
10 1.01 
40.2 1.3/1.0/1.2 
307 .times. 357 
7.61 .times. 10.44 
20.3 .times. 26.6 
0.773 .times. 0.641 
11 1.08 
47.8 1.3/1.1/1.2 
288 .times. 379 
6.36 .times. 10.57 
23.4 .times. 28.7 
0.801 .times. 0.626 
__________________________________________________________________________ 
The data in Table 3 show that as the wt % Hytrel.TM. G4074 thermoplastic 
elastomer compatibilizer was increased, the density of the finished film 
also increased. This appears to indicate that the amount of voiding in the 
film decreased with increasing wt % compatibilizer. This appears to be 
confirmed with SEM micrographs as well as light transmission measurements. 
Light transmission increases as voiding decreases, probably because there 
are fewer or smaller voids around the polypropylene domains to scatter 
light. The above light transmission data has not been normalized for film 
thickness, however. The increase of Hytrel.TM. G4074 thermoplastic 
elastomer compatibilizer concentration appears to reduce the size of the 
largest polypropylene domains, thus affording some control on some 
finished film properties as well as domain size. However, excessive 
Hytrel.TM. G4074 thermoplastic elastomer concentration appears to inhibit 
voiding during film orientation. 
Even though Comparative Examples C1 and C2 appear to have similar physical 
properties compared to the examples of the invention, large polypropylene 
domains are seen in these uncompatibilized Comparative Examples. When this 
film is oriented, large voids appear to form around these domains 
resulting in frequent web breaks during processing which is unacceptable. 
Comparative Example C3 
In Comparative Example C3, film was made as in Comparative Example C1 
except that Exxon 1024 polypropylene (12 mfi) was used, and the film was 
stretched in the MD about 3.28 times by preheating the cast web to about 
200.degree. F. (121.degree. C.). The film was then stretched in the TD 
direction as in C1. The resulting film had a mottled, nonuniform 
appearance and a density of 1.01 g/cc. The resulting web exhibited 
substantial fibrillation of the polypropylene domains at the die surface 
as shown in FIG. 4. FIG. 4 is an SEM micrograph of the MDO web 
cross-section from a sample collected during processing. An MDO web 
surface adjacent to the die during extrusion is visible in the top portion 
of the micrograph; the machine direction is shown by the arrows in the 
micrograph. It can be seen in FIG. 4 that to a depth of about 75 microns 
from the die surface, the polypropylene domains were deformed into fibers 
which are aligned in the machine direction. This excessive fibrillation of 
the polypropylene domains at the web surface was not seen in examples 
utilizing either the 2.5 mfi or 1.6 mfi polypropylenes under similar 
processing conditions, as shown in FIG. 5 for the 1.6 mfi polypropylene. 
FIG. 5 is an SEM micrograph of an unoriented cast web sample of the 
composition described in comparative Example C2. 
Examples 12-15 
In Examples 12-15, additive blends were made as described in Example 1 
except 30 parts Fina 3230 polypropylene was used instead of 30 parts Fina 
3374X polypropylene. The Hytrel.TM. thermoplastic elastomer compatibilizer 
and PET percentages were varied as shown in Table 4. In these examples, 
the Fina 3230 polypropylene and Hytrel.TM. G4074 thermoplastic elastomer 
were dry blended in a drum tumbler for at least 45 minutes and the blend 
was fed to the input of a 4.5 inch (11.43 cm) extruder using a volumetric 
solids feeder to control the rate of addition. Predried PET was also fed 
to the input of the extruder for a total feedrate of approximately 400 
lbs/hr. The extruder had a 31/1 L/D barrel equipped with a high output 
screw which fed an 18-inch (45.72 cm) wide sheeting die with a die gap of 
about 0.065 inches (0.165 cm). The extruder temperature zones were set to 
approximately: zone 1 480.degree. F. (249.degree. C.), zone 2 490.degree. 
F. (254.degree. C.), zone 3 500.degree. F. (260.degree. C.), zone 4,5 and 
6 520.degree. F. (271.degree. C.), gate, filter, gear pump and necktube 
515.degree. F. (268.degree. C.) and die 535.degree. F. (279.degree. C.). A 
static mixer was used in the necktube, close to the die, in order to 
minimize thermal gradients in the melt. These conditions produced a melt 
temperature at the gate of about 545.degree. F. (285.degree. C.). The 
sheet formed by the die was cast onto a temperature controlled casting 
wheel maintained at about 90.degree. F. (32.degree. C.). The cast sheet 
was held in place by electrostatic pinning. A film was then made by 
stretching the cast sheet using conventional polyester film biaxial 
orientation equipment. The cast sheet was stretched in the machine 
direction (MD) about 3.2 times by preheating the cast sheet to about 
180.degree. F. (82.degree. C.) and then stretching the sheet at a 
temperature of about 190.degree. F. (88.degree. C.). The MDO film was then 
stretched in the transverse direction (TD) 3.0-3.2 times in a conventional 
tentering machine. The TD stretch temperature for Examples 12 and 13 was 
about 230.degree. F. (110.degree. C.), for Example 14 about 250.degree. F. 
(121.degree. C.) and Example 15 about 260.degree. F. (127.degree. C.). The 
biaxially stretched films were then subjected to a heat set or annealing 
temperature of about 450.degree. F. (232.degree. C.) for 10-15 sec. while 
the film was restrained. The densities of the resulting films are 
summarized in Table 4. FIG. 6 is an SEM micrograph of the unoriented cast 
web sample described in Example 14. FIG. 6 shows the approximate center of 
the cast web cross-section. The machine direction is shown by the arrows 
in the micrograph. Note the absence of the larger (about 15-20 microns) 
polypropylene domains that were seen in FIG. 1 (Comparative Example C2). 
Comparative Example C4 
In Comparative Example C4, film was made as in Example 12 except that no 
Hytrel.TM. G4074 thermoplastic elastomer was added, and the TD stretch 
temperature was about 210.degree. F. (99.degree. C.). The polypropylene 
percentage remained at 30 wt %. The resulting film density and composition 
is also included in Table 4. 
TABLE 4 
______________________________________ 
Hytrel .TM. 
PET, G4074, Density, 
Example Wt % Wt % g/cc 
______________________________________ 
C4 70.00 0.00 0.75 
12 69.98 0.02 0.76 
13 69.96 0.04 0.89 
14 69.94 0.06 0.92 
15 69.90 0.10 0.96 
______________________________________ 
The data in Table 4 show that low density film can be made at very low 
levels of compatibilizer addition. The films were evaluated for physical 
properties similar to that listed in Table 3 for Examples 1-11. For 
Examples 12-15, samples with similar film densities to those of Examples 
1-11 had similar results for the other properties tested. Values for 
sample roughness, R.sub.q, varied from 1.20 to 1.53 microns. 
Examples 16, 17, 18 
In Examples 16, 17, 18, films were made as in Example 1 except the 
thickness and MD stretch temperature were varied as shown in Table 5. 
TABLE 5 
______________________________________ 
MD Stretch Finished 
Temperature, Density, 
Thickness, 
Ex. .degree.F. g/cc mils 
______________________________________ 
16 210 (99.degree. C.) 
0.86 4.20 
17 210 (99.degree. C.) 
0.98 1.90 
18 255 (124.degree. C.) 
1.06 3.78 
______________________________________ 
The data in Table 5 show that MD stretch temperature is another way of 
controlling finished film density. The density of Example 17 may be higher 
than Example 16 because of its overall lower thickness. As the thickness 
of a film is reduced, the higher density of the surface layers has a 
larger effect on average density. This higher density may be because of 
minimal voiding at or near the surface of the web. 
Comparative Examples C5-C9 
In Comparative Example C5, film was made as in Comparative Example Cl 
except the MD stretch temperature was about 210.degree. F. (99.degree. 
C.). Comparative Example C5 had a thickness of about 5.4 mils (127 
micrometers) and a density of 0.72 g/cc. This film is undesirable because 
of the propensity for web breaks during processing similar to C1 and C2. 
In Comparative Example C6, film was made as in Example 2 except 0.5 wt. % 
Primacor.TM. 3330R adhesive polymer, said to be an ethylene-acrylic acid 
copolymer, (available from Dow Chemical Co.) was added and the MD stretch 
temperature was about 240.degree. F. (116.degree. C.) with a preheat of 
about 200.degree. F. (93.degree. C.). In Comparative Example C7, film was 
made as in Comparative Example C6 except 1.0 wt. % Primacor.TM. 2912R 
adhesive polymer, said to be an ethylene-acrylic acid copolymer, was 
added. In Comparative Example C8, film was made as in Comparative Example 
C6 except Polybond.TM. 3002 functionalized olefin said to be a maleic 
anhydride-modified polypropylene with an unknown percent functionality, 
(available from BP Performance Polymers, Inc.) was used instead of 
Primacor.TM. 3330R adhesive polymer. In Comparative example C9, film was 
made as in Comparative Example C8 except 2.0 wt. % Polybond.TM. 3002 
modified polypropylene was used. Comparative Examples C6-C9 showed no 
obvious change or reduction in polypropylene domain size compared to 
Comparative Example C5 which contained no compatibilizer. However, C6 and 
C7 appeared to show the presence of a third phase at the polypropylene 
interface. 
The films were then evaluated as described above. The test results are 
summarized in Table 6. 
TABLE 6 
__________________________________________________________________________ 
Break Break 
Light MD Shrinkage 
Modulus 
Strength 
Elongation 
Density, 
Transmission, 
Left/Center/Right, 
MD .times. TD, 
MD .times. TD, 
MD .times. TD, 
Roughness 
Ex. 
g/cc 
% % ksi ksi % R.sub.q, microns 
__________________________________________________________________________ 
C5 0.72 
12.5 1.7/1.7/1.7 
246 .times. 199 
9.1 .times. 6.2 
39.1 .times. 17.8 
0.64 .times. 0.76 
C6 0.94 
43.2 1.3/1.0/1.2 
216 .times. 247 
3.72 .times. 4.22 
3.1 .times. 2.2 
2.30 .times. 2.45 
C7 1.03 
57.0 1.3/1.0/1.3 
242 .times. 253 
4.17 .times. 4.14 
2.9 .times. 2.1 
2.63 .times. 2.68 
C8 0.89 
41.7 1.4/1.0/1.2 
209 .times. 236 
3.46 .times. 3.84 
3.4 .times. 2.1 
2.79 .times. 2.82 
C9 1.01 
49.7 1.2/1.0/1.1 
259 .times. 256 
4.64 .times. 4.29 
3.0 .times. 2.0 
2.60 .times. 2.70 
__________________________________________________________________________ 
The results shown in Table 6 for Comparative Examples C6-C9 were 
unacceptable because the films were excessively brittle as shown by the 
low elongation values. Comparative Example C5 was unacceptable because it 
was prone to web breaks. 
Example 19 
In Example 19, a sample was prepared in a 60 ml mixing bowl (available from 
C.W. Brabender, Type: R.E.E. 6-230V 8.5 amp No: A.A. 526 S.B.) with 
heating means and mixing means operated at 50 revolutions per minute (RPM) 
and about 275.degree. C. The following materials were weighed and added to 
the mixing bowl all at once: a) 39.0 grams polyethylene terephthalate 
(PET) as used in Example 1 which had been dried overnight at 130.degree. 
C., b) 18.0 grams FINA 3374X polypropylene and c) 3.0 grams Ecdel.TM. 9966 
elastomer, said to be a copolyester ether, (available from Eastman 
Chemical Co.). The mixture was blended for 5 minutes at 50 RPM and at 
about 275.degree. C. The mixing bowl with the heated mixture was then 
removed from the mixer and the mixture was quickly scraped from the bowl 
and placed directly into a water bath at about 50.degree. F. (10.degree. 
C.) to quench the blend. A batch of only polypropylene was run after each 
mixture to clean the mixing bowl. A sample of the cooled blend was 
fractured by placing the sample in liquid nitrogen and breaking with a 
hammer at liquid nitrogen temperatures. A representative piece showing the 
fractured surface was mounted on a standard Cambridge SEM stub and sputter 
coated with Au/Pd before examination. The electron micrograph shown as 
FIG. 7 was generated using a Hitachi S-530 SEM operated at 20 KV and a 
working distance of 25mm. The electron micrograph was taken at 1000.times. 
and shows a distribution of polypropylene domain sizes ranging from less 
than 1 micron to approximately 10 microns. 
Comparative Example C10 
In Comparative Example C10, a blend was made as in Example 19 except no 
Ecdel.TM. 9966 elastomer was used as a compatibilizer and 18.0 grams of 
the polypropylene and 42.0 grams of PET were used. The resulting electron 
micrograph, taken at 1000.times. (FIG. 8), shows a distribution of 
polypropylene domain sizes ranging from less than 1 micron to 
approximately 20 microns. 
Examples 20-28 
In Examples 20-28, blends were made as in Example 19 except the 
compatibilizer used was as listed in Table 7. The Ecdel.TM. elastomer 
materials were available from Eastman Chemical Co. and differed in mfi 
according to Eastman Chemical Co. literature. The 9965 grade was reported 
to have a mfi measured in grams/10 min. at 230.degree. C. of 15, grade 
9966 mfi was reported as 10 and grade 9967 mfi was reported as 4. The 
Riteflex thermoplastic polyester elastomers were obtained from 
Hoechst-Celanese Corp., and the Hytrel.TM. materials were available from 
E. I. DuPont deNemours & Co., Inc. 
TABLE 7 
______________________________________ 
Size Range Electron 
of PP diam., 
Micrograph 
Ex. Compatibilizer micrometers 
FIG. # 
______________________________________ 
19 Ecdel .TM. 9966 elastomer 
&lt;1-10 7 
20 Ecdel .TM. 9967 elastomer 
&lt;1-10 
21 Ecdel .TM. 9965 elastomer 
&lt;1-9 
22 Riteflex .TM. 672 elastomer 
&lt;1-6 9 
23 Riteflex .TM. 655 elastomer 
&lt;1-11 
24 Hytrel .TM. 7246 elastomer 
&lt;1-3.5 
25 Hytrel .TM. G5544 elastomer 
&lt;1-14 
26 Hytrel .TM. 6356 elastomer 
&lt;1-7 
27 Hytrel .TM. 8238 elastomer 
&lt;1-6 10 
28 Hytrel .TM. G4074 elastomer 
&lt;1-10 11 
C10 no compatibilizer 
&lt;1-20 8 
______________________________________ 
Comparative Example C11 
In Comparative Example C11 a blend was made as in Example 19 except 39 
grams polyethylene terephthalate (PET), which had been dried overnight at 
130.degree. C., 18 grams of PRO-FA.TM. 6723, a 0.8 mfi polypropylene, 
available from Himont, Inc., and 3.0 grams Kraton.TM. FG 1901X (said to be 
a maleic anhydride modified styrene-ethylene/butylene-styrene triblock 
copolymer, available from Shell Chemical Co.), were used as the 
ingredients. The size of polypropylene domains in FIG. 12 were determined 
to be between less than 1 and 8 microns. FIG. 12 indicates a fracturing of 
the polypropylene domains rather than a separation at the domain 
interface. This may indicate an increased adhesion at the domain 
interface. If the interfacial adhesion becomes too strong voids may not 
form during subsequent stretching and the desired density reduction due to 
voiding will not be present. 
Comparative Example C12 
In Comparative Example C12, a blend was made as in Comparative Example C11 
except Kraton.TM. 1652 (said to be a styrene-ethylene/butylene-styrene 
triblock copolymer with a styrene/rubber ratio of 29/71) was used instead 
of Kraton.TM. FG1901X copolymer. The resulting morphology shown in FIG. 13 
appears to indicate a co-continuous morphology and thus, it would be a 
poor compatibilizer for the PET and PP polymer blend as the desired domain 
shape and size distribution were not realized. In this context, 
co-continuous means there is no distinct continuous or discrete phase. 
Micrographs 15 FIG. 1 is an SEM micrograph of the unoriented cast web of 
the composition described in Comparative Example C2 (30 wt % Fina 3230 
polypropylene/70 wt % PET). 
The micrograph is of the approximate center of the sample cross-section. 
The machine direction is shown by the arrows. The magnification is 
1000.times.. 
FIG. 2 is an SEM micrograph of the unoriented cast web of the composition 
described in Example 8 (30 wt % Fina 3230 polypropylene/69.5 wt % PET/0.5 
wt % Hytrel.TM. G4074). The micrograph is of the approximate center of the 
sample cross-section. The machine direction is shown by the arrows. The 
magnification is 1000.times.. 
FIG. 3 is an SEM micrograph of the MDO web of the composition described in 
Example 8 (30 wt % Fina 3230 polypropylene/69.5 wt % PET/0.5 wt % 
Hytrel.TM. G4074). The micrograph is of the approximate center of the 
sample cross-section. The machine direction is shown by the arrow. The 
magnification is 1000.times.. 
FIG. 4 is an SEM micrograph of the MDO web of the composition described in 
Comparative Example C3 (30wt % Exxon 1024 polypropylene/70 wt % PET). The 
micrograph is of the MDO web cross-section with a web surface ("sample 
surface") adjacent the die during extrusion visible in the top portion of 
the micrograph. The machine direction is shown by the arrow. The 
magnification is 500.times.. 
FIG. 5 is an SEM micrograph of the unoriented cast web of the composition 
described in Comparative Example C2 (30 wt % Fina 3230 polypropylene/70 wt 
% PET). The micrograph is of the cast web cross-section with a web surface 
("sample surface") adjacent the die during extrusion visible in the top 
portion of the micrograph. The machine direction is shown by the arrow. 
The magnification is 500.times.. 
FIG. 6 is an SEM micrograph of the unoriented cast web of the composition 
described in Example 14 (30 wt % Fina 3230 polypropylene/69.94 wt % 
PET/0.06 wt % Hytrel G4074 copolymer). The micrograph is of the 
approximate center of the sample cross-section. The machine direction is 
shown by the arrow. The magnification is 1000.times.. 
FIG. 7 is an SEM micrograph of the mixing bowl sample of the composition 
described in Example 19 (30 wt % Fina 3374X polypropylene/65 wt % PET/5 wt 
% Ecdel 9966). The magnification is 1000.times.. 
FIG. 8 is an SEM micrograph of the mixing bowl sample of the composition 
described in Comparative Example C10 (30 wt % Fina 3374X polypropylene/70 
wt % PET). The magnification is 1000.times.. 
FIG. 9 is an SEM micrograph of the mixing bowl sample of the composition 
described in Example 22 (30 wt % Fina 3374X polypropylene/65 wt % PET/5 wt 
% Riteflex 672). The magnification is 1000.times.. 
FIG. 10 is an SEM micrograph of the mixing bowl sample of the composition 
described in Example 27 (30 wt % Fina 3374X polypropylene/65 wt % PET/5 wt 
% Hytrel 8238). The magnification is 1000.times.. 
FIG. 11 is an SEM micrograph of the mixing bowl sample of the composition 
described in Example 28 (30 wt % Fina 3374X polypropylene/65 wt % PET/5 wt 
% Hytrel G4074). The magnification is 1000.times.. 
FIG. 12 is an SEM micrograph of the mixing bowl sample of the composition 
described in Comparative Example C11 (30 wt % Profax 6723 polypropylene/65 
wt % PET/5 wt % Kraton.TM. FG 1901X). The magnification is 5000.times.. 
FIG. 13 is an SEM micrograph of the mixing bowl sample of the composition 
described in Comparative Example C12 (30 wt % Profax 6723 polypropylene/65 
wt % PET/5 wt % Kraton.TM. 1652). The magnification is 150.times.. 
Various modifications and alterations of this invention will become 
apparent to those skilled in the art without departing from the scope and 
spirit of this invention.