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Description  |
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BACKGROUND OF INVENTION
This invention relates to a low density, closed cell foamed thermoplastic
multi-block copolymer elastomer.
Thermoplastic polymers that have been foamed heretofore were not of
sufficiently low density, nor have a substantially uniform cell structure
to be entirely satisfactory for the manufacture of components for athletic
shoes and other sporting equipment, such as innersoles for shoes and
helmet padding nor for use as packaging material for delicate equipment,
such as electronic equipment, that is subjected to severe vibrations.
Prior art foamed polymers were deficient in strength and the foamed
polymers did not have sufficient energy return ratios. The present
invention provides a foamed thermoplastic elastomer having a low density,
high strength, and a high energy return ratio.
SUMMARY OF THE INVENTION
It has now been discovered that certain thermoplastic multi-block copolymer
elastomers that can be foamed to a low density are especially suitable for
components for athletic shoes, e.g., innersoles and other sporting
equipment and packaging material. More specifically, the present invention
is directed to a foamed thermoplastic elastomer having a substantially
uniform cell structure which comprises a foamed thermoplastic multi-block
copolymer elastomer having a closed cell structure and having a specific
gravity of less than about 0.40, an energy return ratio greater than about
0.50, preferably greater than about 0.60, when compressed and released, as
determined by the recommended method of ASTM Committee F08.54 on athletic
footwear, said foam being prepared from a thermoplastic multi-block
copolymer elastomer having a Shore D hardness of from about 25-75 and
selected from the group consisting of (1) copolyetheresters, (2)
copolyesteresters, (3) copolyetherimide esters, and (4) copolyetheramides,
said thermoplastic foam being prepared by mixing said multi-block
copolymer elastomer at a temperature above its melting point to form a
molten mass with a gaseous or low-boiling liquid foaming agent at a
pressure sufficient to dissolve and/or disperse said foaming agent in said
molten elastomer and extruding the resulting mixture through an orifice
into a lower pressure zone whereupon substantially free and uniform
foaming and expansion occur and the elastomer solidifies.
The thermoplastic multi-block copolymer elastomer used to make the foam,
preferably have a melt index not greater than 10 g/10 minutes by the
procedure described in ASTM D1238 (2.16 kg wt.). Most preferably, the
thermoplastic multi-block elastomer has a melt index no greater than 6
g/10 minutes.
The resulting foam thermoplastic elastomer has a surprisingly high energy
return ratio.
DETAILED DESCRIPTION OF THE INVENTION
The foamed thermoplastic multi-block copolymer elastomers have a specific
gravity less than about 0.4, preferably no greater than 0.35, and an
energy return ratio greater than 0.50 preferably greater than 0.60,
provided that the Shore D hardness of the multi-block copolymer elastomer
used to make the foam is from 25-75. The foamed elastomers of the present
invention are especially useful as packaging material and components in
athletic shoes and sports equipment.
The thermoplastic multi-block copolymer elastomers that are used in this
invention to form a thermoplastic foam are (a)copolyetheresters, (b)
copolyesteresters, (c) copolyetherimide esters, and (d) copolyetheramides.
The four types of elastomers are similar to one another in that they all
consist of repeating hard segments which are relatively high melting
polyester or polyamide segments and repeating soft segments which are
relatively low melting polyether or polyester segments. The four types of
polymers described below are well known in the industry.
The copolyetheresters (a) consist essentially of a multiplicity of
recurring long chain ester units and short chain ester units joined
head-to-tail through ester linkages, said long chain ester units being
represented by the formula
##STR1##
and said short chain ester units being represented by the formula
##STR2##
where G is a divalent radical remaining after the removal of terminal
hydroxyl groups from a poly(alkylene oxide) glycol having a number average
molecular weight of about 400-6000 and a carbon to oxygen atomic ratio of
about 2.0-4.3; R is a divalent radical remaining after removal of carboxyl
groups from an aromatic dicarboxylic acid having a molecular weight less
than about 300, and D is a divalent radical remaining after removal of
hydroxyl groups from a diol having a molecular weight less than about 250;
provided said short chain ester units amount to about 20-85 percent by
weight of said copolyetherester.
The term "long-chain ester units" as applied to units in a polymer chain of
the copolyetherester refers to the reaction product of a long-chain glycol
with a dicarboxylic acid. Such "long-chain ester units", which are a
repeating unit in the copolyetheresters, correspond to formula (I) above.
The long-chain glycols are polymeric glycols having terminal (or as nearly
terminal as possible) hydroxy groups and a molecular weight from about
400-6000. The long-chain glycols used to prepare the copolyetheresters are
poly(alkylene oxide) glycols having a carbon-to-oxygen atomic ratio of
about 2.0-4.3. Representative long-chain glycols are poly(ethylene oxide)
glycol, poly(1,2- and 1,3-propylene oxide) glycol, poly(tetramethylene
oxide) glycol, random or block copolymers or ethylene oxide and
1,2-propylene oxide, and random or block copolymers of tetrahydrofuran
with minor amounts of a second monomer such as ethylene oxide.
The term "short-chain ester units" as applied to units in a polymer chain
of the copolyetherester refers to low molecular weight chain units having
molecular weights less than about 550. They are made by reacting a low
molecular weight diol (below about 250) with an aromatic dicarboxylic acid
having a molecular weight below about 300, to form ester units represented
by formula (II) above.
The term "low molecular weight diols" as used herein should be construed to
include equivalent ester-forming derivatives, provided, however, that the
molecular weight requirement pertains to the diol only and not to its
derivatives.
Preferred are diols with 2-15 carbon atoms such as ethylene, propylene,
tetramethylene, pentamethylene, 2,2-dimethyltrimethylene, hexamethylene,
and decamethylene glycols, dihydroxycyclohexane, cyclohexane dimethanol,
and the unsaturated 1,4-butenediol.
The term "dicarboxylic acids" as used herein, includes equivalents of
dicarboxylic acids having two functional groups which perform
substantially like dicarboxylic acids in reaction with glycols and diols
in forming copolyetherester polymers. These equivalents include esters and
ester-forming derivatives, such as acid anhydrides. The molecular weight
requirement pertains to the acid and not to its equivalent ester or
ester-forming derivative.
Among the aromatic dicarboxylic acids for preparing the copolyetherester
polymers, those with 8-16 carbon atoms are preferred, particularly the
phenylene dicarboxylic acids, i.e., phthalic, terephthalic and isophthalic
acids and their dimethyl esters.
The short-chain ester units will constitute about 20-85 weight percent of
the copolyetherester. The remainder of the copolyetherester will be
long-chain ester units comprising about 15-80 weight percent of the
copolyetherester.
Preferred copolyetheresters are those prepared from dimethyl terephthalate,
1,4-butanediol, and poly(tetramethylene oxide) glycol having a molecular
weight of about 600-2000. Optionally, up to about 30 mole percent of the
dimethyl terephthalate in these polymers can be replaced by dimethyl
phthalate or dimethyl isophthalate. Polymers in which a portion of the
butanediol is replaced by butenediol are also preferred.
The dicarboxylic acids or their derivatives and the polymeric glycol are
incorporated into the copolyetherester in the same molar proportions as
are present in the reaction mixture. The amount of low molecular weight
diol actually incorporated corresponds to the difference between the moles
of diacid and polymeric glycol present in the reaction mixture. When
mixtures of low molecular weight diols are employed, the amounts of each
diol incorporated depends on their molar concentration, boiling points and
relative reactivities. The total amount of diol incorporated is still the
difference between moles of diacid and polymeric glycol.
The copolyetheresters described herein are made by a conventional ester
interchange reaction which, preferably, takes place in the presence of a
phenolic antioxidant that is stable and substantially nonvolatile during
the polymerization.
A preferred procedure involves heating the dimethyl ester of terephthalic
acid with a long-chain glycol and 1,4-butanediol in a molar excess and a
phenolic antioxidant and hindered amine photostabilizer in effective
concentrations in the presence of a catalyst at about
150.degree.-260.degree. C. and a pressure of 0.05 to 0.5 MPa, preferably
ambient pressure, while distilling off methanol formed by the ester
interchange. Depending on temperature, catalyst, glycol excess and
equipment, this reaction can be completed within a few minutes, e.g.,
about two minutes, to a few hours, e.g., about two hours. This procedure
results in the preparation of a low molecular weight prepolymer which can
be carried to a high molecular weight copolyetherester by distillation of
the excess of short-chain diol. The second process stage is known as
"polycondensation".
Additional ester interchange occurs during this polycondensation which
serves to increase the molecular weight and to randomize the arrangement
of the copolyetherester units. Best results are usually obtained if this
final distillation or polycondensation is run at less than about 670 Pa,
preferably less than about 250 Pa, and about 200.degree.-280.degree. C.,
preferably about 220.degree.-260.degree. C., for less than about two
hours, e.g., about 0.5 to 1.5 hours. A phenolic antioxidant can be
introduced at any stage of copolyetherester formation or after the polymer
is prepared. As indicated above, preferably, a phenolic antioxidant is
added with the monomers. It is customary to employ a catalyst while
carrying out ester interchange reactions. While a wide variety of
catalysts can be employed, organic titanates such as tetrabutyl titanate
used alone or in combination with magnesium or calcium acetates are
preferred. The catalyst should be present in the amount of about 0.005 to
2.0 percent by weight based on total reactants.
Both batch and continuous methods can be used for any stage of
copolyetherester polymer preparation. Polycondensation of prepolymer
already containing the phenolic antioxidant and hindered amine
photostabilizer can also be accomplished in the solid phase by heating
divided solid prepolymer in a vacuum or in a stream of inert gas to remove
liberated low molecular weight diol. This method has the advantage of
reducing thermal degradation because it must be used at temperatures below
the softening point of the prepolymer.
A more detailed description of suitable copolyetheresters and procedures
for their preparation are further described in U.S. Pat. Nos. 3,023,192,
3,651,014, 3,763,109, 3,766,146, and 4,355,155 the disclosures of which
are incorporated herein by reference.
The copolyesteresters (b) consist essentially of high melting segments
comprised of repeating short-chain ester units of the formula
##STR3##
which are as described for copolyetheresters as disclosed hereinbefore.
The soft segments in the copolyesterester elastomers are derived from low
melting polyester glycols such as poly(butylene adipate) or
poly(caprolactone).
Several procedures have been used to prepare multi-block copolyesterester
elastomers wherein the low melting point blocks are polyesters as well as
the high melting point blocks. One procedure involves carrying out a
limited ester interchange reaction in the presence of an exchange catalyst
between two high molecular weight polymers such as poly(butylene
terephthalate) and poly(butylene adipate) Ester exchange at first causes
the introduction of blocks of one polyester in the other polyester chain
and vice versa. When the desired multi-block polymer structure is formed
the catalyst is deactivated to prevent further interchange which
ultimately would lead to a random copolyester without any blockiness. This
procedure is described in more detail in U.S. Pat. No. 4,031,165 to Saidi
et al. Other useful procedures involve coupling of preformed blocks of
high and low melting point polyester glycols. Coupling can be accomplished
by reaction of a mixture of the blocks with a diisocyanate as described in
European Patent No. 00013461 to Huntjens et al. Coupling can also be
accomplished by heating the mixed blocks in the presence of terephthaloyl
or isophthaloyl bis-caprolactam addition compounds. The caprolactam
addition compounds react readily with the terminal hydroxyl groups of the
polyester blocks, splitting out caprolactam and joining the blocks through
ester linkages. This coupling method is further described in Japanese
Patent Publication No. 73/4115. Another procedure of use when the low
melting blocks are to be provided by polycaprolactone involves reacting a
preformed high melting point block terminated with hydroxyl groups with
epsilon-caprolactone in the presence of a catalyst such as dibutyl tin
dilaurate. The caprolactone polymerizes on the hydroxyl groups of the high
melting point ester block which groups serve as initiators. The resulting
product is a relatively low molecular weight triblock polymer having the
high melting point block in the middle with low melting point
polycaprolactone blocks on each end. The triblock polymer is hydroxyl
terminated and may be joined to give a finished product by reaction with a
diepoxide such as diethylene glycol diglycidyl ether, see Japanese Patent
Publication No. 83/162654.
The copolyetherimide ester elastomers (c) differ from the copolyetheresters
(a) only in that repeating hard segments and soft segments are joined
through imidoester linkages rather than simple ester linkages. The hard
segments in these elastomers consist essentially of multiple short chain
ester units represented by the formula
##STR4##
described hereinbefore. The soft segments in these polymers are derived
from poly(oxyalkylene diimide) diacids which can be characterized by the
following formula:
##STR5##
wherein each R" is independently a trivalent organic radical, preferably a
C.sub.2 to C.sub.20 aliphatic, aromatic or cycloaliphatic trivalent
organic radical; each R' is independently hydrogen or a monovalent organic
radical preferably selected from the group consisting of C.sub.1 to
C.sub.6 aliphatic and cycloaliphatic radicals and C.sub.6 to C.sub.12
aromatic radicals, e.g, benzyl, most preferably hydrogen; and G' is the
radical remaining after the removal of the terminal (or as nearly terminal
as possible) amino groups of a long chain ether diamine having an average
molecular weight of from about 600 to about 12,000, preferably from about
900 to about 4000, and a carbon-to-oxygen ratio of from about 1.8 to about
4.3.
Representative long chain ether glycols from which the polyoxyalkylene
diamine is prepared include poly (ethylene ether)glycol; poly(propylene
ether)glycol; poly(tetramethylene ether) glycol; random or block
copolymers of ethylene oxide and propylene oxide, including propylene
oxide terminated poly(ethylene ether) glycol; and random or block
copolymers of tetrahydrofuran with minor amounts of a second monomer such
as methyl tetrahydrofuran (used in proportion such that the
carbon-to-oxygen mole ratio in the glycol does not exceed about 4.3).
Especially preferred poly(alkylene ether) glycols are poly(propylene
ether) glycol and poly(ethylene ether) glycols end capped with
poly(propylene ether) glycol and/or propylene oxide.
In general, the polyoxyalkylene diamines will have an average molecular
weight of from about 600 to 12,000, preferably from about 900 to about
4000.
The tricarboxylic component is a carboxylic acid anhydride containing an
additional carboxylic group or the corresponding acid thereof containing
two imide-forming vicinal carboxyl groups in lieu of the anhydride group.
Mixtures thereof are also suitable. The additional carboxylic group must
be esterifiable and preferably is substantially nonimidizable.
Further, while trimellitic anhydride is preferred as the tricarboxylic
component, any of a number of suitable tricarboxylic acid constituents
will occur to those skilled in the art including 2,6,7 naphthalene
tricarboxylic anhydride; 3,3',4- diphenyl tricarboxylic anhydride;
3,3'4-benzophenone tricarboxylic anhydride; 1,3,4-cyclopentane
tricarboxylic anhydride; 2,2',3-diphenyl tricarboxylic anhydride; diphenyl
sulfone-3,3',4-tricarboxylic anhydride, ethylene tricarboxylic anhydride;
1,2,5-naphthalene tricarboxylic anhydride; 1,2,4-butane tricarboxylic
anhydride; diphenyl isopropylidene 3,3',4-tricarboxylic anhydride;
3,4-dicarboxyphenyl 3'-carboxylphenyl ether anhydride; 1,3,4-cyclohexane
tricarboxylic anhydride; etc. These tricarboxylic acid materials can be
characterized by the following formula:
##STR6##
where R" is a trivalent organic radical, preferably a C.sub.2 to C.sub.20
aliphatic, aromatic, or cycloaliphatic trivalent organic radical and R' is
preferably hydrogen or a monovalent organic radical preferably selected
from the group consisting of C.sub.1 to C.sub.6 aliphatic and/or
cycloaliphatic radicals and C.sub.6 to C.sub.12 aromatic radicals, e.g.,
benzyl; most preferably hydrogen.
Briefly, the polyoxyalkylene diimide diacids (III) may be prepared by known
imidization reactions including melt synthesis or by synthesizing in a
solvent system. Such reactions will generally occur at temperatures of
from 100.degree.-300.degree. C., preferably at from about 150.degree. to
about 250.degree. C. while drawing off water or in a solvent system at the
reflux temperature of the solvent or azeotropic (solvent) mixture.
Although the weight ratio of the above ingredients is not critical, it is
preferred that the diol be present in at least a molar equivalent amount,
preferably a molar excess, most preferably at least 150 mole percent based
on the moles of dicarboxylic acid and polyoxyalkylene diimide diacid
combined. Such molar excess of diol will allow for optimal yields, based
on the amount of acids, while compensating for the loss of diol during
esterification/condensation.
Further, while the weight ratio of dicarboxylic acid to polyoxyalkylene
diimide diacid is not critical to form the polyetherimide esters,
preferred compositions are those in which the weight ratio of the
polyoxyalkylene diimide diacid to dicarboxylic acid is from about 0.25 to
about 2, preferably from about 0.4 to about 1.4. The actual weight ratio
employed will be dependent upon the specific polyoxyalkylene diimide
diacid used and more importantly, the desired physical and chemical
properties of the resultant polyetherimide ester. In general, the lower
the ratio of polyoxyalkylene diimide diester to dicarboxylic acid the
better the strength, crystallization and heat distortion properties of the
polymer. Alternatively, the higher the ratio, the better the flexibility,
tensile set and low temperature impact characteristics.
Generally, the thermoplastic elastomers comprise the reaction product of
dimethylterephthalate, optimally with up to 40 mole percent of another
dicarboxylic acid; 1,4-butanediol, optionally with up to 40 mole percent
of another saturated or unsaturated aliphatic and/or cycloaliphatic diol;
and a polyoxyalkylene diimide diacid prepared from a polyoxyalkylene
diamine of molecular weight of from about 600 to about 12,000, preferably
from about 900 to about 4000, and trimellitic anhydride. The diol can be
100 mole percent 1,4-butanediol and the dicarboxylic acid 100 mole percent
dimethylterephthalate.
The polyetherimide esters described herein may be prepared by conventional
esterification/condensation reactions for the production of polyesters.
Exemplary of the processes that may be practiced are as set forth in, for
example, U.S. Pat. Nos. 3,023,192; 3,763,109; 3,651,014; 3,663,653 and
3,801,547, incorporated herein by reference.
The preparation of the copolyetherimide ester is more fully described in
U.S. Pat. No. 4,556,705, incorporated herein by reference.
The copolyetheramide elastomers (d) differ from the three types of
elastomers previously described in that their recurring hard segments are
based on repeating amide units rather than short chain ester units. The
repeating amide units may be represented by the formula:
##STR7##
or by the formula
--HN--R'"--NHCORR'"'CO-- (VI)
wherein L is a divalent hydrocarbon radical containing 4-14 carbon atoms,
R'" is a divalent hydrocarbon radical of 6-9 carbon atoms and R'"' is a
divalent hydrocarbon radical of 6-12 carbon atoms.
The hard segments for these polymers are normally prepared in a separate
step in which a suitable lactam or omega-amino acid or a nylon salt are
heated in the presence of a minor amount of a dicarboxylic acid which
controls the molecular weight of the polyamide oligomer formed. In a
second step, the acid-terminated amide hard segments are mixed with an
equivalent amount of a poly(alkylene oxide) glycol and heated in the
presence of a titanate catalyst to form the elastomer. The glycol provides
the soft segments in the polymer. The soft segments can be represented by
the formula
--OGO-- (VII)
wherein G is a divalent radical remaining after the removal of terminal
hydroxy groups from a poly(alkylene oxide) glycol having an average
molecular weight of about 400-3500. The hard and soft segments are joined
through ester linkages. The resulting polymer has an intrinsic viscosity
of about 0.8-2.05. In block copolymers with elastomeric properties the
average molecular weight of the polyamide sequences preferably is in the
range of from about 500 to 3000, most preferably from abut 500 to about
2000. In block copolymers with elastomeric properties, the average
molecular weight of the polyoxyalkylene glycol may vary from about 400 to
about 6000, preferably from about 500 to about 5000, most preferably from
about 400 to about 3000, in particular from about 1000 to about 3000.
The proportion by weight of the polyoxyalkylene glycol with respect to the
total weight of the polyetheramide block copolymer can vary from about 5%
to about 90%, suitably from about 5% to about 85%.
These polymers and their preparation are described in greater detail in
U.S. Pat. No. 4,331,786, incorporated herein by reference.
The thermoplastic elastomer compositions of this invention are foamed into
large slabs having a cross-sectional area of the order of six to ten
square inches or larger and about one to two inches thick. The foamed
thermoplastic elastomers have a low specific gravity of less than about
0.40, usually 0.15-0.25 and have energy return ratios of greater than
about 0.50, preferably 0.60. The slabs of foam made from the thermoplastic
elastomer compositions have a closed cell structure that is substantially
uniform.
The foamed slabs can be made by adding the thermoplastic multi-block
copolymer elastomer, usually in the form of pellets, to an extruder
through a hopper. The elastomer is heated and masticated in the extruder
to produce a molten mass of the elastomer that is mixed and advanced
through the extruder. The temperature necessary to produce the molten mass
will vary with the particular elastomer to be foamed but generally is
within a range of 130.degree.-230.degree. C. The foaming agent is either
injected or incorporated in the thermoplastic elastomer and thoroughly
mixed with the molten elastomer as it advances through the extruder. The
mixture of molten elastomer and foaming agent is cooled as it advances
through the extruder. The mixture is cooled to a temperature at which the
viscosity of the elastomer is adequate to retain the foaming agent when
the mixture is subjected to conditions of lower pressure and is allowed to
expand. After cooling, the mixture is extruded into a holding zone
maintained at a temperature and pressure that prevents foaming of the
mixture. The holding zone has an outlet die having an orifice opening into
a zone of lower pressure, such as atmosphere pressure, where the mixture
foams. The die orifice is externally closable by a gate. The movement of
the gate does not disturb the foamable mixture within the holding zone.
The foamable mixture is extruded from the holding zone by a movable ram
which forces the foamable mixture out of the holding zone through the die
orifice at a rate greater than that at which substantial foaming in the
die orifice occurs and less than at which melt fracture occurs. Generally,
this ranges between about 1000-5000 lbs/hr. Optionally, an extruder that
is sufficiently large can be used to extrude the foamable melt through the
die at a rate great enough to prevent foaming in the die orifice. Upon
passing through the die orifice into the zone of lower pressure, the
foamable mixture is allowed to undergo substantially uniform and free
expansion to produce the desired large size slab of foamed thermoplastic
elastomer having a low specific gravity. Such method for foaming the
thermoplastic multi-block copolymer elastomer to a low density is
disclosed in U.S. Pat. No. 4,323,528, the disclosure of which is
incorporated herein by reference.
As also taught in U.S. Pat. No. 4,323,528, after substantially uniform and
free expansion of the foaming mass has occurred, the hot cellular mass is
still totally deformable and at that stage can be formed if disposed
between two mold halves which are brought together to contact the outer
surfaces of the hot cellular mass. Because the cellular mass is still
capable of limited further expansion while it is totally deformable, the
foam mass fills the mold completely and accurately reproduces the shape of
the mold.
The foaming agents used to make the low density thermoplastic elastomer can
be liquids, solids or inert gases. Suitable foaming agents are
hydrocarbons and partially or fully halogenated hydrocarbons.
Representative liquid foaming agents include halocarbons such as methylene
chloride, trichloromethane, dichlorofluoromethane,
trifluoro-chloromethane, difluorotetrachloro-ethane,
dichlorotetrafluoroethane, chlorotrifluoroethane, difluoro-ethane, and
hydrocarbons such as butane, isobutane, pentane, hexane, and propane.
Solid chemical foaming agents can also be used to foam the thermoplastic
elastomers. Representative chemical foaming agents include
diazodicarbon-amide and other azo, N-nitroso, carbonate and sulfonyl
hydrazides that decompose when heated. Also, inert gases can be used as
foaming agents such as nitrogen and carbon dioxide. The preferred foaming
agents are hydrocarbons, such as isobutane and halogenated hydrocarbons.
The following examples further illustrate the invention.
PROCEDURE FOR DETERMINING ENERGY RETURN RATIO
The energy return ratio of the foams described in the examples were
obtained by a gravity driven drop test following the proposed
recommendations of ASTM Committee F08.54 on Athletic Footwear.
This test was performed on an instrumented impact apparatus identified as
DYNATUP, which is supplied by General Research Corporation The Dynatup
system used for these tests consists of a gravity driven drop weight
machine and an IBM PC computer for analysis and presentation of results.
This system measures the velocity at impact and the force-time record
during impact. From this data, the program generates complete records of
force, deflection, energy, time, and velocity.
The test procedure involves dropping a 8.5 kg weight from a height of 5 cm
on to the sample. The shape of the surface contacting the sample (tup) was
46 mm diameter flat with chamfered edges. The foam samples are positioned
on a rigid steel anvil.
From the force-time and energy-time records stored in the computer, the
computer program can calculate values for (1) the maximum energy imparted
to the foam by the falling weight and (2) the energy returned by the foam.
The ratio of the energy returned by the foam to the maximum energy
imparted to the foam is defined as the "energy return ratio". A perfect
spring would have an energy return ratio of 1.00.
polymers
The thermoplastic multi-block copolymer elastomers used in the examples
were as follows
Elastomer A is a copolyetherester elastomer containing 41.3% by weight
butylene terephthalate short chain ester units, 12% by weight butylene
isophthalate short chain ester units and 46.7% by weight long chain ester
units derived from ethylene oxide-capped poly(propylene oxide) glycol
containing 30% by weight ethylene oxide units and terephthalic/isophthalic
acids. The elastomer has a Shore D hardness of 40 and a melt index at
190.degree. C. of 3g/10 minutes by ASTM D 1238 (2.16 kg weight).
Elastomer B has the same composition and hardness of Elastomer A, but has a
melt index at 190.degree. C. of 7g/10 minutes.
Elastomer C is a copolyetheramide elastomer containing 42% by weight of
polyamide hard segments derived from lauryl lactam and 53% by weight of
soft segments derived from poly(tetramethylene oxide) glycol. The
elastomer has a Shore D hardness of 40 and a melt index at 220.degree. C.
of 1.2g/10 minutes by ASTM D 1238 (2.16 kg weight).
Elastomer D is a copolyetherester elastomer containing 51.9% by weight of
butylene terephthalate short chain ester units and 48.1% by weight long
chain ester units derived from ethylene oxide-capped poly(propylene oxide)
glycol containing 30% by weight ethylene oxide units and terephthalic
acid. The elastomer has a Shore D hardness of 47 and a melt index of 7g/10
minutes at 230.degree. C.
Elastomer E is a copolyetherester elastomer containing 57.4% by weight of
butylene terephthalate short chain ester units, 24.6% by weight butylene
isophthalate short chain ester units and 18.0% by weight of long chain
ester units derived from 1000 MW poly(tetramethylene oxide) glycol and
terephthalic/isophthalic acids. The elastomer has a Shore D hardness of 55
and a melt index of 5 g/10 minutes at 190.degree. C.
Elastomer F is a copolyetherester elastomer containing 60% by weight
butylene terephthalate short chain ester units and 40% by weight of long
chain ester units derived from 1000 MW poly(tetramethylene oxide) glycol
and terephthalic acid. The elastomer has a Shore D hardness of 55 and a
melt index of 7 g/10 minutes at 220.degree. C.
Elastomer G is a copolyetherester elastomer containing 35% by weight of
butylene terephthalate short chain ester units and 65% by weight of long
chain ester units derived from 2000 MW poly(tetramethylene oxide) glycol
and terephthalic acid. It has a Shore D hardness of 40 and a melt index of
8 g/10 minutes at 220.degree. C.
FOAM PREPARATION
The foams described in the following examples were prepared in a 3 inch
diameter, 48:1 extruder. The extruder was equipped with the apparatus
necessary to inject foaming agents and the forward portion of the extruder
barrel was jacketed for cooling using circulating water. The extruder was
attached to a foam accumulator described in U.S. Pat. No. 4,323,528. This
accumulator is equipped with a piston for ejecting (extruding) the
foamable melt through a closable die. The speed of the piston can be
varied to provide various extrusion rates. The use of an accumulator is
not necessary to produce foams of large cross-sections with a large
extruder. However, its use was required with the relatively small foam
extruder used in the examples, which, by itself, would be incapable of
producing large cross-sections. The use of a relatively small extruder
also conserved raw materials as the foamable melt was extruded at rates of
about 1000 to 5000 lbs/hour while the actual output rate of the extruder
was about 120 lbs/hour.
EXAMPLE 1
The foam accumulator was equipped with a bow-tie shaped die measuring 1/8
inch thick in the center by 3" wide. Elastomer A was mixed at the hopper
of the extruder with 0.1% of "Hydrocerol" CF for cell size control.
("Hydrocerol" is an encapsulated mixture of sodium bicarbonate, citric
acid and citric acid salts which liberates carbon dioxide and water under
elevated temperatures in the extruder.) The foaming agent, an 80:20
mixture of dichlorotetrafluoroethane (CFC 114) and dichlorodifluoromethane
(CFC 12) was injected at the rates shown in Table 1. The output of the
extruder was about 120 lbs./hour. After the foaming agent was injected, it
was mixed into the polymer and then the mixture was cooled to the proper
foaming temperature, about 177.degree. C. The foamable melt exiting the
extruder was transferred under pressure to the accumulator where it was
stored and released intermittently at a rate of 3000 lbs/hour. The foam
planks produced were about one inch thick, had a cross-sectional area of 6
to 10 square inches and specific gravities shown in Table 1.
TABLE 1
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Foaming Agent Level
Specific
Number (lbs./hour) Gravity
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1 2 0.32
2 3 0.28
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The foams produced had uniform fine cell structure and had an energy return
ratio in excess of 0.55.
EXAMPLE 2
The same apparatus and elastomer used in Example 1 were used in this
example. Talc was used as a nucleating agent instead of "Hydrocerol" CF
The foaming agents used are enumerated in Table 2 along with specific
gravities of the foams prepared The energy return ratio of the foams is
also given in Table 2.
TABLE 2
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Talc Level Energy
Foaming Agent Foaming Agent Level
(% by weight
Specific
Return
Number
Type (lbs./hour)
of resin)
Gravity
Ratio
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1 CFC-12/CFC-114 20:80
5 .15 0.24 0.597
2 CFC-12/CFC-114 20:80
7 .15 0.19 0.778
3 HCFC-142b 5 .15 0.21 --
4 HCFC-22/HCFC-142b 1.8:1
2.8 .30 0.25 0.812
5 HCFC-22/HCFC-142b 1.8:1
2.8 .15 0.26 0.749
6 HCFC-22 2.5 .15 0.25 0.648
7 HCFC-22 2.5 .30 0.28 0.678
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In the Table,
HCFC142b = chlorodifluoroethane
HCFC22 = chlorodifluoromethane
CFC114 = dichlorotetrafluoroethane
CFC12 = dichlorodifluoromethane
Foam sample numbers 1 and 2 had a thin, smooth "skin" resulting from the
collapse of the outermost bubbles. The "skin" on foam numbers 3 through 7
was thicker and somewhat irregular due to the escape of the foaming agent
from the outermost portions of the foam before air could replace it. As
shown in Table 2, the foams exhibited good resiliency properties and were
useful as innersoles in footwear All samples were about one inch thick and
had 6 to 10 square inches of cross-sectional area.
EXAMPLE 3
Using the same apparatus as in example 1, foams were produced using
Elastomer A and Elastomer B with isobutane as the foaming agent.
Hydrocarbons, such as isobutane, have low permeability through Elastomers
A and B so foam produced using hydrocarbon foaming agents should exhibit
minimal shrinkage and skin-formation as the foaming agent will not leave
the foam faster than air can replace it. The results are shown in Table 3.
TABLE 3
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Isobutane Talc Specific
Number Elastomer Level (pph)
Level (%)
Gravity
______________________________________
1 A 1.0 1.2 0.23
2 A 1.5 1.2 0.18
3 B 1.5 1.2 0.19
4 B 1.0 1.2 0.23
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pph = lbs/hour
Foams 1 though 4 had a uniform cell structure and a very thin smooth skin.
All samples were suitable for use as innersoles in footwear and had energy
return ratios in excess of 0.55. Better results were obtained with
Elastomer B when it was foamed at a lower temperature Elastomer A.
EXAMPLE 4
Using the same apparatus described in Example 1, foam samples were prepared
from Elastomer C using the ingredients shown in Table 4. Specific
gravities of the resulting foams are also given in the table.
TABLE 4
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Foaming Foaming Agent
Talc Specific
Number Agent Level (pph) Level (%)
Gravities
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1 Isobutane
0.8 1.8 0.26
2 Isobutane
1.0 1.8 0.23
3 Isobutane
1.5 1.8 0.18
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Foams 1 and 2 had uniform cell structures and thin smooth skins. Foam 3
showed some evidence of voiding indicating a specific gravity of about
0.18 is about the minimum for this elastomer. The foams have energy return
ratios greater than 0.55 and were suitable for use in athletic footwear
innersoles.
EXAMPLE 5
The same apparatus as Example 1 was used except that the accumulator was
equipped with a smile-shaped die opening with a thickness of 0.165 inches
and a width of about 7 inches. The edges were slightly thicker than the
center of the die so as to produce uniform thickness planks of about 1.0
to 2.0 inches thick and 15 to 20 inches wide. Elastomer D was used with
about 0.8% by weight of talc added at the hopper. With the blowing agent,
a 20:80 mixture of CFC-12/CFC-114 injected at 5 pounds per hour, good foam
was produced with specific gravities of 0.21-0.24 and energy return ratios
greater than 0.50. The foam produced with Elastomer D was relatively firm
It is useful in shock absorbing applications under heavy loads.
EXAMPLE 6
Using the same apparatus as example 5, Hytrel foam was produced using
Elastomer E and isobutane foaming agent. Talc was added at the hopper at
about 1.2% and isobutane was injected at 1 pound per hour. The results are
shown in Table 5.
TABLE 5
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Approximate Specific
Number Foaming Temp. (.degree.C.)
Gravity
______________________________________
1 171 0.26
2 163 0.22
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The higher temperature produced a foam with a higher density, but which was
somewhat softer. These foams are relatively hard at these densities It is
useful for shock absorption of heavy impacts.
EXAMPLE 7
The same apparatus as used in the previous example 5 was used to produce
foam planks from Elastomer F. HCFC-142b was used as a blowing agent. With
2% talc added at the hopper and the HCFC 142b injected at 2.5 pounds per
hour, a foam having a specific gravity of 0.28 was produced. The
temperature window for foaming this elastomer was very narrow. The cell
structure of the foam produced was large and rather irregular. The foam
was hard and would be useful for handling heavy impacts.
EXAMPLE 8
The same apparatus and foaming agent as used in Example 5 were used to
produce foam planks from Elastomer G (except talc was added at 1.6%). The
lowest specific gravity attainable was found to be 0.30-0.32. It had a
very narrow processing window for good foam. The results are shown in
Table 6.
TABLE 6
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Blowing Agent
Approximate Specific
Number Level (pph) Foaming Temp (.degree.C.)
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