Note: Descriptions are shown in the official language in which they were submitted.
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io FOAMS PREPARED FROM BLENDS OF SYNDIOTACTIC POLYPROPYLENES AND
THERMOPLASTIC POLYMERS
FIELD OF THE INVENTION
This invention rotates to foams in general, and more particularly, to foams
prepared
from a blend of syndiotactic polypropylenes and foamable thermoplastic polymer
resins.
BACKGROUND OF THE INVENTION
2o Foams are used in a number of applications, including thermal insulation,
packaging,
and the formation of molded articles such as cups, trays, and the like.
Depending upon the
end-use of the foam, it is desirable that foam exhibit particular properties
or combinations of
properties. For example,when utilized as an insulating material or cushion
packaging
material, expansion of the foam to low densities is quite desirable.
In addition, foams having a high temperature of distortion are desirable for a
number
<-~
of applications, including insulation in high temperature environments. eng
upon the
particular use of such insulating foams, it is also desirable that such foams
be flexible in
addition to having a high temperature of distortion. The degree of flexibility
and the heat
3o distortion requirements vary depending on the end-use of the insulating
foam. For example,
in some automotive uses or for insulation of hot-water pipes, a flexible foam
having a heat
distortion temperature greater than about 90°C, or greater than 110-
120°C in some instances,
is required. In addition, in order to be in compliance with Underwriters
Laboratory Test UL
C44,293 1
,::::
~::::::::::::~:<::::::
AMENDED SHEET ......
CA 02339107 2001-O1-30
WO 00/12594 PCT/US99/19410
AND THERMOPLASTIC POLYMERS
This invention relates to foams in general, and more particu
foams prepared from a blend of syndiotactic polypropylenes and foam
s thermoplastic polymer resins.
Foams are used in a number of applications, in~lGding thermal
insulation, packaging, and the formation of molded articl such as cups, and
trays.
Depending upon the end-use of the foam, it is desir a that the foam exhibits
particular properties or combinations of properti . For example, when utilized
as an
to insulating material or cushion packaging ma rial, expansion of the foam to
low
densities is quite desirable.
In addition, foams h~a~Ging a high temperature of distortion are desirable
for a number of applications, ' cluding insulation in high temperature
environments.
Depending upon the pa ' ular use of such insulating foams, it is also
desirable that
~s such foams be flexib in addition to having a high temperature of
distortion. The
degree of flexibil' and the heat distortion requirements vary depending on the
end-
use of the i lating foam. For example, in some automotive uses or for
insulation of
pipes, a flexible foam having a heat distortion temperature greater than
90°
C,~''greater than 110°C - to 120°C in some instances, is
required. In addition, in
20 1191 Appendix A,
foams used as fillers in personal flotation devices need to withstand
temperatures of
60°C for a prolonged period of time in addition to being very soft and
flexible.
However, it is difficult to achieve the properties of flexibility (that is,
low
modulus of elasticity) and high heat distortion temperature in the same foam.
2s Typically, the flexibility of a given resin (that is, modulus of
elasticity) and the heat
distortion temperature of that resin are both directly related to the melting
point of the
resin. In other words, a resin having a low modulus of elasticity (that is,
high
flexibility) typically requires that the resin have a lower melting point
whereas a resin
having a high temperature of distortion typically requires that the resin have
a higher
3o melting point. In addition, even if properties of flexibility and high heat
distortion
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temperature are found in the same resin or resin blend, the resin or resin
blend may
not be amenable to foaming, or to foaming by a convenient process such as the
extrusion process. Branched-polyolefin resins prepared by the high-pressure-
free-
radical process are foamable to a flexible foam by extrusion, but the foam
lacks the
s temperature resistance for certain applications. Examples of branched-
polyolefin
resins include low-density polyethylene homopolymer resins having densities in
the
range of from 0.915 g/cm3 to 0.932 g/cm3 and copolymers of ethylene with a
vinyl
ester such as vinyl acetate and methyl acrylate. Linear polyolefin homopolymer
resins prepared by a catalytic process (using for example, Ziegler Natta or
io metallocene catalysts), such as high-density polyethylene and isotactic
polypropylene (iPP) resins, have a relatively high heat distortion temperature
but are
difficult to foam by the extrusion process. In addition, the foams made from
such stiff
homopolymer resins lack flexibility. A less stiff linear copolymer resin can
be made
by the catalytic process but the resin suffers from the same lack of
foamability as do
is the homopolymers. The use temperature of a polyolefin resin foam can be
increased
by cross-linking. For example, a cross-linked foam prepared from a low-density
polyethylene resin may be used at a temperature higher than for an uncross-
linked
foam but the use temperature, which is less than 100°C, is not
sufficiently high for
some applications. In addition, a cross-linked foam is costly to manufacture
and is
2o not recyclable.
Foams prepared from a blend of high melting polyolefin resins (for
example, high density polyethylene and iPP) and low density polyethylene
(LDPE)
resin are difficult to expand to a low density foam by extrusion processes,
since the
foam expansion relies on the freezing transition of the high melting resin
which has a
2s poor foamabiiity. When applied to the cross-linking approach, such a blend
causes
another type of difficulty. In that process, a foamable composition is
extruded into a
sheet at a low temperature where the blowing agent and the cross-linking agent
remain substantially unactivated. Often, the required processing temperature
for a
high melting linear polyolefin exceeds the tolerable temperature for the
blowing agent
3o and the cross-linking agent and may prematurely activate them.
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However, depending on the particular end-use, it is not always
desirable that an insulation foam be flexible. Rigid foams having high
temperatures
of distortion are also desirable. Rigid insulation foams are often prepared
from alkyl
aromatic polymers, such as polystyrene, which due to environmental concerns,
are
increasingly expanded with carbon dioxide. However, low density foams, such as
polystyrene, which are expanded with carbon dioxide exhibit a small cell size.
However, in order that a rigid foam be readily formed from the
convenient extrusion process and be easily fabricated, it is necessary that
the foam
has an enlarged cell-size. A foam having a small cell size is not only
difficult to
~o extrude to a large cross-section but is also difficult to fabricate (for
example, slice
and cut to final shapes). In order for ready fabrication, it is desirable that
the foam
have a cell size greater than 0.4 mm.
There have been various attempts to prepare alkyl aromatic foams
having an enlarged cell size by incorporating various additives which enlarge
the cell
is size (see, for example, U.S. Patent Nos. 4,229,396 and 5,489,407). However,
typical cell-enlarging additives are difficult to feed into the extruder and
tend to affect
the heat distortion temperature of the foam product.
In addition to insulation foams having high temperatures of distortion,
which are either 1 ) flexible or 2) rigid with enlarged cell size, flexible
foams which are
2o made from thermoplastic polymers having a T9 above 0°C are desirable
for end-uses
which require noise and vibration damping as well as for cushion packaging.
When
used for cushion packaging or vibration damping, a flexible foam protects the
article
by absorbing the impact and vibration energy in its cell structure. The energy
is
absorbed both in the gas and polymer phase. A foam having cell walls that
2s irreversibly dissipate the mechanical energy into heat is desirable. A
polymer resin
dissipates mechanical energy most effectively at the glass transition
temperature (Tg)
of the resin (see, for example, Properties of Polymers, third edition, Chapter
14,
"Acoustic Properties," ed. By D.W. Van Kreveien, Elsevier, Amserdam-London,
New
York-Tokyo, 1990). Most conventional polyolefin resins such as polyethylene
and
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polypropylene are flexible, but have a relatively low T9, that is, below
0°C and are,
therefore, not useful for cushion packaging or vibration damping end-uses.
Therefore, there remains a need in the art for 1 ) flexible foams having a
high temperature of distortion; 2) rigid alkyl aromatic foams having a high
heat of
distortion and enlarged cell size which are conveniently made and wherein the
heat
of distortion is stable; and 3) flexible thermoplastic foams made from a
thermoplastic
polymer having a T9 above 0°C.
Those needs are met by the present invention. Thus, the present
invention provides polymer foams prepared from a blend of a syndiotactic
io polypropylene (sPP) resin and a foamable thermoplastic polymer resin.
Thus, in a first embodiment of the present invention, there are provided
polymer foams prepared from a blend of a sPP resin and a flexible
thermoplastic
polymer resin which are flexible and have a high temperature of distortion.
The
polymer foams according to the first embodiment of the present invention are
useful
~s as insulating foams in high temperature environments wherein a flexible
foam is
desired, such as some automotive uses and insulation of hot-water pipes. In
addition, since sPP resin has a T9 of 4°C, the polymer foams according
to the first
embodiment of the present invention are also suitable as cushion packaging or
in
noise or vibration damping products.
2o Typical blended polymer foams according to the first embodiment are
as follows:
a blended polymer foam, comprising: a) from 0.1 percent to 60 percent
by weight of a sPP resin; and b) from 40 percent to 99.9 percent by weight of
a
flexible thermoplastic polymer resin;
2s a blended polymer foam, comprising: a) from 10 percent to 50 percent
by weight of a sPP resin; and b) from 50 percent to 90 percent by weight of a
flexible
thermoplastic polymer resin; and
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a blended polymer foam, comprising: a) from 30 percent to 50 percent
by weight of a sPP resin; and b) from 50 percent to 70 percent by weight of a
flexible
thermoplastic polymer resin.
In a second embodiment of the present invention, there are provided
polymer foams prepared from a blend of a sPP resin and a rigid thermoplastic
polymer resin which are rigid, have high temperatures of distortion, and have
enlarged cell size. The sPP resin additive, which enlarges the cell size of
the rigid
thermoplastic polymer foams, is easily fed into the extruder, and does not
affect the
heat distortion temperature of the foam.
io Typical blended polymer foams according to the second embodiment of
the present invention are as follows:
a blended polymer foam comprising: a) from 0.1 percent to 60 percent
by weight of a sPP resin; and b) from 40 percent to 99.9 percent by weight of
a rigid
thermoplastic polymer resin; and
~s a blended polymer foam comprising: a) from 0.2 percent to 5 percent
by weight of a sPP resin; and b) from 95 percent to 99.8 percent by weight of
a rigid
thermoplastic polymer resin.
FIG. 1 depicts the differential scanning calorimetry thermogram of a
foam according to the present invention as extruded.
2o FIG. 2 depicts the differential scanning calorimetry thermogram of a
foam according to the present invention after aging at 120°C for 5
days.
The present invention provides foams prepared from a blend of a sPP
resin and a foamable thermoplastic polymer resin. The blended polymer foams of
the present invention exhibit a combination of desirable properties which have
2s heretofore been difficult, if not impossible, to achieve.
For example, a first embodiment of the present invention provides
polymer foams prepared from a blend of a sPP resin and a flexible
thermoplastic
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polymer resin which foams are flexible and have a high distortion temperature.
The
blended polymer foams according to the first embodiment of the present
invention
are useful as insulating foams in high temperature environments wherein a
flexible
foam is desired, such as some automotive uses and insulation of hot-water
pipes.
s The flexible, insulating foams of the first embodiment of the present
invention exhibit
increased dimensional stability over foams prepared from the flexible
thermoplastic
polymer resin alone. As stated above, flexible foams having a high heat
distortion
temperature are prepared by utilizing a flexible thermoplastic polymer resin
as the
foamable thermoplastic polymer resin in the blend. Although not wishing to be
~o bound by any particular theory, it is believed that the addition of the sPP
resin
provides the blend foam with a high heat distortion temperature while causing
little
disruption of the foam expansion owing to the resin's slow rate of
crystallization. The
slow rate of crystallization of a sPP, which presents a long cycle-time
problem in
injection molding, is advantageously exploited in the preparation of the foams
of the
is present invention. Due to the slow rate of crystallization, a sPP resin
does not
crystallize at the foaming temperature of a flexible thermoplastic polymer
resin, but
crystallizes at an ambient temperature or during secondary heating after a
foam of
the first embodiment of the present invention is prepared from the blend and
stabilized. Once crystallized, the sPP resin component provides the blended
foam
2o with a relatively high heat of distortion due to the high melting point
that is, 130°C) of
the crystals. This phenomenon is demonstrated by differential scanning
calorimetry
as shown in FIG. 1 and FIG. 2. FIG. 1 depicts the differential scanning
calorimetry
thermogram of a foam according to the present invention prepared from a 50/50
by
weight blend of a LDPE resin and a sPP resin as extruded, showing an endotherm
at
2s approximately 113°C and no endotherm at approximately 130°C,
the melting point of
sPP crystals. FIG. 2 depicts the differential scanning calorimetry thermogram
of the
foam of FIG. 1 after it has aged at approximately 120°C for 5 days,
showing an
endotherm at approximately 113°C and an endotherm at approximately
130°C, the
melting point of sPP crystals. The differential scanning calorimetry
thermograms
3o shown in FIG. 1 and FIG. 2 demonstrate that the LDPE resin and the sPP
resin are
not miscible and that the sPP resin phase in the blend undergoes
crystallization
during heating at approximately 120°C.
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In addition, the sPP resin component of the blend does not crystallize
fully during aging of the foam at ambient temperature, but further
crystallization is
observed subsequently upon heating. This secondary crystallization may be
beneficially utilized in thermoforming of the foam product in that the sPP
molecules in
s the amorphous state allow deformation of the foam sheet to conform to the
shape
but become further crystallized during thermoforming thereby helping set the
thermoformed article. The addition of the sPP resin also enhances the
dimensional
stability of the flexible foam. For example, a foam of the present invention
prepared
from a blend of a sPP resin and a LDPE resin expanded with isobutane was found
to
~o be more dimensionally stable than a LDPE resin foam expanded with
isobutane.
This increased dimensional stability is surprising given that at least one sPP
resin
has been reported to have a low crystallinity (about 30 percent) [see Wheat,
W.R.,
"Rheological Explanations for Syndiotactic Polypropylene Behaviors," ANTEC 95
Preprint] and a relatively high permeability to gases and vapors [see Schardl,
J, et
is al., "Syndiotactic Polypropylene Overview Clear Impact Polymer," ANTEC 95
Preprint].
In addition, the flexible, insulating polymer foams according to the first
embodiment of the present invention are also suitable as cushion packaging or
in
noise and vibration damping products. The sPP resins have a T9 of 4-6°C
and would
2o therefore be effective in dissipating mechanical energy into heat. However,
a sPP
resin alone is not readily foamable by the extrusion process. In contrast, the
blends
of a sPP resin and a flexible thermoplastic polymer resin according to the
first
embodiment of the present invention are not only foamable, but the resultant
foams
also possess the properties of the individual component resins. Therefore,
foams
2s prepared from such an immiscible polymer blend are anticipated to posses
different
T9s and thus, are anticipated to beneficially contribute to dampening of noise
and
vibration over a wide range of frequencies and temperatures.
The second embodiment of the present invention provides polymer
foams prepared from a blend of a sPP resin and a rigid thermoplastic polymer
resin
so which foams are rigid, have high temperatures of distortion, and have
enlarged cell
size. Thus, the blended polymer foams of the second embodiment of the present
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CA 02339107 2001-O1-30
WO 00/12594 PCT/US99119410
invention are suitable for use as insulating foams in applications which
require that
the foam be fabricated. The sPP resin additive, which enlarges the cell size
of the
rigid thermoplastic polymer foams, is easily fed into the extruder, and does
not affect
the heat distortion temperature of the foam. Given that polypropylene resins
are not
s known to be compatible with at least one rigid thermoplastic polymer resin,
such as
polystyrene (see, for example, U.S. Patent No. 4,386,187, Examples 18 and 22
and
in U.S. Patent 5,460,818, Example 3) and that foam expansion of an
incompatible
polymer blend is often difficult in the absence of a compatibilizing additive
(see for
example, U.S. patent 4,020,025), the fact that the addition of ax sPP resin to
a
to polystyrene resin does not disrupt, but aid in expansion of the polystyrene
resin, is
somewhat unexpected.
In either embodiment of the present invention, the sPP resin and
foamable thermoplastic polymer resin are typically blended together in weight
ratios
of from 0.1:99.9 to 60:40. In the first embodiment, where the foamable
thermoplastic
is polymer resin is a flexible thermoplastic polymer resin, the preferred
ratios of sPP
resin to flexible thermoplastic polymer resin are from 10:90 to 50:50, with
ratios of
from 30:70 to 50:50 being especially preferred. In the second embodiment,
where
the foamable thermoplastic polymer resin is a rigid thermoplastic polymer
resin, the
preferred ratios of sPP resin to rigid thermoplastic polymer resin are from
0.1:99.9 to
20 5:95.
Suitable sPP resins for use in either embodiment include all
substantially syndiotactic homopolymers of propylene and co-polymers of
propylene
with polymerizable monomers. Typical examples include homopolymers of
polypropylene, copolymers of propylene with ethylene, and copolymers of
propylene
2s with 1-butene, with those homopolymers and co-polymers having a melt flow
rate of
from 0.05 dg/minute to 50 dg/minute being preferred, and those homopolymers
and
co-polymers having a melt flow rate of from 0.1 dg/minute to 10 dg/minute
being
especially preferred. Also preferred are sPP resins having a syndiotacticity
of
greater than 75 percent. An example of suitable sPP resin is a sPP resin
having a
3o melt index of 2 dg/minute(as determined by ASTM D-1238 at 230°C/2.1
fi kg), density
of 0.88 g/cm3, and melting point of 130°C. Examples of such sPP resins
are EOD-
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CA 02339107 2001-O1-30
WO 00/12594 PCTNS99/19410
96-28 and EOD-96-07 grade syndiotactic form copolymer polypropylene resins,
available from Fina Oil and Chemical Company.
Thermoplastic resins suitable for use in the present invention include all
types of thermoplastic polymers that are foamable by extrusion processes.
s Examples of flexible thermoplastic polymer resins suitable for the first
embodiment of
the present invention include, but are not limited to, flexible polyolefin
resins, such as
LDPE resins, ethylene/vinyl acetate copolymer resins, and iPP, with those
resins
having a melt index of from 0.1 dg/minute to 20 dg/minute being preferred, and
those
having a melt index of from 0.2 dg/minute to 10 dg/minute being especially
preferred.
io In addition; when the flexible thermoplastic polymer resin is an
ethylene/vinyl acetate
copolymer, those resins having a vinyl acetate content of from 5 percent to 30
percent are preferred and those resins having a vinyl acetate content of from
8
percent to 20 percent are especially preferred. Further, when the flexible
thermoplastic polymer resin is an iPP, those resins having a high melt
strength when
~s applied to the extrusion process where tan delta is less than 1.5 are
preferred, and
those having a tan delta of less than 1.2 are especially preferred (tan delta
is the
ratio of loss modulus to storage modulus determined using a 2.5 mm thick and
25
mm diameter specimen at 190°C and 1 radian/second oscillating speed as
shown in
U.S. Patent No. 5,527,573). An example of a suitable ethylene/vinyl acetate
2o copolymer resin is ELVAX 460 brand resin, available from Du Pont-Dow Inc.
An
example of a suitable iPP resin is PRO-FAX PF-814 grade high melt strength iPP
resin, available from Montell Polyolefins Co. NV. Examples of rigid
thermoplastic
polymer resins suitable for use in the second embodiment of the present
invention
are alkyl aromatic resins, such as polystyrene resins. An example of a
suitable
2s polystyrene for use in the second embodiment of the invention is a
polystyrene
having an average molecular weight of less than 240,000.
Optionally, a nucleating agent may be added to the foamable blend.
The amount of nucleating agent employed to prepare the foams of the present
invention will vary according to the desired cell size, the foaming
temperature, and
3o the composition of the nucleating agent. Useful nucleating agents include
calcium
carbonate, barium stearate, calcium stearate, talc, clay, titanium dioxide,
silica,
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barium stearate, diatomaceous earth, mixtures of citric, and acid and sodium
bicarbonate. When utilized, the amount of nucleating agent employed may range
from 0.01 to 5 parts by weight per hundred parts by weight of the polymer
resin blend
{Pph)~
Blowing agents useful in making the present foams include all types of
blowing agents known in the art; physical and chemical blowing agents and
mixtures
thereof, including inorganic blowing agents, organic blowing agents, and
chemical
blowing agents. Suitable inorganic blowing agents include carbon dioxide,
nitrogen,
argon, water, air, and helium. Organic blowing agents include aliphatic
~o hydrocarbons having 1-6 carbon atoms, aliphatic alcohols having 1 to 3
carbon
atoms, and fully and partially halogenated aliphatic hydrocarbons having 1 to
4
carbon atoms. Aliphatic hydrocarbons include methane, ethane, propane, n-
butane,
isobutane, n-pentane, and isopentane, neopentane. Aliphatic alcohols include
methanol, ethanol, n-propanol, and isopropanol. Fully and partially
halogenated
is aliphatic hydrocarbons include chlorocarbons, fluorocarbons, and
chlorofluorocarbons. Chlorocarbons for use in this invention include methyl
chloride,
methylene chloride, ethyl chloride, and 1,1,1-trichloroethane. Fluorocarbons
for use
in this invention include methyl fluoride, methylene fluoride, ethyl fluoride,
1,1-
difluoroethane (HFC-152a), 1,1,1-trifluoroethane {HGC-143a), 1,1,1,2-
20 tetrafluoroethane (HFC-134a), 1,1,2,2-tetrafluoroethane (HFC-134),
pentafluoroethane, perfluoroethane, 2,2-difluoropropane, 1,1,1-
trifluoropropane, and
1,1,1,3,3-pentafluoropropane. Partially hydrogenated chlorofluorocarbons for
use in
this invention include chlorodifluoromethane (HCFC-22), 1,1-dichloro-1-
fluoroethane
(HCFC-141 b), 1-chloro-1,1-difluoroethane (HCFC-142b), 1,1-dichloro-2,2,2-
2s trifluoroethane (HCFC-123), and 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-
124).
Fully halogenated chlorofluorocarbons may also be used but are not preferred
for
environmental reasons. Chemical blowing agents for use in this invention
include
azodicarbonamide, azodiisobutyronitrile, benzenesulfonhydrazide, 4,4-
oxybenzene
sulfonyl-semicarbazide, p-toluene sulfonyl semi-carbazide, N,N'-dimethyl-N,N'-
3o dinitrosoterephthalamide, and trihydrazine triazine, sodium bicarbonate,
and
mixtures of sodium bicarbonate and citric acid. Mixtures of all these blowing
agents
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WO 00/12594 PCTNS99/19410
are also contemplated within the scope of this invention. The type of the most
suitable blowing agent depends on the process used to manufacture the foam
body
and the desired density of the foam. Preferred blowing agents for the
extrusion
process and batch process for making moldable beads are physical blowing
agents,
with volatile organic blowing agents being preferred. Preferred blowing agents
for
cross-linked foam processes are decomposable blowing agents and nitrogen.
The amount of blowing agent incorporated into the polymer melt
material to make a faam-forming gel is from 0.1 to 5, preferably from 0.4 to
4, and
most preferably from 0.9 to 3 gram moles per kilogram of polymer.
~o The present foams, optionally, further comprise an infrared absorber
(transmission blocker) such as carbon black, graphite, and titanium dioxide,
to
enhance insulating capability. When utilized, the infrared absorber may
comprise
between 1.0 and 25 weight percent and preferably between 4.0 and 10.0 weight
percent based upon the weight of the polymer blend in the foam. The carbon
black
is may be of any type known in the art such as furnace black, thermal black,
acetylene
black, and channel black. A preferred carbon black is thermal black. A
preferred
thermal black has an average particle size of 150 manometers or more.
It is preferred that the foams of the present invention exhibit
dimensional stability. Although the sPP resin itself acts as a stability
control agent, in
zo some instances, it is desirable to include an additional stability control
agent to
further enhance dimensional stability of the foams of the present invention.
For
example, stability control agents in addition to the sPP resin may be
desirable when
the sPP resin is used at a level of less than 30 percent in a blend with a
polyethylene
or ethylene/vinyl acetate copolymer resin and the blend is expanded with
isobutane.
2s A stability control agent may be especially desirable in producing thick
(that is,
greater than 4 mm) sheet and plank products (thicker than 12 mm) of
substantially
closed-cell structure from the foregoing blend. In contrast, an additional
stability
control agent is probably not necessary or desirable when forming
substantially
open-celled foams.
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Dimensional stability is measured by taking the foam volume during
aging as a percentage of the initial volume of the foam, measured within 30
seconds
after foam expansion. Using this definition, a foam which recovers 80 percent
or
more of the initial volume within a month is tolerable, whereas a foam which
recovers
85 percent or more is preferred, a foam which recovers 90 percent or more is
especially preferred. Volume is measured by a suitable method such as cubic
displacement of water.
Preferred stability control agents include amides and esters of C,o.2,
fatty acids. Such agents are seen in U.S. Patent Nos. 3,644,230 and 4,214,054.
to Most preferred agents include stearyl stearamide, glycerol monostearate,
glycerol
monobenenate, and sorbitol monostearate. Typically, such stability control
agents
are employed in an amount ranging from 0.1 to 10 parts per hundred parts of
the
polymer.
Various additives may also be incorporated in the present foam such
is as inorganic fillers, pigments, antioxidants, acid scavengers, ultraviolet
absorbers,
flame retardants, processing aids, and extrusion aids.
The blended polymer foams of the present invention may be prepared
by techniques and procedures well known to one of ordinary skill in the art
and
include extrusion processes as well as batch processes using a decomposable
2o blowing agent and cross-linking, with extrusion processes being preferred.
The blended polymer foams of the present invention may be cross-
linked or non-cross-linked. Excellent teachings to processes for making
polymer
foam structures and processing them are seen in C.P. Park, "Polyolefin Foam",
Chapter 9, Handbook of Polymer Foams and Technology, edited by D. Klempner
2s and K.C. Frisch, Hanser Publishers, Munich, Vienna, New York Barcelona
(1991.
Non-cross-linked foams of the present invention may be made by a
conventional extrusion foaming process. The foam structure is generally
prepared
by heating a pre-mixed blend of the sPP resin and the thermoplastic polymer
resin
(that is, polymer material) to form a plasticized or melt polymer material,
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incorporating therein a blowing agent to form a foamable gel, and extruding
the gel
through a die to form the foam product. Prior to mixing with the blowing
agent, the
polymer material is heated to a temperature at or above its Tg or melting
point. The
blowing agent may be incorporated or mixed into the melt polymer material by
any
means known in the art, such as with an extruder, mixer, or blender. The
blowing
agent is mixed with the melt polymer material at an elevated pressure
sufficient to
prevent substantial expansion of the melt polymer material and to generally
disperse
the blowing agent homogeneously therein. Optionally, a nucleator may be
blended
in the polymer melt or dry blended with the polymer material prior to
plasticizing or
~o melting. The foamable gel is typically cooled to a lower temperature to
optimize
physical characteristics of the foam structure. The gel is then extruded or
conveyed
through a die of desired shape to a zone of reduced or lower pressure to form
the
foam structure. The zone of lower pressure is at a pressure lower than that in
which
the foamable gel is maintained prior to extrusion through the die. The lower
pressure
is may be superatmospheric or subatmospheric (vacuum), but is preferably at an
atmospheric level.
Non-cross-linked foams of the present invention may be formed in a
coalesced strand form by extrusion of the pre-mixed blend of the sPP resin and
the
thermoplastic polymer resin (that is, polymer material) through a multi-
orifice die.
2o The orifices are arranged so that contact between adjacent streams of the
molten
extrudate occurs during the foaming process and the contacting surfaces adhere
to
one another with sufficient adhesion to result in a unitary foam structure.
The
streams of molten extrudate exiting the die take the form of strands or
profiles, which
desirably foam, coalesce, and adhere to one anther to form a unitary
structure.
2s Desirably, the coalesced individual strands or profiles should remain
adhered in a
unitary structure to prevent strand delamination under stresses encountered in
preparing, shaping, and using the foam. Apparatuses and method for producing
foam structures in coalesced strand form are seen in U.S. Patent Nos.
3,573,152
and 4,324, 720.
3o The present foam structure may also be formed into non-cross-linked
foam beads suitable for molding into articles. The foam beads may be prepared
by
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an extrusion process or a batch process. In the extrusion process, the foam
strands
coming out of a multi-hole die attached to a conventional foam extrusion
apparatus
are granulated to form foam beads. The foam beads, if necessary, are heated
below
the melting point of the sPP resin so that the sPP molecules can crystallize,
thereby
forming a pseudo-network structure that provides thermo-collapse resistance to
the
foam beads. In a batch process, discrete resin particles such as granulated
resin
pellets are suspended in a liquid medium in which they are substantially
insoluble
such as water; impregnated with a blowing agent by introducing the blowing
agent
into the liquid medium at an elevated pressure and temperature in an autoclave
or
io other pressure vessel; and rapidly discharged into the atmosphere or a
region of
reduced pressure to expand to form the foam beads. This process is well taught
in
U.S. Pat. Nos. 4,379,859 and 4,464,484.
Cross-linked foams of the present invention may be prepared by either
the cross-linked foam process employing a decomposable blowing agent or by
is conventional extrusion processes.
When utilizing the cross-linked foam process employing a
decomposable blowing agent, cross-linked foams of the present invention may be
prepared by blending and heating a pre-mixed blend of the sPP resin and the
thermoplastic polymer resin (that is, polymer material) with a decomposable
chemical
2o blowing agent to form a foamable plasticized or melt polymer material,
extruding the
foamable melt polymer material through a die, inducing cross-linking in the
melt
polymer material, and exposing the melt polymer material to an elevated
temperature
to release the blowing agent to form the foam structure. The polymer material
and
the chemical blowing agent may be mixed and the melt blended by any means
2s known in the art such as with an extruder, mixer, or blender. The chemical
blowing
agent is preferably dry-blended with the polymer material prior to heating the
polymer
material to a melt form, but may also be added when the polymer material is in
melt
phase. Cross-linking may be induced by addition of a cross-linking agent or by
radiation. Induction of cross-linking and exposure to an elevated temperature
to
3o effect foaming or expansion may occur simultaneously or sequentially. If a
cross-
linking agent is used, it is incorporated into the polymer material in the
same manner
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as the chemical blowing agent. Further, if a cross-linking agent is used, the
foamable melt polymer material is heated or exposed to a temperature of
preferably
less than 150°C to prevent decomposition of the cross-linking agent or
the blowing
agent and to prevent premature cross-linking. If radiation cross-linking is
used, the
foamable melt polymer material is heated or exposed to a temperature of
preferably
less than 160°C to prevent decomposition of the blowing agent. The
foamable melt
polymer is extruded or conveyed through a die of desired shape to form a
foamable
structure. The foamable structure is then cross-linked and expanded at an
elevated
or high temperature (typically, 150°C to 250°C) such as in an
oven to form a foam
io structure. When radiation cross-linking is used, the foamable structure is
irradiated
to cross-link the polymer material, which is then expanded at the elevated
temperature as described above. The structure can advantageously be made in
sheet or thin plank form according to the above process using either cross-
linking
agents or radiation.
is In addition to use of a cross-linking agent or radiation in the cross-
linked foam process employing a decomposable blowing agent, cross-linking may
also be accomplished by means of silane cross-linking as described in C.P.
Park,
Supra, Chapter 9.
Cross-linked foams of the present invention may also be made into a
2o continuous plank structure by an extrusion process utilizing a long-land
die as
described in GB 2,145,961A. In that process, the polymer, decomposable blowing
agent, and cross-linking agent are mixed in an extruder, heating the mixture
to let the
polymer cross-link and the blowing agent to decompose in a long-land die; and
shaping and conducting away from the foam structure through the die with the
foam
2s structure and the die contact lubricated by a proper lubrication material.
Cross-linked foams of the present invention may also be formed into
cross-linked foam beads suitable for molding into articles. To make the foam
beads,
discrete resin particles such as granulated resin pellets are: suspended in a
liquid
medium in which they are substantially insoluble such as water; impregnated
with a
3o cross-linking agent and a blowing agent at an elevated pressure and
temperature in
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an autoclave or other pressure vessel; and rapidly discharged into the
atmosphere or
a region of reduced pressure to expand to form the foam beads. A version is
that
the polymer beads is impregnated with blowing agent, cooled down, discharged
from
the vessel, and then expanded by heating or with steam. In a derivative of the
above
process, styrene monomer may be impregnated into the suspended pellets along
with the cross-linking agent to form a graft interpolymer with the polymer
material.
Blowing agent may be impregnated into the resin pellets while in suspension,
or
alternatively, in a non-hydrous state. The expandable beads are then expanded
by
heating with steam and molded by the conventional molding method for the
~o expandable polystyrene foam beads.
The foam beads may them be molded by any means known in the art,
such as charging the foam beads to the mold, compressing the mold to compress
the beads, and heating the beads such as with steam to effect coalescing and
welding of the beads to form the article. Optionally, the beads may be pre-
heated
is with air or other blowing agents prior to charging to the mold. Excellent
teachings of
the above processes and molding methods are seen in C.P. Park, Supra, pp. 227-
233, U.S. Pat. Nos. 3,886,100, 3.959,189, 4,168,353, and 4,429,059. The foam
beads can also be prepared by preparing a mixture of polymer, cross-linking
agent,
and decomposable mixtures in a suitable mixing device or extruder and forming
the
2o mixture into pellets, and heating the pellets to cross-link and expand.
There is another process for making cross-linked foam beads suitable
for molding into articles. The polymer material is melted and mixed with a
physical
blowing agent in a conventional foam extrusion apparatus to form an
essentially
continuous foam strand. The foam strand is granulated or pelletized to form
foam
2s beads. The foam beads are then cross-linked by radiation. The cross-linked
foam
beads may then be coalesced and molded to form various articles as described
above for the other foam bead process: Additional teachings of this process
are
seen in U.S. Patent No. 3,616,365 and C.P. Park, Supra, pp. 224-228.
In addition, silane cross-linking technology may be employed in the
3o extrusion process. Teachings of this process are seen in C.P. Park, Supra,
Chapter
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9 and in U.S. Patent No. 4,714,716. When silane cross-linking processes are
utilized
with conventional extrusion processes, a polymer is grafted with a vinyl
functional
silane or an azido functional silane and extruded to foams. The extruded foam
is
then exposed to warm humid air for the cross-linking to develop.
s The cross-linked foams of the present invention may be prepared by
the foam sheet process or foam bun stock process or any process described in
C.P.
Park, Supra, Chapter 9, pages 229 to 235.
Although, typically, substantially closed-celled in nature, the foams of
the present invention may be open-celled or close-celled. In addition, the
foams of
~o the present invention have a cell size (that is, cell diameter) of from
0.01 mm to 10
mm, with 0.1 mm to 5 mm being preferred, and from 0.4 mm to 3 mm being
particularly preferred. In addition, the foams of the present invention have a
density
of from 9 kg/m3 to 200 kg/m3, with densities of 11 kg/m3 to 100 kg/m3 being
preferred,
and 15 kg/m3 to 50 kg/m3 being most preferred.
~s The foams of the present invention may take any physical configuration
known in the art, such as extruded sheet, rod, plank, profiles, beads, and
buns. The
foam structure may also be formed by molding of expandable beads into any of
the
foregoing configurations or any other configuration.
Thus, according to the above, the following foams represent typical
2o foams of the present invention:
a blended polymer foam comprising: a) from 0.1 percent to 60 percent
by weight of a sPP resin; and b) from 40 percent to 99.9 percent by weight of
a
foamable thermoplastic polymer resin;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
2s a sPP resin; and b) from 40% to 99.9% by weight of a foamable thermoplastic
polymer resin, the foam having a density of 9 kg/m3 to 300 kg/m3, preferably
11 kg/m3
to 100 kg/m3, and more preferably 15 kg/m3 to 50 kg/m3;
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a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin; and b} from 40% to 99.9% by weight of a flexible thermoplastic
polymer
resin;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
s a sPP resin; and b) from 40% to 99.9% by weight of a flexible thermoplastic
polymer
resin, the foam having a density of 9 kg/m3 to 300 kg/m3, preferably 11 kg/m3
to 100
kg/m3, and more preferably 15 kg/m3 to 50 kg/m3;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin; and b) from 40% to 99.9% by weight of a rigid thermoplastic
polymer
to resin;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin; and b) from 40% to 99.9% by weight of a rigid thermoplastic
polymer
resin, the foam having a density of 9 kg/m3 to 300 kg/m3, preferably 11 kg/m3
to 100
kg/m3, and more preferably 15 kglm3 to 50 kg/m3;
is a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin; and b) from 40% to 99.9% by weight of a flexible polyolefin
resin;
a blended polymer foam comprising: a} from 0.1 %to 60% by weight of a
sPP resin; and b} from 40% to 99.9% by weight of a flexible polyolefin resin,
the
foam having a density of 9 kg/m3 to 300 kg/m3, preferably 11 kg/m3 to 100
kg/m3, and
2o more preferably 15 kg/m3 to 50 kg/m3;
a blended polymer foam comprising: a) from 0.1 %to 60% by weight of a
sPP resin; and b) from 40% to 99.9% by weight of a LDPE resin;
a blended polymer foam comprising: a) from 0.1 %to 60% by weight of a
sPP resin; and b) from 40% to 99.9% by weight of a LDPE, the foam having a
2s density of 9 kg/m3 to 300 kg/m3, preferably 11 kg/m3 to 100 kg/m3, and more
preferably 15 kg/m3 to 50 kg/m3;
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a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin which is a homopolymer of propylene; and b) from 40% to 99.9% by
weight of a foamable thermoplastic polymer resin;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin which is a homopolymer of propylene; and b) from 40% to 99.9% by
weight of a foamable thermoplastic polymer resin, the foam having a density of
9
kg/m3 to 300 kg/m3, preferably 11 kg/m3 to 100 kg/m3, and more preferably 15
kg/m3
to 50 kglm3;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
io a sPP resin which is a homopolymer of propylene; and b) from 40% to 99.9%
by
weight of a flexible thermoplastic polymer resin;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin which is a homopolymer of propylene; and b) from 40% to 99.9% by
weight of a flexible thermoplastic polymer resin, the foam having a density of
9 kg/m3
~s to 300 kg/m3, preferably 11 kg/m3 to 100 kg/m3, and more preferably 15
kg/m3 to 50
kg/m3;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin which is a homopolymer of propylene; and b) from 40% to 99.9% by
weight of a rigid thermoplastic polymer resin;
2o a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin; and b} from 40% to 99.9% by weight of a rigid thermoplastic
polymer
resin which is a homopolymer of propylene, the foam having a density of 9
kg/m3 to
300 kg/m3, preferably 11 kg/m3 to 100 kg/m3, and more preferably 15 kg/m3 to
50
kg/m3;
2s a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin which is a homopolymer of propylene; and b) from 40% to 99.9% by
weight of a flexible polyolefin resin;
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a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin which is a homopolymer of propylene; and b) from 40% to 99.9% by
weight of a flexible polyolefin resin, the foam having a density of 9 kg/m3 to
300
kg/m3, preferably 11 kg/m3 to 100 kg/m3, and more preferably 15 kg/m3 to 50
kg/m3;
s a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin which is a homopolymer of propylene; and b) from 40% to 99.9% by
weight of a LDPE resin;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin which is a homopolymer of propylene; and b) from 40% to 99.9% by
to weight of a LDPE resin, the foam having a density of 9 kg/m3 to 300 kg/m3,
preferably
11 kg/m3 to 100 kg/m3, and more preferably 15 kg/m3 to 50 kg/m3;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin which is a homopolymer of propylene having a syndiotacticity of
greater
than 75%; and b) from 40% to 99.9% by weight of a foamable thermoplastic
polymer
is resin;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin which is a homopolymer of propylene having a syndiotacticity of
greater
than 75%; and b) from 40% to 99.9% by weight of a foamable thermoplastic
polymer
resin, the foam having a density of 9 kg/m3 to 300 kg/m3, preferably 11 kg/m3
to 100
2o kg/m3, and more preferably 15 kg/m3 to 50 kg/m3;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin which is a homopolymer of propylene having a syndiotacticity of
greater
than 75%; and b) from 40% to 99.9% by weight of a flexible thermoplastic
polymer
resin;
is a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin which is a homopolymer of propylene having a syndiotacticity of
greater
than 75%; and b) from 40% to 99.9% by weight of a flexible thermoplastic
polymer
resin, the foam having a density of 9 kg/m3 to 300 kg/m3, preferably 11 kg/m3
to 100
kg/m3, and more preferably 15 kg/m3 to 50 kg/m3;
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a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin which is a homopolymer of propylene having a syndiotacticity of
greater
than 75%; and b) from 40% to 99.9% by weight of a rigid thermoplastic polymer
resin;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin having a syndiotacticity of greater than 75%; and b) from 40% to
99.9%
by weight of a rigid thermoplastic polymer resin which is a homopolymer of
propylene, the foam having a density of 9 kg/m3 to 300 kg/m3, preferably 11
kg/m3 to
100 kg/m3, and more preferably 15 kg/m3 to 50 kg/m3;
~o a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin; and b) from 40% to 99.9% by weight of an ethylene/vinyl acetate
copolymer resin;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin; and b) from 40% to 99.9% by weight of an ethylene/vinyl acetate
is copolymer resin, the foam having a density of 9 kg/m3 to 300 kg/m3,
preferably 11
kg/m3 to 100 kg/m3, and more preferably 15 kg/m3 to 50 kg/m3;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin; and b) from 40% to 99.9% by weight of an iPP resin;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
2o a sPP resin; and b) from 40% to 99.9% by weight of an iPP resin, the foam
having a
density of 9 kg/m3 to 300 kg/m3, preferably 11 kg/m3 to 100 kg/m3, and more
preferably 15 kg/m3 to 50 kg/m3;
a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin; and b) from 40% to 99.9% by weight of an alkyl aromatic polymer
resin;
2s a blended polymer foam comprising: a) from 0.1 % to 60% by weight of
a sPP resin; and b) from 40% to 99.9% by weight of an alkyl aromatic polymer
resin,
the foam having a density of 9 kg/m3 to 300 kg/m3, preferably 11 kg/m3 to 100
kg/m3,
and more preferably 15 kg/m3 to 50 kg/m3;
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a blended polymer foam comprising: a) from 0.1 percent to 60 percent
by weight of a sPP resin; and b) from 40 percent to 99.9 percent by weight of
a
polystyrene polymer resin;
a blended polymer foam comprising: a) from 0.1 percent to 60 percent
by weight of a sPP resin; and b) from 40 percent to 99.9 percent by weight of
a
polystyrene polymer resin, the foam having a density of 9 kg/m3 to 300 kg/m3,
preferably 11 kg/m3 to 100 kg/m3, and more preferably 15 kg/m3 to 50 kg/m3.
The following are examples of the present invention, and are not to be
construed as limiting the scope of the invention. Unless otherwise indicated,
all
io percentages, parts, or proportions are by weight.
The following examples of foams prepared from sPP resin and
foamable thermoplastic polymer resin blends were prepared using a 19-mm
diameter
screw-type extruder having additional zones for mixing and cooling at the end
of the
usual sequential zones of feeding, melting and metering. An opening for
blowing
~s agent injection is provided on the extruder barrel between the metering and
mixing
zones. At the end of the cooling zone, there is attached a die orifice having
an
opening of rectangular shape. The height of the opening is adjustable while
its width
is fixed at 38 mm.
Example 1 Preparation of a sPP Resin and LDPE Resin Blend
2o Foam
Example 1 demonstrates the preparation of a foam according to the
present invention which was prepared from a 50/50 by weight blend of LDPE
resin
and a sPP resin which had been expanded using isobutane as the blowing agent
by
an extrusion process. Tests performed on the foam prepared according to this
2s example show that the polymer blend is foamable by extrusion, and the foam
is
dimensionally stable and withstands a relatively high temperature.
A 50/50 by weight granular blend of LDPE resin having a melt index of
0.7 dg/minute, (determined by ASTM D-1238 at 190°C/2.16 kg), a density
of 0.923
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g/cm3, and a melting point of 115°C (determined per the differential
scanning
calorimetry (DSC) at the peak of an endotherm during heating at
10°C/minute) and
EOD 96-28 grade syndiotactic form copolymer polyproplyene resin (available
from
Fina Oil and Chemical Company) having a melt flow rate of 2 dg/minute
(determined
by ASTM D-1238 at 230°C/2.16 kg), a density of 0.88 g/cm3, and a
melting point of
130°C was prepared.
The blend of granular resins and an additive package consisting of
talcum powder (nucleating agent) at 0.2 parts per hundred parts of resins
(pph) and
Irganox 1010 brand antioxidant (available from Ciba-Geigy Corp) at 0.1 pph
were fed
~o into the extruder at a uniform rate of 3.26 kilograms per hour (kg/h). The
temperatures at the extruder zones are maintained at 160°C at the
feeding zone,
190°C at the melting zone, 200°C at the metering zone, and
200°C at the mixing
zone. Isobutane (blowing agent) was injected into the mixing zone at a uniform
rate
of 414 g/h (12.7 pph). The temperature of the cooling zone was gradually
reduced
is and the die opening adjusted to make a good foam. For example, at a cooling
zone
temperature of 107°C, die temperature of 105°C, and die opening
of 1.0 mm, an
excellent foam of substantially closed-cell structure (open-cell content
approximately
32 percent per ASTM D-2856 Procedure A) was obtained. The foam had a density
of 24.8 kg/m3, cell size of 1.2 mm, thickness of approximately 12 mm and width
of
2o approximately 19 mm.
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Test 1
Dimensional Stability of the Foam of Example 1
A foam specimen of approximately 15 cm in length was cut from the
freshly prepared foam prepared in Example 1, and the volume of the foam
specimen
s was measured at approximately 2 minutes after extrusion and then,
periodically
thereafter, during aging at an ambient temperature. The foam exhibited an
excellent
dimensional stability with no more shrinkage beyond 30 minutes after extrusion
when
its shrinkage bottomed out to about 97 percent of the original volume. The
foam was
fully recovered to over 100 percent of its original volume within a day.
io Test 2
Heat Stability of the Foam of Example 1
One day after extrusion, the foam prepared in Example 1 was cut to a 8
cm-long specimen. The specimen was put in a convection oven maintained at 121
°
C and its volume was monitored periodically. The foam volume, as a percentage
of
is the original volume, is presented as a function of oven-exposure time as
shown in
Table I.
Table I
Aging Time 0 1.5 hours 1 day 2 days 5 days
Foam 100 78 75 70 71
Volume (%)
As shown, the foam shrinks to 70 percent of the original volume and
2o stays at that volume during a prolonged exposure to the high temperature
whereas a
polyethylene foam based on the same LDPE resin used in Example 1 was observed
to collapse totally at that temperature. The resistance of the blend foam to
high
temperatures is further supported by the DSC thermograms shown in FIG. 1 and
FIG. 2, discussed previously. In FIG. 1 and FIG. 2, the DSC thermograms of an
as-
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extruded foam (FIG. 1 ) and an oven-aged foam (FIG. 2) are compared. The oven-
aged foam was exposed to 121 °C temperature for five days. The oven-
aged foam
shows a sharp peak at approximately 130°C in addition to one at
approximately 113°
C. In contrast, the as-extruded foam does not show a strong peak at
130°C which is
the melting peak of sPP crystals. The thermograms indicate that the LDPE resin
and
the sPP resin used in Example 1 are not miscible and that the sPP resin phase
in the
blend undergoes crystallization during heating at 121 °C.
Test 3
Thermoforming Properties of the Foam of Example 1
to Two 5 cm-long specimens were cut from the foam prepared in Example
1 and heated in a 121 °C oven for 5 minutes. Then, the heated foam
specimens
were taken out of the oven and immediately stacked one on top of the other
with
application of gentle pressure one against the other. The foam specimens
developed satisfactory adhesion without experiencing a noticeable shrinkage,
is indicating that moldable foam beads can be prepared from the foam of
Example 1
and that the foam of Example 1 can be thermoformed.
Comparative Example A Preparation of Foam Prepared from sPP Resin
The foam of Comparative Example A was prepared in order to test the
foam expansion properties of a foam made from sPP resin alone.
2o EOD 96-28 grade syndiotactic form copolymer polyproplyene resin
(available from Fina Oil and Chemical Company) having a melt-flow rate of 2
dg/minute.(determined by ASTM D-1238 at 230°C/2.16 kg), density of 0.88
g/cm3,
and melting point of 130°C, was blended with 0.4 pph talc (nucleating
agent ) and 0.1
pph Irganox 1010(Available from Ciba-Geigy Corp.). The blend was fed into the
2s extruder at a uniform rate of 3.10 kg/h. The temperatures at the extruder
zones were
maintained at 160°C at the feeding zone, 190°C at the melting
zone, 200°C at the
metering zone, and 200°C at the mixing zone. Isobutane (blowing agent)
was
injected into the mixing zone at an uniform rate of 414 g/h (12.7 pph). The
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CA 02339107 2001-O1-30
WO 00/12594 PCT/US99/19410
temperature of the cooling zone was gradually reduced from 160°C to
80°C with a
decrement of approximately 5°C at a time and held for 5 to 10 minutes
at a
temperature in order to see if a good foam can be made. The die temperature
was
maintained at the same temperature as the cooling zone. The die opening was
maintained at 0.8 mm at a cooling zone temperature down to 95°C. Below
95°C, the
die was opened slightly wider to relieve the increasing pressure.
Test 4
Foamability of sPP resin of Comparative Example A
The melt prepared in Comparative Example A above did not expand at
to all at temperatures down to 95°C. At temperatures below 95°C,
the foam expanded
slightly but immediately collapsed. At 80°C, the extruder pressure rose
sharply,
indicating that the melt was too viscous and freezing at the cooling zone. No
further
reduction in the cooling temperature could be tolerated. Conclusion: the sPP
resin
alone can not be expanded into a stable foam by the extrusion process.
is Example 2 and Comparative Example B
Preparation of a sPP Resin and LDPE Resin Blend Foam
Example 2 demonstrates the preparation of foams according to the
present invention which were prepared from a blend of LDPE resin and sPP
resin,
wherein the percentage level of sPP resin is varied in order to examine the
effect of
2o the sPP resin level, in the blend, on the properties of foamability and the
dimensional
stability of the foam. Comparative Example B is a foam prepared from LDPE
resin
only.
Granular blends of LDPE resin having a melt index of 0.7 dg/minute
(determined by ASTM D-1238 at 190°C/2.16 kg ), a density of 0.923
g/cm3, and a
2s melting point of 115°C (determined per the differential scanning
calorimetry (DSC) at
the peak of an endotherm during heating at 10°C/minute) and EOD 96-07
grade
syndiotactic form copolymer polyproplyene resin (Available from Fina Oil and
Chemical Company), having a melt flow rate of 2 dg/minute,(Determined by ASTM
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CA 02339107 2001-O1-30
WO 00/12594 PCTNS99/19410
D-1238 at 230°C/2.16 kg), a density of 0.88 g/cm3, and a melting point
of 130°C in
predetermined ratios, as shown in Table I1, were prepared.
The blend of granular resins and 0.2 pph talcum powder (nucleating
agent) was fed into the extruder at a uniform rate of 3.1 kg/h ( due to a
difference in
s the feeding characteristics among the blends, the actual extrusion rate
varies slightly
in the range from approximately 3 kg/h to 3.2 kg/h, even though an effort is
made to
keep the rate the same by adjusting the screw rotating speed). The
temperatures at
the extruder zones were maintained at 160°C at the feeding zone,
190°C at the
melting zone, 200°C at the metering zone, and 220°C at the
mixing zone. The
io cooling zone temperature was maintained as indicated in Table II. Isobutane
(blowing agent) was injected into the mixing zone at the rate indicated in
Table II.
The temperature of the cooling zone was gradually reduced and the die opening
adjusted to make a good foam. The die temperature was maintained at
110°C for
Comparative Example B, Examples Nos. 2.1 through 2.3, and at 105°C for
Examples
is Nos. 2.4 and 2.5. Foam samples were taken at the optimum cooling zone
temperature for each formulation as shown in Table II and at a die opening
which
varies from 1.1 mm to 1.2 mm.
The dimensional data for the foams are summarized in Table II along
with the density, cell size, and open cell data.
-27-
CA 02339107 2001-O1-30
WO 00/12594 PCT/US99/19410
a~
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-28_
CA 02339107 2001-O1-30
WO 00/12594 PCT/US99/19410
As shown in Table II, the formulations containing up to 40 percent sPP
resin produced good-quality foams. The 50/50 blend foam of LDPE/sPP at the
chosen cooling temperature of 107°C looked slightly hot. The thickness
of the foams
ranged from 6.1 mm to 8.2 mm and the width of the foam ranged from 14.7 mm to
18.4 mm. A specimen of approximately 15 cm in length was cut from each freshly
prepared foam and the volume of the foam specimen was measured at
approximately 2 minutes after extrusion and then periodically thereafter
during aging
at an ambient temperature.
Conclusions:
io The blends tend to give a larger cell size than the pure LDPE resin.
Blends having 40 and 50 percent sPP tend to develop more open cells. The
addition
of the sPP resin is shown to improve the dimensional stability of the foam. A
blend
containing a sPP level of 30 percent or more provided a foam having
satisfactory
dimensional stability with a minimum foam volume during aging greater than 89
~s percent.
Exama~le 3 and Comparative Example C
Preparation of a sPP Resin and LDPE Resin Blend Foam
Example 3 demonstrates the preparation of foams according to the
present invention which were prepared from a blend of LDPE resin and sPP resin
zo wherein the level of blowing agent was varied in order to determine whether
the
foamability of the blends having a high sPP resin level could be improved by a
high
level of blowing agent. The cooling zone temperature was also lowered in order
to
determine its effect on foam expansion.
Granular blends of LDPE resin having a melt index of 0.7 dg/minute,
2s ( determined by ASTM D-1238 at 190°C/2.16 kg) , a density of 0.923
g/cm3, and a
melting point of 115°C (determined per the differential scanning
calorimetry (DSC) at
the peak of an endotherm during heating at 10°C/minute) and EOD 96-07
grade
syndiotactic form copolymer polypropylene resin (available from Fina Oil and
-29-
CA 02339107 2001-O1-30
WO 00/12594 PCT/US99J19410
Chemical Company) having a melt flow rate of 2 dg/minute, ( determined by ASTM
D-1238 at 230°C/2.16 kg), a density of 0.88 g/cm3, and a melting point
of 130°C in a
predetermined ratio, as shown in Table III, were prepared.
The blend of granular resins and 0.2 pph talcum powder (nucleating
s Agent ) was fed into the extruder at a uniform rate of 3.1 kg/h (due to a
difference in
the feeding characteristics among the blends, the actual extrusion rate varies
slightly
in the range from approximately 3 kg/h to 3.2 kg/h even though an effort is
made to
keep the rate the same by adjusting the screw rotating speed). The
temperatures at
the extruder zones was maintained at 160°C at the feeding zone,
190°C at the
~o melting zone, 200°C at the metering zone, and 220°C at the
mixing zone. The
temperature of the cooling zone was maintained as indicated in Table III and
isobutane (blowing agent) was injected into the mixing zone at the levels
indicated in
Table III. The temperature of the cooling zone was gradually reduced and the
die
opening adjusted to make a good foam. The die temperature was maintained at
110
is °C for Comparative Example C and Examples Nos. 3.1 and 3:2, and at
100°C for
Example No. 3.3. Foam samples were taken at the optimum cooling zone
temperature for each formulation as shown in Table III and at a die opening
which
varies from 1.1 mm to 1.2 mm.
The dimensional data for the foams are summarized in Table III along
2o with the density, cell size, and open-cell data.
-30-
CA 02339107 2001-O1-30
WO 00/12594 PCT/US99/19410
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-31-
CA 02339107 2001-O1-30
WO 00/12594 PCT/US99/19410
As shown in Table III, good foams were produced from blends
containing up to 50 percent sPP resin. The 40/60 blend of LDPE/sPP was
marginal
in foam processability. In order to make a foam from the blend, the cooling
zone
temperature had to be lowered to as low as 82°C. The foam was
marginally
s satisfactory with a high level of open cells. All the foams were of
relatively low
density reflecting a high level of blowing agent. Apparent open-cell contents
of the
foams are shown to be relatively high, greater than 36 percent. The ASTM D-
2856-A
open-cell method tends to overestimate the open-cell content for a flexible
foam.
The foams made in these examples are of lower density and of lower modulus
than
io those made in Example 2 resulting in a greater measurement error in the
open cell
content. One explanation for the overestimation of open-cells is seen from the
dimensional stability data for the LDPE foam. In spite of the relatively high
apparent
open cell content (41 percent), the foam shrank as much as 50 percent during
aging
and recovered relatively slowly.
is Example 4 and Comparative Example D
Preparation of Foam Prepared from sPP Resin and EthyleneNinvl Acetate
Copolymer Resin Blend
Example 4 demonstrates the preparation of foams according to the
present invention which were prepared from a blend of ethylene/vinyl acetate
2o copolymer (EVA) resin and varying amounts of sPP resin in order to
determine the
effect of the sPP resin level in the foamability of the blend and the
dimensional
stability of the foam. Comparative Example D was prepared from EVA resin only.
Granular blends of Elvax 460 brand resin (supplied by Du Pont-Dow
Inc.), having a melt index of 2.5 dg/minute (determined by ASTM D-1238 at
230°
25 C/2.16 kg), a density of 0.941 g/cm', and a melting point of 88°C
and EOD 96-07
grade syndiotactic form copolymer polypropylene resin(Available from Fina Oil
and
Chemical Company) having a melt flow rate of 2 dg/minute, a density of 0.88
g/cm',
and a melting point of 130°C in a predetermined ratio, as shown in
Table iV, were
prepared.
-32-
CA 02339107 2001-O1-30
WO 00/12594 PCT/US99/19410
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-33-
CA 02339107 2001-O1-30
WO 00/12594 PCT/US99/19410
The blend of granular resins and 0.4 pph talcum powder (nucleating
agent' was fed into the extruder at a uniform rate of 3 kg/h (due to a
difference in the
feeding characteristics among the blends, the actual extrusion rate varies
slightly as
Shown in Table IV, drifting downward from 3 kg/h to 2.6 kg/h at a fixed screw
rotating
s speed of the extruder). The temperatures at the extruder zones were
maintained at
120°C at the feeding zone, 150°C at the melting zone,
180°C at the metering zone,
and 180°C at the mixing zone.. The temperature of the cooling zone was
maintained
as indicated in Table IV and isobutane (blowing agent) was injected into the
mixing
zone at the levels indicated in Table IV: 380 g/h for Comparative Example D
and
to Examples Nos. 4.1 and4.2 and 450 g/h for Examples Nos. 4.3 and 4.4.{ due to
the
change in the feeding rate of polymer and blowing agent, the level of blowing
agent
in the resin varied from 12.7 pph to 17.3 pph (see Table IV). The die gap was
fixed
at 1.75 mm throughout the tests and the die temperature maintained at
0°C to 5°C
lower than the cooling zone temperature. The dimensional stability data (see
is methods given in Example 1 } for the foams are summarized in Table IV along
with
the density, cell size, and open-cell data.
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CA 02339107 2001-O1-30
WO 00/12594 PCT/US99/19410
As shown in Table IV, the good foams were produced from blends
containing up to 40 percent sPP resin. Contrary to the open cell data, the
foams
made in Comparative Example D and Examples Nos. 4.1 and 4.2 were substantially
close-celled when examined by a squeezing test with fingers. The foams made in
s Examples 4.3 and 4.4 felt open-celled. Again, the open-cell data for the
soft
polyolefin foams were not reliable. The EVA foam made in Comparative Example D
suffered an excessive shrinkage (minimum volume = 25 percent) even though ASTM
D-2856-A indicated that the foam contained 83 percent open cells.
Conclusion:
to Again, blends of sPP resin and a foamable ethylene/vinyl acetate resin
made good foams and sPP resin is shown to improve the dimensional stability
and a
sPP resin level 30 percent or greater yields a foam having satisfactory
dimensional
stability.
Test 5
is Heat Stability of the Foam of Comparative Example D and Example 4
After aging for 16 days, the foams produced in Comparative Example D
and Example 4 were subjected to the heat exposure test as described in Test 2.
The
foam specimens were put in an oven which had been maintained at 90°C.
After 1
hour and then after 8 hours, the samples were removed and measured for changes
2o in volume as shown in Table V.
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CA 02339107 2001-O1-30
WO 00/12594 PCT/US99/19410
Table V
Comp. Ex. or sPP Level (%)' Volume Retention
Ex.
No.
1 h (%)2 8h (%)
D 0 24 16
4.1 10 75 57
4.2 20 37 31
4.3 30 68 69
4.4 40 85 83
'Percentage of sPP resin in the blend
2Volume retention of foam body during aging at 90°C
As shown in Table V, all foams shrank, but the foams containing sPP
resin retained their volume to a greater extent than the foam (Comp. Ex. DJ
not
containing sPP resin. The foam made from a blend containing 40 percent sPP
resin
retained 83 percent volume after 8 hours in the oven.
Example 5 Preparation of Foam Prepared from
sPP Resin and iPP Resin Blend
~o In Example 5, a blend of a foamable high melt strength (HMS) iPP resin
and an sPP resin was used to prepare foams according to the present invention.
A 50/50 by weight granular blend of Pro-fax PF-814 grade high melt
strength iPP resin (available from Montell Polyolefins Co. N.V.) having a melt
index
of 3 dg/minute (determined by ASTM D-1238 at 230°C/2.16 kg), a density
of 0.90
~s g/cm3, and a melting point of 160°C and EOD 96-28 grade syndiotactic
form
copolymer polypropylene resin (available from Fina Oil and Chemical Company)
having a melt flow rate of 2 dg/minute, a density of 0.88 g/cm3, and a melting
point of
130°C was prepared.
The granular blend resins and an additive package consisting of talcum
2o powder ("nucleating agent) at 0.2 parts per hundred parts of resins (pph)
and Irganox
1010 brand antioxidant (available from Ciba-Geigy Corp.) at 0.1 pph, were
premixed
and fed into the extruder at a uniform rate of 4.2 kg/h. The temperatures were
-36-
CA 02339107 2001-O1-30
WO 00!12594 PCT/US99/19410
maintained at the cooling zone, at 160°C at the feeding zone,
190°C at the melting
zone, 200°C at the metering zone, and 200°C at the mixing zone.
Isobutane
(blowing agent) was injected into the mixing zone at a uniform rate of 10.7
pph. The
die opening was maintained at approximately 0.8 mm. The temperature of the
cooling zone was adjusted and the die opening was adjusted to produce foams.
At
cooling zone temperatures in the range of from 170°C to 160°C,
good foams of
substantially closed-cell structure were obtained. For example, a foam made at
160°
C had a density of 26.3 kg/m3, cell size of 1.8 mm, open-cell content of 17
percent,
thickness of approximately 11 mm and width of approximately 20 mm. The foam
to was strong and tough.
Comparative Example E Preparation of Foam Prepared from
sPP Resin and iPP Resin Blend
In Comparative Example E, the procedure of Example 5 was repeated,
but using a 20/80 blend of the same iPP and sPP resins rather than a 50/50
blend.
is At a cooling zone temperature scanned from 180°C down to
150°C, no foam could
be produced.
Example 6 and Comparative Example F Preparation of Foam Prepared from sPP
Resin and Polystyrene Resin Blend
In Example 6, blends of a polystyrene (PS) resin and a sPP resin were
2o expanded with COz, using the same apparatus and essentially the same
procedure
as used in Example 1. Comparative Example F was prepared from PS resin only.
Granular blends of PS resin having an average molecular weight of
150,000, a density of 1.05 g/cm3, and a Tg of 104°C and EOD96-07 Grade
sPP resin
(available from Fina Oil and Chemical Company) having a melt flow rate of 2
2s dg/minute (determined by ASTM D-1238 at 230°C/2.16 kg), a density of
0.88 g/cm3,
and a melting point of 130°C in a predetermined ratio, as shown in
Table VI, were
prepared.
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CA 02339107 2001-O1-30
WO 00/12594 PCTNS99/19410
The blend of granular resins and 0.1 pph barium stearate was
premixed and fed into the extruder at a uniform rate. The temperatures at the
extruder were maintained as follows: 130°C at feeding zone;
160°C at melting zone;
200°C at metering zone; and 200°C at mixing zone. Carbon dioxide
was injected
s into the mixing zone at a uniform rate of 4.6 pph. The temperature of the
cooling
zone was adjusted in the range of from 132°C to 134°C to produce
good foams. The
die temperature was maintained at a uniform 145°C throughout the
processes. The
die opening was maintained at a fixed opening of 1.5 mm. Thickness, foam
density,
cell size, and open cell content are shown in Table VI.
-38-
CA 02339107 2001-O1-30
WO 00/12594 PCT/US99/19410
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-39-
CA 02339107 2001-O1-30
WO 00112594 PCT/US99/19410
As shown in Table VI, the sPP resin makes the cross-sectional size
and the cell size larger. The foams containing 2 percent and 5 percent sPP
resin
are shown to have no open cells. The 80/20 PS/sPP resins blend provides a foam
having some open-cells.
-40-
