U.S. patent application number 16/692792 was filed with the patent office on 2020-03-19 for process for preparing thermoplastic elastomer foam and foamed article.
The applicant listed for this patent is NIKE, Inc.. Invention is credited to Yihua Chang, Richard L. Watkins.
Application Number | 20200087476 16/692792 |
Document ID | / |
Family ID | 56883850 |
Filed Date | 2020-03-19 |
![](/patent/app/20200087476/US20200087476A1-20200319-D00000.png)
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United States Patent
Application |
20200087476 |
Kind Code |
A1 |
Chang; Yihua ; et
al. |
March 19, 2020 |
PROCESS FOR PREPARING THERMOPLASTIC ELASTOMER FOAM AND FOAMED
ARTICLE
Abstract
A thermoplastic elastomer foam is made by incorporating a
gaseous or supercritical blowing agent under pressure into a molten
thermoplastic elastomer comprising polymeric polymeric crystalline
domains, then releasing the pressure to foam the thermoplastic
elastomer.
Inventors: |
Chang; Yihua; (Portland,
OR) ; Watkins; Richard L.; (Portland, OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIKE, Inc. |
Beaverton |
OR |
US |
|
|
Family ID: |
56883850 |
Appl. No.: |
16/692792 |
Filed: |
November 22, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16108923 |
Aug 22, 2018 |
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16692792 |
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15752680 |
Feb 14, 2018 |
10081716 |
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PCT/US2016/046156 |
Aug 9, 2016 |
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16108923 |
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62206906 |
Aug 19, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08J 2429/02 20130101;
C08G 18/3278 20130101; C08J 9/22 20130101; C08J 2300/22 20130101;
C08J 2205/052 20130101; C08J 2203/08 20130101; C08J 9/0061
20130101; C08L 75/04 20130101; C08G 18/3228 20130101; C08J 9/122
20130101; C08J 2375/04 20130101; C08J 9/18 20130101; C08J 2201/03
20130101; C08J 9/236 20130101; C08J 2201/032 20130101; C08J 2300/26
20130101; C08J 2429/04 20130101; C08G 2101/00 20130101; C08G 18/73
20130101; C08J 2423/08 20130101; C08J 9/16 20130101; C08J 2477/00
20130101; C08J 2467/00 20130101; C08J 9/232 20130101; C08G 18/3284
20130101; C08J 2203/06 20130101; C08J 2207/00 20130101 |
International
Class: |
C08J 9/00 20060101
C08J009/00; C08J 9/12 20060101 C08J009/12; C08J 9/16 20060101
C08J009/16; C08J 9/18 20060101 C08J009/18; C08J 9/232 20060101
C08J009/232; C08J 9/236 20060101 C08J009/236; C08L 75/04 20060101
C08L075/04; C08J 9/22 20060101 C08J009/22; C08G 18/32 20060101
C08G018/32; C08G 18/73 20060101 C08G018/73 |
Claims
1.-28. (canceled)
29. A polymeric mixture made by a method comprising: providing a
polymer melt comprising a molten thermoplastic elastomer and a
molten semi-crystalline polymer that is miscible in the molten
thermoplastic elastomer; and cooling the polymer melt to a
temperature below a crystallization temperature, wherein the
crystallization temperature is a temperature at which regions of
the semi-crystalline polymer become immiscible with the
thermoplastic elastomer and phase-separate from the thermoplastic
elastomer, thereby forming a polymeric mixture comprising the
regions of the semi-crystalline polymer distributed in the
thermoplastic elastomer; wherein the semi-crystalline polymer
comprises from 0.1 weight percent to 20 weight percent of total
polymer weight of the polymeric mixture; and wherein the
semi-crystalline polymer comprises a polymer chosen from nylon 11,
nylon 12, or a copolymer of ethylene with at least one vinyl
monomer.
30. The polymeric mixture of claim 29, wherein the thermoplastic
elastomer comprises a thermoplastic polyurethane elastomer.
31. The polymeric mixture of claim 30, wherein polymeric diol
segments of the thermoplastic polyurethane elastomer comprise from
35 weight percent to 65 weight percent of the thermoplastic
polyurethane polymer.
32. The polymeric mixture of claim 30, wherein the thermoplastic
polyurethane elastomer is chosen from a thermoplastic
polyester-polyurethane elastomer, a thermoplastic
polyether-polyurethane elastomer, a thermoplastic
polycarbonate-polyurethane elastomer, or a thermoplastic
polyurethane elastomer comprising polyolefinic segments.
33. The polymeric mixture of claim 29, wherein the thermoplastic
elastomer comprises an elastomer chosen from a thermoplastic
polyurea elastomer, a thermoplastic polyamide elastomer, a
thermoplastic polyester elastomer, a thermoplastic block copolymer
of ethylene and an alpha-olefin having 4 to 8 carbons, or a
thermoplastic styrene block copolymer elastomer.
34. The polymeric mixture of claim 33, wherein the thermoplastic
polyamide elastomer comprises a thermoplastic polyether block
polyamide copolymer.
35. The polymeric mixture of claim 29, wherein the semi-crystalline
polymer comprises the copolymer of ethylene with at least one vinyl
monomer.
36. The polymeric mixture of claim 35, wherein the copolymer of
ethylene with at least one vinyl monomer comprises a copolymer
chosen from an ethylene-vinyl acetate copolymer, an ethylene-vinyl
alcohol copolymer, an ethylene-vinyl chloride copolymer, or any
combination thereof.
37. The polymeric mixture of claim 36, wherein the semi-crystalline
polymer comprises the ethylene-vinyl alcohol copolymer.
38. The polymeric mixture of claim 37, wherein the polymeric
mixture comprises from 0.5 weight percent to 20 weight percent of
the ethylene-vinyl alcohol copolymer.
39. The polymeric mixture of claim 37, wherein the ethylene-vinyl
alcohol copolymer has a ratio of ethylene monomer units to vinyl
alcohol monomer units of from 20 mole percent to 45 mole
percent.
40. The polymeric mixture of claim 29, wherein the semi-crystalline
polymer comprises an ethylene-vinyl alcohol copolymer, and the
thermoplastic elastomer comprises a thermoplastic polyurethane
elastomer.
41. The polymeric mixture of claim 29, wherein the cooling step
comprises forming the polymer melt into an article in a shape
chosen from a pellet, a bead, a particle, a tape, a ribbon, a rope,
a film, a strand, or a fiber.
42. The polymeric mixture of claim 29, wherein the polymer melt is
formed in an extruder, then extruded and pelletized during the
cooling step
43. The polymeric mixture of claim 29, wherein the semi-crystalline
polymer comprises from 1 weight percent to 15 weight percent of
total polymer weight of the polymeric mixture, based on total
polymer weight of the polymeric mixture.
44. The polymeric mixture of claim 29, wherein the semi-crystalline
polymer comprises from 1 weight percent to 10 weight percent of
total polymer weight of the polymeric mixture.
45. The polymeric mixture of claim 29, wherein the method further
comprises impregnating the polymeric mixture with a gas or
supercritical blowing agent.
46. The polymeric mixture of claim 29, wherein the molten mixture
further comprises a gaseous or supercritical blowing agent
incorporated into the molten mixture under pressure.
47. The polymeric mixture of claim 46, wherein the blowing agent
comprises carbon dioxide in gaseous or supercritical state.
48. The polymeric mixture of claim 46, wherein the pressure is
released during the cooling step, thereby foaming the polymeric
mixture.
Description
FIELD AND BACKGROUND OF THE DISCLOSURE
[0001] The present disclosure relates to methods for making
thermoplastic elastomer foams and foamed articles.
[0002] This section provides background information related to this
disclosure but which may or may not be prior art.
[0003] Polyurethane foams are typically prepared by using
chemically-acting blowing agents or physically-acting blowing
agents that are mixed into or injected into the monomer reactants
during polymerization. As an example, chemical blowing agents like
water or formic acid form gaseous products by reaction with
isocyanate groups, while physical blowing agents are dissolved or
emulsified in the monomers and vaporize under polyurethane
polymerization conditions. Other polymer foams may be made using
azo compounds, hydrazine, or sodium bicarbonate. Examples of
physical blowing agents include hydrocarbons, halogenated
hydrocarbons, and carbon dioxide. Physical blowing agents are
typically introduced either in-line, i.e. directly into the mixing
head, or via a stock tank in a batch operation. Such a process is
described, for instance, in Bruchmann et al., US Patent Application
Publication No. US 2011/0275732.
[0004] Many physical properties of foams depend in large part on
the cell morphology of the foam, including compressive strength,
thermal conductivity, dimensional stability, and water absorption
rate. However, it is difficult to control polymer foaming to the
degree necessary for consistent production of a cell morphology
that will produce a partcular foam property, like good compressive
strength, when making uncrosslinked (thermoplastic) foams. Prior
art attempts to make foam micro-structures having desirable cell
morphologies have included the use of powdered nucleation agents.
Among these nucleating agents, inorganic oxides, such as talc,
titanium dioxide, and kaolin have been used. Nucleation efficiency
and, consequently, cell size and shape depend on the nucleating
agent's particle size, shape, and surface treatment and
distribution in the material being foamed. However, adding these
nucleating agents can adversely affect other foam properties.
[0005] A need remains for improved methods of forming polyurethane
foams, especially thermoplastic polyurethane foamed, that provide a
cell structure for improved properties.
DRAWING
[0006] The drawings described herein is for illustrative purposes
only of selected aspects and not all possible implementations, and
is not intended to limit the scope of the present disclosure.
[0007] FIG. 1 shows scanning electron microscopy images B-D of
disclosed thermoplastic elastomer foams compared to a scanning
electron microscopy image A of prior art foam.
DESCRIPTION
[0008] Disclosed are methods of forming foams with a given average
cell size by forming polymeric crystalline domains throughout a
thermoplastic elastomer composition that provide nucleation sites.
The thermoplastic elastomer composition having the polymeric
crystalline domains is combined with a physical blowing agent under
pressure. The pressure is released at a temperature below the
crystallization temperature of the polymeric crystalline domains to
foam the thermoplastic elastomer and form a thermoplastic elastomer
foam. The polymeric crystalline domains serve as nucleation sites
during foaming, and the amount of polymeric crystalline domains
distributed in the thermoplastic elastomer is selected to provide a
certain average cell size. The method and technology now being
disclosed provide an effective way to prepare a foam with more
uniformly sized and uniformly distributed foam cells and to
reliably control cell size and distribution in a straightforward
way without using fillers.
[0009] An aspect is a method of making a thermoplastic elastomer
foam that includes incorporating a gaseous or supercritical blowing
agent, for example gaseous or supercritical carbon dioxide or
nitrogen, under pressure into a thermoplastic elastomer composition
comprising polymeric crystalline domains, then releasing the
pressure to foam the thermoplastic elastomer composition. The
crystalline domains should be uniformly distributed through the
thermoplastic elastomer composition, and the domains may generally
be of uniform or approximately uniform size. The content of the
polymeric crystalline domains and amount of blowing agent may
produce an average cell size from 1 to 20 micrometers in the
thermoplastic elastomer foam. For example, the polymeric
crystalline domains may be provided by from 0.1 wt % to 20 wt %,
based on total polymer weight, of a semi-crystalline polymer (or
from 0.1 wt % or from 0.5 wt % or from 1 wt % up to 5 wt % or up to
10 wt % or up to 15 wt % or up to 20 wt %, based on total polymer
weight, of the semi-crystalline polymer), wherein the
semi-crystalline polymer is at a temperature below the
crystallization temperature (Tc) at the time the pressure is
released to foam the thermoplastic elastomer. The amount of
semi-crystalline polymer incorporated into the thermoplastic
elastomer composition, or the concentration and size of the
polymeric crystalline regions provided by the semi-crystalline
polymer mixed throughout the thermoplastic elastomer composition,
may be selected based on an average cell size produced for the foam
and the crystalline content of the semi-crystalline polymer. The
polymeric crystalline domains of the semi-crystalline polymer act
as nucleating agents. The semi-crystalline polymer may be selected
from copolymers of ethylene with at least one vinyl co-monomer,
polyamides, polyesters, and combinations of these, for example
nylon 11, nylon 12, and ethylene-vinyl alcohol copolymers, and the
thermoplastic elastomer may be a thermoplastic polyurethane
elastomer. The thermoplastic polyurethane foam that is formed by
the method may have a density of 160 kg/m.sup.3 to 300 kg/m.sup.3
and may be either a closed cell foam or an open cell foam. The foam
may be molded during or after foaming or otherwise formed after
foaming into an article, for example an article of clothing,
footwear, protective equipment, a strap, or a component of one of
these.
[0010] Also disclosed is a method of making a thermoplastic
elastomer foam by providing a polymer mixture comprising a
thermoplastic elastomer and from 0.1 wt % to 20 wt %, based on
total polymer weight, of a semi-crystalline polymer; incorporating
a gaseous or supercritical blowing agent into the mixture under
pressure at a temperature at which the thermoplastic elastomer is
molten and that is below the crystallization temperature of the
semi-crystalline polymer; and releasing the pressure to foam the
mixture thereby forming the thermoplastic elastomer foam. The
polymer mixture may be formed by combining a molten thermoplastic
elastomer and from 0.1 wt % to 20 wt %, based on total polymer
weight, of a molten semi-crystalline polymer, for example in an
extruder. The blowing agent is incorporated into the polymer
mixture, then the polymer mixture may be foamed once the
temperature is below the crystallization temperature of the
semi-crystalline polymer and the pressure is released. Again, the
semi-crystalline polymer may be selected from copolymers of
ethylene with at least one vinyl monomer, polyamides, polyesters,
and combinations of these, for example nylon 11, nylon 12, and
ethylene-vinyl alcohol copolymers, and the thermoplastic elastomer
may be a thermoplastic polyurethane elastomer. The thermoplastic
polyurethane foam that is formed by the method may have a density
of 160 kg/m.sup.3 to 300 kg/m.sup.3 and may be either a closed cell
foam or an open cell foam. The foam may be molded during or after
foaming or otherwise formed after foaming into an article, for
example an article of clothing, footwear, protective equipment, a
strap, or a component of one of these.
[0011] In another aspect, a method of preparing a thermoplastic
elastomer foam includes forming a mixture comprising a molten
thermoplastic elastomer and from 0.1 wt % to 20 wt % of a molten
semi-crystalline polymer that is miscible in the thermoplastic
elastomer to form a polymer melt. A gaseous or supercritical
blowing agent is incorporated into the mixture under pressure. The
mixture is cooled to a temperature below the crystallization
temperature of the semi-crystalline polymer to cause crystalline
regions of the semi-crystalline polymer to phase-separate from the
mixture. The pressure is released when the mixture contains these
crystalline regions, and the thermoplastic elastomer is foamed to
form the thermoplastic elastomer foam with the crystalline regions
providing nucleation sites.
[0012] In yet another aspect, a method of preparing a thermoplastic
elastomer foam includes cooling a thermoplastic elastomer
comprising from 0.1 wt % to 20 wt % of a semi-crystalline polymer
to a temperature below the crystallization temperature of the
semi-crystalline polymer, wherein crystalline regions of the
semi-crystalline polymer phase separates from the thermoplastic
elastomer. A gaseous or supercritical blowing agent is incorporated
into the thermoplastic elastomer under pressure before, during, or
after the crystalline regions phase separate. The pressure is
released at a temperature at which the crystalline regions are
present, and the thermoplastic elastomer is foamed to form the
thermoplastic elastomer foam. The polymer mixture should be uniform
so that the crystalline regions are uniformly distributed in the
thermoplastic elastomer. The amount of crystalline regions and
their concentration can be controlled by nature and amount of the
semi-crystalline polymer or polymers used.
[0013] Numerous specific details are given here to provide a
thorough understanding of the technology now being disclosed. The
aspects can be practiced without one or more of the specific
details or with other methods, components, materials, etc. In other
instances, well-known structures, materials, or operations are not
shown or described in detail to avoid obscuring aspects of the
aspects. Reference throughout this specification to "one aspect,"
"an aspect," or "aspects" means that a particular feature,
structure, or characteristic is included in at least one aspect.
Thus, the appearances of the phrases "in one aspect" or "in an
aspect" in various places throughout this specification are not
necessarily all referring to the same aspect. Furthermore, the
particular features, structures, or characteristics may be combined
in other aspects.
[0014] As used in this description, "a," "an," "the," "at least
one," and "one or more" indicate interchangeably that at least one
of the item is present; a plurality of such items may be present
unless the context unequivocally indicates otherwise. All numerical
values of parameters (e.g., of quantities or conditions) in this
specification, including the appended claims, are to be understood
as being modified in all instances by the term "about" whether or
not "about" actually appears before the numerical value. "About"
indicates that the stated numerical value allows some slight
imprecision (with some approach to exactness in the value;
approximately or reasonably close to the value; nearly). If the
imprecision provided by "about" is not otherwise understood in the
technological field with this ordinary meaning, then "about" as
used herein indicates at least variations that may arise from
ordinary methods of measuring and using such parameters. In
addition, disclosures of ranges are to be understood as
specifically disclosing all values and further divided ranges
within the range. The terms "comprising," "including," and "having"
are inclusive and therefore specify the presence of stated
features, steps, operations, elements, or components, but do not
preclude the presence or addition of one or more other features,
steps, operations, elements, or components. Orders of steps,
processes, and operations may be altered when possible, and
additional or alternative steps may be employed. As used in this
specification, the term "or" includes any one and all combinations
of the associated listed items.
[0015] The thermoplastic elastomer foam may be a closed-cell foam
or an open-cell foam. In some aspects, the thermoplastic elastomer
foam is a closed-cell foam with at least 100%, at least 99%, at
least 97%, at least 90%, at least 75%, at least 60%, or at least
50% closed cells.
[0016] Nonlimiting examples of suitable thermoplastic elastomers
include thermoplastic polyurethane elastomers, thermoplastic
polyurea elastomers, thermoplastic polyamide elastomers (in
particular polyether block polyamides (PEBA)), thermoplastic
polyester elastomers, metallocene-catalyzed block copolymers of
ethylene and .alpha.-olefins having 4 to 8 carbon atoms, and
styrene block copolymer elastomers such as
poly(styrene-butadiene-styrene),
poly(styrene-ethylene-co-butylene-styrene), and
poly(styrene-isoprene-styrene).
[0017] Thermoplastic polyurethane elastomers may be selected from
thermoplastic polyester-polyurethanes, polyether-polyurethanes,
polycarbonate-polyurethanes, and polyurethanes made with
polyolefinic segments. Suitable thermoplastic polyurethane
elastomer include, without limitation, polyurethanes polymerized
using as polymeric diol reactants polyethers, polyesters including
polycaprolactone polyesters, polycarbonate diols, and hydrogenated
polybutadiene diols. These polymeric diol-based polyurethanes are
prepared by reaction of the polymeric diol (polyester diol,
polyether diol, polycaprolactone diol, polytetrahydrofuran diol,
polycarbonate diol, hydrogenated polybutadiene diol), one or more
polyisocyanates, and, optionally, one or more chain extension
compounds. Chain extension compounds, as the term is being used,
are compounds having two or more functional groups reactive with
isocyanate groups, such as the diols, amino alcohols, and diamines.
Preferably the polymeric diol-based polyurethane is substantially
linear (i.e., substantially all of the reactants are
difunctional).
[0018] Diisocyanates used in making the polyurethane elastomers may
be aromatic or aliphatic. Useful diisocyanate compounds used to
prepare thermoplastic polyurethanes include, without limitation,
isophorone diisocyanate (IPDI), methylenebis-4-cyclohexyl
isocyanate (H.sub.12MDI), cyclohexyl diisocyanate (CHDI),
m-tetramethylxylene diisocyanate (m-TMXDI), p-tetramethylxylene
diisocyanate (p-TMXDI), 4,4'-methylenediphenyl diisocyanate (MDI,
also known as 4,4'-diphenylmethane diisocyanate), 2,4- and
2,6-toluene diisocyanate (TDI), ethylene diisocyanate,
1,2-diisocyanatopropane, 1,3-diisocyanatopropane,
1,6-diisocyanatohexane (hexamethylene diisocyanate or HDI),
1,4-butylene diisocyanate, lysine diisocyanate,
meta-xylylenediioscyanate andpara-xylylenediisocyanate (XDI),
4-chloro-1,3-phenylene diisocyanate, 1,5-tetrahydro-naphthalene
diisocyanate, 4,4'-dibenzyl diisocyanate, and combinations of
these. Nonlimiting examples of higher-functionality polyisocyanates
that may be used in limited amounts to produce slightly branched
thermoplastic polyurethanes (optionally along with monofunctional
alcohols or monofunctional isocyanates) include 1,2,4-benzene
triisocyanate, 1,3,6-hexamethylene triisocyanate, 1,6,11-undecane
triisocyanate, bicycloheptane triisocyanate, triphenylmethane-4,4',
4''-triisocyanate, isocyanurates of diisocyanates, biurets of
diisocyanates, allophanates of diisocyanates, and the like.
[0019] Useful active hydrogen-containing chain extension agents
generally contain at least two active hydrogen groups, for example,
diols, dithiols, diamines, or compounds having a mixture of
hydroxyl, thiol, and amine groups, such as alkanolamines,
aminoalkyl mercaptans, and hydroxyalkyl mercaptans, among others.
The molecular weight of the chain extenders preferably range from
60 to 400.
[0020] Nonlimiting examples of suitable diols that may be used as
extenders include ethylene glycol and lower oligomers of ethylene
glycol including diethylene glycol, triethylene glycol and
tetraethylene glycol; propylene glycol and lower oligomers of
propylene glycol including dipropylene glycol, tripropylene glycol
and tetrapropylene glycol; cyclohexanedimethanol, 1,6-hexanediol,
2-ethyl-1,6-hexanediol, 1,4-butanediol, 2,3-butanediol,
1,5-pentanediol, 1,3-propanediol, butylene glycol, neopentyl
glycol, dihydroxyalkylated aromatic compounds such as the bis
(2-hydroxyethyl) ethers of hydroquinone and resorcinol;
p-xylene-.alpha.,.alpha.-diol; the bis (2-hydroxyethyl) ether of
p-xylene-.alpha.,.alpha.'-diol; m-xylene-.alpha.,.alpha.'-diol and
combinations of these. Thermoplastic polyurethanes may be made
using small amounts of triols or higher functionality polyols, such
as trimethylolpropane or pentaerythritol, optionally along with
monomeric alcohols such as C.sub.2-C.sub.8 monools or
monoisocyanates such as butyl isocyanate. Suitable diamine
extenders include, without limitation, ethylene diamine, diethylene
triamine, triethylene tetraamine, and combinations of these. Other
typical chain extenders are amino alcohols such as ethanolamine,
propanolamine, butanolamine, and combinations of these.
[0021] In addition to difunctional extenders, a small amount of a
trifunctional extender such as trimethylolpropane,
1,2,6-hexanetriol and glycerol, or monofunctional active hydrogen
compounds such as butanol or dimethyl amine, may also be present.
The amount of trifunctional extender or monofunctional compound
employed is selected so that the product is a thermoplastic
elastomer.
[0022] The polyester diols used in forming a thermoplastic
polyurethane elastomer are in general prepared by the condensation
polymerization of one or more polyacid compounds and one or more
polyol compounds. Preferably, the polyacid compounds and polyol
compounds are di-functional, i.e., diacid compounds and diols are
used to prepare substantially linear polyester diols, although
minor amounts of mono-functional, tri-functional, and higher
functionality materials (perhaps up to 5 mole percent) can be
included to provide a slightly branched, but uncrosslinked
polyester polyol component. Suitable dicarboxylic acids include,
without limitation, glutaric acid, succinic acid, malonic acid,
oxalic acid, phthalic acid, hexahydrophthalic acid, adipic acid,
maleic acid, suberic acid, azelaic acid, dodecanedioic acid, their
anhydrides and polymerizable esters (e.g., methyl esters) and acid
halides (e.g., acid chlorides), and mixtures of these. Suitable
polyols include those already mentioned, especially the diols. In
preferred aspects, the carboxylic acid component includes one or
more of adipic acid, suberic acid, azelaic acid, phthalic acid,
dodecanedioic acid, or maleic acid (or the anhydrides or
polymerizable esters of these) and the diol component includes one
or more of includes 1,4-butanediol, 1,6-hexanediol, 2,3-butanediol,
or diethylene glycol. Typical catalysts for the esterification
polymerization are protonic acids, Lewis acids, titanium alkoxides,
and dialkyltin oxides.
[0023] A polymeric polyether or polycaprolactone diol reactant for
preparing thermoplastic polyurethanes may be obtained by reacting a
diol initiator, e.g., 1,3-propanediol or ethylene or propylene
glycol, with a lactone or alkylene oxide chain-extension reagent.
Lactones that can be ring opened by an active hydrogen are
well-known in the art. Examples of suitable lactones include,
without limitation, c-caprolactone, y-caprolactone,
.beta.-butyrolactone, .beta.-propriolactone, .gamma.-butyrolactone,
.alpha.-methyl-y-butyrolactone, .beta.-methyl-y-butyrolactone,
.gamma.-valerolactone, .delta.-valerolactone,
.gamma.-decanolactone, .delta.-decanolactone, .gamma.-nonanoic
lactone, .gamma.-octanoic lactone, and combinations of these. In
one preferred aspect, the lactone is .epsilon.-caprolactone. Useful
catalysts include those mentioned above for polyester synthesis.
Alternatively, the reaction can be initiated by forming a sodium
salt of the hydroxyl group on the molecules that will react with
the lactone ring.
[0024] In other aspects, a diol initiator may be reacted with an
oxirane-containing compound to produce a polyether diol to be used
in the polyurethane elastomer polymerization. Alkylene oxide
polymer segments include, without limitation, the polymerization
products of ethylene oxide, propylene oxide, 1,2-cyclohexene oxide,
1-butene oxide, 2-butene oxide, 1-hexene oxide, tert-butylethylene
oxide, phenyl glycidyl ether, 1-decene oxide, isobutylene oxide,
cyclopentene oxide, 1-pentene oxide, and combinations of these. The
oxirane-containing compound is preferably selected from ethylene
oxide, propylene oxide, butylene oxide, tetrahydrofuran, and
combinations of these. The alkylene oxide polymerization is
typically base-catalyzed. The polymerization may be carried out,
for example, by charging the hydroxyl-functional initiator compound
and a catalytic amount of caustic, such as potassium hydroxide,
sodium methoxide, or potassium tert-butoxide, and adding the
alkylene oxide at a sufficient rate to keep the monomer available
for reaction. Two or more different alkylene oxide monomers may be
randomly copolymerized by coincidental addition or polymerized in
blocks by sequential addition. Homopolymers or copolymers of
ethylene oxide or propylene oxide are preferred. Tetrahydrofuran
may be polymerized by a cationic ring-opening reaction using such
counterions as SbF.sub.6.sup.-, AsF.sub.6.sup.-, PF.sub.6.sup.-,
SbCl.sub.6.sup.-, BF.sub.4.sup.-, CF.sub.3SO.sub.3.sup.-,
FSO.sub.3.sup.-, and ClO.sub.4.sup.4. Initiation is by formation of
a tertiary oxonium ion. The polytetrahydrofuran segment can be
prepared as a "living polymer" and terminated by reaction with the
hydroxyl group of a diol such as any of those mentioned above.
Polytetrahydrofuran is also known as polytetramethylene ether
glycol (PTMEG).
[0025] Aliphatic polycarbonate diols that may be used in making a
thermoplastic polyurethane elastomer are prepared by the reaction
of diols with dialkyl carbonates (such as diethyl carbonate),
diphenyl carbonate, or dioxolanones (such as cyclic carbonates
having five- and six-member rings) in the presence of catalysts
like alkali metal, tin catalysts, or titanium compounds. Useful
diols include, without limitation, any of those already mentioned.
Aromatic polycarbonates are usually prepared from reaction of
bisphenols, e.g., bisphenol A, with phosgene or diphenyl
carbonate.
[0026] In various aspects, the polymeric diol may have a weight
average molecular weight of at least 500, at least 1000, or at
least 1800 and a weight average molecular weight of up to 10,000,
but polymeric diols having weight average molecular weights of up
to 5000, or up to 4000, may also be suitable. The polymeric diol
may have a weight average molecular weight in the range from 500 to
10,000, from 1000 to 5000, or from 1500 to 4000. The weight average
molecular weights may be determined by ASTM D-4274.
[0027] The reaction of the polyisocyanate, polymeric diol, and diol
or other chain extension agent is typically carried out at an
elevated temperature in the presence of a catalyst. Typical
catalysts for this reaction include organotin catalysts such as
stannous octoate, dibutyl tin dilaurate, dibutyl tin diacetate,
dibutyl tin oxide, tertiary amines, zinc salts, and manganese
salts. Generally, for elastomeric polyurethanes, the ratio of
polymeric diol, such as polyester diol, to extender can be varied
within a relatively wide range in making the polyurethane
elastomer. For example, the equivalent proportion of polyester diol
to extender may be within the range of from 1:0 to 1:12 or from 1:1
to 1:8. In some aspects, the diisocyanate(s) employed are
proportioned such that the overall ratio of equivalents of
isocyanate to equivalents of active hydrogen containing materials
is within the range of from 1:1 to 1:1.05 or from 1:1 to 1:1.02.
The polymeric diol segments typically are from 35% to 65% by weight
of the polyurethane polymer or from 35% to 50% by weight of the
polyurethane polymer.
[0028] The selection of diisocyanate, extenders, polymeric diols,
and the weight percent of the polymeric diols can be varied to
produce a certain density and stability of the finished foam. In
general, a greater content of a polymeric polyol that has a
Hildenbrand solubility parameter closer to that of the
supercritical fluid will permit higher absorption of the
supercritical fluid that results in a lower density foam. In
addition, in general, shorter polymeric diols provide foams that
shrink less after they are first foamed. Use of higher number
average molecular weight polymeric diols allows a higher degree of
swelling, but a molecular weight that is too high may yield a less
stable foam.
[0029] Suitable thermoplastic polyurea elastomers may be prepared
by reaction of one or more polymeric diamines or polyols with one
or more of the polyisocyanates already mentioned and one or more
diamine extenders. Nonlimiting examples of suitable diamine
extenders include ethylene diamine, 1,3-propylene diamine,
2-methyl-pentamethylene diamine, hexamethylene diamine, 2,2,4- and
2,4,4-trimethyl-1,6-hexane diamine, imino-bis(propylamine),
imido-bis(propylamine),
N-(3-aminopropyl)-N-methyl-1,3-propanediamine),
1,4-bis(3-aminopropoxy)butane,
diethyleneglycol-di(aminopropyl)ether),
1-methyl-2,6-diamino-cyclohexane, 1,4-diamino-cyclohexane, 1,3- or
1,4-bis(methylamino)-cyclohexane, isophorone diamine, 1,2- or
1,4-bis(sec-butylamino)-cyclohexane, N,N-diisopropyl-isophorone
diamine, 4,4'-diamino-dicyclohexylmethane,
3,3'-dimethyl-4,4'-diamino-dicyclohexylmethane,
N,N-dialkylamino-dicyclohexylmethane, and
3,3'-diethyl-5,5'-dimethyl-4,4'-diamino-dicyclohexylmethane.
Polymeric diamines include polyoxyethylene diamines,
polyoxypropylene diamines, poly(oxyethylene-oxypropylene) diamines,
and poly(tetramethylene ether) diamines. The amine- and
hydroxyl-functional extenders already mentioned may be used as
well. Generally, as before, trifunctional reactants are limited and
may be used in conjunction with monofunctional reactants to limit
crosslinking.
[0030] Suitable thermoplastic polyamide elastomers may be obtained
by: (1) polycondensation of (a) a dicarboxylic acid, such as oxalic
acid, adipic acid, sebacic acid, terephthalic acid, isophthalic
acid, 1,4-cyclohexanedicarboxylic acid, or any of the other
dicarboxylic acids already mentioned with (b) a diamine, such as
ethylenediamine, tetramethylenediamine, pentamethylenediamine,
hexamethylenediamine, or decamethylenediamine,
1,4-cyclohexanediamine, m-xylylenediamine, or any of the other
diamines already mentioned; (2) a ring-opening polymerization of a
cyclic lactam, such as c-caprolactam or w-laurolactam; (3)
polycondensation of an aminocarboxylic acid, such as 6-aminocaproic
acid, 9-aminononanoic acid, 11-aminoundecanoic acid, or
12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam
with a dicarboxylic acid and a diamine to prepare a carboxylic
acid-functional polyamide block, followed by reaction with a
polymeric ether diol (polyoxyalkylene glycol) such as any of those
already mentioned. Polymerization may be carried out, for example,
at temperatures of from 180.degree. C. to 300.degree. C. Specific
examples of suitable polyamide blocks include, but are not limited
to, NYLON 6, NYLON 66, NYLON 610, NYLON 11, NYLON 12, copolymerized
NYLON, NYLON MXD6, and NYLON 46.
[0031] The effects of the type and molecular weights of the soft
segment polymeric polyols used in making thermoplastic polyurea
elastomers and polyamide elastomers are analogous to the same
effects in making thermoplastic polyurethane elastomers.
[0032] Thermoplastic polyester elastomers have blocks of monomer
units with low chain length that form the crystalline regions and
blocks of softening segments with monomer units having relatively
higher chain lengths. Thermoplastic polyester elastomers are
commercially available under the trade name HYTREL.RTM. from
DuPont.TM..
[0033] Metallocene-catalyzed block copolymers of ethylene and
.alpha.-olefins having from 4 to 8 carbon atoms may be prepared by
single-site metallocene catalysis of ethylene with a softening
comonomer such as hexane-1 or octene-1, for example in a high
pressure process in the presence of a catalyst system comprising a
cyclopentadienyl-transition metal compound and an alumoxane. These
materials are commercially available from ExxonMobil Chemical under
the trade name EXACT.TM. and from the Dow Chemical Company under
the trade name ENGAGE.TM..
[0034] Styrene block copolymer elastomers such as
poly(styrene-butadiene-styrene),
poly(styrene-ethylene-co-butylene-styrene), and
poly(styrene-isoprene-styrene) may be prepared by anionic
polymerization in which the polymer segments are produced
sequentially, first by reaction of an alkyl-lithium initiator with
styrene, then continuing polymerization by adding the alkene
monomer, then completing polymerization by again adding styrene.
S-EB-S and S-EP-S block copolymers are produced by hydrogenation of
S-B-S and S-I-S block copolymers, respectively.
[0035] Examples of suitable semi-crystalline polymers include, but
are not limited to, copolymers of ethylene with at least one vinyl
monomer including ethylene-vinyl acetate copolymers (EVA),
ethylene-vinyl alcohol copolymers (EVOH), ethylene-vinyl chloride
copolymer, ethylene-methyl methacrylate copolymer semi-crystalline
polyamides; semi-crystalline polyesters; and combinations thereof.
To be used in combination, semi-crystalline polymers have a
crystallization temperature below the processing temperature of the
thermoplastic elastomer. In some aspects, the semi-crystalline
polymer comprises a member selected from the group consisting of
nylon 11, nylon 12, polycaprolactone, ethylene-vinyl alcohol
copolymer, and polylactide.
[0036] The molten semi-crystalline polymer is preferably uniformly
distributed in the molten thermoplastic elastomer. In some aspects,
the mixture comprises from 0.1 wt % to 20 wt %, from 0.1 wt % to 15
wt %, from 0.1 wt % to 12 wt %, from 0.1 wt % to 10 wt %, from 0.1
wt % to 8 wt %, from 0.1 wt % to 5 wt %, from 0.1 wt % to 4 wt %,
from 0.1 wt % to 3 wt %, from 0.1 wt % to 2 wt %, from 0.1 wt % to
1 wt %, from 0.2 wt % to 20 wt %, from 0.2 wt % to 15 wt %, from
0.2 wt % to 12 wt %, from 0.2 wt % to 10 wt %, from 0.2 wt % to 8
wt %, from 0.2 wt % to 5 wt %, from 0.2 wt % to 4 wt %, from 0.2 wt
% to 3 wt %, from 0.2 wt % to 2 wt %, from 0.2 wt % to 1 wt %, from
0.3 wt % to 20 wt %, from 0.3 wt % to 15 wt %, from 0.3 wt % to 12
wt %, from 0.3 wt % to 10 wt %, from 0.3 wt % to 8 wt %, from 0.3
wt % to 5 wt %, from 0.3 wt % to 4 wt %, from 0.3 wt % to 3 wt %,
from 0.3 wt % to 2 wt %, from 0.3 wt % to 1 wt %, from 0.4 wt % to
20 wt %, from 0.4 wt % to 15 wt %, from 0.4 wt % to 12 wt %, from
0.4 wt % to 10 wt %, from 0.4 wt % to 8 wt %, from 0.4 wt % to 5 wt
%, from 0.4 wt % to 4 wt %, from 0.4 wt % to 3 wt %, from 0.4 wt %
to 2 wt %, from 0.4 wt % to 1 wt %, from 0.5 wt % to 20 wt %, from
0.5 wt % to 15 wt %, from 0.5 wt % to 12 wt %, from 0.5 wt % to 10
wt %, from 0.5 wt % to 8 wt %, from 0.5 wt % to 5 wt %, from 0.5 wt
% to 4 wt %, from 0.5 wt % to 3 wt %, from 0.5 wt % to 2 wt %, from
0.5 wt % to 1 wt %, from 1 to 10 wt %, from 1 wt % to 5 wt %, from
2 wt % to 5 wt %, or from 3 wt % to 5 wt % of the semi-crystalline
polymer. In some aspects, the mixture comprises from 0.1 wt % or
from 0.2 wt % or from 0.3 wt % or from 0.4 wt % or from 0.5 wt % or
from 0.6 wt % or from 0.7 wt % or from 0.8 wt % or from 0.9 wt % or
from 1 wt % to 2 wt % or to 3 wt % or to 4 wt % or to 5 wt % or to
6 wt % or to 10 wt % or to 12 wt % or to 14 wt % or to 15 wt % or
to 20 wt % of the semi-crystalline polymer. In some aspects, the
mixture comprises less than 20 wt %, less than 10 wt %, less than 8
wt % less than 5 wt %, less than 4 wt %, less than 3 wt %, less
than 2wt %, or less than 1 wt % of the semi-crystalline polymer and
preferably more than 0.1 wt %, more than 0.2 wt %, more than 0.3 wt
%, more than 0.4 wt %, more than 0.5 wt %, more than 0.6 wt %, more
than 0.7 wt %, more than 0.8 wt %, more than 0.9 wt %, or more than
1 wt % of the semi-crystalline polymer.
[0037] In some aspects, the mixture that is foamed comprises a
thermoplastic polyurethane elastomer and a semi-crystalline polymer
component comprising ethylene vinyl alcohol copolymer. In some
aspects, the semi-crystalline polymer is an ethylene vinyl alcohol
copolymer. In some aspects, the ethylene vinyl alcohol copolymer
comprises a ratio of ethylene monomer units to vinyl alcohol
monomer units. In some aspects, the ratio of ethylene monomer units
to vinyl alcohol monomer units in the ethylene vinyl alcohol
copolymer is from 20 mol % to 45 mol %, from 25 mol % to 40 mol %,
from 30 mol % to 40 mol %, from 30 mol % to 35 mol %, or from 20
mol % to 30 mol %. In some aspects, the ratio of ethylene monomer
units to vinyl alcohol monomer units in the ethylene vinyl alcohol
copolymer is from 20 mol % or from 25 mol % to 30 mol % or to 40
mol %. In some aspects, the ratio of ethylene monomer units to
vinyl alcohol monomer units in the ethylene vinyl alcohol copolymer
is from 25 mol % or from 30 mol % to 35 mol % or to 40 mol %.
[0038] In some aspects, the thermoplastic elastomer foam comprises
a thermoplastic polyurethane elastomer and ethylene vinyl alcohol
copolymer, and the ratio of ethylene monomer units to vinyl alcohol
monomer units in the ethylene vinyl alcohol copolymer is from 20
mol % or from 25 mol % or from 30 mol % to 35 mol % or to 40 mol %
or to 45 mol %, and the ethylene vinyl alcohol copolymer is present
in the foam in an amount of from 0.5 wt % or from 1 wt % or from 2
wt % or from 5 wt % or from 10 wt % to 12 wt % or to 15 wt % or to
18 wt % or to 20 wt % of the foam.
[0039] In some aspects, the thermoplastic elastomer foam comprises
a thermoplastic polyurethane elastomer and ethylene vinyl alcohol
copolymer, and the ethylene vinyl alcohol copolymer is present in
the thermoplastic elastomer foam in an amount of from 0.5 wt % or
from 1 wt % or from 2 wt % or from 5 wt % or from 10 wt % to 12 wt
% or to 15 wt % or to 18 wt % or to 20 wt % of the thermoplastic
elastomer foam. In some aspects, the ethylene vinyl alcohol
copolymer is present in the thermoplastic elastomer foam in an
amount of from 0.5 wt % to 20 wt %, from 1 wt % to 15 wt %, from 1
wt % to 10 wt %, from 2 wt % to 10 wt %, from 5 wt % to 10 wt %,
from 1 wt % to 5 wt %, from 10 wt % to15 wt %, from 15 wt % to 20
wt %, less than 20 wt %, less than 15 wt %, less than 10 wt %, or
less than 5 wt % of the thermoplastic elastomer foam.
[0040] The gaseous or supercritical blowing agent should be inert
to the elastomeric polymer mixture. The gaseous or supercritical
blowing agent is incorporated into the thermoplastic elastomer
mixture under pressure, then the pressure is released to foam the
polymer mixture.
[0041] The inert gas or supercritical fluid is not particularly
limited as long as it is inert to the both the thermoplastic
elastomer and the semi-crystalline polymer contained in the
thermoplastic elastomer foam and the thermoplastic elastomer it can
be incorporated into the thermoplastic elastomer-semi-crystalline
polymer mixture. Examples of suitable such blowing agents include
carbon dioxide, nitrogen gas, and air. Note that the inert gas may
be a mixed gas comprising two or more gases. hi some aspects, the
blowing agent is carbon dioxide or nitrogen in gaseous or
supercritical state. When the thermoplastic elastomer is
thermoplastic polyurethane elastomer, gaseous or supercritical
carbon dioxide or a combination of gaseous or supercritical carbon
dioxide with gaseous or supercritical nitrogen may be used to take
advantage of the greater solubility of the carbon dioxide in solid
thermoplastic polyurethane elastomer when the impregnation is done
below the glass transition temperature of the thermoplastic
polyurethane elastomer.
[0042] The rate ofincorporation of the blowing agent into the
thermoplastic: elastomer mixture comprising a semi-crystalline
polymer may be increased by using the blowing agent in a
supercritical state. Supercritical fluids may have increased
solubility in the thermoplastic elastomer mixture and thus may he
used in a higher concentration. At a high concentration, the
supercritical blowing agent generates a larger number of cell
nuclei upon an abrupt pressure drop in foaming the thermoplastic
elastomer, thus working with the crystalline regions in increasing
the cell density.
[0043] Nonlimiting examples of suitable compounds that can be used
as the supercritical fluid include carbon dioxide (critical
temperature 31.1.degree. C., critical pressure 7.38 MPa), nitrous
oxide (critical temperature 36.5.degree. C., critical pressure 7.24
MPa), ethane (critical temperature 32.3.degree. C., critical
pressure 4.88 MPa), ethylene (critical temperature 9.3.degree. C.,
critical pressure 5.12 MPa), nitrogen (critical temperature
-147.degree. C., critical pressure 3.39 MPa), and oxygen (critical
temperature -118.6.degree. C., critical pressure 5.08 MPa).
[0044] Supercritical carbon dioxide fluid can be made more
compatible with the polar thermoplastic elastomers (particularly
thermoplastic polyurethane, polyurea, and polyamide elastomers) by
combining the supercritical carbon dioxide with a polar fluid such
as methanol, ethanol, propanol, or isopropanol. The polar fluid
that is used can have a Hildebrand solubility parameter equal to or
greater than 9 (cal/cm.sup.3).sup.1/2. Increasing the weight
fraction of the polar fluid increases the amount of supercritical
carbon dioxide uptake, but the polar fluid is also taken up, and at
some point there is a shift from a maximum amount of uptake of the
supercritical carbon dioxide to an increasing amount of the
non-foaming agent polar fluid being taken up by the thermoplastic
elastomer article. In certain aspects, from 0.1 mole % to 7 mole %
of the polar fluid is included in the supercritical fluid, based on
total fluid, especially when used to infuse a polyurethane
elastomer, polyurea elastomer, or a polyamide elastomer. In other
aspects, from 0.5 mole % to 6 mole % or from 1 mole % to 5 mole %
of the polar fluid is included in the supercritical fluid, based on
total fluid.
[0045] Supercritical fluids may be used in combination. In some
cases, supercritical nitrogen may be used as an auxiliary
nucleating agent in a small weight percentage along with
supercritical carbon dioxide or another supercritical fluid that
acts as the blowing agent.
[0046] The articles are placed in a vessel that can withstand high
pressure. The vessel is closed and CO.sub.2 or other type of
foaming agent is introduced. The vessel temperature and pressure
are maintained above the critical temperature and pressure of the
foaming agent. Once the article is saturated with the foaming
agent, the vessel is rapidly depressurized. The article is then
removed from the vessel as a foamed part, or heated to produce the
foamed part. When a co-solvent is used, it can be introduced along
with the CO.sub.2 or added to the vessel with the article before
the vessel is closed.
[0047] The thermoplastic article is soaked in the supercritical
fluid under conditions (temperature and pressure) and for a time to
allow it to take up a given amount of the supercritical fluid.
[0048] The process of foaming the thermoplastic elastomer
comprising the semi-crystalline polymer using a high-pressure gas
or supercritical fluid as a foaming agent may be a batch process or
a continuous process. In the batch process, the thermoplastic
elastomer/semi-crystalline polymer composition is formed into an
article suitable for foaming, then the article is impregnated with
a high-pressure gas or supercritical fluid, and then the pressure
is released to allow the gas- or supercritical fluid-impregnated
article to expand to a foam, the continuous system, the
thermoplastic elastomer/semi-crystalline polymer composition is
kneaded under a pressure together with a high-pressure gas or
supercritical fluid, then the kneaded mixture is molded into a
molded article, and, simultaneously, the pressure is released to
allow the gas- or supercritical fluid-impregnated molded article to
expand to a foam.
[0049] In a batch process, the unfoamed thermoplastic elastomer may
be formed into an article by a variety of methods. For example, the
thermoplastic elastomer comprising a semi-crystalline polymer can
be kneaded and extruded with an extruder such as a single-screw
extruder or twin-screw extruder into an article or articles that
may be further cut or shaped; or the thermoplastic elastomer
comprising a semi-crystalline polymer can be uniformly kneaded
beforehand with a kneading machine equipped with one or more blades
typically of a roller, cam, kneader, or Banbury type, and then the
resulting mixture can be press-molded typically with a hot-plate
press to produce a molded sheet article having a predetermined
thickness that may be further cut or shaped; or still further the
thermoplastic elastomer comprising a semi-crystalline polymer can
be molded with an injection molding machine to produce an article
of a given shape. The unfoamed article of thermoplastic elastomer
comprising a semi-crystalline polymer may have at least one thin
dimension (e.g., a thickness or width of 10 mm or less, preferably
5 mm or less). The unfoamed article may be formed using other known
methods to produce a given shape, including pellets (as already
described above), sheets, strands, ropes, tubes, and other shapes,
particularly shapes that include a dimension that is less than 10
mm, for example a dimension in a range of from 0.1 mm or from 0.5
mm up to 5 mm or up to 10 mm. The article that is foamed may have a
regular or irregular shape and may be, for example, a pellet, bead,
particle, cylinder, prolate obloid, cube, sphere, pyramid, tape,
ribbon, rope, film, strand, or fiber. Pellets, beads, or particles
may be generally spherical, cylindrical ellipsoidal, cubic,
rectangular, and other generally polyhedral shapes as well as
irregular or other shapes, including those having circular,
elliptical, square, rectangular or other polygonal cross-sectional
outer perimeter shapes or irregular cross-sectional shapes with or
without uniform widths or diameters along an axis. "Generally" is
used here to indicate an overall shape that may have imperfections
and irregularities, such as bumps, dents, imperfectly aligned
edges, corners, or sides, and so on.
[0050] When the thermoplastic elastomer comprising the
semi-crystalline polymer is subjected to foam molding by the above
batch system, cells are formed in the thermoplastic elastornei
comprising a semi-crystalline polymer through a gas or
supercritical fluid impregnation step of putting the unfoamed
thermoplastic elastomer comprising a semi-crystalline polymer
molded article obtained as described above in a pressure-tight
vessel (high pressure vessel) and injecting or otherwise
introducing a high-pressure gas or supercritical fluid (for example
nitrogen or carbon dioxide) to impregnate the unfoamed
thermoplastic elastomer molded article with the high-pressure gas
or supercritical fluid; a decompression step of releasing the
pressure, typically, but not necessarily, to atmospheric pressure,
when the unfoamed thermoplastic elastomer comprising a
semi-crystalline polymer molded article is sufficiently impregnated
with the high-pressure gas or supercritical fluid to form cell
nuclei in the thermoplastic elastomer comprising in the
semi-crystalline regions; and, optionally, a heating step of
heating the thermoplastic elastomer article to allow the cell
nuclei to grow. The cell nuclei may be allowed to grow at room
temperature without providing the heating step. The
semi-crylstalline phase regions distributed throughout the
thermoplastic elastomer serve as nucleation sites. The even
distribution and selected concentration of these sites produce a
foam with evenly-distributed, uniform foam cells of a certain size
and in a certain concentration. The introduction of the
high-pressure gas may be performed continuously or discontinuously.
Heating to expand the cell nuclei can be carried out, for example,
in a heated oil bath, with a hot roll, in a hot-air oven, or with
infrared or microwave radiation. Water is one suitable medium in
which foaming readily occurs at an appropriate temperature because
water has a high heat capacity and heat transfer rate. In certain
preferred aspects, the thermoplastic elastomer article infused or
saturated with supercritical fluid is submerged in water that is at
a temperature at least 80.degree. higher and, preferably, at least
100.degree. higher than the elastomer's (soft segment) T.sub.g but
less than the elastomer's (hard segment) T.sub.m. Other examples of
suitable mediums are steam or pressurized hot air.
[0051] In one example, the thermoplastic article is soaked under
conditions that result in it becoming saturated with the
supercritical fluid. The article is then removed from the chamber
and immediately either heated to a temperature in a medium with
suitable thermal characteristics for foaming to occur or is exposed
to microwaves or infrared radiation in a tunnel or oven to cause
the foaming to occur. In microwave heating, the material is exposed
to an electromagnetic wave that causes the molecules in the
material to oscillate, thereby generating heat. In a batch process,
the articles saturated with the supercritical fluid are placed in a
microwave oven or a device equipped with an IR lamp or IR lamps.
Preferably the articles are rotated or agitated, when their size is
small enough, to ensure fast and uniform heating. When foaming is
completed, the articles are removed from the system. The heating
can also be done in the continuous process. The articles are placed
on a planar surface such as a belt that moves them through a tunnel
or through a pipe. The system is designed so that the heating
elements (IR lamp or microwave generator) can apply power to
achieve rapid uniform heating. The time of heating is controlled by
the speed by which the articles move through the tunnel or
pipe.
[0052] When the thermoplastic elastomer comprising a
semi-crystalline polymer is molded and foamed in a continuous
process, the process may include kneading the thermoplastic
elastomer comprising the semi-crystalline polymer in an extruder
such as a single-screw extruder or twin-screw extruder and, while
kneading the thermoplastic elastomer polymer, injecting or
otherwise introducing into the polymer the high-pressure gas or
supercritical fluid to impregnate the thermoplastic elastomer
comprising a semi-crystalline polymer with the high-pressure gas or
supercritical fluid; and then extruding the impregnated
thermoplastic elastomer comprising a semi-crystalline polymer
through a die arranged at a distal end of the extruder to release
the pressure, typically but not necessarily to atmospheric
pressure, to mold and foam the extruded article simultaneously.
Like in the batch process, an optional heating step may be carried
out to promote cell growth. The extruder may be coupled with an
injection molding machine or the like to further shape the
extnidate.
[0053] The amount of the gas or supercritical fluid introduced into
the unfoamed thermoplastic elastomer comprising a semi-crystalline
polymer is selected to provide a degree of foaming in the final
article and may be, for example, from 2% or from 2.5% or from 3% up
to 6% or up to 8% or up to 20% by weight, based on the total
polymer weight. For example, the amount of the as or supercritical
fluid used may be from 2% up to 10% by weight or from 2% up to 8%
by weight or from 2% up to 6% by weight or from 2.5% up to 10% by
weight or from 2,5% up to 8% by weight or from 2.5% up to 6% by
weight or from 3% up to 10% by weight or from 3% up to 8% by weight
or from 3% up to 6% by weight, based on the total polymer
weight.
[0054] The pressure at which the unfoamed thermoplastic elastomer
comprising a semi-crystalline polymer is impregnated with a gas or
supercritical fluid is suitably selected according to the type of
gas or supercritical fluid, the viscosity of the polymer
composition at the impregnation temperature, and the equipment
being used. For example.sub.; the pressure may be from 6 IVIPa or
from 8 MPa or from 15 MPa or from 25 MPa to 50 MPa or to 75 MPa or
to 100 MPa., Examples pressure ranges include from 6 MPa to 100
MPa, from 6 MPa to 75 MPa, from 6 MPa to 50 MPa, from 8 MPa to 100
MPa, from 8 MPa to 75 MPa, from 8 MPa to 50 MPa, from 15 MPa. to
100 MPa., from 15 MPa to 75 MPa, from 15 MPa to 50 MPa, from 25 MPa
to 100 MPa, from 25 MPa to 75 MPa, and from 25 MPa to 50 MPa If the
pressure of the gas is lower than 6 IVIPa, considerable cell growth
may occur during foaming. As a result, the number of cell nuclei
formed may be smaller. Because of this, the gas amount per cell
increases rather than decreases, resulting in excessively large
cell diameters. Furthermore, in a region of pressures lower than 6
MPa, only a slight change in impregnation pressure results in
considerable changes in cell diameter and cell density, and this
may often impede the control of cell diameter and cell density.
[0055] The temperature at which the unfoamed thermoplastic
elastomer comprising a semi-crystalline polymer is impregnated with
a gas or supercritical fluid also may be suitably selected
according to the type of gas or supercritical fluid, the particular
polymer composition, and the equipment being used. For example, the
impregnation temperature may be from 10.degree. C. or from
40.degree. C. or from 60.degree. C. or from 100.degree. C. or from
150.degree. C. to 230.degree. C. or to 240.degree. C. or to
250.degree. C. For impregnation with a supercritical fluid, the
temperature and pressure are selected to maintain the fluid in its
supercritical state.
[0056] Further, the decompression rate in the decompressing step
(i.e., releasing the pressure) in the foam molding of the
thermoplastic elastomer comprising a semi-crystalline polymer by
the batch system or continuous system may be from 5 to 300 NIPals
to obtain uniform foam cells. Furthermore, the heating temperature
for promoting cell growth during the foaming step may be, for
example, from 40.degree. C to 250.degree. C.
[0057] In some aspects, the foam of the thermoplastic elastomer
comprising a semi-crystalline polymer has an average cell size of
up to 20 microns. In some aspects, the thermoplastic elastomer foam
has an average cell size of up to 15 microns, or up to 10 micron,
or up to 7.5 microns, or up to 5 microns, or up to 2.5 microns. In
some aspects, the thermoplastic elastomer foam has an average cell
size of from 0.5 microns to 30 microns, or from 0.5 to 20 microns,
or from 1 micron to 20 microns, or from 5 microns to 20 microns, or
from 0.5 microns to 15 microns, or from 1 micron to 15 microns, or
from 1 micron to 10 microns.
[0058] In some aspects, the thermoplastic elastomer foam has a foam
density of from 160 kg/m.sup.3 to 300 kg/ m.sup.3. For example, the
thermoplastic elastomer foam density may be from 50 kg/ m.sup.3 to
500 kg/ m.sup.3, from 75 kg/ m.sup.3 to 400 kg/ m.sup.3, from 100
kg/ m.sup.3 to 300 kg/ m.sup.3, from 125 kg/ m.sup.3 to 300 kg/
m.sup.3, from 140 kg/ m.sup.3 to 300 kg/ m.sup.3, from 200 kg/
m.sup.3 to 300 kg/ m.sup.3, from 250 kg/ m.sup.3 to 400 kg/m.sup.3,
from 250 kg/ m.sup.3 to 350 kg/ m.sup.3, from 250 kg/ m.sup.3 to
300 kg/ m.sup.3, from 160 kg/ m.sup.3 to 250 kg/ m.sup.3, from 180
kg/ m.sup.3 to 225 kg/ m.sup.3, from 200 kg/ m.sup.3 to 225 kg/
m.sup.3, or from 230 kg/ m.sup.3. In some aspects, the
thermoplastic elastomer foam has a foam density of from 50
kg/m.sup.3 or from 75 kg/m.sup.3 or from 100 kg/m.sup.3 or from 125
kg/m.sup.3 or from 130 kg/m.sup.3 or from 140 kg/m.sup.3 to 160
kg/m.sup.3 or to 180 kg/m.sup.3 or to 200 kg/m.sup.3 or to 225
kg/m.sup.3 or to 250 kg/m.sup.3 or to 275 kg/m.sup.3 or to 300
kg/m.sup.3. In some aspects, the thermoplastic elastomer foam has a
foam density of from 150 kg/m.sup.3 or from 175 kg/m.sup.3 or from
200 kg/m.sup.3 to 225 kg/m.sup.3 or to 250 kg/m.sup.3 or to 275
kg/m.sup.3 or to 300 kg/m.sup.3.
[0059] In various aspects, the foam of the thermoplastic elastomer
comprising a semi-crystalline polymer may be further molded or
shaped. In one method, the foamed articles of the thermoplastic
elastomer comprising a semi-crystalline polymer are beads, pellets,
particles, or similar relatively small sizes, which will be
generally referred to in the following discussion as "pellets." In
one example, a mold is filled with the foamed pellets and the
pellets are molded at an appropriate temperature into a shaped
article. The shaped article may be of any dimensions. For example,
the molded foamed elastomer may be sized as a cushion or cushioning
element that can be included in an article of footwear, for example
part of a footwear upper, such as a foam element in a collar or
tongue, as an insole, as a midsole or a part of a midsole, or an
outsole or a part of an outsole; foam padding in shin guards,
shoulder pads, chest protectors, masks, helmets or other headgear,
knee protectors, and other protective equipment; an element placed
in an article of clothing between textile layers; in clothing, in
protective gear such as helmets, chest protectors, and shoulder
pads, or may be used for other known padding applications for
protection or comfort, especially those for which weight of the
padding is a concern; or in furniture or in seats, for example
bicycle seats.
[0060] For example, the thermoplastic elastomer-semi-crystalline
polymer foam may be or be used to make an article of clothing or
footwear. In some aspects, this thermoplastic elastomer foam may
serve as a cushioning element for an article of clothing or
footwear. In some aspects, an article of protective equipment
comprises the thermoplastic elastomer foam including the
semi-crystalline polymer. In some aspects, the thermoplastic
elastomer foam described herein may serve as a cushioning element
for an article of protective equipment. In some aspects, the
thermoplastic elastomer foam comprises a thermoplastic polyurethane
elastomer and the semi-crystalline polymer comprises ethylene vinyl
alcohol copolymer.
[0061] In one aspect, a foamed article, such as a midsole for
footwear, is formed by placing the foamed pellets of thermoplastic
elastomer comprising a semi-crystalline polymer in a compression
mold in the shape of the article. The pellets are heated with
microwave energy to a peak temperature slightly above the melting
temperature of the elastomer, which may be of from 100.degree. C.
to 180.degree. C., over a period of from 60 to 1500 seconds. Within
up to 30 seconds after the peak temperature is reached, the molded
pellets are then cooled to from 5.degree. C. to 80.degree. C. over
a period of from 300 to 1500 seconds. In various aspects, the
thermoplastic elastomer comprising a semi-crystalline polymer foam
pellets may preferably be generally spherical or ellipsoidal. In
the case of non-spherical pellets, for example ellipsoidal beads,
the largest major diameter of a cross-section taken perpendicular
to the major (longest) axis of the ellipsoid. The foam pellets may
preferably have a diameter of from 0.5 mm to 1.5 cm. Ellipsoidal
pellets may be from 2 mm to 20 mm in length and from 1 to 20 mm in
diameter. Each individual pellet may be, for example, from 20 to 45
mg in weight. The foam pellets may have a density of from 100 to
300 Kg/m.sup.3and the molded article may have a density from 100 to
450 Kg/m.sup.3.
[0062] The foam pellets may be coated with an adhesive, for example
a urethane-based adhesive, before being placed in the mold.
Suitable commercially available adhesives include W-104, W-105,
W-01, W-01S and SW07 from Henkel. Other adhesives such as WA-1C and
WP1-116K from Han Young Industry Company can also be used. In
general, these adhesives may be sprayed onto the foamed pellets or
otherwise coated onto the foamed pellets.
[0063] The adhesive-coated foam pellets may be heated with
microwaves or steam to a peak temperature above the melting
temperature of the adhesive, for example to a temperature up
150.degree. C., for example to a temperature of from 70.degree. C.
to 150.degree. C., over a period of from 300 to 1500 seconds. In
general, a longer time may be used for heating a thicker part to
mold the part. Thus, a thicker part may be brought to the peak
molding temperature over a longer period of time compared to the
time in which a thinner part is brought to the peak molding
temperature. In various aspects, the mold is brought to the peak
temperature over a period of from 60 to 1200 seconds or from 60 to
900 seconds. A given skin thickness may be achieved by selection of
the maximum heating temperature within the temperature range. Skin
thickness may be selected to alter cushioning and feel of a molded
midsole as used in an article of footwear. The skin thickness on a
bead may be from 2 to 25 micrometers. The skin thickness on a
molded part may be at least 20 micrometers. In various aspects, the
peak temperature is selected to produce a skin thickness of from 10
to 200 micrometers.
[0064] The mold may then be cooled to a temperature of from
5.degree. C. to 80.degree. C. over a period of from 300 to 1500
seconds. Cooling is typically carried out by moving the mold to the
cold side of the compression molding press between two cold plates.
In general, a longer time may be used for cooling a thicker
part.
[0065] In other aspects, the foamed pellets are molded with a
matrix material of an unfoamed thermoplastic elastomer, which may
include a blowing agent so that it is foamed during the molding
process.
[0066] The molded article may be used as an insert in a further
molding process, such as in a thermoforming process.
[0067] The method and foamed articles are further illustrated in
the following examples.
EXAMPLES
[0068] Samples were prepared comprising 0 wt %, 1 wt %, 3 wt %, and
5 wt %, based on total polymer weight, of ethylene vinyl alcohol
copolymer (EVOH) in ELASTOLLAN.RTM. 1180A10 thermoplastic
polyurethane elastomer (obtained from BASF Polyurethanes GmbH). The
materials were mix-melted in a twin-screw extruder, pelletized, and
then dried in air. The pellets of the samples were impregnated at
200 bar and 40.degree. C. with supercritical carbon dioxide as a
blowing agent and then the pressure was released to foam the
pellets. The uptake of carbon dioxide was measured by weight gain.
The uptake of carbon dioxide did not change significantly with an
increase in EVOH concentration within the pellets of the mixed
samples. The foam density increased at higher concentrations of
EVOH within the mixed samples. This data is presented in Table
1.
TABLE-US-00001 TABLE 1 CO.sub.2 Uptake Density Sample (wt %) (g/cc)
A. ELASTOLLAN .RTM. 1180A10 8.9 0.23 B. ELASTOLLAN .RTM. 1180A10 +
10 0.24 1 wt % EVOH C. ELASTOLLAN .RTM. 1180A10 + 9.4 0.26 3 wt %
EVOH D. ELASTOLLAN .RTM. 1180A10 + 9.3 0.27 5 wt % EVOH
[0069] Cross-sections of the foamed pellets were examined using
scanning electron microscopy (Phenom model from FEI Company) and
are presented in FIGS. 1A-1D. FIG. 1A shows the cell structure of a
foamed pellet prepared without the addition of EVOH. FIG. 1B shows
the cell structure of a foamed pellet prepared 1 wt % of EVOH. FIG.
1C shows the cell structure of a foamed pellet prepared 3 wt % of
EVOH. FIG. 1B shows the cell structure of a foamed pellet prepared
5 wt % of EVOH. The cross-section images of the foamed pellets
reveal finer cell structure when EVOH is present.
[0070] The foregoing descriptions of particular aspects illustrate
features of the invention, but the invention is not limited to any
of the specific aspects that have been described. The features
described for particular aspects are interchangeable and can be
used together, even if not specifically shown or described. The
same may also be varied in many ways. The invention broadly
includes such variations and modifications.
* * * * *