Note: Descriptions are shown in the official language in which they were submitted.
35~8
F-4120
FOAMABLE COMPOSITION CONTAINING
_
NO CHEMICAL NON-POLY~ERIC BLOWING AGENTS
The instant invention is directed to a foamable and foamed
composition and process for forming same. More particularly, the
instant invention is directed to a foamable and foamed composition
which includes an aromatic sulfone polymer, a linear polyester and
an aromatic polycarbonate and a process of forming the compositions.
Of the engineering plastics, which are the high strength
thermoplastics, the class of aromatic sulfone polymers is one of the
most outstanding in terms of high temperature performance. That is,
aromatic sulfone polymers can be utilized at elevated temperatures,
above those at which other engineering plastics fail. This property
suggests many unique uses for this resin. One such `use, recently
developed with the growth of microwave ovens, is food containers for
prepackaged frozen food and the like. In the past frozen food
packages were constructed of aluminum and other light weight
metals. These packages easily withstood the elevated temperatures
of standard gas or electrically heated cooking ovens. However,
these metal containers cannot be used to heat foods contained
therein by microwave energy. As those skilled in the art are aware,
the high dielectric constant of metals result in a preferential
absorption of the microwave energy by the metal covering the food
preventing the heating effect of the microwave energy from
penetrating to the food.
No such detriment exists when plastics are employed. Those
skilled in the art are aware that plastics have very low dielectric
constants. Microwave energy penetrates plastic packages without
absorption so that the energy is focused on heating the foods
contained therein. Thus, the use of a strong, high temperature
resistant plastic such as aromatic sulfone polymers is suggested in
this application.
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F-4120 -2-
The above analysis does not encompass two detrimental effects of
using aromatic sulfone polymers. Engineering plastics, such as
aromatic sulfones, are relatively high priced. In a mass market
such as one involving preprepared foods, the high cost of packaging
material is a critical factor. Equally significant in this
application is handling of these packages. The criticality of
lightweight packaging in handling the large numbers of prepackaged
food containers involved in this application is readily apparent.
Thus, the use of a conventional aromatic sulfone polymer package, in
spite of the advantages noted above, is discouraged.
These detrimental factors can be overcome by using a foamed
aromatic sulfone polymer. A foamed aromatic sulfone polymer is less
dense. The same sized package could be produced at significantly
decreased weight. At the same time the lower density of a foamed
product decreases the aromatic sulfone polymer cost per package in
direct proportion to the decrease in density of the foamed polymer
compared to the density of the unfoamed product. However, prior
success with foaming of sulfone polymers in the prior art would
suggest abandonment of such a project.
As those skilled in the art are aware, typical foaming agents,
often referred to as blowing agents, are usually toxic agents. The
incorporation of these agents in food containers is therefore
unacceptable. Even if non-toxic blowing agents were available which
could pass stringent constraints, still the chemical blowing agents
known in the art present serious processing conditions when added to
engineering plastics. The addition of chemical blowing agents to
engineering plastics require extreme processing conditions. For one
thing, the presence of moisture results in degradation of the
product produced. For another, chemical blowing agents are
typically powders. In order to have a uniform foamed product, the
foaming agent must be uniformly dispersed. To uniformly disperse a
powder is a very difficult, and often, unsolvable problem. Thus,
the utilization of blowing agents oftentimes yields non-uniform
foamed products.
~..2~5~8
F-4120 -3-
While the above problems, associated with engineering plastics
in general, are indeed formidable, they pale when foaming of an
aromatic sulfone is attempted. Aromatic sulfone polymers, like
other engineering plastics, are foamed by extruding the plastic with
a foaming agent. The known chemical blowing agents, howeveT, yield
their gaseous product at relatively low temperatures. On the other
hand, to extrude an aromatic sulfone requires a temperature in the
range of about 250C. At atmospheric pressure, chemical blowing
agents not only react to give off their gaseous product at
temperatures significantly below 25ûC, resulting in premature
foaming, but, more fundamentally, chemical blowing agents decompose
at temperatures below 250C. In sum, ~he known blo~ing agents of the
prior art cannot be employed to foam aromatic sulfone polymers.
The foaming of engineering plastics other than aromatic sulfones
is known in the prior art. Particularly, the foaming of
polyethylene terephthalate is disclosed in U.S. Patent 3,470,114,
issued to Siggel et al. This patent is directed to a process for
producing foamed polyethylene terephthalate by the addition thereto
of an aromatic polycarbonate to which it is reacted at elevated
temperature.
U.S. Patents 4,462,947 and 4,466,933, each issued to the
inventor of the present invention, discloses a similar product, a
foamed polyethylene terephthalate formed by the reaction of
polyethylene terephthalate with an aromatic polycarbonate to produce
a foamed product. This product is subjected to crystallization
annealing to produce lightweight products usable as food containers.
Although these teachings advance the art, those skilled in the
art are aware of the clear superior high temperature properties of
aromatic sulfones, compared to polyethylene terephthalate. However,
the teachinas of the prior art also suggest that making a foamed
aromatic sulfone polymer presents such formidable problems that the
substitution of aromatic sulfone polymer containers for poly-
ethylene terephthalate containers, although desirable, i5 SO
difficult as to make such substitution highly unlikely.
'~"~D,
F-4120 _4_
It has now been discovered that foamable and foamed aromatic
sulfone pOlynErS can ke prepared without the use of chemical blowin~
agents. Thus, the formidable barrier to producing a foamable and
foamed aromatic sulfone polymer is overcome by sidestepping
traditional foaming methods. Instead, a foaming method, using
non-toxic materials, which can be easily handled at elevated
temperatures and which does not result in premature foaming during
resin drying prior to processing overcomes the earlier processing
difficulties associated with making aromatic sulfones in the past.
With the removal of difficult processing barriers, a foamed aromatic
sulfone polymer can be prepared which has superior high temperature
properties making this polymer the material of choice in the
ovenable food container field.
The present invention provides a foamable composition comprising
an admixture of an aromatic sulfone polymer, characterized by the
presence of both aryl ether and aryl sulfone linkages in the polymer
backbone; a high molecular weight linear polyester which is a
polycondensation product of an aromatic dicarboxylic acid and a
glycol; and a high molecular weight linear aromatic polycarbonate
represented by the repeating structural unit of the formula:
_o~}x~-û-c-
where X is a divalent hydrocarbon radical with a total of from 2 to
9 carbon atoms selected from
H C/ \ CH2 C ~ \ CH
~2 H2 CH2 \ /
CH~
in which Rl is hydrocarbon or lower alkyl; and R is phenyl or
Cl-C7 alkyl.
In further accordance with the instant invention a foamed
composition is provided having the same constituency.
.~
3 3~3~38
F-4120 -5-
In still further accordance with this invention a process for
making a foamed article is taught. In this process the three
polymeric components recited above are blended into a homogeneous
mixture. The homogeneous mixture is heated to a temperature in the
range`of 250C to 350C and the heated homogeneous mixture is
extruded into a foamed article.
In yet still further accordance with the present invention a
process for making a foamable composition is disclosed. In this
process the three polymeric compounds, which form the foamable
composition, are blended into a homogeneous mixture. The mixture is
heated to a temperature below 250C and the heated homogeneous
mixture is extruded into a foamable composition.
The present invention is directed to a foamable and foamed
composition comprising an admlxture of an aromatic sulfone polymer,
a linear polyester and an aromatic polycarbonate.
The generic class of compounds denoted as aromatic sulfone
polymers include a class of aromatic sulfone thermoplastic polymers
which are characterized by the incorporation therein of both aryl
ether (ArOAr) and aryl sulfone (ArSO ~ r) linkages in the polymer
backbone. Specific commercial aromatic sulfones within the
contemplation of the present invention include the polymer denoted
as polysulfone. This polymer is formed by the reaction of the sodium
salt of bisphenol A with 4,4'-dichlorodiphenyl sulfone in a mixed
solvent of chlorobenzene and dimethylsulfoxide. Another aromatic
sulfone encompassed by this invention is polyether sulfone, formed
by condensation of diphenyl ether with the disulfonyl chloride of
diphenyl ether. Polyarylsulfone, a copolymer very similar to
polyether sulfone, is characterized by the incorporation of rigid
biphenyl units in the polymer by copolymerizing the sulfonyl
chlorides of biphenyl and diphenyl ether. Polyphenyl sulfone, which
is produced in a method similar to the formation of polysulfone, is
formed by the reaction of an alkali metal salt of bisphenol A,
preferably the sodium salt, with a 4,4'-dichlorodiphenyl- sulfone
having strongly electron-withdrawing groups, such as carbonyl, azo,
sulfonamido and nitro groups, ortho or para to the chlorine atoms.
F-4120 -6-
Obviously, other polymers, outside the group of the commercial
polymers enumerated above but within the generic class of aromatic
sulfones, may be employed in the composition of the present
invention. Thus9 any polymer which have both aryl ether and aryl
sulfone linkages in the polymer backbone is within the contemplation
of the present invention.
Although all aromatic sulfone polymers are within the
contemplation of this invention, polyether sulfone, poly-
sulfone, polyaryl sulfone and polyphenyl sulfone are preferred. ûf
these, polyether sulfone is most preferred.
A second component of the foamed composition of the present
invention is a high molecular weight linear polyester. Linear
polyesters, within the contemplation of the present invention, are
polycondensation products of dicarboxylic acid and a glycol.
Although the linear polyesters of the present invention are
preferably the poly-condensation product of an aromatic dicarboxylic
acid, an aliphatic dicarboxylic acid may be utilized. However, when
an aliphatic dicarboxylic acid is used, it should be used in
combination with an aromatic dicarboxylic acid and then only in a
concentration of not more than 15~, preferably less than 5~ by
weight. A preferred dicarboxylic acid is terephthalic acid. The
glycol, reacted with the dicarboxylic acid to produce the linear
polyester, is generally designated by the formula HO(CH2~nOH,
where n is an integer of 2 to 12. Preferred glycols include
ethylene glycol, 1,4-butanediol and the like.
Of the linear polyesters within the contemplation of the present
invention, polyethylene terephthalate is particularly preferred.
In general, the aromatic polycarbonates of the composition of
this invention are a well-recognized class of polymers, referred to
as "aromatic polyesters of carbonic acid" by H. Schnell in
Angewandte Chemie, Vol. 68, No. 20 pp. 633-660~ ûctober 21, 1956,
and subsequently designated more simply by the term "aromatic
polycarbonates" in the book by the same author entitled " Chemistry
and Physics of Polycarbonates," Interscience Publishers, New York
(1964).
;, . .
5~
F-4120 ~7~
For details concerning the nanner in which the aromatic
polycarbonates are prepared, their physical and chemical properties
and other detailed information ooncerning these polymt rs and their
precursors, the reader is referred b~ the above-n~ntioned Schnell
references. In general, these polycarbonate polymers are essentially
linear synthetic polyesters of organic dicarboxylic acids and
organic dihydroxy ccmpounds.
The preferred aromatic polycarbonates of this invention are the
linear condensation product of carbonic acid with a
4,4'-dihydroxy-diphenyl-alkane, a 4,4'-dihydroxy-triphenyl-alkane or
a 4,4'-dihydroxy-diphenyl-cycloalkane in whlch the bridging group
between the hydroxy-substituted phenyl nuclei contains between 2 and
9 carbon atoms free of aliphatic unsaturation. More particularly,
the preferred aromatic polycarbonates are those linear polymers
defined by the repeating structural unit o~ the ~ormula
-O<~-X~O-~-
where X is a divalent hydrocarbon radical having 2 to 9 carbon atoms
selected ~rom the group consisting of
I
--I
R ~ C- / ~
f , H2 ~ lc~2 and H2~ CH2
R H ~H2 2 \ f 2
in which Rl is hydrogen or lower alkyl; and R is phenyl or
Cl- ~ alkyl. These aro~atic polycarbonates have molecular
,~
.......
F-4120 -8-
weights of from about 18,000 to 50~,0~0 or higher. More desirably,
the average molecular weight of the polycarbonates of this invention
are between 20,00~ and 250,000. Most preferably, the molecular
weight of the polycarbonates of this invention are between 25,ûOO
and 150,000.
In a preferred embodiment, the polycarbonates of the present
invention are obtained from bisphenol A (4,4l-
dihyd~oxy-diphenyl-2,2-propane). Another preferred compound,
reacted with carbonic acid, is 4,4'-dihydroxy-diphenyl-
methyl-phenyl-methane. Other suitabIe, if less preferred, aromatic
polycarbonates include those derived as the carbonic acid esters of
the following dihydroxy aromatic compounds:
4,4'-di-hydroxy-diphenyl-1,1-ethane; 4,4'-dihydroxy-diphenyl-
l,l-butane; 4,4'-dihydroxy-diphenyl-1,1-isobutane; 4,4'-di-
hydroxy-diphenyl-l,l-cyclopentane; 4,4'-dihydroxy-diphenyl-
l,l-cyclohexane; 4,4'-dihydroxy-diphenyl-phenyl-methane;
4,4'-dihydroxy-diphenyl-2,2-butane; 4,4'-dihydroxy-diphenyl-
2,2-pentane; 4,4~dihydroxy-diphenyl-2,2-hexane; 4,4'-di-
hydroxy-diphenyl-2,2-isohexane; 4,4'-dihydroxy-diphenyl-2,2-
heptane; 4,4'-dihydroxy-diphenyl-2,2-octane; 4,4'-dihydroxy-
diphenyl-2,2-nonane; 4,4'-dihydroxy-diphenyl-ethyl-phenyl-
methane; 4,4'-dihydroxy-diphenyl-3,3-pentane; and 4,4'-
dihydroxy-diphenyl-4,4-heptane.
The common feature of all the aromatic poly- carbonates within
the contemplation of this invention are that they decompose and
release carbon dioxide in the presence of the linear polyester when
heated to temperature of about 250C to 3~0C. It is ncted that the
polycarbonates of this invention in the absence of other components
are stable at these temperatures. Thus, the aromatic polycarbonates
of this invention when admixed uniformly with linear polyesters of
the present invention are capable of acting as autogeneous foaming
agents even though the homopolymers of these carbonates require the
addition of a distinct foaming agent or at least a recognizable
unstable gas-liberating compound before any foaming takes place.
~.2~
F-4120 -9-
The composition of the present invention comprises at least 90
weight percent of an aromatic sulfone polymer, based on the total
weight of the composition. More preferably, the composition of the
present invention is at least 95 weight percent aromatic sulfone
polymer, based on the total weight of the composition. Most
preferably, the present composition incorporates at least 97.5
weight percent aromatic sulfone polymer, based on the total weight
of the composition. When recitation of at least 90, 95 and 97.5
weight percent is made, it should be appreciated that implicitly
recitation of less than 100 weight percent is also made. Obviously,
the absence of the linear polyesteraromatic polycarbonate would be
outside the scope of this invention. Correspondingly, the remaining
two constituents, the linear polyester and the aromatic
polycarbonate comprises a.5 to 10 percent by weight of the
composition, based on the total weight of the compûsition. More
preferably, the polyesterpolycarbonate constituent represents 0.75
to 5% by weight of the total composition.
Still more preferably, the linear polyester- aromatic
poly-carbonate contribution to the total weight of the composition
is in the range of between 0.85 and 2.5 percent by weight.
Most preferably, the total concentration of linear polyester and
aromatic polycarbonate in the composition of this invention is in
the range of between about 1 and 2 percent by weight.
In terms of the relative concentration of the linear polyester
and aromatic polycarbonate, these con-
stituents are present such that the weight ratio of linear polyester
to aromatic polycarbonate is in the range of between 1:19 and 19:1,
respectively. More preferably, the weight ratio of linear polyester
to aromatic polycarbonate is in the range of between about 1:3 and
3:1. Still more preferably, the weight ratio of linear polyester to
aromatic polycarbonate is in the range of between about 2:3 and
3:2.
The process of forming the foamed cornposition of the present
invention involves homogeneously mixing the three components of the
composition and heating them above the softening point of the
~ ?d~3~ 3~3
~,
F-4120 -10-
mixture. In general, the reaction for releasing carbon dioxide from
the polycarbonate and thus forming a foamed composition involves
heating the mixture to a temperature of at least 25~C, usually a
temperature in the range of between 250 and 35ûC. Preferably, the
temperature of the composition is raised to between about 270C and
350C. to effect foaming. This heating step occurs in an at least
partially enclosed mold, extruder or similar reaction zone. The
retention time in the reaction zone can be relatively short, e.g.,
from about 1 minute up to about 15 minutes, preferably from about
1.~ to 1.5 minutes at the higher end of the above-recited
temperature range and about 10 to 12 minutes at the lower end of the
usual temperature range for foaming. Temperatures above 350C.
should ordinarily be avoided to prevent unnecessary dama~e to the
linear palyester.
Although mixing and foamin~ may occur in a single operation it
is oftentimes preferred to initially p~epare a fDamable composition
in granule form. In forming a foamable composition the three
components are initially mixed at elevated temperature. Obviously,
the maximum mixing temperature is limited by the temperature above
which foaming occurs. Since foaming is initiated at about 27ûC.,
initial mixing occurs below about 270~., preferably below about
250C. Homogeneous mixing preferably takes place in a screw
extruder, a mixer or a kneader. Of course, any device that effects
homogeneous mixing may be utilized. In a preferred embodiment of
the process of making a foamable composition, the homogeneously
mixed composition is extruded into sheets, rods and the like. The
sheets, rods, etc. are then chopped or granulated into granules for
easy storage and handling. ~s long as the granules are kept below
foamable temperature, i.e., below 250~C, they may be stored for
indefinite periods of time without danger of either foaming or
losing their ability to foam at foamable temperature.
Independent of whether mixing and foaming occurs in a single
step or in separate mixing and foaming steps, the step of foamin~
preferably takes place in a screw injection molding machine. This
F-4120 -11-
machine is preferred in that best homogenization or plasticizing of
the aromatic sulfone~linear polyester-polycarbonate mixture is
achieved in a screw or worm mixer. Moreover, a screw injection
molding machine facilitates both mixing, foaming and molding in a
single continuous operation. The same advantages are achieved by
processing the mixture in an extruder with an attached injection
mold. Another preferred apparatus for conducting the process of the
present invention is a piston injection molding machine, provided
the mixture is first homogenized, at a be~perature below the foamable
temperature range, in an extruder or similar mixing device.
The process of the present invention can also be carried out in
an extruder without an attached injection mold. In this embodiment,
the aromatic sulfone-polyesterpolycarbonate mixture is homogenized
and heated to release carbon dioxide under super atmospheric
pressure in a screw or worm extruder and then extruded or drawn off
therefrom at atmospheric pressure so that the soften extruded mass
rapidly ~oams and resolidify into the desired extruded shape. Thus,
foamed composition can be produced as rods, bands, sheets and the
like with regular or irregular profiles depending upon the die
ooening of the extruder.
Whatever the device employed, the mixture is disposed in the
preferred apparatus and heated to a temperature of preferably
between 270C and 350C. In the preferred embodiment wherein
injection molding occurs, the injection mold may be connected, at
the outlet side of the processing machine, to a vacuum. This
processing step results in a uniform pore size or cell structure.
Thus, in a preferred embodiment, the injection mold is evacuated to
a pressure in the range of between 5 and 3Q0 mm. Hg, and more
pre~erably, about 50 to 100 mm. Hg. Although this evacuation can
occur before or during injectlon of the composition, it is preferred
that evacuation occur after the mold has been injected with the hot
f`oamable mass so as to achieve especially uniform pores or cells.
If different density injection molded foam products are desired,
`~ 35~
F-4120 -12-
this is accomplished by varying the weight of material charged into
a mold of constant volume. Obviously, as the weight of the charge
or "shot capacity" increases in a constant volume mold, the density
of the foam product likewise increases. With this increase in
density there is a corresponding decrease in pore size regardless of
the pressure difference before and after application of the vacuum.
With a sufficiently high density, it is possi~le to achieve a molded
~oam product of the type classified as a rigid, brittle and
open-celled foam structure with a closed outer skin or surface.
In a pre~erred embodiment of the present invention a
thermo~ormed foamable composition is prepared. In this embodiment
the foamable composition is extruded into sheet material. Foaming
generally occurs the instant the softened composition is subjected
to sufficient foaming pressure. That pressure is reached upon
contact with atmospheric pressure which occurs the instant the
composition leaves the extrusion die. The foamed sheet is
immediately cooled on a ohill roll maintained at a temperature in
the range of between about 20C and 50~C. The thus cooled foamed
sheet is then heated to a temperature above the glass transition
temperature of the aromatic sul~one polymeric constituent of said
sheet. Glass transition temperatures for aromatic sulfone
polymers are provided in standard references. For example, the
glass transition temperature for commercially available aromatic
sulfone polymers is provided in Modern Plastics Encyclopedia,
19~4-85 Edition, p.47B, McGraw Hill Publishing Co., New York.
The heated sheet, in turn, is thermo~ormed in a mold under a
pressure of up to 5 atmospheres.
The following examples are provided to illustrate the scope and
spirit of the present invention. Slnce these examples are given for
illustrative purposes only, the scope of the present invention
should not be limited thereto.
, ,~.,
,.", ~,
s:~
i~
F-4120 -13-
EXAMPLE l
A blend of 99.5 parts of Victrex ~trademark] 200P polyether
sulfone (PES); 0.25 parts of Goodyear VFR [trademark~ 10024AS
polyethylene terephthalate (PET); and 0.25 part Merlon ~trademark]
M39-F aromatic polycarbonate (AP~, all parts being by weight, were
dried, blended and extruded in a ll/2 inch extruder equipped with a
water chilled cast roll. The product extruded was a foamed
composition having a density of 1.37 grams per cubic centimeter.
The results o~ this example are summarized in
Table l.
EXAMPLES 2-4
Example l was repeated but for the relative amounts of the three
components of the composition. In Example 2, 99 parts of Victrex
[trademark] 2ûOP; 0.5 part of VFR ~trademark] 10024AS and 0.5 part
of Marlon [trademark] M39F, all parts being by weight, were charged
into the extruder.
In Example 3, using the same brands as in Examples 1 and 2, 98.7
parts by weight of PES; 0.625 parts by weight of PC; 0.625 part o~
PET; and 0.625 part by weight of PC were charged in the extruder.
In Example 4, using the same brand polymers as in Examples 1, 2,
and 3, 97.5 parts by weight of PES; 1.25 parts by weight of PET~ and
1.25 parts by weight of PC were charged into the extruder.
In each case a foamed product resulted whose density was
determined. The resultant density of the foamed product formed in
accordance with each of Examples 2-4 is summarized in Table l.
COMPARATIVE EXAMPLE
A composition constituting only Victrex ~trademark] 2ûOP PES was
charged into the same extruder used in Examples 1-4. No PET or PC
was included in the material charged into the extruder. The
resultant extruded product was unfoamed having a density of 1.41
grams per cc. The results of this example are also incorporated in
Table 1 below.
, ~ . . .
~ .
38
F-4120 -14-
TABLE 1
_ _
Components, parts by wt. _ 1 2 34_
Polyether Sulfone 100 99.5 99.098.75 97.5
Polyethylene Terephthalate 00.25 0.50.625 1.25
Polycarbonate 0.25 0.50.625 1.25
Foamed Density of
Product, ~/cc 1.41 1.37 1.170.81
0.67
Reduction in Density, %
(calculated) --- 3 17 43 52
Unfoamed
The examples establish the ef~ectiveness of poly-
ethylene terephthalate-aromatic polycarbonate as foaming agent in
the foaming of polyether sulfone. In each of Examples 1-4, wherein
these constituents were utilized? foaming was effected. Examples
1-4 evidence reduction in density ranging from 3 to 52 percent
depending upon the concentration of the in-situ foaming agent,
polyethylene terephthalate-aromatic polycarbonate. Clearly, all
concentrations ranges embodied by Examples 1-4 produce attractive
density reductlon.
The above embodiments and examples are given to illustrate the
scope and spirit of the present invention. These embodiments and
examples will make apparent, to those skilled in the art, other
embodiments and examples. These other embodiments and examples are
within the contemplation of the present invention. Therefore, the
instant invention should be limited only by the appended claims.
